A programmable, low noise, multichannel ASIC for readout of pixelated amorphous silicon arrays

Yarema, R.; Zimmerman, T.; Srage, J; Antonuk, L; Berry, J.E.; Huang, Wei; Maolinbay, M.

doi:10.1016/s0168-9002(99)00900-6

Cited by 15 publications

(13 citation statements)

References 3 publications

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“…This technique was employed to explore additive noise reduction. The acquisition system also incorporates full-custom, low noise, 32-channel preamplifier-multiplexer chips 33 operated at two charge capacity settings, resulting in analog-to-digital conversion gains of 550 e / ADC and 4092 e / ADC for PSI-1 and PSI-2/PSI-3, respectively, unless otherwise indicated. A single readout of array data by the G3 system results in a data frame.…”

Section: Iic Electronic Acquisition Systemmentioning

confidence: 99%

Active pixel imagers incorporating pixel‐level amplifiers based on polycrystalline‐silicon thin‐film transistors

El‐Mohri¹,

Antonuk²,

Koniczek³

et al. 2009

Medical Physics

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Active matrix, flat-panel imagers ͑AMFPIs͒ employing a 2D matrix of a-Si addressing TFTs have become ubiquitous in many x-ray imaging applications due to their numerous advantages. However, under conditions of low exposures and/or high spatial resolution, their signal-to-noise performance is constrained by the modest system gain relative to the electronic additive noise. In this article, a strategy for overcoming this limitation through the incorporation of in-pixel amplification circuits, referred to as active pixel ͑AP͒ architectures, using polycrystalline-silicon ͑poly-Si͒ TFTs is reported. Compared to a-Si, poly-Si offers substantially higher mobilities, enabling higher TFT currents and the possibility of sophisticated AP designs based on both n-and p-channel TFTs. Three prototype indirect detection arrays employing poly-Si TFTs and a continuous a-Si photodiode structure were characterized. The prototypes consist of an array ͑PSI-1͒ that employs a pixel architecture with a single TFT, as well as two arrays ͑PSI-2 and PSI-3͒ that employ AP architectures based on three and five TFTs, respectively. While PSI-1 serves as a reference with a design similar to that of conventional AMFPI arrays, PSI-2 and PSI-3 incorporate additional in-pixel amplification circuitry. Compared to PSI-1, results of x-ray sensitivity demonstrate signal gains of ϳ10.7 and 20.9 for PSI-2 and PSI-3, respectively. These values are in reasonable agreement with design expectations, demonstrating that poly-Si AP circuits can be tailored to provide a desired level of signal gain. PSI-2 exhibits the same high levels of charge trapping as those observed for PSI-1 and other conventional arrays employing a continuous photodiode structure. For PSI-3, charge trapping was found to be significantly lower and largely independent of the bias voltage applied across the photodiode. MTF results indicate that the use of a continuous photodiode structure in PSI-1, PSI-2, and PSI-3 results in optical fill factors that are close to unity. In addition, the greater complexity of PSI-2 and PSI-3 pixel circuits, compared to that of PSI-1, has no observable effect on spatial resolution. Both PSI-2 and PSI-3 exhibit high levels of additive noise, resulting in no net improvement in the signal-to-noise performance of these early prototypes compared to conventional AMFPIs. However, faster readout rates, coupled with implementation of multiple sampling protocols allowed by the nondestructive nature of pixel readout, resulted in a significantly lower noise level of ϳ560 e ͑rms͒ for PSI-3.

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Section: Iic Electronic Acquisition Systemmentioning

confidence: 99%

Active pixel imagers incorporating pixel‐level amplifiers based on polycrystalline‐silicon thin‐film transistors

El‐Mohri¹,

Antonuk²,

Koniczek³

et al. 2009

Medical Physics

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“…All arrays were mounted on dedicated printed circuit motherboards, with electrical connections established by means of wirebonding. The electronic acquisition system and the 32-channel preamplifier-multiplexer ASIC used for these measurements have been described previously, 16,17 with modifications performed to the acquisition system, as necessary, to facilitate various types of measurements.…”

Section: Iia Array Designs and Electronic Acquisition Systemmentioning

confidence: 99%

An investigation of signal performance enhancements achieved through innovative pixel design across several generations of indirect detection, active matrix, flat‐panel arrays

et al. 2009

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Active matrix flat-panel imager (AMFPI) technology is being employed for an increasing variety of imaging applications. An important element in the adoption of this technology has been significant ongoing improvements in optical signal collection achieved through innovations in indirect detection array pixel design. Such improvements have a particularly beneficial effect on performance in applications involving low exposures and/or high spatial frequencies, where detective quantum efficiency is strongly reduced due to the relatively high level of additive electronic noise compared to signal levels of AMFPI devices. In this article, an examination of various signal properties, as determined through measurements and calculations related to novel array designs, is reported in the context of the evolution of AMFPI pixel design. For these studies, dark, optical, and radiation signal measurements were performed on prototype imagers incorporating a variety of increasingly sophisticated array designs, with pixel pitches ranging from 75 to 127 microm. For each design, detailed measurements of fundamental pixel-level properties conducted under radiographic and fluoroscopic operating conditions are reported and the results are compared. A series of 127 microm pitch arrays employing discrete photodiodes culminated in a novel design providing an optical fill factor of approximately 80% (thereby assuring improved x-ray sensitivity), and demonstrating low dark current, very low charge trapping and charge release, and a large range of linear signal response. In two of the designs having 75 and 90 microm pitches, a novel continuous photodiode structure was found to provide fill factors that approach the theoretical maximum of 100%. Both sets of novel designs achieved large fill factors by employing architectures in which some, or all of the photodiode structure was elevated above the plane of the pixel addressing transistor. Generally, enhancement of the fill factor in either discrete or continuous photodiode arrays was observed to result in no degradation in MTF due to charge sharing between pixels. While the continuous designs exhibited relatively high levels of charge trapping and release, as well as shorter ranges of linearity, it is possible that these behaviors can be addressed through further refinements to pixel design. Both the continuous and the most recent discrete photodiode designs accommodate more sophisticated pixel circuitry than is present on conventional AMFPIs--such as a pixel clamp circuit, which is demonstrated to limit signal saturation under conditions corresponding to high exposures. It is anticipated that photodiode structures such as the ones reported in this study will enable the development of even more complex pixel circuitry, such as pixel-level amplifiers, that will lead to further significant improvements in imager performance.

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“…(Yarema et al 2000) Readout of all, or of any contiguous part of a prototype by the acquisition system results in a single data frame.…”

Section: Data Acquisitionmentioning

confidence: 99%

Signal behavior of polycrystalline HgI₂at diagnostic energies of prototype, direct detection, active matrix, flat-panel imagers

Antonuk

El‐Mohri

et al. 2008

Phys. Med. Biol.

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Active matrix, flat-panel x-ray imagers based on a-Si:H thin film transistors offer many advantages and are widely utilized in medical imaging applications. Unfortunately, the detective quantum efficiency (DQE) of conventional flat-panel imagers incorporating scintillators or a-Se photoconductors is significantly limited by their relatively modest signal to noise ratio, particularly in applications involving low x-ray exposures or high spatial resolution. For this reason, polycrystalline HgI 2 is of considerable interest by virtue of its low effective work function, high atomic number, and the possibility of large-area deposition. In this study, a detailed investigation of the properties of prototype, flat-panel arrays coated with two forms of this high-gain photoconductor are reported. Encouragingly, high x-ray sensitivity, low dark current, and spatial resolution close to the theoretical limits were observed from a number of prototypes. In addition, input-quantum-limited DQE performance was measured from one of the prototypes at relatively low exposures. However, high levels of charge trapping, lag, and polarization, as well as pixel-to-pixel variations in x-ray sensitivity are of concern. While the results of the current study are promising, further development will be required to realize prototypes exhibiting the characteristics necessary to allow practical implementation of this approach.

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A programmable, low noise, multichannel ASIC for readout of pixelated amorphous silicon arrays

Cited by 15 publications

References 3 publications

Active pixel imagers incorporating pixel‐level amplifiers based on polycrystalline‐silicon thin‐film transistors

Active pixel imagers incorporating pixel‐level amplifiers based on polycrystalline‐silicon thin‐film transistors

An investigation of signal performance enhancements achieved through innovative pixel design across several generations of indirect detection, active matrix, flat‐panel arrays

Signal behavior of polycrystalline HgI₂at diagnostic energies of prototype, direct detection, active matrix, flat-panel imagers

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A programmable, low noise, multichannel ASIC for readout of pixelated amorphous silicon arrays

Cited by 15 publications

References 3 publications

Active pixel imagers incorporating pixel‐level amplifiers based on polycrystalline‐silicon thin‐film transistors

Active pixel imagers incorporating pixel‐level amplifiers based on polycrystalline‐silicon thin‐film transistors

An investigation of signal performance enhancements achieved through innovative pixel design across several generations of indirect detection, active matrix, flat‐panel arrays

Signal behavior of polycrystalline HgI2at diagnostic energies of prototype, direct detection, active matrix, flat-panel imagers

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Signal behavior of polycrystalline HgI₂at diagnostic energies of prototype, direct detection, active matrix, flat-panel imagers