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Fig. 1: Wilson current mirror Fig. 2: Wilson current source. There are three principal metrics of how well a current mirror will perform as part of a larger circuit. The first measure is the static error, i.e., the difference between the input and output currents expressed as a fraction of the input current.
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.
In order to justify the name current mirror, in this circuit the output current has to follow exactly the input current. So, regarding to the current magnitudes, a current mirror is actually a current follower. The Wilson current mirror meets closely this requirement. Circuit-fantasist 15:19, 21 September 2008 (UTC)
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 ...
Download as PDF; Printable version; ... Pages in category "Analog circuits" ... Wilson current mirror; Wunderlich (vacuum tube) Z.
Diagram from Widlar's original patent. 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.
In other words, the input current "programs" the output one and the whole circuit serves as a programmed current source (current-controlled or dependent current source). Obviously, in order to do that, such a current direction inverter (having a more popular name – current mirror ) has to be at least a 3-terminal device (Fig. 2).
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).