ECE 451
Signal Integrity
Jose E. Schutt-Aine
Electrical & Computer Engineering
University of Illinois
jose@emlab.uiuc.edu
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
1
Signal Integrity
Ideal
Transmission
Channel
Common
Transmission
Channel
Noisy
Transmission
Channel
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
2
Signal Integrity
•
•
•
•
•
•
•
•
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)
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
3
The Interconnect Bottleneck
Technology
Generation
ECE 451
MOSFET Intrinsic
Switching Delay
Response
Time
1.0 um
~ 10 ps
~ 1 ps
0.01 um
~ 1 ps
~ 100 ps
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
4
Chip-Level Interconnect Delay
Line
Pulse Characteristics:
Line Characteristics
rise time: 100 ps
fall time: 100 ps
pulse width: 4ns
length : 3 mm
near end termination: 50 
far end termination 65 
Near End Response
Far End Response
1
0.7
0.6
Volts
0.45
Logic
threshold
0.175
Board
VLSI
Submicron
Deep Submicron
0.5
Volts
Board
VLSI
Submicron
Deep Submicron
0.725
0.4
0.3
Logic
threshold
0.2
0.1
0
-0.1
-0.1
0
0.4
0.8
1.2
1.6
2
0
0.4
Time (ns)
ECE 451
0.8
1.2
1.6
2
Time (ns)
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
5
Interconnect Bottleneck
Signal Integrity
Crosstalk
Dispersion
Attenuation
Reflection
Distortion
Loss
Delta I Noise
Ground Bounce
Radiation
Drive Line
Sense Line
Drive Line
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
6
Reflection in Transmission Lines
1.
2.
3.
ECE 451
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7
Metallic Conductors

Area
th
Leng
Re s ist an ce : R
Le ng th
R=
 Are a
Package level:
W=3 mils
R=0.0045 /mm
ECE 451
Submicron level:
W=0.25 microns
R=422 /mm
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
8
Metallic Conductors
Metal
Conductivity
 -1 m 10-7)
Silver
Copper
Gold
Aluminum
Tungsten
Brass
Solder
Lead
Mercury
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
6.1
5.8
3.5
1.8
1.8
1.5
0.7
0.5
0.1
9
Loss in Transmission Lines
RF
SOURCE
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
10
Skin Effect in Transmission Lines

Low Frequency
ECE 451
High Frequency
Very High Frequency
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
11
Skin Effect in Microstrip
.
D
w
y
-
d
t

J=
J oe
y /d
ude
gnit
a
M
/
- jy
d
e
ity
ens
d
t
n
urre
of c
V
er
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
12
Skin Effect
The electric field in a material medium propagates as
E o e z  E oe z e jz
z
where  j. We also have
=

(1+j ) .

Wint
Hint
s
CURRENT AREAS
s
ECE 451
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13
Skin effect and internal inductance
Current density varies as
J  Jo e y /  e  jy / 
Note that the phase of the current density varies as a function of y. The total
current is given by:

I   J o we  y /  e  jy /  dy 
0
 Eo  J o  Eo 
J o w
1 j
Jo

The voltage measured over a section of the conductor of length L is:
V  Eo D 
ECE 451
Jo D

Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
14
Skin effect and internal inductance
The “skin effect” impedance is therefore
Z skin 
V J o D (1  j ) D

 (1  j )  f 
 J o w w
I
1
is the bulk resistivity of the conductor
where  

Z skin  R skin  jX skin
with
Rskin  X skin 
ECE 451
D
 f 
w
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
15
Lossy Transmission Line
I
L
R
+
V
C
G
z
Telegraphers Equation
V

= (R+ jL)I = ZI
z
I
 = (G + jC)V = YV
z
ECE 451
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16
Lossy Transmission Line
z
R, L, G, C,
forward wave
backward wave
ECE 451
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17
Coupled Lines and Crosstalk
w
r
h
V1
s
Cs
I1
Cm
I2
Lm
V2
Cs
ECE 451
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18
Crosstalk noise depends on termination
50 
50 
line 1
line 1
line 2
50 
line 2
line 1
line 1
line 2
line 2
ECE 451
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19
Crosstalk depends on signal rise time
50 
line 1
line 2
50 
tr = 1 ns
tr = 7 ns
line 1
line 2
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
line 1
line 2
20
Crosstalk depends on signal rise time
50 
line 1
line 2
tr = 1 ns
tr = 7 ns
line 1
line 1
line 2
line 2
ECE 451
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21
Sense Line at Near End
Drive Line at Near End
0.2
1
0.15
0.8
0.1
Volts
Volts
0.6
0.05
0.4
0
-0.05
0.2
-0.1
0
-0.15
-0.2
0
0
5
10
15
20
25
30
35
5
10
15
20
25
30
35
40
40
Time (ns)
Time (ns)
ECE 451
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22
7-Line Coupled-Microstrip System
ALS04
ALS240
Drive Line 1
ALS04
Drive Line 2
ALS04
Drive Line 3
ALS240
ALS240
Sense Line 4
ALS04
Drive Line 5
ALS04
Drive Line 6
ALS04
ALS240
ALS240
ALS240
Drive Line 7
z=0
z=l
Ls = 312 nH/m; Cs = 100 pF/m;
Lm = 85 nH/m;
ECE 451
Cm = 12 pF/m.
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23
Drive Line 3
Drive line 3 at Near End
Drive Line 3 at Far End
5
5
4
4
3
3
2
2
1
1
0
0
-1
0
100
Time (ns)
200
0
100
200
Time (ns)
ECE 451
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24
Sense Line
Sense Line at Near End
2
2
Sense Line at Far End
1
1
0
0
-1
-1
0
100
200
0
Time (ns)
ECE 451
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100
200
Time (ns)
25
Multiconductor Simulation
ECE 451
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26
Intersymbol Interference (ISI)
• 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
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
27
Intersymbol Interference
Volts
Ideal waveform beginning transistion
from low to high with no noise on the bus
Timing difference
due to ISI
Receiver switching threshold
Time
Different starting point due to ISI
Waveform beginning transition from low to high
with unsettled noise on the bus
ECE 451
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28
Minimizing ISI
• 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
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
29
Jitter Definition
Jitter is difference in time of when something
was ideally to occur and when it actually did occur.
Some devices specify the amount of marginal jitter and total
jitter that it can take to operate correctly. If the cable adds
more 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
• Timing uncertainties in digital transmission systems
• Utmost importance because timing uncertainties cause bit errors
• There are different types of jitter
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
Jitter Characteristics
• 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)
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
Types 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
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
Jitter Effects
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
Oscillator Phase Noise
 Present in reference clocks or high-speed clocks
 In PLL based clocks, phase noise can be amplified
ECE 451
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Jitter Statistics
 Most 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 lost
 Peak‐to‐peak value depends on observation time
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
Total Jitter Time Waveform
TJ(t)
= PJ(t)
+
RJ(t)
The total jitter waveform is the sum of individual components
ECE 451
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
Jitter Statistics
TJ(x)
= PJ(x)
*
RJ(x)
The total jitter PDF is the convolution of individual components
ECE 451
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Eye Diagram
An eye diagram is a time-folded representation of a signal
that carries digital information
ECE 451
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Eye Diagram Construction
Eye diagram construction in real-time oscilloscope is based
on hardware clock recovery and trigger circuitry
ECE 451
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Eye Diagram Construction
ECE 451
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Eye Diagram Construction
1. Capture of the Waveform Record
2. Determine the Edge Times
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Eye Diagram Construction
3. Determine the Bit Labels
ECE 451
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Eye Diagram Construction
4. Clock Recovery
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Eye Diagram Construction
5. Slice Overlay
6. Display
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Eye Diagram Measurements
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Reference Levels
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Eye Height
Eye Height is the measuremnt of the eye height in volts
Eye Height    PTop  3 PTop     PBase  3 PBase 
 PTop
: mean value of eye top
 PTop
: standard deviation of eye top
 PBase
: mean value of eye base
 PBase
ECE 451
: standard deviation of eye base
Copyright © by Jose E. Schutt‐Aine , All Rights Reserved
46
Eye Width
Eye Width is the measuremnt of the eye width in seconds
Eye Width   TCross 2  3 TCross 2    TCross1  3 TCross1 
Crossing percent measurement is the eye crossing point
expressed as a percentage of the eye height
 PCross1   PBase 

Crossing Percent 
 100%

ECE 451
PTop
  PBase 
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47
Eye Diagram Specifications
PCI Express 2.0 eye diagram specification for
full and deemphasized signals
ECE 451
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Margin Testing
Eye diagram with low margin
ECE 451
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Eye Pattern Analysis
Fiber
Pseudorandom
sequence
generator
Data
Clk
Transmitter
Receiver
Scope
Trig Vert
ECE 451
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Eye Diagram
Typical Eye Diagrams
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Eye Diagram ‐ ADS Simulation
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52
Eye Diagram ‐ ADS Simulation
Ideal Matched Line
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53
Eye Diagram ‐ ADS Simulation
5 GHz Data Transmission
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54
Eye Diagram ‐ ADS Simulation
5 GHz Data Transmission
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55
Eye Diagram ‐ ADS Simulation
10 GHz Data Transmission
ECE 451
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56
Eye Diagram ‐ ADS Simulation
ECE 451
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57
Bit‐Error Rate
• 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 Sparameters obtained in the frequency domain
ECE 451
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58