Stability considerations in a new interface circuit for inductive position sensors

A stable electronic interface circuit for sensing small inductances is discussed in this paper. The main application is for interfacing eddy current displacement sensors. The proposed circuit has been designed and implemented in a 0.35 ¿m BiCMOS process. The frequency of the excitation signal is above 22 MHz, which eliminates the skin effect on the measurement result when using very thin targets. Oscillation stability issues along with an offset cancellation approach for the interface circuit are particularly taken into account. In this design the full-scale displacement range is 1.5 mm. Primary experimental results show that the signal to noise ratio is about 75 dB, with 240 ¿s measurement time and only 9.5 mW power dissipation.