Koji Imamura

A 2.4 GHz ULP OOK Single-Chip Transceiver for Healthcare Applications

This paper describes an ultra-low power (ULP) single chip transceiver for wireless body area network (WBAN) applications. It supports on-off keying (OOK) modulation, and it operates in the 2.36-2.4 GHz medical BAN and 2.4-2.485 GHz ISM bands. It is implemented in 90 nm CMOS technology. The direct modulated transmitter transmits OOK signal with 0 dBm peak power, and it consumes 2.59 mW with 50% OOK. The transmitter front-end supports up to 10 Mbps. The transmitter digital baseband enables digital pulse-shaping to improve spectrum efficiency. The super-regenerative receiver front-end supports up to 5 Mbps with -75 dBm sensitivity. Including the digital part, the receiver consumes 715 μW at 1 Mbps data rate, oversampled at 3 MHz. At the system level the transceiver achieves PER=10 -2 at 25 meters line of site with 62.5 kbps data rate and 288 bits packet size. The transceiver is integrated in an electrocardiogram (ECG) necklace to monitor the hearts electrical property.

A 2.4GHz ULP OOK single-chip transceiver for healthcare applications

Wireless body-area networks (WBAN) are used for communication among sensor nodes operating on, in or around the human body, e.g. for healthcare purposes. In view of energy autonomy, the total energy consumption of the sensor nodes should be minimized. Because of their low complexity, a combination of the super-regenerative (SR) principle [1–3] and OOK modulation enables ultra-low power (ULP) consumption. This work presents a 2.4GHz ULP OOK singlechip transceiver for WBAN applications. A block diagram of the implemented transceiver is shown in Fig. 26.3.1. Next to the direct modulation TX [4] and SR RF [5] front-ends, this work integrates analog and digital baseband, PLL functionality and additional programmability for flexible data rates, and achieves ultra-low power consumption for the overall system.

A 2.7nJ/b multi-standard 2.3/2.4GHz polar transmitter for wireless sensor networks

This paper presents an ultra-low-power (ULP) 2.3/2.4GHz multi-standard transmitter (TX) for wireless sensor networks and wireless body area networks. Several 2.3/2.4GHz wireless standards have been proposed for such applications, including IEEE802.15.6 (BAN) for body area networks, IEEE802.15.4 (Zigbee) and Bluetooth Low Energy (BLE) for sensor networks and IEEE802.15.4g (SUN) for smart buildings. Recent standard compliant short-range TXs [1-6] typically consume DC power in the range of 20 to 50mW. This is rather high for autonomous systems with limited battery energy. Implemented in a 90nm CMOS technology, the presented TX saves at least 75% of power consumption by replacing several power-hungry analog blocks with the digitally-assisted circuits. This TX is compliant with all 4 of these standards, while dissipating only 4.5mA from a 1.2V supply.

Ultra low power wireless and energy harvesting technologies — An ideal combination

Rapid developments of energy harvesting in the past decade have significantly increased the efficiency of devices in converting ambient free energy into usable electrical energy, thus offering opportunities to design energy autonomous systems nowadays. To achieve such energy autonomous systems, a good understanding of the harvesting capability from the source side strongly motivates the design of ultra low power (ULP) systems. In this paper, we focus on wireless body area networks (WBAN) applications and show that ULP wireless is the key technology to enable wireless autonomous transducer solutions (WATS). We first show that the current energy harvesters cannot provide sufficient power for a typical wireless sensor node based on off-the-shelf components. We then point out that the wireless module is the main component whose power consumption needs to be significantly reduced. To address this problem, we present a ULP wireless module that could satisfy the typical performance requirement of WBAN. Using this ULP wireless module, we demonstrate the feasibility of energy autonomous sensor nodes (i.e. WATS) with the current energy harvesting technology. Moreover, with this ULP module, we point out some new research trends on the miniaturization and cost reduction of energy harvesters. Therefore, we conclude that ultra low power wireless system is an ideal application for energy harvesting.

An ultra-low-power 2-step wake-up receiver for IEEE 802.15.4g wireless sensor networks

This paper presents an ultra-low-power 2-step wake-up receiver for the IEEE 802.15.4g. The receiver is composed of an ultra-low-power energy-detection receiver (EDRX) and an address-detection FSK receiver (ADRX). The ADRX is activated only when the EDRX detects a wakeup packet which minimizes power consumption. Fabricated in a 65 nm CMOS process, the receiver achieves an excellent receiver sensitivity of -87 dBm while consuming only 45.5 μW average power.

Performance evaluation of an ultra-low power receiver for body area networks (BAN)

The main bottleneck to achieve energy autonomy in body area networks (BAN) is the design of an ultra low power yet reliable wireless system. In this paper, we first demonstrate the feasibility of an ultra low power receiver by presenting our implemented receiver chip that could operate on a total power of 479.5 uW, which is more than one order of magnitude lower than commercially available low power transceivers working at 2.4 GHz. We then show the reliability of this chip, which can achieve a receiver sensitivity of −72 dBm for a data rate of 1 Mbps. We further demonstrate that this receiver sensitivity is sufficient to guarantee reliability by evaluating this chip in different to-body communication in BAN environments. By using typical BAN channels, simulation results show that our system can provide a reliable link in both the standing and walking situations. With the measured data, we show that a transmit power of −15 dBm is sufficient for our receiver to achieve reliable communication link in different BAN environments. This transmit power requirement is 15 dB lower than the widely known low power Zigbee system. It could thus significantly facilitate the ultra low power transmitter design, and minimize the human exposure to radio frequency electromagnetic fields. The design and evaluation of our receiver presented in this paper therefore provides a way to move towards the energy autonomy of BAN, and opens access to many new applications in BAN.

A 500mW 5Mbps ULP super-regenerative RF front-end

This paper presents an ultra low power superregenerative RF front-end for wireless body area network (WBAN) applications. The RF front-end operates in the 2.36–2.4 GHz medical BAN and 2.4–2.485 GHz ISM bands, and consumes 500 mW. It supports OOK modulation at high data rates ranging from 1–5 Mbps. It achieves a sensitivity of −67 dBm at a BER of 10−3. The combination of digital and analog quench generation and RF front-end optimization provides ultra-low power consumption at high data rates. The RF front end is implemented in a 90 nm CMOS technology and is packaged in a QFN56 package.

A fully integrated 1.7–2.5GHz 1mW fractional-N PLL for WBAN and WSN applications

This paper presents a wide-range low-power fully integrated fractional-N PLL. The PLL consumes 1.13mW to 1mW at 1.2V supply voltage, in a wide frequency range from 1.7GHz to 2.5GHz. It achieves up to -115 dBc/Hz phase noise at 1MHz offset and up to 2.5 degrees RMS phase error. The settling time is 40μs. The PLL is implemented in 90nm CMOS. The PLL can be used for low power wireless body area network (WBAN) and wireless sensor network (WSN) applications at 433MHz, 900MHz and 2.4 GHz.

Autonomous operation of super-regenerative receiver in BAN

Super-regenerative receiver is one of the potential candidates to achieve ultra low power wireless communication in body area network (BAN). The main limitations of the super-regenerative receiver include the difficulty in choosing a good quench waveform to optimize its sensitivity and selectivity, and its significantly degraded performance in the presence of interference. To address the above problems, we first propose a novel quench waveform search algorithm providing good sensitivity and selectivity results. The algorithm avoids the undesirable manual calibration and hence suitable for autonomous operation. In addition, we consider the spectrum sensing algorithm to autonomously avoid data transmission in the presence of unacceptable interferences. The above algorithms enabling autonomous operation of the super-regenerative receiver are implemented in hardware. Our measurement results show that by using the quench waveform calibrated super-regenerative receiver, the system can provide stable probability or mis-detection and probability of false alarm results in different carrier frequencies. This is very desirable for the determination of a good threshold in spectrum sensing. Together with our previously reported chip designed for the super-regenerative receiver, we have developed an autonomously operating super-regenerative receiver based wireless system, which is ideal for many BAN applications.