EMI problems in video frame buffers design

The design of video frame buffer/graphics boards raises difficulties for EMI control, especially because the RGB video signals can't be effectively filtered on the PCB. With high resolution board (like 1920/spl times/1200/spl times/75 and above) the pixel clock is well over 200MHz and almost any filtering will adversely affect the video quality. For a dual head application, the primary video can be provided from the main card, and the secondary video from a daughter card, however the two boards are assembled as one block. Such an assembly creates supplementary EMI problems related both to the digital communications between the two boards and the specific electrical behavior of the main card-daughter card combination. This paper is an overview of the main EMI problems related to graphics boards and the typical trade-off in bandwidth and filtering, local resonances, and connector's effect.