TG3: Diode Read-out

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TG3 Diode Read-out and signal processing C.
Cattadori on behalf of the working group
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Choice of FET and preamps
Strategy has been defined. For Phase I three
possibilities are actually pursued 1 cold FET
and RfCf and warm hybrid preamps a la AGATA near
the crystals (inside the LN bath) pro ready
working (from the electronic point of view)
solution cons problems of radioactive
background from the hybrid themselves and of
the thermally insulated box needed to contain
the hybrids and keep them at proper
temperature. 2 cold FET and RfCf and warm
hybrid preamps outside the LN bath. pro no
problems with background (apart from FET etc)
cons problems from long cables ( 4 m)
?stabilization of amplifying stage, reduced
bandwith, noise increase, noise pick up,
increased possibility of cross talk between
channels, microfonic noise etc.
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Choise of FET and preamps

• 2 possible FET
• InterFET IF1331 tested in HD and MI
• Philips BF862 tested in MI
• 2 Hybrid preamp
• EURYSIS preamp PSC823C
• MARS preamp developed by INFN Milano

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Analog electronics

• Starting point is MARS preamplifier developed by
  A. Pullia University and INFN Milano for AGATA.
• in this month 32 of these preamps will be
  delivered to Cologne to be tested

MARS preamps have extreme low noise figure 130
-150 e- ENC (RMS) at 20 pF input but need to be
slowed down to draw 4m cable from cold FET! (ref
IEEE Trans. on Nucl Sc. 49-5(2002)2436)
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Agata Analog electronics performances
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Choice of FET and preamps
MARS preamps have extreme low noise
characteristics 130 -150 e- ENC (RMS) at 20
pF input and very fast. Can draw 4m cable from
cold FET acting on compensating capacitor in the
cascode stage! For GERDA they will put a
trimmer capacitor 0-3 pF. Remember the preamps
slow down! At HD they have been able to
stabilize the Eurysis preamps connected to FET
through a 4 m. long cable using the same
technique. Needed noise measurements in this
configuration. In Milano we will perform these
measurements before end of february and a full
report will be circulated.
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Analog electronics
25 mW only!
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Noise measurements performed in Milano 15 days
ago, on hybrid ready to be delivered to Cologne
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Choice of FET and preamps (contd)
3. Use JFET based monolithic preamps mod IPA4
developped by Manfredi, Speziali, Re in a
INFN-MURST project, now commercialized by
InterFET co. This can be used cold! (But
noise at LN never measured) ? ongoing Extremely
low noise obtained with buried layer technique
and very high quality silicon. ref. Nucl Phys
B(Proc. Suppl.) 44(1995)613-616 NIMA 380 (1996)
308-311
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Room temperature noise figure of J-FET monolithic
integrated preamps.
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Very good new it works in LN (tested here at
LNGS by myself) Noise measurements at LN ongoing
here at LNGS and then we will perform a
comparative study in Milano of the hybrid
MARS-AGATA preamp versus the JFET monolithic.
This solution will allow to have a voltage signal
in the 100 mV - 5 V range flowing in the cables
from the crystal to the outside of the LN2 bath!
Work is going on and this solution is very
promising.
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4. develop an ad hoc preamps integrated on Si. We
will have an integration test-run at Europractice
(Belgium) within the first semester of 2005 to
make the porting of MARS/AGATA preamp on Si.
(for phase II OK, but not sure for phase I)
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Conclusions

• Work is ongoing to look for the preamps suitable
  to work in our experimental conditions and a
  couple of solution are pursued.
• Open issue
• choice of mounting, cables, gamma ray
  -measurements of feedback components, and of IPA4
  preamplifiers in the die configuration, long term
  stability measurements, etc.