TWI724909B - Ac impedance measurement circuit with calibration function - Google Patents

Abstract

The present invention discloses an AC impedance measurement circuit with a calibration function, which is characterized in that only one calibration impedance is needed, associated with a switch circuit. Based on the measurement results of the two calibration modes, an equivalent impedance of the switch circuit, circuit gain and phase offset can be calculated. Based on the above results, the equivalent impedance of the internal circuit is deducted from the measurement result of the measurement mode to accurately calculate an AC conductance and a phase of the AC conductance for impedance to be measured. In addition, by adjusting a phase difference between an input sine wave signal and a sampling clock signal, impedance of the same phase and impedance of the quadrature phase can be obtained, respectively, and the AC impedance and phase angle of the impedance to be measured can be calculated.

Description

AC impedance measurement circuit with correction function

The present invention relates to an AC impedance measurement circuit, and in particular to a correction function, And calculate the equivalent impedance of the switch circuit, and then compensate the measurement result, improve the measurement accuracy of the measurement circuit.

AC impedance measurement circuit is widely used in human body impedance measurement, allowing users to pay attention to self Body fat content, and then more accurately grasp one's own health status. Compared with the DC impedance measurement circuit, although the DC impedance measurement circuit is simpler, the disadvantage is that the measurement result includes the impedance of the human skin, and the accuracy of the measurement result of the total impedance of the human body becomes worse. The AC impedance measurement circuit can reduce the influence of skin impedance on the measurement results, and accurately analyze the equivalent AC impedance and phase characteristics of the human body.

In Chinese Patent No. 105662411 Invention Patent, an AC impedance measurement is disclosed A measurement circuit in which a sinusoidal current generator is used to generate a sinusoidal excitation current, which is applied to both ends of the human body to be measured, and a sinusoidal voltage signal is generated at both ends of the human body to be measured, and the equivalent impedance of the human body is judged through the output of the rectifier filter circuit.

U.S. Patent No. US10,551,469 discloses an AC impedance The measuring circuit and the correction circuit are designed to connect two correction impedances in parallel with the object to be measured, and the switch can be used to select the measurement correction impedance or the impedance of the object to be measured, and the measurement results of the corrected impedance are used for correction. After the measurement results are corrected, the AC can be improved. The accuracy of impedance measurement.

In the above-mentioned prior art, when the AC impedance measurement circuit is calibrated, an external connection is required. A correction impedance is not convenient in practical applications. In addition, the switch connected in series with the DUT also has impedance, which will affect the accuracy of the measurement result. Therefore, a more convenient correction circuit and correction method are needed, and the equivalent impedance value of the switching circuit is compensated, so as to improve the convenience of practical application and the accuracy of measurement.

The present invention discloses an AC impedance measurement circuit with correction function, including a waveform The generating circuit includes a sine wave signal output terminal for outputting a sine wave signal, and a clock signal output terminal for outputting a clock signal; a first amplifier, the positive input terminal of the first amplifier is connected to the sine wave signal Output terminal; a switch circuit connected to the negative input terminal of the first amplifier and the output terminal of the first amplifier; an impedance to be measured and a correction impedance connected to the switch circuit; a second amplifier, the second The positive input terminal of the amplifier is connected to a reference voltage, the negative input terminal of the second amplifier is connected to the impedance to be measured or the correction impedance; a reference impedance is connected to the negative input terminal of the second amplifier and the second amplifier Between the output terminals; and a sampling circuit that receives the clock signal of the waveform generating circuit and is connected to both ends of the reference impedance; wherein the switch circuit includes a plurality of switches, and by controlling the switches, the first The impedance to be measured or the corrected impedance is connected between an amplifier and the second amplifier, or an additional switch is connected to the corrected impedance.

The AC impedance measurement circuit described above, wherein the switch circuit includes: a first switch, Connected between the negative input terminal of the first amplifier and the correction impedance; a second switch connected between the negative input terminal of the first amplifier and the output terminal of the first amplifier; a third switch connected to Between the output terminal of the first amplifier and the impedance to be measured; and a fourth switch connected between the output terminal of the first amplifier and the correction impedance.

The present invention discloses another AC impedance measurement circuit architecture, including a waveform generating circuit Circuit, including a sine wave signal output terminal, used to output a sine wave signal, and a clock signal output terminal, used to output a clock signal; a reference impedance, directly connected to the sine wave signal output terminal, or through a first An amplifier is connected to the sine wave signal output terminal, wherein the positive input terminal of the first amplifier is connected to the sine wave signal output terminal, the negative input terminal of the first amplifier and the output terminal of the first amplifier are both connected to the reference Impedance; a second amplifier, the positive input of the second amplifier is connected to a reference voltage, the negative input of the second amplifier is connected to the reference impedance; a switch circuit, an impedance to be measured and a correction impedance, connected to Between the negative input terminal and the output terminal of the second amplifier; and a sampling circuit that receives the clock signal generated by the waveform generating circuit and is connected to the output terminal of the second amplifier, the negative input terminal of the second amplifier or The internal terminal of the switch circuit; wherein the switch circuit includes a plurality of switches, and by controlling the switches, the negative input terminal of the second amplifier and the output terminal of the second amplifier are connected to the impedance to be measured or the Correct the impedance, or connect an additional switch to the corrected impedance.

The AC impedance measurement circuit described above, wherein the switch circuit includes: a first switch, One end is connected to the negative input or output end of the second amplifier, and the other end is connected to the correction impedance; a second switch, one end of which is connected to the negative input or output end of the second amplifier; a third switch, It is connected between the impedance to be measured and the other end of the second switch; and a fourth switch, one end of which is connected to the correction impedance, and the other end is connected to the common contact of the second switch and the third switch.

The present invention discloses another AC impedance measurement circuit architecture, including a waveform generating circuit Circuit, including a sine wave signal output terminal, used to output a sine wave signal, and a clock signal output terminal, used to output a clock signal; a reference impedance, directly connected to the sine wave signal output terminal, or through a first An amplifier is connected to the sine wave signal output terminal, wherein the positive input terminal of the first amplifier is connected to the sine wave signal output terminal, the negative input terminal of the first amplifier and the output terminal of the first amplifier are both connected to the reference Impedance; a second amplifier, the positive input of the second amplifier is connected to a reference voltage, the negative input of the second amplifier is connected to the reference impedance; an impedance to be measured and a correction impedance, connected to the second amplifier The negative input terminal; a switch circuit connected between the impedance to be measured or the corrected impedance and the output terminal of the second amplifier; and a sampling circuit that receives the clock signal of the waveform generating circuit and is connected to the The negative input terminal of the second amplifier is connected to the output terminal of the second amplifier or the internal terminal of the switch circuit; wherein the switch circuit includes a plurality of switches, and by controlling the switches, the negative input of the second amplifier The input terminal and the output terminal of the second amplifier are connected to the impedance to be measured or the corrected impedance, or the corrected impedance is connected to a switch.

The AC impedance measurement circuit described above, wherein the switch circuit includes: a first switch, Connected between the output terminal of the second amplifier and the correction impedance; a second switch, one end of which is connected to the output terminal of the second amplifier; a third switch, connected to the impedance to be measured and the second switch Between the other end; and a fourth switch, one end of which is connected to the correction impedance, and the other end is connected to the common contact of the second switch and the third switch.

Various AC impedance measurement circuits of the present invention, wherein the switch circuit includes a first In a calibration mode, the second switch and the fourth switch are turned on; in a second calibration mode, the first switch and the fourth switch are turned on; and in a measurement mode, the second switch and the third switch are turned on; The sampling circuit is connected to the structure of the negative input terminal and the output terminal of the second amplifier, and the second calibration mode does not need to turn on the fourth switch.

Various AC impedance measurement circuits of the present invention, wherein the waveform generating circuit includes: a The digital waveform synthesis circuit is used to output a digital form of sine wave signal, and a digital analog conversion circuit to convert the digital form of the sine wave signal into the analog form of the sine wave signal.

Various AC impedance measurement circuits of the present invention, wherein the sampling circuit includes a digital quantity The conversion circuit converts the sampled signal in analog form into a signal in digital form.

In the various AC impedance measurement circuits of the present invention, by adjusting the sine wave signal and The phase difference of the clock signal controls the sampling time point of the sampling circuit, and then obtains the same-phase sampling or integration result without phase difference for the signal at the output of the second amplifier, which is called the same-phase value, and obtains the phase The quadrature phase sampling or integration result with a difference of 90 degrees is called the quadrature phase value; the above-mentioned integration result can be the result of integrating for one cycle of the clock signal, or for the first half cycle of the clock signal The integral value is subtracted from the result of the second half-period integral value for the clock signal; and the method of calculating the AC conductance value is the square sum of the in-phase value and the quadrature phase value, and the AC conductance is calculated The phase value is divided by the quadrature phase value by the in-phase value, and then substituted into the calculation result of the arctangent function.

In the various AC impedance measurement circuits of the present invention, by adjusting the sine wave signal and For the phase difference of the clock signal, adjust the sampling time point of the sampling circuit, and then obtain the sampling or integration result with no phase difference and a phase difference of 180 degrees for the signal at the output of the second amplifier, and the two integration results are subtracted Obtain in-phase sampling or integration results, which are called in-phase values, and additionally obtain sampling or integration results with a phase difference of 90 degrees and a phase difference of 270 degrees. The two integration results are subtracted to obtain a quadrature phase sampling or integration result, which is called positive Cross-phase value; the above-mentioned integration result can be the result of integrating for one cycle of the sine wave signal, or the value of the integration for the first half cycle of the sine wave signal, minus the integration for the second half cycle of the sine wave signal The result of the numerical value; and the method of calculating the AC conductance value is the in-phase value and the quadrature phase value to the square of the square, and the method of calculating the AC conductance phase value is the quadrature phase value divided by the in-phase value, Then substitute the calculation result of the arctangent function.

The various AC impedance measurement circuits of the present invention further include using the first calibration mode to And the value difference between the AC conductance values obtained in the second calibration mode, and the impedance value of the calibration impedance, calculate the equivalent impedance value of the fourth switch; or use the impedance value of the calibration impedance or the fourth switch, etc. The gain is calculated by the ratio of the effective impedance value to the AC conductance value; or the phase delay of the AC impedance measurement circuit is the AC conductance phase value obtained in the first calibration mode or the AC conductance phase value in the second calibration mode; in addition, the measurement For the AC impedance measurement result of the mode, the equivalent impedance value of the switch connected in series with the impedance to be measured can be deducted to calculate the accurate impedance value of the impedance to be measured.

In the various AC impedance measurement circuits of the present invention, the equivalent impedance of the fourth switch is The calculation method is that the AC conductance value of the second calibration mode is divided by the AC conductance value of the first calibration mode, subtracted by 1, and then multiplied by the resistance value of the calibration impedance, or the gain of the AC impedance measurement circuit is the first The conductance measurement result of the second calibration mode is multiplied by the resistance value of the calibration impedance; in addition, for the configuration where the sampling circuit is connected to the negative input terminal and output terminal of the second amplifier, the equivalent impedance of the fourth switch is calculated as "The AC conductance value of the second calibration mode minus the AC conductance value of the first calibration mode", divided by "The AC conductance value of the first calibration mode multiplied by 2 and minus the AC conductance value of the second calibration mode ", multiplied by the resistance value of the correction impedance, or the gain of the AC impedance measurement circuit is the conductance measurement result of the second correction mode multiplied by "the resistance value of the correction impedance plus the equivalent impedance value of the fourth switch ".

In the AC impedance measurement circuit of the present invention, if the equivalent impedance value of the third switch and the The more matched the equivalent impedance value of the third switch is, the more accurate the correction effect is.

This paragraph text extracts and compiles some features of the present invention; other features will be described In the subsequent paragraphs. Its purpose is to cover the spirit and scope included in the subsequent patent scope, different modifications and similar arrangements.

The present invention will be more specifically described with reference to the following examples. Please note the practicality of the present invention The following description of the embodiments is only for the purpose of description; this does not mean that the present invention has been described in detail or is limited to the form of the disclosure.

Please refer to Figure 1 for the first embodiment of the present invention, which shows an AC impedance measurement The circuit includes a waveform generating circuit 10, including a sine wave signal output terminal for outputting a sine wave signal, and a clock signal output terminal for outputting a clock signal; a first amplifier 20, the positive of the first amplifier 20 The input terminal is connected to the sine wave signal output terminal; a switch circuit 30 is connected to the negative input terminal of the first amplifier 20 and the output terminal of the first amplifier 20; an impedance to be measured 401 and a calibration impedance 402 are connected To the switch circuit 30; a second amplifier 50, the positive input terminal of the second amplifier 50 is connected to a reference voltage, and the negative input terminal of the second amplifier 50 is connected to the impedance to be measured 401 and the correction impedance 402; The reference impedance 403 is connected between the negative input terminal of the second amplifier 50 and the output terminal of the second amplifier 50; and an analog-to-digital conversion circuit 60 is connected to the clock signal output terminal of the waveform generating circuit 10 and the Refer to both ends of impedance 403.

The aforementioned AC impedance measurement circuit, wherein the switch circuit 30 includes: a first switch SW1, connected between the negative input terminal of the first amplifier 20 and the correction impedance 402; a second switch SW2, connected between the negative input terminal of the first amplifier 20 and the output terminal of the first amplifier 20; A third switch SW3 is connected between the output terminal of the first amplifier 20 and the impedance to be measured 401; and a fourth switch SW4 is connected between the output terminal of the first amplifier 20 and the correction impedance 402. By controlling the switches (SW1~SW4), the impedance to be measured 401 or the correction impedance 402 is connected between the first amplifier 20 and the second amplifier 50, or the correction impedance is connected to a switch (SW1~ SW4).

The AC impedance measurement circuit described above, wherein the switch circuit 30 includes a first correction mode Formula, turn on the second switch SW2 and the fourth switch SW4; a second calibration mode, turn on the first switch SW1 and the fourth switch SW4; and a measurement mode, turn on the second switch SW2 and the third switch SW3.

For the above-mentioned first calibration mode, please refer to Fig. 2, turning on the second switch SW2 to And the fourth switch SW4, allowing the negative input terminal of the first amplifier 20 to be connected to the output terminal of the first amplifier 20 through the second switch SW2, and allowing the correction impedance 402 to be connected to the first amplifier 20 through the fourth switch SW4 The output terminal of an amplifier 20. In the first calibration mode, the output terminal of the first amplifier 20 and the negative input terminal of the second amplifier 50 are connected to the fourth switch SW4 and the calibration impedance 402, so that the AC impedance measurement circuit is directed to the fourth switch SW4 The equivalent impedance and the impedance value of the correction impedance 402 in series are measured.

For the above-mentioned second calibration mode, please refer to Figure 3, turning on the first switch SW1 to And the fourth switch SW4, allowing the negative input end of the first amplifier 20 to be connected to the output end of the first amplifier 20 through the first switch SW1 and the fourth switch SW4, and allowing the correction impedance 402 to pass through the fourth The switch SW4 is connected to the output terminal of the first amplifier 20. In the second calibration mode, the first switch SW1 and the fourth switch SW4 can be regarded as the switching circuits of the first amplifier 20, so the AC impedance measurement circuit is allowed to measure the impedance value of the calibration impedance 402.

For the above-mentioned measurement mode, please refer to Figure 4, turning on the second switch SW2 and the The third switch SW3 allows the negative input terminal of the first amplifier 20 to be connected to the output terminal of the first amplifier 20 through the second switch SW2, and allows the impedance to be measured 401 to be connected to the first amplifier 20 through the third switch SW3. The output terminal of the amplifier 20. In the measurement mode, the AC impedance measurement circuit measures the equivalent impedance of the third switch SW3 and the impedance value of the impedance 401 to be measured in series.

The AC impedance measurement circuit mentioned above, by adjusting the sine wave of the waveform generating circuit 10 The phase difference between the signal and the clock signal controls the sampling time point of the sampling circuit 601 of the analog-to-digital converter 60, and then obtains the same-phase sampling or integration result with no phase difference for the signal at the output terminal of the second amplifier 50 , Is called the in-phase value, and the quadrature phase sampling or integration result obtained with a phase difference of 90 degrees is called the quadrature phase value. After the sine wave signal generated by the waveform generating circuit 10 passes through the first amplifier 20, the switch circuit 30, the impedance to be measured 401 or the corrected impedance 402, the reference impedance 403, and the second amplifier 20, the sampling circuit 601 receives If the sine wave signal output by the waveform generating circuit 10 and the clock signal have no phase difference, the sampling time point of the sampling circuit 601 is synchronized with the sine wave signal, and is synchronized with the sine wave signal. The signal at the output terminal of the second amplifier 50 has a phase delay Θ. The sampling circuit 601 can sample at this time point or perform integration of a complete sine wave signal cycle. As shown in FIG. 5A, the same-phase sampling or integration result obtained under the condition of no phase difference is referred to herein as ADC1.

The AC impedance measurement circuit mentioned above, if the sine wave signal of the waveform generating circuit 10 There is a 90-degree phase difference with the clock signal, then the sampling circuit 601 is delayed by 90 degrees from the sine wave signal, and there is a phase delay with the signal at the output of the second amplifier 50 as Θ+90 degrees. The sampling circuit 601 can sample at this point in time or perform integration of a complete sine wave signal cycle. As shown in FIG. 5B, the quadrature phase sampling or integration result obtained with a phase difference of 90 degrees is referred to herein as ADC2. .

The AC impedance measurement circuit mentioned above, when calculating the sampling or integration results of the same phase, In addition, the sine wave signal output by the waveform generating circuit 10 and the clock signal can have a phase difference of 180 degrees. Compared with the sine wave signal, the sampling circuit 601 will be delayed by 180 degrees in timing. The signal at the output end of the second amplifier 50 has a phase delay of Θ+180 degrees. Let the sampling circuit 601 sample instantaneously or perform a complete cycle of integration. As shown in Figure 5C, the result of the sampling or integration is referred to as ADC3 for short. You can use the formula "(ADC1-ADC3)/2" to calculate the same-phase sampling or Integral result; in the same way, the sine wave signal output by the waveform generating circuit 10 and the clock signal can have a phase difference of 270 degrees, and there is a phase delay of Θ+270 degrees with the signal at the output end of the second amplifier 50. Let the sampling circuit 601 sample instantaneously or perform a complete cycle of integration. As shown in Figure 5D, the result of the sampling or integration is referred to as ADC4 for short. The quadrature phase sampling can be calculated using the formula "(ADC2-ADC4)/2" Or integration result.

The above-mentioned in-phase sampling or integration result is referred to as "in-phase value (I)", and quadrature-phase sampling or integration result is referred to as "quadrature phase value (Q)", the method of calculating AC conductance value (Y) It is the one-half power of the sum of the squares of the in-phase value I and the quadrature-phase value Q, the mathematical formula is "Y=(I ² +Q ² ) ^0.5 "; and the way to calculate the AC conductance phase value (Θ) is The quadrature phase value is divided by the in-phase value, and then substituted into the calculation result of the arctangent function. The mathematical formula is "Θ=tan ^-1 (Q/I)".

The above integration result is the result of integrating for one period of the sine wave signal, It can also be the result of subtracting the integral value for the first half period of the sine wave signal and subtracting the integral value for the second half period of the sine wave signal.

For the AC impedance measurement circuit mentioned above, the calculation result of the first correction mode is named Y1 And Θ1, the equivalent conductance value and conductance phase value in parallel corresponding to the correction impedance 402 and the equivalent impedance of the fourth switch SW4 (referred to as Rs); the calculation results of the second correction mode are named Y2 and Θ2, corresponding to For the correction impedance 402, the equivalent conductance value and conductance phase value. In this embodiment, assuming that the impedance value of the correction impedance 402 is 5.1K ohms, the mathematical formula for calculating the equivalent impedance Rs of the fourth switch SW4 is "Rs=5.1K*((Y2/Y1)-1)". And the mathematical formula of gain G is "G=5.1K*Y2".

For the AC impedance measurement circuit mentioned above, the calculation result of this measurement mode is named Y3 and Θ3 corresponds to the parallel equivalent conductance value and conductance phase value of the impedance to be measured 401 and the equivalent impedance of the third switch SW3 (referred to as Rs). When the equivalent impedance values of the third switch SW3 and the fourth switch SW4 match, the measurement result of the measurement mode only needs to subtract the impedance value of Rs to accurately calculate the impedance value of the impedance 401 to be measured. Therefore, the in-phase value of the equivalent impedance of the impedance to be measured is "I3=Y3*cos(Θ3-Θ1)-Rs", where the cos() function represents the cosine function in the trigonometric function, and the quadrature phase value is "Q3 =Y3*sin(Θ3)", where the sin() function represents the sine function in the trigonometric function; the mathematical formula of the equivalent series resistance of the impedance 401 under test is "R3=I3=Y3*cos(Θ3)-Rs ", the mathematical formula of the equivalent series capacitance value of the impedance 401 under test is "C3=1/(2*π*fs*Q3)", where fs represents the frequency of the sine wave signal output by the waveform generating circuit 10.

The aforementioned AC impedance measurement circuit can also calculate the equivalent parallel resistance value and capacitance value of the impedance 401 under test. The equivalent conductance value is "Y4=(I3 ² +Q3 ² ) ^0.5 ", and its equivalent impedance phase The value is "Θ4= tan-1(Q3/I3)", its in-phase value is "I4=Y4*cos(Θ4)", and its quadrature phase value is "Q4=Y4*sin(Θ4)". The equivalent series capacitance value of the impedance 401 under test is "C4=Q4/(2*π*fs)", and the equivalent series resistance value is "R4=1/I4".

For the second embodiment of the present invention, please refer to Figure 6, which shows another AC impedance measurement The quantity circuit includes a waveform generating circuit 10 for outputting a sine wave signal and a clock signal; a first amplifier 20, the positive input terminal of the first amplifier 20 is connected to the sine wave signal output terminal of the waveform generating circuit 10 , The negative input terminal of the first amplifier 20 and the output terminal of the first amplifier 20 are both connected to a reference impedance 403; the other end of the reference impedance 403 is connected to a switch circuit 30 and the negative input terminal of a second amplifier 50 The positive input terminal of the second amplifier 50 is connected to a reference voltage; an impedance to be measured and a correction impedance are connected between the switching circuit 30 and the output terminal of the second amplifier 50; and an analog-to-digital converter 60 , Receiving the clock signal of the waveform generating circuit 10, the output terminal of the second amplifier 50, and the voltage of the negative input terminal of the second amplifier 50.

The aforementioned AC impedance measurement circuit, wherein the switch circuit 30 includes: a first switch SW1 is connected between the negative input terminal of the second amplifier 50 and the correction impedance 402; a second switch SW2, one end is connected to the negative input terminal of the second amplifier 50, the other end is connected to a third switch SW3 and a The fourth switch SW4 is connected; the other end of the third switch SW3 is connected to the impedance to be measured 401; and the other end of the fourth switch SW4 is connected to the correction impedance 402. By controlling the switches (SW1~SW4), the test impedance 401 or the correction impedance 402 is connected between the negative input terminal of the second amplifier 50 and the output terminal of the second amplifier 50, or the correction impedance Connect one more switch (SW1~SW4).

The AC impedance measurement circuit described above, wherein the switch circuit 30 includes a first correction mode Formula, turn on the second switch SW2 and the fourth switch SW4; a second calibration mode, turn on the first switch SW1; and a measurement mode, turn on the second switch SW2 and the third switch SW3.

The above-mentioned first calibration mode turns on the second switch SW2 and the fourth switch SW4 allows the negative input terminal of the second amplifier 50 to be connected to the correction impedance 402 through the second switch SW2 and the fourth switch SW4. In the first calibration mode, the output terminal of the second amplifier 50 and the negative input terminal of the second amplifier 50 are connected to the second switch SW2, the fourth switch SW4, and the correction impedance 402, so that the AC impedance measurement circuit The equivalent impedance of the second switch SW2 and the fourth switch SW4 and the impedance value of the correction impedance 402 in series are measured.

In the above-mentioned second calibration mode, only the first switch SW1 needs to be turned on, so that the second amplifier The negative input terminal of the amplifier 50 is connected to the correction impedance 402 through the first switch SW1. In the second calibration mode, the AC impedance measurement circuit measures the equivalent impedance of the first switch SW1 and the impedance value of the calibration impedance 402 in series.

In the above-mentioned measurement mode, the second switch SW2 and the third switch SW3 are turned on, The negative input terminal of the second amplifier 50 is connected to the impedance to be measured 401 through the second switch SW2 and the third switch SW3. In the measurement mode, the AC impedance measurement circuit measures the equivalent impedance of the second switch SW2 and the third switch SW3 and the impedance value of the correction impedance 402 in series.

The AC impedance measurement circuit mentioned above calculates the sampling or product of the same phase and quadrature phase The method of dividing the results is the same as that described in the first embodiment. The method of calculating the AC conductance value (Y) and the AC conductance phase value (Θ) is also the same as that described in the first embodiment.

For the AC impedance measurement circuit mentioned above, the calculation result of the first correction mode is named Y1 And Θ1, the equivalent conductance value and conductance phase value corresponding to the parallel connection of the correction impedance 402, the equivalent impedance of the second switch SW2 and the fourth switch SW4; the calculation results of the second correction mode are named Y2 and Θ2, The equivalent conductance value and conductance phase value in parallel corresponding to the correction impedance 402 and the equivalent impedance of the first switch SW1. Compared with the first embodiment, in the first calibration mode and the second calibration mode, when the calibration resistor 402 is measured, an additional switch (SW1 or SW2) is connected in series, so the calculation formula is adjusted as follows. In the second embodiment, assuming that the impedance value of the correction impedance 402 is 5.1K ohms, and assuming that the equivalent impedances of the second switch SW2 and the fourth switch SW4 are both Rs, the mathematical formula is "Rs=5.1K *(Y2-Y1)/(2Y1-Y2)". And the mathematical formula of gain G is "G=(5.1K+Rs)*Y2".

In the second embodiment, the calculation results Y3 and Θ3 of the measurement mode correspond to the measurement The equivalent conductance value and conductance phase value of the impedance 401, the equivalent impedance of the second switch SW2 and the third switch SW3 in parallel are connected in parallel. When the equivalent impedance values of the switches (SW1~SW4) match (all referred to as Rs), the measurement result of this measurement mode can be accurately calculated by subtracting 2*Rs from the measurement result of the impedance to be measured 401 . Therefore, the in-phase value of the equivalent impedance of the impedance to be measured is "I3=Y3*cos(Θ3-Θ1)-2*Rs", and the quadrature phase value is "Q3=Y3*sin(Θ3)"; The mathematical formula for the equivalent series resistance of the impedance 401 to be measured is "R3=I3=Y3*cos(Θ3)-2*Rs", and the mathematical formula for the equivalent series capacitance of the impedance 401 to be tested is "C3=1/ (2*π*fs*Q3)".

In the second embodiment, the equivalent parallel resistance and electrical resistance of the impedance 401 to be measured can also be calculated. The capacitance value, as well as the equivalent series resistance value and capacitance value, have the same mathematical formula as in the first embodiment.

The third embodiment of the present invention, please refer to Figure 7, which shows another AC impedance measurement The measurement circuit includes a waveform generating circuit 10 for outputting a sine wave signal and a clock signal; a reference impedance 403, one end of which is connected to the sine wave signal output terminal of the waveform generating circuit 10, and the other end is connected to a switch circuit 30 and a negative input terminal of a second amplifier 50; the positive input terminal of the second amplifier 50 is connected to a reference voltage; an impedance to be measured and a correction impedance are connected to the switch circuit 30 and the output of the second amplifier 50 And an analog-to-digital converter 60 that receives the clock signal of the waveform generating circuit 10, the output terminal of the second amplifier 50 and the voltage of an internal terminal of the switch circuit 30.

The aforementioned AC impedance measurement circuit, wherein the switch circuit 30 includes: a first switch SW1 is connected between the negative input terminal of the second amplifier 50 and the correction impedance 402; a second switch SW2, one end is connected to the negative input terminal of the second amplifier 50, the other end is connected to a third switch SW3 and a The fourth switch SW4 is connected; the other end of the third switch SW3 is connected to the impedance to be measured 401; and the other end of the fourth switch SW4 is connected to the correction impedance 402. The analog-to-digital converter 60 is connected to the common contact of the second switch SW2, the third switch SW3, and the fourth switch SW4. By controlling the switches (SW1~SW4), the test impedance 401 or the correction impedance 402 is connected between the negative input terminal of the second amplifier 50 and the output terminal of the second amplifier 50, or the correction impedance Connect one more switch (SW1~SW4).

The AC impedance measurement circuit described above, wherein the switch circuit 30 includes a first correction mode Formula, turn on the second switch SW2 and the fourth switch SW4; a second calibration mode, turn on the first switch SW1; and a measurement mode, turn on the second switch SW2 and the third switch SW3.

The above-mentioned first calibration mode turns on the second switch SW2 and the fourth switch SW4 allows the negative input terminal of the second amplifier 50 to be connected to the correction impedance 402 through the second switch SW2 and the fourth switch SW4. In the first calibration mode, the AC impedance measurement circuit measures the equivalent impedance of the fourth switch SW4 and the impedance value of the calibration impedance 402 in series.

The above-mentioned second calibration mode turns on the first switch SW1 and the fourth switch SW4 allows the negative input terminal of the second amplifier 50 to be connected to the correction impedance 402 through the first switch SW1. In the second calibration mode, the AC impedance measurement circuit measures the equivalent impedance of the first switch SW1 and the impedance value of the calibration impedance 402 in series. As for the fourth switch SW4, it is just a way for the analog-to-digital converter 60 The equivalent impedance of the receiving voltage path does not affect the measurement result theoretically.

In the above-mentioned measurement mode, the second switch SW2 and the third switch SW3 are turned on, The negative input terminal of the second amplifier 50 is connected to the impedance to be measured 401 through the second switch SW2 and the third switch SW3. In the measurement mode, the AC impedance measurement circuit measures the equivalent impedance of the third switch SW3 and the impedance value of the correction impedance 402 in series.

In the third embodiment, the in-phase value (I), quadrature-phase value (Q), AC conductance are calculated Value (Y), AC conductance phase value (Θ), equivalent impedance Rs, gain G, and the in-phase value (I3), quadrature phase value (Q3), equivalent series of the equivalent impedance of the impedance 401 under test The mathematical formulas of the resistance value (R3), the equivalent series capacitance value (C3), the equivalent parallel resistance value (R4), and the equivalent parallel capacitance value (C4) are the same as in the first embodiment.

The fourth embodiment of the present invention, please refer to Figure 8, which shows another AC impedance measurement The measurement circuit includes a waveform generating circuit 10 for outputting a sine wave signal and a clock signal; a reference impedance 403, one end of which is connected to the sine wave signal output terminal of the waveform generating circuit 10, and the other end is connected to a second The negative input terminal of the amplifier 50 is connected to a measured impedance 401 and a correction impedance 402; the positive input terminal of the second amplifier 50 is connected to a reference voltage; the other end of the measured impedance 401 and the corrected impedance 402 Are respectively connected to a switch circuit 30; the switch circuit 30 is also connected to the output terminal of the second amplifier 50; and an analog-to-digital converter 60 that receives the clock signal of the waveform generating circuit 10 and the second amplifier 50 The voltage of the output terminal and the negative input terminal of the second amplifier 50.

The aforementioned AC impedance measurement circuit, wherein the switch circuit 30 includes: a first switch SW1 is connected between the output terminal of the second amplifier 50 and the correction impedance 402; a second switch SW2, one end is connected to the output terminal of the second amplifier 50, the other end is connected to a third switch SW3 and a fourth The switch SW4 is connected; the other end of the third switch SW3 is connected to the impedance to be measured 401; and the other end of the fourth switch SW4 is connected to the correction impedance 402. By controlling the switches (SW1~SW4), the negative input terminal of the second amplifier 50 and the output terminal of the second amplifier 50 are connected to the impedance to be measured 401 or the correction impedance 402, or further includes at least one Switch (SW1~SW4).

The AC impedance measurement circuit described above, wherein the switch circuit 30 includes a first correction mode Formula, turn on the second switch SW2 and the fourth switch SW4; a second calibration mode, turn on the first switch SW1; and a measurement mode, turn on the second switch SW2 and the third switch SW3.

The above-mentioned first calibration mode turns on the second switch SW2 and the fourth switch SW4 allows the output terminal of the second amplifier 50 to be connected to the correction impedance 402 through the second switch SW2 and the fourth switch SW4. In the first calibration mode, the AC impedance measurement circuit measures the equivalent impedance of the second switch SW2, the equivalent impedance of the fourth switch SW4, and the impedance value of the calibration impedance 402 in series.

In the above-mentioned second calibration mode, the first switch SW1 is turned on, so that the second amplifier The output terminal of 50 is connected to the correction impedance 402 through the first switch SW1. In the second calibration mode, the AC impedance measurement circuit measures the equivalent impedance of the first switch SW1 and the impedance value of the calibration impedance 402 in series.

In the above-mentioned measurement mode, the second switch SW2 and the third switch SW3 are turned on, The output terminal of the second amplifier 50 is connected to the impedance to be measured 401 through the second switch SW2 and the third switch SW3. In the measurement mode, the AC impedance measurement circuit measures the equivalent impedance of the second switch SW3, the equivalent impedance of the third switch SW3, and the impedance value of the correction impedance 402 in series.

In the fourth embodiment, the in-phase value (I), quadrature-phase value (Q), AC conductance are calculated Value (Y), AC conductance phase value (Θ), equivalent impedance Rs, gain G, and the in-phase value (I3), quadrature phase value (Q3), equivalent series of the equivalent impedance of the impedance 401 under test The mathematical formulas of the resistance value (R3), the equivalent series capacitance value (C3), the equivalent parallel resistance value (R4), and the equivalent parallel capacitance value (C4) are the same as in the second embodiment.

Please refer to Figure 9 for the fifth embodiment of the present invention, which shows another AC impedance measurement The circuit structure is similar to that of the fourth embodiment. The difference is that the output terminal of the second amplifier 50 in the fourth embodiment is connected to the analog-to-digital converter 60. In the fifth embodiment, it is changed to the switch circuit 30. The common contact of the second switch SW2, the third switch SW3 and the fourth switch SW4 is connected to the analog-to-digital converter 60. The calculation methods for calculating the in-phase value (I), the quadrature phase value (Q), etc. are the same as in the third embodiment.

The above-mentioned various AC impedance measurement circuits, wherein the waveform generating circuit 10 includes a digital A bit waveform synthesis circuit 101 is used to output a digital form of a sine wave signal; and a digital analog conversion circuit 102 is used to convert the digital form of a sine wave signal into an analog form of sine wave signal.

The above-mentioned various AC impedance measurement circuits, wherein the analog-to-digital converter 60 further includes A digital quantization circuit 602 converts the sampling or integration result in analog form into a digital signal, which is used to calculate the above-mentioned mathematical formulas.

The above-mentioned various AC impedance measurement circuits, wherein the negative input terminal of the second amplifier 50 The voltage value of the connected reference voltage is the same as the average voltage value of the sine wave signal of the waveform generating circuit. For example, if the sine wave signal is an AC signal between 0V and 5V, the voltage value of the reference voltage is 2.5V.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field can make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be subject to the definition of the appended patent scope.

10: Waveform generating circuit

101: Digital Sine Wave Generator

102: Digital Analog Converter

20: The first amplifier

30: Switching circuit

SW1: The first switch

SW2: second switch

SW3: third switch

SW4: fourth switch

401: Impedance to be measured

402: Correction impedance

403: Reference impedance

50: second amplifier

60: Analog-to-digital converter

601: sampling circuit

602: Digital quantization circuit

Figure 1 shows the structure of an AC impedance measurement circuit. Figure 2 shows the switch conduction mode of the first calibration mode of the AC impedance measurement circuit in Figure 1. Figure 3 shows the switch-on mode of the second calibration mode of the AC impedance measurement circuit in Figure 1. Figure 4 shows the switch conduction mode of the measurement mode of the AC impedance measurement circuit in Figure 1. Figure 5 shows the AC impedance measurement circuit, by controlling the clock signal to adjust the sampling circuit Schematic diagram of sampling time points. Figure 6 shows the architecture of the second AC impedance measurement circuit. Figure 7 shows the structure of the third AC impedance measurement circuit. Figure 8 shows the structure of the fourth AC impedance measurement circuit. Figure 9 shows the architecture of the fifth AC impedance measurement circuit.

10: Waveform generating circuit

101: Digital Sine Wave Generator

102: Digital Analog Converter

20: The first amplifier

30: Switching circuit

401: Impedance to be measured

402: Correction impedance

403: Reference impedance

50: second amplifier

60: Analog-to-digital converter

601: sampling circuit

602: Digital quantization circuit

Claims (11)

An AC impedance measurement circuit, including: A waveform generating circuit, including a sine wave signal output terminal for outputting a sine wave signal, and a The clock signal output terminal is used to output a clock signal; A first amplifier, the positive input terminal of the first amplifier is connected to the sine wave signal output terminal; A switch circuit, which is in phase with the negative input terminal of the first amplifier and the output terminal of the first amplifier connection; An impedance to be measured and a correction impedance are connected to the switch circuit; A second amplifier, the positive input of the second amplifier is connected to a reference voltage, the second amplifier The negative input terminal of the amplifier is connected to the impedance to be measured or the calibrated impedance; A reference impedance connected to the negative input terminal of the second amplifier and the output of the second amplifier Between ends; and A sampling circuit that receives the clock signal generated by the waveform generating circuit and connects to the parameter Test the two ends of the impedance; where the switch circuit includes a plurality of switches, and by controlling the switches, the impedance to be measured or the corrected impedance is connected between the first amplifier and the second amplifier, or the corrected impedance is more Connect a switch. The AC impedance measurement circuit described in item 1 of the scope of patent application, wherein the switch circuit includes: A first switch connected between the negative input terminal of the first amplifier and the correction impedance; A second switch connected to the negative input terminal of the first amplifier and the output terminal of the first amplifier between; A third switch connected between the output terminal of the first amplifier and the impedance to be measured; and A fourth switch is connected between the output terminal of the first amplifier and the correction impedance. An AC impedance measurement circuit, including: A waveform generating circuit including a sine wave signal output terminal for outputting a sine wave signal, and The one-clock signal output terminal is used to output one-clock signal; A reference impedance, directly connected to the sine wave signal output terminal, or connected through a first amplifier Connected to the sine wave signal output terminal, wherein the positive input terminal of the first amplifier is connected to the sine wave signal output terminal, the negative input terminal of the first amplifier and the output terminal of the first amplifier are both connected to the reference impedance ； A second amplifier, the positive input of the second amplifier is connected to a reference voltage, the second amplifier The negative input terminal of the amplifier is connected to the reference impedance; A switch circuit, an impedance to be measured and a correction impedance are connected to the negative output of the second amplifier Between the input and output terminals; and A sampling circuit that receives the clock signal generated by the waveform generating circuit and is connected to the second The output terminal of the amplifier, the negative input terminal of the second amplifier or the internal terminal of the switch circuit; wherein the switch circuit includes a plurality of switches, and by controlling the switches, the negative input terminal and the output terminal of the second amplifier Connect the impedance to be measured or the corrected impedance between them, or connect the corrected impedance to one more switch. For the AC impedance measurement circuit described in item 3 of the scope of patent application, the switch circuit includes: A first switch, one end of which is connected to the negative input or output end of the second amplifier, and the other end is connected to Connect to the correction impedance; A second switch, one end of which is connected to the negative input terminal or output terminal of the second amplifier; A third switch connected between the impedance to be measured and the other end of the second switch; and A fourth switch, one end of which is connected to the correction impedance, and the other end is connected to the second switch and the first The common contact of the three switches. For example, the AC impedance measurement circuit described in item 2 or item 4 of the scope of patent application, wherein the switch circuit includes: A first calibration mode, turning on the second switch and the fourth switch; A second calibration mode, turning on the first switch and the fourth switch; and In a measurement mode, the second switch and the third switch are turned on; in addition, the sampling circuit is connected to For the structure of the negative input terminal and the output terminal of the second amplifier, the second calibration mode does not need to turn on the fourth switch. For example, the AC impedance measurement circuit described in item 1, item 2, item 3 or item 4 of the scope of patent application, wherein the waveform generating circuit includes: A digital waveform synthesis circuit for outputting a sine wave signal in digital form; and A digital-to-analog conversion circuit converts the sine wave signal in digital form into the sine wave signal in analog form number. For example, the AC impedance measurement circuit described in item 1, item 2, item 3, or item 4 of the scope of patent application, wherein the sampling circuit includes a digital quantization circuit that converts the sampled signal in analog form into a signal in digital form. For example, the AC impedance measurement circuit described in item 1, item 2, item 3 or item 4 of the scope of patent application, wherein the sampling circuit of the sampling circuit is controlled by adjusting the phase difference between the sine wave signal and the clock signal At the time point, for the signal at the output terminal of the second amplifier, the in-phase sampling or integration result with no phase difference is obtained, which is called the in-phase value, and the quadrature phase sampling or integration result with the phase difference of 90 degrees is obtained, which is called Quadrature phase value; the above integration result can be the result of integrating for one period of the sine wave signal, or the integral value for the first half period of the sine wave signal, minus the second half period for the sine wave signal The result of the integral value; and the method of calculating the AC conductance value is the in-phase value and the quadrature phase value to the square of the square, and the method of calculating the AC conductance phase value is the quadrature phase value divided by the in-phase value , And then substitute the calculation result of the arctangent function. Such as the AC impedance measurement circuit described in item 1, item 2, item 3 or item 4 of the scope of patent application, in which the sampling circuit of the sampling circuit is adjusted by adjusting the phase difference between the sine wave signal and the clock signal At the time point, for the signal at the output of the second amplifier, a sampling or integration result with no phase difference and a phase difference of 180 degrees is obtained. The two integration results are subtracted to obtain the same-phase sampling or integration result, which is called the same-phase value. In addition, the sampling or integration results with a phase difference of 90 degrees and a phase difference of 270 degrees are obtained. The two integration results are subtracted to obtain the quadrature phase sampling or integration result, which is called the quadrature phase value; the above-mentioned integration result can be for the The result of the integration of one cycle of the sine wave signal, or the result of the integration value for the first half cycle of the sine wave signal, and the result of subtracting the integration value for the second half cycle of the sine wave signal; and the method of calculating the AC conductance value is the same phase The value and the quadrature phase value are squared to the power of one-half, and the method of calculating the AC conductance phase value is the quadrature phase value divided by the in-phase value, and then substituted into the calculation result of the arctangent function. For example, the AC impedance measurement circuit described in item 5 of the scope of patent application further includes the numerical difference between the AC conductance values obtained by the first calibration mode and the second calibration mode, and the impedance value of the calibration impedance, to calculate the first calibration mode and the second calibration mode. The equivalent impedance value of the four switches; or use the impedance value of the corrected impedance or the ratio of the equivalent impedance value of the fourth switch to the AC conductance value to calculate the gain; or the phase delay of the AC impedance measurement circuit, that is, the first The AC conductance phase value obtained in the calibration mode or the AC conductance phase value of the second calibration mode; in addition, the AC impedance measurement result of the measurement mode can be deducted from the equivalent impedance value of the switch connected in series with the impedance to be measured, and the calculation is accurate The impedance value of the impedance to be measured. For the AC impedance measurement circuit described in item 10 of the scope of patent application, the equivalent impedance of the fourth switch is calculated by dividing the AC conductance value of the second calibration mode by the AC conductance value of the first calibration mode, After subtracting 1, multiply by the resistance value of the correction impedance, or the gain of the AC impedance measurement circuit is the conductance measurement result of the second correction mode multiplied by the resistance value of the correction impedance; in addition, the sampling circuit is connected to the first The structure of the negative input terminal and output terminal of the second amplifier. The calculation method of the equivalent impedance of the fourth switch is "the AC conductance value of the second calibration mode minus the AC conductance value of the first calibration mode", divided by "The AC conductance value of the first calibration mode is multiplied by 2 and the AC conductance value of the second calibration mode is subtracted", and then multiplied by the resistance value of the calibration impedance, or the gain of the AC impedance measurement circuit is the second calibration The conductance measurement result of the mode is multiplied by the "resistance value of the correction impedance plus the equivalent impedance value of the fourth switch".

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