FANSIC: A Fast ANalog SiPM Interface Circuit for the readout of large silicon photomultipliers

Silicon photomultipliers (SiPMs) have increasingly replaced traditional photomultiplier tubes (PMTs) in a wide range of applications, not subject to excessive radiation or extreme temperatures, due to their benefits in terms of compactness, reliability, granularity, lower operating voltage, cost-effectiveness for mass production and photodetection efficiency (PDE). However, for large-area detection systems, PMTs still remain the preferred choice due to their lower thermal noise and the shorter duration of their output signal, both of which degrade in SiPMs as the sensor size increases. Overcoming these limitations is crucial for the adoption of SiPMs in next-generation gamma-ray observatories. We present FANSIC, a dedicated analog front-end application specific integrated circuit (ASIC) designed to address these challenges and enable the high-speed readout of large-area SiPMs. Developed in 65 nm CMOS technology, FANSIC features an active summation architecture that efficiently combines signals from multiple SiPM channels and mitigates the undesirable effects associated with the capacitance of large sensors. Its functional dynamic range extends up to 800 photoelectrons (p.e.), while a pulse duration of 3 ns and a post-calibration linearity better than ± 5 % are achieved within the range of interest, which goes up to 250 p.e. These performance are obtained while containing the power consumption to 23 mW per pixel, making FANSIC an ideal choice for experiments in which low-power consumption is critical, like in cameras of large-scale telescopes. Designed for versatility, FANSIC offers single-ended and differential output configurations, ensuring compatibility with various digitization solutions and types of SiPMs. Extensive simulations and laboratory measurements confirm its high performance, demonstrating its potential as a key enabling technology for future Cherenkov telescopes.