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© 2014 Microsemi Corporation. COMPANY PROPRIETARY 1 Power Matters. TM Fundamentals of Frequency Reference Oscillators Paul R. Gerry Senior Product Manager, Clocks BU
Power Matters. TM 2 © 2014 Microsemi Corporation. COMPANY PROPRIETARY For Frequency Generation You need… The Earth rotating A pendulum (mechanical oscillator) Electronic Oscillator … a method of generating a repeatable event Atomic resonance
Power Matters. TM 3 © 2014 Microsemi Corporation. COMPANY PROPRIETARY What is Frequency Frequency = the number of cycles per second Ideal frequency source generates a pure, repeatable sine wave Frequency = the number of cycles per second Ideal frequency source generates a pure, repeatable sine wave
Power Matters. TM 4 © 2014 Microsemi Corporation. COMPANY PROPRIETARY 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. TM 5 © 2014 Microsemi Corporation. COMPANY PROPRIETARY 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, semi- conductor and white noise
Power Matters. TM 6 © 2014 Microsemi Corporation. COMPANY PROPRIETARY What is Frequency Stability & Accuracy Courtesy John Vig
Power Matters. TM 7 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Oscillator Stability Over Time Frequency stability typically improves in the short term, stabilizes, then becomes less predictable in the long term
Power Matters. TM 8 © 2014 Microsemi Corporation. COMPANY PROPRIETARY 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. TM 9 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Taking Frequency Measurements Frequency measurements are performed over a time interval: t 1 to t 2 : Signal 1 = Signal 2 t 1 to t 3 : Signal 2 is more stable than Signal 1 Frequency measurements are performed over a time interval: t 1 to t 2 : Signal 1 = Signal 2 t 1 to t 3 : Signal 2 is more stable than Signal 1
Power Matters. TM 10 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Short and Long Term Oscillator Stability Some oscillators perform better short term… others long term
Power Matters. TM 11 © 2014 Microsemi Corporation. COMPANY PROPRIETARY What is Phase Noise Unwanted noise sidebands on either side of the output signal center frequency caused by random variations of the frequency and the phase of the carrier
Power Matters. TM 12 © 2014 Microsemi Corporation. COMPANY PROPRIETARY What is Single Side Band Phase Noise The SSB is defined as the ratio of power in one phase modulation sideband to the total signal power
Power Matters. TM 13 © 2014 Microsemi Corporation. COMPANY PROPRIETARY What is Oscillator Phase Noise Phase noise is a short term noise component indicative of the spectral purity of an oscillator signal
Power Matters. TM 14 © 2014 Microsemi Corporation. COMPANY PROPRIETARY What is one part in 1.0E-10 ? (As in 1 x /day aging) ~1/2 cm out of the circumference of the Earth. ~1/4 second per human lifetime (of ~80 years). Power received on Earth from a GPS satellite, -160 dBW, is as “bright” as a flashlight in Los Angeles when viewed in New York City, ~5000 km away What is -170 dB? (As in -170 dBc/Hz phase noise) -170 dB = 1 part in 1017 ~thickness of a sheet of paper out of the total distance traveled by all the cars in the world in a day Putting the Fundamentals into Perspective… The second is the most precise SI unit of measure!
Power Matters. TM 15 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Frequency Sources Types Quartz Crystal Oscillators Atomic Frequency Standards Emerging Clock Technologies
Power Matters. TM 16 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Crystal Oscillator Types Temperature Sensor Temperature Sensor Compensation Network or Computer Compensation Network or Computer XO Temperature Compensated (TCXO) C +1 ppm -1 ppm C T Oven control Oven control XO Temperature Sensor Temperature Sensor Oven Oven Controlled (OCXO) C +1 x x C T Voltage Tune Output Crystal Oscillator (XO) C -10 ppm +10 ppm 25 0 C T C
Power Matters. TM 17 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Atomic Frequency Standards
Power Matters. TM 18 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Atomic Clock Technologies Rubidium Gas Cell:6,834,682, Hz Cesium Beam: 9,192,631,770 Hz Hydrogen Maser: 1,420,405, Hz Fountains use cesium, rubidium Stored Ions use mercury, ytterbium Optical Clocks use mercury, calcium The resonant frequency of atoms does not age… the apparatus to interrogate or confine atoms can in some atomic clocks
Power Matters. TM 19 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Atomic (Passive) Clock Basics Stimulate an energy state change in the atoms Detect when resonant frequency is achieved Servo the oscillator to maintain optimal performance
Power Matters. TM 20 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Cesium Technology is considered the most comprehensive holdover option against GNSS vulnerabilities Exhibit no frequency drift Maintains 5x 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 Cesium Technology Applications
Power Matters. TM 21 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Rubidium Frequency Standards (Lamp)
Power Matters. TM 22 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Rubidium Frequency Standards (CPT) 10 MHz VCXO synthesizes 3.4 GHZ microwaves Microwave frequency is locked to CPT resonance signal stabilizing the output to 10 MHZ Jinquan Deng, Peter Vlitas, Dwayne Taylor, Larry Perletz, and Robert Lutwak, "A COMMERCIAL CPT RUBIDIUM CLOCK“ EFTF 2008 Toulouse, France. Coherent Population Trapping (CPT) interrogation of Rubidium Laser diode (VCSEL) modulated to achieve CPT resonance Photodiode detects the CPT resonance The MAC uses Coherent Population Trapping (CPT)
Power Matters. TM 23 © 2014 Microsemi Corporation. COMPANY PROPRIETARY 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. TM 24 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Emerging Clock Technologies Fountain Clocks Atoms are cooled and “tossed” upward in Earth’s gravity Used for primary standards where ultimate accuracy is desired Coherent Population Trapping Clocks: Miniature Atomic Clocks (MAC) & CSAC Ultra miniature size and low power requirement-SWaP Optical clocks relying upon optical atomic transitions
Power Matters. TM 25 © 2014 Microsemi Corporation. COMPANY PROPRIETARY 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. TM 26 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Hierarchy of Oscillator Types * Sizes range from 30 liters for Cs standards Costs range from $50,000 for Cs standards ** Including environmental effects (e.g., -40 o C to +75 o C) and one year of aging Oscillator Type*Accuracy**Typical Applications Crystal oscillator (XO) Temperature compensated crystal oscillator (TCXO) Microcomputer compensated crystal oscillator (MCXO) Oven controlled crystal oscillator (OCXO) Small atomic frequency standard (Rb, MAC, CSAC) High performance atomic standard (Cs) to to (with per g option) to Computer timing Frequency control in tactical radios Spread spectrum system clock Navigation system clock & frequency standard, MTI radar C 3 satellite terminals, bistatic, & multistatic radar, T&M Communications Strategic C 3, EW
Power Matters. TM 27 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Frequency and Time Relationship
Power Matters. TM 28 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Time is Derived from Frequency Every clock ever made is an oscillator + a counter The 1 pulse-per-second (PPS) is the epoch or definition of the on-time marker of a clock Further counting of the 1PPS is used to keep track of seconds, minutes, hours, days, and years OSC Counter 1PPS Clock 1PPS rising edge is typically on-time: HH:MM:SS
Power Matters. TM 29 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Accumulated Time Error in Oscillators Clock operating from an OCXO with an offset & aging of 5E-10 and a temperature error of 1 degree C Oscillator errors accumulate impacting clock performance
Power Matters. TM 30 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Cesium Time Error Due to Offset Time error = Freq offset * seconds/day Or 2E-12 x 86400s = ~0.2µs / day Cesium atomic oscillators do not age
Power Matters. TM 31 © 2014 Microsemi Corporation. COMPANY PROPRIETARY GPS Disciplining Phase Plot If we look at the phase error over time we can see just how the Stability and Accuracy are linked Oscillator is key to improving GPS clock performance
Power Matters. TM 32 © 2014 Microsemi Corporation. COMPANY PROPRIETARY Ramki Ramakrishnan Director of Marketing & Business Dev, Clocks BU Thank You Paul R. Gerry Senior Product Manager, Clocks BU Steve Fossi VP and General Manager, Clocks BU
Power Matters. TM 33 © 2014 Microsemi Corporation. COMPANY PROPRIETARY References NIST USNO JPO Time and Frequency User's Manual, National Bureau of Standards Special Publication 559, U.S. Government Printing Office, Washington, DC, 1979
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