Variable threshold scan detector utilizing crossover points on photodetectors of the laser beam to monitor the threshold

摘要

A variable threshold scan detector for use in raster output scan (ROS) systems, whereby the input scanning beam intensity is continually monitored and the threshold is set at a percentage of the signal value. Feedback from a peak detector circuit adjusts the threshold voltage to approximately 55 percent of the peak voltage. When the signal voltage exceeds the threshold voltage, the crossover circuit is enabled and a scan pulse is generated when crossover is detected. The scan detector ignores noise signals below the threshold voltage.