Baseline studies
S. Gleize, B. Martinez & E. Noah
Context
We wanted to study the behaviour of the baseline :
-
SCA mode
Peak-detector mode
Single channel & 2 channels simultaneously
Different time shaper : 37.5 & 12.5 ns
We work in the Dark Counts region
SCA – Negative Baseline
Here we put intentionnally a too high
OR32 value (100). We can see, the kept
value is below the baseline.
The time-clock signal is zero because
we are not doing an acquisition.
SCA – Negative Baseline
Here we can see the previous effect during
an acquisition (the activated channel is inside
the red circle). The baseline is still negative
During an acquisition, the time-clock signal
is not zero anymore. We have a signal for each
channel
Peak-detector Negative Baseline 2CH
Here we enable 2 channel (n2 & n31).
Most of the time, we have a good signal,
but it happens we have a negative baseline.
We suppose it’s due to the chip triggering
on the other channel.
Peak-detector – Negative Baseline 2CH
We see the previous phenomenon effectively
happens when the other channel is triggering.
However this doesn’t happen every time we trig
on the other channel.
Peak-detector – Normal Baseline – 2CH
Here we can see the baseline is not negative
even if we are triggering on the other channel.
We changed the time shaper to 12.5 ns (it was
37.5 before) to see if the baseline changes.
Negative baseline for time shaper = 12.5 ns
We observe the same phenomenon with roughly the
same difference between the negative baseline & the
normal baseline
Back to the plots
Now we observed this negative baseline, we want to know if this is a
phenomenon we can directly see on the data.
For this we take multiple acquisition in different configurations…
Baseline – 2Channels simultaneously
Here we take an acquisition with 2 Ch simultaneously. As you can see, the
baseline distribution looks like a normal gaussian. We don’t see a special
contribution from the negative baseline data.
Ch2
Ch 2
The data were taken on ch2 &
ch31 with a discri 300 in Peakdetector mode
During the acquisition, some
probes were plugged to the
card to observe the signal on a
scope.
Baseline – 16Channels simultaneously
Still following the idea this negative baseline could be linked to the triggering
on other channels, we took data for 16 channels simultaneously. Once again,
we observe no special distribution for the negative baseline.
Ch2
Ch2
The data were taken on ch2 &
ch31 &14Ch with a discri 300
in Peak-detector mode
During the acquisition, some
probes were plugged to the
card to observe the signal on a
scope.
Gap & influence of probes
Taking our data, we observe a «gap» between the first peak & the baseline.
This gap doesn’t seem to change with the discri (first 200 then 180).
Suggesting it could be an effect of the probes fixed to the card, we will try
without it.
Ch2
Ch31
The data were taken on ch2 &
ch31 & 14Ch with a discri 200
then 180 in Peak-detector
mode with a slow shaper time
of 37.5 ns & a HG of 12.
During the acquisition, some
probes were plugged to the
card to observe the signal on a
scope.
Gap & influence of probes
Taking out the probes, we observe no difference in this «gap». We won’t put
these probes again for the rest of the studies.
Ch2
Ch31
The data were taken on ch2 &
ch31 & 14Ch with a discri 200
in Peak-detector mode with a
slow shaper time of 37.5 ns &
a HG of 12.
This time we removed the
probes.
Gap & influence of slow shaper time constant
Now we investigate the influence of the slow shaper time constant on the
gap. We took some data with a 12.5 ns constant instead of the previous 37.5.
Again, no difference in the gap.
Ch2
Ch31
The data were taken on ch2 &
ch31 & 14Ch with a discri 200
in Peak-detector mode with a
slow shaper time of 12.5 ns &
a HG of 1`2.
Gap & influence of High Gain
This time, we look at the high gain possible influence on the gap. It was
previously at 12. Here it is at 1 (maximum value) and in the next slide it’s at
63 (minimum value). Still no difference in the gap.
Ch2
Ch31
The data were taken on ch2 &
ch31 & 14Ch with a discri 200
in Peak-detector mode with a
slow shaper time of 12.5 ns &
a HG of 1.
Gap & influence of High Gain
Ch2
The data were taken on ch2 & ch31 & 14Ch with a discri 200 in Peak-detector
mode with a slow shaper time of 12.5 ns & a HG of 63.
Ch31
Gap & peak-detector mode influence
Finally we changed the peak-detector mode to SCA mode. This time we observe some
difference.
First, the baseline moved. It was around -100 and is now around -50.
Furthermore there is no more gap. This phenomenon seems to be linked to the detector
mode only.
Ch2
Ch31
The data were taken on ch2 &
ch31 & 14Ch with a discri 200
then 250 in SCA mode with a
slow shaper time of 12.5 ns, an
OR32 of 20 ns & a HG of 12.