Development of a low-noise front-end electronics for a multi-channel APD readout system

A fully-active fine grained scintillator tracking detector is being considered as a part of the near detector complex in the Tokai-to-Kamioka (T2K) neutrino oscillation experiment. For the wavelength-shifting (WLS) fiber readout of scintillators, a multi-channel avalanche photo diode (APD) readout system using VA ASIC has been developed. The readout system consists of a front-end electronics board equipped with APD and VA, and a back-end VME module controlling the readout. The analogue information from each APD channel is amplified and sequentially read out via VA. The performance of the APD readout system has been evaluated. The readout electronics has been demonstrated to have good linearity up to 30 fC corresponding to 20 minimum ionizing particles (MIPs). The pedestal width is equivalent to 1,000 to 2,000 electrons depending on the gain of each VA channel. For the light input of 124 photons which is equivalent to the signal from MIPs passing through a scintillator strip of 1.0 cm thickness, the system achieves the signal-to-noise ratio of 7.0 (18.5) at 20degC (-10degC)