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see transistortransistor,
three-terminal, solid-state electronic device used for amplification and switching. It is the solid-state analog to the triode electron tube; the transistor has replaced the electron tube for virtually all common applications.
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McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


(Field Effect Transistor) One of two major categories of transistor; the other is bipolar. FETs use a gate element that, when charged, creates an electromagnetic field that changes the conductivity of a silicon channel and turns the transistor on or off. FETs are fabricated as individually packaged discrete components as well as by the hundreds of millions on a single chip.

FETs vs. Bipolar
FET-based silcon chips are easier to construct than their bipolar counterparts. FETs switch a little slower than bipolar transistors, but use less power. Once the gate terminal on an FET has been charged, no more current is needed to keep that transistor on (closed) for the duration of time required. By comparison, a bipolar transistor requires a small amount of current flowing to keep the transistor on. While the current for one transistor may be negligible, it adds up when millions are switching simultaneously. The heat dissipated on bipolar limits the total number of transistors that can be built on the chip, which is why CMOS logic (based on FETs) is used to build chips with millions of transistors.

The most widely used and widely known FETs are MOSFETs (metal oxide semiconductor FETs), which come in NMOS (n-channel) and PMOS (p-channel) varieties. On a chip, NMOS and PMOS transistors are wired together in a complementary fashion to create CMOS logic, which is the most predominant and used in almost every electronic device today. See MOSFET and n-type silicon.

There Are Many Kinds of FETs
Similar to MOSFETs are JFETs (junction FETs), which use a PN junction gate rather than a poly-crystalline gate. Used for microwave communications, MESFETs (metal semiconductor FETs) are similar to JFETs, but use a Schottky metal gate and are made from gallium arsenide or indium phosphide, not silicon. Evolving from MESFETs for higher-frequency applications are HEMTs and PHEMTs (high electron mobility transistors and pseudomorphic high electron mobility transistors). HEMTs are also called MODFETs, TEGFETs and SDHTs (modulation doped FETs, two-dimensional electron gas FETs and selectively doped heterojunction transistors).

Another high-frequency FET is the gallium arsenide-based CHFET (complementary heterostructure FET), which uses a complementary architecture similar to CMOS.

FETs vs. Bipolar
After the gate is charged in an FET, no more current flows, but the transistor remains closed (turned on) during the required time period. Bipolar transistors (BJTs) require current the entire time the transistor must be closed.
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References in periodicals archive ?
The transit time for the AlGaN/GaN pHEMT is evaluated as
Comparison of the reported pHEMT millimeter-wave double-balanced mixers.
As a leading supplier of high end III/V MMICs and epitaxial wafers the company's fabrication and design, development and production service is based on unique processes such as: 0.18 [micro]m E/D PHEMT, 0.15 [micro]m power PHEMT (12 V, 100 GHz), 0.15 [micro]m metamorphic HEMT (10 V, 150 GHz) and InP HBT (180 GHz).
[4] developed a broadband mixer using three edge and broadside coupled-lines in pHEMT technology.
Pre-production sampling of five new Gallium Arsenide (GaAs) pHEMT low noise amplifiers (LNAs) has been started by RFMD, a manufacturer of RF integrated circuits, with production release expected in September 2006.
The new dual amplifiers can also be used as general-purpose discrete PHEMT devices for other ultra low noise and medium power applications.
On the other hand, recent works from [20, 21] demonstrated wideband amplifier for SDR applications using pHEMT and CMOS technology, providing, however, a lower output power.
TELECOMWORLDWIRE-19 June 2006-RFMD begins pre-production sampling of new GaAs pHEMT LNAs(C)1994-2006 M2 COMMUNICATIONS LTD http://www.m2.com
The model CMQ1432 is a Ku-band GaAs power amplifier module (PAM) that uses GaAs PHEMT device model technology and operates in the 13.75 to 14.5 GHz frequency band.
These RF amplifiers utilize a hybrid microwave integrated circuit design and advanced GaAs pHEMT technology to produce an unconditionally stable module.
has introduced a 0.7- GHz to 1.2 GHz single-die cascode, gallium arsenide (GaAs), pseudomorphic high electron mobility transistor (pHEMT) low-noise amplifier (LNA) for cellular infrastructure applications such as tower-mounted amplifiers, remote radio units, repeaters, and base stations.