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AD7150 - decreasing capacitance while objects are approaching

Question asked by maut on Jul 25, 2012
Latest reply on Jul 25, 2012 by maut

While evaluating different capacitance touch sensors I am wondering about the capacitance behavior shown on AD7150 eval board. The provided SW shows the current capacitance measured on the sensor pads. According to the equivalent circuit one would believe that an approaching object should increase the capacitance. When touching the sensor or at least almost touching it (e.g. with a piece of paper in between) the behavior is as expected and the capacitance is increasing. At greater distances the capacitance is first decreasing while approaching the sensor. Am I missing something?











If anyone should have an explanation I am curious to hear it, otherwise I will keep thinking a bit... :-)