A temperature-compensated CMOS LC-VCO enabling the direct modulation architecture in 2.4GHz GFSK transmitter

The frequency drift of an open-loop PLL is an issue for direct modulation applications such as Bluetooth transceivers. The drift mainly comes from the temperature variation of the VCO during the TX operation. In this paper, we propose the optimum location of the VCO, considering the temperature gradient through full-chip thermal analysis. Moreover, a novel temperature-compensated VCO by employing a new biasing scheme is proposed. The combination of these two techniques enables power reduction of the transmitter by 33% without sacrificing performance.