Noise limits of AToM, a128 channel CMOS readout chip in applications with room temperature high granularity detectors

AToM, a CMOS 128 channel signal processing chip, was originally designed for the readout of the microstrip Silicon Vertex Tracker in the BaBar experiment at SLAC. Each channel in the chip includes an analog section, with low-noise preamplification, shaping, and A/D conversion. A digital section provides data buffering and formatting, and serial sparsified readout. The chip is able to process signals from both electron and hole collecting electrodes on a wide dynamic range. AToM is presently available in both rad-soft and rad-hard implementations. This paper aims at showing that AToM has a much broader application perspective in association with room-temperature high-granularity detectors, for instance in X- and gamma-ray imaging and signal processing for focal plane detectors. The first step toward this extension is the analysis of the intrinsic noise and accuracy limitations in radiation energy measurements. For this purpose the analysis is focused on the noise performances of the analog section, as a function of the detector capacitance, and of the signal peaking time. The effect of series white and 1/f noise and of parallel noise is studied to define the best operating conditions with different detector types.