Status of AGATA preamplifiers

1
Status of AGATA preamplifiers

• A. Pullia
• on behalf of preamplifier team

AGATA week GSI, Germany, 22 October 2004
2
Annual activity of preamplifier team (2004)

• Team meetings
• January 30th Milano
• April 29th Koeln
• in the meetings the circuit structure all
  features have been discussed and decided. The
  circuit architecture of all realized
  preamplifiers is the same.
• Since then the individual groups (GANIL, Milano,
  and Koeln) have developed their prototype
  circuits
• GANIL triple segment preamplifiers on FR4
  substrate
• Milano triple segment preamplifiers on alumina
  substrate
• Koeln core preamplifier built-in pulser on FR4
  substrate

Details available in technical document AGATA
Hybrid Preamplifiers with pulser v. 1.4
3
Developed preamplifiers


Triple segment preamp on FR4 substrate Mod. PACAGA5A GANILB. Cahan et al. Triple segment preamp on alumina substrate Mod. PB-B1 MI MilanoA. Pullia et al. Core preamplifier built-in pulser on FR4 substrate Mod. AGATA core-pulser KoelnG. Pascovici et al.
AGATA_core-pulser (Koeln)
PACAGA5A (GANIL)
PB-B1- MI (Milano)
Top view
Top view
Top view
PZ trimmers
PZ trimmer
Bottom view
Bottom view
Bottom view
PZ trimmers
A. Pullia, G. Pascovici, B. Cahan, D. Weisshaar,
C. Boiano, R. Bassini, M. Petcu, F. Zocca, The
AGATA charge-sensitive preamplifiers with
built-in pulser and active-reset device, Proc.
Nucl. Sci. Symp., October 16-22, 2004, Rome, Italy
4

Development Status Development Status Development Status
Mod. PACAGA5A (GANIL) Mod. PB-B1 MI (Milano) Mod. AGATA_Core-Pulser (Koeln)
- The triple segment preamplifier first prototype (November 2003) 14 triple segment preamplifiers have been realized and tested (April 2004) - 36 segment preamplifiers have been tested with the first AGATA detector (October 2004). The resolutions at low energies (60 keV) are in average 1.1 keV fwhm, and 2.05 keV fwhm on the 60Co lines. - 16 triple segment preamplifiers have been realized and tested (January 2005). These new preamplifiers have been optimized for the stability and the power consumption (306 mW by each preamplifier) - 36 segment preamplifiers will be tested with the second AGATA detector (March 2005) 12 triple segment preamplifiers have been realized and tested (October 2004) 1 triple segment preamplifier has been tested with the first AGATA detector (October 2004). The resolution is 1.1 keV fwhm at 122 keV and 2 keV fwhm on the 60Co lines. However the preamp tends to fall into an oscillatory state, caused by an instability of the LDO voltage regulator used on the 6V power supply. 12 triple segment preamplifiers have been stabilized, fully characterized and optimized (Feb 2005). The power consumption of each preamplifier is 283 mW 36 segment preamplifiers will be tested with the second AGATA detector (March 2005) First prototype of the core preamplifier with built-in pulser (March 2004) Tests of core preamplifier with pulser (April 2004) Core preamplifier is briefly tested with the first AGATA detector (October 2004). The resolution is 1.2 keV fwhm at low energies and 2.26 keV fwhm on the 60Co lines. When used as segment preamplifier the resolution is 1.9 keV fwhm _at_ 1.33 MeV. The principle of using the detector bulk capacitance as test capacitance for the segments has been proved. Ratio of core-to-segment pulser signals 20. Pulser stability is 0.15 keV / 8h. Pulser rise time is 65 ns, fall time 500 µs. Pulser noise is 1.25 keV fwhm.
5
First tests with AGATA detector segment preamps
Cryostat filled with GANIL PACAGA5A segment
preamplifiers (October 2004)
All measurements on single-ended signals Average
resolution _at_ 1.33 MeV 2 keV fwhm Resolution _at_
60 keV 1.1 keV fwhm
6
First tests with AGATA detector segment preamps
With one MILANO PB-B1 segment preamplifier
(October 2004)
Resolution was quite as good (either at low or
high energies), but preamp happened to suddenly
go into an oscillation state
7
First tests with AGATA detector core preamp
AGATA_Core-Pulser - KOELN
Resolution _at_ 1.33 MeV 2.26 keV fwhm Resolution
_at_ 122 keV 1.2 keV fwhm Resolution improves to
1.90 keV _at_ 1.33 MeV fwhm when using it as segment
preamp
8
Features of AGATA preamplifiers
9
One-wire test pulse for all segments
From an idea available in literature
10
A challenging requirement low noise _at_ low power
New FET, mod. BF862 from Philips (proposed by
Milano)
Test performed at Milano using a capacitance to
simulate the detector
Test performed at Koeln with HPGe detector
(courtesy of D. Weisshaar)
FET BF862 performance is adequate, consuming only
1/3 of the power budget of typical FETs for
gamma-ray spectroscopy !
11
A new circuitry automatically resets preamp on
large signals to reduce the dead time
Signal seen at the preamp output
20 MeV event fast reset
1.17 MeV event
Action of fast reset Normal operation of
preamplifier is swiftly recovered (15 us / 100
MeV in AGATA preamplifiers) Requirement posed by
Take R. Saito and J. Gerl - Jan. 2003
12
How does it work
A digital input (not shown) permits to control
fast reset in two ways

1. let it work autonomously on large pulses,
2. activate it upon request from the ADC module

A. Pullia, C. Boiano, R. Bassini, G. Pascovici,
Active Reset of Digitized Preamplifiers for
Ionizing-Radiation Sensors, IEEE Trans. Nucl.
Sci., vol. 51, no. 3, pp. 831-834, June 2004
13
Measurement of large pulses from reset time
ES equivalent energy release T reset time b1,
b2, k1, E0 fitting parameters V1, V2 pre- and
post-pulse baselines

Rate of 60Co events 32 kHz
60Co Event Rate Resolution in Ge FWHM Resolution in Ge FWHM
1 kHz 25.54 keV 0.26
2 kHz 31.86 keV 0.32
4 kHz 29.51 keV 0.30
8 kHz 36.53 keV 0.37
16 kHz 57.26 keV 0.57
32 kHz 56.09 keV 0.56
Measurement performed at Padova with HPGe
detector (courtesy of D. Bazzacco and R.
Isocrate) F. Zocca, A new low-noise
preamplifier for g-ray sensors with smart device
for large signal management, Laurea Degree
Thesis, University of Milano, October 2004 (in
Italian). See http//topserver.mi.infn.it/mies/lab
elet_iii/download_file/capitolo6.doc
14
Extending the energy range by reconstruction of
the large signals from reset time
Prototype preamplifier with fast reset, connected
to detector anodeMeasurement performed at Padova
with HPGe detector - July 2004 (courtesy of D.
Bazzacco and R. Isocrate)
122 keV
344 keV
pulser
1408 keV
2.02 keV fwhm
Extended range
Energy range in normal mode 2MeV
15
Differential output helps reduce RF pickup and
ground bounces
differential
100 MHz pickup
Single ended
A1,A2 dual opamp mod. LM6172
Single-ended to differential stage
Rejection of RF pickup
16
Testing the AGATA 5 m lvds cable
5 m lvds AGATA cable (camera link std)
FETs,RFCF Cdet
Triple preamp
20 cm
Test performed using Milano PB-B1 preamplifier
Feb 2005
17
Rise time role of the differential buffer
5m cable terminated 100 W diff - Cdet23 pF -
FETBF862 is 20 cm far away from preamplifier
differential
differential
Single ended
Single ended
With AD8012 rise time 7.4 ns ! !
With LM6172 rise time 13.2 ns
18
Conclusion

• The first AGATA detector-preamplifier assembly
  was tested succesfully in October 2004
• Optimizations of the preamplifiers and the
  motherboard are being made to get stable, quiet
  and fast preamplifier signals
• New tests with the triple detector system, as
  filled with all types of available preamplifiers,
  will be made in March/April 2005