Resistively variable capacitors using general impedance convertors

The use of general impedance convertors (GICs) for the realisation of resistively variable capacitors (RVCs) is demonstrated. Such elements are useful in analogue-adaptive circuits and for neural networks. Various design concepts have been examined with the aim of finding configurations that are suitable for discrete, and complete, or partial VLSI realisation. A number of useful circuit topologies have been found. Design guidelines are given; simulations and experimental results are compared. The resulting circuits are being considered for use in adaptive telephone hybrid networks for high-speed full-duplex data transmission.