AUTOMATIC TUNING LOW-PASS NOTCH FILTER

An automatic tuning low frequency LC low-pass notch filter is developed. The generalized immittance converter (GIC) is used as a tunable inductor.The notch frequency of the filter can track the control frequency (the frequency of power supply or interference voltage) automatically. This filter can be used to eliminate the power supply noise and to prevent the preamplifier of measurement or data aquisition system from saturating caused by the power supply interference. Experimental results show that the frequency tracking error is less that 0.5Hz in the range from 45Hz to 55Hz, and the notch depth of the filter, i.e. series mode rejection ratio, is 30-40 dB.