Modulation de largeur d'impulsion

La modulation de largeur d'impulsions (MLI ; en anglais : Pulse Width Modulation, soit PWM), est une technique couramment utilisée pour synthétiser des signaux pseudo analogiques à l'aide de circuits numériques (tout ou rien, 1 ou 0), ou plus généralement à états discrets. Elle sert à générer un signal pseudo analogique à partir d'un environnement numérique ou analogique pour permettre un traitement de ce signal par des composants en commutation (se comportant comme des interrupteurs ouverts ou fermés). Le principe général est qu'en appliquant une succession rapide d'états discrets avec des ratio de durée bien choisis, on peut obtenir en ne regardant que la valeur moyenne du signal n'importe quelle valeur intermédiaire Applications Les usages les plus fréquents :

La conversion numérique-analogique
Les amplificateurs de classe D
Les alimentations à découpage
Les variateurs de vitesse
Les onduleurs
Les redresseurs
Plus généralement tous les dispositifs d'é

Gigahertz free-space electro-optic modulators based on Mie resonances

Ileana-Cristina Benea-Chelmus

Electro-optic modulators are essential for sensing, metrology and telecommunications. Most target fiber applications. Instead, metasurface-based architectures that modulate free-space light at gigahertz (GHz) speeds can boost flat optics technology by microwave electronics for active optics, diffractive computing or optoelectronic control. Current realizations are bulky or have low modulation efficiencies. Here, we demonstrate a hybrid silicon-organic metasurface platform that leverages Mie resonances for efficient electro-optic modulation at GHz speeds. We exploit quasi bound states in the continuum (BIC) that provide narrow linewidth (Q = 550 at lambda(res) = 1594 nm), light confinement to the non-linear material, tunability by design and voltage and GHz-speed electrodes. Key to the achieved modulation of Delta T/T-max = 67% are molecules with r(33) = 100 pm/V and optical field optimization for low-loss. We demonstrate DC tuning of the resonant frequency of quasi-BIC by Delta lambda(res) = 11 nm, surpassing its linewidth, and modulation up to 5 GHz (f(EO,- 3dB) = 3 GHz). Guided mode resonances tune by Delta lambda(res) = 20 nm. Our hybrid platform may incorporate free-space nanostructures of any geometry or material, by application of the active layer post-fabrication.

NATURE PORTFOLIO2022

Hybrid continuous-discrete-time multi-bit delta-sigma A/D converters with auto-ranging algorithm

Sergio Pesenti

In wireless portable applications, a large part of the signal processing is performed in the digital domain. Digital circuits show many advantages. The power consumption and fabrication costs are low even for high levels of complexity. A well established and highly automated design flow allows one to benefit from the constant progress in CMOS technologies. Moreover, digital circuits offer robust and programmable signal processing means and need no external components. Hence, the trend in consumer electronics is to further reduce the part of analog signal processing in the receiver chain of wireless transceivers. Consequently, analog-to-digital converters with higher resolutions and bandwidths are constantly required. The ultimate goal is the direct digitization of radio frequency signals, where the conversion would be performed immediately after the front-end amplifier. ΔΣ-modulation-based converters have proved to be the most suitable to achieve the required performance. Switched-capacitor implementations have been widely used over the last two decades. However, recent publications and books have shown that continuous-time architectures can achieve the same performance with lower power consumption. Most designs found throughout the literature use a single- or few-bit internal quantizer with a high-order modulation. As a result, in order to achieve the resolutions and bandwidths required today, the sampling frequency must exceed 100MHz. This approach leads to non-negligible power consumption in the clock generation. Moreover, the presence of such fast squared signals is not suitable for a system-on-chip comprising radio frequency receivers. In this thesis we propose a low-power strategy relying on a large number of internal levels rather than on a high sampling frequency or modulation order. Besides, a hybrid continuous-discrete-time approach is used to take advantage of the accuracy of switched-capacitor circuits and the low power consumption of continuous-time implementation. The sensitivity to clock jitter brought about by the continuous-time stage is reduced by the use of a large number of levels. An auto-ranging algorithm is developed in this thesis to overcome the limitation of a large-size quantizer under low-voltage supply. Finally, the strategy is applied to a design example addressing typical specifications for a Bluetooth receiver with direct conversion.

EPFL2007

Etude formelle pour la synthèse de convertisseurs multiniveaux asymétriques

Jean-Sébastien Mariéthoz

The multilevel converters allow generating a voltage waveform whose magnitude and quality are higher than those of conventional converters. They are devoted to medium and high-voltage, high-switching-frequency applications. Among the series connected cell inverters, the symmetrical multilevel inverters are made of identical cells, which topology is generally the H-bridge inverter. This dissertation deals with asymmetrical multilevel converters, which combine high-voltage cells — made of low conduction loss switches — with low-voltage cells — made of low switching loss switches. The different cells play different roles. The goal is to design a converter that has both better energetic efficiency and higher resolution with the same number of cells. This dissertation develops a set of tools that allows synthesizing an asymmetrical multilevel converter. It develops the cell combination rules, which allow defining several cell association classes. The inverter step uniformity condition determines the finesse that can be reached. The optimized modulation condition allows to reduce the highvoltage cell switching frequency without changing the low-voltage cell switching frequency. This property is essential to derive benefit from combining switches of different characteristics. The power balance condition determine how to control the power sharing between the cells. These association classes are different for the single-phase converters and the three-phase converters — without neutral wire. They allow to select a configuration suitable for a given application. Furthermore, several ways that allow improving the inverter resolution are investigated. The modulation is essential to associate a high-quality signal (which will really be delivered to the load by means of the inverter levels) to the reference signal (which should ideally be applied to the load). The modulator evaluation methods are assessed. An approach—based on the modulated signal decomposition in elementary frames—is proposed. The main modulator drawbacks are highlighted. A modulator—which arrange the frames in order—allows to reduce the modulated signal distortion and number of transitions. The specific control methods that allow to minimize the inverter number of switchings are developed. The active power cell supply implies several conversion stages, which decrease the converter energetic efficiency. Some solutions that allow to reduce these losses are proposed. Finally, this dissertation attempts to determine, which are the more interesting solutions, depending on the application.

EPFL2005