Front-end electronics of the Belle II aerogel ring imaging detector

A proximity focusing RICH detector with an aerogel radiator is used for charged particle identification in the forward end-cap of the Belle II spectrometer. The detector, consisting of a 4 cm aerogel radiator, a 16 cm expansion volume and a photon detector with 420 Hybrid Avalanche Photo Detectors, is mounted in a very confined space between Central Drift Chamber and Electromagnetic Calorimeter, allowing only 5 cm of space for the readout electronics. In our solution, low power front-end read-out boards are mounted at the back side of each of the HAPD photosensors. These boards have each been tested individually before their installation onto the photosensors and into the spectrometer. Most important design issues and first experiences with the aforementioned front-end read-out boards are presented in this contribution.