Circuit for improving small current measurement speed, measurement method and system

Abstract

The invention provides a circuit for improving small current measurement speed, a measurement method and a system, which can be applied to the current measurement requirement of a pA-level range, a first resistor and a first capacitor form a first RC charging and discharging loop, and when small current flows through the first resistor, after the first capacitor is charged, the first resistor is connected with the first RC charging and discharging loop; the output end of the first operational amplifier outputs steady-state measurement voltage, the second resistor and the second capacitor form a second RC charging and discharging loop, and in the charging process of the first capacitor, the second capacitor is controlled to discharge for auxiliary energy charging of the first capacitor. In the invention, the first resistor with a large resistance value is selected to realize indirect measurement of the small current, and meanwhile, the charging speed of the first capacitor is improved through additional RC charging and discharging loop arrangement, so that the single current measurement speed of the source measurement unit in the small current test operation is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of source measurement unit current measurement, and particularly relates to a circuit, a measurement method and a system for improving small current measurement speed. BACKGROUND

[0002] A source measurement unit (SMU for short) is a professional instrument device capable of providing accurate current and voltage sources and capable of simultaneously measuring current and voltage. The SMU is commonly used in an automated test and measurement environment, and is widely applied in the characteristic test and calibration process of semiconductor devices, sensors and other precision electronic components. In the current test process of the source measurement unit, especially when small current measurement (pA range) exists, the response time and time constant of the internal circuit of the source measurement unit will affect the time for the voltage across the to-be-tested resistor to change to a stable value, resulting in that the time for each measurement of small current is relatively long, that is, the small current test time of one point may cover the total time of all large current tests, so that the source measurement unit consumes too much time for single current measurement and has low measurement efficiency in the process of facing small current measurement. SUMMARY

[0003] The present application provides a circuit, a measurement method and a system for improving small current measurement speed to solve the technical problem that the conventional source measurement unit in the prior art consumes too much time for single current measurement and has low measurement efficiency when facing small current measurement.

[0004] To solve the above problems, the technical scheme of the present application is as follows: a circuit for improving small current measurement speed is applied to the current measurement demand of the pA range, and comprises a first resistor, a second resistor, a first capacitor, a second capacitor and a first operational amplifier. A first end of the first resistor is connected with a control voltage output end, and a second end of the first resistor is connected with a load voltage output end. A non-inverting input end of the first operational amplifier is connected with a first common node formed by the first resistor and the load voltage output end, and an inverting input end of the first operational amplifier is connected with an output end thereof. A first end of the first capacitor is connected with the first common node formed by the first resistor and the load voltage output end, and a second end of the first capacitor is connected with the control voltage output end. A first end of the second resistor is connected with the first common node formed by the first resistor and the load voltage output end, a second end of the second resistor is connected with a first end of the second capacitor, and a second end of the second capacitor is connected with the control voltage output end. The circuit for improving small current measurement speed is configured as follows: the first resistance and the first capacitance form a first RC charging and discharging circuit, when the first resistance flows through a small current, after the first capacitance is fully charged, the output end of the first operational amplifier outputs a steady-state measurement voltage; the second resistance and the second capacitance form a second RC charging and discharging circuit, during the charging of the first capacitance, the second capacitance is discharged, and the second capacitance is used to assist the charging of the first capacitance.

[0005] Preferably, the circuit for improving small current measurement speed is further provided with a second operational amplifier and a third resistance, the non-inverting input end of the second operational amplifier is connected with the control voltage output end, the inverting input end of the second operational amplifier is connected with the load voltage output end and forms a second common node, the inverting input end of the second operational amplifier is further connected with the output end in series through the third resistance, and the output end of the second operational amplifier is further connected with a third common node formed by the second capacitance and the second resistance. The circuit for improving small current measurement speed is further configured as follows: when the third resistance flows through a small current, the second operational amplifier outputs a steady-state voltage.

[0006] Preferably, a first switch is arranged between the first common node formed by the first resistance and the load voltage output end and the second common node formed by the inverting input end of the second operational amplifier and the load voltage output end. A second switch is arranged between the inverting input end of the second operational amplifier and the load voltage output end. A third switch is arranged between the second resistance and the second capacitance. A fourth switch is arranged between the output end of the second operational amplifier and the third common node formed by the second capacitance and the third switch.

[0007] Preferably, a fourth resistance is further arranged between the output end of the second operational amplifier and the fourth switch, and the fourth resistance is configured as follows: when the third switch is turned off and the fourth switch is turned on, the second capacitance and the fourth resistance form a third RC charging and discharging circuit, and when the second operational amplifier outputs a steady-state voltage, the second capacitance is charged.

[0008] Preferably, the first resistance and the third resistance have the same resistance value, and the resistance value of the first resistance and the third resistance is limited to 10 GΩ-100 GΩ.

[0009] Based on the same concept, the application further provides a measurement method for improving small current measurement speed, which is applied to the circuit for improving small current measurement speed described in any one of the above embodiments and includes the following steps: S1: the first switch is turned off, the second switch is turned on, the third switch is turned off, and the fourth switch is turned on, so that the output voltage of the control voltage output terminal and the load voltage output terminal is adjusted to be the same; S2: the second operational amplifier charges the second capacitor; S3: after the second capacitor is fully charged, the third switch is turned on, the fourth switch is turned off, and the second capacitor discharges to assist the charging of the first capacitor; S4: after the first capacitor is fully charged, the first switch is turned on, the second switch is turned off, the control voltage output terminal performs adaptive fine tuning on the output voltage, and the output terminal of the first operational amplifier outputs a steady-state measurement voltage; S5: the voltage values of the control voltage output terminal and the output terminal of the first operational amplifier at both ends of the first resistor are obtained, and the current value flowing through the first resistor is solved by Ohm's law.

[0010] Based on the same concept, the application also provides a system for improving the small current measurement speed, which is equipped with any one of the above-mentioned circuits for improving the small current measurement speed, and comprises: a voltage control unit, which is used for outputting a control voltage; a current measurement unit, which is internally provided with a circuit for improving the small current measurement speed, and is externally connected with a host computer, and is used for obtaining a steady-state measurement voltage at both ends of a first resistor and transmitting the voltage to the host computer to realize current value calculation; a measured device unit, which is used for outputting a load voltage of a device to be measured.

[0011] Compared with the prior art, the application has the following advantages and positive effects: The application provides a circuit, a measurement method and a system for improving small current measurement speed. BRIEF DESCRIPTION OF DRAWINGS BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The application provides a structure diagram of the circuit for improving small current measurement speed. Figure 2 The application provides a flowchart of the measurement method for improving small current measurement speed. Figure 3 The application provides a structure diagram of the system for improving small current measurement speed. DETAILED DESCRIPTION

[0013] The application provides a circuit, a measurement method and a system for improving small current measurement speed. The advantages and features of the application will be more apparent according to the following description and claims.

[0014] First embodiment Referring to Figure 1 The embodiment provides a circuit for improving small current measurement speed, which is used for realizing fast and accurate current measurement when a source measurement unit faces small current (pA range) measurement.

[0015] Specifically, the embodiment is provided with a first resistor R1, a second resistor R2, a first capacitor C1, a second capacitor C2 and a first operational amplifier U1. The first end of the first resistor R1 is connected with a control voltage output end Vc, and the second end of the first resistor R1 is connected with a load voltage output end Vout. When current flows through the first resistor R1, the voltage value between the two ends of the first resistor R1 is measured, and the specific current parameter value flowing through the first resistor R1 is indirectly solved and obtained based on the known resistance value of the first resistor R1 and Ohm's law.

[0016] The non-inverting input terminal of the first operational amplifier U1 is connected to the first common node formed by the first resistor R1 and the load voltage output terminal Vout, and the inverting input terminal of the first operational amplifier U1 is connected to the output terminal thereof. The first operational amplifier U1 can serve as a high input impedance source and provide a low output impedance in this embodiment. When a current flows through the first resistor R1, the first operational amplifier U1 can convert the voltage drop generated by the first resistor R1 into a corresponding output voltage Vsense and output the voltage Vsense from the output terminal, thereby achieving the effects of voltage following and buffering. The steady-state measurement voltage Vsense output from the output terminal of the first operational amplifier U1 will be read by the subsequent circuit to perform current value calculation.

[0017] The first end of the first capacitor C1 is connected to the first common node formed by the first resistor R1 and the load voltage output terminal Vout, and the second end of the first capacitor C1 is connected to the control voltage output terminal Vc. In this embodiment, the first resistor R1 and the first capacitor C1 form a first RC charging and discharging circuit. When a current flows through the first resistor R1, the first capacitor C1 first performs a charging process, thereby smoothing voltage changes and reducing the transient response of the circuit. After the first capacitor C1 is fully charged, the output terminal of the first operational amplifier U1 is adjusted to output the steady-state measurement voltage Vsense, thereby satisfying the accurate and stable measurement of the voltage value across the first resistor R1.

[0018] It is worth noting that, in this embodiment, since the embodiment is directed to small current (pA range) measurement, in order to make the actual measured voltage value across the first resistor R1 more accurate and readable, the actual measured voltage value across the first resistor R1 needs to be displayed as a larger value. According to Ohm's law, the resistance value of the first resistor R1 needs to be selected to be larger. Based on the characteristics of the RC charging and discharging circuit, the time constant τ=RC. Therefore, if the first capacitor C1 is only charged by the first RC charging and discharging circuit, the charging speed of the first capacitor C1 is slow, which results in a longer single current measurement time of the source measurement unit. Therefore, the second resistor R2 and the second capacitor C2 are further provided in this embodiment.

[0019] The first end of the second resistor R2 is connected with the first common node formed by the first resistor R1 and the load voltage output terminal Vout, the second end of the second resistor R2 is connected with the first end of the second capacitor C2, the second end of the second capacitor is connected with the control voltage output terminal Vc, in the embodiment, the second resistor R2 and the second capacitor C2 form a second RC charging and discharging circuit, when the current flows through the first resistor R1 and the first capacitor C1 is charged, the second capacitor C2 can be discharged at the same time, and the auxiliary charging of the first capacitor C1 is realized, and in the embodiment, the resistance value of the second resistor R2 is selected as 1KΩ, and the rapid discharge of the second RC charging and discharging circuit can be realized, that is, through the setting of the second capacitor C2, the charging speed of the first capacitor C1 can be rapidly improved, and then the time for the first capacitor C1 to be fully charged is shortened, that is, the time for the output terminal of the first operational amplifier U1 to be adjusted to the output steady-state measurement voltage Vsense is shortened, the overall time for a single current measurement of the source measurement unit in the small current measurement operation is effectively shortened, and the measurement efficiency is improved.

[0020] In the following, the specific structure of the circuit for improving the small current measurement speed provided in the embodiment will be further described in detail. In the circuit for improving the small current measurement speed provided in the embodiment, the second operational amplifier U2 and the third resistor R3 are further provided, the non-inverting input terminal of the second operational amplifier U2 is connected with the control voltage output terminal Vc, the inverting input terminal of the second operational amplifier U2 is connected with the load voltage output terminal Vout and forms a second common node, the inverting input terminal of the second operational amplifier U2 is further connected with the output terminal through the third resistor R3 in series, and the output terminal of the second operational amplifier U2 is further connected with the third common node formed by the second capacitor C2 and the second resistor R2, when the small current flows through the third resistor R3, the output terminal of the second operational amplifier U2 can be adjusted to the output steady-state voltage.

[0021] Further, in the embodiment, the first common node formed by the first resistor R1 and the load voltage output terminal Vout is provided with the first switch K1 between the second common node formed by the inverting input terminal of the second operational amplifier U2 and the load voltage output terminal Vout. The second switch K2 is provided between the inverting input terminal of the second operational amplifier U2 and the load voltage output terminal Vout. The third switch K3 is provided between the second resistor R2 and the second capacitor C2. The fourth switch K4 is provided between the output terminal of the second operational amplifier U2 and the third common node formed by the second capacitor C2 and the third switch K3. In the embodiment, the opening and closing of the first switch K1, the second switch K2, the third switch K3 and the fourth switch K4 can realize the opening and closing control of different lines in the circuit, and further realize the charging and discharging control of the first capacitor C1 and the second capacitor C2. Specifically, when the third switch K3 is disconnected and the fourth switch K4 is connected, the charging operation of the second capacitor C2 can be realized. When the charging of the second capacitor C2 is completed, the third switch K3 is connected and the fourth switch K4 is disconnected, and the discharging of the second capacitor C2 and the charging operation of the first capacitor C1 can be realized.

[0022] Further, in the embodiment, the fourth resistor R4 is further provided between the output terminal of the second operational amplifier U2 and the fourth switch K4. When the third switch K3 is disconnected and the fourth switch K4 is connected, the third RC charging and discharging circuit is formed by the second capacitor C2 and the fourth resistor R4. When the output terminal of the second operational amplifier U2 outputs a steady voltage, the charging operation of the second capacitor C2 can be realized. In the embodiment, the resistance value of the fourth resistor R4 is selected as 1KΩ, which can realize the rapid charging of the third RC charging and discharging circuit and improve the charging speed of the second capacitor C2.

[0023] Preferably, in the embodiment, the resistance values of the first resistor R1 and the third resistor R3 are the same, and the resistance values of the first resistor R1 and the third resistor R3 are limited to 10GΩ-100GΩ. By selecting a large resistor, when a small current flows through the first resistor R1, the voltage value measured at both ends of the first resistor R1 is large, which can improve the accuracy of subsequent current calculation.

[0024] Second embodiment Based on the same concept, the application further provides a measurement method for improving small current measurement speed, which is applied to the circuit for improving small current measurement speed in any one of the first embodiments, and refers to Figure 2 , comprising the following steps: S1: the first switch K1 is disconnected, the second switch K2 is connected, the third switch K3 is disconnected, and the fourth switch K4 is connected, so that the second RC charging and discharging circuit is disconnected, the third RC charging and discharging circuit is connected, and the output voltages of the control voltage output terminal Vc and the load voltage output terminal Vout are adjusted to be the same.

[0025] S2: Wait for the second operational amplifier U2 output end to output adjustment to the steady state voltage, the second capacitor C2 realizes the energy storage.

[0026] S3: After the second capacitor C2 is charged, the third switch K3 is closed, the fourth switch K4 is disconnected, so that the second RC charging and discharging circuit forms a path, the third RC charging and discharging circuit forms a circuit, the second capacitor C2 is charged by discharging to assist the first capacitor C1.

[0027] S4: After the first capacitor C1 is quickly charged, the first switch K1 is closed, the second switch K2 is disconnected, the control voltage output end Vc is self-adapted to the output voltage, and the output end of the first operational amplifier U1 is quickly adjusted to the output steady state measurement voltage Vsense.

[0028] S5: Get the steady state measurement voltage value Vsense of the control voltage output end Vc and the output end of the first resistance R1, and indirectly solve the small current value flowing through the first resistance R1 through Ohm's law.

[0029] Through the measurement method for improving the small current measurement speed provided in the embodiment, the cooperation adjustment of the first switch K1, the second switch K2, the third switch K3 and the fourth switch K4 is used to first realize the fast charging of the second capacitor C2, and then the second capacitor C2 is quickly discharged and the first capacitor C1 is assisted to charge, so that the first capacitor C1 can quickly complete the charging, the output end of the first operational amplifier U1 is quickly adjusted to the output steady state measurement voltage, the adjustment time of the measurement voltage between the first resistance R1 is effectively shortened, and the single current measurement efficiency of the source measurement unit in the face of small current measurement operation is effectively improved.

[0030] Third embodiment Based on the same idea, the application also provides a system for improving the small current measurement speed, which is equipped with the circuit for improving the small current measurement speed in any one of the first embodiment, and refers to Figure 3 , comprising a voltage control unit, a current measurement unit and a measured device unit.

[0031] The voltage control unit is used to output the control voltage Vc to the current measurement unit.

[0032] The current flowing through the current measurement unit and the measured device unit belongs to a series relationship, so the circuit for improving the small current measurement speed is arranged in the current measurement unit, the current measurement unit is connected with the upper computer outside, and the current measurement unit is used to obtain the steady state measurement voltage Vsense between the measurement resistance, and the voltage Vsense is transmitted to the upper computer to realize the current value calculation.

[0033] The measured device unit is used to output the load voltage Vout of the measured device to the current measurement unit.

[0034] To sum up, by the circuit, the measurement method and the system for improving the small current measurement speed provided in the application, the switching cooperation of the first RC charging and discharging circuit, the second RC charging and discharging circuit and the third RC charging and discharging circuit is utilized to realize the fast energy charging of the first capacitor C1, so that the voltage value at both ends of the first resistor R1 with a large resistance value is quickly adjusted to the steady-state measurement voltage Vsense, and then the actual resistance value of the first resistor R1 and the steady-state measurement voltage Vsense are utilized to accurately solve and obtain the specific value of the small current flowing through the first resistor R1 based on the Ohm's law, so as to realize the single-time current fast and accurate measurement function of the source measurement unit when facing the small current measurement operation, and effectively optimize the use performance and manufacturing cost of the source measurement unit.

[0035] The embodiments of the application are described in detail above with reference to the accompanying drawings, but the application is not limited to the above-described embodiments. Even if various changes are made to the application, if the changes belong to the scope of the claims of the application and equivalent technologies thereof, they still fall within the protection scope of the application.

[0036] The term "comprising" and variations thereof as used herein are used inclusively, i.e., "comprising but not limited to". Unless specifically stated, the term "or" means "and / or". The term "based on" means "based at least in part on". The terms "one example embodiment" and "an embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first", "second", etc. can refer to different or the same objects.

Claims

1. A circuit for improving the speed of small current measurement, characterized in that, For current measurement requirements in the pA range, the components include: a first resistor, a second resistor, a first capacitor, a second capacitor, and a first operational amplifier. The first end of the first resistor is connected to the control voltage output terminal, and the second end of the first resistor is connected to the load voltage output terminal. The non-inverting input terminal of the first operational amplifier is connected to the first common junction formed by the first resistor and the load voltage output terminal, and the inverting input terminal of the first operational amplifier is connected to its output terminal. The first end of the first capacitor is connected to the first common junction formed by the first resistor and the load voltage output terminal, and the second end of the first capacitor is connected to the control voltage output terminal. The first end of the second resistor is connected to the first common junction formed by the first resistor and the load voltage output terminal; the second end of the second resistor is connected to the first end of the second capacitor; and the second end of the second capacitor is connected to the control voltage output terminal. A circuit for improving the speed of small current measurement is configured such that the first resistor and the first capacitor form a first RC charging and discharging circuit. When a small current flows through the first resistor, after the first capacitor is fully charged, the output terminal of the first operational amplifier outputs a steady-state measurement voltage. The second resistor and the second capacitor form a second RC charging and discharging circuit. During the charging process of the first capacitor, the second capacitor discharges to assist in charging the first capacitor.

2. The circuit for improving the speed of small current measurement as described in claim 1, characterized in that, It also includes a second operational amplifier and a third resistor. The non-inverting input of the second operational amplifier is connected to the control voltage output, and the inverting input of the second operational amplifier is connected to the load voltage output, forming a second common junction. The inverting input of the second operational amplifier is also connected in series with the third resistor and then connected to its output. The output of the second operational amplifier is further connected to the third common junction formed by the second capacitor and the second resistor. A circuit for improving the speed of small current measurement is further configured such that when a small current flows through the third resistor, the second operational amplifier outputs a steady-state voltage.

3. The circuit for improving the speed of small current measurement as described in claim 2, characterized in that, A first switch is provided between the first common junction formed by the first resistor and the load voltage output terminal and the second common junction formed by the inverting input terminal of the second operational amplifier and the load voltage output terminal; A second switch is provided between the inverting input terminal of the second operational amplifier and the load voltage output terminal; A third switch is provided between the second resistor and the second capacitor; A fourth switch is provided between the output terminal of the second operational amplifier and the third common junction formed by the second capacitor and the third switch.

4. The circuit for improving the speed of small current measurement as described in claim 3, characterized in that, A fourth resistor is provided between the output terminal of the second operational amplifier and the fourth switch. The fourth resistor is configured such that when the third switch is open and the fourth switch is closed, the second capacitor and the fourth resistor form a third RC charging and discharging circuit. When the second operational amplifier outputs a steady-state voltage, the second capacitor is charged.

5. The circuit for improving the speed of small current measurement as described in claim 2, characterized in that, The first resistor and the third resistor have the same resistance value, and the resistance values ​​of the first resistor and the third resistor are limited to 10GΩ-100GΩ.

6. A measurement method for improving the speed of small current measurement, characterized in that, The circuit for improving the speed of small current measurement as described in any one of claims 1-5 includes the following steps: S1: The first switch is open, the second switch is closed, the third switch is open, and the fourth switch is closed, adjusting the output voltage of the control voltage output terminal and the load voltage output terminal to be the same; S2: The second operational amplifier charges the second capacitor; S3: After the second capacitor is fully charged, the third switch is closed and the fourth switch is opened, and the second capacitor assists in charging the first capacitor by discharging; S4: After the first capacitor is fully charged, the first switch is closed, the second switch is open, the control voltage output terminal adaptively fine-tunes the output voltage, and the output terminal of the first operational amplifier outputs a steady-state measurement voltage. S5: Obtain the voltage values ​​of the control voltage output terminal and the output terminal of the first operational amplifier across the first resistor, and solve for the value of the small current flowing through the first resistor using Ohm's law.

7. A system for improving the speed of small current measurement, characterized in that, The circuit for improving the speed of small current measurement according to any one of claims 1-5 includes: Voltage control unit, the voltage control unit being used to output control voltage; The current measurement unit has an internal circuit for improving the speed of small current measurement and is externally connected to the host computer. The current measurement unit is used to obtain the steady-state measurement voltage across the first resistor and transmit the voltage to the host computer to calculate the current value. The device under test (DUT) unit is used to output the load voltage of the device under test.

Images