Physics and Engineering of Radiation Detection

490 Chapter 8. Signal Processing

in succession, as shown in Fig.8.3.12, it results in an output pulse with approxi-
mately linear rising and falling edges. The output pulse then has a shape that looks
like a triangle (see Fig.8.3.13). Such a shaper is referred to as semi-triangular pulse
shaper.

Gaussian

Semi−

Gaussian

Semi−

Gaussian

Semi−

Stage−1 Stage−2 Stage−3

Figure 8.3.12: Step input response at each stage of a three-stage semi-triangle

pulse shaper.

Time

P

ul

se

H

ei

gh

t

Figure 8.3.13: Output of a semi-triangular

pulse shaper.

8.4 Filtering..................................

Due to pickup from external and internal noise sources, it is often desirable to filter
the pulse such that only certain frequencies are allowed to pass through to the next
electronic stage. Though it was not specifically mentioned earlier but the pulse
shapers we just discussed actually perform the filtration function.
There are essentially three classes of filters depending on the frequency range
that needs to be blocked. The low pass filters are perhaps the most commonly used
as they block all the high frequency components from the signal. The high pass
filters, on the other hand, block low frequency components, which may be desirable
in some applications. The combination of these two is called the band pass filter,
which allows only a range of frequencies to pass through. Fig.??shows schematics
of different types of filters.