Splitter/Mixer
The Splitter/Mixer boxes allow
monitoring of PM-tubes of some trigger planes in CHORUS.
Two boxes have been built, for a total of 128 PM tubes.
The general idea is, to have a pulse-height monitor ADC on groups.gz
of 8 Photomultipliers on those Trigger planes, that do not need
individual ADC readout (like the Veto counter, that only uses TDC's).
In this way, the gain of these PM's can be checked, e.g. with the
Gain monitoring system.
From each signal, a negligeable fraction is coupled out,
and summed by a current amplifier, which keeps.gz its input
virtually to Ground-level.
This Sum input monitors a group of 8 PM's.
The amplified sum of 8 signals is output on the
9th Lemo below of each row of 8 Lemo outputs.
A design drawing
((1859-byte PSfile, gzipped) is available, as well as a
detailed electronics schematic
(10718-byte PSfile, gzipped)
for one of the 16 identical 8-channel boards, and a PCB-layout
(2773-byte PSfile, gzipped) for such a board.
Functional Description
The 64 BNC inputs on the backside of the box
should receive the Photo Multiplier signals. They
are connected internally to the corresponding 64 Lemo connectors
on the front-panel, which serve as signal outputs.
Below each row of 8 Lemo's, there is a 9th Lemo, giving the
summed (and amplified) output of the 8 channels above it.
Specifications
- Input level: 0 to -12 Volts (abs max)
- Output level: equal to Input
- Sum level: 0 to -1 Volts (max)
- Sum gain: 1:1 (when only one input driven)
- Sum rise/fall time: ~20 ns.
- Sum amplifier: CLC 401 AJP of Comlinear Inc.
- Sum output DC offset < 5 mV
- Sum inline delay 2.2 ns
Warning
- Input levels should not exceed 0..-1 Volt for
normal summing operation.
- All outputs should be terminated in 50 Ohms.
This also holds for un-used outputs (put a 50Ohm
terminator in), otherwise the Sum-signal will
suffer from reflections.
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JV / 4 May 1994