Adjustable video/raster phasing for horizontal deflection system

Abstract

Adjustment and maintenance of a phase relationship between a video signal and a scan synchronizing signal to assure proper horizontal centering is provided in a horizontal deflection system. A first phase locked loop generates a first timing signal at a first frequency, synchronously with a horizontal synchronizing component in a video signal. A presettable counting circuit operates synchronously with the first timing signal for dividing a clock signal to generate a second timing signal at a second frequency. A second phase locked loop generates a scan synchronizing signal from the second timing signal. A microprocessor may supply different numbers to a register, the output of the register being coupled to the presettable counting circuit. Different numbers change the relative phase between the first and second timing signals by incremental steps. The microprocessor monitors a video source selection switch to gate one of alternative video sources as a video and synchronizing signal output and adjusts the relative phase between the horizontal synchronizing component of the selected video source and a synchronous timing signal by a factor appropriate for the selected video source. A manually operable circuit may be coupled in a feedback path of the second phase locked loop for adjusting the relative phase between the second timing signal and the scan synchronizing signal, over a range corresponding to an incremental step.