Single Photon-Counting Pixel Readout Chip Operating Up to 1.2 Gcps/mm2 for Digital X-Ray Imaging Systems

This paper presents the design of a PXF40-an ultrafast single photon-counting (SPC) readout front-end electronics implemented in a CMOS 40-nm technology dedicated to hybrid pixel detectors. The prototype application specific integrated circuit core is a matrix of 432 pixels (24 × 18) with a 100 μm × 100 μm size. The single processing channel consists of a charge-sensitive amplifier (CSA), a discriminator, and a 24-bit counter with logic circuitry. The input signal is amplified and formed only by the CSA stage. Depending on the CSA input transistor current value, it can operate in two modes: FAST and FAST_HC with higher current. The measured power dissipation per channel P = 45 μW and noise ENC = 212 e ^- rms for the FAST mode, while P = 100 μW and ENC = 185 e rms for the FAST_HC mode, respectively. The readout chip can count up to 1.2 Gcps/mm ² based on 10% dead-time loss input rate parameter, which is currently the fastest SPC-based solution.