The GBT based readout concept for the CBM Silicon Tracking System

The sensors of the CBM Silicon Tracking System (STS) are read out by frontend boards (FEB) with 8 STS-XYTER ASICs for 128 channels each implementing the analog frontend, analog-to-digital conversion and the readout of buffered hits via multiple serial links. A subsequent stage with data aggregation from several ASIC links and an electrical-to-optical interface is required before trans fering the data to the FPGA based data processing boards (DPBs) located in some distance at the detector site where preprocessing and further data transfer occur. The aggregation stage is located in the cooled STS detector box inside the CBM magnet, which implies that the hardware must fulfill conditions in terms of radiation hardness, magnetic field, space contraints and thermal environment.