Progress on the development of a detector mounted analog and digital readout system for the ATLAS TRT

The 430,000 element ATLAS Transition Radiation straw tube Tracker (TRT) is divided into a central barrel tracker consisting of 104,000 axially mounted straws and two radially arranged end caps on either side of the barrel with 160,000 straws each. To achieve a track position resolution of 140μm, the front end electronics must operate at a low (2fC) threshold with a time marking capability of ∼1ns. Two ASICs, the ASDBLR and DTMROC provide the complete pipelined readout chain. Custom designed FBGA packages for the ASICs provide a small enough outline to be detector mounted and the extensive use of low level differential signals make mounting the analog packages on printed circuit boards directly opposite the 40 MHz digital chips feasible. The readout electronics for the barrel occupies a potentially important part of the active tracker volume and an aggressive effort has been made to make it as compact as possible. Utilizing a single board for both analog and digital ASICS a 0.1 cm³ per channel volume has been achieved for the active electronics. This has meant the development of 14 layer boards with four levels of blind vias to separate analog and digital functionality. The design of the packages and boards along with performance measurements is discussed.