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VLSI Design
Volume 11 (2000), Issue 2, Pages 107-113

A Practical Load-optimized VCO Design for Low-jitter 5V 500 MHz Digital Phase-locked Loop

Dept. of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan

Received 5 June 1999; Accepted 1 October 1999

Copyright © 2000 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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 5.0V 500 MHz PLL which is implemented by a 0.6 um 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 that the PLL can be integrated with digital circuits.