Performance study of HGCROC-v2: the front-end electronics for the CMS High Granularity Calorimeter

The High Granularity Calorimeter (HGCAL), presently being designed by the Compact Muon Solenoid collaboration (CMS) to replace the existing endcap calorimeters for the High Luminosity phase of the LHC (HL-LHC), will feature unprecedented transverse and longitudinal readout and triggering segmentation for both electromagnetic and hadronic sections. The requirements for the front-end electronics are extremely challenging, including high dynamic range (0–10 pC), low noise (0~ 200 electrons), high-precision timing information in order to mitigate the pileup effect (25 ps binning) and low power consumption (~ 15 mW/channel). The front-end electronics will face a harsh radiation environment which will reach 200 Mrad at the end of life. It will work at a controlled temperature of 240 K. HGCROC-v2 is the second prototype of the front-end ASIC. It has 72 channels of the full analog chain: low noise and high gain preamplifier and shapers, and a 10-bit 40 MHz SAR-ADC, which provides the charge measurement over the linear range of the preamplifier. In the saturation range of the preamplifier, a discriminator and TDC provide the charge information from TOT (Time Over Threshold) over 200 ns dynamic range using 50 ps binning. A fast discriminator and TDC provide timing information to 25 ps accuracy. Both charge and timing information are kept in a DRAM memory waiting for a Level 1-trigger decision (L1A). At a bunch crossing rate of 40 MHz, compressed charge data are sent out to participate in the generation of the L1-trigger primitives. We report on the performances of the chip in terms of signal-to-noise ratio, charge and timing, as well as results from radiation qualification with total ionizing dose (TID).