Table of Contents
Advertisement
PSI System Controls and Diagnostics
Y2
Y1
300
300
250
250
200
200
150
150
100
100
50
50
0
0
-50
-50
-100
-100
0
Time/nSecs
Figure 13. Circuit simulation, current and voltage waveforms in the D100 input stages, 30 pF
input load.
The red curve is a simulated sodium iodide detector output current pulse, which typically
includes a very fast rise followed by an exponentially falling tail with decay constant around 250
nsec. The blue curve is the current that flows into the amplifier, after some integration by a 30
pF load capacitance, for example from one foot of coaxial cable. The dark green curve is the
voltage output of the first stage, and the orange curve is the signal fed to the ADC.
Capacitive load on the input causes unwanted integration and pulse distortion by any, which is
why this should be minimized. Figure 14 shows the simulation result with 180 pF of load
capacitance, corresponding to about 2 meters (6 feet) of coaxial cable. The distortion appearing
in the pulse shape makes the task of the pulse overlap discrimination algorithms more difficult.
D100 User Manual
100
200
300
D100_UM_081027
400
500
600
700
800
900
100nSecs/div
Page 28 of 46
Advertisement
Table of Contents
