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