Analysis of Phase Noise Degradation Considering Switch Transistor Capacitances for CMOS Voltage Controlled Oscillators

Shoichi HARA
Kenichi OKADA

IEICE TRANSACTIONS on Electronics   Vol.E93-C    No.6    pp.777-784
Publication Date: 2010/06/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E93.C.777
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuits and Related SoC Integration Technologies)
CMOS,  VCO,  inductor,  phase noise,  quality factor,  multiple divide,  switched capacitor,  

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In this paper we present a study on the design optimization of voltage-controlled oscillators. The phase noise of LC-type oscillators is basically limited by the quality factor of inductors. It has been experimentally shown that higher-Q inductors can be achieved at higher frequencies while the oscillation frequency is limited by parasitic capacitances. In this paper, the minimum transistor size and the degradation of the quality factor caused by a switched-capacitor array are analytically estimated, and the maximum oscillation frequency of VCOs is also derived from an equivalent circuit by considering parasitic capacitances. According to the analytical evaluation, the phase noise of a VCO using a 65 nm CMOS is 2 dB better than that of a 180 nm CMOS.