SPACIROC3: A low power 100MHz photon counting ASIC for cosmic ray observatory

SPACIROC (Spatial Photomultiplier Array Counting and Integrating ReadOut Chip) is the front-end ASIC designed for the space-borne fluorescent telescope JEM-EUSO (Extreme Universe Space Observatory onboard Japanese Experiment Module). This ASIC is dedicated to readout 64-channel Multi-Anode Photo-Multiplier Tube (MAPMT). The two main features are the photon counting for each input and the charge conversion for each 8-channel sum. In the photon counting mode, 100% trigger efficiency is achieved for 1/3 photo-electron (p.e.) input charges. In order to avoid pile-up in the case of a large flux of photons, the double pulse separation must be shorter than 10 ns. The high-speed performance is obtained with a low power consumption (1 mW/channel) thanks to the SiGe technology and by integrating photo-electron trigger counters and a dedicated design to improve the double pulse separation up to 100 MHz. For the charge measurement, the ASIC should operate with a large dynamic range (1 p.e. to 100 p.e. per pixel). SPACIROC3 has been designed to improve the double pulse resolution compared to the previous version, which was extensively used in the EUSO balloon campaign of 2014. The architecture and the performance of the photon counting part will be detailed in this presentation.