Specification, design and synthesis of FSK filters using double- resonator monolithic crystal filter (MCF) sections

The design of filter networks with poles as well as zeros satisfying requirements simultaneously in time and frequency domain has been considered analytically by Schussler for the cases of amplitude step or impulse. This paper suggests a general computer-based procedure for designing band-pass filters optimum to a given time-domain specification in terms of step change in frequency (F.S.K.) together with the insertion loss constraints in the frequency domain. The problem of optimizing the step-frequency response subject to insertion loss constraints is reformulated as that of non-linear minimization using a known penalty function technique which converts the constrained optimization problem into a sequence of unconstrained minimisations. As an example, a two-zero, four-pole filter transfer function is optimized using this procedure and synthesized. (11 refs).