Signal Processing in Phase-Domain All-Digital Phase-Locked Loops

PhD Student 
Stefan Mendel

 

 The implementation of wireless transceivers on a single chip in a single technology requires digital realizations of traditional analog building blocks such as phase-locked loops (PLLs). All-digital PLLs (ADPLLs) utilize the zero crossings of signals instead of their amplitudes to realize the frequency synthesizer entirely in digital CMOS technology. This thesis analyzes ADPLLs and highlights the system-level signal processing aspects. A z-domain model and a mixed-signal model are used to develop signal processing algorithms, to perform high-level simulations, and to evaluate the performance of ADPLLs. The impact of imperfections on the output phase noise spectrum are analytically described and compared to event-driven simulation outcomes. Oscillator noise, frequency quantization noise with Sigma-Delta noise shaping, and reference clock jitter raise the output phase noise level, whereas phase quantization and injection pulling manifest themselves as spurs in the output phase noise spectrum. Furthermore, the behavior of a well-known phase-domain ADPLL architecture that employs a periodically time-varying system clock to synchronize the oscillator output clock and the reference clock is extensively investigated and mathematically described. Based on the analysis of injection pulling spurs and the analysis of the time-varying ADPLL operation, an alternative ADPLL architecture, that directly utilizes the uniform reference clock as system clock, is proposed. The advantages are a reduced complexity of the circuits and an improved performance concerning spurs in the phase noise spectrum. Finally, a fast frequency-hopping ADPLL is proposed that enables frequency hops within less than one reference cycle with a frequency resolution of less than 20 ppm of the synthesized frequency. The proposed ADPLL is suitable for Multiband Orthogonal-Frequency-Division-Multiplexing Ultra-Wideband (MB-OFDM-UWB) communication systems, where the time between the recurrence of a frequency band is short and the requirements on the phase noise are not demanding.  

 

This thesis is supervised by Gernot Kubin.