Patent ID: 7265339

Claim:
An interpolating detector for generating a position signal indicating a change in the relative position of a code pattern comprising alternating light and dark stripes, said interpolating detector comprising: a photodiode array comprising a plurality of sets of photodetectors, each set labeled with an index i that runs from 0 to N, said i th set comprising photodiodes that generate four signals: A i =O i +F i sin( x ), B i =O i +F i cos( x ) A i ′=O i −F i sin( x ), and B i ′=O i −F i cos( x ), when said code pattern moves across said photodiode array, wherein F i and O i are constants and x denotes a relative position of said code pattern with respect to said interpolating detector, x changing by 2π when said code pattern moves a distance equal to the width of one light stripe and one dark stripe, and wherein N>2; an interpolation function generator that generates first and second interpolation functions, I 1 (x)=f1cos(x) and I 2 (x)=f2sin(x), respectively, from said photodiode signals wherein f1 and f2 are constants; a detector function generator that generates 4 detector signals, D 1 (x)-D 4 (x), from said photodiode signals, D 1 (x) and D 3 (x) being proportional to sin(x) and −sin(x), respectively, and D 2 (x) and D 4 (x) being proportional to cos(x) and −cos(x), respectively; and a cross-point detector that generates a transition signal when I 1 (x) crosses D 1 or D 3 or when I 2 (x) crosses D 2 or D 4 , wherein said photodiodes have active areas having a shape such that said x values at which said interpolation signals cross said detector signals occur at integer multiples of 2π/m, for m greater than 4.