Need for Current Mirrors in Microelectronics
Proper functioning of electronic circuits dictate that the bias circuits are relatively insensitive to external factors such as voltage and temperature variations. Every chip has a golden reference source for voltage and current generated by a Band Gap Reference circuit, which requires several transistors and is fairly complex to implement. As a result, a design cannot have a multitude of such reference circuits in the chip, wherever a bias supply is required.
A sensible approach to the problem is to generate the golden reference voltage and current on chip using a Band Gap Reference circuit, and simply “copy” or “mirror” the current into other parts of the chip where bias supply is required. This is the main purpose of a Current Mirror. In addition, they tend to have a smaller footprint compared to resistor-based techniques especially when small currents are involved.