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Regenerative circuit

For other uses, see Heat exchanger § Regenerative heat exchanger.
Homebuilt Armstrong one-tube regenerative shortwave radio with construction characteristic of the 1930s - 40s. The controls are (left) regeneration, (lower center) filament rheostat, (right) tuning capacitor.
Rear view of the above radio, showing the simplicity of the regenerative design. The tickler coil is visible inside the tuning coil and is turned by a shaft from the front panel; this type of adjustable transformer was called a variocoupler.

A regenerative circuit is an amplifier circuit that employs positive feedback (also known as regeneration or reaction).[1][2] Some of the output of the amplifying device is applied back to its input to add to the input signal, increasing the amplification.[3] One example is the Schmitt trigger (which is also known as a regenerative comparator), but the most common use of the term is in RF amplifiers, and especially regenerative receivers, to greatly increase the gain of a single amplifier stage.[4][5][6]

The regenerative receiver was invented in 1912[7] and patented in 1914[8] by American electrical engineer Edwin Armstrong when he was an undergraduate at Columbia University.[9] It was widely used between 1915 and World War II. Advantages of regenerative receivers include increased sensitivity with modest hardware requirements, and increased selectivity because the Q of the tuned circuit will be increased when the amplifying vacuum tube or transistor has its feedback loop around the tuned circuit (via a "tickler" winding or a tapping on the coil) because it introduces some negative resistance.

Due partly to its tendency to radiate interference when oscillating,[6][5]: p.190  by the 1930s the regenerative receiver was largely superseded by other TRF receiver designs (for example "reflex" receivers) and especially by another Armstrong invention - superheterodyne receivers[10] and is largely considered obsolete.[5]: p.190 [11] Regeneration (now called positive feedback) is still widely used in other areas of electronics, such as in oscillators, active filters, and bootstrapped amplifiers.

A receiver circuit that used larger amounts of regeneration in a more complicated way to achieve even higher amplification, the superregenerative receiver, was also invented by Armstrong in 1922.[11][5]: p.190  It was never widely used in general commercial receivers, but due to its small parts count it was used in specialized applications. One widespread use during WWII was IFF transceivers, where single tuned circuit completed the entire electronics system. It is still used in a few specialized low data rate applications,[11] such as garage door openers,[12] wireless networking devices,[11] walkie-talkies and toys.

  1. ^ S. W. Amos, R. S. Amos, Newnes Dictionary of Electronics, 4th ed., London, U. K.: Newnes, 1999, p. 265, 269
  2. ^ E. Williams, Thermionic Valve Circuits, 4th ed., London: Sir Isacc Pitman & Sons, 1961, p. 151
  3. ^ W. L. Everitt, Communication Engineering, 2nd ed. New York: McGraw-Hill, 1937, p. 463
  4. ^ J. Scott-Taggart, The Manual of Modern Radio, London: The Amalgamated Press LTD., 1933, p. 94
  5. ^ a b c d Technical Manual TM 11-665: C-W and A-M Radio Transmitters and Receivers. Dept. of the Army, US Government Printing Office. 1952. pp. 187–190.
  6. ^ a b Poole, Ian (1998). Basic Radio: Principles and Technology. Newnes. p. 100. ISBN 0080938469.
  7. ^ Hong, Sungook. "A history of the regeneration circuit: From invention to patent litigation" (PDF). Institute of Electrical and Electronics Engineers. Retrieved March 9, 2014.
  8. ^ US Patent 1113149A, Edwin H. Armstrong, Wireless receiving system, filed October 29, 1913, granted October 6, 1914
  9. ^ Armstrong, Edwin H. (September 1915). "Some recent developments in the Audion receiver" (PDF). Proc. IRE. 3 (9). New York: Institute of Radio Engineers: 215–247. doi:10.1109/JRPROC.1915.216677. S2CID 2116636. Retrieved August 29, 2012.
  10. ^ Malanowski, Gregory (2011). The Race for Wireless: How Radio Was Invented (or Discovered?). AuthorHouse. p. 66. ISBN 978-1463437503.
  11. ^ a b c d Williams, Lyle Russell (2006). The New Radio Receiver Building Handbook. Lulu. pp. 24–26, 31–32. ISBN 1847285260.
  12. ^ Bensky, Alan (2004). Short-range Wireless Communication: Fundamentals of RF System Design and Application. Newnes. p. 1. ISBN 008047005X.

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