Analogue IC design using switched-currents

Most IC signal processors employ digital techniques with an analogue interface to the outside world. Frequently, the analogue interface employs switched-capacitor circuits performing A-D or D-A conversion, sample and hold, filtering etc. Unfortunately, switched-capacitors have never been compatible with VLSI processing as they invariably employ special processing options to make linear capacitors. As IC processing shrinks into the sub-micron region necessitating lower supply voltage working, switched-capacitors will suffer performance degradation. To overcome these problems `switched-currents´ were introduced about one year ago. Since then, the technique has undergone a number of developments. These include re-definition of the integrator structure to improve component sensitivity, noise, speed and linearity. Differentiator structures have also been introduced. Either integrators or differentiators may be used as building blocks for implementing signal processors using design-automation techniques. The circuits have inherent high bandwidth since they do not employ operational amplifiers. The paper will describe these recent developments which make the switched-current technique a real contender to succeed switched-capacitors in future VLSI systems