The upgrade of the ATLAS readout electronics

The ATLAS detector has been designed to study the proton-proton collisions produced at the Large Hadron Collider (LHC) at CERN. The ATLAS trigger consists of a hardware based low-level trigger (L1), and a software based high-level trigger (HLT). A series of upgrades are scheduled to increase the LHC instantaneous luminosity.The overall readout architecture and the trigger structure is being revised to cope with the new LHC parameters. The present L1 trigger will be divided into a L0 and a new L1 using tracker information. This presentation summarizes the readout electronics of the different ATLAS sub-detectors in the present system and the evolution for the ATLAS upgrade. It will include a detailed description of the custom front-end and back-end electronics, the signal reconstruction algorithms and the different timing procedures used to synchronize the acquired data.