Front-end ASIC for a liquid argon TPC

Abstract

We introduce a front-end application specific integrated circuit (ASIC) for a wire based Time-Projection-Chamber (TPC) operating in liquid Argon (LAr). The LAr TPC will be used for long baseline neutrino oscillation experiments. The ASIC must provide low-noise readout of the signals induced on the TPC wires, digitization of those signals at 2 MS/s, compression, buffering and multiplexing. A resolution better than 1000 rms electrons at 200 pF input capacitance for an input range of 300 fC is required, along with low power and operation in LAr (at 87 K). We present the characterization of a commercial technology for operation in cryogenic environment and the first experimental results on the analog front-end. The results demonstrate that CMOS transistors have lower noise and much improved dc characteristics at LAr temperature. Finally, we introduce the concept of “1/f equivalent” to model the low-frequency component of the noise spectral density, for use in the input MOSFET optimization.