An LC-VCO Strongly Suppresses the AM-FM Conversion Caused by Varactor

So Bong SHIN  Sang-Gug LEE  

IEICE TRANSACTIONS on Electronics   Vol.E91-C   No.9   pp.1516-1519
Publication Date: 2008/09/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e91-c.9.1516
Print ISSN: 0916-8516
Type of Manuscript: LETTER
Category: Electronic Circuits
LC-VCO,  AM to FM conversion,  1/f noise,  varactor nonlinearity,  transformer,  CMOS,  

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A differential LC-VCO that adopts a transformer with asymmetric turns-ratio has been proposed. The asymmetric turns-ratio of the transformer leads to the suppression of the AM to FM conversion which is caused by the 1/f noise of the current source transistor. The analysis of the proposed scheme and the improvement in phase noise compare to conventional CMOS LC-VCOs are described. The transformer used in proposed VCO occupies about 430430 µm2 of silicon area while the inductor in compared conventional VCO does 390390 µm2.