Dual-Range Multimode Signal Conditioning Circuits for Resistive Sensors

Wheatstone bridges are the most prominent interface circuits for converting dynamic resistance to voltage. However, conventional voltage bridges are prone to numerous issues, limiting their inclusion in wide-range resistance measurement applications. Primarily, conventional Wheatstone bridges demonstrate a non-linear voltage output, resulting in heightened errors for wide-range resistance measurements. Furthermore, achieving the null condition requires tuning of three reference resistors, and any mismatch in these reference resistors increases the measurement error. This article introduces a bipolar current-excited autobalancing-based resistance measurement circuit with dual-range and programmable sensitivity, designed to enhance range and reduce errors associated with conventional bridges. The proposed circuit seamlessly accommodates floating and grounded resistive sensors. The measurement circuit demonstrates workability within a range of 306 Ω to 1.3 MΩ for floating resistive sensors and 1.5 kΩ to 1.2 MΩ for grounded resistive sensors. The worst-case relative error for the floating sensor is 1.4%, and 1.2% for grounded sensors, demonstrating precision across a wide spectrum of resistance values. The fabricated prototype is tested with a commercial force-sensing resistor and a light-dependent resistor. The worst-case relative errors for these are found to be -0.43% and 0.57%, respectively.