Ring oscillator

Ring oscillator test structures fabricated on silicon using p-type MOSFETs of different sizes.
A schematic of a simple 3-inverter ring oscillator whose output frequency is 1/(6×inverter delay).

A ring oscillator is a device composed of an odd number of NOT gates in a ring, whose output oscillates between two voltage levels, representing true and false. The NOT gates, or inverters, are attached in a chain and the output of the last inverter is fed back into the first.