Here is my basic understanding of common mode range for diff input amplifiers:
As far as I understand the common mode voltage is nothing but the offset at which the diff signal is travelling above a common reference.
And if this CM voltage exceeds the amplifier rail voltages due to capacitive coupling or EMI, this is a problem. So as a remedy, common mode chokes(for high freq.) or filters(for lower freq.) are employed to attenuate this CM voltage so that the amplifier can operate well.
It seems like chokes and filters are frequency dependent and they attenuate CM voltages if the CM voltages are alternating/varying in time.
But can there be an interference or noise source which causes increase in CM voltage as DC? In other words is there a phenomenon called DC common mode interference in practice? If so, what are the ways to eliminate it?