A bilinear analog compressor to adapt the signal dynamic range in the AUGER fluorescence detector

A fluorescence detector, consisting in a PhotoMultiplier Tube (PMT) pixel camera, will be used in the AUGER experiment to study cosmic-ray sources with energies exceeding 10 ¹⁸ eV. The front-end electronics transmits the PMT signals to the ADCs, retaining the timing and amplitude information carried by signals which span a wide (15-16 bits) dynamic range. The analog processing channel consists of a low-noise linear section, including an antialiasing filter, followed by a circuit of original conception, performing a high-accuracy bilinear compression of the signal dynamic range. This allows operation with a 12-bit ADC. Quantization errors can be minimized by correctly choosing the compression parameters. The paper presents the concepts the compressor is based upon, and the experimental behavior of a prototype version.