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betty1007 said:hi friends,
when i design a full differential amp, how to determine the bandwidth of cmfb?
thanks in advance.
betty1007 said:to surianova
what i want to know is how large the bandwidth of the cmfb is needed,when i design a full differential amp with cmfb.
I think in differential amp , common mode noise introduced by output of cmfb opamp will be concel by itself. Is there any other considerations in cmfb bandwidth.surianova said:betty1007 said:to surianova
what i want to know is how large the bandwidth of the cmfb is needed,when i design a full differential amp with cmfb.
the bandwidth of your opamp should less much than the bandwidth of your differential amp. (maybe less than 1 Mhz, i am not sure). bcoz we want the ouput of cmfb opamp to be almost DC, this only can acheive with low bandwidth of cmfb opamp. If the output of the cmfb opamp nosiy, it will cause the output of the diff amp noisy as well bcoz the output of cmfb opamp is connected to the tail of diff amp. If the bandwidth of opamp is low, definitely the slew rate is low as well, so it will longer time for the system to stable when your power supply is ramping up. So, everything is very much depend on the system.
castrader said:In P.R.Gray's book:
make the unity-gain frequency of the DM and CMFB loops about equal.
in pp 857