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Description
This paper presents the design and implementation of the electronic readout system for the CubeSat-based Cosmic X-ray Polarization Detector (CXPD-02), serving as the second-generation prototype verification of the Low Energy X-ray Polarization (LPD) for the Polar-2 experiment. CXPD-02 incorporates the Topmetal-L pixel sensor chip specifically designed for the LPD, featuring the pixel array of the 356 × 512 elements, which represents a 36-fold increase in the number of pixel units compared to the pixel chip used in the previous generation CXPD-01. Thus, the readout design of the system is the critical factor affecting the performance of the detector. To address the challenges posed by large-scale array readout, the system's readout logic is implemented through the digital ASIC on-chip readout of the pixel chip and FPGA algorithms to achieve the Region of Interest Readout Integrated Circuit (ROIRC). The ROIRC employs a sentinel-based detection mechanism to rapidly identify and read out only particle struck pixel regions. This readout process integrates the algorithms: scanning frequency switching, erosion compression, and dynamic background updating, while synchronizing temporally with the signal acquisition from the Gas Microchannel Plate (GMCP). Experimental validation demonstrates that this readout system design significantly enhances overall detector performance, achieving the residual modulation factor of 13.67, exceeding 90% coincidence rate with GMCP events, and 95% data compression efficiency. The detection method of the ROIRC enables the detector to achieve X-ray detection in the low-energy range of 2 to 10 keV.
