Physics and Engineering of Radiation Detection

484 Chapter 8. Signal Processing

t/τd

0123456

out

V

0

0.2

0.4

0.6

0.8

1

CR filter

t/τi

0123456

out

V

0

0.2

0.4

0.6

0.8

1

RC filter

t/τ

0123456

out

V

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

CR-RC filter

Figure 8.3.5: Response of CR (upper), RC (middle), and CR-

RC (bottom) filters to step input pulse. The step input pulse

approximation is valid only for preamplifier-shaper combinations

in which the decay time of the amplifier pulse is much larger than

the shaper’s time constant. In real systems this approximation

is generally not valid and consequently the CR-RC shaper suffers

from small undershoot in the decaying part of the output pulse.

The new pulse will then ride on the decaying pulse whose undershoot will lower its
effective height.