JP2011019285A - Class-d amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a class-D amplifier which reduces a component of direct current voltage in an output, nearly to zero volt, without using a transformer, and has a low distortion and a low loss of electric power.SOLUTION: The class-D amplifier has: an operational amplifier 11 and capacitors C1, C2, which constitute an integrator for integrating a difference between a plus side input signal and minus side input signal as an analogue input signal; delay circuits 21, 22 which delay a phase of a chopping wave by a desired minor angle; resistors R5, R6, R7, R8, R9, R10, R11, and R12 forming a composite circuit which composes an output of the integrator, the chopping wave, and the output of the delay circuits 21, 22; comparators 12, 13 which compare the outputs of the composite circuit each other; AND circuits 31, 32 which constitute a buffer with outputs of the comparators 12, 13 as an input; and resistors R3, R4 which feedback the outputs of the buffer to an input side of the integrator.

Description

  The present invention relates to a class D amplifier.

  The class D amplifier amplifies power by subjecting an input signal to pulse width modulation, and is used for power amplification of an audio signal, for example. As a conventional class D amplifier, an integrator for integrating an analog input signal, a comparator (comparator) for comparing the output of the integrator with a predetermined triangular wave, and amplifying the output of the comparator to output a pulse signal Some have a buffer (pulse amplifier). The buffer output of the conventional class D amplifier is fed back to the input side of the integrator. The buffer output is an analog signal that drives a load such as a speaker through a low-pass filter including a coil and a capacitor.

In addition, as a conventional pulse width modulation amplifier, a comparator for comparing an analog input signal and a predetermined triangular wave, an amplifier for amplifying the output of the comparator, a transformer disposed between the amplifier and a load, (For example, refer patent document 1).
In addition, as a digital amplification circuit using a conventional digital signal processing circuit, a noise shaper for frequency shaping a quantization error of a digital input signal, and a PCM (Pulse Code Modulation) signal which is an output of the noise shaper are PWM (Pulse Width). A converter that converts the signal into a modulation signal, a logic circuit that compensates for the linearity of the output signal of the converter, a switch that is controlled by the output of the logic circuit, and a filter whose input side is connected to the power source by the switch (See, for example, Patent Document 2).

Japanese Patent Publication No.56-27001 Special Table 2000-500625

However, in the conventional class D amplifier, the buffer is composed of two buffers, a plus side buffer and a minus side buffer, and even when there is no input signal, the two buffers output signals of opposite polarity with a duty of 50%. Therefore, the conventional class D amplifier causes a large loss by flowing current into the low-pass filter even when there is no input signal.
In order to avoid the loss at the time of no signal, Patent Document 1 describes a technique for turning off the output amplification element at the time of no signal. However, the conventional pulse width modulation amplifier described in Patent Document 1 requires a transformer for impedance conversion and DC voltage cut, resulting in an increase in size and cost of the device. Furthermore, the conventional pulse width modulation amplifier described in Patent Document 1 has a problem in that distortion of the output signal is large because the comparator compares a simple triangular wave with the input signal.

  The digital amplifier circuit described in Patent Document 2 uses a ternary or quaternary output state (switching state), and the digital input signal is linearized using a digital circuit such as a logic circuit. Amplifying while improving. As a result, the digital amplifier circuit described in Patent Document 2 cannot be configured using an analog circuit, and there is a problem that an analog input signal cannot be amplified with good linearity. That is, in such a conventional digital amplifier circuit, a compensation pulse is added when a small signal pulse is input, thereby compensating for output switch distortion in the logic circuit. However, since the circuit for compensating for the output switch distortion is composed of only a digital circuit such as a logic circuit, the analog input signal cannot be amplified with high linearity.

The present invention has been made to solve the above problems, and provides a class D amplifier with low distortion and low power loss.
The present invention also provides a class D amplifier with low distortion and low power loss without using a transformer.
The present invention also provides a class D amplifier capable of setting the DC voltage component at the output to substantially zero volts.

In order to solve the above problems, the present invention has the following configuration.
That is, the invention according to the class D amplifier described in claim 1 includes an integrator that integrates an analog input signal, a first comparator and a second comparator that compare an output of the integrator with a triangular wave, and the first comparator. Buffer means for receiving the outputs of the comparator and the second comparator, a feedback circuit for feeding back the output of the buffer means to the input side of the integrator, and the output of the second comparator with respect to the output of the first comparator Delay means for delaying, the buffer means has two output terminals connected to a load, and when the analog input signal is no signal, the delay amount of the delay means from the two output terminals Depending on the polarity of the analog input signal, the pulse having a width depending on the output is complementary. One of the output terminals of the two output terminals to a predetermined level, and outputs a pulse signal PWM modulating the analog input signal from the other output terminal.

According to a second aspect of the present invention, there is provided an integrator for integrating an analog input signal, a first comparator for comparing an output of the integrator with a first triangular wave, and an output of the integrator. And a second comparator for comparing the phase of the first triangular wave with a second triangular wave having a waveform shifted by 180 degrees plus or minus a minute angle, and using the output of the first comparator and the output of the second comparator as inputs. Buffer means for outputting a side output signal and a minus side output signal, and a feedback circuit for feeding back the difference between the plus side output signal and the minus side output signal to the input side of the integrator, the buffer means, When there are two output terminals connected to a load and the analog input signal is no signal, the two output terminals depend on the minute angle. When the analog input signal is a valid signal, one output terminal of the two output terminals is set to a predetermined level in a complementary manner according to the polarity of the analog input signal, and the other output A pulse signal obtained by PWM modulating the analog input signal is output from a terminal.
According to the present invention, the integrated value of the analog input signal and the first triangular wave are compared by the first comparator, and the integrated value of the analog input signal and the second triangular wave obtained by inverting the first triangular wave and further delaying by the minute angle are obtained. The comparison can be performed by the second comparator, and the buffer can output the plus side output signal and the minus side output signal based on the comparison result. Here, the plus side output signal and the minus side output signal are fed back to the input side and become the output (PWM output) of the class D amplifier. Thus, according to the present invention, for example, a transformer is used by connecting a load (such as a speaker) to the plus side output (+ OUT) and minus side output (−OUT) of the class D amplifier via a low-pass filter. Therefore, the DC voltage component at the output can be made substantially zero volts, and a class D amplifier with low distortion and low power loss can be provided. That is, according to the present invention, even when there is no analog input signal (no signal), the plus side output and the minus side output can be output in a short time (the duty ratio of the high level period is 0 to several percent), Thereby, a voltage can be output to the low-pass filter little by little. At this time, since (the positive voltage of the low-pass filter) − (the negative voltage of the low-pass filter) is applied to the load, the voltage applied to the load can be zero volts. Therefore, when the analog input terminal changes from a no-signal state to a state in which a small signal is input, the class D amplifier according to the present invention can supply an amplified signal with little distortion to the load even at the time of the change. it can.

According to a third aspect of the present invention, in the invention according to the class D amplifier according to the second aspect, the buffer means performs an AND operation between the output of the first comparator and the output of the second comparator. The first buffer that outputs the calculation result as the minus output signal, and the AND operation of the output of the first comparator and the output of the second comparator, and outputs the calculation result as the plus output signal And a second buffer.
According to the present invention, the first comparator composed of the AND circuit (low active) can generate the minus side output (−OUT) signal that constitutes one of the outputs (PWM outputs) of the class D amplifier, and the second circuit composed of the AND circuit. The comparator can generate a positive output (+ OUT) signal that forms the other of the outputs (PWM output) of the class D amplifier. Therefore, according to the present invention, it is possible to amplify an analog input signal with low distortion and a DC voltage at an output while having a simple circuit configuration that can be easily downsized and realized at low cost. The component can be made substantially zero volts, and a class D amplifier with low power loss can be provided.

According to a fourth aspect of the present invention, in the invention according to the class D amplifier according to the second or third aspect, the feedback circuit amplifies a difference between the positive side output signal and the negative side output signal. It has a differential amplifier.
According to the present invention, the difference between the plus side output signal and the minus side output signal can be amplified with high accuracy and fed back to the input side by the differential amplifier of the feedback circuit. Therefore, according to the present invention, it is possible to amplify an analog input signal with lower distortion, to make a DC voltage component at the output more nearly zero volts with high accuracy, and to easily provide a class D amplifier with less power loss. be able to.

Further, the invention according to the class D amplifier described in claim 5 includes an integrator that integrates a difference between a plus-side input signal that forms an analog input signal and a minus-side input signal, and a phase of a triangular wave by a desired minute angle. A delay circuit for delaying; a synthesis circuit for synthesizing the output of the integrator, the triangular wave and the output of the delay circuit to output a plurality of signals; a comparison means for comparing the outputs of the synthesis circuit; and the comparison means Buffer means for receiving the output of the output, and a feedback circuit for feeding back the output of the buffer means to the input side of the integrator, the buffer means has two output terminals connected to a load, When the analog input signal is no signal, a pulse having a width depending on the minute angle is output from the two output terminals. When the analog input signal is a signal, the analog input signal is output. Complementarily according to the polarity of the input signal, one output terminal of the two output terminals is set to a predetermined level, and a pulse signal obtained by PWM-modulating the analog input signal is output from the other output terminal. .
According to the present invention, the integrated value of the analog input signal, the triangular wave, and the output of the delay circuit are combined, the combined result is compared by the comparator, the comparison result is fed back to the input side, and the output of the class D amplifier is output. (PWM output). Thus, according to the present invention, for example, by connecting a load (speaker or the like) to the outputs (plus output and minus output) of the class D amplifier via a low pass filter, Similarly, a DC voltage component at the output can be made substantially zero volts without using a transformer, and a class D amplifier with low distortion and low power loss can be provided. In the present invention, the difference between the plus side input signal and the minus side input signal forming the analog input signal is integrated by the integrator, so that the analog input signal can be differentially amplified with higher accuracy.

According to a sixth aspect of the present invention, there is provided an integrator for integrating a difference between a positive side input signal and a negative side input signal forming an analog input signal, and an output of the integrator and a triangular wave. A synthesis circuit that synthesizes the output of the integrator and a reverse-phase triangular wave having a phase shifted by 180 degrees with respect to the triangular wave, and outputs a plurality of signals; Comparison means, buffer means for receiving the output of the comparison means, and a feedback circuit for feeding back the output of the buffer means to the input side of the integrator. A plurality of resistors having at least two types, and a phase difference between the plurality of signals, which are outputs of the combining circuit, by the resistors and the input capacitance of the comparison unit; The buffer means has two output terminals connected to a load, and outputs a pulse having a width depending on the phase difference from the two output terminals when the analog input signal is no signal. When the analog input signal is a signal, one output terminal of the two output terminals is set to a predetermined level in a complementary manner according to the polarity of the analog input signal, and the analog input signal is output from the other output terminal. A pulse signal obtained by PWM modulation is output.
According to the present invention, in the synthesis circuit, the integration value of the analog input signal and the triangular wave are synthesized, and the integration value of the analog input signal and the anti-phase triangular wave are synthesized, and the synthesis result is compared by the comparator. Can be fed back to the input side and used as the output (PWM output) of the class D amplifier. Furthermore, the composite circuit in the present invention can be configured with only a plurality of resistors. A phase difference can be generated between the signals input to the comparator by the resistor of the synthesis circuit and the input capacitance of the comparator. This phase difference has the same function as the phase difference (phase difference between signals input to the comparator) generated by the delay circuit according to the fifth aspect of the invention. Thus, according to the present invention, for example, by connecting a load (speaker or the like) to the output (plus side output and minus side output) of the class D amplifier via a low pass filter, Similarly to the invention, the DC voltage component at the output can be made substantially zero volts without using a transformer, and a class D amplifier with low distortion and low power loss can be provided. In the present invention, the difference between the plus side input signal and the minus side input signal forming the analog input signal is integrated by the integrator, so that the analog input signal can be differentially amplified with higher accuracy. Furthermore, the present invention can provide a class D amplifier that has a simple configuration and is easy to manufacture because the composite circuit can be configured with only a plurality of resistors.

According to another aspect of the invention, there is provided a triangular wave generating circuit comprising an integrator for integrating a difference between a positive side input signal and a negative side input signal forming an analog input signal, and a current source and a capacitor. Comparing means for comparing the output of the integrator with the output of the triangular wave generating circuit, buffer means for receiving the output of the comparing means, and feedback for feeding back the output of the buffer means to the input side of the integrator The buffer means has two output terminals connected to a load, and when the analog input signal is no signal, depends on the non-identity of the constituent elements from the two output terminals When a pulse of duty ratio is output and the analog input signal is a signal, one output terminal of the two output terminals is complementarily according to the polarity of the analog input signal And a predetermined level, and outputs a pulse signal PWM modulating the analog input signal from the other output terminal.
According to the present invention, an integrated value of an analog input signal and a triangular wave can be compared by a comparator, and the comparison result can be fed back to the input side and used as an output (PWM output) of the present class D amplifier. Here, since the triangular wave generating circuit includes a current source and a capacitor, a simple and compact configuration can be achieved. Thus, according to the present invention, a DC voltage component at the output can be made substantially zero volts without using a transformer, and a high efficiency, low distortion, class D amplifier having a simple configuration can be provided. it can.

The invention described in claim 8 is the invention according to the class D amplifier described in claim 7, wherein one end of the capacitor in the triangular wave generation circuit is connected to one input terminal of the comparison means. The current source is one that repeatedly switches the direction of the output current so as to repeatedly charge and discharge the capacitor.
According to the present invention, by using a current source to repeatedly charge and discharge a capacitor, the change in potential of the capacitor can be made a triangular wave. Since one end of the capacitor is connected to one input end of the comparator, a triangular wave can be applied to the one input end. Therefore, according to the present invention, the triangular wave generating circuit in the class D amplifier can be simply configured.

The invention described in claim 9 is the invention according to the class D amplifier described in claim 8, wherein one end of the current source is connected to one end of the capacitor, and the current source is When the potential of the capacitor becomes lower than the first potential, a current flows in a direction to charge the capacitor. When the potential of the capacitor becomes higher than the second potential, a current flows in a direction to discharge the capacitor. And the second potential is higher than the first potential.
According to the present invention, when the potential of the capacitor becomes lower than the first potential (VL), the capacitor is charged, and the potential of the capacitor becomes higher (charging period). Then, when the potential of the capacitor becomes higher than the second potential, the capacitor is discharged and the potential of the capacitor becomes lower (discharge period).
. When the capacitance potential becomes lower than the first potential (VL), the charging period starts again. As described above, the triangular wave generation circuit in the class D amplifier of the present invention generates a triangular wave by repeating the charging period and the discharging period.

The invention described in claim 10 is the invention related to the class D amplifier according to any one of claims 7 to 9, wherein the comparing means includes the negative output of the integrator and the triangular wave generation. A first comparator for comparing the output of the circuit, and a second comparator for comparing the positive-side output of the integrator and the output of the triangular wave generating circuit, and the buffer means inverts the output of the first comparator A first buffer that performs an AND operation on the output of the second comparator and an output of the second comparator, and a second buffer that performs an AND operation on the output of the first comparator and the inverted output of the second comparator The feedback circuit includes a first feedback circuit that feeds back the output of the first buffer to a negative input of the integrator, and the second feedback circuit. The output of Ffa characterized by comprising a second feedback circuit for feeding back to the positive input of the integrator.
According to the present invention, it is possible to provide a class D amplifier that has a simple circuit configuration, can be easily made compact, and can be realized at low cost. Furthermore, according to the present invention, an analog input signal can be amplified with low distortion, the DC voltage component at the output can be made substantially zero volts, and a highly efficient class D amplifier can be provided.

  The invention described in claim 11 is the invention according to the class D amplifier described in claim 10, wherein a pulse having a duty ratio depending on non-identity of the constituent elements has a pulse width of the integral. Offset voltage, or a component in the first path from the input of the first comparator to the output of the first buffer and a component in the second path from the input of the second comparator to the output of the second buffer This is due to a delay time difference between the first route and the second route due to non-identity with the second route.

  The invention described in claim 12 is the invention related to the class D amplifier according to any one of claims 1 to 11, wherein the buffer means includes a triangular wave when the analog input signal is a no-signal. A pulse is output in synchronism with.

According to the present invention, it is possible to provide a class D amplifier with low distortion and low power loss.
Further, according to the present invention, it is possible to provide a class D amplifier that can reduce the DC voltage component at the output to almost zero volts without using a transformer, and has low distortion and low power loss.

1 is a circuit diagram illustrating a configuration example of a class D amplifier according to Embodiment 1 of the present invention. FIG. It is a wave form diagram which shows operation | movement when 0 volt is input into the class D amplifier same as the above. It is a wave form diagram which shows operation | movement when a plus value is input into the class D amplifier same as the above. It is a wave form diagram which shows operation | movement when a negative value is input into the class D amplifier same as the above. It is a circuit diagram which shows the structural example of the class D amplifier which concerns on Example 2 of this invention. It is a wave form diagram which shows operation | movement when 0 volt | bolt is input into the class D amplifier which concerns on Example 2 same as the above. It is a figure which shows the example of a waveform in the load when a sine wave is input into the class D amplifier which concerns on Example 1 or Example 2 of this invention. It is a circuit diagram which shows the structural example of the class D amplifier which concerns on Example 3 of this invention. It is a wave form diagram which shows operation | movement when 0 volt is input into the class D amplifier same as the above. It is a wave form diagram which shows operation | movement when a plus value is input into the class D amplifier same as the above. It is a wave form diagram which shows operation | movement when a negative value is input into the class D amplifier same as the above. It is a circuit diagram which shows the structural example of the class D amplifier which concerns on Example 4 of this invention. It is a circuit diagram which shows the structural example of the current source of a D class amplifier same as the above. It is a wave form diagram which shows operation | movement of a current source same as the above. It is a wave form diagram which shows operation | movement when a plus value is input into the class D amplifier of Example 4. It is a wave form diagram which shows operation | movement when 0 volt | bolt is input into the class D amplifier of Example 4. FIG. It is a wave form diagram which shows operation | movement when a negative value is input into the class D amplifier of Example 4. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram showing a configuration example of a class D amplifier according to Embodiment 1 of the present invention. This class D amplifier includes resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, capacitors C1, C2, an operational amplifier (operational amplifier) 11, and comparators 12, 13 , Delay circuits 21 and 22, AND circuit (low active) 31, and AND circuit 32. In addition, predetermined triangular wave signals a and b are respectively applied to one ends of the resistors R9 and R11 in the drawing. The triangular wave signal a and the triangular wave signal b are the same waveform signals whose phases are different from each other by 180 degrees.

  One ends of the resistors R1 and R2 are differential input ends of analog input signals, respectively. One end of the resistor R1 is a plus side input end (+ IN), and one end of the resistor R2 is a minus side input end (−IN). The operational amplifier 11 and the capacitors C1 and C2 constitute an integrator. The analog input signal differentially input by the resistors R1 and R2 is integrated by the integrator and output to the resistors R5, R6, R7, and R8.

The resistors R5, R6, R7, R8, R9, R10, R11, and R12 are triangular waves obtained by delaying the output of the integrator and the triangular wave signals a and b or the triangular wave signals a and b by a minute angle θ (θ << 180 degrees). A synthesis circuit for synthesizing the signals a ′ and b ′ is configured. This synthesis circuit has four types of first circuits.
To generate a fourth synthesized waveform e, f, g, h.
The first combined waveform e is a combination of the negative output of the operational amplifier 11 that forms an integrator and the triangular wave signal a (first triangular wave). The second synthesized waveform f is obtained by synthesizing the plus-side output of the operational amplifier 11 serving as an integrator and the triangular wave signal b (second triangular wave). The third synthesized waveform g is obtained by synthesizing the negative output of the operational amplifier 11 serving as an integrator and the triangular wave signal b ′ obtained by delaying the triangular wave signal b. The fourth composite waveform h is a composite of the plus-side output of the operational amplifier 11 serving as an integrator and the triangular wave signal a ′ obtained by delaying the triangular wave signal a.

The comparator 12 (first comparator) compares the first combined waveform e and the second combined waveform f and outputs the comparison result. The comparator 12 outputs a predetermined “low” level signal (for example, 0 volts) when the first composite waveform e is larger than the second composite waveform f, and the first composite waveform e is greater than the second composite waveform f. If it is smaller, a predetermined “high” level signal is output. The comparator 13 (second comparator) compares the third combined waveform g and the fourth combined waveform h and outputs the comparison result. The comparator 13 outputs a predetermined “low” level signal (for example, 0 volts) when the third synthesized waveform g is larger than the fourth synthesized waveform h, and the third synthesized waveform g is more than the fourth synthesized waveform h. If it is smaller, a predetermined “high” level signal is output.
The comparators 12 and 13 may be realized using an operational amplifier.

The AND circuit 31 is a buffer circuit having a logical product function of negative logic inputs. The AND circuit 31 performs an AND operation (low active) to output a “high” level signal when both the output of the comparator 12 and the output of the comparator 13 are “low”, and the operation result is output to the class D amplifier. Output as negative output -OUT. The resistor R3 forms a first feedback circuit that feeds back the output of the AND circuit 31 that also functions as a buffer to the positive side input of the operational amplifier 11.
The AND circuit 32 is a buffer circuit having an AND operation function, performs an AND operation on the output of the comparator 12 and the output of the comparator 13, and sets the operation result as the plus side output + OUT of the class D amplifier. The resistor R4 forms a second feedback circuit that feeds back the operation result of the AND circuit 32 that also functions as a buffer to the negative side input of the operational amplifier 11.
A load (such as a speaker) is connected between the plus side output + OUT and minus side output −OUT of the class D amplifier via a low-pass filter. With these configurations, this class D amplifier can amplify the analog input signals + IN and −IN with low distortion and drive the load with less power loss without using a transformer.

Next, an example of the operation of the class D amplifier according to the first embodiment having the above configuration will be described with reference to FIGS. 2 to 4 are waveform diagrams showing the operation of each part of the class D amplifier shown in FIG.
FIG. 2 shows waveforms of each part of the class D amplifier when the analog input signal + IN and the analog input signal −IN have the same value, that is, when the differential input has a 0 volt value (no input).
FIG. 3 shows waveforms of each part of the class D amplifier when (analog input signal + IN)> (analog input signal−IN), that is, when the differential input is positive. FIG. 4 shows the waveform of each part of the class D amplifier when (analog input signal + IN) <(analog input signal−IN), that is, when the differential input is negative.

First, FIG. 2, that is, the case of no input (0 volt value input) will be described. The triangular wave signal a and the triangular wave signal b have a phase difference of 180 degrees. Further, the triangular wave signal a ′ is a signal obtained by delaying the triangular wave signal a by a minute angle θ, and the triangular wave signal b ′ is a signal obtained by delaying the triangular wave signal b by a minute angle θ. Here, triangular wave signals a, a ′, b, b
A predetermined noise called dither may be added to each '. In this way, distortion of the output waveform can be corrected. Further, instead of the triangular wave signals a, a ′, b, b ′, a sawtooth wave, an integrated waveform, or the like may be used.

The phase relationship between the triangular wave signals a and a ′ and the plus side output (plus side output of the operational amplifier 11) d of the integrator is substantially the same. Further, the phase relationship between the triangular wave signals b and b ′ and the negative output of the integrator (negative output of the operational amplifier 11) c is substantially the same.
The inputs of the comparators 12 and 13, that is, the first to fourth synthesized waveforms e, f, g, and h are waveforms synchronized with the output of the integrator. The first synthesized waveform e and the second synthesized wave f have a phase difference of about 180 degrees, and the third synthesized waveform g and the fourth synthesized wave h have a phase difference of about 180 degrees. The first synthesized waveform e and the fourth synthesized waveform h are substantially the same waveform, and the phases are different by a minute angle θ. The second synthesized waveform f and the third synthesized waveform g are substantially the same waveform and are different in phase by a minute angle θ.

The output j of the comparator 12 is “low” when (first synthesized waveform e)> (second synthesized waveform f), and “high” when (first synthesized waveform e) <(second synthesized waveform f). It becomes. The output k of the comparator 13 is “low” when (third synthesized waveform g)> (fourth synthesized waveform h), and “high” when (third synthesized waveform g) <(fourth synthesized waveform h). It becomes. The output (−OUT) of the AND circuit 31 becomes “high” when the outputs j and k of the comparators 12 and 13 are both “low”. The output (+ OUT) of the AND circuit 32 becomes “high” when the outputs j and k of the comparators 12 and 13 are both “high”.
That is, during the period from the intersection (time point t1) of the first synthesized waveform e and the second synthesized waveform f to the intersection point (time t2) of the third synthesized waveform g and the fourth synthesized waveform h, the positive side in the class D amplifier The output + OUT becomes high level. Further, in the class D amplifier during the period from the intersection (time point t3) of the next second synthesized waveform f and the first synthesized waveform e to the intersection point (time t4) of the third synthesized waveform g and the fourth synthesized waveform h. The negative output -OUT becomes high level.

Here, the period during which the positive output + OUT or the negative output −OUT is at a high level depends on the phase difference (small angle θ) between the triangular wave signals a and a ′ and the triangular wave signals b and b ′. Therefore, by making the delay time in the delay circuits 21 and 22 sufficiently short to a desired value and reducing the phase difference (small angle θ) between the triangular wave signals a and a ′ and the triangular wave signals b and b ′,
The period during which the plus side output + OUT and the minus side output −OUT are at the high level can be sufficiently shortened to a desired value. At this time, the negative output c and the positive output d of the integrator are very small voltages.

That is, in the case of no input (zero volt value, the same applies hereinafter), the high level period in the plus side output + OUT and the minus side output −OUT can be set to a duty ratio of 0 to several percent. The outputs of the plus side output + OUT and the minus side output −OUT flow into a load such as a speaker via a low-pass filter, for example. Thus, in the case of no input, the plus side output + OUT and the minus side output −OUT have a duty ratio of 0 to several%, so that the current flowing through the filter and the load becomes a very small value. Therefore, when the class D amplifier is used for a small signal, the low-pass filter (LC filter or the like) disposed between the output terminal and the load can be omitted.

Thus, according to the class D amplifier of the first embodiment, when there is no analog input signal (in the case of 0 volt value input), the period during which the output signal is at a high level is sufficiently shortened to a desired value. Therefore, the power loss can be greatly reduced as compared with the conventional one.

Next, the case where (analog input signal + IN)> (analog input signal−IN) shown in FIG. 3, in other words, the case where the differential input is positive will be described. Triangular wave signals a, a ′, b, b ′
Is the same as in FIG. The phase relationship between the triangular wave signals a, a ′, b, b ′ and the outputs of the integrator (outputs of the operational amplifier 11) c, d is the same as in the case shown in FIG. Also in FIG. 3, the first to fourth synthesized waveforms e, f, g, h are waveforms synchronized with the output of the integrator. The first synthesized waveform e and the second synthesized wave f have a phase difference of about 180 degrees, and the third synthesized waveform g and the fourth synthesized wave h have a phase difference of about 180 degrees.

In FIG. 3, the difference between the negative output c of the integrator and the positive output d of the integrator at the same timing is larger than in the case of FIG. The phase difference between the first synthesized waveform e and the fourth synthesized waveform h and the phase difference between the second synthesized waveform f and the third synthesized waveform g are larger than in the case of FIG. Thus, the period from the intersection (time t1 ′) of the first synthesized waveform e and the second synthesized waveform f to the intersection (time t2 ′) of the third synthesized waveform g and the fourth synthesized waveform h is as shown in FIG. It is longer than (from time t1 to time t2), and the period during which the plus side output + OUT is at the high level is longer than in the case of FIG. In FIG. 3, the first synthesized wave e and the second synthesized wave f from the intersection (time t3 ′) between the third synthesized wave g and the fourth synthesized wave h after the time t2 ′.
Also during the period up to the point of intersection (time t4 ′), the positive output + OUT remains at the high level, and thereafter these operations are repeated.

The output j of the comparator 12 is “from the intersection of the first synthesized wave e and the second synthesized wave f (time t1 ′) to the intersection of the next first synthesized wave e and the second synthesized wave f (time t4 ′). "High". Next, the output j of the comparator 12 becomes “low” from the time point t4 ′ to the intersection (time point t5 ′) of the next first synthesized wave e and the second synthesized wave f, and thereafter the above operation is repeated. That is, the output j of the comparator 12 changes its state from “high” to “low” or from “low” to “high” at each intersection of the first synthesized wave e and the second synthesized wave f.
The output k of the comparator 13 is “from the intersection of the third synthesized wave g and the fourth synthesized wave h (time t2 ′) to the intersection of the next third synthesized wave g and the fourth synthesized wave h (time t3 ′). Low ". Next, the output k of the comparator 13 becomes “high” from the time point t3 ′ to the intersection (time point t6 ′) of the next third synthesized wave g and the fourth synthesized wave h, and thereafter the above operation is repeated. That is, the output k of the comparator 13 changes its state from “high” to “low” or from “low” to “high” at each intersection of the third synthesized wave and the fourth synthesized wave.

Since the plus side output + OUT = (output j) AND (output k), the period from time t1 ′ to time t2 ′, the period from time t3 ′ to time t4 ′, and the period from time t5 ′ to time t6 ′ The plus side output + OUT becomes “high” level. Thus, the duty ratio during the period when the positive output + OUT is at the high level is substantially proportional to the magnitude of the positive value (differential value) of the analog input signal. In other words, the plus side output + OUT is a signal obtained by pulse width modulating a plus value (differential value) of the analog input signal.
On the other hand, the negative output -OUT is always at a low level. This is because when (analog input signal + IN)> (analog input signal−IN) shown in FIG. 3, there is no period during which the outputs j and k of the comparators 12 and 13 are both “low”.

Next, the case where (analog input signal + IN) <(analog input signal−IN) shown in FIG. 4, in other words, the differential input is negative will be described. Triangular wave signals a, a ′, b, b
'Is the same as in FIG. The phase relationship between the triangular wave signals a, a ′, b, b ′ and the integrator outputs (outputs of the operational amplifier 11) c, d is the same as in the case shown in FIG.

  However, in the case shown in FIG. 4, the phases of the outputs c and d of the integrator are inverted (shifted by 180 degrees) as compared with the cases of FIGS. 2 and 3. In addition, the time relationship between the intersection of the first synthesized wave e and the second synthesized wave f and the intersection of the third synthesized wave g and the fourth synthesized wave h is opposite to that in the case of FIG. ing.

The output j of the comparator 12 is “from the intersection of the first synthesized wave e and the second synthesized wave f (time t2 ″) to the intersection of the next first synthesized wave e and the second synthesized wave f (time t3 ″). "High". Next, the output j of the comparator 12 becomes “low” from the time point t3 ″ to the intersection (time point t6 ″) of the next first synthesized wave e and the second synthesized wave f, and thereafter the above operation is repeated. That is, the output j of the comparator 12 changes its state from “high” to “low” or from “low” to “high” at each intersection of the first synthesized wave e and the second synthesized wave f.
The output k of the comparator 13 is “from the intersection of the third synthesized wave g and the fourth synthesized wave h (time point t1 ″) to the intersection of the next third synthesized wave g and the fourth synthesized wave h (time point t4 ″). Low ". Next, the output k of the comparator 13 becomes “high” from the time point t4 ″ to the intersection (time point t5 ″) of the next third synthesized wave g and the fourth synthesized wave h, and thereafter the above operation is repeated. That is, the output k of the comparator 13 changes its state from “high” to “low” or from “low” to “high” at each intersection of the third synthesized wave and the fourth synthesized wave.

  Since the positive output + OUT = (output j) AND (output k), the positive output + OUT is always at a low level. The negative output -OUT is “high” when both (output j) and (output k) are “low”, and the duty ratio during the period when the negative output −OUT is high is analog input. It is almost proportional to the negative value (differential value) of the signal. In other words, the negative output -OUT is a signal obtained by pulse width modulating a negative value (differential value) of the analog input signal.

  Thus, according to the class D amplifier of the first embodiment, the analog input signal can be converted into a ternary PWM signal composed of any one of a 0 volt value, a plus value, and a minus value and can be output. Further, according to the class D amplifier of the first embodiment, when the analog input signal becomes equal to or higher than a predetermined value, one of the plus side output + OUT and the minus side output −OUT (one side) as shown in FIGS. Only a switching waveform is obtained. Therefore, the class D amplifier according to the first embodiment can substantially reduce the switching loss by half as compared with the conventional class D amplifier that switches on both the plus side and the minus side.

  Further, according to the class D amplifier of the first embodiment, analog feedback is applied by the resistors R3 and R4, so that the analog input signal is linearly applied without performing digital processing as described in Patent Document 2 above. Can be amplified with good performance. Further, according to the class D amplifier of the first embodiment, unlike the amplifier described in Patent Document 1, the DC output component is set to almost zero volts without requiring a transformer for impedance conversion and DC voltage cut. A class D amplifier with low distortion and low power loss can be provided.

  Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a circuit diagram showing a configuration example of a class D amplifier according to Embodiment 2 of the present invention. The class D amplifier includes resistors R51, R52, R53, R54, R55, and R56, a capacitor C51, operational amplifiers (operational amplifiers) 61 and 64, comparators 62 and 63, an AND circuit (low active) 71, and AND. The circuit 72 is constituted. Further, the triangular wave signal a is applied to the plus side input terminal of the comparator 62, and the triangular wave signal b ′ is applied to the plus side input terminal of the comparator 63.

The triangular wave signal b ′ is obtained by further delaying the phase by the minute angle θ by the delay circuit 81 with respect to the triangular wave signal b obtained by inverting the triangular wave signal a (the phase being delayed by 180 degrees). Therefore, the triangular wave signal a and the triangular wave signal b ′ are the same waveform signals whose phases are different from each other by (180 degrees + small angle θ). Predetermined noise called dither may be added to the triangular wave signals a and b ′. In this way, distortion of the output waveform can be corrected. Further, instead of the triangular wave signals a and b ′, a sawtooth wave, an integrated waveform, or the like may be used.

  One end of the resistor R51 is an input end for an analog input signal. The other end of the resistor R51 is connected to the negative input end of the operational amplifier 61. The operational amplifier 61 and the capacitor C51 constitute an integrator. The comparator 62 compares the triangular wave signal a with the output c of the integrator and outputs the comparison result (output j). The comparator 63 compares the triangular wave signal b 'with the output c of the integrator and outputs the comparison result (output k).

  The AND circuit 71 is a buffer circuit having a row active AND operation function. The AND circuit 71 outputs a “high” level signal when both the output j of the comparator 62 and the output k of the comparator 63 are “low”, and outputs these signals to the minus side output −OUT of the class D amplifier. Output as. The AND circuit 72 is a buffer circuit having an AND operation function. The AND circuit 72 outputs a “high” level signal when both the output of the comparator 62 and the output of the comparator 63 are “high”, and outputs these signals as the positive side output + OUT of the class D amplifier. .

  The operational amplifier 64 and the resistors R53, R54, R55, and R56 constitute a differential amplifier that amplifies the difference between the positive output + OUT and the negative output -OUT. The output 1 of the differential amplifier is fed back to the input side of the operational amplifier 61 (the input side of the class D amplifier) via the resistor R52. Therefore, the operational amplifier 64 and the resistors R52, R53, R54, R55, and R56 form a feedback circuit.

Next, the operation of the class D amplifier according to the second embodiment having the above configuration will be described. When the analog input signal is 0 volts (no input), that is, when IN is 1/2 VDD, positive output + OUT
The negative output -OUT is as shown in FIG. 6, and the duty ratio in the high level period is approximately 0 to several percent. Therefore, when the analog input signal is 0 volt (no input), the current flowing from the class D amplifier to the filter and the load becomes a very small value.

When the analog input signal is positive, the positive output + OUT and the negative output −OUT are the same as those in FIG. Therefore, the plus side output + OUT is a signal obtained by pulse width modulation of a plus value of the analog input signal (plus with 0 volts as a reference value). On the other hand, the negative output -OUT is always at a low level.
When the analog input signal is negative, the positive output + OUT and the negative output −OUT are the same as in FIG. Therefore, the minus side output -OUT is a signal obtained by pulse width modulating a minus value of the analog input signal (minus with 1/2 VDD as a reference value).
On the other hand, the positive output + OUT is always at a low level.

Thus, according to the class D amplifier according to the second embodiment, similarly to the class D amplifier according to the first embodiment, when there is no analog input signal (in the case of 0 volt value input), the output signal is high level. Since the period of time can be sufficiently shortened to a desired value, the power loss can be greatly reduced as compared with the conventional one.

  In addition, according to the class D amplifier according to the second embodiment, an analog input signal can be converted into a ternary PWM signal composed of any one of a 0 volt value, a plus value, and a minus value and output. Further, according to the class D amplifier of the second embodiment, when the analog input signal becomes equal to or higher than a predetermined value, only one (one side) of the plus side output + OUT or the minus side output −OUT as in FIGS. The switching waveform is as follows. Therefore, the class D amplifier according to the second embodiment can reduce the switching loss substantially by half as compared with the conventional class D amplifier that switches on both the plus side and the minus side.

  Further, according to the class D amplifier of the second embodiment, analog feedback is applied by the operational amplifier 64 and the resistors R52, R53, R54, R55, and R56, so that digital processing as described in Patent Document 2 is performed. Without performing this, the analog input signal can be amplified with good linearity. Further, according to the class D amplifier of the second embodiment, unlike the amplifier described in Patent Document 1, the DC output component is set to almost zero volts without requiring a transformer for impedance conversion and DC voltage cut. A class D amplifier with low distortion and low power loss can be provided.

  Next, FIG. 7 shows an example of an output waveform when a sine wave is inputted to the analog input terminal of the class D amplifier according to Example 1 or Example 2 shown in FIG. 1 or FIG. In Example 1 and Example 2, when a sine wave is input to the analog input terminal, the output waveform is the same. FIG. 7A shows a low-pass filter and a load (resistor R) connected to the plus side output + OUT and the minus side output −OUT of the class D amplifier according to the first embodiment or the second embodiment. FIG. 7B shows the waveform after the positive output + OUT in the class D amplifier has passed through the low-pass filter as the output POUT. In FIG. 7B, the waveform after the negative output -OUT in the class D amplifier has passed through the low-pass filter is shown as the output NOUT. Both the outputs POUT and NOUT have waveforms similar to the upper half of the sine wave. However, the output OUT that is a signal applied to the load shown in FIG. 7C is a sine wave. This is because a load (such as a speaker) is connected between the output POUT and the output NOUT (that is, between the plus-side output terminal (POUT) and the minus-side output terminal (NOUT) of the low-pass filter). As shown in FIG. 7C, the output OUT, which is a signal to be added, becomes a difference between the output POUT and the output NOUT (OUT = POUT−NOUT) and becomes a sine wave.

  The class D amplifiers according to the first and second embodiments shown in FIGS. 1 and 5 use at least a triangular wave signal a and a triangular wave signal b 'obtained by inverting and further delaying the triangular wave signal a. Thus, in the class D amplifiers according to the first and second embodiments, the plus side output + OUT and the minus side output −OUT are set to a short time (high level) as shown in FIGS. 2 and 6 even when there is no analog input signal. By outputting the duty ratio of the level period from 0 to several percent, a voltage is output little by little to the low-pass filters (outputs POUT and NOUT). At this time, since the voltage of the output POUT−the output NOUT is applied to the load, the output OUT which is a signal applied to the load becomes zero volts. As a result, when the analog input terminal changes from a no-signal state to a state in which a small signal is input, the class D amplifier according to the first and second embodiments outputs an amplified signal with less distortion even at the time of the change. Can be supplied to the load.

  Next, a third embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a circuit diagram showing a configuration example of a class D amplifier according to Embodiment 3 of the present invention. Unlike the class D amplifier according to the first embodiment, the class D amplifier does not include the delay circuits 21 and 22 as components. In the class D amplifier, the triangular wave signal a is applied to one end of the resistor R10, and the triangular wave signal b is applied to one end of the resistor R12. Other configurations of the class D amplifier shown in FIG. 8 are the same as those of the class D amplifier according to the first embodiment shown in FIG. However, the resistance values of the resistors R5, R6, R7, R8, R9, R10, R11, and R12 forming the synthesis circuit in the class D amplifier are the resistances R5, R6, R7, and R8 of the class D amplifier according to the first embodiment. , R9, R10, R11, and R12 are set under conditions that are not defined. The class D amplifier will be specifically described below.

  This class D amplifier includes resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, capacitors C1, C2, an operational amplifier (operational amplifier) 11, and comparators 12, 13 And an AND circuit (low active) 31 and an AND circuit 32. In addition, a predetermined triangular wave signal a is applied to one end of the resistors R9 and R10 in the figure, and a predetermined triangular wave signal b is applied to one end of the resistors 11 and R12. The triangular wave signal a and the triangular wave signal b are the same waveform signals whose phases are different from each other by 180 degrees. Here, if the triangular wave signal a is a triangular wave in the present invention, the triangular wave signal b is an antiphase triangular wave in the present invention.

  One ends of the resistors R1 and R2 are differential input ends of analog input signals, respectively. One end of the resistor R1 is a plus side input end (+ IN), and one end of the resistor R2 is a minus side input end (−IN). The operational amplifier 11 and the capacitors C1 and C2 constitute an integrator. The analog input signal differentially input by the resistors R1 and R2 is integrated by the integrator and output to the resistors R5, R6, R7, and R8.

The resistors R5, R6, R7, R8, R9, R10, R11, and R12 constitute a synthesis circuit that synthesizes the output of the integrator and the triangular wave signals a and b. This synthesis circuit generates four types of first to fourth synthesized waveforms e, f, g, and h.
The resistance values of the resistors R5, R6, R7, R8, R9, R10, R11, and R12 forming the combining circuit are the resistance values and the input capacitances of the comparator 12 (first comparator) and the comparator 13 (second comparator). Thus, the first and second synthesized waveforms e and f, which are the outputs of the synthesis circuit, and the third and fourth synthesized waveforms g and h have values that give a time difference (phase difference).

  Here, the resistor R5 corresponds to the first resistor in the present invention. The resistor R6 corresponds to the fifth resistor in the present invention. The resistor R7 corresponds to the third resistor in the present invention. The resistor R8 corresponds to the seventh resistor in the present invention. The resistor R9 corresponds to the second resistor in the present invention. The resistor R10 corresponds to the eighth resistor in the present invention. The resistor R11 corresponds to the fourth resistor in the present invention. The resistor R12 corresponds to the sixth resistor in the present invention.

The synthesis circuit has first to fourth synthesis units. The first synthesizing unit synthesizes the negative output of the operational amplifier 11 serving as an integrator and the triangular wave signal a to generate a first synthesized waveform e. The first combining unit includes a resistor R5 (first resistor) having one end connected to the negative output of the operational amplifier 11, and a resistor R9 (second resistor) to which the triangular wave signal a is applied to one end. The other end of the resistor R5 and the other end of the resistor R9 are connected to form an output end.
The second synthesizer synthesizes the plus side output of the operational amplifier 11 and the triangular wave signal b to generate a second synthesized waveform f. The second synthesis unit includes a resistor R7 (third resistor) whose one end is connected to the plus side output of the operational amplifier 11, and a resistor R11 (fourth resistor) to which the triangular wave signal b is applied to one end. The other end of the resistor R7 and the other end of the resistor R11 are connected to form an output end.
The third synthesizer synthesizes the negative output of the operational amplifier 11 and the triangular wave signal b to generate a third synthesized waveform g. The third synthesis unit includes a resistor R6 (fifth resistor) having one end connected to the negative output of the operational amplifier 11, and a resistor R12 (sixth resistor) to which the triangular wave signal b is applied to one end. The other end of the resistor R6 and the other end of the resistor R12 are connected to form an output end.
The fourth synthesizer synthesizes the plus output of the operational amplifier 11 and the triangular wave signal a to generate a fourth synthesized waveform h. The fourth synthesis unit includes a resistor R8 (seventh resistor) having one end connected to the plus side output of the operational amplifier 11, and a resistor R10 (eighth resistor) to which the triangular wave signal a is applied to one end. The other end of the resistor R8 and the other end of the resistor R10 are connected to form an output end.

The resistance values of the resistors R5, R7, R9, and R11 (first to fourth resistors) connected to the comparator 12 are the resistance values of the resistors R6, R8, R10, and R12 (first to fourth resistors) connected to the comparator 13, respectively. Eighth resistor) Each resistance value is preferably set to a value obtained by multiplying a value other than “1”.

For example, the resistance values of the resistors R5, R7, R9, R11 and the resistors R6, R8, R10, R12 are set as follows.
R6 = R8 = R5 × α R5 = R7
R10 = R12 = R9 × α R9 = R11
Here, α ≠ 1.

From the condition of the above formula,
R5 = R7 = R9 = R11
As well as
R5 = R7 ≠ R9 = R11
It is good.
And under the conditions of (R6 = R8) and (R10 = R12), (R6, R8, R10, R1
2) is α times {or (1 / α) times} of (R5, R7, R9, R11).

As a specific example, the resistance values of the resistors R5, R7, R9, and R11 are 1 [KΩ], and the resistance values of the resistors R6, R8, R10, and R12 may be 2 [KΩ] or 500 [Ω]. Good. In this case, α is 2 and 0.5.
The resistance values of the resistors R5, R7, R9, and R11 may be 20 [KΩ], and the resistance values of the resistors R6, R8, R10, and R12 may be 30 [KΩ].
In this case, α is 1.5.
The resistance values of the resistors R5, R7, R9, and R11 are 1 [KΩ], and the resistor R6
, R8, R10, R12 may have a resistance value of 30 [KΩ]. In this case, α is 30.

  As a result, the above-described synthesis circuit is configured so that the resistance values of the resistors R5, R7, R9, and R11 connected to the comparator 12 and the resistors R6, R8, R10, and R12 connected to the comparator 13 are different from each other. With the 13 input capacitors, a time difference (phase difference) can be provided between the first and second combined waveforms e and f and the third and fourth combined waveforms g and h.

The comparator 12 (first comparator) compares the first combined waveform e and the second combined waveform f and outputs the comparison result. The comparator 12 outputs a predetermined “low” level signal (for example, 0 volts) when the first composite waveform e is larger than the second composite waveform f, and the first composite waveform e is greater than the second composite waveform f. If it is smaller, a predetermined “high” level signal is output. The comparator 13 (second comparator) compares the third combined waveform g and the fourth combined waveform h and outputs the comparison result. The comparator 13 outputs a predetermined “low” level signal (for example, 0 volts) when the third synthesized waveform g is larger than the fourth synthesized waveform h, and the third synthesized waveform g is more than the fourth synthesized waveform h. If it is smaller, a predetermined “high” level signal is output.

The AND circuit 31 is a buffer circuit having a logical product function of negative logic inputs. The AND circuit 31 performs an AND operation (low active) to output a “high” level signal when both the output of the comparator 12 and the output of the comparator 13 are “low”, and the operation result is output to the class D amplifier. Output as negative output -OUT. The resistor R3 forms a first feedback circuit that feeds back the output of the AND circuit 31 that also functions as a buffer to the positive side input of the operational amplifier 11.
The AND circuit 32 is a buffer circuit having an AND operation function, performs an AND operation on the output of the comparator 12 and the output of the comparator 13, and sets the operation result as the plus side output + OUT of the class D amplifier. The resistor R4 forms a second feedback circuit that feeds back the operation result of the AND circuit 32 that also functions as a buffer to the negative side input of the operational amplifier 11.
A load (such as a speaker) is connected between the plus side output + OUT and minus side output −OUT of the class D amplifier via a low-pass filter. With these configurations, this class D amplifier can amplify the analog input signals + IN and −IN with low distortion and drive the load with less power loss without using a transformer.

Next, an operation example of the class D amplifier according to the third embodiment having the above configuration will be described with reference to FIGS. 9 to 11 are waveform diagrams showing the operation of each part of the class D amplifier shown in FIG. FIG. 9 shows waveforms of each part of the class D amplifier when the analog input signal + IN and the analog input signal −IN have the same value, that is, when the differential input has a 0 volt value (no input). FIG. 10 shows the waveform of each part of the class D amplifier when (analog input signal + IN)> (analog input signal−IN), that is, when the differential input is positive. FIG. 11 shows waveforms of each part of the class D amplifier when (analog input signal + IN) <(analog input signal−IN), that is, when the differential input is negative.

As shown in FIGS. 9 to 11, the operation of each part of the class D amplifier is often the same as the operation of each part of the class D amplifier according to the first embodiment shown in FIGS. However, the present class D amplifier uses the four triangular wave signals a, a ′, b, and b ′ as the triangular wave, for example, in that the triangular wave signals a and b are used as the triangular wave. This is different from the operation of the class D amplifier. Next, the operation of each part of the class D amplifier will be specifically described.

First, the case of FIG. 9, that is, the case of no input (0 volt value input) will be described. The triangular wave signal a and the triangular wave signal b have a phase difference of 180 degrees. Here, a predetermined noise called dither may be added to each of the triangular wave signals a and b. In this way, distortion of the output waveform can be corrected. Further, instead of the triangular wave signals a and b, a sawtooth wave, an integrated waveform, or the like may be used.

The phase relationship between the triangular wave signal a and the plus side output (plus side output of the operational amplifier 11) d of the integrator is substantially the same. The phase relationship between the triangular wave signal b and the negative output of the integrator (negative output of the operational amplifier 11) c is substantially the same.
The inputs of the comparators 12 and 13, that is, the first to fourth synthesized waveforms e, f, g, and h are waveforms synchronized with the output of the integrator. The first synthesized waveform e and the second synthesized wave f have a phase difference of about 180 degrees, and the third synthesized waveform g and the fourth synthesized wave h have a phase difference of about 180 degrees. The first synthesized waveform e and the fourth synthesized waveform h are substantially the same waveform, and the phases are different by a minute angle θ ′. The second synthesized waveform f and the third synthesized waveform g are substantially the same waveform and are different in phase by a minute angle θ ′.

As described above, the phase difference of the minute angle θ ′ is generated between the first synthesized waveform e and the fourth synthesized waveform h and between the second synthesized waveform f and the third synthesized waveform g. The resistance values of the resistors R5, R7, R9, and R11 connected to are multiplied by a value other than “1” to the resistance values of the resistors R6, R8, R10, and R12 connected to the comparator 13. This is because it is set to a value. That is, the phase difference of the minute angle θ ′ is generated by these resistance values and the input capacitances of the comparators 12 and 13. This minute angle θ ′ corresponds to the minute angle θ in the operation waveform of the class D amplifier according to Embodiment 1 shown in FIG. The minute angle θ ′ can be easily adjusted by adjusting the resistance values of the resistors R5 to R12.

  The outputs J and K of the comparators 12 and 13 have the same waveform as the outputs J and K of the comparators 12 and 13 of the class D amplifier according to Embodiment 1 shown in FIG. Further, the plus side output + OUT and the minus side output −OUT in the class D amplifier have the same waveform as the plus side output + OUT and the minus side output −OUT of the class D amplifier according to the first embodiment shown in FIG. As described above, the operations of the comparators 12 and 13 and the AND circuits 31 and 32 in the class D amplifier are the same as the operations of the comparators 12 and 13 and the AND circuits 31 and 32 of the class D amplifier according to the first embodiment. The operations of the feedback circuit (resistors R3 and R4) and the integrators (the operational amplifier 11, the capacitors C1 and C2) in the class D amplifier are the same as the operations of the feedback circuit and the integrator of the class D amplifier according to the first embodiment. is there.

  Thus, like the class D amplifier according to the first embodiment, the class D amplifier sets the high level period in the plus side output + OUT and the minus side output −OUT to a duty ratio of 0 to several% when there is no input. Can do. Therefore, when the class D amplifier is used for a small signal, the low-pass filter (LC filter or the like) disposed between the output terminal and the load can be omitted.

In addition, as in the case of the class D amplifier according to the first embodiment, this class D amplifier has a period during which the output signal is at a high level when there is no analog input signal (when a 0 volt value is input). Since it can be made sufficiently short, the power loss can be greatly reduced as compared with the conventional one.

  Next, the case where (analog input signal + IN)> (analog input signal -IN) shown in FIG. 10, in other words, the case where the differential input is positive will be described. Comparing FIG. 10 with FIG. 3, the present class D amplifier is different only in that two triangular wave signals a and b are used as triangular waves. Therefore, even when the differential input is positive, this class D amplifier can perform the same operation as the class D amplifier according to the first embodiment except for the synthesis circuit portion. Therefore, in the class D amplifier, when the differential input is positive, the plus side output + OUT is a signal obtained by pulse width modulation of the plus value (differential value) of the analog input signal, and the minus side output −OUT is always at a low level. It has become.

Next, the case of (analog input signal + IN) <(analog input signal −IN) shown in FIG. 11, in other words, the case where the differential input is negative will be described. Comparing FIG. 11 with FIG. 4, the present class D amplifier is different only in that two triangular wave signals a and b are used as triangular waves.
Therefore, even when the differential input is negative, this class D amplifier can perform the same operation as the class D amplifier according to the first embodiment except for the synthesis circuit. Therefore, in the class D amplifier, when the differential input is negative, the negative output -OUT is a signal obtained by pulse width modulation of the negative value (differential value) of the analog input signal, and the positive output + OUT is always at a low level. It has become.

  Thus, according to the class D amplifier of the third embodiment, similarly to the class D amplifier of the first embodiment, an analog input signal is converted into a ternary PWM signal consisting of one of a 0 volt value, a plus value, and a minus value. Can be converted to output. Further, according to the class D amplifier of the third embodiment, when the analog input signal becomes equal to or higher than a predetermined value, one of the plus side output + OUT and the minus side output −OUT (one side) as shown in FIGS. Only a switching waveform is obtained. Therefore, the class D amplifier according to the third embodiment can substantially reduce the switching loss by half as compared with the conventional class D amplifier that switches on both the plus side and the minus side.

  Further, according to the class D amplifier of the third embodiment, since analog feedback is applied by the resistors R3 and R4, the analog input signal is linearly applied without performing digital processing as described in Patent Document 2 above. Can be amplified with good performance. Further, according to the class D amplifier of the third embodiment, unlike the amplifier described in Patent Document 1, the DC output component is set to almost zero volts without requiring a transformer for impedance conversion and DC voltage cut. A class D amplifier with low distortion and low power loss can be provided.

  Furthermore, according to the class D amplifier of the third embodiment, unlike the class D amplifiers of the first and second embodiments, the delay circuits 21, 22, 81 are not used as constituent elements, and the resistance values of the resistors R5 to R12 are adjusted. Thus, a time difference (phase difference) can be provided between the first and second synthesized waveforms e, f and the third and fourth synthesized waveforms g, h. Therefore, the class D amplifier of the third embodiment can be designed and manufactured easily and can provide a high performance class D amplifier.

  Next, a fourth embodiment of the present invention will be described with reference to FIGS. FIG. 12 is a circuit diagram showing a configuration example of a class D amplifier according to Embodiment 4 of the present invention. In FIG. 12, the same components as those in the class D amplifier according to the first embodiment shown in FIG. Unlike the class D amplifiers according to the first and second embodiments, this class D amplifier does not include the delay circuits 21, 22, and 81. Unlike the third embodiment, this class D amplifier has one triangular wave generation circuit. The class D amplifier will be specifically described below.

The class D amplifier includes resistors R1, R2, R3, and R4, capacitors C1, C2, and C100, an operational amplifier (operational amplifier) 11, comparators 112 and 113, and an inverter 121.
, 122, AND circuits 131, 132, and a current source 140. Here, the capacitor 100 and the current source 140 constitute a triangular wave generating circuit, and output the triangular wave to the negative side input terminals of the comparators 112 and 113.

  One ends of the resistors R1 and R2 are differential input ends of analog input signals, respectively. One end of the resistor R1 is a plus side input end (+ IN), and one end of the resistor R2 is a minus side input end (−IN). The operational amplifier 11 and the capacitors C1 and C2 constitute an integrator. The analog input signal differentially input by the resistors R1 and R2 is integrated by the integrator and output to the comparators 112 and 113.

  The negative output of the operational amplifier 11 is connected to the positive input terminal of the comparator 112 (first comparator). The plus output of the operational amplifier 11 is connected to the plus input terminal of the comparator 113 (second comparator). The negative side input ends of the comparators 112 and 113 are both connected to one end of a capacitor (capacitance) 100. One end of the current source 140 is connected to one end of the capacitor 100. The other end of the capacitor 100 is connected to the ground, and the other end of the current source 140 is also connected to the ground. Thus, the comparator 112 compares the negative output of the operational amplifier 11 with the output of the triangular wave generation circuit, and outputs the comparison result. The comparator 113 compares the plus side output of the operational amplifier 11 with the output of the triangular wave generation circuit and outputs the comparison result.

  The output of the comparator 112 is connected to the input terminal of the inverter 121 and one input terminal of the AND circuit 132 (second buffer). The output of the comparator 113 is connected to the input terminal of the inverter 122 and one input terminal of the AND circuit 131 (first buffer). The output of the inverter 121 is connected to the other input terminal of the AND circuit 131. The output of the inverter 122 is connected to the other input terminal of the AND circuit 132. Thus, the AND circuit 131 performs a logical product operation on the signal obtained by inverting the output of the comparator 112 and the output of the comparator 113, and outputs the operation result. The AND circuit 132 performs an AND operation on the signal obtained by inverting the output of the comparator 113 and the output of the comparator 112, and outputs the operation result.

The output of the AND circuit 131 becomes the positive output + OUT of the class D amplifier. This positive output + OUT is fed back to the negative input of the operational amplifier by the resistor R4. The output of the AND circuit 132 becomes the negative output -OUT of the class D amplifier. This negative output -OUT is fed back to the positive input of the operational amplifier by the resistor R3.

  FIG. 13 is a circuit diagram illustrating a specific configuration example of the current source 140. The current source 140 and the capacitor 100 constitute a triangular wave generating circuit. The current source 140 includes transistors T1 and T2, switches S1 and S2, comparators 141 and 142, and NAND circuits 143 and 144.

The transistors T1 and T2 are configured by field effect transistors (FETs). A voltage _VBP is applied to the gate of the transistor T1. This voltage _VBP controls the charging current value of the capacitor 100. A voltage _VBN is applied to the gate of the transistor T2. This voltage V _BN controls the discharge current value of the capacitor 100. The switches S1 and S2 are made of analog switches, for example, and can be constituted by FETs. The switches S1 and S2 switch the direction of the current output from the current source 140, that is, the charge / discharge of the capacitor 100. The current input / output terminal of the transistor T1, the switches S1 and S2, and the current input / output terminal of the transistor T2 are connected in series as shown in FIG. Both the negative input end of the comparator 141 and the positive input end of the comparator 142 are connected to a connection point (hereinafter referred to as “connection point”) between the switch S1 and the switch S2. This connection point is also connected to the capacitor 100 and forms the output point of the triangular wave generation circuit.

  The comparator 142 compares the desired first potential VL with the potential at the connection point, and outputs the comparison result. The comparator 141 compares the desired second potential VH with the potential at the connection point, and outputs the comparison result. Here, it is assumed that the second potential VH is higher than the first potential VL. The difference between the second potential VH and the first potential VL defines the amplitude of the triangular wave. NAND circuits 143 and 144 are connected to form a prop-flop circuit. This flip-flop circuit has outputs from the comparators 141 and 142 as inputs. The opening / closing of the switches S1 and S2 is controlled by the output of the flip-flop circuit. That is, the output of the flip-flop circuit switches between charging and discharging of the capacitor 100 and switching between rising and falling in the triangular wave.

FIG. 14 is a diagram for explaining the operation of the current source 140.
First, the case where the triangular wave G that is the potential of the connection point is lower than the first potential VL, that is, the case of the dotted line K1 will be described. At the dotted line K1, the output of the comparator 142 becomes “L”, the switch S1 is turned on, and the switch S2 is turned off. As a result, a charging current flows through the transistor T1 and the switch S1, and the charging current flows into the capacitor 100. Therefore, the triangular wave G that is the potential of the capacitor 100 rises.

  When the triangular wave G exceeds the first potential VL and reaches the second potential VH, the output of the comparator 141 becomes “L”, the switch S2 is turned on, and the switch S1 is turned off. As a result, the discharge current of the capacitor 100 flows toward the ground via the transistor T2 and the switch S2. Therefore, the triangular wave G that is the potential of the capacitor 100 falls.

When the triangular wave G reaches the first potential VL, the output of the comparator 142 becomes “L”, the switch S1 is turned on, and the switch S2 is turned off. Thereby, a charging current flows again and the triangular wave G rises. Thereafter, by repeating these operations, a triangular wave G as shown in FIG. 14 is generated. The inclination of the triangular wave G when rising can be set by the voltage V _BP for controlling the charging current and the capacitance of the capacitor 100. Also. The slope of the triangular wave G when falling can be set by the voltage _VBN that controls the discharge current and the capacitance of the capacitor 100.

  Next, the case where the triangular wave G is higher than the second potential VH, that is, the case of the dotted line K2 will be described. At the dotted line K2, the output of the comparator 141 becomes “L”, the switch S2 is turned on, and the switch S1 is turned off. As a result, a discharge current of the capacitor 100 flows through the transistor T2 and the switch S2. Therefore, the triangular wave G that is the potential of the capacitor 100 falls. Thereafter, charging and discharging of the capacitor 100 is repeated as described above, and a triangular wave G as shown in FIG. 14 is generated.

  As a result, according to the class D amplifier of this embodiment, the capacitor 100 and the current source 140 can be provided with a triangular wave generation circuit having a simple configuration. Therefore, according to the present embodiment, a class D amplifier having high efficiency and low distortion can be configured at low cost.

Next, an example of the operation of the class D amplifier according to the fourth embodiment having the above configuration will be described with reference to FIGS. 15 to 17 are waveform diagrams showing the operation of each part of the class D amplifier shown in FIG.
FIG. 15 shows waveforms of each part of the class D amplifier when (analog input signal + IN)> (analog input signal−IN), that is, when the differential input is positive. First, as shown in FIG. 14, the triangular wave G is a triangular wave having the first potential VL as a minimum value and the second potential VH as a maximum value.

  The negative output A of the integrator is lower than the positive output B of the integrator. This is because the differential input of the integrator is positive. FIG. 15 shows driving waveforms of the switches S1 and S2 of the current source 140. The switch S1 of the current source 140 is turned on in response to the high level signal during the rising period of the triangular wave G. Further, the switch S1 is turned OFF in response to the low level signal during the descending section of the triangular wave G. The switch S2 of the current source 140 is turned off in response to the low level signal during the rising period of the triangular wave G. Further, the switch S2 is turned on in response to the high level signal during the descending section of the triangular wave G.

  The output C of the comparator 112 is compared with the negative output A of the integrator and the triangular wave G, and becomes “high” when A> G, and “low” when A <G. The output D of the comparator 113 is compared with the positive output B of the integrator and the triangular wave G, and becomes “high” when B> G and becomes “low” when B <G.

The output (+ OUT) E of the AND circuit 131 becomes “high” when the value obtained by inverting the output C of the comparator 112 and the output D of the comparator 113 are both “high”. Thus, the duty ratio during the period when the positive output + OUT is at the high level is substantially proportional to the magnitude of the positive value (differential value) of the analog input signal. In other words, the plus side output + OUT is a signal obtained by pulse width modulating a plus value (differential value) of the analog input signal.
On the other hand, the output (−OUT) F of the AND circuit 132 becomes “high” when both the output C of the comparator 112 and the inverted value of the output D of the comparator 113 are “high”. Therefore, the negative output -OUT is always at a low level.

FIG. 16 shows waveforms of each part of the class D amplifier when (analog input signal + IN) = (analog input signal−IN), that is, when the differential input is not input (0 volt value input). The triangular wave G is the same as the triangular wave G shown in FIG. Further, since the operations of the switches S1 and S2 of the current source 140 with respect to the triangular wave G are the same as in FIG. 15, the drive waveforms of the switches S1 and S2 are omitted in FIG.

  The negative output A of the integrator and the positive output B of the integrator are at the same level. This is because the differential input of the integrator is (+ IN) = (− IN). The output C of the comparator 112 and the output D of the comparator 113 have the same waveform with the same phase. This is because output A = output B.

Since the output (+ OUT) E of the AND circuit 131 is (inverted value of output C) × (output D), it is at the low level for almost the entire period. Since the output (−OUT) F of the AND circuit 132 is (output C) × (inverted value of output D), it is at the low level for almost the entire period. In FIG. 16, the plus side output + OUT and the minus side output −OUT have a slightly high level period. This is due to the difference in delay time due to the offset voltage of the operational amplifier 11 or the non-identity of the constituent elements in the comparators 112 and 113 and the inverters 121 and 122. Therefore, the plus side output + OUT and the minus side output −OUT can be simply and strictly set to a low level over the entire period.

Thus, according to the class D amplifier of the fourth embodiment, when there is no analog input signal (in the case of 0 volt value input), the period during which the output signal is at a high level can be easily and extremely shortened. Therefore, it is possible to significantly reduce the power loss as compared with the conventional one with a simple configuration.

FIG. 17 shows the waveform of each part of the class D amplifier when (analog input signal + IN) <(analog input signal−IN), that is, when the differential input is negative. The triangular wave G is the same as the triangular wave G shown in FIG. Further, since the operations of the switches S1 and S2 of the current source 140 with respect to the triangular wave G are the same as in FIG. 15, the drive waveforms of the switches S1 and S2 are omitted in FIG.

The negative output A of the integrator is higher than the positive output B of the integrator.
This is because the differential input of the integrator is negative. The output C of the comparator 112 is compared with the negative output A of the integrator and the triangular wave G, and becomes “high” when A> G, and “low” when A <G. The output D of the comparator 113 is compared with the positive output B of the integrator and the triangular wave G, and becomes “high” when B> G and becomes “low” when B <G.

The output (−OUT) F of the AND circuit 132 becomes “high” when both the output C of the comparator 112 and the inverted value of the output D of the comparator 113 are “high”. Thus, the duty ratio during the period when the negative output -OUT is at the high level is substantially proportional to the negative value (differential value) of the analog input signal. In other words, the negative output -OUT is a signal obtained by pulse width modulating a negative value (differential value) of the analog input signal.
On the other hand, the output (+ OUT) E of the AND circuit 131 becomes “high” when the value obtained by inverting the output C of the comparator 112 and the output D of the comparator 113 are both “high”. Therefore, the plus side output + OUT is always at a low level.

  Thus, according to the class D amplifier of the fourth embodiment, the analog input signal can be converted into a ternary PWM signal composed of any one of 0 volt value, plus value, and minus value and output. Further, according to the class D amplifier of the fourth embodiment, when the analog input signal is other than 0 volt value, as shown in FIGS. 15 and 17, one of the plus side output + OUT and the minus side output −OUT (one side) ) Only switching waveform. Therefore, the class D amplifier according to the fourth embodiment can reduce the switching loss substantially by half as compared with the conventional class D amplifier that switches on both the plus side and the minus side.

  Further, according to the class D amplifier of the fourth embodiment, analog feedback is applied by the resistors R3 and R4, so that the analog input signal is linearly applied without performing digital processing as described in Patent Document 2 above. Can be amplified with good performance. Further, according to the class D amplifier of the fourth embodiment, unlike the amplifier described in Patent Document 1, the DC output component is set to almost zero volts without requiring a transformer for impedance conversion and DC voltage cut. A class D amplifier with low distortion and low power loss can be provided.

  As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the specific structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.

  For example, in the class D amplifier of the above embodiment, the integrator is configured by a primary integrator. However, the present invention is not limited to this, and the integrator may be configured by a high-order integrator. . In this way, the loop gain can be increased and the distortion rate can be further reduced.

  Although the present invention has been described as a class D amplifier in the above description, the present invention is not limited to this, and the present invention is applied to signal processing circuits other than class D amplifiers, various pulse width modulation amplifiers, and the like. Can do.

11, 61, 64... Operational amplifier (operational amplifier) 12, 13, 62, 63, 112, 1
DESCRIPTION OF SYMBOLS 13 ... Comparator 21, 22, 81 ... Delay circuit 31, 32, 71, 72, 131, 132 ... AND circuit, 121, 122 ... Inverter, 140 ... Current source, C1, C2, C51, C100 ... Capacitor, R1 , R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R51, R52, R53, R54, R55, R56 ... resistors

Claims (12)

An integrator for integrating the analog input signal;
A first comparator and a second comparator for comparing the output of the integrator with a triangular wave;
Buffer means for receiving outputs of the first comparator and the second comparator;
A feedback circuit for feeding back the output of the buffer means to the input side of the integrator;
Delay means for delaying the output of the second comparator with respect to the output of the first comparator;
The buffer means has two output terminals connected to a load;
When the analog input signal is no signal, a pulse having a width depending on the delay amount of the delay means is output from the two output terminals,
When the analog input signal is a signal, one of the two output terminals is set to a predetermined level in a complementary manner according to the polarity of the analog input signal, and the analog input signal is PWMed from the other output terminal. A class-D amplifier that outputs a modulated pulse signal. An integrator for integrating the analog input signal;
A first comparator for comparing the output of the integrator with a first triangular wave;
A second comparator that compares the output of the integrator with a second triangular wave that is a waveform obtained by shifting the phase of the first triangular wave by 180 degrees plus or minus a minute angle;
Buffer means for receiving the output of the first comparator and the output of the second comparator as inputs and outputting a positive side output signal and a negative side output signal;
A feedback circuit that feeds back the difference between the plus side output signal and the minus side output signal to the input side of the integrator;
The buffer means has two output terminals connected to a load;
When the analog input signal is no signal, a pulse having a width depending on the minute angle is output from the two output terminals,
When the analog input signal is a signal, one output terminal of the two output terminals is set to a predetermined level in a complementary manner according to the polarity of the analog input signal, and the analog input signal is PWMed from the other output terminal. A class-D amplifier that outputs a modulated pulse signal.   The buffer means performs an AND operation on the output of the first comparator and the output of the second comparator and outputs the operation result as the minus side output signal; the output of the first comparator; 3. The class D amplifier according to claim 2, further comprising: a second buffer that performs an AND operation on the output of the second comparator and outputs the operation result as the plus-side output signal.   4. The class D amplifier according to claim 2, wherein the feedback circuit includes a differential amplifier that amplifies a difference between the plus side output signal and the minus side output signal. An integrator that integrates the difference between the plus side input signal and the minus side input signal forming the analog input signal;
A delay circuit that delays the phase of the triangular wave by a desired minute angle;
A combining circuit that combines the output of the integrator, the triangular wave, and the output of the delay circuit to output a plurality of signals;
Comparison means for comparing the outputs of the synthesis circuit;
Buffer means for receiving the output of the comparison means;
A feedback circuit for feeding back the output of the buffer means to the input side of the integrator;
The buffer means has two output terminals connected to a load;
When the analog input signal is no signal, a pulse having a width depending on the minute angle is output from the two output terminals,
When the analog input signal is a signal, one of the two output terminals is set to a predetermined level in a complementary manner according to the polarity of the analog input signal, and the analog input signal is PWMed from the other output terminal. A class-D amplifier that outputs a modulated pulse signal. An integrator that integrates the difference between the plus side input signal and the minus side input signal forming the analog input signal;
Combining the output of the integrator and a triangular wave, and combining the output of the integrator and a reverse-phase triangular wave whose phase is shifted by 180 degrees with respect to the triangular wave to output a plurality of signals Circuit,
Comparison means for comparing the outputs of the synthesis circuit;
Buffer means for receiving the output of the comparison means;
A feedback circuit for feeding back the output of the buffer means to the input side of the integrator;
The combining circuit includes a plurality of resistors having at least two types of resistance values, and a phase difference between the plurality of signals that are outputs of the combining circuit is determined by the resistors and the input capacitance of the comparing means. It has a configuration that gives
The buffer means has two output terminals connected to a load;
When the analog input signal is no signal, a pulse having a width depending on the phase difference is output from the two output terminals,
When the analog input signal is a signal, one of the two output terminals is set to a predetermined level in a complementary manner according to the polarity of the analog input signal, and the analog input signal is PWMed from the other output terminal. A class-D amplifier that outputs a modulated pulse signal. An integrator that integrates the difference between the plus side input signal and the minus side input signal forming the analog input signal;
A triangular wave generation circuit comprising a current source and a capacitor;
Comparison means for comparing the output of the integrator and the output of the triangular wave generation circuit;
Buffer means for receiving the output of the comparison means;
A feedback circuit for feeding back the output of the buffer means to the input side of the integrator;
The buffer means has two output terminals connected to a load;
When the analog input signal is no signal, a pulse with a duty ratio depending on the non-identity of the component is output from the two output terminals,
When the analog input signal is a signal, one of the two output terminals is set to a predetermined level in a complementary manner according to the polarity of the analog input signal, and the analog input signal is PWMed from the other output terminal. A class-D amplifier that outputs a modulated pulse signal. In the triangular wave generation circuit,
One end of the capacitor is connected to one input end of the comparison means,
8. The class D amplifier according to claim 7, wherein the current source repeatedly switches the direction of the output current so as to repeatedly charge and discharge the capacitor. One end of the current source is connected to one end of the capacitor,
The current source causes a current to flow in a direction in which the capacitor is charged when the potential of the capacitor becomes lower than the first potential, and discharges the capacitor when the potential of the capacitor becomes higher than the second potential. Has the function of flowing current in the direction
9. The class D amplifier according to claim 8, wherein the second potential is higher than the first potential. The comparison means includes a first comparator that compares the negative output of the integrator and the output of the triangular wave generation circuit, and a second comparator that compares the positive output of the integrator and the output of the triangular wave generation circuit. Consists of
The buffer means includes a first buffer that performs an AND operation on an output obtained by inverting the output of the first comparator and an output of the second comparator, and inverting an output of the first comparator and an output of the second comparator. A second buffer that performs an AND operation with
The feedback circuit includes a first feedback circuit that feeds back the output of the first buffer to the minus side input of the integrator, and a second feedback circuit that feeds back the output of the second buffer to the plus side input of the integrator; The class D amplifier according to any one of claims 7 to 9, characterized by comprising:   The pulse having a duty ratio that depends on the non-identity of the constituent elements has a pulse width of the offset voltage of the integrator or the configuration in the first path from the input of the first comparator to the output of the first buffer. This is due to a delay time difference between the first path and the second path due to non-identity between the element and a component in the second path from the input of the second comparator to the output of the second buffer. The class D amplifier according to claim 10.   The class D amplifier according to any one of claims 1 to 11, wherein the buffer means outputs a pulse in synchronization with a triangular wave when the analog input signal is no signal.

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