The ATLAS FTK Auxiliary Card: A Highly Functional VME Rear Transition Module for a Hardware Track Finding Processing Unit

The ATLAS Fast TracKer is a hardware-based charged particle track finder for the High Level Trigger system of the ATLAS Experiment at the LHC. Using a multi-component system, it finds charged particle trajectories of 1 GeV/c and greater using data from the full ATLAS silicon tracking detectors at a rate of 100 kHz. Pattern recognition and preliminary track fitting are performed by VME Processing Units consisting of an Associative Memory Board containing custom associative memory chips for pattern recognition, and the Auxiliary Card (AUX), a powerful rear transition module which formats the data for pattern recognition and performs linearized fits on track candidates. We report on the design and testing of the AUX, which utilizes six FPGAs to process up to 32 Gbps of hit data, as well as fit the helical trajectory of one track candidate per nanosecond through a highly parallel track fitting architecture. Both the board and firmware design will be discussed, as well as the performance observed in tests at CERN in the Summer of 2014.