A 32-kHz-Reference 2.4-GHz Fractional-<i>N</i> Oversampling PLL With 200-kHz Loop Bandwidth
Junjun Qiu, Zheng Sun, Bangan Liu, Wenqian Wang, Dingxin Xu, Hans Herdian, Hóngyè Huáng, Yuncheng Zhang, Yun Wang, Jian Pang, Hanli Liu, Masaya Miyahara, Atsushi Shirane, Kenichi Okada
Abstract
In this article, a mixed–signal, 32-kHz reference-based 2.4-GHz 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> over-sampling phase-locked loop (OSPLL) is proposed. Different from the conventional <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times $ </tex-math></inline-formula> sampling PLL, which only uses zero-crossing timing information of the reference signal, the proposed OSPLL fully utilizes both the voltage and timing domain information of the reference signal and realizes oversampling ratio (OSR) times phase detection (PD) in one reference cycle. The proposed OSPLL employs the digital-to-analog converter (DAC) to construct the reference-like feedback signal in the voltage domain and utilizes the digital-to-time converter (DTC) to improve PD resolution in the time domain. The adaptive lookup table (LuT)-based calibration is proposed to generate the correct information for DAC and DTC control. A clocked passive comparator works as a bang-bang phase detector (BBPD) for the PLL control and LuTs’ construction. The co-design of low-noise analog circuits and digital calibrations enables good jitter and spur performance. The proposed OSPLL is fabricated in 65-nm CMOS technology, with the core area of 0.58 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the power consumption is 4.97 mW with a 1-V power supply. It achieves 5.79-ps root-mean-square (rms) jitter in 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> modes with the loop-bandwidth (BW <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">loop</sub> ) of 200 kHz, corresponding to the figures of merit (FoMs) of −217.8 dB. The measured fractional spur is less than −36 dBc, and the reference spur is −78 dBc, respectively.