Second-generation Percival sensor and system for upgraded soft X-ray imaging at FELs and synchrotrons

PERCIVAL, “pixellated energy-resolving CMOS imager versatile and large”, is a 2-megapixel soft X-ray imager developed for use at FELs and modern-day synchrotrons. A combination of capabilities is necessary to meet the scientific needs: a large, uninterrupted imaging area with small pixels, high dynamic range, high frame rate, and soft X-ray suitable entrance window to the sensor. A single PERCIVAL sensor offers over 4 cm × 4 cm uninterrupted imaging area (1408 × 1484 pixels of 27 × 27 μm$^2$). Three auto-adapting gains (per pixel per image) provide the large dynamic range from 13 e$^-$ noise to over 3 Me$^-$ signal. The sensor is designed for up to 300 Hz frame rate, and can be operated faster in ROI mode. The first generation of the sensor was hampered by severe crosstalk preventing parallel operation of ADC, streamout, and pixel switches and by non-uniformity of baselines over the sensor. A revised “respin” sensor addresses these issues at the root — and good noise performance at higher frame rates as well as a more uniform baseline can now be provided to users. The first generation DAQ system — still based on existing Virtex5 hardware — had limitations that ultimately prevented handling the fast data rates from a Percival running at full speed, or other complexities such as ROI operation. ... mehrA complete overhaul of the percival-specific DAQ components (FPGA with periphery and firmware) today enables acquisition at envisioned frame rates and in ROI mode. This paper summarizes first laboratory results from the respin sensors in combination with the new DAQ hardware and firmware.