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ORTEC MODEL 863
QUAD TIMING FILTER AMPLIFIER
1. INTRODUCTION
The ORTEC Model 863 Quad Timing Filter Amplifier
incorporates four separate timing filter amplifiers in
a single-width NIM module. This design provides a
compact and cost-effective solution for experiments
where timing is required on a number of detectors.
Together with an ORTEC Model 934 Quad Constant
Fraction Timing Discriminator, the Model 863 can
provide optimum timing for up to four germanium
detectors. The unit can also be used for timing with
other solid-state detectors, or as a general purpose
wide-band amplifier with selectable bandwidth.
The signals from germanium or silicon detectors at
the preamplifier output are not always optimum for
achieving good timing resolution. Before
presentation to a timing discriminator, the signals
normally require amplification with a wide-band
amplifier, and they may need additional pulse
shaping to minimize the noise contribution to the
time resolution. The Model 863 provides a flexible
approach in serving these two functions in order to
handle a wide variety of solid-state detector types.
The gain can be selected as either inverting or
noninverting and is adjustable over the nominal
range of 2 to 250. The fine gain is adjustable from 2
to 50 using a front-panel screwdriver potentiometer,
while a printed wiring board (PWB) jumper selects
a coarse gain of either 1× or 5×. The output will
drive a 50
Ω
load to ±5 V with good linearity. This
ensures that the full
!
50 mV to
!
5 V dynamic range
of a constant fraction timing discriminator can be
used. Excellent dc stability of the output is
maintained by a continuous baseline restorer.
Several means of bandpass limiting are included to
achieve the pulse shaping that yields the optimum
time resolution. With all jumpers in the Out position,
the Model 863 is a wide-band amplifier with an
output rise time <10ns. To reduce low frequency
noise and shorten the output pulse width, the CR
differentiation time constant can be decreased from
0.1 ms (Out position) to 200 ns using a PWB
jumper. Alternatively, two front-panel connectors can
be employed (using a 50
Ω
coaxial cable) to add
delay line clipping. This results in a more abrupt
termination of the output pulse duration while
reducing low frequency noise. Both the CR
differentiation and the cable clip can be used
together to yield a bipolar output signal for fast, zero-
crossing timing.
In some cases it is beneficial to select a 50 ns RC
integration time constant using the PWB jumper
provided for that purpose. This reduces the high
frequency noise while slowing the output rise time to
110 ns.
In addition to the two standard jumper selections
incorporated into each of the Differentiation and
Intergration controls, a third position is provided for
both jumpers. By adding the appropriate
components to each third position, it is possible for
the user to select a customized set of integration
and differentiation time constants.
In order to ensure that the output pulse returns to
baseline as quickly as possible, the differentiation
circuit includes a front-panel pole-zero trimmer. This
control permits compensation for the preamplifier
decay time constant.
Each section of the Model 863 have five sets of
PWB jumpers to control the various functions of the
unit. These jumpers are accessible by removing the
left side panel of the module.
Summary of Contents for 863
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