CMOS integrated circuit for pulse-shaped discrimination

摘要

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 system monitoring stored nuclear materials. The method implemented extracts the pulse tail decay time constant using a leading edge trigger for identifying the start of the pulse and a constant fraction discriminator (CFD) to determine the zero crossing of the 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(mu)m CMOS and operates from a 5-V supply. Specifics of the design including overall topology, charge sensitive preamplifier and CFD characteristics, shaping method and time constant selections, system timing, and implementation are discussed. Circuit performance is presented including dynamic range, timing walk, system dead time, and power consumption.