JP2006262121A - Digital amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital amplifier that is effective to obtain a noise level necessary in a digital amplifier of a high output and a high quality use. <P>SOLUTION: A large capacitor C1 and a small capacitor C2 are connected in parallel to a power line of a class D driver, and a ferrite bead 10 is serially connected between both capacitors. The ferrite bead 10 performs waveform shaping of an output of the class D driver, the large capacitor C1 is made to function as a bypass capacitor of the power line and the small capacitor C2 is made to have bluntness adjustment function of an output of the class D driver. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a digital amplifier, and more particularly to a digital amplifier that is effective in reducing noise.

  In recent years, with the progress of multi-function and high integration of AV equipment, digitalization of composite AV machines has been attracting attention. As this type of composite AV machine, an AV component in which a CD player, an AM / FM radio tuner, an audio amplifier, and the like are configured in the same casing is known.

  Furthermore, recently, switching from an analog amplifier to a digital amplifier has been studied as an audio amplifier incorporated in a composite AV machine as described above. By using a digital amplifier, it is smaller and lower in size than a conventional analog amplifier. Since heat generation, high sound quality, etc. can be expected, digital amplifiers are becoming the mainstream of audio amplifiers for composite AV machines.

In this type of digital amplifier, since an audio signal is amplified by a switching operation, countermeasures against noise and distortion are important. As an approach to these problems, methods described in the following patent documents are known.
JP 2003-258565 A Japanese Patent Laid-Open No. 2004-128662 discloses a configuration in which a digital amplifier is driven during playback of a CD player and a digital amplifier is stopped and an analog amplifier is used when receiving radio. Shows how to shield in a case.

  Patent Document 2 compares the audio input signal and the output signal of the output amplification stage, and modulates the output of the constant voltage power supply circuit based on the comparison result, thereby reducing distortion caused by the output amplification stage. A technique is disclosed.

  Any of the methods described in the above patent documents is considered to be an effective method. However, in order to achieve the noise level required for a high-power / high-quality digital amplifier, further noise reduction is necessary. It was.

On the other hand, a technique for reducing noise by inserting a filter or a ferrite bead into a power line is described in the following patent document.
Japanese Patent Laid-Open No. 7-254824 In this patent document 3, as shown in paragraph 0015 of FIG. 1 and FIG. 1, noise superimposed on a power supply line by connecting a power supply line filter in series to the source of an FET is disclosed. A technique for reducing the above is disclosed. Also, paragraph 0023 of the same document discloses a method for preventing a through current by the action of an inductor constituting a power line filter.

  However, even if this type of power supply line filter is simply applied to a digital amplifier, high-frequency noise cannot be removed without deteriorating the audio band signal, and sufficient characteristics cannot be obtained.

  Further, in Patent Document 4, as described in Paragraph 0044 of the same document, by providing a filter including a ferrite bead FB and a capacitor C2 between the inductor 234 and the smoothing capacitor 235 of the DCDC converter 232, A technique for removing noise generated in the switching operation of the DC-DC converter 232 is disclosed.

  However, it is not enough to remove the switching noise generated from the power supply circuit superimposed on the power supply line. To achieve the noise level required for high-power / high-quality digital amplifiers, further noise reduction is required. It was necessary.

  Accordingly, the present invention provides a digital amplifier that is effective in realizing the noise level required for a high-power / high-quality digital amplifier.

  In order to achieve the above object, a first aspect of the present invention is a digital amplifier that performs switching amplification of an audio signal and outputs the analog signal, and is driven by a pulse modulation circuit that modulates the audio signal and an output of the modulation circuit A class D drive circuit, a filter circuit for smoothing the output of the class D drive circuit, a power line for supplying power to the class D drive circuit, a bypass capacitor connected in parallel to the power line, and the power source And an impedance element connected in series to the line, wherein the impedance element is arranged at a subsequent stage of the bypass capacitor closest to the class D drive circuit.

  As described above, by arranging the impedance element after the bypass capacitor closest to the class D drive circuit, the output pulse of the class D drive circuit becomes dull, and as a result, ringing and overshoot are suppressed, causing ringing. The high-frequency noise that has been generated in can be reduced.

  That is, the output element of the class D drive circuit is shaped into a waveform close to an ideal pulse waveform by the impedance element arranged in the power supply line, and this shaping effect contributes to noise reduction of the digital amplifier. Note that if the output pulse is dulled excessively, the audio signal is distorted. Therefore, it is desirable to select a value for the impedance element so that the output of the class D drive circuit is close to the ideal pulse shape.

  As this impedance element, it is desirable to use a ferrite bead that has a low impedance near the voice band and maintains a high impedance at a frequency where ringing occurs.

  On the other hand, in a configuration in which a ferrite bead is disposed in front of a bypass capacitor, which is generally known as a technique for removing noise superimposed on a power supply line, energy stored in the bypass capacitor is constantly supplied to a class D driver. The effect of dulling the output of the drive circuit cannot be expected, and noise due to ringing occurs.

  The invention according to claim 2 is a digital amplifier for switching and amplifying an audio signal and outputting the analog signal, a pulse modulation circuit for modulating the audio signal, and a class D drive driven by the output of the modulation circuit A circuit, a filter circuit for smoothing the output of the class D drive circuit, a power line for supplying power to the class D drive circuit, first and second capacitors connected in parallel to the power line, and the power source An impedance element connected in series with the line, wherein the first capacitor has a larger capacity than the second capacitor, and the second capacitor is more than the first capacitor in the class D drive circuit. The impedance element is disposed between the first capacitor and the second capacitor.

  In this way, by adding an impedance element after the first capacitor having a large capacity, the output pulse of the class D drive circuit becomes dull, and as a result, ringing and overshoot are suppressed, resulting in ringing. The high frequency noise which has been performed can be reduced.

  Here, even if a second capacitor having a small capacitance is connected to the subsequent stage of the impedance element, the output capability of the class D drive circuit becomes dull because of the low energy supply capability of the second capacitor to the class D driver. , Noise due to ringing can be reduced. The second capacitor is also effective as a means for preventing excessive dullness of the class D drive circuit output.

  According to a third aspect of the present invention, there is provided a digital amplifier for switching and amplifying an audio signal for analog output, a pulse modulation circuit for modulating the audio signal, and a class D drive driven by an output of the modulation circuit A circuit, a filter circuit for smoothing the output of the class D drive circuit, a power supply line for supplying power to the class D drive circuit, a DCDC converter connected to the power supply line, and a series connection to the power supply line An impedance element, and the impedance element is disposed in a subsequent stage of the smoothing capacitor constituting the DCDC converter.

  As described above, when the DCDC converter is used, an effect of shaping the output pulse of the class D drive circuit can be obtained by arranging the impedance element in the subsequent stage of the smoothing capacitor having a large capacity.

  According to a fourth aspect of the present invention, there is provided a digital amplifier for switching and amplifying an audio signal for analog output, a pulse modulation circuit for modulating the audio signal, and a class D drive driven by an output of the modulation circuit A circuit, a filter circuit for smoothing the output of the class D drive circuit, a power supply line for supplying power to the class D drive circuit, a bypass capacitor connected in parallel to the power supply line, and a series connection to the power supply line And ferrite beads.

  Thus, by arranging the ferrite beads in the power supply line, the output waveform of the class D drive circuit can be shaped appropriately. In digital amplifiers, it is necessary to minimize loss of the audio signal band and avoid distortion of the audio signal. Therefore, the impedance is low in the audio signal band and the switching frequency band of the class D drive circuit, and in the ringing frequency band. It is necessary to maintain a high impedance.

  Although it is difficult to obtain such characteristics with a general coil or filter, there are many ferrite beads that match these characteristics, so ferrite beads are used as impedance elements for waveform shaping. It is desirable.

  The invention according to claim 5 is a digital amplifier for switching and amplifying an audio signal and outputting the analog signal, a pulse modulation circuit for modulating the audio signal, and a class D drive driven by the output of the modulation circuit A circuit, a filter circuit for smoothing the output of the class D drive circuit, a power supply line for supplying power to the class D drive circuit, a bypass capacitor connected in parallel to the power supply line, and a series connection to the power supply line The impedance element is characterized in that the Q value on the low frequency side is higher than the Q value on the high frequency side with the switching frequency of the class D drive circuit as a boundary.

  In this way, by using an element whose Q value on the low frequency side is higher than the Q value on the high frequency side, the impedance on the high frequency side can be kept high, minimizing the influence on the audio signal. Ringing can be prevented in the state where

  The invention described in claim 6 is a digital amplifier for switching and amplifying an audio signal and outputting the analog signal, a pulse modulation circuit for modulating the audio signal, and a class D drive driven by the output of the modulation circuit A circuit, a filter circuit for smoothing the output of the class D drive circuit, a power supply line for supplying power to the class D drive circuit, a bypass capacitor connected in parallel to the power supply line, and a series connection to the power supply line The impedance element has the lowest impedance in the band of the audio signal, and the impedance in the audio signal band and the switching frequency in the frequency region equal to or higher than the switching frequency of the class D drive circuit. Impedance higher than any impedance And maintains the dance.

  By using an element having such impedance characteristics, it is possible to prevent ringing while minimizing the influence on the audio signal.

  The invention according to claim 7 is a digital amplifier for switching and amplifying an audio signal and outputting the analog signal, a pulse modulation circuit for modulating the audio signal, and a class D drive driven by the output of the modulation circuit Circuit, a filter circuit for smoothing the output of the class D drive circuit, a power line for supplying power to the class D drive circuit, and a waveform shaping for shaping the output waveform of the class D drive circuit connected to the power line And a circuit.

  In this manner, by inserting the waveform shaping circuit into the power supply line, noise caused by ringing generated in the class D driver circuit can be reduced.

  In the configuration described above, the pulse modulation circuit may include a PWM conversion circuit, a ΔΣ conversion circuit, and the like, and may include a function of performing predetermined arithmetic processing on the audio signal. As a modulation method used in the digital amplifier circuit, there are a pulse width modulation method PWM (Pulse Width Modulation) and a pulse density modulation method PDM (Pulse Density Modulation), and the data format input to the digital amplifier circuit is as follows. PCM (Pulse Code Modulation) used in music CDs.

  Here, the audio signal input to the pulse modulation circuit may be an analog signal or a digital signal. When an analog signal is input, the analog signal is directly input to the pulse modulation circuit. Any of the structures that are converted into a pulse signal, or once converted into a digital signal via an A / D converter and then input into the pulse modulation circuit may be used.

  On the other hand, when a digital signal is input, the digital signal is directly input to the pulse modulation circuit and converted into a pulse signal or once converted into an analog signal via a D / A converter. Any of the configurations that are input to the pulse modulation circuit later may be used.

  As an embodiment of the pulse modulation circuit, an analog input PWM modulation circuit or an analog input ΔΣ circuit is used for an analog signal input, and a digital input PWM modulation circuit or a digital input ΔΣ circuit is used for a digital signal input. Use it.

  The digital amplifier according to the present invention includes any of a switching amplifier, a digital amplifier, and a class D amplifier.

  As described above, according to the present invention, it is possible to prevent ringing while minimizing the influence on the audio signal. Therefore, the noise level required for a high-power / high-quality digital amplifier can be reduced. Can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments described below, and can be modified as appropriate.

  FIG. 1 is a block diagram showing an internal configuration of an audio component in which a digital amplifier according to the present invention is incorporated. As shown in the figure, the audio component includes an AM / FM radio receiving unit 510, an audio tape reproducing unit 520, a CD / DVD player 530, and a digital amplifier module 100 incorporating a digital amplifier circuit. .

  Then, an AM / FM radio reception unit 510 that outputs an audio signal in an analog format and an audio tape reproduction unit 520 are connected to the switch SW1, and a signal selected by the switch SW1 is input to the A / D converter 540.

  The analog audio signal output from the AM / FM radio receiving unit 510 or the audio tape reproducing unit 520 is converted into a digital signal by the A / D converter 540 and input to the pulse modulator 120 in the digital amplifier module 100. Is done.

  On the other hand, a CD / DVD player 530 that outputs an audio signal in digital format and a port P3 for inputting an external digital signal are connected to the switch SW2, and the signal selected by the switch SW2 is stored in the digital amplifier module 100. To the pulse modulator 120.

  The digital amplifier module 100 includes a DCDC converter 100, a pulse modulator 120, a class D driver 130, and a low-pass filter 140, and an AM / FM radio reception unit 510, an audio tape playback unit, a CD / DVD player 530 or The audio signal input from the external port P3 is amplified and output to the speaker 620 provided outside the audio component 500 via the port P2.

  Here, the pulse modulator 120 and the class D driver 130 are driven by the power generated by the DCDC converter 110, and this DCDC converter uses the power supply from the battery 610 provided outside the audio component 500. The voltage VDD2 is generated and supplied to the pulse modulator 120, and the voltage VDD1 is generated and supplied to the class D driver 130. The battery 610 is connected to the port P1 and supplies power to the AM / FM radio reception unit 510, the audio tape playback unit, and the CD / DVD player 530.

  Each of the DCDC converter 110 and the pulse modulator 120 is provided with a switching waveform generation circuit, and these waveform generation circuits generate drive waveforms according to the switching frequency of the DCDC converter and the switching frequency of the class D driver 130, respectively. .

  The ferrite bead 10 is connected in series to the output of the DCDC converter 110, that is, the power line of the class D driver 130. By inserting this ferrite bead, the output waveform of the class D driver 130 is shaped.

  FIG. 2 is a circuit block diagram showing an example of the internal configuration of the digital amplifier module shown in FIG. As shown in the figure, the class D driver 130 incorporated in the digital amplifier module 100 includes a high-side switching element FET1, a low-side switching element FET2, a driver amplifier Amp1 that drives each switching element with a PWM signal, and It is composed of Amp2.

  The signal output from the class D driver 130 passes through a low-pass filter 140 composed of an inductor L and a capacitor C, whereby an analog audio signal is extracted, and the speaker 620 is driven by this audio signal.

  Here, the ferrite bead 10 is connected to the source terminal of the FET constituting the class D driver 130, and the output pulse of the class D driver 130 is shaped by the action of the ferrite bead.

  FIG. 3 is a circuit diagram showing a configuration example of a waveform shaping circuit using ferrite beads and a capacitor. As shown in the figure, the waveform shaping circuit includes a large-capacitance capacitor C1 and a small-capacitance capacitor C2 connected in parallel to the power supply line, and a ferrite bead 10 connected in series between the two capacitors.

  Here, it is desirable for the large-capacitance capacitor C1 to function as a bypass capacitor for the power supply line, and a capacitance value of about 10 to 20 μF is set. Further, it is desirable that the small-capacitance capacitor C2 has a dull adjustment function of the class D driver output, and sets a capacitance value of 0 to 1 μF.

  FIG. 4 is a timing chart showing a state of an output waveform of the class D driver using the waveform shaping circuit shown in FIG. As shown in the figures, when a pulse waveform as shown in FIG. 6A is input to the class D driver, the class D driver including the waveform shaping circuit is shown by the solid line in FIG. A simple waveform. The dotted line waveform corresponds to the input shown in FIG.

  On the other hand, the output of a class D driver without a waveform shaping circuit is a waveform with ringing or overshoot, as shown by the solid line in FIG. 3C, and this ringing or overshoot becomes noise and is superimposed on the audio signal. Will do.

  FIG. 5 is a characteristic diagram showing impedance characteristics of the ferrite beads shown in FIGS. In this characteristic diagram, the vertical axis is composed of impedance, and the horizontal axis is composed of frequency. As shown by the hatched bands in the figure, the signals used in the digital amplifier circuit include, for example, an audio signal Audio having a band of 1 k to 5 kHz, and a switching frequency SW-DCDC of a DCDC converter driven at 300 kHz. And a switching signal SW-Drv of a class D driver having a band of 500 to 700 kHz.

  Among these, the signals that are undesirable to be cut off because they affect the quality of the audio signal are the audio signal Audio and the switching signal SW-Drv of the class D driver. The signals that are desired to be cut off are the switching frequency SW-DCDC of the DCDC converter and the ringing frequency of the class D driver generated in the vicinity of 60 MHz.

  Therefore, the frequency characteristic of the ferrite beads added to the power supply line does not have an impedance up to the switching band of the class D driver, as indicated by the symbol FB in FIG. It is desirable to use a characteristic that increases.

  If the switching frequency SW-DCDC of the DCDC converter is lower than the switching frequency of the class D driver, it cannot be removed by the ferrite bead, so a bypass capacitor or DCDC converter added to the power supply line is used. It is removed by the added smoothing capacitor. If the smoothing capacitor has a value of about 150 μF, noise caused by switching of the DCDC converter can be sufficiently removed.

  On the other hand, as indicated by the dotted line in the figure, it is difficult to secure an impedance near the ringing frequency with the low-pass filter LPF, and the inductor element Inductor affects the voice band. It is not desirable as a noise removal technique for digital filters that require high quality.

  The characteristics of the ferrite bead as shown in the figure are expressed by the characteristic that the resistance component changes depending on the frequency. As a ferrite bead suitable for waveform shaping of the class D driver output, the switching frequency of the class D driver is used. As a boundary, it is desirable to select one having a characteristic that the Q value Q1 on the low frequency side is higher than the Q value Q2 on the high frequency side.

  FIG. 6 is a circuit diagram showing an equivalent circuit of the ferrite beads shown in FIGS. As shown in the figure, in the ferrite bead, a resistance component R (f) that changes according to the frequency is added in series to the inductance L, and a parasitic capacitance Cp is added in parallel with the inductance L and the resistance component R (f). Having an equivalent circuit.

  Here, the ferrite bead 10 has a low impedance on the lower frequency side than the switching frequency of the class D driver and a high impedance on the higher frequency side than the switching frequency of the class D driver due to the action of the resistance component R (f). To maintain the characteristics.

  FIG. 7 is a circuit block diagram showing a configuration example when ferrite beads are inserted in the DCDC converter shown in FIGS. 1 and 2. In the example shown in the figure, the voltage VDD1 output to the class D driver and the voltage VDD2 output to the pulse modulator are common.

  As shown in the figure, the DCDC converter 110 is connected to a capacitor C11 connected to a battery 610, a coil L1, a switching element SW1 that is switched by a switching signal output from the PWM circuit 160, a diode D1, and an output terminal Tout. Smoothing capacitor C12, and resistors R11 and R12 that divide the output voltage and feed it back to PWM circuit 160-1.

  Here, an external clock signal CLK is input to the PWM circuit 160. The PWM circuit monitors the outputs VDD1 and VDD2, and uses the input clock signal CLK to drive a waveform of the switching element SW1. Are generated respectively. The switching element SW1 shown in the figure is preferably composed of an FET, and the clock signal CLK may be generated by providing an oscillator inside the DCDC converter.

  In such a configuration, the ferrite bead 10 is disposed after the smoothing capacitor C12 in order to obtain the waveform shaping effect of the class D drive output. Preferably, VDD1 and VDD2 are also intended for shaping the output waveform of the pulse modulation circuit. To the common line. Of course, when the optimum waveform shaping action is different between the class D drive and the pulse modulation circuit, ferrite beads having different characteristics may be arranged in VDD1 and VDD2.

  FIG. 8 is a circuit diagram showing an example in which the present invention is applied to a digital amplifier for multi-channel use. As shown in the figure, when amplifying audio signals Audio1 to AudioN from a plurality of channels, digital amplifier circuits 102-1 to 102-N are provided for each channel, and ferrite beads 10 are provided to the power supply line of each digital amplifier circuit. A set of bypass capacitors of about −1 to N and about 10 μF are respectively arranged. Note that the DCDC converter 110 is preferably common to each channel.

  FIG. 9 is a circuit diagram showing an internal configuration example of each digital amplifier circuit shown in FIG. As shown in the figure, the digital amplifier circuit 102 has a configuration in which the speaker 620 is differentially driven by two class D drivers 130-1 and 130-2 and two low-pass filters 140-1 and 140-2. In the case of such differential driving, it is desirable to place the ferrite bead 10 on the common line of the class D drivers 130-1 and 130-2.

  According to the present invention, noise caused by ringing of the class D driver output can be reduced, and therefore, application to a composite AV machine that requires a high output and high quality digital amplifier is expected.

It is a block diagram which shows the internal structure of the audio component incorporating the digital amplifier which concerns on this invention. FIG. 2 is a circuit block diagram illustrating an internal configuration example of a digital amplifier module illustrated in FIG. 1. It is a circuit diagram which shows the structural example of the waveform shaping circuit using a ferrite bead and a capacitor | condenser. 4 is a timing chart showing a state of an output waveform of a class D driver using the waveform shaping circuit shown in FIG. 3. FIG. 4 is a characteristic diagram showing impedance characteristics of the ferrite beads shown in FIGS. 1 to 3. FIG. 4 is a circuit diagram showing an equivalent circuit of the ferrite beads shown in FIGS. 1 to 3. FIG. 3 is a circuit block diagram showing a configuration example when ferrite beads are placed in the DCDC converter shown in FIGS. 1 and 2. It is a circuit diagram which shows the example which applied this invention to the digital amplifier of a multichannel use. FIG. 9 is a circuit diagram illustrating an internal configuration example of the digital amplifier circuit illustrated in FIG. 8.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Ferrite bead, 100 ... Digital amplifier module, 102 ... Digital amplifier circuit, 110 ... DCDC converter, 120 ... Pulse modulator, 130 ... Class D driver, 140 ... Low-pass filter, 160 ... PWM circuit, 500 ... Audio component, 510 ... AM / FM radio receiver, 520 ... audio tape player, 530 ... CD / DVD player, 540 ... A / D converter, 610 ... battery, 620 ... speaker

Claims (7)

A digital amplifier that amplifies an audio signal by switching and amplifying it,
A pulse modulation circuit for modulating the audio signal;
A class D drive circuit driven by the output of the modulation circuit;
A filter circuit for smoothing the output of the class D drive circuit;
A power line for supplying power to the class D drive circuit;
A bypass capacitor connected in parallel to the power line;
An impedance element connected in series to the power line,
The digital amplifier according to claim 1, wherein the impedance element is disposed at a subsequent stage of the bypass capacitor closest to the class D drive circuit. A digital amplifier that amplifies an audio signal by switching and amplifying it,
A pulse modulation circuit for modulating the audio signal;
A class D drive circuit driven by the output of the modulation circuit;
A filter circuit for smoothing the output of the class D drive circuit;
A power line for supplying power to the class D drive circuit;
First and second capacitors connected in parallel to the power line;
An impedance element connected in series to the power line,
The first capacitor has a larger capacity than the second capacitor.
The second capacitor is disposed closer to the class D drive circuit than the first capacitor,
The digital amplifier according to claim 1, wherein the impedance element is disposed between the first capacitor and the second capacitor. A digital amplifier that amplifies an audio signal by switching and amplifying it,
A pulse modulation circuit for modulating the audio signal;
A class D drive circuit driven by the output of the modulation circuit;
A filter circuit for smoothing the output of the class D drive circuit;
A power line for supplying power to the class D drive circuit;
A DCDC converter connected to the power line;
An impedance element connected in series to the power line,
The digital amplifier according to claim 1, wherein the impedance element is arranged after a smoothing capacitor that constitutes the DCDC converter. A digital amplifier that amplifies an audio signal by switching and amplifying it,
A pulse modulation circuit for modulating the audio signal;
A class D drive circuit driven by the output of the modulation circuit;
A filter circuit for smoothing the output of the class D drive circuit;
A power line for supplying power to the class D drive circuit;
A bypass capacitor connected in parallel to the power line;
And a ferrite bead connected in series to the power line. A digital amplifier that amplifies an audio signal by switching and amplifying it,
A pulse modulation circuit for modulating the audio signal;
A class D drive circuit driven by the output of the modulation circuit;
A filter circuit for smoothing the output of the class D drive circuit;
A power line for supplying power to the class D drive circuit;
A bypass capacitor connected in parallel to the power line;
An impedance element connected in series to the power line,
A digital amplifier, wherein the impedance element has a Q value on a low frequency side higher than a Q value on a high frequency side with a switching frequency of the class D drive circuit as a boundary. A digital amplifier that amplifies an audio signal by switching and amplifying it,
A pulse modulation circuit for modulating the audio signal;
A class D drive circuit driven by the output of the modulation circuit;
A filter circuit for smoothing the output of the class D drive circuit;
A power line for supplying power to the class D drive circuit;
A bypass capacitor connected in parallel to the power line;
An impedance element connected in series to the power line,
The impedance element has the lowest impedance in the audio signal band, and has an impedance higher than both the impedance in the audio signal band and the impedance in the switching frequency in a frequency region equal to or higher than the switching frequency of the class D drive circuit. A digital amplifier characterized by maintaining. A digital amplifier that amplifies an audio signal by switching and amplifying it,
A pulse modulation circuit for modulating the audio signal;
A class D drive circuit driven by the output of the modulation circuit;
A filter circuit for smoothing the output of the class D drive circuit;
A power line for supplying power to the class D drive circuit;
And a waveform shaping circuit for shaping an output waveform of the class D drive circuit connected to the power supply line.

Images