Speaker
Description
Direct-detection, energy-resolved X-ray imaging at high frame rates and low dead time is challenging for conventional detectors, which typically trade spatial resolution, speed and per-photon spectral information against one another. We present FasXcam, a monolithic active pixel sensor (MAPS) for energy-resolved soft X-ray imaging developed by the CAPADS group as a successor to the X-CHIP and SpacePix detector families.
Fabricated in a 180 nm SOI CMOS process, it integrates the full signal chain on-substrate from charge collection through digitisation and high-speed serial readout. The device comprises two electrically independent chiplets forming a 64 × 64 matrix of 60 µm pixels (≈14.7 mm² active area). Each pixel contains a charge-sensitive amplifier, a peak-detector-hold stage and a discriminator; signals are digitised by column-parallel asynchronous SAR ADCs (8-bit effective, one converter serving two columns) and streamed over high-speed LVDS links. Global- and rolling-shutter readout are supported, the latter reducing dead time to two rows and reaching ≈15,500 frames/s at a ≈300 MHz system clock. On-chip charge injection, a temperature sensor and external ADC test paths enable in-situ characterisation.
We report the first full functional verification of the chip. Pixel noise maps show homogeneous response without structural defects, and per-pixel charge-injection scans define the nonlinear charge-to-ADC transfer used for energy calibration. Spectra acquired with ⁵⁵Fe and ²³⁸Pu resolve the characteristic lines at 5.9/6.4 keV and 13.6/17.1 keV; Gaussian fits yield ≈0.33 keV FWHM at 5.9 keV and confirm near-linear response up to ≈20 keV after nonlinearity correction, validating the architecture for fast, spectroscopic X-ray imaging.