Harold Stephen Black (April 14, 1898 – December 11, 1983) was an American

electrical engineer Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems that use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...

, who revolutionized the field of applied electronics by inventing the

negative feedback amplifier A negative-feedback amplifier (or feedback amplifier) is an electronic amplifier that subtracts a fraction of its output from its input, so that negative feedback opposes the original signal. The applied negative feedback can improve its perfo ...

in 1927. To some, his invention is considered the most important breakthrough of the twentieth century in the field of

electronics Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...

, since it has a wide area of application. This is because all electronic devices (vacuum tubes, bipolar transistors and MOS transistors) are inherently nonlinear, but they can be made substantially linear with the application of negative feedback. Negative feedback works by sacrificing gain for higher linearity (or in other words, smaller

distortion In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...

intermodulation Intermodulation (IM) or intermodulation distortion (IMD) is the amplitude modulation of Signal (electrical engineering), signals containing two or more different frequencies, caused by non-linear, nonlinearities or time variance in a system. ...

). By sacrificing gain, it also has an additional effect of increasing the bandwidth of the amplifier. However, a negative feedback amplifier can be unstable such that it may oscillate. Once the stability problem is solved, the negative feedback amplifier is extremely useful in the field of electronics. Black published a famous paper, ''Stabilized feedback amplifiers'', in 1934.

Biography

He was born in Leominster, Massachusetts in 1898. He went to

Worcester Polytechnic Institute The Worcester Polytechnic Institute (WPI) is a Private university, private research university in Worcester, Massachusetts, United States. Founded in 1865, WPI was one of the United States' first engineering and technology universities and now h ...

(WPI) for his first degree. Subsequently, he received a B.S.S. in Electrical Engineering from WPI in 1921 and then joined

Western Electric Western Electric Co., Inc. was an American electrical engineering and manufacturing company that operated from 1869 to 1996. A subsidiary of the AT&T Corporation for most of its lifespan, Western Electric was the primary manufacturer, supplier, ...

, which was the manufacturing arm of AT&T. He joined

Bell Labs Nokia Bell Labs, commonly referred to as ''Bell Labs'', is an American industrial research and development company owned by Finnish technology company Nokia. With headquarters located in Murray Hill, New Jersey, Murray Hill, New Jersey, the compa ...

(1925), where he was a member of technical staff until his retirement (1963). Black started writing his autobiography with the tentative title "Before the ferry docked". However, he died in December 1983 at age 85 before he could finish it.

Work

Amplifiers are unavoidably non-linear. Therefore, every time a signal is amplified in a telecommunications network, which can happen dozens of times in a circuit, noise and distortion are added. Black first invented the feed-forward amplifier which compares the input and output signals and then negatively amplifies the distortion and combines the two signals, canceling out some of the distortion. This amplifier design improved, but did not solve, the problems of transcontinental telecommunication.Harold Black and the Negative-Feedback Amplifier, Ronald Kline, IEEE Control Systems Magazine, Aug 1993, Volume 13, Issue 4, Pages 82-85 After years of work Black invented the negative feedback amplifier which uses negative feedback to reduce the gain of a high-gain, non-linear amplifier and makes it act as a low-gain, linear amplifier with much lower noise and distortion. The Negative feedback amplifier allowed Bell system to reduce overcrowding of lines and extend its long-distance network by means of carrier telephony. It enabled the design of accurate fire-control systems in World War II, and it formed the basis of early operational amplifiers, as well as precise, variable-frequency audio oscillators. According to Black he got his inspiration to invent the negative feedback amplifier when he was traveling from

New Jersey New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...

New York City New York, often called New York City (NYC), is the most populous city in the United States, located at the southern tip of New York State on one of the world's largest natural harbors. The city comprises five boroughs, each coextensive w ...

by taking a ferry to cross the

Hudson River The Hudson River, historically the North River, is a river that flows from north to south largely through eastern New York (state), New York state. It originates in the Adirondack Mountains at Henderson Lake (New York), Henderson Lake in the ...

in August 1927. Having nothing to write on he sketched his thoughts on a misprinted page of the New York Times and then signed and dated it. At that time,

Bell Laboratories Nokia Bell Labs, commonly referred to as ''Bell Labs'', is an American industrial research and development company owned by Finnish technology company Nokia. With headquarters located in Murray Hill, New Jersey, the company operates several lab ...

headquarters were located in 463 West Street,

Manhattan Manhattan ( ) is the most densely populated and geographically smallest of the Boroughs of New York City, five boroughs of New York City. Coextensive with New York County, Manhattan is the County statistics of the United States#Smallest, larg ...

instead of New Jersey and he lived in New Jersey such that he took the ferry every morning to go to work. Fifty years after his 1927 invention, he published an article in IEEE Spectrum regarding the historical background of his invention.Harold S. Black, "Inventing the negative feedback amplifier", IEEE Spectrum, vol. 14, pp. 54-60, Dec. 1977. (50th anniversary of Black's invention of negative feedback amplifier) He published a classical paper on

negative feedback Negative feedback (or balancing feedback) occurs when some function (Mathematics), function of the output of a system, process, or mechanism is feedback, fed back in a manner that tends to reduce the fluctuations in the output, whether caused ...

amplifier in 1934, which has been re-printed in the Proceedings of IEEE two times in 1984 and 1999 Inside his 1934 classical paper "Stabilized feed-back amplifiers", he mentioned Harry Nyquist's work on stability criterion because a negative feedback amplifier can be unstable and oscillate. Thus, with the help of Nyquist's theory, he managed to demonstrate a stable negative feedback amplifier which can be used in reality.

Bernard Friedland Bernard Friedland is an American professor of engineering. He is Distinguished Professor of Electrical and Computer Engineering at the New Jersey Institute of Technology. Biography Friedland was born in New York City and graduated from Brookly ...

wrote an introduction for the 1999 re-print in Proc. IEEE. James E. Brittain wrote about him in 1997.J.E. Brittain., "Scanning the past: Harold S. Black and the negative feedback amplifier", Proc. IEEE, vol. 85, no. 8, pp. 1335-1336, Aug. 1997. An obituary regarding Black was published by IEEE Transactions on Automatic Control in 1984. He also worked on

pulse-code modulation Pulse-code modulation (PCM) is a method used to digitally represent analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amplitud ...

and wrote a book on "Modulation Theory" ( Van Nostrand, 1953). He held many patents the most famous of which was US Patent 2,102,671 "Wave Translation System", which was issued to Bell Laboratories in 1937, covering the negative feedback amplifier.

Awards

National Inventors Hall of Fame The National Inventors Hall of Fame (NIHF) is an American not-for-profit organization, founded in 1973, which recognizes individual engineers and inventors who hold a US patent of significant technology. Besides the Hall of Fame, it also operate ...

inductee number 25, 1981 * Robert H. Goddard Award from WPI 1981 * AIEE Lamme Medal 1958 * D. Eng. degree (honorary) from WPI 1955 * Research Corporation Scientific Award 1952 * John H. Potts Memorial Award of the

Audio Engineering Society The Audio Engineering Society (AES) is a professional body for engineers, scientists, other individuals with an interest or involvement in the professional audio industry. The membership largely comprises engineers developing devices or product ...

John Price Wetherill Medal The John Price Wetherill Medal was an award of the Franklin Institute. It was established with a bequest given by the family of John Price Wetherill (1844–1906) on April 3, 1917. On June 10, 1925, the Board of Managers voted to create a silv ...

of the

Franklin Institute The Franklin Institute is a science museum and a center of science education and research in Philadelphia, Pennsylvania. It is named after the American scientist and wikt:statesman, statesman Benjamin Franklin. It houses the Benjamin Franklin ...

*Certificate of Appreciation from the US War Department. *WPI gives away the annual Harold S. Black Scholarship (1992-)

References

External links

Harold S. Black Papers at WPI
{{DEFAULTSORT:Black, Harold 1898 births 1983 deaths People from Leominster, Massachusetts American control theorists Cyberneticists American electrical engineers 20th-century American inventors Worcester Polytechnic Institute alumni Scientists at Bell Labs IEEE Lamme Medal recipients