A mixed PLL/DLL architecture for low jitter clock generation

This paper presents a mixed PLL/DLL architecture for low-jitter clock generation that merges phase-locked loop (PLL) and delay-locked loop (DLL) characteristics. It relies on an interpolator to configure the loop to operate more like a PLL or more like a DLL depending on the interpolator´s settings. The ability to vary interpolator settings enables wide range control of the clock generator´s loop bandwidth. Therefore, the loop bandwidth can readily be adjusted to accommodate different noise conditions. A discrete-time Z-domain analysis is provided to illustrate the noise filtering characteristics of the loop in the presence of various noise sources and highlight the potential advantages of the mixed PLL/DLL architecture. Simulation results verify stable operation of the loop designed for a 0.18 μm CMOS process.