With a balanced interface the receiving amplifier just sees two source impedances which are the same. Signal is irrelevant to the "balanced" aspect of the interface. (It seems that's the sticking point for you.)
Regardless, the receiving amplifier has no clue whether one side of the signal is near ground or not. It only acts on the differential voltage between the +/- inputs. One of them need not be varying for nominal operation.
CMR is achieved without signal on one side. Or even both, for that matter. 🙂
Dave.
Regardless, the receiving amplifier has no clue whether one side of the signal is near ground or not. It only acts on the differential voltage between the +/- inputs. One of them need not be varying for nominal operation.
CMR is achieved without signal on one side. Or even both, for that matter. 🙂
Dave.
Of course not! If the impedances of both sources, seen from the receiver, are equal, it doesn't matter whether one line in the end is connected to a zero signal point or not.
Repeating again: the signal the receiver sees is the difference between the two leads. The level at each lead on itself is immaterial as long as it is within the CM range of the receiver.
A balanced line (with equal impedances) is a balanced line no matter what the individual signal levels are with respect to ground.
This is balanced lines 101: the word 'balanced' in balanced lines refers to the impedances. What you mean is symmetrical, which is a different animal altogether. Symmetrical lines help to maximize dynamic range, but in themselves do not help with lowering noise etc.
A line can be balanced, symmetrical or both.
Jan