Low noise and low power preamplifiers for large area avalanche photodiodes - results from the testing of a mass production series with an automatized test system

Modern, high precision EM calorimeters need to run at very high count-rates, require good time and energy resolution, and large dynamic ranges. In addition, newly developed FPGA systems allow the construction of very dedicated experimental triggers in order to select efficiently reactions with low cross sections among high overall reaction rates. Avalanche Photo Diodes (APD's) are used in many of such systems, in particular when magnetic fields are involved. A disadvantage is their relatively low gain which together with other requirements is a challenge for the preamplifier design. Our group has developed special Low Noise / Low Power (LNP) preamplifiers for this purpose. The LNP preamplifier will be used for the upgrade of the Crystal Barrel detector (planned at begining of 2014) at the Bonn ELSA accelerator, mainly aiming at a good time resolution capability (existing readout is with photodiodes without timing information), while conserving the good energy resolution. The 1400 CsI scintillator modules will be equipped with double large area APDs for which special temperature compensation of the gain is necessary. Similar preamplifiers have been also developed by our group for the readout of the PANDA EMC forward end-cap. We report the results from the testing of the first 1500 channels of the preamplifiers for the Crystal Barrel experiment using a specially developed automatized test system.