An Auto-Calibrated Resistive Measurement System With Low Noise Instrumentation ASIC

Abstract

Most of the resistive sensors have a large baseline resistor and a relatively small incremental change in the resistor value due to the measurand. A half-bridge-based versatile ΔR/R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> measurement system for a wide range of resistive sensors is reported in this article. A four-phase auto-calibration-based differential and ratiometric operation is used to compensate for the baseline resistance of the sensor and the mismatches due to the non-ideal circuit parameters. A low-noise application-specific current generator and low noise, high CMRR current-mode instrumentation amplifier is designed and fabricated in UMC 180-nm technology. A prototype board of the ΔR/R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> measurement system is developed and tested. The experimental results show that the proposed system is able to detect even smaller ppm level of about 72 ppm of ΔR/R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> for the base resistor R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> value as high as 0.5 MΩ with a relative error of less than ±1%. The effect of the parasitic capacitors on the sensor response is also tested experimentally. Finally, the proposed system is tested with an in-house fabricated displacement sensor.