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How to determine amplifier's output impedance with Spectre?

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fxxjssc

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determining output impedance

Thanks
 

rout spectre

Put a AC current source with AC magnitude = 1, do AC simulation, then plot the voltage on that node, this is the impedance you want
 
spectre impedance profile

One trick.
Place voltage source with AC magnitude = 1V in series with output between output and load. Do AC analysys and measure current flowing though output terminal - Iout.
The output impedance Zout=1V/Iout.
 
amplifier output impedance

fxxjssc said:
Thanks
Click to expand...

supposing your amplifier has a one dominant pole, you can plot the Bode's diagram of the opamp gain and then calculate:

Rout=Aol/Gm

where Aol is the DC gain you can read from the Bode's plot
and Gm is the global transconductance of the opamp (which value also depends on with how many stages the opamp is built-up).

CBs.
 
You can also do Rout = Rup || Rdown. Find Rup and Rdown .
In the operating point results of MOS ro = 1/gds
 

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