AN IMPROVED LATTICE-BASED ADAPTIVE IIR NOTCH FILTER

A novel lattice-based adaptive IIR notch filter is developed which features independent tuning of the notch frequency and attenuation bandwidth. The internal structure is based on planar rotators, ensuring reliable numerical behavior and high processing rates in CORDIC environments. A simple update law eliminates the need for FIR postfilters and additional gradient filters, thus offering a simpler implementation than previously proposed designs. As opposed to minimizing an output error cost function, the algorithm is designed instead to achieve a stable associated differential equation. This results in a globally convergent unbiased frequency estimator in the single sinusoid case, independent of the notch filter bandwidth. Using a second-order structure in the multiple sinusoid case, unbiased estimation of one of the input frequencies is achieved by thinning the notch bandwidth. The tracking behavior is superior to conventional output error designs, and the estimation of extremal frequencies is less prone to overflow instability than previously reported structures. These attributes make the design suitable for numerically robust, high speed real-time applications.