An improved ROS driver circuit for an electrophotographic printing system includes a sub-pixel clock generator, a parallel to serial converter, and a raster output scanner (ROS) light source. The sub-pixel clock generator generates a sub-pixel clock signal that has a period less than a period of a video data clock and this clock signal is used by the parallel to serial converter to convert a parallel video data stream into a serial video data bit stream. The serial video data bit stream modulates the ROS light source to provide sub-pixel control of the light signal generated by the ROS light source.