An Improved Direct Digital Converter for Bridge-Connected Resistive Sensors

TLDR: In this article, an improved direct digital converter (IDDC) suitable for bridge-connected resistive sensors is presented, where the input stage of a dual-slope analog-to-digital converter is altered to accommodate a resistive sensor bridge, as its integral part and the logic of conversion incorporate automatic compensation for offset, offset drift and gain errors.

Abstract: An improved direct digital converter (IDDC) suitable for bridge-connected resistive sensors is presented in this paper. The input stage of a dual-slope analog-to-digital converter is altered to accommodate a resistive sensor bridge, as its integral part and the logic of conversion incorporate automatic compensation for offset, offset drift, and gain errors. Through a detailed error analysis of the DDC presented earlier, the effects of the non-ideal characteristics of practical components on the performance of the DDC are quantified. From the analysis, it is determined that mismatch between the bridge elements and the input offset of op-amps significantly affect the output. While the earlier version of the DDC requires offline correction for offset and gain errors, the proposed IDDC provides in situ correction for these and hence can also compensate drifts. Simulation studies and experimental results demonstrate the practicality of the proffered scheme and indicate that the worst case error of ±0.2% due to offset in op-amps and mismatch in nominal resistances of sensing elements reduces to ±0.05% with the use of the proposed compensation technique.