A 350 mV, 5 GHz class-D enhanced swing quadrature VCO in 65 nm CMOS with 198.3 dBc/Hz FoM

A new enhanced swing class-D quadrature VCO which operates from a supply voltage as low as 350 mV is presented. The prototype 5 GHz VCO was fabricated in a 65 nm RF CMOS process. The measured phase noise performance is -137.1 dBc/Hz at 3 MHz offset with a power dissipation of 2.1 mW from a 0.35 V supply. The resulting figure-of-merit (FoM) is 198.3 dBc/Hz. Compared to prior CMOS LC VCO designs, the proposed enhanced swing quadrature VCO achieves the best FoM to date at the lowest supply voltage.

I. Introduction

Wireless sensor networks (WSN) have been an important area of interest during recent years. WSN s usually contain numerous independent sensor nodes that power themselves from energy harvesters such as thermoelectric or piezoelectric generators. Energy harvesters usually produce low voltage outputs, necessitating the use of circuits that can operate below 0.5V. The design of RF circuits that can operate in this voltage range is challenging. Most transceivers require a VCO with low phase noise performance, which is difficult to obtain when the output swing is constrained by a low supply voltage. Swing enhancement techniques are needed to increase the oscillation amplitude [1] and improve the phase noise performance.