Low Phase Noise G/109-Boosted Differential Gate-to-Source Feedback Colpitts CMOS VCO Jong-Phil Hong, Student Member , IEEE

Abstract

This paper presents a -boosted differential gate-to- source feedback Colpitts (GS-Colpitts) CMOS voltage-controlled oscillator (VCO) that consumes a lower oscillation start-up cur- rent. The proposed architecture allows a wider range of saturation mode operation for the switching transistors, which helps suppress AM-to-FM conversion by these transistors. In addition, the phase noise contribution of the flicker noise in the switching transistor is reduced through the capacitor feedback network of the Colpitts os- cillator. As a result, the proposed topology can achieve better phase noise performance and a higher figure of merit (FOM) compared to a conventional NMOS-only cross-coupled VCO. The proposed VCO is implemented in a 0.18- m CMOS for 1.78 to 1.93 GHz op- eration. At 1.86 GHz, the measurements show phase noise of 105 and 128 dBc/Hz (corresponding to /70/79/77 /61 /49/57/49 /50) at offsets of 100 kHz and 1 MHz, respectively, while dissipating 1.8 mA from a 0.9-V supply.