The current paradigm of frequency synthesis for short-range wireless transceivers, such as BLE, is to use a crystal oscillator (XO) in the tens-of-MHz range as a frequency reference (FREF) to phase lock an RF oscillator [1-4]. This ensures a sufficiently wide PLL bandwidth of tens to hundreds of kHz to quickly acquire a new channel and to suppress lower-frequency phase noise (PN) of the RF oscillator. The latter requirement can be alleviated by substantially lowering the flicker PN of a digitally controlled oscillator (DCO) thus allowing to freeze its tuning word updates during receive (RX) packets and further directly FM-modulating the DCO during transmit (TX) packets [1]. However, an all-digital PLL (ADPLL) is still needed just to quickly settle the DCO to each new channel.
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