Editing Current mirror (section)

=== Basic idea ===
A bipolar transistor can be used as the simplest ''current-to-current converter'' but its transfer ratio would highly depend on temperature variations, ''β'' tolerances, etc. To eliminate these undesired disturbances, a current mirror is composed of two cascaded ''current-to-voltage'' and ''voltage-to-current'' converters placed at the same conditions and having reverse characteristics. It is not obligatory for them to be linear; the only requirement is their characteristics to be mirrorlike (for example, in the [[Bipolar Junction Transistor|BJT]] current mirror below, they are logarithmic and exponential). Usually, two identical converters are used but the characteristic of the first one is reversed by applying a negative feedback. Thus a current mirror consists of two cascaded equal converters (the first – reversed and the second – direct).
[[File:Simple bipolar mirror.svg|thumbnail|200px|Figure 1: A current mirror implemented with n–p–n bipolar transistors using a resistor to set the reference current ''I''<sub>REF</sub>; ''V''<sub>CC</sub> is a positive voltage.]]