Spread spectrum clocking for emission reduction of charge pump applications

Spread spectrum clock generation (SSCG) techniques are widely used in digital systems as the digital clock signals are considered as one of the major sources for conducted and radiated electromagnetic emission. Although spread spectrum techniques can nowadays be found in many clocked digital system, they are rarely found in clock signals for automotive power systems such as power switches or bridges. In this paper the ability of using SSCG techniques for automotive charge pump applications is investigated. It is shown how this technique can be used to reduce the electromagnetic emission that is caused by the high frequency switching activity of charge pumps. Additionally the assets and drawbacks when using this technique are explained. Based on conducted electromagnetic emission measurements of a charge pump EMC test chip it is shown how typical spread spectrum parameters like frequency deviation, modulation frequency and modulation signal can be optimized in order to maximize the electromagnetic emission reduction in certain frequency ranges.