Performance Consideration of MOS and Junction Diodes for Varactor Application

The engineering and tradeoffs for quality factor, capacitance tuning ratio, capacitance mismatch, and low- frequency noise for different varactor device structures, geometry sizes, and operations have been compared to provide a comprehensive guideline of an optimized structure for the advanced radio-frequency voltage-controlled oscillator (VCO). Compared with junction varactors, n+/n-well (NW) MOS varactors exhibit a higher capacitance tuning ratio (~3) and a superior capacitance mismatch (< 0.1% for a drawn size of 25 mum2). However, a noticeable low-frequency noise (~ 10-18 A2/Hz) was observed in the accumulation-mode n+/NW MOS varactors. A derived figure of merit in selecting a suitable varactor in terms of VCO's phase noise has been proposed for the first time. The measurement was performed by using the 0.18- mum 1P6M with AlCu backend wafer.

[1]  M. Tiebout,et al.  MOS varactors with n- and p-type gates and their influence on an LC-VCO in digital CMOS , 2003, IEEE J. Solid State Circuits.

[2]  T.H. Lee,et al.  Oscillator phase noise: a tutorial , 1999, IEEE Journal of Solid-State Circuits.

[3]  A. Ziel.  Noise in solid state devices and circuits , 1986 .

[4]  B. Razavi.  On the Use of MOS Varactors in RF VCO's , 2003 .

[5]  T. Melly,et al.  Design of high-Q varactors for low-power wireless applications using a standard CMOS process , 2000, IEEE Journal of Solid-State Circuits.

[6]  M.J.M. Pelgrom,et al.  Matching properties of MOS transistors , 1989 .

[7]  Roberto Saletti,et al.  Correlated fluctuations and noise spectra of tunneling and substrate currents before breakdown in thin-oxide MOS devices , 1990 .

[8]  S. Wolf,et al.  Silicon Processing for the VLSI Era , 1986 .

[9]  C. Plett,et al.  The effect of varactor nonlinearity on the phase noise of completely integrated VCOs , 2000, IEEE Journal of Solid-State Circuits.

[10]  A. Hajimiri,et al.  Design issues in CMOS differential LC oscillators , 1999, IEEE J. Solid State Circuits.

[11]  Philip C. H. Chan,et al.  A wide tuning range gated varactor , 2000, IEEE Journal of Solid-State Circuits.

[12]  P. Andreani,et al.  On the use of MOS varactors in RF VCOs , 2000, IEEE Journal of Solid-State Circuits.

[13]  M. Steyaert,et al.  A 1.8 GHz highly-tunable low-phase-noise CMOS VCO , 2000, Proceedings of the IEEE 2000 Custom Integrated Circuits Conference (Cat. No.00CH37044).

[14]  Ali Hajimiri,et al.  A noise-shifting differential Colpitts VCO , 2002, IEEE J. Solid State Circuits.