Electronics and triggering challenges for the CMS High Granularity Calorimeter for HL-LHC

The High Granularity Calorimeter (HGCAL) is presently being designed to replace the CMS endcap calorimeters for the High Luminosity phase at LHC. It will feature six million silicon sensor channels and 52 longitudinal layers. The requirements for the frontend electronics include a 0.3 fC-10 pC dynamic range, low noise (2000 e-) and low power consumption (10 mW /channel). In addition, the HGCAL will perform 50 ps resolution time of arrival measurements to combat the effect of the large number of interactions taking place at each bunch crossing, and will transmit both triggered readout from on-detector buffer memory and reduced resolution real-time trigger data. We present the challenges related to the frontend electronics, data transmission and off-detector trigger preprocessing that must be overcome, and the design concepts currently being pursued.