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 which use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...

, who revolutionized the field of applied electronics by discovering 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 perfor ...

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

electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

, 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 signa ...

intermodulation Intermodulation (IM) or intermodulation distortion (IMD) is the amplitude modulation of signals containing two or more different frequencies, caused by nonlinearities or time variance in a system. The intermodulation between frequency comp ...

). 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 Leominster ( ) is a city in Worcester County, Massachusetts, United States. It is the second-largest city in Worcester County, with a population of 43,782 at the 2020 census. Leominster is located north of Worcester and northwest of Boston. Bo ...

in 1898. He went to

Worcester Polytechnic Institute Worcester Polytechnic Institute (WPI) is a Private university, private research university in Worcester, Massachusetts. Founded in 1865 in Worcester, WPI was one of the United States' first engineering and technology universities and now has 14 ac ...

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

Western Electric The Western Electric Company was an American electrical engineering and manufacturing company officially founded in 1869. A wholly owned subsidiary of American Telephone & Telegraph for most of its lifespan, it served as the primary equipment ma ...

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

Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mul ...

(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 An operational amplifier (often op amp or opamp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op amp produces an output potential (relative to c ...

, 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 state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delawa ...

New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...

by taking a ferry to cross the

Hudson River The Hudson River is a river that flows from north to south primarily through eastern New York. It originates in the Adirondack Mountains of Upstate New York and flows southward through the Hudson Valley to the New York Harbor between Ne ...

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, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial Research and development, research and scientific developm ...

headquarters were located in 463 West Street,

Manhattan Manhattan (), known regionally as the City, is the most densely populated and geographically smallest of the five boroughs of New York City. The borough is also coextensive with New York County, one of the original counties of the U.S. state ...

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 of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by othe ...

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 Harry Nyquist (, ; February 7, 1889 – April 4, 1976) was a Swedish-American physicist and electronic engineer who made important contributions to communication theory. Personal life Nyquist was born in the village Nilsby of the parish Stora ...

'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 Brook ...

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 sampled 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 ...

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 U.S. patent of significant technology. Besides the Hall of Fame, it also oper ...

inductee number 25, 1981 * Robert H. Goddard Award from WPI 1981 * AIEE Lamme Medal 1958 * D. Eng. degree (honorary) from WPI 1955 *

Research Corporation Research Corporation for Science Advancement (RCSA) is an organization in the United States devoted to the advancement of science, funding research projects in the physical sciences. Since 1912, Research Corporation for Science Advancement has id ...

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 silve ...

of the

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

*Certificate of Appreciation from the

US War Department The United States Department of War, also called the War Department (and occasionally War Office in the early years), was the United States Cabinet department originally responsible for the operation and maintenance of the United States Army, a ...

. *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 Control theorists Cyberneticists American electrical engineers 20th-century American inventors Worcester Polytechnic Institute alumni Scientists at Bell Labs IEEE Lamme Medal recipients