Using HF2IS Impedance Spectroscope for FRA, 2-Terminal and 4-Terminal Measurements

Often there are questions from our HF2IS Impedance Spectroscope users on how to configure the HF2IS for frequency response analysis (FRA), 2-Terminal impedance measurement, or 4-Terminal impedance measurement. This short blog will clarify the proper physical connections as well as the setup of the ziControl graphical user interface.

Case I: Frequency Response Analyzer

The physical connection of HF2IS Impedance Spectroscope as a frequency response analyzer is shown below. This is the default setting in the Spectroscope tab. FRA can be used when one simply needs a frequency response of a device-under-test in gain and phase (i.e. a Bode plot). One can also introduce a DC offset to the sweep source by using the auxiliary output to generate an offset and connect it to the Add connector beside the connector Signal Output. The FRA and Add settings are highlighted in the screenshot below.

FRA_ziControl

 

Note: click to enlarge

Case II: 2-Terminal Impedance Measurement

The 2-Terminal configuration is used when the quantity being measured is a current signal. In this case, a transimpedance amplifier like the HF2TA Current Amplifier should be used to convert current into voltage (please click on this link to see how to optimize the HF2TA gain settings). The gain of the HF2TA will be correctly taken into consideration in the measurement when ‘HF2TA 1‘ is selected under the Signal Inputs section of the ziControl.

2T_ziControl

Note: click to enlarge

By default, the impedance sweep display mode is selected in the Sweeper tab when the ‘2-Term-Z‘ mode is chosen in the Spectroscope tab. One is free to select other equivalent display models in the Sweeper. In this example, the sweep result is displayed in impedance magnitude |Z| and phase Phi response. As part of the new ziControl 12.08 release features, the users can now add Sinc filtering during the sweep to eliminate the omega and the 2-omega components. The Sinc filter will automatically turn on when the sweep frequencies are below 10 kHz. All the pertinent settings and features mentioned here are highlighted in the screenshot above.

If you have a very small impedance, then it may not be necessary to use the HF2TA transimpedance amplifier. In this case, you can simply connect the device-under-test directly to the HF2IS Impedance Spectroscope input and turn on the 50 Ω input termination resistor. To calculate the actual current measured, one needs to only scale the measured result by 1/50=0.02 A/V in the Scaling + Units field.

Note: the measured impedance with HF2TA Current Amplifier will be about 100 Ω higher with 2-Terminal measurement. This is due to the fact that there is an internal 50 Ω resistor in series at both the signal output of the HF2IS Impedance Spectroscope and the input of the HF2TA Current Amplifier. These two internal resistor are not subtracted in the 2-Terminal configuration.

Case III: 4-Terminal Impedance Measurement

The 4-Terminal configuration makes use of the second signal input channel of the HF2IS Impedance Spectroscope. Furthermore, the differential voltage across the device-under-test is measured such that it will be much less sensitive to any residual serial resistance outside the device-under-test as in the 2-Terminal configuration. We can see in the 4-Terminal sweep result that the impedance is about 100 Ω less than the 2-Terminal sweep result (the 100 Ω resistance is due to the instrument output and the amplifier input resistors as mentioned above). However, the 4-Terminal configuration is not immune to any parasitic shunt capacitance which have to be taken into account at higher frequencies.

4T_ziControl

Note: click to enlarge

After the connection is set up, one will need to select the  ‘4-Term-Z‘ mode in the Spectroscope tab. In addition, the Diff button should be turned on in order to measure the differential voltage on the second input channel. Note that by default, the channel 1 is configured to receive the HF2TA Current Amplifier input and the channel 2 the different voltage.

Note: It is possible to swap the two inputs but ziControl Filters Input section must be modified accordingly.

Summary

This blog gave an overview on three possible characterization setups that one can be perform with HF2IS Impedance Spectroscope. For more detailed explanations on the Sweeper use, please also see this blog and refer to section 12.4.3 of the HF2 User Manual.