An Injection-Locked Ring-Oscillator-Based Fractional-N Digital PLL Supporting BLE Frequency Modulation
Yuming He, Johan van den Heuvel, Paul Mateman, Erwin Allebes, Stefano Traferro, Johan Dijkhuis, Keigo Bunsen, Peter Vis, Arjan Breeschoten, Yao‐Hong Liu, Tomohiro Matsumoto, Christian Bachmann
Abstract
This article presents an injection-locked (IL) ring-oscillator-based fractional- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula> digital phase locked loop (DPLL) supporting Bluetooth low energy (BLE) frequency modulation with an frequency-shift keying (FSK) error between 2.4% and 3.3%. As the fractional spur cannot be suppressed by IL-DPLL, this work proposes a random edge injection (REI) to reduce the spur. This technique also speeds up the convergence time of gain calibration of the digital-to-time converter (DTC). Furthermore, the proposed background calibration schemes allow the DPLL to achieve stable performance across all BLE channels, including both integer- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula> and fractional- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula> channels. This work was fabricated in the 40-nm CMOS technology occupying a 0.09-mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> area. A fractional spur of −44 dBc and a reference spur of are achieved while consuming 2.76 mW when REI is activated. The background calibrations also ensure stable performance across BLE channels.