An Auto-Calibrated Measurement System for 1-D Matrices of Impedimetric Sensors

Impedance measurement ICs are widely used in embedded systems for single-sensor measurements. Thereby, the impedance value of the target sensor is calculated by comparing its measurement signal with one of a given reference element. This is known as the calibration process. To automate the calibration process for multisensor measurements, multiplexers (MUXs) are recommended. But the switch on-resistances of MUXs cause additional measurement deviations, unless expensive MUXs with very low switch on-resistances or buffer functions are used. To overcome the need for specially designed MUXs, a circuit structure based on two MUXs in the feedback loop of one voltage follower is proposed in this work, with dc bias circuits. This solution is experimentally validated in a prototype system based on the AD5933 chip for a 1-D sensor matrix. Compared to the common single MUX system, the proposed approach has suppressed the average measurement deviation from 6.01% to 0.06% in the impedance magnitude measurements and from 10.75% to 0.13% for the resistive targets.