LC Oscillators

Colpitts and Hartley oscillators use inductor–capacitor tanks to generate RF sine waves.

Intermediate

An LC tank resonates at

$f_0 = \frac{1}{2\pi\sqrt{LC}}$

Colpitts — feedback from a capacitive divider; $C = \dfrac{C_1C_2}{C_1+C_2}$ .
Hartley — feedback from a tapped inductor.
Clapp — adds a series capacitor for better stability.

LC oscillators cover roughly 100 kHz to several GHz and are the basis of RF signal sources and VCOs.

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