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  • 1. Ballabriga, R.
    et al.
    Blaj, G.
    Campbell, M.
    Fiederle, M.
    Greiffenberg, D.
    Heijne, E. H. M.
    Llopart, X.
    Plackett, R.
    Procz, S.
    Tlustos, L.
    Turecek, D.
    Wong, Winnie
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Characterization of the Medipix3 pixel readout chip2011In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 6, no 1Article in journal (Refereed)
  • 2. Ballabriga, R.
    et al.
    Campbell, M.
    Heijne, E.
    Llopart, X.
    Tlustos, L.
    Wong, Winnie
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Medipix3: A 64 k pixel detector readout chip working in single photon counting mode with improved spectrometric performance2011In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 633, no SUPPL. 1, p. S15-S18Article in journal (Refereed)
    Abstract [en]

    Medipix3 is a 256×256 channel hybrid pixel detector readout chip working in a single photon counting mode with a new inter-pixel architecture, which aims to improve the energy resolution in pixelated detectors by mitigating the effects of charge sharing between channels. Charges are summed in all 2×2 pixel clusters on the chip and a given hit is allocated locally to the pixel summing circuit with the biggest total charge on an event-by-event basis. Each pixel contains also two 12-bit binary counters with programmable depth and overflow control. The chip is configurable such that either the dimensions of each detector pixel match those of one readout pixel or detector pixels are four times greater in area than the readout pixels. In the latter case, event-by-event summing is still possible between the larger pixels. Each pixel has around 1600 transistors and the analog static power consumption is below 15 μW in the charge summing mode and 9 μW in the single pixel mode. The chip has been built in an 8-metal 0.13 μm CMOS technology. This paper describes the chip from the pixel to the periphery and first electrical results are summarized.

  • 3.
    De Gaspari, Massimiliano
    et al.
    CERN, Geneva, Switzerland.
    Alozy, Jerome
    CERN, Geneva, Switzerland.
    Ballabriga, Rafael
    CERN, Geneva, Switzerland.
    Campbell, Michael
    CERN, Geneva, Switzerland.
    Fröjdh, Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. CERN, Geneva, Switzerland.
    Idarraga, John
    CERN, Geneva, Switzerland.
    Kulis, S
    CERN, Geneva, Switzerland.
    Llopart, Xavier
    CERN, Geneva, Switzerland.
    Poikela, Toumas
    CERN, Geneva, Switzerland.
    Valerio, P
    CERN, Geneva, Switzerland.
    Wong, Winnie
    CERN, Geneva, Switzerland.
    Design of the analog front-end for the Timepix3 and Smallpix hybrid pixel detectors in 130 nm CMOS technology2014In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 9, p. Art. no. C01037-Article in journal (Refereed)
    Abstract [en]

    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.

  • 4.
    Fröjdh, Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. CERN, Geneva, Switzerland.
    Bisello, F.
    IBA Dosimetty GmbH, Schwarzenhatck, Germany.;FAU Univ Erlangen Nrnberg, Erlangen, Germany..
    Campbell, M.
    CERN, Geneva, Switzerland..
    Damet, J.
    CERN, Geneva, Switzerland.;Univ Lausanne Hosp, Inst Radiat Phys, Lausanne, Switzerland..
    Hamann, E.
    KIT, ANKA Synchrotron Radiat Facil, Karlsruhe, Germany..
    Koenig, T.
    KIT, ANKA Synchrotron Radiat Facil, Karlsruhe, Germany..
    Wong, Winnie S.
    CERN, Geneva, Switzerland.;Univ Lausanne Hosp, Inst Radiat Phys, Lausanne, Switzerland..
    Zuber, M.
    KIT, ANKA Synchrotron Radiat Facil, Karlsruhe, Germany..
    Spectral response of the energy-binning Dosepix ASIC coupled to a 300 mu m silicon sensor under high fluxes of synchrotron radiation2015In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 804, p. 43-49Article in journal (Refereed)
    Abstract [en]

    The Dosepix hybrid pixel detector was designed for dosimetry and radiation monitoring applications. It has three programmable modes of operation: photon counting mode, energy integration mode, and dosimetry mode. The dosimetry mode measures the energy of individual X-ray photons and automatically sorts events into pre-defined energy bins. The output is a histogram representing the measured X-ray energy spectrum, permitting a dose reconstruction that accounts for the attenuation of photons at each energy bin. This presents a potential radiation protection and dosimetry instrument in medical radiodiagnostic practices, including high flux systems such as computed tomography (CT). In this paper, we characterise the Dosepix chip by investigating the energy response and count rate capabilities when coupled to a 300 pm silicon sensor under high fluxes of monochromatic synchrotron radiation. Under nominal settings, the Dosepix detector can detect photons down to 3.5 keV, with an energy resolution of 16.5% FWHM for 8.5 keV photons and 8% FWHM for 40 keV photons. The chip can count up to 1.67 Mcps/mm(2) of 40 keV photons whilst maintaining linear counting behaviour. This count rate range can be further increased by changing the programmable operating settings of the detector, making it suitable for a range of photon dosimetry applications.

  • 5.
    Llopart Cudié, Xavier
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Ballabriga, R
    Campbell, M
    Tlustos, L
    Wong, Winnie
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Timepix, a 65k programmable pixel readout chip for arrival time, energy and/or photon counting measurements2007In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 581, no 1-2, p. 485-494Article in journal (Refereed)
  • 6.
    Reza, Salim
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Wong, Winnie
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Fröjdh, Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Norlin, Börje
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungstörm, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thim, Jan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Smart dosimetry by pattern recognition using a single photon counting detector system in time over threshold mode2012In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 7, no 1, p. Art. no. C01027-Article in journal (Refereed)
    Abstract [en]

    The function of a dosimeter is to determine the absorbed dose of radiation, for those cases in which, generally, the particular type of radiation is already known. Lately, a number of applications have emerged in which all kinds of radiation are absorbed and are sorted by pattern recognition, such as the Medipix2 application in [1]. This form of smart dosimetry enables measurements where not only the total dosage is measured, but also the contributions of different types of radiation impacting upon the detector surface. Furthermore, the use of a photon counting system, where the energy deposition can be measured in each individual pixel, ensures measurements with a high degree of accuracy in relation to the pattern recognition. In this article a Timepix [2] detector system has been used in the creation of a smart dosimeter for Alpha, Beta and Gamma radiation. When a radioactive particle hits the detector surface it generates charge clusters and those impacting upon the detector surface are read out and image processing algorithms are then used to classify each charge cluster. The individual clusters are calculated and as a result, the dosage for each type of radiation is given. In some cases, several particles can impact in roughly the same place, forming overlapping clusters. In order to handle this problem, a cluster separation method has been added to the pattern recognition algorithm. When the clusters have been separated, they are classified by shape and sorted into the correct type of radiation. The algorithms and methods used in this dosimeter have been developed so as to be simple and computationally effective, in order to enable implementation on a portable device. © 2012 IOP Publishing Ltd and SISSA.

  • 7.
    Wong, Winnie
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    A Hybrid Pixel Detector ASIC with Energy Binning for Real-Time, Spectroscopic Dose Measurements2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Hybrid pixel detectors have been demonstrated to provide excellent quality detection of ionising photon radiation, particularly in X-ray imaging. Recently, there has been interest in developing a hybrid pixel detector specifically for photon dosimetry. This thesis is on the design, implementation, and preliminary characterisation of the Dosepix readout chip.

    Dosepix has 256 square pixels of 220 mm side-length, constituting 12.4 mm2 of photo-sensitive area per detector. The combination of multiple pixels provides many parallel processors with limited input flux, resulting in a radiation dose monitor which can continuously record data and provide a real-time report on personal dose equivalent. Energy measurements are obtained by measuring the time over threshold of each photon and a state machine in the pixel sorts the detected photon event into appropriate energy bins. Each pixel contains 16 digital thresholds with 16 registers to store the associated energy bins. Preliminary measurements of Dosepix chips bump bonded to silicon sensors show very promising results. The pixel has a frontend noise of 120 e-. In low power mode, each chip consumes 15 mW, permitting its use in a portable, battery-powered system. Direct time over threshold output from the hybrid pixel detector assembly reveal distinctive photo-peaks correctly identifying the nature of incident photons, and verification measurements indicate that the pixel binning state machines accurately categorise charge spectra. Personal dose equivalent reconstruction using this data has a flat response for a large range of photon energies and personal dose equivalent rates.

  • 8.
    Wong, Winnie
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Design considerations for Area-Constrained In-Pixel Photon counting in Medipix32008In: Topical workshop on Electronics for Particle Physics, 2008, p. 539-543Conference paper (Refereed)
    Abstract [en]

    Hybrid pixel detectors process impinging photons using front-end electronics electrically connected to a segmented sensor via solder bumps. This allows for complex in-pixel processing while maintaining 100% fill factor. Medipix3 is a single photon processing chip whose 55 μm x 55 μm pixels contain analog charge-processing circuits, inter-pixel routing, and digital blocks. While a standard digital design flow would use logic gates from a standard cell library, the integration of multiple functions and configurations within the compact area of the Medipix3 pixel requires a full-custom manual layout. This work describes the various area-saving design strategies which were employed to optimize the use of available space in the digital section of the Medipix3 pixel.

  • 9.
    Wong, Winnie
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Ballabriga, R.
    Campbell, M.
    Llopart, X.
    Tlustos, L.
    Counter architectures for a single photon-counting pixel detector such as Medipix32007In: AIP Conference Proceedings, American Institute of Physics (AIP), 2007, Vol. 958, p. 262-263Conference paper (Refereed)
  • 10. Wong, Winnie S
    et al.
    Anton, G
    ECAP, Erlangen Centre for Astroparticle Physics, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
    Ballabriga, R
    Medipix Team, PH-ESE-ME, CERN, Geneva, Switzerland.
    Blaj, G
    Medipix Team, PH-ESE-ME, CERN, Geneva, Switzerland.
    Böhnel, M
    ECAP, Erlangen Centre for Astroparticle Physics, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
    Campbell, M
    Medipix Team, PH-ESE-ME, CERN, Geneva, Switzerland.
    Gabor, T
    ECAP, Erlangen Centre for Astroparticle Physics, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
    Heijne, E
    Medipix Team, PH-ESE-ME, CERN, Geneva, Switzerland.
    Llopart, S
    Medipix Team, PH-ESE-ME, CERN, Geneva, Switzerland.
    Michel, T
    ECAP, Erlangen Centre for Astroparticle Physics, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
    Ritter, I
    ECAP, Erlangen Centre for Astroparticle Physics, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
    Poikela, T
    Medipix Team, PH-ESE-ME, CERN, Geneva, Switzerland.
    Sievers, P
    ECAP, Erlangen Centre for Astroparticle Physics, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
    Tlustos, L
    Medipix Team, PH-ESE-ME, CERN, Geneva, Switzerland.
    Valerio, P
    Medipix Team, PH-ESE-ME, CERN, Geneva, Switzerland.
    Electrical measurements of a multi-mode hybrid pixel detector ASIC for radiation detection2012In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 7, no 1, p. Art. no. C01056-Article in journal (Refereed)
    Abstract [en]

    We present the first electrical measurements of an application-specific integrated circuit (ASIC) to be used in a hybrid pixel detector intended for dosimetry and radiation detection. The dosimeter has three programmable modes of operation: photon counting mode, energy integration mode, and dosimetry mode. The ASIC comprises a matrix of 16 by 16 (256 total) square pixels of 220 ÎŒm pitch, providing 12.4 mm 2 of segmented active area. Each pixel can be configured to operate in one of the three radiation measurement modes, with programmable-depth counters and shift registers to tailor the data word size and optimise the readout frame-rate in a given mode. The individual energies of impinging photons are determined through programmable analogue energy threshold discrimination, time over threshold measurement, or a combination thereof. Furthermore, the dosimetry mode contains 16 digital energy thresholds and automatically sorts data into 16 corresponding energy bin registers. The chip's output is therefore pre-processed charge spectra of the radiation field. This paper discusses results from measurements taken using programmable test-pulses to inject controlled stimuli into the pixel circuits.

  • 11.
    Wong, Winnie S.
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Anton, G.
    Ballabriga, R.
    Böhnel, M.
    Campbell, M.
    Heijne, E.
    Llopart, X.
    Michel, T.
    Münster, I.
    Plackett, R.
    Sievers, P.
    Takoukam, P.
    Tlustos, L.
    Valerio, P.
    A pixel detector asic for dosimetry using time-over-threshold energy measurements2011In: Radiation Measurements, ISSN 1350-4487, E-ISSN 1879-0925, Vol. 46, no 12, p. 1619-1623Article in journal (Refereed)
    Abstract [en]

    In this work we present the design of a chip which provides the readout of a highly segmented diode array, in which signals induced by individual X-ray photons are processed discretely. There are several benefits to this approach, including the ability to achieve a high signal to noise ratio due to the inherently low sensor capacitance, and the suppression of background noise (e.g. dark current) using an analogue threshold. The segmentation also ensures a linear behaviour even at very high dose rates. A time over threshold (ToT1) energy measurement technique provides an immediate digital value corresponding to the energy deposited onto the diode by each individual photon. Deadtime-free operation is achieved by reading out a subset of the detector segments at a time while the rest of the detector continues to process signals. This paper describes the application-specific integrated circuit (ASIC) chip which was designed to provide pre-processing of photo-induced signals in the detector and readout of the processed digital data.

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