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how to simulate the GM of a rail2rail OPA?

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wjxcom

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Hi all: I am a fresh man to design analog circuit and design a rail2rail OPA. Now I have already finished this OPA, but now I have a question i.e. I do not know how to simulate the GM of rail2rail OPA.

In order to simulate the GM of a rail2rail OPA, I did .AC analysis, i.e. I add a voltage source VIP to the positive port, and the AC voltage of voltage source is 1V, the common voltage of the voltage source is from 0V to 5V.

I simulate the VOUT/VIP, and take the VIP as the abscissa, but the result is not I wanted.

Help me please, how to simulate the GM of a rail2rail OPA?
 

wjxcom said:
Hi all: I am a fresh man to design analog circuit and design a rail2rail OPA. Now I have already finished this OPA, but now I have a question i.e. I do not know how to simulate the GM of rail2rail OPA.

In order to simulate the GM of a rail2rail OPA, I did .AC analysis, i.e. I add a voltage source VIP to the positive port, and the AC voltage of voltage source is 1V, the common voltage of the voltage source is from 0V to 5V.

I simulate the VOUT/VIP, and take the VIP as the abscissa, but the result is not I wanted.

Help me please, how to simulate the GM of a rail2rail OPA?

I think you want to design constant-gm opamp. choose current or other parameter to indirectly measure gm.
 

Hi, renwl: can you explain detailed??
 

Hey you can measure Gm as Iout/Vin, with Vout at an ac zero for the Gm stage.
 

Hi Vamsi Mocherla: can you explain detailed? How can I get an ac zero ?
 

Hi Vamsi Mocherla: you said that I can measure Gm as Iout/Vin, with Vout at an ac zero for the Gm stage. So I use this circuit to simulate the GM. At this circuit, resistance R0 connect to the OUT and GND, voltage source V15 connects to the positive port VIP of the OPA, and the VCM of V15 varies from 0 to 1.5V.

After doing .ac analysis, I get the Iout and I plot Iout/VIP, I think Iout/VIP is GM, but I am wrong, I do not get the wave of GM.

I need help, please!!!
 

wjxcom,

You can remove the resistor and put a DC voltage source of your common mode level and measure the current through the voltage source at the output. The ratio of the output current and the input differntial voltage will give you your Gm.
 

Hi Vamsi Mocherla: I modify my circuit to simulate GM, please look at the circuit in the attachment, but I think the result is not correct.

Hi Vamsi Mocherla, can you help again?
 

to wjxcom: Hello, i also do the rail-to-rail op and have this problem, could we keep contact, my E-mail:yulei_002@163.com
 

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