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Architecture and circuit design of photon counting readout for X-ray imaging sensors
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. (Electronics Design Division, STC)
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Sundsvall: Mittuniversitetet , 2007. , 80 p.
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 22
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:miun:diva-9327OAI: oai:DiVA.org:miun-9327DiVA: diva2:227240
Presentation
(English)
Opponent
Supervisors
Available from: 2009-07-10 Created: 2009-07-10 Last updated: 2011-02-06Bibliographically approved
List of papers
1. Circuit Implementation of Mechanism for Charge-Sharing Suppression for Photon-Counting Pixel Arrays
Open this publication in new window or tab >>Circuit Implementation of Mechanism for Charge-Sharing Suppression for Photon-Counting Pixel Arrays
2005 (English)In: 23rd NORCHIP Conference 2005, IEEE conference proceedings, 2005, 137-140 p., 1597008Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2005
Keyword
read-out electronics
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-3330 (URN)10.1109/NORCHP.2005.1597008 (DOI)000241010100033 ()2-s2.0-33847207475 (Scopus ID)3283 (Local ID)1-4244-0064-3 (ISBN)3283 (Archive number)3283 (OAI)
Conference
23rd NORCHIP Conference 2005; Oulu; Finland; 21 November 2005 through 22 November 2005
Projects
STC - Sensible Things that Communicate
Available from: 2008-09-30 Created: 2009-07-30 Last updated: 2016-10-05Bibliographically approved
2. An Area Efficient Readout Architecture for Photon Counting Color Imaging
Open this publication in new window or tab >>An Area Efficient Readout Architecture for Photon Counting Color Imaging
Show others...
2007 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 576, no 1, 132-136 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
X-ray, photon counting, pixel detectors
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-3904 (URN)10.1016/j.nima.2007.01.140 (DOI)000247330000031 ()2-s2.0-34248171930 (Scopus ID)4265 (Local ID)4265 (Archive number)4265 (OAI)
Conference
8th International Workshop on Radiation Imaging Detectors, Jul 02-06, 2006, Pisa, Italy
Projects
STC - Sensible Things that Communicate
Note

8th International Workshop on Radiation Imaging Detectors, Jul 02-06, 2006, Pisa, Italy

Available from: 2008-11-29 Created: 2008-11-29 Last updated: 2017-12-12Bibliographically approved
3. Architecture and Circuit Design for Color X-Ray Pixal Array Detector Read-Out Electronics
Open this publication in new window or tab >>Architecture and Circuit Design for Color X-Ray Pixal Array Detector Read-Out Electronics
2007 (English)In: 24th Norchip Conference, 2006, New York: IEEE conference proceedings, 2007, 271-276 p., 4126997Conference paper, Published paper (Refereed)
Abstract [en]

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%.

Place, publisher, year, edition, pages
New York: IEEE conference proceedings, 2007
Keyword
Sensor readout electronics
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-3577 (URN)10.1109/NORCHP.2006.329225 (DOI)000245540900064 ()2-s2.0-34547363891 (Scopus ID)4460 (Local ID)978-1-4244-0772-9 (ISBN)4460 (Archive number)4460 (OAI)
Conference
24th Norchip Conference, 2006; Linkoping; Sweden; 20 November 2006 through 21 November 2006
Projects
STC - Sensible Things that Communicate
Available from: 2008-09-30 Created: 2009-07-29 Last updated: 2016-10-05Bibliographically approved
4. Evaluation of Mixed-Signal Noise Effects in Photon Counting X-Ray Image Sensor Readout Circuits
Open this publication in new window or tab >>Evaluation of Mixed-Signal Noise Effects in Photon Counting X-Ray Image Sensor Readout Circuits
2006 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 563, no 1, 88-91 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Photon Counting, Pixel Detector, Noise Effects, Evaluation
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-3433 (URN)10.1016/j.nima.2006.01.098 (DOI)000238764700022 ()2-s2.0-33745000546 (Scopus ID)3432 (Local ID)3432 (Archive number)3432 (OAI)
Conference
7th International Workshop on Radiation Imaging Detectors, Jul 04-07, 2005, Grenoble, France
Projects
STC - Sensible Things that Communicate
Note

7th International Workshop on Radiation Imaging Detectors, Jul 04-07, 2005, Grenoble, France

Available from: 2008-09-30 Created: 2009-01-07 Last updated: 2017-12-12Bibliographically approved

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