how to simulate "gm" of an OTA?

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how to simulate gm

Hi,

As "gm=Io/Vin", AC simulation could get Vout/Vin, but how to get the small signal Io?

I searched here, some thread said to build a RC(1Gohm and 1F) negative feedback to cancel offset, I don't understand that purpose.
 

hspice gm ota

OTA is used in open loop. According to definition of gm, you should add a large capacitor at the output to make it ac ground. Then do ac simulation, you will get small signal Io
 
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    shreza

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ota gm spice

Thanks!

How to print out the Io with hspice? what command I should use?
 

how to simulate ota

Check .print .plot .probe commands in Hspice manual, ex. .probe i(CL), CL is the element name of the large load capacitor.
 

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