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Entry  Wed Jun 1 22:29:01 2016, Dominik Neise, problems when stop cell >= 767 ?? stop_cell_distribution.png
    Reply  Wed Jun 1 23:16:01 2016, Stefan Ritt, problems when stop cell >= 767 ?? 
Message ID: 527     Entry time: Wed Jun 1 23:16:01 2016     In reply to: 526
Author: Stefan Ritt 
Subject: problems when stop cell >= 767 ?? 

I cannot confirm the story with the "stop capacitor > 767". It can be seen from your plots that the distribution of stop cells are even, no holes or bins with double height.

There is an issue with cell 767, but this is when one tries to do simultaneous reading/writing to the chip. This does not really work as writen in the data sheet. Waveforms sometimgs get cut off at cell 767. But the stop cell is always correct, otherwise one could not calibrate the data. If you use the evaluation board for example, which is perfectly calibrated, and introduce an "artifical" shift like

if stop cell > 767 then
  stop cell = stop cell + 1

then you would see that the voltage calibration would become wrong and very noisy.


Dominik Neise wrote:

Hello Stefan,

some colleages told me a story, I was neither able to confirm nor find anything in the datsheet about. According to them:

For some internal reason of the DRS4, if the “stop capacitor” of the DRS4 is >= 767, the true stop channel is one before the stop channel read from the DRS4. In other words, the stop channel which returns the DRS4 shifts after sampling to the capacitor ID 766.

Can you confirm that, or even say a few words about that matter?

I wanted to confirm this by plotting the stop cell distribution for random triggered data, taken with one of the FACT boards. I assumed (possibly misunderstanding the matter), that this would lead to missing values in the area of stop cell 767, but cannot see any significant excess or lack of entries in that area.



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