Enhancing dynamic range in differential log-domain filters based on the two-filters approach

The "two filter" method for designing differential log-domain filters does not allow true class AB operation of filters having complex poles. However, differential log-domain filter structures that pass DC offsets from the input current splitter to each internal state variable can operate linearly to fairly high output modulation indices. New low-V/sub DD/ translinear current-splitter circuits are presented, including a harmonic-mean splitter, which produces increased DC offsets compared to geometric-mean circuits. The increased offsets are shown to allow significant increases in the range of indiscrete signals in differential log-domain filters with appropriate structures.