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Design >> Analog Design >> SC CMFB Design
https://designers-guide.org/forum/YaBB.pl?num=1072971210

Message started by The_One on Jan 1^st, 2004, 7:33am

Title: SC CMFB Design
Post by The_One on Jan 1^st, 2004, 7:33am

<quote>
Hi,

You must define the minimum equivalent resistance your amplifier can drive, this gives the upper limit to the capacitance value - clock frequency product. The lower limit of this product is given by loss of accuracy due to leakage currents and other practical issues.

Paul <quote>

Hi, I create a new thread to accomodate any questions regarding the SC CMFB design.

Title: Re: SC CMFB Design
Post by The_One on Jan 1^st, 2004, 7:38am

Well Paul,

What I mean is as following.

when i only simulate the SC CMFB, the voltage produced is as expected. however, when i combined the full diff opamp and the cmfb, the cmfb cannot work properly. in the end, the opamp cannot work.

i use spectre RF (the pss and pac analysis).

when i use trans analysis from Mentor graphic, the correct dc point of the opamp can be obtained.

is there something wrong with the Spectre RF? or any design rule for SC CMFB?
thx.

Title: Re: SC CMFB Design
Post by Ken Kundert on Jan 1^st, 2004, 10:34am

Rather than speculate, perhaps you can send me both netlists. Be sure to include the full executable netlists (models, analyses, etc.)

-Ken

Title: Re: SC CMFB Design
Post by Ken Kundert on Jan 4^th, 2004, 12:10am

I was able to run a simulation with Spectre from the netlist you sent and did not find anything that would suggest a problem. However, as you did not send a simulatable netlist (there were no analyses, options, etc.), I cannot really know what simulations you ran, or which outputs you observed. Nor have you really described what problems occur (you only say that the simulations cannot work).

If you would like more help, I recommend that you construct a netlist that demonstrates the problem (be sure to test it to assure it both runs and exhibits the problem) and send that to me. Be sure to include a description of the circuit (inputs and outputs, function, etc) and the problem.

-Ken

Title: Re: SC CMFB Design
Post by Paul on Jan 5^th, 2004, 12:03am

Hi The_one,

There's no reason for Eldo and Spectre to give different simulation results. I'm sure the problem is not in the Spectre simulator, but in different simulation conditions between both simulators. As Ken mentions, you should provide more information on the kind of problems you see.

Paul