CN114624500B

CN114624500B - pA-level weak current precise measurement system

Info

Publication number: CN114624500B
Application number: CN202210415557.6A
Authority: CN
Inventors: 宋丽
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2022-04-20
Filing date: 2022-04-20
Publication date: 2023-05-05
Anticipated expiration: 2042-04-20
Also published as: CN114624500A

Abstract

The invention discloses a pA-level weak current precise measurement system which comprises a data acquisition card, a BNC box, an isolation adapter, a low-temperature system and an ammeter, wherein the output end of the data acquisition card comprises two paths, the first path of output end of the data acquisition card and the second path of output end of the data acquisition card are respectively connected with one path of input end of the isolation adapter through the BNC box, one path of output end of the isolation adapter is respectively connected with the low-temperature system to provide a driving signal of gate voltage and drain bias voltage for the low-temperature system, the other path of input end of the isolation adapter is connected with the low-temperature system to receive sound and electricity current provided by the low-temperature system, the other path of output end of the isolation adapter is connected with the ammeter to provide sound and electricity current for the ammeter, and the low-temperature system is used for forming sound and electricity current. The invention provides proper measuring range and stepping gate voltage and source drain bias voltage for the device, eliminates common ground interference and reduces noise floor.

Description

pA-level weak current precise measurement system

Technical Field

The invention relates to the field of pA-magnitude weak current measurement, in particular to a pA-magnitude weak current precise measurement system.

Background

In 1996, shilton et al, university of Cambridge, caladesh laboratory, developed the first gigahertz surface acoustic wave single electron transport (SAW/SET) device using the piezoelectric and split gate technologies of GaAs, enabling the handling of single electrons by Surface Acoustic Waves (SAW), resulting for the first time in a pA-level quantized current: i=nef, where n is a positive integer and f is the microwave frequency with an accuracy of 10 ^-15 The magnitude, e, is the electron charge. Thus, it is possible to establish a quantum reference based on a substantially physical constant using the surface acoustic wave single electron effect. In the experiment, at f=1 GHz, the current signal at the first step of the quantized bioelectric current plateau is about 160 pA. How to measure such weak current signals becomes a key factor for successful experiments.

Disclosure of Invention

Aiming at the problems, the invention provides a pA-magnitude weak current precise measurement system.

The invention is realized by the following technical scheme:

the utility model provides a pA-level weak current's precision measurement system, includes data acquisition card, BNC box, keeps apart adapter, low temperature system and ampere meter, the output of data acquisition card includes two way, the first way output of data acquisition card and the second way output of data acquisition card are respectively through the one way input of BNC box connection isolation adapter, the one way output of keep apart the adapter is through connecting low temperature system, provides the drive signal of gate voltage and drain source offset voltage respectively to low temperature system, the other way input of keep apart the adapter is through connecting low temperature system, and the sound electric current that the low temperature system provided is received to the other way input of keep apart the adapter is through connecting the ampere meter, low temperature system is used for forming sound electric current.

Further, the low-temperature system comprises an interdigital transducer and a surface acoustic wave single-electron transport device, the surface acoustic wave single-electron transport device comprises 6 pins, a drain-source bias voltage output end of the isolation adapter is connected with a source end pin, a gate voltage output end of the isolation adapter is respectively connected with two gate voltage pins, and a current signal input end of the isolation adapter is connected with a measuring end pin.

Furthermore, the input end of the interdigital transducer is connected with the terminal through a microwave signal generator, and the output end of the interdigital transducer outputs the surface acoustic wave for driving the surface acoustic wave single-electron transport device.

Further, the isolation adapter comprises an isolation attenuation superposition circuit, a chip power supply circuit and a power supply voltage indicating circuit, the isolation attenuation superposition circuit comprises a first isolator, a second isolator, resistors R1, R2 and R3 and a summation operation superposition circuit, the input end of the first isolator and the input end of the second isolator are respectively connected with two paths of input voltages, the output end of the first isolator comprises two paths, one path of the output end is connected with one path of the input end of the summation operation superposition circuit, the other path of the output end is connected with the input end of the filter circuit, the output end of the second isolator is connected with R1, the output end of the R1 comprises two paths, one path of the output end is grounded through R2, the other path of the output end of the summation operation superposition circuit is grounded through R3, the output end of the summation operation superposition circuit is connected with the input end of the filter circuit, and the filter circuit is used for outputting filtered gate voltage and drain-source bias voltage.

Furthermore, the isolation attenuation superposition circuit is also respectively connected with a gate voltage isolation attenuation superposition circuit and a drain-source bias voltage isolation attenuation superposition circuit, the gate voltage isolation attenuation superposition circuit is connected with a gate voltage output end of the isolation attenuation superposition circuit, and the drain-source bias voltage isolation attenuation superposition circuit is connected with a drain-source bias voltage output end of the isolation attenuation circuit.

Further, the gate voltage isolation attenuation superposition circuit comprises an isolation attenuation module, the isolation attenuation module comprises an isolation amplifier IC15, an IC16 and resistors R45, R46, R56 and R57, the isolation attenuation module comprises two paths of input ends, one path of input end J7 is attenuated by connecting the R45 and the R56 and then isolated by the IC15, a 38 pin of the IC15 is connected with an output end Uout1, a 37 pin of the IC15 is grounded, the other path of input end is attenuated by the R46 and the R56 and then isolated by the IC16, a 38 pin of the IC16 is connected with an output end Uout2 and a 37 pin of the IC16 is grounded, and the isolation amplifier adopts an AD202 chip with an input range of +/-5V.

Further, the gate voltage isolation attenuation superposition circuit comprises a superposition module, the superposition module comprises an operational amplifier IC10, resistors RV8, RV10, R60, R61 and a reverse proportion operation circuit, the superposition module comprises two paths of input ends Uout1 and Uout2, the Uout1 is connected with the RV8 for gain error adjustment, the Uout2 is connected with the RV10 for gain error adjustment, and then the R60 and the R61 are used for voltage division, the R60, the R61 and the RV8 are connected with the reverse proportion operation circuit for superposition and then reverse phase, the reverse proportion operation circuit is connected with the IC10, the 6 pins of the IC10 are connected with the output ends, and the operational amplifier adopts an OP07 chip.

Further, the drain-source bias voltage isolation attenuation superposition circuit comprises an emitter tracker, a T-shaped resistor network, resistors RV7 and RV9, wherein the input end of the drain-source bias voltage isolation attenuation superposition circuit is matched with resistance through the emitter tracker, superposition attenuation is carried out through the T-shaped resistor network, and the RV7 and the RV9 are arranged on a circuit connected with the emitter tracker and the T-shaped resistor network and used for carrying out error fine adjustment on attenuation multiples.

Further, the isolation adapter further comprises a switch selection circuit, wherein the switch selection circuit is connected with the plurality of the surface acoustic wave single-electron transport devices and is used for independently controlling the grid voltage of the split gate of the surface acoustic wave single-electron transport devices.

The invention has the beneficial effects that:

(1) The invention eliminates common ground interference by utilizing voltage isolation, attenuation and superposition circuits, reduces noise floor, and meets the range and stepping requirements of voltage during device measurement;

(2) The invention provides gear selection for data acquisition by utilizing the switch selection circuit thereof

(3) The invention combines commercial electronic elements to build a weak current measurement system, the measurement precision of the system reaches pA level, and the noise floor is only 0.2 pA.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, it will be apparent that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of a measurement system of a pA-magnitude weak current precision measurement system according to an embodiment of the present invention;

FIG. 2 is a schematic circuit diagram of an isolated adapter according to an embodiment of the present invention;

fig. 3 is a schematic circuit diagram of an isolation attenuation module of a gate voltage isolation attenuation superposition circuit according to an embodiment of the present invention;

fig. 4 is a schematic circuit diagram of a superposition module of a gate voltage isolation attenuation superposition circuit according to an embodiment of the present invention;

fig. 5 is a schematic circuit diagram of a source-drain bias voltage isolation attenuation superposition circuit according to an embodiment of the present invention;

fig. 6 is a schematic circuit diagram of a switch selection circuit according to an embodiment of the present invention;

fig. 7 is a flow chart of a conventional grounding method according to an embodiment of the present invention;

fig. 8 is a flowchart of a method for a terminal device of an improved grounding method according to an embodiment of the present invention;

fig. 9 is a schematic structural diagram of a terminal device of a pA-level weak current precision measurement system according to an embodiment of the present invention.

Detailed Description

For the purpose of making apparent the objects, technical solutions and advantages of the present invention, the present invention will be further described in detail with reference to the following examples and the accompanying drawings, wherein the exemplary embodiments of the present invention and the descriptions thereof are for illustrating the present invention only and are not to be construed as limiting the present invention.

Example 1

As shown in fig. 1, this embodiment provides a precision measurement system of pA magnitude weak current, including data acquisition card, BNC box, isolation adapter, low temperature system and ampere meter, the output of data acquisition card includes two ways, the first way output of data acquisition card and the second way output of data acquisition card are respectively through the one way input of BNC box connection isolation adapter, the one way output of isolation adapter is through connecting low temperature system, provides the drive signal of gate voltage and drain bias voltage to low temperature system respectively, the other way input of isolation adapter is through connecting low temperature system, receives the acoustoelectric current that low temperature system provided, the other way output of isolation adapter is through connecting the ampere meter, low temperature system is used for forming the acoustoelectric current to the ampere meter.

Furthermore, the input end of the interdigital transducer is connected with the terminal through a microwave signal generator, and the output end of the interdigital transducer drives the surface acoustic wave of the surface acoustic wave single-electron transport device.

Further, the gate voltage isolation attenuation superposition circuit comprises an isolation attenuation module, the isolation attenuation module comprises an isolation amplifier IC15, an IC16 and resistors R45, R46, R56 and R57, the isolation attenuation module comprises two paths of input ends J7 and J8, the J7 is attenuated by connecting the R45 and the R56 and then isolated by the IC15, the 38 pin of the IC15 is connected with the output end Uout1, the 37 pin of the IC15 is grounded, the J8 is attenuated by the R46 and the R56 and then isolated by the IC16, the 38 pin of the IC16 is connected with the output end Uout2 and the 37 pin of the IC16 is grounded, and the isolation amplifier adopts an AD202 chip with an input range of +/-5V.

Further, the gate voltage isolation attenuation superposition circuit further comprises a superposition module, the superposition module comprises an operational amplifier IC10, resistors RV8, RV10, R60, R61 and a reverse proportion operation circuit, the superposition module comprises two paths of input ends Uout1 and Uout2, the Uout1 is connected with the RV8 to carry out gain error adjustment, the Uout2 is connected with the RV10 to carry out gain error adjustment, then the R60 and the R61 are connected to carry out voltage division, the R60, the R61 and the RV8 are connected with the reverse proportion operation circuit to carry out superposition and then reverse phase, the reverse proportion operation circuit is connected with the IC10, the 6 pins of the IC10 are connected with the output end, and the operational amplifier adopts an OP07 chip.

Further, the isolation adapter further comprises a switch selection circuit, wherein the switch selection circuit is connected with the surface acoustic wave single-electron transport device and is used for independently controlling the grid voltage of the split gate of the surface acoustic wave single-electron transport device.

The specific implementation principle flow of the embodiment is as follows:

in the surface acoustic wave single electron transport experiment, the signal to be measured is a weak current signal of pA magnitude. Therefore, a high-precision measurement system and a proper measurement scheme are key to the success of the experiment. As shown in FIG. 1, the NI 6289 data acquisition card outputs two voltage signals, enters the self-made isolation adapter through the BNC box, outputs voltage signals meeting measurement requirements, and provides driving of gate voltage and source-drain bias voltage for the device. In the figure, the device interface 6 is used as a source terminal; interface 1 is used as a measuring end; the

interfaces

2, 5 apply a gate voltage. Agilent 8648D is a microwave signal generator that outputs microwave signals to an interdigital transducer (IDT), excites surface acoustic waves, and carries electrons through a quasi-one-dimensional quantum channel to form an acoustic-electric current. The current signal passes through the device interface 1 and enters a Keithley 6430 high-precision ammeter to be measured.

The beneficial effects of this embodiment are:

1. providing a proper range and stepping gate voltage and source-drain bias voltage for the device, eliminating common-ground interference and reducing noise floor;

2. providing more gear options for device data acquisition, such as: when three pairs of split gate devices are measured, the gate voltages of each pair of split gates of the devices can be controlled respectively by using the switch selection circuit of the isolation adapter.

Example 2

Based on embodiment 1, this embodiment further proposes an operation principle of the isolation adapter, where the NI 6289 data acquisition card outputs two voltage signals, and the two voltage signals enter the isolation adapter through the BNC box, where half of the voltage is divided by the resistor, and then the voltage is input into the isolator, and then one of the voltage is divided by the resistor, attenuated by 500 times, and then is overlapped with the other voltage to obtain the gate voltage and the source-drain bias voltage. The voltage signal is also passed through a set of filter circuits before being output by the output terminal. This is because the device is provided with a microwave signal which will cause high frequency interference to the measurement loop, and the set of filter circuits is used to prevent the high frequency interference from affecting the operation of the attenuation superposition circuit.

Furthermore, in order to avoid the interference of commercial power, the isolation adapter is powered by an external nickel-hydrogen rechargeable battery, and a chip power supply circuit and a power supply voltage indicating circuit are arranged on the circuit board besides the isolation attenuation superposition circuit. The chip power supply circuit can generate three voltages of +15V, +7.5V and-7.5V to supply the chip. The power supply voltage indicating circuit ensures that when the voltage of the battery is reduced to below 18V, the light emitting diode turns from green to red, and meanwhile, the buzzer alarms to remind the replacement of the battery. A group of batteries can continuously work for more than 12 hours. The housing of the isolating adapter is made of aluminum plate and has good shielding function.

Example 3

On the basis of embodiment 1, this embodiment further proposes a gate voltage attenuation and superposition circuit, where J7 and J8 are two input ends of the attenuation and superposition circuit in fig. 2 and 3, and are directly connected to a voltage source through a wire. The input voltage is attenuated by half after being divided by the resistors R45, R56, R46 and R57 respectively, then is isolated by the isolation amplifier, and is output at the pins 38 of the IC15 and the IC16, and the output voltage is half of the J7 and J8. IC15 and IC16 are isolation amplifiers that primarily function to cancel common ground disturbances in the circuit because the ground line in the circuit has a resistance and when disturbances are present on the ground line, a common ground loop is formed that produces a deleterious noise voltage in the circuit. The isolation amplifier additionally arranged in the circuit can ensure that the voltages of the input end and the output end of the circuit are consistent, but the circuits of the input end and the output end are mutually independent, thereby cutting off a common ground loop and avoiding common ground interference.

Furthermore, the isolation amplifier adopts an AD202 chip, and the model is a transformer coupling and micro-packaging precision isolation amplifier. Through the coupling of the on-chip transformer, the input and the output of the signals are electrically isolated, and the method has the characteristics of high precision, low power consumption, good common mode performance, small volume, low price and the like. In the input circuit, the on-chip independent amplifier can act as a buffer or amplification of the input signal. The amplified signal is modulated by a modulator and converted into a carrier signal, which is fed via a transformer to a synchronous demodulator so that the signal is reproduced at the output. And the demodulation signal is filtered by a third-order filter, so that noise and ripple in the input signal are minimized, and a good excitation source is provided for a later-stage application circuit. Since the input range of the AD202 is ±5v and the output range of the voltage source is ±10v, half of the voltage is divided by the resistor at the input terminal, and then the AD202 is input. In addition, RV4 and RV5 are used in the circuit to adjust the zero of the output.

Further, as shown in fig. 4, the voltage signals are output Uout1 and Uout2 after passing through the isolation amplifier, one path is connected with RV8, the other path is connected with RV10, and then R60 and R61 (divided by 500 times). RV8 and RV10 are used to adjust the gain error. Plus half the attenuation before isolating the amplifier, the two paths attenuate 1/2 and 1/1000 in total. After attenuation, the two paths of voltages are overlapped by an inverting proportion operation circuit (composed of IC12, R48, R59 and R58) and then are inverted, and the voltage is output at the 6 pin of IC 10. At this point, the 6 pin output voltage of IC10 is isolated, attenuated and superimposed, ranging + -5V, with a minimum step up to 0.3 μV. The operational amplifier required by the emitter tracker and the operational circuit adopts an OP07 chip, and has the characteristics of extremely low input offset voltage, extremely low offset voltage temperature drift, extremely low input noise amplitude, long-term stability and the like.

Example 4

On the basis of embodiment 1, this embodiment further proposes a source-drain bias voltage attenuation and superposition circuit, in which the signal is attenuated by half and then isolated, and then the signal is subjected to emitter tracker (IC 9 and IC 11) to match impedance, and then the attenuation and superposition is directly performed by using the T-shaped resistor network shown in fig. 5. One path through IC11 is attenuated by 1/5000, one path through IC9 is attenuated by 1/500, and the total attenuation is 1/10000 and 1/1000, which is the half of the attenuation before isolation. RV7 and RV9 allow for error fine tuning of the attenuation factor.

Example 5

On the basis of embodiment 1, this embodiment further proposes a switch selection circuit, in which, as shown in fig. 6, the case of plural pairs of gate voltages is the same, and only one pair is shown. Six wires from the device, 1, 3, 4, 6, lead from the source drain pad of the device, and 2, 5 lead from the gate voltage pad of the device (see fig. 1). 1. 3, 4 and 6 are respectively divided into two branches after entering the adapter, and are respectively connected with two single-pole multi-throw switches. The common end of the two switches is respectively connected with the input end of the Keithley 6430 ammeter and the source-drain bias voltage output end on the circuit board. The source drain bias voltage is shown as 6 pins, and the input end of the ammeter is connected with 1 pin. 2. The 5-pin wires are respectively connected to two common ends of a double-pole multi-throw switch. The peripheral ports are respectively connected with gate voltageVg. GND, and a floating end. When the switch is shifted clockwise from left to right, the wiring condition is as follows: first gear, 2-foot connectionVg,5 pin is grounded, at this moment, the bias voltage of source drain is not added, can measure 2 pin and pass the leakage current of the quasi-one-dimensional electronic channel of the device slot; second gear, 5 foot connectionVg, 2 pins are grounded, and leakage current from 2 pins to the quasi-one-dimensional electronic channel can be measured. Third, the 2 and 5 pins are connected with Vg, and the total leakage current from the 2 and 5 pins to the quasi-one-dimensional electronic channel can be measured. Then, the source-drain bias voltage is added, so that the clamping curve of the device can be measured; the acoustoelectric current can be measured by microwave. Fourth gear is the floating end. When the device works, the six grounding switches are all disconnected. When the device is not in operation, the grounding switch is closed to enable all six bonding pads to be grounded.

Example 6

On the basis of embodiment 1, this embodiment further proposes the grounding of the circuit system, wherein, as shown in fig. 7, the grounding method (a) adopts series single-point grounding, that is, the grounding of all devices is connected to the same grounding point, and then is connected to the signal ground through the grounding point. The common ground point of the measurement system is the ground point on the cabinet, and the isolating adapter, the low-temperature system is grounded through the cabinet. Due to the influence on the ground distributed capacitance, a parallel resonance phenomenon can be generated, the impedance of the ground wire is greatly increased, and common impedance coupling interference is generated, so that the measurement accuracy is influenced. When the grounding method is adopted, the noise fluctuation of the measuring system reaches 8 pA, and the measuring requirement is obviously not met. Therefore, we will isolate the adapter, the cryogenic system directly to signal ground, and not through cabinet ground. Thus, the common impedance coupling interference is eliminated, the measurement precision of the system is greatly improved, and when the grounding method shown in fig. 8 is adopted, the noise fluctuation of the measurement system is greatly reduced, the peak-to-peak value is 0.2 pA, and the measurement requirement of the system can be met.

Example 3

As shown in fig. 9, based on embodiment 1, this embodiment proposes a terminal device for precision measurement of pA class weak current, where the terminal device 200 includes at least one memory 210, at least one processor 220, and a bus 230 connecting different platform systems.

Memory 210 may include readable media in the form of volatile memory, such as Random Access Memory (RAM) 211 and/or cache memory 212, and may further include Read Only Memory (ROM) 213.

The memory 210 further stores a computer program, and the computer program may be executed by the processor 220, so that the processor 220 executes any one of the above-mentioned pA-level weak current precision measurement methods in the embodiments of the present application, and a specific implementation manner of the method is consistent with an implementation manner and an achieved technical effect described in the embodiments of the method, and some contents are not repeated. Memory 210 may also include a program/utility 214 having a set (at least one) of program modules 215 including, but not limited to: an operating system, one or more application programs, other program modules, and program data, each or some combination of which may include an implementation of a network environment.

Accordingly, the processor 220 may execute the computer programs described above, as well as the program/utility 214.

Bus 230 may be a local bus representing one or more of several types of bus structures including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, a processor, or using any of a variety of bus architectures.

Terminal device 200 can also communicate with one or more external devices 240, such as a keyboard, pointing device, bluetooth device, etc., as well as one or more devices capable of interacting with the terminal device 200, and/or with any device (e.g., router, modem, etc.) that enables the terminal device 200 to communicate with one or more other computing devices. Such communication may occur through an input/output (I/O) interface 250. Also, terminal device 200 can communicate with one or more networks such as a Local Area Network (LAN), a Wide Area Network (WAN) and/or a public network, such as the Internet, through network adapter 260. Network adapter 260 may communicate with other modules of terminal device 200 via bus 230. It should be appreciated that although not shown, other hardware and/or software modules may be used in connection with terminal device 200, including, but not limited to: microcode, device drivers, redundant processors, external disk drive arrays, RAID systems, tape drives, data backup storage platforms, and the like.

Claims

1. The precise measurement system for pA-level weak current is characterized by comprising a data acquisition card, a BNC box, an isolation adapter, a low-temperature system and an ammeter, wherein the output end of the data acquisition card comprises two paths, the first path of output end of the data acquisition card and the second path of output end of the data acquisition card are respectively connected with one path of input end of the isolation adapter through the BNC box, one path of output end of the isolation adapter is respectively connected with the low-temperature system to provide a driving signal of gate voltage and drain bias voltage for the low-temperature system, the other path of input end of the isolation adapter is connected with the low-temperature system to receive sound and electricity current provided by the low-temperature system, the other path of output end of the isolation adapter is connected with the ammeter to provide sound and electricity current for the ammeter, and the low-temperature system is used for forming sound and electricity current; the low-temperature system comprises an interdigital transducer and a surface acoustic wave single-electron transport device, wherein the surface acoustic wave single-electron transport device comprises 6 pins, a drain-source bias voltage output end of the isolation adapter is connected with a source end pin, a gate voltage output end of the isolation adapter is respectively connected with two gate voltage pins, and a current signal input end of the isolation adapter is connected with a measuring end pin;

the isolation adapter comprises an isolation attenuation superposition circuit, a chip power supply circuit and a power supply voltage indication circuit, wherein the isolation attenuation superposition circuit comprises a first isolator, a second isolator, resistors R1, R2 and R3 and a summation operation superposition circuit, the input end of the first isolator and the input end of the second isolator are respectively connected with two paths of input voltages, the output end of the first isolator comprises two paths, one path of the output end is connected with one path of input end of the summation operation superposition circuit, the other path of output end is connected with the input end of the filter circuit, the output end of the second isolator is connected with R1, the output end of the R1 comprises two paths, one path of output end is grounded through R2, the other path of output end of the summation operation superposition circuit is grounded through R3, the output end of the summation operation superposition circuit is connected with the input end of the filter circuit, and the filter circuit is used for outputting filtered gate voltage and drain source bias voltage;

the isolation attenuation superposition circuit is also respectively connected with a gate voltage isolation attenuation superposition circuit and a drain-source bias voltage isolation attenuation superposition circuit, the gate voltage isolation attenuation superposition circuit is connected with a gate voltage output end of the isolation attenuation superposition circuit, and the drain-source bias voltage isolation attenuation superposition circuit is connected with a drain-source bias voltage output end of the isolation attenuation circuit;

the isolation adapter further comprises a switch selection circuit, wherein the switch selection circuit is connected with the surface acoustic wave single-electron transport devices, and the switch selection circuit is used for independently controlling the grid voltage of the split gate of the surface acoustic wave single-electron transport devices.

2. The precision measurement system of pA-level weak current according to claim 1, wherein the input end of the interdigital transducer is connected with a terminal through a microwave signal generator, and the output end of the interdigital transducer outputs a surface acoustic wave for driving a surface acoustic wave single-electron transport device.

3. The precision measurement system of pA-level weak current according to claim 1, wherein the gate voltage isolation attenuation superposition circuit comprises an isolation attenuation module, the isolation attenuation module comprises an isolation amplifier IC15, an IC16 and resistors R45, R46, R56 and R57, the isolation attenuation module comprises two input ends, one input end is attenuated by connecting R45 and R56 and then isolated by the IC15, a pin 38 of the IC15 is connected with an output end Uout1, a pin 37 of the IC15 is grounded, the other input end is attenuated by R46 and R56 and then isolated by the IC16, a pin 38 of the IC16 is connected with an output end Uout2, a pin 37 of the IC16 is grounded, and the isolation amplifier adopts an AD202 chip with an input range of +/-5V.

4. The precision measurement system of pA-level weak current according to claim 1, wherein the gate voltage isolation attenuation superposition circuit further comprises a superposition module, the superposition module comprises an operational amplifier IC10, resistors RV8, RV10, R60, R61 and a reverse proportion operation circuit, the superposition module comprises two paths of input ends Uout1 and Uout2, the Uout1 is connected with the RV8 to carry out gain error adjustment, the Uout2 is connected with the RV10 to carry out gain error adjustment, then the R60 and the R61 are used for carrying out voltage division, the R60, the R61 and the RV8 are connected with the reverse proportion operation circuit to carry out superposition and then inversion, the reverse proportion operation circuit is connected with the IC10, the 6 pins of the IC10 are connected with the output ends, and the operational amplifier adopts an OP07 chip.

5. The precision measurement system of pA-level weak current according to claim 1, wherein the drain-source bias voltage isolation attenuation superposition circuit comprises an emitter tracker, a T-shaped resistor network and resistors RV7 and RV9, the input end of the drain-source bias voltage isolation attenuation superposition circuit is matched with resistance through the emitter tracker, superposition attenuation is carried out through the T-shaped resistor network, and the RV7 and the RV9 are arranged on a circuit connected with the emitter tracker and the T-shaped resistor network and used for carrying out error fine adjustment on attenuation multiples.