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Detectors and Analog Electronics
Bill Crain
The Aerospace Corporation
310-336-8530
[email protected]
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 1
28 September 2005
Introduction
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Design Overview
Requirements Flowdown
Detector Specification
Signals, Noise, and Processing
Board Descriptions
Interface Diagram
Power Consumption
Trade Studies
Summary
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 2
28 September 2005
Detector Electronics Design Overview
• Electronic Board Designs
– Telescope Board
– Analog Processing Board (APB) in E-box
• Heritage approach from Polar CEPPAD/IPS unchanged from
proposal
– Linear pulse processing system with Amptek front-end
– Circuits designed specifically for CRaTER requirements
• Functional requirements summary
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–
–
–
Measure LET of high LET particles in thin detectors
Measure LET of low LET particles in thick detectors
Provide good resolution for TEP effects
Robust to temperature drift and environments
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 3
28 September 2005
Functional Block Diagram
Detector Boards
Telescope Board
Analog Processing Board
Thin
Thick
Thin
Thick
Thin
Thick
Shaping
Preamps
Scaling
Bias
Networks
Thermistor
Baseline
Restorer
To
Digital
Board
Timing
Trigger
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 4
28 September 2005
Analog Signal Flow Diagram
• Single fixed gain, linear transfer function
• All detector channels use same topology
Bias
Network
Silicon
Detector
Preamp
dv/dt &
Pole-Zero
Cancellation
Shaping
Amp
Analog Pulse
Signals
Scaling
Amp
Amp
Test
Pulser
Timing
Discrim.
Digital Timing
Signals
Baseline
Restorer
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 5
28 September 2005
Requirements Traceability
Electronics Req.
Thin Det.
Thick Det.
Parent Req.
Affectivity
Amplifier strings
3
3
CRaTER-L3-01
Board sizes
Max. Energy Deposit
1 GeV
100 MeV
CRaTER-L3-01
Preamp range, closedloop stability
Low E Threshold
Timing Threshold
2 MeV
<1.3 MeV
200 keV
<130 keV
CRaTER-L3-01
Gain, baseline restorer,
shaping time
Noise (rms)
< 400 keV
< 40 keV
CRaTER-L3-01
CRaTER-L2-08
Preamp, shaping time,
thermal
Max. Singles Rate
1.25 kHz
1.25 kHz
CRaTER-L3-10
Shaping time, preamp
time constant
Integral non-linearity
0.1%
0.1%
CRaTER-L2-08
Preamp, shaping amp
Stability / drift
0.1%
0.1%
CRaTER-L3-01
CRaTER-L2-08
Preamp, bias network,
baseline restorer
Internal Calibration
256:1
256:1
CRaTER-L3-08
Test pulser
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 6
28 September 2005
Detector Specification (1)
• Document 32-05001 released rev 02 August 1, 2005
• Micron Semiconductor Limited
– Lancing Sussex, UK
• 20 years experience in supplying detectors for space physics
– CEPPAD, CRRES, WIND, CLUSTER, ACE, IMAGE, STEREO, and
more…
• Detector Type
– Ion-implanted doping to form P+ junction on N-type silicon
– Very stable technology
– Advantages to science include good carrier lifetime, stable to
environmental conditions, and thin entrance windows
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 7
28 September 2005
Detector Specification (2)
• Circular detectors having active area of 9.6 cm2
• Two different detector thicknesses: thin and thick
– note: state-of-the-art is 20um for thin and 2,000um for thick detectors
• Guard ring on P-side to improve surface uniformity
• Very thin dead layers (windows) reduce energy loss, lower series
resistance, and reduce noise
E-field
~ 1mm
Active
Dimension
(35mm)
Gd/FP
P+ Contact Grid
P+ implant window
Gd/FP
Active Volume
(depletion region)
N window
N contact
0.1 um
Thickness
140 um thin;
1,000 um thick
0.1 um
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 8
28 September 2005
Detector Specification (3)
• Detector drawings (Micron)
– Note: this is not the present mount design
Guard ring
Al. contact
plane
Al. contact grid
reduces surface
resistivity
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 9
28 September 2005
Detector Design Requirements Summary
Requirement
Specification
Active area
9.6 cm2 circular
Active dimension
35 mm
Active dimension tolerance
+/- 0.1 mm
Thickness
Thin = 140 um, Thick = 1000 um
Thickness tolerance
+/- 10 um
Thickness uniformity
+/- 10 um
Window
0.1 um ohmic, 0.1 um junction
Metalization
Ohmic surface and junction grid 3000 Å +/- 1000 Å
Full depletion (FD)
Thin = 20 – 40V, Thick = 150 – 200V
Operating voltage max
Thin = 2 x FD, Thick = FD + 30V
Capacitance
Thin = 700 pF, Thick = 100 pF
Leakage current max (20C)
Drift (max leakage @ 40C)
Thin = 300 nA junction, 200 nA guard
Thick = 1,000 nA junction, 700 nA guard
6 x Ileak @ 20C
Stability
1% Ileak @ 40C for 168 hours
Alpha resolution
Thin = 45 KeV, Thick = 35 KeV FWHM
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 10
28 September 2005
Detector Specification (4)
• ISO9001
– Full traceability and serialization
– Travelers maintained
• Qualification tests prior to flight detector shipment
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–
–
–
Bond pull test
Random vibration test
Thermal cycling
Stability
• Verification matrix specifies test criteria
–
–
–
–
Leakage current
Capacitance
I-V characteristic
Alpha resolution / pulser noise measurement
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 11
28 September 2005
Detector
Verification
Matrix
Eye
Chart
From 32-05001
Rev 02
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 12
28 September 2005
Proton Energy Deposition Simulations
Thin 150MeV
incident E
150 MeV Protons
10000
Nominal Threshold
20,000 incident protons
Thin detectors (140 um)
100
10
0.1
Detector 1
Detector 3
Detector 6
20,000 incident protons
Thick detectors (1000 um)
1000
Events
Events
1000
1
0.01
Thick 150MeV
incident E
150 MeV Protons
10000
Nominal Threshold
GEANT4
100
10
1
10
1
0.01
100
10
100
Thick 1000MeV
incident E
1 GeV Protons
10000
20,000 incident protons
Thin detectors (140 um)
20,000 incident protons
Thick detectors (1000 um)
Detector 2
Detector 4
Detector 5
Detector 1
Detector 3
Detector 6
1000
1000
Events
Events
1
Deposited Energy (MeV)
Thin 1000MeV
incident E
1 GeV Protons
100
10
1
0.01
Detector 2
Detector 4
Detector 5
0.1
Deposited Energy (MeV)
10000
Reference:
M. Looper
100
10
0.1
1
10
Deposited Energy (MeV)
100
1
0.01
0.1
1
10
100
Deposited Energy (MeV)
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 13
28 September 2005
Iron Energy Deposition Simulation
Reference:
J.B. Blake
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 14
28 September 2005
Signal Characteristics
Detector
Min Signal
Max Signal
Collection
Time
Detector
Capacitance
Feedback
Capacitance
Thin
555E3 e-h
pairs
(88 fC)
275E6 e-h
pairs
(44 pC)
3 nsec e-drift
9 nsec h-drift
700 pF
15 pF
Thick
55E3 e-h pairs
(8.8 fC)
27.5E6 e-h
pairs
(4.4 pC)
38 nsec e-drift
115 nsec h-drift
100 pF
1.5 pF
RFB
CFB
PreAmp
Ao
qμnNe(t)E
qμpNh(t)E
Cdet
Vpk = Qtot/CFB
CFB (Ao) >> Cdet
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 15
28 September 2005
Signal Processing (1)
• Combined dynamic range of thin/thick pair is 5,000
• Thin threshold to provide overlap with thick range
• Thin Detector Signal
– Preamp input stage designed for 97% charge collection
• High gain input jFET for large dynamic input capacitance
• 4% drift in operating point will result in 0.1% in output peak
– Large feedback capacitance needed to handle Fe deposit
• Preamp compensation to maintain closed-loop stability
• Thick Detector Signal
– Not as sensitive to detector capacitance
– Designed for low noise to maintain reliable 200 KeV low threshold
and meet resolution requirement
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 16
28 September 2005
Noise Model (1)
Detector
Input
Capacitance
Leakage
Current
Shunt
Resistance
Series
Resistance
Preamp
noise (ena)
Thin
700 pF Det.
160 pF jFET+stray
200 nA @ 20C
800 nA @ 35C
6 Meg ohms 100 ohms
0.6 nV/√Hz
Thick
100 pF Det
10 pF jFET+stray
1000 nA @ 20C
4000 nA @ 35C
6 Meg ohms 100 ohms
2.0 nV/√Hz
+ input cap.
T=peaking time
F=shaping factors
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 17
Reference:
Helmuth Spieler
IFCA Instrumentation Course Notes
2001
28 September 2005
Noise Model (2)
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 18
28 September 2005
Noise Model (3)
20C BOL
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 19
28 September 2005
Signal Processing (2)
• Noise dominated by thick detector leakage current
• Shaping time same for both thin and thick detectors
– ~1 usec for comfortable PHA input timing
– 3-pole gaussian shaping improves symmetry
– 2-complex poles shortens tail
• Coincidence Timing
– Noise occupancy in 1-usec coincidence window < 0.1%
– Threshold to noise ratio (T/N) ~ 3.2 for timing discriminator
– Timing discriminator threshold ~ 130 keV
• Anticipated BOL T/N ratio is ~ 10
• Allows margin for leakage current drift up to 10 uA
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 20
28 September 2005
Signal Processing (3)
• Other factors affecting noise performance
– Bias resistor on thin detector sized to minimize voltage drop
– Bias resistor on thick detector sized to minimize noise
– Detector shot noise doubles every 8 C
• Beneficial to operate cold; preferably below 20 C
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 21
28 September 2005
Signal Processing (4)
• Pileup is rare due to low event rate and relatively short
shaping time
– Exception: occasional periods of high ESP flux
• Coincidence timing uncertainty from leading edge trigger
is small
– Amplified timing discriminator reduces time walk to acceptable
10% uncertainty
• Ballistic deficit is not an issue due to short collection
times relative to peaking time of shaper
• Output voltage scaled for PHA input specifications
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 22
28 September 2005
Telescope Board Details
Negative Bias
Bias
Network
Test Pulser
Test Input
&
Feedback Network
Bias
Network
A250
JFET
G
P-contact
Active Volume
N-contact
G
Signal
• Thin/thick detector pair use
same design topology
• Signal collected on P-contact
• Guard signal shunted to
ground
• No guard leakage noise
• AC coupling to isolate DC
detector leakage current
• Low noise / high gain JFET
input stage (InterFET) with
Amptek A250 hybrid
• MIL-STD-5510 polyimide 8layer construction
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 23
28 September 2005
Analog Processing Board Details
• Single board in E-box contains 3 thin and 3 thick detector
processing channels
– Polyimide laminate, MIL-STD-55110, 8-layers, 0.062 in.
– Interfaces to digital board in same box
• Components
– Linear Technology radiation tolerant opamps for shaping stages, BLR,
and comparators
– Analog Devices rad tolerant op-amp for test pulser interface and bias
monitoring (see trade study chart)
• Pole-zero cancellation circuit included to prevent undershoot
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 24
28 September 2005
Analog Interface Block Diagram
Aerospace
MIT
Analog Processing
Digital Processing & Power
+/- 6V, 5V &
Returns
Power Supply
Detector Bias &
Returns
Shaped Pulse Analog
Signals
3 thin, 3 thick
Timing Digital Triggers
3 thin, 3 thick
Pulse Height
Analysis
System
Temperatures
Spacecraft
Interface
•
•
•
•
ICD 32-02052 rev 01
+/- 6V power, 5V
Thin and thick bias voltages
Unipolar gaussian signals
input to peak-hold circuits
• Low-level triggers for
coincidence timing
• Test pulser level and
clocking signals
Test Pulser Trigger
Test Pulser Level
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 25
28 September 2005
Power Estimate
Detector Boards (total for 3 boards)
Power Source
Analog Processing Board
Total Est. (mA)
Total Max. (mA)
67.980
88.800
97.680
41.800
45.980
41.800
45.980
0.000
1.000
1.100
1.000
1.100
0.030
0.033
0.000
0.000
0.030
0.033
0.075
0.083
0.000
0.000
0.075
0.083
Power Est. (mW)
10% Uncertainty
Power Est. (mW)
10% Uncertainty
Total Est. (mW)
Total Max. (mW)
187.5
206.25
626.6
689.26
814.1
895.51
Current Est. (mA)
10% Uncertainty
Current Est. (mA)
10% Uncertainty
24-May-05
24-May-05
24-May-05
24-May-05
+6V Analog
27.000
29.700
61.800
-6V Analog
0.000
0.000
+5V Digital
0.000
-100V Thin Det Bias
-300V Thick Det Bias
Total Load
Total estimated power dissipation is < 1 Watt
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 26
28 September 2005
Trade Studies
• Considering detector bias current monitor
– Housekeeping item to provide leakage current for each detector
– No impact on noise or failure modes
– Useful for diagnostic purposes especially during environmental
testing of flight units
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 27
28 September 2005
Summary
• Detectors are well-established technology from experienced
supplier
• Detector specification and Analog/Digital ICD documents
have been released
• Electronics design meets requirements of instrument
requirements document 32-01205
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 28
28 September 2005
Cosmic RAy Telescope for the Effects of Radiation
Bill Crain, PDR Slide 29
28 September 2005