Results with the TOFHIR2X Revision of the Front-end ASIC of the CMS MTD Barrel Timing Layer

The CMS Detector will be upgraded for the High-Luminosity LHC to include a MIP Timing Detector (MTD). The MTD will consist of barrel and endcap timing layers, BTL and ETL, respectively, providing precision timing of charged particles. The BTL sensors are based on LYSO:Ce scintillating crystals coupled to SiPMs that are read out by TOFHIR2 ASICs in the front-end system. A resolution of 30 ps for MIP signals is expected at the beginning of HL-LHC operation degrading to 60 ps at the end of operation due to the SiPMs radiation damage. Relative to the first version of the front-end ASIC, TOFHIR2X implements improved circuitry for mitigation of the SiPM dark current noise as well as a new current mode discriminator. We present an overview of the TOFHIR2 requirements and design, simulation results and the first measurements with TOFHIR2X silicon samples coupled to LYSO/SiPM prototype sensors.