Choosing the Right Amplifier for the Application

Choosing the Right Amplifier for the Application

The amplifier is one of the most important components in a pulse processing system for applications in counting, timing, or pulse-amplitude (energy) spectroscopy. Normally, it is the amplifier that provides the pulse-shaping controls needed to optimize the performance of the analog electronics. Figure 1 shows typical amplifier usage in the various categories of pulse processing.

When the best resolution is needed in energy or pulse-height spectroscopy, a linear pulse-shaping amplifier is the right solution, as illustrated in Fig. 1(a). Such systems can acquire spectra at data rates up to 7,000 counts/s with no loss of resolution, or up to 86,000 counts/s with some compromise in resolution.

The linear pulse-shaping amplifier can also be used in simple pulse-counting applications, as depicted in Fig. 1(b). Amplifier output pulse widths range from 3 to 70 µs, depending on the selected shaping time constant. This width sets the dead time for counting events when utilizing an SCA, counter, and timer. To maintain dead time losses <10%, the counting rate is typically limited to <33,000 counts/s for the 3-µs pulse widths and proportionately lower if longer pulse widths have been selected.

Some detectors, such as photomultiplier tubes, produce a large enough output signal that the system shown in Fig. 1(d) can be used to count at a much higher rate. The pulse at the output of the fast timing amplifier usually has a width less than 20 ns. Consequently, maximum counting rates in excess of a few MHz are feasible without suffering more than 10% dead time losses.

The two common schemes for deriving signals to achieve nanosecond and sub-nanosecond time resolution are outlined in Fig. 1(c) and (e). Both applications utilize a fast timing amplifier. Fig. 1(e) illustrates the preferred solution for single-photon or single-ion detection and timing with photomultiplier tubes, electron multipliers, microchannel plates, microchannel plate PMTs, and channeltrons. Although the scheme designated in Fig. 1(c) can also be used with these same types of detectors, it is more commonly employed with high-resolution semiconductor detectors, since such detectors require a low-noise, charge-sensitive preamplifier.

Whatever your application, the brief descriptions of performance characteristics on the next few pages and the selection guide charts that follow will help you to choose the best amplifier for your situation.

Figure 1. Typical Amplifier Applications in Pulse Processing.