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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.

Timepix4 is a 24.7×30.0 mm2hybrid pixel detector readout ASIC which has been designed to permit detector tiling on 4 sides. It consists of 448×512 pixels which can be bump bonded to a sensor with square pixels at a pitch of 55 µm. Like its predecessor, Timepix3, it can operate in data driven mode sending out information (Time of Arrival, ToA and Time over Threshold, ToT) only when a pixel has a hit above a pre-defined and programmable threshold. In this mode hits can be tagged to a time bin of 2/s. In photon counting (or frame-based) mode it can count incoming hits at rates of up to 5 GHz/mm2/s. In both modes data is output via between 2 and 16 serializers each running at a programmable data bandwidth of between 40 Mbps and 10 Gbps. The specifications, architecture and circuit implementation are described along with first electrical measurements and measurements with radioactive sources. In photon counting mode X-ray images have been taken at a threshold of 650 e−(with 90Sr source at a threshold of 800 e−(with ∼120 masked pixels).

This work is dedicated to the study of a technique for hadron identification in the TeV momentum range, based on the simultaneous measurement of the energies and of the emission angles of the Transition Radiation (TR) X-rays with respect to the radiating particles. A detector setup has been built and tested with particles in a wide range of Lorentz factors (from about 1 0 3 to about 4 × 1 0 4 crossing different types of radiators. The measured double-differential (in energy and angle) spectra of the TR photons are in a reasonably good agreement with TR simulation predictions.

This work presents the 8-channel FastIC ASIC developed in CMOS 65 nm technology suitable for the readout of positive and negative polarity sensors in high energy physics experiments, Cherenkov detectors and time-of-flight systems. The front-end can be configured to perform analog summation of up to 4 single-ended channels before discrimination in view of improving time resolution when segmenting a SiPM. The outputs encode the time-of-arrival information and linear energy measurement which captures the peak amplitude of the input signal in the 5 µA–25 mA input peak current range. Power consumption of the ASIC is 12 mW/ch with default settings. Measurements of single photon time resolution with a red-light laser source and a HPK SiPM S13360-3050CS are ≈140 ps FWHM.

New developments of pixel detectors based on GaAs sensors offer effective registration of the transition radiation (TR) X-rays and perform simultaneous measurements of their energies and emission angles. This unique feature opens new possibilities for particle identification on the basis of maximum available information about generated TR photons. Results of studies of TR energy-angular distributions using a 500 |j.m thick GaAs sensor attached to a Timepix3 chip are presented. Measurements, analysis techniques and a comparison with Monte Carlo (MC) simulations are described and discussed.

Growing energies of particles at modern or planned particle accelerator experiments as well as cosmic ray experiments require particle identification at gamma-factors ( γ ) of up to ∼ 105. At present there are no detectors capable of identifying charged particles with reliable efficiency in this range of γ . New developments in high granular pixel detectors allow one to perform simultaneous measurements of the energies and the emission angles of generated transition radiation (TR) X-rays and use the maximum available information to identify particles. First results of studies of TR energy-angular distributions using gallium arsenide (GaAs) sensors bonded to Timepix3 chips are presented. The results are compared with those obtained using a silicon (Si) sensor of the same thickness of 500 μ m. The analysis techniques used for these experiments are discussed.

International audience; We describe the performance of the Timepix silicon detector operation at the SPS and H8 extracted beam line at CERN. Some detector calibration results and tuning will be discussed and a new cluster analysis algorithm, to reconstruct the particle hits, is described as well. We investigated the optimal acquisition setup for the Timepix device in order to use its full capabilities. A setup of 4 planes of the Timepix hybrid silicon pixel detector is tested as a hodoscope in the H8 180 GeV/c extracted pion beam, and also with a special 3 ns channeled proton bunch sequence inside the SPS accelerator. Spatial and angular distributions are measured.

We plan to develop an advanced Transition Radiation Detector (TRD) for hadron identification in the TeV momentum range, based on the simultaneous measurement of the energies and of the emission angles of the Transition Radiation (TR) X-rays with respect to the radiating particles. To study the feasibility of this project, we have carried out a beam test campaign at the CERN SPS facility with 20 GeV/c electrons and muons up to 300 GeV/c. To detect the TR X-rays and the radiating particles, we used a 300 μm thick double-sided silicon strip detector, with a strip readout pitch of 50 μm. A 2 m long helium pipe was placed between the radiators and the detector, in order to ensure adequate separation between the TR X-rays and the radiating particle on the detector plane and to limit the X-ray absorption before the detector. We measured the double-differential (in energy and angle) spectra of the TR emitted by several radiators. The results are in good agreement with the predictions obtained from the TR theory.

X-ray transition radiation detectors (TRDs) are used for particle identification in both high energy physics and astroparticle physics. In most of the detectors, emission of the X-ray transition radiation (TR) starts at Lorentz factors above γ ∼ 500 and reaches saturation at γ ∼ 2 ÷ 3 ⋅ 1 0 3 . However, many experiments require particle identification up to γ ∼ 1 0 5 , which is very difficult to achieve with conventional detectors. Semiconductor pixel detectors offer a unique opportunity for precise simultaneous measurements of spectral and angular parameters of TR photons. Test beam studies of the energy and the angular distributions of TR photons emitted by electrons and muons of different momenta crossing several types of radiators were performed at the CERN SPS with a 480 μ m thick silicon detector bonded to a Timepix3 chip. High resolution images of the e n e r g y − a n g l e phase space of the TR produced by different radiators were obtained and compared with MC simulations. The characteristic interference patterns are in agreement with the theoretical models with an unprecedented level of details. The studies presented in this paper also show that simultaneous measurements of both the energy and the emission angles of the TR X-rays could be used to enhance the particle identification performances of TRDs.

We present the concept of a single-photon imager capable of detecting up to 109 photons per second with simultaneous measurements of position (5–10 μm resolution) and time (few tens of picosecond resolution) for each individual photon over an active area of 7 cm2. The detector is based on a "hybrid" concept: a vacuum tube, with a transparent input window on which a suitable photocathode material is deposited, a micro-channel plate and a pixelated read-out anode designed in 65 nm CMOS technology. These figures of merit will open many important applications allowing significant advances in particle physics, life sciences or other emerging fields where the detection of single photons with excellent timing and position resolutions are simultaneously required.

Power consumption is always a concern in the design of readout chips for hybrid pixel detectors. The Timepix3 chip is capable of dealing with up to 80 Mhits/cm2/sec and tagging each hit within a time bin of 1.56 ns. At full speed the Timepix3 chip will consume 1.3 W. We consider how to reduce power consumption if hit rate and/or time stamp precision is not important. The analog power can be reduced by more than an order of magnitude with little impact on noise by reducing the bias current of the input transistor and increasing the return to zero time of the preamplifier. Digital power consumption might be ~ 6× lower by reducing the clock frequency to 1 MHz from the nominal 40 MHz. Simulations and measurements are presented. In very low power mode Timepix3 could consume only ~150 mW on 2 cm2. The new Timepix4 chip aims at time tagging within a bin of 200 psec. Propagation of a 5 GHz clock around the pixel matrix would be impractical. We present a novel architecture implementing a very low jitter clock to the full pixel matrix. A digital Delay Locked Loop is designed in which the delay chain is distributed along the two columns of each super-pixel with the phase comparator and control located at the base of the double column. The control system locks all super-pixels to the low jitter (

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.

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.

see paper for full list of authors; International audience; We present here the first results obtained employing the Timepix3 for the detection and tagging of annihilations of low energy antiprotons. The Timepix3 is a recently developed hybrid pixel detector with advanced Time-of-Arrival and Time-over-Threshold capabilities and has the potential of allowing precise kinetic energy measurements of low energy charged particles from their time of flight. The tagging of the characteristic antiproton annihilation signature, already studied by our group, is enabled by the high spatial and energy resolution of this detector. In this study we have used a new, dedicated, energy selection beamline (GRACE). The line is symbiotic to the AEgIS experiment at the CERN Antiproton Decelerator and is dedicated to detector tests and possibly antiproton physics experiments. We show how the high resolution of the Timepix3 on the Time-of-Arrival and Time-over-Threshold information allows for a precise 3D reconstruction of the annihilation prongs. The presented results point at the potential use of the Timepix3 in antimatter-research experiments where a precise and unambiguous tagging of antiproton annihilations is required.

While designed primarily for X-ray imaging applications, the Medipix3 ASIC can also be used for charged-particle tracking. In this work, results from a beam test at the CERN SPS with irradiated and non-irradiated sensors are presented and shown to be in agreement with simulation, demonstrating the suitability of the Medipix3 ASIC as a tool for characterising pixel sensors., 16 pages, 13 figures

Hybrid pixel detectors are now widely used in particle physics experiments and at synchrotron light sources. They have also stimulated growing interest in other fields and, in particular, in medical imaging. Through the continuous pursuit of miniaturization in CMOS it has been possible to increase the functionality per pixel while maintaining or even shrinking pixel dimensions. The main constraint on the more extensive use of the technology in all fields is the cost of module building and the difficulty of covering large areas seamlessly [1]. On another hand, in the field of electronic component integration, a new approach has been developed in the last years, called 3D Integration. This concept, based on using the vertical axis for component integration, allows improving the global performance of complex systems. Thanks to this technology, the cost and the form factor of components could be decreased and the performance of the global system could be enhanced. In the field of radiation imaging detectors the advantages of 3D Integration come from reduced inter chip dead area even on large surfaces and from improved detector construction yield resulting from the use of single chip 4-side buttable tiles [2]. For many years, numerous R&D centres and companies have put a lot of effort into developing 3D integration technologies and today, some mature technologies are ready for prototyping and production [3]. The core technology of 3D integration is the TSV (Through Silicon Via) and for many years LETI has developed those technologies for various types of applications [4, 5, 6]. In this paper we will present how one of the TSV approaches developed by LETI, called TSV last, has been applied to a readout wafer containing readout chips intended for a hybrid pixel detector assembly [7, 8].

This paper details the response of a triple GEM detector with a 55 μmetre pitch pixelated ASIC for readout. The detector is operated as a micro TPC with 9.5 cm(3) sensitive volume and characterized with a mixed beam of 120 GeV protons and positive pions. A process for reconstruction of incident particle tracks from individual ionization clusters is described and scans of the gain and drift fields are performed. The angular resolution of the measured tracks is characterized. Also, the readout was operated in a mixed mode where some pixels measure drift time and others charge. This was used to measure the energy deposition in the detector and the charge cloud size as a function of interaction depth. The future uses of the device, including in microdosimetry are discussed.

This paper describes a front-end for hybrid pixel readout chips, which was developed for the Timepix3 and Smallpix ASICs. The front-end contains a single-ended preamplifier with a structure for leakage current compensation which can handle both signal polarities, and a single-threshold discriminator with compensation for pixel-to-pixel mismatch. Preamplifier and discriminator are required to be fast, to allow a Time-Of-Arrival (TOA) measurement with a resolution of 1.56 ns. Time-Over-Threshold (TOT) is also measured; the monotonicity of TOT with respect to the input charge is greatly improved as compared to the previous Timepix chip. The analog area is only 55 μm × 13.5 μm. Timepix3 has already been fabricated and the first test results are also presented in this paper.

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 64x64 square pixels with 25 μm pitch. The main features include simultaneous 4-bit measure- ment of Time-over-Threshold (ToT) and Time-of-Arrival (ToA) with 10 ns accuracy, on-chip data compression and power pulsing capability.

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.

The ATLAS Forward Detectors for Measurement of Elastic Scattering and Luminosity (ALFA) have been fully installed during the 2010–2011 winter LHC shutdown. ALFA consists of 8 mini tracking detectors made of 20 planes of scintillating fibers placed in Roman Pot units near the beam and 240 m away on both sides of the interaction point. The front-end electronics sit directly on top of the PMTs and has been designed to facilitate the connectivity to the ATLAS counting room. The full system consisting of the detectors units, the control electronics and the connections to the ATLAS TTC, TDAQ and DCS systems has been successfully tested.