A practical load-optimized VCO design for low-jitter 5 V 500 MHz digital phase-locked loop

Abstract

In high-speed digital systems and high-resolution display devices, the jitter effect of phase-locked loops (PLL) limits the system performance. Power supply noise coupling is one of the major causes of PLL jitter problems, especially with mixed-signal systems. The paper presents a targeted 5.0 V 500 MHz PLL which is implemented by a 0.6 /spl mu/m 1P3M digital CMOS technology. The features of the proposed design include a load-optimized 3-stage VCO, a frequency limiter RC circuit, and a ratioed VCO controlling current mirror. The jitter, thus, is reduced to 72.693 ps at 600 MHz at the presence of supply noise, while the sensitivity is limited to 286.6 ps/V. This high-noise immunity design allows the PLL to be integrated with digital circuits.