ALTIROC 1, a 25 ps time resolution ASIC for the ATLAS High Granularity Timing Detector

Designed and characterized by the HGTD collaboration, ALTIROC belongs to the family of readout ASICs used at the Large Hadron Collider (LHC) for the High Luminosity-LHC upgrade. ALTIROC1 is a 25-channel ASIC designed in CMOS 130 nm to read out the 5 x 5 matrix of 1.3 mm x 1.3 mm Low Gain Avalanche Diodes (LGAD) of the ATLAS HGTD detector. The targeted combined time resolution of the sensor and its readout electronics from 35 ps/hit (initial) to 70 ps/hit (end of operational lifetime). Each ASIC channel integrates an RF preamplifier followed by a high speed discriminator and two TDCs for Time-of-Arrival and Time-Over-Threshold measurements as well as a local memory. This front-end must exhibit an extremely low jitter noise while keeping a challenging power consumption of less than 4.5 mW per channel. This conference proceeding summarizes the ASIC's architecture, its measured performances compared to simulation, along with the requirements for the HEP experiments.