Start of line detection and synchronization circuit for optical scanning systems

摘要

A circuit is shown for use within an optical scanning system utilizing at least two scanning beams for scanning a grating and a document. A high frequency reference signal is applied to a counter which also receives the grating signal. The grating signal is delayed by a counter to assure that the grating signal has been synchronized with the reference signal. As the scan across the document hits a reference target, a picture element signal is generated which is also applied to the counter. The counter is enabled upon receipt of a positive going signal from both the reference signal and the picture element reference signal. As the reference signal is a much higher frequency than the picture element signal, any error in misalignment between the grating whose signal is synchronized with the reference signal and the target is eliminated by the high frequency reference signal. A further delay counter within the circuit eliminates errors caused by the width of the target signal. An additional counter is utilized to assure that the scan line signal is terminated at the same point after each successive scan.