Fast Digital X-ray Detection System Based on Hybrid Pixel Detectors

P. Maj (AGH Univ. of Science and Techn., Poland)

Hybrid pixel detectors are very popular in the research and industry as they give certain advantages like essentially infinite dynamic range, noiseless imaging if incoming photons are properly discriminated and the sensor material can be adjusted to the application. Another characteristic may be the readout speed, which can be significantly higher than in conventional CMOS sensors, as the digital information is produced in pixels and then it is read-out from the detector. High speed X-ray detection systems should characterize with the fast front-end electronics not to saturate the signal with high photon flux. The size of single pixel is also significant here as the smaller area the better spatial resolution of the detector and also smaller number of events is registered by readout channel. Those two assumptions are contradictory as typically using large-area devices is easier to achieve high speed operation of the readout channel. Another limitations of the high speed readout system is the noise and uniformity of the whole pixel matrix, which both define the energy resolution. Higher uniformity and lower noise is achieved with larger pixels but this is opposite to the trend of having best possible spatial resolution. Nowadays different groups around the world are trying to build hybrid pixel X-ray detectors using sub-micron technologies to be able to shrink the single pixel size and they are trying to use inter-pixel communication to omit the negative effects of charge-sharing. We present the high speed detection system based on one of the fastest hybrid pixel detectors having offset spread below 10 el. rms. and dead-time of the front-end as low as 85ns. The readout speed exceeds 50 000 frames per second with 220 MHz DDR clock sampling the data coming from the detector. Data coming with 440 MBps is processed in FPGA and in a zero-suppressed form sent to the storage. The system operates in time-resolved experiments, namely x-ray photon correlation spectroscopy in Advanced Photon Source synchrotron in Argonne National Laboratory and continuously produces thousands of datasets per day.