The Colpitts oscillator is an LCoscillator whose frequency-determining resonant circuit consists of a coil and the series connection of two capacitors. Unlike the Hartley oscillator, in the Colpitts oscillator the signal to be fed back is tapped between the two capacitors and determined by the ratio of the two capacitors.
The Colpitts oscillator is a three-point circuit with capacitors, instead of a coil as in the Hartley oscillator, and a feedback loop. When the feedback signal is fed into the base of the transistor, the phase of the feedback must be rotated 180° because the transistor in turn rotates it 180°. If the feedback occurs at the emitter, then the signal must not be rotated in phase.
A circuit variant of the Colpitts oscillator is the Clapp oscillator. This oscillator has a series resonant circuit with a capacitive voltage divider connected in parallel.