How much CMRR is required

[calculus_cuthbert]

Hi,

I am trying to some initial calculations for requirements of a receiver.
For a pre-amp (differential) the input signal voltage is 0.2V (voltage spike) and the width of the spike is ~ 500ps. The common mode noise signal is 0.5V (voltage spike) and the width of this spike is also 500ps.
How do I calculate how much CMRR I need from the receiver??
e.g if my receiver provides 90dB CMRR (@ low frequency) and rolls off to 60dB (@ 2.5GHz) is this enough??

How do I calculate the requirements on the CMRR spec???

I would greatly appreciate it if someone helps me out soon!

Thanks.

 

[houly]

Hello
In my opinion, you must fix an output level that you want to have and the noise that you could tolerate (in fact a SNR). Then you could deduce the Amc because you know Ad (which is what you want on output) with your input voltage values...