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Accubeat - Atomic Clock

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For UK Business please contact Melcom Electronics.
T: +44 (0)1932 565544
E: melcomsales@melcom.co.uk
AccuBeat Ltd. designs, develops and manufactures highly accurate Rubidium Frequency Standard, GPS-Rubidium Clocks and Time & Frequency control products. The products provide frequency accuracy in the range of 10-12, frequency stability in the range of 10-13 and time accuracy in the range of nanoseconds.

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Accubeat - Atomic Clock

  1. 1. Atomic Clocks . 1 Time and Frequency 9/20/2007
  2. 2. What is an Atomic Clock? The Most Accurate Man Made Machine! The Atom is the Pendulum of the Clock 1 second in 1000’’s years (Rb) 1 second in 3 million years for Cs fountain Based on a quantum transition which occurs in the atom E 2 E 1 Planck’s law E 1 - E 2 = h 2 Time and Frequency 9/20/2007
  3. 3. Stability of Passive Atomic Standards Internal 5 (10) MHz Atomic Resonator Crystal Oscillator Output: 5 or 10 MHz Error Signal The RF output (5 or 10MHz) is derived from the Crystal Oscillator. On the short term (t tl) the output follows the Crystal Oscillator. On the long term (t tl) the output follows the Atomic Resonator. tl = loop time constant. For Rb: tl =10 to100msec, for Cs: tl =100ms to 1s. This transition of stability from the Crystal to the Atomic Resonator is seen in Phase-Noise and Allan Deviation plots. The same happens for Vibration/Acceleration Sensitivity: For fast acceleration, the Crystal determines the output, and for slow acceleration the Atomic Resonator counts. 3 Time and Frequency 9/20/2007
  4. 4. AccuBeat’’s Digital Loop 10 MHz 6.84 GHz Multiply DDS Atomic Resonator Preamp Micro Processor OCXO DAC RxD, TxD 10 MHz 4 Time and Frequency 9/20/2007
  5. 5. Lamp Rb87 Filter Cell Rb85 Rb Vapor Cell Principles - 1 Microwave Res. Cell Rb87 Photo- Diode 52P1/2 Same difference F=2 52S1/2 F=1 6.834 GHz 3.045 GHz 85Rb 87Rb 52P1/2 F=2 52S1/2 F=1 3 2 1 1. Light from 87Rb lamp contains both 1-3 and 2-3 lines. 2. 85Rb Cell filters out the 2-3 line and transmits the 3-1 line 5 Time and Frequency 9/20/2007
  6. 6. Lamp Rb87 Filter Cell Rb85 Rb Vapor Cell Principles - 2 Microwave Res. Cell Rb87 Photo- Diode Level 3 52P1/2 Level 2 52S1/2 Level 1 Process in Resonance Cell 6.83… GHz Rb87 Microwave stimulated emission 1. The filtered light “optically pumps” 87Rb atoms in the Resonance Cell from level 1 to 3. Optical pumping 2. The injected microwave frequency at 6.84..GHz induces transition from level 2 to 1. 3. When the injected frequency matches the difference 2-1, the photo-diode detects a reduction in the amount of transmitted light. 6 Time and Frequency 9/20/2007
  7. 7. Vapor Cell Atomic Clock Magnetic shield “C-Field” Absorption cell Light 87Rb lamp rf lamp exciter 85Rb + buffer Filter Cell gas Power supplies for lamp, filter and absorption cell thermostats Rb-87 + buffer gas Cavity Photo cell Detector output C-field power supply Frequency input 6.834,685 GHz 7 Time and Frequency 9/20/2007
  8. 8. y()) Log ( -9 -10 -11 -12 -13 Short-Term-Stability of Passive Atomic Standards Example: Rubidium Standard Rubidium Resonator OCXO -1 -1/2 0 +1/2 -2 -1 0 1 2 3 4 5 6 7 Log (), seconds For times shorter than the Loop Time Constant the stability follows the OCXO For times longer than the Loop Time Constant the stability follows the RUBIDIUM resonator 8 Time and Frequency 9/20/2007
  9. 9. Rubidium Performance Summary Miniature Oscillators: 18mm, 150cc Low Aging: 2x10-10 / Year Wide Temp. Range: -40°C to +78°C (+85°C) Temp. Stability: 5x10-11 / 0 to 50°C Low Phase Noise 150dBc/Hz (floor) Digital Freq. Cntrl: 7x10-13 steps Hold-Over, Noise Reduction Smart Clocks: High Reliability: 261,000 Hrs at 25°C 9 Time and Frequency 9/20/2007
  10. 10. DELTA F Frequency Drift Example Aging S/N 402 @ room temperature: (22+/-6) deg C, against house Rb y = 3E-13x + 9E-11 R2 = 0.1856 8.00E-11 6.00E-11 4.00E-11 2.00E-11 0.00E+00 -2.00E-11 -4.00E-11 -6.00E-11 0 10 20 30 40 50 60 70 80 90 DAYS 10 Time and Frequency 9/20/2007
  11. 11. Time Drift Example (Rubidium) 11 Time and Frequency 9/20/2007
  12. 12. Types of Atomic Standards Atomic Frequency Q Principle of Operation Stability Optical pumping and transition 10-9 – 10-11 6.8GHz 107 detection in a Rb vapor cell Detection of Cs beam 10-11– 10-14 9.2GHz 108 trajectories in a magnetic field in a vacuum 1.4GHz 10GHz 9.2GHz Rubidium Vapor Cell Cesium Beam 109 1011 1012 Self-sustaining microwave 10-12– 10-15 oscillator at the atomic H freq. Trapping ions in an electric field 10-14– 10-16 for longer interrogation and for reducing motion Cooled atoms (Cs, Rb) are tossed 10-15– 10-17 up and fall down slowly for longer interrogation Hydrogen Maser Trapped Ions Atomic Fountain 12 Time and Frequency 9/20/2007
  13. 13. y()) Log ( -9 -10 -11 -12 -13 -14 -15 -16 Short Term Stability Ranges of Various Frequency Standards Rubidium Quartz Hydrogen Maser Cesium -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 Log (), seconds 1 day1 month 13 Time and Frequency From Dr John V9ig/2T0u/t2o0ri0al7
  14. 14. Oscillator Comparison Quartz Oscillators Atomic Oscillators Accuracy * (per year) Aging/Year Temp. Stab. (range, 0C) Stability, y() ( = 1s) Size (cm3) Warmup Time (minutes) Power (W) (at lowest temp.) Price (~$) TCXO 2 x 10-6 5 x 10-7 5 x 10-7 (-55 to +85) 1 x 10-9 10 0.03 (to 1 x 10-6) 0.04 10 - 100 OCXO 1 x 10-8 5 x 10-9 1 x 10-9 (-55 to +85) 1 x 10-12 20-200 4 (to 1 x 10-8) 0.6 200-2,000 Rubidium 5 x 10-10 2 x 10-10 3 x 10-10 (-55 to +71) 3 x 10-12 100-800 3 (to 5 x 10-10) 7-20 2,000-8,000 Cesium 2 x 10-11 0 2 x 10-11 (-28 to +65) 5 x 10-11 6,000 20 (to 2 x 10-11) 30 30,000-50,000 Rb+GPS 1 x 10-13 1 x 10-13 Stable T: 1 x 10-13 3 x 10-12 2000 15 15-20 5000-10000 * Including environmental effects (note that the temperature ranges for Rb and Cs are narrower than for quartz). COURTESY OF DR. JOHN VIG 14 Time and Frequency 9/20/2007

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