This document discusses measuring jitter using phase noise techniques. It begins with an overview of jitter and phase noise concepts. It then describes how jitter can be measured in the time domain using an oscilloscope and in the frequency domain using a phase noise analyzer. It explains how phase noise measurements can be used to derive random and deterministic jitter. The document provides examples of measuring very low jitter signals and calculating jitter contributions from phase noise spurs. It concludes with a discussion of calculating peak-to-peak jitter from RMS jitter measurements and references for further information.

1. Measuring Jitter using
Phase Noise Techniques

2. Agenda
• Jitter Review
• Time-Domain and Frequency-Domain Jitter Measurements
• Phase Noise Concept and Measurement Techniques
• Deriving Random and Deterministic Jitter from Phase Noise
• PLL/Filter Weighting of Jitter Spectrum
• Calculating Peak-to-Peak Jitter from RMS Jitter
• Useful References
Phase Noise and Jitter Measurements | 2

3. What is J ii tt tt e rr ?
J
e
• Jitter is the short-term time-domain
variations in clock or data signal timing
• Jitter includes instability in signal period, frequency, phase,
duty cycle or some other timing characteristic
• Jitter is of interest from cycle to cycle, over many
consecutive cycle, or as a longer term variation
• Jitter is equivalent to Phase Noise in the frequency domain
• Variations with frequency components >10Hz are Jitter
• Variations with frequency components <10Hz are Wander
Phase Noise and Jitter Measurements | 3

4. Types of Jitter
• Time Interval Error (TIE)
• Fundamental measurement of jitter
• Time difference between measured
signal edge and ideal edge
• Instantaneous phase of signal
• Period Jitter
• Short-term stability, basic parameter for clocks
• Cycle to Cycle
• Important for parallel data transfer
• N-Cycle
• Important when clock and data routing differ
Phase Noise and Jitter Measurements | 4

5. Jitter Measurement Techniques
• Time Domain (Oscilloscope)
•
•
•
•
•
Direct method for measuring jitter
Measures TIE, Period Jitter, Cycle-to-Cycle Jitter
Measures RMS or Peak-to-Peak Jitter
Measures data or clock signals
Limited sensitivity (100 – 1000 fs)
• Frequency Domain (Phase Noise Analyzer)
•
•
•
•
•
Calculates jitter from phase noise
Measures RMS Jitter
Measures clocks, not random data streams
Easy to separate random and discrete jitter components
Highest sensitivity (<5 fs)
Phase Noise and Jitter Measurements | 5

6. What is Phase Noise?
• Ideal Signal (noiseless)
V(t) = A sin(2
t)
Level
where
t
A = nominal amplitude
= nominal frequency
f
Time Domain
• Real Signal
V(t) = [A + E(t)] sin(2
Frequency Domain
t + (t))
Level
where
E(t) = amplitude fluctuations
(t) = phase fluctuations
t
Phase Noise is unintentional phase modulation that spreads the
signal spectrum in the frequency domain.
Phase Noise is equivalent to jitter in the time domain.
Phase Noise and Jitter Measurements | 6
f

7. Phase Noise – Unit of Measure
• Phase Noise is expressed as L(f)
• L(f) is defined as single sideband power due to
phase fluctuations in a rectangular 1Hz bandwidth
at a specified offset, f, from the carrier
• L(f) has units of dBc/Hz
LOG A
L (f)
AMPLITUDE
LOG f
1 Hz
fc
Phase Noise and Jitter Measurements | 7
fc+f
FREQUENCY

8. Phase Noise Measurement Setup
Clock
Under
Test
Usually Type-N or SMA
connector
Can easily adapt to BNC
Phase Noise and Jitter Measurements | 8

9. Measurement using a Probe
l Provides a means to measure signals within a circuit where no
l
l
l
l
connection point is available
Usually used for troubleshooting, not accurate measurements
Also called an RF Sniffer
Pros: Simple, cheap, and easy to make
Cons: Loads circuit
Simple RF Sniffer
(semi-rigid coax)
Phase Noise and Jitter Measurements | 9

10. Better Measurement using a Probe
l Active scope probe with Probe Adapter
l Probe/Adapter powered by USB cable
l Adapter stores factory probe calibration and provides offset info to
spectrum analyzer (via USB)
l Much less loading effect than simple RF Sniffer
l Useful to 3GHz
+
RT-ZS30 Active
Scope Probe

RTO-ZA9 Probe
Adapter
Phase Noise and Jitter Measurements | 10

11. RJ and DJ Histograms on an Oscilloscope
• Random jitter (RJ) measured on scope shows a Gaussian
distribution
• Relatively easy to derive RMS and Peak-to-Peak jitter
• When deterministic jitter (DJ) is also present the Gaussian curve
forms two (or more) peaks
• Extracting RJ and DJ contributions is more difficult
Jitter Histogram – RJ only
Phase Noise and Jitter Measurements | 11
Jitter Histogram – RJ and DJ

12. Phase Noise (dBc/Hz) 
Example Phase Noise Measurement Plot
Discrete Spurs
Discrete Spurs
Random Phase Noise
Offset from Fundamental Frequency 
Phase Noise and Jitter Measurements | 12

13. Phase Noise Measurement
• Shows phase noise over a
range of offset frequencies: L
(f)
1
2 L ( f )df
• RMS Jitter = 2 f c
• Phase noise including spurs
yields TJ, or Total Jitter
(random plus deterministic)
• Phase noise without spurs
yields RJ, or Random Jitter
Phase Noise and Jitter Measurements | 13

14. Jitter/Phase Noise Measurements: Golden Rule
Oscilloscope or
Phase Noise
Analyzer
• Jitter measured by an oscilloscope or phase noise analyzer is
always the RMS sum of the clock jitter and the internal jitter of
the measuring instrument
• Internal jitter/phase noise limits measurement sensitivity
• Examples:
• Clock Jitter: 1ps
Instrument Jitter: 1ps
• Clock Jitter: 500fs
Instrument Jitter: 300fs  Measured Jitter: 583fs
• Clock Jitter: 500fs
Instrument Jitter: 25fs  Measured Jitter: 500.62fs
Phase Noise and Jitter Measurements | 14
 Measured Jitter: 1.4ps

15. Measurement on FSW Spectrum Analyzer
• Total RMS Jitter (RJ): 61.94 fs
Phase Noise and Jitter Measurements | 15

16. Measurement on FSW Spectrum Analyzer (w/spurs)
• DJ: 29.32 fs
RJ: 82.50 fs
TJ: 87.56 fs
Individual discrete
jitter contributions
Phase Noise and Jitter Measurements | 16

17. Phase Noise Measurement Instruments
• Spectrum analyzer (with a phase noise personality option) can be a
good instrument for measuring phase noise/jitter
• Sensitivity is limited by spectrum analyzer architecture and internal
local oscillator phase noise
• Phase noise analyzer (or Signal Source Analyzer) uses a different
measurement technique to get the best possible sensitivity
FSW Spectrum Analyzer
FSUP Signal Source Analyzer
Phase Noise and Jitter Measurements | 17

18. Phase Noise Measurement on FSUP
• Total RMS Jitter (RJ)
• 43.3 fs
Phase Noise and Jitter Measurements | 18

19. Phase Noise Measurement
Phase Detector Technique
=90°
Clock
Under
Test
Phase
Detector
Ref.
Source
Low Pass
Filter
LNA
Baseband
Analyzer
PLL
PLL Low Pass Filter
(tracks DUT freq,
maintains 90°
offset)
(sets loop BW)
Reference source is tuned to same frequency as clock with 90°
phase offset (quadrature)
Phase Noise and Jitter Measurements | 19

20. Phase Detector with Cross-Correlation
PLL
Noise 2
Ref 2
=90°
Low Pass
Filter
LNA
PD
Clock
Under
Test
ADC
Noise 2
Noise DUT
Correlation
ADC
PD
Ref 1
=90°
Low Pass
Filter
Noise 1
Noise DUT
LNA
Noise 1
PLL
Cross-correlating both measurements effectively reduces
reference source noise – improves measurement sensitivity
Phase Noise and Jitter Measurements | 20

21. Measurement of a Very Low Jitter Device with FSUP
• Crystal based 640MHz oscillator with very low phase noise/jitter
• 4.6fs
• Cross-correlation technique provides this measurement sensitivity
Phase Noise and Jitter Measurements | 21

22. Phase Noise/Jitter Measurement
Spectrum Analyzer vs Phase Detector vs PD with Cross-Correlation
SA: 68.7fs
PD: 13.1fs
PD w/CC: 4.6fs
Same sub-5fs signal
measured using three
different techniques on
the same FSUP analyzer
Phase Detector with Cross-Correlation is the most
sensitive way to measure phase noise and jitter
Phase Noise and Jitter Measurements | 22

23. Jitter Measurement Instruments
Real time (Oscilloscope)
Single-shot or repetitive events (clock or data)
Bandwidths typically 60 MHz to >30 GHz
Lowest sensitivity (highest jitter noise floor)
Measures adjacent cycles
High
Flexibility
Repetitive (Sampling Oscilloscope)
Repetitive events only (clock or data)
Bandwidths typically 20 GHz to 100 GHz
Generally can not discriminate based on jitter frequency
Cannot measure adjacent cycles
Phase noise (SA / Phase Noise Analyzer)
High
Sensitivity
Clock signals only (50% duty cycle)
Integrate phase noise over frequency to measure jitter
Highest sensitivity (lowest jitter noise floor)
Cannot measure adjacent cycles
Phase Noise and Jitter Measurements | 23

24. Phase Noise Measurement (including spurs)
• FSUP Phase Noise Analyzer requires manual calculation of discrete jitter
• Total RMS Jitter (RJ & DJ)
• 67.5 fs
• Total Jitter (TJ) is RMS
sum of RJ and DJ:
TJ
RJ 2
DJ 2
• DJ can be calculated as:
DJ
TJ 2 RJ 2
• TJ = 67.5 fs, RJ = 43.3 fs
• Calculated DJ = 51.8 fs
Phase Noise and Jitter Measurements | 24

25. Measurement of DJ from Individual Contributors
• What is the contribution of individual discrete components (spurs) to
total RMS jitter?
• Use the spur level values from the Spur List
Phase Noise and Jitter Measurements | 25

26. Measurement of DJ from Individual Contributors
• General formula to convert phase noise to jitter is:
• Integral under the square root,
1
2
fc
2 L ( f )df
L ( f )df , is “integrated phase noise”
• For discrete spurs the integrated phase noise is simply the „dBc‟ level
10dBc / 20
• Jitter for a spur can be calculated from its dBc level using:
2
fc
• Example: 20kHz spur at -72.889dBc on a 1GHz clock:
10dBc / 20
2
fc
(exported spur list)
Phase Noise and Jitter Measurements | 26
10( 72.889 / 20)
2
109
51.04 fs

27. Summary of Total Jitter
• TJ is RSS of all contributors
TJ
DJ1
2
DJ 2
2
DJ 3
2
DJ 4
2
DJ 5
2
DJ 6
2
RJ 2
.782 1.992 45.962 3.072 4.752 7.212 42.92
63.6 fs
45.96fs
3.07fs
4.75fs
7.21fs
.78fs 1.99fs
42.9fs
Phase Noise and Jitter Measurements | 27

28. Summary of Total Jitter
• A simple utility can automate these
calculations
45.96fs
3.07fs
4.75fs
7.21fs
.78fs 1.99fs
42.9fs
Phase Noise and Jitter Measurements | 28

29. Frequency Offset Range is Settable
• Measurements in this presentation have used offset range of
1kHz to 10MHz or 30MHz
• Upper offset range can be as high as 30GHz
• Lower offset can be as low as 1Hz on a SA or 10mHz on a
Phase Noise Analyzer
Phase Noise and Jitter Measurements | 29

30. Jitter Calculation over Subset of Measured Range
• By default, jitter is calculated over entire measured offset range
• A subset of the offset range may be specified for the jitter
calculation
• Jitter calculated over full
measured range of
1kHz – 10MHz is 83.09fs
• For reduced range of
5kHz – 2MHz it is 77.51fs
Phase Noise and Jitter Measurements | 30
5kHz – 2MHz

31. Jitter Calculation with PLL Weighting
• Basic measurement shows raw performance of clock
• Real systems use PLLs
• FSUP can apply a weighting function to simulate the frequency
response of a PLL
Define PLL Freq Response
‘PLL1’ weighting curve
Select PLL to apply to measurement
Unweighted Jitter: 4.6fs
Phase Noise and Jitter Measurements | 31
Weighted Jitter: 3.3fs

32. Calculating Peak-to-Peak Jitter from RMS Jitter
• Time-domain histogram of many oscilloscope-based jitter measurements shows
a Gaussian distribution when jitter is purely random (RJ)
• The standard deviation ( ) is the RMS jitter (RJ)
-4*RJRMS
-3*RJRMS
-2*RJRMS
-RJRMS
0
RJRMS
Phase Noise and Jitter Measurements | 32
2*RJRMS
3*RJRMS
4*RJRMS

33. Calculating Peak-to-Peak Jitter from RMS Jitter
• Phase noise measurement doesn‟t provide a histogram, but does provide RMS
jitter value (and therefore standard deviation)
• RJ has a Gaussian distribution so we can calculate pk-pk jitter for a given BER
– Example: if BER=10-6 then we want 999,999 of 1,000,000 jitter measurements to fall
in light shaded region, only 1 in dark shaded region
Jitter measurements in dark
shaded area represent
error-causing jitter values
Most instantaneous
jitter measurements
would be in this region
(1-BER)
Never reaches 0%
probability
-4
-4*RJRMS
-3
-3*RJRMS
-2
-2*RJRMS
-RJRMS
0
RJRMS
Phase Noise and Jitter Measurements | 33
+2
2*RJRMS
+3
3*RJRMS
+4
4*RJRMS

34. Calculating Peak-to-Peak Jitter from RMS Jitter
• We can use the complimentary Gaussian Error Function, erfc(x), to
calculate peak-to-peak random jitter from RMS jitter
RJ pp
* RJ RMS
where is
is derived from:
• Not closed form so use lookup table
Source: Maxim Application Note AN462
Phase Noise and Jitter Measurements | 34
1
erfc
2
2 2
BER

35. vs. BER
• Factors to calculate RJpp from RJRMS based on BER
• Example: RJpp = 9.507*RJRMS for BER = 10-6
14.069*RJRMS (BER=10-12)
11.996*RJRMS (BER=10-9)
9.507*RJRMS (BER=10-6)
6.180*RJRMS(BER=10-3)
Phase Noise and Jitter Measurements | 35

36. Useful References
• “Analysis of Jitter with the R&S FSUP Signal Source Analyzer”
Rohde & Schwarz Application Note 1EF71
• “Converting Between RMS and Peak-to-Peak Jitter at a Specified BER”
Maxim Integrated Application Note HFAN-4.0.2
• “Clock Jitter and Measurement”
SiTime Application Note SiT-AN10007
• “A Primer on Jitter, Jitter Measurement and Phase-Locked Loops”
Silicon Labs Application Note AN687
• “Determining Peak to Peak Frequency Jitter”
Pletronics White Paper
Phase Noise and Jitter Measurements | 36

37. For More Information
• Download complete slide presentation via Slideshare
slideshare.net/rohdeschwarzNA
• Access app notes, white papers and other supporting material via our
Twitter feed
@RohdeSchwarzNA
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