A large dynamic range integrated front-end for photomultiplier tubes

A full custom analog CMOS circuit for obtaining a photomultiplier readout with a 16 bit resolution over 7 V has been developed. It is part of the R&D program for the photomultiplier tube front-end readout of the Pierre Auger Observatory northern site. It performs signal duplication and amplification with three gains: 0.15, 1 and 6. Each amplifier has a resolution of 10 bit and can measure signals with durations of several microseconds with a good baseline stability, for an input charge of up to tens of nano-Coulombs. The amplification is performed by current feedback amplifiers with a bandwidth of 60 MHz.The input impedance, adapted to the coaxial cables, is stable over the whole working range. otype was submitted in April 2004 and successfully tested. The linearity over the working range is less than 1%. It was also successfully tested on the Auger surface detector element installed at Orsay (comprised of a Cherenkov water tank equipped with Photonis XP1805 9” diameter photomultiplier tubes). The resolution over 7 V is 16.6 bit.This circuit is the first step towards a “system-on-a-chip” (SoC) solution for a photomultplier tube readout equipped with a fast ADC for signal digitization. A setup using a single cable for both the signal and the photomultiplier high voltage power supply was shown to be successful.