Physics and Engineering of Radiation Detection

8.2. Signal Transport 475

Cf

Vout

Detector

Comparator

−

Amplitude

Time

(a)

(b)

Threshold Reset Time

Switch

Figure 8.1.10: (a) Sketch of a tran-

sistor based pulsed reset charge sensi-

tive preamplifier. The feedback capac-

itor discharge starts automatically when

the preamplifier output crosses a prede-

fined threshold. The switch (transistor)

closes during the reset and drains the

current to ground. (b) Amplification of

detector pulses for the circuit shown in

(a). During the reset time, the ampli-

fier can not amplify the detector output.

This is referred to as thedead timeof

the preamplifier.

Vout

Cf

−

FET

LED

Trigger

Detector Figure 8.1.11: A typical optical pulsed
feedback charge integrating preampli-
fier. The trigger is issued when the out-
put level crosses some predefined thresh-
old. This lits the LED, which shines
light on the FET, which in this condi-
tion creates a closed circuit to ground,
thus discharging the feedback capacitor
(see also Fig.8.1.10(b)).

be carefully considered while deciding on the signal transport methodology. In the
following we will discuss the most important of these points in relation to typical
radiation detection systems. But before we go on we should note on important
point that, although using a wireless data transport mechanism might at first seem
promising, but in reality it has many pitfalls, the most important of which is the
electromagnetic interference. Therefore wherever possible, physical cables are used
to transport signal. Here also we will concentrate on signal transport through cables.