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Fingerprint sensor employing an integrated noise rejection structure

  • US 9,779,280 B2
  • Filed: 12/24/2014
  • Issued: 10/03/2017
  • Est. Priority Date: 12/24/2014
  • Status: Active Grant
First Claim
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1. A fingerprint sensor system, comprising:

  • a plurality of substantially parallel drive lines;

    a plurality of substantially parallel pickup lines oriented transversely to the plurality of drive lines;

    an insulating layer separating the plurality of pickup lines from the plurality of drive lines;

    a plurality of electrode pairs, each electrode pair being defined at a location where a pickup line crosses a drive line, wherein each electrode pair has an impedance that is sensitive to an object contacting or in close proximity to the electrode pair;

    one or more reference pickup line(s) oriented substantially parallel with the plurality of pickup lines;

    one or more compensation drive line(s) oriented substantially parallel with the drive lines and crossing the pickup lines and the reference pickup line(s) to capacitively couple the compensation drive line(s) into the pickup lines and the reference pickup line(s);

    a reference pickup drive line crossing the reference pickup line to capacitively couple the reference pickup line and the reference pickup drive line;

    wherein each electrode pair has a first impedance when no object is contacting or in close proximity to the electrode pair and wherein the drive lines, the pickup lines, the reference pickup line, the compensation drive line, and the reference pickup drive line are configured such that a second impedance between the compensation drive line and a crossing pickup line, a third impedance between the reference pickup line and a crossing reference pickup drive line, and a fourth impedance between the compensation drive line and the reference pickup line are equal to the first impedance;

    a signal source configured to provide a first signal to one of the drive lines and the reference pickup drive line and to provide a second signal to the compensation drive line, where the second signal is a fixed reference amplitude phase inverted relative to the first signal; and

    a differential amplifier having a first input, a second input, and an output, wherein the first input is connected to a pickup line, the second input is connected to one or more of the reference pickup line(s), and the output of the differential amplifier is indicative of the presence of ridge and valley features of a finger contacting or in close proximity to one or more of the electrode pairs.

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