Submitted by: john ellis (email@example.com).
This low distortion oscillator uses the three phases of a three-phase circuit combined with their inverses to generate an effective six-phase control signal to control the amplitude of the oscillation. This six-phase control circuit requires little additional filtering, enabling a low distortion signal to be obtained with less than one cycle stabilisation period. It operates effectively from 1Hz to 30kHz, but the bandwidth limitation of the op-amps generates slight distortion at higher frequencies that might be eliminated with a faster op-amp.
Performance figures of the prototype circuit show better than -90dB distortion, nothing being visible on a signal anlyser trace at 1Hz and 1kHz, and only a second harmonic at -85dB at 30kHz.