On the structure, performance, and application to modem timing recovery of recursive all-pass filters with adjustable equal-ripple group-delay

A digitally controlled sampled data delay line is implemented with recursive all-pass filter sections. This is in marked contrast to the standard implementation of programmable time delays that use fixed non-recursive polyphase stages or adjustable Farrow FIR filters. The recursive filter exhibits an equal-ripple approximation to constant group delay. The phase slope is programmable to present a continuously variable time delay network. Applications of a continuously adjustable, linear-time delay structure offers unique signal processing options to address various communication system tasks. These include timing recovery in DSP based receivers, adaptive beamforming and steering, communication systems channel modeling, and reverberation modeling in acoustic chambers and instruments.