Diapositiva 1

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Status of integrated preamplifiers for GERDA
F. Zocca, A. Pullia, S.Riboldi, C. Cattadori
GERDA meeting MPI Heidelberg, Feb 20-22, 2006
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Proposed circuit structure (from J. Gal)
J. Gal et al. Realization of charge sensitive
preamplifiers using current feedback operational
amplifier, Nucl. Instrum. And Meth., Vol. A366,
pp. 145-147, 1995
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Test chip
PREAMP 1
MOSFETs
PREAMP 1 pMOS ext RF ext bias Vmax 550mV
(50 Ohm)
TEST struct
PREAMP 2
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 comps
3.3 mm
CSPOS simple CC1.4pF
CSPOS simple CC0.2pF
CSPOS simple CC0.6pF
CSPOS simple CC1pF
CSPOS simple CC0pF
CSP OS simple CSP with new rail-to-rail output
stage. Various comp caps
CSPOS cplx CC1pF
CSPOS cplx CC0pF
CSPOS cplx CC2pF
CSPOS cplx CC0.4pF
CSPOS cplx CC1.4pF
CSP OS cplx CSP with new rail-to-rail output
stage. Various comp caps
OPAMP
OPAMP
OPAMP
OPAMP
3.3 mm
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Test chip with wire bondings in 68LCC package
Setup for cryogenic test
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Output stage dynamic range
The output stage must be able to drive a
coax/twisted pair cable (or a 100 to 200 ? load)
and must provide the largest negative voltage
swing (hole signals)
At T300K, with a negative power supply VEE -
3V, the circuit can drive a 10m coaxial cable of
50 ? still providing a negative voltage swing of
2.5V
At T77K the negative swing reached is of 2.4V
CF 0.15 pF, Ctest 1 pF Cdet 15 pF
Energy sensitivity (in Ge) at the preamp output
370 mV/MeV (185 mV/MeV if 50 ? terminated)
Input dynamic range 6.5 MeV
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Rise time
at T 300 K driving a 50? coaxial cable of
different lengths
13 ns with 1m cable
15 ns with 10m cable
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Rise time
at T 77 K driving a 2m coaxial cable (50?)
7.8 ns with no BW limit
A fast rise time of 8 ns to 13 ns has been
obtained but a little overshoot has still to be
eliminated by a low-pass filter or by reducing
the preamp bandwidth a little bit
13 ns with BW limit (equivalent to Anti-Aliasing
filter)
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Decay time constant
200 ?s both at room temperature and in liquid
nitrogen
T 300 K
CF 0.15 pF RF 1.2 G?
200?s
T 77 K
200?s
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Noise measurements
Cdet 15 pF
Shaping time T300K ENC (el. r.m.s.) T77 K ENC (el. r.m.s.)
0.5 ?s 178 325
1 ?s 148 252
2 ?s 126 191
3 ?s 118 166
6 ?s 110 128
10 ?s 111 112
At T 77 K the substantial increase of the white
series noise is mainly due to the decrease of the
JFET tranconductance
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Tested preamp specs
T 300 K T 77 K
Energy sensitivity (CF 0.15pF) 370 mV/MeV at preamp output 185 mV/MeV after 50 ? termination 370 mV/MeV at preamp output 185 mV/MeV after 50 ? termination
Negative output voltage swing 2.5 V 2.4 V
Input dynamic range 6.7 MeV 6.5 MeV
Rise time 13 ns with 1m coaxial cable 15 ns with 10m coaxial cable 13 ns with 2m coaxial cable (with little overshoot) 15 ns with 10m coaxial cable (with little overshoot)
Loop gain 500 gt 500
Minimum ENC (el. r.m.s.) with Cdet 15pF 110 el. at ? 6?s 112 el. at ? 10?s
Power required 177 mW (VFET 12V ID 14mA VCC 2.5V VEE -3V) 22 mW (VFET 4V ID 3mA VCC 3V VEE -3V)
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Future developments

• Optimization of tested preamplifier
• Tests with different values of Cdet and with
  values of CF ranging from 0.2 to 1 pF
• Tests of more preamplifiers (with different
  values of compensation capacitance)
• Design and test of a miniaturized setup
• Tests with different cable types and lengths

Activity schedule

• March-June 2006 tests/optimization of existing
  chip. Design/realization of miniaturized PCB.
  Design of improved new chip.
• June-September 2006 realization of new chip /
  tests of old chip (continued)
• September-December 2006 tests of new chip