Transcript Fast reset - Agenda INFN

INFN - Milano
University of Milano
Department of Physics
"Fast reset" ASIC Preamplifier
Cutting-edge circuit technology able to boost the
dynamic range of CMOS charge-sensitive
preamplifiers far beyond their saturation limit
Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Oct. 30, 2012
Outline

Context and goal of the research

Large volume HPGe detectors & required specs for charge preamps

The issue of saturation & dynamic range for integrated preamplifiers

Technique to handle saturated signals with low-noise CMOS preamps

Charge information recovery: extending the dynamic range beyond the
saturation limit of the preamplifier

Reset-mode high-resolution spectroscopy

Conclusions
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Context and goal
Context
 New generation of nuclear-physics experiments with highintensity ion beams.
 A technical advance for the new gamma-ray
spectrometers is required.
Goal of the research
 New paradigm: high-resolution spectroscopy is possible
even working with a deeply saturated CSP !
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Large volume HPGe detectors
High-resolution gamma-ray spectroscopy  investigation of
nuclear structure under very extreme conditions of stability
~ 9 cm
Main features:
• operated at cryogenic temperature (liquid nitrogen used as cooling medium @ 77 K)
• electrodes capacitance values: 20-100 pF
• energy of detected gamma-rays: from a few keV to a few tens of MeV
• excellent intrinsic energy resolution: 0.1% - 0.2% in the typical 1 MeV region
• segmentation of the outer electrode  position-sensitivity: ~ 1 mm 3D resolution
Gamma-ray tracking
emitting
radionuclide
Speaker: Stefano Capra
Gamma-ray Compton imaging
can take advantage of the
excellent energy/position
resolution of HPGe
"GASPARD-HYDE-TRACE Workshop 2012 "
Charge-preamplifier specifications
 low noise (gamma spectroscopy grade: 0.1-0.2 % @ 1MeV)
 excellent stability of the gain and of the shape of the preamplifier response
(loop gain ~ 103)
 wide bandwidth: rise time of ~ 20 ns (pulse shape analysis)
 low power consumption (especially for the devices operated in the cryostat)
 LARGE DYNAMIC RANGE:
- at least ~104 : from a few keV to 10-20 MeV
- up to ~30 MeV depending on the physics experiment (i.e. giant resonances)
- minimization of the dead time in a much larger energy range up to 100-200 MeV
extremely hostile background of
highly energetic charge particles
in next-generation nuclear
physics experiments with highintensity exotic beams
Speaker: Stefano Capra
HPGe segmented detectors of AGATA
(Advanced GAmma-ray Tracking Array)
"GASPARD-HYDE-TRACE Workshop 2012 "
The issue of a wide dynamic range
Old-style solution: hybrid DISCRETE preamplifiers
• high flexibility in the design
• use of high voltage power supply (ex: +/- 12 V)
Modern CMOS integrated solutions: a mandatory task
the high segmentation of the read-out electrodes yields a higher
and higher count of read-out channels
• small dimensions & low power dissipation
• radio-purity and full functionality at cryogenic temperature
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
The issue of a wide dynamic range
Old-style solution: hybrid DISCRETE preamplifiers
• high flexibility in the design
• use of high voltage power supply (ex: +/- 12 V)
Modern CMOS integrated solutions: a mandatory task
the high segmentation of the read-out electrodes yields a higher
and higher count of read-out channels
• small dimensions & low power dissipation
• radio-purity and full functionality at cryogenic temperature
Intrinsically low available voltage swing of scaled CMOS technologies
A decrease of the preamplifier sensitivity (energy-to-voltage gain) would
compromise the signal-to-noise ratio and the spectroscopic performances
Saturation of a CMOS preamplifier for HPGe detectors is
expected for input energies > 5-10 MeV
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Time-variant circuit structure*:
typical-amplitude signals
Charge-Sensitive Preamplifier (CSP) Mode
• For “normal” amplitude signals (up to a few MeV) the comparator keeps switch “S” in the
right position
• The circuit is a Low-Noise Charge-sensitive preamplifier
• Allows for high-resolution energy measurements
Normal CSP
External discrete components:
BF862 Si JFET, RF=1GW, CF=0.2pF
X
X
X X X X
CSP Mode
S
Comparator
Threshold of
Comparator
CSP Mode
*see also Radeka, Overload Recovery Circuit for Charge Amplifiers, IEEE Trans. Nucl. Sci., vol. 17, no. 1, p. 269, 1970
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Time-variant circuit structure*:
large signals
Fast-Reset Mode
• Minimizes the preamplifier dead time and prevents from the paralysis of the acquisition
system in the case of extremely high background counting rates
• Allows for charge information even in the saturation condition
• Allows for high-resolution energy measurements  extending the dynamic range of
photons/particles spectroscopy
External discrete components:
BF862 Si JFET, RF=1GW, CF=0.2pF
Q
+ ++ +
Fast Reset Mode
S
Reset Time
Threshold of
Comparator
Comparator
I const
*see also Radeka, Overload Recovery Circuit for Charge Amplifiers, IEEE Trans. Nucl. Sci., vol. 17, no. 1, p. 269, 1970
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
The charge preamplifier
Layout 0.35mm 5V mid-oxide CMOS
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
The Schmitt trigger comparator
Schmitt trigger configuration with a positive feedback loop
lower reset threshold set at 0V
by the ground voltage reference
external feedback
resistances to adjust the
upper reset threshold
(~ preamplifier saturation
voltage)
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
The current sink
the comparator output signal drives a transmission gate
so as to deviate the reset current to the input node of the
preamplifier
Reset current
NMOSFET
inserted into
the negative
feedback
loop of an
operational
amplifier
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Realized chip
Pre OUT
Pre IN
IRESET
-
Curr IN
Comp_INComp_IN+
+
+
VEE
INHIB
RSINK
Comp OUT
VEE
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Charge information recovery
Computer simulation
During saturation, the physical
information, i.e. the charge
released by the germanium
crystal, is not lost but temporarily
stored on the total capacitance at
the input node of the circuit
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Charge information recovery
The bounce of the input node
voltage (virtual ground) is actually
negligible because the capacitance
of HPGe detectors (20-50 pF) is
typically two order of magnitude
larger than the feedback
capacitance (0.2-0.5 pF)
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Charge information recovery
Preamp response to a detector
like test signal (200ns width)
Computer simulation
The bounce of the input node
voltage (virtual ground) is actually
negligible because the capacitance
of HPGe detectors (20-50 pF) is
typically two order of magnitude
larger than the feedback
capacitance (0.2-0.5 pF)
Speaker: Stefano Capra
VG voltage bounce
Computer simulation
"GASPARD-HYDE-TRACE Workshop 2012 "
Charge information recovery
Computer simulation
Computer simulation
The bounce of the input node
voltage (virtual ground) is actually
negligible because the capacitance
of HPGe detectors (20-50 pF) is
typically two order of magnitude
larger than the feedback
capacitance (0.2-0.5 pF)
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Remove Q and measure T
The larger Q the longer the time T needed for complete removal
• Constant current  rate of removed Charge over Time is constant from the
definition of electric current
•  Q and T are proportional
• Nonlinearity of preamplifier working condition must not influence Q vs T linearity
Precise charge measurements are possible in saturated conditions
• Parasitic DC paths
• Virtual ground bounces
So, the issue of the intrinsically low available voltage swing of scaled CMOS
technologies may be skipped through Time-over-Threshold measurements !!
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Active Fast Reset
Computer simulations
Preamplifier output signals of
different amplitudes (negative
holes signals)
Digital pulses delivered by the
comparator: a time-over-threshold
measurement provides the reset time
Proportional relation between input charge and reset time
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Reset time - Input charge Relation
Charge Energy in Ge
The percent error in the fitting mainly
comes from the numerical
approximation of the simulation
program and has to be considered as
a maximum upper limit
Speaker: Stefano Capra
1 pC
2 pC
3 pC
4 pC
5 pC
18.2 MeV
36.4 MeV
54.5 MeV
72.7 MeV
90.9 MeV
"GASPARD-HYDE-TRACE Workshop 2012 "
Reset time - Input charge Relation
Q = (IRESET + VSAT/RF) T + Q0
• (VSAT/RF)T = charge removed (~0.8%)
by the current flowing on RF while the
output signal is saturated
IRESET = constant reset current
VSAT = output saturation voltage
RF = feedback resistance
T = reset time
Q0 = offset term
• Q0= offset term due (i) to the
mismatch between the baseline
voltage and the 2nd reset threshold
(~0V), (ii) to the constant charge
removed by the current flowing in RF
out of the saturation condition
• second-order effects on the bias
conditions of the detector and JFET
p-n junctions, due to the virtual ground
bounce, are found to be negligible in
our computer simulations
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
“Reset-mode” spectroscopy
“Reset-mode” high-resolution spectroscopy has been demonstrated
HV
VCC
RF
IR
RHV
CAC
T
CF
S
C
-1
-1
GAA
CD
A
R0
R2
R1
Detector
Charge-sensitive amplifier
ADC
Hybrid charge
preamplifier with
second-stage
active fast reset
Gain +
Anti-Alias
Pole / Zero + Fast Reset
Reset-mode 241Am+Be spectrum
resolution on Ni line: 0.21% @ 9MeV
See: F.Zocca, A.Pullia, D.Bazzacco, G.Pascovici, “A Timeover-Threshold technique for wide dynamic range gammaray spectroscopy with the AGATA detector”, IEEE Trans.
Nucl. Sci., vol. 56, no. 4, pp. 2384-2391, Aug. 2009
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
“Reset-mode” spectroscopy
Experimental results with “Fast reset” ASIC preamplifier
Excellent linearity also in Fast Reset mode
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
“Reset-mode” spectroscopy
Experimental results with “Fast reset” ASIC preamplifier
ENC: equivalent noise charge with 15 pF (higher value) and 0 pF (lower value) detector capacitance
Series 1/f noise
Parallel white noise
Series white noise
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "
Conclusions
 Design & computer simulation of a JFET-CMOS preamplifier
(0.35mm) for HPGe detectors equipped with a fast reset
device for charge sensing stage de-saturation
 Dead time minimization in the cases of high background
counting rates
 Charge measurements even in a condition of deep
saturation → boost of useful dynamic range for highresolution energy measurements
 Experimental tests performed on the realized test chip
Speaker: Stefano Capra
"GASPARD-HYDE-TRACE Workshop 2012 "