Jitter Separation in High Speed Digital Design
Gustaaf Sutorius
Jitter & Typical Digital Development Process
System
Design
Interconnect
Design
Active Signal
Analysis
• Accurate Design
Analysis
• Test & Analysis
Capability
• Measurement
Automation
Compliance
Test
AGENDA
1. Jitter:
I.
Definition and Description of Jitter
II. Understanding Jitter, its Components, and Separation
III. Jitter Measurement Methods and Tools
2. Actual jitter measurements
Page 3
AGENDA
1. Jitter:
I.
Definition and Description of Jitter
II. Understanding Jitter, its Components, and Separation
III. Jitter Measurement Methods and Tools
2. Actual jitter measurements
Page 4
Jitter Primer: Topics to be Covered
1.
Definition and Description of Jitter
2.
Understanding Jitter, its Components, and Separation
3.
Jitter Measurement Methods and Tools
Page 5
What is Jitter?
• ‘Jitter ‘ is another word for shaky, quiver,
tremulous… speaks of degree of instability of
location.
• In the Digital Design world, jitter has been defined
as:
The short term phase variation of the
significant instants of a digital signal from
their ideal positions in time.
Page 6
What is Jitter: Analyzing an Edge (Transition)
Ideal Location in Time (Reference)
Transition
Instant
Early
Threshold
Late
∆tEarly
0
∆tLate
1
JPP=∆
∆tEarly Pk + ∆tlate Pk
Page 7
Units for expressing Jitter
1) Seconds:
if ∆tEarly =60 ps and ∆tLate=40ps
JPP= 100 pseconds
2) UI:
Referenced to the Data Rate, called Unit Interval (UI):
For 2.5 Gb/s Data Rate, the UI (Period) = 400 pseconds
JPP= 100 pseconds/400 pseconds per UI = 0.25 UI
3) Radians:
where there are 2π
π radians per UI:
JPP= .25 UI x 2π
π= π/2 radians
Page 8
Jitter: Creating the Eye…
E1
Eye Crossing
Points
Single
transition
Left Edge
Nominal
Sampling Point
Right Edge
E0
x=0
The EYE Diagram
Unit Interval
x = 1/2 T
x=T
Oscilloscope Eye
Overlaid
transitions
Total Jitter, JPP
Ideal Sampling Point
Probability Density
Function
Page 9
Why Care about Jitter?
• Bit Errors!
Transmitted
Waveform
1
0
0
1
0
1
1
0
Received
Waveform
1
0
0
1
0
1
1
0
Interpretted
Waveform
1
1
0
1
0
1
1
0
Page 10
Jitter as Horizontal “Timing Noise”
• A low “Signal to Noise Ratio”
causes errors
• Voltage Noise → vertical
fluctuations across the
sampling point
• Undesirable Amplitude
Modulation
• Jitter describes the same
effect but horizontally –
timing noise
• Jitter → horizontal
fluctuations across the
sampling point
• Undesirable Phase
Modulation
Page 11
Jitter – What Causes It?
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Oscillator Topology
PLL Design
Noise
Crystal Performance
Mechanisms
Thermal Noise
Shot Noise
Dispersion
Reference Spurious
System
Radiated or Conducted Signals
Crosstalk
Mechanisms
Duty Cycle Distortion mechanisms
Impedance mismatch
Inter Symbol Interference mechanisms
Data Dependent
Receiver Detector characteristics
Mechanisms
Clock/Data Recovery Design
PRBS Mechanisms
Page 12
Jitter Primer: Topics to be Covered
1.
Definition and Description of Jitter
2.
Understanding Jitter, its Components, and Separation
3.
Jitter Measurement Methods and Tools
Page 13
Representing Jitter
S(t): a general digital jitter signal and P(t): a pulse train
S(t)=P(Asin(2πfDt+ϕ(t)))
Where ϕ(t) is overall system jitter function with many sources.
ϕ(t)= ϕ B(t) +ϕ UB(t)
ϕΒ(t) is composed of functions
that have Deterministic
(Bounded) phase deviations
because their max amplitudes
don’t change
ϕUΒ(t) is composed of functions that
have Random (UnBounded) phase
deviations because their max
amplitudes do change. The functions
are characterized by their statistics
Page 14
Lets Look at the Jitter Sources Again…
Oscillator Topology
PLL Design
Crystal Performance
Noise
RANDOM
Thermal Noise
Shot Noise
Dispersion
Reference Spurious
Radiated or Conducted Signals
System
Crosstalk
Duty Cycle Distortion mechanisms
Impedance mismatch
Inter Symbol Interference mechanisms
Receiver Detector characteristics
Data
Clock/Data Recovery Design
PRBS Mechanisms
/ UNBOUNDED
DETERMINISTIC
BOUNDED
Page 15
Example Random and Deterministic Jitter
σ
Random Jitter (RJ):
Defined by RMS value, σ,
of the Gaussian
distribution
JPPDJ
Deterministic Jitter (DJ): The spacing
between the mean values of the
“earliest” and “latest” traces, JPPDJ
Page 16
Expressing Total Jitter
•
•
Usually represented as root-mean-square, Jrms, and peak-to-peak,
JPP
Most useful to characterize jitter as a combination of JrmsRJ and JPPDJ
at a given Bit Error Ratio (BER)
Random Jitter (RJ) – results from the accumulation of random
processes.
• Assumed to Follow a Gaussian Distribution
RJ contribution to Jrms is JrmsRJ = σ
• Since a Gaussian function is unbounded,
RJ contribution to JPP can be large JPPRJ → ∞
Deterministic Jitter (DJ) – results from systematic effects
•
•
E.g., duty-cycle-distortion (DCD), intersymbol interference
(ISI), periodic jitter (PJ), PRBS effects, and crosstalk
DJ is bounded, JPPDJ is finite.
Page 17
Random jitter: JPPRJ is related to Bit Error Ratio
Unit Interval
Sampling Point
Measure BER(x) = β(x)
Gaussian
Jitter Only!
(No DJ)
x
σL
σR
Overlap indicates BER
µ
Sampling Point
µ
JPPRJ = n×
×σ
Page 18
Random Jitter JPPRJ : What factor to use ?
JPPRJ = n×
×σ
JPPRJ
Random jitter is UNBOUNDED, if we wait long enough we would have “hits” anywhere in the Eyediagram.
We could use any Berr but 10-12 is quite common to use and 10-12 equals to 14.1 sigma.
So if we measure sigma is 10 picoseconds, then we would say the random jitter is 141 Psec.
Page 19
Expressing Total Jitter: RJ & DJ combined
•
•
Since JPPRJ is unbounded, it can be defined by the BER that
would result if there were only RJ. This is where the tails of the
right and left distributions overlap (at the Sampling point):
For a BER = 10-12 → JPPRJ = 14×
×σ
Then JPPRJ ≡ n×
×σ so that JPPRJ =nxJrmsRJ
The Total Jitter (TJ), JTJ, for a given BER is then:
RJ
DJ
J TJ = n × J rms
+ J PP
DJ
= 14 × σ + J PP
This assumes that the Gaussian RJ PDF ‘appends’ to the DJ PDF
This is called the Dual Dirac Assumption
Page 20
The Dual Dirac Assumption
Total Jitter
The ‘RJ’
The ‘DJ’
JPPDJ
7σ
No Jitter values
between deltas
µL
[δ ( x − µ L )
∗
µR
+
δ ( x − µ R )] ∗
σ
 x2 
exp −
2 
 2σ 
=
µL
=
µR
 (x − µ L )2 
 (x − µ R )2 
exp −
 + exp −

2
2
σ
2σ 2 



Page 21
Jitter Probability: BER
J pk − pk = J deterministic
n ×σ random
=
Page 22
Random and Deterministic Jitter
•
•
•
Waveform Observation
Pattern
Note Characteristics
σ = JrmsRJ
JPPDJ
2 Distinct
Falling Edges
2 Distinct
Rising Edges
Threshold
JPP
Jrms
Lots of Zeros
Page 23
Random and Deterministic Jitter
•
Lets Look at Deterministic Component…
σ = JrmsRJ
DJ
J
DJ
J PP
PP
JLPPDJ
JRPPDJ
JLPPDJ + JRPPDJ = JPPDJ
JPP
The Peak-to-Peak Deterministic
value is the DeltaJrms
between
Worst case mean trajectories around a crossing point.
Page 24
Random and Deterministic Jitter
•
Now lets Look at the Random Component…
σ = JrmsRJ
JPPDJ
σRJ
σRJ
σRJ is a measure of the process that makes these traces wide
JPP
Jrms
Page 25
Random and Deterministic Jitter
•
Now lets Summarize Jitter for the Circuit Measured…
DJ
J
DJ
J PP
= JrmsRJRJ
σσ=J
rms
PP
JPPT
JPPT = n x σRJ + JPPDJ
JPP
Jrms
Page 26
Total jitter: Histogram View
Total Jitter is composed of
random and determistic
components
Random Jitter (RJ) unbounded
• Due to thermal noise, shot noise, etc.
• Follows Gaussian distribution
• Requires statistical analysis to be
quantified
• RJpp = 14.1 x Jrms for 10-12 BER
Deterministic Jitter (DJ)
bounded and composed of:
DJ
• Duty-Cycle-Distortion (DCD)
• Inter Symbol Interference (ISI)
• Periodic Jitter (PJ)
RJ
Page 27
Correlated
Decomposing Jitter: The “jitter tree”
TJ
DJ
DDJ
ISI
Uncorr
RJ
PJ
DCD
Signal jitter can be composed of several types from several mechanisms
Data-Correlated
Data-Uncorrelated
Total
ϕB(t) Jitter (TJ)
Deterministic
Jitter (DJ)
Random
Jitter (RJ)
Data Dependent Jitter
(DDJ)
Inter-symbol
Interference (ISI)
Duty Cycle
Distortion (DCD)
Periodic
Jitter PJ
Page 28
Correlated
TJ
Example: Duty Cycle Distortion (DCD)
DJ
RJ
DDJ
Transmitter Threshold Offset Problem
ISI
Uncorr
PJ
DCD
1
1
Actual Threshold
Ideal Threshold
0
0
Clock
+ error
- error
+ error
- error
TIE Trend Waveform
Note: One technique to test for DCD is to stimulate your system/components with a repeating 1-0-1-0… data pattern.
Page 29
This technique will eliminat inter-symbol interference (ISI) jitter and make viewing the DCD within the spectrum display much easier
.
Correlated
TJ
Example: Duty Cycle Distortion (DCD)
DJ
RJ
DDJ
Transmitter Edge Transition Speed Asymmetry
ISI
Uncorr
PJ
DCD
1
1
Threshold
0
Clock
- error
+ error
- error
+ error
TIE Trend Waveform
Page 30
Correlated
TJ
Example: Inter-Symbol Interference (ISI)
DJ
Transmission Line Bandwidth Limitation Problem
C
A
B
1
1
1 1 1 1
DDJ
1
1
1
ISI
Uncorr
RJ
PJ
DCD
1 1
Threshold
0
0
0
0
0
0 0 0 0
0 0
“A” = 0 preceded by string of 1’s = + error
TIE Trend Waveform
“C” = 1 preceded by string of 0’s = + error
“B” = 1 preceded by 0 = - error
Page 31
Correlated
Example: Inter-Symbol Interference (ISI)
TJ
DJ
Transmission Line Reflection / Improper Termination
RJ
DDJ
ISI
Uncorr
PJ
DCD
Data Signal
TIE Trend Waveform
Each arrow shows which bit of data caused a reflection distortion
on a later data bit.
Page 32
Correlated
TJ
Example: Periodic Jitter (PJ)
Uncorr
DJ
System Cross-talk Problem (capacitive coupling)
RJ
DDJ
ISI
PJ
DCD
Corrupter
Threshold
TIE Trend
Page 33
Where Does Jitter Come From?
Correlated
TJ
DJ
DDJ
ISI
Transmitter
Media
Uncorr
RJ
PJ
DCD
Receiver
•Lossy interconnect (ISI)
•Impedance mismatches (ISI)
•Crosstalk (PJ)
•Thermal Noise (RJ)
•DutyCycle Distortion (DCD)
•Power Supply Noise (RJ, PJ)
•On chip coupling (PJ)
•Termination Errors (ISI)
•Thermal Noise (RJ)
•DutyCycle Distortion (DCD)
•Power Supply Noise (RJ, PJ)
•On chip coupling (PJ)
Page 34
Jitter examples for different Jitter Distributions
Different types of jitter ϕ(t) in S(t)=P(Asin(2πfDt+ϕ(t)))
ϕ(t ) = mess
ϕ(t ) = square wave
ϕ(t ) = A Appl sin (2 π fJ t) .
ϕ(t ) = DDJ Only
ϕ(t ) = pulse
Page 35
Jitter Examples Continued
A DCD
C RJ (gaussian)l
B ISI
D Sinusoidal
E ISI and DCD
Page 36
Jitter Primer: Topics to be Covered
1.
Definition and Description of Jitter
2.
Understanding Jitter, its Components, and Separation
3.
Jitter Measurement Methods and Tools
Page 37
Which Eye Has Worse Jitter?
A
B
You can’t know unless you measure the Total
Jitter or measure the jitter components!
Page 38
Jitter Measurement Solutions from Agilent
•
Infiniium Scopes (up to 32 GHz):
• EZJit Software
• EZJit Plus Software
•
DCA-J (86100 Series Infiniium 20-80 GHz Scopes)
• Jitter SW package
•
Infiniimax Probes to 13 GHz
•
N1930 Physical Layer Test System
• Vector Network Analyzer or Time Domain Reflectometer
•
N4900 Series BERTs
• Bathtub curve Extrapolation and RJ/DJ Estimation
•
E443x Signal Sources
• E4438C-SP1 Jitter Injection Software
Page 39
Tools to Measure/Analyze Jitter
Transmitter Media Receiver
Pattern Generator
Bit Error Ratio Tester
X
X
X
X
X
Vector Network analyzer
X
Time domain Reflectometer
X
Real time oscilloscope
X
X
Equivalent time oscilloscope
X
X
Phase Noise Analyzer
X
Time Interval Analyzer
X
X
Page 40
Jitter Tolerance Testing (w/Pattern Generators)
Pros
Low Noise (RJ) available
Standard Patterns and User Definable Patterns
Flexible for wide variety of technologies.
RJ, PJ, and DCD can be created.
Cons
Cost Range: Modestly to Highly Expensive
Intersymbol Interference is not available.
Complex sequencing not available.
Page 41
Tolerance Testing (using a Pattern Generator)
Square
Sinusoidal
Sinusoidal,
RJ and ISI*
* Created with cable length
Page 42
Jitter Analysis (BERTs)
Pros
Measures Total Jitter Directly
Can Provide good estimate of total Jitter quickly with BERTScan method
System Tool: Usable for Media analysis, receiver stress analysis
J-Bert N4903B available for jitter stress test
Cons
Expensive
Time of Measurement of Total Jitter is Long
Need an external clock provided
Page 43
Jitter Analysis: BERT BathTub Curve
Scan the sampling point across the eye
Scan the sampling point, x, across the
eye
Measure BER(x) = β(x)
x
0.5
BER
β(x)
10
Measure the Bit Error
ratio as a function of
sampling point delay,
-3
Gaussian
Tails
10-6
10-9
β(x) ⇒ TJβ
Eye Opening at
BER=10-12
10-12
0
0.5TB
TB
Page 44
Jitter Analysis: N1951A PLTS with Vector Network Analyzers
(VNAs) or Time Domain Reflectometers (TDRs)
VNAs
Expensive
50 GHz BW available yields high
resolution
Highest Accuracy
Full Differential Analysis
analysis to show EMI, mode
conversion locations
Software Modeling and Analysis
Available
S-Parameters for modeling or to
estimate ISI contribution of path
TDRs
InExpensive
Limited by rise time of Pulse
source (35ps)
Accuracy may be sufficient in
many environments. Using
Normalization to increases
accuracy
Only magnitude TDT and TDR
Software Modeling and Analysis
Available
Page 45
N1951A VNA Measurement of XAUI Backplane
Differential Eye Diagram (from Agilent N1951A: VNA System)
Xaui Backplane differences because of transmission line length
15 inches
30 inches
Note increased striation
because of BW limit of path
Note degree of
eye closure
Page 46
Jitter Analysis (Real Time Oscilloscopes)
Pros
•Captures contiguous time record
•No external clock required
•Software clock recovery methods yield precise clock reconstruction
•System Tool: Usable for Debug
•Flexibility for many technologies and usually a growth path provided
•Many views provided for insight: histograms, eyes, fft, trend, data, etc
•Oscilloscope Bandwidths are going higher
Cons
•Expensive
•Limited to current BW of scope
Page 47
Agilent Infiniium Series
Oscilloscopes
High Bandwidth Models up to 32 GHz & 80 GSa/s per channel
Deepest memory in the market up to 2 Gpoint per channel
MegaZoom usable deep memory
Mixed Signal Oscilloscope (MSO) models available
Windows-Based Easy to Use GUI
Drag-and-Drop easurements
Zoom box
Wide variety of analysis options
Page 48
How Do Real Time Scopes Measure Jitter on Data: Ezjit Display
NRZ
Serial
Data
Recovered
Clock
Jitter
Trend
Jitter
Spectrum
Units in Time
Units in Freq.
Jitter
Histogram
Page 49
Agilent E2681A EZJIT Jitter Measurement Application for Infiniium Oscilloscopes
Signal
Histogram
Trend
Spectrum
Page 50
Sampling Techniques
• Real Time (Single-Shot)
• Sequential Sampling (Repetitive)
Page 51
Sampling
Real Time (Single Shot) Technique
• Used with either Repetitive or Single-Shot Signals
• All Samples Are Taken From a Single Trigger
• Samples from Previous Triggers are Erased
• Sample Rate May Limit Scope’s Overall Bandwidth
• Best Resolution Depends Directly on Sample Rate
Each
Trigger
Identical
Page 52
Sampling
Sequential Sampling Technique
• Used ONLY with Repetitive Signals
• One Sample is taken for each Trigger
• Multiple Trigger Events Build Up Waveform
• Used in High Speed Applications with BW >10GHz
• No Pre-Trigger Information
1st Trigger
2nd Trigger
3rd Trigger
Page 53
Jitter Analysis (Equivalent Time Sampling Oscilloscopes)
Pros
InExpensive
Bandwidth is Highest Available
Noise floor is good
TDR options for media analysis
Flexibility for increasing rates
Industry leading jitter separation algorithm (DCA-J)
Cons
External Clock or Clock related trigger is required or
Hardware Clock Recovery Module
Page 54
Jitter Analysis (Equivalent Time Oscilloscopes)
A
B
Page 55
RJ
DJ
J TJ = n × J rms
+ J PP
Which Eye Has Worse Jitter?
A
DJ
= 14 × σ + J PP
B
Page 56
Jitter Measurements on an equivalent Time
Sampling Oscilloscope, 86100C DCA-J
Completely new technique for jitter analysis
Pattern Lock + Eyeline
internally generated pattern trigger + individual trajectories /
averaged eyes
Jitter Mode – jitter analysis at any data rate!
“Swiss army knife”
• Wide bandwidth scope
• eye-diagram analysis
• Time Domain Reflectometer
• Jitter analyzer
Page 57
DCA-J Measurement Architecture
• Eliminate historical weaknesses
• New triggering hardware enables efficient sampling
• Built in pattern trigger – Pattern Lock
• Determines pattern length and counts clock pulses
• Enables precise sampling position within the eye so every
sample is used for jitter analysis
• Minimizes errors from timebase delay
Page 58
Correlated
Separate Correlated and Uncorrelated Jitter
TJ
DJ
DDJ
ISI
Uncorr
RJ
PJ
DCD
Uncorrelated:
•
Counter hardware focuses samples on edges
•
Pattern lock – focus on specific edges
•
Analyze jitter uncorrelated to the pattern:
random jitter and periodic jitter (RJ ∗ PJ)
Correlated:
•
Pattern lock – average every
edge
•
Analyze jitter correlated to the
pattern:
data dependent jitter (DDJ)
Page 59
Correlated
Data Dependent Jitter (DDJ)
TJ
DJ
DDJ
Average out the uncorrelated jitter using Pattern
Lock
• Isolates data-correlated contributions only
ISI
Uncorr
RJ
PJ
DCD
Measure mean position of every edge in pattern
• Ideal edge position defined mean of means
Obtain DDJ vs. Bit record of edge positions
• DDJ for a given edge is the difference
between its average position and the ideal
• Peak-to-peak DDJ is difference between
earliest edge and latest edge
Build histograms for
• All edges
• Rising edges
• Falling edges
Page 60
Duty Cycle Distortion (DCD) &
Inter-Symbol Interference (ISI)
Correlated
TJ
DJ
Uncorr
RJ
DDJ
ISI
PJ
DCD
• Isolate rising edge data from falling edge data
• Difference of average locations is JDCD
• |µ
µFalling - µRising|
• Maximum of the peak-to-peak values is JISI
• Max (P-to-PFalling , P-to-PRising)
µF
DCD
µR
P-PF
P-PR
DDJ
Page 61
Correlated
Data-Uncorrelated Jitter
DJ
Uncorr
RJ
DDJ
Focus on only one edge at a time
• Isolates uncorrelated contributions
Build a time sampled record
• Periodic samples of uncorrelated jitter
ISI
PJ
DCD
Late
Jitter
Counter hardware provides
precise periodic sampling
TJ
Time
Early
Build a histogram of uncorrelated jitter
• RJ, PJ Histogram
Page 62
Correlated
Random Jitter (RJ)
TJ
DJ
Uncorr
RJ
DDJ
ISI
PJ
DCD
Jitter
Late
Early
PJ spikes NOT
used to derive
PJ value
Time
FFT time sampled record
• Aliased jitter frequency spectrum
• Shows RJ & PJ – PJ appears as spikes
Remove PJ spikes from spectrum
• Interpolate across gaps left behind
• Resultant spectrum is made up of RJ
Integrate ‘noise’ power in resultant spectrum…
• This is the random jitter (RJ)
Page 63
Correlated
Periodic Jitter (PJ)
TJ
DJ
Uncorr
RJ
DDJ
ISI
PJ
DCD
Take RJ info from FFT and construct a Dual
Dirac-delta model with appropriate slopes
Match Dual Dirac-delta model to RJ, PJ
histogram so that peak-peak widths match for
99.8% of volume
Separation (offset) of two Gaussians
corresponding to the match is the
periodic jitter (PJ).
Page 64
Correlated
Deterministic Jitter (DJ) and
Total Jitter (TJ)
RJ, PJ
TJ
DJ
Uncorr
RJ
DDJ
ISI
PJ
DCD
DDJ
• DDJ histogram (Data-Correlated)
and RJ, PJ histogram (DataUncorrelated) are measured
directly
• Convolution of these histograms
produces a histogram
representing the PDF of all of the
jitter present – Total Jitter
histogram
*
Aggregate
Jitter
Page 65
Deterministic Jitter (DJ) and
Total Jitter (TJ)
Correlated
DJ
Uncorr
RJ
DDJ
ISI
DJ
TJ
PJ
DCD
Take RJ info from FFT and construct a Dual
Dirac-delta model with appropriate slopes
Match Dual Dirac-delta model to TJ histogram so that
peak-peak widths match for 99.8% of volume
• Same technique as used to get PJ from RJ, PJ PDF
DJ
Separation (offset) of two Gaussians
corresponding to the match is the
deterministic jitter (DJ)
Extrapolate down the resultant Dual Diracdelta model to the effective BER of interest
(typically 10-12) peak-to-peak deviation is TJ
Page 66
Seeing the Complete Jitter Picture
Page 67
New: N5400A EZJIT Plus Jitter Separation
= DCA-J algorithm on a real-time oscilloscope
Page 68
N5400A EZJIT+ simplifies jitter compliance
Page 69
EZJIT and EZJIT Plus Measurements
• E2681A EZJIT Jitter Analysis
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Single-Source
Period
Frequency
Positive/Negative pulse width
Duty cycle
Rise/Fall time
Dual-source
Setup/Hold time
Phase
Clock
Time-interval error (TIE)
Cycle-to-cycle jitter
N-cycle jitter
Cycle-cycle positive/negative pulse width
Cycle-cycle duty cycle
Data
Time-interval error (TIE)
Data rate
Unit Interval
• N5400A EZJIT Plus Additions*
•
•
•
RJ/DJ Separation Components
Random jitter (RJ)
Deterministic jitter (DJ)
• Data-dependent jitter
• Inter-symbol interference (ISI)
• Duty cycle distortion (DCD)
• Periodic jitter
• Total jitter at user-selectable bit error rate
•
•
•
•
•
•
•
•
•
•
•
•
Display Views
RJ/PJ histogram
TJ histogram
DDJ histogram
Composite histogram (TJ, DDJ, RJ/PJ)
Jitter spectrum (zoomable)
DDJ vs. bit (for repeating patterns)
Bathtub curve (eye-opening vs. BER)
N5400A and E2681A common display views
Measurement trend
Histogram
Jitter spectrum
*N5400A includes all features of E2681A
as well as the following
Page 70
Summary
• Jitter is a complex phenomena and understanding and measuring it can be as
well.
• Having a Total Jitter to achieve a desired Bit Error Ratio is the main goal for any
digital interface.
• Jitter Separation is an Enterprise Jitter methodology to deliver an estimate of
Total Jitter quickly.
• There are many methods to separate jitter in our next paper we will see they can
give different results. The results for TJ are often 15-25% in error—almost
always an overestimate of TJ.
• There are many tools that can be used in the testing for jitter. Which ones you
select are dependent on your tasks, future projects, size, and your comfort level.
www.agilent.com/find/jitter
Jitter meas. solutions
www.agilent.com/find/jitter_info
Jitter app. info.
www.agilent.com/find/si
Signal Integrity Solutions
Page 71
Results Agilent Jitter Accuracy Study (Jitterfest 3)
TJ Estimate vs Actual TJ
300
Fast TJ Estimate (ps)
BERT
225
TRUE
DCA-J
DSO81304A/N5400A EZJIT Plus
150
75
0
0
50
100
150
Actual TJ (ps)
200
250
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AGENDA
1. Jitter:
I.
Definition and Description of Jitter
II. Understanding Jitter, its Components, and Separation
III. Jitter Measurement Methods and Tools
2. Actual jitter measurements
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Actual Jitter Measurements
•
86100D as jitter analyzer
•
81134A as pattern generaror
•
Demo 1: measure ISI jitter with bnc cable as “ISI injector”
•
Demo 2 : measure uncorrelated Pj and Resolve Pj frequencies
with MXG as uncorrelated Pj source
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•Questions?
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