PROLOG-based active filter synthesis

The author deals with the novel active filter synthesis method based on generating suitable filter structures by a PROLOG interpreter. Synthesis is organized as a PROLOG program searching for filter structure which satisfies desired input specifications (constraints). Applied PROLOG processing uses symbolic equation transformations to obtain proper filter transfer characteristics, to determine the kind of components and symbolic expressions for polynomial coefficients or desired parameters (for instance quality factor or sensitivities for parasitic elements). The presented synthesis methodology has been developed for filter structures using operational transconductance amplifiers and capacitors only to realize tunable active-C filters without resistors in follow the leader feedback (FLF) and inverse follow the leader feedback (IFLF) structures. The program has been implemented in Turbo PROLOG on an IBM PC/AT computer. An example is presented