An RC Time Constant Auto-Tuning Structure for High Linearity Continuous-Time<tex>$SigmaDelta$</tex>Modulators and Active Filters

TLDR

The paper proposes an automatic RC time‑constant tuning scheme for high‑linearity continuous‑time g_m‑C and active RC circuits operating at low power. The scheme tunes the RC constant by discretely varying integration capacitors using an analog integrator, voltage comparator, and digital tuning engine that generates a control word to set on‑chip capacitors, achieving ±2–10 % accuracy and implemented in a 0.5‑µm CMOS test chip. Experimental results show a peak S/(N+D) of 83 dB and a tuning range exceeding ±40 %.

Abstract

An automatic RC time constant tuning scheme is proposed for high linearity continuous-time g/sub m/-C and active RC circuits in a low power consumption environment. Instead of changing the g/sub m/ (in g/sub m/-C filters), the RC time constant is tuned by discretely varying the integration capacitors to preserve a high linearity. The auto-tuning circuit, consisting of an analog integrator, a voltage comparator, and a digital tuning engine, generates a control word and sets on-chip capacitors to obtain an RC time-constant accuracy of /spl plusmn/2-10%. The proposed scheme is verified by the experimental results of a test chip in a 0.5 /spl mu/m CMOS technology. It achieves a peak S/(N+D) of 83 dB while a tuning range of over /spl plusmn/40% is accomplished.