Search

AMS-2 is an astroparticle experiment designed for a very precise measurement of primary cosmic rays spectrum. The experiment will operate on board of the ISS at a 400 km altitude for a period of about 3 years. The main scientific goals of the experiment are the search for antimatter, for dark matter and the study of gamma rays. In AMS the electromagnetic calorimeter plays a key role for its high capability to measure e/sup +/, e/sup -/ and gamma spectra and to suppress the background generated by p and He nuclei. To directly detect photons the calorimeter is requested to provide a stand alone trigger. The proposed trigger, presented in this article, will have the capability to detect photons with energy above 4 GeV with an efficiency of about 100 %. The hardware implementation foresees an analog section, comparing the photomultiplier signal with a given threshold, and a digital section applying the trigger selection algorithm.

Final results on a CMOS 0.18 µm front-end chip for silicon strips readout are summarized and preliminary results on time measurement are discussed. The status of the next version in 0.13 µm is briefly presented.

The VIRGO signal read-out system is based on a sixteen channels architecture. The system is now installed at the site and the noise of eight of the channels has been measured. The noise at 50 Hz and all its harmonics is coherent with a simultaneous measurement of the power supply. The power supply measurement has been used to remove the 50 Hz line and all its harmonics from the signal read-out noise.

Large interferometers aiming at the detection of gravitational waves are under construction. They use multiple optical cavities and require a coherent control of several mirror positions without spoiling the detector sensitivity. In the case of the VIRGO interferometer several solutions to this problem are currently under study inside the collaboration. In this paper we describe a preliminary study of one of these solutions. We discuss the sensitivity of the controlled interferometer and present some tests done through a simulation of the apparatus. The limitations of the presented solution are discussed.

La filière technologique CMOS représente sans doute la meilleure solution lorsqu'il s'agit de rassembler sur le même substrat des fonctions logiques et des fonctions analogiques moyenne fréquence utilisant le concept de la « commutation de capacités ». L'amplificateur opérationnel est alors l'élément essentiel qui limite les performances de ces dernières (tensions de décalage, gain fini, taux de rejection, bande passante, vitesse de balayage, etc...). Fonctionnant sur charge capacitive, il est possible de retenir des amplificateurs se comportant en sortie, soit comme des sources de tension, soit comme des sources de courant. La première solution est de maniement simple, mais ne conduit pas à des solutions optimums pour une technologie donnée. La seconde solution permet d'obtenir des performances dynamiques meilleures, au prix toutefois d'une plus grande complexité de la conception qui ne peut être menée à bien que par l'emploi d'outils de simulation très performants. L'objet de cet article est l'étude théorique comparative du comportement de ces deux classes d'amplificateurs dans des structures à capacités commutées et la description électrique de leur réalisation technologique.