An Ultra-Compact Differentially Tuned 6-GHz CMOS LC-VCO With Dynamic Common-Mode Feedback

A fully integrated 0.024 mm2 differentially tuned 6-GHz LC-VCO for 6+Gb/s high-speed serial (HSS) links in 90-nm bulk CMOS is presented. It is smaller than any LC-VCO reported to date at this frequency. Its size is comparable with ring oscillators but it has significantly better phase noise. A circuit technique is introduced to dynamically set the common-mode (CM) voltage of the differential varactor control signals equal to the VCO's CM. Compared to other commonly used techniques such as replica biasing, this technique does not dissipate any extra power and it accurately tracks the output common-mode voltage of the VCO during the oscillations. Using a differential control a very wide tuning range from 4.5 GHz to 7.1 GHz (45%) is achieved. The VCO has a measured phase noise of -117.7 dBc/Hz at a 3-MHz offset from a 5.63-GHz carrier while dissipating 14 mW from a 1.6-V supply.

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