Measuring impedance with ltspice

Telstar · 27th January 2011, 01:24 PM

I've searched a bit and came out with this method.
I'd like to know if it is correct.

This is for the input impedance:
1. Do an AC analysis with 1V,decade
2. Plot the current in the AC source
3. Reverse it (1/I(V1) for example)
4. Change the Y axis to linear

I read amperes, but it should be ohms.
Likewise for the output resistance.

Correct or not?

sawreyrw · 27th January 2011, 02:50 PM

A better way to do this is to inject a 1 unit AC current into the node of interest. This won't upset the bias point and the node voltage is equal to the impedance of that node. No need to plot 1/I as in your method.

27th January 2011, 01:24 PM	#1
Telstar diyAudio Member Join Date: Dec 2007	Measuring impedance with ltspice I've searched a bit and came out with this method. I'd like to know if it is correct. This is for the input impedance: 1. Do an AC analysis with 1V,decade 2. Plot the current in the AC source 3. Reverse it (1/I(V1) for example) 4. Change the Y axis to linear I read amperes, but it should be ohms. Likewise for the output resistance. Correct or not? __________________ The response of the inner ear extends to at least 200khz - Dr W. Tempest

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27th January 2011, 02:50 PM	#2
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	A better way to do this is to inject a 1 unit AC current into the node of interest. This won't upset the bias point and the node voltage is equal to the impedance of that node. No need to plot 1/I as in your method.

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