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(Jitter)

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Agenda

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Jitter, what is it?

What is jitter?

the deviation of an edge from where it should bethe deviation of an edge from where it should be

Jitter is caused by:(among other things) Thermal noise Injected noise (EMI/RFI) Circuit instabilities Transmission Losses

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()

()

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Things you should already know:

Period Jitter

Cycle-to-Cycle Jitter

Time Interval Error (TIE)

Clock Jitter

Data Jitter Clock recovery

BER

Three Methods of Jitter Measurement

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Three Methods of Jitter Measurement

1ns

0.8ns 0.8ns 0.8ns 1.2ns 1.2ns 1.2ns 1.2ns 0.8ns 0.8ns

-0.2ns -0.4ns -0.6ns -0.4ns -0.2ns 0ns 0.2ns 0ns -0.2ns

0.8ns

1.2ns

1.0ns

+0.4ns0ns

-0.4ns

-0.2ns

-0.6ns

0ns 0.2ns

-0.4ns -0.4ns

-0.2ns

0ns 0ns

0.8ns

-0.4ns

1.2ns

-0.2ns

1.2ns

0ns

0.8ns

1.2ns

+0.4ns

-0.2ns

-0.4ns

-0.2ns

0ns

()

()

Period Jitter

Time Interval Error (TIE)Jitter

Time Trend forPeriod Jitter

Time Trend forCycle-Cycle Jitter

P(n+1)-P(n)

Time Trend forTIE Jitter()

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TjTotal Jitter in a signal

Estimated jitter for a large population: 1012 bits

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Random Jitter (RJ)

()

Peak-to-Peak(unbounded)!

1-sigma or RMS 7-sigma

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Deterministic Jitter (DJ)

Peak-to-Peak(bounded)!

Peak-to-Peak

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Periodic Jitter (PJ)

RF

Peak-to-Peak

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Duty Cycle Distortion (DCD)

rise-timefall-timeDuty Cycle

0.0v

Peak-to-Peak

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Data-Dependent Jitter (DDJ or ISI)High/Low(Pattern)

DDJ

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BER

Bit Error Rate Ratio of good bits to bad bits

Send 1,000,000,000,000,000,000,000 bits

Receive 999,999,999,999,999,999,999 bits correctly

Yields a BER of 1:10-21 (1x10-21 or 1E-21)

Requires sending as many bits as you are testing for!

You must capture all bits in sequence for this test to be valid, only a BERT can do this!

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Unit Interval and Bit Error Rate

UI: the nominal period of one transmitted bit

Serial Data Source

Transmitter

Connector Cable Connector Amplifier

Channel

Clock DataRecovery

(CDR)

Receiver

END END

BERT System

BER: Ratio of good bits to bad bits Generally specified at 1012 bits

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(01)

1-sigma or RMS 7-sigma

Z

Z = 50.999999 BER=1:10-6

Z = 60.999999999 BER=1:10-9

Z = 70.999999999999 BER=1:10-12

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Total Jitter @ BER

Random components

Deterministic components

Peak-to-Peak

1-sigma or RMS

pdf : Tj = Dj Rj (convolution)

Pk-Pk: Tj = (N*Rj) + Dj , where N =2*Z

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Statistics

Theorem: Sum of Two Independent RVs(Random Variable)

If two RVs are independent, the pdf of the sum is the convolution of the respective pdfs

Central Limit Theorem

If N RVs are independent, the pdf of the sum is Gaussian as N infinity

=

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Histograms vs. Eye Diagrams

How open is the eye, anyway?

(depends how long you watch)

Eye Opening=?

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Eye Opening vs. Bit Error Rate

Cumulative Distribution Function (cdf)

Probability Density Function (pdf)

Eye Open for BER 1:10-12

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BER Estimationusing Eye Diagram Statistics

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Rj/Dj @ Bath Tub Curve

Start with TIE PLL TIE

Perform FFT Determine

frequency and pattern rate

Sum pattern related bins

Sum unrelated periodic bins

Measure RMS of remaining bins

Estimate BER

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TDSJIT3 Factory Correlation

4 BERT Correlation0 A tool is useless if it doesnt agree with accepted standards0 TDSJIT3 correlates to a BER Tester within 2% to 3%

Results for PRBS-7 Data Pattern

Raw Noise (10ps rms) Sinusoidal (100KHz) Sinusoidal (50MHz) JIT3 BERT Diff JIT3 BERT Diff JIT3 BERT Diff JIT3 BERT Diff

Freq 1.0625G 1.0625G 0.0 1.0625G 1.0625G 0.0 1.0625G 1.0625G 0.0 1.0625G 1.0625G 0.0 PRBS-7 BER eye open eye open eye open eye open

(127 bits) 1.00E-02 97.4 97.1 0.3 95.2 95.2 0.0 95.0 95.4 -0.4 95.1 95.4 -0.3 1.00E-03 96.6 96.2 0.4 93.2 93.2 0.0 93.5 93.8 -0.3 93.7 93.7 0.0 1.00E-04 96.0 95.6 0.4 91.8 91.6 0.2 92.3 92.1 0.2 92.5 92.4 0.1 1.00E-05 95.5 95.4 0.1 90.5 90.1 0.4 91.4 91.1 0.3 91.6 91.3 0.3 1.00E-06 95.1 95.2 -0.1 89.4 88.8 0.6 90.6 90.1 0.5 90.8 90.7 0.1 1.00E-07 94.7 95.1 -0.4 88.3 88.3 0.0 89.8 89.4 0.4 90.2 90.0 0.2 1.00E-12 93.2 94.2 -1.0 84.2 82.1 2.1 87.0 85.5 1.5 87.5 85.9 1.6 RJ 3.34ps Noise/Com 22db 7.79ps Noise/Com 12db 5.93ps Noise/Com 17db 5.78ps Noise/Com 17db DJ 24.34ps Sine 27.88ps Sine 56.78ps Sine 53.86ps Sine PJ 5.23ps Freq 100K 3.96ps Freq 100K 37.90ps Freq 100K 33.31ps Freq 50M DCD 4.60ps Mag 1mv 6.10ps Mag 1mv 4.08ps Mag 150mv 4.63ps Mag 150mv DDJ 14.52ps 17.82ps 14.80ps 15.92ps difference in %UI exterpolated

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(setup and hold)

(PLL)

(data)

?

-(Cycle-Cycle)

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Vcc Noise

Ground Bounce

PLL

Dead Band

(Crystal)

(Crosstalk)

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(Histogram)

.

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.

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8

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JavaJavaTM

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T X X X X X X X X

T X X X X X X X X

P1 P2 Period = X1-T,X2-X1,X3-X2,,Xn-Xn-1

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TDS7000/6000/5000TDSJit3

425

:

(Histogram)

(Time Trend)

(Cycle Trend)

(Spectrum)

(BathTub)

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TDS7/6/5000,DPO/DSATDSJit3

: (10) (4) - (3) (8) 425

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: (Mean) (Max) (Min) (Pk-Pk) (Std Dev) (Population) (Max+) (Max-)

6

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(SSC)

32MB

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(Span)

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BER Eye Opening

BER Eye Opening

BER Eye Opening 530.91m Ui

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:

(TDS7000B, 1.2ps RMS)

()

(5.9343ps)

(Delta Time Accuracy)

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(Delta Time Accuracy)

-

DTA(interpolation)

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4 TDS740420GS/s(SR)

1.5ppm

400MHz (2.5ns )

DTA = 0.03 / SR + (DTA = 0.03 / SR + () X () X ()) DTA = 0.03 / 20GS + 1.5ppm x 2.5ns DTA = 1.5ps + 0.00375ps

0.00375ps

DTA

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TDSJIT3 Software Overview

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TDSJIT3 User Interface

Measurement Selection Clock Data Clk-Data General

Users can select measurements from any source

Channel, Math, Ref

User can select the same measurement on multiple channels:

Period(Ch1), Period(Ch2), Period(Ch3), Period(Math1)

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TDSJIT3 Configuration

Configuration Meas Params Source Autoset Gate/Qualify Ref Levels Population Limit

Users configure each Source and Measurement independently Each source has its own settings Each measurement has its own

settings

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TDSJIT3 Autosetting

Vertical Autoset Intended to maximize vertical

dynamic range Each source can be set

independently

Horizontal Autoset Adjusts horizontal settings to

ensure reliable results based on signal risetime

Vert and Horiz Autoset are really fine tuning controls, I normally recommend customers set scope manually for best results

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TDSJIT3 Gates and Qualifiers

Gate Measurements are made only

inside gated region Gate by Cursor Gate by Zoom Limits single shot population

hence Rj/Dj capability

Qualify Measurements are made only

when Qualify input has transitions and state meets criteria

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TDSJIT3 Reference Levels

Sets thresholds for making measurements Each source has its own

settings for rising and falling edges

Autoset-Setup allows changing levels by percentage (e.g., 10-90%)

Autoset All Active is a quick way to go and ensures good results 99% of the time

Hysteresis is an important setting, especially in noisy environments

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TDSJIT3 Population Limit

Sets population limit for making measurements Measurement stops when limit

reached In Run mode (continuous),

acquisitions stop when population limit reach

A handy and customer desired feature

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TDSJIT3 Summaries

Shows a summary of measurements, their configurations and reference levels Handy place to review how the

software is configured

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TDSJIT3 Results Views

Results are displayed differently in TDSJIT3 Results are shown in different

views: All Statistics Min/Max Mean/StdDev TIE Rj/Dj BER

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TDSJIT3 All Statistics

Each measurement is selected independently only results for one measurement are shown All statistics are shown for the

selected measurement The first column is the last

acquisition The second column is the

accumulation of all acquisitions Clear erases all data

Max +/- show the largest pos/negchange on a cycle to cycle basis for every measurement type!

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TDSJIT3 TIE: Rj/Dj - BER

Displays results for Rj/Dj Rj/Dj results are only available

for TIE and PLL TIE measurements

Rj/Dj is a two step process: make the TIE measurement; then calcula