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Capacitive position sensor system

  • US 9,977,061 B2
  • Filed: 09/26/2013
  • Issued: 05/22/2018
  • Est. Priority Date: 10/02/2012
  • Status: Active Grant
First Claim
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1. A capacitive position sensor system for determining the position of an object, in particular on a surface of a contactless smartcard, wherein the object is positioned within a sensitive area of the capacitive position sensor system and changes the capacitance of sensing capacitors being arranged underneath the object, the capacitive position sensor system comprisinga set of sensing elements being arranged in the form of a column, each sensing element comprising a first sensing capacitor having a first electrode and a second electrode and a second sensing capacitor having a first electrode and a second electrode, wherein each first electrode is coupled via a switch to a voltage supply to form a switched capacitor filter, wherein the second electrodes of the first sensing capacitors are coupled to form a first sensing line and the second electrodes of the second sensing capacitors are coupled to form a second sensing line, wherein the electrodes of the first and second sensing capacitors are configured relative to a substrate such that a human finger in close proximity to the substrate causes distortion of a fringe field,a sensing unit, wherein the sensing unit is adapted to sense a voltage level representing the amount of charge being present on the first sensing line and the second sensing line, anda control unit, wherein the control unit is adapted to apply a drive signal to each of the switches being coupled to the first electrodes,wherein a specific sensor position weighting factor is assigned to each sensing capacitor, wherein the capacitances of the first and the second sensing capacitor of one sensing element corresponds to a constant capacitance value, wherein the first sensing capacitors of the set of sensing elements are weighted with sensor position weighting factors that increase relative to each other in one direction along the column and the second sensing capacitors of this set of sensing elements are weighted with sensor position weighting factors that decrease relative to each other in the same direction along the column, wherein the sensor position weighting factor assigned to each sensing capacitor is a multiplier that is a function of the distance of the corresponding sensing capacitor from an origin,wherein the control unit is adapted to, in one integration cycle, close a part of the switches being coupled to the first electrodes so that a part of the first sensing capacitors is driven by a first drive signal and close a part of the switches being coupled to the second electrodes so that a part of the second sensing capacitors is driven by a second drive signal, wherein the sensing unit is adapted to sense the voltage level representing the sum of the amount of charge of the part of the first sensing capacitors and the voltage level representing the sum of the amount of charge of the part of the second sensing capacitors,wherein the control unit is adapted to determine the position of the object in one dimension by analyzing the results of a plurality of sensed voltage levels for the first sensing capacitors and the second sensing capacitors of a plurality of integration cycles, wherein analyzing the results of a plurality of sensed voltage levels comprises multiplying the sensor position weighting factor assigned to a sensing capacitor by a value corresponding to the sensed voltage level of the corresponding sensing capacitor and using the product of the multiplication to determine the position of the object.

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