CN103607206A - Audio digital-to-analog conversion circuit - Google Patents

Abstract

The invention discloses an audio digital-to-analog conversion circuit. The audio digital-to-analog conversion circuit comprises a first clock generation sub-circuit, a common-mode voltage generation sub-circuit and a main conversion circuit, and further comprises a second clock generation sub-circuit and an overturning sub-circuit, wherein the second clock generation sub-circuit is connected with the overturning sub-circuit and is provided with a third output end and a fourth output end, and the third output end and the fourth output end output complementary clock pulses. When a sampling sub-circuit is in a sampling state, the clock pulses output by the second clock generation sub-circuit are overturned, and the overturning sub-circuit is respectively connected with the output end and the input end of a calculation amplifier. When the clock pulses output by the second clock generation sub-circuit are overturned, the overturning sub-circuit overturns the directions of offset voltage and low-frequency noise generated by the calculation amplifier. The audio digital-to-analog conversion circuit reduces the power of the calculation amplifier, eliminates a direct current offset phenomenon and low-frequency 1/f noise of the calculation amplifier, and improves the signal-to-noise ratio.

Description

Audio frequency D/A converting circuit

Technical field

The present invention relates to integrated circuit fields, relate more specifically to a kind of audio frequency D/A converting circuit.

Background technology

Along with the development of multimedia technology, increasing to the demand of audio digital to analog converter (DAC), the key that determines tonequality is audio frequency D/A converting circuit (DAC) and the power amplifier circuit of master control decoding chip the inside.DAC is mainly responsible for the data flow of being convenient to data storage to convert analog signal to, and power amplifier circuit is mainly that the analog signal after DAC conversion is amplified to the power that can promote earphone or loudspeaker, therefore, DAC circuit is as important component part in audio frequency master control decoding chip, its power consumption, performance is the present stage part paid close attention to emphatically of audio digital to analog converter.

In traditional audio frequency D/A converting circuit, in integral process, the charging and discharging currents that sampling capacitance and integrating capacitor need in charge transfer process is all provided by amplifier, has greatly increased the power consumption of amplifier; The Slew Rate of amplifier, speed etc. are had to higher requirement simultaneously.

Therefore, be necessary to provide a kind of improved audio frequency D/A converting circuit to overcome above-mentioned defect.

Summary of the invention

The object of this invention is to provide a kind of audio frequency D/A converting circuit, this audio frequency D/A converting circuit has reduced the power of operational amplifier, has eliminated DC offset voltage and the low frequency 1/f noise of operational amplifier, has improved the signal to noise ratio of audio frequency D/A converting circuit.

For achieving the above object, the invention provides a kind of audio frequency D/A converting circuit, comprise the first clock generating electronic circuit, common-mode voltage produces electronic circuit and conversion main circuit, described the first clock generating electronic circuit is connected with described conversion main circuit, to produce clock pulse, control the work of described conversion main circuit, and described the first clock generating electronic circuit has the first output and the second output, described the first output and the second output are exported complementary clock pulse, described common-mode voltage produces electronic circuit and is connected with described conversion main circuit, to produce the described conversion main circuit required common-mode voltage that works, described conversion main circuit converts the digital differential signal of outside input to analog difference signal output, described conversion main circuit comprises sampling electronic circuit and integration electronic circuit, described integration electronic circuit consists of integrating capacitor and operational amplifier, the input of described sampling electronic circuit is connected with external digital differential signal output, its output is connected with the input of described operational amplifier and one end of integrating capacitor respectively, the other end of described integrating capacitor be connected with described analog signal output and export conversion after analog difference signal, and described conversion main circuit is symmetrical arranged about described operational amplifier, wherein, also comprise that second clock produces electronic circuit, upset electronic circuit, the first Bootstrap electronic circuit and the second Bootstrap electronic circuit, described the first Bootstrap electronic circuit is all connected with described sampling electronic circuit with one end of the second Bootstrap electronic circuit, the other end is all connected with described analog signal output, described second clock produces electronic circuit and is connected with described upset electronic circuit, to produce clock pulse, control the work of described upset electronic circuit, and described second clock produces electronic circuit and has the 3rd output and the 4th output, described the 3rd output and the 4th output are exported complementary clock pulse, and when described sampling electronic circuit is during in sample states, described second clock produces the 3rd output of electronic circuit and the clock pulse of the 4th output output is overturn, described upset electronic circuit is connected with output and the input of described operational amplifier respectively, when described second clock produces the clock pulse upset of electronic circuit output, the offset voltage that described upset electronic circuit produces described operational amplifier and the upset of the direction of low-frequency noise.

Preferably, described upset electronic circuit comprises the first switch, second switch, the 3rd switch, the 4th switch, the 5th switch, the 6th switch, minion is closed and the 8th switch, one end of described the first switch and the 4th switch is connected with an output of described sampling electronic circuit jointly, one end of described second switch and the 3rd switch is connected with another output of described sampling electronic circuit jointly, the other end of described the first switch and the 3rd switch is connected with the normal phase input end of described operational amplifier jointly, the other end of described second switch and the 4th switch is connected with the inverting input of described operational amplifier jointly, one end that described the 5th switch and described minion are closed is connected with the reversed-phase output of described operational amplifier jointly, one end of described the 6th switch and the 8th switch is connected with the positive output end of described operational amplifier jointly, the other end of described the 5th switch and the 8th switch is connected with an output of described analog signal output jointly, and the other end that described the 6th switch and minion are closed is connected with another output of described analog signal output jointly.

Preferably, the control end of described the first switch, second switch, the 5th switch and the 6th switch is also connected with the 3rd output of described second clock generation electronic circuit respectively; Described the 3rd switch, the 4th switch, minion are closed and the control end of the 8th switch is also connected with the 4th output of described second clock generation electronic circuit respectively; And described in each, switch is all closed when the clock pulse of its control end is high level.

Preferably, described the first Bootstrap electronic circuit and the second Bootstrap electronic circuit have identical architectural feature.

Preferably, described the first Bootstrap electronic circuit comprises the first field effect transistor and the first Bootstrap unit, the clock control end of described the first Bootstrap unit is connected with described the second output, the source electrode of its input and described the first field effect transistor is all connected with described analog signal output, its output is connected with the grid of described the first field effect transistor, and the drain electrode of described the first field effect transistor is connected with described sampling electronic circuit.

Compared with prior art, audio frequency D/A converting circuit of the present invention is owing to also comprising that described second clock produces electronic circuit and upset electronic circuit, and described upset electronic circuit is connected with output and the input of described operational amplifier respectively, when described second clock produces the clock pulse upset of electronic circuit output, the offset voltage that described upset electronic circuit produces described operational amplifier and the upset of the direction of low-frequency noise; Thereby make within a clock cycle, the DC maladjustment of described operational amplifier input and low frequency 1/f noise thereof to be offset, also within a clock cycle, eliminate DC maladjustment and the low frequency 1/f noise thereof of operational amplifier input, further improved the signal to noise ratio of audio frequency D/A converting circuit; And described the first Bootstrap electronic circuit and the second Bootstrap electronic circuit have reduced the harmonic distortion of whole audio frequency D/A converting circuit.

By following description also by reference to the accompanying drawings, it is more clear that the present invention will become, and these accompanying drawings are used for explaining the present invention.

Accompanying drawing explanation

Fig. 1 is the structured flowchart of audio frequency D/A converting circuit of the present invention.

Fig. 2 is the circuit structure diagram of audio frequency D/A converting circuit of the present invention.

Fig. 3 is the equivalent operating state that second clock produces the front operational amplifier of clock pulse upset of electronic circuit output.

Fig. 4 is the equivalent operating state that second clock produces the rear operational amplifier of clock pulse upset of electronic circuit output.

Embodiment

With reference now to accompanying drawing, describe embodiments of the invention, in accompanying drawing, similarly element numbers represents similar element.As mentioned above, the invention provides a kind of audio frequency D/A converting circuit, this audio frequency D/A converting circuit has reduced the power of operational amplifier, has eliminated DC maladjustment and the low frequency 1/f noise of operational amplifier, the signal to noise ratio that has improved audio frequency D/A converting circuit, has reduced the harmonic distortion of circuit.

Please refer to Fig. 1, Fig. 1 is the structured flowchart of audio frequency D/A converting circuit of the present invention.As shown in the figure, audio frequency D/A converting circuit of the present invention comprises that conversion main circuit, the first clock generating electronic circuit, second clock produce electronic circuit, common-mode voltage produces electronic circuit, the first Bootstrap electronic circuit, the second Bootstrap electronic circuit and upset electronic circuit; Described conversion main circuit comprises sampling electronic circuit and integration electronic circuit, described sampling electronic circuit is connected with described integration electronic circuit and external digital differential signal output respectively, digital differential signal to outside digital differential signal output part output is sampled, and exports the signal after sampling to described integration electronic circuit; Described integration electronic circuit is also connected with analog signal output, and described integration electronic circuit carries out integration to the signal after sampling, and by the analog difference signal after described analog signal output output conversion; Described the first clock generating electronic circuit is connected with the sampling electronic circuit of described conversion main circuit, thereby the clock pulse of described the first clock generating electronic circuit output is controlled the work of described sampling electronic circuit; Described common-mode voltage produces electronic circuit and is connected with the sampling electronic circuit of described conversion main circuit, with output common mode voltage, to guarantee described sampling electronic circuit, works; Described second clock produces electronic circuit and is connected with described upset electronic circuit, controls the work of described upset electronic circuit to produce clock pulse; Described upset electronic circuit is connected with the integration electronic circuit of described conversion main circuit, at described second clock, produce under the control of electronic circuit, within a clock cycle, described upset electronic circuit overturns the direction of the offset voltage of described integration electronic circuit and low-frequency noise, make within a clock cycle, the offset voltage of described integration electronic circuit and low-frequency noise can be cancelled; Described the first Bootstrap electronic circuit is connected with described sampling electronic circuit with one end of the second Bootstrap electronic circuit, the other end is connected with described analog signal output, in integral process, described the first Bootstrap electronic circuit and the second Bootstrap electronic circuit can reduce the harmonic distortion of audio frequency D/A converting circuit.

Particularly, please again in conjunction with reference to figure 2.CLK is the input clock of described the first clock generating electronic circuit, and described the first clock generating electronic circuit has the first output Φ 1 and the second output Φ 2, the clock pulse that described the first output Φ 1 and the second output Φ 2 outputs are complementary,, when described the first output Φ 1 is output as high level, described the second output Φ 2 is output as low level, and vice versa.CHOP_CLK is the input clock that described second clock produces electronic circuit, and described second clock produces electronic circuit and has the 3rd output Φ 3 and the 4th output Φ 4, the clock pulse that described the 3rd output Φ 3 and the 4th output Φ 4 outputs are complementary,, when described the 3rd output Φ 3 is output as high level, described the 4th output Φ 4 is output as low level, and vice versa; In the present invention, the upset that described second clock produces the pulse of electronic circuit output clock occurs in described sampling electronic circuit when outside digital differential signal is sampled.Described common-mode voltage produces electronic circuit and is connected with external power source, and output common mode voltage VCM.Described integration electronic circuit comprises integrating capacitor Cintp and operational amplifier OP; In a preferred embodiment of the invention, described operational amplifier OP is Full differential operational amplifier.Described sampling electronic circuit comprises the 9th switch S 9, the tenth switch S the 10, the 11 switch S 11 and sampling capacitance Csp; One end of described the 9th switch S 9 (being the input of described sampling electronic circuit) is connected with external digital differential signal output, the other end is connected with one end of sampling capacitance Csp and the first Bootstrap electronic circuit, external digital differential signal output output digital differential signal VINP is to described sampling electronic circuit, and when described the 9th switch S 9 closure, described sampling capacitance Csp samples to digital differential signal VINP, and the signal after sampling is kept; The other end of described sampling capacitance Csp is connected with one end of described the tenth switch S 10 and the 11 switch S 11, the other end of described the tenth switch S 10 is connected with the output that described common-mode voltage produces electronic circuit, and described common-mode voltage produces circuit by described the tenth switch S 10 output common mode voltage VCM described sampling electronic circuit extremely; The other end of described the 11 switch S 11 (being the output of described sampling electronic circuit) is connected with one end of described integrating capacitor Cintp and the normal phase input end of operational amplifier OP, thereby when described the 11 switch S 11 closure, described integrating capacitor Cintp and operational amplifier OP can carry out Integral Transformation to the digital differential signal after sampling; The other end of described integrating capacitor Cintp is connected with the other end of described analog signal output and described the first Bootstrap electronic circuit, thereby by this output, the analog difference signal VOUTN after Integral Transformation is exported.In the present invention, described conversion main circuit is symmetrical arranged about described operational amplifier OP, and described conversion main circuit comprises two groups of sampling electronic circuits and integrating capacitor, and is arranged at respectively the both sides of described operational amplifier OP; The sampling electronic circuit of organizing separately comprises the 13 switch S the 13, the 14 switch S the 14, the 15 switch S 15 and sampling capacitance Csn, and the integrating capacitor of organizing separately is Cintn; These two groups of structures are identical, annexation is identical, difference is only, external digital differential signal output output digital differential signal VINN is to described sampling electronic circuit, described the 15 other end of switch S 15 and one end of described integrating capacitor Cintn are connected with the inverting input of described operational amplifier OP, the other end of described integrating capacitor Cintn is connected with another output port of described analog signal output, and the analog difference signal VOUTP after output conversion.Wherein, the control end of described the 9th switch S 9, the tenth switch S the 10, the 13 switch S 13 and the 14 switch S 14 is all connected with the first output Φ 1 of described the first clock generating electronic circuit, thereby the clock pulse of described the first output Φ 1 output is controlled closure and the disconnection of switch described in each; Described the 11 switch S 11, twelvemo are closed the control end that S12, the 15 switch S 15 and sixteenmo close S16 and are all connected with the second output Φ 2 of described the first clock generating electronic circuit, thereby the clock pulse that described the second output Φ 2 exports is controlled closure and the disconnection of switch described in each; And described in each, switch is all closed when the clock pulse of its control end is high level, during low level, disconnects.Described upset electronic circuit comprises the first switch S 1, second switch S2, the 3rd switch S 3, the 4th switch S 4, the 5th switch S 5, the 6th switch S 6, minion pass S7 and the 8th switch S8; One end of described the first switch S 1 and the 4th switch S 4 is connected with the other end (output of the electronic circuit of sampling) of described the 11 switch S 11 jointly, one end of described second switch S2 and the 3rd switch S 3 is connected with the other end (another output of the electronic circuit of sampling) of described the 15 switch S 15 jointly, the other end of described the first switch S 1 and the 3rd switch S 3 is connected with the normal phase input end of described operational amplifier OP jointly, and the other end of described second switch S2 and the 4th switch S 4 is connected with the inverting input of described operational amplifier OP jointly; One end that described the 5th switch S 5 and described minion are closed S7 is connected with the reversed-phase output of described operational amplifier OP jointly, one end of described the 6th switch S 6 and the 8th switch S8 is connected with the positive output end of described operational amplifier OP jointly, the other end of described the 5th switch S 5 and the 8th switch S8 is connected with an output of described analog signal output jointly, and the other end that described the 6th switch S 1 and minion are closed S1 is connected with another output port of described analog signal output jointly.In addition, the control end of described the first switch S 1, second switch S2, the 5th switch S 5 and the 6th switch S 6 is also connected with the 3rd output Φ 3 of described second clock generation electronic circuit respectively; The control end that described the 3rd switch S 3, the 4th switch S 4, minion are closed S7 and the 8th switch S8 is also connected with the 4th output Φ 4 of described second clock generation electronic circuit respectively; And described in each, switch is all closed when the clock pulse of its control end is high level, during low level, disconnects.Described the first Bootstrap electronic circuit comprises the first field effect transistor M1 and the first Bootstrap unit, the clock control end of described the first Bootstrap unit is connected with described the second output Φ 2, the source electrode of its input and described the first field effect transistor M1 is all connected with described analog signal output VOUTN, its output is connected with the grid of described the first field effect transistor M1, and the drain electrode of described the first field effect transistor M1 is connected with the other end of the 9th switch S 9 of described sampling electronic circuit; When the clock pulse of described the second output Φ 2 outputs is high level, the output VOUT of described the first Bootstrap unit is output as high level, and certain voltage difference between the input VIN of itself and described the first Bootstrap unit, now described the first field effect transistor M1 conducting; When the clock pulse of described the second output Φ 2 outputs is low level, the output VOUT of described the first Bootstrap unit is output as low high level, makes described the first field effect transistor M1 cut-off.When described the first field effect transistor M1 conducting, while that is to say described integration electronic circuit work, can make described sampling capacitance Csp is described integrating capacitor Cintp charging.Described the first Bootstrap unit can improve the linearity of the conducting resistance of the first field effect transistor M1, reduces the conducting resistance R of the first field effect transistor M1 simultaneously _m1thereby, make the conducting resistance R of the first field effect transistor M1 _m1with the time constant of integrating capacitor Cintp (be R _m1* Cintp) keep constant, and the first field effect transistor M1 conducting resistance R _m1reduce, can make time constant R _m1* Cintp is less, accelerates the speed that discharges and recharges of integrating capacitor Cintp, thereby has reduced harmonic distortion.In a preferred embodiment of the invention, described the first Bootstrap electronic circuit and the second Bootstrap electronic circuit have identical architectural feature, be that described the second Bootstrap electronic circuit also comprises the second field effect transistor M2 and the second Bootstrap unit, at this, no longer carefully state.Wherein, architectural feature and the function of Bootstrap unit are well known to the skilled person, and are repeating no more.

Below, in conjunction with Fig. 2-4, introduce the course of work of audio frequency D/A converting circuit of the present invention.Because described conversion main circuit is symmetrical arranged about described operational amplifier OP, the structure of make to sample electronic circuit and integration electronic circuit is upper and lower symmetrical structure, when the course of work is introduced, only the first half is described, and the latter half is identical.Sampling instant, when the clock pulse of the first output Φ 1 output is high level, the clock pulse of the second output Φ 2 outputs is low level, the 9th switch S 9 and the tenth switch S 10 conductings, the 11 switch S 11 disconnects and described the first Bootstrap unit makes described the first field effect transistor M1 cut-off, now described sampling capacitance Csp samples to the digital differential signal VINP of input, and becomes electric charge to be kept in sampling capacitance Csp the voltage transitions obtaining after sampling.Integration constantly, when the clock pulse of the first output Φ 1 output is low level, the clock pulse of the second output Φ 2 outputs is high level, the 9th switch S 9 and the tenth switch S 10 disconnect, the 11 switch S 11 closures and described the first Bootstrap unit make described the first field effect transistor M1 conducting, now sampling capacitance Csp is in parallel with integrating capacitor Cintp, and sampling capacitance Csp transfer part sampled charge is to integrating capacitor Cintp, and operational amplifier OP charges to the right pole plate of integrating capacitor Cintp simultaneously; In the present invention, described sampling capacitance Csp also provides Partial charge to integrating capacitor Cintp, thereby makes the charging of described integrating capacitor Cintp and not only rely on described operational amplifier OP, the driving power consumption of therefore having saved operational amplifier OP.

When the clock pulse that produces the 3rd output Φ 3 outputs of electronic circuit when described second clock is high level, the clock pulse of the 4th output Φ 4 outputs is low level, described the first switch S 1, second switch S2, the 5th switch S 5 and the 6th switch S 6 closures, described the 3rd switch S 3, the 4th switch S 4, minion close S7 and the 8th switch S8 disconnects; Now the operating state of described operational amplifier OP as shown in Figure 3, wherein Veq1 is that the clock pulse of the 3rd output Φ 3 outputs is high level, operational amplifier OP equivalent input noise when the clock pulse of the 4th output Φ 4 outputs is low level, Vn1 is offset voltage and the low frequency 1/f noise of operational amplifier OP, Vn2 is the equivalent input noise of the power amplifier that connects below of audio frequency D/A converting circuit of the present invention, if the gain of described operational amplifier OP is A, equivalent input noise so is now

${\mathrm{<figure-callout\; id="1"\; label="v\; eq"\; filenames="HDA0000421812440000021.png"\; state="\{\{state\}\}">v</figure-callout>}}_{\mathrm{eq}}=v_{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="HDA0000421812440000021.png"\; state="\{\{state\}\}">n</figure-callout>}1}+\frac{v_{n2}}{A}---\left(1\right)$

When described sampling electronic circuit is during in sample states, the clock pulse that is the first output Φ 1 output of described the first clock generating electronic circuit is high level, the clock pulse of the second output Φ 2 outputs is low level, described second clock produces the clock pulse of electronic circuit output and overturns, also the clock pulse that makes described second clock produce the 3rd output Φ 3 outputs of electronic circuit is low level, and the clock pulse of the 4th output Φ 4 outputs is high level; And, described the first switch S 1, second switch S2, the 5th switch S 5 and the 6th switch S 6 disconnect, described the 3rd switch S 3, the 4th switch S 4, minion close S7 and the 8th switch S8 is closed, now, the operating state of described operational amplifier OP as shown in Figure 4, wherein Veq2 is the equivalent input noise of described operational amplifier OP now, and now the equivalent input noise of operational amplifier OP is

${\mathrm{<figure-callout\; id="1"\; label="v\; eq"\; filenames="HDA0000421812440000021.png"\; state="\{\{state\}\}">v</figure-callout>}}_{\mathrm{eq}}=-v_{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="HDA0000421812440000021.png"\; state="\{\{state\}\}">n</figure-callout>}1}+\frac{v_{n2}}{A}---\left(2\right)$

, within a clock cycle, the average equivalent input noise Veq of the operational amplifier OP of audio frequency D/A converting circuit of the present invention is the mean value of formula (1) and formula (2) summation,

$v_{\mathrm{eq}}=\frac{{\mathrm{<figure-callout\; id="1"\; label="v\; eq"\; filenames="HDA0000421812440000021.png"\; state="\{\{state\}\}">v</figure-callout>}}_{\mathrm{eq}}+{\mathrm{<figure-callout\; id="2"\; label="v\; eq"\; filenames="HDA0000421812440000021.png"\; state="\{\{state\}\}">v</figure-callout>}}_{\mathrm{eq}}}{2}=\frac{v_{n2}}{A}---\left(3\right)$

By (3) formula, can be found out, described upset electronic circuit overturns to the input noise of described operational amplifier within every half clock cycle, thereby the offset voltage of described operational amplifier and low frequency 1/f noise sum are 0 within a clock cycle, make audio frequency D/A converting circuit of the present invention within a clock cycle, eliminate DC maladjustment and the low frequency 1/f noise thereof of operational amplifier OP, further improved the signal to noise ratio of audio frequency D/A converting circuit.

In addition, when the clock pulse of described the second output Φ 2 outputs is high level, the equiva lent impedance of the conducting of described the first field effect transistor pipe M1 is

$R_{M1}=\frac{1}{k*{(W/L)}_{M1}*(\mathrm{VGS}-\mathrm{VTH})}---\left(4\right)$

Wherein k is the constant relevant to technique, (W/L) _m1be the breadth length ratio of the first field effect transistor M1, VTH is the threshold voltage of the first field effect transistor M1, and VGS is the gate source voltage of the first field effect transistor M1.For reducing the harmonic distortion of audio frequency D/A converting circuit, need to improve precision and the speed of the first field effect transistor M1, needing (4) formula is a relatively constant value, equiva lent impedance has high linearity, needs time constant R simultaneously _m1c _intpas much as possible little, to guarantee fast electric charge dispensing rate; And sampling capacitance Cintp is constant, so will make time constant R _m1c _intpas much as possible little, need equiva lent impedance R _m1as far as possible little.After the breadth length ratio of technique and field effect transistor is selected, the k in (4) formula, (W/L) _m1, VTH is for changing very little value, therefore in order to guarantee the equiva lent impedance R of sampling switch _m1constant and as far as possible little, in needs (4) formula, gate source voltage is constant and large as far as possible; And the function of Bootstrap unit is to guarantee that the gate source voltage of the first field effect transistor M1 is a fixed value VC, therefore, under the control of described Bootstrap unit, the conducting resistance of described the first field effect transistor M1 is

${\mathrm{<figure-callout\; id="1"\; label="R\; M"\; filenames="HDA0000421812440000021.png"\; state="\{\{state\}\}">R</figure-callout>}}_M=\frac{1}{k*{(W/L)}_{M1}*(\mathrm{VC}-\mathrm{VTH})}---\left(5\right)$

Therefore,, by VC value large as far as possible in selecting circuit allowed band, can guarantee the resistance value R in (5) formula _m1as far as possible little, and be relatively constant value, the harmonic distortion of audio frequency D/A converting circuit reduced.Described the second Bootstrap electronic circuit also has above-mentioned functions, at this, is no longer repeated in this description.

Invention has been described for above combination most preferred embodiment, but the present invention is not limited to the embodiment of above announcement, and should contain the various modifications of carrying out according to essence of the present invention, equivalent combinations.

Claims (5)

1. an audio frequency D/A converting circuit, comprise the first clock generating electronic circuit, common-mode voltage produces electronic circuit and conversion main circuit, described the first clock generating electronic circuit is connected with described conversion main circuit, to produce clock pulse, control the work of described conversion main circuit, and described the first clock generating electronic circuit has the first output and the second output, described the first output and the second output are exported complementary clock pulse, described common-mode voltage produces electronic circuit and is connected with described conversion main circuit, to produce the described conversion main circuit required common-mode voltage that works, described conversion main circuit converts the digital differential signal of outside input to analog difference signal output, and comprise sampling electronic circuit and integration electronic circuit, described integration electronic circuit consists of integrating capacitor and operational amplifier, the input of described sampling electronic circuit is connected with external digital differential signal output, its output is connected with the input of described operational amplifier and one end of integrating capacitor respectively, the other end of described integrating capacitor be connected with analog signal output and export conversion after analog difference signal, and described conversion main circuit is symmetrical arranged about described operational amplifier, it is characterized in that, also comprise that second clock produces electronic circuit, upset electronic circuit, the first Bootstrap electronic circuit and the second Bootstrap electronic circuit, described the first Bootstrap electronic circuit is all connected with described sampling electronic circuit with one end of the second Bootstrap electronic circuit, the other end is all connected with described analog signal output, described second clock produces electronic circuit and is connected with described upset electronic circuit, to produce clock pulse, control the work of described upset electronic circuit, and described second clock produces electronic circuit and has the 3rd output and the 4th output, described the 3rd output and the 4th output are exported complementary clock pulse, and when described sampling electronic circuit is during in sample states, described second clock produces the 3rd output of electronic circuit and the clock pulse of the 4th output output is overturn, described upset electronic circuit is connected with output and the input of described operational amplifier respectively, when described second clock produces the clock pulse upset of electronic circuit output, the offset voltage that described upset electronic circuit produces described operational amplifier and the upset of the direction of low-frequency noise.

2. audio frequency D/A converting circuit as claimed in claim 1, it is characterized in that, described upset electronic circuit comprises the first switch, second switch, the 3rd switch, the 4th switch, the 5th switch, the 6th switch, minion is closed and the 8th switch, one end of described the first switch and the 4th switch is connected with an output of described sampling electronic circuit jointly, one end of described second switch and the 3rd switch is connected with another output of described sampling electronic circuit jointly, the other end of described the first switch and the 3rd switch is connected with the normal phase input end of described operational amplifier jointly, the other end of described second switch and the 4th switch is connected with the inverting input of described operational amplifier jointly, one end that described the 5th switch and described minion are closed is connected with the reversed-phase output of described operational amplifier jointly, one end of described the 6th switch and the 8th switch is connected with the positive output end of described operational amplifier jointly, the other end of described the 5th switch and the 8th switch is connected with an output of described analog signal output jointly, and the other end that described the 6th switch and minion are closed is connected with another output of described analog signal output jointly.

3. audio frequency D/A converting circuit as claimed in claim 2, is characterized in that, the control end of described the first switch, second switch, the 5th switch and the 6th switch is also connected with the 3rd output of described second clock generation electronic circuit respectively; Described the 3rd switch, the 4th switch, minion are closed and the control end of the 8th switch is also connected with the 4th output of described second clock generation electronic circuit respectively; And described in each, switch is all closed when the clock pulse of its control end is high level.

4. audio frequency D/A converting circuit as claimed in claim 1, is characterized in that, described the first Bootstrap electronic circuit and the second Bootstrap electronic circuit have identical architectural feature.

5. audio frequency D/A converting circuit as claimed in claim 4, it is characterized in that, described the first Bootstrap electronic circuit comprises the first field effect transistor and the first Bootstrap unit, the clock control end of described the first Bootstrap unit is connected with described the second output, the source electrode of its input and described the first field effect transistor is all connected with described analog signal output, its output is connected with the grid of described the first field effect transistor, and the drain electrode of described the first field effect transistor is connected with described sampling electronic circuit.

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