1. GERDA Phase I: Status GERDA FE Phase II meeting
Milano Bicocca 16 april 2010
Carla Cattadori, Alberto Pullia, Stefano Riboldi, Alessio D’Andragora, Francesca Zocca,
M. Barnabe-Heider, K. Gusev, D. Budjas
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

2. 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
CMOS ASIC PZ0
CMOS ASIC PZ1
Commercial CMOS OPAMP
Radiopurity issues
Conclusion
Outlook and next steps
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

3. GERDA Phase I FE electronic:
Speca as in year 2005 (1st meeting at Milano Celoria Physic Department, and subsequent refinements)
Charge Sensitive Amplifier
Sensitivity: ~ 150 mV / MeV
Range Dynamic: > 5-6 MeV (now 8-9 MeV)
Criogenic T
Large Open loop gain (~ 105) to guarantee stability (but cryogenics helps)
Noise: <1 keV in Ge (< 150 e- 1 MeV, t = ms, at T= 77°K
Rise time: < 30 ns to allow PSD of ionization events in Ge detectors
Compact / integrated as possible
Drive 50 W 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 mBq 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.)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

4. GERDA Phase I detectors & detector assembly
8 enrGe + 6 natGe p-type coaxial Ge detector
mass:1-3 kg
Cdet = 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

5. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Phase I detectors
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)
Drawing of phase I detector array:
All Phase-I detectors reprocessed and mounted in a low-mass holder.
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

6. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
The chosen strategy
First rule to reduce significantly background is to minimize mass of each component close to crystals  integrated front end.
As a trade-off of noise, radioactivity and other specs a semi-integrated architecture was chosen and pursued: external JFET 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

7. 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

8. CSA based on PZ0 (Pullia Zocca 0)
ASIC CMOS circuit designed by A. Pullia in 2005
Produced by AMS foundry in 0.8 mm 5V CZX CMOS technology
Single ended circuit
External feedback components
Tested circuit structure: external BF862 JFET + 0.8m 5V CMOS single-ended preamplifier
+3V
-3V
VCC
Closed loop gain A = gm x RD x G
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

9. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Test chip
TEST struct
PREAMP 1
PREAMP 2
MOSFETs
PREAMP 1
pMOS + ext RF + ext bias
Vmax = 550mV (50 Ohm)
resistors
PREAMP 2
pMOS + ext RF + int bias
Vmax = 550mV (50 Ohm)
MOSFETs
PREAMP 3
TEST struct
PREAMP 4
MOSFETs
PREAMP 3
pMOS + reset pMOS + shaper
MOSFETs
PREAMP 4
pMOS + ext RF + ext bias
Vmax = 2V (1 kOhm)
HIGH VOLTAGE comp’s
3.3 mm
CSP+OS simple CC=1.4pF
CSP+OS simple CC=0.2pF
CSP+OS simple CC=0.6pF
CSP+OS simple CC=0pF
CSP+OS simple CC=1pF
CSP + OS simple
CSP with new rail-to-rail output stage. Various comp cap’s
CSP+OS cplx CC=0pF
CSP+OS cplx CC=2pF
CSP+OS cplx CC=0.4pF
CSP+OS cplx CC=1.4pF
CSP+OS cplx CC=1pF
CSP + OS cplx
CSP with new rail-to-rail output stage. Various comp cap’s
OPAMP
OPAMP
OPAMP
OPAMP
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
3.3 mm

10. Working temperature
from -196°C to 55°C
(from 77 K to 328 K)
Negative output voltage swing on W 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 150W termination
Input dynamic range
~ 8.6 MeV
Rise time
~ 16 ns with ~ 10m terminated coaxial cable
Fall time
~ 250 ms ( RF = 1.2 GW )
Open-loop gain
~ 3.5 *105
Loop gain
~ 600
Resolution at T= 77 K (  = 6s )
MeV ( 60Co )
keV pulser line
Power required at T=77K
23.4 mW
(VFET = +4V ID = 3mA
VCC= +3.6V VEE = -2.8V)
Comparison between noise measured at room temperature (T=300°K) and in LN (T=77°K)
Acquired output signal driving a 50  coaxial cable of ~ 10 m : rise time of ~ 15 ns
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Working temperature
(from 77 K to 328 K)
from -196°C to 55°C
Negative output voltage swing on W impedance
~ 2.5 V (against a negative power supply of -2.7V)
Energy sensitivity
(CF = 0.2 pF)
~ 217 mV/MeV after 150W termination
~ 290 mV/MeV at preamp output
Input dynamic range
~ 8.6 MeV
Rise time
~ 16 ns with ~ 10m terminated coaxial cable
Fall time
~ 250 ms ( RF = 1.2 GW )
Open-loop gain
~ 3.5 *105
Loop gain
~ 600
Resolution at T= 77 K (  = 6s )
keV pulser line
MeV ( 60Co )
Power required at T=77K
(VFET = +4V ID = 3mA
23.4 mW
VCC= +3.6V VEE = -2.8V)

11. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Spectroscopic performances of prototype PZ0 with prototype Cryotemp T
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: Co
Best resolution obtained with (encapsulated) prototype crystal and cold PZ0 CSA
1ch CSA based on PZ0 ASIC (in ceramic carrier)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

12. 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

13. Experimental Setup 1 Test Input Cable
7 LVPS Cables (connected to the Power Supply Unit, through a “filters box”)
3 Output Cables (50 W terminated)
JFET Power Supply = 3.7 v
LV Power Supply = ±3.1 V; V
Power Consumption ~ 40 mW 3 ch
Dynamic Range ~ 8 MeV on high imp.
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)
Ch1 Ch2 Ch3
GND
GND
HPGe LN
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

14. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
CSA, Cu EM shield
~ 40 cm from 1st detector (+15 cm 2nd, +15 cm 3rd)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

15. RIN FADC removed Working Temperature 89 K Rise Time SM 50 + RG 174
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
Fall Time
250 ms (RF = 1 GW, CF = 0.3 pF)
Resolution
1.2 1 MeV pulser line
Ch-3
(DETECTOR)
MeV (60Co)
2.3 1 MeV pulser line
Power Required (T=77K)
~ 40 mW (VFET = +3.7 V, ID = 3 mA; VCC= +3.1 V; VEE = -2 V)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

16. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
PZ0 solved issues
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 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 W for 10 m), and to PSRR of PZ0 circuit
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

17. PZ1 chip (PZ0 modified to drive 50W terminated cables at 77K)
Chip area ~5 mm2
Chip includes 3 versions of TRIPLE PZ1 and one TRIPLE PZ0 (as spare)
PZ1 prototype mounting (single channel, ceramic carrier, only for testing purpose)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
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.

18. PZ1 chip (PZ0 modified to drive 50W terminated cables at 77K)
Two PS needed for 3 ch array: 1
OK when removed
VCC, -VEE 2
VC, -VE
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
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

19. PZ1 chip (PZ0 modified to drive 50W terminated cables at 77K)
First 300K and 77K of a single PZ1 very promising
No need of RC stabilizing network
Able to drive 50 W cable at 300K and 77K
Noise ok (same as PZ0: ~1.1 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
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
*tests performed in March 2010

20. 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.
PCB material: Cuflon© (PTFE embedded in two Cu foils) for PCBs
Selected a company: PCB production process & electrogalvanic Ni/Au deposition (for ASIC bonding) qualified for radiopourity.
The ASIC is bonded directly on board and sealed by a radiopure Cu cup, providing both the EM shield and the protection of the bonding wires.
SMD Resistors and capacitors are of 0402 and 0603 size to reduce mass, and protection diodes have been added at the FET input (Philips BF862).
All the components (FET, C, R, Rf (high values), solder paste) screened and selected for radiopurity
Qualified the contacting pins.
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

21. 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 mBq/PCB
U < 3 mBq/PCB
8 x 3-ch circuit in production
U-238/Ra Th-232/Ra Th-232/Th K-40
[mBq/PCB] [mBq/PCB] [mBq/PCB] [mBq/PCB]
0.54 +/ / / /-0.8
Pb-210:
< 5.3 Bq/PCB
Pins for PCB to Habia Cable connection
U-238/Ra Th-232/Ra Th-232/Th K-40
[mBq/PCB] [mBq/PCB] [mBq/PCB] [mBq/PCB]
< < 0, ,060+/ /- 0.2
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

22. CSA Based on Commercial CMOS OPAMP Architecture: external JFET + CMOS OPAMP and Rf,Cf
Tested with encapsulated SUB detector along 3 weeks
In test in these days at LNGS GDL with naked BEGe detector
PCB manufactured in FR4 material (2 layers)
Same size as PZ0 for compatibility purpose (65 mm x 40 mm)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

23. Experimental Setup Test Input Cable
3 LVPS Cables (directly to the Power Supply Unit, no need for the “filters box” in between)
3 Output Cables (50 Ohm terminated)
JFET Power Supply = V
LV Power Supply = ± 2.5 V
Power Consumption < 140 mW
Dynamic Range > 15 MeV
7 cables used
All cables 10 meters long
Ch1 and Ch3 : 33 pF cap.
Ch2 : SUB HPGe detector
Acquired data with both MCA and Flash ADCs (Caen)
Ch1 Ch2 Ch3
GND
GND
HPGe LN
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

24. Summary of CC2 measured characteristics
Best energy LNT : kev FWHM (0 pF Cdet) kev FWHM (33 pF Cdet)
(with 1 Mev pulser signal, 12 us shaping time)
Best energy LNT : 1.96 kev FWHM for 22 Na (12 us shaping time, 5k counts acquisition)
15 MeV guaranteed energy dynamic range
50 W drive capability with 10 m long cables
Power consumption < 140 mW (down to 100 mW for 10 Mev dynamic range)
Rise time : less then 55 ns with 50 Ohm terminated, long cables and energy up to 15 Mev
Cross-talk : < 0.1%
Power Supply Rejection Ratio : should allow HPGe spectroscopy within the Gerda setup
Expected reduction on CSA radio-activity < 150 mBq for both 232Th & 238U
Operated (in Milano) with 7 cables (3 for power supplies, 3 for outputs, 1 for input test)
Small size, no bonding wires, no PCB copper shield, no LVPS “filters box”, simple and robust
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

25. CC2- PCB Redesigned Reduced PCB Size (38 mm x 50 mm)
Pin Connector
Reduced PCB Size (38 mm x 50 mm)
Mechanical Stability (4 distributed holes: M25) (no need for Teflon Layer in Copper Shield)
Reduced Connector Pin Number (11 vs 14)
Eliminated Feedback and Test Capacitors (implemented with PCB copper traces, after Alessio’s work)
Various BOM configurations to trade-off between:
Radiopurity and Channel Crosstalk
CSA BOM (as tested in Milano)
3 JFET
3 Operational Amplifiers
11 Tantalum Capacitors (LV decoupling)
22 Resistors
3 Discharge Protection Devices (JFET)
Less than 0.1% measured crosstalk
Redesigned CC2 PCB
First CC2 PCB (same size as PZ0)
Minimum CSA BOM
3 JFET
3 Operational Amplifiers
3 Tantalum Capacitors (LV decoupling)
13 Resistors
3 Discharge Protection Devices (JFET)
Crosstalk ? ? ?
Detector Input Contacts
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

26. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
CC2-PCB Redesigned
PCB capacitors
Component layer Bottom layer
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

27. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
Conclusions
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 mBq for a 3 ch circuit) the CSA can be approached 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

28. 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

29. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
EXTRA slides
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

30. 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 mBq / PCB (for both Th & Ra) pins included
as a result of:
- 3 BF862 JFET (228Th= 15 ± 4 mBq / PCB, 226Ra= 14 ± 4 mBq / PCB)
- 3 OpAmp (228Th < 11 mBq / PCB, 226Ra= 6.3 ± 1.2 mBq / PCB)
- 0 NP0 Ceramic Capacitor (for test and feed-back) replaced by PCB Capacitors
- 11 max. (down to 3 min.) Tantalum Capacitors for LVPS decoupling (228Th= 88 ± 22 mBq / PCB , 226Ra= <33 mBq / PCB, 40K=770 ± 330 mBq / PCB)
- Cuflon for PCB (228Th <12 mBq / PCB , 226Ra <3 mBq / PCB, 40K =200 ± 62 mBq / PCB)
- 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 mBq / PCB , 226Ra= < 53 mBq / PCB, 40K= 280 ± 140 mBq / PCB) but research of better pins in progress
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

31. CSA Intrinsic Energy Resolution
Room Temperature
LN Temperature
Circle : 6 V JFET Power Supply Triangle : 12 V JFET Power Supply
Cdet = 33 pF
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

32. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010
CSA Rise Time
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

33. Spectroscopy with CC2 CSA
Analog Amplifier (10 us Shaping Time)
MCA
Reproducible Energy Resolution (σ = 0.03 kev over 20 short measurements)
Irradiation with 22Na source.
FWHM = 2.15 kev
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

34. Spectroscopy with CC2 CSA
Analog Amplifier (10 us Shaping Time)
MCA
Background long acquisition (over the night)
FWHM = 2.75 kev (232 Th)
FWHM = 2.28 kev (40 K)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

35. Digital Spectroscopy with CC2 CSA
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
FWHM = 2.27 keV
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

36. Crosstalk between Channels
Between Ch2 (detector) and Ch1
Same procedure as for PZ0: Ch1 and Ch2 through analog shaper (10us) Gain amplification for Ch2 = 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

37. 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)
C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010