fully differential op amp simulation

[henrywent]

op amp simulator

when we perform simulation on fully differential op amps in close loop configuration,do we need to add cmfb circuit? or how to simulate fully differential op amps in close loop configuration? please help me out, many thanks!

 

[yschuang]

differential op amp

I think CMFB is definitely needed for simulation like differential or common mode.
One way to split differential and common mode is to use balun. For simplicity, you can implement an ideal CMFB like VCVS to simulatate differential behaviors. Please refer the following link for VCVS.
Happy 2009
**broken link removed**

 

[henrywent]

fully differential opamp

thanks for your information, it hleped me a lot. but could anyone give me some popular cmfb configurations. do the cmfb circuitry in gray's book work good enough?

Added after 1 hours 18 minutes:

please tell me what's the function of the 0.3pf capacitor in the cmfb circuitry you posted. thanks

 

[LvW]

opamp simulation

when we perform simulation on fully differential op amps in close loop configuration,do we need to add cmfb circuit? or how to simulate fully differential op amps in close loop configuration? please help me out, many thanks!

It depends on your requirements resp the aims of your simulation.
If you only want to see the properties of an ideal (symmetrical) FD amplifier, CMFB is not necessary. However, if you are going to simulate the real behaviour including asymmetric effects, it is necessary, of course.

 

[alicia8283]

op amp simulation

Then how should we actually simulate for whole system ( fully diff amp togather with the CMFB) if the CMFB is switch cap type? i read from this forum that we have to use spectreRF to simulate it, but how if the cadence tools i used do not have spectreRF license? Do we have another way to simulate it?
thanks a lot

 

[erikl]

differential op amps

Then how should we actually simulate for whole system ( fully diff amp togather with the CMFB) if the CMFB is switch cap type? i read from this forum that we have to use spectreRF to simulate it, but how if the cadence tools i used do not have spectreRF license? Do we have another way to simulate it?
thanks a lot

Sure; you don't need spectreRF. You may simulate your circuit with spectre e.g. within ADE .

 

[leehying]

fully differential op amp

Return ratio may help.

 

[alicia8283]

differential op amp

Return ratio may help.

Thanks a lot. Do you have any reference on the test bench?