Integrated analog sensor for automatic alignment

Currently many optical alignment systems use digital signal and image processing to detect an alignment marking and compute misalignment. These methods work well, but their speed is limited by the large amount of data in a two-dimensional image that must be acquired, transmitted, and processed to extract the alignment error. The alignment sensor with on-chip analog signal processing presented in this paper improves alignment speed. The sensor uses photodiodes to detect the misalignnent of an image of a surveyor´s mark. The integrated circuitry combines and amplifies the photocurrents to create output currents proportional to alignment error and independent of illumination level.