ALTIROC2 is a 225-channel ASIC designed in CMOS 130 nm to read out a 15 × 15 matrix of 1.3 mm × 1.3 mm Low Gain Avalanche Diodes (LGAD) for the ATLAS HGTD (High Granularity Timing Detector). The targeted combined time resolution of the sensor and its readout electronics range from 35 ps/hit (initial) to 65 ps/hit (end of operational lifetime). Each ASIC channel integrates a high-speed 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 a small jitter while keeping a challenging power consumption of less than 4.5 mW per channel. This conference proceeding summarizes the ASIC architecture, its measured performances compared to simulation, along with the requirements for the ATLAS HGTD experiments.

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The development of detectors that provide high resolution in four dimensions has attracted wide-spread interest in the scientific community for applications in high-energy physics, nuclear physics, medical imaging, mass spectroscopy as well as quantum information. However, finding a technology capable of fulfilling such aspiration proved to be an arduous task. Among other silicon-based candidates, the Low-Gain Avalanche Diode (LGAD) has already shown excellent timing performances but proved to be unsuitable for fine pixelization. Therefore, the AC-coupled LGAD (AC-LGAD) approach was introduced to provide high resolution in both time and space, making it a promising candidate for future 4D detectors. However, appropriate readout electronics must be developed to match the sensor's fast-time and fine-pitch capabilities. This is currently a major technological challenge. In this paper, we test AC-LGAD prototypes read out by the fast-time ASIC ALTIROC 0, originally developed for the readout of DC-coupled LGADs for the ATLAS experiment at the High Luminosity-LHC. Signal generated by either betas from a 90Sr source or a focused infra-red laser were analyzed. This paper details the first successful readout of an AC-LGAD sensor using a readout chip. This result will pave the way for the design and construction of a new generation of AC-LGAD-based 4D detectors.