Dynamic Current Requirements in Single-Ended Log-Domain Filters

Abstract

Single-ended log-domain filters must operate Class A: the amplitude of any symmetric signal must be less than the bias current. Even so, peak internal dynamic current requirements can be much greater than the bias currents. Worst-case peak current demands in a second-order log-domain filter are related to modulation index by simple expressions that allow transistor geometries to be optimized for specified signal levels. Several circuit topologies are considered, and some circuit topologies are shown to be better able to supply larger internal currents than others.