US Patent 7521669 Multi-bit absolute position optical encoder with reduced number of tracks

An optical encoder includes a coding element having a track with a track pattern that comprises multiple optically distinguishable sections. The optical encoder compares photodetector outputs with transition-specific thresholds that correspond to transitions between the optically distinguishable sections of the track. The comparisons are used to determine when the transition between two optically distinguishable sections of the track has passed the photodetector. Knowledge of the transition between two optically distinguishable sections is then translated into digital position information.