Improved switched tuning of differential CMOS VCOs

Varactors for continuous frequency tuning are typically used in LC-oscillators. However, they have some drawbacks for large tuning ranges, such as high tuning sensitivity causing high sensitivity to noise and disturbances on the control voltage. Furthermore, large metal-oxide-semiconductor (MOS) varactors have high conversion of harmless amplitude noise into harmful phase noise. To reduce these problems a small varactor can be used in combination with MOS-transistors that switch fixed capacitors in and out of the oscillator. The limitations due to the imperfect complementary metal-oxide-semiconductor (CMOS) switches are investigated, and an improved structure for use with the popular differential CMOS LC-oscillator is presented.

[1]  F. Torrisi,et al.  Impact of indirect stability on phase noise performance of fully–integrated LC tuned VCOs , 1999, Proceedings of the 25th European Solid-State Circuits Conference.

[2]  E. Hegazi,et al.  23.4 A Filtering Technique to Lower Oscillator Phase Noise , 2008 .

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

[4]  Asad A. Abidi,et al.  RF-CMOS oscillators with switched tuning , 1998, Proceedings of the IEEE 1998 Custom Integrated Circuits Conference (Cat. No.98CH36143).

[5]  A.A. Abidi,et al.  A broad-band tunable CMOS channel-select filter for a low-IF wireless receiver , 1999, IEEE Journal of Solid-State Circuits.