Multiple-input translinear element log-domain filters

Abstract

Describes the implementation of log-domain filters with multiple-input translinear elements (MITEs). Such circuit elements produce output currents that are exponential in a weighted sum of their input voltages. The author discusses the operation of the MITE building block circuit from which he constructs MITE log-domain filters. Then, he analyzes the behavior of a first-order low-pass MITE log-domain fitter, the simplest such circuit. He also presents a fully tunable second-order low-pass MITE log-domain filter with experimental measurements of a version of the second-order filter that was fabricated in a 1.2-/spl mu/m double-poly CMOS process with an npn bipolar option. The author also describes a simple procedure for synthesizing MITE log-domain filters from state-space descriptions. He can obtain such state-space descriptions from a variety of sources; the procedure described can be used regardless of the source of the description. We can often derive such descriptions conveniently from already extant filters that have been previously implemented within a different class of filters. The synthesis procedure is illustrated by deriving two simple MITE log-domain filters from single-ended voltage-mode operational transconductance amplifier C filter prototypes.