Thesis (D.Sc.)--University of the Witwatersrand, Faculty of Science, 1959.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1978. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / B.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Vita. / Includes bibliographical references. / by David Michael Papurt. / Ph.D.

Photocopy of typescript. / Digitized by Kansas Correctional Industries

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Power minimization in wireless transceivers has become increasingly critical in recent years with the emergence of standards for short-distance applications in the 900 MHz and 2.4 GHz industrial, scientific and medical (ISM) radio bands. The demand for long battery life and better portability in such applications has led to extensive research on low power radio architectures. This dissertation introduces receiver topologies for low-power systems and presents a theoretical performance analysis of the topologies. Two fully integrated receiver down-converters that demonstrate the concept are implemented in a 0.13-[mu]m CMOS technology. These topologies employ merged mixers and IF amplifiers in order to reduce power dissipation for a given dynamic range performance. In the described topologies, the input stage of a mixer is used to simultaneously provide conversion gain and baseband amplification. This is achieved by applying the down-converted IF signal to input of the mixer. Consequently, the effective conversion gain of the design is greatly enhanced with current requirement primarily determined by the input transconductor. Potential degradation mechanisms related to instability and second-order distortion are identified and solved by the use of appropriate circuit techniques. Noise and linearity performance of the down-converters is analyzed and compared to that of conventional cascaded design counterparts. The potential for enhancement of IIP3 performance through cancellation of nonlinear products is discussed. Potential extensions of the above work including feedback-based architectures that exploit multiple loops for further maximizing the power efficiency of receiver front-ends are also presented.

No description available.

In the energy-limited wireless sensor node applications, wake-up radios are required to reduce the average power consumption of the node. Energy-detecting receivers are the best fit for such low power operations. This thesis presents the energy-detecting receiver design; challenges; techniques to enhance sensitivity, selectivity; and multi-access operation. Self-mixers instead of the conventional envelope detectors are proposed and proved to be optimal for signal detection. A fully integrated wake-up receiver uses the self-mixer and time-encoded baseband signal processing to provide a sensitivity of -79.1dBm at 434MHz with 420pW of power, providing an 8dB better sensitivity at 10dB lower power consumption compared to the SoA. A novel approach using narrowband interferers as local oscillators will be presented to further enhance sensitivity and selectivity, effectively operating the energy-detector receiver as a direct down-conversion receiver. Additionally, a clockless continuous-time analog correlator will be introduced to enhance the selectivity to wide-band AM interferers. The architecture uses pulse-position-encoded analog signal processing with VCOs as integrators and pulse-controlled relaxation delays; it operates as a code-domain matched filter to de-spread asynchronous wake-up codes. This code-domain matched filtering also provides code-division multiple access (CDMA) for simultaneous wakeups. Additional enhancement in the link can be achieved using directional antennas, providing spatial gain and selectivity. Certain applications can leverage a nearby reflector similar to a Yagi antenna to enhance the directivity. A low power directional backscatter tag is proposed, it uses multiple antennas acting as a reflectarray by configuring constant phase gradients depending on the direction of arrival (DoA) of the signal. Thus, instead of harvesting energy, the same energy and the surrounding environment can be leveraged to enhance functionality (e.g. interferer as LO, using a backscatter tag on a wall) for low power operation. Innovations spanning both system and circuit architectures that leverage the ambient energy and environment to enable power-efficient solutions for next-generation wake-up radios are presented in this work.

The ever-increasing demand for wireless throughput requires modern handset receivers to aggregate signals from multiple non-contiguously allocated RF carriers. This poses significant receiver design challenges, including concurrent signal reception, RF input interface, out-of-band (OB) linearity, and suppression of spurious responses. Commercial solutions use external antenna switches and off-chip RF multiplexers to provide non-tunable, narrowband filtering and impedance matching. The RF signal is then divided into separate signal chains, each with a dedicated receiver for signal reception. Although this solution allows the selection of any carrier combinations supported by the available RF filters, as the number of aggregation band combinations increases, the scale of the passive front-end module grows rapidly, leading to increased system complexity, extra signal loss, and degraded performance. This thesis presents the design and implementation of two receiver architectures that support reconfigurable operations and flexible, concurrent reception from two inter-band carriers with a tuned RF interface. We first present a multi-branch receiver with modulated mixer clocks (MMC). It unifies the functions of single-carrier and dual-carrier reception, as well as compressive-sampling spectrum scanning into a single architecture. With continuous-wave-modulated mixer clocks, the receiver supports concurrent reception from two distinct bands and realizes tuned impedance matching that greatly improves the OB linearity. With pseudo-noise-modulated mixer clocks, the receiver supports spectrum scanning. Disabling modulation reverts the receiver into a single-carrier receiver with good OB linearity. The 65nm CMOS prototype is developed that operates from 300 to 1300MHz and offers 2.7dB minimum NF, -1.3dBm B1dB, and +8.0dBm IIP3 for single-carrier reception. Concurrent dual-carrier reception is demonstrated that offers -8.4dBm B1dB and sub-6dB NF with the two carriers separated from 200 to 600MHz apart. For spectrum scanning, the receiver achieves a 66dB dynamic range with -75dBm sensitivity over a 630MHz RF span. In addition, a discussion of the higher-order MMC technique is included to improve the receiver’s spurious and noise performance by suppressing the higher-order responses and mitigating the noise-folding effect. Next, we present an IF-filterless, double-conversion receiver. The concurrent, narrowband RF interface is realized with two layers of passive mixing in its mixer-first branches, which translate the low-pass, baseband impedance twice to two distinct bands and improve the OB linearity. Branches with DDS-modulated LNTAs for multi-phase, switched-Gm mixing offer rejection of spurious responses and improved noise performance. The 65nm CMOS prototype is developed that operates from 100 to 1200MHz. For single-carrier reception, the receiver delivers 4.8dB minimum NF, +7.9dBm B1dB, and +22.8dBm IIP3. For concurrent signal reception, two arbitrarily-allocated RF carriers, separated from 200 to 600MHz apart, can be received concurrently. The receiver delivers a +1.9dBm B1dB and supports 8-/16-phase DDS modulation with a 30dB spurious rejection across its operating range. In addition, a theoretical study of a modified, mixer-first branch is included. By re-arranging the connections of the baseband termination resistors, the baseband noise can be fully cancelled, thus improving the receiver’s noise performance.

Cognitive radio (CR) is a multi-disciplinary field that makes use of knowledge from a multitude of specialties such as antenna design, circuits, systems and digital signal processing among many others. CR has emerged as an area of interest over 20 years ago and in the years since has evolved to encompass both realizable theory and physical hardware. Key among the latter are reconfigurable, software defined radios and embedded sensors that incorporate flexible parameters, allowing a CR to operate in a wide variety of electromagnetic (EM) environments. The ideal cognitive radio would be capable of adapting to a changing EM environment without any specific knowledge or direction from the operator. This would require the radio itself to be aware of the EM environment and ideally, to sense the EM environment and act upon it in a semi-autonomous or autonomous way. While most research in this field has focused on the spectrum sensing aspects of the domain, development of the above-described "ideal CR" would require that the EM environment be characterized in domains such as angular, time and polarization among others. Signal dependent parameters can also be characterized such as bandwidth and modulation. The multi-dimensionality of the environment and the signals present within entail challenges with scalability and efficiency. This work focuses on the efficient sensing of signals in the angular domain also known as direction-of-arrival (DOA). There are a multitude of ways to find a signal's DOA. All require multiple antennas connected to a single or multiple radio nodes, antennas with patterns that gather energy in a particular direction, or multiple single antenna radios. The methods that utilize multiple antennas exploit the phase and/or amplitude relationships between the antennas themselves for a signal's DOA. The principal tradeoff between DOA methods typically converges to scan time vs. number of antenna elements. For many DOA architectures, this also means a scan time tradeoff with angular resolution as well. Since fast and accurate measurements are important for characterizing a quickly changing EM environment, sensing speed becomes a key requirement in designing a CR and associated sensing architecture. In this work, we present a DOA sensing architecture suitable for use in CR systems called the Direct Space to Information Converter (DSIC). Unlike current state-of-the art DOA methods, the DSIC breaks the tradeoff between scan time and the number of antenna elements needed for a given angular resolution when compared to other DOA and beamforming architectures. By randomly modulating the received signals in space, across multiple antenna elements and taking a few, compressed sensing (CS) measurements, the DSIC is able to angularly scan a wide field of view in an order of magnitude less time than other DOA methods. These CS measurements correspond to different random perturbations of the DSIC's antenna factor and can be quantized in as little as a single bit of resolution in the DSIC's phaseshifters/vector modulators. The DSIC is able to create multiple user-specified nulls in the antenna pattern to reduce the impact of strong known interferers while also simultaneously scanning the full field of view. Additionally, the designer has the option of performing simultaneous reception or nulling while sensing. If nulling, a few different methods are available each suitable for varying EM environments and potential use cases. We show in detail the multi-disciplinary process in designing a complete end-to-end hardware solution, selecting the parameters necessary to design the DSIC as well as test and characterize it. The benefits of the DSIC are discussed and compared to the current state-of the art with an emphasis on architectures suitable for use in interferer rich environments. We demonstrate that the energy usage of the DSIC is lower than comparable CR architectures by a large factor and scales much more favorably in terms of energy and physical complexity as the number of antenna elements increase. At the conclusion of this work we also discuss future areas of exploration in extending the DSIC's capability by incorporating an ability to sense the spectrum as well as the DOA of a signal.