CN101465622A - D-genus audio power amplifier - Google Patents

Abstract

The invention provides a class D audio power amplifier and a modulator for class D audio power amplifier; the modulator comprises a first transconductance amplifier, a second transconductance amplifier, a capacitor and a comparator unit; wherein, the negative input end of the first transconductance amplifier is used for receiving a first audio signal and a second feedback signal of a class D amplifier, and the positive input end thereof is used for receiving reference input voltage; the negative input end of the second transconductance amplifier is used for receiving a second audio signal contrary to the first audio signal and a first feedback signal of the class D amplifier, and the positive input end thereof is used for receiving reference input voltage; the capacitor is connected between the output ends of the first transconductance amplifier and the second transconductance amplifier, and is combined with the first transconductance amplifier and the second transconductance amplifier to perform integral towards the output signal of the first transconductance amplifier and the output signal of the second transconductance amplifier; the comparator unit is used for respectively comparing the output signal of the first transconductance amplifier and the output signal of the second transconductance amplifier with the output signal of a first current source and the output signal of a second current source, and outputting a first control signal, a second control signal, a third control signal and a fourth control signal which are modulated into digital signals.

Description

The D genus audio power amplifier

Technical field

The present invention relates to audio power and amplify, more particularly, relate to the D genus audio power amplifier that a kind of spread spectrum self-oscillation that can reduce electromagnetic interference (EMI) does not need filter.

Background technology

D genus audio power amplifier (hereinafter to be referred as the D class A amplifier A) is the same with traditional category-A, category-B, class ab ammplifier, all is used for producing again on the sounding output element with the volume that requires and power level the audio input signal of true, efficient and low distortion.But compare with category-A, category-B, class ab ammplifier, the D class A amplifier A has significant advantage in many application, and is less because low-power consumption produces heat, saves printed circuit board (PCB) (PCB) area and cost, and can prolong the battery life of portable system.

Specifically, the D class audio amplifier has adopted pulse modulation technology PWM (Pulse WidthModulation) or pulse duty factor modulation technique PDM (Pulse Duty cycle Modulation), that is, the amplitude of use simulated audio signal is modulated the width or the duty ratio of series of rectangular pulse.Like this, simulated audio signal just become that a series of width are modulated or duty ratio is modulated etc. the amplitude pulse signal.And original simulated audio signal is not to be included among the amplitude of this pulse signal, and is included among its width or duty ratio.So,, produce distortion on the amplitude and can't make original audio signal produce distortion if when amplifying.Amplifier in this case just can be fully operational on off state.Transistor can not be fully operational in cut-off state when having signal, thereby obtains very high efficient, as is higher than 90% conversion efficiency.

Fig. 1 shows the theory diagram of traditional D class A amplifier A.Audio input signal is through the modulation of modulator, thus the generation pwm signal.Pwm signal is input to power output stage (using the H bridge circuit usually).Between output stage and loud speaker, be inserted with low pass filter,, and avoid driving loud speaker with too many high-frequency energy so that electromagnetic interference is reduced to minimum.

Because therefore the high efficiency and the low distortion of D class A amplifier A are widely used at battery powered various portable electric appts with under to the space requirement condition with higher, for example mobile phone, DVD, MP3, LCD TV etc.Most of D class A amplifier A is the PWM modulation of adopting traditional fixed frequency on the market now.Because power output stage is worked (as 250KHz) on a fixed frequency f, the high order harmonic component of its generation concentrates on the frequency nf (n is an integer), thus electromagnetic interference (30MHz～300MHz) also higher.

In order to reduce electromagnetic interference, the spread spectrum on people will communicate by letter (Spread Spectrum) is used for the design of D class A amplifier A, is US 6,847 as publication number, 257 U.S. Patent application.Yet, in actual applications, still need further to reduce electromagnetic interference, and require the volume of D class A amplifier A and cost further to reduce.

Summary of the invention

To be partly articulated other aspect of the present invention and/or advantage in the following description, by describing, it can become clearer, perhaps can understand by implementing the present invention.

According to an aspect of the present invention, a kind of modulator of the D of being used for genus audio power amplifier is provided, described modulator comprises: first trsanscondutance amplifier, its negative input end receives second feedback signal of first audio signal and D genus audio power amplifier, and its positive input terminal receives reference input voltage; Second trsanscondutance amplifier, second audio signal that its negative input end receives and first audio signal is anti-phase and first feedback signal of D genus audio power amplifier, its positive input terminal receives reference input voltage; Capacitor is connected between the output of first trsanscondutance amplifier and second trsanscondutance amplifier, combines with first trsanscondutance amplifier and second trsanscondutance amplifier, so that the output signal of first trsanscondutance amplifier and the output signal of second trsanscondutance amplifier are carried out integration; And comparator unit, to compare with the output signal of first current source and second current source respectively via the output signal of the output signal of first trsanscondutance amplifier of capacitor integration and second trsanscondutance amplifier, output is modulated to first control signal, second control signal, the 3rd control signal and the 4th control signal of digital signal.

According to a further aspect in the invention, a kind of D genus audio power amplifier is provided, described D genus audio power amplifier comprises: preamplifier, difference input audio signal inverting each other is carried out preposition amplification, and export first audio signal and second audio signal of difference output inverting each other; Modulator, first feedback signal and second feedback signal of first audio signal of receiving preamplifier output and second audio signal and D genus audio power amplifier feedback, described a plurality of signals are modulated, be modulated to first control signal, second control signal, the 3rd control signal and the 4th control signal of digital signal with output; Logic control and drive circuit, receive first control signal, second control signal, the 3rd control signal and the 4th control signal of modulator output, according to certain logic rules described a plurality of control signals are carried out logic control, with output first grid drive signal, second grid drive signal, the 3rd gate drive signal and the 4th gate drive signal; With the bridge-type power switch, comprise and be used to export a H bridge circuit of first feedback signal and second feedback signal and be used to export first output signal of driving load and the 2nd H bridge circuit of second output signal, wherein, the grid of a P type metal-oxide-semiconductor of a side and a N type metal-oxide-semiconductor in first grid drive the one H bridge circuit, the grid of the 2nd P type metal-oxide-semiconductor of opposite side and the 2nd N type metal-oxide-semiconductor in second grid drive the one H bridge circuit, the 3rd gate drive signal drives a P type metal-oxide-semiconductor of a side in the 2nd H bridge circuit and the grid of a N type metal-oxide-semiconductor, and the 4th gate drive signal drives the 2nd P type metal-oxide-semiconductor of opposite side in the 2nd H bridge circuit and the grid of the 2nd N type metal-oxide-semiconductor.

The D genus audio power amplifier of realizing according to the present invention, because its balance negative feedback fb1, fb2 that adopts and the floating empty integrating capacitor C that discharges and recharges, therefore when not having the audio frequency input, electric current is zero in the load, thereby common-mode rejection ratio and Power Supply Rejection Ratio have been improved, reduce electromagnetic interference (EMI) greatly, and can under the situation that need not add filter, directly drive load.

Description of drawings

By the description of embodiment being carried out below in conjunction with accompanying drawing, these and/or other aspect of the present invention and advantage will become clear and be easier to and understand, wherein:

Fig. 1 shows the theory diagram of traditional D class A amplifier A;

Fig. 2 is the structured flowchart that illustrates according to the spread spectrum self oscillating class D amplifier of the embodiment of the invention;

Fig. 3 is the circuit diagram that illustrates according to the preamplifier of the spread spectrum self oscillating class D amplifier of the embodiment of the invention;

Fig. 4 A to Fig. 4 C is the circuit diagram that illustrates according to the internal structure of the modulator of the spread spectrum self oscillating class D amplifier of the embodiment of the invention;

Fig. 5 shows the equivalent circuit diagram that is connected across the electric capacity between the trsanscondutance amplifier;

Fig. 6 shows the charging and discharging process according to the electric capacity two ends of the spread spectrum self oscillating class D amplifier of the embodiment of the invention;

Fig. 7 A shows the waveform of the negative input end of when audio input signal is 0 electric capacity two ends and first comparator and second comparator;

Fig. 7 B and Fig. 7 C show the waveform of the negative input end of the negative input end of electric capacity two ends, first comparator and second comparator when audio input signal is not 0 and the 3rd comparator and the 4th comparator;

Fig. 8 is the circuit diagram that illustrates according to the bridge-type power switch of the spread spectrum self oscillating class D amplifier of the embodiment of the invention;

Fig. 9 shows the output waveform that audio input signal is a bridge-type power switch under 0 the situation;

Figure 10 shows the output waveform that audio input signal is a bridge-type power switch under 0 the situation; With

Figure 11 shows the output waveform that audio input signal is a bridge-type power switch under 0 the situation.

Embodiment

Now the embodiment of the invention is described in detail, its example shown in the accompanying drawings, wherein, identical label is represented same parts all the time.Below with reference to the accompanying drawings embodiment is described to explain the present invention.

Spread spectrum self oscillating class D amplifier according to the embodiment of the invention can be embodied as a kind of integrated chip based on CMOS technology or BiCMOS technology.

Fig. 2 is the structured flowchart that illustrates according to the spread spectrum self oscillating class D amplifier of the embodiment of the invention.With reference to Fig. 2, described spread spectrum self oscillating class D amplifier comprises preamplifier 201, modulator 202, logic control and drive circuit 203, bridge-type power switch 204 and protective circuit 205.In D class A amplifier A according to the present invention, reference voltage V _REFBe D class A amplifier A supply voltage V _DDA1/2nd, i.e. V _REF=1/2V _DDA

Followingly operation according to each building block of the spread spectrum self oscillating class D amplifier of the embodiment of the invention is described with reference to Fig. 3 to Figure 11.

Fig. 3 is the circuit diagram that illustrates according to the preamplifier 201 of the spread spectrum self oscillating class D amplifier of the embodiment of the invention.With reference to Fig. 3, preamplifier 201 adopts the amplifier of differential-input differential output, and in1 and in2 are the audio signal of anti-phase input, and wherein, in1 is V _MSin ω t, in2 is-V _MSin ω t, V _MMaximum for audio signal.Resistance R ₁And R ₂Be used to set the gain of preamplifier 201.Simultaneously, resistance R ₁And R ₂Capacitance (not shown) in the time of can using with the D class A amplifier A comes together to determine the low frequency flex point of the audio signal of input.The audio signal of 201 pairs of inputs of preamplifier is carried out preposition amplification, and the reversed-phase output signal pa1 and the pa2 of amplification are imported into modulator 202.Here, with V _REFAs the quiescent point of preamplifier 201, can get R ₁=R ₂Thereby the gain amplifier of preamplifier 201 is 0dB.Output signal pa1 is-V _MSin ω t, pa2 are V _MSin ω t, and the static direct current operating voltage of in1, in2, pa1 and pa2 all will be V _REF, i.e. 1/2V _DDA

Fig. 4 A to Fig. 4 C is the circuit diagram that illustrates according to the internal structure of the modulator 202 of the spread spectrum self oscillating class D amplifier of the embodiment of the invention.With reference to Fig. 4 A to Fig. 4 C, modulator comprises: trsanscondutance amplifier Amp1 and Amp2, its mutual conductance is G _mBuffer Buf1 and Buf2 all adopt the unit gain buffer amplifier; First current source: ${\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="A200710301270E00232.png,A200710301270E00241.png"\; state="\{\{state\}\}">I</figure-callout>}}_1=\frac{V_{\mathrm{DDA}}+{\mathrm{<figure-callout\; id="1"\; label="V\; pa"\; filenames="A200710301270E00232.png,A200710301270E00241.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{pa}}}{4R},$ Second current source: ${\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="A200710301270E00191.png,A200710301270E00241.png"\; state="\{\{state\}\}">I</figure-callout>}}_2=\frac{V_{\mathrm{DDA}}-{\mathrm{<figure-callout\; id="1"\; label="V\; pa"\; filenames="A200710301270E00232.png,A200710301270E00241.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{pa}}}{4R};$ And comparator C om1, Com2, Com3 and Com4 that sluggishness is arranged.

The effect of modulator 202 is that the audio signal with preposition amplification is converted to the high-frequency pulse signal through ovennodulation, comprises the audio signal of needs and the important high-frequency energy relevant with modulated process in the frequency content of pulse.Comparing with traditional PWM modulator, is variable according to the modulated carrier frequencies of the modulator 202 of the embodiment of the invention, does not need custom-designed oscillator.That is, can realize the spread spectrum self-oscillation in the modulator 200, thereby high-frequency harmonic is distributed to wider frequency that therefore the electromagnetic interference that is in 30MHz～300MHz frequency band can be reduced significantly.The following operation of describing modulator 202 with reference to Fig. 4 A to Fig. 4 C in detail.

The differential output signal pa1 of preamplifier 201 and pa2 are input to the negative input end of trsanscondutance amplifier Amp1 and Amp2 respectively, wherein, and V _Pa1=-V _Pa2Fb1 and fb2 are the feedback signals of bridge-type power switch 205 states sampling, also are the negative feedback input signals of trsanscondutance amplifier Amp2 and Amp1.According to the structure of bridge-type power switch 205, the magnitude of voltage of fb1 and fb2 can be 0 or V _DDA, and fb1=-fb2.The positive input terminal of trsanscondutance amplifier Amp1 and Amp2 is connected to reference voltage V _REFCapacitor C is connected across between the output B of the output terminals A of trsanscondutance amplifier Amp1 and Amp2.As shown in Figure 5, capacitor C is equivalent to the series connection of the electric capacity of two 2C, and the tie point of the electric capacity of these two 2C can be considered virtual earth.By input signal pa1, pa2, fb1 and fb2, can charge to capacitor C, thereby realization is to the integration of input signal pa1, pa2, fb1 and fb2.By such integration, can be with the radio-frequency component filtering of carrier wave, low frequency audio frequency component that is comprised among elimination feedback input signal fb2 and the fb1 and the error between pa1 and the pa2.When feedback signal fb2 (or fb1) is high level VDDA, to the capacitor C charging, during for low level GNDA, the capacitor C discharge.The cycle that discharges and recharges of capacitor C is determined according to following equation.Basis is that in one-period, switching frequency is far longer than audio signal frequency, as the 300KHz switching frequency.V _Pa2, V _Pa1Can be considered to fixed value with fb1, fb2, so linear in the voltage and the time at electric capacity two ends.Can be descended equation by the I*T=C*V formula, wherein, I=G _m(V _Pa1+ V _Fb2), V=(V _DDA-V _Pa1)/4.

$T=\frac{2C(\frac{V_{\mathrm{<figure-callout\; id="2"\; label="DDA"\; filenames="A200710301270E00191.png,A200710301270E00241.png"\; state="\{\{state\}\}">DDA</figure-callout>}}^2}{2}+{2V}_{\mathrm{pa}1}^2)}{G_m(\frac{V_{\mathrm{<figure-callout\; id="2"\; label="DDA"\; filenames="A200710301270E00191.png,A200710301270E00241.png"\; state="\{\{state\}\}">DDA</figure-callout>}}^2}{4}-V_{\mathrm{pa}1}^2)}$

By to the discharging and recharging of capacitor C, realized the self-oscillation of input signal, i.e. the self-oscillation of modulator, the free-running frequency of modulator can be determined by following equation.

$f=\frac{1}{T}=\frac{G_m\left(\frac{V_{\mathrm{<figure-callout\; id="2"\; label="DDA"\; filenames="A200710301270E00191.png,A200710301270E00241.png"\; state="\{\{state\}\}">DDA</figure-callout>}}^2}{4}{-V}_{\mathrm{pa}1}^2\right)}{2C(\frac{V_{\mathrm{<figure-callout\; id="2"\; label="DDA"\; filenames="A200710301270E00191.png,A200710301270E00241.png"\; state="\{\{state\}\}">DDA</figure-callout>}}^2}{2}+2V_{\mathrm{pa}1}^2)}$ Wherein, $\left|V_{\mathrm{pa}1}\right|\&le;\frac{V_{\mathrm{<figure-callout\; id="2"\; label="DDA"\; filenames="A200710301270E00191.png,A200710301270E00241.png"\; state="\{\{state\}\}">DDA</figure-callout>}}}{2}.$

This shows that the free-running frequency of modulator will be along with the variation of the amplitude of input signal (pa1) and changed, and has further realized the spread spectrum self-oscillation of modulator thus.

If get V _DDA=5V, C=8p, G _m=9.6 * 10 ^-6S is then when input signal (pa1) is 0.The modulator self-oscillating frequency is about 300KHz.

Because modulator 202 free-running frequencies are far longer than the frequency of audio signal, therefore in one-period, audio input signal pa1 and pa2 can be approximately constant D. C. value, and it is constant that the value of feedback signal fb1 and fb2 also can be considered.Because feedback signal fb1 and fb2 are the mirror value of the output signal out1 and the out2 of bridge-type power switch 205, so can eliminate owing to the influence of transistor conduct resistance in the bridge-type power switch 205 to audio distortion.As mentioned above, in one-period, capacitor C ends A, B are in charging and discharging state, and alternately charge and discharge, and Fig. 6 shows the charging and discharging process at A, B two ends.At this moment, the common-mode noise at electric capacity two ends can be cancelled out each other.

The output B of the output terminals A of trsanscondutance amplifier Amp1 and Amp2 is connected respectively to buffer amplifier Buf1 and Buf2, and the output of buffer amplifier Buf1 and Buf2 is respectively up and do.Buffer amplifier is used to isolate the input signal of the comparator of the signal at A, B two ends and back, thereby makes the trsanscondutance amplifier of modulator 202 not be subjected to the influence of load and stably work.

Shown in Fig. 4 B and Fig. 4 C, the output up of buffer amplifier Buf1 is imported into the positive input terminal of comparator C om1 and Com3, and the output do of buffer amplifier Buf2 is imported into the positive input terminal of comparator C om2 and Com4.In addition, current source I ₁Output signal be input to the negative input end (D) of comparator C om2 and same current source I ₁Output signal be input to the negative input end (E) of comparator C om3, and current source I ₂Output signal be input to the negative input end (C) of comparator C om1 and same current source I ₂Output signal be input to the negative input end (F) of comparator C om4.Between the negative input end of the positive input terminal of comparator C om1 and Com2, between the positive input terminal of the negative input end of Com1 and Com2, all be connected with resistance R between the negative input end of the positive input terminal of Com3 and Com4 and between the positive input terminal of the negative input end of Com3 and Com4, its size is generally tens kilo-ohms.Current source I ₁And I ₂Satisfy following equation.

Equation 1: ${\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="A200710301270E00232.png,A200710301270E00241.png"\; state="\{\{state\}\}">I</figure-callout>}}_1=\frac{V_{\mathrm{DDA}}+V_{\mathrm{pa}1}}{4R}$

Equation 2: ${\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="A200710301270E00191.png,A200710301270E00241.png"\; state="\{\{state\}\}">I</figure-callout>}}_2=\frac{V_{\mathrm{DDA}}-V_{\mathrm{pa}1}}{4R}$

Wherein, V _Pa1Be V _MSin ω t.

When the positive input terminal of comparator was higher than negative input end, the output signal of comparator was a high level.With comparator C om1 is example, and when the voltage of the output up of buffer amplifier Buf1 was higher than the C point voltage, the output signal m1 of comparator C om1 was a high level.When audio input signal changed, the waveform of the output signal of each comparator will change.By the compare operation of comparator, make the triangular wave envelope that discharges and recharges on the capacitor tightly follow audio input signal, thereby make the modulated square wave of comparator output not be subjected to The noise, audio distortion can drop to minimum.To omit its detailed description because therefore the compare operation of comparator it is known to the person skilled in the art that.Fig. 7 A shows when audio input signal is 0, the waveform that A, B, C, D are 4, this moment 2 of E, F waveform the waveform with 2 of C, D is identical respectively.Fig. 7 B and Fig. 7 C show when audio input signal is not 0, the waveform that A, B, C, D, E, F are 6.

Output m1, m2, m3 and the m4 of comparator C om1, Com2, Com3 and Com4 is input in logic control and the drive circuit 203.Logic control and drive circuit 203 can have stronger antijamming capability, thereby it can less be subjected to the interference of noise that comprises in the audio input signal.Logic control and drive circuit 203 couples of m1, m2, m3 and m4 signal carry out comprehensively, output G1, G2, G3 and these four gate drive signals of G4, and wherein, G1 and G2 inversion signal, G2 and G3 are in-phase signal.

The temperature of 204 pairs of chips of protective circuit monitors that when the too high phenomenon of temperature took place, the output cut-off signals was given logical circuit, the work of rupturing duty switch.Protective circuit is the electric current of monitor flows overpower switch also, when the output short-circuit phenomenon takes place, exports cut-off signals immediately and gives logical circuit, the work of rupturing duty switch.Its circuit is realized and can be realized by overcurrent protection and overtemperature protection device commonly used.

Fig. 8 is the circuit diagram that illustrates according to the bridge-type power switch 205 of the spread spectrum self oscillating class D amplifier of the embodiment of the invention.With reference to Fig. 8, bridge-type power switch 205 is made up of two H bridge circuits, and wherein, H bridge circuit output feeds back to the feedback signal fb1 and the fb2 of modulator 202, and the 2nd H bridge circuit output out1 and out2 are connected to load (for example, loudspeaker, loud speaker).In a H bridge circuit, MP1 is the P type metal-oxide-semiconductor with identical channel length and width with MP2.MN1 is the N type metal-oxide-semiconductor with identical channel length and width with MN2.The grid of MP1 and MN1 is driven by gate drive signal G1, and the grid of MP2 and MN2 is driven by gate drive signal G2.R _sBe the resistance that is integrated on the chip, its size is load resistance R _LIntegral multiple.For example, if the load loudspeaker are 4 ohm, R then _sIt can be 4000 ohm.In the 2nd H bridge circuit, MP3 and MP4 are the P type metal-oxide-semiconductor with same channel length and width, and the channel length of MP3 is identical with MP1, but width is 1000 times of MP1, MN3 and MN4 are the N type metal-oxide-semiconductor with same channel length and width, and the channel length of MN3 is identical with the channel length of MN1, but width is 1000 times of MN1.The grid of MP3 and MN3 is driven by gate drive signal G3, and the grid of MP4 and MN4 is driven by gate drive signal G4.Use the method, on off state, the magnitude of voltage of the output fb2 of a H bridge circuit is consistent with the value of the 2nd H bridge circuit output out1, and fb1=-fb2.Like this, the state value (high or low) of feedback fb1, fb2 directly is the sampling of the state value of load two ends out1, out2, thereby can offset the influence of power switch conducting resistance to distortion.

Below the course of work according to the D class A amplifier A of the embodiment of the invention is briefly described.When audio input signal was 0, the output signal pa1 of preamplifier 201 also was 0.As the negative-feedback signal of trsanscondutance amplifier Amp1, when fb2 is V _DDAThe time, the A point is charged B point discharge this moment.When fb2 is 0, the discharge of A point, and the charging of B point.

When A point charging voltage rises to when equating with the C point voltage, the output m1 of comparator C om1 is a high level, and the rising edge of m1 triggers logic control and drive circuit 203, and output gate drive signal G1 be a height, and G2 is low.At this moment, fb2 is from V _DDABe reduced to 0, the A point begins discharge, and the B point begins charging.When B point charging voltage rises to when equating with the D point voltage, the output m2 of comparator C om2 is a high level, and the rising edge of m2 triggers logic control and drive circuit 203, and output gate drive signal G1 is low, and G2 be a height.At this moment, fb2 rises to V from 0 _DDA, the A point begins charging once more, and the B point begins discharge.More than be described at feedback signal fb2, feedback signal fb1 carries out work in the mode similar to aforesaid way.As mentioned above, in this case, output signal out1, out2 all equate with feedback signal fb2.Fig. 9 shows the output waveform that audio input signal is a bridge-type power switch 205 under 0 the situation.

When audio input signal is not 0, can be divided into following two kinds of situations and considers.With audio input signal be 0 o'clock identical, the rising edge of m1 will trigger logic control and drive circuit 203, output gate drive signal G3 is low, G4 is low, thus the output out1 of bridge-type power switch 205 be high, out2 also is a height.In addition, the rising edge of m2 will trigger logic control and drive circuit 203, and output gate drive signal G3 is high, thereby the output out1 of bridge-type power switch 205 is low.As audio input signal V _Pa1Less than 0 o'clock, current source I ₁Less than current source I ₂, A point charging interval this moment, the B point charging interval was less than (see figure 10) discharge time greater than discharge time.When A point charging voltage rises to when equating with the E point voltage, the output m3 of comparator C om3 is a high level, and the rising edge of m3 triggers logic control and drive circuit 203, and output gate drive signal G4 be a height, and output signal out2 is a low level.Figure 10 shows the output waveform of bridge-type power switch 205 under the above-mentioned situation, this moment feedback signal fb2 duty ratio greater than 1/2, and the duty ratio of feedback signal fb1 is less than 1/2.As audio input signal V _Pa1Greater than 0 o'clock, current source I ₁Greater than current source I ₂, A point discharge time this moment is greater than the charging interval, and B point discharge time is less than the charging interval.When B point charging voltage rises to when equating with the F point voltage, the output m4 of comparator C om4 is a high level, and the rising edge of m4 triggers logic control and drive circuit 203, and output gate drive signal G4 be a height, and output signal out2 is a low level.Figure 11 shows the output waveform of bridge-type power switch 205 under the above-mentioned situation, this moment feedback signal fb2 duty ratio less than 1/2, and the duty ratio of feedback signal fb1 is greater than 1/2.

When the negative feedback of D class A amplifier A according to the present invention reaches balance, in a self-oscillation period T, audio input signal pa1, feedback signal fb2 and reference voltage V _REFTo satisfy following equation.

${\&Integral;}_0^T(V_{\mathrm{REF}}-V_{\mathrm{pa}1}-V_{\mathrm{fb}2})\mathrm{dt}=0$

Therefore, when audio input signal pa1 was 0, the duty ratio that can draw feedback signal fb2 was $\mathrm{duty}=\frac{1}{2}.$ When audio input signal pa1 was not equal to 0, the duty ratio of feedback signal fb2 was $\mathrm{duty}=\frac{1}{2}+\frac{V_{\mathrm{pa}1}}{V_{\mathrm{DDA}}}.$ Because fb1=-fb2 is so when audio input signal was not equal to 0, the duty ratio of feedback signal fb1 was $\mathrm{duty}=\frac{1}{2}-\frac{V_{\mathrm{pa}1}}{V_{\mathrm{DDA}}}.$ Hence one can see that, and the variation along with the size of audio input signal changes according to the free-running duty cycle square wave of D class A amplifier A of the present invention, is 1 to the maximum, and minimum is 0.

D genus audio power amplifier according to the present invention has following advantage:

First, by utilizing the intersection negative feedback to form free-running modulator, reduced the common-mode noise that traditional single sided pulse width modulator brought (as common-mode noise) greatly, thereby improved common-mode rejection ratio and Power Supply Rejection Ratio and reduced the asymmetry problem of output voltage from the power ground wire of HF switch.

The second, control the frequency of oscillation of differential variation at random by the amplitude of utilizing input audio signal, the Harmonic Distribution that makes the generation of bridge-type power switch is in the frequency range of a broad, and the electromagnetic interference (EMI) of puzzlement D class power amplifier is reduced greatly.Therefore, described D genus audio power amplifier can be applied to the field that some are had relatively high expectations to EMI.

The 3rd, because adopted the H bridge technology of enjoying a double blessing at the bridge-type power switch, the performance state that promptly connects the H bridge circuit of load is fed back by the H bridge circuit pass of another mirror image, so when reducing distortion, can be under the situation that need not add filter, directly drive load (as loudspeaker), thereby reduced the application cost of described D genus audio power amplifier widely.

Though represented and described some embodiments of the present invention, but those skilled in the art should understand that, without departing from the principles and spirit of the present invention, can make amendment to these embodiment, scope of the present invention is limited by claim and equivalent thereof.

Claims (21)

1, a kind of modulator that is used for the D genus audio power amplifier, described modulator comprises:

First trsanscondutance amplifier, its negative input end receive second feedback signal of first audio signal and D genus audio power amplifier, and its positive input terminal receives reference input voltage;

Second trsanscondutance amplifier, second audio signal that its negative input end receives and first audio signal is anti-phase and first feedback signal of D genus audio power amplifier, its positive input terminal receives reference input voltage;

Capacitor is connected between the output of first trsanscondutance amplifier and second trsanscondutance amplifier, combines with first trsanscondutance amplifier and second trsanscondutance amplifier, so that the output signal of first trsanscondutance amplifier and the output signal of second trsanscondutance amplifier are carried out integration; With

Comparator unit, to compare with the output signal of first current source and second current source respectively via the output signal of the output signal of first trsanscondutance amplifier of capacitor integration and second trsanscondutance amplifier, output is modulated to first control signal, second control signal, the 3rd control signal and the 4th control signal of digital signal.

2, modulator according to claim 1 also comprises:

First buffer is used for the output signal via first trsanscondutance amplifier of first trsanscondutance amplifier and capacitor integration is cushioned; With

Second buffer is used for the output signal via second trsanscondutance amplifier of second trsanscondutance amplifier and capacitor integration is cushioned,

Wherein, first buffer and second buffer are the unit gain buffer amplifiers.

3, modulator according to claim 1, wherein, first feedback signal and second feedback signal of D genus audio power amplifier are inverting each other.

4, modulator according to claim 1, wherein, the size of reference input voltage be modulator supply voltage 1/2nd.

5, modulator according to claim 1, wherein, the cycle of described integration is definite according to following equation,

$T=\frac{2C(\frac{V_{\mathrm{DDA}}^2}{2}+{2V}_{\mathrm{pa}1}^2)}{G_m(\frac{V_{\mathrm{DDA}}^2}{4}-V_{\mathrm{pa}1}^2)},$

Wherein, C is the capacitance of capacitor, and Gm is the mutual conductance of first trsanscondutance amplifier and second trsanscondutance amplifier, V _DDABe the supply voltage of modulator, V _Pa1It is the ac voltage of first audio signal.

6, modulator according to claim 1, wherein, first current source and second current source are definite according to following equation,

First current source $I_1=\frac{V_{\mathrm{DDA}}+V_{\mathrm{pa}1}}{4R},$

Second current source $I_2=\frac{V_{\mathrm{DDA}}-V_{\mathrm{pa}1}}{4R},$

Wherein, V _DDABe the supply voltage of modulator, V _Pa1Be the magnitude of voltage of first audio signal, R is the resistance value that is connected the resistor between current source and the comparator unit.

7, modulator according to claim 1, wherein, comparator unit comprises:

First comparator, its positive input terminal receives the output signal via first trsanscondutance amplifier of capacitor integration, and its negative input end receives the output signal of second current source, and exports first control signal;

Second comparator, its positive input terminal receives the output signal via second trsanscondutance amplifier of capacitor integration, and be connected to the negative input end of first comparator via resistor, its negative input end receives the output signal of first current source, and be connected to the positive input terminal of first comparator, and export second control signal via resistor;

The 3rd comparator, its positive input terminal receives the output signal via first trsanscondutance amplifier of capacitor integration, and its negative input end receives the output signal of first current source, and exports the 3rd control signal; With

The 4th comparator, its positive input terminal receives the output signal via second trsanscondutance amplifier of capacitor integration, and be connected to the negative input end of first comparator via resistor, its negative input end receives the output signal of second current source, and be connected to the positive input terminal of first comparator, and export the 4th control signal via resistor.

8, a kind of D genus audio power amplifier, described D genus audio power amplifier comprises:

Preamplifier carries out preposition amplification to difference input audio signal inverting each other, and exports first audio signal and second audio signal of difference output inverting each other;

Modulator, first feedback signal and second feedback signal of first audio signal of receiving preamplifier output and second audio signal and D genus audio power amplifier feedback, described a plurality of signals are modulated, be modulated to first control signal, second control signal, the 3rd control signal and the 4th control signal of digital signal with output;

Logic control and drive circuit, receive first control signal, second control signal, the 3rd control signal and the 4th control signal of modulator output, according to certain logic rules described a plurality of control signals are carried out logic control, with output first grid drive signal, second grid drive signal, the 3rd gate drive signal and the 4th gate drive signal; With

The bridge-type power switch, comprise and be used to export a H bridge circuit of first feedback signal and second feedback signal and be used to export first output signal of driving load and the 2nd H bridge circuit of second output signal, wherein, the grid of a P type metal-oxide-semiconductor of a side and a N type metal-oxide-semiconductor in first grid drive the one H bridge circuit, the grid of the 2nd P type metal-oxide-semiconductor of opposite side and the 2nd N type metal-oxide-semiconductor in second grid drive the one H bridge circuit, the 3rd gate drive signal drives a P type metal-oxide-semiconductor of a side in the 2nd H bridge circuit and the grid of a N type metal-oxide-semiconductor, and the 4th gate drive signal drives the 2nd P type metal-oxide-semiconductor of opposite side in the 2nd H bridge circuit and the grid of the 2nd N type metal-oxide-semiconductor.

9, D genus audio power amplifier according to claim 8 also comprises: protective circuit, overcurrent protection and overtemperature protection are carried out in logic control and drive circuit.

10, D genus audio power amplifier according to claim 8, wherein, the gain amplifier of preamplifier is set to 0dB.

11, D genus audio power amplifier according to claim 8, wherein, modulator comprises:

First trsanscondutance amplifier, its negative input end receive first audio signal and second feedback signal, and its positive input terminal receives reference input voltage;

Second trsanscondutance amplifier, its negative input end receive second audio signal and first feedback signal, and its positive input terminal receives reference input voltage;

Capacitor is connected between the output of first trsanscondutance amplifier and second trsanscondutance amplifier, combines with first trsanscondutance amplifier and second trsanscondutance amplifier, so that the output signal of first trsanscondutance amplifier and the output signal of second trsanscondutance amplifier are carried out integration; With

Comparator unit, to compare with the output signal of first current source and second current source respectively via the output signal of the output signal of first trsanscondutance amplifier of capacitor integration and second trsanscondutance amplifier, output is modulated to first control signal, second control signal, the 3rd control signal and the 4th control signal of digital signal.

12, D genus audio power amplifier according to claim 11 also comprises:

First buffer, buffering is via the output signal of first trsanscondutance amplifier of first trsanscondutance amplifier and capacitor integration; With

Second buffer cushions the output signal via second trsanscondutance amplifier of second trsanscondutance amplifier and capacitor integration,

Wherein, first buffer and second buffer are the unit gain buffer amplifiers.

13, D genus audio power amplifier according to claim 11, wherein, first feedback signal and second feedback signal are inverting each other.

14, D genus audio power amplifier according to claim 11, wherein, the size of reference input voltage be modulator supply voltage 1/2nd.

15, modulator according to claim 11, wherein, the cycle of described integration is definite according to following equation,

$T=\frac{2C(\frac{V_{\mathrm{DDA}}^2}{2}+{2V}_{\mathrm{pa}1}^2)}{G_m(\frac{V_{\mathrm{DDA}}^2}{4}-V_{\mathrm{pa}1}^2)},$

Wherein, C is the capacitance of capacitor, and Gm is the mutual conductance of first trsanscondutance amplifier and second buffer, V _DDABe the supply voltage of modulator, V _Pa1It is the ac voltage of first audio signal.

16, D genus audio power amplifier according to claim 11, wherein, first current source and second current source are definite according to following equation,

First current source $I_1=\frac{V_{\mathrm{DDA}}+V_{\mathrm{pa}1}}{4R},$

Second current source $I_2=\frac{V_{\mathrm{DDA}}-V_{\mathrm{pa}1}}{4R},$

Wherein, V _DDABe the supply voltage of modulator, V _Pa1Be the magnitude of voltage of first audio signal, R is the resistance value that is connected the resistor between current source and the comparator unit.

17, D genus audio power amplifier according to claim 11, wherein, comparator unit comprises:

First comparator, its positive input terminal receives the output signal via first trsanscondutance amplifier of capacitor integration, and its negative input end receives the output signal of second current source, and exports first control signal;

Second comparator, its positive input terminal receives the output signal via second trsanscondutance amplifier of capacitor integration, and be connected to the negative input end of first comparator via resistor, its negative input end receives the output signal of first current source, and be connected to the positive input terminal of first comparator, and export second control signal via resistor;

The 3rd comparator, its positive input terminal receives the output signal via first trsanscondutance amplifier of capacitor integration, and its negative input end receives the output signal of first current source, and exports the 3rd control signal; With

The 4th comparator, its positive input terminal receives the output signal via second trsanscondutance amplifier of capacitor integration, and be connected to the negative input end of first comparator via resistor, its negative input end receives the output signal of second current source, and be connected to the positive input terminal of first comparator, and export the 4th control signal via resistor.

18, D genus audio power amplifier according to claim 11, wherein, described logic rules comprise following rule:

The rising edge of first control signal triggers column signal down: the first grid drive signal is a high level, and second grid drive signal, the 3rd gate drive signal and the 4th gate drive signal are low level;

The rising edge of second control signal triggers column signal down: the first grid drive signal is a low level, and second grid drive signal and the 3rd gate drive signal are high level;

The rising edge of the 3rd control signal triggers column signal down: the 4th gate drive signal is a high level; With

The rising edge of the 4th control signal triggers column signal down: the 4th gate drive signal is a high level.

19, D genus audio power amplifier as claimed in claim 8, wherein, P type metal-oxide-semiconductor in the one H bridge circuit has identical channel length and width with the 2nd P type metal-oxide-semiconductor, and the N type metal-oxide-semiconductor in the H bridge circuit has identical channel length and width with the 2nd N type metal-oxide-semiconductor; P type metal-oxide-semiconductor in the 2nd H bridge circuit has identical channel length and width with the 2nd P type metal-oxide-semiconductor, and the N type metal-oxide-semiconductor in the 2nd H bridge circuit has identical channel length and width with the 2nd N type metal-oxide-semiconductor; The channel width of the P type metal-oxide-semiconductor in the channel width of the P type metal-oxide-semiconductor in the 2nd H bridge circuit and the H bridge circuit is identical, and the channel length of the P type metal-oxide-semiconductor in the 2nd H bridge circuit is 1000 times of channel width of the P type metal-oxide-semiconductor in the H bridge circuit; The channel width of the N type metal-oxide-semiconductor in the channel width of the N type metal-oxide-semiconductor in the 2nd H bridge circuit and the H bridge circuit is identical, and the channel length of the N type metal-oxide-semiconductor in the 2nd H bridge circuit is 1000 times of channel width of the N type metal-oxide-semiconductor in the H bridge circuit.

20, D genus audio power amplifier as claimed in claim 8, wherein, an integrated resistor between the H bridge circuit output, its resistance is the integral multiple of the load resistance of D genus audio power amplifier.

21, D genus audio power amplifier as claimed in claim 20, wherein, described integer is 1000.

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