The common mode feedback circuit of switching capacitor system
Technical field
The present invention relates to a kind of common mode feedback circuit that is used for switching capacitor system, belong to the technical field of operation amplifier circuit design.
Background technology
By switch, the switching capacitor system structure that electric capacity and operational amplifier are formed, at filter, be widely used in modulus and the digital to analog converter, but at the common common mode feedback circuit that is used for switching capacitor system, the initial voltage that detects output voltage electric capacity heavily distributes by electric charge and obtains, when giving the charging of detection output voltage electric capacity, switching capacity is used as resistance, thereby charge constant RC is increased, cause the speed of setting up of common-mode feedback to reduce, simultaneously, because output common mode control end parasitic capacitance produces the right influence at zero point of a pair of utmost point, has further reduced the speed of setting up of common-mode feedback again.In addition, in the common mode feedback circuit of common switched-capacitor circuit, because operational amplifier has different output loadings with transmission mutually mutually in sampling, make differential operational amplifier have different frequency responses mutually with transmission mutually in sampling, when using at multi channels time interlacing pattern number converter circuit, can cause the different passages in some clock phases to be in different operating states, different interchannels produce mismatch, finally cause output to produce error.
Summary of the invention
Technical problem: the objective of the invention is to solve above-mentioned problems of the prior art, a kind of common mode feedback circuit that is used for switching capacitor system is provided, improve the speed of setting up of common-mode feedback, reduce the output error of multi channels time interlacing pattern number converter.
Technical scheme: for solving the problems of the technologies described above, the present invention is achieved by the following technical solutions: sampling phase common mode feedback circuit is set respectively and transmits common mode feedback circuit mutually, become common mode feedback circuit of the present invention by their mutual group, make circuit sample mutually and transmit the common-mode feedback that hockets respectively mutually.Wherein, the first input end of the first input end of sampling phase common mode feedback circuit and transmission phase common mode feedback circuit links to each other afterwards as the first input end of this common mode feedback circuit; Second input of second input of sampling phase common mode feedback circuit and transmission phase common mode feedback circuit links to each other afterwards as second input of this common mode feedback circuit; The 3rd input of the 3rd input of sampling phase common mode feedback circuit and transmission phase common mode feedback circuit links to each other afterwards as the 3rd input of this common mode feedback circuit; The four-input terminal of transmission phase common mode feedback circuit is as the four-input terminal of this common mode feedback circuit; The output of the output of sampling phase common mode feedback circuit and transmission phase common mode feedback circuit links to each other afterwards as the output of this common mode feedback circuit.Common mode feedback circuit of the present invention, sampling mutually and transmitting the common-mode feedback that hockets respectively mutually, changed the common-mode feedback structure of transmission phase time operational amplifier output terminal load, with switch the difference output end of detection output voltage electric capacity in the conventional structure and operational amplifier is isolated, eliminated in the conventional common mode feedback circuit, set up the utmost point right influence at zero point that end produces in common-mode feedback, thereby improved the speed of setting up of operational amplifier output common mode level; On the other hand, because the present invention can make operational amplifier have identical output loading with the transmission phase time mutually in sampling, when therefore being used for multi channels time interlacing pattern number converter, different interchannel mismatches can not occur, can reduce output error greatly.
At the common mode feedback circuit that is used for switching capacitor system of the present invention, the first input end of described sampling phase common mode feedback circuit, first switch, first electric capacity, second electric capacity, the 3rd switch, second input of sampling phase common mode feedback circuit is linked in sequence, first end of second switch connects the tie point of first switch and first electric capacity, first end of the 4th switch connects the tie point of second electric capacity and the 3rd switch, second end of second switch and second end of the 4th switch link together, as the 3rd input of sampling phase common mode feedback circuit, draw the sampling output of common mode feedback circuit mutually from first electric capacity and the tie point of second electric capacity; The first input end of described transmission phase common mode feedback circuit, minion is closed, the 3rd electric capacity, octavo is closed, twelvemo is closed, the 4th electric capacity, the 11 switch, second input of transmission phase common mode feedback circuit is linked in sequence, first end of the 5th switch connects the tie point of minion pass and the 3rd electric capacity, first end of the 9th switch connects the tie point of the 4th electric capacity and the 11 switch, second end of the 5th switch and second end of the 9th switch link together, the 3rd input as transmission phase common mode feedback circuit, first end of the 6th switch connects the tie point of the 3rd electric capacity and octavo pass, first end of the tenth switch connects the tie point of twelvemo pass and the 4th electric capacity, second end of the 6th switch and the tenth switch second end link together, as the four-input terminal of transmission phase common mode feedback circuit, close the tie point that closes with twelvemo from octavo and draw the transmission output of common mode feedback circuit mutually.In the above circuit, first switch, the 3rd switch, the 5th switch, the 6th switch, the 9th switch, the tenth switch closure when sampling phase P1 is opened when transmission phase P2; Minion pass, octavo pass, the 11 switch, twelvemo pass, second switch, the 4th switch closure when sampling phase P2 is opened when transmission phase P1.When sampling phase P1, the 3rd electric capacity and the charging of the 4th electric capacity, first electric capacity and second electric capacity are realized common-mode feedback; When transmission phase P1, first electric capacity and the charging of second electric capacity, the 3rd electric capacity and the 4th electric capacity are realized common-mode feedback; By with upper type, operational amplifier in sampling mutually and the transmission realization common-mode feedback that alternates.
In multi channels time interlacing pattern number converter, when sampling and transmission output loading mutually are unequal, each interchannel will produce mismatch, cause output error.In sampling phase common mode feedback circuit of the present invention and transmission mutually in the common mode feedback circuit circuit, the capacitance of first electric capacity, second electric capacity, the 3rd electric capacity, the 4th electric capacity is equated, then sampling has identical output loading mutually with output, can avoid different interchannels mismatch to occur, thereby can reduce output error greatly.
Beneficial effect: the common mode feedback circuit that is used for switching capacitor system of the present invention, by sampling phase common mode feedback circuit and transmission mutually two of common mode feedback circuits partly form, by the common-mode feedback that hockets respectively mutually in sampling phase and transmission, on the one hand owing to changed the common-mode feedback structure of transmission phase time operational amplifier output terminal load, with switch the difference output end of detection output voltage electric capacity in the conventional structure and operational amplifier is isolated, it is right zero point to have avoided common-mode feedback to set up the utmost point of holding, thereby has improved the speed of setting up of operational amplifier output common mode level; On the other hand, when being used for multi channels time interlacing pattern number converter, can make operational amplifier have identical output loading mutually with transmission mutually, therefore in sampling, can avoid different interchannels mismatch to occur, thereby can reduce output error greatly.
Description of drawings
Fig. 1 is conventional common-mode feedback and operation amplifier circuit.
Fig. 2 is that common mode feedback circuit of the present invention is connected block diagram with operational amplifier.
Fig. 3 is a sampling phase common mode feedback circuit of the present invention.
Fig. 4 is a transmission phase common mode feedback circuit of the present invention.
Fig. 5 is the comparison of experimental result of the present invention and routine techniques experimental result.
Have among the above figure: operational amplifier 1, common mode feedback circuit 2, sampling phase common mode feedback circuit 21, transmission phase common mode feedback circuit 22, the speed of setting up 51 of routine techniques common-mode feedback, common-mode feedback is set up speed 52.First switch 211, second switch 212, the 3rd switch 213, the 4th switch 214, the 5th switch 221, the 6th switch 222, minion pass 223, octavo are closed the 224, the 9th switch 225, the tenth switch the 226, the 11 switch 227, twelvemo pass 228.
Embodiment
Below in conjunction with accompanying drawing and embodiment the present invention is described in further detail.
Fig. 1 is conventional common-mode feedback and operation amplifier circuit.Wherein, the first input end A of common mode feedback circuit 2 meets the second output OUT+ of operational amplifier 1 with output signal V
0+; The second input B of common mode feedback circuit 2 meets the first output OUT-of operational amplifier 1 with input signal V
0-, the 3rd input C of common mode feedback circuit 2 meets common-mode reference level V
REF, the four-input terminal E of common mode feedback circuit 2 meets bias voltage V
BIAS, the 3rd input CM that the output D of common mode feedback circuit 2 connects operational amplifier 1 regulates level V with output common mode
CMFB, the first input end IN+ of operational amplifier 1 meets analog input signal V
IN+, the second input IN-of operational amplifier 1 meets analog input signal V
IN-.In this circuit, detect the output voltage capacitor C
C1And C
C2Initial voltage heavily distribute by electric charge and obtain, give C
C1And C
C2During charging, switching capacity C
S1And C
S2Be used as resistance, thereby charge constant RC is increased, simultaneously, because output common mode control end V
CMFBParasitic capacitance produces the right influence at zero point of a pair of utmost point, has further reduced the speed of setting up of common-mode feedback again.In addition, in the common mode feedback circuit of common switched-capacitor circuit, because operational amplifier has different output loadings with transmission mutually mutually in sampling, the sampling phase time is a capacitor C
C1And C
C2, and the transmission phase time be C
S1, C
S2, C
C1And C
C2And then make differential operational amplifier have different frequency responses mutually with transmission mutually in sampling, when using at multi channels time interlacing pattern number converter circuit, can cause different passages to be in different operating states in some clock phases, make different interchannels produce mismatch, finally cause output to produce error.
Fig. 2 is that common mode feedback circuit of the present invention is connected block diagram with operational amplifier.Common mode feedback circuit 2 of the present invention by sampling phase common mode feedback circuit 21 and transmission mutually common mode feedback circuit 22 form, wherein, the first input end A of the phase of sampling common mode feedback circuit 21
SWith the transmission first input end A of common mode feedback circuit 22 mutually
HLink to each other the back as the first input end A of this common mode feedback circuit 2 with input signal V
0+; The second input B of sampling phase common mode feedback circuit 21
SWith the transmission second input B of common mode feedback circuit 22 mutually
HLink to each other the back as the second input B of this common mode feedback circuit 2 with input signal V
0-; The 3rd input C of sampling phase common mode feedback circuit 21
SWith transmission the 3rd input C of common mode feedback circuit 22 mutually
HLink to each other the back as the 3rd input C of this common mode feedback circuit 2 to insert common-mode reference level V
REFThe four-input terminal E of transmission phase common mode feedback circuit 22
HAs the four-input terminal E of this common mode feedback circuit 2 to insert bias voltage V
BIASThe output D of sampling phase common mode feedback circuit 21
SWith the transmission output D of common mode feedback circuit 22 mutually
HOutput D as this common mode feedback circuit 2 after linking to each other regulates level V with output common mode
CMFB Operational amplifier 1 receives analog differential input signal V by differential input end IN+, IN-
IN+ and V
IN-, produce analog differential output signal V at difference output end OUT+, OUT-
0+ and V
0-, the 3rd input CM of operational amplifier 1 is connected to the adjusting level V of common-mode feedback
CMFBThe output common mode of operational amplifier 1 is remained on a stable current potential.Common mode feedback circuit of the present invention, by utilizing sampling phase common mode feedback circuit 21 and transmitting mutually common mode feedback circuit 22 common-mode feedback that hockets respectively, changed the common-mode feedback structure of transmission phase time operational amplifier output terminal load, with the difference output end V of switch with detection output voltage electric capacity in the conventional common mode feedback circuit and operational amplifier
0+ and V
0-isolate, thus the utmost point of breaking common-mode feedback foundation end is right zero point, reduces the settling time of common-mode feedback, improves the speed of setting up of operational amplifier output common mode level significantly.Fig. 5 is the comparison of experimental result of the present invention and routine techniques experimental result, and as can be seen from the figure, common-mode feedback of the present invention is set up speed, approximately than routine techniques common-mode feedback to set up speed fast again.
Referring to Fig. 3 and Fig. 4, Fig. 3 is a sampling phase common mode feedback circuit of the present invention, and Fig. 4 is a transmission phase common mode feedback circuit of the present invention.The first input end A of sampling phase common mode feedback circuit 21
S, first switch 211, first capacitor C 1, second capacitor C 2, the 3rd switch 213, the second input B
SBe linked in sequence, first end of second switch 212 connects the tie point of first switch 211 and first capacitor C 1, first end of the 4th switch 214 connects the tie point of second capacitor C 2 and the 3rd switch 213, second end of second end of second switch 212 and the 4th switch 214 links together, as the 3rd input C of sampling phase common mode feedback circuit 21
S, draw the sampling output D of common mode feedback circuit 21 mutually from first capacitor C 1 and the tie point of second capacitor C 2
SThe first input end A of transmission phase common mode feedback circuit 22
H, minion closes that the 223, the 3rd capacitor C 3, octavo close 224, twelvemo is closed the 228, the 4th capacitor C the 4, the 11 switch 227, the second input B
HBe linked in sequence, first end of the 5th switch 221 connects the tie point that minion is closed the 223 and the 3rd capacitor C 3, first end of the 9th switch 225 connects the tie point of the 4th capacitor C 4 and the 11 switch 227, second end of second end of the 5th switch 221 and the 9th switch 225 links together, as the 3rd input C of transmission phase common mode feedback circuit 22
HFirst end of the 6th switch 222 connects the tie point of the 3rd capacitor C 3 and octavo pass 224, first end of the tenth switch 226 connects the tie point that twelvemo is closed the 228 and the 4th capacitor C 4, second end of the 6th switch 222 and the tenth switch 226 second ends link together, as the four-input terminal E of transmission phase common mode feedback circuit 22
H, draw the transmission output D of common mode feedback circuit 22 mutually from the tie point of octavo pass 224 and twelvemo pass 228
HConcrete operation principle of the present invention is as follows: the 5th switch 221 switches, the 6th switch 222, first switch 211, the 9th switch 225, the tenth switch 226, the 3rd switch 213, and closure when sampling phase P1 is opened when transmission phase P2; Minion is closed 223 switches, octavo pass 224, second switch the 212, the 11 switch 227, twelvemo pass the 228, the 4th switch 214 closure when sampling phase P2, opens when transmission phase P1.When sampling phase P1, the 3rd capacitor C 3 and 4 chargings of the 4th capacitor C, first capacitor C 1 and second capacitor C 2 realize common-mode feedback; When transmission phase P1, first capacitor C 1 and 2 chargings of second capacitor C, the 3rd capacitor C 3 and the 4th capacitor C 4 realize common-mode feedback.By with upper type, operational amplifier in sampling mutually and the transmission realization common-mode feedback that alternates.
In multi channels time interlacing pattern number converter, because of different with the output loading of transmission phase in sampling, each interchannel will produce mismatch, causes output error.In sampling phase common mode feedback circuit 21 of the present invention and transmission mutually in common mode feedback circuit 22 circuit, the output loading of sampling phase is C1 and C2, the output loading of transmission phase is C3 and C4, the capacitance of first capacitor C 1, second capacitor C 2, the 3rd capacitor C 3,4 four electric capacity of the 4th capacitor C is equated, then has identical output loading mutually with transmission in sampling, can avoid different interchannels mismatch to occur, thereby can reduce output error greatly.
The making work of common mode feedback circuit of the present invention can realize by the CMOS technology of prior art.