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HighQ MOS Varactor Models for QuasiMillimeterWave LowNoise LCVCOs
Yuka ITANO Shotaro MORIMOTO Sadayuki YOSHITOMI Nobuyuki ITOH
Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences
Vol.E97A
No.3
pp.759767 Publication Date: 2014/03/01 Online ISSN: 17451337
DOI: 10.1587/transfun.E97.A.759 Print ISSN: 09168508 Type of Manuscript: Special Section PAPER (Special Section on Analog Circuit Techniques and Related Topics) Category: Keyword: MOS varactor, quasimillimeter wave, modeling, LCVCO,
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Summary:
This paper presents the strategy of MOS varactor's highQ optimization, a novel scalable model for the quasimillimeterwave MOS varactors, and confirmation results by discrete MOS varactors and VCO measurements. To realize a highQ MOS varactor in the quasimillimeterwave region, low MOS varactor capacitance and low series resistance of unit cell are essential. Downsizing is a key to realize both low capacitance and low resistance. However, it is induced by C_{max}/C_{min} reduction, simultaneously. Therefore, scalable MOS varactor model is necessary to use optimum MOS varactor to cover various application requirements using same process. Decreasing the MOS varactor's size of W/L =2µm/2µm to 0.5µm/0.26µm, the Q factor increased sevenfold at f =20GHz but C_{max}/C_{min} is reduced by 60%, by using conventional PSP model, an error of approximately 20% is shown. Proposed model has been improved its accuracy from 18.9% to 0.2% for N^{+} MOS varactor and from 22.1% to 0.8% for P^{+} MOS varactor, for minimum size of MOS varactor even if model covers wide dimension range. Also, it has been confirmed this model is covered in two types of layouts. Oscillation frequency and phase noise also have been confirmed by three types of 22GHz VCOs. The accuracy of oscillation frequency is less than 2.5% and that of phase noise at 1MHz offset from carrier is less than 5dB.

