JP2006054545A - Digital gain control device, audio signal power amplification device using the same, and methods thereof - Google Patents

Abstract

A gain control with a simpler configuration and less quality degradation than in the prior art is possible.
A digital gain control device subtracts output signals from digital filters 111, 112, and 113 from a digital signal input from an oversampling circuit 102 by a subtractor 108, and requantizes the digital signal resulting from the subtraction. A delta-sigma modulator that outputs the signal after requantization by 109 and subtracts the digital signal resulting from the subtraction from the requantized digital signal by the subtractor 110 and outputs the result to the subtractor 108 via the digital filters 11, 112, and 113. 103. Here, as the attenuation coefficient of the volume control signal increases, one of them is selected so that the quantization step width of the requantizer 109 is increased and the order of the digital filters 111, 112, 113 is increased. The switches SW1 and SW2 are switched and controlled.
[Selection] Figure 1

Description

  The present invention relates to a digital gain control apparatus for controlling the gain of a digital signal such as a digital audio signal, an audio signal power amplifying apparatus for power amplifying an audio signal using the same, and a method thereof.

  A power amplifier in an acoustic device modulates a DC voltage supplied from a DC power source based on an input signal and supplies a waveform similar to the input signal to a speaker as a load. In such a power amplifier, an input signal is converted into a binary signal and the signal is power amplified (switched) to reduce power loss as much as possible and improve power conversion efficiency. It is called a class power amplifier (class D amplifier or digital amplifier). Among them, an input audio signal (power-amplified input signal) is directly input without converting the digital audio signal read from a medium on which a digital audio signal such as a CD (Compact Disc) is recorded into an analog signal. What is processed as a signal is called a full digital amplifier (for example, see Non-Patent Documents 1 and 2).

  The full digital amplifier according to the first conventional example will be described below with reference to FIG.

  In FIG. 6, the digital volume 502 multiplies the signal input from the input terminal 501 by an attenuation coefficient according to the attenuation instruction of the volume control signal to attenuate the signal amplitude, and then in the noise shaper 505. The data is output to the oversampling circuit 503. The noise shaper 505 includes an oversampling circuit 503 and a delta sigma modulator 504. The oversampling circuit 503 oversamples the output signal from the digital volume 502 at a predetermined oversampling rate, and then outputs it to the delta sigma modulator 504. Next, the delta sigma modulator 504 requantizes the oversampled signal by delta sigma modulation and outputs the resampled signal to a pulse width modulator (PWM) 506. The pulse width modulator 506 performs pulse width modulation on the input signal, thereby converting the input signal into a binary signal whose pulse width changes according to the input signal, and outputs the binary signal to the power amplifier power switch circuit 507. Further, the output voltage variable DC power supply 510 changes the output voltage according to the amount of attenuation in accordance with the volume control signal and outputs it to the power amplifier power switch circuit 507. The power amplifying unit power switch circuit 507 amplifies the signal output from the pulse width modulator 506 using the output voltage from the output voltage variable DC power supply 510 and performs low-pass filtering of the audible audio signal. The signal is output to an output terminal 509 via a band pass filter (LPF) 508.

  The mechanism of volume attenuation in the full digital amplifier configured as described above is such that the output voltage of the output voltage variable DC power supply 510 is changed according to the instruction of the volume control signal. That is, when the volume is increased, the power supply voltage value is increased, and when the volume is decreased, the power supply voltage value is decreased. Therefore, the amplitude of the output signal from the power amplification unit power switch circuit 507 changes according to the volume control. That is, when the volume is increased, the amplitude is increased, and when the volume is reduced, the amplitude is decreased. As a result, the amplitude of the output signal from the low-pass filter 508 can be controlled.

  However, when the power supply voltage is changed according to the volume control, the power supply voltage becomes zero when the volume is reduced to the maximum, and the power amplification unit power switch circuit 507 to which no power is supplied is supplied from the pulse width modulator 506. A signal is supplied, and there is a possibility of destroying the elements constituting the power amplifier power switch circuit 507. Therefore, a lower limit is set for volume control (particularly attenuation control) by changing the power supply voltage, and for volume attenuation beyond that, the input signal is attenuated by the digital attenuator 502, so that the volume is controlled to zero. It is set as the structure which can implement.

  Further, a configuration in which power is amplified after attenuating the digital signal as it is can be considered. For this purpose, if a digital attenuator is used for the master volume of a preamplifier or mixing device, a stable volume adjustment characteristic can always be obtained, and sound quality changes and deterioration over time occur as in the case of using a resistance-attenuator. It is known that there are no advantages. As such a digital attenuator, for example, a digital attenuator disclosed in Patent Document 1 has been proposed.

  FIG. 7 is a block diagram showing a configuration of a digital attenuator according to the second conventional example. In FIG. 7, input digital audio data input via an n-bit input terminal 601 oversampled at an appropriate magnification as required is input to a digital attenuator 602. The digital attenuator 602 multiplies the input digital audio data by attenuation data which is output from a controller (not shown), and changes in magnitude according to the user's volume reduction operation or increase operation. Is output as digital data having a length of (n + m) bits. Here, the attenuation amount data takes a value in the range of 1 to 0. When the volume is maximum, the attenuation amount data is 0 dB = 1, and when the volume is minimum, the attenuation amount is 0. The volume-adjusted digital audio data is D / A converted by a k-bit D / A converter 603 and output to an output terminal 605 via a low-pass filter (LPF) 604. Specifically, the upper k bits of the digital signal from the digital attenuator 602 are output as digital audio data to the D / A converter 603, and the D / A converter 603 converts the input digital audio data to D The analog signal output is passed through the low-pass filter 604, and signal processing such as smoothing and aliasing noise removal is executed and output to the output terminal 605.

  When this digital attenuator is applied to a class D power amplifier, instead of the D / A converter 603, a binary signal generating means 606 for converting a multilevel digital signal into a binary signal and the power of the binary signal are amplified. A circuit 610 comprising a power amplifier 607 is used. The digital volume 502 in FIG. 5 performs the same operation as the digital attenuator 602.

JP-A-8-330869. “Production of 100W + 100W Audio Digital Amplifier <Part 1> Birth of Full Digital Amplifier”, Transistor Technology, September 2002, CQ Publishing Co., pp. 265-271. “Manufacture of Digital Amplifier for 100W + 100W Audio <Part 2> Manufacture of Full Digital Amplifier”, Transistor Technology October 2002, CQ Publishing Co., pp. 242-254. Yoshio Yamazaki, “High-Speed 1-bit Signal Processing”, JAS Journal, April 1997 Special Issue, Japan Audio Society, Vol. 34, no. 4.

  However, since the volume control of the full digital amplifier according to the first conventional example changes the power supply voltage, the configuration of the power supply section that supplies a stable power supply and makes the output voltage variable becomes complicated, and the There has been a problem that the power supply unit is very expensive for a power source that converts a lamp power supply (AC100V of 50 Hz or 60 Hz in the case of Japan) to a direct current by a rectifier circuit after stepping down with a transformer.

  In the digital attenuator according to the second conventional example described above, if the amount of attenuation at the digital attenuator 602 is large even if the value of the audio data input to the digital attenuator 602 is the same, the digital attenuator 602. Output signal is shifted to the lower bit side. Therefore, in order to perform D / A conversion with high resolution even when the volume is reduced, the word length of the D / A converter 603 may be (n + m) bits, but the internal configuration of the D / A converter 603 is not limited. It is very difficult to have a performance commensurate with the complexity and data word length, and even if the performance can be achieved, it becomes very expensive and unrealistic. Therefore, in general, the word length of the D / A converter is the word length before performing the volume attenuation process. For example, in FIG. 7, n = 20 and m = 10.

  When listening to actual audio, the volume is reduced, and as the amount of attenuation in the digital attenuator 602 increases, the dynamic range of the output signal of the digital attenuator 602 becomes narrower and the quality deteriorates. It was.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a digital gain control device that has a simpler configuration than that of the conventional example and can perform gain control with little quality deterioration, and audio signal power using the same. An object of the present invention is to provide an amplification device and a method thereof.

According to a first aspect of the present invention, a digital gain control apparatus subtracts an output signal from a digital filter from an input digital signal by a first subtracter, and requantizes the digital signal resulting from the subtraction by a requantizer. And a delta-sigma modulator that subtracts the subtraction result digital signal from the requantized digital signal by a second subtracter and outputs the subtracted digital signal to the first subtractor via the digital filter. In the digital gain control device,
Control means for controlling to increase the quantization step width of the requantizer and to increase the order of the digital filter as the attenuation coefficient of the gain control signal increases based on the input gain control signal It is provided with.

An audio signal power amplifying device according to a second aspect of the invention comprises oversampling means for oversampling and outputting an input digital audio signal;
The digital gain control device for controlling and outputting the gain of the output signal from the oversampling means;
Power amplifying means for amplifying and outputting an output signal from the digital gain control device;
And filtering means for filtering an audio signal of a predetermined band from the output signal from the power amplifying means.

An audio signal power amplifying device according to a third aspect of the invention comprises oversampling means for oversampling and outputting an input digital audio signal;
The digital gain control device for controlling and outputting the gain of the output signal from the oversampling means;
Pulse width modulation means for pulse-modulating and outputting a predetermined pulse signal in accordance with an output signal from the digital gain control device;
A power amplifying means for amplifying and outputting an output signal from the pulse width modulation means;
And filtering means for filtering an audio signal of a predetermined band from the output signal from the power amplifying means.

According to a fourth aspect of the present invention, there is provided a digital gain control method, wherein an output signal from a digital filter is subtracted from an input digital signal by a first subtracter, and the digital signal resulting from the subtraction is requantized by a requantizer. And a delta-sigma modulator that subtracts the subtraction result digital signal from the requantized digital signal by a second subtracter and outputs the subtracted digital signal to the first subtractor via the digital filter. In a digital gain control method for a digital gain controller,
The step of controlling to increase the quantization step width of the requantizer and increase the order of the digital filter as the attenuation coefficient of the gain control signal increases based on the input gain control signal. It is characterized by including.

An audio signal power amplification method according to a fifth aspect of the present invention includes a step of oversampling and outputting an input digital audio signal;
Using the digital gain control method to control and output the gain of the oversampled signal; and
Amplifying and outputting the signal whose gain is controlled; and
Filtering the audio signal of a predetermined band from the power amplified signal.

An audio signal power amplification method according to a sixth aspect of the present invention includes a step of oversampling and outputting an input digital audio signal;
Using the digital gain control method to control and output the gain of the oversampled signal; and
A step of performing pulse width modulation of a predetermined pulse signal according to the signal in which the gain is controlled, and outputting,
Power amplifying and outputting the pulse width modulated signal;
Filtering the audio signal of a predetermined band from the power amplified signal.

  Therefore, according to the digital gain control apparatus and method of the present invention, the quantization step width of the requantizer is increased as the attenuation coefficient of the gain control signal increases based on the input gain control signal. In addition, since the order of the digital filter is increased, the order of the delta-sigma modulator can be increased to reduce the quantization noise power, thereby suppressing the increase in noise of the requantizer as well as dynamic. The narrowing of the range can be prevented, and the SN ratio of the entire apparatus can be increased.

  Also, an audio signal power amplifying apparatus having a simple configuration compared to the conventional example and capable of realizing an improved S / N ratio by configuring the audio signal power amplifying apparatus using the digital gain control apparatus and method is provided. Can be provided.

  Further, by providing a pulse width modulator or a pulse width modulation step, the dynamic range of the delta sigma modulator can be increased, and the quantization noise generated by the requantizer is used for the pulse width modulation. Compared to the conventional binary signal example, the whiteness is high, the correlation with the input signal can be reduced, and the operation can be stably performed. As a result, a high-performance audio signal power amplifier is provided compared to the conventional example. it can.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected about the same component.

<First Embodiment>
FIG. 1 is a block diagram showing a configuration of an audio signal power amplifying apparatus according to the first embodiment of the present invention. The audio signal power amplifying apparatus according to the first embodiment subtracts the output signals from the digital filters 111, 112, and 113 from the digital signal input from the oversampling circuit 102 by the subtractor 108, and the digital signal of the subtraction result. The signal is re-quantized by the re-quantizer 109 and output, and the digital signal resulting from the subtraction is subtracted from the re-quantized digital signal by the subtracter 110 and subtracted through the digital filters 11, 112 and 113. The delta-sigma modulator 103 that outputs to the comparator 108 constitutes a digital gain control device, and two switches SW1, SW1 that selectively switch the digital filters 111, 112, and 113 between the subtractor 108 and the subtractor 110. SW2 is provided, and the volume control is an input gain control signal Based on the signal, as the attenuation coefficient of the volume control signal increases, the digital filter 111, 112, 113 increases the order of the digital filter 111, 112, 113 so that the quantization step width of the requantizer 109 increases. The switches SW1 and SW2 are controlled so as to select one of 112 and 113.

  In FIG. 1, the oversampling circuit 102 oversamples the digital audio signal input via the input terminal 101 at a predetermined oversampling rate, and then outputs the digital audio signal to the subtracter 108 of the delta sigma modulator 103.

The delta-sigma modulator 103 includes two subtracters 108 and 110, a requantizer 109, three digital filters 111, 112, and 113, and two switches SW1 and SW2 (for example, Non-patent document 3). Here, the digital filter 111 is a primary digital filter having a transfer function z ^−1, for example, and the digital filter 112 is a secondary digital filter having a transfer function 2z ⁻¹ −z ^−2, for example. Is, for example, a third-order digital filter having a transfer function 3z ⁻¹ -3z ⁻² −z ⁻³ . In the delta sigma modulator 103, the subtractor 108 subtracts the output signal output from the digital filters 111, 112, and 113 through the switch SW2 from the digital signal input from the oversampling circuit 102, and The subtraction result digital signal is requantized by the requantizer 109 and output to the pulse width modulator 104, and the subtraction result digital signal is subtracted from the requantized digital signal by the subtractor 110. , Output to the subtractor 108 via the switch SW1, one of the digital filters 11, 112, 113, and the switch SW2. Note that the subtractor 110 performs subtraction after converting the signal after requantization into a quantization step before requantization at the time of subtraction. Here, according to the volume control signal, for example, the requantizer 109 and the switches SW1 and SW2 are controlled as follows.

(1) When the volume is relatively large and the volume control signal is 0.67 or more and 1 or less (its attenuation coefficient is the reciprocal of the volume control signal): Switch SW1 and SW2 to contact a and switch to 1 The next digital filter 111 is selected, and the quantization step width of the requantizer 109 is set to 1.
(2) When the volume is relatively intermediate and the volume control signal is not less than 0.33 and less than 0.67 (the attenuation coefficient is the reciprocal of the volume control signal): the switches SW1 and SW2 are respectively set. Switch to the contact point b to select the secondary digital filter 112 and set the quantization step width of the requantizer 109 to 2.
(3) When the sound volume is relatively large and the sound volume control signal is 0 or more and less than 0.33 (the attenuation coefficient is the reciprocal of the sound volume control signal): Switch SW1 and SW2 to contact c respectively. The next digital filter 113 is selected, and the quantization step width of the requantizer 109 is set to 3.

  That is, in the delta-sigma modulator 103, the quantization step width of the requantizer 109 is increased as the attenuation coefficient of the volume control signal increases based on the volume control signal that is an input gain control signal. In addition, the switches SW1 and SW2 are controlled so as to select one of the digital filters 111, 112, and 113 so as to increase the order of the digital filters 111, 112, and 113.

  Therefore, the delta sigma modulator 103 requantizes the oversampled signal by delta sigma modulation and outputs the resampled signal to the pulse width modulator (PWM) 104. The pulse width modulator 104 performs pulse width modulation on the input signal, thereby converting the input signal into a binary signal whose pulse width changes according to the input signal, and outputs the binary signal to the power amplification unit power switch circuit 105. The power amplifying unit power switch circuit 105 amplifies the signal output from the pulse width modulator 104 and supplies the audible audio signal to the output terminal 107 via a low-pass filter (LPF) 106 that performs low-pass filtering. Output.

  FIG. 2 is a block diagram showing a configuration of the power amplification unit power switch circuit 105 of FIG. In FIG. 2, the power amplification unit power switch circuit 105 includes a driver circuit 121 and two power MOS field effect transistors (hereinafter referred to as MOSFETs) 122 and 123 having a CMOS configuration. As shown in FIG. 2, the driver circuit 121 drives the MOSFET 122 in the same phase in accordance with the digital signal input via the input terminal T1, while driving the MOSFET 123 in the opposite phase to amplify the power of the input digital signal.

  Here, since the two MOSFETs 122 and 123 can only be turned on / off, the two MOSFETs 122 and 123 and the driver circuit 121 for driving the MOSFETs 122 and 123 are configured as described above. The input signal to the power amplifier power switch circuit 105 is preferably a 1-bit binary signal. The reason is that if a plurality of power switches are combined, the input signal to the power amplifying unit power switch circuit 105 can be multi-valued, but the number of parts increases, resulting in an increase in cost and impracticality.

  3 is a diagram showing the operation of the audio signal power amplifying apparatus of FIG. 1, in which FIG. 3 (a) is a waveform diagram showing an input signal, and FIGS. 3 (b1) to 3 (d1) are volume control. 3 is a waveform diagram of each signal when not performing (when the quantization step width of the requantizer 109 is 1), and FIG. 3B1 is a waveform diagram of an output signal of the delta-sigma modulator 103, and FIG. (C1) is a waveform diagram of the output signal of the power amplification unit power switch circuit 105, FIG. 3 (d1) is a waveform diagram of the output signal of the low-pass filter 106, and FIGS. 3 (b2) to 3 (d2) ) Is a waveform diagram of each signal when the volume control signal is 1/2 (when the quantization step width of the requantizer 109 is 2), and (b2) is an output signal of the delta-sigma modulator 103. FIG. 3 (c2) is a power amplifying unit power switch circuit. 05 is a waveform diagram of the output signal of FIG. 3 (d2) is a waveform diagram of the output signal of the low-pass filter 106.

  In the present embodiment, the number of output bits (gradation) of the requantizer 109 is left as it is, and the quantization level is set to be proportional to the inverse of the volume attenuation coefficient of the volume control signal. This operation will be described below with reference to FIG. Here, in order to simplify the description, as shown in FIG. 3A, the signal input to the input terminal 101 is a DC signal whose amplitude is full scale (+1). Even if this signal is oversampled, the amplitude value remains full scale.

  First, the case where the volume is not attenuated will be described. The input signal is requantized by the delta sigma modulator 103. The requantizer 109 sets the quantization number to three (quantization level is 0, 0.5, 1). Here, since the amplitude value of the signal is full scale, the data after re-quantization is also a full-scale DC signal as shown in FIG. The same applies to the PWM waveform. When the signal is amplified by the power amplifying unit power switch circuit 105, the output signal becomes a DC signal whose amplitude is the power supply voltage value + Vdd (FIG. 3 (c1)). Even if the signal is band-limited using the low-pass filter 106, there is no effect on the direct current component, so that a signal having an amplitude value of + Vdd appears at the output terminal 107 (FIG. 3 (d1)).

  Next, a case where the volume is attenuated by half (1/2) will be described. First, since the volume attenuation coefficient is ½, the quantization level of the requantizer 109 is set to the reciprocal of the volume attenuation coefficient (FIG. 3 (b2)). That is, the signs of the output signals of the requantizer 109 are 0, 1, and 2. Here, when the signal is quantized by the requantizer 109, the +1 direct current signal is converted into a signal having a waveform as shown in FIG. When this signal is input to the pulse width modulator 104, it is converted into a binary signal having a duty ratio of 50% (FIG. 3 (c2)). In this case, since the quantization number of the requantizer 109 is ternary, the PWM signal is a signal having a period at least half the sampling period of the delta-sigma modulator 103. When the output signal from the pulse width modulator 104 is amplified by the power amplifying unit power switch circuit 105, a signal having an amplitude of + Vdd and a duty ratio of 50% is output (FIG. 3 (d2)). Further, when the signal is passed through the low-pass filter 106, a signal having an average value (+ Vdd / 2) is output from the output terminal 107 (FIG. 3 (d2)). Thereby, it can be seen that the input signal is attenuated by half.

  Therefore, as apparent from FIG. 3, the input audio signal can be attenuated by increasing the quantization step width of the requantizer 109 as the signal level of the volume control signal is decreased.

  As described above, according to the present embodiment, the quantization step width of the requantizer 109 increases as the attenuation coefficient of the volume control signal increases based on the volume control signal that is an input gain control signal. And switches SW1 and SW2 so as to select one of the digital filters 111, 112, and 113 so that the order of the digital filters 111, 112, and 113 is increased. As a result, as the attenuation coefficient of the volume control signal increases, the order of the delta sigma modulator 103 can be increased to reduce the quantization noise power, thereby suppressing the increase in noise of the requantizer. The dynamic range can be prevented from being narrowed, and the SN ratio of the entire apparatus can be increased.

  Further, by configuring the audio signal power amplifying apparatus as in the present embodiment, it is possible to provide an audio signal power amplifying apparatus that has a simple configuration compared to the conventional example and can realize an improved SN ratio.

<Second Embodiment>
FIG. 4 is a block diagram showing the configuration of an audio signal power amplifying apparatus according to the second embodiment of the present invention. The audio signal power amplifying apparatus according to the second embodiment has a pulse width that is obtained by setting the quantization number of the requantizer 109 to be binary as compared with the audio signal power amplifying apparatus according to the first embodiment. This is because the modulator 104 has been deleted, and may be configured in this way.

  FIG. 5 is a diagram showing the operation of the audio signal power amplifying apparatus of FIG. 4, wherein (a) is a waveform diagram showing an input signal, and FIGS. 5 (b1) to 5 (d1) are when volume control is not performed. FIG. 5B is a waveform diagram of each signal when the quantization step width of the requantizer 109 is 1, and FIG. 5B1 is a waveform diagram of an output signal of the delta-sigma modulator 103. FIG. ) Is a waveform diagram of an output signal of the power amplification unit power switch circuit 105, FIG. 5 (d1) is a waveform diagram of an output signal of the low-pass filter 106, and FIGS. 5 (b2) to 5 (d2) are diagrams. FIG. 5B is a waveform diagram of each signal when the volume control signal is 1/2 (when the quantization step width of the requantizer 109 is 2), and FIG. 5B2 is an output signal of the delta-sigma modulator 103. FIG. 5 (c2) is a power amplifying unit power switch circuit. 05 is a waveform diagram of the output signal of FIG. 5 (d2) is a waveform diagram of the output signal of the low-pass filter 106.

  As is apparent from FIG. 5, the input audio signal can be attenuated by increasing the quantization step width of the requantizer 109 as the signal level of the volume control signal is decreased.

  In the audio signal power amplifying apparatus of FIG. 4, the pulse width modulator 104 is omitted, but in the audio signal power amplifying apparatus of FIG. 1, the pulse width modulator 104 is inserted. This is due to the following reason. When the requantizer is multi-valued, it needs to be converted into a binary signal, so the pulse width modulator 104 is used as the conversion means. Since the quantization step width of the requantizer 109 is larger in the configuration having the pulse width modulator 104, the dynamic range of the delta sigma modulator 103 is larger if the configurations of the digital filters 111, 112, and 113 are the same. An audio signal power amplifying apparatus with higher performance can be configured. In addition, the whiteness is high, that is, the correlation with the input signal is small as compared with the binary quantization noise generated by the requantizer 109. Therefore, the delta-sigma modulator 103 can be stabilized even if the orders of the digital filters 111, 112, and 113 are increased. As a result, a higher-performance audio signal power amplifier can be easily realized.

  As described above, according to the digital gain control apparatus and method of the present invention, as the attenuation coefficient of the gain control signal increases based on the input gain control signal, the quantization step of the requantizer Since the control is performed so that the width is increased and the order of the digital filter is increased, it is possible to increase the order of the delta-sigma modulator to reduce the quantization noise power and suppress the increase in noise of the requantizer. In addition, the dynamic range can be prevented from being narrowed, and the SN ratio of the entire apparatus can be increased.

  Also, an audio signal power amplifying apparatus having a simple configuration compared to the conventional example and capable of realizing an improved S / N ratio by configuring the audio signal power amplifying apparatus using the digital gain control apparatus and method is provided. Can be provided.

  Further, by providing a pulse width modulator or a pulse width modulation step, the dynamic range of the delta sigma modulator can be increased, and the quantization noise generated by the requantizer is used for the pulse width modulation. Compared to the conventional binary signal example, the whiteness is high, the correlation with the input signal can be reduced, and the operation can be stably performed. As a result, a high-performance audio signal power amplifier is provided compared to the conventional example. it can.

1 is a block diagram showing a configuration of an audio signal power amplifying apparatus according to a first embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration of a power amplification unit power switch circuit 105 in FIG. 1. FIG. 2 is a diagram illustrating an operation of the audio signal power amplifying apparatus in FIG. 1, where (a) is a waveform diagram illustrating an input signal, and (b1) to (d1) are when the volume control is not performed (quantization of the requantizer 109). (B1) is a waveform diagram of an output signal of the delta-sigma modulator 103, and (c1) is an output signal of the power amplifier unit power switch circuit 105. (D1) is a waveform diagram of the output signal of the low-pass filter 106, and (b2) to (d2) are graphs when the volume control signal is ½ (the quantizer of the requantizer 109). (B2) is a waveform diagram of an output signal of the delta-sigma modulator 103, and (c2) is an output signal of the power amplifying unit power switch circuit 105. (D2) is low It is a waveform diagram of the output signal of the pass filter 106. It is a block diagram which shows the structure of the audio signal power amplification apparatus which concerns on the 2nd Embodiment of this invention. FIG. 5 is a diagram illustrating an operation of the audio signal power amplifying apparatus of FIG. 4, where (a) is a waveform diagram illustrating an input signal, and (b1) to (d1) are when the volume control is not performed (quantization of the requantizer 109) (B1) is a waveform diagram of an output signal of the delta-sigma modulator 103, and (c1) is an output signal of the power amplifier unit power switch circuit 105. (D1) is a waveform diagram of the output signal of the low-pass filter 106, and (b2) to (d2) are graphs when the volume control signal is ½ (the quantizer of the requantizer 109). (B2) is a waveform diagram of an output signal of the delta-sigma modulator 103, and (c2) is an output signal of the power amplifying unit power switch circuit 105. (D2) is low It is a waveform diagram of the output signal of the pass filter 106. It is a block diagram which shows the structure of the full digital amplifier based on a 1st prior art example. It is a block diagram which shows the structure of the digital attenuator which concerns on a 2nd prior art example.

Explanation of symbols

101: Input terminal,
102: Oversampling circuit,
103 Delta sigma modulator,
104: Pulse width modulator (PWM),
105: Power amplifier power switch circuit,
106 ... Low-pass filter (LPF),
107 ... output terminal,
108 ... subtractor,
109 ... requantizer,
110 ... subtractor,
111... Primary digital filter,
112 ... secondary digital filter,
113: Third-order digital filter,
SW1, SW2 ... switch.

Claims (6)

From the input digital signal, the output signal from the digital filter is subtracted by the first subtracter, the digital signal resulting from the subtraction is requantized and output by the requantizer, and the requantized digital signal is output. A digital gain control device comprising a delta-sigma modulator that subtracts a digital signal of the subtraction result from the second subtractor and outputs the subtracted digital signal to the first subtractor via the digital filter;
Control means for controlling to increase the quantization step width of the requantizer and to increase the order of the digital filter as the attenuation coefficient of the gain control signal increases based on the input gain control signal A digital gain control device comprising: Oversampling means for oversampling and outputting an input digital audio signal;
The digital gain control apparatus according to claim 1, wherein the gain of the output signal from the oversampling means is controlled and output.
Power amplifying means for amplifying and outputting an output signal from the digital gain control device;
An audio power amplifying apparatus comprising: filtering means for filtering an audio signal in a predetermined band from an output signal from the power amplifying means. Oversampling means for oversampling and outputting an input digital audio signal;
The digital gain control apparatus according to claim 1, wherein the gain of the output signal from the oversampling means is controlled and output.
Pulse width modulation means for pulse-modulating and outputting a predetermined pulse signal in accordance with an output signal from the digital gain control device;
A power amplifying means for amplifying and outputting an output signal from the pulse width modulation means;
An audio power amplifying apparatus comprising: filtering means for filtering an audio signal in a predetermined band from an output signal from the power amplifying means. From the input digital signal, the output signal from the digital filter is subtracted by the first subtracter, the digital signal resulting from the subtraction is requantized and output by the requantizer, and the requantized digital signal is output. A digital gain control method for a digital gain control apparatus comprising a delta-sigma modulator that subtracts a digital signal resulting from the subtraction from a second subtracter and outputs the result to the first subtractor via the digital filter In
The step of controlling to increase the quantization step width of the requantizer and increase the order of the digital filter as the attenuation coefficient of the gain control signal increases based on the input gain control signal. A digital gain control method comprising: Oversampling and outputting the input digital audio signal;
Using the digital gain control method according to claim 4 to control and output the gain of the oversampled signal;
Amplifying and outputting the signal whose gain is controlled; and
Filtering the audio signal of a predetermined band from the power amplified signal. Oversampling and outputting the input digital audio signal;
Using the digital gain control method according to claim 4 to control and output the gain of the oversampled signal;
A step of performing pulse width modulation of a predetermined pulse signal according to the signal in which the gain is controlled, and outputting,
Power amplifying and outputting the pulse width modulated signal;
Filtering the audio signal of a predetermined band from the power amplified signal.

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