A CMOS integrated circuit for pulse-shape discrimination

A CMOS integrated circuit (IC) for pulse-shape discrimination (PSD) has been developed. The IC performs discrimination of gamma-rays and neutrons as part of a monitoring system for stored nuclear materials. The method extracts the pulse tail decay time constant using a leading edge trigger for identifying the start of the pulse and a zero-crossing discriminator to determine the zero crossing of the bipolar shaped signal. The circuit is designed to interface with two photomultiplier tubes-one for pulse processing and one for coincidence detection. Two outputs from the IC, a start and stop, can be used with a high speed timing system for pulse characterization with minimal external control. The circuit was fabricated in Orbit 1.2 μm CMOS and operates from a 5-V supply. Specifics of the design including overall topology, charge-sensitive preamplifier and discriminator characteristics, shaping method and time constant selections, system timing, and implementation are discussed. Circuit performance is presented including timing walk, system dead time, and power consumption