Dithered timing spread spectrum clock generation for reduction of electromagnetic radiated emission from high-speed digital system

In modern digital systems, the most amount of radiation from the system is caused by the high-speed digital clock signal. As a method to reduce the electromagnetic radiation from the system clock, a spread spectrum clock technique that modulates the system clock frequency had been introduced. The conventional spread spectrum clock is realized by controlling the period or the frequency using a phase locked loop. Because of the inherent jitter of the phase locked loop, the attenuation of the spectrum decreased and the realization is very difficult at the higher clock frequency near the GHz. In this paper, the authors propose a dithered timing spread spectrum clock. The proposed dithered timing spread spectrum clock is realized by controlling the transition timing-difference using a delayer. The proposed dithered timing spread spectrum clock has more effective suppression of the electromagnetic radiation from the high-speed digital system than the conventional spread spectrum clock.