Balanced log-domain filters for VHF applications

General transfer characteristics of log-domain integrators necessary to realize different log-domain filter topologies, based on LC ladder synthesis, are described. As an example, a transistor-level all-NPN differential log-domain integrator is proposed and used to implement a fully tunable balanced 600 MHz biquad. The integrator is then used to implement 4/sup th/ and 6/sup th/-order balanced bandpass filters. The sensitivity of log-domain integrators to DC biasing offsets is discussed. These offsets are minimized using a BiCMOS common mode feedback circuit. Simulation results are presented with an emphasis on distortion analysis.