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how to calculate gain and bandwitdth of switch capacitor common mode feedback.....?

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ASHUTOSH RANE

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hello friends
I have designed the folded cascode opamp...(fully-differential)....i have added SC-CMFB circuit to Amplifier ....but i am getting problem in simulating with PSS and PAC analysis..
my detailed steps for the analysis are as follows...
set pss simulation for
clock of 2.56MHz and
input signal of 256K
beat freq=256k
no of harmonics=1 (don't know how to set this Can Anybody tell me??)
tstab=1m


now how to calculate the gain and bandwidth of common mode feedback loop.....?????
 

now how to calculate the gain and bandwidth of common mode feedback loop.....?????
Click to expand...

Break the loop at some point with an iprobe component from analogLib and run stb analysis.That's all!

no of harmonics=1 (don't know how to set this Can Anybody tell me??)
Click to expand...

Dig into SpectreRF manual (it is located in your cadence installation folder),they explain well the meaning of this option.In brief,it is the number of harmonics of the clock signal that pss will take into account during simulation,given that
the clock is a pulse (not a pure sine signal).

Some remarks :

1.)In pss analysis you should insert only the clock signal.At the small-signal pac analysis you will pass the other one with freq. 256KHz.As far as i know,you can't simulate two tones with pss...for this case you need qpss analysis.
2.)tstab=1m is huge!!Use a smaller value of some nsec or μsec.
 
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