CN101958715B - Audio digital-to-analog converter - Google Patents

Abstract

The invention provides an audio digital-to-analog converter, which comprises an operational amplifier, a first resistor-capacitor circuit, a second resistor-capacitor circuit and a current mirror circuit. The operational amplifier outputs an output voltage to the output terminal according to the first input signal and the second input signal of the first input terminal and the second input terminal. The first resistor-capacitor circuit is coupled between the first input end and the output end of the operational amplifier, and the second resistor-capacitor circuit is coupled between the second input end of the operational amplifier and a common mode voltage. The first current mirror path of the current mirror circuit is coupled to the second input terminal of the operational amplifier, and the second current mirror path thereof is coupled to the first input terminal of the operational amplifier.

Description

Audio Digital to Analog Converter

technical field

The present invention relates to an audio digital-to-analog converter (Audio DAC), especially an audio digital-to-analog converter that improves the input range of its internal operational amplifier and improves performance by adding a current mirror circuit.

Background technique

Digital-to-analog Converter (DAC) is an indispensable circuit component in today's communication systems, and there are quite a few types. Generally speaking, the current-controlled digital-to-analog converter (Current-Steering Digital- to-analog Converter) is a relatively common and high-speed digital-to-analog converter. Its basic concept is to use a current source to switch the required current to the output terminal through switch control. However, with the development of semiconductor technology, the supply voltage (Vdd) keeps decreasing, which causes the voltage working range of the transistor to become narrower and narrower, thus causing the transistor to operate in an incorrect working region.

In order to solve the problems that the input range of the operational amplifier is insufficient when the input amplitude of the operational amplifier is too large, and the working range of the transistor in the front circuit is insufficient when the transistor in the front circuit operates in the saturation region, many scholars have proposed some methods. . For example, Kim Fai Wong, Ka IanLei, Seng-Pan U, and R.P. Martins et al proposed a solution disclosed in the following references:

[1]Kim Fai Wong, Ka Ian Lei, Seng-Pan U and R.P.Martins, "1-V 90dB DRAudio Stereo DAC with Embedding Headphone Driver" in Proc.of IEEE AsiaPacific Conference on Circuit and Systems(APCCAS),pp.1160 -1163, Dec. 2008.

In reference [1], they added two resistor elements before the two input terminals of the operational amplifier to reduce the input amplitude of the operational amplifier. Please refer to FIG. 1 , which is a schematic diagram of an audio DAC 100 in the prior art. The audio DAC 100 includes an operational amplifier 110 , a first resistor-capacitor circuit 120 , a second resistor-capacitor circuit 130 and two resistor elements R2 . The operational amplifier 110 has a first input terminal 111, a second input terminal 112 and an output terminal 113, which is based on a first input signal S _IN1 of the first input terminal 111 and a second input of the second input terminal 112 Signal S _IN2 to output an output voltage V _OUT . The first resistor-capacitor circuit 120 and the second resistor-capacitor circuit 130 each include a resistor R1 and a capacitor C connected in parallel, wherein the first resistor-capacitor circuit 120 is coupled to the first input terminal 111 and the output of the operational amplifier 110 The second resistor-capacitor circuit 130 is coupled between the second input terminal 112 of the operational amplifier 110 and a common mode voltage terminal V _CM .

Please note that when the audio digital-to-analog converter 100 is used for low-frequency operation, by adding two resistor elements R2 before the first input terminal 111 and the second input terminal 112 of the operational amplifier 110, the input amplitude of the operational amplifier 110 can be determined by It is represented by the following formula:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; IN</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="H2009101500901E00011.png,H2009101500901E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="H2009101500901E00011.png,H2009101500901E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="H2009101500901E00011.png,H2009101500901E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

由此可知，将两电阻元件R2分别加入运算放大器110的第一输入端111与第二输入端112之前，可缩小运算放大器110的输入振幅 $V_{\mathrm{IN}}(\frac{1}{2}(I\&times;R1)<I\&times;R1)).$ Wherein, V _IN represents the input amplitude of the operational amplifier 110 , and I represents the current flowing through the first input terminal 111 (or the second input terminal 112 ). When the resistance values of R2 and R1 are the same, the input amplitude V _IN of the operational amplifier 110 is equal to

It can be seen from this that the input amplitude of the operational amplifier 110 can be reduced by adding the two resistance elements R2 before the first input terminal 111 and the second input terminal 112 of the operational amplifier 110 respectively. $V_{\mathrm{IN}}(\frac{1}{2}(I\&times;R1)<I\&times;R1)).$

Please refer to FIG. 2 . FIG. 2 is a schematic diagram of an audio digital-to-analog converter 200 with switching current architecture in the prior art. The architecture of the audio DAC 200 shown in FIG. 2 is similar to the audio DAC 100 shown in FIG. 1 , the difference between the two is that the audio DAC 200 further includes a current source circuit 220 and a bias voltage circuit 240. As shown in FIG. 2 , the current source circuit 220 has a switching current architecture, which includes a plurality of switching current sources 230 , a plurality of first switches SW1 , a plurality of second switches SW2 and two transistors M1 , M2 . Multiple switching current sources 230 and two transistors M1, M2 are used to provide multiple sets of switching currents, and the bias circuit 240 (including at least one bias transistor M _Bias ) is used to provide a bias voltage V _Bias to the current source circuit 220 Transistors M1, M2. Each first switch SW1 is coupled between the corresponding switching current source 230 and the first input terminal 111 of the operational amplifier 110 for controlling whether the corresponding switching current source 230 is allowed to be electrically connected to the first input terminal of the operational amplifier 110 111; and each second switch SW2 is coupled between the corresponding switching current source 230 and the second input terminal 112 of the operational amplifier 110, and is used to control whether to allow the corresponding switching current source 230 to be electrically connected to the second input terminal 110 of the operational amplifier 110. Two input terminals 112 .

Although the aforementioned audio digital-to-analog converters 100 and 200 can solve the problems of insufficient input range of the operational amplifier and insufficient working range when the transistors of the front circuit operate in the saturation region under low-frequency operation, they will greatly reduce the performance of the operational amplifier. Like adding output noise.

Contents of the invention

One object of the present invention is to provide an audio digital-to-analog converter to solve the problems in the prior art.

The embodiment of the invention discloses an audio digital-to-analog converter. The audio digital-to-analog converter includes an operational amplifier, a first resistor-capacitor circuit, a second resistor-capacitor circuit and a current mirror circuit. The operational amplifier has a first input terminal, a second input terminal and an output terminal, and is used to output an output voltage according to a first input signal of the first input terminal and a second input signal of the second input terminal . A first resistor-capacitor circuit is coupled between the first input terminal and the output terminal of the operational amplifier, and a resistor and a capacitor in the first resistor-capacitor circuit are connected in parallel. A second resistor-capacitor circuit is coupled between the second input terminal of the operational amplifier and a common-mode voltage, and a resistor and a capacitor in the second resistor-capacitor circuit are connected in parallel. The current mirror circuit includes a first current mirror path and a second current mirror path, the first current mirror path is coupled to the second input terminal of the operational amplifier, and the second current mirror path is coupled to at the first input of the operational amplifier. Wherein the current mirror circuit includes a first transistor and a second transistor. A first transistor is located in the first current mirror path. The first terminal of the first transistor is coupled to the second input terminal of the operational amplifier, the second terminal of the first transistor is coupled to a ground terminal, and the first transistor The control terminal is coupled to the first terminal. A second transistor is located in the second current mirror path. The first terminal of the second transistor is coupled to the first input terminal of the operational amplifier, the second terminal of the second transistor is coupled to the ground terminal, and the second The control terminal of the transistor is coupled to the control terminal of the first transistor.

According to the audio digital-to-analog converter provided by the present invention, it can solve the problems of insufficient input range of its internal operational amplifier and insufficient working range when the transistor of the front circuit operates in the saturation region under low-frequency operation. The audio digital-to-analog converter improves the input range of the operational amplifier without affecting the performance of the operational amplifier. The audio digital-to-analog converter is also applicable to a switching current structure, and there is no need to additionally arrange a bias voltage circuit to provide a bias voltage to the current source circuit, so as to achieve the purpose of saving cost and area.

Description of drawings

FIG. 1 is a schematic diagram of an audio DAC in the prior art.

FIG. 2 is a schematic diagram of an audio DAC with switched current architecture in the prior art.

FIG. 3 is a schematic diagram of a first embodiment of an audio digital-to-analog converter of the present invention.

FIG. 4 is a schematic diagram of a second embodiment of an audio digital-to-analog converter of the present invention.

Reference number

Detailed ways

Please refer to FIG. 3 , which is a schematic diagram of a first embodiment of an audio digital-to-analog converter 300 of the present invention. As shown in FIG. 3 , the audio DAC 300 includes an operational amplifier 310 , a first resistor-capacitor circuit 320 , a second resistor-capacitor circuit 330 and a current mirror circuit 340 . The operational amplifier 310 is a differential to single-ended (differential to single-ended) amplifier, which has a first input terminal 311, a second input terminal 312 and an output terminal 313, and the operational amplifier 310 is based on the first input terminal 311 The first input signal S _IN1 ′ of the second input terminal 312 and the second input signal S _{IN2 ′} of the second input terminal 312 are used to output an output voltage V _OUT ′. The first resistor-capacitor circuit 320 and the second resistor-capacitor circuit 330 each include a resistor R1 and a capacitor C connected in parallel, wherein the first resistor-capacitor circuit 320 is coupled to the first input terminal 311 and the output of the operational amplifier 310 The second resistor-capacitor circuit 330 is coupled between the second input terminal 312 of the operational amplifier 310 and a common-mode voltage terminal V _CM . The current mirror circuit 340 includes a first current mirror path PA1 and a second current mirror path PA2, the first current mirror path PA1 is coupled to the second input terminal 312 of the operational amplifier 310, and the second current mirror path PA2 is coupled to the The first input terminal 311 of the operational amplifier 310 .

In this embodiment, the current mirror circuit 340 includes a first transistor M11 and a second transistor M22. Wherein, the first transistor M11 is located in the first current mirror path PA1, the first terminal 351 of the first transistor M11 is coupled to the second input terminal 312 of the operational amplifier 310, and the second terminal 352 of the first transistor M11 is coupled to a ground terminal, and the control terminal 353 of the first transistor M11 is coupled to the first terminal 351; the second transistor M22 is located in the second current mirror path PA2, and the first terminal 361 of the second transistor M22 is coupled to the first terminal of the operational amplifier 310 In the input terminal 311 , the second terminal 362 of the second transistor M22 is coupled to the ground terminal, and the control terminal 363 of the second transistor M22 is coupled to the control terminal 353 of the first transistor M11 .

Please note that each of the above-mentioned first transistor M11 and second transistor M22 can be an N-type transistor, but the present invention is not limited thereto, and can also be a P-type transistor in other design variations of the current mirror circuit.

Please note again that when the audio digital-to-analog converter 300 is applied to low-frequency operation, by adding the first transistor M11 and the second transistor M22 of the current mirror circuit 340 to the second input terminal 312 and the first input terminal of the operational amplifier 310 respectively Before 311, the input amplitude of the operational amplifier 310 can be expressed by the following formula:

${{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; IN</span>}}}^{<span\; class="notranslate">\; \text{'}</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="H2009101500901E00011.png,H2009101500901E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; G\; m</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="H2009101500901E00011.png,H2009101500901E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; G\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

此外，当电导值Gm愈大时，运算放大器310的输入振幅V_IN’会愈小。Wherein, V _IN ′ represents the input amplitude of the operational amplifier 310, I represents the current flowing through the first input terminal 311 (or the second input terminal 312), and Gm represents the conductance value of the first transistor M11. It can be seen that adding the first transistor M11 and the second transistor M22 of the current mirror circuit 340 before the second input terminal 312 and the first input terminal 311 of the operational amplifier 310 can greatly reduce the input amplitude of the operational amplifier 310

In addition, when the conductance value Gm is larger, the input amplitude V _IN ′ of the operational amplifier 310 is smaller.

Next, the audio DAC 300 disclosed in this embodiment is compared with the audio DAC 100 shown in FIG. 1 to further illustrate various advantages of the audio DAC of the present invention. It is worth noting that the comparisons of output noise and linearity mentioned below are only established in low frequency analysis.

(A) Comparison against the output noise of the op amp:

First, the output noise of the operational amplifier 110 in FIG. 1 can be expressed by the following formula:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out\; noise</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; opnoise</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

Wherein, V _outnoise represents the output noise of the operational amplifier 110 after the resistor element R2 is added, and V _opnoise represents the output noise of the original operational amplifier 110 before the resistor element R2 is added. When the resistance values of R2 and R1 are the same, the output noise V _outnoise of the operational amplifier 110 is equal to 2×V _opnoise .

On the other hand, the output noise of the operational amplifier 310 in FIG. 3 can be expressed by the following formula:

${{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out\; noise</span>}}}^{<span\; class="notranslate">\; \text{'}</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; DS</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; opnoise</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

Wherein, V _outnoise ' represents the output noise of the operational amplifier 310 after adding the current mirror circuit 340, V _opnoise represents the output noise of the original operational amplifier 310 before the current mirror circuit 340 is added, and r _DS represents the on-resistance of the second transistor M22 . When r _DS is much larger than R1, the output noise V _outnoise ′ of the operational amplifier 310 is approximately equal to V _opnoise . Comparing the output noise V _outnoise of the operational amplifier 110 and the output noise V _outnoise ′ of the operational amplifier 310 , it can be known that the output noise V _outnoise of the operational amplifier 310 is better than the output noise V _outnoise of the operational amplifier 110 .

(B) Compare the linearity of the op amp:

First, the input voltage (input amplitude) and output voltage of the operational amplifier 110 in FIG. 1 can be represented by the following formulas respectively:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; IN</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="H2009101500901E00011.png,H2009101500901E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="H2009101500901E00011.png,H2009101500901E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="H2009101500901E00011.png,H2009101500901E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; IN</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="H2009101500901E00011.png,H2009101500901E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; IN</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

Among them, V _IN represents the input voltage of the operational amplifier 110, and V _OUT represents the output voltage of the operational amplifier 110. Substituting the input voltage V _IN in the formula (5-1) into the formula (5-2), the operation can be obtained The output voltage V _OUT of the amplifier 110 is equal to 2×I×R1.

On the other hand, the input voltage and output voltage of the operational amplifier 310 in FIG. 3 can be represented by the following formulas respectively:

${{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; IN</span>}}}^{<span\; class="notranslate">\; \text{'}</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="H2009101500901E00011.png,H2009101500901E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; G\; m</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="H2009101500901E00011.png,H2009101500901E00031.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; G\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

V _OUT '=(GmV _IN '+I)×R1+V _IN '=2×I×R1 (6-2);

Wherein, V _IN ' represents the input voltage of the operational amplifier 310, and V _OUT ' represents the output voltage of the operational amplifier 310, and the input voltage V _IN ' in the formula (6-1) is brought into the formula (6-2) , it can be obtained that the output voltage V _OUT ' of the operational amplifier 310 is also equal to 2×I×R1. Then comparing the output voltage V _OUT of the operational amplifier 110 and the output voltage V _OUT ′ of the operational amplifier 310 , it can be seen that the linearity of the two is the same.

Please refer to FIG. 4 , which is a schematic diagram of a second embodiment of an audio digital-to-analog converter 400 of the present invention. The architecture of the audio DAC 400 shown in FIG. 4 is similar to that of the audio DAC 300 shown in FIG. 3 , except that the audio DAC 400 further includes a current source circuit 420 . The current source circuit 420 is coupled to the first input terminal 311 and the second input terminal 312 of the operational amplifier 310 for providing a first current I1 to the first input terminal 311 of the operational amplifier 310 as the first input signal S _IN1 ′ , and provide a second current I2 to the second input terminal 312 of the operational amplifier 310 as the second input signal S _IN2 ′. As shown in FIG. 4 , the current source circuit 420 has a switching current structure, which includes a plurality of switching current sources 430 , a plurality of first switches SW11 and a plurality of second switches SW22 . Wherein, a plurality of switching current sources 430 respectively provide a plurality of switching currents; each first switch SW11 is coupled between the corresponding switching current source 430 and the first input terminal 311 of the operational amplifier 310, and is used to control whether to allow the first The corresponding switching current source 430 of the switch SW11 is electrically connected to the first input terminal 311 of the operational amplifier 310; and each second switch SW22 is coupled between the corresponding switching current source 430 and the second input terminal 312 of the operational amplifier 310 , is used to control whether to allow the corresponding switching current source 430 of the second switch SW22 to be electrically connected to the second input terminal 312 of the operational amplifier 310 .

Comparing the audio digital-to-analog converter 400 shown in FIG. 4 with the audio digital-to-analog converter 200 in FIG. 2, it can be known that the audio digital-to-analog converter 400 does not need an additional bias circuit 240 (including at least one transistor M _Bias ) To provide the bias voltage V _Bias to the current source circuit 420, and in low-noise applications (such as audio digital-to-analog converters), a large transistor element is required to achieve the effect of reducing noise, so if the bias voltage circuit 240 can be reduced for Cost savings as well as area savings can help a lot.

The above-mentioned embodiments are only used as examples of the present invention, and are not limitations of the present invention. Those skilled in the art should understand that, without departing from the spirit of the present invention, the audio digital-to-analog converters 300, 400 Various changes are possible, which also belong to the scope of the present invention.

The above-mentioned embodiments are only used to illustrate the technical features of the present invention, and are not intended to limit the scope of the present invention. From the above, the present invention provides an audio digital-to-analog converter. By adding a current mirror circuit to the audio digital-to-analog converter, the problems of insufficient input range of its internal operational amplifier and insufficient working range when the transistor of the front circuit operates in the saturation region can be solved under low-frequency operation. In addition, the audio digital-to-analog converter disclosed in the present invention improves the input range of the operational amplifier without affecting the performance (such as linearity and output noise) of the operational amplifier. Furthermore, the audio digital-to-analog converter disclosed in the present invention is also applicable to a switching current structure, and does not need an additional bias circuit to provide a bias voltage to the current source circuit, so as to save cost and area.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the claims of the present invention shall fall within the scope of the present invention.

Claims (8)

1. a digital audio analog converter is characterized in that, described digital audio analog converter comprises:

One operational amplifier has a first input end, one second input and an output, is used for exporting an output voltage according to one first input signal of described first input end and one second input signal of described the second input;

One first resistance-capacitance circuit is coupled between the described first input end and described output of described operational amplifier, and resistance is connected with Capacitance parallel connection in described the first resistance-capacitance circuit;

One second resistance-capacitance circuit is coupled between described second input and a common-mode voltage end of described operational amplifier, and resistance is connected with Capacitance parallel connection in described the second resistance-capacitance circuit; And

One current mirroring circuit, comprise one first current mirror path and one second current mirror path, described the first current mirror path is coupled to described second input of described operational amplifier, and described the second current mirror path is coupled to the described first input end of described operational amplifier.

2. digital audio analog converter as claimed in claim 1 is characterized in that, described current mirroring circuit comprises:

One the first transistor, be positioned at described the first current mirror path, described the first transistor has a first end, one second end and a control end, the described first end of described the first transistor is coupled to described second input of described operational amplifier, described second end of described the first transistor is coupled to an earth terminal, and the described control end of described the first transistor is coupled to described first end; And

One transistor seconds, be positioned at described the second current mirror path, described transistor seconds has a first end, one second end and a control end, the described first end of described transistor seconds is coupled to the described first input end of described operational amplifier, described second end of described transistor seconds is coupled to described earth terminal, and the described control end of described transistor seconds is coupled to the described control end of described the first transistor.

3. digital audio analog converter as claimed in claim 2 is characterized in that, described the first transistor and described transistor seconds respectively are a P transistor npn npn.

4. digital audio analog converter as claimed in claim 2 is characterized in that, described the first transistor and described transistor seconds respectively are a N-type transistor.

5. digital audio analog converter as claimed in claim 1 is characterized in that, described digital audio analog converter comprises in addition:

One current source circuit, be coupled to described first input end and described second input of described operational amplifier, be used to provide one first electric current to the described first input end of described operational amplifier with as described the first input signal, and provide one second electric current to described second input of described operational amplifier with as described the second input signal.

6. digital audio analog converter as claimed in claim 5 is characterized in that, described current source circuit has one and switches the electric current framework.

7. digital audio analog converter as claimed in claim 6 is characterized in that, described current source circuit comprises:

A plurality of switchable current sources are used for providing respectively a plurality of switch currents;

A plurality of the first switches, each first switch is coupled between the described first input end of a corresponding switchable current source and described operational amplifier, is used for controlling the described first input end that the described corresponding switchable current source that whether allows described the first switch is electrically connected to described operational amplifier; And

A plurality of second switches, each second switch is coupled between described second input of a corresponding switchable current source and described operational amplifier, is used for controlling described the second input that the described corresponding switchable current source that whether allows described second switch is electrically connected to described operational amplifier.

8. digital audio analog converter as claimed in claim 1 is characterized in that, described operational amplifier is a differential single-ended amplifier that turns.

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