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2011 Stanford PNT Symposium November 18, 2011
Menlo Park, CA
THE SA.45S CHIP-SCALE ATOMIC CLOCK
Robert Lutwak Symmetricom - Technology Realization Center [email protected]
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CSAC for PNT
2001
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Physics in REALLY small cells?
J. Kitching, S. Knappe, and L. Hollberg, "Performance of small-scale frequency references," presented at IEEE International Frequency Control Symposium, New Orleans, LA, 2002.
J. Kitching, S. Knappe, and L. Hollberg, "Miniature vapor-cell atomic-frequency references," Applied Physics Letters, vol. 81, pp. 553-555, 2002.
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DARPA MTO CSAC Program
• Target Specifications • Device Volume: < 1cm3 • Total Power Consumption: < 30 mW • Stability:
• Multiple Competitive Contracts • National Institute of Standards and Technology (NIST)/U. of Colorado
• Symmetricom/Draper/Sandia • Teledyne Scientific/Rockwell Collins/Agilent • Honeywell • Sarnoff/Princeton/Frequency Electronics
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The CSAC Challenge
CSAC
Lower Power & Better Performance
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Navigation Applications
• Enhanced GPS Receivers – Navigation with
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Other Applications
• Secure Communications – Time-Sequence Code Acquisition in GPS-denied environments – Frequency-hopping radios
• Datalogging – Time-tagging – Synthesized aperture arrays of sensors (seismology) – Traingulation of signals
• Underwater timing applications – Data-logging
• Automobile collision avoidance systems • Telecom/Enterprise – GPS timing holdover – Clean-up timing source for PTP
• Time/Frequency in high vibration environments
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A bit of History
Era Activity Result Reporting
2001-2003 DARPA CSAC Phase-I Basic physics MEMS Components PTTI 2002 PTTI 2003
2004 DARPA CSAC Phase-II 10 mW Physics Package PTTI 2004
2005 DARPA CSAC Phase-II Autonomous CSAC PTTI 2005
2006-2007 DARPA CSAC Phase-III Build of 10X prototypes 30 mW 1 cm3 demo PTTI 2007
2008-2010 DARPA CSAC Phase-IV Ruggedization and environmental testing
2008-2011 Symmetricom Productization SA.45s 1/18/2011 Product Announcement
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The 10 mW Physics Package
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Ditch the cavity Cyr & Tetu 1993
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RF vs. CPT
Requires Resonant Cavity High-Bandwidth VCSEL is Enabling Technology
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The 10 mW Physics Package
Tensioned polyimide suspension Microfabricated Silicon vapor cell Low-power Vertical-Cavity Surface Emitting Laser (VCSEL) Vacuum-packaged to eliminate convection/conduction Overall Thermal Resistance 5000°C/W
M. Mescher, et. Al., "An Ultra-Low-Power Physics Package for a Chip-Scale Atomic Clock," Proceedings of the 13th International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers '05), Seoul, Korea, June 5-9, 2005, pp. 311-316.
US Patent #7215213
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Polyimide Suspension
Photos courtesy of Draper Laboratory
VCSEL and Thermistor on Polyimide suspension
Polyimide suspension
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SA.45s Physics Package
Frame Spacer
Cover
Photodiode
Cell Spacer
Lower Suspension
VCSEL
LCC
Upper Suspension
Resonance Cell
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Physics Package Performance
PPIII CPT Resonance
Resonance “Q” = 5x107
Stability vs. Time
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Production Statistics: Physics Package Power
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SA.45s CSAC
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Control System
Laser Servo - Lock laser wavelength to optical absorption resonance via DC Bias Temperature Servo - Optimize optical power via temperature Clock Servo – Lock local oscillator to CPT resonance Power Servo - Optimize CPT signal amplitude via µWave power
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SA.45s CSAC Block Diagram
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7 Microwave System: 50 mW
1
1
1 Control System: 40 mW
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1
1 1
5
1
1
2
6
Total: 115 mW
Regulators & Passives: 15 mW
2
11
10
Physics: 10 mW
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SA.45s CSAC
Lid
Physics Package
PCB
Lower Shield
Baseplate
Top Shield
C‐Field Coil
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SA.45s Performance
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Short-term Stability
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Production Statistics: 1-second Stability
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Production Statistics: 10-second Stability
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Timing Error
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Medium- to Long-Term Stability
SN 1008CS00066 – Now on ISS
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Impact of Drift on Timing Error
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REALLY Long-term Stability
SN 084 – Early functional prototype
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Typical Temperature Sensitivity
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Production Statistics: Temperature Sensitivity
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Production Statistics: Power Consumption
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Other interesting measurements
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1 Pulse-per-Second System
Synchronization Resolution +/- 50 ns
GPS-dominated regime σy(τ)≈10-8/ τ
CSAC-dominated regime σy(τ)≈10-10/ τ1/2
Discipline to GPS
Self-calibration to reference 1 PPS Initial phase and frequency error steered away within 1000 seconds
Initial synchronization +/- 50 ns Internal 1 PPS measurement system Resolution ≈ 400 ps
(better than CSAC for τ > 10 s) Self-calibration for mission initialization Discipline to GPS as holdover oscillator
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Performance under Vibration
5X Production SA.45s CSACs tested to Mil-STD-810 Fig. 514.6E-1, 7.7 gRMS and 15.4 gRMS All 5X Units hold lock up to 15.4 gRMS Most units meet static ADEV spec in most axes up to 7.7 gRMS !
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Exposure to Ionizing Radiation
2X Production SA.45s CSACs were exposed to Total Ionizing Dose (TID) Gamma radiation testing Both units failed between 11 kRad and 12 kRad TID due to same op-amp (not Physics!) Minimal additional mu-metal shielding should permit LEO orbit applications at 50-100 kRad TID
Frequency Shift ≈ 2.5x10-11/kRad
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Status and Future History
• SA.45s CSAC is available now – $1500 list price – Lead times are still a little long (6-8 weeks)
• Manufacturing Technology (ManTech) program underway – Funded by USArmy/OSD/GPS-W – Objective: $100 sell price, Threshold: $300 sell price
• Tactical-Grade Atomic Clock (TGAC) Program – Funded by Office of Naval Research – Objective is smaller, lower-power, improved performance
• Integrated Micro-Primary Atomic Clock (IMPACT) Program – Funded by DARPA MTO – Objective is CSAC with 1000X improvement in drift, retrace, and
temperature sensitivity
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Acknowledgements
CSAC Development Team: Symmetricom: A. Rashed, P. Vlitas, J. Deng, D. Emmons, T. Gebrewold, and
R.M. Garvey Draper Laboratory: M. Varghese, G. Tepolt, J. Leblanc, and M. Mescher Sandia National Laboratories: G.M.Peake, K.M. Geib, and D.K. Serkland
Symmetricom Productization Team: Design and Process Engineering: M. Silveira, D. Taylor, S. Chang, M. Juppe, J. McCartney, E. Saw, N. Dao, E.
Arena, R. Dumont, M. Jiang, M. Stanczyk, L. Zanca, J. Malcolmson, and J. Dansereau
Manufacturing Engineering and Operations: M-J. Bennett, S. Wilson, R. Dumont, S. Fox, E. Arena, T. Iovanella, J. McGuire,
and M. Duval
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Symmetricom, Inc. 2300 Orchard Parkway San Jose, CA 95131‐1017 Tel: +1 408‐428‐7907 Fax: +1 408‐428‐6960
www.symmetricom.com
Robert Lutwak [email protected]
…and the rest of the CSAC Team.