Indirect X-ray photon-counting image sensor with 27T pixel and 15e&lt;sup&gt;&amp;#x2212;&lt;/sup&gt;&lt;inf&gt;rms&lt;/inf&gt; accurate threshold

Dierickx, B.; Dupont, Benoît; Defernez, Arnaud; Ahmed, Nayera

doi:10.1109/isscc.2011.5746243

Cited by 12 publications

(12 citation statements)

References 6 publications

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“…The threshold dispersion of 530 sample pixels without calibration is 188erms , which is much smaller than 1875erms from [3]. Unlike prior papers [2][3][4], which showed only the IC test results, functionality of our work is successfully demonstrated using real X-ray images, as shown in the bottom of Fig. 6.1.5.…”

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confidence: 80%

“…Thanks to the compact SAL ADC, the pixel pitch of the chip is 60μm despite its 3-level energy detection (color X-ray imaging) capability. Each pixel consumes a static power of 4.6μW, which is a reduction of over 70% with respect to pixels in [2][3][4]. The measured electronic noise according to [6] is 110erms .…”

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confidence: 99%

“…The direct-type photon-counting method [1][2][3] has higher X-ray-to-charge conversion efficiency and position resolution compared with the indirect-type detection method [4]. Therefore, direct-type detection is more suitable for medical imaging applications for which the dose efficiency and the image quality are especially important.…”

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confidence: 99%

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A sampling-based 128×128 direct photon-counting X-ray image sensor with 3 energy bins and spatial resolution of 60μm/pixel

Kim

Han

Yang

et al. 2012

2012 IEEE International Solid-State Circuits Conference

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The photon-counting method is one of several useful image-detection methods for digital X-ray imaging. The direct-type photon-counting method [1][2][3] has higher X-ray-to-charge conversion efficiency and position resolution compared with the indirect-type detection method [4]. Therefore, direct-type detection is more suitable for medical imaging applications for which the dose efficiency and the image quality are especially important. Figure 6.1.1 shows a lateral view of a direct-type X-ray photon-counting image sensor and the conceptual diagram of a unit pixel. When the X-ray-to-charge conversion occurs in the photoconductor, a charge packet drifts toward the input pad of the unit pixel. Then, the CMOS circuit generates a voltage signal corresponding to the received charge amount, and the voltage is compared with a certain threshold so as to determine its validity for X-photon counting. The grayscale X-ray image is generated using all pixels' counted data. Figure 6.1.1 also shows a conventional charge preamplifier [5], which converts the charge information into voltage (V out ) via C FB . The DC-feedback loop resets V out slowly for subsequent signal processing. One major drawback of this circuit is that the sensitivity and the reset speed must be traded off, because fast DC feedback impedes the amplification operation, while slow DC feedback slows down the photon counting rate. Moreover, the DC feedback makes circuit design difficult due to the loop stability issue and PVT variations due to sub-nA bias current design.In this paper, we present a direct X-ray photon-counting image sensor with 3 energy bins for high-quality color X-ray medical imaging. A sampling-based charge preamplifier operates with high charge-to-voltage gain and a fast hardreset scheme. The successive-approximation-like (SAL) ADC discriminates three levels of X-photon energy with high spatial resolution and low power consumption. Figure 6.1.2 shows the circuit diagram of the X-photon-counting pixel. Unlike the preamplifier in Fig. 6.1.1, this preamplifier works on the sampling base with a reset switch, M 1 . The charge packet (-Q) transmitted from the photoconductor is trapped on the feedback capacitor, C FB , without any charge loss owing to not having DC feedback. All the disadvantages related to DC feedback, such as loop instability and PVT sensitivity issues, are eliminated in the circuit. This samplingbased operation enhances the reliability of the circuit function because V OUT stays constant at its peak value until reset. After the energy discrimination period is complete, C FB can be reset quickly by switch M 1 in order to prepare the next signal detection. This fast hard-reset scheme enables the enhancement of the photon-counting rate. For high charge-to-voltage conversion gain, a small C FB of 1.5fF was chosen, which corresponds to a gain of 107mV/ke -. Since C FB is very small, charge-injection from switch M 1 must be kept as small as possible. In addition to the dummy switch M 2 , an optimized switching-level generator was implem...

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A sampling-based 128×128 direct photon-counting X-ray image sensor with 3 energy bins and spatial resolution of 60μm/pixel

Kim

Han

Yang

et al. 2012

2012 IEEE International Solid-State Circuits Conference

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“…Unlike X-ray photon-counting ICs which feature larger pixel pitch due to their need for complex pixel-level chargesensitive amplifiers [6][7][8], we achieve very small pixel sizes by using an integration-mode pixel constructed from a compact four-transistor active pixel sensor (4T APS) and pixel-level capacitor. Integration mode imagers are preferred in high-flux radiographic applications where it becomes difficult to distinguish individual charge pulses, typically leading to paralysis for photon-counting circuits.…”

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confidence: 99%

Direct-Conversion CMOS X-Ray Imager With <inline-formula> <tex-math notation="LaTeX">$5.6 ~\mu \text{m} \times 6.25~\mu \text{m}$ </tex-math></inline-formula> Pixels

Parsafar

Scott

El-Falou

et al. 2015

IEEE Electron Device Lett.

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“…The main inconvenient of direct detection is that conversion crystals are available today only in small surfaces of few . In contrast, scintillators are easily manufactured in large surfaces, and the corresponding indirect technique, using a scintillator and a photodiode has been proposed [7]. However, indirect detection creates fewer electrons per absorbed X-ray photon than direct detection.…”

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confidence: 99%

Sphinx1: Spectrometric Photon Counting and Integration Pixel for X-Ray Imaging With a 100 Electron LSB

Habib

Arques

Dupont

et al. 2015

IEEE Trans. Nucl. Sci.

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Sphinx1 is a novel pixel architecture adapted for X-ray imaging that can detect radiation by photon counting and by charge integration. In photon counting mode, each photon is compensated by one or more counter-charge packets which can be dimensioned at a level as low as 100 electrons and the number of injected counter-charge packets indicates the incoming photon energy, thus allowing a spectrometric detection. The pixel is also able to detect radiation by integrating the charges deposited by all incoming photons and converting this analog value into a digital data with a least significant bit (LSB) of 100 electrons through the use of the counter-charge concept. In this paper, Sphinx1 pixel architecture is presented with emphasis on the counter-charge design, and the two modes of operation are described in detail. The pixel was simulated using Eldo simulator. Simulation results indicate an equivalent noise charge (ENC) of 48 electrons-rms for a detector capacitance of 75 fF. The LSB linearity and the ENC are further studied for different values of detector capacitances. The analog and digital power consumptions are calculated to be less than W in static conditions, proving the architecture to be suitable for large area detectors. Finally, corner simulations show a consistent performance against transistors mismatch. Proof of concept test chip of mm mm. test chip is being designed fabricated in CMOS m technology, with a pixel pitch of m.

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Indirect X-ray photon-counting image sensor with 27T pixel and 15e<sup>−</sup><inf>rms</inf> accurate threshold

Cited by 12 publications

References 6 publications

A sampling-based 128×128 direct photon-counting X-ray image sensor with 3 energy bins and spatial resolution of 60μm/pixel

A sampling-based 128×128 direct photon-counting X-ray image sensor with 3 energy bins and spatial resolution of 60μm/pixel

Direct-Conversion CMOS X-Ray Imager With <inline-formula> <tex-math notation="LaTeX">$5.6 ~\mu \text{m} \times 6.25~\mu \text{m}$ </tex-math></inline-formula> Pixels

Sphinx1: Spectrometric Photon Counting and Integration Pixel for X-Ray Imaging With a 100 Electron LSB

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Indirect X-ray photon-counting image sensor with 27T pixel and 15e<sup>&#x2212;</sup><inf>rms</inf> accurate threshold

Cited by 12 publications

References 6 publications

A sampling-based 128&#x00D7;128 direct photon-counting X-ray image sensor with 3 energy bins and spatial resolution of 60&#x03BC;m/pixel

A sampling-based 128&#x00D7;128 direct photon-counting X-ray image sensor with 3 energy bins and spatial resolution of 60&#x03BC;m/pixel

Direct-Conversion CMOS X-Ray Imager With <inline-formula> <tex-math notation="LaTeX">$5.6 ~\mu \text{m} \times 6.25~\mu \text{m}$ </tex-math></inline-formula> Pixels

Sphinx1: Spectrometric Photon Counting and Integration Pixel for X-Ray Imaging With a 100 Electron LSB

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Indirect X-ray photon-counting image sensor with 27T pixel and 15e<sup>−</sup><inf>rms</inf> accurate threshold

A sampling-based 128×128 direct photon-counting X-ray image sensor with 3 energy bins and spatial resolution of 60μm/pixel

A sampling-based 128×128 direct photon-counting X-ray image sensor with 3 energy bins and spatial resolution of 60μm/pixel