FETs

P N P

P N P

extra electronsmissing

electrons

P N P

P N P

P N P

No extra or missing electrons

prevents charges from flowingIons

Depletion Zones

source

drain

gategate

source

drain

gategate

electron flow

conventional flow

What happens if … ?

source

drain

gategate

source

drain

gategate

source

drain

gategate

source

drain

gategate

signal

input

source

drain

gategate

signal

input

source

drain

gategate

signal

input

source

drain

gategate

signal

input

signal

output

FET properties

• Field effect transistors control current flow by

varying voltage level

– Voltage controlled device

• Practically no current to operate

– Ideal amplifier draws no current from a source

• High input impedance

– no gate/source current because reverse biased

• Low output impedance

– Easy current flow through center channel

N channel JFET P channel JFET

source

drain

gategate

MOSFET

Metal Oxide Semiconductor Field Effect Transistor

thin silicon

metal oxide

layer

between

N and P

material

source

drain

gategate

depletion mode MOSFET

source

drain

gategate

enhancement mode MOSFET

MOSFET properties

• Nearly infinite impedance

– Does not load a source

– Very low current draw

• Low noise

• Ruined by static discharge

– Shipped in protective foil and conductive foam

– Handle by case not pins

– Everything grounded when working with them

– Power off when inserting or removing

depletion mode enhancement mode

N Channel MOSFET N channel MOSFET

depletion mode enhancement mode

P Channel MOSFET P channel MOSFET