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.