Tablet digitizer with untethered stylus

Claim 1

A digitizing tablet for use with an unattached stylus instrument, comprising a piezoelectric film membrane having corners, said piezoelectric film membrane having a resistive conductive and resistive film coating on its upper and lower surface, the upper and lower surface each having separate conductive leads connected to the upper and lower surfaces respectively at each corner of the film membrane, each corner upper and lower leads being coupled via a resistance coupling in the form of a voltage divider, voltage measurement means being coupled to the upper and lower leads at each corner, said piezoelectric film membrane being deformable and having the property that when subjected to deformation that the film generates a voltage that encounters a varying resistance to leads at the corners of the film membrane depending on its location from these corners, comparison means for comparing the ratios of the voltages detected at each corner of the film for determining the relative coordinates of a pressure point provided by a stylus pressed against said piezoelectric film membrane.