ATLAS Pixel Detector and readout upgrades for the improved LHC performance

Since the moment it was first started in 2008, the LHC particle accelerator at CERN continued to constantly increase its center-of-mass energy and luminosity. During next years, LHC will undergo two major series of upgrades; after the first one it will reach the design energy of 14 TeV and a luminosity of 2-3·10^34cm-2s-1 (Phase-I ), and in the last phase (Phase-II ) the luminosity will be increased to ~7·10^34cm-2 s-1 . To keep up with the augmented detector performance, the LHC detectors where (and will be) upgraded as well. This work will focus on the ATLAS detector - one of the four main experiments of LHC - and in particular on its Pixel Detector. The ATLAS Pixel Detector was first upgraded in 2015, with the introduction of a new pixel layer - called IBL - to compensate for the B-layer inefficiencies and to increase the tracking performance for Phase-0 and Phase-I. The detector layout, combined with the higher LHC luminosity, led to an increased amount of data to be transmitted and analyzed, constituting a challenge for the read-out system. For this reason the previous readout chain was renovated and two new boards, called IBL-ROD and IBL-BOC, were designed to interface IBL. The second major upgrade involving the ATLAS Pixel Detector will be in 2024-2026, when the Inner Detector will be completely replaced by ITk, entirely made of silicon sensors. To be able to sustain the more difficult conditions, another readout upgrade will be required; the final design has not been decided yet and is still under consideration. This work will give an overview on the ATLAS Pixel Detector and will analyze the motivations that led to its upgrades. The current and future DAQ systems will also be discussed, focusing on the technologies adopted, the detector requirements and the results obtained.