FET amplifier

Generalised FET as an 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.

In detail

The transconductance is given by

On rearranging, we get

Equivalent circuit

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

Voltage gain

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

From the equivalent circuit,

and from the definition of transconductance,

we get[1]

Types of FET amplifiers

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]

History

Further information: Field-effect transistor and Amplifier

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

Main article: MOSFET
1957, Diagram of one of the SiO2 transistor devices made by Frosch and Derrick[6]

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]

See also

References

  1. ^ a b 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. ^ a b "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. ^ a b 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.