So I have spent days reading about specifics of op-amps, instrumentation amps, and ECG circuitry and it just isn't clicking for me.
As I understand it, the common mode signal gets amplified and added to the differential output voltage. I don't see how this will be a problem since all it will do is provide a DC shift.
There seem to be several ways of compensating for DC shifts so why is it so important to have a high CMRR?
For example, in the following ECG circuit we already have the RLD and the output DC feedback loop for DC shift correction, so CMRR shouldn't be that big of a concern.
Despite this ECGs seem to have a minimum CMRR standard of 80dB.
Can someone please help clear up these concepts a bit for me?