  The Phase-I trigger readout electronics upgrade of the ATLAS Liquid Argon
calorimeters enhances the physics reach of the experiment during the upcoming
operation at increasing Large Hadron Collider luminosities. The new system,
installed during the second Large Hadron Collider Long Shutdown, increases the
trigger readout granularity by up to a factor of ten as well as its precision
and range. Consequently, the background rejection at trigger level is improved
through enhanced filtering algorithms utilizing the additional information for
topological discrimination of electromagnetic and hadronic shower shapes. This
paper presents the final designs of the new electronic elements, their custom
electronic devices, the procedures used to validate their proper functioning,
and the performance achieved during the commissioning of this system.
