CN101989836B - High Efficiency Audio Amplifier and Related Methods - Google Patents

Abstract

The invention relates to a high efficiency audio amplifier and related methods. The high-efficiency audio amplifier comprises an input end, a first amplifier, a second amplifier and a third amplifier, wherein the input end is used for receiving an input audio signal; a signal generator coupled to the input end for determining a frequency of an oscillation signal according to a distribution of the input audio signal and a reference voltage, and generating the oscillation signal with a corresponding frequency; a waveform converter, coupled to the input terminal and the signal generator, for comparing the input audio signal with the oscillation signal to generate a pulse modulation signal; a pre-driving circuit for generating a pre-driving signal according to the pulse modulation signal; an output stage, coupled to the pre-driving circuit, for generating an output signal according to the pre-driving signal; and a filter for filtering the output signal to generate the output audio signal to an output terminal. The audio amplifier of the invention can effectively improve the condition of poor amplification efficiency at low output power.

Description

High Efficiency Audio Amplifier and Related Methods

technical field

The invention relates to a high-efficiency audio amplifier and its related method, in particular to an audio amplifier whose efficiency is improved by adjusting the oscillation frequency and its related method.

Background technique

The power amplifier is mainly used to amplify the power of the signal. Generally speaking, it can be divided into A, B, AB, C and D according to the output stage used. Among them, the class-D audio power amplifier using switching output stage has been widely used in various consumer electronic products, such as notebook computers, LCD screens, mobile phones, multimedia playback devices, etc.

Please refer to FIG. 1A , which is a schematic diagram of a conventional class-D audio amplifier 10 . The class D audio amplifier 10 includes an input terminal 102 , a reference signal terminal 104 , a comparator 106 , a gate driving circuit 108 , an output stage 110 , a filter 112 and a speaker 114 . The input terminal 102 is used for receiving an audio input signal S _IN . The reference signal terminal 104 is used for receiving a triangular wave reference signal S _T . The comparator 106 is used for comparing the audio input signal S _IN with the fixed-frequency triangular wave reference signal S _T to generate a pulse width modulation signal S _P , and transmits the pulse width modulation signal S _P to the gate driving circuit 108 . The gate driving circuit 108 generates a gate driving signal S _G according to the pulse width modulation signal S _P to drive the switch of the output stage 110 , so that the output stage 110 outputs an output signal S _AP . Then, the output signal S _AP is filtered by the filter 112 to generate an audio output signal S _O , which is sent to the speaker 114 for output.

However, in practice, please refer to FIG. 1B , which is a schematic diagram of the working efficiency of the class-D audio amplifier 10 . Compared with other types of audio amplifiers, the class D audio amplifier 10 has an amplification efficiency of over 90% at higher output power, and has a fairly good amplification efficiency performance. However, in the case of low output power, the class-D audio amplifier 10 cannot effectively obtain better efficiency performance. Therefore, how to improve the amplification efficiency performance of the audio amplifier when the output power is low is really a problem to be solved.

Contents of the invention

Therefore, the main purpose of the present invention is to provide a high-efficiency audio amplifier and its related method.

The invention discloses a high-efficiency audio amplifier, which includes: an input end, used to receive an input audio signal; an output end, used to output an output audio signal; a signal generator, coupled to the input end, used for To determine the frequency of an oscillating signal according to the distribution of the input audio signal and a reference voltage, and thereby generate the oscillating signal of a corresponding frequency; a waveform converter, coupled to the input terminal and the signal generator, It is used to compare the input audio signal and the oscillating signal to generate a pulse modulation signal (PWM signal); a pre-drive circuit, coupled to the waveform converter, is used to generate a pre-drive signal according to the pulse modulation signal; an output stage, coupled to the pre-driver circuit, for generating an output signal according to the pre-driver signal; and a filter, coupled to the output stage, for filtering the output signal to generate the output Audio signal to this output.

The present invention also discloses a method for improving the efficiency of an audio amplifier, which includes determining the frequency of an oscillating signal according to the distribution of an input audio signal and a reference voltage, and accordingly generating the oscillating signal of a corresponding frequency; comparing the Input an audio signal and the oscillating signal to generate a pulse modulation signal; generate a pre-drive signal according to the pulse modulation signal; generate an output signal according to the pre-drive signal; and filter the output signal to generate the output audio signal.

According to the signal characteristics of the input audio signal, the invention elastically adjusts the frequency of the oscillation signal to reduce the loss power of the audio amplifier and further improve the amplification efficiency of the audio amplifier. In this way, the audio amplifier of the embodiment of the present invention can effectively improve the poor amplification efficiency at low output power.

Description of drawings

FIG. 1A is a schematic diagram of a known class D audio amplifier.

FIG. 1B is a schematic diagram of the operating efficiency of a known class D audio amplifier.

FIG. 2 is a schematic diagram of an audio amplifier according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of the signal generator in FIG. 2 .

FIG. 4 is a schematic diagram of an audio amplifier with two-channel output according to an embodiment of the present invention.

FIG. 5 is a schematic diagram of a process in Embodiment 1 of the present invention.

Description of main component symbols:

10D Class Audio Amplifier

102, 202, 402 input terminals

104 Reference signal terminal

106 Comparator

108 Gate drive circuit

110, 210, 414, 416 output stages

112, 212, 418, 420 filters

114, 216, 424 Speakers

20, 40 audio amplifier

204, 404 Signal generator

206, 406, 408 Wave Converter

208, 410, 412 Pre-driver circuit

214, 422 output terminals

302, 426 Judgment circuit

304, 428 Waveform Generator

306, 430 detection circuit

308, 432 selection circuit

434 first comparator

436 Second Comparator

438 OR gate

50 Process

500, 502, 504, 506,

508, 510, 512 steps

L ₁ , L ₂ inductance

C ₁ , C ₂ capacitance

S _AP , S _AP1 , S _AP2 output signal

S _G , S _G1 , S _G2 gate drive signals

S _IN audio input signal

S _O , S _O1 , S _O2 output audio signal

S _P , S _P1 , S _P2 pulse width modulation signal/pulse modulation signal

S _R oscillation signal

S _T triangle wave reference signal

V _ref reference voltage

S _C control signal

_SD detection signal

Detailed ways

Please refer to FIG. 2 , which is a schematic diagram of an audio amplifier 20 according to an embodiment of the present invention. The audio amplifier 20 includes an input terminal 202 , a signal generator 204 , a waveform converter 206 , a pre-driver circuit 208 , an output stage 210 , a filter 212 , an output terminal 214 and a speaker 216 . The input terminal 202 is used for receiving an input audio signal S _IN . The signal generator 204 is coupled to the input terminal 202, and is used to determine the frequency of an oscillating signal S _R according to the distribution of the input audio signal S _IN and a reference voltage V _ref , and generate an oscillating signal S _R corresponding to the frequency. . The waveform converter 206 is coupled to the input terminal 202 and the signal generator 204 for comparing the input audio signal S _IN and the oscillation signal S _R to generate a pulse modulation signal S _P . The pre-driving circuit 208 is coupled to the waveform converter 206 for generating a pre-driving signal S _G according to the pulse modulation signal S _P . The output stage 201 is coupled to the pre-driving circuit 208 for generating an output signal S _AP according to the pre-driving signal S _G . The filter 212 is coupled to the output stage 210 for filtering the output signal S _AP to generate an output audio signal S _O , and transmits the output audio signal S _O to the speaker 216 through the output terminal 214 . In other words, the signal generator 204 can adjust the frequency of the oscillating signal _SR according to the magnitude of the input audio signal S _IN , so as to improve the performance of the amplification efficiency of the audio amplifier 20 .

Generally speaking, the efficiency performance of an amplifier is inversely proportional to the loss power P _loss , and the loss power P _loss usually includes three parts, which are the switching loss P _sw of the transistor in the amplifier, the conduction loss P _cond of the transistor, and the loss of parasitic capacitance. P _gd , where the loss power P _loss is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; loss</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; sw</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; cond</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; gd</span>}}$

$<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; oss</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="V\; BUS"\; filenames="H2009101624266E00021.png"\; state="\{\{state\}\}">V</figure-callout></span><figure-callout\; id="2"\; label="V\; BUS"\; filenames="H2009101624266E00021.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}^{\mathrm{<span\; class="notranslate">BUS</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; pwm</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; pwm</span>}}<span\; class="notranslate">\; )</span>}_{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; sw</span>}}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; DS</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; )</span>}_{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; cond</span>}}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; gs</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; pwm</span>}}<span\; class="notranslate">\; )</span>}_{{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; gd</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them, C _oss is the output capacitance value of the transistor, V _BUS is the supply voltage of the transistor, _ID is the conduction current, t _f is the rising and falling time of the pulse signal, f _pwm is the pulse modulation frequency of the pulse modulation signal _SP , R _L load impedance, R _DS is the conduction resistance of the transistor, P _O is the output power, Q _g is the gate capacitance of the transistor, and Vgs is the conduction voltage of the transistor. According to formula (1), in practical application, the above parameters are all fixed values. In this case, the loss power of the amplifier can be changed by changing the pulse modulation frequency f _pwm . Furthermore, the pulse modulation frequency f _pwm is mainly changed according to the frequency of the oscillating signal _SR . Therefore, in the audio amplifier 20 , by adjusting the frequency of the oscillating signal _SR (and thus changing the pulse modulation frequency f _pwm ), the loss power P _loss of the audio amplifier 20 can be changed, thereby controlling the efficiency performance of the audio amplifier 20 . For example, when the output power is low, the power loss P _loss can be reduced by reducing the frequency of the oscillating signal _SR . In this way, the amplification efficiency performance of the audio amplifier 20 can be improved.

On the other hand, the audio signal input by the Class D audio amplifier is usually proportional to the output audio signal, therefore, in order to solve the poor amplification efficiency at low output power, embodiments of the present invention are based on the signal strength of the input audio signal S _IN , to adjust the frequency of the oscillating signal _SR . Please continue to refer to Figure 3. FIG. 3 is a schematic diagram of the signal generator 204 in FIG. 2 . The signal generator 204 includes a judgment circuit 302 and a waveform generator 304 . The judging circuit 302 is coupled to the input terminal 202 for determining the frequency of the oscillating signal S _R according to the distribution of the input audio signal S _IN and the reference voltage V _ref . When the input audio signal S _IN is smaller (larger) than the reference voltage V _ref , the judging circuit 302 lowers (increases) the frequency of the oscillating signal, and generates the control signal S _C accordingly. For example, when the signal strength of the input audio signal S _IN in the form of a continuous sine wave exceeds the reference voltage V _ref for a time ratio smaller (larger) than a first preset value, the judging circuit 302 can adjust down (increase) The frequency of the oscillating signal S _R . In addition, the judging circuit 302 can also lower (or increase) the frequency of the oscillating signal _SR when the average magnitude of the input audio signal S _IN is smaller (larger) than the reference voltage V _ref , but not limited thereto. In short, the embodiment of the present invention adjusts the frequency of the oscillating signal according to the signal characteristics of the input audio signal S _IN , thereby improving the poor amplification efficiency at low output power.

For further description of the judging circuit 302 , please continue to refer to FIG. 3 . The judgment circuit 302 includes a detection circuit 306 and a selection circuit 308 . The detection circuit 306 is coupled to the input terminal 202 and is mainly used to determine the distribution of the input audio signal S _IN according to the input audio signal S _IN and the reference voltage V _ref to generate a detection signal S _D . The selection circuit 308 is coupled to the detection circuit 306 and the waveform generator 304 for selecting the frequency of the oscillating signal S _R according to the detection signal _SD and generating the control signal S _C accordingly. For example, the selection circuit 308 can be implemented as a multiplexer. When the detection signal _SD is received, the control signal S _C is selected by switching from multiple candidate control signals representing different oscillation signal frequencies according to the detection signal S _D , to provide to the waveform generator 304 . Therefore, the waveform generator 304 generates an oscillating signal S _R with a corresponding frequency according to the control signal S _C .

It should be noted that the audio amplifier 20 is only an example of the present invention, and those skilled in the art can make various modifications accordingly, and is not limited thereto. For example, please refer to FIG. 4 , which is a schematic diagram of an audio amplifier 40 with dual-channel output according to an embodiment of the present invention. It is worth noting that since the audio amplifier 20 of FIG. 2 and the components with the same name in the audio amplifier 40 of FIG. The connection relationship of the above is shown in FIG. 4 , which will not be repeated here. The audio amplifier 40 includes an input terminal 402 , a signal generator 404 , waveform converters 406 , 408 , pre-driver circuits 410 , 412 , output stages 414 , 416 , filters 418 , 420 , output terminal 422 and a speaker 424 . The signal generator 404 includes a judging circuit 426 and a waveform generator 428 . The judgment circuit 426 includes a detection circuit 430 and a selection circuit 432 . The detection circuit 430 uses the first comparator 434 and the second comparator 436 to generate a first comparison result and a second comparison result, and then performs an OR logic operation by an OR gate 438 to generate a detection signal _SD to the waveform generator 428. As shown in FIG. 4 , the positive and negative input terminals of the first comparator 434 respectively receive the reference voltage V _ref and the input audio signal S _IN , so that the (first) of the reference voltage V _ref and the input audio signal S _IN is output from the output terminal. Comparing results. The positive and negative input terminals of the second comparator 436 receive the input audio signal S _IN and the reference voltage V _ref respectively, so as to output the (second) comparison result of the input audio signal S _IN and the reference voltage V _ref through the output terminal. In other words, the detection circuit 430 can estimate whether the absolute value of the signal strength of the input audio signal S _IN exceeds the level of the reference voltage V _ref as a reference for selecting the frequency of the oscillating signal _SR . Of course, the detection circuit 430 can be implemented in various ways or circuits, and those skilled in the art should be able to make various modifications accordingly. In addition, in FIG. 4, the selection circuit 432 can be realized by a multiplexer. The output stages 414, 416 are a totem-pole output formed by connecting two metal-oxide-semiconductor transistors in series. The filters 418 and 420 are low-pass filters respectively composed of an inductor L ₁ and a capacitor C ₁ , an inductor L ₂ and a capacitor C ₂ .

In addition, preferably, components such as the pre-driver circuit, the output stage, or the filter in the audio amplifier 20 can be modified and designed according to the operating conditions of the audio amplifier. The reference voltage V _ref can be a DC voltage. The oscillating signal _SR can be a triangular wave signal, a sawtooth wave signal or other forms of oscillating signal according to different system designs. In addition, in the audio amplifier 20, according to the number of channels of the system, those skilled in the art should be able to make corresponding modifications accordingly.

Regarding the working mode of the audio amplifier 20 , please refer to FIG. 5 , which is a schematic diagram of a process 50 according to Embodiment 1 of the present invention. Process 50 comprises the following steps:

Step 500: start.

Step 502: The signal generator 204 determines the frequency of the oscillating signal _SR according to the distribution of the input audio signal S _IN and the reference voltage V _ref , and generates an oscillating signal _SR corresponding to the frequency.

Step 504: The waveform converter 206 compares the input audio signal S _IN with the oscillating signal S _R to generate a pulse modulation signal S _P .

Step 506: The pre-driving circuit 208 generates a pre-driving signal S _G according to the pulse modulation signal S _P .

Step 508: The output stage 201 generates an output signal S _AP according to the pre-drive signal S _G .

Step 510: The filter 212 filters the output signal S _AP to generate an output audio signal S _O .

Step 512: end.

The process 50 is used to illustrate the working mode of the audio amplifier 20 , and the detailed description and related changes can refer to the foregoing description, and will not be repeated here.

To sum up, the present invention flexibly adjusts the frequency of the oscillating signal according to the signal characteristics of the input audio signal, so as to reduce the power loss of the audio amplifier, thereby improving the amplification efficiency of the audio amplifier. In this way, the audio amplifier of the embodiment of the present invention can effectively improve the poor amplification efficiency at low output power.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the claims of the present invention shall fall within the scope of the present invention.

Claims (31)

1. Audio Frequency Amplifer comprises:

One input is used for receiving an input audio signal;

One output is used for exporting an output audio signal;

One signal generator is coupled to said input, is used for a distribution situation and a reference voltage according to said input audio signal, determines the frequency of an oscillator signal, and produces the said oscillator signal of corresponding frequency according to this;

One waver is coupled to said input and said signal generator, is used for more said input audio signal and said oscillator signal, to produce a pulse-modulated signal;

One predrive circuit is coupled to said waver, is used for producing a pre-drive signal according to said pulse-modulated signal;

One output stage is coupled to said predrive circuit, is used for according to said pre-drive signal, produces an output signal; And

One filter is coupled to said output stage, is used for said output signal is carried out filtering, to produce said output audio signal to said output.

2. audio frequency amplifier as claimed in claim 1, wherein said signal generator comprises:

One decision circuitry is coupled to said input, is used for distribution situation and said reference voltage according to said input audio signal, determines the frequency of said oscillator signal, and produces a control signal according to this; And

One waveform generator is coupled to said decision circuitry and said waver, is used for producing said oscillator signal according to said control signal.

3. audio frequency amplifier as claimed in claim 2, wherein said decision circuitry are, to heighten the frequency of said oscillator signal, and produce said control signal according to this during greater than said reference voltage at said input audio signal.

4. audio frequency amplifier as claimed in claim 3, wherein said decision circuitry are the time scales during greater than one first preset value that surpasses said reference voltage at said input audio signal, heighten the frequency of said oscillator signal, and produce said control signal according to this.

5. audio frequency amplifier as claimed in claim 3, wherein said decision circuitry are mean sizes at said input audio signal during greater than said reference voltage, heighten the frequency of said oscillator signal, and produce said control signal according to this.

6. audio frequency amplifier as claimed in claim 2, wherein said decision circuitry are, to downgrade the frequency of said oscillator signal, and produce said control signal according to this during less than said reference voltage at said input audio signal.

7. audio frequency amplifier as claimed in claim 6, wherein said decision circuitry are the time scales during greater than one second preset value that is lower than said reference voltage at said input audio signal, downgrade the frequency of said oscillator signal, and produce said control signal according to this.

8. audio frequency amplifier as claimed in claim 6, wherein said decision circuitry are mean sizes at said input audio signal during less than said reference voltage, downgrade the frequency of said oscillator signal, and produce said control signal according to this.

9. audio frequency amplifier as claimed in claim 2, wherein said decision circuitry comprises:

One testing circuit is coupled to said input, is used for judging the distribution situation of said input audio signal, to produce a detection signal according to said input audio signal and said reference voltage; And

One selects circuit, is coupled to said testing circuit and said waveform generator, is used for selecting the frequency of said oscillator signal according to said detection signal, and produces said control signal according to this.

10. audio frequency amplifier as claimed in claim 9, wherein said testing circuit comprises:

One first comparator comprises a positive input terminal, is used for receiving said reference voltage; One negative input end is coupled to said input, is used for receiving said input audio signal; Reach an output, be used for exporting one first comparative result of said positive input terminal and said negative input end;

One second comparator comprises a positive input terminal, is coupled to said input; Be used for receiving said input audio signal, a negative input end is used for receiving said reference voltage; Reach an output, be used for exporting one second comparative result of said positive input terminal and said negative input end; And

One or door, be coupled to the said output and the said selection circuit of the said output of said first comparator, said second comparator, be used for said first comparative result and said second comparative result are carried out the logic OR computing, to produce said detection signal.

11. audio frequency amplifier as claimed in claim 9, wherein said selection circuit comprises:

One MUX is coupled to said testing circuit and said waveform generator, is used for according to said detection signal, selects said control signal by switching in a plurality of candidate's control signals of the different oscillation signal frequencies of expression, to provide to said waveform generator.

12. audio frequency amplifier as claimed in claim 1, wherein said output stage comprises:

One the first transistor comprises one first end, is coupled to said predrive circuit; Be used for receiving said pre-drive signal, one second end, and one the 3rd end; Be coupled to a power end, be used for according to the conducting state between said second end of the signal controlling of said first end to said the 3rd end; And

One transistor seconds comprises one first end, is coupled to said predrive circuit; Be used for receiving said pre-drive signal; One second end is connected to earth terminal, and one the 3rd end; Be coupled to second end of said the first transistor, be used for according to the conducting state between said second end of the signal controlling of said first end to said the 3rd end;

Wherein said filter is coupled to said second end of said the first transistor and said the 3rd end of said transistor seconds, to export said output signal.

13. audio frequency amplifier as claimed in claim 12, wherein said the first transistor are a NMOS transistor, said first end is a grid, and said second end is a source electrode, and said the 3rd end is drain electrode.

14. audio frequency amplifier as claimed in claim 12, wherein said transistor seconds are a NMOS transistor, said first end is a grid, and said second end is a source electrode, and said the 3rd end is drain electrode.

15. audio frequency amplifier as claimed in claim 1, wherein said filter are a low pass filter.

16. audio frequency amplifier as claimed in claim 1, wherein said reference voltage are a direct current voltage.

17. audio frequency amplifier as claimed in claim 1, wherein said oscillator signal are a triangular signal or a sawtooth signal.

18. audio frequency amplifier as claimed in claim 1 also comprises a loud speaker, is coupled to said output, is used for playing said output audio signal.

19. a method that promotes an audio frequency amplifier efficient comprises:

A distribution situation and a reference voltage according to an input audio signal determine the frequency of an oscillator signal, and produce the said oscillator signal of corresponding frequency according to this;

More said input audio signal and said oscillator signal are to produce a pulse-modulated signal;

According to said pulse-modulated signal, produce a pre-drive signal;

According to said pre-drive signal, produce an output signal; And

Said output signal is carried out filtering, to produce said output audio signal.

20. like the method for claim 19, wherein, determine the frequency of said oscillator signal, and the step that produces the said oscillator signal of corresponding frequency according to this comprises according to the distribution situation and the said reference voltage of said input audio signal:

Distribution situation and said reference voltage according to said input audio signal determine the frequency of said oscillator signal, and produce a control signal according to this; And

According to said control signal, produce said oscillator signal.

21. like the method for claim 20, wherein, determine the frequency of said oscillator signal, and the step that produces said control signal according to this comprises according to the distribution situation and the said reference voltage of said input audio signal:

, heighten the frequency of said oscillator signal, and produce said control signal according to this during at said input audio signal greater than said reference voltage.

22. like the method for claim 21, wherein, determine the frequency of said oscillator signal, and the step that produces said control signal according to this comprises according to the distribution situation and the said reference voltage of said input audio signal:

The time scale that surpasses said reference voltage at said input audio signal is heightened the frequency of said oscillator signal, and is produced said control signal according to this during greater than one first preset value.

23. like the method for claim 21, wherein, determine the frequency of said oscillator signal, and the step that produces said control signal according to this comprises according to the distribution situation and the said reference voltage of said input audio signal:

, heighten the frequency of said oscillator signal, and produce said control signal according to this during at the mean size of said input audio signal greater than said reference voltage.

24. like the method for claim 20, wherein, determine the frequency of said oscillator signal, and the step that produces said control signal according to this comprises according to the distribution situation and the said reference voltage of said input audio signal:

, downgrade the frequency of said oscillator signal, and produce said control signal according to this during at said input audio signal less than said reference voltage.

25. like the method for claim 24, wherein, determine the frequency of said oscillator signal, and the step that produces said control signal according to this comprises according to the distribution situation and the said reference voltage of said input audio signal:

The time scale that surpasses said reference voltage at said input audio signal downgrades the frequency of said oscillator signal, and produces said control signal according to this during less than one first preset value.

26. like the method for claim 24, wherein, determine the frequency of said oscillator signal, and the step that produces said control signal according to this comprises according to the distribution situation and the said reference voltage of said input audio signal:

, downgrade the frequency of said oscillator signal, and produce said control signal according to this during at the mean size of said input audio signal less than said reference voltage.

27. like the method for claim 20, wherein, determine the frequency of said oscillator signal, and the step that produces said control signal according to this comprises according to the distribution situation and the said reference voltage of said input audio signal:

According to said input audio signal and said reference voltage, judge the distribution situation of said input audio signal, to produce a detection signal; And

According to said detection signal, select the frequency of said oscillator signal, and produce said control signal according to this.

28. like the method for claim 27,, judge the distribution situation of said input audio signal, comprise with the step that produces said detection signal according to said input audio signal and said reference voltage:

Whether the amplitude of the positive edge of more said input audio signal and negative edge is greater than said reference voltage, to produce one first comparative result and one second comparative result respectively; And

The comparative result that said first comparative result and said second comparator are exported carries out the logic OR computing, to produce said detection signal.

29. like the method for claim 19,, select the frequency of said oscillator signal, and the step that produces said control signal according to this comprises wherein according to said detection signal:

According to said detection signal, select said control signal by switching in a plurality of candidate's control signals of the different oscillation signal frequencies of expression.

30. like the method for claim 19, wherein said reference voltage is a direct current voltage.

31. like the method for claim 19, wherein said oscillator signal is a triangular signal or a sawtooth signal.

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