JP2007104285A - Digital amplifier and switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital amplifier which is effective in attaining a noise level required by a digital amplifier for high-output/high quality use. <P>SOLUTION: A ripple extracting circuit 10 which generates an opposite-phase waveform of a ripple component included in a class D driving circuit 130 is connected behind the driving circuit 130, and the opposite-phase waveform generated by the ripple extracting circuit is loaded in a rear stage of a coil L1 constituting a low-pass filter 140. In this constitution, source voltages V1 and V2 of a main line and a subordinate line, and inductance values L1 and L2 of coils L1 and L2 are so set that "V1/L1=V2/V2", and then a ripple component on the main line is canceled. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital amplifier and a switching power supply, and more particularly to a digital amplifier and a switching power supply effective for 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. Similarly, since the switching power driver circuit is used in the switching power supply as well as the digital amplifier, a fundamental wave residual component called carrier ripple noise exists in the output stage of the switching circuit.

  Since this remaining ripple noise often becomes an unwanted noise and adversely affects other circuits, it is necessary to reduce the ripple noise. However, as a technique, a method of increasing the time constant or order of the output stage filter is generally used. Is applied to.

  However, increasing the time constant and order of the filter affects the cost and size, so it is desirable to configure the filter with the smallest possible time constant and order.

Here, as an approach to noise reduction other than increasing the time constant and the order of the filter, for example, a method described in the following patent document is 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 method for removing a switching component superimposed on an audio signal of a digital amplifier is described in the following patent document.
JP, 2002-368554, A The method indicated in this patent document shows the method of removing a fundamental wave component by synthesize | combining a non-inverted PWM waveform and the inverted PWM waveform.

  However, with this method, if the phase of the non-inverted PWM waveform and the inverted PWM waveform are out of phase, the audio signal is distorted and reactive power is likely to be generated, and two non-inverted and inverted drive circuits are prepared. There is a need to.

Further, a method for removing a ripple component caused by a switching component of a switching power supply is described in the following patent document.
US Pat. No. 5,929,692 The technique described in this patent document is a technique in which a ripple component of the main path is extracted to create a waveform having a phase opposite to that of the main path, and this is put on the main path to cancel the ripple voltage. It is shown.

  However, this method also requires two drive circuits, non-inverted and inverted, as in the above-mentioned Patent Document 3, and a coil with a large inductance value is used to extract a ripple component from the output of the inverted drive circuit. Is required.

  Accordingly, the present invention provides a digital amplifier and a switching power supply that are effective in reducing ripple components with a simple configuration.

  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 First drive circuit, a filter including a first coil and a first capacitor for smoothing the output of the first drive circuit, a speaker driven by the output of the filter, and the first drive A second drive circuit supplied with a power supply voltage different from the circuit, and adding the output of the second drive circuit to a signal passing through the filter via a series circuit of a second coil and a second capacitor And a means for performing the above.

  As described above, by providing the second drive circuit to which the power supply voltage different from the first drive circuit is supplied, two high power drive drive circuits as described in Patent Document 4 are provided. Even if it does not take the structure to provide, the ripple cancellation effect can be acquired.

  Here, a line connected from the output of the first drive circuit to the speaker via the filter is a main path, and a line connected to the filter from the second drive circuit via the second coil and the second capacitor. Is a sub-path, a reverse-phase waveform of the ripple component included in the output of the first trie circuit is generated by this sub-path, and this anti-phase waveform is added to the main path to reduce output ripple. Figured.

  According to a second aspect of the present invention, in the first aspect of the present invention, the power supply voltage supplied to the first drive circuit is V1, and the voltage on the speaker side of the first coil is V1 ′. When the power supply voltage supplied to the drive circuit is V2, the voltage on the speaker side of the second coil is V2 ′, the inductance of the first coil is L1, and the inductance of the second coil is L2. V1-V1 ′) / L1 = (V2−V2 ′) / L2 is satisfied.

  Thus, the power supply voltage of the main path and the inductance value of the coil, and the power supply voltage of the sub path and the inductance value of the coil are in the condition of “(V1−V1 ′) / L1 = (V2−V2 ′) / L2”. By setting, the slopes of the currents flowing through both coils can be matched, so that the ripple component can be canceled effectively.

  Here, the values of V1 ′ and V2 ′ vary with the audio signal, but the ratio of V1-V1 ′ and V2-V2 ′ is approximately constant, so that V1, V2, L1, When L2 is determined, it may be determined under the condition of “V1 / L1 = V2 / L2”, and the intermediate voltage “(1/2) · V1 / L1 = (1/2) · V2 / L2” may be set. It is good also as conditions of ".

  According to a third aspect of the present invention, in the first aspect of the present invention, the power supply voltage supplied to the first drive circuit is V1, the power supply voltage supplied to the second drive circuit is V2, and the first drive circuit is the second drive circuit. When the inductance of one coil is L1, and the inductance of the second coil is L2, the relationship of V1> V2 and L1> L2 is satisfied.

  Thus, by setting the power supply voltage of the main path and the inductance value of the coil and the power supply voltage of the sub path and the inductance value of the coil under the conditions of “V1> V2 and L1> L2,” a low voltage, small size A ripple canceling effect suitable for the configuration can be obtained.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the inductance of the first coil is L1, the inductance of the second coil is L2, the capacitance value of the first capacitor is C1, When the capacitance value of the second capacitor is C2, the relationship of L1 · C1 <L2 · C2 is satisfied.

  In this way, the inductance value of the coil and the capacitance value of the capacitor provided in the main path, and the inductance value and the capacitance value of the capacitor provided in the sub-path under the condition “L1 · C1 <L2 · C2”. By setting, a more preferable ripple canceling effect can be obtained. In this condition, it is desirable to satisfy the conditions of C2 ≧ C2 ′ / 4 and L1 · C1 = L2 · C2 ′.

  In addition, the capacitance value C2 of the capacitor provided in the sub path is equal to or more than a quarter of the capacitance value having the same resonance frequency as the inductance value L1 of the coil provided in the main path and the capacitance value C1 of the capacitor. It is desirable to set.

  According to a fifth aspect of the present invention, in the first aspect of the invention, the power supply voltage supplied to the first drive circuit and the power supply voltage supplied to the second drive circuit are linked. Features.

  In this way, by linking the power supply voltages of the drive circuits, the ripple canceling effect can be maintained even if the power supply voltage fluctuates due to some factor.

  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 Circuit, a filter for smoothing the output of the class D drive circuit, a speaker driven by the output of the filter, and a ripple component included in the output of the class D drive circuit using the output of the class D drive circuit And means for generating a negative phase waveform and means for adding the negative phase waveform to a signal passing through the filter.

  In this way, by generating an antiphase waveform using the output of the class D drive circuit, ripple cancellation can be achieved without having to provide two high power drive circuits as described in Patent Document 4 above. An effect can be obtained.

  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 A circuit, a filter including a first coil and a first capacitor for smoothing the output of the class D drive circuit, a speaker driven by the output of the filter, and means for branching the output of the class D drive circuit Level adjusting means for adjusting the level of the branched signal, phase inverting means for inverting the phase of the branched signal, and the signal after the phase inversion via a series circuit of a second coil and a second capacitor. And means for adding to the subsequent stage of the first coil.

  In this way, by adjusting the level of the signal branched from the class D drive circuit, there is no configuration in which two high power drive drive circuits as described in Patent Document 4 described above are provided, and the low voltage A negative-phase ripple waveform can be generated by driving. As the level adjusting means, means such as an attenuator and an amplifier can be used.

  The invention according to claim 8 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 for smoothing the output of the class D drive circuit, a speaker driven by the output of the filter, and an inverse of the ripple component included in the output of the class D drive circuit using the output of the pulse modulation circuit And means for generating a phase waveform and means for adding the negative phase waveform to a signal passing through the filter.

  In this way, by generating the anti-phase component using the output of the pulse modulation circuit, the ripple canceling effect can be obtained without using two high-power drive circuits as described in Patent Document 4 above. Can be obtained.

  According to a ninth 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 Circuit, a filter including a first coil and a first capacitor for smoothing the output of the class D drive circuit, a speaker driven by the output of the filter, and a level adjusting means for adjusting the output level of the modulation circuit Phase inverting means for inverting the output phase of the modulation circuit; means for adding the signal after the phase inversion to a subsequent stage of the first coil via a series circuit of a second coil and a second capacitor; It is characterized by comprising.

  In this way, by adjusting the output level of the modulation circuit, there is no configuration in which two drive circuits of high power drive as described in Patent Document 4 described above are provided, and the anti-phase ripple is low-voltage driven. Waveforms can be generated. As the level adjusting means, means such as an attenuator and an amplifier can be used.

  The invention according to claim 10 is a switching power supply for converting an input voltage into a predetermined output voltage, a switching circuit for switching the input voltage, a first coil for smoothing the output of the switching circuit, and A first capacitor; means for branching the output of the switching circuit; level adjusting means for adjusting the level of the branched signal; phase inverting means for inverting the phase of the branched signal; Means for adding a signal to a subsequent stage of the first coil through a series circuit of a second coil and a second capacitor.

  In this way, by adjusting the level of the signal branched from the switching circuit, a negative-phase ripple waveform can be generated without using two switching circuits driven by high power as described in Patent Document 4 above. can do.

  The invention according to claim 11 is a switching power supply for converting an input voltage into a predetermined output voltage, wherein the switching circuit performs switching of the input voltage according to a predetermined pulse waveform, and smoothes the output of the switching circuit. A first coil and a first capacitor; level adjusting means for adjusting the level of the pulse waveform; phase inverting means for inverting the phase of the pulse waveform; and And means for adding to the subsequent stage of the first coil through a series circuit of two capacitors.

  In this way, by adjusting the level of the pulse waveform that is the driving waveform of the switching circuit, the anti-phase ripple can be obtained without providing two switching circuits of high power driving as described in Patent Document 4 described above. Waveforms can be generated.

  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 configurations 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 through a D / A converter. Any configuration that is 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, since the ripple component superimposed on the output of the switching circuit can be extracted effectively, the noise level of the digital amplifier and the switching power supply can be reduced with a simple configuration. .

  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, a low-pass filter 140, and a ripple extraction circuit, and an AM / FM radio reception unit 510, an audio tape playback unit, a CD / Amplifies the audio signal input from the DVD player 530 or the external port P3, and differentially drives the speaker 620 provided outside the audio component 500 via the port P2 with an analog output.

  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. Thus, the voltage V1 is supplied to the pulse modulator 120 and the class D driver 130, and the voltage V2 is supplied to the noise extraction circuit 10. 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 (not shown). 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. Generate.

  The ripple extraction circuit 10 generates a negative-phase waveform of a ripple component included in the output from the output of the class D driver 130 using the power supply voltage V2, and the low-pass filter 140 that uses the generated negative-phase waveform as a main path. By adding to the output, the ripple component superimposed on the main path is canceled. That is, this ripple extraction circuit constitutes a sub route for generating a reverse phase waveform of the ripple component included in the main route.

  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 pulse signal output from the class D driver 130 passes through a low-pass filter 140 composed of a coil L1 and a capacitor C1, and an analog audio signal is extracted. An anti-phase waveform of the included ripple component is generated, and this anti-phase waveform is added to the output of the low-pass filter 140 to remove the ripple component included in the analog audio signal.

  The ripple extraction circuit 10 constituting the sub-path includes an attenuator 12 that attenuates the output of the class D driver 130, an inverter 14 that inverts the output phase of the attenuator, and a sub that drives the output of the inverter with the power supply voltage V2. The drive circuit 16 includes a coil L2 and a capacitor C2 that generate a reverse-phase waveform of a ripple component included in the main path from the output of the sub drive circuit and add it to the main path.

  Here, the power supply voltage V2 is set to a voltage value lower than the power supply voltage V1 of the class D drive circuit 130, and the coil L2 is set to an inductance value smaller than the coil L1 provided on the main path side.

  FIG. 3 is a timing chart showing the principle of ripple removal of the digital amplifier circuit shown in FIG. As shown in FIGS. 9A and 9B, the output signal A of the class D driver 130 and the output signal B of the sub drive circuit 16 are in an inverted relationship, as shown in FIGS. In addition, the current IL1 flowing in the coil L1 by the output signal A of the class D driver 130 and the current IL2 flowing in the coil L2 by the output signal B of the sub drive circuit 16 are in a state in which the current gradients are mutually inverted.

  Here, as shown in FIG. 5F, the current IL2 flowing through the coil L2 becomes a signal in which only the change is taken out due to the capacitor C2 decoupling effect, and the power supply voltages V1 and V2 and the coils L1 and L2 By setting the inductance values L1 and L2 to the conditions of the following equation, the peak values of IL1 and IL2 become the same. In the figure, “I0” is a steady portion of the current flowing through the coil L1.

V1 / L1 = V2 / L2
Therefore, the ripple component of the current IL1 flowing through the coil L1 is canceled by adding the current IL2 flowing through the coil L2 to the current IL1 flowing through the coil L1.

  The above equation is expressed as (V1−V1 ′) / L1 = (V2−V2 ′) / L2 where the speaker side voltage of the coil L1 is V2 ′ and the speaker side voltage of the coil L2 is V2 ′. It may be configured.

  Furthermore, by setting the power supply voltages V1 and V2 and the inductance values L1 and L2 of the coils L1 and L2 to the following conditions, the ripple extraction circuit 10 can be configured to be driven at a low voltage and use a low inductance element. .

V1> V2
L1> L2
By configuring according to the conditions described above, a mechanism for canceling the ripple component can be obtained with a simple configuration.

  Hereinafter, supplementing the principle that the ripple component is canceled by satisfying the condition of “V1 / L1 = V2 / L2”. First, the current IL1 flowing through the coil L1 can be expressed by the following equation.

IL1 = (V1-Vout1) · ton / L1
Here, Vout1: the output voltage of the speaker line, and ton: the ON time of the class D drive circuit 130.

  Further, the current IL2 flowing through the coil L2 can be expressed by the following equation.

IL2 = (V2-Vout2). (T-ton) / L2
Here, Vout2 is the output voltage of the sub drive circuit 16, T is the switching period, and Vout2 is a voltage smoothed by the coil L2 and the capacitor C2.

  Here, the ripple voltage Vripple as a noise generation source can be generally expressed by the following equation.

Vripple = 1 / C · ∫IL · dt
Accordingly, if the coil ripple current IL is made zero, it is equivalent to making the ripple voltage zero, so that the condition of “IL1 = IL2”, that is, the condition of “V1 / L1 = V2 / L2” is satisfied. The ripple component can be canceled by setting, and if V2 and L2 are reduced while maintaining this condition, the voltage can be reduced and the size can be reduced.

  FIG. 4 is a characteristic diagram showing the relationship between the value of the capacitor C2 provided in the ripple extraction circuit and the ripple removal effect. FIG. 5A is a diagram showing the relationship between the value of the capacitor C2 and the ripple voltage Vripple after ripple removal, and FIG. 5B is the relationship between the value of the capacitor C2 and the ripple current Iripple after ripple removal. FIG.

  As shown in the figures, since the ripple voltage and ripple current after cancellation change depending on the capacitance value of the capacitor C2, the capacitance value of the capacitor C2 is divided into four quarters of the capacitance value having the same resonance frequency as the coil C1 and the capacitor C. By setting the capacitance to 1 or more, a suitable ripple canceling effect can be obtained. Desirably, the configuration satisfies the following conditions.

L1 ・ C1 <L2 ・ C2
C2 ≧ C2 ′ / 4
L1 ・ C1 = L2 ・ C2 '
With this configuration, a more suitable ripple removal effect can be obtained.

  FIG. 5 is a circuit block diagram showing an example in which the configuration of FIG. 2 is applied to BTL. As shown in the figure, when the present invention is applied to a BTL configuration in which the speaker 620 is differentially driven using two class D drive circuits 130-1 and 130-2, the output of each class D drive circuit is used. Ripple extraction circuits 10-1 and 10-2 may be provided respectively. Other configurations and conditions are the same as those in FIG.

  FIG. 6 is a circuit block diagram showing a configuration example in consideration of fluctuations in the power supply voltage of the class D drive circuit. If the power supply voltage V1 of the class D drive circuit 130 fluctuates due to some operating factor, the condition of “V1 / L1 = V2 / L2” is not satisfied, and as shown in FIG. By providing the voltage fluctuation detection circuit 18 for detecting the fluctuation of the voltage V1 and linking the detected fluctuation with the power supply voltage V2 of the sub drive circuit 16 through the resistor R, the ripple removal effect can be maintained.

  FIG. 7 is a circuit block diagram showing a first configuration example in the case of generating a reverse-phase waveform of a ripple component using the output of the pulse modulator 120 shown in FIG. As shown in the figure, the ripple canceling effect can also be obtained by inputting a small amplitude PWM signal output from the pulse modulator 120 to the noise extraction circuit 10 without going through an attenuator. Others are the same as FIG.

  FIG. 8 is a circuit block diagram showing a second configuration example in the case of generating a reverse-phase waveform of a ripple component using the output of the pulse modulator 120 shown in FIG. As shown in the figure, when an inverted PWM signal is obtained from the pulse modulator 120, a ripple canceling effect can also be obtained by inputting the inverted PWM signal to the noise extraction circuit 10 without passing through an attenuator and an inverter. be able to. Others are the same as FIG.

  FIG. 9 is a circuit block diagram showing a first configuration example when the present invention is applied to a switching power supply. As shown in the figure, when the present invention is applied to a switching power supply that converts an input voltage V1 into a predetermined voltage and supplies it to a load 622, subsequent stages of switching elements S1 and S2 that perform a switching operation according to the PWM circuit 20 The ripple extraction circuit 10 may be connected to and the extracted anti-phase ripple component may be added before the capacitor C1. Other configurations and conditions are the same as those in FIG.

  FIG. 10 is a circuit block diagram showing a second configuration example when the present invention is applied to a switching power supply. As shown in the figure, the ripple cancellation effect can also be obtained by inputting the output of the PWM circuit 20 to the inverter 14 in the ripple extraction circuit 10. Other configurations are the same as those in FIG.

  According to the present invention, since a ripple component can be removed from an output signal of a digital amplifier or a switching power supply with a simple configuration, application to a high-quality digital amplifier or switching power supply 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. 3 is a timing chart showing the principle of ripple removal of the digital amplifier circuit shown in FIG. 2. It is a characteristic view which shows the relationship between the value of the capacitor | condenser C2 provided in the ripple extraction circuit, and the ripple removal effect. FIG. 3 is a circuit block diagram showing an example when the configuration of FIG. 2 is applied to BTL. It is a circuit block diagram which shows the structural example at the time of considering the fluctuation | variation of the power supply voltage of a class-D drive circuit. FIG. 2 is a circuit block diagram showing a first configuration example in the case of generating a reverse phase waveform of a ripple component using the output of the pulse modulator 120 shown in FIG. 1. FIG. 6 is a circuit block diagram illustrating a second configuration example in the case of generating a reverse phase waveform of a ripple component using the output of the pulse modulator 120 illustrated in FIG. 1. It is a circuit block diagram which shows the 1st structural example at the time of applying this invention to a switching power supply. It is a circuit block diagram which shows the 2nd structural example at the time of applying this invention to a switching power supply.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Ripple extraction circuit, 12 ... Attenuator, 14 ... Inverter, 16 ... Sub drive circuit, 18 ... Voltage fluctuation detection circuit, 20 ... PWM circuit, 100 ... Digital amplifier module, 102 ... Digital amplifier circuit, 110 ... DCDC converter, DESCRIPTION OF SYMBOLS 120 ... Pulse modulator, 130 ... Class D driver, 140 ... Low-pass filter, 160 ... PWM circuit, 500 ... Audio component, 510 ... AM / FM radio receiving part, 520 ... Audio tape reproducing part, 530 ... CD / DVD player 540 ... A / D converter, 610 ... battery, 620 ... speaker, 622 ... load

Claims (11)

A digital amplifier that amplifies an audio signal by switching and amplifying it,
A pulse modulation circuit for modulating the audio signal;
A first drive circuit driven by the output of the modulation circuit;
A filter including a first coil and a first capacitor for smoothing the output of the first drive circuit;
A speaker driven by the output of the filter;
A second drive circuit supplied with a power supply voltage different from the first drive circuit;
And a means for adding the output of the second drive circuit to a signal passing through the filter via a series circuit of a second coil and a second capacitor.   The power supply voltage supplied to the first drive circuit is V1, the voltage on the speaker side of the first coil is V1 ′, the power supply voltage supplied to the second drive circuit is V2, and the voltage of the second coil is When the speaker-side voltage is V2 ′, the inductance of the first coil is L1, and the inductance of the second coil is L2, the relationship of (V1−V1 ′) / L1 = (V2−V2 ′) / L2 The digital amplifier according to claim 1, wherein:   The power supply voltage supplied to the first drive circuit is V1, the power supply voltage supplied to the second drive circuit is V2, the inductance of the first coil is L1, and the inductance of the second coil is L2. 2. The digital amplifier according to claim 1, wherein the relationship of V1> V2 and L1> L2 is satisfied.   When the inductance of the first coil is L1, the inductance of the second coil is L2, the capacitance value of the first capacitor is C1, and the capacitance value of the second capacitor is C2, L1 · C1 <L2 2. The digital amplifier according to claim 1, wherein the relationship of C2 is satisfied.   2. The digital amplifier according to claim 1, wherein a power supply voltage supplied to the first drive circuit and a power supply voltage supplied to the second drive circuit are linked to each other. 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 for smoothing the output of the class D drive circuit;
A speaker driven by the output of the filter;
Means for generating an anti-phase waveform of a ripple component included in the output of the class D drive circuit using the output of the class D drive circuit;
Means for adding the negative phase waveform to a signal passing through the filter. 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 including a first coil and a first capacitor for smoothing the output of the class D drive circuit;
A speaker driven by the output of the filter;
Means for branching the output of the class D drive circuit;
Level adjusting means for adjusting the level of the branched signal;
Phase inversion means for inverting the phase of the branched signal;
And a means for adding the phase-inverted signal to a subsequent stage of the first coil through a series circuit of a second coil and a 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 for smoothing the output of the class D drive circuit;
A speaker driven by the output of the filter;
Means for generating an antiphase waveform of a ripple component included in the output of the class D drive circuit using the output of the pulse modulation circuit;
Means for adding the negative phase waveform to a signal passing through the filter. 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 including a first coil and a first capacitor for smoothing the output of the class D drive circuit;
A speaker driven by the output of the filter;
Level adjusting means for adjusting the output level of the modulation circuit;
Phase inversion means for inverting the output phase of the modulation circuit;
And a means for adding the phase-inverted signal to a subsequent stage of the first coil through a series circuit of a second coil and a second capacitor. A switching power supply that converts an input voltage into a predetermined output voltage,
A switching circuit for switching the input voltage;
A first coil and a first capacitor for smoothing the output of the switching circuit;
Means for branching the output of the switching circuit;
Level adjusting means for adjusting the level of the branched signal;
Phase inversion means for inverting the phase of the branched signal;
And a means for adding the phase-inverted signal to a subsequent stage of the first coil through a series circuit of a second coil and a second capacitor. A switching power supply that converts an input voltage into a predetermined output voltage,
A switching circuit for switching the input voltage according to a predetermined pulse waveform;
A first coil and a first capacitor for smoothing the output of the switching circuit;
Level adjusting means for adjusting the level of the pulse waveform;
Phase inversion means for inverting the phase of the pulse waveform;
And a means for adding the phase-inverted signal to a subsequent stage of the first coil through a series circuit of a second coil and a second capacitor.

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