Electronics for PMTs

Abstract

Photomultipliers (PMTs) are current generators characterized by high gain, wide bandwidth, and high-output impedance. The role of preamplifiers and amplifiers is generally one of conditioning the PMT output. Either the time signature is preserved using a fast voltage preamplifier, or a voltage proportional to the charge in each event is generated with a charge-sensitive preamplifier. Both preamplifier types are generally of low-output impedance, suitable for driving matched coaxial cable. Preamplifiers and amplifiers are available as modular units (e.g. nuclear instrument module), stand alone, or are incorporated in a module including the PMT. Shaping amplifiers are used to further condition preamplifier signals, using integrating and differentiating circuits—particularly relevant to scintillation spectrometers. Discrete-component amplifiers and current-feedback operational amplifiers serve fast applications. Digital signal processing has overtaken many of the classical electronic techniques involving resolution and in pulse shape discrimination. Electronic circuitry for generating fast LED pulses is discussed.