CN101605287B - Integrated circuit for providing a microphone interface - Google Patents

Abstract

An integrated circuit for providing a programmable microphone interface, comprising an input terminal for receiving an input signal and an output terminal for providing an output audio signal, the integrated circuit comprising a bias circuit, an amplifier circuit and two feedback circuits; the bias circuit provides a microphone bias signal to the microphone and provides a sense microphone signal; the amplifier circuit comprises a first input end, a second input end and an output end; the first input terminal is configured to receive a sensing microphone signal, a first feedback signal and a second feedback signal; the second input terminal is configured to receive a first reference signal; the feedback circuit is communicated with the output end and the first input end of the amplifier circuit; in a particular embodiment, the first feedback circuit includes an RC circuit and the second feedback circuit includes an integrator.

Description

Integrated circuit for providing a microphone interface

technical field

The present invention relates to an integrated circuit. More specifically, the present invention provides an integrated circuit related to a programmable microphone interface.

Background technique

Sound and audio band applications often use microphones to receive sound or audio energy from the environment and convert it into voltage or current. There is a very popular type of microphone called an "electret condenser" type microphone. This microphone typically requires a DC bias to operate. Figure 1 shows a schematic diagram of an example of an existing CODEC microphone interface circuit. As shown, the electret microphone 102 often requires many off-chip components to interface with the CODEC integrated circuit 150 . For example, microphone 102 is biased with resistor 112 and resistor 114 and capacitor 122 for noisy DC bias and power supply filtering. A gain stage is often used to interface with the CODEC die 150 . In FIG. 1 , the gain stage includes discrete components, such as capacitor 142 , capacitor 144 , capacitor 146 , and capacitor 148 , and resistor 132 , resistor 134 , resistor 136 , and resistor 138 . Although existing interface circuit technology is widely used, it suffers from a number of limitations, as discussed in more detail below.

Therefore, there is a need for an improved technique for microphone interface circuits.

Contents of the invention

This invention relates to integrated circuits. More specifically, the present invention provides a method and apparatus for an integrated circuit of a microphone interface. Merely as an example, the present invention has been applied to an interface circuit of an electret microphone. It should be appreciated, however, that the invention has much broader applicability. For example, the present invention can be applied to interface circuits of other types of microphones or interface circuits of other signal sources.

According to an embodiment of the present invention, an integrated circuit for a microphone interface is provided. An integrated circuit includes input terminals for receiving input signals, output terminals for providing output signals, and bias circuits. A bias circuit is coupled to the input terminal for providing a bias signal at the input terminal and is configured to provide a sense input signal. The integrated circuit also includes a first amplifier circuit having a first input, a second input, and an output. The first input terminal is configured to receive a sensing input signal, a first feedback signal and a second feedback signal. The second input is configured to receive the first reference signal, and the output is configured to provide an output signal to the output terminal. The integrated circuit also includes two feedback circuits. The first feedback circuit communicates with the output terminal of the first amplifier circuit and the first input terminal and provides a first feedback signal to the first input terminal of the first amplifier circuit. The second feedback circuit communicates with the output terminal of the first amplifier circuit and the first input terminal and provides a second feedback signal to the first input terminal of the first amplifier circuit. The second feedback circuit further includes an integrator circuit.

In a particular embodiment of the integrated circuit, the input terminal is configured to receive an input signal from an electret microphone without external components. In an embodiment, the bias circuit includes a reference circuit for providing a second reference signal, which may be a reference voltage or a reference current. The bias circuit includes a first input resistor in communication with the input terminal and the reference circuit, and a second input resistor in communication with the input terminal and the second input of the first amplifier circuit.

In some embodiments, the first feedback circuit includes a first feedback resistor and a first feedback capacitor in a parallel configuration. In some embodiments, the integrator circuit includes an inverting amplifier coupled to an output of the first amplifier circuit and a second amplifier circuit. The second amplifier circuit includes a first input terminal, a second input terminal and an output terminal. The second input terminal is coupled to the third reference signal. The first feedback circuit also includes a second feedback resistor coupled to the output terminal of the unity gain inverting amplifier and the first input terminal of the second amplifier circuit, and a second feedback resistor coupled to the first input terminal and the output terminal of the second amplifier circuit. feedback capacitor. In an embodiment, the output terminal of the second amplifier circuit is coupled to the second input terminal of the first amplifier circuit via a third feedback resistor.

In some embodiments, the integrator circuit includes a switched capacitor circuit and a second amplifier circuit. The switched capacitor circuit includes a switch capacitor and a first switch, a second switch, a third switch and a fourth switch. The first switch and the second switch are coupled to the first terminal of the switched capacitor, and the third switch and the fourth switch are coupled to the second terminal of the switched capacitor. In addition, the second switch and the fourth switch are coupled to the first reference signal. The second amplifier circuit includes a first input terminal, a second input terminal and an output terminal. The first input communicates with the third switch of the switched capacitor circuit. The second input terminal is coupled to the first reference signal. The second amplifier circuit also includes a second feedback capacitor communicated with the first input terminal and the output terminal of the second amplifier circuit.

In an embodiment, the integrated circuit also includes a supply voltage. The first reference signal is about half the supply voltage in magnitude for providing the maximum signal swing at the output terminal allowed by the supply voltage. In some embodiments, the integrated circuit is characterized by a DC loop gain that is sufficiently large to cause the voltage at the output of the first amplifier to be substantially equal to the first reference voltage. In a particular example, the integrated microphone interface circuit is characterized by a DC loop gain in the range of about 80 dB to about 140 dB. In some embodiments, the integrated circuit is characterized by a large DC loop gain and a low alternating current (AC) loop gain, causing the DC output voltage at the output terminals to be substantially equal to the first reference voltage, and the AC output voltage to be consistent with the first feedback The impedance of the circuit is linearly proportional to the AC input current or voltage across the input terminals. In another embodiment, the bias circuit provides a programmable voltage or current reference, and the first feedback resistor and the second feedback resistor are programmable.

According to another embodiment of the present invention, an integrated circuit for providing a microphone interface includes a first input terminal and a second input terminal for respectively receiving a first differential input signal (differential input signal) and a second differential input signal . The integrated circuit also includes a first output terminal and a second output terminal for respectively providing a first differential output signal and a second differential output signal. The integrated circuit further includes two bias circuits. The first bias circuit communicates with the first input terminal and the first reference signal, and provides a first sensing input signal. The second bias circuit communicates with the second input terminal and the second reference signal, and provides a second sensing input signal. The integrated circuit further includes a first amplifier circuit having a first input terminal, a second input terminal and a third input terminal. The first input terminal receives a first sensing input signal, the second input terminal receives a second sensing input signal, and the third input terminal receives a common-mode reference signal. The first amplifier circuit also has a first output terminal and a second output terminal. The first output terminal and the second output terminal respectively provide the first differential output audio signal and the second differential output audio signal to the first output terminal and the second output terminal. Additionally, the integrated circuit includes a feedback circuit in communication with the first and second inputs and the first and second outputs of the first amplifier circuit.

In a particular embodiment, the first input terminal and the second input terminal are configured to receive an input signal from an electret microphone. In an embodiment, the first bias circuit includes a third resistor in communication with the first input terminal and the source of the microphone reference signal and a fourth resistor in communication with the first input terminal and the third resistor, the fourth resistor providing the first sense input signal. In an embodiment, the second bias circuit includes a fifth resistor in communication with the second input terminal and the ground reference voltage source, and a sixth resistor in communication with the second input terminal and the fifth resistor, the sixth resistor providing the second inductance. Measure the input signal.

In some embodiments, the feedback circuit also includes three feedback circuits. The first feedback circuit communicates with the first output terminal and the first input terminal of the first amplifier. In a specific example, the first feedback circuit includes a first resistor and a first capacitor connected in parallel. The second feedback circuit communicates with the second output terminal and the second input terminal of the first amplifier. In an example, the second feedback circuit includes a second resistor and a second capacitor connected in parallel. In an embodiment, the third feedback circuit is a differential feedback circuit. The differential feedback circuit includes a first input terminal and a second input terminal respectively coupled to the first output terminal and the second output terminal of the first amplifier circuit. The differential feedback circuit also includes a first output terminal and a second output terminal respectively coupled to the first input terminal and the second input terminal of the first amplifier circuit.

In a specific embodiment, the differential feedback circuit further includes the following components. The differential amplifier includes a first input terminal, a second input terminal and a third input terminal, and a first output terminal and a second output terminal. The third input terminal receives the common mode reference signal. The first resistor is connected to the first input terminal of the differential amplifier. The second resistor is connected to the first output terminal of the differential amplifier. The first capacitor is connected to the first input terminal and the first output terminal of the differential amplifier. The third resistor is connected to the second input terminal of the differential amplifier. The fourth resistor is connected to the second output terminal of the differential amplifier. The second capacitor is connected to the second input end and the second output end of the differential amplifier. In an embodiment, the integrated circuit also includes a supply voltage. The common mode reference signal is approximately half the supply voltage in magnitude for providing the maximum signal swing at the output terminals allowed by the supply voltage.

According to an alternative embodiment of the invention, an integrated circuit for a microphone interface comprises an input terminal for receiving an input signal, an output terminal for providing an output signal, and a programmable reference circuit for providing a bias signal. The integrated circuit also includes a first amplifier circuit having a first input, a second input, and an output. The first input terminal is configured to receive a bias signal, a first feedback signal, and a second feedback signal. The second input terminal is configured to receive the first reference signal. The output terminal is configured to provide an output signal to the output terminal. The integrated circuit further includes two feedback circuits. The first feedback circuit communicates with the output terminal of the first amplifier circuit and the first input terminal, and provides a first feedback signal to the first input terminal of the first amplifier circuit. The second feedback circuit communicates with the output terminal of the first amplifier circuit and the first input terminal, and provides a second feedback signal to the first input terminal of the first amplifier circuit. The second feedback circuit also includes an integrator circuit.

In a particular embodiment of the above integrated circuit, the input terminal is configured to receive an input signal from an electret microphone without external components. In an embodiment, the bias circuit includes a reference circuit for providing a second reference signal, which may be a reference voltage or a reference current. The bias circuit includes a first input resistor in communication with the input terminal and the reference circuit, and a second input resistor in communication with the input terminal and the second input of the first amplifier circuit.

In some embodiments, the first feedback circuit includes a first feedback resistor and a first feedback capacitor in a parallel configuration. In some embodiments, the integrator circuit includes an inverting amplifier coupled to the output of the first amplifier circuit and a second amplifier circuit. The second amplifier circuit includes a first input terminal, a second input terminal and an output terminal. The second input terminal is coupled to the third reference signal. The first feedback circuit also includes a second feedback resistor coupled to the output terminal of the unity gain inverting amplifier and the first input terminal of the second amplifier circuit, and a second feedback resistor coupled to the first input terminal and the output terminal of the second amplifier circuit. feedback capacitor. In an embodiment, the output terminal of the second amplifier circuit is coupled to the second input terminal of the first amplifier circuit via a third feedback resistor.

In some embodiments, the integrator circuit includes a switched capacitor circuit and a second amplifier circuit. The switched capacitor circuit includes a switched capacitor and a first switch, a second switch, a third switch and a fourth switch. The first switch and the second switch are coupled to the first terminal of the switched capacitor, and the third switch and the fourth switch are coupled to the second terminal of the switched capacitor. In addition, the second switch and the fourth switch are coupled to the first reference signal. The second amplifier circuit includes a first input terminal, a second input terminal and an output terminal. The first input communicates with the third switch of the switched capacitor circuit. The second input terminal is coupled to the first reference signal. The second amplifier circuit also includes a second feedback capacitor communicated with the first input terminal and the output terminal of the second amplifier circuit.

In an embodiment, the integrated circuit also includes a supply voltage. The first reference signal size is approximately half of the supply voltage for providing the maximum signal swing at the output terminal allowed by the supply voltage. In some embodiments, the integrated circuit is characterized by a DC loop gain that is sufficiently large to cause the voltage at the output of the first amplifier to be substantially equal to the first reference voltage. In a particular example, the integrated microphone interface circuit is characterized by a DC loop gain in the range of about 80 dB to about 140 dB. In some embodiments, the integrated circuit is characterized by a large DC loop gain and a low AC loop gain, causing the DC output voltage at the output terminals to be substantially equal to the first reference voltage, and the AC output voltage to be equal to the impedance of the first feedback circuit And the AC input current or voltage through the input terminal is linearly proportional. In another embodiment, the bias circuit provides a programmable voltage or current reference, and the first feedback resistor and the second feedback resistor are programmable.

In a particular embodiment, the present invention provides an integrated circuit for providing a programmable microphone interface. The integrated circuit includes input terminals for receiving input signals and output terminals for providing output audio signals. The integrated circuit includes a bias circuit in communication with the input terminal. The integrated circuit also includes a first amplifier circuit and a plurality of feedback circuits. For example, in an embodiment, the integrated circuit includes two feedback circuits. The first amplifier circuit includes a first input terminal, a second input terminal and an output terminal. In the first amplifier, the first input terminal communicates with the first feedback circuit, and can be programmed to receive an input signal or a feedback signal. For example, the first input terminal receives an input signal in response to a first mode control signal and a feedback signal in response to a second mode control signal. The second input terminal receives a feedback signal in response to the first mode control signal and an input signal in response to the second mode control signal. The output terminal provides an output signal to an output terminal. The first feedback circuit communicates with the output end of the first amplifier and the first input end, and the first feedback circuit includes a first resistor and a first capacitor connected in parallel. The second feedback circuit includes an integrator circuit in communication with the output of the first amplifier circuit. A second feedback circuit provides a feedback signal.

In an integrated circuit embodiment, the integrator includes a switched capacitor circuit, an amplifier, and a capacitor. The switched capacitor circuit includes a second capacitor and a first switch, a second switch, a third switch and a fourth switch. The first switch and the second switch are coupled to the first terminal of the second capacitor, and the third switch and the fourth switch are coupled to the second terminal of the second capacitor. The first switch and the third switch respond to the first clock signal, and the second switch and the fourth switch respond to the second clock signal. The amplifier circuit includes a first input terminal, a second input terminal and an output terminal. The first input terminal and the second input terminal are respectively communicated with the third switch and the fourth switch of the switched capacitor circuit, and the second input terminal is also communicated with the second reference voltage signal. The third capacitor communicates with the first input terminal and the output terminal of the amplifier. In an embodiment, the second reference voltage signal is approximately half the supply voltage for providing maximum signal swing at the output.

In a particular embodiment, the integrated circuit is characterized by a large DC loop gain and a low AC loop gain, causing the DC output voltage at the output terminals to be substantially equal to the second reference voltage, and the AC output voltage to be equal to the impedance of the first feedback circuit And the AC input current through the input terminals is linearly proportional. In an embodiment, the third capacitor is a MOS sandwich capacitor. In an embodiment, the microphone reference voltage source circuit provides a programmable microphone reference voltage source.

In another embodiment, the present invention provides an integrated microphone interface circuit comprising an input terminal for receiving an input signal and an output terminal for providing an output audio signal. The integrated microphone interface circuit includes a first resistor communicated with the input terminal and a first reference circuit coupled to the first resistor. The integrated microphone interface circuit also includes a first amplifier circuit and two feedback circuits. The first amplifier circuit includes a first input for receiving an input signal, a second input and an output for providing an output signal to an output terminal. The first feedback circuit communicates with the output terminal of the first amplifier and the first input terminal. The first feedback circuit includes a second resistor and a first capacitor connected in parallel. The second feedback circuit includes an integrator circuit and communicates with the output terminal of the first amplifier and the second input terminal. In an embodiment, the first reference voltage or current is independent of the first feedback circuit and the second feedback circuit.

In the integrated circuit embodiments above, the integrated circuits are provided in a single integrated circuit die. In a particular embodiment of the integrated microphone interface circuit, the input terminal is configured to receive an input signal from an electret microphone without the need for an external capacitor. In an embodiment, the microphone reference is programmable. Embodiments of the invention include various implementations of integrators. In one example, the integrator includes a second amplifier including a first input, a second input, and an output. The first input terminal is coupled to the third resistor. The second input terminal is coupled to the second reference voltage signal, and the second capacitor is coupled to the first input terminal and the output terminal of the amplifier. In another example, an integrator includes a switched capacitor circuit, an amplifier, and a capacitor. The switched capacitor circuit includes a second capacitor and a first switch, a second switch, a third switch and a fourth switch. The first switch and the second switch are coupled to the first terminal of the second capacitor, and the third switch and the fourth switch are coupled to the second terminal of the second capacitor. The first switch and the third switch respond to the first clock signal, and the second switch and the fourth switch respond to the second clock signal. The amplifier circuit includes a first input terminal, a second input terminal and an output terminal. The first input terminal and the second input terminal are respectively communicated with the third switch and the fourth switch of the switched capacitor circuit, and the second input terminal is also communicated with the second reference voltage signal. The third capacitor communicates with the first input terminal and the output terminal of the amplifier.

In a particular embodiment, the integrated circuit is characterized by a large DC loop gain and a low AC loop gain, causing the DC output voltage at the output terminals to be substantially equal to the second reference voltage, and the AC output voltage to be equal to the impedance of the first feedback circuit And the AC input current through the input terminals is linearly proportional. In an embodiment, the third capacitor is a MOS interlayer capacitor. In an embodiment, the microphone reference voltage source circuit provides a programmable microphone reference voltage source.

In an alternative embodiment, the present invention provides an integrated microphone interface circuit comprising an input terminal for receiving an input signal and an output terminal for providing an output audio signal. The integrated microphone interface circuit includes a first resistor communicated with the input terminal and a first reference circuit coupled to the first resistor. The microphone interface circuit also includes a first amplifier circuit, and the first amplifier circuit includes a first input terminal, a second input terminal and an output terminal. In the first amplifier, the second input terminal receives the input signal, and the output terminal provides the output signal to the output terminal. The microphone interface circuit also includes two feedback circuits. The first feedback circuit communicates with the output terminal of the first amplifier and the first input terminal, and includes a second resistor and a first capacitor connected in parallel. A second feedback circuit is in communication with the output of the first amplifier and the first input, and includes an integrator circuit. In an embodiment, the integrated circuits are provided in a single integrated circuit die. In a particular embodiment, the input terminal is configured to receive an input signal from an electret microphone without the need for an external capacitor. In another embodiment, the microphone reference voltage or current is programmable, and the first resistor and the second resistor are programmable. In certain embodiments, the microphone reference voltage or current is independent of the first feedback circuit and the second feedback circuit.

Numerous benefits over the prior art are achieved by means of the present invention. For example, in certain embodiments, a method for integrating DC bias and AC coupling (AC coupling) in a single integrated circuit die without external components is provided and saves integrated circuit packaging by combining AC and DC signals. technology on the pins. In an embodiment, techniques are provided for reduced DC bias noise and improved power supply rejection to prevent interface circuits from interfering with microphone signals. In an embodiment, circuitry is provided to prevent the microphone reference voltage source from being forced on the amplifier output and to limit the signal swing for large bias voltage requirements so that the signal at the output may not be in the back of the integrated circuit technique that saturates at the input of the stage. In some embodiments, the method provided by the present invention can save the bill of materials (B.O.M.) cost and PCB area in the application. In particular embodiments, techniques to reduce the impact of external noise sources as well as power supply noise are provided. In some embodiments, a method for a differential interface circuit is also provided. In some embodiments, the AC and DC characteristics of the interface circuit are determined by on-chip capacitance and resistance, and circuit layout techniques can be used such that precise matching can be achieved that may yield precise gain and time-constant parameters. These parameters are critical in applications such as beamforming. Additionally, tuning or calibration methods may be employed in accordance with embodiments of the present invention, if desired. In an embodiment, a technique for programmable audio squelch by changing the clock frequency of switched capacitors in the feedback stage is provided. Depending on the embodiment, one or more of these benefits may be achieved. These and other benefits will be described in more detail throughout this specification and more particularly below.

Various additional objects, features, and advantages of the present invention can be more fully understood with reference to the embodiments and the following drawings.

Description of drawings

FIG. 1 is a schematic diagram of a conventional microphone CODEC interface circuit.

Figure 2a is a simplified schematic diagram of an integrated microphone interface circuit according to an embodiment of the present invention.

Fig. 2b is a simplified diagram of a gain transfer function of an integrated microphone interface circuit according to an embodiment of the present invention.

FIG. 3 is a simplified schematic diagram of an integrated microphone interface circuit according to another embodiment of the present invention.

4 is a simplified schematic diagram of an integrated differential microphone interface circuit according to an alternative embodiment of the present invention.

FIG. 5 is a simplified schematic diagram of an integrated microphone interface circuit according to yet another embodiment of the present invention.

6 is a simplified schematic diagram of an integrated microphone interface circuit according to another alternative embodiment of the present invention.

FIG. 7 is a simplified schematic diagram of an integrated microphone interface circuit according to yet another embodiment of the present invention.

8 is a simplified schematic diagram of an integrated microphone interface circuit according to another alternative embodiment of the present invention.

FIG. 9 is a simplified schematic diagram of an integrated microphone interface circuit according to yet another embodiment of the present invention.

10 is a simplified schematic diagram of an integrated microphone interface circuit according to another alternative embodiment of the present invention.

11 is a simplified schematic diagram of an integrated circuit for a programmable microphone interface circuit according to an embodiment of the present invention.

Reference number

100: Microphone interface circuit 102: Electret microphone

112: Resistance 114: Resistance

122: capacitor 132: resistor

134: Resistance 136: Resistance

138: Resistance 142: Capacitance

144: capacitor 146: capacitor

148: capacitor 150: CODEC integrated circuit

200: Integrated microphone interface circuit 202: Input node

204: output node 206: input terminal

207: Input terminal 208: Microphone reference voltage source

211: Integrator circuit 213: Amplifier

215: Amplifier 217: Amplifier

221: Resistance 222: Resistance

223: Resistance 224: Resistance

225: Resistance 231: Capacitance

232: Capacitor 261: Feedback path

262: Feedback path 300: Microphone interface circuit

311: Integrator circuit 315: Amplifier

320: Switched capacitor circuit 330: MOS interlayer capacitor

335: capacitor 400: integrated microphone interface circuit

401: Input node 402: Input node

403: output node 404: output node

407: Microphone reference voltage source 411: Differential feedback circuit

413: Amplifier 415: Amplifier

421: Resistance 422: Resistance

423: Resistance 424: Resistance

425: Resistance 431: Capacitance

432: capacitor 441: input terminal

442: Input terminal 451: Resistor

452: Resistance 453: Resistance

454: Resistance 455: Resistance

457: Ground voltage 461: Feedback path, capacitance

462: Feedback path, capacitor 463: Feedback path

464: Feedback path 500: Integrated microphone interface circuit

502: Node 504: Output node

507: Microphone reference voltage source 511: Integrator circuit

513: Amplifier 515: Amplifier

517: Amplifier 521: Resistor

522: Resistance 524: Resistance

531: capacitance 532: capacitance

541: input terminal 542: input terminal

561: Feedback path 562: Feedback path

600: Microphone interface circuit 611: Integrator circuit

620: Switched capacitor network 630: MOS interlayer capacitor

635: capacitor 700: integrated microphone interface circuit

702: Input terminal 704: Output node

706: input terminal 707: second input terminal

708: Microphone reference voltage source 711: Integrator circuit

713: Amplifier 715: Amplifier

721: Resistance 722: Resistance

725: Resistance 731: Capacitance

732: capacitor 761: feedback path

762: Feedback circuit 800: Microphone interface circuit

811: Integrator circuit 815: Amplifier

820: Switched capacitor circuit 830: MOS interlayer capacitor

835: capacitor 900: integrated microphone interface circuit

902: Input terminal 904: Output node

906: Second input terminal 907: Input terminal

908: Microphone reference voltage source 911: Integrator circuit

913: Amplifier 915: Amplifier

917: amplifier circuit 921: resistor

922: Resistance 924: Resistance

925: Resistance 931: Capacitance

932: capacitor 961: feedback path

962: Feedback path 1000: Microphone interface circuit

1011: Integrator circuit 1015: Amplifier

1020: Switched capacitor circuit 1030: MOS interlayer capacitor

1035: capacitor 1100: microphone interface circuit

1102: Input terminal 1104: Output terminal

1106: first input terminal 1107: second input terminal

1108: Microphone reference voltage source 1111: Integrator circuit

1113: amplifier circuit 1115: amplifier

1120: Switched capacitor circuit 1122: Resistor

1124: Resistance 1125: Resistance

1130: MOS interlayer capacitor 1132: capacitor

1135: Second capacitor 1141: Switching device

1142: switch device 1161: first feedback circuit

1162: Second feedback circuit 1163: Node

S ₁ : Switch S ₂ : Switch

S ₃ : Switch S ₄ : Switch

Detailed ways

The present invention relates to an integrated circuit. More specifically, the present invention provides a method and apparatus for an integrated circuit of a microphone interface. Merely by way of example, the present invention has been applied to an interface circuit for an electret microphone. It should be appreciated, however, that the invention has much broader applicability. For example, the present invention can be applied to interface circuits of other types of microphones or interface circuits of other signal sources.

Depending on the embodiment, the invention includes various features that may be used. Such characteristics include the following:

1. On-chip integration of DC bias and AC coupling without the need for external components.

2. Programmable control for selecting two operating modes;

3. Allows signal calibration and provision of a common mode reference voltage for providing maximum signal swing at the output;

4. Low pin count;

5. Circuit design for reducing the influence of external noise sources and power supply noise;

6. Alternative differential interface circuit design;

7. Better gain and time-constant control provided by matching on-chip components; and

8. Programmable squelch.

FIG. 2a is a simplified schematic diagram of an integrated microphone interface circuit 200 according to an embodiment of the present invention.

As shown, an integrated microphone interface circuit (MIC) 200 includes an input node 202 for receiving an input signal Vin and an output node 204 for transmitting an output signal Vout. The MIC 200 includes a microphone reference voltage source 208 coupled to Vin via a resistor 225 . The MIC 200 also includes a first amplifier 213 having an input 206 coupled to Vin via a resistor 223 and an output coupled at 204 to Vout. The amplifier 213 includes a second input terminal 207 coupled to the common mode reference voltage V _commonmode . According to an embodiment of the present invention, MIC 200 includes a feedback path communicating between an input terminal and an output terminal of amplifier 213 . In the particular example shown in FIG. 2 a , MIC 200 includes two feedback paths 261 and 262 in communication with output 204 and input 206 of amplifier 213 . Feedback path 261 includes a parallel combination of resistor 222 (R2) and capacitor 232 (C2). Feedback path 262 includes amplifier 217 , integrator circuit 211 , and resistor 224 ( R4 ) connected in series between output 204 and input 206 of amplifier 213 . In a particular embodiment, the integrator circuit 211 includes an amplifier 215, a resistor 221 (R1) connected to a first input terminal of the amplifier 215, and a capacitor 231 (C1) connected between the first input terminal and the output terminal of the amplifier 215 . In a specific embodiment, the reference voltage V _commonmode is connected to the second input terminal of the amplifier 215 .

In a preferred embodiment, amplifiers 213, 215, and 217 in MIC 200 may be operational amplifiers. However, other suitable amplifiers may also be used. In certain embodiments of the invention, Vin may be an output signal from the microphone 102 (eg, an electret microphone). For example, Vin can be a sound-band or audio-band signal. In an embodiment, Vout may be coupled to an analog-to-digital converter (ADC) of the CODEC (not shown). In some embodiments, the microphone reference voltage source 208 may be a programmable voltage source. In a particular embodiment, the on-die (programmable) microphone reference voltage source 208 provides DC current to the external microphone via the programmable on-die resistor 225 . In an embodiment, resistors 223 and 225 form a microphone bias circuit in communication with input terminal 202 and microphone reference voltage source 208 . The bias circuit provides the sense input signal to the input 206 of the amplifier 213 . As shown in FIG. 2 a , resistor 225 communicates with input terminal 202 and microphone reference voltage source 208 . Similarly, resistor 223 communicates with input terminal 202 and resistor 225 . In this example, resistor 223 provides the sense input signal to input 206 of amplifier 213 . In a particular embodiment, amplifier 217 has a gain of -1. Of course, there may be other variations, modifications, and substitutions.

According to certain embodiments of the present invention, the gain transfer function of the MIC 200 can be represented by the following equation.

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="s"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">s</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="4"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="C"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}$

Figure 2b is a simplified diagram of a gain transfer function for a microphone interface circuit according to an embodiment of the invention. As shown in the figure, at high frequencies, the gain function can be approximated by the following formula.

$\frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}$

In the sound or audio band frequency range, this AC loop gain of the feedback loop is small, allowing the AC signal to pass through. At lower frequencies, the gain function can be approximated by the following equation.

$\frac{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}$

According to an embodiment of the present invention, MIC 200 is characterized by a DC loop gain large enough to force the common mode output voltage of the gain stage to V _commonmode . For example, in a particular embodiment, MIC 200 may have a DC loop gain of approximately 80 dB to 140 dB.

In an embodiment of the present invention, microphone interface circuit (MIC) 200 provides DC bias and AC coupling in a single integrated circuit chip without the need for external components. In an embodiment, the circuit providing the DC bias is independent of the feedback circuit. In certain embodiments, the desired switching characteristics can be obtained, for example, by selecting appropriate resistors and capacitors. As an example only, resistor 221 (R1) typically has a high resistance in the range of 100 MΩ to 500 MΩ, while resistor 222 (R2), resistor 223 (R3), and resistor 224 (R4) may have a high resistance in the range of 1 kΩ to 500 kΩ. resistance. Capacitor 231 ( C1 ) and capacitor 232 ( C2 ) may have a capacitance in the range of 3 pF to 600 pF. Of course, one of ordinary skill in the art will recognize other variations, modifications, and substitutions.

FIG. 3 is a simplified schematic diagram of an integrated microphone interface circuit according to another embodiment of the present invention. As shown, the microphone interface circuit 300 is similar to the microphone interface circuit 200 discussed above with reference to FIG. 2a. In MIC 300 , integrator circuit 311 is used in place of integrator circuit 211 in MIC 200 . As shown in the figure, the integrator circuit 311 includes an amplifier 315 , a switched capacitor circuit 320 , and a MOS interlayer capacitor 330 . This design results in a substantial reduction in device area. The switched capacitor circuit 320 includes a capacitor 335 and four switches S ₁ , S ₂ , S ₃ and S ₄ . As shown, S ₁ and S ₂ are coupled to the first terminal of the capacitor 335 . S ₃ and S ₄ are coupled to the second terminal of the capacitor 335 . In a specific embodiment, S ₂ and S ₄ are also coupled to the common mode reference voltage V _commonmode . In an embodiment, S ₁ and S ₃ respond to the first clock signal Φ ₁ , while S ₂ and S ₄ respond to the second clock signal Φ ₂ . The amplifier circuit 315 includes a first input terminal, a second input terminal, and an output terminal. The first input terminal communicates with S ₃ , and the second input terminal communicates with S ₂ and S ₄ of the switched capacitor circuit 320 . In the integrator circuit 311, the capacitor 330 communicates with the first input terminal and the output terminal of the amplifier.

Note that in the integrator stage in MIC 200, resistor 221 is often a large resistor (eg, 100MΩ to 500MΩ), which requires a large device area. In MIC 300, this resistance is provided by switched capacitor network 320, which can be implemented in a relatively small device area in an integrated circuit. Also, since this is a sampling system, the feedback capacitor on the gain stage will provide anti-aliasing filtering and the large integrator capacitor will provide smoothing. In an embodiment, the switched capacitor network is controlled by on-chip clock signals _Φ1 and _Φ2 . By changing the clock frequency, the squelch function can also be implemented.

As also shown in FIG. 3 , the MOS interlayer capacitor 330 is used in the MIC 300 to replace the feedback capacitor 231 in the MIC 200 . The feedback capacitor 231 is usually large, for example, 100pF-300pF. According to an embodiment of the present invention, the MOS interlayer capacitance used in the MIC 300 offers the advantage of a smaller device area. Non-linearity is less of an issue with this capacitor because in-band signals are highly attenuated across it.

4 is a simplified schematic diagram of an integrated differential microphone interface circuit according to an alternative embodiment of the present invention.

As shown in the figure, an integrated microphone interface circuit (MIC) 400 includes a differential input node 401 and a differential input node 402 for receiving a differential input signal Vin. The MIC 400 includes a differential output node 403 and a differential output node 404 for providing a differential output signal Vout. In an embodiment, the MIC 400 includes a first microphone bias circuit including a resistor 423 and a resistor 425 . The microphone reference voltage source 407 is coupled to the input node 401 via a resistor 425 . The MIC 400 also includes a second microphone bias circuit, and the second microphone bias circuit includes a resistor 453 and a resistor 455 . Resistor 455 couples input node 402 to ground voltage 457 . In an alternative embodiment, 457 may be another reference voltage. The MIC 400 also includes a first amplifier 413 having an input 441 and an input 442 coupled to 401 and 402 via a resistor 423 and a resistor 453 , respectively. That is, the input terminal 441 and the input terminal 442 of the amplifier 413 respectively receive the sensing input signals provided by the first microphone bias circuit and the second microphone bias circuit. The amplifier 413 includes an input terminal coupled to the common mode reference voltage V _commonmode . According to an embodiment of the present invention, MIC 400 includes a feedback path communicating between an input terminal and an output terminal of amplifier 413 . In the particular example shown in FIG. 4 , MIC 400 includes four feedback paths 461 , 462 , 463 , and 464 in communication with the input and output of amplifier 413 , respectively. For example, the feedback path 461 between the output terminal 404 and the input terminal 442 includes a parallel combination of the resistor 422 and the capacitor 432 . Feedback path 462 between output 404 and input 441 of amplifier 413 includes resistor 424 connected in series with an integrator comprising amplifier 415 , resistor 421 and capacitor 431 . The feedback path 463 between the output terminal 403 and the input terminal 441 includes a parallel combination of the resistor 452 and the capacitor 462 . A feedback path 464 between output 403 and input 442 of amplifier 413 includes resistor 454 connected in series with a second integrator including amplifier 415 , resistor 451 , and capacitor 461 . In a particular embodiment, the common mode reference voltage V _commonmode is connected to the input of the amplifier 415 . Alternative descriptions of MIC 400 may be made in terms of differential signals. For example, feedback path 461 and feedback path 463 provide a differential feedback signal from the output of amplifier 413 to the input of amplifier 413, and feedback path 462 and feedback path 464 provide another differential feedback signal from the output of amplifier 413 is provided to the input of the amplifier 413. As shown in FIG. 4 , feedback path 462 and feedback path 464 form a differential feedback circuit 411 .

In a preferred embodiment, the amplifier 413 and the amplifier 415 in the MIC 400 can be operational amplifiers. However, other suitable amplifiers may also be used. In certain embodiments of the invention, Vin may be an output signal from a microphone (eg, an electret microphone). For example, Vin can be a sound or audio band signal from a microphone. In an embodiment, Vout may be coupled to an analog-to-digital converter (ADC) such as a CODEC. In some embodiments, the microphone reference voltage source 407 may be a programmable voltage source. In a particular embodiment, the on-die (programmable) microphone reference voltage source 407 provides DC current to the external microphone via the (programmable) on-die resistor 425 .

According to an embodiment of the present invention, MIC 400 provides a differential feedback path. Similar to MIC 200, in the sound or audio band frequency range, the AC loop gain of the feedback loop in MIC 400 is small, allowing the AC signal to pass through the input terminal to the output. According to an embodiment of the present invention, MIC 400 is characterized by a DC loop gain large enough to force the common mode output voltage of the gain stage to V _commonmode . For example, in a particular embodiment, MIC 400 may have a DC loop gain of approximately 80 dB to 140 dB. Therefore, according to an embodiment of the present invention, the microphone interface circuit 400 provides DC bias and AC coupling on a single integrated circuit chip without the need for external components. In an embodiment, the circuit providing the DC bias is independent of the feedback circuit.

FIG. 5 is a simplified schematic diagram of a microphone interface circuit according to yet another embodiment of the present invention. As shown, an integrated microphone interface circuit (MIC) 500 includes an input node 502 for receiving an input signal Vin and an output node 504 for transmitting an output signal Vout. The MIC 500 includes a microphone reference voltage source 507 . The MIC 200 also includes a first amplifier 513 having an input 541 and an input 542 and an output coupled to Vout at 504 . The input terminal 542 is coupled to Vin, and the second input terminal 541 is coupled to the microphone reference voltage source 507 . According to an embodiment of the present invention, the MIC includes a feedback circuit between the input and output of the amplifier 513 . In the particular example shown in FIG. 5 , MIC 500 includes two feedback paths in communication with the input and output of amplifier 513 . The feedback path 561 includes a parallel combination of a resistor 522 and a capacitor 532 . Feedback path 562 includes integrator circuit 511 and resistor 524 connected in series between the output and input of amplifier 513 . In a particular embodiment, integrator circuit 511 includes amplifier 517 , amplifier 515 , resistor 521 and capacitor 531 . The resistor 521 is connected to the input terminal of the amplifier 515 , and the capacitor 531 is connected between the input terminal and the output terminal of the amplifier 515 . In a particular embodiment, the reference voltage V _commonmode is connected to the input of the amplifier 515 .

In a preferred embodiment, the amplifier in MIC 500 may be an operational amplifier. However, other suitable amplifiers may also be used. In certain embodiments of the invention, Vin may be an output signal from a microphone (eg, an electret microphone). For example, Vin can be a sound or audio band signal from a microphone. In an embodiment, Vout may be coupled to an analog-to-digital converter (ADC) such as a CODEC. In some embodiments, the microphone reference voltage source 507 may be a programmable voltage source. In an embodiment, amplifier 517 has a gain of -1.

According to an embodiment of the invention, the MIC 500 includes a feedback path 561 and a feedback path 562 that perform functions similar to the feedback path in the MIC 200 described above with reference to FIG. 2a. In the MIC 500, in the sound or audio band frequency range, the AC loop gain of the feedback loop is small, allowing the AC signal to pass through the input terminal to the output. According to an embodiment of the invention, the MIC 500 is characterized by a DC loop gain large enough to force the output voltage to the common mode voltage. For example, in certain embodiments, MIC 500 may have a DC loop gain of approximately 80 dB to 140 dB. Therefore, according to an embodiment of the present invention, the microphone interface circuit 500 provides DC bias and AC coupling in a single integrated circuit chip without the need for external components. In an embodiment, the circuit providing the DC bias is independent of the feedback circuit.

6 is a simplified schematic diagram of an integrated microphone interface circuit according to another alternative embodiment of the present invention. As shown, the microphone interface circuit 600 is similar to the microphone interface circuit 500 discussed with reference to FIG. 5 . Note that MIC 600 includes integrator circuit 611 in place of integrator circuit 511 in MIC 500. As shown, the integrator circuit 611 includes a switched capacitor network 620 and a MOS interlayer capacitor 630 . The general operation of integrator circuit 611 can be understood with reference to the discussion above with respect to MIC 500 and FIG. 5 . However, compared to the MIC 500, the MIC 600 has the advantage of providing a smaller device area, which can be provided by, for example, switched capacitor networks as well as MOS interlayer capacitors.

FIG. 7 is a simplified schematic diagram of a microphone interface circuit according to yet another embodiment of the present invention. As shown, an integrated microphone interface circuit (MIC) 700 includes an input terminal 702 for receiving an input signal Vin and an output node 704 for providing an output signal Vout. The MIC 700 includes a microphone reference voltage source 708 coupled to Vin via a resistor 725 ( R3 ). Depending on the embodiment, the microphone reference voltage source 708 may provide a reference voltage or a reference current. The MIC 700 also includes a first amplifier 713 having an input 706 coupled to Vin to receive a current Iin and an output coupled to the output terminal 704 . Amplifier 713 includes a second input 707 that receives a feedback signal from feedback circuit 762 as discussed below. According to an embodiment of the present invention, MIC 700 includes a feedback circuit in communication with the input and output of amplifier 713 . In the particular example shown in FIG. 7 , MIC 700 includes two feedback paths 761 and 762 in communication with output 704 and input 706 and input 707 of amplifier 713 , respectively. Feedback path 761 includes a parallel combination of resistor 722 (R2) and capacitor 732 (C2). Feedback path 762 includes integrator circuit 711 connected between output 704 and input 707 of amplifier 713 . In a particular embodiment, the integrator circuit 711 includes an amplifier 715 , a resistor 721 ( R1 ) connected to the input of the amplifier 715 , and a capacitor 731 ( C1 ) connected between the input and output of the amplifier 715 . In an embodiment, the resistor 722 and the resistor 725 are programmable resistors. In a specific embodiment, the reference voltage V _commonmode is connected to the second input terminal of the amplifier 715 .

In a preferred embodiment, the amplifier in MIC 700 may be an operational amplifier. However, other suitable amplifiers may also be used. In certain embodiments of the invention, the signal Vin at the input terminal 702 may be an output signal from a microphone (eg, an electret microphone). For example, other types of microphones may also be used. Depending on the application, Vin can be a sound band signal or an audio band signal. In an embodiment, the output signal Vout may be an audio band signal coupled to an analog-to-digital converter (ADC) of the CODEC. In some embodiments, the microphone reference voltage source 708 may be a programmable voltage source. In a particular embodiment, the on-chip programmable reference 708 provides DC current to the external microphone via the on-chip resistor 725 . In an embodiment, resistor 725 is a programmable resistor. Thus, in an embodiment, the present invention provides an on-die microphone bias circuit including resistor 725 and microphone reference voltage source 708 .

According to an embodiment of the present invention, the gain conversion function of the MIC 700 can be expressed by the following formula.

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="s"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">s</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}$

At high frequencies, the gain transfer function of MIC 700 can be approximated by the following formula.

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}$

At lower frequencies, the gain function can be approximated by the following equation.

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&ap;</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}$

According to an embodiment of the invention, the AC loop gain of the feedback loop is small and the DC loop gain is large in the sound or audio band frequency range. For example, in certain embodiments, MIC 700 may have a DC loop gain of approximately 80 dB to 140 dB. More specifically, the MIC 700 is characterized by a large DC loop gain as well as a low AC loop gain, causing the DC output voltage at the output terminals to be substantially equal to the second reference voltage, and the AC output voltage to be consistent with the impedance of the first feedback circuit and AC input current or voltage across the input terminals is linearly proportional.

In an embodiment of the present invention, microphone interface circuit (MIC) 700 provides DC bias and AC coupling in a single integrated circuit chip without the need for external components. In an embodiment, the circuit providing the DC bias is independent of the feedback circuit. In certain embodiments, desired conversion characteristics (such as microphone bias voltage, high DC loop gain, and low AC loop gain) can be obtained by selecting appropriate resistors and capacitors. As an example only, resistor 721 ( R1 ) typically has a high resistance in the range of 100 MΩ to 500 MΩ, while resistor 722 ( R2 ) and resistor 723 ( R3 ) may have resistance in the range of 1 kΩ to 500 kΩ. Capacitor 731 ( C1 ) and capacitor 732 ( C2 ) may have a capacitance in the range of 3 pF to 500 pF.

FIG. 8 is a simplified schematic diagram of an integrated microphone interface circuit according to another embodiment of the present invention. As shown, microphone interface circuit (MIC) 800 is generally similar to microphone interface circuit 700 discussed above with reference to FIG. 7 . In FIG. 8 , MIC 800 includes integrator circuit 811 instead of integrator circuit 711 in MIC 700 . As shown, the integrator circuit 811 includes an amplifier 815 , a switched capacitor network 820 and a MOS interlayer capacitor 830 . This design results in a substantial reduction in device area. The switched capacitor circuit 820 includes a capacitor 835 and four switches S ₁ , S ₂ , S ₃ and S ₄ . As shown, S ₁ and S ₂ are coupled to the first terminal of the capacitor 835 . S ₃ and S ₄ are coupled to the second terminal of the capacitor 835 . In a specific embodiment, S ₂ and S ₄ are also coupled to the common mode reference voltage V _commonmode . In an embodiment, S ₁ and S ₃ respond to the first programmable clock signal Φ ₁ , while S ₂ and S ₄ respond to the second programmable clock signal Φ ₂ . The amplifier circuit 815 includes a first input terminal, a second input terminal and an output terminal. The first input terminal communicates with S ₃ , and the second input terminal communicates with S ₂ and S ₄ of the switched capacitor circuit 820 . In the integrator circuit 811, the capacitor 830 communicates with the first input terminal and the output terminal of the amplifier.

According to an embodiment of the present invention, the gain conversion function of the MIC 800 can be expressed by the following formula.

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&ap;</span>\frac{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 835</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="s"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">s</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 835</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; .</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 835</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}$

In embodiments of the present invention, the operation of microphone interface circuit MIC 800 is generally similar to the operation of MIC 700. For example, the feedback circuit in the MIC 800 provides high DC loop gain and low AC loop gain. The MIC 800 provides DC bias and AC coupling on-chip without the need for external components. In addition, the MIC 800 has the advantage of providing a smaller device area compared to the MIC 700.

As discussed above, in the integrator stage in MIC 700, resistor 721 is often a large resistor (eg, 100 MΩ to 500 MΩ), which requires a large device area. In MIC 800, this resistance is provided by switched capacitor network 820, which can be implemented using a smaller device area than a large resistor. Also, since this is a sampling system, the feedback capacitor on the gain stage will provide anti-aliasing filtering and the large integrator capacitor will provide smoothing. In an embodiment, the switched capacitor network is controlled by on-chip clock signals _Φ1 and _Φ2 . By changing the clock frequency, the squelch function can also be implemented.

As also shown in FIG. 8, a MOS interlayer capacitor 830 is used in the MIC 800 to replace the feedback capacitor 731 in the MIC 700 in FIG. 7. The feedback capacitor 731 is usually large, eg, 100pF-300pF. According to an embodiment of the present invention, the MOS interlayer capacitance used in the MIC 800 provides the desired capacitance with a smaller device area.

In embodiments of the present invention, the operation of microphone interface circuit MIC 800 is generally similar to the operation of MIC 700. For example, the feedback circuit in the MIC 800 provides high DC loop gain and low AC loop gain. The MIC 800 provides DC bias and AC coupling in a single integrated circuit chip without the need for external components. In an embodiment, the circuit providing the DC bias is independent of the feedback circuit. In addition, the MIC 800 has the advantage of providing a smaller device area compared to the MIC 700.

FIG. 9 is a simplified schematic diagram of an integrated microphone interface circuit according to yet another embodiment of the present invention. As shown, an integrated microphone interface circuit (MIC) 900 includes an input terminal 902 for receiving an input signal Vin and an output node 904 for providing an output signal Vout. MIC 900 also includes microphone reference 908 coupled to Vin via resistor 925 (R3). Depending on the embodiment, microphone reference 908 may provide a reference voltage or a reference current. The MIC 900 also includes a first amplifier 913 having an input 907 coupled to Vin and an output coupled to the output terminal 904 . Amplifier 913 includes a second input 906 that receives a feedback signal from a feedback circuit as discussed below. According to an embodiment of the present invention, MIC 900 includes a feedback circuit in communication between an input terminal and an output terminal of amplifier 913 . In the particular example shown in FIG. 9 , MIC 900 includes two feedback paths 961 and 962 in communication with output 904 and inputs 906 and 907 of amplifier 913 . Feedback path 961 includes a parallel combination of resistor 922 (R2) and capacitor 932 (C2). Feedback path 962 includes amplifier circuit 917 , integrator circuit 911 , and resistor 924 ( R4 ) connected in series between output 904 and input 906 of amplifier 913 . In a particular embodiment, the integrator circuit 911 includes an amplifier 915 , a resistor 921 ( R1 ) connected to the input of the amplifier 915 , and a capacitor 931 ( C1 ) connected between the input and output of the amplifier 915 . In an embodiment, the resistor 922 and the resistor 925 are programmable resistors. In a specific embodiment, the reference voltage V _commonmode is connected to the second input terminal of the amplifier 915 .

In a preferred embodiment, the amplifier in MIC 900 may be an operational amplifier. However, other suitable amplifiers may also be used. In an embodiment, amplifier circuit 917 has a gain of -1. In certain embodiments of the invention, input terminal 902 may receive Vin as an output signal from a microphone (eg, an electret microphone). Depending on the embodiment, other types of microphones may also be used. Depending on the application, Vin can be a sound band signal or an audio band signal. In an embodiment, the output signal Vout may be an audio band signal coupled to an analog-to-digital converter (ADC) of the CODEC. In some embodiments, microphone reference 908 may be a programmable voltage source. In a particular embodiment, on-die programmable microphone reference 908 provides DC current to an external microphone via on-die resistor 925 . In an embodiment, resistor 925 is a programmable resistor. Thus, in an embodiment, the present invention provides an on-die microphone bias circuit including resistor 925 and microphone reference voltage source 908 .

According to an embodiment of the present invention, the gain conversion function of the MIC 900 can be expressed by the following formula.

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Vout</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; Vin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="4"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="C"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="s"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">s</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="4"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="C"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}$

According to an embodiment of the present invention, at a high frequency, the gain conversion function of the MIC 900 can be approximated by the following formula.

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}$

At lower frequencies, the gain function can be approximated by the following formula.

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="4"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}$

以及输入端子处的AC输入电压成线性比例。According to an embodiment of the invention, the AC loop gain of the feedback loop is small and the DC loop gain is large in the sound or audio band frequency range. For example, in a particular embodiment, MIC 900 may have a DC loop gain of approximately 80 dB to 140 dB. More specifically, the MIC 900 is characterized by a large DC loop gain as well as a low AC loop gain, causing the DC output voltage at the output terminals to be substantially equal to the second reference voltage, and the AC output voltage in the audio frequency band to be equal to

and linearly proportional to the AC input voltage at the input terminals.

In an embodiment of the present invention, microphone interface circuit (MIC) 900 provides DC bias and AC coupling in a single integrated circuit chip without the need for external components. In an embodiment, the circuit providing the DC bias is independent of the feedback circuit. In certain embodiments, the desired switching characteristics can be achieved by selecting appropriate resistors and capacitors. As an example only, resistor ( R1 ) typically has a high resistance in the range of 100 MΩ to 500 MΩ, while resistor 922 ( R2 ), resistor 923 ( R3 ), and resistor 924 ( R4 ) may have resistance in the range of 1 kΩ to 500 kΩ. Capacitor 931 ( C1 ) and capacitor 932 ( C2 ) may have a capacitance in the range of 3 pF to 500 pF. Of course, one of ordinary skill in the art will recognize other variations, modifications, and substitutions.

FIG. 10 is a simplified schematic diagram of an integrated microphone interface circuit according to another embodiment of the present invention. As shown, microphone interface circuit (MIC) 1000 is generally similar to microphone interface circuit 900 discussed above with reference to FIG. 9 . In FIG. 10 , MIC 1000 includes integrator circuit 1011 instead of integrator circuit 911 in MIC 900 . As shown in the figure, the integrator circuit 1011 includes an amplifier 1015 , a switched capacitor circuit 1020 and a MOS interlayer capacitor 1030 . This design results in a substantial reduction in device area. The switched capacitor circuit 1020 includes a capacitor 1035 and four switches S ₁ , S ₂ , S ₃ and S ₄ . As shown, S ₁ and S ₂ are coupled to the first terminal of the capacitor 1035 . S ₃ and S ₄ are coupled to the second terminal of the capacitor 1035 (C ₁₀₃₅ ). In a specific embodiment, S ₂ and S ₄ are also coupled to the common mode reference voltage V _commonmode . In an embodiment, S ₁ and S ₄ respond to the first programmable clock signal Φ ₁ , while S ₂ and S ₃ respond to the second programmable clock signal Φ ₂ . The amplifier circuit 1015 includes a first input terminal, a second input terminal, and an output terminal. The first input terminal communicates with S ₃ , and the second input terminal communicates with S ₂ and S ₄ of the switched capacitor circuit 1020 . In the integrator circuit 1011 , the capacitor 1030 communicates with the first input terminal and the output terminal of the amplifier 1015 .

According to an embodiment of the present invention, the gain transfer function of the MIC 1000 can be expressed by the following formula.

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&ap;</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1035</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="4"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="C"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="s"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">s</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1035</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="4"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="C"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1035</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="S2008101101108E00021.png,S2008101101108E00061.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2008101101108E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}$

In embodiments of the present invention, the operation of microphone interface circuit MIC 1000 is generally similar to the operation of MIC 900. For example, the feedback circuit in the MIC 1000 provides high DC loop gain and low AC loop gain. The MIC 1000 provides DC bias and AC coupling in a single integrated circuit chip without the need for external components. In an embodiment, the circuit providing the DC bias is independent of the feedback circuit. In addition, the MIC 1000 has the advantage of providing a smaller device area compared to the MIC 900.

As discussed above, in the integrator stage in MIC 900, resistor 921 is often a large resistor (eg, 100 MΩ to 500 MΩ), which requires a large device area. In MIC 1000, this resistance is provided by switched capacitor network 1020, which can be implemented using a smaller device area than a large resistor. Also, since this is a sampling system, the feedback capacitor on the gain stage will provide anti-aliasing filtering and the large integrator capacitor will provide smoothing. The switched capacitor network is controlled by on-chip clock signals Φ ₁ and Φ ₂ . By changing the clock frequency, the squelch function can also be implemented.

As also shown in FIG. 10 , MIC 1000 includes MOS interlayer capacitor 1030 in place of feedback capacitor 931 in MIC 900 in FIG. 9 . The feedback capacitor 931 is usually large, eg, 100pF-300pF. According to an embodiment of the present invention, the MOS interlayer capacitor used in the MIC 1000 provides the desired capacitance but requires a smaller device area.

11 is a simplified schematic diagram of an integrated circuit for a programmable microphone interface according to an embodiment of the present invention. As shown, MIC 1100 is an integrated circuit for providing a programmable microphone interface. The MIC 1100 includes an input terminal 1102 for receiving an input signal Vin and an output terminal 1104 for providing an output audio signal Vout. MIC 1100 also includes a bias circuit in communication with input terminal 1102. As shown, the bias circuit includes a microphone reference voltage source 1108 and a resistor 1125 . In an embodiment, 1108 is a programmable reference circuit. Depending on the embodiment, the microphone reference voltage source 1108 may provide a reference voltage or a reference current. The MIC 1100 includes a first amplifier circuit 1113 that includes a first input 1106, a second input 1107, and an output coupled to an output terminal 1104. The MIC 1100 further includes a first feedback path 1161 , and the first feedback path 1161 includes a resistor 1122 and a capacitor 1132 connected in parallel. The first feedback circuit is coupled to the output end of the amplifier 1113 and the first input end. The MIC 1100 also includes a second feedback path 1162 including an integrator circuit 1111 and a resistor 1124. The second feedback path 1162 provides a feedback signal at node 1163 . In an embodiment, the resistor 1122 and the resistor 1125 are programmable resistors.

As shown in the figure, the integrator circuit 1111 includes an amplifier 1115 , a switched capacitor circuit 1120 , and a MOS interlayer capacitor 1130 . The structure and function of the integrator circuit 1111 are generally similar to those of the integrating circuit 1011 in FIG. 10 and the integrating circuit 811 in FIG. 8 . The switched capacitor circuit 1120 and the MOS interlayer capacitor 1130 provide the desired resistance and capacitance while consuming a relatively small device area.

The feedback circuit in the MIC 1100 provides high DC loop gain as well as low AC loop gain. More particularly, the MIC 1100 is characterized by a large DC loop gain as well as a low AC loop gain, causing the DC output voltage at the output terminals to be substantially equal to the second reference voltage, and the AC output voltage to be consistent with the impedance of the first feedback circuit and AC input current or voltage across the input terminals is linearly proportional. According to an embodiment of the present invention, the MIC 1100 is capable of providing DC bias and AC coupling in a single integrated circuit die without the need for external components. In an embodiment, the circuit providing the DC bias is independent of the feedback circuit.

As described above by way of example only, the present invention has been applied to an interface circuit for an electret microphone. It should be appreciated, however, that the invention has much broader applicability. For example, the present invention can be applied to interface circuits of other types of microphones or interface circuits of other signal sources.

Although selected groups of components of the microphone interface circuit have been set forth above, many alternatives, modifications and variations are possible. For example, some components may be extended and/or combined. Other components may be inserted to the above-mentioned components. Depending on the embodiment, configurations of components may be swapped with other configurations instead. Additional details of these components can be found throughout this specification.

It should also be understood that the examples and embodiments described herein are for illustrative purposes only, and that various modifications or changes based on the examples and embodiments will be proposed to those skilled in the art, and that the various modifications or changes It shall be included in the spirit and scope of this specification and the category of a claim.

Claims (23)

1. An integrated circuit for providing a microphone interface, characterized in that the integrated circuit comprises: an input terminal for receiving an input signal; an output terminal for providing an output signal; a bias circuit coupled to the input terminal to provide a bias signal at the input terminal, the bias circuit configured to provide a sense input signal; A first amplifier circuit comprising a first input terminal, a second input terminal and an output terminal, the first input terminal configured to receive the sensing input signal, the first feedback signal and the second feedback signal, the second an input configured to receive a first reference signal, the output configured to provide the output signal to the output terminal; A first feedback circuit in communication with the output terminal of the first amplifier circuit and the first input terminal, the first feedback circuit providing the first feedback signal to the first amplifier circuit of the a first input terminal; and a second feedback circuit in communication with the output terminal of the first amplifier circuit and the first input terminal, the second feedback circuit providing the second feedback signal to the At the first input, the second feedback circuit includes an integrator circuit. 2. The integrated circuit for providing a microphone interface as claimed in claim 1, wherein the input terminal is configured to receive an input signal from an electret microphone without external components. 3. The integrated circuit for providing a microphone interface as claimed in claim 1, wherein the bias circuit comprises: a reference circuit, configured to provide a second reference signal, the second reference signal comprising a reference voltage or a reference current; a first input resistor in communication with the input terminal and the reference circuit; and A second input terminal resistor communicates with the input terminal and the second input terminal of the first amplifier circuit. 4. The integrated circuit for providing a microphone interface as claimed in claim 1, wherein the first feedback circuit comprises a first feedback resistor and a first feedback capacitor in parallel configuration. 5. The integrated circuit for providing a microphone interface as claimed in claim 1, wherein the integrator circuit comprises: an inverting amplifier coupled to the output terminal of the first amplifier circuit; a second amplifier circuit, the second amplifier circuit includes a first input terminal, a second input terminal and an output terminal, the second input terminal is coupled to a third reference signal; a second feedback resistor coupled to the output of the inverting amplifier and the first input of the second amplifier circuit; and a second feedback capacitor coupled to the first input terminal and the output terminal of the second amplifier circuit; Wherein the output terminal of the second amplifier circuit is coupled to the second input terminal of the first amplifier circuit via a third feedback resistor. 6. The integrated circuit for providing a microphone interface as claimed in claim 1, wherein the integrator circuit comprises: A switched capacitor circuit, comprising a switched capacitor and a first switch, a second switch, a third switch, and a fourth switch, the first switch and the second switch are coupled to the first terminal of the switched capacitor, the The third switch and the fourth switch are coupled to the second terminal of the switched capacitor, the second switch and the fourth switch are coupled to the first reference signal; The second amplifier circuit includes a first input terminal, a second input terminal and an output terminal, the first input terminal communicates with the third switch of the switched capacitor circuit, and the second input terminal is coupled to the the first reference signal; and The second feedback capacitor communicates with the first input terminal and the output terminal of the second amplifier circuit. 7. The integrated circuit for providing a microphone interface as claimed in claim 1 , further comprising a supply voltage, wherein said first reference signal is approximately half of said supply voltage in magnitude for providing said output The maximum signal swing allowed at the terminals by the supply voltage. 8. The integrated circuit for providing a microphone interface according to claim 1 , characterized in that the integrated circuit for providing a microphone interface is characterized by a DC loop gain in the range of about 80 dB to about 140 dB, wherein The DC loop gain is sufficiently large to cause a voltage at the output of the first amplifier to be substantially equal to the first reference signal. 9. The integrated circuit for providing a microphone interface according to claim 1, characterized in that said integrated circuit is characterized by a large DC loop gain and a low AC loop gain, resulting in a DC output at said output terminal The voltage is substantially equal to the first reference signal, and the AC output voltage is linearly proportional to the impedance of the first feedback circuit and the AC input current or voltage through the input terminal. 10. An integrated circuit for providing a microphone interface, characterized in that, the integrated circuit for providing a microphone interface comprises: The first input terminal and the second input terminal are respectively used to receive the first differential input signal and the second differential input signal; The first output terminal and the second output terminal are respectively used to provide a first differential output signal and a second differential output signal; a first bias circuit, communicated with the first input terminal and a first reference signal, the first bias circuit provides a first sensing input signal; a second bias circuit, communicated with the second input terminal and a second reference signal, the second bias circuit provides a second sensing input signal; A first amplifier circuit, the first amplifier has a first input terminal, a second input terminal and a third input terminal, the first input terminal receives the first sensing input signal, and the second input terminal receives the first input terminal Two sensing input signals, the third input terminal receives a common mode reference signal, the first amplifier circuit also has a first output terminal and a second output terminal, and the first output terminal and the second output terminal are respectively providing the first differential output signal and the second differential output signal to the first output terminal and the second output terminal; and A feedback circuit in communication with the first and second input terminals and the first and second output terminals of the first amplifier circuit. 11. The integrated circuit for providing a microphone interface as claimed in claim 10, wherein the first input terminal and the second input terminal are configured to be connected from an electret without external components. The microphone receives the input signal. 12. The integrated circuit for providing a microphone interface as claimed in claim 10, wherein the first bias circuit comprises: a third resistor in communication with the first input terminal and a microphone reference signal source; and A fourth resistor communicates with the first input terminal and the third resistor, and the fourth resistor provides the first sensing input signal. 13. The integrated circuit for providing a microphone interface as claimed in claim 10, wherein the second bias circuit comprises: a fifth resistor in communication with the second input terminal and a ground reference voltage source; and The sixth resistor communicates with the second input terminal and the fifth resistor, and the sixth resistor provides the second sensing input signal. 14. The integrated circuit for providing a microphone interface as claimed in claim 10, wherein the feedback circuit further comprises: a first feedback circuit communicating with the first output terminal and the first input terminal of the first amplifier, the first feedback circuit comprising a first resistor and a first capacitor connected in parallel; a second feedback circuit in communication with the second output terminal and the second input terminal of the first amplifier, the second feedback circuit comprising a second resistor and a second capacitor connected in parallel; and a differential feedback circuit, the differential feedback circuit includes a first input terminal and a second input terminal respectively coupled to the first output terminal and the second output terminal of the first amplifier circuit, the differential The feedback circuit also includes a first output terminal and a second output terminal respectively coupled to the first input terminal and the second input terminal of the first amplifier circuit. 15. The integrated circuit for providing a microphone interface as claimed in claim 14, wherein the differential feedback circuit further comprises: a differential amplifier having a first input terminal, a second input terminal, and a third input terminal, and a first output terminal and a second output terminal, the third input terminal receiving the common mode reference signal; a first resistor connected to the first input terminal of the differential amplifier; a second resistor connected to the first output terminal of the differential amplifier; a first capacitor connected to the first input terminal and the first output terminal of the differential amplifier; a third resistor connected to the second input terminal of the differential amplifier; a fourth resistor connected to the second output terminal of the differential amplifier; and The second capacitor is connected to the second input end and the second output end of the differential amplifier. 16. An integrated circuit for providing a microphone interface, characterized in that the integrated circuit for providing a microphone interface comprises: an input terminal for receiving an input signal; an output terminal for providing an output signal; a bias circuit for providing a bias signal; The first amplifier circuit includes a first input terminal, a second input terminal and an output terminal, the first input terminal is configured to receive the bias voltage signal, the first feedback signal and the second feedback signal, the second input terminal a terminal configured to receive a first reference signal, the output terminal configured to provide the output signal to the output terminal; A first feedback circuit, the first feedback circuit communicates with the output terminal of the first amplifier circuit and the first input terminal, the first feedback circuit provides the first feedback signal to the first feedback circuit said first input of an amplifier circuit; and A second feedback circuit, the second feedback circuit communicates with the output terminal of the first amplifier circuit and the first input terminal, the second feedback circuit provides the second feedback signal to the first amplifier circuit On said first input of an amplifier circuit, said second feedback circuit includes an integrator circuit. 17. The integrated circuit for providing a microphone interface of claim 16, wherein the input terminal is configured to receive an input signal from an electret microphone without external components. 18. The integrated circuit for providing a microphone interface as claimed in claim 16, wherein the bias circuit comprises: a reference circuit, configured to provide a second reference signal, where the second reference signal is a reference voltage or a reference current; a first input resistor in communication with the input terminal and the reference circuit; and A second input terminal resistor communicates with the input terminal and the second input terminal of the first amplifier circuit. 19. The integrated circuit for providing a microphone interface as claimed in claim 16, wherein the first feedback circuit comprises a first feedback resistor and a first feedback capacitor in a parallel configuration. 20. The integrated circuit for providing a microphone interface as claimed in claim 16, wherein said integrator circuit comprises: an inverting amplifier coupled to the output terminal of the first amplifier circuit; The second amplifier circuit includes a first input terminal, a second input terminal and an output terminal, the second input terminal is coupled to a third reference signal; a second feedback resistor coupled to the output of the inverting amplifier and the first input of the second amplifier circuit; and a second feedback capacitor coupled to the first input terminal and the output terminal of the second amplifier circuit; Wherein the output terminal of the second amplifier circuit is coupled to the second input terminal of the first amplifier circuit via a third feedback resistor. 21. The integrated circuit for providing a microphone interface as claimed in claim 16, wherein said integrator circuit comprises: A switched capacitor circuit, comprising a switched capacitor and a first switch, a second switch, a third switch, and a fourth switch, the first switch and the second switch are coupled to the first terminal of the switched capacitor, the The third switch and the fourth switch are coupled to the second terminal of the switched capacitor, the second switch and the fourth switch are coupled to the first reference signal; A second amplifier circuit, the second amplifier circuit includes a first input terminal, a second input terminal and an output terminal, the first input terminal communicates with the third switch of the switched capacitor circuit, and the second an input coupled to the first reference signal; and The second feedback capacitor communicates with the first input terminal and the output terminal of the second amplifier circuit. 22. The integrated circuit for providing a microphone interface as recited in claim 16, wherein the integrated circuit for providing a microphone interface is characterized by a DC loop gain in the range of about 80 dB to about 140 dB, wherein The DC loop gain is sufficiently large to cause a voltage at the output of the first amplifier to be substantially equal to the first reference signal. 23. An integrated circuit for providing a microphone interface as claimed in claim 16, characterized in that said integrated circuit is characterized by a large DC loop gain and a low AC loop gain, resulting in a DC output at said output terminal The voltage is substantially equal to the first reference signal, and the AC output voltage is linearly proportional to the impedance of the first feedback circuit and the AC input current or voltage through the input terminal.

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