Transcript Testing of the TriP chip in DAB3 J. Estrada, C. Garcia, B

AFEII in the test cryostat at DAB
J. Estrada, C. Garcia, B. Hoeneisen, P. Rubinov
MICE Fiber Tracker Workshop
Fermilab
July 15, 2003
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First VLPC spectrum with the TriP chip
Z measurement using the TriP chip
Conclusion and plans
(more detail about the electronics in Paul’s talk)
J. Estrada - Fermilab
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Short history of AFEII
• Two summers ago the design of AFEII started. AFEI does not work
at 132 nsec (at that point 132nsec was still alive).
• A new front end chip (TriP: Trigger and Pipeline) was designed to
replace the SIFT+SVX combination. The new system uses a
commercial ADC for the charge readout.
• MCMII was designed for the TriP chip, MCMII mounts on the
existing AFE. We have been using MCMII for 1.5 years, three
existing versions.
• Last summer we received the TriP chips, they were mounted on
MCMII and readout using the existing AFE (SASeq). Extensive tests
of 8 chips were done in the bench (see DØNote 004009 and
DØNote 4076), high yield ~90%. We have enough TriP chips for the
full AFE replacement.
• This summer we have the 4-cassette cryostat to look at real signals
from the VLPC.
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Why do we still bother with AFEII?
(132nsec is not a possibility anymore)
• The situation is as follows:
– we have the TriP chip, we have enough of them.
– we have seen that it works, and maybe it solves many of the
issues with AFEI (split pedestals, tick to tick variations).
• After some discussion with DØ management we agreed
to:
– build a real AFEII and populate it with 8 MCMII (J. Anderson)
– at the end of the year, with the information from our tests and our
knowledge of the performance of AFEI, we will make a decision
on the possible replacement of the CFT electronics.
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VLPC spectrum
VLPC signal with the TriP chip (132 nsec - cass 109, LH, @7.2 V)
We have a high gain
cassette (~55K in Don’s
units), from our spares.
Without seriously
optimizing the parameters
for the operation of the
TriP in these conditions,
we got a nice sprectrum.
Notice the very little spread
between channels and the
uniformity in the gain.
2500
2000
1500
1000
500
0
0
50
100
150
200
250
charge (ADC counts)
Same channels as seen by the stereo board, after
very hard work to reduce the noise.
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Fits to the spectra
Mysterious deformation
around 128 counts
We measure a gain of around 21 counts/p.e., from our previous studies of
the chip we believe this means that the VLPC are running at ~75K, a bit
higher than what we were expecting…
Other typical parameters: pedestal width=0.18 p.e., gain dispersion=0.17
p.e., pedestal spread (RMS-16 channels)= 0.05 p.e.
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Z measurement
The TriP seems to be working, we will keep testing it to have the
information to make the correct decision in December.
One idea: a minor modification to the TriP that would allow us to
measure the time when the discriminators fired with respect to the
crossing clock , (see DØNote 004009) . This will give a
measurement of the Z position of the hit along the fiber, could help
for tracking (tracking algorithm experts need to evaluate how useful
this will be).
We are now measuring the resolution that we can achieve for this z
measurement using the current version of the TriP (we can only look
at ½ the channels of the TriP and we needed to implement an
external readout for the timing).
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Cosmic Muon Trigger

ADC information
Discriminator signal
AFEII-prototype
VLPC
scope
ethernet
timing information
SASeq
bit3
ADC information
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Our events
DISCR. from TriP
CROSSING(132nsec)
SCINT.1
SCINT.2
This is how me measure timing of the discriminator, with respect to the muon trigger
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and the crossing clock. The green line is the OR of 16 channels.
Charge injection, integration window
30 nsec
t1= time from crossing clock to charge injection
The TriP has an internal mechanism to inject charge in any channel. We
used this system to inject 60 and 30 fC (~ 7 and 3.5 p.e.) at a ramdom time
with respect to the 132 nsec crossing to see the integration window and the
internal timing resolution in the TriP discriminator.
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Charge Injection, timing resolution in the TriP.
A)
B)
C)
A) The time walk of the
discriminator as a function of
injected charge is very small.
B) The timing spread in the
discriminator is 420 ps for 60 fC.
C) The timing spread in the
discriminator is 662 ps for 30 fC.
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Integration window
We open a 30 nsec integration window and scan it with respect to the
132nsec clock.
Looking at the average signal (ADC output) we determine position for the
optimal integration window, and we use this window to measure the
timing resolution.
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Signal with muon trigger
For events outside this window
the charge does not get
completely integrated in the TriP
and we could be missing the first
photons from our signal.
This data corresponds to 2 different runs,
our setup had a timing problem during the
first run that made us miss part of the
interesting events.
T4= time from crossing clock to muon trigger
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Our signal
We are using the 11m
waveguides, and are getting in
average approx. 5 p.e.
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Time walk
The photons from the
scintillating fibers have some
timewalk (~0.83 nsec/pe), we
correct for this timewalk.
As the number of photons
increases the timing spread
reduces.
The integration window cut is
already applied to this data.
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Results, with a cut at 5 p.e.
The width of the peak is about 4
nsec wide, and there is a tail that
makes the RMS 3.3 nsec. This
could come from muons at large
angle that have a different Z
Corrected discr. timing (nsec)
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Results as a function of the cut in the ADC
we start to get a measurement
only above 5 p.e., and for the
large signal pulses we get
about RMS=2.8 nsec
(2.8 nsec x 16 cm/nsec = 48cm)
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Result for different timing
The integration window,
according to the ADC, shows
a plateau in the width of the
timing distribution.
When pulses are delayed the
spread becomes larger
because we start missing the
first photons.
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Conclusion and Plans
• The TriP still looks good. The noise and the channel to channel
differences look ok (so far we looked at a small number of
channels). It is amazing how easy it is to operate this chip compared
to SVX+TriP .
• For the moment we get σ=48cm for the Z measurement of the hit in
the fiber. We will continue trying to understand if this is the best we
can do (part of this resolution could come from cosmic muons at
large angle, that actually have a different Z). We are waiting for input
from our tracking experts to tell us how useful will this information be
for track reconstruction ( reduction of fakes, reduction of CPU time
for tracking algorithm, resolution improvement).
• Now moving to 396 nsec operation of the TriP, the performance of
the TriP has not been studied in detail with this timing…
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