Microwave, biquadratic, active-RC filter development

We present a number of computer-simulated results for a recently developed family of active-RC, microwave, biquadratic filters. These circuits are gyrator-based and contain negative second-generation current conveyors (CCII−s) realized as cascades of MMIC GaAs FETs. First, the circuit family is extended to include asymmetric band-reject filters. As with the previous circuits of the group, we use optimization to obtain an accurate frequency response when the CCII−s are implemented as cascaded pairs of GaAs FETs. Second, we illustrate how cascades of three or four devices become necessary for the CCII−s of bandpass biquads as their center frequencies are increased. Next, we show how third- and fourth-order filters may be obtained by cascading optimized lower-order sections. In our examples, the slight interaction between the stages is eliminated by adjusting a single element. Finally, we discuss the topological origins of the biquad family and consider alternative circuit structures which may possess particular practical advantages.