Automatic Tuning of Time Constants in Continuous-Time Delta–Sigma Modulators

We describe a digital technique for estimating and correcting time constant shifts in continuous-time delta-sigma modulators. The proposed method is based on the principle that the in-band gain and the out-of-band performance of a modulator are related. If the modulator output is denoted as v(n), we show that the variance of p(n)equivv(n)-v(n-1) is a good indicator of the modulator RC time constants. An alternative indicator, which is easier to implement in hardware is proposed. Simulation results demonstrating the effectiveness of the proposed techniques are given