Cold electronics for the liquid argon hadronic endcap calorimeter of ATLAS

This paper describes the on-detector electronics of the ATLAS hadronic end-cap calorimeter (HEC). The electronics is working in liquid argon; therefore the attention is paid to its performance at low temperatures. The calibration and signal cables have been studied in laboratory conditions and signal distortion is modeled. The core of the electronics are GaAs preamplifiers. We present the design, layout and measured characteristics of preamplifier chips and summing boards. The on-module signal distribution is also described. All parts of the electronics have been produced, tested and assembled on the calorimeter modules. The summary of commissioning tests is presented.