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Field Effect Transistor

The FET consists of a semiconductor channel with electrodes at either end referred to as the drain and the source.  A control electrode called the gate is placed in very close proximity to the channel so that its electric charge is able to affect the channel.  The semiconductor channel where the current flow occurs may be either P-type or N-type. So there are two types or categories of FET known as P-Channel and N-Channel. FETs are also known as unipolar transistors as they involve single-carrier-type operation.

The field effect transistor is said to be the most like the triode vacuum tube.  A vacuum tube has a cathode emitter which emits the electrons (negative terminal), and a collector plate which collects the electrons (positive terminal).  The triode tube control grid will speed up or slow down electrons moving past it depending on polarity.  Positive grid voltage will accelerate the electrons.  The N type field effect transistor works the same way without the need for a heated filament.

The bipolar PNP and NPN transistor existed before the field effect transistor.  Bipolar transistors have low input impedance.  In a search for something with the high input impedance of the vacuum tube and the solid state durability and efficiency of a transistor, scientists came up with the FET. 

A FET uses voltage to control an electrostatic field within the transistor while the bipolar transistor  uses bias current between base and emitter to control conductivity.  Because the FET is voltage-controlled it is the most like the old triode vacuum tube.  

==FET Types==
===MOSFET===
In the world of radio the MOSFET is the power.  MOSFET RF transistors are metal-oxide field effect transistors (MOSFETs) that are designed to handle high-power radio frequency (RF) signals.  

[[Category:Electronics]]
[[Category:Electronic Components]]