3-D Depth Finding Imager with Digital Readout

The objective of the project is the design of an imager chip for laser-scanned 3-D depth/range finding. The project is divided into two modules: Pixel Array/Centroid Detection and Analog-to-Digital Conversion (ADC). The pixel array/centroid detector tracks the centroid of the laser beam as its scans the object while the ADC converts the analog out
3-D Depth Finding Imager with Digital Readout - schematic

put of the centroid into digital format. The conversion into digital ensures that the result is readily available for further processing in the digital domain. The pixel array/centroid detector is described first. The pixel and centroid system works in the following way. A laser is scanned across an object continuously in the vertical direction and discretely in the horizontal direction. The laser beam reflects off the surface of the target. Because the imager observes the object from a different angle than that of the laser source, the surface depth is recorded as a horizontal deflection of the projected laser beam. The figure below illustrates the system overview. As the laser illuminates more than a single pixel, a distribution of the incident light intensity is recorded on the imager. The discrete distribution is observed as photocurrents along columns of pixels of the imager. If we were to just use a winner-takes-all decision circuit to extract the horizontal deflection of the laser beam, we would be getting single pixel accuracy. By finding the center of this distribution we find our deflection value with sub-pixel accuracy. Only deflections in one axis are recorded and used. Therefore there is no need for a full N x N array of photo pixels. At the same time, the decision circuit will require that all the pixel output currents in a single column be summed together. Rather than summing the pixel outputs, a single large...

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