JP2007209038A - Power amplifier circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power amplifier circuit using a PWM modulation circuit that prevents variations of the circuit gain. <P>SOLUTION: The PWM modulation circuit 10a comprises a comparator 11, and an integrator 20, whose integrated output is compared with an input signal from a signal source 16 via an amplifier 15 by the comparator 11 to produce a PWM signal having an advanced phase characteristic due to differentiation of the input signal. A switching circuit 21 amplifies the PWM modulation signal The amplified PWM modulation signal is supplied to a speaker 27 via an LC filter 26, and it is also negatively fed back to the input side of the PWM modulation circuit. In this case, a positive source voltage and a negative source voltage of the switching circuit 21 are respectively switched depending on an output of the comparator 11, and input terminals of the comparator 11 receives signals. Thus, variations in the circuit gain are prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power amplifier circuit including a PWM modulation circuit.

  FIG. 10 is a block diagram showing a power amplifier circuit using a conventional PWM modulation circuit. In this figure, an input signal such as an audio signal input from a signal source 31 is applied to a PWM modulation circuit 33 via a resistor 32 and subjected to PWM modulation. The switching circuit 34 is driven by the PWM signal output from the PWM modulation circuit 33, and the switching output is applied to the speaker 36 through the LC filter 35.

  The PWM modulation circuit 33 includes an integrator 39 including an operational amplifier 37 and a capacitor 38, and a comparator 43 including an operational amplifier 40 and resistors 41 and 42 having hysteresis characteristics, and a PWM signal output from the comparator 43. Is fed back to the integrator 39 via the resistor 44. The switching circuit 34 includes an N-type field effect transistor 45 and a P-type field effect transistor 46, and the LC filter 35 includes an inductance 47 and a capacitor 48.

  The PWM modulation circuit 33 outputs a pulse signal having a duty ratio of 50% when no input signal is input. When an input signal is input, an integrated output of the integrator 39 as shown in FIG. 11 is obtained, and this integrated output is added to the comparator 43 having hysteresis characteristics, so that the pulse signal is input from the comparator 43 to the input signal. In response to this, a pulse width modulated PWM signal is output. The transistors 45 and 46 of the switching circuit 34 are alternately turned on and off by this PWM signal, whereby the PWM signal is amplified, and the speaker 36 is driven via the LC filter 35 by this amplified PWM signal.

  When the speaker 36 is directly driven by the PWM signal, the carrier component of the PWM signal flows into the speaker, which may deteriorate the efficiency or destroy the speaker. Therefore, the LC filter 35 is provided to remove the carrier component of the PWM signal. I have to.

The power amplifier circuit using the above-described conventional PWM modulation circuit operates as a self-excited class D amplifier circuit and can generally obtain a flat frequency characteristic as shown in FIG. As shown in the figure, although the slope of the curve differs depending on the characteristics and order of the integrator, a steep characteristic close to that of a multi-order low-pass filter can be obtained, and the carrier component can be effectively removed.
JP 59-125105 A

  Audio power amplifier circuits are required to have low distortion and low output impedance in order to eliminate the influence on sound quality. Conventionally, when a normal linear amplifier is used for the power amplifier circuit, since negative feedback is applied from the output side of the amplifier, distortion and output impedance on the output side can be extremely reduced. Similarly, when a PWM modulation circuit is used for the power amplifier circuit, it is desired to apply negative feedback. However, since the input signal is an analog signal and the PWM signal is a digital signal, negative feedback cannot be applied directly. It is conceivable to use an LC filter as a low-pass filter for conversion to an analog signal and to negatively feed back the output of the LC filter. However, when the output of the LC filter is negatively fed back, the LC filter causes distortion and an increase in output impedance.

  In addition, the LC filter has a secondary or higher order composed of one inductance and one capacitor, and even if the second order is used, a phase rotation of 180 ° occurs in a high region. Furthermore, since the PWM modulation circuit has a low-pass filter characteristic by an integrator, a phase rotation of 180 ° or more occurs in the signal that has passed through the LC filter. Therefore, the analog signal that has passed through the LC filter is negatively affected by the input signal. There was a problem that it was not possible to return.

  Furthermore, the power amplifier circuit shown in FIG. 10 has the following problems. That is, the gain G between the input terminal P of the comparator 43 and the output terminal Q of the switching circuit 34 is set such that the maximum value of the integral output input to the input terminal P is VP and the minimum value is VM. If the voltages are VPX (+ power supply) and VMX (−power supply), the amplitude of the signal at the input terminal P is (VP−VM), and the amplitude of the signal at the output terminal Q is (VPX−VMX). = (VPX-VMX) / (VP-VM) (1) Here, the power supply voltages VPX and VMX may vary. When the power supply voltages VPX and VMX fluctuate, the above-described gain G fluctuates. As a result, the stability of the system changes and the stability must be taken more than necessary.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a PWM modulation circuit and a power amplification circuit capable of reducing phase rotation and performing stable negative feedback. Another object of the present invention is to provide a power amplifier circuit that can suppress fluctuations in circuit gain and thus can obtain stable operation.

  A power amplifying circuit according to the present invention as claimed in claim 1, comprising: an integrator for integrating a PWM signal; and a comparator for outputting the PWM signal by comparing an output of the integrator with an input signal. A switching circuit that is driven by an output signal of the PWM modulation circuit and outputs an amplified PWM signal, a low-pass filter to which a PWM signal output from the switching circuit is input, and an output of the low-pass filter that is the PWM signal A negative feedback circuit that negatively feeds back to the modulation circuit; and a voltage input circuit that switches the positive power supply voltage and the negative power supply voltage of the switching circuit according to the output of the comparator and inputs them to the input terminal of the comparator, The voltage input circuit is between the positive power supply terminal of the switching circuit and the input terminal of the comparator. A first series connection circuit including an inserted first resistor and first switch means; a second resistor inserted between a negative power supply terminal of the switching circuit and an input terminal of the comparator; And a first common terminal connected to the positive power supply voltage via the first resistor, and an input terminal of the comparator. When the output of the comparator corresponds to the positive power supply voltage, the first common terminal is connected to the first contact. When the first contact is connected to the first contact and the output of the comparator corresponds to the negative power supply voltage, the first common terminal is connected to the second contact, and the second switch means ,in front A second common terminal connected to the negative power supply voltage via a second resistor, a first contact connected to the input terminal of the comparator, and a second contact connected to the ground terminal When the output of the comparator corresponds to the negative power supply voltage, the second common terminal is connected to the first contact, and the output of the comparator corresponds to the positive power supply voltage. In this case, the second common terminal is connected to the second contact.

  A power amplifier according to a second aspect of the present invention includes a PWM modulation circuit including an integrator that integrates an input signal, and a comparator that outputs a PWM signal by comparing an output of the integrator with a predetermined voltage; A switching circuit that is driven by the output signal of the PWM modulation circuit and outputs an amplified PWM signal, a low-pass filter to which the PWM signal output from the switching circuit is input, and an output of the switching circuit to the integrator A negative feedback circuit that performs negative feedback, and a voltage input circuit that switches a positive power supply voltage and a negative power supply voltage of the switching circuit according to an output of the comparator and inputs the input to the input terminal of the comparator, and the voltage input circuit includes: A first resistor inserted between a positive power supply terminal of the switching circuit and an input terminal of the comparator; A first series connection circuit by a first switch means, a second resistor interposed between a negative power supply terminal of the switching circuit and an input terminal of the comparator, and a second series connection circuit by a second switch means The first switch means includes a first common terminal connected to the positive power supply voltage via the first resistor, and a first contact connected to the input terminal of the comparator. And a second contact connected to a ground terminal, and when the output of the comparator corresponds to the positive power supply voltage, the first common terminal is connected to the first contact, When the output of the comparator corresponds to the negative power supply voltage, the first common terminal is connected to the second contact, and the second switch means is connected via the second resistor. Negative A second common terminal connected to a source voltage; a first contact connected to the input terminal of the comparator; and a second contact connected to a ground terminal. The second common terminal is connected to the first contact when it corresponds to the power supply voltage, and the second common terminal when the output of the comparator corresponds to the positive power supply voltage. Is connected to the second contact.

  A power amplifier circuit according to a third aspect of the present invention is the power amplifier circuit according to the first or second aspect, wherein the low-pass filter is configured by an LC filter, and an output of the LC filter is supplied to a load. And

  According to the present invention, the PWM signal is compared with the integrated output of the PWM signal and the input signal, and the PWM signal is positively fed back, and the PWM modulation circuit is provided with a comparator configured to have hysteresis characteristics. Since the circuit becomes a phase advance circuit, phase rotation can be reduced by combining the characteristics of the PWM modulation circuit and a low-pass filter such as an LC filter in the subsequent stage. Therefore, the output of the low-pass filter can be stably negatively fed back, and distortion and output impedance on the output side of the power amplifier circuit can be reduced.

  According to the present invention, since the voltage input circuit for switching the positive power supply voltage and the negative power supply voltage of the switching circuit according to the output of the comparator and inputting the voltage to the input terminal of the comparator is provided. The fluctuation of the circuit gain based on the fluctuation of the power supply voltage can be suppressed, so that a stable operation can be obtained.

  According to the present invention, the voltage obtained by dividing the positive power supply voltage of the switching circuit by a constant voltage dividing ratio and the voltage obtained by dividing the negative power supply voltage by the constant voltage dividing ratio are switched according to the output of the comparator. Since the signal is input to the input terminal of the comparator, fluctuations in circuit gain based on fluctuations in the power supply voltage of the switching circuit can be suppressed, and stable operation can be obtained.

  Further, according to the present invention, the triangular wave having the maximum value and the minimum value respectively obtained by dividing the positive power supply voltage of the switching circuit by a constant voltage division ratio and the voltage obtained by dividing the negative power supply voltage by the constant voltage division ratio, respectively. Since there is provided a triangular wave generating circuit for output and a switching means for selectively supplying the output of the triangular wave generating circuit or the output of the switch means to the input terminal of the comparator, it operates as a self-excited type or separately excited type power amplifier. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a PWM modulation circuit according to a first embodiment of the present invention. In FIG. 1, the PWM modulation circuit 10 is composed of a comparator 11, a resistor 12, and an integrator 13, which are operational amplifiers and have hysteresis characteristics. The output signal (PWM signal) of the comparator 11 is output from the output terminal 14 and positively fed back to the comparator 11 via the resistor 12. The integration output of the integrator 13 is input to one input terminal of the amplifier 15, and an input signal from the signal source 16 is input to the other input terminal of the amplifier 15. The output of the amplifier 15 is applied to one input terminal of the comparator 11 via the resistor 17, and the other input terminal of the comparator 11 is grounded. The amplifier 15 is a linear amplifier for obtaining a loop gain.

  FIG. 2 is a block diagram showing a PWM modulation circuit according to the second embodiment of the present invention. The PWM modulation circuit 10 according to the present embodiment is composed of an operational amplifier as shown in the figure and an integrator 20 including a comparator 11 having a hysteresis characteristic, a resistor 12, a resistor 18, and a capacitor 19. The integration output of the integrator 20 is input to one input terminal of the comparator 11, and an input signal from the signal source 16 is input to the other input terminal of the comparator 11 via the resistor 17.

  According to the PWM modulation circuit 10 according to the first and second embodiments, a hysteresis in which the PWM signal output from the comparator 11 and the integration outputs of the integrators 13 and 20 are positively fed via the resistor 12 is applied. A PWM signal having a characteristic obtained by differentiating the input signal is output by being compared by the comparator 11 having the characteristic. That is, the PWM modulation circuit 10 has a differential characteristic in which the frequency response increases with a slope of +6 dB / oct, and the phase of the PWM signal advances by 90 ° with respect to the input signal of the PWM modulation circuit 10.

  FIG. 3 shows a power amplifier circuit according to a third embodiment of the present invention, which is a power amplifier circuit configured as a self-excited class D amplifier circuit using a PWM modulation circuit 10 similar to FIG. In FIG. 3, the PWM signal output from the PWM modulation circuit 10 is obtained by alternately switching the transistors 22 and 23 of the switching circuit 21 via the inverter 30 to be amplified to ± 50 V, for example. This PWM signal is applied to the speaker 27 via an LC filter 26 including an inductance 24 and a capacitor 25. The output of the LC filter 26 is negatively fed back to the amplifier 15 (inversion buffer) through the resistor 28. An input signal from the signal source 16 is applied to the amplifier 15 via a resistor 29, and the amplified output is input to the comparator 11 via the resistor 17.

  FIG. 4 shows the frequency characteristics of the power amplifier circuit according to this embodiment. In FIG. 4, a characteristic a indicates the frequency characteristic of the PWM modulation circuit 10, and a high-frequency rising characteristic having a slope of +6 dB / oct is obtained as shown in the figure, which is a leading phase characteristic. The characteristic b indicates the frequency characteristic of the LC filter 26, and is a delayed phase characteristic having an inclination of −12 dB / oct with a cutoff frequency fc (for example, 50 KHz). The characteristic c is an overall characteristic in which the slopes of the characteristics a and b are combined, and has a slope of −6 dB / oct which is 0 dB at the frequency f1 (for example, 500 KHz).

  That is, in the power amplifier circuit according to the present embodiment, the PWM modulation circuit 10 can obtain a differential characteristic of +6 dB / oct at a frequency about 10 times (20 dB) the cut-off frequency fc of the LC filter 26. Then, by combining the PWM modulation circuit 10 serving as the first-order advance system and the LC filter 26 serving as the second-order delay system, phase rotation can be reduced and stable negative feedback can be applied. In the present embodiment, the configuration of the PWM modulation circuit 10 in FIG. 2 is used, but the configuration of the PWM modulation circuit 10 in FIG. 1 may be used.

  Incidentally, in the third embodiment described above, as described above, when the power supply voltages VPX and VMX of the switching circuit 21 fluctuate, the gain between the input terminal P of the comparator 11 and the output terminal Q of the switching circuit 21 is increased. It will fluctuate. In order to suppress this gain fluctuation, a highly stabilized power supply may be used as the power supply for the switching circuit 21, but this makes the power supply circuit complicated and expensive. The following fourth embodiment is a circuit that prevents gain fluctuations without using a highly stabilized power supply.

  FIG. 5 is a circuit diagram showing a fourth embodiment of the present invention. The circuit shown in this figure is different from the circuit shown in FIG. 3 in that the positive power supply voltage VPX of the switching circuit 21 is connected to the common terminal of the switch 53 via the resistor 52, and the first contact of the switch 53 is not connected to the comparator 11. The second contact is connected to the inverting input terminal and the ground terminal, the negative power supply voltage VMX of the switching circuit 21 is connected to the common terminal of the switch 54 via the resistor 55, and the first contact of the switch 54 is connected to the non-contact of the comparator 11. The second contact point is connected to the inverting input terminal and the ground terminal. In this case, the switch 53 is driven by the output of the comparator 11, and when the output is “H”, the common terminal and the first contact are connected, and when the output is “L”, the common terminal and the second contact are connected. The switch 54 is driven by the output of the inverter 56 that inverts the output of the comparator 11. When the output is “H”, the common terminal and the first contact are connected, and when the output is “L”, the common terminal and the second contact are connected. Connected.

  According to the above configuration, the maximum value VP and the minimum value VM of the signal input to the input terminal P of the comparator 11 are voltages proportional to the power supply voltages VPX and VMX of the switching circuit 21, respectively. As a result, the gain between the input terminal P of the comparator 11 and the output terminal Q of the switching circuit 21 becomes a constant unrelated to the power supply voltages VPX and VMX (see the above formula (1)), and the circuit based on the power supply voltages VPX and VMX. Gain variation can be prevented.

FIG. 6 is a circuit diagram showing the configuration of the fifth embodiment of the present invention. In this figure, 61 is an input terminal to which an analog input signal is input, 62 is an integrating circuit composed of an operational amplifier 63 and a capacitor 64, 65 is a comparator, and 66 is a switch. This switch 66 is driven by the signal at the non-inverting output terminal R2 of the comparator 65. When the signal at the non-inverting output terminal R2 is "H", the common terminal is connected to the first contact, and when it is "L". Has a common terminal connected to the second contact. The common terminal of the switch 66 is connected to the non-inverting input terminal of the comparator 65, and the voltage VM3 is supplied to the first contact and the voltage VP3 is supplied to the second contact. In this case, the voltages VM3 and VP3 are respectively the following voltages.
VM3 = VMX / a (2)
VP3 = VPX / a (3)
However, a is a positive constant.

  A switching circuit 67 is a series connection of a switch 68 that is on / off controlled by the signal at the inverting output terminal R1 of the comparator 65 and a switch 69 that is on / off controlled by the signal at the non-inverting output terminal R2 of the comparator 65. The positive power supply voltage VPX is supplied to one end of the switch 68, and the negative power supply voltage VMX is supplied to one end of the switch 69. The signal at the output terminal Q of the switching circuit 67 is applied to the speaker 27 via the LC filter 26 composed of the inductance 24 and the capacitor 25, and is fed back to the integrating circuit 62 via the resistor 70. The feedback amount is determined by the resistor 70 and the resistor 71. The capacitor 72 is a capacitor for cutting off direct current. The integration circuit 62, the comparator 65, the switch 66, the resistors 70 and 71, and the capacitor 72 described above constitute the PWM modulation circuit 10b.

  In such a configuration, each time the signals at the output terminals R1 and R2 of the comparator 65 are inverted, the switches 68 and 69 of the switching circuit 67 are repeatedly turned on / off, and the integration circuit is turned on according to the on / off of the switches 68 and 69. 62 capacitors 64 are repeatedly charged and discharged. FIG. 7 is a diagram showing a signal waveform at the output terminal (input terminal of the comparator 11) P of the integrating circuit 62 and the signal at the output terminals R1 and R2 of the comparator 65 when the input signal is “0”. Here, when the input signal is input to the input terminal 61, the charge / discharge time of the capacitor 64 changes according to the input signal. As a result, the pulse widths of the signals at the output terminals R1 and R2 of the comparator 65 become the input signal. Will change accordingly.

In the circuit described above, the gain G1 between the output terminal Q of the switching circuit 67 and the input terminal P of the comparator 65 is:
G1 = (1 / 2πf · Cf) / Rf (4)
However, Cf; capacitance of the capacitor 64 Rf; resistance value of the resistor 70. Further, the gain G between the input terminal P of the comparator 65 and the output terminal Q of the switching circuit 67 can be obtained by referring to the expressions (1), (2), and (3).
G = (VPX-VMX) / (VP3-VM3)
= (VPX-VMX) / (VPX / a-VMX / a)
= A ... (5)
Thus, the value is not affected by the power supply voltages VPX and VMX of the switching circuit 67.

  FIG. 8 is a block diagram showing the configuration of the sixth embodiment of the present invention. The embodiment shown in this figure is different from the embodiment shown in FIG. 6 in the configuration of the PWM modulation circuit 10c. That is, the non-inverting input terminal of the comparator 65 is connected to the common terminal of the manual changeover switch 75, the first contact of the switch 75 is connected to the common terminal of the switch 66, and the second contact of the switch 75 is the output of the triangular wave generation circuit 74. Connected to the end.

  In such a configuration, when the manual changeover switch 75 is turned on to the first contact side, the operation is the same as the circuit of FIG. 6, and the PWM modulation circuit 10c operates as a self-excited PWM modulation circuit. When the manual changeover switch 75 is turned on to the second contact side, the output of the triangular wave generation circuit 74 is input to the non-inverting input terminal of the comparator 65, whereby the PWM modulation circuit 10c operates as a separately excited PWM modulation circuit. . Here, if the maximum value and the minimum value of the output triangular wave of the triangular wave generating circuit 74 are determined according to the power supply voltages VPX and VMX of the switching circuit 67, the power supply voltage VPX of the switching circuit 67 is the same as the circuit of FIG. , A circuit that is not affected by VMX.

  FIG. 9 is a block diagram showing the configuration of the seventh embodiment of the present invention. The embodiment shown in this figure is an improvement of the circuit shown in FIG. 10 described above, and is different from the circuit shown in FIG. 10 as follows. First, the positive power supply voltage VPX of the switching circuit 34 is connected to the common terminal of the switch 82 via the resistor 81, the first contact of the switch 82 is connected to the non-inverting input terminal of the comparator 40, and the second contact is connected to the ground terminal. The negative power supply voltage VMX of the switching circuit 34 is connected to the common terminal of the switch 84 via the resistor 83, the first contact of the switch 84 is connected to the non-inverting input terminal of the comparator 40, and the second contact is connected to the ground terminal. Has been. In this case, the switch 82 is driven by the output of the comparator 40. When the output is “H”, the common terminal and the first contact are connected, and when the output is “L”, the common terminal and the second contact are connected. The switch 84 is driven by the output of the inverter 85 that inverts the output of the comparator 40. When the output is “H”, the common terminal and the first contact are connected, and when the output is “L”, the common terminal and the second contact are connected. Connected.

  The output of the comparator 40 is input to the gates of the transistors 45 and 46 via the inverter 86, and the signal at the output terminal Q of the switching circuit 34 is fed back to the integrating circuit 39 via the resistor 87.

  According to the above configuration, as in the circuit of FIG. 5 described above, the maximum value VP and the minimum value VM of the integral output (triangular wave) input to the input terminal P of the comparator 40 are the power supply voltage VPX of the switching circuit 34, respectively. The voltage is proportional to VMX. As a result, the gain between the input terminal P of the comparator 40 and the output terminal Q of the switching circuit 34 becomes a constant unrelated to the power supply voltages VPX and VMX (see the above formula (1)), and the circuit based on the power supply voltages VPX and VMX. Gain variation can be prevented.

It is a block diagram which shows the PWM modulation circuit by the 1st Embodiment of this invention. It is a block diagram which shows the PWM modulation circuit by the 2nd Embodiment of this invention. It is a block diagram which shows the power amplifier circuit by the 3rd Embodiment of this invention. It is a characteristic view of the power amplifier circuit by 3rd Embodiment. It is a block diagram which shows the power amplifier circuit by the 4th Embodiment of this invention. It is a block diagram which shows the power amplifier circuit by the 5th Embodiment of this invention. FIG. 7 is a waveform diagram for explaining the operation of the power amplifier circuit of FIG. 6. It is a block diagram which shows the power amplifier circuit by the 6th Embodiment of this invention. It is a block diagram which shows the power amplifier circuit by the 7th Embodiment of this invention. It is a block diagram which shows the power amplifier circuit using the conventional PWM modulation circuit. It is a wave form diagram which shows operation | movement of the power amplifier circuit using the conventional PWM modulation circuit. It is a frequency characteristic diagram of a power amplifier circuit using a conventional PWM modulation circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... PWM modulation circuit 11, 65 ... Comparator, 12 ... Resistance, 13, 62 ... Integrator, 15 ... Amplifier, 16 ... Signal source, 20 ... Integrator, 21 ... Switching circuit, 26 ... LC filter, 27 ... Speaker 52, 55, 81, 83... Resistor, 53, 54, 66, 82, 84... Switch, 74.

Claims (3)

A PWM modulation circuit having an integrator for integrating the PWM signal, and a comparator for outputting the PWM signal by comparing the output of the integrator with an input signal;
A switching circuit driven by an output signal of the PWM modulation circuit and outputting an amplified PWM signal;
A low-pass filter to which a PWM signal output from the switching circuit is input;
A negative feedback circuit that negatively feeds back the output of the low-pass filter to the PWM modulation circuit;
A voltage input circuit that switches the positive power supply voltage and the negative power supply voltage of the switching circuit according to the output of the comparator and inputs the input to the input terminal of the comparator,
The voltage input circuit includes: a first series connection circuit including a first resistor and a first switch unit interposed between a positive power supply terminal of the switching circuit and an input terminal of the comparator; and a negative power supply of the switching circuit. A second resistor connected between the terminal and the input terminal of the comparator and a second series connection circuit by the second switch means,
The first switch means is connected to a first common terminal connected to the positive power supply voltage via the first resistor, a first contact connected to the input terminal of the comparator, and a ground terminal. The first common terminal is connected to the first contact when the output of the comparator corresponds to the positive power supply voltage, and the output of the comparator is If it corresponds to the negative power supply voltage, the first common terminal is connected to the second contact,
The second switch means is connected to a second common terminal connected to the negative power supply voltage via the second resistor, a first contact connected to the input terminal of the comparator, and a ground terminal. The second common terminal is connected to the first contact when the output of the comparator corresponds to the negative power supply voltage, and the output of the comparator In the case of a voltage corresponding to a positive power supply voltage, the second common terminal is connected to the second contact point. A PWM modulation circuit having an integrator that integrates an input signal, and a comparator that outputs a PWM signal by comparing the output of the integrator with a predetermined voltage;
A switching circuit driven by an output signal of the PWM modulation circuit and outputting an amplified PWM signal;
A low-pass filter to which a PWM signal output from the switching circuit is input;
A negative feedback circuit for negatively feeding back the output of the switching circuit to the integrator;
A voltage input circuit that switches the positive power supply voltage and the negative power supply voltage of the switching circuit according to the output of the comparator and inputs the input to the input terminal of the comparator;
The voltage input circuit includes: a first series connection circuit including a first resistor and a first switch unit interposed between a positive power supply terminal of the switching circuit and an input terminal of the comparator; and a negative power supply of the switching circuit. A second resistor connected between the terminal and the input terminal of the comparator and a second series connection circuit by the second switch means,
The first switch means is connected to a first common terminal connected to the positive power supply voltage via the first resistor, a first contact connected to the input terminal of the comparator, and a ground terminal. The first common terminal is connected to the first contact when the output of the comparator corresponds to the positive power supply voltage, and the output of the comparator is If it corresponds to the negative power supply voltage, the first common terminal is connected to the second contact,
The second switch means is connected to a second common terminal connected to the negative power supply voltage via the second resistor, a first contact connected to the input terminal of the comparator, and a ground terminal. The second common terminal is connected to the first contact when the output of the comparator corresponds to the negative power supply voltage, and the output of the comparator In the case of a voltage corresponding to a positive power supply voltage, the second common terminal is connected to the second contact point. The power amplifier circuit according to claim 1, wherein the low-pass filter includes an LC filter, and an output of the LC filter is supplied to a load.

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