A method for producing a digital video signal from an analog video signal, the analog video signal including an analog video data signal that is raster scanned in lines across a CRT screen to form consecutive frames of video information, the raster scanning controlled by use of a horizontal synchronizing...http://www.google.com/patents/US5767916?utm_source=gb-gplus-sharePatent US5767916 - Method and apparatus for automatic pixel clock phase and frequency correction in analog to digital video signal conversion 
