Copyright © by Jose E. Schutt‐Aine , All Rights ReservedECE 451 1
ECE 451Signal Integrity
Jose E. Schutt-AineElectrical & Computer Engineering
University of [email protected]
Copyright © by Jose E. Schutt‐Aine , All Rights ReservedECE 451 2
TransmissionChannel
TransmissionChannel
TransmissionChannel
Ideal
Common
Noisy
Signal Integrity
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• Attenuation & Loss (skin effect, on-chip loss)• Crosstalk (interconnect proximity, coupling)• Dispersion (frequency dependence of parameters)• Reflection (unmatched loads, reactive loads, ISI)• Distortion (nonlinear loads)• Interference & Radiation (EMI/EMC)• Rise time degradation• Clock skew (different electrical path lengths)
Signal Integrity
Copyright © by Jose E. Schutt‐Aine , All Rights ReservedECE 451 4
The Interconnect BottleneckThe Interconnect Bottleneck
TechnologyGeneration
MOSFET IntrinsicSwitching Delay
ResponseTime
1.0 um
0.01 um
~ 10 ps
~ 1 ps
~ 1 ps
~ 100 ps
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ChipChip--Level Interconnect DelayLevel Interconnect DelayLine
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Vol
ts
0 0.4 0.8 1.2 1.6 2Time (ns)
Far End Response
BoardVLSISubmicronDeep Submicron
-0.1
0.175
0.45
0.725
1
0 0.4
Vol
ts
0.8 1.2 1.6 2Time (ns)
Near End Response
BoardVLSISubmicronDeep Submicron
Pulse Characteristics: rise time: 100 ps fall time: 100 ps pulse width: 4ns
Line Characteristics length : 3 mm near end termination: 50 far end termination 65
LogicthresholdLogic
threshold
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Signal Integrity
Crosstalk Dispersion Attenuation
Reflection Distortion Loss
Delta I Noise Ground Bounce Radiation
Sense Line
Drive Line
Drive Line
Interconnect BottleneckInterconnect Bottleneck
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Reflection in Transmission Lines
1.
2.
3.
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Metallic Conductors
Length
Area
Re sist an ce : R
Package level:W=3 milsR=0.0045 /mm
R = Le ng th Are a
Submicron level:W=0.25 micronsR=422 /mm
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Metal Conductivity -1 m 10-7)
Silver 6.1Copper 5.8Gold 3.5Aluminum 1.8Tungsten 1.8Brass 1.5Solder 0.7Lead 0.5Mercury 0.1
Metallic Conductors
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RF SOURCE
Loss in Transmission Lines
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Low Frequency High Frequency Very High Frequency
Skin Effect in Transmission Lines
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.
Magnitude of current density
y
w
t
e
D
V
J = Joe- y /d e
- jy / d
d
Skin Effect in Microstrip
r
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The electric field in a material medium propagates as
z
Eoez Eoeze jz
where j. We also have
= (1+j) .
Skin EffectSkin Effect
Wint
s
s
Hint
CURRENT AREAS
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Current density varies as
J Joey / e jy /
Note that the phase of the current density varies as a function of y. The total
current is given by:
/ /
0 1y jy o
oJ wI J we e dy
j
oo o o
JE J E
The voltage measured over a section of the conductor of length L is:
oo
J DV E D
Skin effect and internal inductance
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The “skin effect” impedance is therefore
(1 ) (1 )oskin
o
J DV j DZ j fI J w w
where 1
is the bulk resistivity of the conductor
Zskin Rskin jXskin
with
skin skinDR X fw
Skin effect and internal inductance
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Vz
= (R+ jL)I = ZI
Iz
= (G+ jC)V = YV
Lossy Transmission LineL
z
C
I
V
+
-
G
R
Telegraphers Equation
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z
R, L, G, C,
Lossy Transmission Line
forward wave
backward wave
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Coupled Lines and Crosstalk
r
w s
h
Cs
V1
V2
I1
I2
Cs
Cm Lm
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50 line 1
line 2
50
line 1
line 2
50 line 1
line 2
line 1
line 2
Crosstalk noise depends on termination
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50 line 1
line 2
50
line 1
line 2
line 1
line 2
tr = 1 ns tr = 7 ns
Crosstalk depends on signal rise time
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tr = 1 ns tr = 7 ns
Crosstalk depends on signal rise time
50 line 1
line 2
line 1
line 2
line 1
line 2
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-0.2
0
0.2
0.4
0.6
0.8
1
Vol
ts
0 5 10 15 20 25 30
Time (ns)
Drive Line at Near End
35 40
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
Vol
ts
0 5 10 15 20 25 30
Time (ns)
Sense Line at Near End
35 40
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ALS04 ALS240Drive Line 1
Drive Line 2
z=0 z=l
Drive Line 3
Sense Line 4
Drive Line 5
Drive Line 6
Drive Line 7
ALS04
ALS04
ALS04
ALS04
ALS04
ALS240
ALS240
ALS240
ALS240
ALS240
7-Line Coupled-Microstrip System
Ls = 312 nH/m; Cs = 100 pF/m;
Lm = 85 nH/m; Cm = 12 pF/m.
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20010000
1
2
3
4
5Drive line 3 at Near End
Time (ns)2001000
-1
0
1
2
3
4
5Drive Line 3 at Far End
Time (ns)
Drive Line 3
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2001000-1
0
1
2Sense Line at Near End
Time (ns)2001000
-1
0
1
2Sense Line at Far End
Time (ns)
Sense Line
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Multiconductor Simulation
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• Signal launched on a transmission line can be affected by previous signals as result of reflections
• ISI can be a major concern especially if the signal delay is smaller than twice the time of flight
• ISI can have devastating effects
• Noise must be allowed to settled before next signal is sent
Intersymbol Interference (ISI)
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Volts
Time
Waveform beginning transition from low to highwith unsettled noise on the bus
Different starting point due to ISI
Receiver switching threshold
Timing differencedue to ISI
Ideal waveform beginning transistionfrom low to high with no noise on the bus
Intersymbol Interference
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• Minimize reflections on the bus by avoiding impedance discontinuities
• Minimize stub lengths and large parasitics from package sockets or connectors
• Keep interconnects as short as possible (minimize delay)
• Minimize crosstalk effects
Minimizing ISI
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• Timing uncertainties in digital transmission systems• Utmost importance because timing uncertainties cause bit errors• There are different types of jitter
Jitter DefinitionJitter DefinitionJitter is difference in time of when somethingwas ideally to occur and when it actually did occur.
Some devices specify the amount of marginal jitter and totaljitter that it can take to operate correctly. If the cable addsmore jitter than the receiver’s allowed marginal jitter and total jitter the signal will not be received correctly. In this case the jitter is measured as in the below diagram
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• Jitter is a signal timing deviation referenced to a recovered clock from the recovered bit stream
• Measured in Unit Intervals and captured visually with eye diagrams
• Two types of jitter– Deterministic (non Gaussian)– Random
• The total jitter (TJ) is the sum of the random (RJ) and deterministic jitter(DJ)
Jitter CharacteristicsJitter Characteristics
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Types of JitterTypes of Jitter
•Deterministic Jitter (DDJ)Data‐Dependent Jitter (DDJ)Periodic Jitter (PJ)Bounded Uncorrelated Jitter (BUJ)
• Random Jitter (RJ)Gaussian Jitter f Higher‐Order Jitter
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Bandwidth Limitations Cause intersymbol interference (ISI) ISI occurs if time required by signal to completely charge is longer
than bit interval Amount of ISI is function of channel and data content of signal
Jitter EffectsJitter Effects
Oscillator Phase Noise Present in reference clocks or high-speed clocks In PLL based clocks, phase noise can be amplified
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Jitter StatisticsJitter StatisticsMost common way to look at jitter is in statistical domain
Because one can observe jitter histograms directly on oscilloscopes
No instruments to measure jitter time waveform or frequency spectrum directly
Jitter Histograms and Probability Density Functions (PDF)Built directly from time waveforms Frequency information is lostPeak‐to‐peak value depends on observation time
Copyright © by Jose E. Schutt‐Aine , All Rights ReservedECE 451
Total Jitter Time WaveformTotal Jitter Time Waveform
The total jitter waveform is the sum of individual components
TJ(t) = PJ(t) + RJ(t)
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Jitter StatisticsJitter Statistics
TJ(x) = PJ(x) * RJ(x)
The total jitter PDF is the convolution of individual components
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An eye diagram is a time-folded representation of a signal that carries digital information
Eye DiagramEye Diagram
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Eye Diagram ConstructionEye Diagram Construction
Eye diagram construction in real-time oscilloscope is based on hardware clock recovery and trigger circuitry
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Eye Diagram ConstructionEye Diagram Construction
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1. Capture of the Waveform Record
2. Determine the Edge Times
Eye Diagram ConstructionEye Diagram Construction
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Eye Diagram ConstructionEye Diagram Construction
3. Determine the Bit Labels
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4. Clock Recovery
Eye Diagram ConstructionEye Diagram Construction
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Eye Diagram ConstructionEye Diagram Construction
5. Slice Overlay
6. Display
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Eye Diagram MeasurementsEye Diagram Measurements
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Reference LevelsReference Levels
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Eye HeightEye HeightEye Height is the measuremnt of the eye height in volts
3 3PTop PTop PBase PBaseEye Height
PTop
PBasePBasePTop
: mean value of eye top
: standard deviation of eye top
: mean value of eye base
: standard deviation of eye base
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Eye WidthEye WidthEye Width is the measuremnt of the eye width in seconds
2 2 1 13 3TCross TCross TCross TCrossEyeWidth
1Crossing Percent 100%PCross PBase
PTop PBase
Crossing percent measurement is the eye crossing point expressed as a percentage of the eye height
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Eye Diagram SpecificationsEye Diagram Specifications
PCI Express 2.0 eye diagram specification for full and deemphasized signals
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Margin TestingMargin Testing
Eye diagram with low margin
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Pseudorandomsequencegenerator
Transmitter Receiver
Scope
Trig Vert
Clk
Data
Fiber
Eye Pattern AnalysisEye Pattern Analysis
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Typical Eye Diagrams
Eye DiagramEye Diagram
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Eye Diagram ‐ ADS Simulation
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Eye Diagram ‐ ADS SimulationIdeal Matched Line
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Eye Diagram ‐ ADS Simulation5 GHz Data Transmission
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Eye Diagram ‐ ADS Simulation5 GHz Data Transmission
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Eye Diagram ‐ ADS Simulation10 GHz Data Transmission
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Eye Diagram ‐ ADS Simulation
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• The Bit-error rate (BER) quantifies the likelihood of a bit being interpreted at the receiver incorrectly due to jitter- or amplitude-induced degradation on the received signal
• No higher than a 10-16 BER is tolerable no more than 1 error out of 1016 bits.
• BER can be measured directly or quantified with statistical calculations
• Deterministic jitter(DJ) can be easily measured via S-parameters obtained in the frequency domain
Bit‐Error Rate
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