Design of the front-end electronics for the fluorescence detector of the AUGER experiment

P.F. Manfredi, M. Manghisoni, L. Ratti, V. Re, V. Speziali The AUGER experiment is concerned with the study of cosmic rays with energies ranging between 1019 and 1021 eV. The extended air showers produced in the earth atmosphere by cosmic radiation give rise to fluorescence phenomena, which will be measured by a purposely developed detection system. In the present design the fluorescence detector which is to be used in the AUGER experiment is made of 30 modules; each module consists of an array of 20 × 22 photomultiplier tubes (PMTs). The front-end electronics employed in the PMTs' readout is required to preserve time and amplitude information of the original fluorescence signal, without significantly degrading the noise performance of the system with respect to the noise level due to sky background. Furthermore the measurement channel is expected to handle a 16 bit input dynamic range. After analog processing the waveforms will be sampled at a rate of 10 MHz with 12 bit resolution. A compression circuit with bilinear transfer characteristic has been designed to adapt the dynamic range of the PMT signals to the input dynamic range of the ADC and to adjust the gain to compensate for the gain spread of the PMTs. A prototype detector module, consisting of 100 complete channels, have been successfully tested at the end of 2000. In 2001 two modules of 440 channels each have been installed at the experiment site in Argentina and has begun taking data.

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