CN101277094A - Operational amplifier capable of compensating offset voltage - Google Patents

Abstract

An operational amplifier capable of compensating for offset voltage comprises an input stage circuit, comprising a positive input terminal, a negative input terminal, a first current output terminal and a second current output terminal, for outputting corresponding currents from the first current output terminal and the second current output terminal according to the voltages received by the positive input terminal and the negative input terminal; an output stage circuit, coupled to the first current output terminal and the second current output terminal of the input stage circuit, for outputting voltages according to the currents of the first current output terminal and the second current output terminal; and an adjustment device, coupled between the input stage circuit and the output stage circuit, for adjusting the currents of the first current output terminal and the second current output terminal to compensate for the influence of the offset voltage.

Description

Operational Amplifier Compensated for Offset Voltage

technical field

The invention relates to an operational amplifier capable of compensating offset voltage, in particular to an operational amplifier capable of compensating the influence caused by offset voltage by adjusting the magnitude of the current between the input stage circuit and the output stage circuit in the operational amplifier.

Background technique

An operational amplifier is an important circuit component in various electronic devices, and it is widely used in home appliances, industrial and scientific instruments and other fields. Circuit designers can often use operational amplifiers to implement many different operational functions such as buffers, filters, analog-to-digital converters, and more.

An ideal operational amplifier has the following characteristics: infinite input impedance, zero output impedance, infinite open-loop gain, infinite Common Mode Rejection Ratio, and infinite bandwidth. However, due to the limitations of semiconductor technology and integrated circuit technology, in practice, it is difficult to realize an ideal operational amplifier. In order to represent the characteristics of a real operational amplifier, known techniques use an offset voltage (Offset Voltage) to represent the non-ideality of the operational amplifier.

Please refer to FIG. 1 , which is a schematic diagram of a known operational amplifier 10 . The operational amplifier 10 includes an input stage circuit 100 , an output stage circuit 102 and an equivalent voltage source 104 . The operational amplifier 10 receives a differential signal through a positive input terminal Vp and a negative input terminal Vn, and outputs an amplified result through an output terminal Vo. The equivalent voltage source 104 is used to represent the non-ideality of the operational amplifier 10 (does not exist in the actual circuit), and the voltage Vos generated by it represents when the output terminal Vo is coupled to the negative input terminal Vn (forming a unity gain feedback structure). , the voltage difference between the output terminal Vo and the positive input terminal Vp, that is, the offset voltage of the operational amplifier 10 . There are many reasons for the offset voltage, such as semiconductor physical characteristics, process defects, component mismatch, etc.

Please refer to FIG. 2 , which is a schematic diagram of the input stage circuit 100 in FIG. 1 . The input stage circuit 100 is used for generating currents Id1 and Id2 to the output stage circuit 102 according to the voltages of the positive input terminal Vp and the negative input terminal Vn, and includes input transistors P1 and P2 and a current source 200 . The input transistors P1 and P2 are both P-type MOS transistors, forming a common-source differential pair with a common-mode voltage Vc. In an ideal situation, the channel length and channel width of the input transistors P1 and P2 are exactly the same, then the current Ib generated by the current source 200 will flow to the sources of the input transistors P1 and P2 on average, so that the input transistors P1 and P2 The voltages from the source to the gate are exactly the same, that is, the voltage Vos is 0, and the current Id1 and Id2 are equal. However, in practice, when the input transistors P1 and P2 are not completely matched due to certain characteristics of the process, the threshold voltages (ThresholdVoltage) of the input transistors P1 and P2 will be unequal, so that the source to gate of the input transistors P1 and P2 If the pole voltages are not equal, the offset voltage Vos is not equal to 0, and the currents Id1 and Id2 are not equal.

In short, due to factors such as semiconductor physical characteristics, process defects, and component mismatches, the offset voltage of known operational amplifiers is not equal to 0, which affects its performance. Therefore, how to reduce the influence of the offset voltage of the operational amplifier has become one of the subjects that the industry strives for.

Contents of the invention

Therefore, the main objective of the present invention is to provide an operational amplifier capable of compensating offset voltage.

The present invention discloses an operational amplifier capable of compensating offset voltage, which includes an input stage circuit, including a positive input terminal, a negative input terminal, a first current output terminal and a second current output terminal, which are used according to the positive input terminal. The voltage received by the input terminal and the negative input terminal outputs a corresponding current from the first current output terminal and the second current output terminal; an output stage circuit is coupled to the first current output terminal of the input stage circuit and the second current output terminal, used to output a voltage according to the currents of the first current output terminal and the second current output terminal; and an adjustment device, coupled between the input stage circuit and the output stage circuit, for to adjust the currents of the first current output terminal and the second current output terminal to compensate the influence of the offset voltage.

The present invention also discloses a rail-to-rail operational amplifier capable of compensating offset voltage, which includes an input stage circuit, including a positive input terminal, a negative input terminal, a first current output terminal, a second current output terminal, A first current receiving end and a second current receiving end, used to output current from the first current output end and the second current output end according to the voltage received by the positive input end and the negative input end, and by The first current receiving end and the second current receiving end receive current; an output stage circuit is coupled to the first current output end, the second current output end, the first current receiving end and the second current receiving end end, used to generate a corresponding voltage according to the currents of the first current output end, the second current output end, the first current receiving end and the second current receiving end; and an adjusting device, coupled to the input stage Between the circuit and the output stage circuit, it is used to adjust the current output by the first current output terminal and the second current output terminal and the current received by the first current receiving terminal and the second current receiving terminal to compensate Effect of Offset Voltage.

Description of drawings

FIG. 1 is a schematic diagram of a known operational amplifier 10 .

FIG. 2 is a schematic diagram of the input stage circuit 100 in FIG. 1 .

FIG. 3 is a schematic diagram of an operational amplifier 30 capable of compensating offset voltages according to an embodiment of the present invention.

FIG. 4 shows a functional block diagram of the adjusting device 304 in FIG. 3 .

FIG. 5 is a schematic diagram of the first current mode digital-to-analog converter in FIG. 4 .

6 and 7 are schematic diagrams of operational amplifiers 60 and 70 according to embodiments of the present invention, respectively.

FIG. 8 is a schematic diagram of a rail-to-rail operational amplifier 80 capable of compensating offset voltages according to an embodiment of the present invention.

FIG. 9 is a schematic diagram of the input stage circuit 800 in FIG. 8 .

FIG. 10 shows a functional block diagram of the adjusting device 804 in FIG. 8 .

FIG. 11 is a schematic diagram of the first current mode digital-to-analog converter in FIG. 10 .

Description of reference symbols

10, 30, 60, 70, 80 operational amplifiers

100, 300, 600, 700, 800 input stage circuit

102, 302, 802 output stage circuit

104, 310, 814 equivalent voltage source

Vp Positive input terminal

Vn Negative input terminal

Vo output terminal

Id1, Id2, Id3, Id4 Current

Vos Offset Voltage

Vc Common Mode Voltage

P1, P2, N1, N2 Transistors

200 Current Source

304, 606, 706, 804 adjustment device

306, 806 The first current output terminal

308, 808 Second current output terminal

Vctrl control signal

400, 900 First current mode digital to analog converter

402, 902 Second current mode digital to analog converter

404, 904 control unit

SW1～SWn, SWU1～SWUn, SWD1～SWDn switch

CS1～CSn, CSU1～CSUn, CSD1～CSDn current source

810 The first current receiving end

812 Second current receiving terminal

Detailed ways

Please refer to FIG. 3 . FIG. 3 is a schematic diagram of an operational amplifier 30 capable of compensating offset voltage according to an embodiment of the present invention. The operational amplifier 30 includes an input stage circuit 300 , an output stage circuit 302 and an adjustment device 304 . The input stage circuit 300 receives voltage signals from a positive input terminal Vp and a negative input terminal Vn, and outputs corresponding currents Id1 and Id2 to the output stage circuit 302 through a first current output terminal 306 and a second current output terminal 308 . The output stage circuit 302 outputs a voltage amplification result from an output terminal Vo according to the currents Id1 and Id2 of the first current output terminal 306 and the second current output terminal 308 . In addition, in FIG. 3 , an equivalent voltage source 310 is used to represent the non-ideality of the operational amplifier 30 (which does not exist in the actual circuit), and the voltage Vos generated by it represents the offset voltage of the operational amplifier 30 . The adjustment device 304 is used to adjust the currents Id1 and Id2 outputted by the first current output terminal 306 and the second current output terminal 308 to compensate the influence of the offset voltage.

Therefore, in the operational amplifier 30 , the adjustment device 304 can compensate the influence of the offset voltage caused by factors such as semiconductor physical characteristics, process defects, and component mismatches by adjusting the currents Id1 and Id2 . For example, if the current Id1 is greater than the current Id2 , the adjusting device 304 can draw or output current from the first current output terminal 306 to the second current output terminal 308 so that the current Id1 is approximately equal to the current Id2 . Conversely, when the current Id1 is smaller than the current Id2 , the adjusting device 304 can output a current to the first current output terminal 306 or draw a current from the second current output terminal 308 so that the current Id1 is approximately equal to the current Id2 . In this case, even if the operational amplifier 30 produces an offset voltage due to factors such as semiconductor physical characteristics, process defects, and component mismatches, the present invention does not need to change the design of the input stage circuit 300 and the output stage circuit 302. The means 304 compensates for the effect of the offset voltage.

Please refer to FIG. 4 , which shows a functional block diagram of the adjusting device 304 in FIG. 3 . The adjusting device 304 includes a first current-mode digital-to-analog converter 400 , a second current-mode digital-to-analog converter 402 and a control unit 404 . The first current-mode digital-to-analog converter 400 and the second current-mode digital-to-analog converter 402 are respectively coupled to the first current output terminal 306 and the second current output terminal 308 for controlling signals output by the control unit 404 Vctrl outputs or receives current through the first current output terminal 306 and the second current output terminal 308 . The control unit 404 can output the control signal Vctrl according to the current difference between the first current output terminal 306 and the second current output terminal 308 to control the first current mode digital-to-analog converter 400 to output or receive through the first current output terminal 306 The magnitude of the current is the same as the magnitude of the current output or received by the second current mode digital-to-analog converter 402 through the second current output terminal 308 . Therefore, when the current Id1 and Id2 of the operational amplifier 30 are not equal due to the offset voltage, the control unit 404 can control the first current-mode digital-to-analog converter 400 and the second current-mode digital-to-analog converter 402 through the control signal Vctrl, To adjust the current input to the output stage circuit 302, so that the current (Id1±dI) and (Id2±dI) are equal. In this way, the influence caused by the offset voltage can be effectively compensated.

It should be noted that FIG. 4 is only a functional block diagram of the adjusting device 304 , and those skilled in the art can design a circuit with the same function in conjunction with other components. For example, as shown in FIG. 5 , the first current-mode digital-to-analog converter 400 may be composed of switches SW1˜SWn and current sources CS1˜CSn. The switches SW1˜SWn can connect the first current output terminal 306 to the corresponding current source according to the control signal Vctrl, so as to adjust the magnitude of the current drawn or output by the first current output terminal 306 . Therefore, when the currents Id1 and Id2 are not equal, the control unit 404 can control the switches SW1-SWn to connect a specific current source among the current sources CS1-CSn to the first current output terminal 306 to make the currents Id1 and Id2 equal.

Therefore, in the operational amplifier 30 , the adjusting device 304 can adjust the currents Id1 and Id2 so that the currents flowing into the output stage circuit 302 are equal to compensate the influence of the offset voltage. Of course, those skilled in the art can design an appropriate adjustment device 304 according to the required input stage circuit. For example, please refer to FIG. 6 and FIG. 7 . FIG. 6 and FIG. 7 respectively show schematic diagrams of operational amplifiers 60 and 70 according to embodiments of the present invention. The operational amplifiers 60 and 70 are both derivatives of the operational amplifier 30, wherein the input stage circuit 600 of the operational amplifier 60 is composed of P-type metal oxide semiconductor transistors P1 and P2, and the input stage circuit 700 of the operational amplifier 70 is composed of N-type The metal oxide semiconductor transistors N1 and N2 are composed, and the adjustment units 606 and 706 of the two are designed according to the first current mode digital-to-analog converter 400 in FIG. 5 , and its operation principle is as described above. For example, taking the operational amplifier 60 as an example, when certain characteristics of the transistors P1 and P2 are not fully matched, the threshold voltages of the transistors P1 and P2 will be unequal, and thus the currents Id1 and Id2 will be unequal. In this case, the adjustment unit 606 can make the currents Id1 and Id2 close to equal by turning on the current source.

The operational amplifiers 60 and 70 shown in FIG. 6 and FIG. 7 are embodiments derived from the operational amplifier 30 and are not intended to limit the scope of the present invention, and designers can make appropriate changes. For example, the number of current sources in the adjustment units 606 and 706 can be adjusted according to the required accuracy, and the current generated by each current source can be set to be consistent or gradually decreasing.

In addition, for the rail-to-rail operational amplifier, the present invention provides another embodiment for compensating the influence of the offset voltage. Please refer to FIG. 8 , which is a schematic diagram of a rail-to-rail operational amplifier 80 capable of compensating offset voltages according to an embodiment of the present invention. The rail-to-rail operational amplifier 80 includes an input stage circuit 800 , an output stage circuit 802 and an adjustment device 804 . The input stage circuit 800 receives voltage signals from a positive input terminal Vp and a negative input terminal Vn, and outputs corresponding currents Id1 and Id2 to the output stage circuit 802 through a first current output terminal 806 and a second current output terminal 808, And the currents Id3 and Id4 output by the output stage circuit 302 are received by a first current receiving end 810 and a second current receiving end 812 . The output stage circuit 802 outputs a voltage from an output terminal Vo according to the current Id1, Id2, Id3, and Id4 of the first current output terminal 806, the second current output terminal 808, the first current receiving terminal 810, or the second current receiving terminal 812. Zoom in on the results. In addition, in FIG. 8 , an equivalent voltage source 814 is used to represent the non-ideality of the rail-to-rail operational amplifier 80 (which does not exist in the actual circuit), and the voltage Vos generated by it represents the rail-to-rail operational amplifier 80 the offset voltage. The adjusting device 804 is used to adjust the current Id1 and Id2 output by the first current output terminal 806 and the second current output terminal 808 or the current Id3 and Id4 received by the first current receiving terminal 810 and the second current receiving terminal 812 to compensate Effect of Offset Voltage.

The operation mode of the rail-to-rail operational amplifier 80 is similar to that of the operational amplifier 30. The difference is that the rail-to-rail operational amplifier 80 has more than the operational amplifier 30 a first current receiving terminal 810 and a second current receiving terminal 812 for receiving output The currents Id3 and Id4 output by the stage circuit 802. Therefore, as long as the operational amplifier 30 is properly modified, the offset voltage of the rail-to-rail operational amplifier 80 can be compensated.

First, please refer to FIG. 9 , which is a schematic diagram of an input stage circuit 800 . The input stage circuit 800 includes a differential pair composed of PMOS transistors P1 and P2 and a differential pair composed of NMOS transistors N1 and N2. The differential pair composed of transistors P1 and P2 can output current Id1 and Id2 to the output stage circuit 802 through the first current output terminal 806 and the second current output terminal 808, while the differential pair composed of transistors N1 and N2 can output currents Id1 and Id2 to the output stage circuit 802 through the first current output terminal 806 and the second current output terminal 808. A current receiving end 810 and a second current receiving end 812 receive the currents Id3 and Id4 output by the output stage circuit 802 .

Please continue to refer to FIG. 10 , which is a schematic diagram of the adjusting device 804 . Like the adjusting device 304 shown in FIG. 4 , the adjusting device 804 also includes a first current-mode digital-to-analog converter 900 , a second current-mode digital-to-analog converter 902 and a control unit 904 . The first current mode digital-to-analog converter 900 is coupled between the first current output terminal 806 and the first current receiving terminal 810 for outputting through the first current output terminal 806 according to the control signal Vctrl output by the control unit 904 The current is received through the first current receiving terminal 810 . The second current mode digital-to-analog converter 902 is coupled between the second current output terminal 808 and the second current receiving terminal 812 , and is used to pass the second current output terminal 808 according to the control signal Vctrl output by the control unit 904 Output current and receive current through the second current receiving end 812 . Therefore, when the currents Id1 and Id2 and Id3 and Id4 are not equal due to the offset voltage of the rail-to-rail operational amplifier 80, the control unit 904 can control the first current mode digital-to-analog converter 900 and the second current mode through the control signal Vctrl. mode DAC 902 to adjust the current input to the output stage circuit 802 and the current input to the input stage circuit 800 . In this way, the influence caused by the offset voltage can be effectively compensated.

Of course, the adjustment device 804 can be any circuit with the same function, and those skilled in the art can design a circuit with the same function in conjunction with other components. For example, as shown in FIG. 11 , the first current-mode digital-to-analog converter 900 may be composed of switches SWU1 -SWUn, SWD1 -SWDn and current sources CSU1 -CSUn, CSD1 -CSDn. The switches SWU1-SWUn can connect the first current output terminal 806 to the corresponding current source according to the control signal Vctrl, thereby adjusting the magnitude of the current output by the input stage circuit 800 through the first current output terminal 806; and the switches SWD1-SWDn Then, according to the control signal Vctrl, the connection between the first current receiving end 810 and the corresponding current source can be turned on, so as to adjust the magnitude of the current received by the input stage circuit 800 through the first current receiving end 810 . Likewise, the second current-mode digital-to-analog converter 902 can also be implemented with the architecture shown in FIG. 11 . In this way, the control unit 904 can make Id1 equal to or close to Id2 and Id3 equal to or close to Id4 by outputting the control signal Vctrl, so that the influence caused by the offset voltage can be effectively compensated. Of course, the number of the current sources CSU1-CSUn, CSD1-CSDn can be adjusted according to the required accuracy, and the current generated by each current source can be set to be consistent or gradually decrease.

To sum up, the present invention compensates the influence caused by the offset voltage by adjusting the current between the input stage circuit and the output stage circuit in the operational amplifier. Therefore, without changing the input stage circuit and the output stage circuit, the present invention can compensate the influence caused by the offset voltage, thereby improving the circuit performance.

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

Claims (25)

1. but the operational amplifier of a compensating migration voltage includes:

One input stage circuit, include a positive input terminal, a negative input end, one first current output terminal and one second current output terminal, be used for the voltage that receives according to this positive input terminal and this negative input end, by this first current output terminal and the corresponding electric current of this second current output terminal output;

One output-stage circuit is coupled to this first current output terminal and this second current output terminal of this input stage circuit, is used for electric current according to this first current output terminal and this second current output terminal, output voltage; And

One adjusting device is coupled between this input stage circuit and this output-stage circuit, is used for adjusting the electric current of this first current output terminal and this second current output terminal, with the influence of compensating migration voltage.

2. operational amplifier as claimed in claim 1, wherein this input stage circuit includes:

One current source;

One the first transistor includes a drain electrode, is coupled to this first current output terminal, and one source pole is coupled to this current source, and a grid, is coupled to this positive input terminal; And

One transistor seconds includes a drain electrode, is coupled to this second current output terminal, and one source pole is coupled to this current source, and a grid, is coupled to this negative input end.

3. operational amplifier as claimed in claim 2, wherein this first transistor and this transistor seconds are all P type metal-oxide semiconductor transistor.

4. operational amplifier as claimed in claim 2, wherein this first transistor and this transistor seconds are all N type metal-oxide semiconductor transistor.

5. operational amplifier as claimed in claim 1, wherein this adjusting device includes:

One first current-mode digital to analog converter is coupled to this first current output terminal, is used for according to a controlling signal, by this output of first current output terminal or received current;

One second current-mode digital to analog converter is coupled to this second current output terminal, is used for according to this controlling signal, by this output of second current output terminal or received current; And

One control unit, be coupled to this first current-mode digital to analog converter and this second current-mode digital to analog converter, be used for difference between current according to this first current output terminal and this second current output terminal, export this controlling signal, to control the size of current that size of current that this first current-mode digital to analog converter exports or receive by this first current output terminal and this second current-mode digital to analog converter are exported or received by this second current output terminal.

6. operational amplifier as claimed in claim 5, wherein this first current-mode digital to analog converter includes:

A plurality of current sources; And

A plurality of switches, each switch includes one first end and is coupled to this first current output terminal, one second end is coupled to this control unit, and one the 3rd end is coupled to a current source of these a plurality of current sources, be used for this controlling signal of being received according to this second end, control of the binding of this first end to the 3rd end.

7. operational amplifier as claimed in claim 6, wherein the size of current exported of this a plurality of current source is all identical.

8. operational amplifier as claimed in claim 6, wherein the size of current exported of this a plurality of current source is step relation.

9. operational amplifier as claimed in claim 5, wherein this second current-mode digital to analog converter includes:

A plurality of current sources; And

A plurality of switches, each switch includes one first end and is coupled to this second current output terminal, one second end is coupled to this control unit, and one the 3rd end is coupled to a current source of these a plurality of current sources, be used for this controlling signal of being received according to this second end, control of the binding of this first end to the 3rd end.

10. operational amplifier as claimed in claim 9, wherein the size of current exported of this a plurality of current source is all identical.

11. operational amplifier as claimed in claim 9, wherein the size of current exported of this a plurality of current source is step relation.

12. but the track to track formula operational amplifier of a compensating migration voltage includes:

One input stage circuit, include a positive input terminal, a negative input end, one first current output terminal, one second current output terminal, one first electric current receiving terminal and one second electric current receiving terminal, be used for the voltage that receives according to this positive input terminal and this negative input end, by this first current output terminal and this second current output terminal output current, and by this first electric current receiving terminal and this second electric current receiving terminal received current;

One output-stage circuit, be coupled to this first current output terminal, this second current output terminal, this first electric current receiving terminal and this second electric current receiving terminal, be used for electric current according to this first current output terminal, this second current output terminal, this first electric current receiving terminal or this second electric current receiving terminal, produce corresponding voltage; And

One adjusting device, be coupled between this input stage circuit and this output-stage circuit, be used for adjusting the electric current that electric current that this first current output terminal or this second current output terminal export and this first electric current receiving terminal or this second electric current receiving terminal are received, with the influence of compensating migration voltage.

13. track to track formula operational amplifier as claimed in claim 12, wherein this input stage circuit includes:

One first current source;

One the first transistor includes a drain electrode, is coupled to this first current output terminal, and one source pole is coupled to this first current source, and a grid, is coupled to this positive input terminal;

One transistor seconds includes a drain electrode, is coupled to this second current output terminal, and one source pole is coupled to this first current source, and a grid, is coupled to this negative input end;

One second current source;

One the 3rd transistor includes a drain electrode, is coupled to this first electric current receiving terminal, and one source pole is coupled to this second current source, and a grid, is coupled to this positive input terminal; And

One the 4th transistor includes a drain electrode, is coupled to this second electric current receiving terminal, and one source pole is coupled to this second current source, and a grid, is coupled to this negative input end.

14. track to track formula operational amplifier as claimed in claim 13, wherein this first transistor and this transistor seconds are all P type metal-oxide semiconductor transistor, and the 3rd transistor AND gate the 4th transistor is all N type metal-oxide semiconductor transistor.

15. track to track formula operational amplifier as claimed in claim 12, wherein this adjusting device includes:

One first current-mode digital to analog converter is coupled between this first current output terminal and this first electric current receiving terminal, is used for according to a controlling signal, by this first current output terminal and output of this first electric current receiving terminal or received current;

One second current-mode digital to analog converter is coupled between this second current output terminal and this second electric current receiving terminal, is used for according to this controlling signal, by this second current output terminal and output of this second electric current receiving terminal or received current; And

One control unit, be coupled to this first current-mode digital to analog converter and this second current-mode digital to analog converter, be used for according to the difference between current of this first current output terminal and this second current output terminal and the difference between current of this first electric current receiving terminal and this second electric current receiving terminal, export this controlling signal, to control the size of current that size of current that this first current-mode digital to analog converter exports or receive by this first current output terminal and this first electric current receiving terminal and this second current-mode digital to analog converter are exported or received by this second current output terminal and this second electric current receiving terminal.

16. track to track formula operational amplifier as claimed in claim 15, wherein this first current-mode digital to analog converter includes:

A plurality of first current sources;

A plurality of first switches, each first switch includes one first end and is coupled to this first current output terminal, one second end is coupled to this control unit, and one the 3rd end is coupled to one first current source of these a plurality of first current sources, be used for this controlling signal of being received according to this second end, control of the binding of this first end to the 3rd end;

A plurality of second current sources;

A plurality of second switches, each second switch includes one first end and is coupled to this first electric current receiving terminal, one second end is coupled to this control unit, and one the 3rd end is coupled to one second current source of these a plurality of second current sources, be used for this controlling signal of being received according to this second end, control of the binding of this first end to the 3rd end.

17. track to track formula operational amplifier as claimed in claim 16, wherein the size of current exported of these a plurality of first current sources is all identical.

18. track to track formula operational amplifier as claimed in claim 16, wherein the size of current exported of these a plurality of first current sources is step relation.

19. track to track formula operational amplifier as claimed in claim 16, wherein the size of current exported of these a plurality of second current sources is all identical.

20. track to track formula operational amplifier as claimed in claim 16, wherein the size of current exported of these a plurality of second current sources is step relation.

21. track to track formula operational amplifier as claimed in claim 15, wherein this second current-mode digital to analog converter includes:

A plurality of first current sources;

A plurality of first switches, each first switch includes one first end and is coupled to this second current output terminal, one second end is coupled to this control unit, and one the 3rd end is coupled to one first current source of these a plurality of first current sources, be used for this controlling signal of being received according to this second end, control of the binding of this first end to the 3rd end;

A plurality of second current sources;

A plurality of second switches, each second switch includes one first end and is coupled to this second electric current receiving terminal, one second end is coupled to this control unit, and one the 3rd end is coupled to one second current source of these a plurality of second current sources, be used for this controlling signal of being received according to this second end, control of the binding of this first end to the 3rd end.

22. track to track formula operational amplifier as claimed in claim 21, wherein the size of current exported of these a plurality of first current sources is all identical.

23. track to track formula operational amplifier as claimed in claim 21, wherein the size of current exported of these a plurality of first current sources is step relation.

24. track to track formula operational amplifier as claimed in claim 21, wherein the size of current exported of these a plurality of second current sources is all identical.

25. track to track formula operational amplifier as claimed in claim 21, wherein the size of current exported of these a plurality of second current sources is step relation.

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