JP5733838B2 - Class D amplifier - Google Patents

Description

  The present invention relates to a class D amplifier for use in an acoustic amplifier, a signal amplifier, or the like included in a home electronic device or a commercial electronic device, and in particular, a class D that can suppress electromagnetic interference generated from the electronic device and reduce the cost of the device. It relates to an amplifier.

  Conventionally, a class D amplifier using a switching technique is known. Unlike analog amplifiers that control the current of amplifier elements to an intermediate state, class D amplifiers have the advantage of greatly reducing excess heat generated by the amplifier elements by turning on / off the switching amplifier elements. It is used in equipment (one-bit AD converter).

  FIG. 1 is a circuit showing a configuration of a class D amplifier of Conventional Example 1 (Patent Document 1). The class D amplifier of Conventional Example 1 converts the signal from the signal source 101a into a pulse signal by a pulse width modulator (PWM) 110a, amplifies the pulse signal by a first pulse amplifier 105a, and a first low-pass filter (LPF). ) 107a removes the pulse component, extracts the frequency component of the original input signal, and outputs it to the load 109a. Further, in general, in order to increase the driving power of the load 109a, the inverted pulse signal obtained by inverting the pulse signal of the pulse width modulator 110a by the inverter 111a is amplified by the second pulse amplifier 106a, and the second low-pass signal is obtained. Output to the other end of the load 109a through the filter (LPF) 108a.

When the input signal _VIN shown in FIG. 2 (a) is input, if the power supply voltage applied to the first pulse amplifier circuit 105a is V, the output pulse voltage shown in FIG. 2 (b) becomes the first pulse amplifier circuit. The output pulse voltage further inverted from 105a is output from the second pulse amplifier circuit 106a, and the output voltage Vo1 and Vo1 obtained through the first low-pass filter 107a and the second low-pass filter 108a are inverted. A voltage is applied to the load 109a. This circuit system is called a BTL (Balance Transformerless or Bridged Transformerless) circuit. In the BTL circuit, the output pulse voltage applied to the load 109a from the first low-pass filter 107a and the second low-pass filter 108a is a binary value of + V and −V, as shown in FIG. The voltage change width is twice the power supply voltage. For this reason, the electromagnetic unnecessary radiation noise accompanying switching becomes large, and as shown in FIG. 2C, the frequency component of the output pulse spreads to a very high frequency.

  In order to suppress the generation of electromagnetic radiation noise accompanying switching, it is necessary to cover the class D amplifier with an electromagnetic shield plate or to insert a filter circuit in each part of the class D amplifier. However, the electromagnetic shield plate is expensive, and it is necessary to provide an expensive element as the noise level at which the filter circuit is generated is large and the noise frequency is high. This increases the manufacturing cost of the class D amplifier.

  Therefore, as a class D amplifier that solves the above problem, a configuration of a class D amplifier of Conventional Example 2 shown in FIG. 3 is known (Patent Document 2). The class D amplifier of Conventional Example 2 includes a first pulse width modulator 103 and a second pulse width modulator 104 connected to a reference signal source 131 that outputs a triangular wave or a sawtooth wave. The first pulse width modulator 103 is directly connected to the signal source 101. The second pulse width modulator 104 is connected to the input signal source 101 via the signal inverter 102. The outputs of the first pulse width modulator 103 and the second pulse width modulator 104 are connected to different terminals of the load 109 via the first low-pass filter 107 and the second low-pass filter 108, respectively.

According to the class D amplifier of Conventional Example 2, as shown in FIG. 4B, the differential pulse voltage Vo ′ obtained between the outputs of the first pulse amplification circuit 105 and the second pulse amplification circuit 106 has its polarity. Are modulated according to the polarity of the input signal _{VIN and} are always output with reference to the ground level. For this reason, the amplitude of the differential pulse voltage Vo ′ is always suppressed to the same magnitude as the power supply voltage V. Therefore, this circuit system is also called a pulse polarity modulation system. In the pulse polarity modulation method, as shown in FIG. 4B, the amplitude of the differential pulse voltage Vo ′ is halved with respect to the output pulse voltage by the amplifier of Conventional Example 1 shown in FIG. Further, as shown in FIG. 4C, the odd-order harmonic component of the frequency spectrum of the output pulse corresponding to the dotted line portion disappears. Further, the pulse frequency of the differential pulse voltage Vo ′ shown in FIG. 4B is twice that of Vo1′−Vo2 in FIG. 2B, so that the cutoff frequency of the low-pass filter is designed to be high and small. And cost can be reduced.

JP-A-7-221564 JP 2009-212902 A

  However, in the actual class D amplifier of the second embodiment, for example, there is a propagation delay amount due to insertion of a signal inverting circuit, and therefore, it is not possible to sufficiently reduce the odd-order harmonics forming the main component of the frequency component of the pulse output. It was.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an amplifier that can significantly reduce odd-order harmonics, which are the main component of the frequency component of pulse output, and can greatly reduce electromagnetic radiation, and that is inexpensive.

In order to solve the above problems, a class D amplifier according to a first technical aspect of the present invention includes a signal inverter that generates an inverted signal obtained by inverting an input signal from a signal source, and an input signal from the signal source. A first pulse width modulator that performs pulse width modulation on the power source, a first switching amplification element and a second switching amplification element connected in series to both ends of the power source, and the first switching amplification element and the first switching amplification element A first pulse amplifier that amplifies the pulse width modulation signal from the first pulse width modulator by alternately turning on and off the two switching amplifier elements, and a second pulse width modulation that applies pulse width modulation to the inverted signal alternating with vessels, and a third switching amplifier element and the fourth switching amplifier element connected in series to both ends of the power supply, and the third switching amplifier element and said fourth switching amplifier element On / off and the second pulse amplifier for amplifying the pulse width modulated signal from the second pulse width modulator by a first low pass only low frequency components of the pulse width modulation signal from the first pulse amplification device a band pass filter, is connected to the second low-pass filter which passes only low frequency components of the pulse width modulation signal from the second pulse amplification unit, between the signal source and the first pulse width modulator, the signal source And a signal delay unit that outputs the generated delay signal to the first pulse width modulator, and the signal delay unit includes an input signal from the signal source, A delay signal obtained by delaying the input signal by a delay time corresponding to the delay time between the inverted signal inverted by the signal inverter and the signal from the first low-pass filter and the second low-pass filter is generated. To the load To.

  With such a configuration, it is possible to reduce odd-order harmonics that form the main frequency component of the pulse output.

  With such a configuration, the delay of the inverted signal by the signal inverter is canceled by the signal delay by the signal delay device, and the in-phase component of the output pulse voltage applied to the load is accurately canceled. For this reason, it is possible to greatly reduce the odd-order harmonics that form the main component of the frequency component of the pulse output. As a result, electromagnetic radiation is greatly reduced and the cost is reduced. At that time, the output differential component of both amplifier circuits including the amplified signal component is applied to the load as usual.

A class D amplifier according to a second technical aspect of the present invention includes a signal inverter that generates an inverted signal obtained by inverting an input signal from a signal source, and performs pulse width modulation on the input signal from the signal source. A first pulse width modulator; a first switching amplification element and a second switching amplification element connected in series at both ends of the power supply; and alternately switching the first switching amplification element and the second switching amplification element. A first pulse amplifier that amplifies the pulse width modulation signal from the first pulse width modulator by turning on / off, a second pulse width modulator that applies pulse width modulation to the inverted signal, and both ends of the power supply A third switching amplifying element and a fourth switching amplifying element connected in series; and alternately turning on / off the third switching amplifying element and the fourth switching amplifying element. A second pulse amplifier that amplifies the pulse width modulation signal from the two-pulse width modulator and one of the first pulse amplifier and the second pulse amplifier, and is a low-pass filter that passes only a low frequency component of the pulse width modulation signal. A band-pass filter, connected between the signal source and the first pulse width modulator, generates a delayed signal obtained by delaying an input signal from the signal source for a predetermined time, and the generated delayed signal is converted into the first pulse width modulator. The signal delay unit delays the input signal by a delay time corresponding to the delay time between the input signal from the signal source and the inverted signal inverted by the signal inverter. It generates a signal, and a signal from the pulse width modulation signal and a low-pass filter from which is not connected to the low-pass filter of the first pulse amplifier circuit and the second pulse amplifier device to a load.

  With such a configuration, it is possible to reduce odd-order harmonics that form the main frequency component of the pulse output.

  With such a configuration, the delay of the inverted signal by the signal inverter is canceled by the signal delay by the signal delay device, and the in-phase component of the output pulse voltage applied to the load is accurately canceled. For this reason, it is possible to greatly reduce the odd-order harmonics that form the main component of the frequency component of the pulse output. As a result, electromagnetic radiation is greatly reduced and the cost is reduced. At that time, the output differential component of both amplifier circuits including the amplified signal component is applied to the load as usual.

FIG. 1 is a circuit diagram showing the configuration of the class D amplifier of the first conventional example. 2 (a) to 2 (c) are diagrams showing waveforms of respective parts of the class D amplifier of the conventional example 1 shown in FIG. FIG. 3 is a circuit diagram showing a configuration of a conventional class D amplifier of the second example. 4 (a) to 4 (c) are diagrams showing waveforms of respective parts of the class D amplifier of the conventional example 2 shown in FIG. FIG. 5 is a circuit diagram illustrating a configuration of the class D amplifier according to the first embodiment. FIG. 6 is a diagram showing output waveforms of the class D amplifier of the second conventional example shown in FIG. 3 and the class D amplifier according to the first embodiment shown in FIG. FIG. 7 is a diagram showing a pulse output and an output waveform of the class D amplifier of the conventional example 2 shown in FIG. FIG. 8 is a diagram illustrating a pulse output and an output waveform of the class D amplifier according to the first embodiment illustrated in FIG. 5. FIG. 9 is a circuit diagram illustrating a configuration of a class D amplifier according to the second embodiment. FIG. 10 is a circuit diagram illustrating a configuration of a class D amplifier according to the third embodiment. FIG. 11 is a circuit diagram illustrating a configuration of a class D amplifier according to the fourth embodiment.

  Hereinafter, a class D amplifier according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 5 is a circuit diagram showing a configuration of the class D amplifier according to Embodiment 1 of the present invention. The class D amplifier shown in FIG. 5 is for amplifying an input signal from the signal source 1 and outputting the amplified signal to the load 8. The signal delay unit 2, the signal inverter 3, and the first pulse width modulation (PWM) unit 4, second pulse width modulator 5, first pulse amplifier 10, second pulse amplifier 11, first low pass filter (LPF) 6, second low pass filter (LPF) 7, triangular wave or sawtooth wave A triangular wave generator 9 for output is provided. The signal inverter 3 inverts the input signal from the input signal source 1 and outputs the inverted signal to the second pulse width modulator 5.

  The signal delay unit 2 delays the input signal from the input signal source 1 by a delay time corresponding to the phase difference between the input signal from the input signal source 1 and the inverted signal inverted by the signal inverter 3. Output to the pulse width modulator 4.

  As the signal delay device 2, a non-inverting amplifier having an amplification factor of 1, or a low-pass filter composed of a resistor, a capacitor, or a coil, connected in one or more stages can be used. The low pass filter may be a passive circuit or an active circuit. Further, the number of stages of the non-inverting amplifier having an amplification factor of 1 is set in accordance with the delay time. When a low-pass filter is used, the time constant between the resistor and the capacitor may be set according to the delay time.

  The first pulse width modulator 4 is composed of a comparator, performs pulse width modulation by comparing the delayed signal from the signal delay device 2 with the triangular wave signal from the triangular wave generator 9, and converts the pulse width modulated signal into the first pulse width modulation signal. Output to the pulse amplifier 10.

  The first pulse amplifier 10 includes, for example, a switching amplifier element composed of a first MOSFET and a second MOSFET connected in series to both ends of the power supply V, and is based on a pulse width modulation signal from the first pulse width modulator 4. The pulse width modulation signal amplified by alternately turning ON / OFF the first MOSFET and the second MOSFET is output to the first low-pass filter 6. As the switching amplifying element, any amplifying element such as an IGBT or a bipolar transistor can be applied in addition to the MOSFET.

  The first low-pass filter 6 includes, for example, a first coil and a first capacitor, or a resistor and a capacitor. Among the pulse width modulation signals from the first pulse width modulator 4, the first coil By passing only the low frequency component below the cutoff frequency determined by the first capacitor, the frequency component of the original input signal is extracted and output to the load 8.

  The second pulse width modulator 5 is composed of a comparator having the same characteristics as the first pulse width modulator 4, and compares the inverted signal from the signal inverter 3 with the triangular wave signal from the triangular wave generator 9 to compare the pulse. The width modulation is performed, and the pulse width modulation signal is output to the second pulse amplifier 11.

  The second pulse amplifier 11 includes, for example, a switching amplification element composed of a third MOSFET and a fourth MOSFET connected in series to both ends of the power supply V, and is based on a pulse width modulation signal from the second pulse width modulator 5. The pulse width modulation signal amplified by alternately turning on / off the third MOSFET and the fourth MOSFET is output to the second low-pass filter 7.

  The second low-pass filter 7 includes, for example, a second coil and a second capacitor, or a resistor and a capacitor. Among the pulse width modulation signals from the second pulse width modulator 5, the second coil By passing only the low-frequency component below the cutoff frequency determined by the second capacitor, the frequency component of the original input signal is extracted and output to the load 8.

  FIG. 6 is a diagram showing output waveforms of the class D amplifier of the second conventional example shown in FIG. 3 and the class D amplifier according to the first embodiment shown in FIG. In FIG. 6, the non-inverted output Vo1 'of Conventional Example 2 is the pulse output of the first pulse amplifier 105 shown in FIG. 3, and the inverted output Vo2 of Conventional Example 2 is the pulse output of the first pulse amplifier 106 shown in FIG. In the inverting output Vo2 of the conventional example 2, a phase change with respect to the non-inverting output Vo1 ′ of the conventional example 2 occurs due to the propagation delay amount DL of the inverter 102 (signal inverting circuit) which is a delay of Vsr with respect to Vs ′. ing. In the first embodiment, the non-inverted output Vo1 is the pulse output of the first pulse amplifier 10 shown in FIG. 5, and the inverted output Vo2 is the pulse output of the second pulse amplifier 11 shown in FIG. Vs is an output of the signal delay unit 2, and Vsr is an output of the signal inverter 3.

  Since the pulse P1 of the inverting output Vo2 of the conventional example 2 is shifted to the right from the center of the pulse of the non-inverting output Vo1 ′ of the conventional example 2, as shown in FIG. 7, the first pulse amplifier 105 and the second pulse amplifier 106 The differential pulse (Vo2-Vo1 ′) between the outputs also has the effect of the pulse P1, and the odd-order harmonics are increased, and electromagnetic radiation is increased. In FIG. 7, the pulse indicated by the alternate long and short dash line is the non-inverted output Vo1 'of the second conventional example.

  On the other hand, in the class D amplifier according to the first embodiment, as shown in FIG. 6, the same delay occurs in the output Vs of the signal delay unit 2 and the output Vsr of the signal inverter 3, and the propagation delay amount The difference in DL is zero. That is, since the pulse P2 of the inverted output Vo2 is adjusted so as to be positioned at the center of the pulse of the non-inverted output Vo1, the interval between the outputs of the first pulse amplifier 10 and the second pulse amplifier 11 is adjusted as shown in FIG. The pulse P2 appears at the center of the pulse signal of the differential pulse (Vo2-Vo1). As a result, in the class D amplifier according to the first embodiment, odd-order harmonics are greatly reduced, and electromagnetic unnecessary radiation is greatly reduced. In FIG. 8, the pulse indicated by the alternate long and short dash line is the non-inverted output Vo1.

  That is, the in-phase component of the output pulse voltage applied to the load 8 is accurately canceled by canceling the delay of the inverted signal by the signal inverter 3 by the signal delay by the signal delay device 2. As a result, in the class D amplifier according to the first embodiment, the odd-order harmonics that form the main component of the frequency component of the pulse output can be greatly reduced, and the even-order harmonics and the sideband components are electromagnetic radiation. Therefore, in the class D amplifier according to the first embodiment, the generated noise is almost halved, and electromagnetic unnecessary radiation can be greatly reduced. In the differential output voltage waveform that actually drives the load, the pulse voltage amplitude is halved, and the pulse polarity is controlled according to the polarity of the signal, so that the conventional output power can be secured.

  Further, the electromagnetic shield plate can be configured with a simple shape at an acceptable level, the mounting portion thereof can be omitted, and the filter circuit can be greatly reduced. Further, even from the viewpoint of the occurrence of noise disturbance, since interference with wireless connections of mobile phones, computers, etc. can be greatly reduced, this technology is extremely highly compatible with the information society. Thus, the industrial and social effects of the present invention are extremely high.

Table 1 is a table showing a comparison of output frequency spectra of the conventional example 1, the conventional example 2, and the pulse polarity modulation method of the first example. In Table 1, Conventional Example 1 shows the output frequency spectrum of the Class D amplifier of Conventional Example 1 shown in FIG. 1, Conventional Example 2 shows the output frequency spectrum of the Class D amplifier of Conventional Example 2 shown in FIG. Example 1 shows an output frequency spectrum of the class D amplifier of Example 1 shown in FIG.

  From the results shown in Table 1, it can be seen that by inserting the signal delay device 2 (non-inverting circuit) in the pulse polarity modulation system circuit, the signal propagation delay can be canceled and the odd harmonics can be reduced to −35 dB or less of the fundamental wave. Can be confirmed.

  FIG. 9 is a circuit diagram showing a configuration of a class D amplifier according to Embodiment 2 of the present invention. The class D amplifier according to the second embodiment illustrated in FIG. 9 is different from the class D amplifier according to the first embodiment illustrated in FIG. 5 in that the signal delay device 2 is deleted, and the first low-pass filter 6 and the second low-pass A third low-pass filter 6a and a fourth low-pass filter 7a are used instead of the pass filter 7, and a triangular wave generator 9a is used instead of the triangular wave generator 9.

  The other configuration shown in FIG. 9 is the same as the configuration shown in FIG. Here, the first pulse width modulator 4, the second pulse width modulator 5, the triangular wave generator 9a, the third low-pass filter 6a, and the fourth low-pass filter 7a will be described.

  The triangular wave generator 9 a generates a triangular wave signal having a period sufficiently longer than the delay time of the signal inverter 3 (period in which the delay time can be ignored).

  The first pulse width modulator 4 is connected to the input signal source 1 and has a triangular wave signal from the triangular wave generator 9 a having a period sufficiently longer than the delay time of the signal inverter 3, and an input signal from the input signal source 1. Are compared to generate a pulse signal having a period sufficiently longer than the delay time of the signal inverter 3, that is, a pulse width modulation is applied to the input signal from the input signal source, and the first pulse amplifier 10 is output.

  The second pulse width modulator 5 is connected to the signal inverter 3 and includes a triangular wave signal from the triangular wave generator 9 a having a period sufficiently longer than the delay time of the signal inverter 3 and an inverted signal from the signal inverter 3. Are compared to generate a pulse signal having a period sufficiently longer than the delay time of the signal inverter 3, that is, the pulse width modulation is applied to the inverted signal from the signal inverter 3 to generate the second pulse. Output to the amplifier 11.

  Since the frequency of the output pulse also decreases as the period of the triangular wave signal generated by the triangular wave generator 9a increases, the cutoff frequencies of the third low-pass filter 6a and the fourth low-pass filter 7a are also set low.

  The delay time of the signal inverter 3 is the propagation delay amount DL described in the class D amplifier according to the first embodiment, that is, the level of the input signal from the input signal source 1 and the inverted signal inverted by the signal inverter 3. This is the delay time corresponding to the phase difference.

  The delay time τ of the signal inverter 3 is determined based on the following formula (1) so as to be sufficiently shorter than the pulse period T.

τ << T = 1 / (2 · f · D) (1)
f is the frequency of the triangular wave signal, and D is the dynamic range of the on / off duty ratio of the pulse signal. The period T is 10 times or more of the delay time τ, and more preferably 100 times or more.

  The first pulse amplifier 10 and the second pulse amplifier 11 alternately turn on / off switching amplifying elements composed of a plurality of MOSFETs or the like by a pulse signal having a period sufficiently longer than the delay time of the signal inverter 3.

  Thus, according to the class D amplifier according to the second embodiment, the first pulse width modulator 4 generates a pulse signal having a period sufficiently longer than the delay time of the signal inverter 3, and the second pulse width Since the modulator 5 generates a pulse signal having a period sufficiently longer than the delay time of the signal inverter 3, the signal delay time due to the signal inversion can be ignored in the output pulse signal. That is, the output pulse signal has the same waveform as that when there is no signal delay due to signal inversion.

  For this reason, the delay time of the output pulse voltage applied to the load 8 is canceled out, and the odd-order harmonics that form the main component of the frequency component of the pulse output can be greatly reduced, so that unnecessary electromagnetic radiation can be greatly reduced. That is, in the class D amplifier according to the second embodiment, the same effect as that of the class D amplifier according to the first embodiment can be obtained.

  FIG. 10 is a circuit diagram showing a configuration of a class D amplifier according to Embodiment 3 of the present invention. The class D amplifier according to the third embodiment shown in FIG. 10 deletes the second low-pass filter 7 from the class D amplifier according to the first embodiment shown in FIG.

  When the output voltages of the first pulse width modulator 4 and the second pulse width modulator 5 do not have such a large amplitude or distortion that noise generation becomes a problem, only the noise component included in the output current may be removed. . In this case, noise generation can be suppressed by deleting the second low-pass filter 7 and providing only the third low-pass filter 6. For this reason, electromagnetic unnecessary radiation can be significantly reduced.

  The same effect can be obtained by deleting the first low-pass filter 6 and providing only the second low-pass filter 7 instead of deleting the second low-pass filter 7.

  FIG. 11 is a circuit diagram showing a configuration of a class D amplifier according to Embodiment 4 of the present invention. The class D amplifier according to the fourth embodiment shown in FIG. 11 is characterized in that the fourth low-pass filter 7a is deleted from the class D amplifier according to the second embodiment shown in FIG.

  When the output voltages of the first pulse width modulator 4 and the second pulse width modulator 5 do not have such a large amplitude or distortion that noise generation becomes a problem, only the noise component included in the output current may be removed. . In this case, noise generation can be suppressed by deleting the fourth low-pass filter 7a and providing only the third low-pass filter 6a. For this reason, electromagnetic unnecessary radiation can be significantly reduced.

  The same effect can be obtained by deleting the third low-pass filter 6a and providing only the fourth low-pass filter 7a instead of deleting the fourth low-pass filter 7a.

  The present invention can be used for an acoustic amplifier, a signal amplifier, or the like included in a home electronic device or a commercial electronic device.

Claims (2)

A class D amplifier,
A signal inverter that generates an inverted signal obtained by inverting the input signal from the signal source;
A first pulse width modulator that performs pulse width modulation on the input signal from the signal source;
A first switching amplifying element and a second switching amplifying element connected in series to both ends of the power supply, and the first switching amplifying element and the second switching amplifying element are alternately turned on / off to A first pulse amplifier for amplifying a pulse width modulation signal from the one pulse width modulator;
A second pulse width modulator that applies pulse width modulation to the inverted signal;
A third switching amplifying element and a fourth switching amplifying element connected in series to both ends of the power supply, and the third switching amplifying element and the fourth switching amplifying element are alternately turned on / off A second pulse amplifier for amplifying the pulse width modulation signal from the second pulse width modulator;
A first low-pass filter which passes only low frequency components of the pulse width modulation signal from the first pulse amplification device,
A second low-pass filter which passes only low frequency components of the pulse width modulation signal from the second pulse amplification device,
Connected between the signal source and the first pulse width modulator, generates a delay signal obtained by delaying the input signal from the signal source for a predetermined time, and generates the delayed signal as the first pulse width modulator. A signal delay device that outputs to
The signal delay unit generates the delayed signal obtained by delaying the input signal by a delay time corresponding to a delay time between the input signal from the signal source and the inverted signal inverted by the signal inverter. And
A class-D amplifier that outputs a signal from the first low-pass filter and a signal from the second low-pass filter to a load. A class D amplifier,
  A signal inverter that generates an inverted signal obtained by inverting the input signal from the signal source;
  A first pulse width modulator that performs pulse width modulation on the input signal from the signal source;
  A first switching amplifying element and a second switching amplifying element connected in series at both ends of the power supply, and the first switching amplifying element and the second switching amplifying element are alternately turned on / off to turn the first switching amplifying element on and off; A first pulse amplifier for amplifying a pulse width modulation signal from the one pulse width modulator;
  A second pulse width modulator that applies pulse width modulation to the inverted signal;
  A third switching amplifying element and a fourth switching amplifying element connected in series to both ends of the power supply, and the third switching amplifying element and the fourth switching amplifying element are alternately turned on / off A second pulse amplifier for amplifying the pulse width modulation signal from the second pulse width modulator;
  A low-pass filter connected to one of the first pulse amplifier and the second pulse amplifier and passing only a low-frequency component of a pulse width modulation signal;
  Connected between the signal source and the first pulse width modulator, generates a delay signal obtained by delaying the input signal from the signal source for a predetermined time, and generates the delayed signal as the first pulse width modulator. A signal delay device that outputs to
  The signal delay unit generates the delayed signal obtained by delaying the input signal by a delay time corresponding to a delay time between the input signal from the signal source and the inverted signal inverted by the signal inverter. And
  A pulse width modulation signal from a side of the first pulse amplifier and the second pulse amplifier not connected to a low-pass filter and a signal from the low-pass filter are output to a load. Class D amplifier.

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