How to calculate the circuit's output resistance in SPICE?

[jluhzw]

spice resistance

hello ,everybody

Now I am learning the analog design.During studying, I encounter a question so I

need your help.

When I am caculate a circuit's output resistance,how do I check the result

in SPICE.

In my opinion,the output resistor is the parameter in the small-signal,so I should

use the AC analysis.Is it right?Second,how to set the input signal,if should set it to

zero?.Third,how to display the result in the SPICE?

If you know,would tell me how can I do?

Thank you!

 

[ambreesh]

how to calculate input resistance pspice

You are right.
Use a ac source of unit magnitude as input at the node u want to see the output resistance.
Connect Input to AC ground
Do an ac analysis.
Plot the inverse of current from the ac source. that would be your output resistance plot

 

[flamingo]

calculate output resistance in spice

three methods:
1. USE definition of output impedence: input source ZERO(DC on, AC off), plus a test current(AC on 1A, DC off, in order not to disturb DC operating point) to output, then AC analysis, plot vout(m), and it is output impedence
2.USE .tf analysis, you will get ROUT based on DC analysis
3.USE .AC anylysis plus a .NET command, plot ZOUT(m) ZOUT(i) ZOUT(r), you will magnitud. imaginary, and real part of ZOUT.

U can comparate the above three mothods, judge by yourself.
Best Regards