Tests of AGATA preamplifiers and hints to improve their performanceTests of AGATA preamplifiers and hints to improve their performance

A. Pullia on behalf of preamplifier team

AGATA Digital Processing workshopAGATA Digital Processing workshop –– Milano,Milano, Italy,Italy, 22 22 -- 2323 SeptemberSeptember 20052005

Outline

• Tests of segment preamps at IKP

• Tests of built-in fast-reset device

• Tests of a digital deoscillator filter

• Tests of a digital baseline controller

• Conclusions

Outline

• Tests of segment preamps at IKP

• Tests of built-in fast-reset device

• Tests of a digital deoscillator filter

• Tests of a digital baseline controller

• Conclusions

AGATA Detector CSP Set ( 12 Segments + 1 Core)

new solid GND concept for the mother board of 12+1 CSPs / Agata_Detector

GND_Layer

Top_Layer

MDR26 connectors

Segment preamplifiers

Segment preamplifiersCore

preamplifier

Tests made with one segmented detector housed in triple cryostat

• 14 – 18 March 2005: GANIL preampssuccesful after damping of a 75 MHz oscillation by increasing the compensation capacitance. Detailed report available upon request.

• 11 – 15 April 2005: MILANO preampssuccesful after damping of a 120 MHz oscillation by reducing bias current of FET and increasing the compensation capacitance. Detailed report available upon request.

FWHM of 122keV-line

0,00

0,20

0,40

0,60

0,80

1,00

1,20

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39

Segment index

FWHM

[keV

] Reihe1

Reihe2

FWHM of 59.5keV-line

0,00

0,20

0,40

0,60

0,80

1,00

1,20

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39

segment index

FWHM

[keV

]

Reihe1

Reihe2

GANIL

Milano

GANIL

Milano

Mean FWHM is 1 keV with GANIL and Milano preamplifiers

Mean FWHM is 0.94 keV with GANIL and Milano

preamplifiers

Comparison of Milano and Ganil preamplifiersMeasurements made by D. Weisshaar

(April 2005)

FWHM of Corewith segments equipped with preamplifiers from

Ganil Milano 122keV: 1.15keV 1.15keV1.3MeV: 2.14keV 2.15keV

Some segment resolutions:Ganil Milano

C2 122keV 0.91keV 0.92keV1.3MeV 1.85keV 1.83keV

C3 122keV 0.90keV 0.90keV1.3MeV 1.81keV 1.81keV

D5 122keV 1.02keV 1.04keV1.3MeV 1.99keV 1.97keV

D6 122keV 1.07keV 1.12keV1.3MeV 1.93keV 1.92keV

Absolute best result

Energy resolution of 1.71/1.77 keV fwhm on 60Co lines (12 April 2005) isone of the best ever obtained withGe detectors !

Outline

• Tests of segment preamps at IKP

• Tests of built-in fast-reset device

• Tests of a digital deoscillator filter

• Tests of a digital baseline controller

• Conclusions

Random arrival of 16.65 MeV events

provided by a poissonian pulser BNC mod. DB-2

The random distribution of negative tails yields a random distribution of reset times, each of

which is smaller than that obtained with no tail

Tests made with MILANO preamplifiers

Negative tails

Inhsignals

Reset time

An accidental AC-coupling in the pulser module causes the output signal to have a zero DC component and so

to assume also negative values

Measurements of the event energy from the reset time

( ) OS EVVkTbTbE +−−+= 2112

21EESS = = photonphoton energyenergy (or (or equivalentequivalent))

T = reset timeT = reset time

bb11, b, b22, k, k11, E, E00 = fitting parameters= fitting parameters

VV11, V, V22 = pre= pre-- and postand post--pulse baselines correction of the tail of the previous events pulse baselines

Francesca Zocca, ”Francesca Zocca, ”A new A new lowlow--noisenoise preamplifierpreamplifier forfor γγ--rayray sensorssensors with smart with smart devicedevice forfor largelarge signal managementsignal management”, ”, Laurea Laurea DegreeDegree ThesisThesis, University of Milano, , University of Milano, OctoberOctober 2004 (in 2004 (in ItalianItalian),), http://http://topserver.mi.infn.ittopserver.mi.infn.it//miesmies//labelet_iiilabelet_iii//download_filedownload_file/capitolo6.doc/capitolo6.doc

Energy resolution in auto-reset mode

Event count rate

Energy resolution @ 16.65 MeV

in HPGe (fwhm)

140 Hz 0.26 %

470 Hz 0.29 %

1.14 kHz 0.30 %

1.44 kHz 0.30 %

2.65 kHz 0.34 %

4.87 kHz 0.44 %

Outline

• Tests of segment preamps at IKP

• Tests of built-in fast-reset device

• Tests of a digital deoscillator filter

• Tests of a digital baseline controller

• Conclusions

A simple approach exists to improve the preamplifier response

PREAMP ADCNUMERICAL

“DEOSCILLATOR” FILTER (FIR)

Insufficient compensation capacitance

The filter goal is to eliminate the ringingswhile preserving the high-frequency content

of the preamplifier output signal

Weights of the numerical “deoscillator”

filter

as obtained from the DECONVOLUTION between the oscillating signal of the preamplifier and the wanted

ideal response

Example: deoscillator filter removes ringings from a disturbed pulse shape

Outline

• Tests of segment preamps at IKP

• Tests of built-in fast-reset device

• Tests of a digital deoscillator filter

• Tests of a digital baseline controller

• Conclusions

Tests of a digital BL controller

in

out

out - in

in

out

ADC input

200 mV /

1 µs /

0.5 V /

0.5 ms /

in outADC input

12 bit 100 MHz

14 bit 100 MHz

In XILINX Spartan 3

A. Pullia, S. Riboldi, G.M. Franchi, F. ZoccaActive control of the baseline of digitized preamplifiers with sliding-scale correction2004 IEEE Nucl. Sci. Symp. Conference Record, Rome, ITALY, 16-22 Oct. 2004

The baseline can now walk across the preamplifier full range without causing ADC saturation !

Analysis of observed signals

Noise of output signal is 0.85 mV (1.75 LSB) r.m.s.

For slow input signals an amplitude-folding effect occurs, which yields an extended input dynamic range…

...which in turn yields an extended range on the individual signals

The extended range (bit gain) increases as the input signal gets

slower

Conclusion

• Full sets of Ganil and Milano segment preamplifiers have been installed in triple cryostat and operated succesfully in conjunction with one segmented detector

• All preamplifiers are equipped with over-threshold fast-reset device. Energy measurements are still possible in reset mode (up to 50 MeV) and energy resolution is good (0.26 to 0.44% @ 17 MeV)

• Techniques to improve integrity and reduce randomwalks of preamplifier signals are available