Self-Dithered Digital Delta-Sigma Modulators for Fractional-N PLL

Zule XU
Jun Gyu LEE
Shoichi MASUI

IEICE TRANSACTIONS on Electronics   Vol.E94-C    No.6    pp.1065-1068
Publication Date: 2011/06/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E94.C.1065
Print ISSN: 0916-8516
Type of Manuscript: BRIEF PAPER
digital delta-sigma modulator (DDSM),  fractional-N PLL,  dither,  

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Digital delta-sigma modulators (DDSMs) applied in fractional-N frequency synthesizers suffer from spurious tones which undermine the synthesizer's spectral purity. We propose a solution featuring no hardware overhead while achieving equivalent spur elimination effect as using LFSR-dithering. This method can be implemented on MASH and single-loop DDSMs of 3rd- and 2nd-order.