Ultra Low Power FM-UWB Transceiver for High-Density Wireless Sensor Networks

The WiseSkin project aims to provide a non-invasive solution for restoration of a natural sense of touch to persons using prosthetic limbs. By embedding sensor nodes into the silicone coating of the prosthesis, which acts as a sensory skin, WiseSkin targets to provide improved gripping, manipulation and mobility for amputees. Flexibility, freedom of movement and comfort demand unobtrusive, highly miniaturized, low-power sensing capabilities built into the artificial skin, which is then integrated with a sensory feedback system. Wireless communication between the sensor nodes provides more flexibility, better scalability and robustness compared to wired solution, and is therefore a preferred approach for WiseSkin. Design of an RF transceiver tailored for the specific needs of WiseSkin is the topic of this work. The properties of FM ultra-wide band (FM-UWB) modulation make it a good candidate for High-Density Wireless Sensor Networks (HD-WSN). The proposed FM-UWB receivers take advantage of short range to reduce power consumption, and exploit robustness of this wideband modulation scheme. The LNA, identified as the biggest consumer, is removed and signal is directly converted to dc, where amplification and demodulation are performed. Owing to 500 MHz bandwidth, frequency offset and phase noise can be tolerated, and a low-power, free-running ring oscillator can be used to generate the LO signal. The receiver is referred to as an approximate zero-IF receiver. Two receiver architectures are studied. The first one performs quadrature downconversion, and owing to the demodulator linearity, provides the multi-user capability. In the second receiver, quadrature demodulation is replaced by the single-ended one. Due to the nature of the demodulator, sensitivity degrades, and multiple FM-UWB signals cannot be resolved, but the consumption is almost halved compared to the first receiver. The proposed approach is verified through two integrations, both in a standard 65 nm bulk CMOS process. In the first run, a standalone quadrature receiver was integrated. Power consumption of 423 uW was measured, while achieving -70 dBm sensitivity. Good narrow-band interference rejection and multiuser capability with up to 4 FM-UWB channels could be achieved. In the second run, a full transceiver is integrated, with both quadrature and single-ended receivers and a transmitter, all sharing a single IO pad, without the need for any external passive components or switches. The quadrature receiver, with on-chip baseband processing and multi-user support, in this case consumes 550 uW, with a sesensitivity of -68 dBm. The low power receiver consumes 267 uW, and provides -57 dBm sensitivity, at a single FM-UWB channel. The implemented trantransmitter transmits a 100 kb/s FM-UWB signal at -11.4 dBm, while drawing 583 uW from the 1 V supply. The on-chip clock recovery allows reference frequency offset up to 8000 ppm. Since state of the art on-chip RC oscillators can provide below 2100 ppm across the temperature range of interest, the implemented transceiver demonstrates the feasibility of a fully integrated FM-UWB radio with no need for a quartz reference or any external components. In addition, the transceiver can tolerate up to 3 dBm narrow-band interferer at 2.4 GHz. Such a strong signal can be used to remotely power the sensor nodes inside the artificial skin and enable a truly wirelessWiseSkin solution

A 2.4-GHz low power polar transmitter for wireless body area network applications

A 2.4GHz low power polar transmitter is proposed in this paper. A dynamic biasing circuit, controlled by a digital envelope signal, is used as a direct digital-to-RF envelope converter. It effectively linearizes the input-output characteristic of the overdriven cascode class-C power amplifier used as the output stage, by dynamically adjusting the bias voltage of the cascode transistor. An equivalent baseband model of the transmitter is presented and used to optimize system parameters and give initial assessment of the achievable performance in terms of efficiency and linearity. Based on these simulations, parameters for transistor-level implementation of the bias circuit are derived. The transmitter is designed in a 65nm CMOS technology. The post layout simulations indicate that the transmitter successfully meets the requirements of the IEEE 802.15.6 standard for wireless body area networks. The simulated amplifier consumes 4.75mA from a 1.2V supply while delivering 1.45dBm of output power with a peak efficiency of 24%. The entire transmitter, including the PLL, consumes 7.5mA

FM-UWB: Towards a Robust, Low-Power Radio for Body Area Networks

The Frequency Modulated Ultra-Wideband (FM-UWB) is known as a low-power, low-complexity modulation scheme targeting low to moderate data rates in applications such as wireless body area networks. In this paper, a thorough review of all FM-UWB receivers and transmitters reported in literature is presented. The emphasis is on trends in power reduction that exhibit an improvement by a factor 20 over the past eight years, showing the high potential of FM-UWB. The main architectural and circuit techniques that have led to this improvement are highlighted. Seldom explored potential of using higher data rates and more complex modulations is demonstrated as a way to increase energy efficiency of FM-UWB. Multi-user communication over a single Radio Frequency (RF) channel is explored in more depth and multi-channel transmission is proposed as an extension of standard FM-UWB. The two techniques provide means of decreasing network latency, improving performance, and allow the FM-UWB to accommodate the increasing number of sensor nodes in the emerging applications such as High-Density Wireless Sensor Networks

An Approximate Zero IF FM-UWB Receiver for High Density Wireless Sensor Networks

A low-power frequency modulated-ultra-wideband (FM-UWB) receiver for short-range communications, capable of simultaneously demodulating multiple FM-UWB signals located at the same frequency, is presented in this paper. The proposed receiver utilizes an "approximate zero IF" architecture that uses a low-power, free-running ring oscillator as the RF LO to first convert the input signal into baseband, where it is then amplified and demodulated. Moving the most power-hungry blocks from RF to IF results in reduction of power consumption by more than one order of magnitude compared to previous implementations using the delay-line demodulator. Integrated in a 65-nm CMOS technology, the whole receiver chain consumes 423 mu W from a 1-V supply while achieving -70-dBm sensitivity at a data rate of 100 kb/s at 4 GHz. Communication with up to four FM-UWB users, operating in the same band, is demonstrated, making this receiver suitable for high-density wireless sensor networks

A 2.4-GHz low power polar transmitter for wireless body area network applications

A 2.4 GHz low power polar transmitter is proposed in this paper. A dynamic biasing circuit, controlled by a digital envelope signal, is used as a direct digital-to-RF envelope converter. It effectively linearizes the input-output characteristic of the overdriven cascode class-C power amplifier used as the output stage, by dynamically adjusting the bias voltage of the cascode transistor. An equivalent baseband model of the transmitter is presented and used to optimize system parameters and give initial assessment of the achievable performance in terms of efficiency and linearity. Based on these simulations, parameters for transistor-level implementation of the bias circuit are derived. The transmitter is designed in a 65 nm CMOS technology. The post layout simulations indicate that the transmitter successfully meets the requirements of the IEEE 802.15.6 standard for wireless body area networks. The simulated amplifier consumes 4.75 mA from a 1.2 V supply while delivering 1.45 dBm of output power with a peak efficiency of 24 %. The entire transmitter, including the PLL, consumes 7.5 mA

The WiseSkin artificial skin for tactile prosthetics: A power budget investigation

The use of prosthetic hands are limited partly due to the fact that they lack the provision of sensory feedback to the user. A first step to providing sensory feedback is having adequate sensors in the prosthesis. The WiseSkin project targets the use of artificial skin embedding ultra-low power wireless sensor nodes. This paper provides an overview of the WiseSkin artificial skin for tactile prosthetics and specifically addresses the power consumption by the sensor nodes

A 2.4-GHz low complexity polar transmitter using dynamic biasing for IEEE 802.15.6

A 2.4 GHz polar transmitter compliant with the IEEE 802.15.6 standard is presented in this paper. A Linearized class-C power amplifier, employing dynamic biasing is used to minimize the adjacent channel interference and satisfy the defined spectrum mask requirements. An FBAR based frequency synthesizer enables fast startup and channel switching times. It is capable of addressing all the channels within the MBAN and ISM bands (2.36-2.48 GHz). The transmitter was integrated in 65 nm CMOS technology. It provides 0 dBm of output power while drawing 8.7 mA of current from a 1.2 V supply. The standalone power amplifier exhibits peak efficiency of 16%. © 2015 IEEE

Randomness scores and conflict groups.

<p>Mean randomness scores as a function of conflict groups. Vertical bars denote 1 standard error of the mean. If not otherwise stated (non-significant, ns), the pairwise comparisons were significant.</p