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Common Mode and Differential Mode Signals
Data can be transmitted as common mode or differential mode signals. Read on to find out what that means and why differential mode signals are so much better for data transmission than common mode signals.
Common mode signal transmission is an unbalanced transmission, which means one of the two wires is connected to ground and the other isn’t. Because of this external noise causes big problems as the electrical potential of the wire that is not grounded changes whereas the potential of the grounded one doesn’t. This changes the voltage level between the two wires at the receiver which in this very simplified example can only detect “1” but not a single “0”.
Example for common mode signal (CM) transmission (very simplified schematic diagram, voltage levels randomized).
Differential mode signal transmission is a balanced transmission, which means none of the two wires is connected to ground. External noise causes small problems as the receiver only detects the voltage difference between the wires but not against ground. As neither of the two wires is grounded, both are affected by external noise the same way and thus the voltage difference between the two is not affected.
Example for differential mode signal (DM) transmission (very simplified schematic diagram, voltage levels randomized).
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Dirk Traeger
