J. Alozy

Bio: J. Alozy is an academic researcher from CERN. The author has contributed to research in topics: Detector & Transition radiation. The author has an hindex of 9, co-authored 22 publications receiving 537 citations.

The Medipix3RX: a high resolution, zero dead-time pixel detector readout chip allowing spectroscopic imaging

Abstract: The Medipix3 chips have been designed to permit spectroscopic imaging in highly segmented hybrid pixel detectors. Spectral degradation due to charge sharing in the sensor has been addressed by means of an architecture in which adjacent pixels communicate in the analog and digital domains on an event-by-event basis to reconstruct the deposited charge in a neighbourhood prior to the assignation of the hit to a single pixel. The Medipix3RX chip architecture is presented. The first results for the characterization of the chip with 300 μm thick Si sensors are given. ~ 72e− r.m.s. noise and ~ 40e− r.m.s. of threshold dispersion after chip equalization have been measured in Single Pixel Mode of operation. The homogeneity of the image in Charge Summing mode is comparable to the Single Pixel Mode image. This demonstrates both modes are suitable for X-ray imaging applications.

Review of hybrid pixel detector readout ASICs for spectroscopic X-ray imaging

Abstract: Semiconductor detector readout chips with pulse processing electronics have made possible spectroscopic X-ray imaging, bringing an improvement in the overall image quality and, in the case of medical imaging, a reduction in the X-ray dose delivered to the patient. In this contribution we review the state of the art in semiconductor-detector readout ASICs for spectroscopic X-ray imaging with emphasis on hybrid pixel detector technology. We discuss how some of the key challenges of the technology (such as dealing with high fluxes, maintaining spectral fidelity, power consumption density) are addressed by the various ASICs. In order to understand the fundamental limits of the technology, the physics of the interaction of radiation with the semiconductor detector and the process of signal induction in the input electrodes of the readout circuit are described. Simulations of the process of signal induction are presented that reveal the importance of making use of the small pixel effect to minimize the impact of the slow motion of holes and hole trapping in the induced signal in high-Z sensor materials. This can contribute to preserve fidelity in the measured spectrum with relatively short values of the shaper peaking time. Simulations also show, on the other hand, the distortion in the energy spectrum due to charge sharing and fluorescence photons when the pixel pitch is decreased. However, using recent measurements from the Medipix3 ASIC, we demonstrate that the spectroscopic information contained in the incoming photon beam can be recovered by the implementation in hardware of an algorithm whereby the signal from a single photon is reconstructed and allocated to the pixel with the largest deposition.

Photon Counting Detectors for X-Ray Imaging With Emphasis on CT

Abstract: X-ray imaging is a widely used imaging modality in the medical diagnostic field due to its availability, low cost, high spatial resolution, and fast image acquisition X-ray photons in standard X-ray sources are polychromatic Detectors that allow to extract the “color” information of the individual X-rays can lead to contrast enhancement, improved material identification or reduction of beam hardening artifacts at the system level, if we compare them with the widely spread energy integrating detectors Today, in the field of computed tomography (CT), prototypes of clinical grade systems based on spectral photon counting detectors are currently available for clinical research from different companies One of the key system components in that development is the X-ray photon detector This article reviews the photon detection hardware, from the conversion of X-rays into electrical signals to the pulse processing electronics A review of available photon counting application specific integrated circuits (ASICs) for spectroscopic X-ray imaging is presented with emphasis on the CT medical imaging application

Towards a new generation of pixel detector readout chips

Abstract: The Medipix3 Collaboration has broken new ground in spectroscopic X-ray imaging and in single particle detection and tracking. This paper will review briefly the performance and limitations of the present generation of pixel detector readout chips developed by the Collaboration. Through Silicon Via technology has the potential to provide a significant improvement in the tile-ability and more flexibility in the choice of readout architecture. This has been explored in the context of 3 projects with CEA-LETI using Medipix3 and Timepix3 wafers. The next generation of chips will aim to provide improved spectroscopic imaging performance at rates compatible with human CT. It will also aim to provide full spectroscopic images with unprecedented energy and spatial resolution. Some of the opportunities and challenges posed by moving to a more dense CMOS process will be discussed.

A prototype hybrid pixel detector ASIC for the CLIC experiment

Abstract: A prototype hybrid pixel detector ASIC specifically designed to the requirements of the vertex detector for CLIC is described and first electrical measurements are presented. The chip has been designed using a commercial 65 nm CMOS technology and comprises a matrix of 64 × 64 square pixels with 25 μm pitch. The main features include simultaneous 4-bit measurement of Time-over-Threshold (ToT) and Time-of-Arrival (ToA) with 10 ns accuracy, on-chip data compression and power pulsing capability.

The ATLAS Experiment at the CERN Large Hadron Collider

Abstract: This paper describes the ATLAS experiment as installed in i ts experimental cavern at point 1 at CERN. It also presents a brief overview of the expec ted performance of the detector.

Dual- and Multi-Energy CT: Principles, Technical Approaches, and Clinical Applications

Abstract: The ability of dual- and multi-energy CT to differentiate materials of different effective atomic numbers makes possible several new and clinically relevant CT applications.

The alice experiment at the CERN LHC

Abstract: ALICE is a general-purpose heavy-ion detector designed to study the physics of strongly interacting matter and the quark-gluon plasma in nucleus-nucleus collisions at the LHC at a center of mass energy of 5.5 TeV/nucleon. It is currently under construction and will be ready for data taking at LHC turn-on in 2007. The collaboration currently includes more than 900 physicists, both from nuclear physics and high-energy physics, from over 70 institutions in 27 countries.

Timepix3: a 65K channel hybrid pixel readout chip with simultaneous ToA/ToT and sparse readout

Abstract: The Timepix3, hybrid pixel detector (HPD) readout chip, a successor to the Timepix \cite{timepix2007} chip, can record time-of-arrival (ToA) and time-over-threshold (ToT) simultaneously in each pixel. ToA information is recorded in a 14-bit register at 40 MHz and can be refined by a further 4 bits with a nominal resolution of 1.5625 ns (640 MHz). ToT is recorded in a 10-bit overflow controlled counter at 40 MHz. Pixels can be programmed to record 14 bits of integral ToT and 10 bits of event counting, both at 40 MHz. The chip is designed in 130 nm CMOS and contains 256 × 256 pixel channels (55 × 55 μm2). The chip, which has more than 170 M transistors, has been conceived as a general-purpose readout chip for HPDs used in a wide range of applications. Common requirements of these applications are operation without a trigger signal, and sparse readout where only pixels containing event information are read out. A new architecture has been designed for sparse readout and can achieve a throughput of up to 40 Mhits/s/cm2. The flexible architecture offers readout schemes ranging from serial (one link) readout (40 Mbps) to faster parallel (up to 8 links) readout of 5.12 Gbps. In the ToA/ToT operation mode, readout is simultaneous with data acquisition thus keeping pixels sensitive at all times. The pixel matrix is formed by super pixel (SP) structures of 2 × 4 pixels. This optimizes resources by sharing the pixel readout logic which transports data from SPs to End-of-Column (EoC) using a 2-phase handshake protocol. To reduce power consumption in applications with a low duty cycle, an on-chip power pulsing scheme has been implemented. The logic switches bias currents of the analog front-ends in a sequential manner, and all front-ends can be switched in 800 ns. The digital design uses a mixture of commercial and custom standard cell libraries and was verified using Open Verification Methodology (OVM) and commercial timing analysis tools. The analog front-end and a voltage-controlled oscillator for 1.5625 ns timing resolution have been designed using full custom techniques.

Towards high-capacity fibre-optic communications at the speed of light in vacuum

Abstract: Wide-bandwidth signal transmission with low latency is emerging as a key requirement in a number of applications, including the development of future exaflop-scale supercomputers, financial algorithmic trading and cloud computing. Optical fibres provide unsurpassed transmission bandwidth, but light propagates 31% slower in a silica glass fibre than in vacuum, thus compromising latency. Air guidance in hollow-core fibres can reduce fibre latency very significantly. However, state-of-the-art technology cannot achieve the combined values of loss, bandwidth and mode-coupling characteristics required for high-capacity data transmission. Here, we report a fundamentally improved hollow-core photonic-bandgap fibre that provides a record combination of low loss (3.5 dB km-1) and wide bandwidth (160 nm), and use it to transmit 373 x 40 Gbit s-1 channels at a 1.54 ms km-1 faster speed than in a conventional fibre. This represents the first experimental demonstration of fibre-based wavelength division multiplexed data transmission at close to (99.7%) the speed of light in vacuum