Distortion compensation in log-domain filters using state-space techniques

A new state-space method is proposed for the synthesis of "quasilog-domain" filters where the parasitic emitter resistance of transistors is built into the equation formulation. The explicit exponential maps for log domain filters are replaced with implicit exponential maps yielding nodal equations for active filters. The theory, which unifies a class of externally linear filters including log domain filters as a subset, is shown to be applicable to general higher order filters. Circuit realization is discussed, some example circuit topologies are proposed, and simulation results are offered to show the potential of the approach in improving log-domain filter performance.