Voltage transfer curve (VTC)
Beginner
A graph showing what a gate outputs for every input, from fully low to fully high.
Novice
A plot of a gate’s steady-state output voltage against its input voltage. For an inverter it is high for low inputs, falls steeply in the middle and is low for high inputs.
Expert
The DC transfer characteristic , found where pull-up and pull-down currents are equal. Its steep middle (high gain) is what gives a gate noise margin and lets logic restore degraded levels. Five regions follow from which device is off, linear or saturated.
Explained in CMOS logic (Transistors).
See also: Switching threshold (VM), Noise margin.