A PLL-based eddy current displacement sensor for button applications

Abstract

This thesis presents an Eddy current sensor (ECS) for button readout applications. By employing a Phase-locked loop to perform a frequency readout, it was possible to significantly reduce the power consumption of the interface while achieving resolutions comparable to prior arts making it a more suitable solution for portable applications. The sensor achieves more than 12bit effective resolution, which translates into an equivalent displacement resolution in excess of 10nm RMS. The interface consumes less than 235µA from a 1.8V supply, achieving resolution similar to current state-of-the-art readout systems while consuming 20x less power.