gm simulation in a rail to rail opamp

[rosaeidi]

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?

 

[meitolake]

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

 

[jecyhale]

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

I agree. So it should be an OTA.

 

[rosaeidi]

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

 

[meitolake]

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

 

[rosaeidi]

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

 

[gte582w]

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.