Upgrade of the ATLAS Thin Gap Chamber Electronics for HL-lHC

The High-Luminosity LHC (HL-LHC) is planned to start the operation in 2026 with an instantaneous luminosity of $7.5 \times 10^{34} \mathrm{cm}^{-2} \mathrm{s}^{-1}$. To cope with the event rate higher than that of LHC, the trigger and readout electronics of ATLAS Thin Gap Chamber (TGC) will need to be replaced. An advanced first-level trigger with fast tracking will be implemented with the transfer of all hit data from the frontend to the backend boards. Studies with the data taken by ATLAS indicate that the advanced trigger could reduce the event rate by 25% for a single muon trigger with $p_{\mathrm{T}}$ threshold of 20 GeV while maintaining similar efficiency. First prototype of the TGC frontend board has been developed with most of the functions required for HL-LHC. The data transfer has been demonstrated with charged particle beam at the CERN SPS beam facility.