A Revised Version of the ATLAS Tile Calorimeter Link Daughterboard for the HL-LHC

The ATLAS Tile Calorimeter (TileCal) readout link and control daughterboard (DB) is the central on-detector hub of the new TileCal electronics upgrade for the high-luminosity large hadron collider (HL-LHC). The DB, which has undergone gradual redesigns during development, provides the connection between the on- and off-detector electronics via bidirectional fiber-optic links. Two CERN-developed, radiation hard GBTx application specified integrated circuits (ASICs) receive LHC timing signals and configuration commands through 4.8-Gb/s downlinks, which are in turn propagated to the front end through Xilinx Kintex Ultrascale field-programmable gate arrays (FPGAs). The Kintex FPGAs also continuously perform real-time readout and transmission of digitized photomultiplier (PMT) samples, detector control system (DCS) signals, and monitoring data through redundant pairs of 9.6-Gb/s uplinks. The DB design aims at minimizing single points of failure and improving the performance and reliability of the board. Apart from the GBTx devices, the DB design relies on radiation-qualified commercial off-the-shelf (COTS) components. Mitigation of radiation-induced single-event upsets (SEUs) in the FPGAs is performed by a combination of the Xilinx soft error mitigation (SEM) controller and triple-mode redundancy (TMR) schemes in the FPGA firmware. Data integrity is protected through forward error correction (FEC) in the downlinks and cyclic redundancy check (CRC) error verification in the redundant uplinks. This article presents the latest revision of the DB (version 6), a redesign that addresses single-event latch-up (SEL) behavior observed in the Kintex Ultrascale+ FPGAs used in the previous revision, and features a more robust power circuitry combined with an improved current monitoring scheme, enhanced performance of the analog-to-digital converter (ADC) read-out, and improved timing performance.