Design of the ANTARES4 Readout ASIC for the Second Flight of the GAPS Experiment: Motivations and Requirements

The General AntiParticle Spectrometer is a balloon borne experiment designed to search for low energy cosmic ray antinuclei as a potential indirect signature of dark matter. Over the course of at least three long duration flights over Antarctica, it will explore the sub 250 MeV per nucleon energy range with sensitivity to antideuterons and antihelium, while also extending antiproton measurements below 100 MeV. The instrument features a tracker built from more than one thousand lithium drifted silicon detectors, each read out by a dedicated custom integrated circuit. With the first flight scheduled for the austral summer of 2025, a new prototype chip, ANTARES4, has been developed using a commercial 65 nm complementary metal oxide semiconductor process for use in the second flight. It integrates eight independent analog channels, each incorporating a low noise charge sensitive amplifier with dynamic signal compression, a CR RC shaping stage with eight selectable peaking times, and on chip calibration circuitry. The charge sensitive amplifier uses metal oxide semiconductor feedback elements with voltage dependent capacitance to support the wide input energy range from 10 keV to 100 MeV. Four alternative feedback implementations are included to compare performance and design trade offs. Leakage current compensation up to 200 nA per detector strip is provided by a Krummenacher current feedback network. This paper presents the design and architecture of ANTARES4, highlighting the motivations, design drivers, and performance requirements that guided its development.