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gm simulation in a rail to rail opamp

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rosaeidi

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opamp gm simulation

Hi
How can I measure the total gm of a rail to rail opamp? My friend said me to ground the output and measure the output currents, then gm=d(Io)/v(vin). Is it true?
 

If the output of an operational amplifier is current mode, you can use this method to measure the transconductance.
 

meitolake said:
If the output of an operational amplifier is current mode, you can use this method to measure the transconductance.
Click to expand...

I agree. So it should be an OTA.
 

Hi
Thanks.
I use the folowing gm. What should I do in output to measure the total gm?
 

You can ground the output, but need to handle the DC operation carefully.
Why do you want to measure the transconductance?
 

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    rosaeidi

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Hi again,

I wanted to measure the gm variation of opamp against the input common mode voltage. I grounded ac voltage of outputs and measured the gms. Finally I could find the desired results.

TX
 

since the total gm is the sum of the gm of upper and lower input stages, you can simply add their
gm up while sweeping the input common-mode.
 

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