Low Phase Noise G(m)-Boosted Differential Gate-to-Source Feedback Colpitts CMOS VCO

Abstract

This paper presents a g(m)-boosted differential gate-to-source feedback Colpitts (GS-Colpitts) CMOS voltage-controlled oscillator (VCO) that consumes a lower oscillation start-up current. 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 oscillator. 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-mu m CMOS for 1.78 to 1.93 GHz operation. At 1.86 GHz, the measurements show phase noise of -105 and -128 dBc/Hz (corresponding to FOM = 191.2) at offsets of 100 kHz and 1 MHz, respectively, while dissipating 1.8 mA from a 0.9-V supply.