|
Response Details:
CURRENT MIRROR:
A current mirror is a circuit designed to copy a 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 current amplifier.
There are three main specifications that characterize a current mirror.
The first is the current level it produces. The second is its AC output
resistance, which determines how much the output current varies with
the voltage applied to the mirror. The third specification is the
minimum voltage drop across the mirror necessary to make it work
properly. This minimum voltage is dictated by the need to keep the
output transistor of the mirror in active mode. The range of voltages
where the mirror works is called the compliance range and the voltage marking the boundary between good and bad behavior is called the compliance voltage. There are also a number of secondary performance issues with mirrors, for example, temperature stability.
USES:
The current mirror is used to provide bias currents and active loads to circuits..A current mirror may be thought of as an adjustable current regulator, the current limit being easily set by a single resistance. It is a rather crude current regulator circuit, but one that finds wide use due to its simplicity.
|