JP2006217109A - Audio amplifier device and power unit for audio amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an audio amplifier device that can keep constant a peak value of a pulse signal after current amplification to improve sound quality and a power unit for an audio amplifier. <P>SOLUTION: This audio amplifier device includes an audio amplifier section 1 as a class D amplifier and a power supply section 2 which controls a source voltage to a current amplification section 12 so that a peak value of the output voltage of a pulse-modulated signal of a current amplification section 12 in the audio amplifier section 1 is as constant as possible. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an audio amplifier device and an audio amplifier power supply device.

  FIG. 3 is a block diagram showing an example of a conventional audio amplifier device. The conventional audio amplifier device shown in FIG. 3 includes an audio amplifier unit 101 that is a D-class amplifier, and a power supply unit 102 that supplies power to the current amplification unit 112 of the audio amplifier unit 101.

  In the audio amplifier unit 101, the PWM circuit 111 performs PWM modulation (pulse width modulation) on the analog or digital audio input signal, and the current amplification unit 112 current-amplifies the pulsed signal after PWM modulation, The low-pass filter 113 removes the high-frequency component of the pulse-like signal after current amplification and outputs an analog signal in the audio frequency band.

  The power supply unit 102 is applied with a voltage Vcc from a power supply (not shown) such as a DC power supply device or a battery that obtains DC power from a commercial power supply, and supplies a power supply voltage to the current amplification unit 112 with a predetermined constant voltage equal to or lower than the voltage Vcc. Apply.

  In addition to the device shown in FIG. 3, a power amplifier having a current amplifying unit that amplifies an analog signal instead of a pulse signal, the output voltage value of the current amplifying unit is monitored, and the output voltage value exceeds a predetermined threshold value And switching the power supply voltage applied to the current amplifying unit has been proposed (see, for example, Patent Document 1).

  In addition, a power amplifying apparatus has been proposed in which a power supply voltage is detected directly from a power supply side terminal of a switching element constituting a current amplifying unit, and the power supply voltage applied to the switching element is made exactly constant (for example, a patent) Reference 2).

JP 10-150325 A (summary, FIGS. 1 and 2) JP 2002-94340 A (summary)

  However, in an amplifier device such as a D-class amplifier that once modulates and amplifies an analog audio signal into a pulse signal, and then converts the analog audio signal back to an analog audio signal by a low-pass filter, a back electromotive current caused by an inductor in the low-pass filter There is a problem that the peak value of the output signal of the switching element of the current amplification stage fluctuates due to the saturation and the on-operation resistance, and the sound quality is deteriorated.

  To deal with the above problem, it may be possible to use a power MOSFET having a low resistance during the on-operation as the switching element of the current amplification stage, but the cost increases. In order to suppress the fluctuation of the power supply voltage of the current amplification stage with respect to the above problem, it is conceivable to provide a large capacity capacitor, but the cost increases.

  The power amplifier described in Patent Document 1 is an amplification circuit that amplifies an analog signal as it is, and modulates an analog audio signal such as a D class amplifier into a pulse signal and amplifies it, and then returns it to the analog audio signal by a low-pass filter. It is difficult to apply to an amplifier device.

  Further, in the power amplifying device described in Patent Document 2, since the power supply voltage is adjusted by detecting the voltage of the power supply side terminal of the switching element, the counter electromotive current and current caused by the inductor in the low pass filter are still present. The peak value of the output signal of the switching element in the current amplification stage fluctuates due to saturation of the switching element in the amplification stage and resistance during the on operation.

  An object of the present invention is to provide an audio amplifier device and an audio amplifier power supply device that can maintain a constant peak value of a pulse signal after current amplification and improve sound quality.

  In order to solve the above problems, the present invention is configured as follows.

  One audio amplifier device according to the present invention includes a D-class amplifier and a power supply unit that controls a power supply voltage to the current amplification unit so that the peak value of the output voltage of the current amplification unit in the D-class amplifier approaches a constant value. Prepare.

  Also, one of the audio amplifier devices according to the present invention is arranged in a subsequent stage of a pulse modulation unit that performs pulse modulation of an audio signal, a current amplification unit that amplifies the signal pulse-modulated by the pulse modulation unit, and a current amplification unit Filter, a power supply circuit for applying a power supply voltage to the current amplification unit, a peak value detection unit for detecting a peak value of the output voltage from the current amplification unit to the filter, and a current according to a detection value by the peak value detection unit And a control unit that controls a power supply voltage to the amplification unit.

  Furthermore, the audio amplifier device according to the present invention may be configured as follows in addition to any of the above audio amplifier devices. That is, in this case, the peak value detection unit detects the peak value by peak-holding and / or bottom-holding the pulsed output voltage from the current amplification unit.

  Furthermore, the audio amplifier device according to the present invention may be configured as follows in addition to any of the above audio amplifier devices. That is, in this case, the time constant of peak hold and / or bottom hold in the peak value detection unit is set so that the reciprocal of the time constant is higher than the upper limit of the required audio frequency band.

  Furthermore, the audio amplifier device according to the present invention may be configured as follows in addition to any of the above audio amplifier devices. That is, in this case, the power supply circuit is a PWM power supply circuit capable of both sink operation and source operation, and the control unit controls the duty of the PWM power supply circuit based on the peak value of the output voltage of the current amplification unit. Generate a signal.

  An audio amplifier power supply device according to the present invention includes a peak value detection unit that detects a peak value of an output voltage of a current amplification unit in a D-class amplifier, and a current so that the peak value detected by the peak value detection unit approaches a constant value. And a power supply unit that controls a power supply voltage to the amplification unit.

  According to the present invention, the peak value of the pulse signal after current amplification can be kept constant, and the sound quality can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of an audio amplifier apparatus according to an embodiment of the present invention. In FIG. 1, an audio amplifier unit 1 is a D class amplifier that amplifies and outputs an audio signal. The power supply unit 2 is a circuit group that supplies power to the audio amplifier unit 1, in particular, the current amplification unit 12 with a direct current.

  In the audio amplifier unit 1, the PWM circuit 11 is a circuit that functions as a pulse modulation unit that performs pulse modulation on an audio signal. The PWM circuit 11 outputs a pulse with a duty corresponding to the amplitude of the audio input signal in time series.

  The current amplifying unit 12 includes a current amplification switching element that performs a switching operation according to the output voltage of the PWM circuit 11, and is a circuit that amplifies the output signal of the PWM circuit 11. For example, the current amplifying unit 12 is composed of a pair of complementary power MOSFETs.

  The low-pass filter 13 is a filter circuit including an inductor L between the input end and the output end, and a capacitor C between the output end and the ground. The low-pass filter 13 transmits signals in the audio frequency band and attenuates signals having a frequency higher than the audio frequency band.

  In the power supply unit 2, the power supply circuit 21 is a power supply circuit that controls the power supply voltage to the current amplification unit 12 so that the peak value of the output voltage of the current amplification unit 12 in the audio amplifier 1 approaches a certain reference value. In this embodiment, the power supply circuit 21 is a PWM power supply circuit capable of both sink operation and source operation.

  In the power supply circuit 21, the reference signal generating circuit 31 is a circuit that generates a sawtooth wave or a triangular wave as a reference signal. The comparator 32 compares the reference signal from the reference signal generation circuit 31 with the output of the error amplifier 24, and is high (voltage value at which the switching element of the switching circuit 33 is turned on) or low (switching) according to the comparison result. This is a circuit that generates an output voltage of a voltage value at which the switching element of the circuit 33 is turned off. The reference signal generation circuit 31 and the comparator 32 realize pulse width modulation.

  The switching circuit 33 has a switching element that performs a switching operation in accordance with the output voltage of the comparator 32 and generates a pulse having the amplitude of the DC voltage Vcc and the ground GND by current amplification. The smoothing circuit 34 is a low-pass filter including an inductor L and a capacitor C.

  The peak hold circuit 22 is a circuit that functions as a peak value detection unit that detects the voltage at the connection position between the current amplification unit 12 and the low-pass filter 13, that is, the peak value of the output voltage of the current amplification unit 12. The peak hold circuit 22 peak-holds the pulse voltage output from the current amplifier 12 and detects the peak value. For example, the time constant of the peak hold in the peak hold circuit 22 is set so that the reciprocal of the time constant is higher than the upper limit (for example, 20 kHz) of the audio frequency band (audible band). The peak hold time constant in the peak hold circuit 22 may be set so that the reciprocal of the time constant is higher than the upper limit of the required audio frequency band. For example, even when the audible band is 20 Hz to 20 kHz, the upper limit When it is desired to improve the acoustic characteristics up to 10 kHz, the peak hold time constant may be set so that the reciprocal of the time constant is higher than 10 kHz.

  The reference voltage generation circuit 23 is a circuit that generates a reference voltage Vref corresponding to the target voltage value of the output voltage of the current amplifier 12. The error amplifier 24 generates an output voltage obtained by multiplying the difference between the peak value of the output voltage of the current amplifier 12 detected by the peak hold circuit 22 and the reference voltage Vref by the reference voltage generation circuit 23 by a predetermined amplification factor. Circuit. The reference voltage generation circuit 23 and the error amplifier 24 function as a control unit that controls the output voltage of the power supply circuit 21.

  Next, the operation of the above apparatus will be described.

  First, the operation of the audio amplifier unit 1 will be described.

  In the audio amplifier unit 1, the PWM circuit 11 performs PWM modulation (pulse width modulation) on the analog audio input signal. Next, the current amplifying unit 12 amplifies the pulse-shaped signal after PWM modulation.

  The output voltage of the current amplifying unit 12 is pulsed, and the peak value of the pulse is determined from the voltage value applied by the power supply unit 2 when the switching element of the current amplifying unit 12 is turned on (drain in the case of FET). • The voltage value is reduced by the voltage drop due to the resistance between the sources.

  Then, the low pass filter 13 removes the high frequency component of the pulse-like signal after current amplification and outputs an analog signal in the audio frequency band.

  Next, the operation of the power supply unit 2 will be described.

  In the power supply unit 2, the peak hold circuit 22 peaks the pulsed voltage output from the current amplification unit 12 and detects the peak value of the output voltage of the current amplification unit 12.

  The error amplifier 24 generates an output voltage obtained by multiplying the difference between the peak value of the output voltage of the current amplifier 12 detected by the peak hold circuit 22 and the reference voltage Vref by the reference voltage generation circuit 23 by a predetermined amplification factor. And applied to the comparator 32 of the power supply circuit 21.

  In this embodiment, since the output voltage of the peak hold circuit 22 is applied to the negative side input of the error amplifier 24 and the reference voltage Vref from the reference voltage generation circuit 23 is applied to the positive side input, the amplification factor is assumed to be A. The output voltage Ve of the error amplifier 24 is expressed by the following equation.

  Ve = A × (Vref−Vp)

  The comparator 32 of the power supply circuit 21 compares the reference signal from the reference signal generation circuit 31 with the output of the error amplifier 24, generates an output voltage according to the comparison result, and outputs a switching element (not shown) of the switching circuit 33. Let it be a gate signal.

  In this embodiment, since the output voltage of the reference signal generation circuit 31 is applied to the negative input of the comparator 32 and the output voltage Ve of the error amplifier 24 is applied to the positive input, the output voltage Ve of the error amplifier 24 is applied. Increases, the duty of the output voltage of the comparator 32 increases, and when the output voltage Ve decreases, the duty of the output voltage of the comparator 32 decreases.

  A switching element (not shown) of the switching circuit 33 performs a switching operation according to the voltage of the gate signal. The pulsed output voltage of the switching circuit 33 is smoothed by the smoothing circuit 34, and a DC power supply voltage is applied to the current amplification unit 12 of the audio amplifier unit 1.

  Here, the control for keeping the pulse peak value of the output voltage of the current amplifying unit 12 constant will be described. FIG. 2 is a diagram showing the peak value of the output voltage of the current amplifying unit 12 and the reference voltage Vref of the reference voltage generating circuit 23 in the embodiment of the present invention.

  When the pulse peak value Vp of the output voltage of the current amplifier 12 is lower than the reference voltage Vref (in the case of FIG. 2A), the output voltage of the error amplifier 24 depends on the difference between the reference voltage Vref and the pulse peak value Vp. Positive value. For this reason, the duty of the output voltage of the comparator 32 becomes high. Thereby, the ON period of the switching element of the switching circuit 33 is increased, and the power supply voltage to the current amplifying unit 12 is increased. When the power supply voltage to the current amplification unit 12 increases, the output voltage of the current amplification unit 12 when the switching element of the current amplification unit 12 is turned on increases.

  On the other hand, when the pulse peak value Vp of the output voltage of the current amplifier 12 is higher than the reference voltage Vref (in the case of FIG. 2B), the output voltage of the error amplifier 24 is the difference between the reference voltage Vref and the pulse peak value Vp. Negative value according to. For this reason, the duty of the output voltage of the comparator 32 becomes low. Thereby, the ON period of the switching element of the switching circuit 33 decreases, and the power supply voltage to the current amplifying unit 12 decreases. When the power supply voltage to the current amplifier 12 decreases, the output voltage of the current amplifier 12 when the switching element of the current amplifier 12 is turned on decreases.

  In this manner, when the pulse peak value Vp of the output voltage of the current amplifier 12 is lower than the reference voltage Vref, the pulse peak value Vp increases, and when the pulse peak value Vp is higher than the reference voltage Vref, The peak value Vp decreases. Thereby, the pulse peak value Vp of the output voltage of the current amplifying unit 12 is kept constant.

  As described above, the audio amplifying apparatus according to the above embodiment is configured to amplify the current so that the peak value of the output voltage of the audio amplifying unit 1 as the D class amplifier and the current amplifying unit 12 in the audio amplifying unit 1 approaches a constant value. And a power supply unit 2 that controls a power supply voltage to the unit 12.

  In particular, the audio amplifier device according to the above embodiment includes a PWM circuit 11 as a pulse modulation unit that performs pulse modulation on an audio signal, a current amplification unit 12 that amplifies a signal pulse-modulated by the PWM circuit 11, and a current amplification. A low-pass filter 13 disposed downstream of the unit 12, a power supply circuit 21 that applies a power supply voltage to the current amplifier 12, and a peak value detector that detects a peak value of the output voltage from the current amplifier 12 to the low-pass filter 13. And a reference voltage generating circuit 23 and an error amplifier 24 as a control unit for controlling the power supply voltage to the current amplifying unit 12 in accordance with a value detected by the peak hold circuit 22.

  Thereby, it is possible to suppress fluctuation of the peak value of the pulse signal after the current amplification due to the influence from the load side or the characteristics of the switching element of the current amplification unit 12, and the peak value of the pulse signal after the current amplification is reduced. Can be kept constant. As a result, even if the switching element of the current amplifying unit 12 and the capacitor C of the smoothing circuit 34 of the power supply circuit 21 are not expensive, distortion is prevented during amplification of the audio signal and the sound quality is improved. Can be.

  Further, according to the above embodiment, the peak hold circuit 22 holds the pulse voltage at the connection position between the current amplifying unit 12 and the low-pass filter 13 to obtain the peak value of the output voltage of the current amplifying unit 12. To detect.

  As a result, even if the output voltage of the current amplifying unit 12 fluctuates like a rectangular wave, the power supply voltage can be continuously controlled according to the peak value of the output voltage of the current amplifying unit 12, and the current amplification The peak value of the subsequent pulse signal can be kept well constant.

  Further, according to the above embodiment, the power supply circuit 21 is a PWM power supply circuit that can perform both a sink operation and a source operation, and the error amplifier 24 is configured to supply power based on the peak value of the output voltage of the current amplifying unit 12. A control signal for setting the duty of the circuit 21 is generated.

  As a result, since the power supply circuit 21 can perform both the sink operation and the source operation, the peak of the output voltage of the current amplifying unit 12 regardless of whether the peak value of the output voltage of the current amplifying unit 12 is higher or lower than the reference value. The value can be brought close to the reference value well.

  The above-described embodiments are preferred examples of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. is there.

  For example, in the above-described embodiment, the peak hold circuit 22 as the peak value detection unit performs a peak hold operation, but instead of the peak hold circuit 22, a bottom hold circuit is provided to detect the detected value (that is, a negative peak). Value) may be a peak value. Alternatively, a circuit that simultaneously performs both the peak hold operation and the bottom hold operation may be provided as the peak value detection unit. In that case, the difference (that is, peak-to-peak value) between the peak hold value and the bottom hold value is detected by the differential amplifier and used as the peak value.

  In the above embodiment, the power supply circuit 21 is a PWM power supply circuit, but may be a constant voltage power supply circuit or a stabilized power supply circuit of another type.

  In the above embodiment, the audio amplifier unit 1 performs pulse width modulation by the PWM circuit 11, but a pulse modulation unit that performs pulse density modulation may be provided instead of the PWM circuit 11.

  In addition, by applying the above embodiment, a peak hold circuit 22 as a peak value detection unit for detecting a peak value of the output voltage of the current amplification unit 12 in the D class amplifier, and a peak value detected by the peak hold circuit 22 It is also possible to configure an audio amplifier power supply device including the power supply unit 2 that controls the power supply voltage to the current amplifying unit 12 so as to be close to constant.

  The present invention is applicable to, for example, an amplifier device or a power supply device of a portable audio player.

FIG. 1 is a block diagram showing a configuration of an audio amplifier apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing the peak value of the output voltage of the current amplification unit and the reference voltage of the reference voltage generation circuit in the embodiment of the present invention. FIG. 3 is a block diagram showing an example of a conventional audio amplifier device.

Explanation of symbols

1 Audio amplifier (D class amplifier)
2 Power supply section 11 PWM circuit (pulse modulation section)
12 Current amplifier 13 Low-pass filter (filter)
21 Power supply circuit 22 Peak hold circuit (peak value detector)
23 Reference voltage generation circuit (part of control unit)
24 Error amplifier (part of control unit)

Claims (6)

A D-class amplifier,
A power supply unit that controls a power supply voltage to the current amplification unit so that a peak value of an output voltage of the current amplification unit in the D class amplifier approaches a constant value;
An audio amplifier device comprising: A pulse modulator for pulse-modulating an audio signal;
A current amplifying unit for amplifying the signal pulse-modulated by the pulse modulating unit;
A filter disposed in a subsequent stage of the current amplification unit;
A power supply circuit for applying a power supply voltage to the current amplification unit;
A peak value detection unit for detecting a peak value of an output voltage from the current amplification unit to the filter;
A control unit for controlling the power supply voltage to the current amplification unit according to the detection value by the peak value detection unit;
An audio amplifier device comprising:   3. The audio amplifier device according to claim 2, wherein the peak value detection unit detects a peak value by performing peak hold and / or bottom hold on the pulsed output voltage from the current amplification unit.   4. The audio amplifier device according to claim 3, wherein the reciprocal of the time constant of peak hold and / or bottom hold in the peak value detection unit is higher than the upper limit of the required audio frequency band. The power supply circuit is a PWM power supply circuit capable of both sink operation and source operation,
The control unit generates a control signal for setting a duty of the PWM power supply circuit based on a peak value of an output voltage of the current amplification unit;
The audio amplifier device according to claim 2. A peak value detector for detecting a peak value of the output voltage of the current amplifier in the D class amplifier;
A power supply unit that controls the power supply voltage to the current amplification unit so that the peak value detected by the peak value detection unit approaches a constant value;
An audio amplifier power supply device comprising:

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