ORTEC 109A - Linear Output; Fig. 1. Bias Resistor Value (Megohms); Fig. 2. Rise Time as a Function of Input Capacitance

PARALLEL BIAS RESISTOR
A 10Mi2 resistor is provided, shipped in a plastic bag with
the 109A, to be plugged into the two single pin sockets
near the lOOIVlJl resistor (R2) on the printed circuit. This
resistor will reduce the voltage required from the bias
supply, but should be used only for very high leakage
detectors. When it is instal led in parallel with R2, the total
series resistance between the Detector Bias connector and
the Detector Input connector is reduced to 10MJ2, and the
compensation is 10 V per microampere of detector leakage
current. However, this circuit will increase the zero pF
noise by approximately 0.5 keV (silicon equivalent) and
should not be used unless necessary. See Fig. 1.
4.2 Linear Output
The output of the 109A is a "step" of voltage of 150
mV/MeV with the gain switch in the X10 position, or
15 mV/MeV in the XI position (silicon detector equivalents).
The pulse rise time is a function of input capacitance (see
Fig. 2). The dynamic range of the output is 7 V either
polarity, when the output is "sending-end" terminated.
"Receiving-end" termination will result in a 3.5-V dynamic
range, but this may be preferable to sending-end termina
tion. The integral nonlinearity in the preamplifier is
specified at not greater than 0.1% over the 0- to 10-MeV
range.
EXT;
M EXT
EXT.
f'EXT
600_
10 20
50 100 200 500 ^ 000 2000 5000
Fig. 1. Bias Resistor Value (l\/112).
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--
1
-
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;
--
1
~r
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I ! : ;
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....
1
—
1
L|j 1 . .
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—
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■ t-
109A
& 118
. . .
A
—
4 6 8 10 20 40 60 80 100
INPUT CAPACITANCE (pf|
400 600 1000
Fig. 2, Rise Time as a Function of Input Capacitance.