On delay structures for the analog adaptive filters with long filter taps

Adaptive filtering of the time-domain signals requires delayed versions of the input signals. For example, adaptive filter for AEC (Acoustic Echo Cancellation) often has more than 1000 filter taps to correctly model a room impulse response. In analog-domain, first-order low-pass filters as well as the mixture of first-order low-pass and all-pass filter have been implemented for the approximation of ideal delay. In this paper, we investigate the accumulated noise problems of the analog adaptive filters that occur when nonideal delay filters are cascaded for a large number of filter taps. Group delay properties of various delay networks using low-pass and band-pass delay filters are also discussed.