Testbeam for the CMS ECAL upgrade for the High Luminosity phase of LHC

With the incoming High Luminosity phase of LHC some upgrades for the CMS ECAL are in line. As a part of the characterization process, data was taken using either a laser as light source or electrons at the testbeam H4. Dependance of gain in terms of voltage and temperature were studied, which allowed later to compare the measurements obtained with the VFEs working at 120 MHz and 160 MHz. Additionally, the electron beam used for the test was studied after the characterization was done, allowing for a first reconstruction of energy.