Quartz Crystal Oscillators and Phase Locked Loops. Dominik Schneuwly Yves Schwab

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1 Quartz Crystal Oscillators and Phase Locked Loops Dominik Schneuwly Yves Schwab Ed D. Schneuwly Slide 1

2 Content 1. Quartz Crystal Resonator Technology Quartz, crystal lattice and piezo-electric effect Vibration modes and equivalent circuit Cuts Ageing mechanisms 2. Quartz Crystal Oscillator (XO) Technology TCXO MCXO OCXO DOCXO 3. XO Performance vs. Telecom Requirements Frequency holdover Phase holdover 4. Phase Locked Loops (PLL) Ed D. Schneuwly Slide 2

3 1. Quartz Crystal Resonator Technology Ed D. Schneuwly Slide 3

4 Quartz Crystal Quartz = SiO 2 Pink = silicon atoms Blue = oxygen atoms Quartz lattice Ed D. Schneuwly Slide 4

5 Cuts Small disks are cut out of the crystal at given angles. Z z z X y y Y x Single rotated cut (e.g. AT-cut) x Double rotated cut (e.g. SC-cut) Ed D. Schneuwly Slide 5

6 Cuts Angle accuracy: + 10 (for SC-cut) Ed D. Schneuwly Slide 6

7 Vibration Modes Flexure Mode Extensional Mode Face Shear Mode Thickness Shear Mode Fundamental Mode Thickness Shear Third Overtone Thickness Shear Ed D. Schneuwly Slide 7

8 Piezo-electric Effect Piezo-electric effect: Mechanical strain voltage Voltage mechanical deformation = Silicon atom = Oxigen atom Ed D. Schneuwly Slide 8

9 Piezo-electric Effect Strain Axis Field Axis & Mode (A) (B) (C) x x x y x y z y Ed D. Schneuwly Slide 9

10 Equivalent Circuit C 0 L 1 R 1 C 1 Vibration mode 1 L 2 R 2 C 2 Vibration mode 2 L 3 R 3 C 3 Vibration mode 3 Ed D. Schneuwly Slide 10

10 Frequency [MHz] Frequency [MHz] Note: Exaggerated resistance

11 Admittance [mho] Arg(Admittance) [rad] Admittance Y(f) Y(f) Arg ( Y(f) ) 1E-2 1E-3 2 /2 1 1E-4 1E-5 0 1E-6-1 /2 1E Frequency [MHz] Frequency [MHz] Note: Exaggerated resistance values R 1, R 2 and R 3 for better readability Ed D. Schneuwly Slide 11

12 Quartz Crystal Oscillator (XO) L R C I IN G U IN = 0 U OUT = G I IN Open Loop Gain: H G Y G 1 j L R j C 1 1 If G and 0 then H 0 1 R LC 0 f0 resonance frequency 2 Ed D. Schneuwly Slide 12

Fractional frequency deviation [1] Frequency Drift Due to Ageing 3E-10 2E-10 Positive ageing 1E-10

13 Fractional frequency deviation [1] Frequency Drift Due to Ageing 3E-10 2E-10 Positive ageing 1E E-10 Ageing reversal - 2E-10-3E Time [day] Negative ageing Ed D. Schneuwly Slide 13

14 Ageing Mechanisms Mass transfer due to contamination (e.g. electrode metal atoms into the crystal Stress relief in the resonator's mounting and bonding structure, electrodes, and in the quartz Other mechanisms: 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 Ed D. Schneuwly Slide 14

BVA Resonator Electrodes not in direct contact with the resonator body contamination of the resonator body is stopped Ageing improves by a factor of 10 or

15 BVA Resonator Electrodes not in direct contact with the resonator body contamination of the resonator body is stopped Ageing improves by a factor of 10 or more Other performance parameters improve also (Q, temperature sensitivity, phase noise, etc.) Courtesy Jean-Pierre Aubry Ed D. Schneuwly Slide 15

16 AT-cut Resonator AT-cut: Θ = 35 Φ = 0 Δf/f as a function of temperature (parameter: ΔΘ = deviation from reference angle) Lower Turnover Point (LTP) Inflection Point (IP) Upper Turnover Point (UTP) Ed D. Schneuwly Slide 16

17 SC-cut Resonator SC-cut: Θ = 34 Φ = 22 Δf/f as a function of temperature (parameter: ΔΘ = deviation from reference angle) Lower Turnover Point (LTP) Inflection Point (IP) Upper Turnover Point (UTP) Ed D. Schneuwly Slide 17

18 SC- versus AT-cut Advantages of the SC-cut Thermal transient compensated (allows faster warm-up OCXO) Static and dynamic f(t) allow higher stability OCXO Planar stress compensated; lower f due to edge forces and bending Better f(t) repeatability allows higher stability OCXO (less f for oscillator reactance changes) Lower drive level sensitivity Higher Q for fundamental mode resonators of similar geometry Higher capacitance ratio (less f for oscillator reactance changes) Less sensitive to plate geometry - can use wide range of contours Far fewer activity dips Lower sensitivity to radiation Disadvantages of the SC-cut More difficult to manufacture Ed D. Schneuwly Slide 18

19 2. Quartz Crystal Oscillator (XO) Technology Ed D. Schneuwly Slide 19

20 XO Categories rel. Temp. Control XO, Crystal Oscillator: LTP centered in the operation temperature range > 1E-7 / C Ed D. Schneuwly Slide 20

21 XO Categories rel. Temp. Control TCXO, Temperature Compensated XO: Resonance frequency is modified by a varactor diode so as to compensate temperature sensitivity 5E-8 to 5E-7 over [-55 C to 85 C] Temp. Sensor Temp. Control U CONTROL Ed D. Schneuwly Slide 21

22 XO Categories rel. Temp. Control MCXO, Microcomputer Compensated XO: Dual mode oscillator generating fundamental (f 1 ) and third overtone (f 3 ). Difference between f 3 and 3 x f 1 is used to measure temperature and compensate temperature sensitivity of f 3. f 1 x 3 3 x f 1 f C = 3 x f 1 - f 3 ~ Temp. -1 Mixer Temp. Control Synthesizer f OUT f 3 Ed D. Schneuwly Slide 22

23 Heating XO Categories rel. Temp. Control OCXO, Oven Controlled XO: A control loop maintains the oven containing the XO at (nearly) constant temperature. 5E-9 to 5E-8 over [-30 C to 60 C] Oven Temp. Control XO Temp. Sensor Ed D. Schneuwly Slide 23

24 Heating Heating XO Categories rel. Temp. Control DOCXO, Double Oven Controlled XO: Two temperature controlled ovens, one inside the other. 2E-10 to 5E-9 over [-30 C to 60 C] BVA resonator: 1E-10 over [-30 C to 60 C], 5E-11 over [-15 C to 60 C] Outer Oven Inner Oven Temp. Control Temp. Control XO Temp. Sensor Temp. Sensor Ed D. Schneuwly Slide 24

25 Typical XOs SOCXO: DOCXO: BVA-DOCXO: mm Ed D. Schneuwly Slide 25

26 3. XO Performance vs. Telecom Requirements Ed D. Schneuwly Slide 26

27 Frequency Holdover Autonomy How long can the SSU stay in holdover mode until the MTIE hits the Network Limit for PRC-traceable SSU outputs (G.823)? Ed D. Schneuwly Slide 27

28 Frequency Holdover Autonomy Holdover autonomy for different oscillator types and for different temperature conditions (temp. change during holdover): Const. Temp. OCXO 1 DOCXO 2 BVA- DOCXO 3 Rb 4 9 h 21 h 51 h 9 days 2 C 1.4 h 17 h 46 h 5.5 days 5 C 30 min 13 h 39 h 67 h 10 C 15 min 8.3 h 31 h 33 h Notes: 1) OSA ) OSA ) OSA ) TNT RMO Ed D. Schneuwly Slide 28

29 Fractional Frequency Deviation Due to Temperature Variations [1] Phase Holdover Autonomy (e.g. 1PPS) Holdover Autonomy T of cdma2000 Base Stations Temperature variation: + 10 C Criterion: phase-time accumulation < 7 microseconds T = 6 h T = 12 h T = 24 h T = 48 h T = 72 h 1.0E-09 DOCXO 1.0E-10 Rb BVA-DOCXO 1.0E E E E E E-08 Frequency Drift Due to Ageing [1/day] Ed D. Schneuwly Slide 29

30 4. Phase Locked Loops (PLL) Ed D. Schneuwly Slide 30

31 PLL: Working principle u () IN t Phase Comparator Loop Filter P P NOM IN OUT u K x x uc() t up t g t Voltage Controlled Oscillator uout () t 0 OUT uk C V x IN t IN t u ( t) Asin 2 t Asin 2 IN NOM 0, IN NOM xou T t O t uout ( t) Asin 2 t Asin 2 UT 0, OUT Ed D. Schneuwly Slide 31

32 Phase-time deviation x(t) nominal signal sin 2 actual signal sin 2 x(t 1 ) NOM NOM t x t t t t 1 t 1 + x(t 1 ) Ed D. Schneuwly Slide 32

PLL: Transfert function IN OUT ht H s u t u t h t OUT U s U s H s IN where impulse response transfer function 20 log H j 2 f [db] Laplace h t 20 10-5 10-4 10-3

33 PLL: Transfert function IN OUT ht H s u t u t h t OUT U s U s H s IN where impulse response transfer function 20 log H j 2 f [db] Laplace h t f [Hz] Red curve = PLL transfer function Blue curve = transfer function for oscillator noise Ed D. Schneuwly Slide 33

PLL: Jitter filtering x IN (t) [s] x OUT (t) [s] 1 x 10-6 5 x 10-7 0

34 PLL: Jitter filtering x IN (t) [s] x OUT (t) [s] 1 x x t [s] - 5 x x Ed D. Schneuwly Slide 34

35 PLL with Direct Digital Synthesis Phase Comparator Loop Filter M Counts from 0 to 2 N -1 in steps of M Sine Look-up Table Digital-to- Analog Converter ν OUT ν OSC Replaces the VCO! Free-running Oscillator OUT where M M N 2 N output of the digital loop filter (integer) size of the counter in bits (integer) frequency of output signal u Ed D. Schneuwly Slide 35 OUT OSC OSC OUT t free-run frequency of the oscillator

36 PLL with VCO and with DDS compared PLL with VCO PLL with DDS Pros Very low phase noise Configurable pull-in range Requires only freerunning oscillator Cons PLL s pull-in range depends on VCO s pulling range Requires VCO Some quantization phase noise Ed D. Schneuwly Slide 36

37 Thank you Ed D. Schneuwly Slide 37

Fundamentals: Frequency & Time Generation

Fundamentals: Frequency & Time Generation Dominik Schneuwly Oscilloquartz SA slide 1 v.1.0 24/10/12 SCDO Content 1. Fundamentals 2. Frequency Generation Atomic Cesium Clock (Cs) Rubidium Oscillator (Rb)