LNGS, 3-4 february 2005C.Cattadori GERDA meeting - TG3 report TG3: Diode Read-out and signal processing C. Cattadori on behalf of the working group

LNGS, 3-4 february 2005 C.Cattadori GERDA meeting - TG3 report

TG3: Diode Read-out

and signal processing

C. Cattadori on behalf of the working group


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) solutioncons: 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.


Choise of FET and preamps

• 2 possible FET InterFET IF1331 tested in HD and MIPhilips BF862 tested in MI

• 2 Hybrid preamp EURYSIS preamp PSC823CMARS preamp developed by INFN Milano


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 inputbut need to be slowed down to draw 4m cable from cold FET!(ref IEEE Trans. on Nucl Sc. 49-5(2002)2436)


Agata Analog electronics performances


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.


Analog electronics

25 mW only!


Noise measurements performed in Milano 15 days ago, on hybrid ready to be delivered to Cologne



Choice of FET and preamps (cont’d)

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)613-616NIMA 380 (1996) 308-311


Room temperature noise figure of J-FET monolithic

integrated preamps.



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.


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)


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….

Documents

LNGS, 3-4 february 2005C.Cattadori GERDA meeting - TG3 report TG3: Diode Read-out and signal processing C. Cattadori on behalf of the working group