Ultra haute fréquence | EPFL Graph Search

La bande des ultra hautes fréquences (ultra high frequency/UHF) est la bande du spectre radioélectrique comprise entre et , soit les longueurs d'onde de à . Vocabulaire La bande UHF est le terme officiel désignant les fréquences radio de 300 à , mais la partie haute appartient plus généralement au domaine technique des « hyperfréquences » qui s'étend de () à . On y trouve donc des appellations anciennes et largement utilisées comme la Bande L et la Bande S. Strictement, au-dessus de , on considère qu'on entre dans le domaine des micro-ondes, même si cette limite d'1 GHz n'est qu'empiriquement fixée. L'UHF est connu par le grand public pour les antennes TV dites "râteau" et les antennes d'intérieur, servant à capter la TNT. En France entre 470 et 694 MHz. En Espagne, ce terme servait à désigner la TVE 2 du 1er janvier 1965 au 14 novembre 1966. Propriétés générales thumb|200px|Groupement d'antennes pour les bandes des et Les fréquences de type UHF se prop

A Cryo-CMOS Oscillator With an Automatic Common-Mode Resonance Calibration for Quantum Computing Applications

Edoardo Charbon, Yue Chen, Fabio Sebastiano

This article presents a 4-to-5 GHz LC oscillator operating at 4.2K for quantum computing applications. The phase noise (PN) specification of the oscillator is derived based on the control fidelity for a single-qubit operation. To reveal the substantial gap between the theoretical predictions and measurement results at cryogenic temperatures, a new PN expression for an oscillator is derived by considering the shot-noise effect. To reach the optimum performance of an LC oscillator, a common-mode (CM) resonance technique is implemented. Additionally, this work presents a digital calibration loop to adjust the CM frequency automatically at 4.2K, reducing the oscillator's PN and thus improving the control fidelity. The calibration technique reduces the flicker corner of the oscillator over a wide temperature range (10 x and 8 x reduction at 300K and 4.2K, respectively). At 4.2K, our 0.15-mm(2) oscillator consumes a 5-mW power and achieves a PN of -153.8dBc/Hz at a 10MHz offset, corresponding to a 200-dB FOM. The calibration circuits consume only a 0.4-mW power and 0.01-mm(2) area.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2022

System Design and Advanced Circuit Techniques for Bi-Directional Brain-Machine Interfaces

Wen-Yang Hsu

Bi-directional brain-machine interfaces (BBMIs) that can capture electrophysiological signals and provide feedback through electrical stimulation are emerging tools with various applica-tions in fundamental neuroscience research as well as in clinical treatments of neurological dis-orders. The strict requirements originating from the specific and vast application range of these systems pose severe constraints to the development of portable or implantable microelectronic devices in terms of safety and reliability, autonomy, critical physical dimensions. The power consumption of BBMI systems should be minimized to comply with safety require-ments and enable long-term operations in an energy-constraint environment. In addition, specific physical dimensions and the interconnect reduction are crucial to fully exploit novel MEMS technologies to forge BBMIs aiming at different applications. Both bottom-up and top-down improvements are mandatory contributors of innovations on critical circuit blocks and system-level optimization, respectively. The first part of this thesis presents a BBMI targeting for a specific clinical application, namely, deep brain stimulation which has been proven to effectively alleviate neurological disorders such as essential tremor and Parkinsonâs disease. A novel MEMS technology which encom-passes a 3-dimensional brain region is employed to enhance the localization of the stimulation site. In order to fully exploit this technology, system requirements such as the strict device di-mension, highly-limited inter-connects and simultaneous recordings from 5 channels at low-power consumption pose several challenges on the custom electronics. Using a single supply voltage, an application-specific integrated circuit (ASIC) shaped into a specific aspect ratio is presented to tackle the aforementioned challenges. While the presented work is suitable for open-loop operations which demand frequent post-surgery programming for optimized therapeutic effects, closed-loop approaches directly re-sponding to the recorded signals offers better patient experience. Such autonomous BBMIs require long-term operation in an energy-constrained environment as well as intensive compu-tations on data processing. Innovations on critical blocks such as recording front-ends and stimulators are thus highly desirable to achieve an aggressive power reduction. A novel high-frequency, switched-capacitor (HFSC) stimulation and active charge balancing scheme is proposed. It achieves a high energy efficiency and well-controlled stimulation charge in the presence of large electrode impedance variations. Furthermore, the HFSC can be imple-mented in a compact size without any external component to simultaneously enable multi-channel stimulation by deploying multiple stimulators. The proposed design shows significant benefits over the constant-current and voltage-mode stimulation methods. Finally, a time-based and digitally-intensive recording front-end is presented, which employs the pulse-width modulation (PWM) to generate a timing-encoded binary output. The proposed design achieves low-power operation using a highly scaled technology with a sin-gle 0.5V supply voltage, favorable for system integration in energy-constraint BBMI applications.

EPFL2018

Effect of intelligent antennas on radio system planning and on mitigation

Juliane Iten Chaves Simoes

Smart antennas have been recently applied to improve the capacity and the performance of second generation wireless mobile communication systems. In general, smart antennas reduce the effects of multipath fading and improve the signal-to-noise-plus-interference ratio (SNIR). Additional advantages such as channel capacity increase in urban areas, coverage extension in urban areas and spectrum efficiency in general can be obtained with the aid of smart antennas at the base station. Drawbacks are the cost, and both hardware and software complexity. Smart antennas promise a clear advantage in multi-service traffic scenario in comparison with non-adaptive antenna techniques. It is generally accepted that the adaptive antennas technique will be a key enable for the success of the European third generation mobile communication system known as Universal Mobile Telecommunication System (UMTS). The first part of this thesis presents two types of smart antenna systems: switched beam antennas and adaptive arrays. It introduces statistical models for them and investigates the performance measures of cellular radio systems with and without smart antennas deployed at base stations. Employing Monte-Carlo methodology, a tool has been developed to analyze the interference between two different systems that share the same geographical area and have neighboring frequency channels. The statistical smart antennas model has been used to verify the mitigation of the interference compared with others antennas used at the base station. These simulations have been done for TDMA, FDMA and CDMA systems. Wireless communication operating at different frequencies on the non-ionizing radiation (NIR) region of the electromagnetic spectrum has greatly increased in the last few decades, with important benefits for the population. These include mobile communication, such as cellular telephone systems. However, the radiated electromagnetic field levels increased substantially in areas where people may stay during long periods each day. This may result in long-term exposure to the population. International guidelines and standards were developed aiming at protecting the population, and limiting the maximum radiation produced. The methods used by regulation authorities to evaluate the field levels at places of sensitive use yield very conservative results. They need thus to be refined prior to the introduction of adaptive antennas. In the second part of the thesis, a 3D ray tracing tool is developed to predict the propagation for real scenarios using UMTS systems. This tool takes into account 3D radiation diagrams and multipath propagation. It was used in real scenarios to compare the real field levels with the levels obtained by the approximate methods defined by the regulation standards. Finally, this tool was used to predict the field levels in a scenario containing smart antennas. Scenario not foreseen in the method described in the standards.

EPFL2008