阅读说明：本技术 一种电压电阻电容自动测量的方法及电路 (Method and circuit for automatically measuring voltage resistance capacitance ) 是由 周治富 严王军 许为来 黄海龙 陈志武 罗伟绍 于 2021-07-05 设计创作，主要内容包括：本发明涉及电子元器件测量技术,公开了一种电压电阻电容自动测量的方法及电路；其包括外部信号输入电路、内部开关网络电路、基准信号输出与电流源产生电路、通道切换与ADC采集电路和比较器输出电路；外部信号输入电路与内部开关网络电路连接,内部开关网络电路与通道切换与ADC采集电路和基准信号输出与电流源产生电路连接,外部信号输入电路包括电阻R5和输入端口A1、电阻R6和输入端口A2、电阻R7和输入端口A4。本发明简化了电压电阻电容表的测量电路,只需三个电阻就能进行电压电阻电容的自动测量,无需使用继电器和表盘切换档位,内部自动判断量程进行测量；设计安全可靠,体积小,降低厂家生产成本和提高生产效率。(The invention relates to the electronic component measuring technology, and discloses a method and a circuit for automatically measuring voltage resistance and capacitance; the circuit comprises an external signal input circuit, an internal switch network circuit, a reference signal output and current source generating circuit, a channel switching and ADC acquisition circuit and a comparator output circuit; the external signal input circuit is connected with the internal switch network circuit, the internal switch network circuit is connected with the channel switching and ADC acquisition circuit and the reference signal output and current source generation circuit, and the external signal input circuit comprises a resistor R5, an input port A1, a resistor R6, an input port A2, a resistor R7 and an input port A4. The invention simplifies the measuring circuit of the voltage resistance capacitance meter, can automatically measure the voltage resistance capacitance by only three resistors, does not need to use a relay and a dial plate to switch gears, and automatically judges the measuring range inside to measure; the design is safe and reliable, the volume is small, the production cost of a manufacturer is reduced, and the production efficiency is improved.)

1. A circuit for automatically measuring voltage resistance and capacitance comprises an external signal input circuit, an internal switch network circuit, a reference signal output and current source generating circuit, a channel switching and ADC acquisition circuit and a comparator output circuit; the external signal input circuit is connected with the internal switch network circuit, and the internal switch network circuit is connected with the channel switching and ADC acquisition circuit and the reference signal output and current source generation circuit;

the external signal input circuit is characterized by comprising a resistor R5, an input port A1, a resistor R6, an input port A2, a resistor R7 and an input port A4; the internal switch network circuit comprises resistors R1, R2, R3, R4, switches K1, K2, K3, K4, K5, K6, K7, K8, K9, K10 and K11; one end of A1 is connected to resistors R4, R3, R2 and R1 through switches K1, K3, K5 and K7 respectively, the resistor R1 is connected with the switch K11, and the other port of K11 is connected with a COM port; one end of A2 is connected to resistors R4, R3, R2 and R1 through switches K2, K4, K6 and K8 respectively, and the resistor R1 is connected with the switch K12; the AVDDR is connected with the common end of the resistor R3 and the resistor R2 through a switch K9; VSS is connected to the common terminal of resistors R3 and R2 through switch K10.

2. The automatic voltage resistor capacitor measuring circuit as claimed in claim 1, wherein the reference signal output and current source generating circuit comprises switches K12, K13, K14, K15, K16, NMOS Q1 and PMOS Q2, operational amplifier OPA and channel switching MUX 1; the switch K12 is connected with the switch K13, and the other end of the switch K13 is connected with the output end OPOUT of the operational amplifier OPA; the negative input end of the operational amplifier OPA is connected to the common end of the switch K12, the switch K13, the NMOS transistor Q1 and the PMOS transistor Q2, the positive input end of the operational amplifier OPA is connected with the OPIN and connected to the switch K16, and the other end of the switch K16 is connected with the output end of the channel switching MUX 1; one end of the switch K14 is connected with the output end OPOUT of the operational amplifier OPA, and the other end is connected with the grid electrode of the NMOS tube Q1; one end of the switch K15 is connected to the output end OPOUT of the OPA, and the other end is connected to the gate of the PMOS transistor Q2.

3. The automatic voltage resistor capacitor measuring circuit as claimed in claim 1, wherein the channel switching and ADC collecting circuit comprises a channel switching MUX2 and an analog-to-digital converter ADC; the voltages of VA, VB, VC and VD points select V1P and V1N to collect signals at the input end of the ADC through a control channel switching MUX2 respectively.

4. The automatic voltage resistor capacitor measuring circuit as claimed in claim 1, wherein the comparator output circuit comprises comparators CMPH, CMPL and LATCH; the port a4 is connected to the positive input of comparator CMPH and the negative input of comparator CMPL, the negative input port of comparator CMPH is connected to the COM port, the output CMPH _ OUT of comparator CMPH is connected to the LATCH input, the positive input port of comparator CMPL is connected to VDR22, the output CMPL _ OUT of comparator CMPL is connected to the other input of LATCH, the LATCH output LATCH _ OUT is connected to the capture block.

5. The automatic measurement circuit of claim 1, wherein when the CMPH comparator outputs a high level and the CMPL comparator outputs a low level, the input signal is determined to be a voltage signal; when the CMPH comparator outputs a low level and the CMPL comparator outputs a high level, the input signal is judged to be a capacitance signal; when the CMPH comparator outputs a low level and the CMPL comparator outputs a low level, the input signal is determined to be a resistance signal.

6. A method for automatic measurement of voltage resistance capacitance, comprising a circuit for automatic measurement of voltage resistance capacitance according to any one of claims 1-5, the method comprising;

measuring a voltage signal, wherein the voltage signal is connected to an A1 port through a resistor R5, an A1 port is connected with an internal switch network and is switched according to different measuring ranges, an R1 resistor is connected with a switch K11, and a switch K11 is connected to COM; and, Res1 ═ R1; res2 ═ R1+ R2; res3 ═ R1+ R2+ R3; res4 ═ R1+ R2+ R3+ R4;

measuring a resistance signal, wherein the resistance signal is connected to an A2 port through a resistor R6, an A2 port is connected with an internal switch network, switching is carried out according to different measuring ranges, an R1 resistor is connected with a switch K12, a switch K12 is connected with a switch K13, and the other end of the switch K13 is connected with the output end of an operational amplifier OPA; the voltage of the operational amplifier output end is Vop, the voltage of the COM end is Vcom,

the resistance to be measured is Rx, and the internal reference resistance is Rr;

measuring a capacitance signal, wherein AVDDR is connected to a resistor R2 through a switch K9, the other end of the resistor R2 is connected to a resistor R1, the resistor R1 is connected to a switch K12, a switch K12 is connected to the source electrode of a PMOS tube Q2, the grid electrode of the PMOS tube Q2 is connected to a switch K15, and the other end of the switch K15 is connected with an output end OPOUT of an operational amplifier OPA; the drain electrode of the PMOS tube Q2 is connected to the A2 port, and the A2 port is connected with the resistor R6 to the end of the capacitor to be tested to supply the capacitor;

V_OP、V_CMPHall are a partial pressure of AVDDR, and the coefficients are respectively set as a and b, namely: v_OP＝a×AVDDR；V_CMPH＝b×AVDDR；Rc＝R1+R2

Converting into the following steps:

the coefficients a, b are determined by the set voltage division ratio, Δ t is obtained by the calibrated clock count inside the chip, R_CObtained by calibration.

Technical Field

The invention relates to the technology of electronic component measurement, in particular to a method and a circuit for automatically measuring voltage resistance and capacitance.

Background

With the development of electronic industry technology and measurement and control technology, the demand of measuring instruments is getting bigger and bigger, and the measurement of voltage, resistance and capacitance is often needed in different application occasions.

In the production and maintenance of circuits, the measurement of voltage, resistance and capacitance is often a crucial link, and a good electronic product must be composed of qualified electronic components, among which the power chip, resistance and capacitance are the most basic ones. For this reason, the detection of voltage, resistance and capacitance is an unavoidable step. Therefore, the design of safe, reliable and convenient voltage, resistance and capacitance testing instruments has great practical necessity.

The voltage resistance capacitance meter on the market at present has the characteristics of complex circuit design, too many gears, larger volume, complex operation in use, trouble and the like. Along with the development of electronic industrial technology, measurement and control technology and the pressure of competition in the instrument industry, the characteristics of simple design circuit, convenient operation, small volume and low production cost of a measuring instrument are increasingly required.

The patent names are: an automatic measurable multimeter having the application number: CN201911119788.7, application date: 2019-11-15, the patent application discloses an automatically measurable multimeter comprising: an input terminal for receiving a signal to be measured; the signal monitoring circuit is used for monitoring the voltage of the signal to be detected; the micro-control unit is used for sending out a measurement instruction according to the source of the signal to be measured; the function switching driving unit is used for switching the measurement gear according to the measurement instruction sent by the micro-control unit; the low-voltage switching circuit comprises a reed switch, and when the function switching driving unit is switched to a low-voltage measurement mode, the reed switch is closed; and the high-voltage prevention protection device is connected with the input terminal and the low-voltage switching circuit and is used for preventing the high-voltage signal to be detected from entering the low-voltage switching circuit. Aiming at the problem that a peripheral protection circuit is complex, the operation is troublesome by adopting a reed switch;

for example, the patent names: a digital multimeter having an application number of: CN200610062667.X, application date is: 2006-09-18. The patent needs additional auxiliary program control voltage or current source, voltage dividing network and electronic switch, and the design circuit is complex.

Disclosure of Invention

Aiming at the problems that the prior art has complex peripheral protection circuit and adopts a reed switch, the operation is troublesome; the problem of complex design circuit of the voltage or capacitance automatic measurement method and circuit is that auxiliary program control voltage or current source, voltage dividing network and electronic switch are needed to be added.

In order to solve the technical problem, the invention is solved by the following technical scheme:

a circuit for automatically measuring voltage resistance and capacitance comprises an external signal input circuit, an internal switch network circuit, a reference signal output and current source generating circuit, a channel switching and ADC acquisition circuit and a comparator output circuit; the external signal input circuit is connected with the internal switch network circuit, and the internal switch network circuit is connected with the channel switching and ADC acquisition circuit and the reference signal output and current source generation circuit.

The external signal input circuit comprises a resistor R5, an input port A1, a resistor R6, an input port A2, a resistor R7 and an input port A4; the internal switch network circuit comprises resistors R1, R2, R3, R4, switches K1, K2, K3, K4, K5, K6, K7, K8, K9, K10 and K11; one end of A1 is connected to resistors R4, R3, R2 and R1 through switches K1, K3, K5 and K7 respectively, the resistor R1 is connected with the switch K11, and the other port of K11 is connected with a COM port; one end of A2 is connected to resistors R4, R3, R2 and R1 through switches K2, K4, K6 and K8 respectively, and the resistor R1 is connected with the switch K12; the AVDDR is connected with the common end of the resistor R3 and the resistor R2 through a switch K9; VSS is connected to the common terminal of resistors R3 and R2 through switch K10.

Through the measuring circuit and the protection circuit of simplifying the voltage resistance electric capacity table, only need three resistance R5, R6, R7 to carry out the automatic measure of voltage resistance electric capacity, need not to use relay and dial plate switching gear, inside automatic judgement range is measured. The three large resistors are designed to be safe and reliable, the chip can be prevented from being damaged by high voltage, the size is small, the production cost of a manufacturer is reduced, and the production efficiency is improved.

Preferably, the reference signal output and current source generating circuit comprises switches K12, K13, K14, K15, K16, an NMOS transistor Q1 and a PMOS transistor Q2, an operational amplifier OPA and a channel switching MUX 1; the switch K12 is connected with the switch K13, and the other end of the switch K13 is connected with the output end OPOUT of the operational amplifier OPA; the negative input end of the operational amplifier OPA is connected to the common end of the switch K12, the switch K13, the NMOS transistor Q1 and the PMOS transistor Q2, the positive input end of the operational amplifier OPA is connected with the OPIN and connected to the switch K16, and the other end of the switch K16 is connected with the output end of the channel switching MUX 1; one end of the switch K14 is connected with the output end OPOUT of the operational amplifier OPA, and the other end is connected with the grid electrode of the NMOS tube Q1; one end of the switch K15 is connected to the output end OPOUT of the OPA, and the other end is connected to the gate of the PMOS transistor Q2.

Preferably, the channel switching and ADC collecting circuit includes a channel switching MUX2 and an analog-to-digital converter ADC; the voltages of VA, VB, VC and VD points select V1P and V1N to collect signals at the input end of the ADC through a control channel switching MUX2 respectively.

Preferably, the comparator output circuit includes comparators CMPH, CMPL and a LATCH; the port a4 is connected to the positive input of comparator CMPH and the negative input of comparator CMPL, the negative input port of comparator CMPH is connected to the COM port, the output CMPH _ OUT of comparator CMPH is connected to the LATCH input, the positive input port of comparator CMPL is connected to VDR22, the output CMPL _ OUT of comparator CMPL is connected to the other input of LATCH, the LATCH output LATCH _ OUT is connected to the capture block.

Preferably, when the CMPH comparator outputs a high level and the CMPL comparator outputs a low level, the input signal is determined to be a voltage signal; when the CMPH comparator outputs a low level and the CMPL comparator outputs a high level, the input signal is judged to be a capacitance signal; when the CMPH comparator outputs a low level and the CMPL comparator outputs a low level, the input signal is determined to be a resistance signal.

A method for automatically measuring voltage resistance capacitance comprises a circuit for automatically measuring voltage resistance capacitance, and the method comprises the following steps;

measuring a voltage signal, wherein the voltage signal is connected to an A1 port through a resistor R5, an A1 port is connected with an internal switch network and is switched according to different measuring ranges, an R1 resistor is connected with a switch K11, and a switch K11 is connected to COM; and, Re s1 ═ R1; re s2 ═ R1+ R2; re s3 ═ R1+ R2+ R3; re s4 ═ R1+ R2+ R3+ R4;

measuring a resistance signal, wherein the resistance signal is connected to an A2 port through a resistor R6, an A2 port is connected with an internal switch network, switching is carried out according to different measuring ranges, an R1 resistor is connected with a switch K12, a switch K12 is connected with a switch K13, and the other end of the switch K13 is connected with the output end of an operational amplifier OPA; the voltage of the operational amplifier output end is Vop, the voltage of the COM end is Vcom, the resistance to be detected is Rx, and the internal reference resistance is Rr;

measuring a capacitance signal, wherein AVDDR is connected to a resistor R2 through a switch K9, the other end of the resistor R2 is connected to a resistor R1, the resistor R1 is connected to a switch K12, a switch K12 is connected to the source electrode of a PMOS tube Q2, the grid electrode of the PMOS tube Q2 is connected to a switch K15, and the other end of the switch K15 is connected with an output end OPOUT of an operational amplifier OPA; the drain electrode of the PMOS tube Q2 is connected to the A2 port, the A2 port is connected with the resistor R6 to the end of the capacitor to be measured for supplying the capacitor,

V_OP、V_CMPHall are a partial pressure of AVDDR, and the coefficients are respectively set as a and b, namely: v_OP＝a×AVDDR.V_CMPH＝b×AVDDR；Rc＝R1+R2

Converting into the following steps:

the coefficients a, b are determined by the set voltage division ratio, Δ t is derived from the calibrated clock count inside the chip, R_CObtained by calibration.

Due to the adoption of the technical scheme, the invention has the remarkable technical effects that: according to the invention, by simplifying the measuring circuit and the protection circuit of the voltage resistance capacitance meter, only three resistors R5, R6 and R7 are needed for automatically measuring the voltage resistance capacitance, a relay and a dial are not needed for switching gears, and the internal automatic judgment range is used for measuring.

Meanwhile, the measuring circuit designed by the invention is safe and reliable, can prevent the chip from being damaged by high voltage through three peripheral large resistors, has small volume, reduces the production cost of manufacturers and improves the production efficiency.

Drawings

Fig. 1 is a circuit diagram of the present invention.

Fig. 2 is a circuit diagram of the internal switching network of the present invention.

FIG. 3 is a circuit diagram of the reference signal output and current source generation circuit of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples.

Example 1

A circuit for automatically measuring voltage resistance and capacitance comprises an external signal input circuit, an internal switch network circuit, a reference signal output and current source generating circuit, a channel switching and ADC acquisition circuit and a comparator output circuit; the external signal input circuit is connected with the internal switch network circuit, and the internal switch network circuit is connected with the channel switching and ADC acquisition circuit and the reference signal output and current source generation circuit.

The external signal input circuit comprises a resistor R5, an input port A1, a resistor R6, an input port A2, a resistor R7 and an input port A4; the internal switch network circuit comprises resistors R1, R2, R3, R4, switches K1, K2, K3, K4, K5, K6, K7, K8, K9, K10 and K11; one end of A1 is connected to resistors R4, R3, R2 and R1 through switches K1, K3, K5 and K7 respectively, the resistor R1 is connected with the switch K11, and the other port of K11 is connected with a COM port; one end of A2 is connected to resistors R4, R3, R2 and R1 through switches K2, K4, K6 and K8 respectively, and the resistor R1 is connected with the switch K12; the AVDDR is connected with the common end of the resistor R3 and the resistor R2 through a switch K9; VSS is connected to the common terminal of resistors R3 and R2 through switch K10.

Through the measuring circuit and the protection circuit of simplifying the voltage resistance electric capacity table, only need three resistance R5, R6, R7 to carry out the automatic measure of voltage resistance electric capacity, need not to use relay and dial plate switching gear, inside automatic judgement range is measured. The three large resistors are designed to be safe and reliable, the chip can be prevented from being damaged by high voltage, the size is small, the production cost of a manufacturer is reduced, and the production efficiency is improved.

The reference signal output and current source generating circuit comprises switches K12, K13, K14, K15, K16, an NMOS tube Q1, a PMOS tube Q2, an operational amplifier OPA and a channel switching MUX 1; the switch K12 is connected with the switch K13, and the other end of the switch K13 is connected with the output end OPOUT of the operational amplifier OPA; the negative input end of the operational amplifier OPA is connected to the common end of the switch K12, the switch K13, the NMOS transistor Q1 and the PMOS transistor Q2, the positive input end of the operational amplifier OPA is connected with the OPIN and connected to the switch K16, and the other end of the switch K16 is connected with the output end of the channel switching MUX 1; one end of the switch K14 is connected with the output end OPOUT of the operational amplifier OPA, and the other end is connected with the grid electrode of the NMOS tube Q1; one end of the switch K15 is connected to the output end OPOUT of the OPA, and the other end is connected to the gate of the PMOS transistor Q2.

The channel switching and ADC acquisition circuit comprises a channel switching MUX2 and an analog-to-digital converter ADC; the voltages of VA, VB, VC and VD points select V1P and V1N to collect signals at the input end of the ADC through a control channel switching MUX2 respectively.

The comparator output circuit comprises comparators CMPH, CMPL and a LATCH LATCH; the port a4 is connected to the positive input of comparator CMPH and the negative input of comparator CMPL, the negative input port of comparator CMPH is connected to the COM port, the output CMPH _ OUT of comparator CMPH is connected to the LATCH input, the positive input port of comparator CMPL is connected to VDR22, the output CMPL _ OUT of comparator CMPL is connected to the other input of LATCH, the LATCH output LATCH _ OUT is connected to the capture block.

The CMPH comparator outputs a high level, and the CMPL comparator outputs a low level, which is a voltage signal; the CMPH comparator outputs a low level, and the CMPL comparator outputs a high level, which is a capacitance signal; the CMPH comparator outputs a low level, and the CMPL comparator outputs a low level, which is a resistance signal.

Example 2

On the basis of the embodiment 1, the method for realizing the automatic voltage resistance and capacitance measuring circuit comprises the following steps of;

measuring a voltage signal, wherein the voltage signal is connected to an A1 port through a resistor R5, an A1 port is connected with an internal switch network and is switched according to different measuring ranges, an R1 resistor is connected with a switch K11, and a switch K11 is connected to COM; and order: re s1 ═ R1; re s2 ═ R1+ R2; re s3 ═ R1+ R2+ R3; re s4 ═ R1+ R2+ R3+ R4;

measuring a resistance signal, wherein the resistance signal is connected to an A2 port through a resistor R6, an A2 port is connected with an internal switch network, switching is carried out according to different measuring ranges, an R1 resistor is connected with a switch K12, a switch K12 is connected with a switch K13, and the other end of the switch K13 is connected with the output end of an operational amplifier OPA; the voltage of the operational amplifier output end is Vop, the voltage of the COM end is Vcom, the resistance to be detected is Rx, and the internal reference resistance is Rr;

measuring a capacitance signal, wherein AVDDR is connected to a resistor R2 through a switch K9, the other end of the resistor R2 is connected to a resistor R1, the resistor R1 is connected to a switch K12, a switch K12 is connected to the source electrode of a PMOS tube Q2, the grid electrode of the PMOS tube Q2 is connected to a switch K15, and the other end of the switch K15 is connected with an output end OPOUT of an operational amplifier OPA; the drain electrode of the PMOS tube Q2 is connected to the A2 port, and the A2 port is connected with the resistor R6 to the end of the capacitor to be tested to supply the capacitor;

V_OP、V_CMPHall are a partial pressure of AVDDR, and the coefficients are respectively set as a and b, namely: v_OP＝a×AVDDR；V_CMPH＝b×AVDDR；Rc＝R1+R2

Converting into the following steps:

the coefficients a, b are determined by the set voltage division ratio, Δ t is derived from the calibrated clock count inside the chip, R_CObtained by calibration.

Example 3

On the basis of the above embodiments, the chip internal resistor string of the present embodiment is named as R1, R2, R3, and R4 in sequence from small to large.

And order: re s1 ═ R1; re s2 ═ R1+ R2; re s3 ═ R1+ R2+ R3; re s4 ═ R1+ R2+ R3+ R4; assuming that the meter is calibrated;

an external voltage resistor capacitor signal is connected to two input ports V/omega/F and COM of the instrument, firstly, which signal is input needs to be judged, a signal to be detected is connected to an A4 port through a resistor R7, and an A4 port is connected to the input ends of two comparators. The COM voltage is 1.2V and the VDR22 voltage is 0.825V.

If the CMPH comparator outputs a high level and the CMPL comparator outputs a low level, the voltage signal is judged. If the CMPH comparator outputs a low level and the CMPL comparator outputs a high level, the capacitance signal is judged to be the capacitance signal. If the CMPH comparator outputs a low level and the CMPL comparator outputs a low level, the resistance signal is judged.

After detecting the voltage signal, the voltage signal is connected to the port A1 through a resistor R5, the port A1 is connected with an internal switch network, switching is carried out according to different measuring ranges, the resistor R1 is connected with a switch K11, and the switch K11 is connected to COM. The ADC collects signals on the internal switch resistance network, and a voltage signal measurement calculation formula is as follows (Vin refers to a voltage signal to be measured):

after the resistance signal is detected, the resistance signal is connected to an A2 port through a resistor R6, an A2 port is connected with an internal switch network and is switched according to different measuring ranges, the R1 is connected with a switch K12 in a resistance mode, a switch K12 is connected with a switch K13, and the other end of the switch K13 is connected with an output end OPOUT of an operational amplifier OPA; the negative input end of the operational amplifier OPA is connected to the common end of the switch K12, the switch K13, the NMOS transistor Q1 and the PMOS transistor Q2, the positive input end of the operational amplifier OPA is connected to the OPIN and connected to the switch K16, the other end of the switch K16 is connected to the output end of the channel switching MUX1, and the MUX1 selects the reference voltage VDR20 (0.75V). And the ADC acquires a signal on the internal switch resistance network and a signal on an external resistor to be measured (between A4 and COM) to perform proportional calculation.

Assume that the voltage generated by the operational amplifier is Vop, the voltage at the COM terminal is Vcom, the resistance to be measured is Rx, and the internal reference resistance is Rr. The output voltage Vop of the operational amplifier in different gears may be different, and one principle is to make the voltage division on Rx as large as possible. Using the ADC to measure the voltage division on Rx and Rr, the resistance signal measurement calculation formula is as follows:

rebuke brief description:

after a capacitance signal is detected, firstly, the capacitor is charged, the AVDDR is connected to a resistor R2 through a switch K9, the other end of the resistor R2 is connected with a resistor R1, the resistor R1 is connected with a switch K12, a switch K12 is connected to the source electrode of a PMOS tube Q2, the grid electrode of the PMOS tube Q2 is connected with a switch K15, and the other end of the switch K15 is connected with the output end OPOUT of the operational amplifier OPA; the negative input end of the operational amplifier OPA is connected to the common end of the switch K12, the switch K13, the NMOS transistor Q1 and the PMOS transistor Q2, the positive input end of the operational amplifier OPA is connected to the OPIN and connected to the switch K16, the other end of the switch K16 is connected to the output end of the channel switching MUX1, and the MUX1 selects the reference voltage VDR40 (1.5V). The AVDDR voltage and the voltage of the output end of the operational amplifier are fixed, a constant current source is formed and is connected to the A2 port through the drain electrode of the PMOS tube Q2, and the A2 port is connected with the resistor R6 to the end of the capacitor to be tested to charge the capacitor.

VSS is connected to a resistor R2 through a switch K10, the other end of the resistor R2 is connected to a resistor R1, the resistor R1 is connected to a switch K12, a switch K12 is connected to the source electrode of an NMOS tube Q1, the grid electrode of the NMOS tube Q1 is connected to a switch K14, and the other end of the switch K14 is connected with the output end OPOUT of the operational amplifier OPA; the drain electrode of the NMOS tube Q1 is connected to the A2 port, and the A2 port is connected with the resistor R6 to the end of the capacitor to be tested to discharge the capacitor.

And charging the capacitor by using a constant current, keeping the charging current unchanged, increasing the voltage of the capacitor end along with the charging, stopping charging when the voltage of the capacitor end reaches a threshold value set by the comparator, and recording time. The voltage output by the internal operational amplifier is set as V_OPThe threshold voltage of the comparator is V_CMPHAnd the charging time is delta t, then:

wherein V_OP、V_CMPHAll are a partial pressure of AVDDR, and the coefficients are respectively set as a and b, namely:

V_OP＝a×AVDDR

V_CMPH＝b×AVDDR

Rc＝R1+R2

thus, it is converted into:

the coefficients a, b are determined by the set voltage division ratio, Δ t is obtained by the calibrated clock count inside the chip, R_CThe accuracy is guaranteed by calibration, and therefore theoretically, the measured value can be obtained without extra calibration of the capacitance gear.

The voltage resistance capacitance can be automatically measured by using three peripheral resistors (R5 is 10M, R6 is 390k, and R7 is 1M), the traditional relay and dial switching gear method is not needed, the interior judges which signal to be measured is according to the comparator result, and the measurement is carried out by automatically judging the measuring range through the internal program control switch network after the signal to be measured is detected.