2011 Stanford PNT Symposium November 18, 2011

Menlo Park, CA

THE SA.45S CHIP-SCALE ATOMIC CLOCK

Robert Lutwak Symmetricom - Technology Realization Center Rlutwak@Symmetricom.com

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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 RLutwak@Symmetricom.com

…and the rest of the CSAC Team.