Triggerless charge measurement system for fast characterization with APDs and PMTs

Abstract

Particle detectors based on the response of sensitive material (plastic scintillator, saturated gas, etc.) usually need characterization and test procedures before final installation. Cosmic ray particles are normally used to perform those preliminary tests which includes a detailed inspection of the readout electronics and a data acquisition to obtain a charge distribution of cosmic ray detection.

The Data Processing Interface is implemented in an FPGA (ALTERA family), designed to test the acquisition of digitized signals from light sensors, fotomultipliers (PMTs)  and Avalanche photodiodes (APDs) are the most common ones. The architecture is based on a medium density FPGA that continuously reads the data coming from a 10-bit, 40MHz ADC. Input data is stored in a dual port memory designed to search for valid pulses and compress them by removing data below a programmable voltage threshold. The Interface can produce two types of data packets, non-Zero packets and empty packets. Data in non-zero packets are compressed with a lossless technique and they are marked with a start of data, time stamp, valid data and data size information for reconstruction purposes. Empty events are generated when the maximum waiting time for a valid pulse is exceeded and information is added to preserve the time continuity.