JP2004229215A - Digital switching amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an unwanted phenomenon even when muting is performed to set a mute state initially. <P>SOLUTION: In the initial operation of a digital switching amplifier 10, muting is performed by a ΔΣ modulation circuit 13, and a switching circuit 20 negatively feeds an output 1-bit signal from the ΔΣ modulation circuit 13 to input side adders 16a, 16b via a second feedback path 19. A constant voltage circuit 22 stops supplying a constant voltage to a constant voltage switching circuit 14. When canceling the muting to start an ordinary operation, first of all, the constant voltage is supplied from the constant voltage circuit 22 to the constant voltage switching circuit 14, and the switching circuit changes over the feedback path to perform the negative feedback via a first feedback path 18. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a digital switching amplifier capable of converting an analog signal such as an audio signal or a multi-bit signal into a 1-bit digital signal by delta-sigma modulation and amplifying the signal with high efficiency.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as one of methods for converting an analog signal into a digital signal, a method using a delta-sigma (denoted as “ΔΣ” in the drawing) modulator is known. In a basic analog-to-digital conversion method using a delta-sigma modulator, an analog signal is input to an integrator, and the output is quantized by one bit and converted into a bit stream signal having time information. This is returned to an analog signal by digital / analog conversion, and negatively fed back to the input side of the integrator. Due to the negative feedback, the input of the integrator becomes an error between the original analog signal and the digitally converted signal, and a digital output comes out so as to suppress this error. The quantization step may be performed with three or more values to obtain a 1-bit bit stream signal as an output (for example, see Patent Document 1).
[0003]
The 1-bit signal obtained by the delta-sigma modulation is used not only for recording an audio signal and transmitting between devices, but also for directly inputting the 1-bit signal to a semiconductor power amplifier, and using a method called class D amplification. Power amplification can also be performed. The semiconductor power amplifying element performs a switching operation based on the 1-bit signal, and a power-amplified demodulated analog signal can be obtained by passing the obtained high-voltage switching pulse through a low-pass filter. Moreover, the semiconductor power amplifier element is used not in a linear region (unsaturated region) but in a non-linear region (saturated region) in terms of operating characteristics as in a conventional analog signal amplifier. Such a switching type amplifier using delta sigma modulation has an advantage that power amplification can be performed with extremely high efficiency.
[0004]
3 and 4 show an example of a schematic configuration of a digital switching amplifier using a conventional delta-sigma modulation signal. Corresponding parts in FIGS. 3 and 4 are denoted by the same reference numerals. As shown in FIGS. 3 and 4, in the conventional digital switching amplifier, a differential signal composed of a pair of a positive analog audio signal and a negative analog audio signal is applied to a pair of input terminals 1a and 1b. Each of them is input, amplifies an analog audio signal, and outputs it from the output terminals 2a and 2b to drive a speaker or the like. The negative polarity analog audio signal is a signal obtained by inverting only the polarity of the positive polarity analog audio signal. The digital switching amplifier includes a delta-sigma modulation circuit 3, a constant voltage switching circuit 4, a low-pass filter network circuit 5, a negative feedback circuit, and the like. The negative feedback circuit includes adders 6a, 6b and attenuator 7, and feedback path 8 or feedback path 9. In the adders 6a and 6b, the input analog audio signal and the signal that is negatively fed back from the feedback path 8 or the feedback path 9 are added. Since the input signal and the negative feedback signal have opposite polarities, the subtraction is performed substantially.
[0005]
The delta-sigma modulation circuit 3 quantizes the analog audio signal obtained by subtracting the feedback signal from the analog audio signals input to the input terminals 1a and 1b by delta-sigma modulation to generate a 1-bit signal. Although not shown, the delta-sigma modulation circuit 3 includes an integrator and an adder group, and a quantizer. The group of integrators and adders integrates and adds the analog audio signals after being subtracted by the adders 6a and 6b on the input side, and outputs the obtained signal to the quantizer. The quantizer determines the polarity of the signal obtained by the integrator / adder group based on the quantization threshold, and converts it into a 1-bit signal as binary quantization. Here, the quantization threshold of the quantizer is set to be an optimum value for an assumed sampling frequency. The quantizer operates in response to the clock signal.
[0006]
Although not shown, the constant voltage switching circuit 4 includes a constant voltage power supply that outputs a positive DC constant voltage + V and a negative DC constant voltage −V having an absolute value equal to the DC constant voltage + V. It is connected. The constant voltage switching circuit 4 performs switching of the constant voltages + V and -V supplied from the constant voltage power supply based on the 1-bit signal, that is, by using the 1-bit signal as a switching control signal, thereby converting the 1-bit signal into power. Amplify.
[0007]
In FIG. 3, a power-amplified 1-bit signal obtained by power-amplifying the 1-bit signal by the constant voltage switching circuit 4 is output to a low-pass filter network circuit 5 and a negative feedback circuit including a negative feedback path 8. This negative feedback circuit is for negatively feeding back the 1-bit power amplified signal to the input side of the delta-sigma modulation circuit 3. By applying the negative feedback, it is possible to prevent the audio performance from deteriorating due to the fluctuation of the constant voltages + V and -V supplied from the constant voltage power supply to the constant voltage switching circuit 4.
[0008]
The low-pass filter network circuit 5 interpolates the amplified 1-bit signal by band-limiting the input signal to a low frequency band, and demodulates the amplified 1-bit signal into an analog sound signal. The low-pass filter network circuit 5 outputs an analog audio signal from the output terminals 2a and 2b.
[0009]
As shown in FIG. 4, in the conventional digital switching amplifier, a negative feedback circuit negatively feeds a 1-bit signal output from the delta-sigma modulation circuit 3 from a feedback path 9 to the input side of the delta-sigma modulation circuit 3. Some make it work.
[0010]
By the way, in the delta-sigma modulation circuit 3 described above, a mute state is taken by a reset signal or the like at the time of startup in order to initialize the internal integration / addition operation and to suppress noise generation at the time of the initial operation. ing.
[0011]
[Patent Document 1]
JP-A-10-233634
[0012]
[Problems to be solved by the invention]
In the digital switching amplifier as shown in FIG. 3, a problem occurs when the mute state of the delta-sigma modulation circuit 3 is released. At the moment when the mute state is released, the loop in which the power-amplified 1-bit signal is negatively fed back to the input side of the delta-sigma modulation circuit 3 is interrupted, so that the delta-sigma modulation circuit 3 cannot maintain the transfer characteristics according to the algorithm. As a result, the residual noise increases, and the maximum allowable amount of the input signal with respect to the feedback signal (oscillation limit value) changes, so that the semiconductor power amplifying element in the constant voltage switching circuit 3 becomes too large at the moment of applying the constant voltage. There is a possibility that a large amount of current flows and the semiconductor power amplifying element is destroyed.
[0013]
Further, in the digital switching amplifier as shown in FIG. 4, the constant voltage switching circuit 4 is not included in the negative feedback loop. Since the constant voltage fluctuation of the constant voltage switching circuit 4 cannot be corrected, the SN (signal-to-noise) ratio decreases due to an increase in the noise floor, and a desired frequency band or dynamic range may not be obtained. There is.
[0014]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a digital switching amplifier capable of preventing occurrence of an undesired phenomenon even when performing a muting operation or the like for setting a mute state at an initial operation.
[0015]
[Means for Solving the Problems]
The present invention provides a delta-sigma modulator that performs delta-sigma modulation on an input signal to generate a quantized signal.
A power supply to supply voltage;
A power amplifier that receives a quantized signal from a delta-sigma modulator and switches a voltage supplied from a power supply based on the quantized signal to switch and amplify the quantized signal to generate a pulse signal;
A low-pass filter that converts the pulse signal amplified by the power amplifier into an analog signal by low-pass filtering and outputs the analog signal;
An attenuator to which a pulse signal amplified by a power amplifier is input and attenuates a peak value of the pulse signal,
A first feedback path for negatively feeding back the pulse signal output from the attenuator to the input side of the delta-sigma modulator, or negatively feeding back the quantized signal output from the delta-sigma modulator to the input side of the delta-sigma modulator A switching circuit for switching any one of the second feedback paths so as to select the second feedback path.
[0016]
According to the present invention, a digital switching amplifier using delta-sigma modulation includes a delta-sigma modulator, a power supply, a power amplifier, a low-pass filter, an attenuator, and a switching circuit. The delta-sigma modulator generates a quantized signal by performing delta-sigma modulation on an input signal. The power amplifier generates a switching-amplified pulse signal by switching a constant voltage supplied from a power supply based on the quantized signal generated by the delta-sigma modulator. The low-pass filter converts the pulse signal amplified by the power amplifier into an analog signal by low-pass filtering and outputs the analog signal. The attenuator attenuates the peak value of the pulse signal that is switched and amplified by the power amplifier. The switching circuit includes a first feedback path for negatively feeding back the pulse signal output from the attenuator to the input side of the delta-sigma modulator, and a quantizing signal output from the delta-sigma modulator to the input side of the delta-sigma modulator. And the second return path for negative feedback. Since the pulse signal output from the power amplifier is fed back to the first feedback path, if the switching circuit is switched to the first feedback path, even if the voltage supplied from the power supply fluctuates, it is stable. Can work. If the switching circuit is switched to the second feedback path, the power amplifier is not included in the negative feedback circuit. Therefore, even when the muting operation is cancelled, occurrence of an undesired phenomenon can be avoided.
[0017]
Further, in the present invention, the delta-sigma modulator uses a differential signal composed of a pair of a first signal and a second signal having opposite polarities as an input signal.
[0018]
According to the present invention, since the differential signal is used as the input signal of the delta-sigma modulator, the influence of the potential fluctuation of the circuit ground is equally affected and cancels out the pair of input terminals, and the switching noise of the power amplifier and the like is eliminated. Does not affect the input signal via the circuit ground or the like, and the S / N ratio as a digital switching amplifier can be sufficiently obtained.
[0019]
Also, in the present invention, the delta-sigma modulator is characterized in that the quantized signal is a binary or multi-level quantized signal.
[0020]
According to the present invention, by performing delta-sigma modulation by multi-level quantization of two or more values, even when the amplitude of an input signal is small, a quantized output signal based on a small quantization threshold can be extracted. A switching operation set to a low voltage level becomes possible. Further, even if the amplitude of the input signal is small, the quantization noise can be drastically reduced.
[0021]
In the present invention, the switching circuit switches so as to select the first feedback path during a normal operation.
[0022]
According to the present invention, the first feedback path is selected during the normal operation, so that the pulse signal switched and amplified by the power amplifier is subjected to negative feedback to the input side of the delta-sigma modulator by attenuating the peak value by the attenuator. , The noise shaping operation of the delta-sigma modulator can be stabilized, and the fluctuation of the voltage supplied from the power supply to the power amplifier can be corrected.
[0023]
In the present invention, the switching circuit switches so as to select the second feedback path during a muting operation.
[0024]
According to the present invention, during the muting operation, the quantized signal output from the delta-sigma modulator is negatively fed back to the input side of the delta-sigma modulator via the second feedback path. It is possible to stabilize the shaping operation, prevent an excessive noise signal from being included in the quantized signal output from the delta-sigma modulator, and prevent an excessive current from flowing through a switching element or the like of the power amplifier. Even when the muting operation is canceled, noise output can be avoided.
[0025]
In the present invention, the power supply cuts off the supply of the voltage to the power amplifier during the muting operation.
[0026]
According to the present invention, at the time of the muting operation, the power supply cuts off the supply of the voltage for switching and amplifying the quantized signal by the power amplifier to generate the pulse signal, so that the noise is output from the power amplifier during the muting operation. Power consumption can be reduced.
[0027]
Further, in the present invention, during the muting operation, the power amplifier is supplied with a voltage from the power supply in a state where the transition to the normal operation is switched so as to select the second feedback path. After that, the switching circuit further includes control means for performing the control by performing switching so as to select the first return path from the second return path.
[0028]
According to the present invention, the transition from the muting operation to the normal operation is performed after the switching circuit supplies the voltage from the power supply to the power amplifier while the switching circuit is switching to the second feedback path. Since the feedback path is switched to the first feedback path, an excessive noise component is not included in the output of the delta-sigma modulator, so that an excessive current does not flow through the switching element of the power amplifier and switching noise is not output. Then, the operation can be switched.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic electrical configuration of a digital switching amplifier 10 according to the present invention. The digital switching amplifier 10 is a switching amplifier using delta-sigma modulation. An input audio signal from an input signal source is input as a differential signal to a pair of input terminals 11a and 11b. It is converted into a 1-bit digital signal, and can be output from the output terminals 12a and 12b as power for driving a speaker or the like. In the digital switching amplifier 10, a delta-sigma modulation circuit 13, a constant voltage switching circuit 14, a low-pass filter network circuit 15, adders 16a and 16b, an attenuator 17, a first feedback path 18, and a second feedback path. 19, a switching circuit 20, a power supply 21, a constant voltage circuit 22, and a control circuit 23.
[0030]
Although not shown, the delta-sigma modulation circuit 13, which is a delta-sigma modulator, for example, cascade-connects an integrator that sequentially integrates an input audio signal and outputs from each integrator to each other. An integrator / adder group including an adder for adding, and a quantizer for quantizing an output from the adder into a 1-bit signal are included. The constant voltage switching circuit 14 serving as a power amplifier switches a constant voltage supplied from the power supply 21 and made constant by the constant voltage circuit 22 using the quantized 1-bit signal output from the delta-sigma modulation circuit 13, Outputs a voltage pulse signal. The attenuator 17 attenuates the peak value of the large voltage pulse signal from the constant voltage switching circuit 14 so as to decrease. The switching circuit 20 includes a pulse signal output from the attenuator 17 and input from the first feedback path 18, and a quantized 1-bit signal output from the delta-sigma modulation circuit 13 and input from the second feedback path 19. Are switched and input to the adders 16a and 16b. The adders 16a and 16b perform an operation of subtracting the negative feedback signal input from the switching circuit 20 from the input signal supplied to the input terminals 12a and 12b.
[0031]
The constant voltage switching circuit 14 is supplied with a positive constant voltage + V and a negative constant voltage −V having an absolute value equal to the constant voltage + V from the constant voltage circuit 22. Although two types of power supply voltages having different polarities are used here, a single power supply may be used as ground (0 V) instead of a constant voltage having either positive or negative polarity. The constant voltage circuit 22 may be provided inside the digital switching amplifying device 10 or may be provided outside the digital switching amplifying device 10 and connected via a power line.
[0032]
The constant voltage switching circuit 14 performs switching of the constant voltages + V and −V supplied from the constant voltage circuit 22 by using a 1-bit signal output from the delta-sigma modulation circuit 13 as a switching control signal, and performs a 1-bit signal. To amplify the power. Further, the constant voltage switching circuit 14 outputs a power amplified 1-bit signal obtained by power amplification of the 1-bit signal to the low-pass filter network circuit 15 and the attenuator 17 of the feedback circuit.
[0033]
The low-pass filter network circuit 15 limits the band to a low-frequency band, interpolates the power-amplified 1-bit signal, and demodulates the power-amplified 1-bit signal into an analog acoustic signal. The low-pass filter network circuit 15 outputs an analog audio signal from the output terminals 12a and 12b.
[0034]
The first feedback path 18 is for returning the power-amplified 1-bit signal to the input side of the delta-sigma modulation circuit 13 in a negative way. The attenuator 17 is provided on the first feedback path 18 and attenuates the pulse peak value of the power amplified 1-bit signal.
[0035]
The second feedback path 19 directly feeds back the 1-bit signal output from the delta-sigma modulation circuit 13 to the input side of the delta-sigma modulation circuit 13 via the adders 16a and 16b.
[0036]
Next, the operation of the digital switching amplifier 10 having the above configuration will be described. After a feedback signal is subtracted by an adder 16a or 16b from an analog signal such as an audio signal or a multi-bit signal input to the input terminals 11a and 11b, the obtained signal is converted into a 1-bit signal by a delta-sigma modulation circuit 13. Is converted to
[0037]
Specifically, the difference signal after the feedback signal is subtracted by the integrator / adder group as described above is integrated, then added, noise-shaped, and added by the quantizer. Is determined and converted to a 1-bit signal having a logical value of “1” or “0”. The one-bit signal is input to the constant voltage switching circuit 14 as a switching control signal, and is power-amplified into a power-amplified one-bit signal having a voltage width of a constant voltage + V and a constant voltage -V given from the constant voltage circuit 22.
[0038]
The 1-bit power amplified signal obtained by the constant voltage switching circuit 14 is input to a low-pass filter network circuit 15, demodulated into an analog sound signal by the low-pass filter network circuit 15, and connected to a speaker connected between the output terminals 12a and 12b. And so on. On the other hand, the peak value of the 1-bit power-amplified signal is attenuated by the attenuator 17 and negatively fed back to the input side of the delta-sigma modulation circuit 13 as a feedback signal.
[0039]
Although the configuration of the above embodiment includes the low-pass filter network circuit 15 for demodulating a 1-bit signal to be power-amplified into an analog acoustic signal, the configuration as a demodulation unit for demodulating the amplified 1-bit signal to an analog signal. , A circuit other than the low-pass filter network circuit.
[0040]
Further, the demodulation unit for demodulating the amplified 1-bit signal into an analog signal may be omitted, and the amplified 1-bit signal may be digitally output as it is.
[0041]
Furthermore, the quantizer in the delta-sigma modulation circuit does not need to have one quantization threshold, and may be configured to perform multi-level quantization. By performing multi-level quantization in the delta-sigma modulation circuit 13, even when the amplitude of the input signal is small, a quantized output signal based on a low quantization threshold can be taken out. A switching operation can be performed. Therefore, there is an effect that the power efficiency is dramatically improved. In addition, when the amplitude of the input signal is small, the quantization noise is remarkably reduced, and a sufficient SN ratio can be obtained.
[0042]
Further, the input signal is a differential signal composed of a pair of a first signal and a second signal having opposite polarities, but may be a single signal based on the ground voltage level (0 V). If it is a single signal, it is not necessary to provide the pair of adders 16a and 16b, and the configuration of the feedback circuit and the like can be simplified. In the present embodiment, since a differential signal is used as an input signal, high-frequency noise such as switching noise generated in the constant voltage switching circuit 14 does not affect the input signal via the circuit ground, and digital switching is performed. The SN ratio of the amplification device 10 can be sufficiently obtained.
[0043]
The digital switching amplifier 10 configured as described above enters a normal operation state after a muting operation, such as when power is turned on.
[0044]
FIG. 2 schematically shows a procedure at the time of canceling the muting operation performed under the control of the control circuit 23 of FIG. That is, control is started from step s0. In step s1, the output of the delta-sigma modulation circuit 13 is input to the adders 16a and 16b via the second feedback path 19 in a state where the delta-sigma modulation circuit 13 has risen. The switching circuit 20 is switched as described above. The constant voltage circuit 22 does not supply the constant voltages + V and -V to the constant voltage switching circuit 14. Next, in step s2, the constant voltage circuit 20 is controlled to apply the constant voltages + V and -V to the constant voltage switching circuit 14. Then, in step s3, the switching circuit 20 is controlled to switch the return path to the first return path 18, and the control ends in step s4.
[0045]
According to the above operation procedure, the 1-bit signal output from the delta-sigma modulation circuit 13 is fed back without passing through the constant voltage switching circuit 14 during the muting operation, so that the noise shaping operation of the delta-sigma modulation circuit 13 is stable. However, no excessive noise component is included in the output of the delta-sigma modulation circuit 13, so that an excessive current does not flow through the semiconductor power amplifying element of the constant voltage switching circuit 14 and no noise is output when the muting operation is canceled.
[0046]
When the switching circuit 20 switches the feedback path to the first feedback path 18 and the muting operation is released, the signal amplified by the constant voltage switching circuit 14 and further attenuated by the attenuator 17 is added to the adders 16a and 16b. A signal loop in which the signal subtracted from the input signal is further delta-sigma modulated is formed, the noise shaping operation of the delta-sigma modulation circuit 13 is stabilized, and the output of the delta-sigma modulation circuit does not contain excessive noise components. An excessive current does not flow through the semiconductor power amplifier element of the voltage switching circuit 14, and no noise is output when the muting operation is canceled. Further, since the voltage fluctuation supplied from the constant voltage circuit 22 is corrected by negative feedback through the first feedback path 18 including the constant voltage switching circuit 14 in the signal loop, the residual noise component can be removed, and the sufficient noise can be eliminated. An SN ratio can be taken. The constant voltage circuit 22 cannot perform a complete constant voltage operation, and the output voltage fluctuates, but the effect can be reduced by negative feedback. In addition, it is possible to reduce the influence of noise and operate with only a smoothing circuit using a large-capacity capacitor without using the constant voltage circuit 22.
[0047]
Further, since the clock of the delta-sigma modulation circuit 13 is not stopped, the muting release operation is performed without performing complicated control on the operation timing of the delta-sigma modulation circuit 13, and the delta-sigma modulation is performed even after the muting is released. The output of the circuit 13 does not include an excessive noise component, so that there is an advantage that an excessive current does not flow through the semiconductor power amplifier element of the constant voltage switching circuit 14 and no noise is output when the muting operation is canceled. I have.
[0048]
【The invention's effect】
As described above, according to the present invention, even when a muting operation is performed at the time of initial operation start-up, the noise shaping operation of the delta-sigma modulator and the operation of the power amplifier can be performed by switching the feedback path by the switching circuit. Can be stabilized. Excessive noise components are not included in the output of the delta-sigma modulator even after the muting operation is released, and excessive current flows to the semiconductor power amplifier that performs switching operation in the power amplifier, or noise is output when the muting operation is released. This has the advantage that undesired phenomena such as inconvenience do not occur.
[0049]
Further, according to the present invention, since a differential signal is used as an input signal, high-frequency noise such as switching noise generated in a power amplifier does not affect an input signal via a circuit ground. The S / N ratio of the device can be sufficiently obtained.
[0050]
Further, according to the present invention, by performing multi-level quantization by the delta-sigma modulator, even when the amplitude of the input signal is small, a quantized output signal based on a low quantization threshold can be extracted. The switching operation can be performed by setting the voltage level. Therefore, there is an effect that the power efficiency is dramatically improved. In addition, when the amplitude of the input signal is small, the quantization noise is remarkably reduced, and a sufficient SN ratio can be obtained.
[0051]
Further, according to the present invention, the noise shaping operation of the delta-sigma modulator can be stabilized and the fluctuation of the voltage supplied to the power amplifier can be corrected during the normal operation such as after the start-up of the operation. Components can be removed, and a sufficient SN ratio can be obtained.
[0052]
Further, according to the present invention, the muting operation is performed before the operation is started to stabilize the noise shaping operation of the delta-sigma modulator, the output of the delta-sigma modulator does not include an excessive noise component, and the power amplifier is switched. It is possible to prevent an excessive current from flowing through the semiconductor power amplifier element included as an element, and prevent noise from being output when the muting operation is canceled.
[0053]
Further, according to the present invention, the power supply does not output noise in a state where it is supplied to the power amplifier during the muting operation to switch and amplify the quantized signal, and also has a power saving effect because unnecessary power is not used. .
[0054]
Further, according to the present invention, the output of the delta-sigma modulator does not include an excessive noise component even after the muting operation is released, and an excessive current flows through a semiconductor power amplifier element or the like that performs switching in the power amplifier, or a mu current is generated. The normal operation can be switched so that no noise is output at the time of canceling the singing operation.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic electrical configuration of a digital switching amplifier 10 according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a schematic control procedure when muting is released by a control circuit 23 of FIG. 1;
FIG. 3 is a block diagram showing a schematic electrical configuration of a conventional digital switching amplifier.
FIG. 4 is a block diagram showing a schematic electrical configuration of a conventional digital switching amplifier.
[Explanation of symbols]
10 Digital switching amplifier
13 Delta-sigma modulation circuit
14. Constant voltage switching circuit
15 Low-pass filter network circuit
16a, 16b adder
17 Attenuator
18 First return path
19 Second return path
20 Switching circuit
22 Constant voltage circuit
23 Control circuit

Claims (7)

A delta-sigma modulator that generates a quantized signal by performing delta-sigma modulation on an input signal;
A power supply to supply voltage;
A power amplifier that receives a quantized signal from the delta-sigma modulator and switches a constant voltage supplied from a constant voltage power supply based on the quantized signal, thereby switching and amplifying the quantized signal to generate a pulse signal; ,
A low-pass filter that converts the pulse signal amplified by the power amplifier into an analog signal by low-pass filtering and outputs the analog signal;
An attenuator to which a pulse signal amplified by a power amplifier is input and attenuates a peak value of the pulse signal,
A first feedback path for negatively feeding back the pulse signal output from the attenuator to the input side of the delta-sigma modulator, or negatively feeding back the quantized signal output from the delta-sigma modulator to the input side of the delta-sigma modulator A switching circuit for switching one of the second feedback paths so as to select it. 2. The digital switching amplifier according to claim 1, wherein the delta-sigma modulator receives, as an input signal, a differential signal composed of a pair of a first signal and a second signal having opposite polarities. . 2. The digital switching amplifier according to claim 1, wherein the delta-sigma modulator is a binary or multi-level quantized signal as the quantized signal. 2. The digital switching amplifier according to claim 1, wherein the switching circuit switches so as to select the first feedback path during a normal operation. 2. The digital switching amplifier according to claim 1, wherein the switching circuit switches so as to select the second feedback path during a muting operation. The digital switching amplifier according to claim 5, wherein the power supply cuts off the supply of the voltage to the power amplifier during the muting operation. At the time of the muting operation, the power amplifier is supplied with a voltage from the power supply while the switching to the normal operation is switched so that the switching circuit selects the second feedback path. 7. The digital switching amplifying device according to claim 6, further comprising control means for performing the control by switching the circuit to select the first return path from the second return path.

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