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Digital subpixel algorithm for small pixel photon counting devices

Krzyżanowska Aleksandra, Otfinowski Piotr

Opto-Electronics Review

2025

Vol. 33, No. 1

art. no. e152768

Hybrid pixel detectors are segmented devices widely used for photon detection. They consist of a sensor and readout electronics bonded together. Due to their hybrid structure, sensors of different materials can be used to register a wide range of photon energies. Moreover, the devices working in a single photon counting (SPC) mode allow registering each incoming photon separately, providing noiseless imaging. The spatial resolution of the detectors and photon count rate registered per unit area can be improved by reducing pixel size. However, small-pixel devices suffer from charge sharing. The charge sharing between pixels can be observed if the charge cloud generated in the photon-sensor event spreads due to diffusion and repulsion. Several anti-charge-sharing algorithms exist and some have been successfully implemented inside the ASICs readout. Even though they allow the allocation of the event to the proper pixel and reconstruction of the total photon energy, the detector resolution is limited by the readout channel area which must be large enough to fit the complex mixed-mode functionality. The article presents the simulations of an alternative solution which can improve both spatial resolution and high-count-rate performance. In the authors’ approach, charge sharing is regarded as a positive effect which can be used to estimate the photon interaction position with subpixel resolution. The algorithm is evaluated to improve detection efficiency and required pixel area for implementation in deep submicron technologies.

Simulation study on improving the spatial resolution of photon-counting hybrid pixel X-ray detectors

Krzyżanowska Aleksandra, Szczygieł Robert

Opto-Electronics Review

2021

Vol. 29, No. 4

187--191

Hybrid pixel radiation detectors with a direct photon-to-charge conversion working in a single photon counting mode have gained increasing attention due to their high dynamic range and noiseless imaging. Since sensors of different materials can be attached to readout electronics, they enable work with a wide range of photon energies. The charge-sharing effect observed in segmented devices, such as hybrid pixel detectors, is a phenomenon that deteriorates both spatial resolution and detection efficiency. Algorithms that allow the detection of a photon irrespective of the charge-sharing effect are proposed to overcome these limitations. However, the spatial resolution of the detector can be further improved beyond the resolution determined by the pixel size if information about the chargé proportions collected by neighbouring pixels is used to approximate the interaction position. In the article, an approach to achieve a subpixel resolution in a hybrid pixel detector working in the single photon counting mode is described. Requirements and limitations of digital inter-pixel algorithms which can be implemented on-chip are studied. In the simulations, the factors influencing the detector resolution are evaluated, including size of a charge cloud, number of virtual pixel subdivisions, and detector parameters.