LAPAS: A SiGe Front End Prototype for the Upgraded ATLAS LAr

We have designed and fabricated a very low noise preamplifier and shaper with a (RC)2 – CR response to replace the existing ATLAS Liquid Argon readout for use at SLHC. IBM’s 8WL 130nm SiGe process was chosen for its radiation tolerance wide voltage range and potential for use in other LHC detector subsystems. The required dynamic range of 15 bits is accomplished by utilization of a single stage, low noise, wide dynamic range preamp connected to a dual range shaper. The low noise of the preamp (~.01nA / √Hz) is achieved by utilizing the process Silicon Germanium bipolar transistors. The relatively high voltage rating of the npn transistors is exploited to allow a gain of 650V/A. With this gain the equivalent input voltage noise requirement on the shaper to about 2.2nV/ √Hz. Each shaper stage is designed as a cascaded differential op amp doublet with a common mode operating point regulated by an internal feedback loop. The shaper outputs are designed to be compatible with the 130nm CMOS ADC being developed in parallel with this effort. Preliminary measurement of the fabricated circuits indicates their performance is consistent with the design specifications.