FREE LESSON · Semiconductors & electronics · 2 OF 4
How a CMOS Inverter Works
The CMOS inverter — Complementary devices restore a bit
Two complementary networks make a robust NOT gate.
A CMOS inverter pairs a pull-up network with a pull-down network. A low input turns on the path toward the supply and turns off the path to ground, producing high; a high input does the reverse. Around the switching threshold both may partly conduct, but stable endpoints restore strong logic levels.
Complementary action gives high gain and very low ideal static power at stable 0 and 1.
Where switching energy goes
To change the output, the circuit must move charge onto or off its effective capacitance. Roughly, dynamic energy grows with capacitance and the square of supply voltage, and power also grows with switching frequency. More activity, larger loads, or higher voltage therefore costs heat.
Power is workload-dependent: an idle circuit and a toggling circuit with the same transistor count behave differently.