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Practical Guide to Making Advanced Jitter

Measurements

Get results you can live with!

Pascal GRISON

Digital Application Engineer

[email protected]

2

Validating Design Performances

through accurate measurements

PCIe 1.1, 2.5 GT/s

16” Channel

PCIe 2.0, 5.0 GT/s

16” Channel

PCIe 3.0, 8.0 GT/s

16” Channel

3

There are Three faces to the problem

• How much jitter should the transmit side be allowed to generate

• How much jitter can the receiver side tolerate

• How much degradation is acceptable from transmission line

in the case of local Chip to Chip interconnect (PCI-Express)

in the case of Rack Backplane (ATCA,PCI-Express, AXI-e, VPX…)

in the case of an external cable (SATA,HDMI,DISPLAYPORT,USB…)

A well designed Serial Link mustspecifies properly these 3 points

to guarantee system level performance (bit-error-ratio)

High Speed Serial Link

Design for Success

4

The easiest way to get an overall idea of the quality of the serial signal

Using Oscilloscope Software Clock Recovery with PLL Emulation to recover Signal Clock

Eye Diagram is the superposition in the middle of the screen of 3 consecutive bits

Multiple case combined form the Eye (000,001,010,011,100,101,110,111)

Evaluate overall impact of Channel, Crosstalk and RJ/PJ

Fundamental Signal Integrity Analysis:

The Eye Diagram

101 Sequence 011 Sequence Overlay of all combinations

Using OFFLINE Oscilloscope GUI to Analyse ChannelSim

DIA2 1Gb/s Differential signal

ChannelSim N8900A

Simulation –> Infiniiview ChannelSim ADS

Simulation –> Front Panel

Measurement vs Simulated Eye Diagram Analysis

ChannelSim –> Infiniiview DUT DSAX93304A Scope Meas

Note

User error on DIA2 Amplitude register

setting during Scope Meas

800mV instead of 1200mV

Using ChannelSim to evaluate Xtalk impact

from SIGA79 Single-Ended signal

DIA2_Xtlk_DIA1_SIGA79_ChannelSimTB_AMI

200 Mbps DSAX93304A Measurements Simulation – Infiniiview

Note

User error on DIA2 Amplitude register

setting during Scope Meas

800mV instead of 1200mV

DIA2_Xtlk_DIA1_SIGA79_ChannelSimTB_AMI

400 Mbps Oscilloscope Measurements Simulation – Infiniiview

10

The eye-mask is the common industry approach to measure the eye opening

Failures usually occur at mask corners

What represents “good enough”?

Violating USB FS 12Mb/s Eye Diagram Good 2.5Gb /sDisplayport Eye Diagram

But How is Defined the Mask Template?

11

AGILENT SI Seminar 2012

by Pascal GRISON

Measure DUT Receiver Minimum Eye at BER 10E-12

Rx latch

DLL

Rx

PLL

ISI

Channel

Receiver RX Data

Semiconductor Vendors are Using bert to Caracterize SERDES BER susceptibility

to ISI, Random Jitter and Frequency dependant Periodic Jitter Eye Closure

Tx latch

Tx

DLL

Transmitter

DUT SerDes in

LoopBack Mode

TX Data

BERT up to 28Gb/s PRBS Generation

with Calibrated Jitter insertion

and integrated adjustable ISI channel

JBERT Realtime Error Detector allow

thorough BER Analysis and BER Eye

Opening

12

Analysing a serial Link

TX RX Channel

Clean Source Signal Closed Eye

Received Signal Channel

Frequency Response

We are going to analyse a 12Gb/s Link

Channel will be 9 Inch FR4 PCB

13


by Pascal GRISON

Transmiter 12Gb/s

Intrinsic Jitter Analysis

33GHz 80GSa/s Scope

RJ: 500fs (RMS)

PJ: 740fs

DCD: 660fs

ISI: 10.52ps

Scope Eye & Jitter BreakDown Analysis on TX output

14


by Pascal GRISON


by Pascal GRISON

Depending on Link

Target Datarate &

Transmission Channel

Losses

Even with Perfect TX

Eye Opening…

You may end up with a

completely closed

at Receiver Side

Why is the RX Eye

Closed? ISI Jitter!

Does that mean that this

link will never Work?

Well it Depends….

Black GUI Offline Analysis Application: Infiniiview

Eye Diagram on TX output and Channel Output

15


by Pascal GRISON

ISI Jitter is coming from Signal Distorsions in Transmission Channel

What are Inter-Symbol Interferences?

16


by Pascal GRISON

To reduce ISI at RX Side, Most TX implement De-Emphasis

Press ESC during Video to Skip Video

Impact of TX De-Emphasis on RX Signal

17


by Pascal GRISON

From Zero RX Eye

Opening with no TX

De-Emphasis

RX Eye Opening of

25mV X 27.5ps

Was achieved with

-12dB De-Emphasis

Note: Measure is

done on D+ only

So Differential Eye

Opening is 2X SE

Opening

=50mV X 27.ps

Much better!

But is it enough?

Infiniiview Offline Eye Diagram Analysis of Waveform captured on scope

-12dB TX De-Emphasis -> RX Eye Opening

18


by Pascal GRISON

Modern SerDes are embbeding

RX EQUALIZATION

Using Oscilloscope Equalization

we can emulate most DUT RX EQ

configurations:

FeedForward EQ

Continuous Time EQ

Decision Feedabck EQ

Let’s Emulate a Typical configuration:

Upper Eye:

FFE 2Taps -> CDR

DFE 5 Taps ->Data

Lower Eye

FFE 2Taps -> CDR (no EQ on DATA)

Scope can Emulate Receiver EQUALIZATION

DSO91304A#014 or N5465A

19


by Pascal GRISON

From almost Zero

RX Eye Opening

with no TX De-

Emphasis and

No RX EQ

RX Eye Opening of

132mV X 65ps

Was achieved with

EQUALIZATION

Note: Measure is

done on D+ only

So Differential Eye

Opening is 2X SE

Opening

=264mV X 65ps

Very Good Eye

opening !!

You MUST Emulate your RX Equalization in Oscilloscope to Analyze True RXEye Diagram

Press ESC during Video to Skip Video

Emulate Receiver EQUALIZATION on Oscilloscope

20

Total Jitter

(TJ)

Deterministic

Jitter (DJ)

Random Jitter

(RJ)

Correlated with

Data (DDJ)

Uncorrelated

with Data (BUJ)

DutyCycle

Distortion

(DCD)

InterSymbol

Interference

(ISI)

Periodic

(PJ)

Non

Periodic

(ABUJ)

Gaussians

(s, RJRMS)

Jitter Components

Xtalk

Non Linear

CR

Events

Thermal

Shot

1/f

Burst

Tr, Tf

D Settling Time

Reflections

Clocks

Bounded UnBounded

Non flat Freq

Response

Xtalk

21

Where Does Jitter Come From?

Transmitter Receiver

•Thermal Noise (RJ)

•Local Oscillator (RJ/PJ)

•Bias shift (DCD)

•Power Supply Noise (RJ, PJ)

•On chip coupling (PJ, ISI)

•Lossy Channel interconnect (ISI)

•Impedance mismatches (ISI)

•Crosstalk with ABC Lanes (BUJ)

•Termination Errors (ISI)

Aggressor Lane A

Lane under Study

Aggressor Lane B

Aggressor Lane C

High Probability Determinisic Jitter

is reported as Peak-Peak Ideal Location in Time (Reference)

Threshold Late

Early

DtEarly

JPP=DtEarly Pk + Dtlate Pk

DtLate

0 1

Transition

Instant

22

• JPPRJ is unbounded

• For pure random jitter the BER defines the JPPRJ: BER = 10-12 = JPP

RJ = 14.1 JrmsRJ

• Total Jitter (TJ), JTJ, for a given BER:

Random Jitter is Measured as RMS

DJ

PP

RJ

rms

DJ

PP

TJ

JJn

JnJ

s

23

Page #

Pure random or periodic jitter:

Relation between RMS and PP Jitter

For 6 Sigma Statistics (BER=3.4*10-6) and pure random jitter:

Jitter pp ~ 9 * Jitter RMS.

For pure periodic Time Intervall Error (Jitter):

Jitter pp ~ 2*sqrt(2) Jitter RMS ~ 2.828 * Jitter RMS

For BER = 10-12 and pure random Jitter

Jitter pp = 14.1 * Jitter RMS

Topics

Review of Jitter Measurement

Jitter Decomposition

Four Critical Areas

• Your control of the jitter measurement

• Examples and tips for Good Measurements

Evaluating ‘BUJ’ from Crosstalk

Other Considerations

Tx

f Noise

Pre-emphasis

Delay

Ground Bounce

ISI

Skew

Frequency Response

Crosstalk

Reflections

Skew

Noise

Match

Equalization modeling

Clock Recovery/PLL Performance

Review of Jitter Measurement

On an oscilloscope we monitor the waveform transitions and note the jitter at

each transition point. This is called the Time Interval Error record

The Problem with Jitter…

42

44

46

48

50

52

54

56

58

0.25 0.5 1 2 4 8 16

Jitterpk-pk

(ps)

Transitions (M) [Acquisition Length constant at 8MPt]

Jitter pk-pk vs # Transitions (fixed record length)

Max

Average

Minimum

40

50

60

70

80

90

100

248163264

Jitterpk-pk

Acquisition Length(MPt)

Jitter for 1 Million Transitions

Max

Average

Minimum

Jitter will statistically grow over:

• increasing number of Acquired Waveforms

• Increasing observation time

Phase Noise Plot

Character of Jitter

Many contributors to Jitter

• Most of these are Bounded… they have limited distributions of jitter.

• Others are grouped in the UnBounded classification…

Unbounded Jitterpkpk will grow over time of measure

The distributions of these contributors convolve together to

compose the Total Jitter Histogram.

Total Jitter

(TJ)

Deterministic

Jitter (DJ)

Random Jitter

(RJ)

Correlated with

Data (DDJ)

Uncorrelated

with Data (BUJ)

DutyCycle

Distortion

(DCD)

InterSymbol

Interference

(ISI)

Periodic

(PJ)

Non

Periodic

(ABUJ)

Gaussians

(s, RJRMS)

Jitter Components

Xtalk

Non Linear

CR

Events

Thermal

Shot

1/f

Burst

Tr, Tf D Settling Time

Reflections

Clocks

Bounded UnBounded

Non flat Freq

Response

Xtalk

Approach to Resolve ‘random nature’:

the Dual Dirac Assumption

R

L

sR

sL

DJDD

Fit the tails of the jitter PDF to two Gaussian curves

Jitterpp(BER) =DJDD + n s

N = f(target BER)

For instance for BER = 10-12 n ~ 14

The jitter that composes DJDD

comes from the deterministic

components… 7s for 10-12 BER.

Evaluate TIE

DDJ Analysis

RJ Extraction

Clock

Reference

Dual Dirac

Analysis

Waveform

Acquisition

Jitter Decomposition Overview

Complete T.I.E Record

DDJ: T.I.E per Bit

RJ/PJ T.I.E Record

Reported Values of TJ, RJ, DJDD

Four Critical Areas

Evaluate TIE

DDJ Analysis

RJ Extraction

Clock

Reference

Dual Dirac

Analysis

Waveform

Acquisition 1 2

3

4

Inattention to these areas will compromise your result.

1

2

3

4

Signal Fidelity in Connection

Oscilloscope Settings

Clock Recovery Type &Setting

PLL Parameters

Pattern Type/Length Expected

Gaussian Jitter Estimation

Method

Measurement Signal Fidelity

Connection path to signal isn’t perfect Waveform

Acquisition 1

Scope Probe/Connection Flatness

Test Point Access Fixture BW/Flatness

Skew

Match

Test

Fixture Your Device Tx

Degradation in performance of any of these will cause DDJ increase

in your result, and affect RJ as well.

You want

not

Frequency Response of Infiniium DSO91304A

Key Observations

• Agilent meets specified bandwidth will all of it settings.

• Agilent provides the flattest frequency response by using the DSP magnitude and phase compensation technology.

• Notice the amplitude gain/attenuation variations are controlled to the minimum amount throughout the bandwidth,

Agilent DSO91304A 13GHz FLAT Response

Magnitude Flatness +/-0.25dB up to

32GHz

Agilent DSOX93204A 32GHz ULTRA-FLAT Response

Oscilloscope Settings Waveform

Acquisition 1

Scale Setting

Threshold Settings

Hysteresis

Acquisition Length

Test

Fixture

Your Device

Oscilloscope settings: Input Scaling

Scaling = Volts/division selection

A poor selection will Amplify scope noise floor to affect your

measurement….

Choose a scale that gets the ‘raw’ signal close to full screen.

Push Knob to access Vernier DO NOT OVERDRIVE the SCOPE

Waveform

Acquisition 1

Tip for Good Measurement

Oscilloscope Settings: Scale and Jitter

Dependent on slope of

signal, noise on signal and

noise of scope

Waveform

Acquisition 1

0

10

20

30

40

50

60

70

80

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Full Half Qtr Eighth

Jit

ter

Pk

-Pk

RJrm

s

Scale

Jitter vs Full Scale

RJ

TJ

Why is your Oscilloscope Vertical Noise

Floor Impacting your Jitter Results? Let’s consider a theoretical signals with Zero jitter, fixed voltage noise

presenting three different edge speed and crossing a Threshold at

50%

1. Voltage noise translate directly in Jitter

2. Higher Vertical Noise Floor translate in Higher Jitter

3. Slow Edges will dramatically transform vertical Noise into Jitter

4. At constant Edge Speed, best Measurement Noisefloor translate into

Lowest RJ and TJ Jitter, Best Eye Diagram Opening and more repeatable

results!

Oscilloscope Noise Impacts Measured Jitter Measure AC rms measurement at proper Volts/Div scale for DUT signal

Agilent 90K X-Series: ~ 6.1 mV

(at 137 mV/div and 32 GHz BW Setting) Agilent 86100D/86108B Series: ~ 640 uV

(at 35 GHz BW Setting) & 140mV/div setting

Note - single-ended noise measurements since we’re performing a comparison using single-

ended signals (analyzing P and N from the same DUT)

Manually Determine Induced Jitter due to Scope

Noise and Signal’s Slew Rate

Induced Jitter due to scope noise:

1. 86100D / 86108B DCA-X Noise = 640 uV

Slew Rate = 173.3 mV / 8.34 ps

= 20.8 V/ns

Induced Jitter = RN / SlewRate

= 640uV / 20.8V/ns

Induced Jitter = 31 fs

2. 90K X-Series Oscilloscope Noise = 6.1 mV

Slew Rate = 26 V/ns

Induced Jitter = RN /SlewRate

= 6.1mV / 26 V/ns

Induced Jitter = 234 fs

The faster the edge, the smaller the problem! And vice-versa!

RN = Random Noise(rms)

Slew Rate = rate of change of signal in V / ns

= Delta V/ Delta T

Delta V

Delta T

Estimate Jitter due to Intrinsic Scope Jitter/Noise

and Signal’s Slew Rate (AM-to-PM Conversion)

Measured Jitter = SQRT [(Timing Jitter)^2 + (AM-to-PM Jitter)^2)]

Example: 86100D / 86108B

1. DUT Random Jitter = 200 fs

2. Scope Random Jitter = 50 fs

Random Timing Jitter = 206 fs = SQRT [(200^2)+(50^2)]

Example: 90K X-Series

1. DUT Random Jitter = 200 fs

2. Scope Random Jitter = 75 fs

Random Timing Jitter = 213 fs = SQRT [(200^2)+(75^2)]

Scope jitter results include noise induced jitter (AM-to-PM conversion).

Results change due to signal slew rate and random noise.

Measured Jitter

= SQRT [(213)^2 + (234)^2)]

= 317 fs

Measured Jitter

= SQRT [(206)^2 + (31)^2)]

= 208 fs

3. Noise Induced Jitter from scope

= 31 fs (see previous page)

3. Noise Induced Jitter from scope

= 234 fs (see previous page)

Summary - BaNoise / Slew Rate

As random noise (RN) increases, random jitter

increases. Especially problematic with slower

edge speeds!

Minimize oscilloscope noise. Use only enough

BW to capture signal.

43

Case Study: Observing the 4.8Gbps (FB-DIMM like)

Signal with Various Edge Rates (at 55ps)

4.8Gbps: Fundamental Freq = 2.4GHz, 3rd Harmonics = 7.2GHz, 5th Harmonics = 12GHz

6GHz Scope

8GHz Scope

12GHz Scope

6GHz scope only captures fundamental frequency.

8GHz scope captures both fundamental and 3rd harmonics, but not 5th. The eye pattern changes dramatically.

Although 12GHz scope captures 3rd and 5th harmonics, at 55ps rise time, there is no difference between eye patterns of 8 and

12GHz scope even the signal rate stays at 4.8Gbps. This is because the signal has no 5th harmonics freq content.

It is the “edge rate” that determines required BW, not 3rd and 5th harmonics.

45

• A simple calculation matrix to determine the required scope bandwidth and the sampling rate to characterize a given signal accurately.

• Notice, due to the different amount of “out of bandwidth” signal frequency contents that each filter response captures (i.e. becomes the source of aliasing), in order to characterize the signal with desired accuracy, a scope with a “Gaussian” filter response requires more bandwidth and more sampling rate than a scope with a “Brickwall” filter response.

Rise Time vs. Bandwidth and Required Sampling Rate

Scope BW and Measurement Accuracy

fmax 0.5 / Rise Time (10%-90%)

0.4 / Rise Time (20%-80%)

Scope Digital Filter Type Gaussian Brickwall

Measurement Error of Tr Scope BW

20% 1.0 fmax 1.0 fmax

10% 1.3 fmax 1.2 fmax

3% 1.9 fmax 1.4 fmax

Sampling Speed (With sin (x)/x interpolation feature)

4 x BW 2.5 x BW

For more info, see application note 5988-8008EN

Oscilloscope Settings:

Threshold Settings

Choose:

• Fixed Threshold ONLY

• Threshold Value

Use halfway point in the signal swing. Most differential buses will

stipulate 0 volts as the threshold. Examine rise and fall time differences.

Waveform

Acquisition 1

0.0 mV threshold 10.0 mV threshold


Setting Hysteresis: You are setting how you discern an edge.

If the setting is too low:

the scope will interpret multiple edges.

If the setting is too high:

the scope will miss edges altogether.

threshold

Hysteresis settings

1 region

0 region

threshold

Hysteresis settings

1 region

0 region

1

0

Waveform

Acquisition 1

Use Halfway point between threshold value and the smallest 0-1-0 or 1-0-1

swing



Hysteresis Settings

Use the Setup Wizard. Experiment for repeatable and consistent

results.

Waveform

Acquisition 1

It’s a balance:

If the setting is too low:

- can’t do PLL clock recovery

- won’t see enough of the signal edges

If the setting is too high:

- the scope responsiveness suffers

- may start including more 1/f noise than you want



Memory Depth

Check things out…

You can quickly analyze the T.I.E. Trend...

Before performing Jitter separation, check the T.I.E trend, spectrum

for ‘reasonableness’.

? !!


Checking for ‘Reasonableness’

More on T.I.E. Trend….

Unsmoothed

Smoothed

Smoothed and Expanded

Peak to Peak trend measurements will let you know if you are in the ballpark…

If you get something like 10nSeconds on a 2Gbs signal, you likely have issues

you need to resolve before doing jitter decomposition

Analyze the T.I.E. Spectrum….

Short time record Longer (32x) record

T.I.E. Spectrum measurement will let you see frequency components. Higher

resolution may demonstrate frequency spacings of clock harmonics, DDJ

spacings, or multiple jitter sources.

Checking for ‘Reasonableness’

Clock Reference

Jitter measurement demands a reference. It may be:

From previous edges in the signal

Externally Available

Recovered from a Hardware clock recovery unit

Constant Clock estimation

Software PLL

Clock

Reference 2

SW PLL and Constant Clock Clock

Reference 2

Constant Clock 2nd Order SW PLL

0.5 MHz Sine wave is reduced 18 dB

and there is no other low freq content

0.5 MHz Sine injected.

1/f noise content seen

Quick Review - Clock Recovery (CR) Basics

Phase DetectorVoltage Controlled

Oscillator (VCO)Data Input Recovered Clock

Phase

Error

Amplifier

o Provides a recovered clock for receiver

o Manages jitter in the system

o Standards specify CR Phase Locked Loop (PLL) order, bandwidth, peaking, or damping factor

0

0.2

0.4

0.6

0.8

1

1.2

1.0E+3 10.0E+3 100.0E+3 1.0E+6 10.0E+6 100.0E+6

Jitte

r M

ultip

lier

Frequency (Hz)

Clock Recovery PLL Response Jitter Transfer Function (JTF)

and Observed Jitter Transfer Function (OJTF)

PLL “Jitter Transfer Function” (JTF) • indicates how much of the jitter on the

input signal is “transferred” to the

recovered clock (output)

• low-pass filter function (LPF)

“Observed Jitter Transfer Function” (OJTF) • indicates the jitter that is “observed” by the

receiver (scope)

• high frequency jitter on the data stream is

“transferred” to the receiver (HPF)

Sampler

(Receiver)

Input

Signal

)()()()(1

)(

gain loop Closed JTF

sj

in

outesGsG

sA

sA f

f

f

)()(1)(-1

1OJTF

sjesGsG

JTF

f

Basic CR Block Diagram Narrow

CR Loop

BW

Wide CR

Loop BW

Data relative to a

“clean” clock

(narrow loop BW)

Data relative to

recovered clock

(wide loop BW)

OR

OR

Agilent 86100C/D Sampling Scope

CR loop BW setting configures JTF

JTF Example: Ethernet, SONET/SDH

Agilent 90K Series Real-time Scope

CR loop BW setting configures OJTF

OJTF : SATA/SAS

BEWARE of Clock Recovery

(PLL) Definitions!

Standards (and scopes)

describe PLL requirements

differently.

Jitter Spectrum To understand how the CR PLL response impacts low frequency jitter, it is

useful to observe jitter in the frequency domain

Magnitude

Frequency

Offset frequency

Jitter Spectrum Shows distribution of low frequency jitter and impact of clock recovery

Spectral lines indicate deterministic jitter (including SSC and its odd harmonics)

Observe all incoming jitter

Wide CR loop bandwidth

Jitter floor (without tones)

is random jitter

Clock Recovery response greatly impacts amount of jitter

seen by receiver, and/or measured by an oscilloscope!

Narrow CR loop bandwidth

Track out low frequency jitter

Clock Recovery Models

86108B

FTD_DCA_22

4

Agilent

Restricted

March 2012

1st Order PLL:

JTF BW = OJTF BW

Peaking/DF = none

Roll-Off: 20 dB/decade - Less ability to track out low

frequency jitter and stay locked

- Real hardware CR does not

behave this way

2nd Order, Type 2 PLL:

Bandwidth: JTF BW > OJTF BW

Peaking/Damping Factor: need to specify

Roll-Off: 40 dB/decade

(tracks out low jitter more than 1st order PLL)

3rd Order PLL:

JTF BW > OJTF BW

- Specify zero, gain, pole

frequencies.

- Roll-Off: 60 dB/decade

below zero frequency

- Use “PLL Response Tutorial”

workbook to model.

HW CR Loop Response Desired SW CR Loop Response e.g. match a standard exactly HW CR response may

have higher peaking in

OJTF than “desired”.

This will amplify jitter in

this region.

Note – significance

depends on DUT jitter

spectrum.

Jitter Spectrum Jitter Spectrum

Less Peaking

Jitter Spectrum Analysis and SW Clock Recovery

Emulation using Agilent 86100D/86108B-JSA

Ideal Software

Clock Recovery

Emulation

Device

Under

Test

86108A/B Module

• “Real” CR PLL response

• Adjustable Loop Bandwidth

• Adjustable Peaking (discrete)

• “Ideal”, flexible CR PLL response

• Adjustable Loop Bandwidth

• Adjustable Peaking (continuous)

Integrated

Hardware

Clock

Recovery

Data or Clock

Signal

Filtered

Signal (“Jitter Fitler”) (“Jitter Filter”)

Jitter Spectrum Jitter Spectrum

Apply “ideal” PLL

using Software

Clock Recovery

Emulation

Hardware only clock recovery “Ideal” SW Clock Recovery Model

Higher

Accuracy

Desired SW CR Loop Response e.g. match a standard exactly

HW CR response may

have higher peaking in

OJTF than “desired”.

Jitter amplification will

occur in region where

unwanted peaking

exists.

Note – “how much” of

an increase depends

on DUT jitter spectrum.

Less Peaking

90000 X-Series

59

Clock Recovery Comparison Always use similar clock recovery models – “Apples-to-Apples” setup

Agilent 90K X-Series Agilent 86100D with 86108B

10 Gb/s Jitter Measurement – Matching CDR

We are using the same CR setup now, but are there other things we should look at?

OJTF: 2nd Order 10 MHz Loop BW, 0.707 DF JTF: 2nd Order, 20 MHz Loop BW, 2dB Peaking

OJTF: 2nd Order 10 MHz Loop BW, 0.707 DF

10G Pattern

Generator

D+ D-

“Perform a jitter measurement using 2nd Order CR response with

10MHz OJTF and 0.707 DF.”

Pattern Type/Length Data

Dependence

Analysis 3

Data Out

Repeating

Non Repeating

Extraction Data Out Pattern

Arbitrary

Periodic/Arbitrary

Arbitrary

Short: 27, 29, 211, 215

Long: 223, 231

ISI Channel Your Device Tx

Periodic Pattern

is generally preferred

algorithm is robust/efficient

Arbitrary Pattern

requires dynamic estimation

of ISI channel so is less

efficient.

If Arbitrary mode is a must, analyze step response if possible.


Pattern Type/Length Data

Dependence

Analysis 3

Data Out ISI Channel Your Device Tx

Arbitrary Data: Analyze Step

Measure step length in terms

of Unit Intervals, N. Use value

as starting point in determining

optimal setting for Arbitrary

Mode ISI Filter. PRBS 231 3Gbs

N RJ

4

6

8

10

Minimize RJ

Trade off with time

RJ Extraction RJ

Extraction 4

We are here

We will now deal with your

algorithmic options in the

evaluation of the RJ component

Evaluate TIE

DDJ

Analysis

RJ

Extraction

Clock

Reference

Waveform

Acquisition 1 2

3

4 Characterize the tails

of the distribution

RJ Extraction RJ

Extraction 4

Jitter Measurement

Algorithm on

Oscilloscope

Gaussian Tail Fit

Rationale Extraction Method

General Purpose/

ABUJ (Xtalk) Conditions

Spectral

Narrow Bandwidth

Wide Bandwidth Known Bounded Noise

Presence of Low Freq RJ

Speed/Consistency to Past

Accuracy in low BUJ cases

Spectral Extraction Method tim

e e

rror

freq0

0

likely to contain PJ

PJ threshold

tim

e e

rror

freq0

0

likely to contain PJ

PJ threshold

RJ

Extraction 4

Integrate PSD to derive d,

or, RJRMS. Sum the PJ

components for PJRMS

PJ threshold is

chosen by

experimentation.

Measurement Detail

Spectral Extraction RJ

Extraction 4

Separation occurs

as described…

What do you do in

this case?

Is it RJ

or PJ?

Spectral Extraction RJ

Extraction 4

Wide RJ BW analysis Narrow RJ BW analysis

RJ=.88ps

PJDD=10.4ps RJ=1.68ps

PJDD=4.0ps

Non-linear Threshold in limited acquisition sizes can help this…

Choosing longer sampling time and/or selecting Narrow Mode

will spread the spectrum around (greatly alias) and will have the

effect of the flattening the noise.


RJ Spectral Extraction: Wide vs Narrow RJ

Extraction 4

Analyze the bathtub plot for slope continuity between measured data

and extrapolated result


ABUJ: Crosstalk or Ground bounce

Amplitude interference uncorrelated with data

and not periodic in nature.

Crosstalk Interference Model

No crosstalk

With crosstalk

Dv

Victim

Aggressor

Dt

Victim Out

Dt = Dv/Slopevictim

ABUJ Observations and Measurement (ABUJ= Aperiodic Bounded Uncorrelated Jitter)

1. View ABUJ in time domain

2. Techniques to Evaluate

Something is wrong here..

Using the slope continuity concept we expect

the extrapolated curve to look like this.

The RJ/PJ spectral extraction doesn’t deal with ABUJ well.

The RJ is overestimated severely.

RJ Extraction with Crosstalk (ABUJ) Spectral vs Gaussian RJ Extraction.

X

RJ

Extraction 4

Analyze the bathtub plot with both extraction modes to explore

presence of crosstalk or ground bounce.


Spectral Extraction

Gaussian Tailfit

Extraction

No Crosstalk w/Crosstalk

Compare actual Data with RJ estimates of both methods Spectral Extraction

Gaussian Tailfit

Extraction

Examine slope continuity

What makes Tail fitting hard

0 5 10 15-0.2

0

0.2

0.4

0.6

0.8

1

1.2Histogram Object

High Statistical Precision

Low accuracy Extrapolation

Lower Precision

Statistics

Higher accuracy

Extrapolation

Fit Window

DJ end Noisy data

RJ

Extraction 4

Measurement Detail

More data may be required to get reliable consistent results

Aperiodic Bounded Uncorrelated Jitter

Crosstalk, time aligned for illustration.

Time Domain Views

Aggressor

Victim

Victim

Aggressor

Aggressor

Aggressor at transition

Aggressor in middle of eye

Adjusting the Crosstalk in phase

Two Ways to Analyze ABUJ

1. Two Pass Spectral Extraction Approach

Assumes you have control of the Xtalk interferer(s)

Assumes conveyed jitter of interferer is all ABUJ

2. If Interferers cannot be desactivated

Use Gaussian Tailfit Extraction

ABUJ/Crosstalk Analysis

1. Two Pass approach

a) Turn off crosstalk element(s).

b) Measure Jitter components

c) Turn on crosstalk element(s)

d) Enter RJrms value for RJ (‘specify’)

e) Crosstalk (ABUJ) will go into

bounded portion of jitter which will prevent

overestimation of RJ and Total Jitter.

1.47 ps

Victim

Aggressor


ABUJ/Crosstalk Analysis Two Pass Approach

No interferer With interferer

Victim

Aggressor


ABUJ/Crosstalk Analysis

2. Gaussian Single Pass RJ Tailfit Extraction

No interferer With interferer

Total Jitter TailFit estimation in this case is within 2% of Two Pass Analysis!

ABUJ is a bit tricky. Use every tool you have available.

Other Jitter Measurement Considerations

Gain Margin by removal of Scope contribution to RJ

ISI

Channel

DUT Tx

DUT Tx

With no Scope RJ removal With Scope RJ removal


Simulate Crosstalk to Evaluate Effect of Aggressor on Victim

Tx

Tx

Tx

Tx

.s2p or

.s4p +

.s2p or

.s4p

Tx

Tx

Ch A

Ch B .snp

+

Scope Front End HW

Actual Measurement Simulation

Great correlation


Analyze the Amplitude components of your signal

Analyze anywhere in the Unit Interval

Summary

Tx

f Noise

Pre-emphasis

Delay

Ground Bounce

ISI

Skew

Frequency Response

Crosstalk

Reflections

Skew

Four Critical Areas

Your device and Environment

Dual Dirac Model 2 4 6 8 10 12 14

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Histogram Fits. True RJrms = 2, PJmax = 5

ABUJ (Crosstalk) Analysis

Use tools available

Agilent’s Oscilloscope Portfolio Real-time Bandwidth from 50 MHz to 63 GHz

Handheld

U1600B

USB

U2700

2000X

DSO/MSO

3000X

DSO/MSO

6000A

DSO/MSO

7000B

DSO/MSO

9000A

DSO/MSO

90000A

DSO/DSA

90000X

DSO/DSA

90000Q

DSO/DSA

InfiniiVision Series Infiniium Series Entry

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• Up to 80 GS/s sample rate

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Documents

Practical Guide to Making Advanced Jitter Measurementsscopetools.free.fr/Agilent_Signal_Integrity/HighSpeedSerialDigital... · Practical Guide to Making Advanced Jitter ... The easiest