Thesis. 1976. B.S.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / Microfiche copy available in Archives and Engineering. / Bibliography: leaf 21. / B.S.

Digital transmitters offer several advantages over conventional analog transmitters such as reconfigurability, elimination of scaling-unfriendly, power hungry and bulky analog blocks and portability across technology. The rapid advancement of technology in CMOS processes also enables integration of complex digital signal processing circuitry on the same die as the digital transmitter to compensate for their non-idealities. The use of this digital assistance can, for instance, enable the use of highly efficient but nonlinear switching-class power amplifiers by compensating for their severe nonlinearity through digital predistortion. While this shift to digitally intensive transmitter architectures is propelled by the benefits stated above, several pressing challenges arise that vary in their nature depending on the frequency of operation - from RF to mmWave. Millimeter wave CMOS power amplifiers have traditionally been limited in output power due to the low breakdown voltage of scaled CMOS technologies and poor quality of on-chip passives. Moreover, high data-rates and efficient spectrum utilization demand highly linear power amplifiers with high efficiency under back-off. However, linearity and high efficiency are traditionally at odds with each other in conventional power amplifier design. In this dissertation, digital assistance is used to relax this trade-off and enable the use of state-of-the-art switching class power amplifiers. A novel digital transmitter architecture which simultaneously employs aggressive device-stacking and large-scale power combining for watt-class output power, dynamic load modulation for linearization, and improved efficiency under back-off by supply-switching and load modulation is presented. At RF frequencies, while the problem of watt-class power amplification has been long solved, more pressing challenges arise from the crowded spectrum in this regime. A major drawback of digital transmitters is the absence of a reconstruction filter after digital-to-analog conversion which causes the baseband quantization noise to get upconverted to RF and amplified at the output of the transmitter. In high power transmitters, this upconverted noise can be so strong as to prevent their use in FDD systems due to receiver desensitization or impose stringent coexistence challenges. In this dissertation, new quantization noise suppression techniques are presented which, for the first time, contribute toward making watt-class fully-integrated digital RF transmitters a viable alternative for FDD and coexistence scenarios. Specifically, the techniques involve embedding a mixed-domain multi-tap FIR filter within highly-efficient watt-class switching power amplifiers to suppress quantization noise, enhancing the bandwidth of noise suppression, enabling tunable location of suppression and overcoming the limitations of purely digital-domain filtering techniques for quantization noise.

The demand for broadband wireless communication is growing rapidly, requiring more spectrum resources. However, spectrum usage is inefficient today because different frequency bands are allocated for different communication standards and most of the bands are not highly occupied. Cognitive radio systems with dynamic spectrum access improve spectrum efficiency, but they require wideband tunable receiver hardware. In such a system, a preselect filter is required for the RF receiver front end, because an out-of-band (OB) interferer can block the front end or cause distortion, desensitizing the receiver. In a conventional solution, off-chip passive filters, such as surface-acoustic-wave (SAW) filters, are used to reject the OB interferer. However, such passive filters are hardly tunable, have large area, and are very expensive. On-chip, high-selectivity, linearly tunable RF filters are, therefore, a hot topic in RF front-end research. Switched-capacitor (SC) RF filters, such as N-path filters, feature good linearity and tunability, making them good candidates for tunable RF filters. However, N-path filters have some drawbacks: notably, a poor harmonic response and limited close-by blocker tolerance. This thesis presents the design and implementation of several interferer-tolerant receivers based on SC technology. We present an RF receiver with a harmonic-rejecting N-path filter to improve the harmonic response of the N-path bandpass filter. It features tunable narrowband filtering and high attenuation of the third- and fifth-order LO harmonics at the LNA output, which improves the blocker tolerance at LO harmonics. The 0.2-1 GHz RF receiver is implemented in a 65 nm CMOS process. The blocker 1 dB compression point (B1dB) is -2.4 dBm at a 20 MHz offset, and remains high at the third- and fifth-order LO harmonics. The LNA’s reverse isolation helps keep the LO emission below -90 dBm. A two-stage harmonic-rejection approach offers a > 51 dB harmonic-rejection ratio at the third- and fifth-order LO harmonics without calibration. To improve tolerance for close-by blockers, we further present an SC RF receiver achieving high-order, tunable, highly linear RF filtering. We implement RF input impedance matching, N-path filtering, high-order discrete-time infinite-impulse response (IIR) filtering and downconversion using only switches and capacitors in a 0.1-0.7 GHz prototype with tunable center frequency, programmable filter order, and very high tolerance for OB blockers. The 40 nm CMOS receiver consumes 38.5-76.5mA, achieves 40 dB gain, 24 dBm OB IIP3, 14.7 dBm B1dB for a 30MHz blocker offset, 6.8-9.7 dB noise figure, and > 66dB calibrated harmonic rejection ratio. The key drawback of our earlier SC receiver is the relatively high theoretical lower limit of the noise figure. To improve the noise performance, we developed a 0.1-0.6 GHz chopping SC RF receiver with an integrated blocker detector. We achieve RF impedance matching, high-order OB interferer filtering, and flicker-noise chopping with passive SC circuits only. The 34-80 mW 65 nm receiver achieves 35 dB gain, 4.6-9 dB NF, 31 dBm OB-IIP3, and 15 dBm B1dB. The 0.2 mW integrated blocker detector detects large OB blockers with only a 1 us response time. The filter order can be adapted to blocker power with the blocker detector.

This thesis examines the functional connectivity of the hippocampus with the rest of the brain, with a focus on the neocortex. The hypothesis explored, in an animal model, is whether the frequency-dependent behaviour of certain brain connectivity relationships applies to hippocampal-neocortical connections. To encompass the temporal and spatial resolution necessary to do this, two main techniques are used in combination in most of the experimental work hereby presented: (1) electrophysiological recordings of local field potentials (LFPs), and (2) functional activity recordings of blood oxygenation level dependent (BOLD) signal using functional magnetic resonance imaging (fMRI). The main hypothesis is that the frequency-dependent behaviour of specific hippocampal synapses imposes the rules of extra-hippocampal activity propagation and hippocampal-neocortical interactions. The main discovery is that short and long-term plasticity modulates network activation, a finding suggesting a possible mechanism that could mediate the encoding and consolidation of memory traces. Chapters 1 to 3 introduce the vast literature review in which this project lies, and the general methods utilised. Chapter 4 (first experimental chapter) describes, using electrophysiology in rats, the evoked response of the main hippocampal output (CA1 neurons) when its major input (CA3 pyramidal cells) is activated at frequencies that in subsequent experiments were used to build brain-wide functional maps. CA1 spiking activity is found to be optimal in maintaining the amplitude of the population spike (PS) at beta frequencies (10-20 Hz), whereas lower (< 10 Hz) and higher (> 20 Hz) frequencies are normally less effective. Chapter 5 describes, using fMRI, how these intra-hippocampal activity patterns relate to long-range activity propagation in fMRI experiments. Hippocampal activation exhibits a linear monotonic increase with evoked frequency, whilst a network of selected structures is activated preferentially when beta frequencies are applied (mainly neocortical structures like the prefrontal and parietal cortices, motor and sensory cortices, and some subcortical structures like the nucleus accumbens and the striatum). This data is highly correlated with the PS recorded in CA1 and with multi-unit activity (MUA) and single-unit activity (SUA) simultaneously recorded in the medial prefrontal cortex (mPFC), one of the structures receiving propagated activity at beta frequencies, as described in Chapter 6. As mPFC also receives hippocampal input at a restricted beta frequency range stimulation of the dorsal hippocampus, Chapter 7 describes the use of a combined electrophysiology/fMRI approach to identify the pathway responsible for activity propagation. We performed microsurgery lesions to investigate the pathway responsible for the polysynaptic propagation of activity. Findings indicate that the septo-temporal longitudinal pathway is the one leading information transfer from dorsal to ventral hippocampus in the rat, and from there directly to the ventral subiculum, apparently by-passing entorhinal cortex. Last, in Chapter 8 the effect of durable modifications of synaptic weights by long-term potentiation (LTP) in the previously described frequency-dependent activity propagation is also described and contextualized in the memory trace consolidation framework, both electrophysiologically (Chapter 5) and with fMRI (Chapter 6). LTP is a long-lasting change in synaptic weights that, at the CA3-CA1 synapse, is capable of modifying hippocampal-neocortical connections such as to open the opportunity for higher frequency patterns (> 40 Hz) to propagate to neocortical structures. These results suggest that, by means of frequency-coding, the hippocampus normally regulates propagation of selected information to the neocortex, but that at specific moments (e.g. when the hippocampus undergoes LTP) this regulation broadens to permit high-frequency information to pass through and affect neural activity in the cortex. It is a beautifully simple mechanism that merits further detailed examination in a multi-disciplinary manner as outlined in Chapters 9 and 10.

No description available.

[pt] Radares são sistemas eletromagnéticos de detecção e localização de objetos refletores. Sua operação consiste na transmissão de formas de onda e na detecção e processamento do sinal refletido no alvo, visando extrair algumas características deste (e.g. posição, velocidade, direção, tipo de alvo). Radares de ruído, por sua vez, são sistemas que transmitem sinais com forma de onda aleatória e que, por este motivo, apresentam elevado desempenho em presença de interferências externas, intencionais ou não, e supressão da ambiguidade em distância na detecção de alvos. O presente trabalho desenvolve inicialmente uma modelagem probabilística dos sinais envolvidos em radares de ruído. Esta modelagem permite a obtenção de expressões fechadas para funções autocorrelação, densidades espectrais de potência, funções correlação cruzada e ganhos de processamento associadas aos diversos sinais envolvidos. Com base nesta modelagem, e feita uma análise comparativa de radares que utilizam compressão de pulso e integração em sua cadeia de recepção. Mais especificamente, são comparados radares de ruído com radares tradicionais (que utilizam formas de onda determinísticas - chirps) operando em cenários que permitem avaliar aspectos como a resolucao em distância, o nível de lóbulos secundários e a eliminação de ambiguidades. / [en] Radars are electromagnetics systems used for detecting and locating reflecting objects. Their operation is based on the transmition of waveforms and on the detection and processing of the reflected signal so that some targets can be estimated (e.g. position, velocity, direction and type of target). Noise radars are systems that use random signals as the transmitting waveform and that for this reason present high performance against external interference, intentional or not, and the suppression of range ambiguity in the detection of targets. The present work initially develops a probabilistic model for the random signals involved in Noise Radars. This model allows for derivation of closed forms expressions for autocorrelation functions, power spectral densities, processing gains, and cross-correlation functions of the random signals involved. Based on this model, a comparison of radars that employ pulse compression and integration in their receivers. More specifically, Noise Radars are compared to traditional radars that use deterministic waveforms (chirps) under different scenarios which are chosen so that some specific aspects like range resolution, side-lobe levels and range ambiguity elimination can be evaluated.

Quadrature amplitude modulation (QAM) is a highly bandwidth efficient transmission technique for digital communications. It makes use of multiple signal phase and amplitude levels to carry multiple bits per symbol. This requires accurate and robust carrier phase and frequency estimation in the receiver. / Thesis (PhDElectronicEngineering)--University of South Australia, 2002

No description available.

L.B. Arguimbau ... [et al.]. / "September 20, 1954." / Bibliography: p. 49. / Army Signal Corps Contract DA36-039 sc-42607 Project 132B Dept. of the Army Project 3-99-12-022

R.D. Stuart ... [et al.]. / "July 6, 1953." / Bibliography: p. 10. / Army Signal Corps Contract No. DA36-039 sc-100 Project No. 8-102B-0 Dept. of the Army Project No. 3-99-10-022