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Tablet for use in a coordinate digitizer

  • US 3,974,332 A
  • Filed: 03/10/1975
  • Issued: 08/10/1976
  • Est. Priority Date: 12/03/1974
  • Status: Expired due to Term
First Claim
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1. In a coordinate digitizer tablet of the type including a matrix of conductors comprised of a first group of spaced conductors disposed to define a first coordinate axis, and a second group of spaced conductors disposed to define a second coordinate axis, said first group and said second group of conductors being superposed and mutually oriented so that the conductors comprising said two groups cross to define lattice points of said matrix at the cross-over points of the respective conductors defining said matrix;

  • and means mutually electrically insulating said conductors;

    said conductors sequentially receiving in operation electrical pulses which are sensed by capacitive coupling with the matrix to indicate the position on said matrix with respect to the coordinate axes to which the capacitive coupling is made;

    the improvement which comprises;

    an electrically conductive shield layer disposed overlying said matrix and defining an electrical shield, said shield having means defining therethrough apertures positioned to expose said lattice points and dimensioned to define unshielded segments of said matrix for capacitive coupling therewith and to substantially prevent capacitive coupling with other portions of said matrix thereby to substantially prevent sensing of electrical signals applied to the respective electrical conductors defining other lattice points of said matrix;

    means electrically insulating said shield from said matrix; and

    a surface insulative layer disposed on a major surface of said shield opposite said matrix.

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