Continuous-time analog CMOS circuits are being developed to realize infinite-impulse-response (IIR) adaptive filters that were recently developed. These structures are all based on notch biquads that have good sensitivity properties and are easy to adapt while guaranteeing that the filter is stable. Previous research has concentrated on the theoretical analysis of these structure, where global convergence was proved and it was shown the structures have very small biases. he future research will focus on the development of the adaptive filters for practical applications. These include FM demodulators, frequency- assisted phase-locked-loops and Costas-loops, carrier and clock- extraction circuits, efficient channel-banks for spectral analysis and periodic noise cancellation circuits, to name only a few. In many ways, these new circuits represent a generalization of the phase-locked-loop to the multi-sinusoidal case. As such, they will be the first ever analog circuits capable of isolating individual sinusoids having unknown frequencies from a multisinusoidal input signal, in real- time.
