ams AS5920M Photon Counting Module
Product status: Pre-Production
The AS5920M is a 72x24 pixel, four-side buttable module solution for photon counting applied for spectral computed tomography detectors. The 1728-channel proprietary Buttable System-In-Package (BSIP) integrates three AS5920 photon counting ICs as well as passive components.
The BSIP allows on the top side to form electrical connections to the direct conversion CdTe or CZT sensor material, which converts each X-ray photon into charge pulses. The bottom side of the BSIP forms the digital interface to the FPGA, supply connections as well as the thermal heat dissipation to the carrier.
During a CT scan, the AS5920 IC counts the X-ray photon generated charge pulses with an amplitude proportional to the energy deposited by the photon. 576-channel per AS5920 discriminates the incoming photon energy by counting the number of pulses exceeding 5 different energy thresholds. The threshold levels are adjustable by 8-bit DACs with a step size of typ. 0.7 keV/LSB, the number of comparators enabled per channel are selectable for power optimizations. Lowest power dissipation with all 5 comparators enabled is as low as typ. 0.64 mW/pixel in non-paralyzable mode having BLR enabled and typ. 0.58 mW/pixel in paralyzable mode with only static leakage compensation.
A 15-bit counter register accumulates the comparator output events and transmits 14/16-bit LVDS data within an integration time of minimum 104 µs. During its maximum frame rate of 9615 Fps, the AS5920 transfers the output data via a high-speed LVDS interface to the FPGA, the device operates up to an input count rate of 250 Mcps per pixel (2 Gcps/mm²). The AS5920 has both paralyzable and non-paralyzable counting mode implemented that are selectable via SPI. In paralyzable mode, it allows for a maximum output count rate of 15 Mcps/pixel (120 Mcps/mm²) at 25 keV and exceeding 40 Mcps/pixel (>320 Mcps/mm²) in non-paralyzable mode.
The signal chain of the AS5920 with its low-noise charge sensitive amplifier (CSA) and its high-speed shaper allows for lowest electronic noise of 330 electrons resulting in an ASIC-intrinsic energy resolution of the measured photon of 3.5 keV FWHM.
The photon counting IC AS5920 features an on-chip voltage reference and internal temperature sensor and is embedded in the AS5920M. The AS5920M is delivered as 1728-channel, 4-side buttable module integrating three ICs in one 24.52 mm x 8.75 mm Buttable System-In-Package (BSIP). Pixel sizes of the BSIP are 341 µm x 365 µm and customizable for pixel pitch of 340 µm and above. The performance temperature range of AS5920 and AS5920M is specified from 20°C to 70°C.
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