JP2008048262A - Switching amplifier unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching amplifier unit of low distortion rate by restraining a distortion due to crosstalk through a power supply circuit. <P>SOLUTION: The switching amplifier unit includes a first and a second switching amplifier circuit each having a PWM converter 17 for converting either an analog input signal or a digital input signal into a PWM signal, switching amplification stage 22, 26, and low pass filter 23, 27 for eliminating a high frequency component from the output signal of the above switching amplification stages, so as to demodulate into an audio signal. The switching amplifier unit further includes one direct-current power supply circuit 51 for supplying a direct current voltage in common to each switching amplification stage 22, 26, and a means for performing negative feedback of the audio signal demodulated in the first switching amplifier circuit to the input side of the PWM converter in the second amplifier circuit, so as to restrain the distortion generated in the second switching amplifier circuit following a varied output of the first switching amplifier circuit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a switching amplifying device, and more particularly to a switching amplifying device that converts an input signal into a PWM signal and then amplifies the signal by a switching method.

  An audio amplifier is required to faithfully amplify an input signal. The measurement item that serves as a fidelity guideline is the distortion rate. Usually, the noise component is also regarded as a kind of distortion and is expressed as THD (Total Harmonic Distortion).

  As a conventional technique for suppressing the distortion rate in a switching system amplifier, a negative feedback system generally used in an analog linear amplifier or the like, and an arithmetic algorithm that reduces a conversion error generated when an input signal is converted into a PWM signal are used. Known is a system, a predistortion system in which a distortion that is the inverse of the distortion characteristics generated in the switching element is programmed in advance, and is calculated by a DSP (Digital Signal Processor) or the like and applied to an input signal.

  By using these conventional distortion suppression techniques, even a switching type amplifier can achieve a distortion rate of 0.01% or less in static characteristics. In the case of a stereo amplifier, the distortion rate in the static characteristic is measured by adding the same signal to both the L and R channels or adding the signal to only one channel.

  In addition, a method of using a digital attenuator is known for volume adjustment in a switching amplifier. In this method, before the PCM digital audio signal is converted into the PWM signal, the digital attenuator performs, for example, bit shift from higher to lower according to the volume adjustment value for the digital audio signal. is doing.

  As another volume adjustment method, there is a method of changing the power supply voltage supplied to the output stage in accordance with the set value of the volume. These volume adjustment methods are disclosed in Patent Document 1, for example. However, in other words, this type of volume adjustment method is particularly vulnerable to fluctuations in the power supply voltage. For this reason, the power supply voltage must be used with a constant voltage by a voltage variable stabilization circuit. The stabilization circuit is generally a circuit that controls the power supply voltage to be constant by negative feedback.

  Note that an audio amplifier having a switching output stage often adjusts the volume by controlling the power supply voltage. This is due to the following reason. (1) In a digital amplifier of a digital signal input method such as PCM (Pulse Code Modulation), a conversion operation from a PCM signal to a PWM signal is performed when a digital audio signal reproduced from a CD is input, and a 16-bit signal is converted from 8 to 10 Since an algorithm that shifts bits to about bits and corrects the conversion error is employed, the conversion error increases as the input signal data becomes lower in volume, that is, lower bit data. For this reason, volume adjustment by control of the power supply voltage is more advantageous in terms of PWM conversion accuracy than volume adjustment by digital computation before conversion from a PCM signal to a PWM signal. (2) In a class D amplifier that converts an analog input signal into a PWM signal and amplifies it, it becomes difficult to improve the performance by the negative feedback technique because the amplification factor changes with a change in power supply voltage. On the other hand, since the analog input signal is not significantly smaller than the reference triangular wave used for PWM signal conversion, the linearity and accuracy of the reference triangular wave are unlikely to be a problem. For this reason, the volume adjustment by controlling the power supply voltage is more advantageous than adjusting the volume by attenuating the analog input signal before converting it to the PWM signal. (3) In both digital signal processing and analog signal processing, the power supply voltage can be lowered when the input signal is no signal or when the volume is low, and the peak value of the PWM signal that is switched at the output stage can be reduced. This is advantageous in terms of S / N ratio and unnecessary width.

  By the way, when the power supply circuit is shared by the L and R channels, the power supply circuit is affected by the current flowing through the speaker load accompanying the amplification operation of one channel, and the power supply voltage varies to some extent. . This fluctuation in the power supply voltage adds distortion to the signal of the other channel. Therefore, it is best to provide a constant voltage circuit for each channel. However, since power consumed in the output stage is large, it is often difficult in terms of circuit scale, space, and cost.

Patent Document 2 is known as a technique for suppressing the influence of mutual interference between channels in a switching amplifier having a plurality of channels.
JP 2001-202696 A JP 2004-320325 A

  FIG. 5 is a diagram for explaining that distortion is added to the signal of the other channel by the amplification operation of one channel when the power supply circuit is shared by both the L and R channels. In FIG. 5A, 51 is a power supply circuit, 54 is an output stage for amplifying an L channel signal, 55 is an output stage for amplifying an R channel signal, Vin1 is an L channel input signal, and Vout1 is an L channel output. The signal, Vin2, is an R channel input signal, and Vout2 is an R channel output signal.

  As shown in FIG. 5B, a sound input signal is input to the L channel, and a silence input signal is input to the R channel. The L-channel and R-channel output stages include a converter (not shown) for converting an audio signal into a PWM signal, a driver, a switching element (MOS-FET), and an LPF. The power supply circuit 51 supplies a common power supply voltage to the L-channel and R-channel output stages 54 and 55.

  Assuming that the output of the power supply circuit 51 is constant, when the input signal Vin1 having a voltage waveform having a peak as shown in FIG. 5B is input to the L channel, the output stage 54 An output signal Vout1 having a peak as shown in 5 (B) is output. The waveform of the output signal Vout1 is similar to the waveform of the input signal Vin1, and is amplified by the gain. If the L channel speaker is a pure resistor, the current waveform of the audio signal output from the L channel output stage is similar to the current waveform of the input audio signal.

  When the input signal Vin2 having a voltage waveform (silence signal) as shown in FIG. 5B is input to the R channel, the output stage 55 outputs a silence output signal Vout2 as shown in the figure. .

  However, when the output voltage Vcc of the power supply circuit 51 that should be a constant voltage fluctuates due to the influence of the internal impedance R of the power supply circuit 51 or the response delay of the stabilization circuit, the signal output from the R channel output stage. Will be added to the distortion. That is, in a switching type amplifier that adjusts the volume by changing the power supply voltage, the power supply voltage Vcc that varies due to the output fluctuation of the L channel is supplied to the R channel output stage as the power supply voltage. For this reason, distortion is added to the signal output from the R channel.

  For this reason, although the input signal Vin2 having a voltage waveform (silent signal) as shown in FIG. 5B is input, the output signal having the voltage waveform shown in FIG. Vout2 ′ is output. For this reason, a noise sound is output from the R channel speaker. Further, due to the fluctuation of the power supply voltage Vcc, distortion is also added to the output signal Vout1 output from the L channel output stage, resulting in a signal Vout1 'as shown in FIG. In other words, the waveform peak is crushed and an undershoot occurs.

  In this way, crosstalk occurs from other channels through the power supply circuit, which causes distortion.

  The present invention has been made in view of such problems, and provides a switching amplification device having a low distortion rate by suppressing distortion due to crosstalk.

  In order to solve the above problems, the present invention employs the following means.

  PWM converter for converting analog input signal or digital input signal into PWM signal, switching amplification stage for switching amplification of output signal of PWM converter, and high frequency component from output signal of switching amplification stage for demodulation to audio signal A switching amplifier circuit that switches and amplifies the audio signal of the first channel, a PWM converter that converts an analog input signal or a digital input signal into a PWM signal, and amplifies the output signal of the PWM converter A switching amplifier circuit, and a switching amplifier circuit that switches and amplifies the audio signal of the second channel, comprising: a switching amplifier stage; A DC power supply circuit commonly supplying a DC voltage to each of the switching stages constituting the switching amplifier circuit and the second switching amplifier circuit, and the demodulated audio signal of the first switching amplifier circuit as the second switching amplifier circuit. The switching amplifier circuit includes a filter circuit that performs negative feedback on the input side of the PWM converter, and suppresses distortion generated in the second switching amplifier circuit due to output fluctuation of the first switching amplifier circuit.

  Since the present invention has the above-described configuration, it is possible to provide a switching amplification device with a low distortion rate by suppressing distortion based on crosstalk through a power supply circuit.

  Hereinafter, the best embodiment will be described with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a switching amplification device according to an embodiment of the present invention. In FIG. 1, a digital input signal input to an input terminal 12 is input via a digital interface circuit 15 to an arithmetic circuit 17 formed by a DSP or a PLD (Programmable Logic Device) element. The analog input signals input to the input terminals 11 and 13 are converted into digital signals by the A / D converters 14 and 16 and then input to the arithmetic circuit 17 through the digital interface circuit 15. The arithmetic circuit 17 converts the input digital signal into a PWM signal, and the converted PWM signal is input to the driver circuits 18 and 21. The driver circuit performs a DC level shift as necessary to drive the output amplification stages 22 and 26 including the output switching elements FET1 and FET2.

  As the output amplification stages 22 and 26, MOS-FETs having excellent high-speed switching characteristics and low ON resistance are used. The PWM signal switched and amplified by the output amplification stage removes a carrier wave by LPF (Low Pass Filter) 23 and 27, demodulates it into an audio signal, and drives the speakers 30 and 31.

  The volume is adjusted by controlling the power supply voltage Vcc of the output amplification stages 22 and 26. As described above, the power supply circuit 51 that supplies the power supply voltage Vcc is shared by the L channel and the R channel due to cost or installation space.

  The crosstalk generated through the power supply circuit 51 does not occur at a constant rate at any frequency, but depends mainly on the frequency characteristics of the impedance of the power supply circuit, and the crosstalk increases at frequencies where the impedance becomes high.

  In the present embodiment, after the output signal from the LPF 23 of one channel (for example, Lch) is attenuated by the attenuator 28 formed by a resistance voltage dividing circuit, distortion due to crosstalk is caused by the filter 24 corresponding to the impedance characteristic of the power supply circuit. A factor component (distortion factor signal) is extracted. Next, the extracted distortion factor signal is A / D converted by the A / D converter 19 and input to the arithmetic circuit 17. The arithmetic circuit 17 inverts the extracted distortion factor signal and adds it to the input signal of the other channel (Rch in this example).

  Further, after the output signal from the LPF 27 of the other channel (for example, Rch) is attenuated by the attenuator 29 formed by the resistance voltage dividing circuit, the filter 25 corresponding to the impedance characteristic of the power supply circuit causes distortion due to crosstalk. A component (distortion factor signal) is extracted. Next, the extracted distortion factor signal is A / D converted by the A / D converter 20 and input to the arithmetic circuit 17. The arithmetic circuit 17 inverts the extracted distortion factor signal and adds it to the input signal of the other channel (Lch in this example). Thereby, the crosstalk which generate | occur | produces between each channel can be suppressed. The filters 24 and 25 may be constituted by an arithmetic circuit in the arithmetic circuit 17.

  In the example of FIG. 1, the number of output channels has been described as 2 for simplification of description. However, when the number of channels is 3 or more, output signals from LPFs of all channels other than the channel are input to the attenuator. It is good to add.

  FIG. 4 is a diagram illustrating an example of impedance characteristics of the power supply circuit (FIG. 4A) and filter characteristics corresponding to the impedance characteristics (FIG. 4B). The filters 24 and 25 corresponding to the power supply circuit having the impedance characteristics as shown in FIG. 4A have a relatively Q (the sharpness of the frequency characteristics) having a center frequency at 45 Hz which is the peak center frequency of the impedance characteristics. ) High band pass filter.

  FIG. 2 is a diagram for explaining another embodiment of the present invention. The L channel analog signal input to the input terminal 11 is amplified by the differential amplifier 32 to the most efficient signal level when converted to a PWM signal, then converted to a PWM signal by the converter 34, and the driver circuit 18. The output amplification stage 22 is switched and amplified via The amplified PWM signal removes the carrier wave in the LPF 23, demodulates it into an audio signal, and drives the speaker 30.

  The R channel analog signal input to the input terminal 13 is amplified by the differential amplifier 33 to the most efficient signal level when converted to a PWM signal, and then converted to a PWM signal by the converter 36. Switching amplification is performed in the output amplification stage 26 through the circuit 21. The amplified PWM signal removes the carrier wave in the LPF 27, demodulates it into an audio signal, and drives the speaker 31.

  In the example of this figure, the distortion factor signal extracted from the filter 24 of one channel (Lch) is added to the (−) input terminal of the differential amplifier 33 that amplifies the analog signal input to the other channel (Rch). . Further, the distortion factor signal extracted from the filter 25 of the other channel (Rch) is applied to the (−) input terminal of the differential amplifier 32 that amplifies the analog signal input to the one channel (Lch).

  In this manner, the distortion component signal is canceled by adding the distortion factor signal extracted from one channel to the (−) input terminal of the differential amplifier of the other channel that amplifies the input analog signal. Thereby, the crosstalk which generate | occur | produces between each channel can be suppressed.

  In the example of FIG. 2, the number of output channels has been described as 2 for simplification of explanation. However, when the number of channels is 3 or more, all the channels other than the channel are connected to the (−) input terminal of the differential amplifier. An output signal from the LPF may be added.

  FIG. 3 is a diagram illustrating still another embodiment of the present invention. In FIG. 3, 37 and 38 are filters, and 39 and 40 are attenuators. Note that the filters 37 and 38 are formed of bandpass filters having a relatively high Q and having a center frequency at the peak center frequency of the impedance characteristic of the power supply circuit 51.

  In the example of this figure, the distortion factor signal extracted from the filter 37 of one channel (Lch) is amplified by the (−−) of the differential amplifier 33 that amplifies the analog signal input to the other channel (Rch) via the attenuator 39. ) Add to the input terminal. Further, the distortion factor signal extracted from the filter 38 of the other channel (Rch) is applied to the (−) input terminal of the differential amplifier 32 that amplifies the analog signal input to the one channel (Lch) via the attenuator 40. Add.

  The level of distortion that the fluctuation of the output current that drives the speaker of one channel adds to the other channel through the power supply circuit varies depending on the output current that drives the speaker of one channel. For this reason, when the power supply voltage is high (volume is high), the attenuation is reduced, and the crosstalk component added to the differential amplifier is increased. When the power supply voltage is low (volume is low), the attenuation is reduced. Increase the crosstalk component to be added to the differential amplifier. That is, the microcomputer 52 controls the power supply voltage Vcc according to the value of the volume operation by the volume operation unit 53 and also controls the attenuation amount by the attenuators 39 and 40.

  Unlike the technique for suppressing the crosstalk by feeding back the distortion factor signal extracted from the output signals from the LPFs 23 and 27 as described with reference to FIGS. 2 and 3, the present embodiment is a kind of predistortion. Therefore, it is possible to obtain an amplifying apparatus with excellent transient response with no time difference between the occurrence of distortion and the correction thereof.

  As described above, according to the embodiments of the present invention, a multi-channel switching amplifier that shares the power supply circuit for the output amplification stage of each channel and adjusts the volume by controlling the power supply voltage of the power supply circuit. The distortion factor signal extracted from the output signal of one channel is fed back to the input signal of the other channel, or the distortion factor signal extracted from the input signal of one channel is inverted and supplied to the input signal of the other channel. Therefore, the distortion due to the signal component (crosstalk) of the other channel added through the power supply circuit can be removed, and a switching amplification device with less distortion can be realized.

It is a figure explaining the switching amplifier concerning embodiment of this invention. It is a figure explaining other embodiment. It is a figure explaining other embodiment. It is a figure which shows an example of the impedance characteristic and filter characteristic of a power supply circuit. It is a figure explaining distortion being added to the signal of the other channel by amplification operation of one channel.

Explanation of symbols

15 Digital interface 17 Arithmetic circuit 18, 21 Driver circuit 22, 26 Output amplification stage 23, 27 LPF
28, 29 Attenuator 30, 31 Speaker 32, 33 Differential amplifier circuit 34, 36 Modulator 35 Reference triangular wave oscillator 37, 38 Filter 39, 40 Attenuator 51 Power supply circuit 52 Microcomputer 53 Volume control section

Claims (3)

PWM converter for converting analog input signal or digital input signal into PWM signal, switching amplification stage for switching amplification of output signal of PWM converter, and high frequency component from output signal of switching amplification stage for demodulation to audio signal A switching amplifier circuit for switching and amplifying the audio signal of the first channel;
PWM converter for converting analog input signal or digital input signal into PWM signal, switching amplification stage for switching amplification of output signal of PWM converter, and high frequency component from output signal of switching amplification stage for demodulation to audio signal A switching amplifier circuit for switching and amplifying the audio signal of the second channel;
One DC power supply circuit for commonly supplying a DC voltage to each of the switching stages constituting the first switching amplifier circuit and the second switching amplifier circuit;
A filter circuit for negatively feeding back the demodulated audio signal of the first switching amplifier circuit to the input side of the PWM converter of the second switching amplifier circuit, and accompanying an output fluctuation of the first switching amplifier circuit; A switching amplifying device characterized by suppressing distortion generated in the second switching amplifying circuit. PWM converter for converting analog input signal or digital input signal into PWM signal, switching amplification stage for switching amplification of output signal of PWM converter, and high frequency component from output signal of switching amplification stage for demodulation to audio signal A switching amplifier circuit for switching and amplifying the audio signal of the first channel;
PWM converter for converting analog input signal or digital input signal into PWM signal, switching amplification stage for switching amplification of output signal of PWM converter, and high frequency component from output signal of switching amplification stage for demodulation to audio signal A switching amplifier circuit for switching and amplifying the audio signal of the second channel;
One DC power supply circuit for commonly supplying a DC voltage to each of the switching stages constituting the first switching amplifier circuit and the second switching amplifier circuit;
A filter circuit and an attenuator for supplying an inverted signal of the input signal of the first switching amplifier circuit to the input side of the second switching amplifier circuit; A switching amplifying device characterized by suppressing distortion generated in the switching amplifying circuit. The switching amplification device according to claim 1 or 2,
The switching amplification device according to claim 1, wherein the frequency characteristic of the filter circuit has a low-impedance pass band in a frequency band where the impedance of the DC power supply circuit exhibits a high impedance.

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