Precision Oscillator Overview

Transcription

1 Precision Oscillator Overview Hugo Fruehauf April 2007

2 Discussion Outline Quartz Crystal Oscillators Atomic Oscillators Atomic Oscillator Size History & Future Performance Characteristics 2

3 Main Categories of Precision Quartz Oscillators Temperature Sensor Compensation Network f f 25 c 1 x c 100 c XO Temperature Compensated (TCXO) -1 x 10-7 Oven f f 1 x 10-9 Oven Control XO Temperature Sensor -45 c -1 x c Oven Controlled (OCXO) Ovens f f 1 x Oven Controls XO Temperature Sensors Double Oven Controlled (DOCXO) -45 c -1 x Quartz Crystal Oscillators have no wear out mechanism. If manufactured properly, should last 25 years or more 100 c 3

4 Precision Crystal Oscillators from raw materials Resonator Z Dynamic Cleaning Crystal Cutting i.e. SC, AT, FC, etc Rounding Polishing X Plating Mounting Qz Disc Crystal Oscillator Y Tuning Sealing Testing Typically 0.75 x 1.5 x 1.5 Piezoelectric properties of quartz 4

5 Typical Resonator Package Examples 5

6 6 The piezoelectric effect provides a coupling between the mechanical properties of a piezoelectric crystal and an electrical circuit. Un-deformed lattice X Strained lattice X - Y Y Courtesy, John Vig (Ft. Monmouth NJ) The Piezoelectric Effect The Piezoelectric Effect

7 Modes of Piezoelectric Motion Flexure Mode Extensional Mode Face Shear Mode Thickness Shear Mode Fundamental Mode Thickness Shear Third Overtone Thickness Shear Courtesy, John Vig (Ft. Monmouth NJ) 7

8 Zero Temperature Coefficient Quartz Cuts 90 o θ z θ 60 o 30 o 0-30 o -60 o AT FC IT BT SBTC SC x Singly Rotated Cut Doubly Rotated Cut φ θ x l -90 o 0 o 10 o 20 o 30 o y φ The AT, FC, IT, SC, BT, and SBTCcuts are some of the cuts on the locus of zero temp. coefficient cuts. Courtesy, John Vig (Ft. Monmouth NJ) 8

9 Oven Effect on Temperature Coefficient TURNOVER POINT OVEN SET POINT Frequency OVEN OFFSET 2 To OVEN CYCLING RANGE TURNOVER POINT Typical f vs. T characteristic for AT and SC-cut resonators Temperature Courtesy, John Vig (Ft. Monmouth NJ) 9

10 Aging Mechanisms Mass transfer due to contamination Since f 1/t, f/f = - t/t; e.g., f 5MHz 10 6 molecular layers, therefore, 1 quartz-equivalent monolayer f/f 1 ppm Stress relief in the resonator's: mounting and bonding structure, electrodes, and in the quartz (?) Other effects Quartz outgassing Diffusion effects Chemical reaction effects Pressure changes in resonator enclosure (leaks and outgassing) Oscillator circuit aging (load reactance and drive level changes) Electric field changes (doubly rotated crystals only) Oven-control circuitry aging 10

11 Summary - Most Significant Effects Temperature Control temperature deltas with ovens Frequency Aging Control aging with superior manufacturing technology Dynamic Environments (vibration, shock, acceleration) Control sensitivity with: - Superior manufacturing technology - Shock mounts - Electronic g-compensation technology 11

12 Typical Loiter Aircraft and Helicopter Random Vibration 0.5 5g 2 /Hz 0.4 V i b r a t i o n g 2 / H z Loiter Aircraft Helicopter g 2 /Hz 0.04g 2 /Hz Frequency (Hz) 12

13 g-compensation Technology [2] Sensing devices mounted in each axis Vibration applied to the Oscillator [3] Quartz Disk Y Z Quartz Crystal Resonator base Г = (x 2 y 2 z 2 ) ½ X [1] The actual product encloses the disk with a cap Sensing devices respond Quartz Resonator responds [4] [5] [6] Electronic Compensation [7] Oscillator Output 13

14 g-compensation & Shock Mount Approach Acceleration sensitivities better than 2E-12/g Improvements of greater than 30dB Optimized compensation from DC to 200 Hz Broadband compensation from DC to 2 KHz is possible Economies in manufacturability Small package < 5in 3 Compensated Uncompensated Uncompensated Compensated 14

15 Discussion Outline Quartz Crystal Oscillators Atomic Oscillators Atomic Oscillator Size History & Future Performance Characteristics 15

16 Stand-alone alone Precision Oscillator Technologies Rubidium Vapor Atomic Oscillator Quartz Crystal Oscillator Qz Osc. Principle Oscillator in use today Precision Quartz Crystal Oscillators Rb Vapor Phy Pkg Cs Beam Phy Pkg Qz Osc. Qz Osc. Out Cesium Beam Atomic Standard Out Hydrogen Maser Atomic Oscillator Hm Fountain Phy Pkg Atomic Oscillators Qz Osc. Out Qz oscillator frequency-locked to Hyperfine Rb frequency of ~6.8 GHz Qz oscillator frequency-locked to Hyperfine Cs frequency of ~9.2 GHz Qz oscillator frequency-locked to Hyperfine Hm frequency of ~1.4 GHz (Passive Hm) or Phase-locked to ~1.4 GHz (Active Hm) 16

17 Atomic Energy Levels Electron Energy Levels - Electrostatic interaction between Proton and Electron ( and - charges) Collapsing the orbit releases energy Expanding orbit requires energy (Energy out or in is generally in the infrared-visible-uv frequencies) Fine Structure - Interaction between electron spin dipole moment and the magnetic field due to the electron s orbital motion. ~1/50 of the first energy level. (Energy out or in is generally in the microwave frequency area) Hyperfine Structure - Magnetic dipole interaction between the electron spin dipole moment with the nucleus. ~1/1000 of fine structure interaction. N S S N (Energy out or in is generally in the microwave frequencies and below) f 1.4 GHz for Hydrogen f 6.8 GHz for Rubidium f 9.2 GHz for Cesium Zeeman Effect - Magnetic interaction between external magnetic field and electron and proton spin dipoles. (Energy out or in is generally in the audio frequency area and above) (Courtesy: Ed Mattison, Smithsonian from his tutorial (a H. Fruehauf modification of his chart) 17

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19 Atomic Vapor Oscillator (5) Glass Cells (3) Photo Cell (7) Heaters (2) DCMod Freq 87 Rb 85 Rb Lamp (4) (could also be a Laser Diode) ~6.8 GHz Rubidium (1) Servo (8) Synth (8a) (6) (could also be a Cesium Source) Qz Osc (9) Output 10 MHz Atomic Vapor Oscillators have no wear out mechanism. If manufactured properly, should last 25 years or more (1) Active Element of Choice (2) Controlled Environment (3) Element Container (4) Atomic Pump (5) Resonator (6) Irradiation Source (7) State Detector(s) (8) Control Electronics (9) Frequency Source 19

20 Optical Pumping Process f c <f Rb Dip Due to Rb Resonance f c >f Rb Cavity (6.834, 682, 613 GHz) Photo Current f m t f c =f Rb f m t 2f m t Modulated Photo Current Output Resonance Cell Filter 87 Cell Rb 85 Rb 87 Rb Lamp f f m f m f m t t t f c <f Rb f c =f Rb f c >f Rb S N Frequency Modulation Microwave Frequency f c Photo Detector 6.8 GHz from Osc. (20 to 50 ns) Spectral Line Filtered C Spectral Line Excited N B A 6.8 GHz Separation S (~0.15 ns) 20

21 Modulation Scheme Dip Due to Rb Resonance f c <f Rb f c >f Rb Photo Current f m t ~500 Hz f c =f Rb f m t 2f m t Modulated Photo Current Output f t t f m t Frequency Modulation f c <f Rb f c =f Rb f c >f Rb Microwave Frequency f c 21

22 Rubidium Vapor Atomic Oscillator Physics Package Size: ~1.5 x ~3 x ~3 22

23 Cesium Beam Atomic Frequency Standard State Selection Magnets (7) Hot Wire Ionizer (7) DCMod Freq (2) Cesium Oven (4) Servo (8) Cesium Source (1) Beam Tube (3) (5) (6) ~9.2 GHz (10) (1) Active Element of Choice (2) Controlled Environment (3) Element Container (4) Atomic Pump (5) Resonator (6) Irradiation Source (7) State Detector(s) (8) Control Electronics (9) Frequency Source (10) Ion Pump and Getters Synth (8a) 5 MHz Cesium Oscillators have a wear out mechanism, mainly due to the detector getting noisy from ungettered ions. It begins to show up in 7 to 10 years Qz Osc (9) Output 23

24 Passive Hydrogen Maser Atomic Oscillator (2) Bulb (3) (5) ~1.4 GHz Receiving Antenna (7) ~1.4 GHz (10) Synth (8a) (6) State Selection Magnets (7) Servo (8) Qz Osc (9) H 2 Disassociator (4) Passive H-Maser Oscillators have a wear out mechanism, mainly Output from Hydrogen depletion and Ion Pump failures, which begin to show up in 5 to 7 years H H 2 (2) Hydrogen Source (1) (1) Active Element of Choice (2) Controlled Environment (3) Element Container (4) Atomic Pump (5) Resonator (6) Irradiation Source (7) State Detector(s) (8) Control Electronics (9) Frequency Source (10) Ion Pump and Getters 24

25 Active Hydrogen Maser Atomic Oscillator Receiving Antenna (7) (5) & (9) (2) Bulb (3) ~1.4 GHz (10) (6) State RCVR & Selection PLL (8a) Magnets (7) (1) Active Element of Choice (2) Controlled Environment H (3) Element Container (2) (4) Atomic Pump (5) Resonator H H 2 Disassociator (4) 2 (6) Irradiation Source (7) State Detector(s) Hydrogen Source (1) (8) Control Electronics Qz Osc (9) Frequency Source (8) (10) Ion Pumps and Getters Output Active H-Maser Oscillators have a wear out mechanism, mainly from Hydrogen depletion and Ion Pump failures, which begin to show up in 3 to 5 years (6) No Irradiation Source; the Cavity Oscillates and thus is the Frequency Source, not the Qz Oscillator as in previous configurations 25

26 Discussion Outline Quartz Crystal Oscillators Atomic Oscillators Atomic Oscillator Size History & Future Performance Characteristics 26

27 Volume History of Rubidium and Cesium Osc Vapor Std's Vapor Std Best Guess Beam Std Beam Std. Best Guess 10 4 ~5500 in3 (Lab) Volume (size) in Cubic Inches ~2400 in3 (HP, TRACOR, GENRAD) (1 in 3 = 16.4 cm 3 ) 10 3 ~350 in 3 (FTS) 10 2 ~64 in 3 (Efratom) Cesium Beam 47 in 3 (Efratom) ~ 180 in 3 60 in in 3 (Efratom, EG&G) Rb Vapor ~13 in 3 (FEI, TNT) ~6.4 in 3 (AccuBeat) ~7.35 in 3 (Symmetricom) ~1 in 3? (DARPA Man-Pac Spec, Low Pwr) ~1.0 cm 3 (my guess, HF)

28 Discussion Outline Quartz Crystal Oscillators Atomic Oscillators Atomic Oscillator Size History & Future Performance Characteristics 28

29 Accuracy, Precision, and Stability Precise but not accurate Not accurate and not precise Accurate but not precise Accurate and precise f f f f 0 Time Time Time Time Stable but not accurate Not stable and not accurate Accurate but not stable Stable and accurate 29

30 Qz Osc Best-in in-class Frequency Domain Noise (Phase Noise for a 10 MHz Carrier) CMAC CFPO-LN dbc/hz FEI State of Art FEI-Zyfer 10 MHz- LN Module (- 4036) HP Qz Hz 10 Hz 100 Hz Frequency (Hz) 1KHz 10KHz 100KHz 30

31 FEI 6.3 MHz LN Osc. Test Plot, FEI State of Art Equivalent for 10 MHz Measurement problem; should be at -165 floor HP Qz Frequency FrequencyElectronics ElectronicsInc. Inc

32 10-8 Qz Osc Best-in in-class Time Domain Noise (Short-term term Stability for 10 MHz) 10-9 Allan Variance ½, σ y (τ) HP Qz FEI-Zyfer 10 MHz- LN Module (- 4036) FEI State of Art Hr 1 Day 10 Hrs Averaging Time, T(Sec.) 32

33 Comparison of Qz, Rb, GPS, Cs, and Maser Time Domain Noise Sym 5061A, Cs Good Qz Osc Sym 5071A, Cs GPS-Disciplined Qz/Rb High Performance Rb ( ) 2 ( ) 1 τ y,σ AllanVariance VREMYA (FEI) VCH-1006 Passive Maser Kvarz Passive Maser Kvarz Active Maser Sym 5071A Option 001 Cs Hr 1 Day 10 Hrs. 1 Week 1 Mo Averaging Time, T(Sec.) 33

34 Stability & Accuracy of Precision Oscillators Short & Long Term Stability Approx. Time Error at One Day (Lab Conditions) ~250 ms TCXO TCXO Accuracy Range (Allan Variance) ½ [σγ(τ)] Low Cost Rb STD. Cs GPS/Rb (Cs Substitute) Space Qz & Super OCXO MCXO OCXO Passive - Hm STD. Cs Hi-Perf. Rb Hi-Perf. Cs & Space Rb ~10 ms ~300 µs ~90 µs ~30 µs ~10 µs ~1 µs ~86 ns ~25 ns ~3 ns ~1 ns MCXO OCXO Active - HM Super OCXO Space Qz Low Cost Rb Hi-Perf. Rb Low Cost Space Rb Hi-Perf. Cs Passive - HM Hi-Perf. Space Rb GPS/Rb (Cs Subst) & STD. Cs Active - Hm ~100 ps Averaging Time in Seconds 1-Day Elapsed Time 1-Year 34

35 500 MHz Osc Output; Best-in in-class Frequency Domain Noise (Qz and SAW combo) 35 35

36 Typical Specs for Precision Quartz Oscillators Basic Parameters TCXO OCXO (0.5 High) OCXO (0.75 High) DOCXO For Reference Only (Temp. Comp. XO) (Oven Control XO) (Oven Control XO) (Double Oven XO) Rubidium Osc. Output 10 MHz, Sine 0.5Vrms, 50 Ω 10 MHz, Sine 0.5 Vrms, 50 Ω 10 MHz, Sine 0.5 Vrms, 50 Ω 10 MHz, Sine 0.5 Vrms, 50Ω 10 MHz, Sine 0.5 Vrms, 50 Ω Short Term Stab. 1s 10s 100s 1 E-9 5 E-10 5 E-10 1E-11 1E-11 1E-10 5E-12 1E-11 1E-11 5E-12 1E-11 1E-11 3E-11 7E-12 3E-12 Phase Noise, 1Hz 100Hz 1000Hz - 55 dbc/hz -115 dbc/hz -130 dbc/hz - 80 dbc/hz -135 dbc/hz -145 dbc/hz - 90 dbc/hz -135 dbc/hz -145 dbc/hz - 90 dbc/hz -135 dbc/hz -145 dbc/hz -75 dbc/hz -125 dbc/hz -145 dbc/hz Aging/Day/Month/Year --- 5E-7/yr 5E-10/day 2E-7/yr 2E-10/day 2E-8/yr 2E-10/day 2E-8/yr 5E-11/day 5E-10/yr Temp Range Frequency Stability 0 to 75 C 5E-7 0 to 75 C 2E-8* 0 to 75 C 2E-9* 0 to 70 C 2E-10 0 to 60 C 3E-10 Power Consumption Warm-up Time 50 miliwatts 50 milisec 2 watts 10 min, 1E watts 10 min, 1E watts 10 min, 1E-8 8 watts 4 min, ~1E-9 Magnetic Field Sensitivity Input Volts Range Supply Volts Sensitivity Vdc± 0.25% 1E-8 for /-10% Vdc± 10% Vdc± 10% Vdc± 10% 2E-11/Gauss 15 to 28 Vdc 1E-9 for /-10% 1E-9 for /-10% 1E-9 for /-10% 2E-11 for /-10% Size Volume Weight 1.0 x 0.7 x 0.22 H in 3 < 0.1 lbs 1.5 x 1.5 x 0.5 H in 3 < 0.15 lbs 2.0 x 2.0 x 0.75 H 3 in 3 < 0.22 lbs 2.0 x 2.0 x 1.0 H 4 in 3 < 0.3 lbs 3.0 x 3.0 x 1.4 H 13 in lbs * With GPS learning algorithm, X20 improvement 36