3_1_Module 3 Lecture 2B (MOSFET)

3_1_Module 3 Lecture 2B (MOSFET) - Field Effect Transistors...

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Field Effect Transistors Many types: JFET (Junction FET) MOSFET (metal-oxide-semiconductor FET) DGMOSFET (Dual Gate MOSFET) MESFET (Metal-Semiconductor FET) HFET, MODFET, IGBT, FREDFET, ISFET, DNAFET MOSFETs rule.
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Start with an Analogy Large pipe carrying water at high volume. In the pipe is a gate that restricts the flow of water. The gate is controlled by a small amout of force (think frictionless, massless gate). Now, let a small signal control the gate. For every small change in signal at the gate, we get a large change in current through the pipe. small Δ signal LARGE Δ FLOW
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Analogy Description The pipe with water flowing is the channel . The top of the pipe is the source . The bottom of the pipe is the drain . The gate that controls the flow is the gate . The gate carries the input signal. The drain current is the output .
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MOSFET Construction CONVENTIONAL current flow
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MOSFET Symbols P-channel N-channel +V -V -V -V -V +V +V +V
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N+ N+ P V D = 0 V G = 0 V G = V D = 0: two P-N junctions, two depletion regions, I DS = 0. NOTE: even if there were nonzero voltage on the drain, I DS would still be zero, because V G = 0 prevents a path from existing between source and drain. MOSFET Operation (Cutoff) DEPLETION REGION D S G
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N+ N+ P V D = 0 0 < V G < V T - - - 0 < V G < V T : A few electrons from N+ regions move into a third depletion region, very close to the oxide, attracted by + voltage on gate. Still, even if V D > 0, I DS 0 because not enough electrons are close to the oxide to establish substantial current. S
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This note was uploaded on 04/04/2010 for the course EE 3 taught by Professor Staff during the Winter '08 term at UCLA.

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3_1_Module 3 Lecture 2B (MOSFET) - Field Effect Transistors...

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