Developments in switched-current filter design

Current domain sampled-data techniques are receiving considerable attention, finding application in both general signal processing and A-D/D-A conversion. Potentially, current domain operation offers greater ease for algebraic manipulation of signals, lower voltage operation and simpler IC processing than voltage domain operation (i.e. switched-capacitors). A family of switched-current integrator cells for building larger systems, e.g. filters, was described by Hughes et al. (see IEEE International Symposium on Circuits and Systems, p.1584 (1989)) and was developed subsequently by Hughes et al. (see IEE Proceedings Part G, no.2 (1990)) into a circuit configuration for a universal integrator. This performed an identical algorithm to a well known switched-capacitor counterpart, and could be used to map known switched-capacitor filter structures into equivalent switched-current arrangements. In the paper, some shortcomings of that circuit configuration are discussed and an improved integrator configuration is proposed