A Spread-Spectrum Clock Generator Using Fractional-N PLL with an Extended Range ΣΔ Modulator

Yi-Bin HSIEH  Yao-Huang KAO  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E89-C   No.6   pp.851-857
Publication Date: 2006/06/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e89-c.6.851
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Integrated Electronics
Keyword: 
spread spectrum,  ΣΔ modulator,  phase-locked loop,  fractional-N,  

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Summary: 
A spread-spectrum clock generator (SSCG) using fractional-N phase-locked loop (PLL) with an extended range sigma-delta (ΣΔ) modulator is presented in this paper. The proposed ΣΔ modulator simply adds an extra output bit in the first stage modulator. It can enlarge the input range about three times as compared to the conventional modulator and solve the saturation problem when the input exceeds the boundary of the conventional modulator. A flexible digital modulation controller can generate center and down spread-spectrum modulation and each has spread ratios of 0.4%, 0.8%, 1.6% and 3.2%. The proposed SSCG has been fabricated in TSMC 0.35-µm double-poly quadruple-metal CMOS process with output frequency of 300 MHz. The active area is 0.630.62 mm2 and the power consumption is 17.5 mW.