An Injection-Locked Ring-Oscillator-Based Fractional-N Digital PLL Supporting BLE Frequency Modulation

• Published in: IEEE journal of solid-state circuits 2022-06, Vol.57 (6), p.1765-1775
• Main Authors: He, Yuming, van den Heuvel, Johan, Mateman, Paul, Allebes, Erwin, Traferro, Stefano, Dijkhuis, Johan, Bunsen, Keigo, Vis, Peter, Breeschoten, Arjan, Liu, Yao-Hong, Matsumoto, Tomohiro, Bachmann, Christian
• Format: Article
• Language: English
• Subjects: Bluetooth; Calibration; Channels; Converters; Delays; fractional-<italic xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">N digital phase locked loop (DPLL); Frequency locking; Frequency modulation; Frequency shift keying; frequency-shift keying (FSK) modulation; injection locking; Keying; Oscillators; Phase locked loops; Phase noise; ring oscillator (RO); Time-frequency analysis
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2022.3154752

This article presents an injection-locked (IL) ring-oscillator-based fractional- {N} 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- {N} and fractional- {N} channels. This work was fabricated in the 40-nm CMOS technology occupying a 0.09-mm 2 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.