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Real Time Jitter Measurement

Live webinar from 2/11/14
View the On-Demand webinar, http://ubm.io/LywVYU
Overview
ı Background jitter measurement methods
Batch mode jitter measurement
 Triggered measurement
 Real –time digita...
What is Jitter?

Data
Clk

Setup
Time

Hold
Time

Q

l Jitter includes instability in signal period, frequency, phase, dut...
Serial digital data transmitter
Time Interval Error (TIE)

TIE is the difference between the measured clock edge and the ideal clock edge
locations
TIE is...
Jitter Measurement Instruments
Real time (Oscilloscope)
Single-shot or repetitive events (clock or data)
Bandwidths typica...
Spectrum Analyzer Method

7
Phase Detector Method
PLL-Controlled Reference
⊗√=90°
DUT
PD
Low Pass
Filter

LNA

Spectrum
Analyzer

PLL
PLL Low Pass Fil...
Phase Detector Method
Input signals of the mixer (having 90° offset, i.e. in “Quadrature“):

Output signals of the mixer:
...
Relationship between phase noise and jitter
Timing Measurement in Oscilloscopes
Threshold crossing time
interpolation
threshold

50 ps

50 ps

ı Time is measured at t...
Jitter Measurement: Histogram
ı Collection of measurements
arranged in an x-y plot value
vs. frequency of occurrence
ı App...
Jitter Measurement: Jitter Track

t1

t2

t3

t4

t

t

ı Jitter measurement over time
ı Synchronous sampling with signal ...
Jitter as a Random Variable
ı Jitter is a combination of random and deterministic sources and can be treated
as a random v...
The Random Component of Jitter
# Measurements
100
1,000
5,000
10,000
100,000
1,000,000
5,000,000
100,000,000
1,000,000,000...
Probability Density Functions
ı The PDF is a function that gives the probability that a random variable takes on
a specifi...
The Dual Dirac Jitter Model
ı Fit Gaussian curve to the left and

ı
ı
ı
ı
ı

right sides of estimated jitter PDF
(i.e. the...
Jitter and Bit Error Rate

BER

Jitter PDF

0

UI

1
Total Jitter Curve
ı The specified BER is
another way of expressing a
confidence interval or
observation time
ı Total jitt...
Summary of Histogram Analysis
ı Histograms are used to estimate the PDF of random variables such as jitter
ı Jitter consis...
Jitter measurement methods
ı Oscilloscope is the primary instrument for jitter measurement
Measurement of clock and data s...
Real time jitter measurement
ı Hardware clock recovery
ı Separate trigger circuit
ı Timing uncertainty introduced via CDR,...
Batch Mode Jitter Measurement
ı Analyze long signal acquisition
ı Software clock recovery applied
to timing data
ı Many an...
Jitter Noise Floor

Batch mode
Typ. 330 fs
Noise

Sampling clock jitter

Triggered
Typ. 1.5 ps
Noise

Sampling clock jitte...
Real time Digital Clock Recovery
ı Real time acquisition similar to triggered mode
ı No CDR or trigger jitter
ı Loop bandw...
Limitations of Batch Mode Jitter Measurement
ı
ı
ı
ı

Inherent low frequency cutoff due to windowing
Large time gaps in ac...
Jitter transfer function

N measurements
FFT Bin Response
Jitter transfer function

Each bin has a sin(x)/x response
Low frequency cutoff at the first FFT bin
Jitter transfer function

1 MHz carrier with 10 KHz sinusoidal jitter measured over a 100 us time window
Jitter transfer function

1 MHz carrier with 10 KHz sinusoidal jitter measured over a 50 us time window
Transient jitter
Example of transient jitter

histograms of low rate jitter measured using batch and continuous modes. Jitter
Injected at 1...
Example of Jitter on a Long Pattern

Histograms of jitter measured on a PRBS31 data pattern. The linear trend lines
on the...
Summary
ı Oscilloscope jitter measurements rely mainly on batch mode processing
lowest jitter noise floor
 time and frequ...
Learn More
ı For more information on the instruments seen in this presentation, please visit


www.rohde-schwarz-scopes.c...
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Real-Time Jitter Measurements

Jitter measurements are commonly done taking small snapshots in time, yet systems often experience jitter from sources that occur over relatively long time intervals, which may not be accounted for using short time interval measurements methods.

In this webinar we will present the application of a real time, digital clock recovery and trigger system to the measurement of jitter on clock and data signals. Details of the measurement methodology will be provided along with measurement examples on both clock and data signals.

You Will Learn:
- What is Jitter
- Different types of Jitter
- Jitter measurement techniques
- Benefits of Jitter analysis using real-time DDC techniques

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Real-Time Jitter Measurements

  1. 1. Real Time Jitter Measurement Live webinar from 2/11/14 View the On-Demand webinar, http://ubm.io/LywVYU
  2. 2. Overview ı Background jitter measurement methods Batch mode jitter measurement  Triggered measurement  Real –time digital clock recovery ı Jitter transfer function (real time vs. batch) ı Transient and low rate jitter events ı Measurement examples  Low rate jitter  PRBS31 
  3. 3. What is Jitter? Data Clk Setup Time Hold Time Q l Jitter includes instability in signal period, frequency, phase, duty cycle or some other timing characteristic l Jitter is of interest from pulse to pulse, over many consecutive pulses, or as a longer term variation l Very long term variations (<10Hz) are a separate class of pathologies referred to as wander (Telecommunication only)
  4. 4. Serial digital data transmitter
  5. 5. Time Interval Error (TIE) TIE is the difference between the measured clock edge and the ideal clock edge locations TIE is essentially the instantaneous phase of the signal
  6. 6. Jitter Measurement Instruments Real time (Oscilloscope) Single-shot or repetitive events (clock or data) Bandwidths typically 60 MHz – 30+ GHz Lowest sensitivity (highest jitter noise floor) Measures adjacent cycles Repetitive (Sampling Oscilloscope) Repetitive events only (clock or data) Bandwidths typically 20 GHz - 100 GHz Generally can not discriminate based on jitter frequency Cannot measure adjacent cycles Phase noise (Phase noise test set) Sensitivity Clock signals only Must integrate phase noise over frequency to measure jitter Highest sensitivity (lowest jitter noise floor) Cannot measure adjacent cycles Flexibility
  7. 7. Spectrum Analyzer Method 7
  8. 8. Phase Detector Method PLL-Controlled Reference ⊗√=90° DUT PD Low Pass Filter LNA Spectrum Analyzer PLL PLL Low Pass Filter Reference Source 8
  9. 9. Phase Detector Method Input signals of the mixer (having 90° offset, i.e. in “Quadrature“): Output signals of the mixer: After low-pass filtering and assuming ƒL= ƒR we get: For small changes in phase (simplification allowed for this kind of noise): 9
  10. 10. Relationship between phase noise and jitter
  11. 11. Timing Measurement in Oscilloscopes Threshold crossing time interpolation threshold 50 ps 50 ps ı Time is measured at the point where the waveform amplitude crosses a predefined threshold ı Samples are spaced at the sample interval (50 ps at 20 Gs/s for example) ı Sin(x)/x or cubic interpolation is used on the waveform transition followed by linear interpolation of the points nearest the crossing to find the exact time
  12. 12. Jitter Measurement: Histogram ı Collection of measurements arranged in an x-y plot value vs. frequency of occurrence ı Approximation of a PDF when normalized ı Analyzed to "measure" total jitter and jitter components (random, deterministic, etc.)
  13. 13. Jitter Measurement: Jitter Track t1 t2 t3 t4 t t ı Jitter measurement over time ı Synchronous sampling with signal transitions ı Used to measure jitter spectrum t5
  14. 14. Jitter as a Random Variable ı Jitter is a combination of random and deterministic sources and can be treated as a random variable ı The jitter histogram is used as an estimate of the probability density function (PDF) of the timing values – usually TIE ı A model is fit to the estimated PDF and is used to predict the range of timing values for any sample size  Referred to as the total jitter  The sample size is defined in terms of an equivalent bit error rate
  15. 15. The Random Component of Jitter # Measurements 100 1,000 5,000 10,000 100,000 1,000,000 5,000,000 100,000,000 1,000,000,000,000 Peak-to peak (σ) ±2.1 ±2.9 ±3.4 ±3.5 ±4.1 ±4.6 ±5.1 ±6.0 ±7.0 Theoretically, the peak to peak value of random jitter will grow without bound. To define the random jitter you must specify a measurement time.
  16. 16. Probability Density Functions ı The PDF is a function that gives the probability that a random variable takes on a specific value ı In the case of jitter, this is the probability that a transition happens at a specific time from its expected location ı The cumulative density function is the integral of the PDF and gives the total probability of a transition happening within a certain time range of the expected transition time ı The histogram of a random measurement is an estimate of the PDF for that measurement
  17. 17. The Dual Dirac Jitter Model ı Fit Gaussian curve to the left and ı ı ı ı ı right sides of estimated jitter PDF (i.e. the measured normalized histogram) Separation of the mean values gives Dj(δ−δ) Standard deviation gives Rj Dj(δ−δ) and σ are chosen to best fit the measured histogram in the tails Model Predicts jitter for low bit error rates Note that the model does not fit the central part of the measured distribution
  18. 18. Jitter and Bit Error Rate BER Jitter PDF 0 UI 1
  19. 19. Total Jitter Curve ı The specified BER is another way of expressing a confidence interval or observation time ı Total jitter is determined by integrating the probability density function (PDF) separately from the left and right sides to determine the cumulative probability density (CDF) ı The width of this curve at the specified BER (or confidence interval) gives the total jitter CDF (total jitter) PDF Total jitter and PDF for a Gaussian distribution with standard deviation = 1
  20. 20. Summary of Histogram Analysis ı Histograms are used to estimate the PDF of random variables such as jitter ı Jitter consists of both random and “deterministic” components Random jitter is assumed to have a Gaussian PDF  Deterministic jitter is actually bounded and is modeled by a pair of Dirac delta functions ı The Dual Dirac model is used to extrapolate a small set of jitter measurements in order to predict the peak to peak range of a much larger sample ı The sample size is expressed in terms of bit error rate  BER of 1e-12 equals a sample size of approximately 2e12 bits  Ratio of ‘1’ to ‘0’ values is assumed to be ½ ı Rj and Dj from the Dual Dirac jitter model are specified in all serial data standards for jitter 
  21. 21. Jitter measurement methods ı Oscilloscope is the primary instrument for jitter measurement Measurement of clock and data signals  Wide range of measurement types (period, cycle to cycle, TIE, etc) ı Measurement methods used in oscilloscopes  Real time (triggered)  Batch mode 
  22. 22. Real time jitter measurement ı Hardware clock recovery ı Separate trigger circuit ı Timing uncertainty introduced via CDR, trigger and ADC sampling clock
  23. 23. Batch Mode Jitter Measurement ı Analyze long signal acquisition ı Software clock recovery applied to timing data ı Many analysis features (frequency, time, statistical)
  24. 24. Jitter Noise Floor Batch mode Typ. 330 fs Noise Sampling clock jitter Triggered Typ. 1.5 ps Noise Sampling clock jitter Clock recovery jitter Trigger jitter
  25. 25. Real time Digital Clock Recovery ı Real time acquisition similar to triggered mode ı No CDR or trigger jitter ı Loop bandwidth not limited by acquisition window
  26. 26. Limitations of Batch Mode Jitter Measurement ı ı ı ı Inherent low frequency cutoff due to windowing Large time gaps in acquisition obscure transient jitter Generally impossible to measure long stress data patterns Discontinuous phase tracking can cause phase "slipping"
  27. 27. Jitter transfer function N measurements
  28. 28. FFT Bin Response Jitter transfer function Each bin has a sin(x)/x response Low frequency cutoff at the first FFT bin
  29. 29. Jitter transfer function 1 MHz carrier with 10 KHz sinusoidal jitter measured over a 100 us time window
  30. 30. Jitter transfer function 1 MHz carrier with 10 KHz sinusoidal jitter measured over a 50 us time window
  31. 31. Transient jitter
  32. 32. Example of transient jitter histograms of low rate jitter measured using batch and continuous modes. Jitter Injected at 1/3208 rate
  33. 33. Example of Jitter on a Long Pattern Histograms of jitter measured on a PRBS31 data pattern. The linear trend lines on the histogram on a log scale estimate the total jitter
  34. 34. Summary ı Oscilloscope jitter measurements rely mainly on batch mode processing lowest jitter noise floor  time and frequency domain analysis ı Batch mode jitter analysis has limitations  transient jitter  long repeating patterns ı Applying digital methods to real time jitter analysis provides significant benefits for jitter measurements  low jitter noise floor  large statistical sample  capture of transient jitter 
  35. 35. Learn More ı For more information on the instruments seen in this presentation, please visit  www.rohde-schwarz-scopes.com ı If you’re interested in a free demo of our products, please visit  http://www.rohde-schwarz-usa.com/FASTDemo.html

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  • auvro

    Jun. 21, 2014
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    Aug. 14, 2014
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    Apr. 15, 2018
  • WilliamLee423

    Nov. 16, 2020

Jitter measurements are commonly done taking small snapshots in time, yet systems often experience jitter from sources that occur over relatively long time intervals, which may not be accounted for using short time interval measurements methods. In this webinar we will present the application of a real time, digital clock recovery and trigger system to the measurement of jitter on clock and data signals. Details of the measurement methodology will be provided along with measurement examples on both clock and data signals. You Will Learn: - What is Jitter - Different types of Jitter - Jitter measurement techniques - Benefits of Jitter analysis using real-time DDC techniques

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