PT Journal AU ATLAS Collaboration (Aad, Gea Aparisi Pozo, JA Bailey, AJ Cabrera Urban, S Castillo, FL Castillo Gimenez, V Cerda Alberich, L Costa, MJ Escobar, C Estrada Pastor, O Ferrer, A Fiorini, L Fullana Torregrosa, E Fuster, J Garcia, C Garcia Navarro, JE Gonzalez de la Hoz, S Gonzalvo Rodriguez, GR Guerrero Rojas, JG Higon-Rodriguez, E Lacasta, C Lozano Bahilo, JJ Madaffari, D Mamuzic, J Marti-Garcia, S MiƱano, M Mitsou, VA Moreno Llacer, M Rodriguez Bosca, S Rodriguez Rodriguez, D Ruiz-Martinez, A Salt, J Santra, A Soldevila, U Sanchez, J Valero, A Valls Ferrer, JA Vos, M TI Performance of the upgraded PreProcessor of the ATLAS Level-1 Calorimeter Trigger SO Journal of Instrumentation JI J. Instrum. PY 2020 BP P11016 - 48pp VL 15 IS 11 DI 10.1088/1748-0221/15/11/P11016 LA English DE Calorimeters; Trigger concepts and systems (hardware and software) AB The PreProcessor of the ATLAS Level-1 Calorimeter Trigger prepares the analogue trigger signals sent from the ATLAS calorimeters by digitising, synchronising, and calibrating them to reconstruct transverse energy deposits, which are then used in further processing to identify event features. During the first long shutdown of the LHC from 2013 to 2014, the central components of the PreProcessor, the Multichip Modules, were replaced by upgraded versions that feature modern ADC and FPGA technology to ensure optimal performance in the high pile-up environment of LHC Run 2. This paper describes the features of the new Multichip Modules along with the improvements to the signal processing achieved. ER