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A current mirror is a circuit designed to copy a current through one active ... transistor Q 2 is replaced with its hybrid-pi model; a test current I X at the output ...
A Wilson current mirror is a three-terminal circuit ... Fig. 3 shows a small signal model of a Wilson current mirror drawn with a test voltage source, ...
in parallel with the collector–emitter junction of the transistor. This resistor can thus account for the finite output resistance of a simple current mirror or an actively loaded common-emitter amplifier. In keeping with the model used in SPICE and as discussed above using the resistance becomes:
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.
An ideal current source generates a current that is independent of the voltage changes across it. An ideal current source is a mathematical model, which real devices can approach very closely. If the current through an ideal current source can be specified independently of any other variable in a circuit, it is called an independent current source.
In textbooks, channel length modulation in active mode usually is described using the Shichman–Hodges model, accurate only for old technology: [2] where = drain current, ′ = technology parameter sometimes called the transconductance coefficient, W, L = MOSFET width and length, = gate-to-source voltage, =threshold voltage, = drain-to-source voltage, =, and λ = channel-length modulation ...
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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).