David D. Wentzloff

Design considerations for ultra-low energy wireless microsensor nodes

This tutorial paper examines architectural and circuit design techniques for a microsensor node operating at power levels low enough to enable the use of an energy harvesting source. These requirements place demands on all levels of the design. We propose architecture for achieving the required ultra-low energy operation and discuss the circuit techniques necessary to implement the system. Dedicated hardware implementations improve the efficiency for specific functionality, and modular partitioning permits fine-grained optimization and power-gating. We describe modeling and operating at the minimum energy point in the subthreshold region for digital circuits. We also examine approaches for improving the energy efficiency of analog components like the transmitter and the ADC. A microsensor node using the techniques we describe can function in an energy-harvesting scenario.

Gaussian pulse Generators for subbanded ultra-wideband transmitters

This paper presents calculations for approximating the measured spectrum of pulsed signals in the high and low pulse-repetition-frequency (PRF) region. Experimentally verified peak and average power calculations are presented for pulse trains with no modulation and when modulated by random data using binary phase-shift keying (BPSK). A pulse generator is presented that is built using commercially available discrete components. BPSK pulses are generated at a PRF of 50 MHz. The output spectrum has a center frequency of 5.355 GHz and a -10-dB bandwidth of 550 MHz. A technique for pulse shaping is presented that approximates a Gaussian pulse by exploiting the exponential behavior of a bipolar junction transistor. This technique is demonstrated by a pulse generator fabricated in a 0.18-/spl mu/m SiGe BiCMOS process. BPSK pulses are generated by inverting a local oscillator signal as opposed to the reference pulse, improving matching. Pulses are transmitted at a PRF of 100 MHz and centered in 528-MHz-wide channels equally spaced within the 3.1-10.6-GHz ultra-wideband band. Measurement results for both transmitters match well with calculated values.

A 47pJ/pulse 3.1-to-5GHz All-Digital UWB Transmitter in 90nm CMOS

An all-digital UWB TX is presented that generates PPM pulses with a center frequency tunable to 3 channels in the 3.1-to-5GHz band without the use of an RF oscillator. A delay-based spectral scrambling technique is proposed that exploits the digital architecture. The circuit achieves 47pJ/b at a data rate of 10Mb/s.

System design considerations for ultra-wideband communication

This article discusses issues associated with high-data-rate pulsed ultra-wideband system design, including the baseband processing, transmitter, antenna, receiver, and analog-to-digital conversion. A modular platform is presented that can be used for developing system specifications and prototyping designs. This prototype modulates data with binary phase shift keyed pulses, communicates over a wireless link using UWB antennas and a wideband direct conversion front-end, and samples the received signal for demodulation. Design considerations are introduced for a custom chipset that operates in the 3.1-10.6 GHz band. The chipset is being designed using the results from the discrete prototype.

Recent advances in IR-UWB transceivers: An overview

Modern Ultra-Wide Band (UWB) regulations have recently been adopted worldwide allowing for unlicensed operation within 3.1 and 10.6 GHz, using an appropriate wideband signal format with a low Effective Isotropic Radiated Power (EIRP) level. UWB characteristics are suitable to transmit data using pulses instead of continuous-waves such as in narrowband radio links. It has the potential to be the right technology for high data-rate, low-power and short-to-medium range communication systems. We will focus on Impulse Radio-UWB (IR-UWB) systems and show their suitability for many different applications, including sensor networks, ad-hoc networks, cognitive radio, home networking, etc. We will also discuss the difficulties and challenges of designing IR-UWB systems. We present a tutorial overview of UWB regulations and usable signals. We present the existing standards and recommendations, and we review recently published results, highlighting trends in UWB transceiver power consumption and the impact of CMOS scaling on performance.

Low-Power Impulse UWB Architectures and Circuits

Ultra-wide-band (UWB) communication has a variety of applications ranging from wireless USB to radio frequency (RF) identification tags. For many of these applications, energy is critical due to the fact that the radios are situated on battery-operated or even batteryless devices. Two custom low-power impulse UWB systems are presented in this paper that address high- and low-data-rate applications. Both systems utilize energy-efficient architectures and circuits. The high-rate system leverages parallelism to enable the use of energy-efficient architectures and aggressive voltage scaling down to 0.4 V while maintaining a rate of 100 Mb/s. The low-rate system has an all digital transmitter architecture, 0.65 and 0.5 V radio-frequency (RF) and analog circuits in the receiver, and no RF local oscillators, allowing the chipset to power on in 2 ns for highly duty-cycled operation.

Body Sensor Networks: A Holistic Approach From Silicon to Users

Body sensor networks (BSNs) are emerging cyber-physical systems that promise to improve quality of life through improved healthcare, augmented sensing and actuation for the disabled, independent living for the elderly, and reduced healthcare costs. However, the physical nature of BSNs introduces new challenges. The human body is a highly dynamic physical environment that creates constantly changing demands on sensing, actuation, and quality of service (QoS). Movement between indoor and outdoor environments and physical movements constantly change the wireless channel characteristics. These dynamic application contexts can also have a dramatic impact on data and resource prioritization. Thus, BSNs must simultaneously deal with rapid changes to both top-down application requirements and bottom-up resource availability. This is made all the more challenging by the wearable nature of BSN devices, which necessitates a vanishingly small size and, therefore, extremely limited hardware resources and power budget. Current research is being performed to develop new principles and techniques for adaptive operation in highly dynamic physical environments, using miniaturized, energy-constrained devices. This paper describes a holistic cross-layer approach that addresses all aspects of the system, from low-level hardware design to higher level communication and data fusion algorithms, to top-level applications.

A 98nW wake-up radio for wireless body area networks

A 0.13μm CMOS low power wake-up radio is presented. The wake-up radio operates with -41dBm sensitivity at 915MHz using OOK modulation with a data rate of 100kbps while consuming 98nW active power, 11pW sleep power, and has an energy efficiency of 0.98pJ/bit. The wake-up radio occupies 0.03mm2 and uses two off-chip components (an inductor and a capacitor). All biasing and calibration for process variation and mismatch is included on-chip. The entire radio operates from a single 1.2V supply.

An All-Digital 12 pJ/Pulse IR-UWB Transmitter Synthesized From a Standard Cell Library

This paper presents an all-digital impulse radio ultra-wideband (IR-UWB) transmitter. All functional blocks in the transmitter are implemented with digital standard cells and automatically place-and-routed by design tools. The center frequency and the bandwidth of the UWB pulses are digitally tuned to compensate for variations, or target different applications. This paper also proposes a calibration scheme and modeling of a cell-based digitally controlled oscillator (DCO), which takes systematic mismatch from automatic place-and-route into account. The transmitter is fabricated in a 65 nm CMOS process, and occupies a core area of 0.032 mm2. The transmitter operates in the 3.1-5.0 GHz UWB band with leakage power of 170 μW and active energy consumption ranges from 8 pJ/pulse to 16 pJ/pulse, which combine to a total minimum energy/pulse of 12 pJ/pulse at 50 Mb/s.

Design and experimental verification of a direct-drive interior PM synchronous machine using a saturable lumped-parameter model

This paper presents the design and experimental verification of a 6 kW interior permanent magnet (IPM) synchronous machine intended for an automotive direct-drive starter/alternator application. The machine was designed using a saturable lumped-parameter magnetic circuit model in combination with a Monte Carlo optimization process that minimized the machine-plus-converter cost. An experimental IPM machine has been constructed based on the resulting design specifications. Laboratory tests have confirmed the accuracy of the analytical models for predicting the q-axis inductance L/sub q/ (including saturation effects) and the torque production characteristics, but discrepancies between the predicted and measured d-axis inductance L/sub d/ were revealed. The impact of these differences on machine performance is discussed, as well as potential adjustments in the IPM analytical model to improve the performance of future machines.