Microsemi Atomic Clock Technology

Transcription

1 Power Matters. Microsemi Atomic Clock Technology DCF China Clock Conference Bryan Owings and Ramki Ramakrishnan November 6 and 7, 2014

2 About Microsemi Corporation (Nasdaq: MSCC) Global provider of semiconductor solutions for applications focused on delivering power, reliability, security and performance. High-value, high barrier-entry markets: Communications Defense & Security Aerospace Industrial FY 2013 Revenue: $976 million Corporate headquarters in Aliso Viejo, CA Power Matters. 2

3 Agenda Definitions of terms Principles of atomic clocks & architecture Cesium beam atomic clocks Hydrogen maser atomic clocks Rubidium gas cell atomic clocks Positioning of various atomic clock technologies Time Scales & Emerging clock technologies Conclusion Power Matters. 3 3

4 Terms: Normalized Frequency Normalized frequency: Also called fractional frequency offset y = (ν ν 0) ν 0 Example: -1 Hz offset at 5 MHz ( Hz) is -2e-7 Power Matters. 4 4

5 Terms: Allan Deviation The Allan deviation is a statistical measure (analogous to the well known standard deviation) of frequency stability. i 1 1 = M 2 y ( ) = σ τ ( y i + 1 y i ) 2( 1) M i= 1 1/ 2 Allan deviation can be predicted from basic atomic resonance parameters (more on this later) Power Matters. 5 5

6 Why Atomic Clocks? Atoms of a given element and isotope are identical Properly designed apparatus can interrogate atomic resonances to form precise and stable frequency references The best atoms are hydrogen like in their atomic structure: 1 H, 133 Cs, 87 Rb. While cesium defines the SI second, stored ions and optical transitions in other atoms ( 199 Hg +, 171 Yb +, 88 Sr +, Ca) may be candidates for evolutionary laboratory standards. Power Matters. 6 6

7 Basic (Passive) Atomic Clock Synthesizer Atoms Detector RF Output Oscillator Clock Output Divider Servo Cesium: ν 0 = Hz (definition) Hydrogen: ν 0 = (3) Hz Rubidium: ν 0 = (9) Hz Power Matters. 7 7

8 Atomic Energy Levels and Resonance E 2 E 2 -E 1 = hv 0 E 1 --Atoms can reside only in well defined energy states --Transitions between energy states define a resonance, usually in the microwave region Power Matters. 8 8

9 Related Frequency Definitions Offset the frequency error from the ideal (fast or slow) Accuracy refers to frequency offset of a device Stability how well an oscillator produces time or frequency over a given time interval Aging change of frequency over time (also called drift) Temperature Stability the change of frequency over temperature Accumulated Time Error total of all the above characteristics acting on a clock Power Matters. 9

10 Performance Definitions Short Term Stability the change of frequency over seconds from noise and vibration. Sometimes called flicker or jitter Long Term Stability the change of frequency over hours, days, or months. Result due to age and temperature Phase Noise The rapid, short-term, random fluctuations in the phase of a sine wave due to oscillator quality, semiconductor and white noise Power Matters. 10

11 What is Frequency Stability & Accuracy Courtesy John Vig Power Matters. 11

12 Oscillator Stability Over Time Frequency stability typically improves in the short term, stabilizes, then becomes less predictable in the long term Power Matters. 12

13 What are the Influences on Oscillator Frequency Time Short term (noise) Long term (aging) Temperature Static frequency versus temperature Dynamic frequency versus temperature (warm-up) Thermal history (retrace) Acceleration Gravity, vibration, shock Other Power supply variation Humidity Power Matters. 13

14 Design Considerations Accuracy: preserve the intrinsic accuracy of the atomic resonance Short Term Stability: extract information with highest signalto-noise from the atoms Characterized with Allan deviation Long Term Stability: control the effects of time (aging) and environment (e.g. temperature) on the atomic interrogation? Accuracy and stability are usually interrelated. How do we achieve reasonable size, cost, and operational reliability? Power Matters

15 Calibration vs Accuracy vs Stability Calibration does not guarantee accuracy indefinitely The second is the duration of periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom 13th Conférence Général des Poids et Mesures (1967) Clarification of 1997: cesium atoms at rest at a temperature of 0 K. Stability implies absence of noise or change says nothing about accuracy Power Matters

16 Atomic Resonance Requirements Narrow resonance we seek resonances with high quality factor Q = v W o ν 0 is resonance frequency and W is atomic linewidth High signal-to-noise ratio good short term stability σ ( τ ) y S : 1 N * Q Power Matters

17 Atomic State Populations -- Atoms can reside only in discrete energy states -- States populations are essentially equal for microwave resonances in thermal equilibrium -- Signal-to-Noise considerations require we alter the population distribution E 2 hv 0 hv 0 E 2 -E 1 = hv 0 -- Common techniques to alter the population distribution include optical pumping and state selection E 1 Goal: deplete one state, induce transitions back into this state, detect the results Power Matters

18 Power Matters. Cesium Beam Frequency Standards

19 Cesium Beam Frequency Standards Cesium (caesium) resonance forms the internationally acknowledged definition of the SI second interval of time Mature technology,excellent reliability and stability and performance at reasonable cost Two levels of performance in commercial products today Device of choice when superior long term stability (and environmental immunity) or when autonomy is required Intrinsic accuracy--calibration not required No aging of frequency Power Matters

20 Cesium Beam Tube 9192 MHz Detector F=3 + F=4 S F=3 F=4 F=3 + F=4 S F=3 F=4 N N "A" Magnet "B" Magnet Magnetically-Selected CBT Power Matters

21 Cesium Beam Tube Power Matters

22 Cesium Spectrum Power Matters

23 Cesium Spectrum (high resolution) Linewidth 450 Hz Atomic line Q 20 million ν 0 = Hz Power Matters

24 Cesium Beam Block Diagram Servo including DACs, ADCs, microprocessor Direct Digital Synthesizer RS-232 Oven Controlled Quartz Oscillator 5 MHz Frequency Mulitplier/Synthesizer Hz User Output Power Matters

25 Atomic Beam Pluses and Minuses + Cesium beam is a primary standard and does not require calibration + Beam has no interaction with its confinement Most accurate and most stable atomic clock, in long term + No first order Doppler frequency offsets in properly designed and built apparatus + Beam density is low enough for minimal self-interaction - Relatively complex and expensive apparatus - Linewidth limited by time-of-flight through the apparatus +/- Lifetime: 6 years for high performance; 12+ years for standard performance Power Matters

26 Cesium Instrument Evolution <5E-11 Accuracy <5E-13 Accuracy NPL HP 5060 $20, HP A 2001 CsIII 1958 The National Company Atomichron $20,000 in 1964 = ~$143,000 in 2009 Based on CPI over this period Power Matters. 26

27 Cesium Technology Applications Cesium Technology is considered the most comprehensive holdover option against GNSS vulnerabilities Exhibit no frequency drift Maintains 5x10-15 accuracy over the life of the instrument Critical for long-term autonomous operation No on-going calibration required More expensive than Rubidium and OCXO Consumes more power and space Typical applications Fixed wireline communications infrastructure Under sea (Submarine) Satellite ground stations Metrology and Time Keeping Power Matters. 27

28 Power Matters. Active Hydrogen Maser Frequency Standards

29 Active Hydrogen Masers Excellent frequency stability up to 1 day 40X superior to high performance cesium Mature technology with good operating lifetime and reliability Design of choice when the ultimate frequency stability is required Applications: National Timescale and Radio Astronomy MASER: Microwave Amplification by Stimulated Emission of Radiation MHM 2010 Power Matters. 29

30 Hydrogen Maser Maser Signal (-105 dbm) Cavity Magnetic Shields Hydrogen Maser Physics Package Tuning Varactor Switching Varactor Quartz Bulb State Selector Hydrogen Dissociator Source Discharge Oscillator Power Matters

31 Maser Block Diagram MPG Hz Varactor Control IF Amp L.O. Multiplier Receiver Amplifier -105 dbm KHz Phase Detector & KHz 10 MHz VCXO 14 digit Maser Tuning 10 MHz Synthesizer Physics Varactor Package 10 MHz 10 MHz Signal Buffers 405 KHz Hz Synchronous Detectors 10 MHz U/D Cavity Register Switching Varactor 24 V Battery Power Module Source Pressure Control Hydrogen Source 110 VAC 110 VAC VDC H 2 supply Palladium Purifier 31 Power Matters. 31

32 Maser Accuracy and Stability Thermal motion of the atoms induces a second-order Doppler effect of approximately - 5e-11. Confinement ( wall shift ) of hydrogen atoms induces a frequency offset of approximately - 3 e-11. Cavity pulling dependent on cavity tuning error Spin-exchange frequency shift Magnetic field in the atomic environment Best performance requires that these effects be constant to better than 10 ppm/day Power Matters

33 Applications Metrology Where? International timekeeping laboratories Why a Maser? Provides superior frequency stability out to one day Stability is the key attribute in a timescale application and today s primary standards research Time scale reference clock steered to the cesium ensemble Radio Astronomy Where? VLBI Very long baseline interferometry VLBA Very large baseline arrays Why a Maser? Offers frequency stability for multiple VLBA stations to operate as a single instrument Perfect Clock : Maser (short term) + Cesium (long term) Power Matters. 33

34 Power Matters. Rubidium Gas Cell Frequency Standards

35 Rubidium Gas Cell Frequency Standards Most widely used type of atomic clock Smallest, lightest, lowest power Least complex, least expensive, longest life Excellent performance, stability & reliability Device of choice when better stability is needed compared to crystal oscillator Lower aging, lower temperature sensitivity Faster warm-up, excellent retrace Used as an inexpensive holdover technology Power Matters. 35

36 Gas Cell Confinement Nitrogen Rubidium --Nitrogen atoms immobilize the rubidium atoms, slowing their velocity and minimizing wall collisions --Interaction between rubidium and buffer gas introduces large frequency offset (which must be calibrated) Power Matters

37 Optical Pumping --Incident pumping photons stimulate transitions into an excited optical state Excited Optical State --Atoms in the excited state decay to the ground states with equal probability --Continued pumping out of one ground state effectively moves the atoms into the other state hν Optical pumping photons hν hν hν E 2 E 1 E 2 -E 1 = hv 0 Power Matters

38 Rubidium Frequency Standard Basics Magnetic Shield Lamp Oven Filter Oven Cavity Oven Lamp Filter Absorption RF Excitation Lamp Exciter Rb-87 Lamp Rb-85 Rb-87 Photo- Detector Signal Out Coil Cell Cell C-Field Coil C-Field Current (3) Oven Temperature Sensors and Heaters Physics Package µw Interrogation RF Chain Servo Modulation Discriminator Signal Frequency Lock Loop Servo Amplifier Control Voltage Crystal Oscillator O/P Amp O/P Power Matters. 38

39 Rubidium Gas Cells The cells in the latest commercial RFS designs have (along with their cavities) gotten much smaller. While this comes at the expense of a broader line, lower Q and poorer short-term stability, good performance e.g. σ y (τ)= 1e- 11 at 1 second can still be realized. Comparison between classic 1 long (LPRO) and latest ultra-miniature (X72) integrated Rb gas cells Power Matters

40 Gas Cell Atomic Clock Pluses and Minuses + Buffer gas confinement allows small size and economical construction + Rubidium has a fortuitous isotope overlap to allow optical pumping - Buffer gas introduces a large frequency shift which results in poor accuracy, is difficult to perfectly stabilize over time (aging) and environment (temperature, barometric, etc) Buffer gas mixtures can reduce thermal effects, one gas with a positive temperature coefficient (N 2 ) and one with a negative temperature coefficient (Ar) Barometric effects (1e-10/atmosphere) are small and non-cumulative Power Matters

41 Traditional Rubidium Products XPRO Traditional lamp-based Rb atomic clock Highest-performance clock SA.22c Traditional lamp-based Rb atomic clock Legacy clock aimed at telecom applications. Being replaced by CPT Clocks. Power Matters. 41

42 Atomic Clock Technologies Technology Intrinsic Accuracy Stability (1s) Stability (floor) Aging (/day) initial to ultimate Cost Hydrogen Maser ~10-11 ~10-13 ~ to ~150X Cesium Beam ~10-13 ~10-11 ~10-14 nil ~20X Passive H Maser ~10-10 ~ x ~40X Rb Gas Cell ~10-9 ~10-11 ~ to ~X Hi-quality Qz 10-6 to 10-8 ~10-12 ~ to ~0.5X 42 Power Matters. 42

43 Power Matters. Time Scales & Emerging clock technologies

44 What is Precise Time-Scale System 5MHz UTC(k) Cesium (5071A) BIPM 5MHz Correction H-Maser(s) Precise Time-Scale System The frequency stability of atomic clocks enables high resolution measurements ensuring the accuracy of the world s time Power Matters. 44

45 How Does a Time Scale Work Step 1 Measure the time differences between all the clocks and the reference clock Step 2 Use a Kalman filter to estimate the time, frequency, and aging differences between all the clocks and the reference clock Step 3 Apply the time scale algorithm (KAS-2*) to calculate the corrections to the reference clock s time, frequency, and aging in order to render it equal the time scale Step 4 *KAS-2 Microsemi Patented Time Scale Algorithm Connect a synthesizer to the reference clock and steer the output of the synthesizer to approximate the time scale using corrections from step 3 Power Matters. 45

46 Precise Time-Scale System Description Real Time Clock Hitless switch capability Clock steering device GNSS receiver IRIG-B, 1PPS, 5MHz Multiple clocks support Cesium External Hydrogen Maser Server with RAID & Ethernet Networking Control & Monitor Storage Modular Measurement System 8 channel measurement Database Keyboard & Monitor Battery charger, batteries, and UPS for total power backup Power Matters. 46

47 Precise Time-Scale System Block Diagram Power Matters. 47

48 Precise Time-Scale User Interface & Database Web-Based User Interface Configure MMS Manage Clocks Retrieve and manipulate Data Add User Accounts Database (includes Manager) 10 years of data storage capacity TCP/IP interface to MMS w/listener process Every sec data from MMS is sent to listener for data processing and storing RAID GB Disk Array On-line striped for 360 GB actual storage 1 Auto-failover hot spare Web Interface for database and measurement systems Clock Steering GUI with estimated offset from UTC Front Panel of Database w/raid 5 disk array Power Matters. 48

49 Precise Time-Scale System Sample Performance Performance vs. UTC UTC - UTC(lab) ns August 2007 through 11 June 2008 RMS = 5 ns Mean = 2.5 ns MJD Power Matters. 49

50 Performance of a 6-Cesium Time Scale (Upgrade Option) Power Matters. 50

51 Performance of a 3-Maser Time Scale (Upgrade Option) UTC(lab) Power Matters. 51

52 Emerging Clock Technologies Miniature Atomic Clocks (MAC) & CSAC using CPT technology Power Matters. 52

53 CPT Physics Comparison Conventional Rb Physics - Requires resonant microwave cavity Lamp Filter Absorption RF Source - RF Discharge lamp (1 Watt) - 3 (or 2) cells, ovens, controllers Lamp Exciter Rb-87 Lamp Coil Rb-85 Cell Rb-87 Cell Photo- Detector RF Discharge Lamp Resonance Cell In Microwave Cavity Coherent Population Trapping (CPT) Physics - High-bandwidth Vertical-Cavity Surface Emitting Laser (VCSEL) - Microwaves applied directly to VCSEL (No cavity) - Potential for very small oven assembly Power Matters

54 SA.31m Laser Pumped Rb & Chip Scale Atomic Clock (CSAC) Rb Miniature Atomic Clock (MAC) Small form factor: 51mm x 51mm x 18mm (H) Lower power: 25 o C Stability 1s <3E-11; 100s <8E-12 Aging: <3E-10/month Temp Stability: <1E-10 ( 10 o C to +75 o C) CSAC (Chip Scale Atomic Clock) Volume: <17 cc Weight : 35g Very Low power: <120 mw Stability 1s <2E-10; 100s <2E-11 Aging: <3E-10/month Temp Stability: <5E-10 (0 to +75 o C) Power Matters. 54

55 Microsemi Portfolio of Atomic Clocks Spec\Type Dimensions (cm) Volume X72 Precision Rubidium Oscillator XPRO High- Performance Rubidium Oscillator SA.35m Miniature Atomic Clock 8.9 x 7.6 x x 9.2 x x 5.1 x cm cm 3 47 cm 3 Quantum Chip Scale Atomic Clock (CSAC) 1.6 x 1.39 x 0.45 < 17 cm 3 C 10 W 13 W 5 W <120 mw 1 sec < 3 x <1 x <3 x <1.5 x Microsemi s atomic clocks meet a variety of application needs Power Matters. 55

56 Conclusion Microsemi is a leader in atomic clock technology with on-going investments to research and development We contribute to many metrology and time keeping labs worldwide with atomic clock technology and precise instrumentation We are committed to our customers in China and the metrology/time keeping community in the country Power Matters

57 Thank You Bryan Owings Engineering Manager, Frequency & Time Division Ramki Ramakrishnan Director Product Management & Business Dev, Clocks BU Power Matters. 57