What Is an Impedance Analyzer?
An impedance analyzer is an analyzer of impedance (resistance).
Impedance is the ratio of voltage to current in an AC circuit and is an indicator of the resistance to current flow. Impedance is expressed as a vector quantity in the complex plane, with reactance on the imaginary axis and resistance on the real axis.
When the current is direct current, there is only a resistance component, expressed as V=IR, which is represented by Ohm’s law. There are two main types of resistance in reactance, inductive reactance for the L (inductor) component representing a coil or other winding, and capacitive reactance for the C (capacitor) component representing a capacitor. The impedance analyzer is a machine that analyzes the impedance, which is the electrical resistance including the AC component.
Uses of Impedance Analyzers
Impedance analyzers are used to analyze the details of impedance, which is electrical resistance that includes an AC component.
For example, most impedance analyzers display a graph of the analysis results on the screen of the impedance analyzer, with the horizontal axis representing frequency and the vertical axis representing the parameters (variables) that the user wants, such as voltage and current. A similar device called an LCR meter is also available.
However, an LCR meter only displays pinpoint results numerically, while an impedance analyzer can display graphs showing various parameters over a wide range of frequency bands.
Principle of Impedance Analyzers
Impedance analyzers can measure the resistance and reactance components of impedance by applying AC signals of various frequencies and measuring current, voltage, and phase differences. There are various measurement methods such as the resonance method, I-V method, and automatic balanced bridge method.
The measurement method using the automatic balanced bridge circuit is described here as a typical example. The automatic balanced bridge circuit uses a signal source, two voltmeters, and a current-to-voltage converter. The impedance of the sample can be measured by calculating the ratio of the voltage flowing through the sample to the voltage flowing through the reference resistance.
The automatic balanced bridge method can measure a wide range of frequencies below 110 MHz. The RF I-V method is used to measure impedance at higher frequencies.
The obtained data is analyzed by plotting it graphically as a Bode diagram with frequency plotted on the horizontal axis and impedance plotted on the vertical axis, or as a Cole-Cole plot with resistance plotted on the horizontal axis and reactance plotted on the vertical axis. By analyzing these equivalent circuits, it is possible to design circuits and isolate resistance components such as electrodes.
Other Information on Impedance Analyzers
1. Difference between an Impedance Analyzer and a Network Analyzer
Impedance analyzers and network analyzers are both devices that measure the impedance components of a DUT (DUT under test) by inputting signals to the DUT and comparing the signal strength and phase that appear on the output side with the input.
Impedance analyzers are used to accurately measure high impedances of 10 kΩ or higher. However, the frequency range that can be measured is limited to about 100 MHz.
Network analyzers can measure up to about 10 GHz and are suitable for measuring impedances of 10 kΩ or lower. Devices for communication equipment require measurement of characteristics up to the high-frequency range, so network analyzers are used.
2. How to Use an Impedance Analyzer
These four terminals are used for impedance measurement:
- Terminal for applying input current
- Terminal for measuring input side voltage
- Terminal for measuring output side current
- Terminal for measuring output side voltage
The object to be measured (DUT) is placed between the input and output sides, but for more accurate measurement, a measurement jig called a fixture is used. The fixture is an important measurement jig used to hold the DUT stable, reduce extraneous noise, and prevent attenuation of signal propagation.