Most analog functions can be built using almost only three building blocks. These blocks are:
These blocks perform respectively the following transfer characteristics:
The fourth transfer, Current to voltage, is performed by an impedance.
These building blocks are interesting since their behavior depends on their topology and their performance depend on their sizing.
These building blocks are typical from IC design since their proper operation is based on good components matching which is difficult to grant using discrete devices.
A current mirror is built from two transconductors. The first one with input shorted to output to perform a current to voltage conversion, the second one with input connected to input of first transconductor to perform voltage to current conversion.