CN108037341B - Low leakage current reset device for capacitance integral weak current measurement circuit - Google Patents
Low leakage current reset device for capacitance integral weak current measurement circuit Download PDFInfo
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/16—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using capacitive devices
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- G—PHYSICS
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Abstract
The invention belongs to the technical field of weak current measurement, and particularly relates to a low leakage current reset device for a capacitance integration type weak current measurement circuit, which is connected to a capacitance integration type weak current measurement circuit (2) for measuring weak current (1) to be measured and comprises a reset current circuit (3), a multiplexer (4), a D/A converter (5), a voltage follower (6) and a logic control unit (7); the voltage follower (6) can copy the voltage of weak current (1) to be detected as the turn-off voltage of the reset current circuit (3), and the D/A converter (5) can provide the turn-on voltage with adjustable polarity and size for the reset current circuit (3); the device also comprises a logic control unit (7) for controlling the multiplexer (4) to selectively output an off voltage or an on voltage and controlling the polarity and the magnitude of the on voltage output by the D/A converter (5). The invention can greatly improve the measurement lower limit and the minimum resolution of the capacitance integral weak current measurement circuit system.
Description
Technical Field
The invention belongs to the technical field of weak current measurement, and particularly relates to a low leakage current reset device for a capacitance integration type weak current measurement circuit.
Background
Currents of the order nA (10 -9 a) or less are generally referred to as weak currents. In scientific research work in the fields of radiation detection, electrochemistry, new materials, etc., weak current measurements are often required. Weak current measurement suffers from not only the very small signal amplitude to be measured, but also from the extreme susceptibility to various types of interference, sometimes even being inundated with interference noise. The types of interference sources are not only electronic noise, but also electric field, magnetic field and electromagnetic field, even friction electrification effect generated by mechanical vibration, piezoelectric effect generated by applying external force, electrochemical noise formed by mixing electrochemical substances and moisture and leakage current introduced by insulating materials can seriously influence the measurement result of weak current, and even measurement cannot be performed normally. These effects are particularly pronounced when weak current measurements are made at pA (10 -12 a) level or even fA (10 -15 a) level. The current weak current measurement method mainly comprises two main types:
one type is an I-V conversion method, which converts a weak current signal to be measured into a voltage signal which is easier to measure through a high-value resistor (usually in the order of 10 9 Ω to 10 11 Ω according to the magnitude of the current to be measured) through a formula The current value can be calculated;
The other type is a capacitance integration method (the capacitance integration weak current measurement circuit adopting the method is shown in figure 1), the method collects charges by using an integration capacitor, the voltage at two ends of the capacitor is gradually increased along with the accumulation of the charges on a capacitor plate, the change rate of the voltage at the capacitor end with a known capacitance value within a certain time is calculated, and the formula is adopted The average value of the current over the period of time can be calculated. The stability of the capacitor is better and the temperature coefficient is lower than that of the capacitor with a relatively high value, and the capacitor can restrain the influence of part of electronic noise and external interference in an integral mode. Therefore, compared with the I-V conversion method, the capacitance integration method is more suitable for occasions with higher measurement accuracy, for example, the measurement device based on the capacitance integration method is widely used in the field of ionization radiation measurement to finish the measurement of weak ionization current signals output by various types of ionization chambers.
In measurement schemes based on capacitive integration, one important process is to release the charge accumulated on the capacitance for the next measurement. To release this part of the charge, an additional reset device needs to be added. At present, the implementation form of the reset device is mainly two types of switch mode and current source mode. The switch mode is that a switch is used to be connected with an integrating capacitor in parallel, and when the switch is conducted, the two ends of the capacitor are short-circuited to release charges. The method has simple structure, but the common transistor type switch can not meet the requirement because of higher requirement on leakage current introduced when the switch is disconnected, so a mechanical reed switch is generally adopted as the switch. The method has the defects that a large current impact is formed at the moment that a large amount of charge relays are accumulated in a capacitor and are conducted and discharged, the current impact can possibly cause chip damage, and the mechanical relay is disconnected at the moment to generate charges due to mechanical contact and friction, voltage change is generated after the integration capacitor is collected, and the generated charge quantity is uncontrollable, so that the measurement is influenced. Therefore, a current source mode is generally adopted in the method, the current source is used for outputting the current with the polarity opposite to that of the input current to reversely charge the capacitor, so that the charge of the integrating capacitor is released, the constant current source circuit is mostly composed of a field effect transistor or a transistor, potential difference exists between the potential of the constant current source circuit formed by the constant current source circuit when the constant current source circuit is turned off and the input end, for example, the potential of a charge collector (namely a current output end) of an ionization chamber commonly used in the radiation detection field is usually tens of millivolts, a larger potential difference exists between the potential of the charge collector and the zero potential (or PN junction reverse bias potential) of the constant current source when the constant current source is turned off, leakage current is formed, and the leakage current is mostly of pA (10 -12 A) or even nA (10 -9 A), and the leakage current can not only generate measurement errors, but also influence the measurement lower limit and the minimum resolution capability of the measurement circuit.
Disclosure of Invention
Aiming at the problems that the current integral weak current reset device is large in leakage current and seriously affects the lower limit and the minimum resolution capability of circuit measurement, the invention develops a low leakage current reset device, the leakage current of the low leakage current reset device is smaller than 1fA (10 - 15 A), and the output of bipolar reset current with adjustable size can be realized, so that the influence of the low leakage current reset device on the lower limit and the minimum resolution capability of the weak current measurement system is greatly reduced, and the performance index of the weak current measurement system is greatly improved.
In order to achieve the above purpose, the technical scheme adopted by the invention is that the low leakage current reset device for the capacitance integration type weak current measurement circuit is connected to the capacitance integration type weak current measurement circuit for measuring weak current to be measured, and comprises a multiplexer, wherein the output end of the multiplexer is connected with the input end of the reset current circuit, the input end of the multiplexer is connected with the output end of a voltage follower and a D/A converter, and the output end of the reset current circuit and the input end of the voltage follower are connected with the input end of the capacitance integration type weak current measurement circuit; the voltage follower can copy the voltage of the weak current to be detected as the turn-off voltage of the reset current circuit, and the D/A converter can provide the turn-on voltage with adjustable polarity and size for the reset current circuit; when the multiplexer outputs the turn-off voltage, the reset current circuit is turned off, and when the multiplexer outputs the turn-on voltage, the reset current circuit is turned on and outputs a reset current to the capacitance integration type weak current measurement circuit; the device further comprises a logic control unit for controlling the multiplexer to selectively output the turn-off voltage or the turn-on voltage and controlling the polarity and the magnitude of the turn-on voltage output by the D/A converter.
Further, the circuit board of the low leakage current restorer uses a high insulation performance board, and the board at least comprises a ceramic plate.
Further, a guard ring is arranged around the wire for outputting the reset current on the output end of the reset current circuit, the guard ring adopts the turn-off voltage output by the voltage follower as clamping voltage, the guard ring is subjected to windowing and gold deposition process, and the gap between the wire for outputting the reset current and the wire of the guard ring is 15mil.
Further, a potential difference between the turn-off voltage provided by the voltage follower and the voltage of the weak current to be measured is smaller than 10 mu V.
Further, when the logic control unit selects the on-voltage output by the D/a converter, the reset current output by the reset current circuit is a μa level reset current, and the polarity and magnitude of the reset current are determined by the polarity and magnitude of the on-voltage output by the D/a converter.
Further, the method comprises the steps of,
The reset current circuit comprises a resistor R1 and a resistor R2 which are connected in parallel between the input end and the output end of the reset current circuit; the resistor R1 is connected in series with a diode D2, the diode D2 is positioned between the resistor R1 and the input end, and the resistor R1 is positioned on the positive electrode side of the diode D2; the resistor R2 is connected in series with a diode D1, the diode D1 is positioned between the resistor R2 and the input end, the resistor R2 is positioned on one side of the cathode of the diode D1, the resistor R1 and the resistor R2 are used as current limiting resistors when the reset current circuit is conducted to prevent the reset current from being overlarge, and are also used as voltage dividing resistors when the reset current circuit is turned off to reduce the voltage of the diode end;
the resistor R1 and the resistor R2 are metal film resistors, and the resistance value is 1MΩ;
The diode D1 and the diode D2 are low reverse bias leakage current diodes PAD1;
The circuit composed of the resistor R1 and the diode D2 and the circuit composed of the resistor R2 and the diode D1 are respectively used for the reset currents with different polarities output by the D/A converter;
The reset current I Reset output by the reset current circuit is obtained by a formula (V DAC-VDiode)/R, wherein V DAC is the conducting voltage output by the D/A converter, V Diode is the voltage when the diode D1 and the diode D2 are conducted, and R is the resistance value of the current limiting resistor.
Further, an absolute value of the on voltage output by the D/a converter is not less than 1V.
Further, the voltage follower adopts an amplifier with JFET stage ultralow bias current I b and low offset voltage V os, and the amplifier is prepared into a positive phase follower.
Further, the reset current circuit formed by the reset current circuit and the voltage follower is arranged in the metal shielding box and is close to the capacitance integration type weak current measuring circuit.
The invention has the beneficial effects that:
1. According to the invention, the voltage follower 6 with low bias current I b and low offset voltage V os is adopted, the voltage at the weak current output end, namely the voltage at the input end of the voltage follower 6, is used as the turn-off voltage of the low leakage current reset device for the capacitance integration type weak current measuring circuit, the turn-off voltage of the reset current circuit 3 and the voltage difference at the input end of the capacitance integration type weak current measuring circuit 2 are reduced from mV magnitude (10 -3 V) to mu V magnitude (10 -6 V), and the leakage current level of the reset current circuit 3 is greatly reduced.
2. The reset current circuit 3 adopts a connection mode that a low reverse bias leakage current diode is connected with a high-value resistor in series, so that the equivalent resistance of a low leakage current reset device used for a capacitance integration type weak current measurement circuit in an off state is greatly increased.
3. The invention adopts the turn-off voltage output by the voltage follower 6 as the clamping voltage of the guard ring and is matched with the ceramic high-performance insulating material as the substrate material of the circuit board, thereby greatly reducing the leakage current of the reset current circuit 3 caused by the insulating material.
4. The leakage current of the low leakage current reset device for the capacitance integration type weak current measurement circuit in the off state does not exceed 1fA, and the bipolar reset current output by the reset current circuit 3 and the mu A level reset current with adjustable size can be realized through the adjustment of the polarity and the size of the output potential by the D/A converter 5.
5. The invention can improve the measurement lower limit and the minimum resolution of the capacitance integration type weak current measurement circuit from the pA level (10 -12 A) to the fA level (10 -15 A), thereby greatly improving the measurement performance of the capacitance integration type weak current measurement circuit.
Drawings
FIG. 1 is a schematic diagram of a capacitive integrated weak current measurement circuit according to the background art;
FIG. 2 is a block diagram of a low leakage current reset device for a capacitive integrated weak current measurement circuit according to an embodiment of the present invention; in fig. 2: 1-weak current to be measured, 2-capacitance integral weak current measuring circuit, 3-reset current circuit, 4-multiplexer, 5-D/A converter, 6-voltage follower and 7-logic control unit;
FIG. 3 is a circuit diagram of a voltage follower according to an embodiment of the present invention;
FIG. 4 is a circuit diagram of a reset current circuit according to an embodiment of the present invention;
FIG. 5 is a circuit diagram of an output buffer and a proportional voltage inverter in a D/A converter according to an embodiment of the present invention;
Fig. 6 is a schematic diagram of a multiplexer MAX4518 according to an embodiment of the present invention.
Detailed Description
The invention is further described below with reference to the drawings and examples.
The invention provides a low leakage current reset device (shown in figure 2) for a capacitance integration type weak current measuring circuit, which is connected to a capacitance integration type weak current measuring circuit 2 for measuring weak current 1 to be measured and comprises a reset current circuit 3, a multiplexer 4, a D/A converter 5, a voltage follower 6, a logic control unit 7 and the like.
The output end of the reset current circuit 3 is connected with the input end of the capacitance integration type weak current measurement circuit 2, and the input end of the reset current circuit 3 is connected with the output end of the multiplexer 4 and is used for closing or conducting the capacitance integration type weak current measurement circuit 2 according to the turn-off voltage or the turn-on voltage of the output of the multiplexer 4;
The output end of the multiplexer 4 is connected to the input end of the reset current circuit 3, the input ends of the multiplexer 4 are multiple, and are respectively connected with the output end of the voltage follower 6 and the output end of the D/A converter 5, the multiplexer 4 is also connected with the logic control unit 7 and is controlled by the logic control unit 7, and is used for outputting an off voltage or an on voltage (the off voltage is generated by the voltage follower 6, and the on voltage is generated by the D/A converter 5) to the reset current circuit 3 according to the control of the logic control unit 7;
The input end of the voltage follower 6 is connected to the input end of the capacitance integration type weak current measuring circuit 2, the output end of the voltage follower 6 is connected to one input end of the multiplexer 4, and the voltage follower 6 can copy the voltage of the weak current 1 to be measured as the turn-off voltage of the reset current circuit 3 (the turn-off voltage is transmitted to the reset current circuit 3 through the multiplexer 4);
The output end of the D/A converter 5 is connected with the other input end of the multiplexer 4, the D/A converter 5 can provide a conduction voltage with adjustable polarity and magnitude for the reset current circuit 3 (the conduction voltage is transmitted to the reset current circuit 3 through the multiplexer 4), and the D/A converter 5 is also connected with the logic control unit 7 and is controlled by the logic control unit 7, and is used for providing the conduction voltage according to the control of the logic control unit 7 and adjusting the polarity and magnitude of the conduction voltage;
when the multiplexer 4 outputs the turn-off voltage, the capacitance integration type weak current measuring circuit 2 measures the weak current 1 to be measured when the reset current circuit 3 is turned off; when the multiplexer 4 outputs the on-voltage, the reset current circuit 3 is turned on, and outputs the reset current to the capacitance integration type weak current measurement circuit 2.
The circuit board of the low leakage current restorer uses a high-insulation-performance board, and the board at least comprises a ceramic plate.
A guard ring is arranged around the wiring for outputting the reset current on the output end of the reset current circuit 3, the guard ring adopts the turn-off voltage output by the voltage follower 6 as the clamping voltage, the guard ring is subjected to windowing and gold deposition process, and the gap between the wiring for outputting the reset current and the wiring of the guard ring is 15mil.
The potential difference between the off voltage provided by the voltage follower 6 and the voltage of the weak current 1 to be measured is smaller than 10 mu V.
When the logic control unit 7 selects the on-voltage output by the D/a converter 5, the reset current output by the reset current circuit 3 is a μa-level reset current, and the polarity and magnitude of the reset current are determined by the polarity and magnitude of the on-voltage output by the D/a converter 5.
The reset current circuit composed of the reset current circuit 3 and the voltage follower 6 is arranged in the metal shielding box and is close to the capacitance integration type weak current measuring circuit 2.
The reset current circuit 3 (see fig. 4) includes a resistor R1 and a resistor R2 connected in parallel between an input terminal and an output terminal of the reset current circuit 3; the resistor R1 is connected in series with a diode D2, the diode D2 is positioned between the resistor R1 and the input end of the reset current circuit 3, and the resistor R1 is positioned at one side of the positive electrode of the diode D2; the resistor R2 is connected in series with a diode D1, the diode D1 is positioned between the resistor R2 and the input end of the reset current circuit 3, and the resistor R2 is positioned on one side of the cathode of the diode D1; when the reset current circuit 3 is conducted, the resistor R1 and the resistor R2 serve as current limiting resistors of the reset current circuit 3 to prevent the reset current from being overlarge; when the reset current circuit 3 is turned off, the resistor R1, the resistor R2 reduce the diode-end voltage (the diode includes the diode D1 and the diode D2) as the voltage dividing resistor of the reset current circuit 3;
The resistor R1 and the resistor R2 are metal film resistors, and the resistance value is 1MΩ;
The diode D1 and the diode D2 are low reverse bias leakage current diodes PAD1 (the diode D1 and the diode D2 can also be replaced by JFET type and MOS type field effect transistors of the same type, such as PN 4117A);
The circuit composed of the resistor R1 and the diode D2 and the circuit composed of the resistor R2 and the diode D1 are respectively used for resetting currents with different polarities output by the D/A converter 5;
The magnitude I Reset of the reset current outputted by the reset current circuit 3 is obtained by the formula V DAC-VDiode/R, where V DAC is the on voltage outputted by the D/a converter 5, V Diode is the voltage (about 0.7V) when the diodes (i.e., the diode D1 and the diode D2) are turned on, and R is the resistance of the current limiting resistor (i.e., the resistance when the resistor R1 and the resistor R2 are used as the current limiting resistor).
The voltage follower 6 (see U1 in fig. 3) adopts an amplifier with JFET stage ultra-low bias current I b and low offset voltage V os (in the specific embodiment of the invention, the amplifier of the voltage follower 6 adopts LMC6001AIN, or can also adopt lmp7721, LMC6042AIN and other similar indexes to replace the same), and the amplifier is configured as a normal phase follower, so that the influence of the voltage follower 6 on the capacitance integration type weak current measurement circuit 2 is negligible due to the ultra-low bias current. The pins 4 and 7 of the amplifier LMC6001AIN are respectively connected to a power supply, the pin 3 is a positive input terminal, and is connected to an input terminal of the capacitance integration type weak current measurement circuit 2 in fig. 2 (i.e. connected to the weak current 1 to be measured in fig. 2), the pin 2 is a negative input terminal, and is connected to the pin 6 as an output terminal and is connected to the multiplexer 4 (in the embodiment of the present invention, the type of the multiplexer 4 is MAX4518, and the output terminal of the amplifier LMC6001AIN is specifically the pin 11 connected to MAX4518, see fig. 6).
The D/a converter 5 is controlled by the logic control unit 7, the absolute value of the on voltage output by the D/a converter 5 is not less than 1V, so that the diode in the reset current circuit 3 is turned on, in the embodiment of the invention, the D/a converter 5 adopts a microcontroller stm32f103rct chip, the output end of the D/a converter 5 (i.e. the pin PB4 of the microcontroller stm32f103 rct) is respectively connected to an output buffer consisting of the amplifier U2A and a same-proportion inverting amplifier (see fig. 5) configured by the amplifier U2B, thereby outputting voltage signals with the same polarity and the same magnitude, the output of the output buffer is connected to the pin 4 of the MAX4518 (i.e. the multiplexer), and the output of the inverting amplifier is connected to the pin 5 of the MAX4518 (see fig. 6). The D/A converter 5 has no special requirement, and adopts an on-chip DAC module of a microcontroller stm32f103rct chip, and can also be replaced by other general models. The model numbers of the amplifier U2A and the amplifier U2B are OPA2277U; the resistor R3 and the resistor R4 are metal film resistors, and the resistance values are 10k.
The multiplexer 4 (i.e., U3 in fig. 6) uses a multiplexer of model MAX4518ESD, which has analog power supply pin 3 and pin 12 connected to ±5v low noise power supply, pin 2 connected to +3.3v high level, pin 4 connected to positive polarity voltage of D/a converter 5, pin 5 connected to negative polarity voltage of D/a converter 5, pin 11 connected to voltage follower 6 output as off voltage, and pin 10 connected to zero potential, see fig. 6.
The logic control unit 7 adopts a 32bit Microcontroller (MCU) with the model number of stm32f103rct, adopts +3.3V to supply power, completes communication with the D/A converter 5 through an SPI2 bus and sets output potential, the pins PC1 and PC2 of the logic control unit are respectively connected with the pin 1 and the pin 14 of the multiplexer 4 (U3 in FIG. 6), and the logic control unit 7 selects the output logic states of the pins PC1 and PC2 to realize different outputs of the multiplexer;
The logic control unit 7 adopts an rs232 communication interface, and an upper computer can send an instruction to configure the reset current and the state of the reset device;
the logic controller 7 configures the multiplexer 4 to select different voltage signals as output to the reset current circuit 3 according to specific requirements, and realizes the turn-off or turn-on of the reset current circuit 3 so as to meet different requirements of the capacitance integration type weak current measurement circuit 2.
When the PC1 and PC2 of the logic control unit 7 output low level, the multiplexer 4 outputs positive polarity voltage, at this time, the diode D1 of the reset current circuit 3 is turned on, and the reset current circuit 3 outputs positive polarity reset current; when the PC1 of the logic control unit 7 outputs a low level and the PC2 outputs a high level, the multiplexer 4 outputs a negative polarity voltage, and at this time, the diode D2 of the reset current circuit 3 is turned on, and the reset current circuit 3 outputs a negative polarity reset current; when the output of the PC1 of the logic control unit 7 is at a high level and the output of the PC2 is at a low level, the output of the multiplexer 4 is at a weak current input end potential (i.e., the off voltage output by the voltage follower 6), the diode D1 and the diode D2 of the reset current circuit 3 are both turned off, no current is output, and the capacitance integration type weak current measurement circuit 2 can perform current measurement on the weak current 1 to be measured.
When the low leakage current reset device for the capacitance integration type weak current measurement circuit is in an off state, namely the output of the multiplexer 4 is the potential of the voltage follower 6, the voltage difference between two ends of the diode of the reset current circuit 3 is far smaller than the threshold voltage of the diode conduction, and the diode is cut off. The potential difference across the series circuit (i.e., the line in series with resistor R1 and diode D2 and the line in series with resistor R2 and diode D1) is mainly determined by the offset voltage of voltage follower 6, typically in the μv (10 -6 V) level, with the high-value resistors (resistor R1 and resistor R2) acting as a voltage divider in the series circuit. In this state, the current in the PN junction of the diode is formed by the thermal motion of the hole electron pair, and the equivalent resistance value formed by the junction resistance and the megaohm resistance connected in series is extremely high. The current formed by the voltage difference and the equivalent high-value resistor is not more than 1fA, so that the extremely low leakage current of the low leakage current reset device for the capacitance integration type weak current measurement circuit is realized. When the low leakage current reset device for the capacitance integration type weak current measurement circuit is in a conducting state, namely, the output of the multiplexer 4 is the output potential of the D/A converter 5, the absolute value of the output potential is larger than 1V, the diode of the reset current circuit 3 is conducted, the magnitude of the reset current is equal to the quotient of the difference between the output voltage of the multiplexer 4 and the diode voltage of the reset current circuit 3 and the current limiting resistance value, so that the reset current is in a mu A (10 -6 A) level, and the output voltage of the D/A converter 5 can be regulated according to requirements to realize the regulation of the magnitude of the reset current.
The device according to the invention is not limited to the examples described in the specific embodiments, and a person skilled in the art obtains other embodiments according to the technical solution of the invention, which also belong to the technical innovation scope of the invention.
Claims (8)
1. The low leakage current reset device for the capacitance integration type weak current measuring circuit is connected to a capacitance integration type weak current measuring circuit (2) for measuring weak current (1) to be measured, and is characterized in that: the device comprises a multiplexer (4) with an output end connected with an input end of a reset current circuit (3), an input end connected with a voltage follower (6) and an output end of a D/A converter (5), wherein the output end of the reset current circuit (3) and the input end of the voltage follower (6) are connected with the input end of the capacitance integration type weak current measuring circuit (2); the voltage follower (6) can copy the voltage of the weak current (1) to be detected as the turn-off voltage of the reset current circuit (3), and the D/A converter (5) can provide the turn-on voltage with adjustable polarity and size for the reset current circuit (3); when the multiplexer (4) outputs the turn-off voltage, the reset current circuit (3) is turned off, and when the multiplexer (4) outputs the turn-on voltage, the reset current circuit (3) is turned on and outputs a reset current to the capacitance integration type weak current measurement circuit (2); further comprising a logic control unit (7) for controlling the multiplexer (4) to selectively output the off-voltage or the on-voltage, and controlling the polarity and magnitude of the on-voltage output by the D/a converter (5);
The reset current circuit (3) comprises a resistor R1 and a resistor R2 which are connected in parallel between the input end and the output end of the reset current circuit (3); the resistor R1 is connected in series with a diode D2, the diode D2 is positioned between the resistor R1 and the input end, and the resistor R1 is positioned on the positive electrode side of the diode D2; the resistor R2 is connected in series with a diode D1, the diode D1 is positioned between the resistor R2 and the input end, the resistor R2 is positioned on one side of the cathode of the diode D1, the resistor R1 and the resistor R2 are used as current limiting resistors when the reset current circuit (3) is conducted to prevent the reset current from being overlarge, and are also used as voltage dividing resistors when the reset current circuit (3) is turned off to reduce the diode end voltage;
the resistor R1 and the resistor R2 are metal film resistors, and the resistance value is 1MΩ;
The diode D1 and the diode D2 are low reverse bias leakage current diodes PAD1;
The circuit composed of the resistor R1 and the diode D2 and the circuit composed of the resistor R2 and the diode D1 are respectively used for the reset currents with different polarities output by the D/A converter (5);
The reset current I Reset output by the reset current circuit (3) is obtained by a formula (V DAC-VDiode)/R, wherein V DAC is the conducting voltage output by the D/A converter (5), V Diode is the voltage when the diode D1 and the diode D2 are conducted, and R is the resistance value of the current limiting resistor.
2. The low leakage current reset device for a capacitive integrated weak current measurement circuit of claim 1, wherein: the circuit board of the low leakage current restorer uses a high-insulation-performance board, and the board at least comprises a ceramic plate.
3. The low leakage current reset device for a capacitive integrated weak current measurement circuit of claim 1, wherein: and a protection ring is arranged around a wire for outputting the reset current on the output end of the reset current circuit (3), the protection ring adopts the turn-off voltage output by the voltage follower (6) as clamping voltage, the protection ring is subjected to windowing and gold deposition process, and the gap between the wire for outputting the reset current and the wire of the protection ring is 15mil.
4. The low leakage current reset device for a capacitive integrated weak current measurement circuit of claim 1, wherein: the potential difference between the turn-off voltage provided by the voltage follower (6) and the voltage of the weak current (1) to be measured is smaller than 10 mu V.
5. The low leakage current reset device for a capacitive integrated weak current measurement circuit of claim 1, wherein: when the logic control unit (7) selects the conduction voltage output by the D/A converter (5), the reset current output by the reset current circuit (3) is a mu A level reset current, and the polarity and the magnitude of the reset current are determined by the polarity and the magnitude of the conduction voltage output by the D/A converter (5).
6. The low leakage current reset device for a capacitive integrated weak current measurement circuit of claim 1, wherein: the absolute value of the on voltage output by the D/A converter (5) is not less than 1V.
7. The low leakage current reset device for a capacitive integrated weak current measurement circuit of claim 1, wherein: the voltage follower (6) adopts an amplifier with JFET stage ultralow bias current I b and low offset voltage V os, and the amplifier is prepared into a positive phase follower.
8. The low leakage current reset device for a capacitive integrated weak current measurement circuit of claim 1, wherein: the reset current circuit formed by the reset current circuit (3) and the voltage follower (6) is arranged in the metal shielding box and is close to the capacitance integration type weak current measuring circuit (2).
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| CN113711064B (en) * | 2019-04-10 | 2024-03-08 | Iee国际电子工程股份公司 | Multichannel capacitance sensing measurement circuit |
| CN112213554B (en) * | 2020-09-04 | 2021-12-21 | 中国原子能科学研究院 | Weak current measuring circuit and method based on current frequency conversion method |
| CN113238088B (en) * | 2021-05-08 | 2023-01-20 | 中国测试技术研究院辐射研究所 | High-precision weak current measuring circuit and method based on charge balance |
| CN115373011A (en) * | 2022-09-20 | 2022-11-22 | 北京康科达科技有限公司 | Radiation therapy dosimeter |
| CN116699463B (en) * | 2023-07-28 | 2024-02-06 | 珠海禅光科技有限公司 | MLCC capacitor leakage current measuring method, device, control device and medium |
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