Bande de base

Résumé

thumb|right|Spectre d'un signal en bande de base Dans le jargon des télécommunications, le terme de bande de base ou base de bande (ou en anglais baseband) désigne une technique de transmission dans laquelle le signal est envoyé directement sur le canal après Codage en ligne sans passer par un codage canal (sans modulation). Le signal transmis peut être analogique ou numérique. Dans le cas d'une transmission numérique, le signal transmis est alors sous la forme simple d'un signal codé par exemple en NRZ, Manchester ou AMI, avec les caractéristiques suivantes : *Suite de bits représentant les données numériques, *Changement d'états discret d'amplitude du signal physique (tension électrique, intensité lumineuse), *Un signal en bande de base ne subit pas de transposition en fréquence ; de même, la durée de chaque bit est constante. En bande de base, le spectre du signal transmis démarre à partir de la fréquence zéro, ce qui distingue ce procédé de la modulation qui utilise une onde po

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Publications associées (10)

It has already been a few years since the first appearance of micro-electromechanical systems (MEMS) in academic research. Since then, a broad number of devices have been designed under this generic term. Bulk-acoustic wave (BAW) resonators are among the few of them which have become exploited at industrial level. They are mainly used to implement filters for mainstream telecommunication applications. In a different domain, potential applications for integrated wireless transceivers are flourishing. While some of them require always higher data rates, others need devices with low data rate but even lower power consumption. The goal of this thesis is to explore ways of using BAW resonators to implement building blocks for such a low-power radio and actually verify the postulate that this could help improving power consumption as well as miniaturize key functionalities. For the active integrated circuit part, the choice of a standard digital 0.18µm CMOS process established itself for its low cost and ubiquity. The specifications for the developed radio receiver are calculated for a physical layer derived from the well known Bluetooth communication protocol in the 2.4GHz ISM band with similar applications scenarii but with much lower data rates and wider channel spacing. After presenting the advantages and limitations of the devices, the implications for using BAWresonators to implement a low-power radio are investigated at circuit and system levels and a super-heterodyne architecture is proposed. A selective low-noise amplifier (LNA) is used at the circuit front-end to yield image and blocker rejection. Measurements for the RF front-end comprising an external balun, the selective LNA, a first downconversionmixer and an intermediate-frequency (IF) amplifier showed an overall noise figure of 11dB for a current consumption of 1.5mA under 1.2V. The high selectivity of the design yields an image rejection ratio of at least 50dB and allows to decrease linearity requirements and thus power consumption. A slightly improved version of the same front-end integrated together with the analog baseband signal processing chain but still using external local oscillators showed sensitivities of -96dBm at 100kbps symbol rate and -93dBm at 200kbps with an external state-of-the art FSK demodulator, allowing to extrapolate a global noise figure of 12.2dB for a global current consumption of 2.3mA under 1.2V. The proposed solution for the frequency synthesis uses both a BAW oscillator for the first downconversion to IF and a quadrature quasi-harmonic relaxation oscillator to translate the signals to baseband. The relaxation oscillator is embedded within a phase-locked loop (PLL) for which all the required blocks are discussed. Particularly, a novel modular multi-modulus frequency divider is presented, which does not necessitate complicated logic to yield the wanted division ratio and uses dynamic logic. The necessary digital circuitry to control the frequency generation is discussed as well. Finally, measurements for the complete receiver using the proposed frequency synthesis as well as digital control and demodulator implemented on FPGA are presented.

EPFL2008

Chargement

A 49 mu W 6th-Order Chebyshev SSF-based Low-Pass Analog Filter for IEEE 802.11ax

Daniel Mathias Bold, Salvatore Collura, Christian Enz, Alessandro Pezzotta

In this paper a continuous-time low-pass analog filter based on the Cascoded Super Source Follower (C-SSF) architecture, implemented in a 28-nm bulk CMOS process, is presented. The target application is the transceiver analog baseband for the next-generation IEEE 802.11ax WiFi standard. To comply with the high-selectivity requirements, a 6th-order Chebyshev transfer function has been implemented as a cascade of three biquadratic cells. The high quality factors required by such topology have been achieved by cascoding the feedback transistor in the standard SSF cell, reducing the quality factor dependence on the output conductance of the source follower transistor. Designed with the Inversion-Coefficient (IC) methodology, the filter is able to operate for channel bandwidths ranging from 10 MHz to 20 MHz by changing its bias current. Measurement results show that the filter has a minimum noise power of -55.1 dBm and a maximum IIP3 of 14 dBm consuming 49 mu W, i.e. 8.17 mu W per pole, occupying an area of 0.0099 mm(2).

IEEE2020

Chargement

A 51.4 Mb/s FSK Transmitter Employing a Phase Domain Digital Synthesizer with 1.5 mu s Start-up for Energy Efficient Duty Cycling

Christian Enz, David Ruffieux, Nicola Scolari, Raghavasimhan Thirunarayanan

This paper presents a low start-up latency Transmitter (TX) that can achieve FSK data rates of upto 51.4 Mb/s for deployment in duty cycled microsensor nodes. Utilizing a Phase Domain Digital Synthesizer with an FBAR frequency reference, this TX has a start-up latency of just 1.5 mu s. It has been integrated in a 65nm technology and outputs upto 3 dBm power. It achieves a phase noise of -110 dBc/Hz at 1 MHz offset and has a frequency coverage of 2.17 - 2.47 GHz. The power consumption of this TX (including the Digital Baseband) varies from 15 mW at 1.2 Mb/s to 21.4 mW at 51.4 Mb/s. At peak data rate, this leads to an Duty-Cycling-Energy/bit (which takes into account the start-up energy) of 500 pJ/b for transmitting packets of length 32 bytes. Moreover, the TX incorporates a Hybrid Requantizer circuit which helps to trade off in-band noise with the spurs due to the non-linearity induced Sigma Delta noise folding.

Ieee2016

Chargement

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EPFL2008