Tutorial: Quartz Crystal Oscillators & Phase- Locked Loops

Transcription

1 Tutorial: Quartz Crystal Oscillators & Phase- Locked Loops Greg Armstrong (IDT) Dominik Schneuwly (Oscilloquartz) June 13th,

2 Content 1. Quartz Crystal Oscillator (XO) Technology Quartz Crystal Overview Ageing and Temperature XO, TCXO, OCXO, DOCXO 2. Phase Locked Loops (PLL) PLL Overview Response To Injected Noise 3. PLL with 2 inputs 2

3 1. Quartz Crystal Oscillator (XO) Technology 3

4 Quartz Crystal Quartz = SiO 2 Pink = silicon atoms Blue = oxygen atoms Piezo-electric effect: Mechanical strain voltage Inverse Piezo-electric effect: Voltage mechanical deformation = Silicon atom = Oxigen atom 4

5 Vibration Modes, Resonance Frequency, High Q, Cutting Orientation Flexure Mode Extensional Mode Face Shear Mode Thickness Shear Mode Fundamental Mode Thickness Shear Third Overtone Thickness Shear 5

6 Fractional frequency deviation [1] Frequency Drift Due to Ageing Frequency vs. Temperature 3E-10 2E-10 1E E-10 Positive ageing Ageing reversal SC-cut: Θ = 34 Φ = 22 Δf/f as a function of temperature (parameter: ΔΘ = deviation from reference angle) - 2E-10-3E-10 Negative ageing Time [day] Lower Turnover Point (LTP) Inflection Point (IP) Upper Turnover Point (UTP) 6

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

8 Heating Heating 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 DOCXO, Double Oven Controlled XO: Two temperature controlled ovens, one inside the other. 5E-11 to 5E-9 over [-30 C to 60 C] Outer Oven Inner Oven Temp. Control XO Temp. Control Temp. Control XO Temp. Sensor Temp. Sensor Temp. Sensor 8

9 Summary Oscillator type Temperature sensitivity (fractional frequency vs temperature) XO 1E-7 / C TCXO 5E-8 to 5E-7 [-55 C to 85 C] OCXO 5E-9 to 5E-8 [-30 C to 60 C] DOCXO 5E-11 to 5E-9 [-30 C to 60 C] 9

10 2. Phase-Locked Loops (PLL) 10

11 PLL: Working principle uin () 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 OUT uk C V 0 xin t IN t u ( t) A sin 2 t A sin 2 IN NOM 0, IN NOM xou T t O t uout ( t) A sin 2 t A sin 2 UT 0, OUT 11

12 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 DAC & LPF ν OUT ν OSC Replaces the VCO! Free-running Oscillator DAC = Digital-to-Analog Converter LPF = Low-pass Filter OUT M N 2 where M N OUT OSC output of the digital loop filter (integer) size of the counter in bits (integer) OSC frequency of output signal u OUT t free-run frequency of the oscillator 12

13 PLL with Digitally Controlled Oscillator Free-running Oscillator ref(t) PFD & TDC Digital Loop Filter Digitally Controlled Oscillator (DCO) out(t) Divider PFD Phase & Frequency Detector TDC Time-to-Digital Converter 13

14 PLL with VCO, DDS, and DCO compared Pros Cons PLL with VCO PLL with DDS Very low phase noise Configurable pull-in range Requires only free-running oscillator PLL s pull-in range depends on VCO s pulling range Requires VCO Some quantization phase noise PLL with DCO Fully programmable Configurable pull-in range Configurable low pass filter range Requires only free-running oscillator Requires APLL to clean up jitter Precision of TDC affects close-in phase noise 14

15 PLL Response to Injected Noise Oscillator Transfer function «Input-to-Output» Phase Noise (In) PD LPF DCO Phase Noise (Out) Phase Noise (Out) Phase Noise (In) F L Transfer function «Oscillator-to-Output» Phase Noise (Oscillator) Ref (In) PD LPF DCO Phase Noise (Out) Phase Noise (Out) Phase Noise (Osc) F H 15

16 PLL: Jitter & Wander filtering x IN (t) [s] x OUT (t) [s] 1 x x t [s] - 5 x x

17 3. PLL with 2 Inputs 17

18 Imagine the following: Phase Noise (In2) PD LPF DCO Phase Noise (Osc2) Phase Noise (Out2) Phase Noise (Out2) Phase Noise (In2) Phase Noise (Out2) Phase Noise (Osc2) F 2 Phase Noise (In1) Phase Noise (Osc1) PD LPF DCO Phase Noise (Out1) Phase Noise (Out1) Phase Noise (In1) Phase Noise (Out1) Phase Noise (Osc1) F 1 18

19 What do the transfer functions look like? Phase Noise (In2) PD LPF DCO Phase Noise (Osc2) Phase Noise (Out2) F 1 F 2 Phase Noise (In1) PD LPF DCO Phase Noise (Out) 19

20 Imagine three spectral densities (phase-time): (log-log scales) IN 1 IN 2 OUT OSC S IN1 (f) S IN2 (f) S OSC (f) f [Hz] 20

21 combined by the 2 input PLL: (log-log scales) S OUT (f) IN 1 IN 2 OSC OUT f [Hz] 21

22 Physical Layer Support for Telecom Boundary Clock G calls for Telecom Boundary Clock (T-BC) to use the physical layer as the basis for the PTP clock frequency G

23 SyncE + IEEE 1588 Filtering in Combination SyncE Noise (In) PD 1.1Hz LPF DCO SyncE (Out) A band-pass filter for SyncE Noise Amplitude, db TCXO Frequency, Hz offsetfrommaster 92mHz LPF DCO PTP (Out) PTP Stack Time Stamp Unit (TSU) PTP Network Very little PDV PRTC T-GM T-BC1 T-BC2 T-BC9 End App. 23

24 Oscillator Phase Drift (ns) Response (ns) Response to Oscillator Drift (Noise) Loop Response to Oscillator Drift 6,000 3,000 Oscillator drift on this axis 5, Hz Loop Response Alone 2,500 Loop response on this axis 4,000 2,000 3,000 Oscillator Drift 1,500 EEC1 Osc Drift (Variable Temp) 0.1Hz Loop Response Combo Response with 1.7Hz SyncE Combo Response with 7Hz SyncE 2,000 1,000 1 μs 1, Hz Loop Response with BPF Time (s) First order PLL responses 24

25 Thank You Analog Mixed Signal Product Leadership in Growth Markets 25