Analysis and simulation of the SLD WIC (Warm Iron Calorimeter) PADS hybrid preamplifier circuitry Page: 3 of 8
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(a-
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a 40-- -
10Hz 1.OkHz 100kHz 10MHz
Frequency07
160
120
80
40
0
10Hz
1.0kHz 100kHz
Frequency10MHz
(a)
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00
45
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a5
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Time (ps)15 20
(b)
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. nW
Fig. 3 Simulated (a) and measured (b) input impedances of
the hybrid preamplifier.
The third region in the curves (2 MHz to 100 MHz)
also shows general agreement between the model and the
measurements. The amplifier shows a parallel low Q res-
onance which raises the input impedance to a maximum.
The model and lab results both show the resonance (simu-
lation resonance at 7 MHz, lab measurement at 15 MHz),
and the model predicts a lower maximum impedanc: of
105 Q versus the measured 150 Q. This discrepancy is
largely due to the simplified representation of the output
impedance and the absence of parasitic elements in the
Boyle model (such as lead inductance and parasitic ca-
pacitance) that would be significant in this 10-100 MHz
range. The unity gain frequency of the preamplifier is
600 ItHz, so that the major effect of these high-frequency
resonances involves the interaction of the physical detec-
tor with the input integrator. In our system the capaci-
tance of the detector system is in parallel with the input
impedance, so that the input detector capacitance dom-
inates the input impedance at this resonance. For the
frequencies where the system has gain, there is very good
agreement between the simulation and laboratory mea-
surements.
Figs. 4(a) and 4(b) show the simulated and measured
transient responses of the amplifier without any input ca-
pacitance CPAD. Note the 5 ps peaking time in both
figures and the excellent agreement for the overall pulse
shape. Table I shows the sensitivity of the system to vari-
ations in sampling time relative to the maximum. The
required time stability for 1% accuracy is easy to achieve.Fig. 4 Simulated (a) and measured (b) transient responses for
full-scale (3400 pC) input charge and zero pad capacitance.
Table I
Time Shift of Sampling Edge Relative to 5 ps
for Specified Errors
ERROR - Shift (ps) + Shift (ps)
1% --0.63 0.71
5% -1.36 1.68
V. INPUT CHARGE DISTRIBUTION EFFECTS
Figure 5(a) shows the response of the system (with a
nominal 10 nF pad capacitance) to 3400 pC input charges
with 50, 100, 200 and 300 ns total duration. Note that
the variation in output amplitude at the 6 ps sampling
time is less than 0.2%. Figures 5(b) and 5(c) show the
waveforms at the input node and at the first stage inte-
grator output during these short intervals. The dominant
effect of the charge duration is to change the amplitude
of the transient voltage developed at the input node, and
to change slightly the voltage ramp waveform at the first
stage output. Thus the overall shape of the input charge3
- (b)
+c 40
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Fox, J.D. & Horelick, D. Analysis and simulation of the SLD WIC (Warm Iron Calorimeter) PADS hybrid preamplifier circuitry, article, October 1, 1990; Menlo Park, California. (https://digital.library.unt.edu/ark:/67531/metadc1206669/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.