The FEB/A_v2 board has one TOFPET2 ASIC with 64 channels (Fig 2). The two versions of the Front-End Module use the FEB/A v2 board as core component. The Front-End Module with 128 channels has two FEB/A_v2 boards and the 256 channels version has four boards. The FEB/A_v2 boards are mounted perpendicular to the SiPM arrays, and this geometry makes it easier to control and stabilise the temperature of the SiPM array. The board also has a temperature sensor near to the ASIC.
The FEB/S board is a purely passive board adapting the SiPM array to the input connector on FEB/A_v2 boards . This board will be different for different SiPM arrays models. The version of the board shown on figure 1 has two pairs of connectors that directly take the Hamamatsu S13361-3050AS-08 8x8 MPPC array, or the KETEK 8x8 array PA3325-WB-0808. Each FEB/S measures 53.1 x 25.4 mm and is four-side buttable such as to allow forming a continuously sensitive area with almost no dead space. The FEB/S also has two temperature sensors, each located in the middle of the pair of connectors taking one SiPM array. The Front-End Module with 256 channels has two FEB/S boards identical to the ones used in the 128 channel version.
