A superposition operation circuit and floating voltage digital-to-analog conversion circuit

Abstract

The present application provides a superposition operation circuit and a floating voltage digital-to-analog conversion circuit, which realizes the superposition of analog quantities by using the indirect current superposition principle. Among them, the negative phase input terminal and the output terminal of the first operational amplifier are connected, so that the first operational amplifier has the characteristics of a voltage follower, and its output terminal is embedded to the voltage inputted by the positive phase input terminal, that is, the analog quantity to be superimposed; then, the voltage signal is converted into a current signal by the current generating circuit, and the current signal generates a voltage drop on the first resistor connected to the output terminal of the first operational amplifier, and the voltage drop is superimposed with the voltage signal outputted by the first operational amplifier. It can be seen that the output operating point of the first operational amplifier in the superposition operation circuit is always fixed at the analog quantity to be superimposed, thereby ensuring the output accuracy of the operational amplifier; moreover, the high-precision current superposition amount is obtained by converting the voltage signal with low absolute accuracy, rather than being directly generated by the digital-to-analog conversion circuit, therefore, the input accuracy of the current generating circuit is relaxed, and then the requirements of the current generating circuit on power consumption and area are relaxed.

Description

Technical Field

[0001] The invention belongs to the field of electronic technology, and in particular relates to a superposition operation circuit and a floating voltage digital-to-analog conversion circuit. Background Art

[0002] In electronic control applications, in many cases, it is necessary to superimpose and adjust a certain analog quantity with another digital control analog quantity. The digital control analog quantity can be obtained through a digital analog converter (DAC). Figure 1 , showing a schematic diagram of the principle of superimposing analog quantity A and analog quantity B, such as Figure 1 As shown, after receiving the digital control signal, the DAC generates a corresponding analog quantity A, which is superimposed with the analog quantity B to be superimposed through a superposition operation circuit to obtain the signal C required in the final application, that is, C=A+B.

[0003] The superposition operation circuit is usually realized by an operational amplifier, and the digital control analog quantity can be a voltage type analog quantity or a current type analog quantity. Figure 2 to Figure 4 Introduce the superposition operation principle of the superimposed quantity and two different control analog quantities. Figure 2 A schematic diagram showing the principle of a traditional direct voltage superposition method is shown. Figure 3 Shows Figure 2 The equivalent schematic diagram of the operational amplifier in Figure 4 A schematic diagram showing the principle of a traditional indirect current superposition method.

[0004] like Figure 2 As shown, the analog quantity VDAC controlled by the digital control signal and the analog quantity VS to be superimposed are directly added by using a dual-input operational amplifier. The analog quantity VDAC is input into one pair of input terminals of the dual-input operational amplifier, and the positive phase of the other pair of input terminals is input into the superimposed quantity VS, and the negative phase is connected to the output terminal VO. Figure 3 As shown, the MOS tubes controlled by a pair of inputs V+ and V- of the operational amplifier can be equivalent to a voltage-controlled current source respectively. The output voltage is the voltage drop caused by the current generated by the controlled current source passing through the resistor. Therefore, the output of the dual-input operational amplifier is shown in Formula 1:

[0005] V O =[gm1×V DAC +gm2×(V S -V O )]×R (Formula 1)

[0006] In Formula 1, gm1 represents the gain of the MOS tube controlled by the first pair of input terminals, gm2 represents the gain of the MOS tube controlled by the second pair of input terminals, and R represents the resistance value of the equivalent resistor.

[0007] If formula 1 satisfies the linear requirement VO≈VDAC+VS, then gm1=gm2 must be satisfied. However, the gm of the actual device is related to the input voltage applied to the device. Obviously, in actual applications, VDAC and VS are not equal. The greater the difference between VDAC and VS, the greater the error between gm1 and gm2. Therefore, the actual output is less consistent with VO≈VDAC+VS. Excluding the inherent error of the inconsistency between VS and VDAC, when VDAC changes greatly, the input voltage also has a great impact on the state change of the MOS tube. The change of the MOS tube state will cause gm to change, which in turn leads to the nonlinear error of the superposition amount. It can be seen that the voltage superposition circuit is simple and has low power consumption, but the achievable absolute accuracy is low, at the mV level.

[0008] like Figure 4 As shown, the positive input terminal of the operational amplifier inputs the amount to be superimposed Vs, and the negative input terminal is connected to the output terminal, so that the output terminal V1 of the operational amplifier is fixed to Vs, and the output of the upper end of the resistor is the output of the entire superposition operation circuit VO = V1 + R × IDAC = VS + R × IDAC. In this superposition method, the output of the operational amplifier is always fixed at VS, and the operating point is fixed, so the output accuracy is relatively high, but the current accuracy requirements of the IDAC are very high. Providing a high-precision superposition operation circuit with low input signal accuracy requirements has become a technical problem that needs to be solved urgently. Summary of the invention

[0009] In view of this, the purpose of the present invention is to provide a superposition operation amplifier circuit and a floating voltage digital-to-analog conversion circuit, which can improve the accuracy of the superposition operation output signal and reduce the input signal accuracy requirement without increasing the power consumption of the superposition operation circuit.

[0010] In the first aspect, the present application provides a superposition operation circuit, comprising: a current generating circuit and a first operational amplifier; the current generating circuit comprises a first input terminal, a second input terminal and an output terminal, the first input terminal inputs a first voltage signal, the second input terminal inputs a second voltage signal, the current generating circuit is used to convert the first voltage signal into a first current signal, convert the second voltage signal into a second current signal, and output the current difference between the first current signal and the second current signal via the output terminal; the positive phase input terminal of the first operational amplifier inputs the analog quantity to be superimposed, the negative phase input terminal of the first operational amplifier is connected to the output terminal of the first operational amplifier, and the output terminal is connected to the output terminal of the current generating circuit through a first resistor, and the first operational amplifier is used to superimpose the analog quantity to be superimposed with the voltage drop on the first resistor.

[0011] In a first possible implementation of the first aspect, the current generating circuit includes a first voltage-current conversion circuit, a second voltage-current conversion circuit and a current replication circuit; the first voltage input terminal of the first voltage-current conversion circuit is input with the first voltage signal, and the first voltage-current conversion circuit is used to convert the first voltage signal into the first current signal and then output it through the first current output terminal; the second voltage input terminal of the second voltage-current conversion circuit is input with the second voltage signal, and the second voltage-current conversion circuit is used to convert the second voltage signal into the second current signal and then output it through the second current output terminal; the input terminal of the current replication circuit is connected to the second current output terminal, the output terminal of the current replication circuit is connected to the first current output terminal, and the current replication circuit is used to reverse the second current signal and superimpose it with the first current signal to obtain the current difference.

[0012] In a second possible implementation of the first aspect, the first voltage-current conversion circuit includes: a second operational amplifier, a first switch tube, a second switch tube, and a second resistor; the first voltage signal is input into the positive input terminal of the second operational amplifier, the output terminal of the second operational amplifier is connected to the control terminal of the first switch tube, and the output terminal of the first switch tube is the output terminal of the first voltage-current conversion circuit; the control terminal of the second switch tube is connected to the output terminal of the second operational amplifier, the output terminal of the second switch tube is connected to the negative input terminal of the second operational amplifier, and the input terminal of the second switch tube and the input terminal of the first switch tube are both connected to a power supply; the negative input terminal of the second operational amplifier is connected to the ground terminal through the second resistor.

[0013] In a third possible implementation of the first aspect, the second voltage-current conversion circuit includes: a third operational amplifier, a third switch tube, a fourth switch tube and a third resistor; the second voltage signal is input into the positive phase input terminal of the third operational amplifier, the output terminal of the third operational amplifier is connected to the control terminal of the third switch tube, the negative phase input terminal of the third operational amplifier is connected to the output terminal of the third switch tube, and the negative phase input terminal of the third switch tube is connected to the ground terminal through the third resistor; the control terminal of the fourth switch tube is connected to the output terminal of the third operational amplifier, the output terminal of the fourth switch tube is the output terminal of the second voltage-current conversion circuit, and the input terminals of the fourth switch tube and the third switch tube are connected to a power supply.

[0014] In a fourth possible implementation manner of the first aspect, the current replication circuit is a standard current mirror circuit composed of a fifth switch tube and a sixth switch tube; the control end of the fifth switch tube is connected to the control end of the sixth switch tube, the output end of the fifth switch tube and the output end of the sixth switch tube are both connected to the ground end, the input end of the fifth switch tube is connected to the control end of the fifth switch tube, the input end of the fifth switch tube is the input end of the current replication circuit, and the input end of the sixth switch tube is the output end of the current replication circuit.

[0015] In a fifth possible implementation of the first aspect, the current generating circuit also includes a common-mode resistor; the negative phase input terminal of the second operational amplifier is connected to the first end of the common-mode resistor through the second resistor, and the second end of the common-mode resistor is connected to the ground terminal; the negative phase input terminal of the third operational amplifier is connected to the first end of the common-mode resistor through the third resistor.

[0016] In a sixth possible implementation manner of the first aspect, the first switch tube and the second switch tube are both P-type metal-oxide-semiconductor MOS field effect tubes; or, the third switch tube and the fourth switch tube are both P-type MOS tubes.

[0017] In a seventh possible implementation manner of the first aspect, the fifth switch tube and the sixth switch tube are both N-type MOS tubes.

[0018] In a second aspect, the present application provides a floating voltage digital-to-analog conversion circuit, comprising a digital-to-analog conversion circuit and any one of the superposition operation circuits provided in the first aspect; a digital control signal is input into the input end of the digital-to-analog conversion circuit, a first output end of the digital-to-analog conversion circuit is connected to the first input end of the current generating circuit, a second output end of the digital-to-analog conversion circuit is connected to the second input end of the current generating circuit, and the digital-to-analog conversion circuit is used to convert the digital control signal into the first voltage signal and the second voltage signal and provide them to the current generating circuit in the superposition operation circuit.

[0019] The superposition operation circuit provided in this embodiment adopts the indirect current superposition principle to realize the superposition of analog quantities. Among them, the negative phase input terminal and the output terminal of the first operational amplifier are connected, so that the first operational amplifier has the characteristics of a voltage follower, and its output terminal is embedded to the voltage inputted by the positive phase input terminal, that is, the analog quantity to be superimposed; then, the voltage signal is converted into a current signal by the current generating circuit, and the current signal generates a voltage drop on the first resistor connected to the output terminal of the first operational amplifier, and the voltage drop is superimposed with the voltage signal outputted by the first operational amplifier. It can be seen that the output operating point of the first operational amplifier in the superposition operation circuit is always fixed at the analog quantity to be superimposed, thereby ensuring the output accuracy of the operational amplifier; moreover, the high-precision current superposition amount is obtained by converting the voltage signal with low absolute accuracy, rather than being directly generated by the digital-to-analog conversion circuit, therefore, the input accuracy of the current generating circuit is relaxed, and then the requirements of the current generating circuit on power consumption and area are relaxed. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a schematic diagram of the principle of analog quantity superposition;

[0022] Figure 2 This is a schematic diagram of the circuit principle of the traditional direct voltage superposition method;

[0023] Figure 3 It is the equivalent principle diagram of a dual-input operational amplifier;

[0024] Figure 4 It is a schematic diagram of the circuit principle of the traditional indirect current superposition method;

[0025] Figure 5 It is a schematic diagram of the principle of a superposition operation circuit according to an embodiment of the present application;

[0026] Figure 6 It is a schematic diagram of another principle of a superposition operation circuit according to an embodiment of the present application;

[0027] Figure 7 It is a schematic diagram of the principle of a floating voltage digital-to-analog conversion circuit according to an embodiment of the present application. DETAILED DESCRIPTION

[0028] Figure 2The direct voltage superposition method shown in the figure is limited by the parameters of the operational amplifier itself, and the absolute superposition accuracy that can be achieved is low, at the mV level; Figure 4 The indirect current superposition method shown can achieve high precision, but it faces the problem of high-precision current input. The present application provides a superposition operational amplifier circuit, which uses an indirect current superposition method in which the output operating point of the operational amplifier is always fixed to the input analog quantity to be superimposed, thereby ensuring the output accuracy of the operational amplifier. Moreover, the high-precision current superposition amount is obtained by the current generating circuit according to the input low absolute precision voltage signal conversion, rather than being directly generated by the digital-to-analog conversion circuit. Therefore, the input accuracy of the current generating circuit is relaxed, and then the requirements of the current generating circuit on power consumption and area are relaxed. Finally, a superposition operational circuit with high precision and low requirements on input signal accuracy is realized.

[0029] See also Figure 5 , shows a schematic diagram of the circuit principle of a superposition operation circuit in an embodiment of the present application, such as Figure 5 As shown, the superposition operation circuit includes an operational amplifier 1 (i.e., a first operational amplifier) ​​and a current generating circuit 100, wherein the current generating circuit 100 includes a first voltage-current conversion circuit 101, a second voltage-current conversion circuit 102 and a current replication circuit 103;

[0030] The analog quantity Vs to be superimposed is input to the positive input terminal of the operational amplifier 1, and the negative input terminal is connected to the output terminal. Meanwhile, the output terminal of the operational amplifier 1 is connected to the output terminal of the current generating circuit 100 through the resistor RD (ie, the first resistor).

[0031] The current generating circuit 100 includes two input terminals, wherein a voltage signal VDACA is input to one input terminal and a voltage signal VDACB is input to the other input terminal. The current generating circuit 100 is used to convert VDACA and VDACB into current signals respectively and output the difference between the two current signals via an output terminal.

[0032] The first voltage-to-current conversion circuit is used to convert VDACA into a corresponding current signal, and includes an operational amplifier 2, a switch tube Ma (i.e., a first switch tube), Mb (i.e., a second switch tube) and a resistor RA (i.e., a second resistor);

[0033] In one embodiment of the present application, Ma and Mb are PMOS tubes, the source of the PMOS tube is the input terminal, the drain is the output terminal, and the gate is the control terminal. In other embodiments of the present application, Ma and Mb can use other types of switch tubes. Of course, the corresponding circuit schematic diagram will be changed accordingly. Those skilled in the art can obtain the corresponding circuit schematic diagram of other types of switch tubes according to this embodiment without creative labor, and will not be repeated here.

[0034] The positive input terminal of the operational amplifier 2 serves as an input terminal of the current generating circuit, and is input with a voltage signal VDACA. The negative input terminal of the operational amplifier 2 is connected to the drain of Mb. At the same time, the negative input terminal is grounded through RA. The output terminal of the operational amplifier 2 is connected to the gates of Ma and Mb, and the drain of Ma is connected to the output terminal of the current copy circuit; the sources of Ma and Mb are connected to the power supply VDD.

[0035] The second voltage-to-current conversion circuit is used to convert VDACB into a corresponding current signal, and includes an operational amplifier 3 (i.e., the third operational amplifier), a switch tube Mc (i.e., the third switch tube), Md (i.e., the fourth switch tube), and a resistor RB (i.e., the third resistor). Mc and Md are PMOS tubes, and the source of the PMOS tube is the input terminal, the drain is the output terminal, and the gate is the control terminal.

[0036] The positive input terminal of the operational amplifier 3 serves as another input terminal of the current generating circuit, and is input with a voltage signal VDACB. The negative input terminal of the operational amplifier 3 is connected to the drain of Mc. At the same time, the negative input terminal is grounded through RB. The output terminal of the operational amplifier 3 is connected to the gates of Mc and Md. The sources of Mc and Md are connected to the power supply VDD. The drain of Md is connected to the input terminal of the current replication circuit.

[0037] The current replication circuit is used to reverse the current signal inputted at the input end, and its circuit structure is a standard current mirror circuit composed of a switch tube Me (i.e., the sixth switch tube) and Mf (i.e., the fifth switch tube). The drain of Me is the output end of the current mirror, the sources of Me and Mf are both connected to the ground end, the gates of Me and Mf are connected and connected to the drain of Mf, and the drain of Mf is the input end of the current mirror.

[0038] The following will be combined with the attached Figure 5 The circuit schematic diagram shown in the figure introduces the working process of the superposition operation circuit in detail:

[0039] Assuming the output of operational amplifier 1 to be V1 and the amplification factor to be A, the input-output relationship of operational amplifier 1 is V1=A(Vs-V1), that is, V1 / Vs=A / (1+A). Usually, when A is in the order of 1000 to 10000, V1=Vs, that is, the output of operational amplifier 1 changes with the input. In this way, the output of operational amplifier 1 is always fixed to Vs, thus improving the output accuracy.

[0040] The function of operational amplifier 1 is to superimpose the voltage signal output by itself with the voltage drop on resistor RD, wherein the voltage drop on RD is generated by the current output by the current generating circuit flowing through RD. If the current output by the current generating circuit is set to IO, the output voltage of operational amplifier 1 and the voltage drop on RD are superimposed at the VO terminal to obtain VO=Vs+RD*IO. It can be seen that operational amplifier 1 adopts an indirect current superposition method, but the current superposition amount is not directly generated by DAC, but is converted by the current generating circuit according to the voltage signal generated by DAC.

[0041] The output of operational amplifier 2 is connected to the gate of Mb to control the output current IB of Mb. The current IB flows through the resistor RA to generate a voltage that is fed back to the negative input of operational amplifier 2 to form a closed loop. According to the characteristics of the operational amplifier, under the premise of A>>1, the voltages at the positive and negative ends of operational amplifier 2 are equal, that is, VA=VDACA. Similarly, VB=VDACB.

[0042] The gate voltage and source voltage of Ma and Mb are the same, and the size of the two tubes is the same, so the current IA flowing through Ma is equal to the current IB flowing through Mb, that is, IA = IB; similarly, ID = IC. Among them, the current directions of IA, IB, IC and ID are as follows Figure 5 As shown in the direction of the arrow,

[0043] Me and Mf are a pair of simple standard current mirrors. The output current IE of Me is equal to the input current IF of Mf (IF = IE). The current directions of IE and IF are as follows: Figure 5 Indicated by the direction of the arrow.

[0044] Mf and Md are connected in series, so IF = ID, and because ID = IC, IF = IC. Therefore, the static current IO generated from Ma and Me and flowing to the resistor RD has a current direction from the upper end to the lower end of RD, so IO is the difference between IA and IE, that is, IO = IA-IE = IA-IF = IB-IC.

[0045] Under the premise of VA=VDACA, VB=VDACB, RA=RB=R, IB=VA / R, IC=VB / R, then the output current IO is as shown in formula 2:

[0046]

[0047] The final output of the superposition operation circuit is V O As shown in Formula 3:

[0048]

[0049] According to Formula 2 and Formula 3, we can know that by selecting a suitable R, adjusting (V A -V B ) range, the function of outputting the voltage superimposed on the output Vs can be realized. When V O That is equivalent to the VS superimposed voltage DAC output voltage (V DACA -V DACB )of The coefficient N relaxes the absolute accuracy limit of the voltage DAC, and a voltage DAC with a minimum accuracy of Err can be used to eventually produce a voltage superposition with a minimum equivalent accuracy of Err / N. The minimum current I_LSB of the current DAC equivalent to the voltage DAC after the superposition operation circuit is calculated is determined by the minimum V_LSB of the voltage DAC divided by R. There is no longer a matching and power consumption compromise between I_LSB and I_MSB as in the previous current DAC, so it can be as low as nA level.

[0050] The superposition operation circuit provided in this embodiment adopts an indirect current superposition method to always fix the output voltage of the superposition operation amplifier at the analog quantity to be superimposed, thereby improving the output accuracy of the superposition operation circuit. However, the high-precision superposition current is generated by the current generating circuit according to the low-precision voltage signal, not directly by the DAC, so the input accuracy of the current generating circuit is relaxed, and the requirements of the current generating circuit on power consumption and area are relaxed.

[0051] See also Figure 6 , shows a schematic diagram of another principle of a superposition operation circuit according to an embodiment of the present application, such as Figure 6 As shown, the superposition operation circuit provided in this embodiment is Figure 5 A common mode resistor RC is added to the superposition operation circuit shown, and both RA and RB are connected to the ground terminal through RC.

[0052] When VA = VDACA, VB = VDACB, RA = RB = RC = R, and the resistance of resistor RC is VC, the voltage at the connection end of RC, resistors RA and RB is VC, then IB and IC are as shown in Formula 4 and Formula 5:

[0053]

[0054]

[0055] Therefore, the output current IO of the current generating circuit is still as shown in Formula 2. It can be seen that after the common-mode resistor RC is introduced, IO does not change, but the absolute values ​​of IB and IC are reduced. Therefore, compared with the solution without the common-mode resistor, the common-mode resistor introduced reduces the absolute value of the operation current under the premise of unchanged output dynamic range, reduces the operation current power consumption, and further reduces the power consumption of the entire superposition operation circuit.

[0056] See also Figure 7 , shows a schematic diagram of the principle of a floating voltage DAC provided by an embodiment of the present application, wherein the floating voltage DAC Figure 5 or Figure 6 A DAC is added to the superposition operation circuit shown, and the voltage signal output by the DAC is provided to the superposition operation circuit for superposition operation, thereby realizing that the DAC outputs a floating voltage.

[0057] In a possible implementation of the present application, the voltage signals VDACA and VDACB input to the superposition operation circuit are respectively generated by the digital-to-analog conversion circuit DAC_A (i.e., the first digital-to-analog conversion circuit) and the digital-to-analog conversion circuit DAC_B (i.e., the second digital-to-analog conversion circuit) according to the digital control signal.

[0058] In another possible implementation of the present application, the voltage signal V DACA and V DACB It can be generated by the same digital-to-analog conversion circuit according to a digital control signal.

[0059] It can be seen from the technical content disclosed by the above-mentioned superposition operation circuit embodiment that in order to achieve voltage superposition with minimum accuracy Err / N, this embodiment does not directly generate a high-precision current with minimum accuracy Err / (NR) by the current DAC, but converts the voltage with minimum accuracy Err generated by the DAC into an equivalent current with minimum accuracy Err / (NR) for superposition through a current generating circuit, thereby relaxing the matching accuracy (i.e., chip area) and power consumption requirements.

[0060] It should be noted that each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other. For the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0061] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0062] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

[0063] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A superposition operation circuit, characterized in that: include: a current generating circuit and a first operational amplifier; The current generating circuit comprises a first voltage-current conversion circuit, a second voltage-current conversion circuit and a current replication circuit; A first voltage signal is input to a first voltage input terminal of the first voltage-to-current conversion circuit, and the first voltage-to-current conversion circuit is used to convert the first voltage signal into a first current signal, and then output the first current signal via a first current output terminal; A second voltage signal is input to a second voltage input terminal of the second voltage-to-current conversion circuit, and the second voltage-to-current conversion circuit is used to convert the second voltage signal into a second current signal and then output the second current signal via a second current output terminal; The input end of the current replication circuit is connected to the second current output end, the output end of the current replication circuit is connected to the first current output end, and the current replication circuit is used for superimposing the second current signal and the first current signal to obtain a current difference and then outputting it; The analog quantity to be superimposed is input to the positive phase input terminal of the first operational amplifier, the negative phase input terminal of the first operational amplifier is connected to the output terminal of the first operational amplifier, and the output terminal is connected to the output terminal of the current generating circuit through a first resistor, and the first operational amplifier is used to superimpose the analog quantity to be superimposed with the voltage drop on the first resistor. The current generating circuit further includes a common mode resistor, and the current generating circuit is connected to a ground terminal through the common mode resistor.

2. The superposition operation circuit according to claim 1, characterized in that: The resistance of the common mode resistor is greater than the resistance of the first resistor.

3. The superposition operation circuit according to claim 1, characterized in that: The first voltage-current conversion circuit includes: a second operational amplifier, a first switch tube, a second switch tube and a second resistor; The first voltage signal is input to the non-inverting input terminal of the second operational amplifier, the output terminal of the second operational amplifier is connected to the control terminal of the first switch tube, and the output terminal of the first switch tube is the output terminal of the first voltage-current conversion circuit; The control end of the second switch tube is connected to the output end of the second operational amplifier, the output end of the second switch tube is connected to the negative input end of the second operational amplifier, and the input end of the second switch tube and the input end of the first switch tube are both connected to a power supply; The negative phase input terminal of the second operational amplifier is connected to the ground terminal through the second resistor.

4. The superposition operation circuit according to claim 3, characterized in that: The second voltage-current conversion circuit includes: a third operational amplifier, a third switch tube, a fourth switch tube and a third resistor; The second voltage signal is input to the positive phase input terminal of the third operational amplifier, the output terminal of the third operational amplifier is connected to the control terminal of the third switch tube, the negative phase input terminal of the third operational amplifier is connected to the output terminal of the third switch tube, and the negative phase input terminal of the third operational amplifier is connected to the ground terminal through the third resistor; The control end of the fourth switch tube is connected to the output end of the third operational amplifier, the output end of the fourth switch tube is the output end of the second voltage-current conversion circuit, and the input ends of the fourth switch tube and the third switch tube are connected to a power supply.

5. The superposition operation circuit according to claim 1, characterized in that: The current replication circuit is a standard current mirror circuit composed of a fifth switch tube and a sixth switch tube; The control end of the fifth switch tube is connected to the control end of the sixth switch tube, the output end of the fifth switch tube and the output end of the sixth switch tube are both connected to the ground end, the input end of the fifth switch tube is connected to the control end of the fifth switch tube, the input end of the fifth switch tube is the input end of the current replication circuit, and the input end of the sixth switch tube is the output end of the current replication circuit.

6. The superposition operation circuit according to claim 4, characterized in that: The negative phase input terminal of the second operational amplifier is connected to the first end of the common mode resistor through the second resistor, and the second end of the common mode resistor is connected to the ground terminal. The negative phase input terminal of the third operational amplifier is connected to the first end of the common mode resistor through the third resistor.

7. The superposition operation circuit according to claim 6, characterized in that: The second resistor, the third resistor and the common mode resistor have equal resistance values.

8. The superposition operation circuit according to claim 6 or 7, characterized in that: The resistance values ​​of the second resistor, the third resistor and the common-mode resistor are all greater than the first resistor.

9. The superposition operation circuit according to claim 3, characterized in that: The first switch tube and the second switch tube are both P-type metal-oxide-semiconductor MOS field effect tubes.

10. The superposition operation circuit according to claim 4, characterized in that: The third switch tube and the fourth switch tube are both P-type MOS tubes.

11. The superposition operation circuit according to claim 5, characterized in that: The fifth switch tube and the sixth switch tube are both N-type MOS tubes.

12. A floating voltage digital-to-analog conversion circuit, characterized in that: It comprises a digital-to-analog conversion circuit and the superposition operation circuit according to any one of claims 1 to 11; A digital control signal is input to the input end of the digital-to-analog conversion circuit, a first output end of the digital-to-analog conversion circuit is connected to the first input end of the current generating circuit, a second output end of the digital-to-analog conversion circuit is connected to the second input end of the current generating circuit, and the digital-to-analog conversion circuit is used to convert the digital control signal into the first voltage signal and the second voltage signal and provide them to the current generating circuit in the superposition operation circuit.

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