JP2002162985A - Device and method for reproducing speech - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to control more easily and surely deterioration in tone quality of reproduced speech accompanied by fluctuations of a power source or the like. SOLUTION: It is made possible to eliminate the need for a strict synchronous control compared with the correction by feeding back a pulse signal, and facilitate the feedback control of the pulse width of the PWM signal, by feeding back to an output stage of a DAC part 1 an analog audio signal generated by LPF 13 for performing low-pass filter processing to an audio signal amplified by a power amplifier 12 according to a PWM signal, and generating the PMW signal corrected with a variation of a power source voltage Vp of the power amplifier 12 using the fed-back analog audio signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio reproducing apparatus and method, and more particularly, to a digital power amplifier for reproducing digital audio data recorded on a digital signal recording medium such as a CD (compact disk) and outputting the analog output. It is suitable.

[0002]

2. Description of the Related Art Conventionally, as means for expressing audio information, which is originally an analog signal, as a digital signal, a PC has been used.
The M multi-bit system (hereinafter abbreviated as PCM system) has been adopted. Currently widely used CDs are also
The CM system is adopted. In the PCM method, an operation according to the quantization characteristic is performed at each sampling frequency (44.1 kHz), an analog signal is replaced with a digital signal, and the absolute amount of data is recorded on a CD at all sample points.

On the other hand, recently, by controlling the distribution of quantization noise using ΔΣ modulation, the PC
The 1-bit system, which has improved restoration from a digital signal to an original analog signal as compared with the M system, has attracted attention.
In the 1-bit system, only the amount of change with respect to the immediately preceding data is recorded as a binary signal, and there is no thinning out or interpolation of the amount of information unlike the PCM system.
The bit signal has characteristics very similar to analog.

[0004] Therefore, unlike a PCM system, a sound reproducing apparatus (digital power amplifier) based on the 1-bit system, that is, a 1-bit amplifier, does not require a D / A converter.
An advantage is that the original analog signal can be reproduced by a simple process of removing the digital signal of the high-frequency component by the low-pass filter provided at the last stage.

FIG. 3 is a block diagram schematically showing a configuration of a conventional one-bit amplifier. In FIG. 3, a ΔΣ modulation unit 52 performs a conversion process based on Δ１ modulation on a 1-bit signal of digital audio reproduced from the CD 51, and performs PWM (Pulse Width Modulation).
Get the signal. Then, the obtained PWM signal is output as a control signal for driving the power amplifier 53.

[0006] The power amplifier 53 is composed of a full-bridge switching circuit, and amplifies and outputs an audio signal based on the supplied power supply voltage by controlling the ON time of each switching element. As a signal for controlling this switching, a PWM signal having an analog width on a time axis is used. This power amplifier 5
The audio signal amplified by 3 becomes an analog audio signal through a low-pass filter (LPF) 54 and is output from a speaker 55.

As described above, if the 1-bit amplifier having such a configuration is used, the original analog signal can be simply removed by the low-pass filter 54 without performing the D / A conversion operation during reproduction. The signal can be reproduced. However, in such a configuration, an error or distortion occurs in the amplified audio signal due to a change in the power supply voltage of the power amplifier 53 or the like, which causes a bad influence on the sound quality of the reproduced sound.

That is, when a loud sound is output, for example, a very large amount of current flows through the output impedance of the power supply, so that the power supply voltage decreases. When the power supply voltage drops, the output level of the audio signal peaks and clips, resulting in waveform distortion. In addition, even when a relatively small sound is output, when a signal having a sharp rising edge or a falling edge is output, the power supply voltage is reduced or increased, which causes a distortion in an output waveform.

Therefore, in order to solve such a problem, an output signal of the power amplifier 53 whose power supply voltage can fluctuate is fed back to the ΔΣ modulator 52, and the fluctuation of the power supply voltage is corrected using this feedback signal. After doing PW
One-bit amplifiers have been proposed in which a pulse width of a PWM signal is adjusted in real time by generating an M signal.

[0010]

In the conventional 1-bit amplifier having the above-mentioned feedback loop, a pulse signal generated in the ΔΣ modulation section 52 based on a 1-bit signal reproduced from the CD 51 and a power amplifier 53 The pulse width of the PWM signal is adjusted by comparison with a pulse signal that includes a feedback fluctuation error. Therefore, it is necessary to perform high-precision timing control for accurately synchronizing both pulse signals.

However, it is actually very difficult to accurately synchronize two pulse signals. In addition, there is a problem that a circuit configuration for this becomes complicated, and an expensive device that operates at a high speed is required, thereby increasing the manufacturing cost. Further, although it is good that the synchronization is accurately obtained, once the synchronization is deviated, there is a problem that the pulse width of the PWM signal cannot be adjusted properly, and the reproduced sound quality may be significantly deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem. The present invention makes it possible to easily perform feedback control of the pulse width of a PWM signal, and to reduce the sound quality of reproduced sound due to fluctuations in power supply voltage. It is an object of the present invention to provide an audio reproducing device capable of more easily and surely suppressing the sound reproduction.

[0013]

SUMMARY OF THE INVENTION An audio reproducing apparatus according to the present invention amplifies an audio signal according to a pulse width modulation signal generated based on a digital audio signal, and outputs an analog audio signal by performing a filtering process. An audio reproducing apparatus, wherein an analog audio signal generated by the filtering process is fed back to a pulse width modulation signal generation unit, and the pulse width modulation signal is corrected using the fed back analog audio signal. It is characterized by.

In another aspect of the present invention, modulation processing means for performing conversion processing based on modulation on an input digital audio signal to generate an analog pulse width modulation signal, and modulation processing means for generating an analog pulse width modulation signal. Amplifying means for amplifying the audio signal based on the pulse width modulation signal; filtering means for generating an analog audio signal by performing a filtering process on the signal output from the amplifying means; And a feedback unit that feeds back the analog audio signal to an output stage of the modulation processing unit and corrects the pulse width modulation signal using the fed back analog audio signal.

In another aspect of the present invention, the correction means includes means for converting the analog pulse width modulation signal into a digital pulse width modulation signal when correcting the pulse width modulation signal; The driving of the amplifying means is controlled based on the pulse width modulation signal.

According to another aspect of the present invention, there is provided a modulation processing means for performing conversion processing based on modulation on an input digital audio signal to generate a pulse width modulation signal, and a pulse width modulation signal generated by the modulation processing means. Amplifying means for amplifying an audio signal based on a modulation signal; filter means for generating an analog audio signal by performing a filtering process on a signal output from the amplifying means; and an analog signal generated by the filter means A for analog / digital conversion of audio signal
/ D conversion means, wherein the digital audio signal generated by the A / D conversion means is fed back to the modulation processing means, and the pulse width modulation signal is corrected using the fed back digital audio signal. It is characterized by.

In another aspect of the present invention, the modulation processing means includes ΔΣ modulation processing means for performing conversion processing based on ΔΣ modulation, and the digital audio signal generated by the A / D conversion means is subjected to the ΔΣ modulation processing. It is characterized in that feedback is provided to the means.

According to another aspect of the present invention, a digital audio signal is subjected to conversion processing based on ΔΣ modulation,
ΔΣ modulation processing means for generating a digital pulse width modulation signal, first filter means for performing low-pass filter processing on the output signal of the ΔΣ modulation processing means to generate an analog pulse width modulation signal, A triangular wave generating means for generating a triangular wave signal based on the clock signal; a triangular wave signal generated by the triangular wave generating means; and an analog pulse width modulation signal generated by the first filter means. A driving unit that drives an amplification unit that amplifies an audio signal based on the pulse width modulation signal, and the amplification unit that amplifies the audio signal according to a drive time controlled by the driving unit.
A second filter for generating an analog audio signal by performing a low-pass filter process on the signal output from the amplifier; an analog pulse width modulation signal generated by the first filter; Correcting means for correcting the pulse width modulation signal using the analog audio signal generated by the second filter means.

In another aspect of the present invention, the correcting means digitally converts the analog pulse width modulated signal using the triangular wave signal generated by the triangular wave generating means when correcting the pulse width modulated signal. And a means for returning the pulse width modulated signal to the above-mentioned drive control signal.

According to another aspect of the present invention, a digital audio signal is subjected to conversion processing based on ΔΣ modulation,
ΔΣ modulation processing means for generating a digital pulse width modulation signal, first filter means for performing low-pass filter processing on the output signal of the ΔΣ modulation processing means to generate an analog pulse width modulation signal, A triangular wave generating means for generating a triangular wave signal based on the clock signal; a triangular wave signal generated by the triangular wave generating means; and an analog pulse width modulation signal generated by the first filter means. A driving unit that drives an amplification unit that amplifies an audio signal based on the pulse width modulation signal, and the amplification unit that amplifies the audio signal according to a drive time controlled by the driving unit.
A second filter for generating an analog audio signal by performing low-pass filtering on the signal output from the amplifier; and an analog / digital conversion of the analog audio signal generated by the second filter. And A / D conversion means for supplying the resulting digital audio signal to the ΔΣ modulation processing means.

In another aspect of the present invention, the predetermined clock signal used when the triangular wave generating means generates the triangular wave signal is the same clock signal as a clock signal for controlling the operation timing of the ΔΣ modulation processing means. It is characterized by being.

According to another aspect of the present invention, a digital audio signal is subjected to conversion processing based on ΔΣ modulation,
ΔΣ modulation processing means for generating a pulse width modulation signal, driving means for driving amplification means for amplifying an audio signal based on the pulse width modulation signal generated by the ΔΣ modulation processing means, and control by the driving means Amplifying means for amplifying the audio signal according to the driving time to be performed, a filter means for generating an analog audio signal by performing a low-pass filter process on the signal output from the amplifying means, and a filter means for generating an analog audio signal. A / D conversion means for performing analog-to-digital conversion of the analog audio signal thus obtained, and supplying the resulting digital audio signal to the ΔΣ modulation processing means.

The audio reproducing method according to the present invention is an audio reproducing method for amplifying an audio signal in accordance with a pulse width modulation signal generated based on a digital audio signal, and further performing an filtering process to output an analog audio signal. The analog audio signal generated by the filtering process is fed back to the pulse width modulation signal generator, and the pulse width modulation signal is corrected using the fed back analog audio signal. .

According to another aspect of the present invention, there is provided a sound reproducing method for amplifying an audio signal in accordance with a pulse width modulation signal generated based on a digital audio signal, and further performing a filtering process to output an analog audio signal. Converting the analog audio signal generated by the filtering process from analog to digital, feeding back the obtained digital audio signal to the pulse width modulation signal generation unit, and using the fed back digital audio signal to generate the pulse width modulation signal. Is corrected.

According to the present invention constructed as described above, an audio signal including an error caused by a change in the power supply voltage of the amplifying means is fed back, and the error is corrected using this feedback signal, and the pulse is corrected. Since the width modulation signal is generated, the pulse width of the pulse width modulation signal can be adjusted in real time.
Further, since the audio signal to be fed back is an analog signal that has passed through the filter means, stricter synchronization control is not required as compared with a case where the correction is performed by feeding back a pulse signal.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration example of a 1-bit amplifier according to the present embodiment in which the audio reproducing device of the present invention is implemented. As shown in FIG. 1, the 1-bit amplifier according to the present embodiment includes a DAC unit 1, a power amplifier 12, an LPF 13
And controls the amplification time of the power amplifier 12 based on the PWM signal generated by the DAC unit 1 based on the digital audio signal reproduced from the CD 51, and passes the obtained amplified signal to the LPF 13. As a result, an analog audio signal is obtained.

The DAC unit 1 performs a conversion process based on ΔΣ modulation and a low-pass filter process on a 1-bit digital audio signal reproduced from the CD 51 to obtain an analog PWM signal. This DAC unit 1
Includes an interface (I / F) 2 with a CD 51, a digital filter (DF) 3, a ΔΣ modulation processing unit 4, an LPF 5, and a timing controller 6.

The I / F 2 inputs a digital 1-bit signal reproduced from the CD 51 to the DAC unit 1. The digital filter 3 performs a low-pass filter process on the 1-bit signal input by the I / F 2, and outputs the result to the ΔΣ modulation processing unit 4. The ΔΣ modulation processing unit 4 performs a conversion process based on the ΔΣ modulation on the signal output from the digital filter 3 to generate a digital PWM signal.

The LPF 5 performs a low-pass filter process on the digital PWM signal generated by the ΔΣ modulation processing unit 4 to obtain an analog PWM signal.
The analog PWM signal thus generated is the first PWM signal.
Then, the signal passes through the second comparators 9 and 10 and becomes a corrected digital PWM signal.
Is output to the drive circuit 11 in order to generate a drive control signal for driving.

The timing controller 6 supplies a clock signal generated by the crystal oscillator 7 to the I / F 2, the digital filter 3, and the ΔΣ modulation processing unit 4, and controls the operation timing of each of the units 2 to 4. Further, the timing controller 6 also supplies the same clock signal to the triangular wave generator 8 provided outside the DAC 1.

The triangular wave generator 8 generates a triangular wave signal by repeating an operation of integrating and resetting the signal for the time corresponding to the pulse width for each pulse of the clock signal output from the timing controller 6. I do. As an original signal for generating a triangular wave signal, the DAC unit 1
By using the same clock signal as the clock signal controlling each of the blocks 2 to 4 in, unnecessary interference caused by using a plurality of clocks can be prevented.

The first comparator 9 compares the analog signal output from the LPF 5 in the DAC unit 1 with the analog signal fed back from the LPF 13, generates a difference signal and outputs the difference signal to the second comparator 10. I do. The second comparator 10 compares the differential signal output from the first comparator 9 with the triangular wave signal generated by the triangular wave
It generates a digital PWM signal having a pulse width in which an error due to a fluctuation of the power supply voltage in the inside is corrected. The PWM signal generated in this way is output to the drive circuit 11.

The drive circuit 11 generates a drive control signal based on the PWM signal supplied from the second comparator 10. Using this drive control signal, each switching element (pMOS transistors Q1, Q2 and nMO
The time during which the S transistors Q3 and Q4) are turned on is controlled and driven. Thereby, the power amplifier 12 amplifies and outputs the audio signal based on the power supply voltage Vp for the controlled driving time.

The audio signal amplified by the power amplifier 12 becomes an analog audio signal through the LPF 13 and is output from the speaker 55. The analog audio signal generated in this manner is a signal having an error including a variation in the power supply voltage Vp of the power amplifier 12, and the positive and negative portions of the signal are input to the third comparator 14, and the analog noise is output. The exponent NF is obtained and fed back to the first comparator 9.

As described above, in this embodiment, the DAC unit 1
To generate an analog PWM signal, and L
The analog audio signal generated by the PF 13 is fed back to the first comparator 9 provided at the output stage of the DAC unit 1 to generate a PWM signal in which the fluctuation of the power supply voltage Vp is corrected by comparing the analog signals. ing. This eliminates the need for strict synchronization control as compared with the conventional example in which the pulse width of the PWM signal is adjusted by comparing the pulse signals, and the feedback control of the pulse width of the PWM signal can be performed more easily. .

Further, when feedback control is performed using an analog signal, the quality of reproduced sound is slightly reduced due to a slight phase shift. Extreme sound quality degradation such as a case where the synchronization of the signals is greatly shifted does not occur. Therefore, according to the present embodiment, it is possible to simply and more reliably suppress the sound quality deterioration of the reproduced sound due to the fluctuation of the power supply voltage Vp or the like.

FIG. 2 is a diagram showing another configuration example of the 1-bit amplifier according to the present embodiment. Components having the same functions as the components shown in FIG. 1 are denoted by the same reference numerals. . In the 1-bit amplifier shown in FIG. 2, the analog audio signal output from the LPF 13 is converted to an A / D converter 15.
To a digital signal, which is converted into a digital signal by the Δ
フ ィ ー ド バ ッ ク Feedback is provided to the modulation processing unit 4.

The .DELTA..SIGMA. Modulation processing section 4 synthesizes the digital audio signal after low-pass filter processing supplied from the digital filter 3 with a digital audio signal including an error due to the fluctuation of the power supply voltage Vp, and the synthesized signal. To generate a digital PWM signal by performing a conversion process based on ΔΣ modulation. The digital PWM signal generated here is supplied to the LPF 5.

Analog PW generated by LPF 5
The M signal is directly input to the second comparator 10 and is compared with a triangular wave signal input from the triangular wave generator 8 to generate a digital PWM signal in which an error due to a change in the power supply voltage Vp or the like is corrected.

Even in the case of such a configuration, strict synchronization control is not required as compared with the conventional example in which the pulse width of the PWM signal is adjusted by comparing the pulse signals.
Feedback control of the pulse width of the WM signal can be performed more easily. Also, it is possible to suppress extreme deterioration in sound quality.

The above-described embodiment is merely an example of an embodiment for carrying out the present invention, and the technical scope of the present invention should not be interpreted in a limited manner. is there. That is, the present invention can be embodied in various forms without departing from the spirit or main features thereof.

For example, in the configuration shown in FIG.
5, the triangular wave generator 8 and the second comparator 10 are omitted, and the output signal of the ΔΣ modulation processor 4 is supplied to the drive circuit 11
May be supplied directly to the server.

[0043]

As described above, according to the present invention, the analog audio signal generated by the filter means is fed back, and the error caused by the fluctuation of the power supply voltage of the amplifier means is corrected using the fed back analog audio signal. Since the pulse width modulation signal is generated, the pulse width of the pulse width modulation signal can be adjusted in real time. Also, since the audio signal to be fed back is an analog signal that has passed through the filter means, stricter synchronization control is not required as compared with the case where the correction is performed by feeding back the pulse signal, and the feedback of the pulse width of the pulse width modulation signal is performed. Control can be easily performed. As a result, it is possible to more easily and reliably suppress the sound quality deterioration of the reproduced sound due to the fluctuation of the power supply voltage or the like.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of a 1-bit amplifier according to a first embodiment that implements an audio reproduction device of the present invention.

FIG. 2 is a diagram illustrating another configuration example of the 1-bit amplifier according to the embodiment;

FIG. 3 is a diagram illustrating a configuration of a conventional 1-bit amplifier.

[Explanation of symbols]

 Reference Signs List 1 DAC section 2 I / F 3 Digital filter 4 ΔΣ modulation processing section 5 LPF 6 Timing controller 7 Crystal oscillator 8 Triangular wave generation section 9 First comparator 10 Second comparator 11 Drive circuit 12 Power amplifier 13 LPF 14 Third Comparator 15 A / D converter 51 CD 55 Speaker

Claims (12)

[Claims] 1. An audio reproducing apparatus for amplifying an audio signal in accordance with a pulse width modulation signal generated based on a digital audio signal and outputting an analog audio signal by performing a filtering process, the audio reproducing device comprising: An audio reproducing apparatus characterized in that the analog audio signal obtained is fed back to the pulse width modulation signal generating section, and the pulse width modulation signal is corrected using the fed back analog audio signal. 2. A modulation processing means for performing a conversion process based on modulation on an input digital audio signal to generate an analog pulse width modulation signal, and based on the pulse width modulation signal generated by the modulation processing means. Amplifying means for amplifying an audio signal by performing a filtering process on an output signal from the amplifying means to generate an analog audio signal; and an analog audio signal generated by the filtering means, Feedback to the output stage of the modulation processing means,
An audio reproducing apparatus comprising: a correction unit that corrects the pulse width modulation signal using the analog audio signal that has been fed back. 3. The correction means includes means for converting the analog pulse width modulation signal into a digital pulse width modulation signal when correcting the pulse width modulation signal, and converting the analog pulse width modulation signal into the digital pulse width modulation signal. 3. The audio reproducing apparatus according to claim 2, wherein the driving of the amplifying means is controlled based on the signal. 4. A modulation processing means for performing a conversion process based on modulation on an input digital audio signal to generate a pulse width modulation signal, and an audio signal based on the pulse width modulation signal generated by the modulation processing means. Amplifying means for amplifying a signal; filtering means for generating an analog audio signal by performing a filtering process on the signal output from the amplifying means; analog / digital conversion of the analog audio signal generated by the filtering means A / D conversion means for converting the digital audio signal, the digital audio signal generated by the A / D conversion means is fed back to the modulation processing means, and the pulse width modulation signal is corrected using the fed back digital audio signal. An audio playback device characterized by the following. 5. The modulation processing means includes ΔΣ modulation processing means for performing conversion processing based on ΔΣ modulation, and feeds back the digital audio signal generated by the A / D conversion means to the ΔΣ modulation processing means. The audio reproducing device according to claim 4, wherein 6. A ΔΣ modulation processing means for performing conversion processing based on ΔΣ modulation on a digital audio signal to generate a digital pulse width modulation signal, and a low-pass filter processing for an output signal of said ΔΣ modulation processing means. A first filter means for generating an analog pulse width modulation signal; a triangular wave generating means for generating a triangular wave signal based on a predetermined clock signal; a triangular wave signal generated by the triangular wave generating means; A driving means for driving an amplification means for amplifying an audio signal based on a pulse width modulation signal generated by using the analog pulse width modulation signal generated by the first filter means; Amplifying means for amplifying the audio signal in accordance with a driving time, and a low-pass filter for the signal output from the amplifying means. A second filter for generating an analog audio signal by performing a filtering process; an analog pulse width modulation signal generated by the first filter; and an analog audio signal generated by the second filter. And a correcting means for correcting the pulse width modulation signal using the above. 7. The correction means, when correcting the pulse width modulation signal, converts the analog pulse width modulation signal into a digital pulse width modulation signal using a triangular wave signal generated by the triangular wave generation means. 7. The audio reproducing apparatus according to claim 6, further comprising: means for returning the signal as the drive control signal. 8. A ΔΣ modulation processing means for performing a conversion processing based on ΔΣ modulation on a digital audio signal to generate a digital pulse width modulation signal; and a low-pass filter processing for an output signal of the ΔΣ modulation processing means. A first filter means for generating an analog pulse width modulation signal; a triangular wave generating means for generating a triangular wave signal based on a predetermined clock signal; a triangular wave signal generated by the triangular wave generating means; A driving means for driving an amplification means for amplifying an audio signal based on a pulse width modulation signal generated by using the analog pulse width modulation signal generated by the first filter means; Amplifying means for amplifying the audio signal in accordance with a driving time, and a low-pass filter for the signal output from the amplifying means. A second filter for generating an analog audio signal by performing a filtering process; an analog / digital conversion of the analog audio signal generated by the second filter; and a digital audio signal obtained as a result of the Δ 上 記 modulation. A sound reproducing apparatus comprising: A / D conversion means for supplying to a processing means. 9. The clock signal used when the triangular wave generating means generates the triangular wave signal is the same clock signal as a clock signal for controlling the operation timing of the ΔΣ modulation processing means. The audio reproduction device according to claim 6. 10. Δ デ ジ タ ル for a digital audio signal
ΔΣ modulation processing means for performing a conversion process based on modulation to generate a pulse width modulation signal; and driving for driving amplification means for amplifying an audio signal based on the pulse width modulation signal generated by the ΔΣ modulation processing means. Means, the amplifying means for amplifying the audio signal according to a driving time controlled by the driving means, and a filter for generating an analog audio signal by performing a low-pass filter process on the signal output from the amplifying means. Means, and A / D conversion means for performing analog / digital conversion of the analog audio signal generated by the filter means and supplying the resulting digital audio signal to the ΔΣ modulation processing means. Audio playback device. 11. A sound reproducing method for amplifying an audio signal in accordance with a pulse width modulation signal generated based on a digital audio signal and outputting an analog audio signal by performing a filtering process, wherein the analog reproduction signal is generated by the filtering process. An audio reproduction method, wherein the analog audio signal thus fed back is fed back to the pulse width modulation signal generator, and the pulse width modulation signal is corrected using the fed back analog audio signal. 12. A sound reproducing method for amplifying an audio signal in accordance with a pulse width modulation signal generated based on a digital audio signal and outputting an analog audio signal by performing a filtering process. The obtained analog audio signal is subjected to analog / digital conversion, and the obtained digital audio signal is fed back to the pulse width modulation signal generator, and the pulse width modulation signal is corrected using the fed back digital audio signal. A sound reproduction method characterized by the above-mentioned.