A SiGe front-end prototype for the upgraded ATLAS liquid argon calorimeter

We have designed and fabricated a very low noise preamplifier and shaper to replace the existing ATLAS Liquid Argon readout for use at the Large Hadron Collider upgrade (SLHC). IBM's 8WL 130nm SiGe process was chosen for its radiation tolerance, low noise bipolar NPN devices, wide voltage range and potential use in other SLHC detector subsystems. Although the requirements for the final design have not been yet finalized, the prototype was designed to accommodate a 16 bit dynamic range. This was accomplished by using a single stage, low noise, wide dynamic range preamplifier followed by a dual range shaper. The low noise of the preamp is made possible by the low base spreading resistance of the silicon germanium NPN bipolar transistors. The relatively high voltage rating of the NPN transistors is exploited to allow a gain of 650V/A in the preamplifier which eases the input voltage noise requirement on the shaper. Each shaper stage is designed as a cascaded differential operational amplifier pair with a common mode operating point regulated by an internal feedback loop. Measurement of the fabricated circuits indicates their performance is consistent with the design specifications including the radiation tolerance targets.