1856 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 62, NO. 9, SEPTEMBER 2014 A Reference-Less Injection-Locked Clock-Recovery Scheme for Multilevel-Signaling-Based Wideband BCC Receivers Vishal V. Kulkarni, Member, IEEE, Junghyup Lee, Jun Zhou, Member, IEEE, Chee Keong Ho, Member, IEEE, Jia Hao Cheong, Member, IEEE, Wei-Da Toh, Peng Li, Xin Liu, Member, IEEE, and Minkyu Je, Senior Member, IEEE Abstract—Body channel communication (BCC) integrated circuits for emerging wireless body area network multimedia applications call for the need of high-speed inter-device data com- munication at ultra-low-power consumption and smaller device footprint. In this paper, a novel low-power injection-locking-based clock-recovery circuit (CRC) is proposed for BCC transceivers that employ multilevel direct digital signaling for high data rates. The CRC utilizes transition detection for generating pulses from transmitted digital data and injects them directly into the VCO to recover the clock. The pulse-based direct injection-locking architecture achieves instantaneous clock recovery from random multilevel data with a sensitivity of up to 43 dBm, and elim- inates the need for a reference crystal used in conventional phase-locked-loop-based CRC circuits. Measured results verify that the proposed CRC achieves clock recovery for two- and three-level signals for data rates up to 160 Mb/s. Implemented in 65-nm CMOS technology, the CRC consumes 0.84 mW with a footprint of 0.12 mm . Index Terms—Body channel communication (BCC), clock recovery, injection-locked oscillator, multilevel signaling, wireless body area network (WBAN). I. INTRODUCTION T HE LAST decade has seen explosive growth in the research of wearable computing technology. Up until recently, the focus of this research has been utilizing a wireless Manuscript received March 21, 2014; revised June 04, 2014 and July 15, 2014; accepted July 18, 2014. Date of publication August 05, 2014; date of cur- rent version September 02, 2014. This work was supported by the Agency for Science, Technology and Research (A*STAR) and the Science and Engineering Research Council (SERC), Singapore, under NeuroDevices Program 102 171 0161/0162/0163. This paper is an expanded version from the IEEE MTT-S In- ternational Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications, Singapore, December 9–11, 2013. V. V. Kulkarni, J. Lee, J. Zhou, C. K. Ho, J. H. Cheong, and X. Liu are with the Integrated Circuits and Systems (ICS) Laboratory, Agency for Science, Technology and Research (A*STAR), Institute of Microelec- tronics (IME), Singapore 117685 (e-mail: kulkarnivv@ ime.a-star.edu.sg; leejh@ime.a-star.edu.sg; zhouj@ime.a-star.edu.sg; hockm@ime.a-star.edu.sg; cheongjh@ime.a-star.edu.sg; liux@ime.a-star.edu.sg). W.-D. Toh was with DSO National Laboratories, Singapore 118230. He is now with Temasek Polytechnic, Singapore 529757 (e-mail: tohweida@gmail. com). P. Li is with the Inspur Group, Jinan 250101, China. M. Je is with the Department of Information and Communication En- gineering, Daegu Gyeongbuk Institute of Science and Technology, Daegu 711873, Korea (e-mail: minkyu.je@dgist.ac.kr). Digital Object Identifier 10.1109/TMTT.2014.2342654 body area network (WBAN) for sensing applications within and over the human body. These devices, which include neural recording microprobes, blood flow monitoring sensors, and electrocardiogram (ECG) and body temperature monitoring systems to name a few, operate at a low data rate ranging from a few kilobits/second to a few megabits/second and at low power [1]–[4]. With the advent of wearable applications such as smart glasses and smart watches, demand for personal multimedia content to be transferred over the body in a fast and energy efficient way is gaining momentum. For such applications, data rates on the order of 100 Mb/s are expected to soon become a reality. However, limited bandwidth in the usable BCC frequency spectrum and interference from existing wireless broadcast systems make the realization of such a systems extremely challenging. In addition, the ever-present need for an ultra-small device footprint calls for an overhaul of conventional wireless transceiver system design. A number of studies have made efforts in this direction such as frequency shift keying (FSK) or orthogonal frequency divi- sion multiplexing (OFDM) based signaling to get higher data rates from 10 Mb/s up to 14.55 Mb/s [5]–[7]. In [8], a direct digital signaling scheme is presented that eliminates complexi- ties arising from a carrier-based modulation and demodulation scheme and achieves high energy efficiency. In a recent work from the authors, a multilevel direct digital nonreturn to zero (NRZ) transmission and transition-detection based demodula- tion scheme is demonstrated that helps realize even higher data rates up to 60 Mb/s and energy efficiency up to 150 pJ/b with a band-limited data signal [9]. While the direct digital trans- mission and multilevel signaling enable realization of higher data rates for a band-limited signal, the improvement in en- ergy efficiency is attributed to an injection-locking-based carrier recovery scheme that complements the multilevel direct-dig- ital data-transmission- and transition-detection-based demod- ulation. This paper elaborates on the injection-locking-based carried recovery scheme described in [9] and presents detailed analysis of circuit design and injection-locking behavior along with measured results. Injection locking has recently gained wide popularity as a vi- able alternative for phase-locked-loop (PLL)-based frequency generation circuits due to reduced area overhead and power consumption that arise from complex phase detectors, divider circuits, and loop filters used in PLLs. Moreover, PLL-based 0018-9480 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. 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