An Auto-Calibrated Resistive Measurement System With Low Noise Instrumentation ASIC
Meraj Ahmad, Shahid Malik, Sourya Dewan, A. K. Bose, Dinesh Maddipatla, Binu B. Narakathu, Massood Z. Atashbar, Maryam Shojaei Baghini
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.