Gm- and Swing-Enhanced Colpitts VCO by Optimization of Capacitance Ratio

This letter presents a negative conductance (G_m)and swing-enhanced Colpitts voltage-controlled oscillator (VCO) based on optimization of the capacitance ratio. In the proposed VCO structure, a current source typically used in conventional VCOs is replaced with an inductor to increase the output voltage swing. A current-reuse configuration is also adopted to decrease power consumption. Theoretical analyses and simulations show that the devised VCO with an optimized capacitance ratio exhibits enhanced G_m and swing when compared to a conventional VCO. Measurements revealed a phase noise of -129.67 dBc/Hz at a 1-MHz offset frequency from the 2.2-GHz carrier, while power consumption was 2.2 mW from a 1.2-V supply voltage. This resulted in a figure-of-merit of -193.1 dBc/Hz. The proposed device was implemented using a 65-nm CMOS process.

I. Introduction

The voltage-controlled oscillator (VCO) is a crucial component in radio frequency (RF) systems. Among the various parameters to consider in VCO design, phase noise is known to be utmost importance. In general, the best phase noise performance is achieved at the maximum attainable peak amplitude. The startup time, which is inversely proportional to negative conductance (), is also an important parameter in applications such as impulse radio ultrawideband (IR-UWB) communication systems, where the VCO operates at approximately ten cycles of the carrier frequency and repetitive ON/OFF switching occurs [1].