I'm trying to check the differential and common-mode impedance modelled on the spice model of AD620.I'm using Pspice.
By using a DC sweep, looking at the input current and take the slope, I found about 5 MOhms which is very smaller than the datasheet (10 GOhms).
Could somebody help me to find if the model is wrong or if it's my method of measuring input impedance.
Below the circuit for differential impedance measurement
I will look into the spice model.
Ok, please let me know when you have an answer.
I checked the spice model of AD620 and input impedance was not modeled.
I used ac source and ac analysis instead to measure input impedance.
I used LTspice and I think it will be the same in Pspice.
At DC or very low frequencies, resistance dominates the impedance but as frequency increases, capacitive reactance starts to kick in to dominate impedance. The phase approaches -90deg as input impedance becomes capacitive.