Sigma delta ADC with a dynamic reference for accurate temperature and voltage sensing

A second-order sigma-delta analog-to-digital converter (ADC) with 12-bit absolute accuracy has been designed using a 0.7 mum CMOS technology. The ADC is part of a temperature sensor, and they both share a dynamic band-gap reference voltage, which is trimmed at room temperature. By using precision techniques such as chopping, correlated double-sampling and dynamic element matching, this reference voltage has a temperature coefficient of 3.5 ppm/degC over the range -40degC to 125degC. Its curvature error is corrected at the system level by means of a look-up-table-driven feedback loop. The result is an accurate temperature sensor with, in addition, accurate voltage sensing capability. The ADC´s input dynamic range extends from 0 to V_DD, for V_DD ranging from 2.5 V to 5.5 V. The chip has an active area of 4.9 mm², and a current consumption of 85 muA.