Frequency Synthesizers Based on Fast-Locking Bang-Bang PLL for Cellular Applications

The fractional-N frequency synthesis based on Digital Phase Locked Loop (DPLLs) has become a conventional design approach for the new radio wireless applications. The advantage of the digitally-intensive design style is the possibility to implement low-power and very accurate digital calibration techniques. Most of these algorithms run in the background tracking PVT variations and either relax or, in some cases, completely remove the performance limitations due to analog impairments. Moreover, the digital loop filter area is practically negligible with respect to the one in analog PLLs. These benefits become even more relevant in the scaled CMOS technology nodes. This chapter identifies the design parameters of a standard DPLL architecture and proposes a novel locking scheme to overcome the intrinsic limitations of the digital frequency synthesizers approach. To prove this new scheme a sub-6GHz fractional-N synthesizer has been implemented in 65nm CMOS. The synthesizer has an output frequency from 3.59GHz to 4.05GHz. The integrated output jitter is 182fs and the power consumption of 5.28mW from 1.2V power supply leads to a FoM of -247.5dB. This topology exploits a novel locking technique that guarantee a locking time of 5.6s, for a frequency step of 364MHz, despite the use of a single bit phase detector.