HVMUX, high voltage multiplexing for the ATLAS strip tracker upgrade

The currently adopted HV biasing solution in the ATLAS detector uses one HV conductor for each sensor. This approach allows disabling malfunctioning sensors without affecting the others, but, for the Upgraded detector, space constraints and material budget considerations renders this approach impractical. Also, the increased luminosity of the Upgraded LHC will require more channels in the upgraded ATLAS Tracker, as a result of the finer detector segmentation. An alternative approach, named HVMUX, to provide the HV biasing to the detector that consists of using the same HV line shared among several sensors, individually selectable using semiconductor switches, has been successfully investigated. This solution is now baseline for the HV biasing of ATLAS Strip Tracker Upgrade. Beside the size constraints, particular attention had to be paid to the radiation tolerance of all the components of the HVMUX circuitry, which, for the strips detector, is required to operate properly up to fluences of 2× 1015 Φeq [n1 MeV/cm2] and TID of 600 kGy(Si). In this paper, a detailed description of the final HVMUX solution, along with latest radiation tests results will be presented and discussed.