Nyquist, Harry

SUBJECT AREA: Electronics and information technology, Recording

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b. 7 February 1889 Nilsby, Sweden

d. 4 April 1976 Texas, USA

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Swedish-American engineer who established the formula for thermal noise in electrical circuits and the stability criterion for feedback amplifiers.

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Nyquist (original family name Nykvist) emigrated from Sweden to the USA when he was 18 years old and settled in Minnesota. After teaching for a time, he studied electrical engineering at the University of North Dakota, gaining his first and Master's degrees in 1915 and 1916, and his PhD from Yale in 1917. He then joined the American Telegraph \& Telephone Company, moving to its Bell Laboratories in 1934 and remaining there until his retirement in 1954. A prolific inventor, he made many contributions to communication engineering, including the invention of vestigial-side band transmission. In the late 1920s he analysed the behaviour of analogue and digital signals in communication circuits, and in 1928 he showed that the thermal noise per unit bandwidth is given by 4 kT, where k is Boltzmann's constant and T the absolute temperature. However, he is best known for the Nyquist Criterion, which defines the conditions necessary for the stable, oscillation-free operation of amplifiers with a closed feedback loop. The problem of how to realize these conditions was investigated by his colleague Hendrik Bode.

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Principal Honours and Distinctions

Franklin Institute Medal 1960. Institute of Electrical and Electronics Engineers Medal of Honour 1960; Mervin J.Kelly Award 1961.

Bibliography

1924, "Certain factors affecting telegraph speed", Bell System Technical Journal 3:324. 1928, "Certain topics in telegraph transmission theory", Transactions of the American

Institute of Electrical Engineers 47:617.

1928, "Thermal agitation of electric charge in conductors", Physical Review 32:110. 1932, "Regeneration theory", Bell System Technical Journal 11:126.

1940, with K.Pfleger, "Effect of the quadrature component in single-sideband transmission", Bell System Technical Journal 19:63.

Further Reading

Bell Telephone Laboratories, 1975, Mission Communications.

See also: Shannon, Claude Elwood

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