PLL performance comparison with application to spread spectrum clock generator design

This paper presents performance, power and area comparisons of LC vs. Ring VCO-based PLL designs in order to determine the best option for high-speed spread spectrum clock generator (SSCG) designs. Analytical performance, power and area comparisons of LC versus Ring VCO-based PLL designs demonstrate that a Ring VCO can be used to meet the requirements of SATA and SAS applications at rates up to 6 Gbps. The designed SSCG operating frequency range is 2-4.25 GHz with RMS RJ jitter <1.3 and <1.5 pS for non-SSC and SSC modes, respectively, at 3 GHz. The measured EMI reduction is 18 and 21 dB for 2,300 and 4,600 ppm SSC, respectively, also at 3 GHz.