I'm studying on my own for an exam. I bumped into this problem that really got me. My answer just doesn't match.
Find the CMRR of the operational amplifier above, consider Ad = 1000000 (Answer CMRR= 100000)
- From the theory I know that
CMRR = 20*log(Ad/Acm)where Ad is the gain in differential mode and Acm is the gain in common mode.
- I notice that the answer doesn't seem to be in dBs so I assume the answer is given by simply
CMRR = Ad/Acm
- Why do they give me Ad? since I can get it from a circuit analysis.
- I got from the picture that
Vo/ΔVi = 1/100, so if
Vo/ΔVi = Admy Ad doesn't match with the given Ad
- How can I get Acm, I think this data is inherent of the op-amp and have to be given information.
I think there's something wrong with the problem, but since I don't have a way to confirm it I think I am missing something. Any help will be appreciated.
The source pdf (ES) Page 6, number 4.