Crystal-Less WBAN Receiver Consumes Just 0.24 nJ/b

To meet the requirements of IEEE 802.15.6 wireless body area network (WBAN) applications, this transceiver provides low energy consumption, low system cost, and high QoS scalability.

Due to an aging population and increasingly sedentary lifestyles around the world, cardiovascular disease and diabetes are affecting a larger number of people. Because of the asymptomatic or intermittent properties of these diseases, long-term continuous and ubiquitous real-time health monitoring—without limiting the patient’s activities—are critical to their detection and treatment. Such continuous and automated monitoring demands ultra-low-power wireless connectivity among devices placed in, on, and around the human body. At the Korea Advanced Institute of Science and Technology (KAIST), an energy-efficient, crystal-less, double-frequency-shift-keying (double-FSK) transceiver for wireless-body-area-network (WBAN) sensor nodes has been designed by Joonsung Bae, Kiseok Song, Hyungwoo Lee, Hyunwoo Cho, and Hoi-Jun Yoo.

In a WBAN, which consists of a hub node (base station) and several sensor nodes, body-worn sensor nodes periodically send physiological or multimedia data to a central hub node. According to the IEEE 802.15.6 standard, energy efficiency is a top priority for WBAN sensor nodes. The lifetime of sensor nodes is expected to extend to five years for implants and one week for a wearable device using limited energy resources, such as coin batteries. Among other design challenges is the need for a low-power transceiver with fast turn-on time with tight duty-cycle control between sleep and active modes.

To lower the cost of their device and its energy consumption, the researchers replaced the crystal oscillator with an injection-locking digitally controlled oscillator (DCO). By choosing a calibration method that uses an injection-locking detector, they found that the frequency drift of that DCO could be calibrated within 100-kHz accuracy over a 100° temperature variation. To satisfy WBAN requirements like quality of service (QoS), they adopted the double-FSK modulation scheme with a divider-based transmitter by a power-efficient switching modulator. Upon its fabrication, the resulting crystal-less, double-FSK, WBAN-compatible sensor-node transceiver consumed 1 and 2 mW in calibrating and transmitting modes, respectively, at a data rate to 10 Mb/s. It provided an 80-MHz reference source with 100-kHz accuracy by auto-calibrated digitally controlled oscillator. The transceiver, which was fabricated in 0.18-μm CMOS technology, measured 2.5 x 5.0 mm. See “A Low-Energy Crystal-Less Double-FSK Sensor Node Transceiver for Wireless Body-Area Network,” IEEE Journal Of Solid-State Circuits, Nov. 2012, p. 2678.

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