All-Digital PLL with Variable Loop Type Characteristics

Abstract

A fully-digital frequency synthesizer for RF wireless applications has recently been proposed. It replaces the conventional VCO with a digitally-controlled oscillator with sufficiently fine frequency resolution. The conventional phase/frequency detector, charge pump and RC loop filter are replaced by a time-to-digital converter and a simple digital loop filter. In this paper, we present novel techniques used in the all-digital PLL to achieve ultra-fast frequency acquisition of < 50 mus while maintaining excellent phase noise and spurious performance during transmission and reception. This approach has been validated and incorporated in commercial single-chip Bluetooth and GSM radios realized in deep-submicron CMOS