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 mu m thick Si sensors are given. similar to 72e super(-) r.m.s. noise and similar to 40e super(-) 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.
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.
Abstract
Timepix4 is a 24.7 × 30.0 mm
2
hybrid 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 <200 ps and Timepix4 can record hits correctly at incoming rates of ∼3.6 MHz/mm
2
/s. In photon counting (or frame-based) mode it can count incoming hits at rates of up to 5 GHz/mm
2
/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 <10 masked pixels). In data driven mode images were taken of ToA/ToT data using a
90
Sr source at a threshold of 800 e
−
(with ∼120 masked pixels).
This manuscript describes the optimization of the front-end readout electronics for high granularity hybrid pixel detectors. The theoretical study aims at minimizing the noise and jitter. The model ...presented here is validated with both circuit post layout simulations and measurements on the Timepix4 Application Specific Integrated Circuit (ASIC). The analog front-end circuit and the procedure to optimize the dimensions of the main transistors are described with detail.
The Timepix4 is the most recent ASIC designed in the framework of the Medipix4 Collaboration. It was manufactured in 65nm CMOS process, and consists of a four side buttable matrix of 448 × 512 pixels with 55µm pitch. The analog front-end has a gain of ∼36mV/ke- when configured in High Gain Mode, and ∼20mV/ke- when configured in Low Gain Mode. The Equivalent Noise Charge (ENC) is ∼68e-rms and ∼80e-rms in High Gain Mode and in Low Gain Mode respectively. In event driven mode the incoming hits can be time stamped within a ∼ 200ps time bin and the chip can deal with a maximum flux of ∼ 3.6MHzmm−2s−1. In photon counting mode, the chip can deal with up to ∼ 5GHzmm−2s−1.
The routine designed to optimize the Timepix4 front-end is then used to analyze the performance limits in terms of jitter and noise for Charge Sensitive Amplifiers in pixel detectors.
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.
The Timepix2 ASIC (application-specific integrated circuit) is the upgraded successor to the Timepix 1 hybrid pixel detector readout chip. Like the original, Timepix2 contains a matrix of 65k square ...pixels of 55 μm pitch that can be coupled to a similarly segmented semiconductor sensor, or integrated in an ionising gas detector. The pixels are programmable, with several operation modes and selectable counter depths (up to 18 bits for time-of-arrival, ToA, and up to 14 bits for time-over-threshold, ToT). In ToT and ToA mode, each pixel records the arrival time and energy deposited by particles interacting with the corresponding sensor segment, with an optional separation of timing resolution for ToT and ToA: down to 10 ns each. The gain of the frontend circuit can be programmed to adapt to the quantity of energy deposited in the sensor, yielding a large dynamic range of 0.38 ke− to 950 ke−. The frontend noise in adaptive gain mode is 380 e− rms. The design also introduces some power optimisation features to the Timepix portfolio, such as power masking on selectable parts of the pixel matrix. With all pixels powered on, using 100 MHz for both ToT and ToA clock frequencies, and assuming a sparse particle interaction with the pixels, the matrix is estimated to consume less than 900 mW based on simulation.
New architecture for the analog front-end of Medipix4 Sriskaran, V.; Alozy, J.; Ballabriga, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2020, Letnik:
978
Journal Article
Recenzirano
The Medipix4 chip is the latest member of the family of Medipix pixel detector readout chips aimed at high rate spectroscopic X-ray imaging. Unlike its predecessors, it will be possible to tile the ...chip on all 4 sides permitting seamless large area coverage. This paper focuses on the development of the new Medipix4 front-end architecture capable of event-by-event data processing allowing accurate photon energy reconstruction, with charge sharing correction at an increased rate compared to Medipix3. The architecture is particularly well adapted for readout of pixelated high-Z detector materials allowing accurate energy binning of incoming hits at a fine pixel pitch. The new front-end architecture has a linear response up to 150 keV (CdTe), a count-rate capability up to 5.1×108 photons.mm−2s−1 for 10% dead time loss at 10 keV (CdTe) , and an energy resolution aiming for 2.2 keV FWHM (Full Width Half Maximum) at 60 keV (CdTe). The layout accommodates sensors with either 70μm or 140μm pitch of contacts.
•New architecture for the analog front-end of Medipix4.•Electronics to improve dynamic range, rate capability and energy resolution.•Photon processing with charge summing and single pixel arbitration mode.•Aim for spectroscopic X-ray imaging at rates compatible with medical CT scans.
A pixelated 2-D detector combining chemical-vapor-deposited diamond and the Timepix3 chip ("Diamondpix") is presented. Its conceptual design with a brief description of the Timepix3 chip acquisition ...modes is outlined. The performance has been tested with fluorescence X-rays, fast neutrons, and electron beam. A first energy calibration has been obtained with X-rays and compared with an equivalent silicon Timepix3 detector. Measurements on fast neutrons and other radioactive source demonstrated a good gamma/neutron rejection capability. Moreover, Diamondpix has been exposed to a beam of ultrarelativistic electrons showing that it can act as a very powerful monitor of beam position, measuring simultaneously the charge released inside the detector and the time of arrival (ToA) of the particles by reconstructing the time profile of the beam bunches. Finally, high-intensity measurements show some delayed signals probably related to the trap defects inside the diamond. The first study of their spatial distribution correlated with the measurements of the charge released inside the diamond and ToA is also discussed.
The development of a single-photon detector based on a vacuum tube, transmission photocathode, microchannel plate and CMOS pixelated read-out anode is presented. This imager will be capable of ...detecting up to 1 billion photons per second over an area of 7 cm
2
, with simultaneous measurement of position and time with resolutions of about 5 microns and few tens of picosecond, respectively. The detector has embedded pulse-processing electronics with data-driven architecture, based on the Timepix4 ASIC, producing up to 160 Gb/s data that will be handled by a high-throughput FPGA-based external electronics and data acquisition system. These performances will enable significant advances in particle physics, life sciences, quantum optics or other emerging fields where the detection of single photons with excellent timing and position resolutions are simultaneously required.
Abstract
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.
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