Sigma-Delta Approach in Direct Interface Circuits for Readout of Resistive Sensors

The simplest versions of direct interface circuits (DICs) allow resistive sensors to be read with reasonable accuracy, along with reduced acquisition time and energy consumption. However, the options available to the designer in terms of modifying the values of previous figures of merit are very limited. Indeed, the only possibility is to modify the value of the capacitor used in the DIC. This article proposes a new readout method that can improve performance using the same circuits as several DICs present in the literature and the well-known sigma-delta (Sigma-Delta) technique. This would give the designer greater flexibility by allowing a tradeoff between accuracy, acquisition time, and energy consumption through two design parameters, M and N. M selects the number of measurements needed to obtain an estimate, while N is related to the charging time of the capacitor used. Experimental results show that the new Sigma-Delta DICs can improve on the performance of their conventional counterparts. It is also possible to find some combinations of M and N that simultaneously improve all figures of merit. The number of M and N combinations that achieve these improvements increases significantly if the calibration, necessary in the DICs, can be carried out sporadically.