阅读说明：本技术 消除电荷测试电路漏电流的电路及方法 (Circuit and method for eliminating leakage current of charge test circuit ) 是由 陆去疾 曹晨 刘亚国 于 2021-09-10 设计创作，主要内容包括：本发明涉及一种消除电荷测试电路漏电流的电路及方法,包括输入保护电路、运算放大电路、反馈电路、比例运算电路及数模转换电路,通过采样被测件的两次电荷量,算出漏电流的大小,从而计算出数模转换电路应该补偿的电压值,再将数模转换电路叠加补偿值输出,将失调电压抵消掉,从而消除漏电流。本发明的消除电荷测试电路漏电流的电路及方法,通过实时采样测试值,计算漏电流大小,调节DAC的大小改变测试电路输入端的电压,从而消除运放的输入失调电压以及输入偏置电流产生的漏电流,使得测试达到稳定准确的状态,保证了测试精度和测试效率。(The invention relates to a circuit and a method for eliminating leakage current of a charge test circuit, which comprises an input protection circuit, an operational amplifier circuit, a feedback circuit, a proportional operation circuit and a digital-to-analog conversion circuit, wherein the magnitude of the leakage current is calculated by sampling the charge amount of a tested piece twice, so that the voltage value which should be compensated by the digital-to-analog conversion circuit is calculated, then the digital-to-analog conversion circuit is superposed with the compensation value to be output, offset voltage is offset, and thus the leakage current is eliminated. According to the circuit and the method for eliminating the leakage current of the charge test circuit, the test value is sampled in real time, the size of the leakage current is calculated, the size of the DAC is adjusted, and the voltage of the input end of the test circuit is changed, so that the leakage current generated by the input offset voltage and the input bias current of the operational amplifier is eliminated, the test is stable and accurate, and the test precision and the test efficiency are guaranteed.)

1. A circuit for eliminating leakage current of a charge test circuit, comprising: the device comprises an input protection circuit, an operational amplification circuit, a feedback circuit, a proportional operation circuit and a digital-to-analog conversion circuit;

the input protection circuit comprises a protection tube consisting of two diodes, the input voltage is clamped, large voltage is prevented from being input instantly, and a post-stage circuit is protected;

the feedback circuit is connected with the input protection circuit and comprises a standard range capacitor for generating voltage;

the operational amplification circuit is respectively connected with the input protection circuit and the feedback circuit, comprises a plurality of operational amplifiers, resistors and capacitors, and can calculate a test value according to the voltage of the feedback circuit;

the digital-to-analog conversion circuit comprises a digital-to-analog converter and is used for outputting a voltage value;

the proportional operation circuit is respectively connected with the digital-to-analog conversion circuit and the operational amplification circuit, comprises a plurality of operational amplifiers and resistors and is used for outputting the compensation voltage output by the digital-to-analog converter after proportional operation.

2. The circuit of claim 1, wherein the digital-to-analog converter is a 16-bit digital-to-analog converter with a voltage output range of 0-5V.

3. A method of eliminating leakage current in a charge test circuit, using a circuit as claimed in claim 1 or 2, comprising the steps of: the charge quantity of the tested piece is marked as Q, the tested piece is connected to a test circuit, after passing through an input protection circuit, the charge of the tested piece flows through a standard range capacitor C1, the current of the tested piece is the same as that of the standard range capacitor C1, and the current is the integral of the current with respect to time according to the charge value, namely:

Q＝∫I dt

the charge quantity of the tested part is the same as that of the standard measuring range capacitor, and the formula is shown as follows:

Q＝C*U

the voltage on the sampling standard range capacitor is multiplied by the standard range capacitor to obtain the charge quantity;

in a time period, the two times of electric charge amount of the tested piece are sampled, the magnitude of leakage current is calculated according to the change values of the two times of electric charge amount, so that the voltage value which should be compensated by the digital-to-analog conversion circuit is calculated, then the digital-to-analog conversion circuit is superposed with the compensation value to output, offset voltage is offset, and the leakage current is eliminated.

The technical field is as follows:

the invention relates to the technical field of electronic measurement, in particular to a circuit and a method for eliminating leakage current of a charge test circuit, which can measure stable, accurate and stable charge quantity.

Background art:

at present, when the electric charge quantity of components is tested, analysis finds that the components in the circuit have individual difference, and theoretical states such as an integrated operational amplifier cannot exist, so that leakage current exists in the test circuit due to reasons such as component temperature drift and integrated operational amplifier offset voltage, the test electric charge is reduced, the test electric charge quantity is reduced along with the increase of test time, and the test value has deviation.

Therefore, a leakage current compensation circuit needs to be added to the charge test circuit, and the circuit is adjusted in real time by matching with a software algorithm, so that the leakage current is compensated, and the test is stable and accurate.

The invention content is as follows:

according to the invention, a digital-to-analog conversion (DAC) circuit is added in a common charge test circuit, the magnitude of leakage current is calculated by sampling a test value in real time, and the magnitude of the DAC is adjusted to change the voltage of the input end of the test circuit, so that the input offset voltage of the operational amplifier and the leakage current generated by input bias current are eliminated, and the test value is stable.

In order to solve the above technical problems, the present invention provides a circuit for eliminating leakage current of a charge test circuit, which includes an input protection circuit, an operational amplifier circuit, a feedback circuit, a proportional operational circuit, and a digital-to-analog conversion circuit.

The input protection circuit comprises a protection tube consisting of two diodes, the input voltage is clamped, large voltage is prevented from being input instantly, and a post-stage circuit is protected.

The feedback circuit is connected with the input protection circuit and comprises a standard range capacitor used for generating voltage.

The operational amplification circuit is respectively connected with the input protection circuit and the feedback circuit, comprises a plurality of operational amplifiers, resistors and capacitors, and can calculate a test value according to the voltage of the feedback circuit.

The digital-to-analog conversion circuit comprises a digital-to-analog converter and is used for outputting a voltage value.

The proportional operation circuit is respectively connected with the digital-to-analog conversion circuit and the operational amplification circuit, comprises a plurality of operational amplifiers and resistors and is used for outputting the compensation voltage output by the digital-to-analog converter after proportional operation.

The invention also provides a method for eliminating the leakage current of the charge test circuit, which adopts the circuit and comprises the following steps: the charge quantity of the tested piece is marked as Q, the tested piece is connected to a test circuit, after passing through an input protection circuit, the charge of the tested piece flows through a standard range capacitor C1, the current of the tested piece is the same as that of the standard range capacitor C1, and the current is the integral of the current with respect to time according to the charge value, namely:

Q＝∫I dt

the charge quantity of the tested part is the same as that of the standard measuring range capacitor, and the formula is shown as follows:

Q＝C*U

the voltage on the sampling standard range capacitor is multiplied by the standard range capacitor to obtain the charge quantity.

The invention obtains a primary charge quantity test value by an input protection circuit, a proportional operation circuit (integral operation circuit), a feedback circuit and an operational amplification circuit;

testing once again at the time of delta t to obtain a second charge quantity test value;

calculating the magnitude of leakage current generated on the input protection circuit D1 at the moment by a software algorithm according to the two electric charge quantity test values;

obtaining the voltage corresponding to the leakage current according to the calculated leakage current and the U-I curve of the input protection circuit, wherein the voltage is the total offset voltage and the negative compensation voltage;

the digital-to-analog conversion circuit superposes the compensation voltage on the original basic value, and the compensation voltage is output after passing through the proportional operation circuit, and can be offset with the original offset voltage at the moment, so that the two ends of the input protection circuit tend to be equal, and the leakage current tends to 0.

The invention can realize real-time negative feedback and continuous adjustment in the test process, so that the test value is stable and accurate. The circuit can be applied to charge quantity testing.

In a time period, the two times of electric charge amount of the tested piece are sampled, the magnitude of leakage current is calculated according to the change values of the two times of electric charge amount, so that the voltage value which should be compensated by the digital-to-analog conversion circuit is calculated, then the digital-to-analog conversion circuit is superposed with the compensation value to output, offset voltage is offset, and the leakage current is eliminated.

The invention has the beneficial effects that: according to the circuit and the method for eliminating the leakage current of the charge test circuit, the test value is sampled in real time, the size of the leakage current is calculated, the size of the DAC is adjusted, and the voltage of the input end of the test circuit is changed, so that the leakage current generated by the input offset voltage and the input bias current of the operational amplifier is eliminated, the test is stable and accurate, and the test precision and the test efficiency are guaranteed.

Description of the drawings:

FIG. 1 is a schematic block diagram of a circuit for eliminating leakage current of a charge test circuit according to the present invention;

FIG. 2 is a schematic circuit diagram of a circuit for eliminating leakage current of the charge test circuit according to the present invention;

FIG. 3 is a graph of a test of the present invention;

fig. 4 is a UI graph of the input protection circuit device of the present invention.

The specific implementation mode is as follows:

the following detailed description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings, will make the advantages and features of the invention more readily understood by those skilled in the art, and thus will more clearly and distinctly define the scope of the invention.

The circuit for eliminating the leakage current of the charge test circuit shown in fig. 1 includes an input protection circuit, an operational amplifier circuit, a feedback circuit, a proportional operation circuit and a digital-to-analog conversion circuit.

As shown in fig. 2, the input protection circuit includes: the protection tube D1 composed of two diodes clamps the input voltage, prevents the instantaneous input of large voltage and protects the post-stage circuit.

The operational amplifier circuit includes: the operational amplifier U1, the resistor R2, the resistors R3, U2, C2, U3, the resistor R9, the resistor R10 and the resistor R11 can calculate the test value according to a feedback circuit.

The feedback circuit includes: the standard range capacitor C1(R1 off, not used at this time).

The digital-to-analog conversion circuit includes: and a 16-bit digital-to-analog converter U4 for outputting a voltage value.

The proportional operation circuit includes: the operational amplifier U5, the resistor R4, the resistor R5, the operational amplifier U6, the resistor R6, the resistor R7 and the resistor R8 are used for carrying out proportional operation on the compensation voltage output by the 16-bit digital-to-analog converter U4 and then outputting the compensation voltage.

The method for measuring the amount of charge is as follows: the charge quantity of the tested piece is Q, the tested piece is connected to the test circuit, after passing through the input protection circuit, the charge of the tested piece flows through the standard range capacitor C1, the current of the tested piece is the same as that of the C1, and the charge value is the integral of the current with respect to time, namely:

Q＝∫I dt

the charge quantity of the tested part is the same as that of the standard measuring range capacitor, and the formula is shown as follows:

Q＝C*U

the voltage on the standard range capacitor is sampled, and the magnitude of the standard range capacitor is multiplied to obtain the charge quantity.

The working principle of the invention is as follows:

as shown in fig. 2, when the tested device is connected to the test circuit, Imeas enters the operational amplifier circuit, and passes through the input protection circuit D1, and then passes through the standard-range capacitors C1 and C1 of the feedback circuit to generate a voltage Uc, the charge amount of the tested device at this time is equal to the charge amount of the standard-range capacitor C1, according to the formula:

Q＝∫I dt＝C1*Uc

the operation amplifying circuit can obtain the value of the voltage Uc generated on the standard range capacitor C1, the standard range capacitor C1 is a known quantity, and the electric charge quantity can be calculated according to the formula.

In this ideal state, at this time, the 16-bit digital-to-analog converter DAC outputs 2.5V, and through the proportional operation circuit, the output terminal of the operational amplifier U6 outputs 0V voltage, the left side of the resistor R3 is also 0V, the resistor R3 is connected to the + terminal of the operational amplifier U2, which is also 0V, according to the characteristics of the virtual short virtual break of the input terminal of the operational amplifier, the-terminal and the + terminal of the operational amplifier U2 are both 0V, and according to the virtual short virtual break, the-terminal of the operational amplifier U2 has no current, i.e., the two terminals of R2 are 0V, the operational amplifier U1 is used as a follower, so that the-terminal and the + terminal of the operational amplifier U1 are both 0V (virtual short virtual break), and the ground (0V) is connected below the input protection circuit D1, so there is no current on the D1, and Imeas to be equal to the current flowing through the standard capacitor C1 of the measurement range.

However, offset voltages are inevitably generated at the + terminal and the-terminal of the operational amplifier U6, U2 and U1, so that the terminal voltage of the operational amplifier U6-terminal is Uu6 ≈ 0 (not equal to 0), then the terminal voltage of the operational amplifier U2-terminal is Uu2 ≈ 0 (not equal to 0) through the operational amplifier U2, and then the terminal voltage of the operational amplifier U1+ Uu1 ≈ 0 (not equal to 0) through the U1. At this time, the upper end of the D1 is connected to the U1+ end of the operational amplifier, the voltage is Uu6+ Uu2+ Uu1, and the lower end of the D1 is 0V, so that a voltage drop occurs, and at this time, a current Id, that is, a leakage current, is generated on the protective tube D1, so that Imeas becomes Imeas. When there is leakage current, the current is reduced, so that the charge value is floated down.

To solve the problem, an algorithm is needed to calculate, two times of electric charge amount are sampled in a time period, the magnitude of leakage current is calculated according to the change values of the two times of electric charge amount, so that the voltage value which should be compensated by the digital-to-analog conversion circuit is calculated, then the analog-to-analog conversion circuit is superposed with the compensation value to output, offset voltage and the like are offset, and therefore the leakage current is eliminated.

As shown in fig. 3:

	test point 1	Test point 2	Interval value
				Test value	Q1	Q2	ΔQ＝Q2–Q1
Time	t1	t2	Δt＝t2–t1

Q1 and Q2 are sampled at times t1 and t2, wherein the values are Q2-Q1 and t 2-t 1.

By the formula:

ΔQ＝∫I dt＝0.5*I*Δt

it can be found that:

I＝(2*ΔQ)/Δt

since Δ Q and Δ t are known, the magnitude of the leakage current can be calculated.

At this time, it is known that the current flowing through the input protection D1 is the leakage current value, and D1 is a diode device, so according to the U-I curve of the device (as shown in fig. 4, this is a positive half cycle waveform, and the negative half cycle is the same, and will not be described again), the voltage corresponding to D1 at this time, that is, the compensation voltage Udac of this test, can be obtained.

The output range of the 16-bit DAC is 0-5V, the default output is 2.5V, after the compensation voltage is obtained, the output of the DAC is adjusted to be (2.5-Udac) in time, Q is sampled twice every delta t (fixed) in a test to obtain the current compensation voltage value, and negative feedback adjustment is continuously carried out, so that the test value can be stable and accurate.

While particular embodiments of the present invention have been described in the foregoing specification, the various illustrations do not limit the spirit of the invention, and one of ordinary skill in the art, after reading the description, can make modifications and alterations to the particular embodiments described above without departing from the spirit and scope of the invention.