Diode connected transistor

A diode-connected transistor is a method of creating a two-terminal rectifying device (a diode) out of a three-terminal transistor. A characteristic of diode-connected transistors is that they are always in the saturation region for MOSFETs and in the active region for BJTs.

A diode-connected transistor is made by

Diode-connected transistors are used in current mirrors to provide a voltage drop that tracks that of the other transistor as temperature changes. They also have very low reverse leakage currents