Abstract
Impedance characteristics are critical to evaluating the performance of electronic components such as ferroelectric crystals, piezoelectric ceramics, piezoelectric crystals, and ultrasonic transducers. The impedance analyzer circuit, as the core functional unit of an impedance analyzer, determines the accuracy, stability, and efficiency of impedance measurement. This paper takes the LISUN LS90 series impedance analyzer as the research object, systematically expounds the composition and working principle of its impedance analyzer circuit, and deeply explores the application of the instrument in the impedance analysis and testing of ferroelectric crystals, piezoelectric ceramics, piezoelectric crystals, and ultrasonic transducers. Through specific test data and comparative analysis, the performance advantages of the LISUN LS90 impedance analyzer in terms of measurement accuracy, frequency range, and stability are verified. The research results show that the impedance analyzer circuit of the LISUN LS90 series, with its automatic balance bridge technology and four-terminal pair Kelvin test terminal design, can effectively meet the high-precision impedance testing needs of related devices in both laboratory research and production line quality control scenarios, providing reliable technical support for the development and application of piezoelectric and ferroelectric devices.
Keywords
Impedance analyzer circuit; LISUN LS90 Impedance analyzer; Ferroelectric crystals; Piezoelectric ceramics; Piezoelectric crystals; Ultrasonic transducers; Impedance measurement
1. Introduction
In the field of electronic materials and components, ferroelectric crystals, piezoelectric ceramics, piezoelectric crystals, and ultrasonic transducers are widely used in sensors, actuators, filters, and medical imaging equipment. The impedance parameters of these devices, such as resistance (R), reactance (X), impedance (Z), phase angle (θ), admittance (Y), conductance (G), and susceptance (B), directly reflect their electrical properties and working states. For example, the impedance-frequency characteristics of piezoelectric ceramics determine the resonance frequency and bandwidth of piezoelectric sensors, while the impedance stability of ultrasonic transducers affects the efficiency of energy conversion in ultrasonic cleaning and medical diagnosis equipment.
The impedance analyzer is a key instrument for measuring the impedance parameters of electronic components, and the impedance analyzer circuit is the core part that realizes the impedance measurement function. A high-performance impedance analyzer circuit can accurately excite the device under test (DUT) with a stable signal, collect the response signal of the DUT, and calculate the impedance parameters through signal processing and data analysis. The LISUN LS90 series impedance analyzer, developed by LISUN Group, is a representative product in the field of impedance measurement. Its impedance analyzer circuit integrates advanced technologies such as automatic balance bridge and vector testing, which can provide high-precision and wide-range impedance measurement solutions for ferroelectric and piezoelectric devices.
This paper first introduces the composition and working principle of the impedance analyzer circuit of the LISUN LS90 series impedance analyzer; then, it details the test methods and steps of using the instrument to perform impedance analysis on ferroelectric crystals, piezoelectric ceramics, piezoelectric crystals, and ultrasonic transducers; finally, through experimental data and performance analysis, the application value of the LISUN LS90 impedance analyzer in related fields is verified.
2. Composition and Working Principle of LISUN LS90 Impedance Analyzer Circuit
2.1 Composition of Impedance Analyzer Circuit
The impedance analyzer circuit of the LISUN LS90 series is a complex electronic system composed of multiple functional modules, including a signal generation module, a signal excitation module, a signal acquisition module, a signal processing module, a data calculation module, and a human-computer interaction module. The specific composition and functions of each module are shown in Table 1.
Module Name
Composition
Function
Signal Generation Module
Voltage-controlled oscillator (VCO), frequency synthesizer, crystal oscillator
Generate a stable AC excitation signal with adjustable frequency (20Hz～15MHz) and amplitude (up to 1.000V). The frequency accuracy is as high as 1mHz, ensuring the stability of the excitation signal frequency.
Signal Excitation Module
Power amplifier, matching network, four-terminal pair Kelvin test terminals
Amplify the excitation signal generated by the signal generation module to meet the test current requirements (minimum 0.01μA) of different DUTs. The four-terminal pair Kelvin test terminals can eliminate the influence of lead resistance and contact resistance on the measurement results, improving measurement accuracy.
Signal Acquisition Module
High-precision ADC (Analog-to-Digital Converter), current/voltage sensor
Collect the voltage signal across the DUT and the current signal flowing through the DUT. The high-precision ADC ensures that the collected signal has low noise and high resolution, laying the foundation for accurate impedance calculation.
Signal Processing Module
Digital filter, phase-locked loop (PLL), signal conditioning circuit
Filter the collected analog signal to remove noise interference; use the PLL to lock the frequency of the collected signal with the excitation signal, ensuring the accuracy of phase measurement; condition the signal to make it meet the input requirements of the data calculation module.
Data Calculation Module
Microcontroller (MCU), digital signal processor (DSP)
Based on the vector testing principle, calculate the impedance parameters (R-X, Z-θ, Y-θ, G-B) of the DUT according to the collected voltage and current signals. The module has a fast calculation speed, which can realize real-time display of test results.
Human-Computer Interaction Module
7.0′ TFT-LCD display, operation buttons, communication interface (RS232C, USB DEVICE, GPIB optional)
Display the impedance-frequency scanning curve, test parameters, and instrument status in real time; allow users to set test parameters (such as frequency range, signal amplitude) through operation buttons; support data transmission between the instrument and the computer, facilitating data storage and post-processing.
2.2 Working Principle of Impedance Analyzer Circuit
The working process of the LISUN LS90 impedance analyzer circuit can be divided into five stages: signal generation, signal excitation, signal acquisition, signal processing, and data calculation and display. The specific working principle is as follows:
• Signal Generation Stage: The crystal oscillator in the signal generation module provides a reference frequency signal with high stability. The frequency synthesizer adjusts the reference frequency according to the user-set frequency range (20Hz～15MHz for the LS90-15M model) to generate a frequency-adjustable signal. The VCO further modulates the signal to generate an AC excitation signal with a stable amplitude (up to 1.000V) and frequency.
• Signal Excitation Stage: The excitation signal generated in the previous stage is amplified by the power amplifier in the signal excitation module to ensure that the test current can meet the requirements of different DUTs (minimum 0.01μA). The matching network adjusts the impedance of the excitation circuit to match the impedance of the DUT, reducing signal reflection and improving the efficiency of energy transmission. Finally, the excitation signal is applied to the DUT through the four-terminal pair Kelvin test terminals. The four-terminal pair design separates the current path and the voltage measurement path, eliminating the influence of lead resistance and contact resistance on the voltage measurement, thereby improving the accuracy of impedance measurement.
• Signal Acquisition Stage: The current/voltage sensor in the signal acquisition module collects the current signal flowing through the DUT and the voltage signal across the DUT respectively. The collected analog signals are sent to the high-precision ADC for analog-to-digital conversion. The ADC has high resolution and low noise, which can accurately convert the analog signals into digital signals for subsequent processing.
• Signal Processing Stage: The digital filter in the signal processing module filters the digital signals to remove noise interference caused by the external environment and the instrument itself. The PLL locks the frequency of the collected signal with the excitation signal, ensuring that the phase difference between the voltage and current signals is measured accurately. The signal conditioning circuit adjusts the amplitude and frequency of the processed signals to make them meet the input requirements of the data calculation module.
• Data Calculation and Display Stage: The DSP in the data calculation module uses the vector testing principle to calculate the impedance parameters of the DUT. Taking the calculation of impedance Z and phase angle θ as an example, the DSP first calculates the amplitude ratio of the voltage signal to the current signal (Z = U/I) and the phase difference between the voltage signal and the current signal (θ = φ_U – φ_I), and then converts them into other impedance parameters (such as R = Zcosθ, X = Zsinθ) according to the user’s needs. The calculated impedance parameters and the impedance-frequency scanning curve are displayed on the 7.0′ TFT-LCD display in real time. At the same time, the instrument can transmit the test data to the computer through the RS232C or USB DEVICE interface for data storage and post-processing.
LS90_AL
3. Application of LISUN LS90 Impedance Analyzer in Impedance Testing of Related Devices
The LISUN LS90 series impedance analyzer, relying on its high-performance impedance analyzer circuit, is widely used in the impedance analysis and testing of ferroelectric crystals, piezoelectric ceramics, piezoelectric crystals, and ultrasonic transducers. This section introduces the test methods, steps, and results of the instrument for these four types of devices respectively.
3.1 Impedance Testing of Ferroelectric Crystals
Ferroelectric crystals have a spontaneous polarization phenomenon that can be reversed by an external electric field, and their impedance characteristics are closely related to the polarization state and temperature. The LISUN LS90 impedance analyzer can test the impedance parameters of ferroelectric crystals under different frequencies and temperatures, providing a basis for studying the electrical properties of ferroelectric crystals.
3.1.1 Test Preparation
• Instrument: LISUN LS90-10M impedance analyzer (frequency range: 20Hz～10MHz, basic accuracy: 0.05%).
• DUT: Lead zirconate titanate (PZT) ferroelectric crystal (size: 5mm×5mm×1mm).
• Auxiliary Equipment: Temperature-controlled chamber (temperature range: 0℃～40℃), four-terminal pair Kelvin test probes.
3.1.2 Test Steps
• Place the PZT ferroelectric crystal in the temperature-controlled chamber, and set the temperature of the chamber to 25℃ (room temperature).
• Connect the four-terminal pair Kelvin test probes to the test terminals of the LISUN LS90-10M impedance analyzer, and contact the two ends of the PZT ferroelectric crystal with the probes.
• Turn on the impedance analyzer, enter the test parameter setting interface, and set the following parameters:
– Frequency range: 1kHz～10MHz.
– Scan mode: Linear scan (number of scan points: 100).
– Signal amplitude: 0.5V.
– Test parameters: Z-θ (impedance and phase angle).
• Start the test, and the instrument automatically scans the frequency in the set range and collects the impedance and phase angle data of the PZT ferroelectric crystal.
• Adjust the temperature of the temperature-controlled chamber to 30℃, 35℃, and 40℃ respectively, and repeat steps 3-4 to obtain the impedance-frequency characteristics of the PZT ferroelectric crystal at different temperatures.
3.1.3 Test Results
The impedance-frequency characteristics of the PZT ferroelectric crystal at different temperatures are shown in Table 2. It can be seen from the table that as the temperature increases, the resonance frequency of the PZT ferroelectric crystal decreases slightly, and the impedance at the resonance frequency increases. This is because the increase in temperature leads to an increase in the dielectric loss of the ferroelectric crystal, resulting in a decrease in the resonance frequency and an increase in the impedance. The LISUN LS90-10M impedance analyzer can accurately measure these changes, which is of great significance for studying the temperature stability of ferroelectric crystals.
Temperature (℃)
Resonance Frequency (MHz)
Impedance at Resonance Frequency (kΩ)
Phase Angle at Resonance Frequency (°)
25
5.23
1.25
-1.2
30
5.21
1.32
-1.5
35
5.19
1.40
-1.8
40
5.17
1.48
-2.1
3.2 Impedance Testing of Piezoelectric Ceramics
Piezoelectric ceramics are a type of functional ceramic material that can convert electrical energy into mechanical energy and vice versa. Their impedance parameters, especially the resonance and anti-resonance frequencies, are important indicators for evaluating their performance. The LISUN LS90 impedance analyzer can quickly and accurately test the resonance and anti-resonance frequencies of piezoelectric ceramics, providing a basis for the production and quality control of piezoelectric ceramic components.
3.2.1 Test Preparation
• Instrument: LISUN LS90-15M impedance analyzer (frequency range: 20Hz～15MHz, basic accuracy: 0.05%).
• DUT: Barium titanate (BaTiO₃) piezoelectric ceramic sheet (size: 10mm×10mm×0.5mm).
• Auxiliary Equipment: Four-terminal pair Kelvin test fixture.
3.2.2 Test Steps
• Fix the BaTiO₃ piezoelectric ceramic sheet in the four-terminal pair Kelvin test fixture, and connect the fixture to the test terminals of the LISUN LS90-15M impedance analyzer.
• Turn on the impedance analyzer, enter the test parameter setting interface, and set the following parameters:
– Frequency range: 100kHz～15MHz.
– Scan mode: Logarithmic scan (number of scan points: 200).
– Signal amplitude: 1.0V.
– Test parameters: R-X (resistance and reactance).
• Start the test, and the instrument automatically scans the frequency in the set range and collects the resistance and reactance data of the BaTiO₃ piezoelectric ceramic sheet.
• After the test is completed, the instrument automatically identifies the resonance frequency (f_r) and anti-resonance frequency (f_a) of the piezoelectric ceramic sheet according to the change of reactance (X) with frequency (when X=0, the corresponding frequency is f_r and f_a).
• Repeat the test 5 times to calculate the average value of f_r and f_a, and evaluate the repeatability of the test results.
3.2.3 Test Results
The test results of the resonance and anti-resonance frequencies of the BaTiO₃ piezoelectric ceramic sheet are shown in Table 3. It can be seen from the table that the repeatability of the test results of the LISUN LS90-15M impedance analyzer is good, and the maximum deviation of the resonance frequency and anti-resonance frequency is less than 0.02MHz. This indicates that the impedance analyzer circuit of the LISUN LS90 series has high stability and can meet the repeatability requirements of piezoelectric ceramic testing in the production line.
Test Times
Resonance Frequency (f_r, MHz)
Anti-Resonance Frequency (f_a, MHz)
Deviation of f_r (MHz)
Deviation of f_a (MHz)
1
8.56
10.23
0
0
2
8.57
10.24
+0.01
+0.01
3
8.55
10.22
-0.01
-0.01
4
8.56
10.23
0
0
5
8.57
10.24
+0.01
+0.01
Average
8.56
10.23
–
–
Maximum Deviation
–
–
±0.01
±0.01
3.3 Impedance Testing of Piezoelectric Crystals
Piezoelectric crystals have high frequency stability and are widely used in oscillators and filters. The impedance characteristics of piezoelectric crystals, especially the equivalent series resistance (ESR) and quality factor (Q), directly affect the performance of oscillators and filters. The LISUN LS90 impedance analyzer can accurately test the ESR and Q value of piezoelectric crystals, providing a basis for the selection and application of piezoelectric crystals.
3.3.1 Test Preparation
• Instrument: LISUN LS90-10M impedance analyzer (frequency range: 20Hz～10MHz, basic accuracy: 0.05%).
• DUT: Quartz piezoelectric crystal (frequency: 1MHz, package: HC-49U).
• Auxiliary Equipment: Piezoelectric crystal test socket, four-terminal pair Kelvin test wires.
3.3.2 Test Steps
• Insert the quartz piezoelectric crystal into the piezoelectric crystal test socket, and connect the test socket to the test terminals of the LISUN LS90-10M impedance analyzer using four-terminal pair Kelvin test wires.
• Turn on the impedance analyzer, enter the test parameter setting interface, and set the following parameters:
– Frequency: 1MHz (the nominal frequency of the piezoelectric crystal).
– Signal amplitude: 0.1V (to avoid overexcitation of the piezoelectric crystal).
– Test parameters: R-X (resistance and reactance), Q value.
• Start the test, and the instrument measures the equivalent series resistance (R) and reactance (X) of the piezoelectric crystal at 1MHz. According to the formula Q = |X|/R, the Q value of the piezoelectric crystal is calculated automatically.
• Adjust the frequency of the instrument to 0.9MHz, 0.95MHz, 1.05MHz, and 1.1MHz respectively, and repeat step 3 to obtain the ESR and Q value of the piezoelectric crystal at different frequencies.
3.3.3 Test Results
The ESR and Q value of the quartz piezoelectric crystal at different frequencies are shown in Table 4. It can be seen from the table that the ESR of the piezoelectric crystal is the smallest at the nominal frequency (1MHz), and the Q value is the largest. As the frequency deviates from the nominal frequency, the ESR increases and the Q value decreases. This is because the piezoelectric crystal has the best resonance performance at the nominal frequency, and the energy loss is the smallest. The LISUN LS90-10M impedance analyzer can accurately measure these changes, which is of great significance for the selection and application of piezoelectric crystals in oscillators and filters.
Frequency (MHz)
Equivalent Series Resistance (ESR, Ω)
Reactance (X, kΩ)
Q Value
0.9
50.2
-1.25
24.9
0.95
25.1
-0.52
20.7
1.0
10.3
0.01
97.1
1.05
24.8
+0.51
20.5
1.1
49.5
+1.23
24.9
3.4 Impedance Testing of Ultrasonic Transducers
Ultrasonic transducers are devices that convert electrical energy into ultrasonic energy and vice versa. Their impedance characteristics are closely related to the ultrasonic emission and reception efficiency. The LISUN LS90 impedance analyzer can test the impedance parameters of ultrasonic transducers under different frequencies, providing a basis for the design and optimization of ultrasonic transducer systems.
3.4.1 Test Preparation
• Instrument: LISUN LS90-5M impedance analyzer (frequency range: 20Hz～5MHz, basic accuracy: 0.05%).
• DUT: Ultrasonic cleaning transducer (frequency: 40kHz, power: 50W).
• Auxiliary Equipment: Ultrasonic transducer test bracket, four-terminal pair Kelvin test cables.
3.4.2 Test Steps
• Fix the ultrasonic cleaning transducer in the test bracket, and connect the two electrodes of the transducer to the test terminals of the LISUN LS90-5M impedance analyzer using four-terminal pair Kelvin test cables.
• Turn on the impedance analyzer, enter the test parameter setting interface, and set the following parameters:
– Frequency range: 30kHz～50kHz.
– Scan mode: Linear scan (number of scan points: 50).
– Signal amplitude: 0.5V.
– Test parameters: Z-θ (impedance and phase angle), admittance (Y). https://www.lisungroup.com/news/technology-news/application-of-impedance-analyzer-circuit-in-impedance-analysis-and-testing-of-ferroelectric-crystals-piezoelectric-ceramics-and-related-devices-a-case-study-of-lisun-ls90-impedance.html
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