Design and Investigation of a Self-Tuning Circuit for Integrated Active-RC Filter

In this article, an integrated filter’s self-tuning circuit based on time-constant detection for series- and parallel-connected resistor banks (SPRB) with discrete-step control is investigated and validated. Process, voltage and temperature compensation using SPRB structures can greatly reduce the layout area of the resistor tuning bank, while maintaining the same tuning range and maximum control step compared to the more classic structures of the tuning banks, such as series, parallel or R-2R. The proposed self-tuning circuit implements a two-step search approach and signal delay compensation to achieve precise tuning results for the filter using SPRB structure. Mean value of bandwidth variation equal to 1.4% is achieved at all process corners and temperatures ranging from −40°C to 80°C. The self-tuning circuit was validated with a reconfigurable 6th order low-pass filter, and designed using 65nm CMOS process, while using a 1.2 V supply.