| 1. |
- Abdalla, Suliman A
(författare)
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Architecture and circuit design of photon counting readout for X-ray imaging sensors
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hybrid pixel array detectors for X-ray imaging are based on different technologies for sensor and readout electronics. The readout electronics are based on standard CMOS technologies that are experiencing continuously rapid improvements by means of down-scaling the feature sizes, which in turn lead to higher transistor densities, lower power consumption, and faster circuits. For pixel-array imaging sensors the improvements in CMOS technology opens up new possibilities of integrating more functionality in the pixels for local processing of the sensor data. However, new issues related to the tight integration of both analog and digital processing circuits within the small area of a pixel must also be evaluated. The advantages of down-scaling the CMOS technology can be utilized to increase the spatial resolution by reducing the pixel sizes. Recent research indicates however that the bottleneck in reaching further spatial resolution in X-ray imaging sensors may not be limited by the circuit area occupied by the functions necessary in the pixels, but are instead related to problems associated with charge-sharing of charges generated by the sensor which are distributed over a neighbourhood of pixels and will limit the spatial resolution and lead to a distortion of the energy spectrum. In this thesis a mechanism to be implemented in the readout circuits is proposed in order to suppress the charge-sharing effects. The proposed architecture and its circuit implementation are evaluated with respect to circuit complexity (area) and power consumption. For a photon-counting pixel it is demonstrated that the complete pixel, with charge-sharing suppression mechanism, can be implemented using 300 transistors with an idle power consumption of 2.7μW in a 120nm CMOS technology operating with a 1.2V power supply. The improvements in CMOS technology can also be used for increasing the range of applications for X-ray imaging sensors. In this thesis, an architecture is proposed for multiple energy discrimination, called color X-ray imaging. The proposed solution is the result of balancing the circuit complexity and the image quality. The method is based on color sub-sampling with intensity biasing. For three-level energy discrimination, that corresponds to color imaging systems for visible light with R, G, and B color components, the increase in circuit complexity will be only 20% higher than that for the Bayer method but results in significantly better image quality. As the circuit complexity in the digital processing within each pixel is increased, the digitally induced noise may play an increasingly important role for the signal-to-noise ratio in the measurements. In this thesis an initial study is conducted regarding how the digital switching noise affects the analog amplifiers in the photon-counting pixel.
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| 2. |
- Abdalla, Suliman, et al.
(författare)
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Architecture and Circuit Design for Color X-Ray Pixal Array Detector Read-Out Electronics
- 2007
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Ingår i: 24th Norchip Conference, 2006. - New York : IEEE conference proceedings. - 9781424407729 ; , s. 271-276
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Konferensbidrag (refereegranskat)abstract
- This paper proposes an area- and power-efficient implementation of the read-out electronics for color X-ray pixel detectors for imaging. Introducing multiple levels of energy discrimination will increase the complexity of the read-out electronics in each pixel. The proposed architecture has full resolution for the intensity and reduced resolution for the energy spectrum (color), which leads to a good compromise of image quality and circuit complexity. We show that the increase in complexity, compared to single energy-range pixel, will lead to increase in circuit area of less than 20%.
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| 3. |
- Abdalla, Suliman, et al.
(författare)
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Circuit Implementation of Mechanism for Charge-Sharing Suppression for Photon-Counting Pixel Arrays
- 2005
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Ingår i: 23rd NORCHIP Conference 2005. - : IEEE conference proceedings. - 1424400643 ; , s. 137-140
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Konferensbidrag (refereegranskat)abstract
- This work proposes an efficient circuit implementation of a mechanism for charge-sharing suppression in photon-counting pixel arrays based on current-mode circuits for the analog parts. The additional circuits needed for charge-sharing suppression in a four-pixel cluster, leads to an increase in power consumption of 36% and only a marginal increase in circuit area. The implemented pixel with window-discrimination, managing charge-sharing in a four-pixel cluster and with an event-counter of 13 bits, consists of 300 transistors and has a power consumption of 2.7 μW when idle. It is implemented in a 120nm CMOS process and the presented results are based on simulations.
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| 4. |
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| 5. |
- Lundgren, Jan, et al.
(författare)
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An Area Efficient Readout Architecture for Photon Counting Color Imaging
- 2007
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 576:1, s. 132-136
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Tidskriftsartikel (refereegranskat)abstract
- The introduction of several energy levels, namely color imaging, in photon counting X-ray image sensors is a trade-off between circuit complexity and spatial resolution. In this paper we propose a pixel architecture that has full resolution for the intensity and uses sub-sampling for the energy spectrum. The results show that this sub-sampling pixel architecture produces images with an image quality which is, on average, 2.4 dB (PSNR) higher than those for a single energy range architecture and with half the circuit complexity of that for a full sampling architecture.
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| 6. |
- Lundgren, Jan, et al.
(författare)
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Evaluation of Mixed-Signal Noise Effects in Photon Counting X-Ray Image Sensor Readout Circuits
- 2006
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 563:1, s. 88-91
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Tidskriftsartikel (refereegranskat)abstract
- In readout electronics for photon counting pixel detectors, the tight integration between analog and digital blocks causes the readout electronics to be sensitive to on-chip noise coupling. This noise coupling can result in faulty luminance values in grayscale X-ray images, or as color distortions in a color X-ray imaging system. An exploration of simulating noise coupling in readout circuits is presented which enables the discovery of sensitive blocks at as early a stage as possible, in order to avoid costly design iterations. The photon counting readout system has been simulated for noise coupling in order to highlight the existing problems of noise coupling in X-ray imaging systems. The simulation results suggest that on-chip noise coupling should be considered and simulated in future readout electronics systems for X-ray detectors.
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| 7. |
- Lundgren, Jan, et al.
(författare)
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Power Distribution and Substrate Noise Coupling Investigations on the Behavioral Level for Photon Counting Imaging Readout Circuits
- 2007
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 576:1, s. 113-117
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Tidskriftsartikel (refereegranskat)abstract
- In modern mixed-signal system design, there are increasing problems associated with noise coupling caused by switching digital parts to sensitive analog parts. As a consequence, there is a growing necessity to understand these problems. In order to avoid costly design iterations, noise coupling simulations should be initiated as early as possible in the design chain. The problems associated with on-chip noise coupling have been discovered in photon counting pixel detector readout systems, where the level of integration of analog and digital circuits is very high on a very small area, and it would appear that these problems will continue to increase for future system designs in this field. This paper deals with the functionality of utilizing behavioral level models for simulating noise coupling in these readout systems. The methods and models are described and simulation results are shown for a photon counting pixel detector readout system.
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| 8. |
- Oelmann, Bengt, et al.
(författare)
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All-Digital Window Discriminator for Photon Counting Pixel Detectors
- 2001
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Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 0013-5194. ; 37:6, s. 373-374
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Tidskriftsartikel (refereegranskat)abstract
- An all-digital window discriminator is presented. It is event-driven and does not rely on any external or internal timing references. In addition, it provides an area-efficient implementation of photon counting pixel detectors. The transistor-level implementation of the circuit is presented with its circuit area and timing performance.
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| 9. |
- Thim, Jan, et al.
(författare)
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Realizing increased sub-pixel spatial resolution in X-ray imaging using displaced multiple images
- 2011
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 633:Suppl 1, s. S247-S249
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Tidskriftsartikel (refereegranskat)abstract
- A method, generally called oversampling, to reach sub-pixel resolution by taking slightly displaced images of an object is investigated for X-ray applications. By mounting the sensor on a high precision step motor table it is possible to increase the spatial resolution from 55 Όm×55 Όm to at least 20 Όm×20 Όm, which is required for quality assurance measurements in several industry processes. The performance compared to physically smaller pixels is shown, and the effects of charge sharing on the method are investigated. The suggested method is relatively cost effective compared to using X-ray microscopy. © 2010 Elsevier B.V. All rights reserved.
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| 10. |
- Thim, Jan, et al.
(författare)
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Realizing increased sub-pixel spatial resolution in X-ray imaging using displaced multiple images
- 2009
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Ingår i: 11th International Workshop on Radiation Imaging Detectors.
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Konferensbidrag (refereegranskat)abstract
- In X-Ray imaging with pixel detector systems, the resolution of the image taken is dependant on the pixel size in the detector readout electronics. Depending on the functionality of the readout electronics, the surface space on the readout chip for each pixel has a minimum size, which sets the spatial resolution of the taken images. For applications where it is required to image extremely small structures in a material, the spatial resolution of the X-Ray detector system sets the limit, and readout systems with high functionality cannot be considered. One way to reach sub-pixel resolution is to use a nanofocus source to achieve an X-ray microscopy setup [1]. However, this type of X-ray source is still too expensive to be an alternative for quality assurance systems used in the industry. In this paper we focus on a much simpler way of increasing spatial resolution that has proven effective in images for visible light. By mounting either the objects for imaging or the image sensor system on a step motor table and take multiple images slightly dislocated from one another, an increase in sub-pixel spatial resolution can be achieved. Consider the case that an image sensor system with a pixel size of 55x55 µm is available for an imaging application that requires a resolution of 20x20 µm. The application is material characterization and allows for multiple images to be taken for one sample. In this case, increasing the sub-pixel resolution by nine times (3x3) will result in a pixel size of about 18x18 µm, which would meet the requirements. This can be realized by taking nine images dislocated 1/3 of the pixel width from each other. If the upper left pixel of the centre image has coordinates (0,0) the upper left pixel of all the nine images will have coordinates (-1/3,1/3), (0,1/3), (1/3,1/3), (-1/3,0), (0,0), (1/3,0), (-1/3,-1/3), (0,-1/3) and (1/3,-1/3). The result of a direct combination of these images is illustrated in Figure 1, where one of nine images is shown at the left. Combining the images without images processing with an algorithm will yield the image in the centre, which can be compared to how the image would look in full 9x resolution (right image). As can be seen, some details are lost and the image is blurred compared to a full resolution image. However, with an image processing algorithm in the combination phase this effect can be reduced and the image quality increased. This paper shows simulated and measured results from using dislocation imaging in X-Ray imaging systems, where the test case system will be the MEDIPIX2 system [2]. An investigation of different image processing algorithms suitable for this type of imaging is conducted. An investigation is also done to show whether detectors with large size pixels compared to the standard size in a MEDIPIX system can be combined with the described sub-pixel scaling technique. The result of this combination is used to investigate the charge sharing effects on the MEDIPIX system. [1] Norlin B., Fröjdh C., Nuclear Instruments and Methods, sect. A (2009), doi:10.1016/j.nima.2009.03.155[2] Llopart X., Campbell M., Dinapoli R., san Segundo D., Pernigotti E., IEEE Transactions on Nuclear Science, Vol. 49, Issue 5, Part 1, pp. 2279-2283, October 2002. Figure 1. Image (left) with 50x50 pixels, with the resulting combination of nine images forming an image with a sub-pixel resolution of 150x150 pixel (centre), compared to a full resolution reference image (right).
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