Transistor-only frequency-selective circuits

The possibility of implementing frequency-selective circuits using only MOS transistors is considered. The advantages of such circuits are small chip area, good matching properties for individual elements, a potential for very high frequency of operation, and suitability for fabrication using standard digital VLSI processes. Disadvantages include the implementation of automatic tuning schemes that reliably eliminate unpredictabilities and variations, device modeling difficulties of common simulators, and nonlinearity cancellation. A procedure for the topology development of filters in which transistors are used as URC elements is presented together with a technique which uses transistors as capacitors, along with first-order correction for the nonidealities of such `capacitors´ and of the active elements. Measured results from three experimental chips are reported in the 1-100-MHz range