A dedicated digital unit for event recognition and centroiding in photon counting intensified CCDs

A dedicated digital electronic system for real time acquisition and processing of data arrays with input rate as high as 20 MHz is presented. The system identifies and determines the center coordinates, to sub-pixel accuracy of events produced by a photon counting intensified CCD. Each photon event is represented, on the CCD matrix, by a charge distribution of approximately Gaussian profile. Identification is performed by a morphological analysis of the event profile. A number of characteristics of the expected profile is checked by dedicated units, operating in parallel, with an internal pipeline architecture that renders it possible to produce a result every 50 ns. System operation is managed by a microprogrammable control unit. The system prototype has been implemented by means of field programmable gate arrays (FPGA).