US Patent 7145371 Variable frequency generator

A digital circuit generates very precise varying clock frequencies for applications that can tolerate a small degree of jitter but require exact longer term frequencies, e.g. a video clock for a laser printer. Some subpixel jitter is acceptable, but the overall pixel rate remains exact and consistent. In some applications, the jitter may be desirable to smear the EMI spectrum. For example, if the high frequency input clock is modulated, the edges of the video clock will also be modulated yet remain within the jitter and frequency specification.