Editing Current mirror (section)

{{short description|Circuit designed to copy a current through one active device}}
{{Use dmy dates|date=June 2023}}
A '''current mirror''' is a circuit designed to copy a [[electric current|current]] through one [[active device]] by controlling the current in another active device of a circuit, keeping the output current constant regardless of loading. The current being "copied" can be, and sometimes is, a varying signal current. Conceptually, an ideal current mirror is simply an ideal ''inverting current amplifier'' that reverses the current direction as well, or it could consist of a [[amplifier#Ideal|current-controlled current source (CCCS)]]. The current mirror is used to provide bias currents and [[active load]]s to circuits. It can also be used to model a more realistic current source (since ideal current sources do not exist).

The circuit topology covered here is one that appears in many monolithic ICs. It is a [[Widlar current source|Widlar mirror]] without an emitter degeneration resistor in the follower (output) transistor. This topology can only be done in an IC, as the matching has to be extremely close and cannot be achieved with discretes.

Another topology is the [[Wilson current mirror]]. The Wilson mirror solves the [[Early effect]] voltage problem in this design.

Current mirrors are applied in both analog and mixed [[Very Large Scale Integration|VLSI]] circuits.