Some display devices create an image by scanning a beam of varying intensity across a display surface. For example, in cathode ray tubes (CRTs), an electron beam is scanned across a surface in a row and column pattern. Further, some projection display devices scan a light beam across a surface in a row and column pattern. In these display devices, the beam intersects each pixel location as it paints the image row by row. The intensity of the scanned light beam is then modulated as it passes over each display pixel location.
Pixels are typically displayed at times specified by a “pixel clock”. The pixel clock is typically generated by phase locking the output of a voltage controlled oscillator (VCO) to a sync signal that describes the position of the scanned beam. VCOs used for this purpose are typically sensitive analog circuits that are susceptible to electromagnetic interference (EMI).