Ultralow-frequency design of the Wien bridge oscillator using switched capacitors

An ultralow-frequency oscillator and automatic gain controller circuitry are proposed in which switched capacitors (SC) are used in place of resistors of the frequency-determining arm in the Wien bridge oscillator. The oscillation frequency f is widely varied only by adjusting the SC clock frequency f_c. Experimental results show that the oscillator is stable over the oscillation frequency range from 10 μHz to 100 Hz and that f is proportional to f_c, which agrees with theoretical results. The oscillation voltage distortion is estimated to be less than -35 dB within the oscillation frequency range from 100 μHz to 100 Hz. The distortion increases at frequencies below 100 μHz, where an increase of output offset voltage has been observed. The very short rise time of the stable oscillation has been achieved by changing the clock frequency to a lower value after getting the stable oscillation at a higher clock frequency