How CMRR can be improved?
Answer: CMRR is the ratio of differential voltage gain (Ad) to the common mode voltage gain (Ac), so we can improve the CMRR by either increasing differential voltage gain or by decreasing common mode voltage gain.
To increase CMRR, emitter resistance RE should be increased. Higher the value of RE , more is the negative feedback and less is the common mode gain. Thus with the increase in RE , common mode voltage gain decreases and CMRR increases.