AD2 + Impedance Analyzer Adapter + Reference Resistor

[Lars Lindner]

Hello everybody,

first of all thank you for your valuable time and effort. I have a simple question and I hope, this is the right place to ask.

How do I choose the correct reference resistor value in WaveForms, when performing an Impedance measurement, using the AD2 and the Impedance Analyzer Adapter for a mixed load characteristics circuit (when I don't have a single capacitance or inductance) ?

 

Thanks again Digilent team for your help,

Lars

 

 

[attila]

Hi @Lars Lindner

The resistor value should be a comparable value to the DUT impedance. Ideally equal but in range of 0.01 to 100. This to have measurable voltage on DUT/R divider.

Like here with 100k it goes from 16 (1.6M) to 0.01 (1k)

 

With the IA Adept module, for wide impedance variation you can also use the Constant Voltage/Current which adjusts the stimulus signal amplitude and selects the suitable resistor on the fly.

[Lars Lindner]

Hi @attila,

thank you very much for your fast answer. I looked into that and did a test, using a 4MHz oscillator and measuring the Impedance and Phase response using the Amplitude and Constant Voltage Mode. All of the other parameters are identical. However, the results of both measurements are slightly different. Please see the following pictures:

Amplitude Mode:

 

Constant Voltage Mode:

 

Why they are different? What is causing the difference? How can I prevent these differences? 

 

Thanks again for your help attila and with best wishes

Lars

 

 

 

 

[attila]

Hi @Lars Lindner

With Constant Voltage option it tries to maintain 1Vrms on the DUT event before the 4MHz threshold. Increases the output amplitude and accordingly sets the input range to high, but the DUT voltage is low so it has low resolution on the input.
Use constant Amplitude or set lower RMS value for CV.