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A FET amplifier is an amplifier that uses one or more field-effect transistors (FETs). The most common type of FET amplifier is the MOSFET amplifier, which uses metal–oxide–semiconductor FETs (MOSFETs). The main advantage of a FET used for amplification is that it has very high input impedance and low output impedance.

In detail[edit]

The transconductance is given by

${\displaystyle g_m=\frac{I_{\mathrm{D}}}{V_{\mathrm{G}\mathrm{S}}}}$

On rearranging, we get

${\displaystyle I_{\mathrm{D}}=g_m{V}_{\mathrm{G}\mathrm{S}}}$

Equivalent circuit[edit]

The internal resistance R_gs, between gate and source appears between drain and source. R_ds is internal resistance between drain and source.As R_gs is very high, it is taken to be infinite and R_ds is neglected.^[1]

Voltage gain[edit]

For ideal FET equivalent circuit, voltage gain is given by,

From the equivalent circuit,

and from the definition of transconductance,

we get

Types of FET amplifiers[edit]

There are three types of FET amplifiers: which terminal is the common input and output? (This is similar to a bipolar junction transistor (BJT) amplifier.)

Common gate amplifier[edit]

The gate is common to both input and output.

Common source amplifier[edit]

The source is common to both input and output.

Common drain amplifier[edit]

Fet Amp

The drain is common to both input and output. It is also known as a 'source follower'.^[2]

History[edit]

The basic principle of the field-effect transistor (FET) amplifier was first proposed by Austro-Hungarian physicist Julius Edgar Lilienfeld in 1925.^[3] However, his early FET concept was not a practical design.^[4] The FET concept was later also theorized by Oskar Heil in the 1930s and William Shockley in the 1940s,^[5] but there was no working practical FET built at the time.^[4]

MOSFET amplifier[edit]

A breakthrough came with the work of Egyptian engineer Mohamed M. Atalla in the late 1950s.^[6] He developed the method of surface passivation, which later became critical to the semiconductor industry as it made possible the mass-production of siliconsemiconductor technology, such as integrated circuit (IC) chips.^[7][4][8] For the surface passivation process, he developed the method of thermal oxidation, which was a breakthrough in silicon semiconductor technology.^[9] The surface passivation method was presented by Atalla in 1957.^[10] Building on the surface passivation method, Atalla developed the metal–oxide–semiconductor (MOS) process,^[7] with the use of thermally oxidized silicon.^[11][12] He proposed that the MOS process could be used to build the first working silicon FET, which he began working on building with the help of Korean recruit Dawon Kahng.^[7]

The MOS field-effect transistor (MOSFET) amplifier was invented by Mohamed Atalla and Dawon Kahng in 1959.^[5] They fabricated the device in November 1959,^[13] and presented it as the 'silicon–silicon dioxide field induced surface device' in early 1960,^[14] at the Solid-State Device Conference held at Carnegie Mellon University.^[15] The device is covered by two patents, each filed separately by Atalla and Kahng in March 1960.^[16][17]

See also[edit]

References[edit]

Fet Amplifier Experiment

1. ^ ^abThomas L. Floyd (2011). Electronic Devices. Dorling Kinersley (India) Pvt. Ltd., licensees of Pearson Education in South Asia. p. 252. ISBN978-81-7758-643-5.
2. ^Allen Mottershead (2003). Electronic Devices and circuits. Prentice-Hall of India, New Delhi-110001. ISBN81-203-0124-2.
3. ^Lilienfeld, Julius Edgar (1926-10-08) 'Method and apparatus for controlling electric currents' U.S. Patent 1745175A
4. ^ ^abc'Dawon Kahng'. National Inventors Hall of Fame. Retrieved 27 June 2019.CS1 maint: discouraged parameter (link)
5. ^ ^ab'1960: Metal Oxide Semiconductor (MOS) Transistor Demonstrated'. The Silicon Engine: A Timeline of Semiconductors in Computers. Computer History Museum. Retrieved August 31, 2019.CS1 maint: discouraged parameter (link)
6. ^Puers, Robert; Baldi, Livio; Voorde, Marcel Van de; Nooten, Sebastiaan E. van (2017). Nanoelectronics: Materials, Devices, Applications, 2 Volumes. John Wiley & Sons. p. 14. ISBN9783527340538.
7. ^ ^abc'Martin (John) M. Atalla'. National Inventors Hall of Fame. 2009. Retrieved 21 June 2013.CS1 maint: discouraged parameter (link)
8. ^Lojek, Bo (2007). History of Semiconductor Engineering. Springer Science & Business Media. pp. 321–3. ISBN9783540342588.
9. ^Huff, Howard (2005). High Dielectric Constant Materials: VLSI MOSFET Applications. Springer Science & Business Media. p. 34. ISBN9783540210818.
10. ^Lojek, Bo (2007). History of Semiconductor Engineering. Springer Science & Business Media. p. 120. ISBN9783540342588.
11. ^Deal, Bruce E. (1998). 'Highlights Of Silicon Thermal Oxidation Technology'. Silicon materials science and technology. The Electrochemical Society. p. 183. ISBN9781566771931.
12. ^U.S. Patent 2,953,486
13. ^Bassett, Ross Knox (2007). To the Digital Age: Research Labs, Start-up Companies, and the Rise of MOS Technology. Johns Hopkins University Press. p. 22. ISBN9780801886393.
14. ^Atalla, M.; Kahng, D. (1960). 'Silicon–silicon dioxide field induced surface devices'. IRE-AIEE Solid State Device Research Conference. Carnegie Mellon University Press.
15. ^'Oral-History: Goldey, Hittinger and Tanenbaum'. Institute of Electrical and Electronics Engineers. 25 September 2008. Retrieved 22 August 2019.CS1 maint: discouraged parameter (link)
16. ^U.S. Patent 3,206,670 (1960)
17. ^U.S. Patent 3,102,230 (1960)