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offset of fully differential amplifier

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manissri

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how to measure the offset of fully differential amplifier.
any test bench doc or pdf available would be appreciable.
regards
 

hi
see the following connection, and the out will be the offset

hope it helped to you.
 

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HI Spring thanz for reply.
can u tell me what wud be the value of resistance which has connected into the feedfback and how it will measure the offset of the amp.
regards
 

Connect the OPAMP with buffer structure, can simulate the offset volt. Use montecalo analysis can track the change of offset volt.
 

manissri said:
HI Spring thanz for reply.
can u tell me what wud be the value of resistance which has connected into the feedfback and how it will measure the offset of the amp.
regards
Click to expand...

hi
r1=r3,r2=r4. RL and CL is the load of your circuit. CMFB must work.
do OP analysis and the difference between VON and VOP ( VON - VOP)is the offset of total ckt. then , r1/(r1+r2)*(VON-VOP) will be the offset of the amp.
B.R.
 

To measure the differential amplifier's offset. You can use R2=R4=0 and remove the R1 & R4. Then measure the voltage different between Von & Vop
 

What is Vcom (the 3rd input of amp)? If my Vdd=2.5, so my Vcom = 1.25V?
 

udintbr said:
What is Vcom (the 3rd input of amp)? If my Vdd=2.5, so my Vcom = 1.25V?
Click to expand...
Sometimes it is! In fact, Vcom is the voltage that the op can work well base on it. And the value of Vcom is in a certain range. Vdd/2 is usually a suitable value, but isn't the only choice.
 

i fully agree with the above discussion that we if put the diff amp into the buffer configuration and put the vcm (common mode voltage) at the both input of amp the diff bet the both output is the offset of diff amp
but the issue arises :
if we put the diff amp into the buffer mode the gain error will also come at the output ---> is it?
coz the gain error wud be 1-(1/A) where A is the open loop gain of diffamp
so the offset we are measuring is the correct offset.
please clarify this
regards
 

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