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Q: What is Single Ended Signaling?

A: Single ended signaling is the result of using a single individual wire to transport a signal in a circuit. Capacitance is this case is encountered from the nearest ground plane as the wire is charged. This effect is called stray capacitance because it strays from the axis of the cable and seeks the nearest ground. This can greatly impact the signals but for most low speed, short length circuits it is of lesser concern. If the ground plane distance varies along the traversed length of the cable then the capacitance varies as the signal builds along the length. This will either degrade or completely impede the signal. However, in the case of coax, the nearest ground plane is the shield. Typically the shield is negative and the conductor is positive. This sort of configuration is called a differential pair. Since the geometry creates a perfect concentric distance between the capacitive plates (i.e. the conductor and the shield) then the overall affect is a controlled capacitance throughout the length of the run and it is far more impervious to stray capacitance. Single ended signals that encounter high capacitance will often end up looking more like “Saw-teeth” that a clear square wave. The same is true of differential signal which will exhibit eye patterns that are not as well defined. An excellent article can be found here on the subject.

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