Approaches for single channel large area silicon photomultiplier array readout

We present the results of experiments applying a large area tiled array of silicon photomultipliers (SiPM) to gamma ray spectroscopy with 50.8 mm diameter NaI(Tl) and CsI(Tl) scintillators and 25.4 mm diameter CeBr3. These scintillators are many times larger than an individual SiPM, the largest of which are 36 mm2 at present. This work compares two methods of summing 64 SiPMs into a single output signal for use with standard charge integration electronics. The methods are a straightforward passive method, which simply combines all anode and cathodes together, and an active method, which employs high bandwidth op-amps in a summing topology. Comparisons are also made to a high quantum efficiency photomultiplier tube (PMT) for both resolution and pulse shape. Resolution and noise floor are satisfactorily comparable to the PMT from 21 keV to 2614 keV. The passive method provides the most straightforward approach, and slightly better energy resolution than the active method. The active method shows a substantially faster pulse rise time and undistorted fall time compared to the passive method.