Effects of transistor nonidealities on high-order log-domain ladder filter frequency responses

The nonideality studies on biquadratic log-domain filters are extended to cover high-order filter deviations. It is shown that the log-domain filter nonidealities can be classically understood as integrator magnitude and phase errors, which also bear direct relationship to the component drifts and parasitic dissipations experienced by their passive ancestors. This insight allows us to apply the well-proven LC ladder nonideality theories to our relatively unexplored log-domain regime. We quantify the high-order log-domain filter deviations due to major transistor nonidealities such as parasitic junction resistances, finite beta, and Early effect. SPICE simulations are performed to verify the results. By promoting physical understandings based on the passive ladder, effective and straightforward compensation schemes are proposed.