John B. Johnson
Encyclopedia
John Bertrand "Bert" Johnson (October 2, 1887 – November 27, 1970) (né Johan Erik Bertrand) was a Swedish
-born American
electrical engineer and physicist. He first explained in detail a fundamental source of random interference
with information traveling on wires.
paper "Thermal Agitation of Electricity in Conductors". In electronic systems, thermal noise (now also called Johnson noise) is the noise
generated by thermal agitation of electrons in a conductor. Johnson's papers showed a statistical fluctuation of electric charge
occur in all electrical conductor
s, producing random variation of potential
between the conductor ends (such as in vacuum tube
amplifier
s and thermocouple
s). Thermal noise power, per hertz
, is equal throughout the frequency
spectrum
. Johnson deduced that thermal noise is intrinsic to all resistors and is not a sign of poor design or manufacture, although resistors may also have excess noise.
's US Patent 1,900,018 of 1928. In sworn testimony to the U.S. patent office in 1949, Johnson reported "...although the modulation index of 11 per cent is not great,...the useful output power is substantial...it is in principle operative as an amplifier". On the other hand, in an article in 1964 he denied the operability of Lilienfeld's patent, saying "I tried conscientiously to reproduce Lilienfeld’s structure according to his specification and could observe no amplification or even modulation."
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
-born American
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
electrical engineer and physicist. He first explained in detail a fundamental source of random interference
Noise
In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise...
with information traveling on wires.
Career
In 1928, while at Bell Telephone Laboratories he published the journalAcademic journal
An academic journal is a peer-reviewed periodical in which scholarship relating to a particular academic discipline is published. Academic journals serve as forums for the introduction and presentation for scrutiny of new research, and the critique of existing research...
paper "Thermal Agitation of Electricity in Conductors". In electronic systems, thermal noise (now also called Johnson noise) is the noise
Noise
In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise...
generated by thermal agitation of electrons in a conductor. Johnson's papers showed a statistical fluctuation of electric charge
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
occur in all electrical conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
s, producing random variation of potential
Potential
*In linguistics, the potential mood*The mathematical study of potentials is known as potential theory; it is the study of harmonic functions on manifolds...
between the conductor ends (such as in vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
s and thermocouple
Thermocouple
A thermocouple is a device consisting of two different conductors that produce a voltage proportional to a temperature difference between either end of the pair of conductors. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a...
s). Thermal noise power, per hertz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, is equal throughout the frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
. Johnson deduced that thermal noise is intrinsic to all resistors and is not a sign of poor design or manufacture, although resistors may also have excess noise.
Field-effect transistor
Johnson was possibly among the first people to make a working field effect transistor, based on Julius Edgar LilienfeldJulius Edgar Lilienfeld
Julius Edgar Lilienfeld was an Austro-Hungarian physicist. He was born in Lemberg in Austria-Hungary , moved to the United States in the early 1920s, and became American citizen in 1934...
's US Patent 1,900,018 of 1928. In sworn testimony to the U.S. patent office in 1949, Johnson reported "...although the modulation index of 11 per cent is not great,...the useful output power is substantial...it is in principle operative as an amplifier". On the other hand, in an article in 1964 he denied the operability of Lilienfeld's patent, saying "I tried conscientiously to reproduce Lilienfeld’s structure according to his specification and could observe no amplification or even modulation."
See also
- Johnson–Nyquist noiseJohnson–Nyquist noiseJohnson–Nyquist noise is the electronic noise generated by the thermal agitation of the charge carriers inside an electrical conductor at equilibrium, which happens regardless of any applied voltage...
- Timeline of thermodynamics, statistical mechanics, and random processesTimeline of thermodynamics, statistical mechanics, and random processesA timeline of events related to thermodynamics.- Before 1800 :* 1650 – Otto von Guericke builds the first vacuum pump* 1660 – Robert Boyle experimentally discovers Boyle's Law, relating the pressure and volume of a gas...
External articles and references
- J. B. Johnson, "Thermal Agitation of Electricity in Conductors". The American Physical Society, 1928.
- Federal Standard 1037CFederal Standard 1037CFederal Standard 1037C, titled Telecommunications: Glossary of Telecommunication Terms is a United States Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended....
and MIL-STD-188MIL-STD-188MIL-STD-188 is a series of U.S. military standards relating to telecommunications.-Purpose:Faced with “past technical deficiencies in telecommunications systems and equipment and software…that were traced to basic inadequacies in the application of telecommunication standards and to the lack of a...