C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 GERDA Phase I: Status Carla Cattadori, Alberto Pullia, Stefano Riboldi, Alessio D’Andragora, Francesca Zocca, M. Barnabe-Heider, K. Gusev, D. Budjas GERDA FE Phase II meeting Milano Bicocca 16 april 2010
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C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 GERDA Phase I: Status Carla Cattadori, Alberto Pullia, Stefano Riboldi, Alessio D’Andragora,
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C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
GERDA Phase I: Status
Carla Cattadori, Alberto Pullia, Stefano Riboldi, Alessio D’Andragora, Francesca Zocca,
M. Barnabe-Heider, K. Gusev, D. Budjas
GERDA FE Phase II meeting
Milano Bicocca 16 april 2010
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Outline
• GERDA Phase I specs• GERDA Phase I Detectors & Detector Assembly• The developed CSA based on semi-integrated
architecture (further integration see S. Riboldi talk)• Exp. Results for CSA based on
• Radiopurity issues• Conclusion• Outlook and next steps
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
• Charge Sensitive Amplifier– Sensitivity: ~ 150 mV / MeV– Range Dynamic: > 5-6 MeV (now 8-9 MeV) – Working @ Criogenic T– Large Open loop gain (~ 105) to guarantee stability (but cryogenics helps)– Noise: <1 keV in Ge (< 150 e- r.m.s) @ 1 MeV, = 8 -10 s, at T= 77°K– Rise time: < 30 ns to allow PSD of ionization events in Ge detectors– Compact / integrated as possible– Drive 50 load through 6 m (later 10 m and then 20 m) long cables – Power dissipation: < 50 mW /ch (as low as possible)– Output stage: Better differential (later single ended)
• PCB requirements– 3ch modularity to serve 1 string– Radiopurity: as low as possible later set limit < 500 Bq 232Th and 2.5 mBq 238U
for distance– Interconnection with input detector and output/LV cables by pins– Cryogenic (stable vs deformations for thermal cycles etc.)
GERDA Phase I FE electronic:
Speca as in year 2005 (1st meeting at Milano Celoria Physic Department, and subsequent refinements)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
GERDA Phase I detectors & detector assembly
• 8 enrGe + 6 natGe p-type coaxial Ge detector
• mass:1-3 kg
• Cdet = 30-50 pF
• Deployed in strings
• Mounted in low-mass Cu holders
• Cable from Detector to CSA Input & HV : Cu unshielded strip insulated in Teflon pipe
• HV contact: on Li surface by pressure
• Readout contact: in borehole spring-loaded
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Phase I detectors
Drawing of phase I detector array:
•above:Non-enriched prototype detector assembly (p-type, 1.6 kg). Same performance as in a vacuum cryostat.
•IGEX and HDM crystals after dismounting from cryostat (prior to reprocessing at manufacturer)
•All Phase-I detectors reprocessed and mounted in a low-mass holder.
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
The chosen strategy
First rule to reduce significantly background is to minimize First rule to reduce significantly background is to minimize mass of each component close to crystals mass of each component close to crystals integrated integrated front end.front end.As a trade-off of noise, radioactivity and other specs a semi-integrated architecture was chosen and pursued: external JFET external JFET first stage followed by an ASIC second stage amplifier.first stage followed by an ASIC second stage amplifier.
• First stage FET: Philips BF862 as:
• Noise good
• Bandwidth good
• Can work at VGS =0
• FET can be replaced
@ cryo -T
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
BF862 characterization at room and cryo-T:gm drops ~ 2-3 at cryo-T
• Parallel white noise contribution substantially decreases at 77K as expected.
•The decreased temperature only partially compensates the effect of decreased transconductance
the overall series white noise is higher at 77 K than at room temperature.
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
•ASIC CMOS circuit designed by A. Pullia in 2005•Produced by AMS foundry in 0.8 m 5V CZX CMOS technology•Single ended circuit•External feedback components
Closed loop gain A = gm x RD x G
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
CSP + OS simpleCSP with new rail-to-rail output stage. Various comp cap’s
CSP + OS cplxCSP with new rail-to-rail output stage. Various comp cap’s
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Acquired output signal driving a 50 coaxial cable of ~ 10 m : rise time of ~ 15
ns
Comparison between noise measured at room
temperature (T=300°K) and in LN (T=77°K)
Working temperature
from -196°C to 55°C
(from 77 K to 328 K)
Negative output voltage swing on 150 impedance
~ 2.5 V (against a negative power supply of -2.7V)
Energy sensitivity
(CF = 0.2 pF)
~ 290 mV/MeV at preamp output
~ 217 mV/MeV after 150 termination
Input dynamic range
~ 8.6 MeV
Rise time~ 16 ns with ~ 10m
terminated coaxial cable
Fall time ~ 250 s ( RF = 1.2 G )
Open-loop gain ~ 3.5 *105
Loop gain ~ 600
Resolution at T= 77 K ( = 6s )
2.2 keV @ 1.332 MeV ( 60Co )
1.6 keV @ 932 keV pulser line
Power required at T=77K
23.4 mW
(VFET = +4V ID = 3mA
VCC= +3.6V VEE = -2.8V)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Spectroscopic performances of prototype PZ0 with prototype detectors @ Cryotemp T
Best resolution obtained with Best resolution obtained with (encapsulated) prototype crystal (encapsulated) prototype crystal and cold PZ0 CSAand cold PZ0 CSA
•With encapsulated SUB detector: R = 2.06 keV (best); 2.2 keV (typical) in LN (both CSA & Detector)
•With prototype naked detector in LAr in Gerda Underground Detector Lab: 2.6 keV @ 60Co
1ch CSA based on PZ0 ASIC (in ceramic carrier)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
The 3ch CSA based on PZ0
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Experimental Setup
HPGeLN
Ch1 Ch2 Ch3
3 Output Cables (50 terminated)
7 LVPS Cables (connected to the Power Supply Unit,
through a “filters box”)
1 Test Input Cable
• 11 cables used
• All cables 10/20 meters long
• Ch1 and Ch3 : 33 pF cap.
• Ch2 : Prototype HPGe detector
• Acquired data with both MCA and Flash ADCs (Caen)
JFET Power Supply = 3.7 v
LV Power Supply = ±3.1 V; - 2.0 V
Power Consumption ~ 40 mW 3 ch
Dynamic Range ~ 8 MeV on high imp.
GND GND
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
~ 40 cm from 1st detector (+15 cm 2nd, +15 cm 3rd)
CSA, Cu EM shield
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Working Temperature
89 K
Rise Time SM 50 + RG 174
SM 50
Ch-1 (CDET=33 pF, on board )
74 ns 40 ns
Ch-2 (CDET=33 pF, short leg
~1 cm)
72 ns 41 ns
Ch_3 (DETECTOR) 73 ns 41 ns
Fall Time 250 s (RF = 1 G, CF = 0.3 pF)
Resolution Ch-1(CDET=33 pF, on board )
1.2 keV @ 1 MeV pulser line
Ch-2 (CDET=33 pF, short leg
~1 cm)
1.2 keV @ 1 MeV pulser line
Ch-3 (DETECTOR)
2.7 keV @ 1.332 MeV (60Co)2.3 keV @ 1 MeV pulser
line
Power Required (T=77K)
~ 40 mW (VFET = +3.7 V, ID = 3 mA; VCC= +3.1 V; VEE = -2 V)
RIN FADC removed
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
PZ0 open issuesPZ0 open issues
• Large number of physical components needed on PCB• Some mortality of CSA due to not fully optimized technology of ASIC
gluing on PCB and Cu cup sealing
• Some x-talk among channels (~1 %) going through LV ASIC VCC & VEE PS in relation to the 10 m long resistive Habia SM50 cables (10 for 10 m), and to PSRR of PZ0 circuit
• Removed ceramic carrier and ASIC bonded on board
• Defined technology for chip gluing
• Sealing of Cu cup to protect the ASIC and its bonding wires
• En res and x-talk among ASIC on same chip OK for high impedence load
PZ0 solved issuesPZ0 solved issues
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
PZ1 chip (PZ0 modified to drive 50 terminated cables at 77K)
Chip includes 3 versions of TRIPLE PZ1 and one TRIPLE PZ0 (as spare)
PZ1 prototype mounting (single channel, ceramic carrier, only for testing purpose)
Response of PZ1 at room T, Cdet=33pF, 12.5m cables and 50 ohm terminations. Transition time = 88ns.
Response of PZ1 at 77K, Cdet=33pF, 12.5m cables and 50 ohm terminations. Transition time = 21ns.
Chip area ~5 mm2
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
PZ1 chip (PZ0 modified to drive 50 terminated cables at 77K)
OK when removed
• Power supply of output buffer (VC, -VE) separated from first stage (VCC, -VEE)
• Bulk connection separated from power supply of output buffer
• Output buffer optimized
VCC, -VEE
VC, -VE
Two PS needed for 3 ch array:
1
2
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
PZ1 chip (PZ0 modified to drive 50 terminated cables at 77K)
• First tests* @ 300K and 77K of a single PZ1 very
promising
• No need of RC stabilizing network
• Able to drive 50 cable at 300K and 77K
• Noise ok (same as PZ0: ~1.1 keV @ 6us shaping time with
Cdet=33pF)
• Dynamic range ok (8MeV with CF=0.2pF, still to be tested with
0.3pF)
• Triple channel / cross-talk still to be measured
• Still to be tested with Ge detector
*tests performed in March 2010
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
PCBs
A high degree of radiopurity is required for the CSA, long R&D on physical components & PCBs materials to make a radiopure CSA.
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Radioisotopes concentration in FE circuits
FE circuits: available at LNGS 3 x 3 ch PZ0 circuits (tested). Result of individual radioactivity measurement (reference value for B = 10-3 c/keV kg y):Th < 500 Bq/PCBU < 3 mBq/PCB
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
CC2-PCB Redesigned
Component layer Bottom layer
PCB capacitors
• Value of PCB copper traces capacitors (FR4 PCB) reproducible. (Cf=0.7 pF,Ct= 0.2pF) • a 3 ch CC2 CSA will be coupled to a naked BEGe detector in the next days•
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
ConclusionsConclusions
• 2 CSA available semi-integrated architecture: external JFET BF862 + CMOS ASIC PZ0-1 / Commercial OPAMP with adequate performances for GERDA specs (cryo-T).
• R&D to produce low radioactivity PCB and selected physical components to produce CSA with radionuclide concentrations << limit value for Phase I Background index (10-3 c/kg y keV); valid for both options.
• Implementation of printed Cu traces Capacitors instead of C physical components allow to produce a very low background CSA (expected <150 Bq for a 3 ch circuit) the CSA can be the CSA can be approached to detector stringapproached to detector string
possible to separate the Very FE (VFE= FET,Cf,Rf) to detectors to reduce Cu strip cable length i.e. reduce microphonism, pick-up etc.
• Very good solution for Phase II unsegmented detectors• Can be a solution for Phase II segmented detctors, but PCB needs
to be re-designed +………
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Outlook and next steps
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
EXTRA slides
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Radioactivity issues
• CC2 CSA expected to improve the radioactivity issues related to the FE electronics
• Radioactivity budget estimated on the base of already measured components is:
< 150 < 150 Bq / PCB (for both Th & Ra) pins includedBq / PCB (for both Th & Ra) pins included
- 0 NP0 Ceramic Capacitor (for test and feed-back) replaced by PCB Capacitors - 0 NP0 Ceramic Capacitor (for test and feed-back) replaced by PCB Capacitors
- 22 max. (down to 13 min.) resistors (3 for feed-back; 19 for polarization and LVPS decoupling) Only upper limit available, but from integral radioactivity of PZ0 are not dominant
- 7 (for signals) + 4 (for ground) PCB Pins for cable connection (228Th = 42 ±14 Bq / PCB , 226Ra= < 53 Bq / PCB, 40K= 280 ± 140 Bq / PCB) but research of better pins in progress
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
CSA Intrinsic Energy Resolution
2 4 6 8 10 120.5
1
1.5
2
2.5
3
3.5
Shaping Time [us]
Ene
rgy
Res
olut
ion
[kev
]
2 4 6 8 10 120.5
1
1.5
2
2.5
3
3.5
Shaping Time [us]
Ene
rgy
Res
olut
ion
[kev
]
Circle : 6 V JFET Power Supply Triangle : 12 V JFET Power Supply
Cdet = 33 pF
Room Temperature LN Temperature
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
CSA Rise Time
0 2 4 6 8 10 12 14 16 18 2035
40
45
50
55
60
Equivalent Input Energy [Mev]
10%
- 9
0% R
ise
Tim
e [n
s]
• Blue line: CSA + 10 m long output cables (50 Ohm terminated)
• Red line: CSA + 1 m long output cables (50 Ohm terminated)
• Pulser signal 5 ns rise time
• Rise time defined as time interval between 10% and 90% of CSA output signal
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Spectroscopy with CC2 CSA
Irradiation with 22Na source.
FWHM = 2.15 kev
• Analog Amplifier (10 us Shaping Time)
• MCA
• Reproducible Energy Resolution (σ = 0.03 kev over 20 short measurements)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Spectroscopy with CC2 CSA
• Analog Amplifier (10 us Shaping Time)
• MCA
• Background long acquisition (over the night)
FWHM = 2.28 kev (40 K)
FWHM = 2.75 kev (232 Th)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Digital Spectroscopy with CC2 CSA
FWHM = 2.27 keV
• CAEN FADC
• Off-line processing
• Digital FIR filtering with symmetric weighting function for baseline
• CSA output signals with 700 us decaying time
(from 10% to 90%)
• Good agreement with single-pole exponentially decaying pulse model
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Crosstalk between Channels
• Between Ch2 (detector) and Ch1
• Same procedure as for PZ0: Ch1 and Ch2 through analog shaper (10us) Gain amplification for Ch2 = 200 Gain amplification for Ch1 = 1000
• Experimental Result:
ΔCh1 / ΔCh2 = (15 mV / 5 V) / 5 = 0.06 %
• Very similar results for cross-talk measurement between Ch2 and Ch3
• Because cross-talk is low, it is also difficult to estimate because of the electronic noise
• As a conservative assumption :
Cross-talk < 0.1%
Inducing signal:Ch2
Inducted signal:Ch1
256 Scope Averages: Ch1
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
CSA Power Supply Rejection Ratio
• Important parameter to be evaluated (because of unavoidable LVPS variation across long and resistive cables)
• Low PSRR may cause: cross-talk between channels noise on output signals as a result of disturbances on LVPS
• In order to practically estimate the CSA PSRR: we measured the 22Na peak shift on the energy spectrum for ± 10% variation of each LVPS
Less than 1/4000 shift of the centroid of the peak (5k counts)