Regenerative receiver

A regenerative circuit is one that employs an amount of positive feedback (which is also known as regeneration or regen), that is: part of the output is fed back to the input without phase inversion, to reinforce the signal. 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 increase the gain of a single stage - effectively allowing an electronic signal to be amplified many times by the same active device. This circuit was widely used in radio receivers, called regenerative receivers, between 1915 and World War II. The regenerative receiver was invented in 1912 and patented in 1914 by American electrical engineer Edwin Armstrong when he was an undergraduate at Columbia University. Advantages of regenerative receivers include increased sensitivity with modest hardware requirements, and increased selectivity because the Q factor 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to radiate interference if the regeneration control is set too high, by the 1930s the regenerative receiver was largely superseded by other TRF receiver designs (for example "reflex" receivers) and especially by another Armstrong invention - superheterodyne receivers and is largely considered obsolete,. Regeneration (now called positive feedback) is still widely used in other areas of electronics, such as in oscillators and active filters, and bootstrapped amplifiers.

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