Distance measurement with capacitive sensor

摘要

Circuits and methods to read out capacitive sensors for distance measurement used by a position control system having a high accuracy and low noise have been disclosed. The ratio or difference of the capacitances of two sensor capacitors is used to determine the distance of an object from a target position. A sense amplifier is using auto-zero methods to achieve a long term stability. A sample-and-hold circuit using double correlated sampling methods minimizes noise. Low cost capacitors can be used with the sample-and-hold circuit because not the absolute value of capacitances but only the ratio of capacitances are relevant. A high resolution is ensured also by significant over-sampling of the control loop.