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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.
A Wilson current mirror is a three-terminal circuit (Fig. 1) that accepts an input current at the input terminal and provides a "mirrored" current source or sink output at the output terminal. The mirrored current is a precise copy of the input current.
A Widlar current source is a modification of the basic two-transistor current mirror that incorporates an emitter degeneration resistor for only the output transistor, enabling the current source to generate low currents using only moderate resistor values. [1] [2] [3]
The output part of the simple current mirror is an example of such a current source widely used in integrated circuits. The common base, common gate and common grid configurations can serve as constant current sources as well. A JFET can be made to act as a current source by tying its gate to its source. The current then flowing is the I DSS of ...
Most commonly the active load is the output part of a current mirror [1] and is represented in an idealized manner as a current source. Usually, it is only a constant-current resistor that is a part of the whole current source including a constant voltage source as well (the power supply V CC on the figures below).
The current sourced or sunk at the inverting input is sensed by current mirrors inserted between the buffer and its power supply rails, and its mirrored copy is sourced or sunk into an internal high-impedance node. [4] The resulting positive or negative voltage at this node is interfaced to the outside world with the output buffer. [4]
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The Blackmer cell is a direct descendant of a two-transistor log-antilog circuit, itself a derivative of the simple current mirror.Normally, the bases of two transistors of a mirror are tied together to ensure the collector current I 2 of the output transistor T2 exactly mirrors the collector current I 1 of the input transistor T1.