The Compact Muon Solenoid detector was originally designed to operate for about ten years, for LHC instantaneous luminosities up to 1β 1034 cmβ2 sβ1 and integrated luminosity of 500 fbβ1. The High Luminosity LHC will increase the instantaneous luminosity by about a factor of 5 from current levels and CMS will accumulate an integrated luminosity of 3000 fbβ1 by about 2035. With such high luminosity the electromagnetic calorimeter of CMS will have to cope with a challenging increase in the number of interactions per bunch crossing and in radiation levels. The front-end readout electronics will be completely redesigned, with the goals of providing precision timing, low noise and added flexibility in the trigger system. It will use a faster pre-amplifier, increase the sampling frequency from 40 MS/s to 160 MS/s and implement a trigger system that resides entirely off-detector