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Multi-touch sensing method

  • US 9,104,273 B1
  • Filed: 03/02/2009
  • Issued: 08/11/2015
  • Est. Priority Date: 02/29/2008
  • Status: Active Grant
First Claim
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1. An apparatus comprising:

  • a drive circuit to generate a drive signal on a first plurality of sensor elements oriented in a first direction;

    a second plurality of sensor elements oriented in a second direction, wherein intersections of the first plurality of sensor elements and the second plurality of sensor elements form a plurality of sensor locations;

    a first voltage divider coupled to a first sensor element of the second plurality of sensor elements and coupled to ground, wherein the first voltage divider is configured to decrease a first voltage at the first sensor element to a second voltage at an output of the first voltage divider;

    a second voltage divider coupled to a second sensor element of the second plurality of sensor elements and coupled to the ground, wherein the second voltage divider is configured to decrease a third voltage at the second sensor element to a fourth voltage at an output of the second voltage divider;

    a voltage subtractor comprising a first input coupled to the output of the first voltage divider and a second input coupled to the output of the second voltage divider, the voltage subtractor configured to generate a difference signal based on a difference in measured signals on the first sensor element and the second sensor element, wherein the measured signals represent mutual capacitances at the intersections of the first sensor element and the second sensor element, wherein, responsive to proximity of a conductive object closer to the first sensor element than the second element, the difference signal is a positive signal, and wherein, responsive to proximity of the conductive object closer to the second sensor element than the first element, the difference signal is a negative signal; and

    an amplitude detect circuit configured to receive the drive signal and to receive the difference signal, the amplitude detect circuit configured to reject noise in the difference signal that is out of phase with the drive signal.

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