A Simple Noninverting Amplifier for Three-Wire Resistive Sensors Using a Single-Supply Ratiometric Measurement

This letter presents a simple and accurate interface circuit for three-wire resistive sensors based on a non-inverting amplifier and a two-phase ratiometric measurement technique. The circuit is excited by a single positive reference voltage, while an analog switch alternates two current paths to produce distinct steady-state output levels corresponding to different lead-wire configurations. Digital averaging of these steady-state output levels enables effective compensation of lead-wire resistance, op-amp offset, and switch on-resistance effects, with averaging performed digitally after direct ADC sampling. Experimental results demonstrate excellent linearity over the 490–3,026 Ω range, corresponding to approximately −130°C to 525°C for a Pt1000 sensor, with a maximum relative error of 0.22% and nonlinearity below 0.16% FSS. These results confirm the circuit's accuracy, simplicity, and suitability for compact, low-power resistive sensor instrumentation.