Minutes of the forward endcap EMC meeting, 13th of October 2014, SeeVogh, 10:30 - 11:40

Topics are not in the order of discussion but by subject.

  • Basel: Werner
  • Bochum: Claudius, Fritz-Herbert, Malte (via SeeVogh), Matthias, Patrick, Stefan, Tobias H., Tobias T.
  • Bonn: excused
  • Groningen: excused
  • Uppsala: Pawel

Preamp ringing

It was suggested the the higher ringing probability is caused by the shorter rise time of the APD preamps (Myroslav by mail and rise time measurements by Malte/Matthias). To confirm: Measure rise time of old and new preamps in Bochum.

In the proto192 about 2/3 are ringing, 1/3 of the preamps are stable at -25 degree C (Matthias).

Comments from Werner:
  • Measurements with APD require to put HV to get correct capacitance (load). (The test pulse measurements in Bochum use equivalent capacitor as load).
  • to reduce ringing behavior increase the compensation capacitor from 100 pF to 200 pF or 470 pF
  • Put capacitors on the HV and LV supplies for decoupling. Observe the LV/HV when ringing starts (difficult to do).
  • Old preamps have scratched serial numbers, new one have glued serial numbers. Also version is important to distinguish different preamps.

Ringing of preamps could not be reproduced in the lab. It was decided to built a test setup identical to the APD alveole in the proto192:
  • Werner will sent 33 APD preamps (same version as in proto192) this or next week to Bochum
  • At RUB the APDs will be mounted in an old APD alveole. Modify it to same setup as in the proto192.
  • It will be tested in the fridge. If ringing is observed:
  • Modify the preamps (increased capacitor for the compensation).
  • Check that this can solve the problem

Gain of APD preamps: From ELSA beam time we observe two classes: 170 mV/MeV and 350 mV/MeV. For the higher number the current gain is ok. Need to clarify the reason for the two classes.

Preamp gain for VPTT

Tobias: gain response at B=0.9 T and HV=1000 V about 60% of signal without magnetic field (tbc. by Bonn measurements). From ELSA test beam: 145 mV/GeV thus maximum 1044 mV. Some tubes have higher gain, so expect maximum 1442 mV with current preamp. Conclusion: 34% more gain would be better = 0.63 V/pC. Werner will produce two preamps, Bochum will test them.

Note (Malte): the preamp with factor 2 higher gain has longer rise time (30 ns) and fall time decreased by factor 2. Waveform after shaper not yet checked.

Preamps for APD test setup

Werner will produce 22 APD preamps with standard gain 0.5 V/pC for GSI APD test lab.


Pawel: ADC debugging complicated due to problems with new Xilinx Vivado tools. Will try to use old ISE tools. Concerning crate design: An ADC size of 180mm x 65 mm would be possible.


Matthias, Claudius: Backplate is mounted in frame in Lab at Bochum. Test of space for LP etc. ongoing. Modification of LP housing needed.

-- FritzHerbertHeinsius - 14 Oct 2014
Topic revision: r2 - 2014-10-15, FritzHerbertHeinsius
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