hi all:
Recently I am designing a telescopic opamp with gainboost.
I meet the problems in CMRR.
1. How to acquire the spec of CMRR? That is to say the influence of opamp's CMRR in their applicant, such as in data converter.
2. (May be the 2 is another saying of 1.
![Smiley Smiley](https://designers-guide.org/forum/Templates/Forum/default/smiley.gif)
)
From text, we can get Acm = gm*R/ (1+2*gm*Rtail),where Acm is gain of commom mode, gm is transconduct of opamp, R is the
output res of opamp and Rtail is the output res of the tail current. With gainboost, the R will increase 100 times and so do the Acm, that is means that CMRR will decrease to 100 times. Do we need to consider the influence of gainboost?
Many thanks!