A signal power amplification module for impedance measurement

Abstract

The application aims to provide a signal power amplification module for impedance measurement. The application comprises a power amplification circuit and an output control circuit, the power amplification circuit is connected with the output control circuit, the power amplification circuit and the output control circuit are both connected with a feedback control circuit, the power amplification circuit outputs input sine wave or direct current signal according to a set function, the output control circuit outputs direct current or alternating current as an excitation signal, when the system output signal is alternating current, DC_Input is set as 0, AC_Input is the excitation signal, Mux_EN is 1, Mux_ADDR_A0 is 1, at this time, the feedback loop integrates the alternating current signal, so that the direct current bias of the power amplifier is close to 0; when the system output signal is direct current, DC_Input is set as the excitation signal, AC_Input is 0, Mux_EN is 1, and Mux_ADDR_A0 is 0. The application is applied to the technical field of impedance measurement.

Description

Technical Field

[0001] This invention applies to the technical field of impedance measurement, and particularly relates to a signal power amplification module for impedance measurement. Background Technology

[0002] Impedance measurement is widely used in passive device testing, PCB measurement, electrochemical analysis, biosensing, and other fields. The basic principle of impedance measurement is to apply a known excitation signal to the object under test and measure its response signal, thereby calculating the impedance magnitude and phase angle. The quality and controllability of the excitation signal directly affect the measurement accuracy and repeatability.

[0003] In impedance measurement systems, the signal source output control circuit is a crucial component. It needs to possess the following capabilities: output AC or DC bias signals; control the amplitude of the output signal; achieve a "high impedance" state at the output terminal; and exhibit low noise, low distortion, and fast response characteristics. However, commercially available excitation signal source driving technologies require isolation capacitors of 1000uF or larger to meet the low-frequency requirement of 20Hz; otherwise, the accuracy of AC impedance testing will be affected. Due to the use of large-sized components in the output, the overall test module is too large, making it difficult to meet the requirements of low-frequency miniaturization measurement. For example, Chinese patent CN122043070A discloses a method for measuring the impedance of a common-mode inductor under DC bias. In one parallel branch, an impedance analyzer, an isolation capacitor, and an AC bias inductor are connected in series and then connected to the positive terminal of a DC bias source; in another parallel branch, an isolation capacitor is connected in series and then connected to the negative terminal of the DC bias source, forming a closed loop. However, this scheme requires isolation capacitors of 1000uF or more, resulting in a large number of modules, which is difficult to meet the requirements of low-frequency miniaturization measurement. Therefore, it is necessary to provide a signal power amplification module and measurement method for impedance measurement that is highly reliable, free from mechanical wear, has a long lifespan, is small in size, has low power consumption, and has a large and small output capacitance, thus meeting the requirements for low-frequency measurement. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a signal power amplification module for impedance measurement, which has high reliability, no mechanical wear, long life, small size, low power consumption, and large output capacitance, thus meeting the requirements of low frequency measurement.

[0005] The technical solution adopted in this invention is as follows: This invention includes a power amplifier circuit and an output control circuit. The power amplifier circuit is connected to the output control circuit, and both the power amplifier circuit and the output control circuit are connected to a feedback control circuit. The power amplifier circuit outputs the input sine wave or DC signal according to a set function. The output control circuit outputs DC or AC as an excitation signal. When the system output signal is AC, DC_Input = 0, AC_Input is the excitation signal, Mux_EN = 1, and Mux_ADDR_A0 = 1. At this time, the feedback loop integrates the AC signal, making the DC bias of the power amplifier close to 0. When the system output signal is DC, DC_Input is the excitation signal, AC_Input = 0, Mux_EN = 1, and Mux_ADDR_A0 = 0.

[0006] As can be seen from the above scheme, the feedback control circuit serves as a servo drive circuit. This application adds a servo drive circuit to the power amplifier circuit, which effectively reduces the capacitance of the isolation capacitor without affecting the signal quality at low frequencies, thus effectively improving the system's testing accuracy. The introduction of servo feedback and solid-state relays, combined with software, meets the requirements for device miniaturization and impedance measurement. This application has the following significant advantages: high reliability, no mechanical wear, theoretically unlimited lifespan, suitable for long-life equipment such as medical and aerospace applications. Small size and low power consumption: the output capacitance is significantly small, requiring only tens of microseconds (µF), which meets the requirements for 20Hz low-frequency measurement, allowing for miniaturization and modularization. With a servo feedback system and programmable servo feedback control, it can meet the requirements for rapid settling time for both DC and AC voltages.

[0007] In a preferred embodiment, the feedback control circuit includes an operational amplifier U2, which is connected to resistors R2, R3, R6, R7, and capacitor C2; and the power amplifier circuit includes an operational amplifier U3, which is connected to resistors R8, R9, R11, R12, and R13. Let the voltage of AC_input be Vac, the reference voltage be Vref, and the voltage of DC_input be Vdc. When the output excitation signal is AC voltage and there is no DC bias, the system is set as follows: Vdc_input = 0V, Mux_EN = 1, Mux_ADDR_A0 = 1, VOutput = Vout_ac. Let the output voltage of U2 be V1. According to Kirchhoff's current law, we have: Vac / R11 + Vref / R9 + V1 / R8 = -Vout_ac / (R12 + R13); Assuming the integral voltage of the servo feedback loop on the output voltage of U3 is V2, then the servo feedback loop has: V1 = V2 * (1 / (ω*C2) / (1 / (ω*C2) +R6) = V2* / (1+ω*C2*R6) R11 = 3 Kohm, R9 = 3.6 Kohm, R8 = 1.8 Kohm, R6 = 49.9 Kohm, C2 = 1uF, R11 + R12 = 3.3 Kohm. Solving the two equations above simultaneously, we have: Vout_ac= (R12 + R13) *Vac / R11 +Vref / R9 + V2* / ((1+ω*C2*R6) *R8) = -1.1Vac + 2.5 / 3.6 * 10-3 - V2* / (1600 +78.94ω); Where ω is the system response frequency of U2, when the output of the power amplifier is a small DC plus a sine wave signal, since the long-term integral voltage of the sine wave by the feedback control circuit is 0, only the DC component remains. The feedback control circuit feeds this DC component back to the input of the power amplifier, forcing 2.5 / 3.6 *10-3 - V2* / (1600 +78.94ω) in the Vout equation to approach zero, thereby eliminating the DC bias in the sine wave signal and achieving the purpose of eliminating the low-frequency isolation capacitor.

[0008] A preferred approach is to configure the system as follows when the output excitation signal is a DC voltage with no AC component: With Vdc_input = Vdc, Mux_EN = 1, Mux_ADDR_A0 = 0, and VOutput = 0V, a smaller integrating capacitor is selected to improve the DC test response time.

[0009] The corresponding servo feedback circuit is: Vdc / R2 -Vref / R7 = -Vout_dc / R3. From the schematic diagram, we know that R2 = 100Kohm and R7 = R3 = 200Kohm. The formula for calculating DC output is: Vout = R3* Vref / R7 - R3*Vdc / R2 = 2.5–2Vdc; The input range of Vdc is 0-2.5V, and the actual output range of the power drive circuit is [-2.5~2.5]V.

[0010] In a preferred embodiment, the signal power amplification module for impedance measurement further includes a DDS signal generator and a high-order signal filtering circuit. The DDS signal generator is connected to the power amplification circuit via the high-order signal filtering circuit. The DDS signal generator generates a sinusoidal excitation signal or a DC voltage, and the high-order signal filtering circuit filters out the higher harmonics of the sinusoidal signal. Attached Figure Description

[0011] Figure 1 This is a system block diagram of the present invention; Figure 2 This is the circuit schematic diagram of the present invention; Figure 3 This is a schematic diagram illustrating the application of the present invention to the impedance testing of an LCR module. Detailed Implementation

[0012] like Figures 1 to 2 As shown, in this embodiment, the present invention includes a power amplifier circuit 1 and an output control circuit 2. The power amplifier circuit 1 is connected to the output control circuit 2, and both the power amplifier circuit 1 and the output control circuit 2 are connected to a feedback control circuit 3. The power amplifier circuit 1 outputs the input sine wave or DC signal according to a set function. The output control circuit 2 outputs DC or AC as an excitation signal. When the system output signal is AC, DC_Input = 0, AC_Input is the excitation signal, Mux_EN = 1, and Mux_ADDR_A0 = 1. At this time, the feedback loop integrates the AC signal, making the DC bias of the power amplifier close to 0. When the system output signal is DC, DC_Input is the excitation signal, AC_Input = 0, Mux_EN = 1, and Mux_ADDR_A0 = 0. The output of this circuit is a pure DC voltage, and it meets the test time requirements for DC balance level changes. The power amplifier circuit 1 uses an OPA891 integrated operational amplifier as the power driver to output the input sine wave or DC signal according to a set function. The output control circuit 2 serves as an AC or DC output control circuit, controlling the system to output DC or AC as an excitation signal according to the system's settings.

[0013] like Figures 1 to 2 As shown, in this embodiment, the feedback control circuit 3 includes an operational amplifier U2, which is connected to resistors R2, R3, R6, R7, and capacitor C2. The power amplifier circuit 1 includes an operational amplifier U3, which is connected to resistors R8, R9, R11, R12, and R13. Let the voltage of AC_input be Vac, the reference voltage be Vref, and the voltage of DC_input be Vdc. When the output excitation signal is AC voltage and there is no DC bias, the system is set as follows: Vdc_input = 0V, Mux_EN = 1, Mux_ADDR_A0 = 1, VOutput = Vout_ac. Let the output voltage of U2 be V1. According to Kirchhoff's current law, we have: Vac / R11 + Vref / R9 + V1 / R8 = -Vout_ac / (R12 + R13); Assuming the integral voltage of the servo feedback loop on the output voltage of U3 is V2, then the servo feedback loop has: V1 = V2 * (1 / (ω*C2) / (1 / (ω*C2) +R6) = V2* / (1+ω*C2*R6) R11 = 3 Kohm, R9 = 3.6 Kohm, R8 = 1.8 Kohm, R6 = 49.9 Kohm, C2 = 1uF, R11 + R12 = 3.3 Kohm. Solving the two equations above simultaneously, we have: Vout_ac= (R12 + R13) *Vac / R11 +Vref / R9 + V2* / ((1+ω*C2*R6) *R8) = -1.1Vac + 2.5 / 3.6 * 10-3 - V2* / (1600 +78.94ω); Where ω is the system response frequency of U2, when the output of the power amplifier is a small DC plus a sine wave signal, since the long-term integral voltage of the sine wave by the feedback control circuit 3 is 0, only the DC component remains. The feedback control circuit 3 feeds this DC component back to the input of the power amplifier, forcing 2.5 / 3.6 *10-3 - V2* / (1600 +78.94ω) in the Vout equation to approach zero, thereby eliminating the DC bias in the sine wave signal and achieving the purpose of eliminating the low-frequency isolation capacitor.

[0014] like Figures 1 to 2 As shown, in this embodiment, when the output excitation signal is a DC voltage with no AC component, the system is set as follows: With Vdc_input = Vdc, Mux_EN = 1, Mux_ADDR_A0 = 0, and VOutput = 0V, a smaller integrating capacitor is selected to improve the DC test response time.

[0015] The corresponding servo feedback circuit is: Vdc / R2 -Vref / R7 = -Vout_dc / R3. From the schematic diagram, we know that R2 = 100Kohm and R7 = R3 = 200Kohm. The formula for calculating DC output is: Vout = R3* Vref / R7 - R3*Vdc / R2 = 2.5–2Vdc; The input range of Vdc is 0-2.5V, and the actual output range of the power drive circuit is [-2.5~2.5]V.

[0016] The theoretical analysis of the circuit above shows that adding a servo drive circuit to a traditional power amplifier circuit can eliminate the DC bias in the output sine wave to near zero through the feedback circuit. Therefore, when using low-frequency signals for measurement, a DC measurement method can be used, applying a low-frequency AC test signal to both ends of the DUT to perform impedance measurement. At the system level, software cooperation is also required. Because the type of DUT is unknown in actual use, the firmware needs to determine whether the DUT is a passive or active device (such as a 4.2V single-cell lithium battery test) by acquiring the signals at both ends of the DUT before performing normal measurements, thereby improving the reliability of the impedance measurement module.

[0017] like Figures 1 to 2 As shown, in this embodiment, the signal power amplification module for impedance measurement further includes a DDS signal generator 4 and a high-order signal filtering circuit 5. The DDS signal generator 4 is connected to the power amplification circuit 1 via the high-order signal filtering circuit 5. The DDS signal generator 4 generates a sinusoidal excitation signal or DC voltage, and the high-order signal filtering circuit 5 filters out higher harmonics of the sinusoidal signal. The DDS signal generator 4 serves as a signal generation circuit, generating a sinusoidal excitation signal or DC voltage through a high-precision DAC or DDS. The high-order signal filtering circuit 5 is a seventh-order passive low-pass filter, capable of filtering out higher harmonics in the sinusoidal signal and improving the output signal quality.

[0018] In this embodiment, Figure 2 The formula for calculating the output voltage is: Figure 3 The amplitude of the voltage source is calculated in complex form because the firmware uses IQ demodulation. Figure 2 The circuit output voltage is copied three times, and each copy is connected to the voltage source indicated by SEV, QBV, and PBV respectively. SEV is used as the excitation signal, and PBV and QBV are used as reference signals. Figure 3As shown, SEV_SRC: Excitation source signal output, a programmable signal source provided in this technical solution, with an internal resistance of 100 ohms. QBV_SRC: Imaginary part reference excitation signal source, a programmable signal source provided in this technical solution, with built-in values ​​of 100 ohms, 1 Kohm, 10 Kohm, and 50 Kohm, denoted as RQ. PBV_SRC: Real part reference excitation signal source, a programmable signal source provided in this technical solution, with built-in values ​​of 100 ohms, 1 Kohm, 10 Kohm, and 50 Kohm, denoted as RP. VND: Error signal, the output signal of the error current after three-source balancing amplification by TIA, with built-in values ​​of 100 ohms, 1 Kohm, 10 Kohm, and 50 Kohm, denoted as RF.

[0019] The impedance calculation formula is: VSEV_SRC / Z = VQBV_SRC / RQ +VPBV_SRC / RP + VVND / RF Where VSEV_SRC, VQBV_SRC, VPBV_SRC, and VVND are voltage signals calculated through IQ demodulation, which are complex numbers. Finally, the complex impedance of the DUT is calculated using the above formula.

[0020] Although the embodiments of the present invention are described with reference to actual solutions, they do not constitute a limitation on the meaning of the present invention. Modifications to the embodiments and combinations with other solutions based on this specification will be obvious to those skilled in the art.

Claims

1. A signal power amplification module for impedance measurement, comprising a power amplification circuit (1) and an output control circuit (2), wherein the power amplification circuit (1) is connected to the output control circuit (2), characterized in that: Both the power amplifier circuit (1) and the output control circuit (2) are connected to a feedback control circuit (3). The power amplifier circuit (1) outputs the input sine wave or DC signal according to a set function. The output control circuit (2) outputs DC or AC as the excitation signal. When the system output signal is AC, DC_Input = 0, AC_Input is the excitation signal, Mux_EN = 1, and Mux_ADDR_A0 = 1. At this time, the feedback loop integrates the AC signal to make the DC bias of the power amplifier close to 0. When the system output signal is DC, DC_Input is the excitation signal, AC_Input = 0, Mux_EN = 1, and Mux_ADDR_A0 = 0.

2. The signal power amplification module for impedance measurement according to claim 1, characterized in that, The feedback control circuit (3) includes an operational amplifier U2, which is connected to resistors R2, R3, R6, R7 and capacitor C2. The power amplifier circuit (1) includes an operational amplifier U3, which is connected to resistors R8, R9, R11, R12 and R13. Let the voltage of AC_input be Vac, the reference voltage be Vref, and the voltage of DC_input be Vdc. When the output excitation signal is AC voltage and there is no DC bias, the system is set as follows: Vdc_input = 0V, Mux_EN = 1, Mux_ADDR_A0 = 1, VOutput = Vout_ac. Let the output voltage of U2 be V1. According to Kirchhoff's current law, we have: Vac / R11 + Vref / R9 + V1 / R8 = -Vout_ac / (R12 + R13); Assuming the integral voltage of the servo feedback loop on the output voltage of U3 is V2, then the servo feedback loop has: V1 = V2 * (1 / (ω*C2) / (1 / (ω*C2) +R6) = V2* / (1+ω*C2*R6) R11 = 3 Kohm, R9 = 3.6 Kohm, R8 = 1.8 Kohm, R6 = 49.9 Kohm, C2 = 1uF, R11 + R12 = 3.3 Kohm. Solving the two equations above simultaneously, we have: Vout_ac= (R12 + R13) *Vac / R11 +Vref / R9 + V2* / ((1+ω*C2*R6) *R8) = -1.1Vac + 2.5 / 3.6 * 10-3 - V2* / (1600 +78.94ω); Where ω is the system corresponding frequency of U2. When the output of the power amplifier is a small DC plus a sine wave signal, since the long-term integral voltage of the sine wave by the feedback control circuit (3) is 0, only the DC component remains. The feedback control circuit (3) feeds the DC component back to the input of the power amplifier, forcing 2.5 / 3.6 *10-3 - V2* / (1600 +78.94ω) in the Vout equation to approach zero, thereby eliminating the DC bias in the sine wave signal and achieving the purpose of eliminating the low-frequency isolation capacitor.

3. The signal power amplification module for impedance measurement according to claim 2, characterized in that, When the output excitation signal is a DC voltage with no AC component, the system is set as follows: Vdc_input = Vdc, Mux_EN = 1, Mux_ADDR_A0 = 0, VOutput = 0V. In this case, a smaller integrating capacitor is selected to improve the DC test response time. The corresponding servo feedback circuit is: Vdc / R2 -Vref / R7 = -Vout_dc / R3. From the schematic diagram, we know that R2 = 100Kohm and R7 = R3 = 200Kohm. The formula for calculating DC output is: Vout = R3* Vref / R7 - R3*Vdc / R2 = 2.5–2Vdc; The input range of Vdc is 0-2.5V, and the actual output range of the power drive circuit is [-2.5~2.5]V.

4. The signal power amplification module for impedance measurement according to claim 1, characterized in that, The signal power amplification module for impedance measurement also includes a DDS signal generator (4) and a high-order signal filtering circuit (5). The DDS signal generator (4) is connected to the power amplification circuit (1) via the high-order signal filtering circuit (5). The DDS signal generator (4) generates a sine wave excitation signal or DC voltage, and the high-order signal filtering circuit (5) filters out the high-order harmonics of the sine wave signal.

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