Analysis and compensation of log-domain biquadratic filter response deviations due to transistor nonidealities

Abstract

A translinear log-domain integrator, the powerhouse of log-domain filtering techniques, is analyzed to determine its deviations due to major time-invariant bipolar transistor imperfections, such as parasitic emitter and base resistances, finite beta, Early effect, and area mismatches. The results are used to predict the transfer function deviations of biquad filters, for both lowpass and bandpass filter responses. It will be shown that the errors can be understood and categorized into integrator scalar and negative feedback errors, and how they can be electronically compensated. SPICE simulations, both large and small-signal analysis, are performed to verify the results.