Abstract

This paper presents a drift-resilient time-based resistive sensor interface in a 0.18-mu m CMOS technology. The interface is built around only two oscillators, a phase detector, a digital filter, and a digital-to-analog converter (DAC), resulting in a simple first-order Delta-Sigma design with a predictable transfer function. The highly digital approach not only results in a small area but also implies that only a few analog circuits are sensitive to drift. The holistic drift-resilience strategy implemented combines time-based chopping and voltage-controlled oscillator (VCO) tuning to remove the dc and low-frequency errors introduced by VCO nonidealities and drift. These techniques do not introduce a significant area and power overhead. Silicon measurements show that the proposed bang-bang phase-locked loop (BBPLL)-based sensor interface exhibits ppm-level gain drift and offset drift for the entire -40 degrees C-175 degrees C temperature range while using a single-temperature calibration scheme and no external accurate references nor components for this drift stability. The interface provides a 15-effective number of bits conversion for a 100-ms conversion time and consumes 3.41 mW of power and occupies only 0.23 mm(2) of the active area.