Multi-channel device for rapidly measuring extra-small unit current

Abstract

The invention discloses a multi-channel device for rapidly measuring extra-small unit current. The multi-channel device is an integral multi-channel measuring device composed of a plurality of single-channel measuring modules. The single-channel measurement module comprises a gear switching module, a sampling module, an absolute value module, an ADC module, an MCU module and a human-computer interface module. The gear switching module is connected with a measured load. Positive and negative currents can be rapidly measured, and the current value can be extremely small. The main aspect of the device is characterized in that a floating ground technology and an absolute value circuit are adopted, other devices can rapidly realize filtering rectification, and a current value can be rapidly measured.

Description

Technical Field

[0001] The invention relates to a multi-channel fast measurement device for ultra-small unit current. Background Art

[0002] When measuring smaller unit currents, such as nanoampere (nA) currents, conventional RC filtering is usually used in existing technologies. The existing technologies mainly have the following defects: 1. The ADC conversion time is too long, about 200mS; 2. There are many filter capacitors, and the sampling current signal filtering takes a long time to stabilize; 3. There are many filter capacitors, and the capacitor discharge time is long, and the next cycle test time is too long; 4. The voltage signal across the sampling resistor has large ripple. Summary of the invention

[0003] The object of the present invention is to provide a device which can quickly measure positive and negative currents and can quickly measure very small unit currents with extremely small current values.

[0004] The technical solution of the present invention is:

[0005] A multi-channel fast measurement device for ultra-small unit current, characterized in that: it is an integral multi-channel measurement device composed of multiple single-channel measurement modules; the single-channel measurement module includes a gear switching module, which is used to measure the size of the current value, and the MCU selects a suitable gear according to the size of the measured current value; the gear switching module is connected to a sampling module, the sampling module is used to collect the signal of the measured current value, and amplify the signal and then filter it; the sampling module is connected to an absolute value module, the absolute value module mainly performs absolute value calculation and then filters the signal collected by the sampling module, and it can quickly perform filtering processing; the absolute value module The output is connected to the input of the ADC module. The ADC module is an isolated ADC, which is used to separate the floating ground F from the system ground GND and convert the analog quantity of the measured current value into a digital quantity; the ADC module is connected to the MCU module. The MCU module is the control center. The selection of the range is implemented by the MCU module. The MCU module selects the corresponding gear range according to the size of the received current value, and transmits the measured current value to the human-machine interface for display; the MCU module is connected to the human-machine interface module, which plays a display role and displays the measured current value on the human-machine interface;

[0006] The gear switching module is connected to the load to be measured.

[0007] The entire multi-channel measurement device is controlled by the same MCU module, or multiple MCU modules control a single-channel measurement module respectively.

[0008] The first end of the resistor Rp1 in the gear switching module is connected to the voltage input terminal VIN, and the second end is connected to the first end of the switching switch Sp1, and the second end of the switching switch Sp1 is connected to the floating ground F; the first end of the resistor Rp2 is connected to the voltage input terminal VIN, and the second end is connected to the first end of the switching switch Sp2, and the second end of the switching switch Sp2 is connected to the floating ground F; the first end of the resistor Rpn is connected to the voltage input terminal VIN, and the second end is connected to the first end of the switching switch Spn, and the second end of the switching switch Spn is connected to the floating ground F; the first end of the resistor Rs1 is connected to the voltage output terminal VOUT, and the second end is connected to the first end of the switching switch Ss1, and the second end of the switching switch Ss1 is connected to the floating ground; the first end of the resistor Rs2 is connected to the voltage output terminal VOUT, and the second end is connected to the first end of the switching switch Ss2, and the second end of the switching switch Ss2 is connected to the floating ground; the first end of the resistor Rsn is connected to the voltage output terminal VOU T, the second end is connected to the first end of the switch Ssn, and the second end of the switch Ssn is connected to the floating ground; multiple switches Sp1 / Sp2 / ... / Spn / Ss1 / Ss2 / ... / Ssn are used to control the range switching, each switch has a third end pin, the third end of the switch Sp1 is connected to the third end of the switch Ss1 and the MCU, the two switches are controlled by the MCU at the same time, and are connected or disconnected at the same time; the third end of the switch Sp2 is connected to the third end of the switch Ss2 and the MCU, the two switches are controlled by the MCU at the same time, and are connected or disconnected at the same time; the third end of the switch Spn is connected to the third end of the switch Ssn and the MCU, the two switches are controlled by the MCU at the same time, and are connected or disconnected at the same time; the module circuit is also provided with a filter capacitor C3, the first end of the filter capacitor C3 is connected to the floating ground F, and the second end is connected to the voltage output terminal VOUT. IO1 / IO2 / ... / IOn in the module are respectively connected to IO1 / IO2 / ... / IOn of the MCU module for switching range selection.

[0009] The sampling module is mainly composed of an operational amplifier, a capacitor, and two resistors; the first end pin of the operational amplifier U3 is connected to the first end of the capacitor C2, the second end of the resistor R5, the first end of the resistor R1, the first end pin of the operational amplifier U1, and the first end of the resistor R6; the second end of the capacitor C2 is connected to the floating ground, the third end pin of the operational amplifier U3 is connected to the voltage output terminal VOUT, the second end pin of the operational amplifier U3 is connected to the first end of the resistor R5, the second end of the resistor R4, and the first end of the resistor R4 is connected to the floating ground F.

[0010] The absolute value module consists of 4 resistors, 3 diodes, 2 operational amplifiers and 1 filter capacitor; the third end pin of the operational amplifier U1 is connected to the floating ground F, and the second end pin is connected to the first end of the resistor R1, the first end of the resistor R6 and the output end of the module; the first end pin of the operational amplifier U1 is connected to the cathode of the diode D1 and the anode of the diode D3; the anode of the diode D1 is connected to the second end of the resistor R1 and the first end of the resistor R2; the cathode of the diode D3 is connected to the second end of the resistor R6 and the third end pin of the operational amplifier U2; the second end pin of the operational amplifier U2 is connected to the second end of the resistor R2 and the first end of the resistor R3; the first end pin of the operational amplifier U2 is connected to the anode of the diode D2; the cathode of the diode D2 is connected to the second end of the resistor R3 and the first end of the capacitor C1 and the input end of the ADC module; the second end of the capacitor C1 is connected to the floating ground F.

[0011] The present invention can quickly measure positive and negative currents, and the current value can be extremely small, the minimum is PA (picoampere level). Its main performance is the use of floating ground technology and absolute value circuit, and the other can quickly achieve filtering and rectification, so as to quickly measure the current value.

[0012] The advantages of the present invention also lie in:

[0013] 1. Use advance filtering to make the sampled current signal quickly stable. However, the existing technology has poor effect and accuracy in post-filtering.

[0014] 2. Use floating ground technology to sample on high-voltage lines, so that the voltage of the op amp is lower and the output signal can be faster and more stable. However, in the existing technology, the voltage requirement of the op amp is too high and the stability is poor.

[0015] 3. After the absolute value current signal is converted into a positive signal, a diode is placed to rectify and prevent reverse flow, and then a wave capacitor is added, so that other capacitors cannot discharge reversely, and a stable sampling signal can be quickly achieved. However, this is not seen in the prior art.

[0016] 4. Using extremely small leakage current of the operational amplifier, the current value measured is highly accurate. However, the operational amplifier value current of the prior art is relatively large. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0018] Figure 1 It is a schematic diagram of a single-channel module of the present invention.

[0019] Figure 2 It is a simplified module diagram of multiple channels.

[0020] Figure 2 illustrate:

[0021] Figure 2A in is equivalent to the combination of module 1, module 2, module 3, and module 4 in a single channel. The module TQ under test is the same as Q in module 7.

[0022] VIN is connected to the input of A1\A2\An, the output of A1 is connected to the GATE of TQ1, and the D and S terminals of TQ1 are connected to the ground GND (it should be noted that the example here is to measure the IGSS (leakage current of the G pole) of MOS. The connection method will be different according to the requirements of the test item and can be simplified to a resistor for illustration).

[0023] The A2 output terminal is connected to the GATE terminal of TQ2, and the D and S terminals of TQ2 are connected to the ground GND; the An output terminal is connected to the GATE terminal of TQn, and the D and S terminals of TQn are connected to the ground GND; the MCU and the human-machine interface are shared.

[0024] The whole device is controlled by the same MCU or multiple MCUs, such as the control of displaying test values ​​and range switching. DETAILED DESCRIPTION

[0025] A multi-channel fast measurement device for ultra-small unit current is an overall multi-channel measurement device composed of multiple single-channel measurement modules; the single-channel measurement module includes a gear switching module 1, which is used to measure the size of the current value. According to the size of the measured current value, the MCU selects a suitable gear (range); the gear switching module is connected to a sampling module 2, and the sampling module is used to collect the signal of the measured current value, and amplify the signal and then filter it; the sampling module is connected to an absolute value module 3, and the absolute value module mainly performs absolute value calculation and then filtering on the signal collected by the sampling module, and it can quickly implement the filtering process; the output of the absolute value module is connected to the absolute value module 3, and the absolute value module ... The input connection of the ADC module, the ADC module 4 is an isolation ADC, which is used to separate the floating ground F from the system ground GND, and convert the analog quantity of the measured current value into a digital quantity; the ADC module is connected to the MCU module (control module) 5, the MCU module is the control center, the range selection is implemented by the MCU module, the MCU module selects the corresponding gear range according to the size of the received current value, and transmits the measured current value to the human-machine interface for display; the MCU module is connected to the human-machine interface module 6, the human-machine interface module plays a display role, and displays the measured current value on the human-machine interface;

[0026] The gear switching module is connected to the load 7 under test.

[0027] The entire multi-channel measurement device is controlled by the same MCU module, or multiple MCU modules control a single-channel measurement module respectively.

[0028] The first end of the resistor Rp1 in the gear switching module is connected to the voltage input terminal VIN, and the second end is connected to the first end of the switching switch Sp1, and the second end of the switching switch Sp1 is connected to the floating ground F; the first end of the resistor Rp2 is connected to the voltage input terminal VIN, and the second end is connected to the first end of the switching switch Sp2, and the second end of the switching switch Sp2 is connected to the floating ground F; the first end of the resistor Rpn is connected to the voltage input terminal VIN, and the second end is connected to the first end of the switching switch Spn, and the second end of the switching switch Spn is connected to the floating ground F; the first end of the resistor Rs1 is connected to the voltage output terminal VOUT, and the second end is connected to the first end of the switching switch Ss1, and the second end of the switching switch Ss1 is connected to the floating ground; the first end of the resistor Rs2 is connected to the voltage output terminal VOUT, and the second end is connected to the first end of the switching switch Ss2, and the second end of the switching switch Ss2 is connected to the floating ground; the first end of the resistor Rsn is connected to the voltage output terminal VOU T, the second end is connected to the first end of the switch Ssn, and the second end of the switch Ssn is connected to the floating ground; multiple switches Sp1 / Sp2 / ... / Spn / Ss1 / Ss2 / ... / Ssn are used to control the range switching, each switch has a third end pin, the third end of the switch Sp1 is connected to the third end of the switch Ss1 and the MCU, the two switches are controlled by the MCU at the same time, and are connected or disconnected at the same time; the third end of the switch Sp2 is connected to the third end of the switch Ss2 and the MCU, the two switches are controlled by the MCU at the same time, and are connected or disconnected at the same time; the third end of the switch Spn is connected to the third end of the switch Ssn and the MCU, the two switches are controlled by the MCU at the same time, and are connected or disconnected at the same time; the module circuit is also provided with a filter capacitor C3, the first end of the filter capacitor C3 is connected to the floating ground F, and the second end is connected to the voltage output terminal VOUT. IO1 / IO2 / ... / IOn in the module are respectively connected to IO1 / IO2 / ... / IOn of the MCU module for switching range selection.

[0029] The sampling module is mainly composed of an operational amplifier, a capacitor, and two resistors; the first end pin of the operational amplifier U3 is connected to the first end of the capacitor C2, the second end of the resistor R5, the first end of the resistor R1, the first end pin of the operational amplifier U1, and the first end of the resistor R6; the second end of the capacitor C2 is connected to the floating ground, the third end pin of the operational amplifier U3 is connected to the voltage output terminal VOUT, the second end pin of the operational amplifier U3 is connected to the first end of the resistor R5, the second end of the resistor R4, and the first end of the resistor R4 is connected to the floating ground F.

[0030] The absolute value module consists of 4 resistors, 3 diodes, 2 operational amplifiers and 1 filter capacitor; the third end pin of the operational amplifier U1 is connected to the floating ground F, and the second end pin is connected to the first end of the resistor R1, the first end of the resistor R6 and the output end of the module; the first end pin of the operational amplifier U1 is connected to the cathode of the diode D1 and the anode of the diode D3; the anode of the diode D1 is connected to the second end of the resistor R1 and the first end of the resistor R2; the cathode of the diode D3 is connected to the second end of the resistor R6 and the third end pin of the operational amplifier U2; the second end pin of the operational amplifier U2 is connected to the second end of the resistor R2 and the first end of the resistor R3; the first end pin of the operational amplifier U2 is connected to the anode of the diode D2; the cathode of the diode D2 is connected to the second end of the resistor R3 and the first end of the capacitor C1 and the input end of the ADC module; the second end of the capacitor C1 is connected to the floating ground F.

[0031] like Figure 2 As shown, the core of the device is to measure the current value flowing through the device. The voltage at both ends of the ammeter cannot be too large, because a large voltage at both ends of the ammeter will reduce the voltage on the device under test, resulting in poor measurement accuracy. Therefore, the gear switching module adopts a graded range. The smaller the current, the larger the ammeter sampling resistor is selected. On the contrary, the larger the current, the smaller the sampling resistor range is selected. R0 represents the internal resistance of the ammeter, V0 represents the voltage between the two ammeters, and I0 represents the current flowing through the sampling resistor, then:

[0032] V0=R0*I0[Formula 1]

[0033] In this example, V0 is set to 180mV. When the voltage across UAB received by the control unit exceeds 180mV, the MCU will switch to a gear with a smaller sampling resistor.

[0034] For example: sampling resistors Rs1 = 1.8MΩ, Rs2 = 180KΩ, Rs3 = 18KΩ, a total of 3 ranges. For the initial test, use Rs1 = 1.8MΩ. At this time, the MCU controls Sp1 / Ss1 to connect and Sp2 / Ss2 / Sp3 / Ss3 to disconnect. When the current flowing through Rs1 exceeds 100nA:

[0035] UAB=100nA*1.8MΩ=180mV

[0036] When UAB reaches the 180mV limit, the MCU controls the switch Sp2 / Ss2 in the gear switching module to connect and the switch Sp1 / Ss1 / Sp3 / Ss3 to disconnect. If the voltage of UAB still exceeds 180mV at this time, the same logic applies. If it still exceeds the last maximum current level, the human-machine interface displays an error. The measurement ends.

[0037] The measurement order in the above definition is from small to large. In some other test methods, the measurement order may be from large to small. For example, start the test at the third gear. At this time:

[0038] UAB=100nA*18KΩ=1.8mV,

[0039] At this time, the MCU determines that the current is small and needs to be switched to a smaller gear. This gear range can only be used when 180mV>UAB>10mV, otherwise the gear needs to be switched.

[0040] C3 in the gear switching module is mainly used for initial filtering. This capacitor is used to speed up the measurement. When measuring extremely small unit current, the sampling resistor is relatively large, generally with a resistance value of more than one megabyte. With such a large resistance, even a small change in the amount of electricity will cause a large ripple. If this capacitor is missing, the peak-to-peak value of the ripple input of the early sampling is large, and the transmission to the next stage exceeds the limit, which prolongs the filtering time of the next stage. This capacitor is shared with Rp to form an RC filter.

[0041] After the voltage UAB is collected by the gear switching module, this voltage is amplified and filtered by the sampling module. The sampling module adopts a floating amplification mode. The advantage of the floating mode is that the power supply voltage of the operational amplifier U3 does not need to be too high, and the low output voltage accelerates filtering. The characteristic of the amplifier U3 in the sampling module is that the input current of the same phase or opposite phase is less than 1pA (picoampere). For measuring currents greater than 1pA, such as 1nA, the influence of the operational amplifier shunt can be ignored, making its measurement accuracy high. C2 is used for filtering, and R4 / R5 / U3 form a proportional amplifier. After amplification, the accuracy of the measured current is improved. Suppose the amplification factor of this sampling module is A1. The output voltage is UO1.

[0042] U01=A1*UAB

[0043] The absolute value module is an absolute value circuit. If the output voltage of this module is U02, then

[0044] U02=|U01|

[0045] The output voltage of this circuit is always positive, and the diode half-wave rectifier is used for fast rectification. The voltage is rectified by the diode and then filtered efficiently by capacitor C1. Because the diode has a reverse effect, the current of C1 cannot flow back, thus achieving fast, stable and smooth voltage signals. This is another fast and stable feature.

[0046] The function of the ADC module is to convert analog signals into digital signals, and to perform conversion and isolation.

[0047] The load under test is mainly SIC, but can also be MOS (metal oxide semiconductor), other semiconductor devices or any device parts.

Claims

1. A multi-channel rapid measurement of ultra-small unit current device, characterized in that: An overall multi-channel measuring device composed of multiple single-channel measuring modules; the single-channel measuring module includes a gear switching module for measuring the size of the current value, and the MCU selects a suitable gear according to the size of the measured current value; the gear switching module is connected to the sampling module, the sampling module is used to collect the signal of the measured current value, and amplify the signal and then filter it; the sampling module is connected to the absolute value module, the absolute value module mainly performs absolute value calculation and then filtering on the signal collected by the sampling module, and it can quickly perform real-time filtering processing; the output of the absolute value module is connected to the input of the ADC module, the ADC module is an isolation ADC, which is used to separate the floating ground F from the system ground GND, and convert the analog quantity of the measured current value into a digital quantity; the ADC module is connected to the MCU module, the MCU module is the control center, the range selection is implemented by the MCU module, the MCU module selects the corresponding gear range according to the size of the received current value, and transmits the measured current value to the human-machine interface for display; the MCU module is connected to the human-machine interface module, the human-machine interface module plays a display role, and displays the measured current value on the human-machine interface; The gear switching module is connected to the load to be measured.

2. A multi-channel fast measurement of ultra-small unit current device according to claim 1, characterized in that: The entire multi-channel measurement device is controlled by the same MCU module, or multiple MCU modules control a single-channel measurement module respectively.

3. A multi-channel fast measurement device for ultra-small unit current according to claim 1 or 2, characterized in that: The first end of the resistor Rp1 in the gear switching module is connected to the voltage input terminal VIN, and the second end is connected to the first end of the switching switch Sp1, and the second end of the switching switch Sp1 is connected to the floating ground F; the first end of the resistor Rp2 is connected to the voltage input terminal VIN, and the second end is connected to the first end of the switching switch Sp2, and the second end of the switching switch Sp2 is connected to the floating ground F; the first end of the resistor Rpn is connected to the voltage input terminal VIN, and the second end is connected to the first end of the switching switch Spn, and the second end of the switching switch Spn is connected to the floating ground F; the first end of the resistor Rs1 is connected to the voltage output terminal VOUT, and the second end is connected to the first end of the switching switch Ss1, and the second end of the switching switch Ss1 is connected to the floating ground; the first end of the resistor Rs2 is connected to the voltage output terminal VOUT, and the second end is connected to the first end of the switching switch Ss2, and the second end of the switching switch Ss2 is connected to the floating ground; the first end of the resistor Rsn is connected to the voltage output terminal VOUT, and the second end is connected to the first end of the switching switch Ssn, and the switching switch Ssn The second end of the switching switch Sp1 / Sp2 / ... / Spn / Ss1 / Ss2 / ... / Ssn is connected to the floating ground; a plurality of switching switches Sp1 / Sp2 / ... / Spn / Ss1 / Ss2 / ... / Ssn are used to control the range switching, each switching switch has a third end pin, the third end of the switching switch Sp1 is connected to the third end of the switching switch Ss1 and the MCU, the two switching switches are controlled by the MCU at the same time, and are connected or disconnected at the same time; the third end of the switching switch Sp2 is connected to the third end of the switching switch Ss2 and the MCU, the two switches are controlled by the MCU at the same time, and are connected or disconnected at the same time; the third end of the switching switch Spn is connected to the third end of the switching switch Ssn and the MCU, the two switches are controlled by the MCU at the same time, and are connected or disconnected at the same time; a filter capacitor C3 is also provided in the module circuit, the first end of the filter capacitor C3 is connected to the floating ground F, and the second end is connected to the voltage output terminal VOUT; the ports IO1 / IO2 / ... / IOn are respectively connected to the ports IO1 / IO2 / ... / IOn of the MCU module for switching the range selection.

4. A multi-channel fast measurement device for ultra-small unit current according to claim 1 or 2, characterized in that: Sampling Module It is mainly composed of 1 operational amplifier, 1 capacitor and two resistors; the first end pin of the operational amplifier U3 is connected to the first end of the capacitor C2, the second end of the resistor R5, the first end of the resistor R1, the first end pin of the operational amplifier U1 and the first end of the resistor R6; the second end of the capacitor C2 is connected to the floating ground, the third end pin of the operational amplifier U3 is connected to the voltage output terminal VOUT, the second end pin of the operational amplifier U3 is connected to the first end of the resistor R5 and the second end of the resistor R4, and the first end of the resistor R4 is connected to the floating ground F.

5. A multi-channel fast measurement device for ultra-small unit current according to claim 1 or 2, characterized in that: The absolute value module consists of 4 resistors, 3 diodes, 2 operational amplifiers and 1 filter capacitor; the third end pin of the operational amplifier U1 is connected to the floating ground F, and the second end pin is connected to the first end of the resistor R1, the first end of the resistor R6 and the output end of the module; the first end pin of the operational amplifier U1 is connected to the cathode of the diode D1 and the anode of the diode D3; the anode of the diode D1 is connected to the second end of the resistor R1 and the first end of the resistor R2; the cathode of the diode D3 is connected to the second end of the resistor R6 and the third end pin of the operational amplifier U2; the second end pin of the operational amplifier U2 is connected to the second end of the resistor R2 and the first end of the resistor R3; the first end pin of the operational amplifier U2 is connected to the anode of the diode D2; the cathode of the diode D2 is connected to the second end of the resistor R3 and the first end of the capacitor C1 and the input end of the ADC module; the second end of the capacitor C1 is connected to the floating ground F.

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