A new CMOS VCO topology with capacitive degeneration and transformer feedback

This paper presents a new voltage controlled oscillator (VCO) topology for radio frequency operation. The low phase noise differential CMOS VCO uses capacitive degeneration and transformer coupling between the gate and source of the negative conductance transistor. An on chip transformer in positive feedback is used to increase the voltage swing in resonator and to improve the phase noise. The VCO is tunable from 2.85 GHz to 3.35 GHz with 16% tuning range, and has been fabricated with 0.18um CMOS technology. The measured phase noise at 1 MHz offset is -119 dBc/Hz at the operation frequency of 3 GHz. The circuit draws 10 mA from a 1.8V supply.