A low noise high dynamic range analog front-end ASIC for the AGIPD XFEL detector

In this paper we present a low noise high dynamic range analog front-end ASIC designed for the Adaptive Gain Integrating Pixel Detector (AGIPD) being developed for the European X-ray Free Electron Laser (XFEL) facility. The ASIC has 64 × 64 pixels with a pixel size of 200 × 200 μm², and is bump bonded to a silicon sensor for X-ray imaging. Each pixel includes an adaptive gain charge integrating amplifier (AGCIA) and 352 analog storage cells. The gain of the AGCIA dynamically adapts to the number of photons arriving at the sensor in order to achieve a single photon resolution and a dynamic range of more than 10⁴ 12 keV photons. The XFEL bunch trains consist of up to 2700 bunches separated by 220 ns (600 us in total) followed by an idle time of 99.4 ms. The AGCIA operates in a 220 ns repeating cycle by storing images and the gain information into the pixel memory during the pulse train. The stored images are read out during the breaks of the bunch trains. Several prototypes are designed and fabricated in IBM 130 nm CMOS technology. The measurements showed an input equivalent noise charge (ENC) lower than 300 e^- and a dynamic range of 7000 photons.