1. C osmic R Ay T elescope for the E ffects of R adiation Detectors and Analog Electronics Bill Crain The Aerospace Corporation 310-336-8530 Bill.crain@aero.org

2. C osmic R Ay T elescope for the E ffects of R adiation Introduction Design Overview Requirements Flowdown Detector Specification Signals, Noise, and Processing Board Descriptions Interface Block Diagram Power Consumption Trade Studies Summary

3. C osmic R Ay T elescope for the E ffects of R adiation Detector Electronics Design Overview Detector electronics comprised of two board designs –Detector Boards in Telescope assembly –Analog Processing Board (APB) in E-box Heritage approach from Polar CEPPAD/IPS unchanged from proposal –Linear pulse processing system utilizing Amptek hybrids –Circuits re-designed for CRaTER requirements Functional requirements summary –Measure LET of high LET particles in thin detectors –Measure LET of low LET particles in thick detectors –Provide good resolution for TEP effects –No fast timing requirements –Robust to temperature drift and environments

4. C osmic R Ay T elescope for the E ffects of R adiation Analog Signal Flow Diagram Single fixed gain, linear transfer function All detector channels use same topology –Differences in preamp input transistor, detector biasing, and gain settings are made to optimize thin and thick channels

5. C osmic R Ay T elescope for the E ffects of R adiation Requirements Flowdown Electronics reqs. derived from Level 2 reqs. and detector sims. Electronics Req.Thin Det.Thick Det.Level 2 Req.Affectivity Amplifier strings33TEP analysisSystem design Stability / drift0.1% (1 bit) ResolutionPreamp, bias network, baseline restorer Max. Energy Deposit1 GeV for Fe100 MeV for H+LET spectrum range Preamp range, closed- loop stability Low E Threshold2 MeV200 keVLET spectrum range Gain, baseline restorer, shaping time Noise (rms)< 500 keV (1/2bit) < 50 keV (1/2bit)ResolutionPreamp, shaping time, thermal Max. Singles Rate 10 kHz ESP eventsShaping time, preamp time constant OutputLinear ResolutionOutput amplifier Internal Calibration1000:1 OperationsTest pulser

6. C osmic R Ay T elescope for the E ffects of R adiation Detector Specification (1) 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

7. C osmic R Ay T elescope for the E ffects of R adiation Detector Specification (2) Circular detectors having active area of 9.6 cm 2 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 GuardP+ ContactGuard Active Volume (depletion region) P+ window N window 0.1 um 140 um thin; 1,000 um thick 35 mm, diam. N contact E-field

8. C osmic R Ay T elescope for the E ffects of R adiation Detector Specification (3) Detector drawings (Micron) Guard ring Al. contact grid reduces surface resistivity Al. contact plane

9. C osmic R Ay T elescope for the E ffects of R adiation Detector Specification (4) ISO9001 –Full traceability and serialization –Travelers maintained Verification and test prior to detector shipment –Random vibration test –Thermal cycling and thermal vacuum –Stability Test criteria –Leakage current –I-V characteristic –Alpha resolution / pulser noise measurement (final test)

10. C osmic R Ay T elescope for the E ffects of R adiation Proton Energy Deposition Simulations Reference: M. Looper Thin 150MeV incident EThick 150MeV incident E Thin 1000MeV incident EThick 1000MeV incident E Nominal Threshold GEANT4

11. C osmic R Ay T elescope for the E ffects of R adiation Iron Energy Deposition Simulation Reference: J.B. Blake

12. C osmic R Ay T elescope for the E ffects of R adiation Signal Characteristics DetectorMin SignalMax SignalCollection Time Detector Capacitance Feedback Capacitance Thin555E3 e-h pairs (88 fC) 275E6 e-h pairs (44 pC) 3 nsec e-drift 9 nsec h-drift 700 pF10 pF Thick55E3 e-h pairs (8.8 fC) 27.5E6 e-h pairs (4.4 pC) 38 nsec e-drift 115 nsec h-drift 100 pF1.0 pF qμ n N e(t) Eqμ p N h(t) E C det C FB R FB C FB (A o ) >> C det Ao V pk = Q tot /C FB

13. C osmic R Ay T elescope for the E ffects of R adiation 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 to raise dynamic input capacitance 4% drift in operating point will result in 0.1% in output peak (< 1 bit) –Large feedback capacitance needed to handle Fe deposit Preamp compensation to maintain closed-loop stability Thick Detector Signal –Not as sensitive to detector capacitance –Design for low noise to maintain reliable 200 KeV low threshold and achieve < 1-bit resolution

14. C osmic R Ay T elescope for the E ffects of R adiation Noise Model (1) Reference: Helmuth Spieler IFCA Instrumentation Course Notes 2001 DetectorInput Capacitance Leakage Current Shunt Resistance Series Resistance Preamp noise (e na ) Thin700 pF Det. 160 pF jFET+stray 200 nA @ 20C 800 nA @ 35C 260 kohm100 ohms0.6 nV/√Hz Thick100 pF Det 10 pF jFET+stray 200 nA @ 20C 800 nA @ 35C 260 kohm100 ohms2.0 nV/√Hz + input cap. T=peaking time F=shaping factors

15. C osmic R Ay T elescope for the E ffects of R adiation Noise Model (2) Optimum

16. C osmic R Ay T elescope for the E ffects of R adiation Signal Processing (2) Noise dominated by detector leakage and input jFET Shaping time for both thin and thick detectors set at thick optimum point –~1 usec –Compatible with A/D signal acquisition timing –3-pole gaussian shaping improves symmetry and 2-complex poles shortens tail Shaping reduces noise but also impacts signal level –S/N at thick detector threshold for this design ~ 4 –Translates to a noise occupancy in the coincidence window of < 0.1% for time period not greater than shaping time

17. C osmic R Ay T elescope for the E ffects of R adiation Signal Processing (3) Other factors affecting noise performance –Bias resistor sized to minimize voltage drop (i.e., maintain stable operating point) –Detector shot noise doubles every 8 C –Beneficial to operate cold; preferably below 20 C

18. C osmic R Ay T elescope for the E ffects of R adiation Signal Processing (4) Pileup is rare due to low event rate and relatively short shaping time –Exception: occasional periods of high ESP flux Leading edge trigger technique causes timing uncertainty but coincidence window is large by comparison –Amplified low-level discriminator available to reduce walk Ballistic deficit is not an issue due to short collection times relative to peaking time of shaper Output voltage scaled for A/D input specifications

19. C osmic R Ay T elescope for the E ffects of R adiation Detector Board Thin/thick detector pair use same design topology Signal collected on P-contact Negative bias Guard signal shunted to ground No guard leakage noise AC coupling to isolate DC detector leakage current Low noise / high gain JFET input stage

20. C osmic R Ay T elescope for the E ffects of R adiation Analog Processing Board Single board in E-box contains 3 thin and 3 thick detector processing channels Flight proven pulse processing components –Amptek A250 preamp hybrid utilizing external jFET on detector board –Shaping amps use Amptek A275 for active filtering –Baseline restorer, Amptek BLR1, compensates for baseline shifts on interface to A/D Pole-zero cancellation circuit for correcting preamp pulse decay to eliminate undershoot Test pulser injects ΔQ at preamp input jFET

21. C osmic R Ay T elescope for the E ffects of R adiation Analog Interface Block Diagram

22. C osmic R Ay T elescope for the E ffects of R adiation Power Estimate Total estimated power dissipation is < 1 Watt

23. C osmic R Ay T elescope for the E ffects of R adiation Trade Studies Determine if one detector board can be implemented instead of three Determine if A250 device should be located on detector board Determine sensitivity of APB to detector performance –Want to avoid rework of APB when selecting/changing detectors during development Determine how best to isolate chassis noise from detectors and preamp

24. C osmic R Ay T elescope for the E ffects of R adiation Summary Detectors are well-established technology from experienced supplier Detector electronics design meets requirements of Level 2 mission and satisfies energy deposition levels determined by detector/TEP simulations Trade studies in progress