On the Reconfigurability of All-Digital Phase-Locked Loops for Software Defined Radios

A new all-digital phase-locked loop (ADPLL) for wireless applications has recently been proposed and commercially demonstrated. It replaces conventional phase/frequency detector and charge pump with a time-to-digital converter (TDC). Analog frequency tuning of a VCO is replaced with an all- digital tuning of a digitally-controlled oscillator (DCO). Due to its digital intensive structure, the ADPLL is well suited for single-chip radio solutions fabricated using state-of-the- art low cost and power nanometer-scale CMOS processes. Being integrated with a digital signal processor (DSP), the ADPLL parameters can be properly controlled and seamlessly reconfigured using the available on-chip DSP unit making the ADPLL a software defined radio (SDR) platform. In this paper, we present a DSP based technique for the fully dynamic control of the ADPLL settling performance that allows the loop band width to be seamlessly widened or narrowed allowing for fast frequency acquisition or tracking with excellent phase noise and spurious performance, respectively. The arbitrary and dynamic control of the frequency synthesizer loop bandwidth will address the dynamically varying nature of a multi-radio multi- standard SDR environment.