CN114624500A

CN114624500A - Precision measurement system for pA-level weak current

Info

Publication number: CN114624500A
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: 2022-06-14
Anticipated expiration: 2042-04-20
Also published as: CN114624500B

Abstract

The invention discloses a pA-level weak current precision measurement system which comprises a data acquisition card, a BNC (bayonet nut connector) box, an isolation adapter, a low-temperature system and an ammeter, wherein the output end of the data acquisition card comprises two paths, a first path of output end of the data acquisition card and a 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 through being connected with a driving signal of gate voltage and drain source bias voltage, the other path of input end of the isolation adapter is connected with the low-temperature system through being connected with the low-temperature system and receives acoustoelectric current provided by the low-temperature system, the other path of output end of the isolation adapter is connected with the ammeter and provides acoustoelectric current for the ammeter, and the low-temperature system is used for forming acoustoelectric current. The invention provides proper range and stepping gate voltage and source-drain bias voltage for the device, eliminates common ground interference and reduces background noise.

Description

Precision measurement system for pA-level weak current

Technical Field

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

Background

In 1996, Shilton et al, cavendish laboratory of cambridge university, developed the first gigahertz surface acoustic wave single electron transport (SAW/SET) device by using the piezoelectric property and split gate technology of GaAs, realized the transport of a single electron by Surface Acoustic Wave (SAW), obtained the pA-level quantized current for the first time: i = nef, where n is a positive integer and f is the microwave frequency, with an accuracy of up to 10^-15Magnitude, e is the electron charge. Therefore, it is good forIt is possible to establish a quantum reference based on basic physical constants by using the surface acoustic wave single electron effect. In the experiment, the current signal at the first step of the quantized acoustoelectric current plateau is about 160 pA when f =1 GHz. How to measure such weak current signals becomes a key factor for the success of the experiment.

Disclosure of Invention

Aiming at the problems, the invention provides a precision measurement system for pA-level weak current.

The invention is realized by the following technical scheme:

the utility model provides a precision measurement system of pA magnitude weak current, includes data acquisition card, BNC box, keeps apart adapter, cryogenic system and ampere meter, data acquisition card's output includes two the tunnel, the first output of the same kind of output of data acquisition card and data acquisition card's second way output are connected the input of the same kind of isolation adapter through the BNC box respectively, keep apart the output of the same kind of adapter through connecting cryogenic system, provide the drive signal of gate voltage and leakage source offset voltage respectively to cryogenic system, another input of keeping apart the adapter is through connecting cryogenic system, receives the acoustoelectric current that cryogenic system provided, another output of keeping apart the adapter is through connecting the ampere meter, provides the acoustoelectric current to the ampere meter, cryogenic system is used for forming the acoustoelectric 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 connected with two gate voltage pins respectively, and a current signal input end of the isolation adapter is connected with a measurement end pin.

Furthermore, 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 and drives the surface acoustic wave of the surface acoustic wave single electron transport device.

Furthermore, 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, a resistor R1, a resistor R2, a resistor 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 voltage, the output end of the first isolator comprises two paths, one path is connected with one input end of the summation operation superposition circuit, the other path is connected with the input end of the filter circuit, the output end of the second isolator is connected with the R1, the output end of the R1 comprises two paths, one path is grounded through the R2, the other path is connected with one input end of the summation operation superposition circuit, the other output end of the summation operation superposition circuit is grounded through the R3, and the output end of the summation operation superposition circuit is connected with the input end of the filter circuit, the filter circuit is used for outputting the filtered gate voltage and drain-source bias voltage.

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

Further, the gate voltage 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 J7 is connected with R45 and R56 for attenuation and then isolated through an IC15, a pin 38 of the IC15 is connected with an output end U out1, a pin 37 of the IC15 is grounded, the other input end is attenuated through R46 and R56 and then isolated through an IC16, a pin 38 of the IC16 is connected with the output end U out2, a pin 37 of the IC16 is grounded, and the isolation amplifier adopts an AD202 chip with an input range of +/-5V.

Further, the gate voltage attenuation superposition circuit comprises a superposition module, the superposition module comprises an operational amplifier IC10, a resistor RV8, an RV10, an R60, an R61 and an inverse proportion operation circuit, the superposition module comprises two input ends U out1 and U out2, the Uout1 carries out gain error adjustment by being connected with the RV8, the Uout2 carries out gain error adjustment by being connected with the RV10 and then carries out voltage division by virtue of R60 and R61, the R60, the R61 and the RV8 carry out superposition and phase inversion by being connected with the inverse proportion operation circuit, the inverse proportion operation circuit is connected with the IC10, a 6 pin of the IC10 is connected with an output end, and the operational amplifier adopts an OP07 chip.

Furthermore, the leakage-source bias voltage isolation attenuation superposition circuit comprises an emitter tracker, a T-shaped resistor network, resistors RV7 and RV9, the input end of the leakage-source bias voltage isolation attenuation superposition circuit is matched with an impedance through the emitter tracker and then is subjected to superposition attenuation 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 performing error fine adjustment on attenuation multiples.

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

The invention has the beneficial effects that:

(1) the invention utilizes the voltage isolation, attenuation and superposition circuit to eliminate common ground interference and reduce background noise so as to meet the voltage measuring range and step requirements when the device is measured;

(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 measuring system, the measuring precision of the system reaches pA magnitude, and the background noise is only 0.2 pA.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.

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

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

fig. 3 is a schematic circuit diagram of an isolation and attenuation module of a gate voltage isolation and 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 flowchart of a conventional grounding method according to an embodiment of the present invention;

fig. 8 is a flowchart of a method of 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

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.

Example 1

As shown in fig. 1, this embodiment provides a pA-class weak current precision measurement system, including data acquisition card, BNC box, isolation adapter, cryogenic system and ampere meter, the output of data acquisition card includes two ways, the first output of data acquisition card and the second output of data acquisition card are connected the input of the same kind of isolation adapter through the BNC box respectively, the output of the same kind of isolation adapter is through connecting cryogenic system, provides the drive signal of gate voltage and leakage source offset voltage to cryogenic system respectively, another input of isolation adapter is through connecting cryogenic system, receives the acoustoelectric current that cryogenic system provided, another output of isolation adapter is through connecting the ampere meter, provides the acoustoelectric current to the ampere meter, cryogenic system is used for forming the acoustoelectric current.

Furthermore, 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 measurement end pin.

Furthermore, 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 drives the surface acoustic wave of the surface acoustic wave single electron transport device.

Further, the gate voltage 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 J7 and J8, the J7 is connected with R45 and R56 for attenuation and then isolated through an IC15, a 38 pin of the IC15 is connected with an output end U out1, a pin 37 of the IC15 is grounded, the J8 is attenuated through R46 and R56 and then isolated through an IC16, a 38 pin of the IC16 is connected with the output end U out2, a pin 37 of the IC16 is grounded, and the isolation amplifier adopts an AD202 chip with an input range of +/-5V.

Further, the gate voltage attenuation superposition circuit further comprises a superposition module, the superposition module comprises an operational amplifier IC10, a resistor RV8, an RV10, an R60, an R61 and an inverse proportion operation circuit, the superposition module comprises two input ends U out1 and U out2, the Uout1 is connected with the RV8 to adjust gain errors, the Uout2 is connected with the RV10 to adjust the gain errors, voltage division is performed through the R60 and the R61, the R60, the R61 and the RV8 are connected with the inverse proportion operation circuit to perform superposition and phase inversion, the inverse proportion operation circuit is connected with the IC10, a 6 pin of the IC10 is connected with an output end, and the operational amplifier adopts an OP07 chip.

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

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

in the acoustic surface wave single electron transport experiment, the signal to be detected is a weak current signal with 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, which enter the self-made isolation adapter through the BNC box, and outputs a voltage signal meeting the measurement requirement, so as to provide the device with the driving of the gate voltage and the source-drain bias voltage. In the figure, the device interface 6 is used as a source terminal; the interface 1 is used as a measuring end; the

interfaces

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

The beneficial effect of this embodiment does:

1. the device is provided with a proper range and a stepping gate voltage and a source-drain bias voltage, common ground interference is eliminated, and background noise is reduced;

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

Example 2

On the basis of embodiment 1, this embodiment further provides a working principle of the isolation adapter, in which the NI 6289 data acquisition card outputs two paths of voltage signals, the voltage signals enter the isolation adapter through the BNC box, are divided by half by the resistor and then input into the isolator, and then one of the paths is divided by the resistor, attenuated by 500 times, and then superposed with the other path of the summation operation circuit to obtain the gate voltage and the source-drain bias voltage. The voltage signal also passes through a set of filter circuits before being output by the output terminal. This is because the microwave signal is applied to the device, which will generate high frequency interference to the measuring loop, and this set of filter circuits is used to prevent the high frequency interference from affecting the operation of the attenuation and superposition circuit.

Furthermore, in order to avoid mains supply interference, the isolation adapter adopts an external nickel-hydrogen rechargeable battery for power supply, 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 + 15V, + 7.5V and-7.5V to supply three voltages to 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 the buzzer gives an alarm to remind of replacing the battery. A battery pack can operate continuously for more than 12 hours. The shell of the isolation adapter is made of aluminum plates and has a good shielding function.

Example 3

On the basis of embodiment 1, this embodiment further proposes a gate voltage attenuation and superposition circuit, where, as shown in fig. 2 and 3, J7 and J8 are two input terminals of the attenuation and superposition circuit, and are directly connected to a voltage source through a wire. The input voltage is respectively attenuated by half after being divided by resistors R45 and R56, R46 and R57, then is isolated by an isolation amplifier, and is output at pins 38 of IC15 and IC16, and the output voltage is half of J7 and J8. IC15 and IC16 are isolation amplifiers that are primarily designed to eliminate common ground interference in the circuit, because the ground line has a resistance in the circuit, and when there is interference in the ground line, a common ground loop is formed, which can generate a harmful noise voltage in the circuit. The isolation amplifier additionally arranged in the circuit can ensure that the voltage of the input end and the voltage of the output end of the circuit are consistent, but the input end circuit and the output end circuit are mutually independent, so that a common ground loop is cut off, and common ground interference is avoided.

Furthermore, the isolation amplifier adopts an AD202 chip, and the type is a transformer coupling and micro-packaging precision isolation amplifier. The input and the output of the signal are electrically isolated by the coupling of the transformer in the chip, and the circuit has the characteristics of high precision, low power consumption, good common mode performance, small volume, low price and the like. In the input circuit, an on-chip independent amplifier can be used for buffering or amplifying an input signal. The amplified signal is modulated by a modulator to convert the signal into a carrier signal, which is fed to a synchronous demodulator via a transformer so that the signal is reproduced at an output. And the demodulated signal is filtered by a third-order filter, so that the noise and the 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 before the AD202 is input. In addition, RV4 and RV5 are used in the circuit to adjust the zero point of the output.

Further, as shown in fig. 4, the voltage signal passes through the isolation amplifier and then outputs U out1 and U out2, one path is connected to RV8, the other path is connected to RV10, and then passes through R60 and R61 (voltage division is 500 times). RV8 and RV10 are used to adjust the gain error. Plus half of the attenuation before the isolation amplifier, the two paths total attenuations 1/2 and 1/1000. The two paths of voltages after attenuation are superposed through an inverse proportion operation circuit (composed of IC12, R48, R59 and R58), and then are inverted, and the voltage is output at a pin 6 of the IC 10. At this time, the 6-pin output voltage of the IC10 is isolated, attenuated and superimposed, the range is +/-5V, and the minimum step is 0.3 mu V. 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 provides a source-drain bias voltage attenuation and superposition circuit, in which a signal is attenuated by half and then isolated, and then is attenuated and superposed directly by using a T-shaped resistor network shown in fig. 5 after being impedance-matched by emitter trackers (IC 9 and IC 11). One path through IC11 attenuates 1/5000, one path through IC9 attenuates 1/500, plus half the attenuation before isolation, for both attenuations 1/10000 and 1/1000. RV7 and RV9 can carry out error fine adjustment on the attenuation multiple.

Example 5

On the basis of embodiment 1, this embodiment further proposes a switch selection circuit, wherein, as shown in fig. 6, the situation of multiple pairs of gate voltages in the figure is the same, and only one pair is shown. Six wires from the device, 1, 3, 4, 6 from the source drain pad of the device, and 2, 5 from the gate voltage pad of the device (see fig. 1). 1. 3, 4 and 6 enter the adapter and then are respectively divided into two branches which are respectively connected with two single-pole multi-throw switches. And the common ends of the two switches are 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 at 6 feet,the input end of the ammeter is connected with a pin 1. 2. The 5-pin leads are respectively connected with two public ends of a double-pole multi-throw switch. The peripheral ports are respectively connected with gate voltagesVg. GND, and a floating terminal. When the switch is shifted clockwise from left to right, the wiring condition is as follows: first gear, 2-pin jointVg, grounding the 5 pins, not adding source-drain bias voltage at the moment, and measuring leakage current from the 2 pins to the quasi-one-dimensional electronic channel through the device groove; second gear, 5-pin jointVg, grounding the 2 pin, and measuring the leakage current from the 2 pin to the quasi-one-dimensional electronic channel. In the third step, the

pins

2 and 5 are connected with Vg, so that the total leakage current from the

pins

2 and 5 to the quasi-one-dimensional electronic channel can be measured. Then, the source-drain bias voltage is added, and the clamping curve of the device can be measured; the acoustoelectric current can be measured by adding microwaves. The fourth gear is the floating end. When the device works, the six grounding switches are all disconnected. When the circuit does not work, the grounding switch is closed to enable the six bonding pads to be grounded.

Example 6

On the basis of embodiment 1, this embodiment further proposes grounding of the circuit system, wherein, as shown in fig. 7, the grounding method (a) is to use a series single-point grounding, i.e., the grounds of all the devices are connected to the same grounding point, and then connected to the signal ground through the grounding point. The common grounding point of the measurement system is the grounding point on the cabinet, and the isolation adapter and the cryogenic system are 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 the 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 obviously, the measuring requirement cannot be met. Therefore, we connect the isolation adapter, the cryogenic system, directly to signal ground and no longer to ground through the cabinet. Therefore, the common impedance coupling interference is eliminated, the measurement precision 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 can be met.

Example 3

Referring to 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 for connecting different platform systems.

The 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 can be executed by the processor 220, so that the processor 220 executes any one of the pA-level weak current precision measurement methods in the embodiments of the present application, and the specific implementation manner of the method is consistent with the implementation manner and the achieved technical effect described in the embodiments of the method, and details of the method 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 of which, or some combination thereof, may comprise an implementation of a network environment.

Accordingly, processor 220 may execute the computer programs described above, as well as may execute programs/utilities 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 any other type of bus structure.

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

Claims

1. A precision measurement system of pA magnitude 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, a first path of output end of the data acquisition card and a 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 and provides a gate voltage and a drain source bias voltage driving signal for the low-temperature system, the other path of input end of the isolation adapter is connected with the low-temperature system and receives acoustoelectric current provided by the low-temperature system, the other path of output end of the isolation adapter is connected with the ammeter and provides acoustoelectric current for the ammeter, and the low-temperature system is used for forming acoustoelectric 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.

2. The system of claim 1, wherein the input terminals of the interdigital transducer are connected to the terminal through a microwave signal generator, and the output terminals of the interdigital transducer output a surface acoustic wave that drives a surface acoustic wave single electron transport device.

3. The precision measurement system of pA-class weak current according to claim 1, wherein the isolation adapter comprises an isolation attenuation superposition circuit, a chip power supply circuit and a power supply voltage indication circuit, the isolation attenuation superposition circuit comprises a first isolator, a second isolator, resistors R1, R2, 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 input voltages, the output end of the first isolator comprises two paths, one path is connected with the input end of the summation operation superposition circuit, the other path is connected with the input end of a filter circuit, the output end of the second isolator is connected with R1, the output end of R1 comprises two paths, one path is grounded through R2, the other path is connected with the input end of the summation operation superposition circuit, and the other path 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.

4. The pA-level weak current precision measurement system according to claim 3, wherein the isolation attenuation superposition circuit is further connected with a gate voltage isolation attenuation superposition circuit and a drain-source bias voltage isolation attenuation superposition circuit respectively, 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.

5. The precision measurement system of a pA-level weak current according to claim 4, wherein the gate voltage 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 is isolated by an IC15, a pin 38 of the IC15 is connected with an output end U out1, a pin 37 of the IC15 is grounded, the other input end is attenuated by connecting R46 and R56 and is isolated by an IC16, a pin 38 of the IC16 is connected with an output end U out2, a pin 37 of the IC16 is grounded, and the isolation amplifier adopts an AD202 chip with an input range of +/-5V.

6. The precision measurement system of a pA-level weak current according to claim 4, wherein the gate voltage attenuation superposition circuit further comprises a superposition module, the superposition module comprises an operational amplifier IC10, a resistor RV8, an RV10, an R60, an R61 and an inverse proportion operation circuit, the superposition module comprises two input ends U out1 and U out2, the Uout1 performs gain error adjustment by connecting to the RV8, the Uout2 performs gain error adjustment by connecting to the RV10, and then performs voltage division by connecting to R60 and R61, the R60, the R61 and the RV8 perform superposition re-inversion by connecting to the inverse proportion operation circuit, the inverse proportion operation circuit is connected to the IC10, the 6 pin of the IC10 is connected to the output end, and the operational amplifier adopts an OP07 chip.

7. The precision measurement system for the pA-level weak current according to claim 4, 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 subjected to matched impedance through the emitter tracker and then subjected to superposition attenuation through the T-shaped resistor network, and the RV7 and the RV9 are arranged on a circuit formed by connecting the emitter tracker and the T-shaped resistor network and used for carrying out error fine adjustment on attenuation multiple.

8. The system of claim 1, wherein said isolation adapter further comprises a switch selection circuit, said switch selection circuit is connected to a plurality of surface acoustic wave single electron transport devices, said switch selection circuit is used for individually controlling the gate voltage of the split gate of the surface acoustic wave single electron transport device.