Clapp oscillator

The Clapp oscillator is one of several types of LC electronic oscillator constructed from a transistor (or vacuum tube) and a positive feedback network, using the combination of an inductance with a capacitor for frequency determination.

It was published by James Kilton Clapp in 1948. According to Vačkář, oscillators of this kind were independently developed by several inventors, and one developed by Gouriet had been in operation at the BBC since 1938.

Referring to the notional circuit in the figure, the network comprises a single inductor and three capacitors. Capacitors C1 and C2 form a voltage divider that determines the amount of feedback voltage applied to the transistor input. The Clapp oscillator is a Colpitts oscillator that has an additional capacitor placed in series with the inductor. The oscillation frequency in Hertz (cycles per second) for the circuit in the figure, which uses a field-effect transistor (FET), is

$f_{0}={1 \over 2\pi }{\sqrt {{1 \over L}\left({1 \over C_{0}}+{1 \over C_{1}}+{1 \over C_{2}}\right)}}\ .$ $f_{0}={1 \over 2\pi }{\sqrt {{1 \over L}\left({1 \over C_{0}}+{1 \over C_{1}}+{1 \over C_{2}}\right)}}\ .$

...
Wikipedia