Design of eddy current sensor IC for large displacement

This article presents two types of circuits used for eddy current sensors capable of detecting objects at large distances (12mm). The first one uses an operational amplifier oscillator with positive feedback and the second one is based on a cross-coupled oscillator with negative transconductance. Both operate at a frequency of 257 kHz. Due to its advantages, such as small silicon area and low-power consumption, the second one proved to be the best solution and was chosen to be implemented in a 0.6μm CMOS technology with the chip-on-board (COB) packaging solution. Its thermal drift was analyzed for different sensing distances.