A Full Current-Mode AFE With Dark Noise Suppression Using Differential Leading-Edge Discrimination for the CMS/LHC Timing Detector at CERN

In this article, we present a full current-mode analog front-end (AFE) of the time-of-flight at high-rate (TOFHiR) front-end application specific integrated circuit (ASIC) designed for the new barrel timing layer (BTL) timing detector that will feature in the Compact Muon Solenoid (CMS) experiment of the upgraded high-luminosity Large Hadron Collider (HL-LHC) accelerator at CERN. The AFE features for the first time, in silicon, the differential leading-edge discrimination (DLED) operation to suppress the increasing radiation induced dark noise and stabilize the baseline, leading to a time resolution of 25 ps at the beginning-of-life (BoL) and 55 ps at the end-of-life (EoL) of the detector. The proposed current-mode AFE is less sensitive to parameter spread and parasitics since the signal flows through low impedance nodes, hence also reducing channel-to-channel mismatches. This feature is of utmost importance since TOFHiR is a multichannel ASIC and the BTL will feature over 10k TOFHiR ASICs totaling 330k channels. These assumptions were validated by measurements taken on 100 dies and more than 3100 channels, and this achievement was key to the commissioning of the BTL detector. The TOFHiR ASIC was designed in a standard mainstream CMOS 130-nm technology, has a total die area of 8.5 x 5 mm² and 32 channels, and dissipates less than 12 mW per channel. As this article was finalized more than 5000 TOFHiR ASICs have been measured, 3600 have been assembled in 1800 front-end boards, and 200 burned-in boards have already been shipped to CERN for assembling in the BTL detector.