Overview and innovations of the electronics of the New Small Wheel of the ATLAS Muon Spectrometer

The New Small Wheel upgrade of the ATLAS Muon Spectrometer at the LHC collider employs two detector technologies, the resistive strip Micromegas chambers and the ``small'' Thin Gap Chambers (sTGC), with a total of 2.45 M analog readout channels. The electronics is required to support the two different detector technologies and provide both precision readout for tracking and a fast trigger. It will operate in a high background radiation region up to about 20 kHz/cm^2 at the expected HL-LHC luminosity of 7.5×10^34 /cm^2 /s. A difficult constraint is that the trigger decision must be ready about 1.1 µsec after the collision. The architecture of the system is strongly defined by the CERN GBTx data aggregation ASIC and the newly-introduced FELIX data router of the ATLAS detector and the software-based data acquisition they enable. The NSW electronics was designed and developed over the last ten years and consists of multiple radiation hard Application Specific Integrated Circuits, multiple front-end boards, dense boards with FPGA's and purpose-built Trigger Processor boards within the ATCA standard. The NSW has been installed in 2021 and is undergoing integration within ATLAS for LHC Run 3. It must operate through the end of Run 4 (December 2032). The presentation will focus on the more innovative aspects of the electronics.