Digitizer with serpentine conductor grid having non-uniform repeat

Abstract

Disclosed herein are position determining apparatus and conductor structures or grids therefor. The conductor structure for each axis includes a number of conductors, at least one of which is run in a serpentine path with a non-uniform repeat increment. The repeat increment, which is the spacing between one run and the next of the same serpentine conductor, is constrained by a maximum repeat increment, or a minimum repeat increment, or a maximum change in repeat increments between consecutive runs of a same conductor, or combinations thereof. In the preferred embodiments, there is at least a constraint on the maximum repeat increment to provide noise immunity. The conductors are arranged for each axis of the grid in a pattern such that signals obtained for that axis may be processed to provide binary members in a Gray-type code each unique to a small region of the active area in which the coil center is located. The small region for a given axis corresponds to the space between two immediately adjacent, active conductor portions for that axis, with a possible ambiguity of one space. Smal regions in each axis define the coarse location of the coil center. Fine location within a region may be determined from the magnitudes of currents induced in selected runs by interpolation, or from the phase relationship of current induced in selected runs.