Instrumentation Amplifier Based Linearizing Front-End for Differential Inductive Sensors With Polynomial Transfer Equation

This paper introduces a simple and efficient linearizing instrumentation amplifier (LIA) for processing differential inductive sensors (DIS) with polynomial characteristics. The proposed circuitry employs a unique, low-complexity instrumentation amplifier (IA) based design that eliminates the need for a separate linearizer circuit in the subsequent signal conditioning chain. The circuit features a novel topology combining a classical IA with dual multipliers. The IA inputs are connected to the nonlinear signals from the DIS, while its reference terminal is linked to the feedback voltage from the multiplier stage. The mathematical methodology that shows the ability of the LIA to perform inverse polynomial synthesis is established in the paper. Furthermore, an LIA-based application circuit for LVDT processing is discussed. The performance of the LIA is evaluated using a practical LVDT module. Experimental tests of the LIA-LVDT system demonstrate a nonlinearity (NL) of 0.93 % over a 100 mm span, representing a six-fold improvement in NL compared to the inherent NL of the LVDT. The signal-to-noise ratio of the hardware LIA model was found to exceed 61 dB. This proposed scheme shows significant potential for applications in aerospace and other industries to enhance the linearity and range of DIS topologies.