A monolithic c.c.d. programmable transversal filter for analogue signal processing

This paper describes the operational features and performance of a fully-integrated programmable transversal filter (p.t.f.), using c.c.d./m.o.s.t. technology. The choice of filter architecture for a prototype realization is discussed with particular reference to a novel multiplier array implementation using a single, time-multiplexed m.o.s. transistor. The performance characteristics of a prototype, 64-point filter design based on this approach are detailed with reference to frequency- and matched- filtering. Techniques for optimizing the performance of this analogue filter structure under microprocessor control are suggested, through the iterative adaption of the filter impulse response, and equivalent results are given to show the improvement gained. An alternative technique for improving the filter characteristics which enables it to optimize the processing of signals under certain conditions has also been demonstrated. This adaptive filter configuration is based on the linear Widrow least-mean-square (W.l.m.s.) algorithm, and has been realized using the p.t.f. with minimal additional circuitry, without the requirement for a microprocessor. A general signal-processing module of 256-points using four cascaded filters is described; and results are presented when it is used in a sonar, matched-filtering experiment. Also a 64-point adaptive filter based on a prototype p.t.f. is described and its application to inverse filtering and self-tuning filtering is demonstrated. Finally, the potential of this miniature integrated filter for sonar-type applications is reviewed against new developments. In particular, a 256-point monolithic p.t.f.currently in development, and the concept of a dedicated adaptive filter in single chip form.