Dynamic currents in log-domain filters

Single-ended log-domain filters must operate class A: the amplitude of any symmetric signal must be less than the bias current. Even so, internal dynamic current requirements can be much higher than the bias currents. Worst-case peak current demands are related to the modulation index by simple expressions that allow transistor geometries to be optimized for specified signal levels. Some circuit topologies are shown to be better able to supply large internal currents than others.