Preamplifier – Ortec

Matching the Preamplifier to the Detector and the Application

The primary function of a preamplifier is to extract the signal from the detector without significantly degrading the intrinsic signal-to- noise ratio. Therefore, the preamplifier is located as close as possible to the detector, and the input circuits are designed to match the characteristics of the detector. Different pulse processing techniques are typically employed, depending on whether the arrival time or the amplitude (energy) of the detected event must be measured. Pulse shaping for either application is normally implemented in a subsequent module. This module can be located at some distance from the preamplifier, provided that the signal fidelity is not degraded due to the length of the interconnecting coaxial cable. Several types of detectors produce moderately large signals at their outputs, and this relaxes the restrictions on the noise contribution from the preamplifier. Detectors that typically fall in this category are: photodiodes operating with intense light pulses, photomultiplier tubes (PMT), scintillation detectors (scintillator mounted on a PMT), microchannel plate PMTs, microchannel plates, channeltrons, and electron multipliers. For such detectors, a wideband amplifier with a low input impedance can be used directly at the detector output to generate short, fast-rising pulses for timing or counting purposes. For pulse-amplitude (or energy) spectroscopy, a relatively inexpensive preamplifier, such as the Model 113 or the Model 142IH, can be used to integrate the charge in the pulse at the detector output. Three basic types of preamplifiers are available: the current-sensitive preamplifier, the parasitic-capacitance preamplifier, and the charge-sensitive preamplifier.

Read more about counters in the counter catalog or go to the ORTEC website.