SPACIROC: A front-end readout ASIC for Spatial Cosmic Ray Observatory
Abstract
The SPACIROC ASIC is designed for the JEM-EUSO fluorescence imaging telescope onboard of the In- ternational Space Station. Its goal is the detection of Giant Air Showers above a few 1019 eV, developing at a distance of about 400 km, downward in the troposphere. From such distance, most of the time, the number of the photons ex- pected in the pixels is very weak, ranging from a few units to a few tens. For such running conditions, we propose a low-power, rad-hard ASIC which is intended for reading out a 64-channel Multi-Anode Photomultiplier. The two main features of this ASIC are the photon counting mode for each input and the charge-to-time (Q-to-T) conversions for the multiplexed channels. In the photon counting mode, the 100% triggering efficiency is achieved for 50fC input charges. For the Q-to-T converter, the ASIC requires a minimum input of 2pC. Moreover SPACIROC is required to have a low power dissipation which is around 1mW/channel. We will describe in details the architecture of this ASIC and how the required specifications are satisfied. SPACIROC is a result of the collaboration between OMEGA/LAL- Orsay, France, RIKEN, ISAS/JAXA and Konan University, Japan on behalf of the JEM-EUSO consortium.