Abstract: An optical shaft encoder has a light detector configuration that includes the function of a phase plate. The light detectors are one-half the width of a code wheel transmissive section and are arranged in groups of four so that each group corresponds to one pitch of the code wheel. The light detectors are interdigitated such that they are adjacent to one another and receive information from two channels. One light beam illuminates the four light detectors producing four electrical signals. The physical layout of the light detectors causes the output signals to be phase shifted 90.degree. from each other. These signals are combined electronically in pairs forming quadrature push pull signals.