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Measure Transconductance Gm of a circuit in Hspice or ADS

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gm transconductance

I am designing an input stage of an Op Amp. I need to measure the Transconductance Gm of the whole input stage. Can somebody give me a suggestion how to get Gm in Hspice or ADS? Thank you very much in advance.
 

hspice transconductance

I think since you are simulaing the Gm of whole state, I think you should performed a DC sweep of output current as input voltage, then take derivatives using your simulator.
 

how to measure gm

try this in Hspice
.meas dc GM1 DERIV i(xop.vp) when v(op)=1

to measure the GM at V(op)=1
 

transconductance gm

terryssw said:
I think since you are simulaing the Gm of whole state, I think you should performed a DC sweep of output current as input voltage, then take derivatives using your simulator.
Click to expand...

Thank you for you replay.

When measure Gm, we should short the output. If we short the output, the biasing will change.
 

how to measure transconductance

These measurements are done with AC. You can use capacitors to short the output without affecting the bias.
 

measure gm

may I use awaves "express" for gm measure in .tran simulation?

gm = Ids / Vgs

we can measure Ids & Vgs ..
then use awaves express function
 

short circuit transconductance

In ADS, after you define Idif=Ip-In and Vdif=Vip-Vin
Then sweep Idif versus Vdif . Then with another plot add a diff() , eg
diff(Idif), then you'll get the differential Gm.
 

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