Mechatronic Systems Engineering 2201A/B Lecture Notes - Lecture 23: Darlington Transistor, Transconductance, Electric Field
16 Jan 2020
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Darlington pair: a circuit made by two bipolar transistors connected in such a way that the current amplified by the first transistor is amplified further by the second one. The current gain of a darlington pair can exceed 10,000. Fets operate on a different principle than the bjts but serve a similar role in mechatronic system design. The basis of the operation of fets is that an external electric field may be used to vary the conductivity of a narrow region called a channel. A fet is a "transconductance amplifier": the output current is controlled by input voltage. Metal-oxide semiconductor field-effect transistors (mosfets): enhancement-mode mosfets depletion-mode mosfets. An n-channel enhancement-mode mosfet has three terminals: the gate (analogous to the base in a bjt) the drain (analogous to the collector) the source (analogous to the emitter) The gate consists of a metal film layer, separated from the p-type bulk by a thin oxide layer (hence the terminology metal-oxide semiconductor)
