FET amplifier

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.

The transconductance is given by

g_{m}={I_{\mathrm {D} } \over V_{\mathrm {GS} }}

On rearranging, we get

I_{\mathrm {D} }=g_{m}V_{\mathrm {GS} }

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

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

$A_{v}={\frac {V_{DS}}{V_{GS}}}$

From the equivalent circuit,

$V_{DS}=I_{D}\cdot R_{D}$

and from the definition of transconductance,

$V_{GS}={\frac {I_{D}}{g_{m}}}$

we get^[1]

$A_{V}=g_{m}\cdot R_{D}$

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

Common gate amplifier

The gate is common to both input and output.

Common source amplifier

The source is common to both input and output.

Common drain amplifier

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

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

In 1955, Carl Frosch and Lincoln Derrick accidentally grew a layer of silicon dioxide over the silicon wafer, for which they observed surface passivation effects.^[7] By 1957 Frosch and Derrick, using masking and predeposition, were able to manufacture silicon dioxide transistors and showed that silicon dioxide insulated, protected silicon wafers and prevented dopants from diffusing into the wafer.^[7]^[8] J.R. Ligenza and W.G. Spitzer studied the mechanism of thermally grown oxides and fabricated a high quality Si/SiO₂ stack in 1960.^[9]^[10]^[11]

Following this research, Mohamed Atalla and Dawon Kahng proposed a silicon MOS transistor in 1959^[12] and successfully demonstrated a working MOS device with their Bell Labs team in 1960.^[13]^[14] Their team included E. E. LaBate and E. I. Povilonis who fabricated the device; M. O. Thurston, L. A. D’Asaro, and J. R. Ligenza who developed the diffusion processes, and H. K. Gummel and R. Lindner who characterized the device.^[15]^[16]

[1]
Thomas L. Floyd (2011). Electronic Devices. Dorling Kinersley (India) Pvt. Ltd., licensees of Pearson Education in South Asia. p. 252. ISBN 978-81-7758-643-5.
[2]
Allen Mottershead (2003). Electronic Devices and circuits. Prentice-Hall of India, New Delhi-110001. ISBN 81-203-0124-2.
[3]
Lilienfeld, Julius Edgar (1926-10-08) "Method and apparatus for controlling electric currents" U.S. patent 1745175A
[4]
"Dawon Kahng". National Inventors Hall of Fame. Retrieved 27 June 2019.
[5]
"1960: Metal Oxide Semiconductor (MOS) Transistor Demonstrated". The Silicon Engine: A Timeline of Semiconductors in Computers. Computer History Museum. Retrieved August 31, 2019.
[6]
Frosch, C. J.; Derick, L (1957). "Surface Protection and Selective Masking during Diffusion in Silicon". Journal of the Electrochemical Society. 104 (9): 547. doi:10.1149/1.2428650.
[7]
Huff, Howard; Riordan, Michael (2007-09-01). "Frosch and Derick: Fifty Years Later (Foreword)". The Electrochemical Society Interface. 16 (3): 29. doi:10.1149/2.F02073IF. ISSN 1064-8208.
[8]
Frosch, C. J.; Derick, L (1957). "Surface Protection and Selective Masking during Diffusion in Silicon". Journal of the Electrochemical Society. 104 (9): 547. doi:10.1149/1.2428650.
[9]
Ligenza, J. R.; Spitzer, W. G. (1960-07-01). "The mechanisms for silicon oxidation in steam and oxygen". Journal of Physics and Chemistry of Solids. 14: 131–136. doi:10.1016/0022-3697(60)90219-5. ISSN 0022-3697.
[10]
Deal, Bruce E. (1998). "Highlights Of Silicon Thermal Oxidation Technology". Silicon materials science and technology. The Electrochemical Society. p. 183. ISBN 978-1566771931.
[11]
Lojek, Bo (2007). History of Semiconductor Engineering. Springer Science & Business Media. p. 322. ISBN 978-3540342588.
[12]
Bassett, Ross Knox (2007). To the Digital Age: Research Labs, Start-up Companies, and the Rise of MOS Technology. Johns Hopkins University Press. pp. 22–23. ISBN 978-0-8018-8639-3.
[13]
Atalla, M.; Kahng, D. (1960). "Silicon-silicon dioxide field induced surface devices". IRE-AIEE Solid State Device Research Conference.
[14]
"1960 – Metal Oxide Semiconductor (MOS) Transistor Demonstrated". The Silicon Engine. Computer History Museum. Retrieved 2023-01-16.
[15]
KAHNG, D. (1961). "Silicon-Silicon Dioxide Surface Device". Technical Memorandum of Bell Laboratories: 583–596. doi:10.1142/9789814503464_0076. ISBN 978-981-02-0209-5.
[16]
Lojek, Bo (2007). History of Semiconductor Engineering. Berlin, Heidelberg: Springer-Verlag Berlin Heidelberg. p. 321. ISBN 978-3-540-34258-8.

[Prathamesh-1] [1]
Thomas L. Floyd (2011). Electronic Devices. Dorling Kinersley (India) Pvt. Ltd., licensees of Pearson Education in South Asia. p. 252. ISBN 978-81-7758-643-5.

[2] [2]
Allen Mottershead (2003). Electronic Devices and circuits. Prentice-Hall of India, New Delhi-110001. ISBN 81-203-0124-2.

[p1-3] [3]
Lilienfeld, Julius Edgar (1926-10-08) "Method and apparatus for controlling electric currents" U.S. patent 1745175A

[kahng-4] [4]
"Dawon Kahng". National Inventors Hall of Fame. Retrieved 27 June 2019.

[computerhistory-5] [5]
"1960: Metal Oxide Semiconductor (MOS) Transistor Demonstrated". The Silicon Engine: A Timeline of Semiconductors in Computers. Computer History Museum. Retrieved August 31, 2019.

[6] [6]
Frosch, C. J.; Derick, L (1957). "Surface Protection and Selective Masking during Diffusion in Silicon". Journal of the Electrochemical Society. 104 (9): 547. doi:10.1149/1.2428650.

[:0-7] [7]
Huff, Howard; Riordan, Michael (2007-09-01). "Frosch and Derick: Fifty Years Later (Foreword)". The Electrochemical Society Interface. 16 (3): 29. doi:10.1149/2.F02073IF. ISSN 1064-8208.

[8] [8]
Frosch, C. J.; Derick, L (1957). "Surface Protection and Selective Masking during Diffusion in Silicon". Journal of the Electrochemical Society. 104 (9): 547. doi:10.1149/1.2428650.

[9] [9]
Ligenza, J. R.; Spitzer, W. G. (1960-07-01). "The mechanisms for silicon oxidation in steam and oxygen". Journal of Physics and Chemistry of Solids. 14: 131–136. doi:10.1016/0022-3697(60)90219-5. ISSN 0022-3697.

[Deal2-10] [10]
Deal, Bruce E. (1998). "Highlights Of Silicon Thermal Oxidation Technology". Silicon materials science and technology. The Electrochemical Society. p. 183. ISBN 978-1566771931.

[11] [11]
Lojek, Bo (2007). History of Semiconductor Engineering. Springer Science & Business Media. p. 322. ISBN 978-3540342588.

[Bassett222-12] [12]
Bassett, Ross Knox (2007). To the Digital Age: Research Labs, Start-up Companies, and the Rise of MOS Technology. Johns Hopkins University Press. pp. 22–23. ISBN 978-0-8018-8639-3.

[13] [13]
Atalla, M.; Kahng, D. (1960). "Silicon-silicon dioxide field induced surface devices". IRE-AIEE Solid State Device Research Conference.

[14] [14]
"1960 – Metal Oxide Semiconductor (MOS) Transistor Demonstrated". The Silicon Engine. Computer History Museum. Retrieved 2023-01-16.

[15] [15]
KAHNG, D. (1961). "Silicon-Silicon Dioxide Surface Device". Technical Memorandum of Bell Laboratories: 583–596. doi:10.1142/9789814503464_0076. ISBN 978-981-02-0209-5.

[16] [16]
Lojek, Bo (2007). History of Semiconductor Engineering. Berlin, Heidelberg: Springer-Verlag Berlin Heidelberg. p. 321. ISBN 978-3-540-34258-8.

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Common gate amplifier

Common source amplifier

Common drain amplifier

MOSFET amplifier

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FET amplifier

Common gate amplifier

Common source amplifier

Common drain amplifier

MOSFET amplifier

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In detail

Equivalent circuit

Voltage gain

Types of FET amplifiers

History

See also

References