An Analog Delay Compensation System to Reduce the Effect of Variable Transit Time in PMTs

Photomultiplier transit time variation due to different high-voltage settings is a significant problem that degrades the performance of the systems that try to recognize fast image patterns in arrays of this type of photosensors. This effect is especially harmful for the performance of the trigger system of Cherenkov telescope cameras. With the aim of overcoming this effect, an electronic system has been designed, manufactured, and tested. This system can reduce the delay differences by introducing the appropriate variable delay for each photomultiplier (PMT), which is calculated by making use of a delay meter specially designed for this application. The specifications of the system have been defined by means of simulations and the measurements fulfill the requirements. The circuits used in this delay compensation system, as well as the simulations and measurements of the prototypes, are presented in this paper.