Essential principles of jitter part 2 the components of jitter

WEBINAR: Essential Principles of Jitter Part II Components of Jitter Thank you for joining us. We will begin at 2pm ET. NOTE: This presentation includes Q&A. We will be taking questions during the presentation with answers at the end using the questions section of your control panel.

LeCroy founded in 1964 by Walter LeCroy Origins are high speed digitizers for particle physics

research Teledyne LeCroy corporate headquarters is located in

Chestnut Ridge, NY Teledyne LeCroy has the most advanced technology

and widest line of Real-Time digital oscilloscopes (from 40 MHz to 100 GHz)

Long History of Innovation in Digital Oscilloscopes Teledyne LeCroy became the world leader in

protocol analysis with the purchase of CATC and Catalyst, and creating a protocol analyzer division based in Santa Clara, CA.

In August 2012, LeCroy became Teledyne LeCroy through an acquisition by Teledyne Technologies

Teledyne LeCroy Overview

Teledyne LeCroy Signal Integrity Acadamy 2

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About the Presenters

Dr. Eric Bogatin • Signal Integrity Evangelist with the Teledyne LeCroy Front Range

Signal Integrity Lab • Adjunct Professor, University of Colorado, Boulder, ECEE • Soon to be: Dean, Teledyne LeCroy Signal Integrity Academy Email: [email protected] www.beTheSignal.com

Dr. Alan Blankman Signal Integrity Product Marketing Manager, Teledyne LeCroy • B.A. Northwestern University • PhD University of Pennsylvania • MBA New York University, Stern School of Business • Has been with Teledyne LeCroy for over 16 years Email: [email protected]


Essential Principles of Jitter part 2 Dr. Alan Blankman Product Manager, High Speed Serial Data Products, Teledyne LeCroy and Dr. Eric Bogatin, Dean, Teledyne LeCroy Signal Integrity Academy, Teledyne LeCroy

Check out the Teledyne LeCroy Signal Integrity Academy at www.beTheSignal.com

Where to get a copy of the slides: www.beTheSignal.com


Essential Principles of Jitter, or Jitter 101

1 Introduction to Jitter: The Time Interval Error: TIE

2 Jitter Synthesis: The Jitter Components

3 Jitter Analysis Extrapolation and Decomposition


Jitter part 1: The Time Interval Error (TIE)

The actual edge arrival times – the expected edge arrival times, for each edge

Expected arrival times from CDR circuitry

Plotted over time: the TIE track Apply the power of statistics to

analyze the TIE track


Jitter part 2: The Jitter Components

The power of statistical analysis

The five fundamental types of jitter: ISI, DCD, Periodic, Random, Other

Their statistical “signature”

The jitter “tree”

Synthesizing examples based on their root cause

Check out Alan’s new app note: “Understanding Jitter Calculations, why Dj can be less than DDj (or Pj)”


How Can We Characterize Jitter?

What figures of merit do we use to characterize the TIE Track (jitter) waveform?

Look at a histogram distribution of the jitter over some time period What terms characterize the waveform?

Average Peak to peak (over some interval) Spectral density RMS, standard deviation (only has meaning if Gaussian) Best figures of merit to use depend on the features of the TIE Track


Explore Jitter Analysis of Many NRZ Data Signals: look for patterns

Take an NRZ data pattern

Recover clock and calculate TIE Track

Plot a histogram of jitter over some time interval

Plot the spectral density of jitter over some time interval

Tpk-pk


Best Figure of Merit Depends on the “Signature” of the Jitter

Peak-Peak is not a useful figure of merit for Gaussian (random) Jitter Random jitter is unbounded

Peak-Peak grows as we increase

the measured time interval

Expected pk-pk

Typically, the more samples, the farther the outliers…but it’s statistical


Inter Symbol Interference (ISI): information from one bit leaks into others

200 psec UI

(described by S-parameter matrix)

ISI

“echoes of bits past”

One root cause of ISI jitter: reflection noise


Another root cause of ISI jitter: frequency dependent loss rise time degradation vertical noise and horizontal jitter

SBR for extreme bit patterns, 11111010000000

00000010000000

5 Gbps, RT = 50 psec

Switching threshold time for the “1” bit is different when previous bits were all 0 or all 1

The more rise time degradation, the more deterministic jitter

20 inch interconnect:

40 inch interconnect:

No interconnect

And every bit pattern combination between Teledyne LeCroy Signal Integrity Acadamy 14

Jitter from Inter Symbol Interference (ISI) Signature: Jitter of an edge depends on the bit history

TIE Track repeats for a repeating bit pattern (e.g., PRBS7)

Features of jitter from ISI Discrete peaks corresponding to specific, finite bit patterns Bounded, pk to pk is a good FoM Broadens a little with increasing repeat bit pattern Complex spiky histogram pattern characterizes ISI jitter Tpk-pk= DDj


Duty Cycle Distortion (DCD)

Caused by: Variation in crossing level and/or

shift in signal’s offset If rising, falling edge is symmetric about level, no DCD

Signature: two states in TIE Track and histogram Measures difference in bit width for 0 and 1 bits Bounded Figure of Merit: center to center of average of each

distribution

0 1 1 0

DCD = ∆T


Periodic Jitter Caused by:

Coupling from other periodic signals in system, Noise on the power rails, Instability in a feedback loop

Signature: bowl-shape histogram, pks in spectrum

Bounded Contributed by ALL the frequency components of periodic jitter Characterized by the peak to peak jitter from all periodic sources

TIE track Pk-Pk periodic = Pj


Random Jitter: root cause- “death by a thousand cuts”

2

2

1 tPDF(t) exp22

= − σπσ

Probability of an edge arriving a time t from the mean is a Gaussian distribution

Random jitter can have large excursions… just at low probability

Typically, the more samples, the farther the outliers…but it’s statistical

Peak to peak

Random jitter pk-pk grows with sample size


Gaussian Statistics in 4 minutes

2

2

1 tPDF(t) exp22

= − σπσ

n

n

PDF(t)dt+ σ

− σ

= ∫n

n n

1 PDF(t)dt 2 x PDF(t)dt+ σ ∞

− σ + σ

= − =∫ ∫

Confidence interval measured in units of σ

outliers

Two regions: (the fraction in each region)

• Confidence interval defined as between +/-n σ: fraction of events occurring within the confidence interval =

• Outliers (outside the confidence interval): fraction of events occurring as outlier =


What is the Connection between Outlier Fraction and Confidence Interval Width?

0

2

4

6

8

10

12

14

16

18

1.E-

16

1.E-

15

1.E-

14

1.E-

13

1.E-

12

1.E-

11

1.E-

10

1.E-

09

1.E-

08

1.E-

07

1.E-

06

1.E-

05

1.E-

04

1E

03

Alph

a (#

of s

igm

a)

Outlier Fraction

confidence interval width = α x σ

Confidence interval measured in units of σ

outliers

n

n

1 PDF(t)dt fraction of bits outside confidence int erval+ σ

− σ

− =∫

For an outlier fraction of 10-12, need α = 14.069 Rule #9: what do we expect? Teledyne LeCroy Signal Integrity Acadamy 20

So What?

δT

δT

UI

If strobe point is located δT from beginning of UI or end of UI, any edge with arrival time > δT will be an error (the outliers) For a given strobe location, the confidence interval is (2 x δT) and the fraction of outliers is the BER For a target BER of 10-12 , confidence interval is = α x σ = 14.069 x σ The σ characterizes the Gaussian distribution of jitter

wash on, wash off Teledyne LeCroy Signal Integrity Acadamy 21

Four Kinds of Jitter: They don’t always play well together

Periodic Jitter Intersymbol Interference

Duty Cycle Distortion Random Jitter


The Fifth Type of Jitter: “Other”

Other: catch all grab bag Bounded in extent (not Gaussian) Uncorrelated to the data… Not Gaussian, not periodic… OBUJ

Other Bounded Uncorrelated Jitter Crosstalk / interference, switching noise, cavity noise

Interference translates into jitter Potentially broadband; spectral noise floor rises:

w/XTALK


Classification of Jitter Types: Our Five Friends

Total Jitter – “Tj”

Intersymbol interference

“ISI”

Duty Cycle Distortion

“DCD”

Bounded Deterministic (not random)

“Dj”

Correlated Jitter Data Dependent Jitter

“DDj”

Periodic “Pj”

Unbounded, Random

“Rj”

Bounded, uncorrelated Jitter

“BUJ”

Other, bounded, uncorrelated with the data,

jitter “OBUJ”


Alan Blankman Product Manager, High Speed Serial Data Products,

Teledyne LeCroy


ISI


DCD


Periodic


Random


Multiple


Four General Patterns from Different Causes of Jitter (5th is “other”)

Periodic Jitter Intersymbol Interference

Duty Cycle Distortion Random Jitter


Essential Principles of Jitter, or Jitter 101

1 Introduction to Jitter: The Time Interval Error: TIE

2 Jitter Synthesis: The Jitter Components

3 Jitter Analysis Extrapolation and Decomposition


For More Information

www.BeTheSignal.com

The Signal Integrity Academy

Online video training

Published by Prentice Hall, 2009

Check out Alan’s new app note: “Understanding Jitter Calculations, why Dj

can be less than DDj” Visit www.TeledyneLeCroy.com


Q&A

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Essential principles of jitter part 2 the components of jitter

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