CN219871544U

CN219871544U - Impedance measuring device

Info

Publication number: CN219871544U
Application number: CN202321023873.5U
Authority: CN
Inventors: 欧兴钦; 覃光; 吴旭明
Original assignee: Nanning Fulian Fugui Precision Industrial Co Ltd
Current assignee: Nanning Fulian Fugui Precision Industrial Co Ltd
Priority date: 2023-04-28
Filing date: 2023-04-28
Publication date: 2023-10-20
Anticipated expiration: 2033-04-28

Abstract

An impedance measuring device comprises a switch circuit, a constant current generating circuit, a reference resistance circuit, an analog-to-digital conversion circuit and a main control circuit. The switch circuit is used for being electrically connected to a point to be measured of the circuit to be measured, the constant current generation circuit sets the output constant current according to a first control signal output by the main control circuit, the reference resistance circuit sets the impedance connected to a loop formed by the constant current generation circuit according to a second control signal output by the main control circuit, the analog-to-digital conversion circuit carries out analog-to-digital conversion on the voltage of the common connection end of the reference resistance circuit and the constant current generation circuit to obtain a digital signal, when the switch circuit is disconnected, the main control circuit determines the impedance of the reference resistance circuit according to the digital signal input by the analog-to-digital conversion circuit, and when the switch circuit is conducted, the initial impedance of the point to be measured is determined according to the digital signal input by the analog-to-digital conversion circuit and the impedance of the reference resistance circuit. The utility model is applicable to the measurement of impedance in different ranges and has high accuracy of impedance measurement.

Description

Impedance measuring device

Technical Field

The present utility model relates to the field of circuit board assembly detection, and in particular, to an impedance measurement device.

Background

At present, the functions of electronic products tend to be diversified, the circuit system of the electronic products is increasingly complex, and the number of the included electronic components is increasingly large. In order to ensure that the electrical performance of the circuit board assembly meets the design requirement after the surface mount technology (surface mount technology, SMT) is finished, bad products are screened out, and a large amount of manpower and material resources are required to be input by a production enterprise to test the electrical performance of the products.

Open/short/impedance measurement is a fundamental test procedure for circuit board assemblies, including but not limited to open/short/impedance measurement of power lines, signal lines, etc. and major devices on the board. The existing impedance measurement scheme mainly tests the impedance of different ranges by using multi-branch quantity, namely, one measurement branch is designed corresponding to each impedance range, so that the circuit layout area of the test fixture is increased, the manufacturing cost is increased, the maintainability and the intellectualization of the fixture are low, and the use of the test fixture is inconvenient for the test personnel.

Disclosure of Invention

In view of the foregoing, it is desirable to provide an impedance measuring device that is suitable for measuring impedances in different ranges.

The embodiment of the utility model discloses an impedance measuring device which comprises a switch circuit, a constant current generating circuit, a reference resistance circuit, an analog-to-digital conversion circuit and a main control circuit. The switch circuit comprises an input end, an output end and a control end, wherein the input end of the switch circuit is used for being electrically connected with a point to be measured of the circuit to be measured; the constant current generation circuit is electrically connected to the output ends of the main control circuit and the switch circuit, and is used for setting the output constant current according to a first control signal output by the main control circuit; the reference resistance circuit is electrically connected with the output end of the switch circuit, the constant current generation circuit and the main control circuit, the reference resistance circuit and the constant current generation circuit form a loop, and the reference resistance circuit is used for setting impedance connected to the loop according to a second control signal output by the main control circuit; the analog-to-digital conversion circuit is electrically connected to a common connection end of the reference resistance circuit and the constant current generation circuit, and is used for performing analog-to-digital conversion on the voltage of the common connection end to obtain a digital signal, and inputting the digital signal to the main control circuit; the main control circuit is used for determining the impedance accessed by the reference resistance circuit according to the digital signal converted by the analog-to-digital conversion circuit when the switch circuit is disconnected; the main control circuit is also used for determining the initial impedance of the point to be measured according to the digital signal converted by the analog-to-digital conversion circuit and the impedance accessed by the reference resistance circuit when the switch circuit is conducted.

By adopting the technical scheme, the measuring environment matched with the point to be measured can be constructed according to the impedance of the point to be measured, the measuring environment can be suitable for measuring the impedance in different ranges, and the calibration of the impedance measuring environment can be carried out before the impedance test is carried out on the point to be measured, so that the accuracy of impedance measurement can be improved.

In some embodiments, the reference resistance circuit comprises a plurality of reference resistance units, and the master control circuit is used for determining the reference resistance units matched with the point to be measured according to the initial impedance of the point to be measured; and if the reference resistance unit matched with the point to be measured is the reference resistance unit currently connected to the impedance measuring device, taking the initial impedance as the final measured impedance of the point to be measured.

By adopting the technical scheme, by setting different reference resistance units, the different reference resistance units correspond to different impedance measurement ranges, the accuracy of measuring the impedance of the point to be measured can be improved, and if the currently accessed reference resistance unit is matched with the impedance of the point to be measured, the initial impedance measured initially can be used as the final measured impedance of the point to be measured.

In some embodiments, if the reference resistance unit matched with the point to be measured is not the reference resistance unit currently connected to the impedance measurement device, the reference resistance circuit is further configured to connect the reference resistance unit matched with the point to be measured to the loop under the control of the master control circuit, and the master control circuit is further configured to determine, when the switch circuit is turned off, the impedance of the reference resistance unit matched with the point to be measured according to the digital signal converted by the analog-to-digital conversion circuit; the main control circuit is also used for determining the final measured impedance of the point to be measured according to the digital signal converted by the analog-to-digital conversion circuit and the impedance of the reference resistance unit matched with the point to be measured when the switch circuit is conducted.

By adopting the technical scheme, if the currently accessed reference resistance unit is not matched with the impedance of the point to be measured, the reference resistance unit can be switched, the calibration and measurement can be performed again, or the measurement can be performed again directly (the calibration is performed after the power-on), so that the accuracy of measuring the impedance of the point to be measured can be improved.

In some embodiments, the reference resistance unit currently connected to the impedance measurement device is a reference resistance unit having the largest impedance among the plurality of reference resistance units.

By adopting the technical scheme, before impedance measurement is carried out on the point to be measured, the reference resistance unit with the largest measuring range is connected into the impedance measurement device, and then the reference resistance unit is switched based on the initial measuring result, so that the problem that the impedance of the point to be measured cannot be estimated accurately due to the over-measuring range is avoided, and the reference resistance unit cannot be switched accurately is avoided.

In some embodiments, the reference resistor circuit further includes a first electronic switch, each reference resistor unit of the plurality of reference resistor units is composed of one or more resistors, the first electronic switch includes a first end, a plurality of second ends and a plurality of control ends, the first end of the first electronic switch is electrically connected to the output end of the switch circuit and the constant current generation circuit, the plurality of control ends of the first electronic switch are all electrically connected to the main control circuit, each second end of the plurality of second ends of the first electronic switch is electrically connected to one end of each reference resistor unit in a one-to-one correspondence manner, and the other end of each reference resistor unit is grounded.

By adopting the technical scheme, the electronic switch is controlled by the main control circuit to gate different reference resistance units, so that the switching of impedance range is realized.

In some embodiments, the magnitude of the constant current output by the constant current generation circuit is inversely related to the impedance of the reference resistance circuit connected to the loop.

By adopting the technical scheme, the voltage requirement of the analog signal input to the analog-to-digital conversion circuit is met by setting the magnitude of the constant current and the impedance connected to the loop (the loop formed by the reference resistance circuit and the constant current generation circuit) to be inversely related.

In some embodiments, the constant current generating circuit includes a reference voltage source, a constant current generating unit and a constant current switching unit, the constant current generating unit is electrically connected to the reference voltage source and the constant current switching unit, the constant current generating unit is configured to set a magnitude of an output constant current according to a reference voltage output by the reference voltage source and a resistance value accessed by the constant current switching unit, the constant current switching unit is electrically connected to the main control circuit, and the constant current switching unit is configured to set the accessed resistance value according to a first control signal output by the main control circuit.

By adopting the technical scheme, the constant current with different current magnitudes is generated through the reference voltage source, the constant current generation unit and the constant current switching unit.

In some embodiments, the constant current generation unit includes: the first amplifier comprises a positive input end, a negative input end and an output end, wherein the positive input end of the first amplifier is electrically connected with the output end of the switch circuit and the reference resistance circuit, and the negative input end of the first amplifier is electrically connected with the output end of the first amplifier; the second amplifier comprises a positive input end, a negative input end, a detection end, a reference end and an output end, wherein the positive input end of the second amplifier is electrically connected with the reference voltage source, the negative input end of the second amplifier is grounded, and the output end of the second amplifier is electrically connected with the output end of the first amplifier and the detection end of the second amplifier; the constant current switching unit comprises a first end, a second end and a control end, wherein the first end of the constant current switching unit is electrically connected with the positive input end of the first amplifier, the second end of the constant current switching unit is electrically connected with the reference end of the second amplifier, and the control end of the constant current switching unit is electrically connected with the main control circuit.

By adopting the technical scheme, the constant current source is combined by two amplifiers (for example, a differential operational amplifier and a common operational amplifier) and a reference voltage source.

In some embodiments, the constant current switching unit includes: one end of each matching resistor in the plurality of matching resistors is electrically connected with the reference end of the second amplifier; the first ends of the second electronic switches are electrically connected to the positive input end of the first amplifier, each of the second ends of the second electronic switches is electrically connected to the other end of each matching resistor in a one-to-one correspondence mode, and the control ends of the second electronic switches are electrically connected to the main control circuit.

By adopting the technical scheme, the constant current with different current magnitudes is generated by adjusting the voltage connected to the reference end of the second amplifier (for example, the differential operational amplifier). For example, the first end of the second electronic switch may be used as the first end of the constant current switching unit, the common connection end of each matching resistor may be used as the second end of the constant current switching unit, and the control end of the second electronic switch may be used as the control end of the constant current switching unit.

In some embodiments, the analog-to-digital conversion circuit comprises an analog-to-digital converter, and the master control circuit comprises a micro control unit, and the micro control unit receives a digital signal input by the analog-to-digital converter through an SPI bus or an I2C bus _。

By adopting the technical scheme, the micro control unit can receive the digital signals input by the analog-to-digital converter through buses such as SPI, I2C and the like.

Drawings

FIG. 1 is a functional block diagram of an impedance measuring apparatus according to an embodiment of the present utility model.

FIG. 2 is a functional block diagram of an impedance measuring apparatus according to another embodiment of the present utility model.

FIG. 3 is a circuit diagram of an impedance measuring apparatus according to an embodiment of the utility model.

Detailed Description

The technical solutions in the embodiments of the present utility model will be clearly described below with reference to the drawings in the embodiments of the present utility model.

It is understood that the connection relationship described in the present utility model refers to direct or indirect connection. For example, the connection between a and B may be a direct connection between a and B or an indirect connection between a and B via one or more other electrical components. For example, a may be directly connected to C, and C may be directly connected to B, so that a connection between a and B is achieved through C. It is also understood that "a-connection B" as described herein may be a direct connection between a and B, or an indirect connection between a and B via one or more other electrical components.

In the description of the present utility model, "/" means "or" unless otherwise indicated, for example, A/B may mean A or B. "and/or" herein is merely an association relationship describing an association object, and means that three relationships may exist, for example, a and/or B may mean: a exists alone, A and B exist together, and B exists alone.

In the description of the present utility model, the words "first", "second", etc. are used only to distinguish different objects, and are not limited to numbers and execution orders, and the words "first", "second", etc. are not necessarily different. Furthermore, the terms "comprising," "including," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion.

The technical scheme of the utility model is further described in detail below with reference to the accompanying drawings.

Referring to fig. 1, an impedance measuring apparatus 10 is provided according to an embodiment of the present utility model, and the impedance measuring apparatus 10 can be used for measuring the impedance of a point to be measured of a circuit 20 to be measured, so as to determine whether an open circuit or a short circuit occurs, perform signal quality analysis, and the like. For example, the impedance of a certain point/pin on a certain line on the circuit 20 to be tested is measured and compared with a preset impedance value to evaluate whether the quality of the circuit 20 to be tested meets the requirement.

The circuit 20 to be tested may be a circuit in an electronic device, and the electronic device may be a mobile phone, a tablet computer, a television, a notebook computer, etc., which is not limited in type according to the embodiment of the present utility model.

The impedance measuring device 10 may include a switch circuit 101, a constant current generating circuit 102, a reference resistance circuit 103, an analog-to-digital conversion circuit 104, and a main control circuit 105.

The switching circuit 101 includes an input terminal, an output terminal, and a control terminal. The input terminal of the switch circuit 101 is used for being electrically connected to a point to be measured of the circuit to be measured 20.

The constant current generation circuit 102 is electrically connected to the output terminals of the main control circuit 105 and the switch circuit 101, and the constant current generation circuit 102 is configured to set the magnitude of the output constant current according to the first control signal output by the main control circuit 105. The magnitude of the constant current output by the constant current generation circuit 102 is related to the reference impedance of the reference resistance circuit 103 connected to the impedance measuring device 10, so that the voltage requirement of the analog signal input to the analog-to-digital conversion circuit 104 at the rear end can be met.

The reference resistor circuit 103 is electrically connected to the output terminal of the switch circuit 101, the constant current generation circuit 102, and the master circuit 105, and the reference resistor circuit 103 and the constant current generation circuit 102 may form a loop, that is, a constant current output from the constant current generation circuit 102 may flow to the ground terminal via the reference resistor circuit 103. For example, the reference resistor circuit 103 may include a first end, a second end and a control end, the first end of the reference resistor circuit 103 is electrically connected to the common connection end of the output end of the switch circuit 101 and the constant current generating circuit 102, the second end of the reference resistor circuit 103 is grounded, the control end of the reference resistor circuit 103 is electrically connected to the main control circuit 105, and the constant current output by the constant current generating circuit 102 may flow to the second end via the first end of the reference resistor circuit 103. The reference resistance circuit 103 is configured to set the impedance connected to the loop according to the second control signal output by the main control circuit 105, that is, for the points to be measured with different impedances, the reference resistance circuit 103 is set to connect different reference impedances to the impedance measurement device 10, so that the accuracy of measuring the impedance of the points to be measured can be improved, and the measurement of the impedance applicable to different ranges can be realized.

The analog-to-digital conversion circuit 104 is electrically connected to a common connection end of the reference resistor circuit 103 and the constant current generation circuit 102, and the analog-to-digital conversion circuit 104 is configured to perform analog-to-digital conversion on a voltage of the common connection end to obtain a digital signal, and input the digital signal to the main control circuit 105.

The main control circuit 105 is configured to determine the impedance of the reference resistor circuit 103 according to the digital signal converted by the analog-to-digital conversion circuit 104 when the switch circuit 101 is turned off. For example, when the switch circuit 101 is turned off, the main control circuit 105 may calculate the impedance to which the reference resistance circuit 103 is connected based on the voltage of the current common connection terminal and the magnitude of the constant current output from the constant current generation circuit 102. The main control circuit 105 is further configured to determine an initial impedance of the point to be measured according to the digital signal converted by the analog-to-digital conversion circuit 104 and the impedance accessed by the reference resistance circuit when the switch circuit 101 is turned on. For example, when the switch circuit 101 is turned on, the main control circuit 105 may calculate, based on the voltage at the current common connection terminal and the constant current output by the constant current generation circuit 102, the parallel impedance between the impedance of the reference resistance circuit 103 and the impedance of the point to be measured, and may further calculate, based on the parallel impedance and the impedance of the reference resistance circuit 103, the impedance of the point to be measured.

In some embodiments, the master circuit 105 may process the digital signal using an existing algorithm to obtain the impedance of the point to be measured. The impedance of the point to be measured can be transmitted to other devices with display screens by the main control circuit 105 for display, or the impedance measuring device 10 can be integrated with a display screen module, and the main control circuit 105 can transmit the impedance of the point to be measured to the display screen module for display.

Referring to fig. 2, an impedance measuring apparatus 10 is provided according to another embodiment of the present utility model.

As shown in fig. 2, the reference resistance circuit 103 may include a plurality of reference resistance units 103_1 to 103—n, each of the reference resistance units 103_1 to 103—n may have a different resistance value, and each of the reference resistance units 103_1 to 103—n may be composed of one or more resistors. The main control circuit 105 can also determine a reference resistance unit matched with the point to be measured according to the initial impedance of the point to be measured; if the reference resistance unit matched with the point to be measured is the reference resistance unit currently connected to the impedance measuring device 10, the reference resistance unit currently connected is indicated to meet the range requirement of the point to be measured, and the initial impedance can be used as the final measured impedance of the point to be measured.

For example, the reference resistor circuit 103 includes four reference resistor units 103_1 to 103_4, the resistance value of the reference resistor unit 103_1 is 1mΩ, the resistance value of the reference resistor unit 103_2 is 10kΩ, the resistance value of the reference resistor unit 103_3 is 1kΩ, and the resistance value of the reference resistor unit 103_4 is 100 Ω. That is, the range corresponding to the reference resistor 103_4 is set to (0, 100deg.C ], the range corresponding to the reference resistor 103_3 is set to (100deg.C, 1KΩ), the range corresponding to the reference resistor 103_2 is set to (1KΩ,10KΩ ], the range corresponding to the reference resistor 103_1 is set to (10KΩ,1MΩ), or the reference resistor 103_1 may be used for measuring the range of 1MΩ or more.

Assuming that the currently accessed reference resistance unit is the reference resistance unit 103_1, the main control circuit 105 calculates that the initial impedance of the point to be measured is 50kΩ, that is, the reference resistance unit matched with the point to be measured is also the reference resistance unit 103_1, and the initial impedance can be used as the final measured impedance of the point to be measured without switching the reference resistance unit.

In some embodiments, in order to improve accuracy of impedance measurement range of a point to be measured, multiple measurements may be performed on the point to be measured to obtain multiple impedance values, and final measured impedance of the point to be measured based on the multiple impedance values. For example, an average value of the impedance values may be calculated, where the average value is used as the final measured impedance of the point to be measured, or the maximum value and the minimum value of the preset number are removed, and the average value of the remaining impedance values is used as the final measured impedance of the point to be measured.

If the reference resistance unit matched with the point to be measured is not the reference resistance unit currently connected to the impedance measuring device 10, the reference resistance circuit 103 is further configured to connect the reference resistance unit matched with the point to be measured to the loop under the control of the main control circuit 105 to re-measure the impedance of the point to be measured. After the reference resistance unit matched with the point to be measured is connected to the loop, the main control circuit 105 can determine the impedance of the reference resistance unit matched with the point to be measured according to the digital signal converted by the analog-to-digital conversion circuit 104 when the switch circuit 101 is disconnected; when the switch circuit is turned on 101, the main control circuit 105 determines the final measured impedance of the point to be measured according to the digital signal converted by the analog-to-digital conversion circuit 104 and the impedance of the reference resistance unit matched with the point to be measured.

In some embodiments, after the impedance measuring apparatus 10 is powered on, the constant currents output by the reference resistor units 103_1 to 103—n or the constant current generating circuit 102 may be calibrated uniformly, so that after the reference resistor unit matched with the point to be measured is connected to the loop, the switch circuit is controlled to be turned on 101, and the main control circuit 105 may determine the final measured impedance of the point to be measured directly according to the digital signal converted by the analog-to-digital conversion circuit 104 and the impedance of the reference resistor unit matched with the point to be measured.

Assuming that the currently connected reference resistance unit is the reference resistance unit 103_1, the main control circuit 105 calculates that the initial impedance of the point to be measured is 500Ω, that is, the reference resistance unit matched with the point to be measured should be the reference resistance unit 103_3, the main control circuit 105 can control the reference resistance unit 103 to connect the reference resistance unit 103_3 to the loop, and then control the switch circuit to conduct 101, so that the main control circuit 105 can determine the final measured impedance of the point to be measured according to the digital signal converted by the analog-to-digital conversion circuit 104 and the impedance of the reference resistance unit 103_3.

In some embodiments, before impedance measurement is performed on a point to be measured, a reference resistance unit with a maximum measurement range may be connected to a loop, for example, the reference resistance unit 103_1 described above, and then the reference resistance unit is switched based on an initial measurement result, so as to avoid that the impedance of the point to be measured cannot be estimated accurately due to the over measurement range, and the reference resistance unit cannot be switched accurately.

In some embodiments, the analog-to-digital conversion circuit 104 may include an analog-to-digital converter, where the magnitude of the constant current output by the constant current generation circuit 102 is inversely related to the impedance of the reference resistor circuit 103 connected to the loop, so as to meet the voltage requirement of the analog signal input to the analog-to-digital converter at the back end, improve the accuracy of impedance measurement, limit the high voltage caused by the high impedance, and prevent the withstand voltage of the back end device from being damaged insufficiently. Taking the example that the reference resistor circuit 103 includes the four reference resistor units 103_1 to 103_4 described above, the constant current generation circuit 102 can output four constant currents of 1uA, 100uA, 1mA, and 10mA, respectively. 1uA corresponds to the reference resistance unit 103_1, 100uA corresponds to the reference resistance unit 103_2,1mA corresponds to the reference resistance unit 103_3, and 10mA corresponds to the reference resistance unit 103_4.

As shown in fig. 2, the constant current generation circuit 102 may include a reference voltage source 1021, a constant current generation unit 1022, and a constant current switching unit 1023. The constant current generation unit 1022 is electrically connected to the reference voltage source 1021 and the constant current switching unit 1023, and the constant current generation unit 1022 is configured to set the magnitude of the output constant current according to the reference voltage output by the reference voltage source 1021 and the resistance value of the resistor connected to the constant current switching unit 1023. The constant current switching unit 1023 is electrically connected to the main control circuit 105, and the constant current switching unit 1023 is configured to set a resistance value connected to the constant current generating unit 1022 according to a first control signal output by the main control circuit 105.

The voltage of the reference voltage source 1021 can be set according to actual requirements, the utility model is not limited to this, and taking the constant current generation circuit 102 as an example, which can correspondingly output four constant currents of 1uA, 100uA, 1mA and 10mA, the reference voltage source 1021 can be a voltage source of 2.5V, for example, can output a voltage of 2.5V based on a REF5025 chip.

The constant current switching unit 1023 may include a plurality of resistance branches, each having a different resistance value. Taking a voltage source of 2.5V as an example, the resistances of the four resistive branches may be 2.5mΩ, 25kΩ, 2.5kΩ, 250 Ω, respectively, to generate constant currents of 1uA, 100uA, 1mA, 10 mA.

Referring to fig. 3, a circuit diagram of an impedance measuring apparatus 10 according to an embodiment is provided.

The master control circuit 105 may include a chip with control and signal processing capabilities, such as an MCU, or a single-chip microcomputer. Fig. 3 illustrates an example in which the master circuit 105 includes an MCU U0, for example, the MCU U0 may be an MCU chip based on Arm Cortex-M and RISC-V cores. The switch circuit 101 may include an electronic gating switch S1, and the electronic gating switch S1 may be set to a single channel input or a dual channel input according to a control signal output from the MCU U0. The electronic gating switch S1 may include an input end, an output end and a control end, the input end of the electronic gating switch S1 may be used for being electrically connected to a point to be measured, and the control end (fig. 3 illustrates 3 control ends ct1, ct2, ct3, but not limited to this) of the electronic gating switch S1 may be connected to a general-purpose input/output (GPIO) pin of the MCU U0, so as to receive a control signal output by the MCU U0, and realize a connection between a certain input end and an output end of the electronic gating switch S1. For example, the electronic gating switch S1 may be a TMUX7208 chip, and the electronic gating switch S1 may also select other multiplexer chips, which is not limited in the embodiment of the present utility model.

The reference resistor circuit 103 may include a first electronic switch S2 and a plurality of reference resistors RA1 to RAn (fig. 3 illustrates four reference resistors RA1 to RA4, but not limited thereto). Each of the reference resistors RA1 to RAn (each of the reference resistors RA1 to RAn may have a different resistance value) may be used as one of the reference resistor units 103_1 to 103—n. The first electronic switch S2 includes a first end, a plurality of second ends and a plurality of control ends (fig. 3 illustrates 2 control ends ct4 and ct5, but not limited thereto), the first end of the first electronic switch S2 is electrically connected to the output end of the electronic gating switch S1 and the constant current generating circuit 102, the plurality of control ends of the first electronic switch S2 are all electrically connected to the MCU U0 (for example, connected to the GPIO pin of the MCU U0), each of the plurality of second ends of the first electronic switch S2 is electrically connected to one end of each of the reference resistors RA1 to RAn in a one-to-one correspondence manner, and the other end of each of the reference resistors RA1 to RAn is grounded. The first electronic switch S2 can gate different reference resistors RA1 to RAn under the control of the MCU U0 to adapt the measurement of the impedance in different ranges. The first electronic switch S2 may be a TMUX7208 chip, and the reference resistors RA1 to RAn may be resistors with higher precision, for example, resistors with resistance errors within 1%.

In some embodiments, the first electronic switch S2 and the plurality of reference resistors RA1 to RAn may be replaced by a digital potentiometer (programmable resistor), which is not limited in the present utility model.

The constant current generation circuit 102 may include a first amplifier U1, a second amplifier U2, a second electronic switch S3, and a plurality of matching resistors RB1 to RBn (fig. 3 illustrates four matching resistors RB1 to RB4, but not limited thereto). The first amplifier U1 includes a positive input end, a negative input end and an output end, the positive input end of the first amplifier U1 is electrically connected to the output end of the gating switch S1 and the first end of the first electronic switch S2, and the negative input end of the first amplifier U1 is electrically connected to the output end of the first amplifier U1. The second amplifier U2 includes a positive input terminal (in+), a negative input terminal (IN-), a detection terminal (SENSE), a reference terminal (REF), and an output terminal (OUT). The positive input end of the second amplifier U2 is electrically connected to the reference voltage source 1021, the negative input end of the second amplifier U2 is grounded, and the output end of the second amplifier U2 is electrically connected to the output end of the first amplifier U1 and the detection end of the second amplifier U2. One end of each of the plurality of matching resistors RB1 to RBn is electrically connected to the reference end of the second amplifier U2. The second electronic switch S3 includes a first end, a plurality of second ends and a plurality of control ends (fig. 3 illustrates 2 control ends ct6 and ct7, but not limited thereto), the first end of the second electronic switch S3 is electrically connected to the positive input end of the first amplifier U1, each of the plurality of second ends of the second electronic switch S3 is electrically connected to the other end of each of the matching resistors RB1 to RBn in a one-to-one correspondence manner, and the plurality of control ends of the second electronic switch S3 are electrically connected to the MCU U0 (for example, connected to GPIO pins of the MCU U0). The second electronic switch S3 may gate different matching resistors RB1 to RBn (each matching resistor RB1 to RBn may have different resistance values) under the control of the MCU U0, so as to change the voltage value connected to the reference terminal of the second amplifier U2, thereby changing the magnitude of the constant current output by the constant current source composed of the first amplifier U1 and the second amplifier U2. The second electronic switch S3 can adopt a TMUX7208 chip, and the matched resistors RB 1-RBn can select resistors with higher precision, such as resistors with resistance errors within 1%.

In some embodiments, the second electronic switch S3 and the plurality of matching resistors RB1 to RBn may also be replaced by a digital potentiometer (programmable resistor).

In some embodiments, the first amplifier U1 may be a general purpose operational amplifier, e.g., the first amplifier U1 may employ an OPA180 chip, and the second amplifier U2 may be a differential amplifier, e.g., the second amplifier U2 may be an INA592 chip.

Analog-to-digital conversion circuit 104 may include an analog-to-digital converter (ADC) U3, and MCU U0 may receive digital signals input by analog-to-digital converter U3 via an SPI, I2C, etc. bus (fig. 3 illustrates receiving digital signals via an SPI bus, and pins include CS, CLK, DO, D1). The analog-digital converter U3 can select analog-digital converter chips with different precision according to the measurement precision requirement, for example, the low-precision requirement can select 12-Bit analog-digital converter chips, the model can be ADC121S021 or ADS7951, the high-precision requirement can select 24-Bit analog-digital converter chips, and the model can be AD7172.

In some embodiments, the analog-to-digital converter U3 may be integrated in the MCU U0, or may be an analog-to-digital conversion chip independent of the MCU U0, which is not limited in the present utility model.

In the actual measurement process, after the impedance measurement apparatus 10 is powered on, the MCU U0 controls the electronic gating switch S1 to be turned off, and then the MCU U0 controls the first electronic switch S2 and the second electronic switch S3 to switch, so as to select the reference resistor and the constant current corresponding to the reference resistor, and calibrate each constant current output by each reference resistor unit 103_1 to 103—n or the constant current generation circuit 102 in a unified manner (for example, if the resistance errors of each reference resistor unit 103_1 to 103—n are ignored, that is, calibrate each constant current output by the constant current generation circuit 102, that is, calibrate each reference resistor unit 103_1 to 103—n if the current errors of each constant current output by the constant current generation circuit 102 are ignored). After calibration is completed, the MCU U0 controls the electronic gating switch S1 to be conducted so as to connect a point to be measured into the impedance measuring device 10, controls the first electronic switch S2 to select the largest impedance range, controls the second electronic switch S3 to select constant current corresponding to the largest impedance range, reads a digital signal input by the analog-to-digital converter U3 to obtain initial impedance of the point to be measured, controls the first electronic switch S2 to select the corresponding impedance range according to the initial impedance, controls the second electronic switch S3 to select the corresponding constant current, and reads a digital signal input by the analog-to-digital converter U3 to obtain final measured impedance of the point to be measured, and can also perform multiple measurements on the corresponding impedance range to obtain the final measured impedance of the point to be measured based on the calculation of the multiple measurements.

Other corresponding changes and modifications will occur to those skilled in the art from the present disclosure and the application conception and the practical need for production, and are intended to be within the scope of the present disclosure.

Claims

1. The impedance measuring device is characterized by comprising a switch circuit, a constant current generating circuit, a reference resistance circuit, an analog-to-digital conversion circuit and a main control circuit;

the switch circuit comprises an input end, an output end and a control end, wherein the input end of the switch circuit is used for being electrically connected with a point to be measured of the circuit to be measured;

the constant current generation circuit is electrically connected to the output ends of the main control circuit and the switch circuit, and is used for setting the output constant current according to a first control signal output by the main control circuit;

the reference resistance circuit is electrically connected with the output end of the switch circuit, the constant current generation circuit and the main control circuit, the reference resistance circuit and the constant current generation circuit form a loop, and the reference resistance circuit is used for setting impedance connected to the loop according to a second control signal output by the main control circuit;

the analog-to-digital conversion circuit is electrically connected to a common connection end of the reference resistance circuit and the constant current generation circuit, and is used for performing analog-to-digital conversion on the voltage of the common connection end to obtain a digital signal, and inputting the digital signal to the main control circuit;

the main control circuit is used for determining the impedance accessed by the reference resistance circuit according to the digital signal converted by the analog-to-digital conversion circuit when the switch circuit is disconnected;

the main control circuit is also used for determining the initial impedance of the point to be measured according to the digital signal converted by the analog-to-digital conversion circuit and the impedance accessed by the reference resistance circuit when the switch circuit is conducted.

2. The impedance measurement device of claim 1, wherein the reference resistance circuit comprises a plurality of reference resistance units, and the master circuit is configured to determine a reference resistance unit matching the point to be measured according to an initial impedance of the point to be measured; and if the reference resistance unit matched with the point to be measured is the reference resistance unit currently connected to the impedance measuring device, taking the initial impedance as the final measured impedance of the point to be measured.

3. The impedance measurement device according to claim 2, wherein if the reference resistance unit matched with the point to be measured is not the reference resistance unit currently connected to the impedance measurement device, the reference resistance circuit is further configured to connect the reference resistance unit matched with the point to be measured to the loop under the control of the master circuit, and the master circuit is further configured to determine the impedance of the reference resistance unit matched with the point to be measured according to the digital signal converted by the analog-to-digital conversion circuit when the switch circuit is turned off;

the main control circuit is also used for determining the final measured impedance of the point to be measured according to the digital signal converted by the analog-to-digital conversion circuit and the impedance of the reference resistance unit matched with the point to be measured when the switch circuit is conducted.

4. The impedance measurement device of claim 2, wherein the reference resistance unit currently connected to the impedance measurement device is a reference resistance unit having a largest impedance among the plurality of reference resistance units.

5. The impedance measurement device of claim 2, wherein the reference resistor circuit further comprises a first electronic switch, each reference resistor unit of the plurality of reference resistor units is composed of one or more resistors, the first electronic switch comprises a first end, a plurality of second ends and a plurality of control ends, the first end of the first electronic switch is electrically connected to the output end of the switch circuit and the constant current generation circuit, the plurality of control ends of the first electronic switch are electrically connected to the master control circuit, each second end of the plurality of second ends of the first electronic switch is electrically connected to one end of each reference resistor unit in a one-to-one correspondence manner, and the other end of each reference resistor unit is grounded.

6. The apparatus of claim 1, wherein the magnitude of the constant current output from the constant current generating circuit is inversely related to the impedance of the reference resistor circuit connected to the loop.

7. The impedance measuring device according to claim 1, wherein the constant current generating circuit comprises a reference voltage source, a constant current generating unit and a constant current switching unit, the constant current generating unit is electrically connected to the reference voltage source and the constant current switching unit, the constant current generating unit is used for setting the output constant current according to the reference voltage output by the reference voltage source and the resistance value accessed by the constant current switching unit, the constant current switching unit is electrically connected to the main control circuit, and the constant current switching unit is used for setting the accessed resistance value according to the first control signal output by the main control circuit.

8. The impedance measuring device according to claim 7, wherein the constant current generating unit includes:

the first amplifier comprises a positive input end, a negative input end and an output end, wherein the positive input end of the first amplifier is electrically connected with the output end of the switch circuit and the reference resistance circuit, and the negative input end of the first amplifier is electrically connected with the output end of the first amplifier;

the second amplifier comprises a positive input end, a negative input end, a detection end, a reference end and an output end, wherein the positive input end of the second amplifier is electrically connected with the reference voltage source, the negative input end of the second amplifier is grounded, and the output end of the second amplifier is electrically connected with the output end of the first amplifier and the detection end of the second amplifier;

the constant current switching unit comprises a first end, a second end and a control end, wherein the first end of the constant current switching unit is electrically connected with the positive input end of the first amplifier, the second end of the constant current switching unit is electrically connected with the reference end of the second amplifier, and the control end of the constant current switching unit is electrically connected with the main control circuit.

9. The impedance measuring device of claim 8, wherein the constant current switching unit comprises:

one end of each matching resistor in the plurality of matching resistors is electrically connected with the reference end of the second amplifier;

the first ends of the second electronic switches are electrically connected to the positive input end of the first amplifier, each of the second ends of the second electronic switches is electrically connected to the other end of each matching resistor in a one-to-one correspondence mode, and the control ends of the second electronic switches are electrically connected to the main control circuit.

10. The impedance measurement device of claim 1, wherein the analog-to-digital conversion circuit comprises an analog-to-digital converter, and the master control circuit comprises a micro control unit, the micro control unit receiving the digital signal input by the analog-to-digital converter through an SPI bus or an I2C bus.