A low power consumption CMOS differential-ring VCO for a wireless sensor

This paper describes a new three-stage voltage controlled ring oscillator (VCO) based on 0.35???m standard CMOS technology. The VCO was designed for a transmitter operating in the 863?C870?MHz European band for wireless sensor applications. The transmitter is designed for binary frequency-shift keying (BFSK) modulation, communicating a maximum data rate of 20?kb/s. In addition to the VCO, the transmitter combines a BFSK modulator, an up conversion mixer, a power amplifier and an 863?C870?MHz band pass filter. The modulator uses the frequency hopping spread spectrum and it is intended for short range wireless applications, such as wireless sensor networks. The oscillation frequency of the VCO is controlled by a voltage V_CTRL. Simulation results of the fully differential VCO with positive feedback show that the estimated power consumption, at desired oscillation frequency and under a supply voltage of 3.3?V, is only 7.48?mW. The proposed VCO exhibits a phase noise lower than ?126?dBc/Hz at 10?MHz offset frequency.