An adaptive analog continuous-time CMOS biquadratic filter

An adaptive analog continuous-time biquadratic filter is realized in a 2- mu m digital CMOS process for operation at 300 kHz. The biquad implements the notch, bandpass, and lowpass transfer functions. The update method is based on a LMS algorithm which adapts the notch frequency to minimize the power at the notch filter output. Applications include FM demodulators (linear and frequency shift keying), clock extractors, and frequency acquisition aids for phase-locked loops and Costas loops. Measured results from experimental prototypes are presented.<<ETX>>