A 2.5-3.2GHz CMOS differentially-controlled continuously-tuned varactor-less LC-VCO

The design and implementation of a 2.5-3.2 GHz LC-VCO incorporating a varactor-less tuning technique is presented. The VCO´s oscillation frequency is tuned differentially by varying the effective inductance of the oscillators. Fabricated in a 0.18 mum CMOS process, the prototype VCO achieves 24% continuous tuning range without varactors. The circuit draws 7-15 mA current from a 1.8 V power supply. The measured phase noise is varying between -102 dBc/Hz and -111 dBc/Hz at 1 MHz offset across the tuning range.