The MINOS near detector front end electronics

The near detector for the MINOS experiment at Fermilab is composed of alternating planes of scintillator strips and steel plates, and is read out with 64-channel, multi-anode photomultiplier tubes. The instrumentation uses a custom ASIC designed at Fermilab for the front end analog processing, called the QIE. The system can measure single photoelectrons to high precision with a dynamic range of 16 bits. The electronics operates in two modes. It records all events that occur during the 10 microsecond ´fast spill´ of the beam from the Fermilab main injector at a rate of 53 MHz, using a gate from the beamline controls to force data acquisition. The system can also acquire data from cosmic rays that pass through the detector for calibration. In this case, dynode signals from the photomultipliers are used as the trigger, causing digitization and readout of the associated channels. Zero suppression and normalization are done in the front-end electronics. The system is ´trigger-less´ in that there is no global hardware trigger. Instead, each event is tagged with a ´timestamp´, which is used in post-processing to reconstruct events and discard noise hits. The system of 10,000 channels is now built, and installation is in progress at Fermilab. The components of the system are described and preliminary system performance is reported.