Selecting and designing the front-end amplifier for high-gain photomultiplier detectors with optimal timing performance

High-gain photomultiplier detectors are employed in an increasing number of applications in different fields to evaluate with great accuracy the occurrence time of light flashes composed by few or even single photons. Examples of these application fields are medical imaging, astroparticle and high energy physics, laser spectroscopy and LIDAR. To fulfill a good single photon timing accuracy, in the range of few hundreds of picoseconds, not only detectors with intrinsic excellent timing resolution (photomultiplier tubes, microchannel plated detectors, silicon photo multipliers, etc.) must be used, but the very first front-end amplifier (FEA) stage, used to read-out the detector, must also be carefully chosen and designed. We compare here three commonly used solutions for the FEA, from the point of view of the best achievable timing resolution: the charge sensitive amplifier (CSA), the voltage amplifier (VA) and the current buffer (CB). The results show that the CSA solution is limited in terms of frequency response by the usually large equivalent capacitance of the detector and that, surprisingly, the presence of the parasitic inductance L, due to interconnection detector–FEA, has a noise shaping effect which favorably affects the timing accuracy of the CB over the VA configuration. To support this study, simulations of simple implementations of the compared FEA solutions have been performed, under the same conditions. Moreover, with reference to a given detector and to a particular value of L, we show how the best timing accuracy of the CB is obtained by selecting an appropriate combination of input resistance and bandwidth of the FEA.