JP2007060510A - Digital amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital amplifier which is valid for realizing a noise level requested for a digital amplifier for the purpose of high output/high fidelity. <P>SOLUTION: In this digital amplifier for performing the differential driving of a speaker 620 by BTL configuration; the post-stage of a D class driver 130-1 and the post-stage of a coil LB configuring a low pass filter 140-2 are connected through the series circuit of a coil Lb and a capacitor Cb, and the post-stage of a D class drive 130-2 and the post-stage of a coil LA configuring a low pass filter 140-1 are connected through the series circuit of a coil La and a capacitor Ca, so that ripple components superimposed on each differential line can be mutually canceled. <P>COPYRIGHT: (C)2007,JPO&INPIT

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. 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.

  Therefore, the present invention provides a digital amplifier that is effective in reducing switching 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 A first class D drive circuit, a first filter for smoothing the output of the first class D drive circuit, a second class D drive circuit driven by the inverted output of the modulation circuit, A second filter for smoothing the output of the second class D drive circuit, a speaker differentially driven by the outputs of the first and second filters, and a ripple component from the output of the first class D drive circuit And extracting the ripple component from the output of the second class D drive circuit and adding it to the signal passing through the first filter. Characterized by including and.

  In this way, by using the differential output of the digital amplifier, the switching components superimposed on each differential line can be interchanged, thereby effectively canceling with a simple configuration.

  According to a second 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 first driven by the output of the modulation circuit. A D-class drive circuit, a first coil connected to a subsequent stage of the first D-class drive circuit, a first capacitor connected to a subsequent stage of the first coil, and an inverted output of the modulation circuit. A second class D drive circuit to be driven; a second coil connected to a subsequent stage of the second class D drive circuit; a second capacitor connected to a subsequent stage of the second coil; A first path connected from the front stage of the first coil to the rear stage of the second coil through a series circuit of a coil and a capacitor, and from a front stage of the second coil through a series circuit of the coil and the capacitor The first Characterized by comprising a second path connected to the subsequent yl.

  In this way, the ripple component is extracted from the previous stage of the coil constituting the filter through the series circuit of the coil and the capacitor, and added to the subsequent stage of the coil constituting the filter, so that the ripple component superimposed on the audio signal is effectively obtained. Can be reduced.

  The invention according to claim 3 is the coil according to claim 2, wherein the coil constituting the first path has the same inductance as the second coil, and constitutes the second path. Has the same inductance as the first coil.

  In this way, by matching the inductance of the coil constituting the filter and the inductance of the coil for extracting the ripple component, the slope of the current flowing in both coils can be matched, so that the ripple component can be canceled effectively. can do.

  According to a fourth aspect of the present invention, in the second aspect of the present invention, the invention further includes means for changing the inductance of the coil constituting the first path and / or the inductance of the coil constituting the second path. It is characterized by doing.

  Thus, by changing the inductance of the ripple component extraction coil, it is possible to adjust the cancellation effect that varies depending on various factors. For example, when direct current superposition or current saturation occurs in a coil or when a duty change affects the cancellation effect, the inductance of the coil for extracting ripple components is changed to adjust the slope of the current flowing through the coil. Thus, an optimum canceling effect is obtained.

  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 for smoothing the output of the class D drive circuit, and a means for adjusting the level of the inverted output of the pulse modulation circuit and adding it to a signal passing through the filter via a series circuit of a coil and a capacitor; It is characterized by comprising.

  Thus, by using the inverted output of the pulse modulation circuit, the switching component can be effectively canceled even when only one side of the drive circuit is provided.

  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 switching component superimposed on the audio signal can be extracted effectively, the noise level of the digital amplifier 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, class D drivers 130-1 and 130-2, and low-pass filters 140-1 and 140-2, and an AM / FM radio reception unit 510. The audio signal input from the audio tape reproducing unit, the CD / DVD player 530 or the external port P3 is amplified, and the speaker 620 provided outside the audio component 500 is differentially driven with an analog output via the port P2. .

  Here, the pulse modulator 120 and the class D drivers 130-1 and 130-2 are driven by the power generated by the DCDC converter 110, and this DCDC converter is supplied from a battery 610 provided outside the audio component 500. Is used to supply the voltage VDD to the pulse modulator 120 and the class D drivers 130-1 and 130-2. 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.

  The DCDC converter 110 and the pulse modulator 120 are each provided with a waveform generation circuit for switching. These waveform generation circuits are respectively a switching frequency of the DCDC converter and a switching frequency of the class D drivers 130-1 and 130-2. To generate a drive waveform.

  Audio signal input to one terminal of the speaker 620 through the class D driver 130-1 and the low pass filter 140-1, and input to the other terminal of the speaker 620 through the class D driver 130-2 and the low pass filter 140-2. The audio signal has a phase inversion relationship, and takes a BTL configuration in which the speakers are differentially driven by both drivers.

  Here, in the BTL configuration, the ripple component extracted from the output of the class D driver 130-1 is added to the signal passing through the low pass filter 140-2, and the ripple component extracted from the output of the class D driver 130-2 is low pass. The switching components added to the signal passing through the filter 140-1 and superimposed on each differential line cancel each other.

  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 drivers 130-1 and 130-2 incorporated in the digital amplifier module 100 include a high-side switching element FET1, a low-side switching element FET2, and each switching element as a PWM signal. The driver amplifiers Amp1 and Amp2 are driven.

  The pulse signal output from the class D driver 130-1 passes through a low-pass filter 140-1 composed of a coil LA and a capacitor CA, whereby an analog audio signal on the non-inversion side is extracted, and the class D driver 130- 2 passes through a low-pass filter 140-2 composed of a coil LB and a capacitor CB, so that an inversion-side analog audio signal is extracted, and the non-inverted and inverted audio signals are used as a speaker 620. Are driven differentially.

  Here, the subsequent stage of the class D driver 130-1 and the subsequent stage of the coil LB constituting the low pass filter 140-2 are connected by a series circuit of the coil Lb and the capacitor Cb, and the subsequent stage of the class D driver 130-2 and the low pass filter are connected. The subsequent stage of the coil LA constituting 140-1 is connected by a series circuit of a coil La and a capacitor Ca. The inductance value of each coil is preferably LA = La and LB = Lb in order to make the slope of the ripple current to be canceled the same.

  The series circuit of the coil Lb and the capacitor Cb extracts the switching component contained in the output of the class D driver 130-1, adds it to the signal passing through the low-pass filter 140-2, and the series circuit of the coil La and the capacitor Ca. Extracts the switching component included in the output of the class D driver 130-2 and adds it to the signal passing through the low-pass filter 140-1. As a result, it is possible to preferably cancel the ripple component between the differential lines in which signals having phases opposite to each other flow.

  FIG. 3 is a timing chart showing the principle of noise 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 130-1 and the output signal B of the class D driver 130-2 are in an inverted relationship, and FIGS. ), The current ILA that flows through the coil LA by the output signal A of the class D driver 130-1 and the current ILB that flows through the coil LB by the output signal B of the class D driver 130-2 have a current gradient. It will be in a mutually inverted state. In the figure, “I0” is a steady portion of the current flowing through the coil.

  In addition, as shown in FIGS. 5E and 5F, the currents ILb and ILa flowing through the branches of the coils Lb and La become signals from which changes are extracted by the decoupling effect of the capacitors Cb and Ca.

  Therefore, by adding the current ILa extracted from the branch of the coil La to the current ILA flowing through the coil LA, the ripple component of the current ILA flowing through the coil LA is canceled, and the current ILB flowing through the coil LB is extracted from the branch of the coil Lb. By adding the current ILb, the ripple component of the current ILB flowing through the coil LB is canceled.

  FIG. 4 is a circuit block diagram illustrating an example in which the ripple component extraction coil is varied. As shown in the figure, by varying the inductances of the coils Lb and La, the slope of the current flowing through each coil can be adjusted, so that the canceling effect according to various fluctuation factors such as DC superposition and duty change can be achieved. Adjustment is possible. The ratio of changing the inductance can be determined based on the output current level of the coil constituting the low-pass filter and the output voltage level of the audio signal. The other configuration is the same as in FIG.

  FIG. 5 is a circuit diagram showing an example in which the speaker is unbalanced. As shown in the figure, when the speaker is driven by one-end grounding, an inverted signal of the PWM signal output from the pulse modulator is input to the amplifier Amp, the level is adjusted by the amplifier Amp, and then the coil La and An inversion ripple component for cancellation is generated via the capacitor Ca, and the generated inversion ripple component is added to the subsequent stage of the coil LA.

  Here, the level of the inverted PWM signal is adjusted to a value in which the slope of the current flowing in the coil LA and the slope of the current flowing in the coil La are the same in consideration of the amplification factor of the class D driver 130-1. Specifically, while setting the inductances of the coil LA and the coil La to the same value, the amplification factor of the amplifier Amp is set so that the output voltage value of the class D driver 130-1 and the output voltage value of the amplifier Amp are the same. Set.

  According to the present invention, since a switching component can be removed from an audio signal with a simple configuration, application to a 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. 3 is a timing chart showing the principle of noise removal of the digital amplifier circuit shown in FIG. It is the circuit block diagram which showed the example in the case of varying the coil for ripple component extraction. It is a circuit diagram which shows the example in the case of carrying out unbalanced drive of a speaker.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 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 (5)

A digital amplifier that amplifies an audio signal by switching and amplifying it,
A pulse modulation circuit for modulating the audio signal;
A first class D drive circuit driven by the output of the modulation circuit;
A first filter for smoothing the output of the first class D drive circuit;
A second class D drive circuit driven by the inverted output of the modulation circuit;
A second filter for smoothing the output of the second class D drive circuit;
A speaker that is differentially driven by outputs of the first and second filters;
Means for extracting a ripple component from the output of the first class D drive circuit and adding it to a signal passing through the second filter;
Means for extracting a ripple component from the output of the second class D drive circuit and adding it to a signal passing through the first filter. A digital amplifier that amplifies an audio signal by switching and amplifying it,
A pulse modulation circuit for modulating the audio signal;
A first class D drive circuit driven by the output of the modulation circuit;
A first coil connected to a subsequent stage of the first class D drive circuit;
A first capacitor connected downstream of the first coil;
A second class D drive circuit driven by the inverted output of the modulation circuit;
A second coil connected to a subsequent stage of the second class D drive circuit;
A second capacitor connected downstream of the second coil;
A first path connected from the front stage of the first coil to the rear stage of the second coil through a series circuit of a coil and a capacitor;
A digital amplifier comprising: a second path connected from the front stage of the second coil to the rear stage of the first coil via a series circuit of a coil and a capacitor.   The coil constituting the first path has the same inductance as the second coil, and the coil constituting the second path has the same inductance as the first coil. Item 3. A digital amplifier according to Item 2.   3. The digital amplifier according to claim 2, further comprising means for changing the inductance of the coil constituting the first path and / or the inductance of the coil constituting the second path. 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;
Means for adjusting the level of the inverted output of the pulse modulation circuit and adding it to the signal passing through the filter via a series circuit of a coil and a capacitor;
A digital amplifier comprising:

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