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

An ultralow-frequency Wien bridge oscillator, in which resistors are replaced by switched capacitors and automatic gain controller circuitry, is reported. The oscillation frequency f is varied only by adjusting the SC clock frequency f/sub c/ without changing any element values. Experimental results show that the oscillator is stable over the oscillation frequency range from 10 /spl mu/Hz to 100 Hz. The linearity between f and f/sub c/ agrees with theoretical results. The device exhibits output voltage distortion of less than -40 dB within the frequency range from 100 /spl mu/Hz to 100 Hz. The distortion increases at frequencies below 100 /spl mu/Hz, resulting from an increase in output offset voltage. Very short rise times for stable oscillation is achieved by lowering the clock frequency after achieving stable oscillation at a higher clock frequency. Experiments and computer simulations are also discussed.<
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