Intel: Anodes Crosstalk Overview

Urban and Civil

Nov 16, 2013 (4 years and 6 months ago)

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Crosstalk

Overview and Modes

2

Crosstalk Overview

What is Crosstalk?

Crosstalk Induced Noise

Effect of crosstalk on transmission line
parameters

Crosstalk Trends

Design Guidelines and Rules of Thumb

Overview

3

Crosstalk Overview

Crosstalk Induced Noise

Key Topics:

Mutual Inductance and capacitance

Coupled noise

Circuit Model

Transmission line matrices

4

Crosstalk Overview

Crosstalk is the coupling of energy from one line
to another via:

Mutual capacitance (electric field)

Mutual inductance (magnetic field)

Mutual Inductance and Capacitance

Zs

Zo

Zo

Zo

Mutual Capacitance
, C
m

Mutual Inductance
, L
m

Zs

Zo

Zo

Zo

C
m

L
m

near

far

near

far

5

Crosstalk Overview

The circuit element that represents this
transfer of energy are the following familiar
equations

Mutual Inductance and Capacitance

Mechanism of coupling”

dt
dI
L
V
m
Lm

dt
dV
C
I
m
Cm

The mutual inductance will induce current on the
victim line opposite of the driving current (Lenz’s
Law)

The mutual capacitance will pass current through
the mutual capacitance that flows in both
directions on the victim line

6

Crosstalk Overview

The near and far end victim line currents sum to
produce the near and the far end crosstalk
noise

Crosstalk Induced Noise

Coupled Currents”

Zs

Zo

Zo

Zo

Zs

Zo

Zo

Zo

I
Cm

L
m

near

far

near

far

I
Lm

Lm
Cm
far
Lm
Cm
near
I
I
I
I
I
I

7

Crosstalk Overview

Near end crosstalk is always positive

Currents from Lm and Cm always add and flow into the
node

For PCB’s, the far end crosstalk is “usually”
negative

Current due to Lm larger than current due to Cm

Note that far and crosstalk can be positive

Crosstalk Induced Noise

Voltage Profile of Coupled Noise”

Driven Line

Un
-
driven Line

“victim”

Driver

Zs

Zo

Zo

Zo

Near End

Far End

8

Crosstalk Overview

Graphical Explanation

TD

2TD

~Tr

~Tr

far end

crosstalk

Near end

crosstalk

Zo

V

Time = 2TD

Zo

Near end current

terminated at T=2TD

V

Time = 0

Zo

Near end crosstalk pulse at T=0 (I
near
)

Far end crosstalk pulse at T=0 (I
far
)

Zo

Zo

V

Time= 1/2 TD

Zo

V

Time= TD

Zo

Far end of current

terminated at T=TD

9

Crosstalk Overview

Crosstalk Equations

Driven Line

Un
-
driven Line

“victim”

Driver

Zs

Zo

Zo

Zo

Near End

Far End

Driven Line

Un
-
driven Line

“victim”

Driver

Zs

Zo

Zo

Near End

Far End

LC
X
TD

C
C
L
L
V
A
M
M
input
4

C
C
L
L
T
LC
X
V
B
M
M
r
input
2
TD

2TD

Tr

~Tr

Tr

A

B

TD

2TD

Tr

~Tr

~Tr

A

B

C
C
L
L
V
A
M
M
input
4
C
B
2
1

C
C
L
L
T
LC
X
V
C
M
M
r
input
C

Terminated Victim

Far End

Open Victim

10

Crosstalk Overview

Crosstalk Equations

Driven Line

Un
-
driven Line

“victim”

Driver

Zs

Zo

Zo

Near End

Far End

Near End Open Victim

TD

2TD

Tr

Tr

Tr

A

B

C

3TD

C
C
L
L
V
A
M
M
input
2

C
C
L
L
T
LC
X
V
B
M
M
r
input
2

C
C
L
L
V
C
M
M
input
4

The Crosstalk noise characteristics are
dependent on the termination of the victim line

11

Crosstalk Overview

Creating a Crosstalk Model

Equivalent Circuit”

The circuit must be distributed into N segments as
shown in chapter 2

K1

L
11
(1)

L
22
(1)

C
1G
(1)

C
12
(1)

K1

L11(2)

L
22
(2)

C
1G
(2)

C
12
(2)

C
2G
(2)

C
2G
(1)

K1

L
11
(N)

L
22
(N)

C
1G
(N)

C
12
(n)

C
2G
(N)

C
1G

C
2G

C
12

22
11
12
L
L
L
K

Line 1

Line 2

Line 1

Line 2

12

Crosstalk Overview

The transmission line Matrices are used to
represent the electrical characteristics

The Inductance matrix is shown, where:

LNN = the self inductance of line N per unit length

LMN = the mutual inductance between line M and N

Creating a Crosstalk Model

Transmission Line Matrices”

Inductance Matrix =

NN
N
N
L
L
L
L
L
L
L
1
22
21
1
12
11
...
13

Crosstalk Overview

The Capacitance matrix is shown, where:

C
NN

= the self capacitance of line N per unit length
where:

C
NG

= The capacitance between line N and ground

C
MN

= Mutual capacitance between lines M and N

Creating a Crosstalk Model

Transmission Line Matrices”

Capacitance Matrix =

NN
N
N
C
C
C
C
C
C
C
1
22
21
1
12
11
...

mutuals
NG
NN
C
C
C
12
1
11
C
C
C
G

For example, for the 2 line circuit shown earlier:

14

Crosstalk Overview

Example

Calculate near and far end crosstalk
-
induced noise magnitudes and sketch the
waveforms of circuit shown below:

Vsource=2V, (Vinput = 1.0V), Trise = 100ps.

Length of line is 2 inches. Assume all terminations are 70 Ohms.

Assume the following capacitance and inductance matrix:

L / inch =

C / inch =

The characteristic impedance is:

Therefore the system has matched termination.

The crosstalk noise magnitudes can be calculated as follows:

nH
nH
nH
nH
869
.
9
103
.
2
103
.
2
869
.
9

pF
pF
pF
pF
051
.
2
239
.
0
239
.
0
051
.
2

4
.
69
051
.
2
869
.
9
11
11
pF
nH
C
L
Z
O
v

R
1

R
2

15

Crosstalk Overview

Example (cont.)

V
pF
pF
nH
nH
V
C
C
L
L
V
V
input
near
082
.
0
051
.
2
239
.
0
869
.
9
103
.
2
4
1
4
11
12
11
12

V
pF
pF
nH
nH
ps
pF
nH
inch
V
C
C
L
L
T
LC
X
V
V
rise
input
far
137
.
0
051
.
2
239
.
0
869
.
9
103
.
2
100
*
2
051
.
2
*
869
.
9
*
2
*
1
2
)
(
11
12
11
12

Near end crosstalk voltage amplitude (from slide 12):

Far end crosstalk voltage amplitude (slide 12):

Thus,

100ps/div

200mV/div

The propagation delay of the 2 inch line is:

ns
nH
nH
inch
LC
X
TD
28
.
0
051
.
2
*
869
.
9
(
*
2

16

Crosstalk Overview

Effect of Crosstalk on
Transmission line Parameters

Key Topics:

Odd and Even Mode Characteristics

Microstrip vs. Stripline

Modal Termination Techniques

Modal Impedance’s for more than 2 lines

Effect Switching Patterns

Single Line Equivalent Model (SLEM)

17

Crosstalk Overview

Electromagnetic Fields between two driven coupled lines will
interact with each other

These interactions will effect the impedance and delay of the
transmission line

A 2
-
conductor system will have 2 propagation modes

Even Mode (Both lines driven in phase)

Odd Mode (Lines driven 180
o

out of phase)

The interaction of the fields will cause the system electrical
characteristics to be directly dependent on patterns

Odd and Even Transmission Modes

Even Mode

Odd Mode

18

Crosstalk Overview

Potential difference between the conductors lead to an
increase

of the effective Capacitance equal to the mutual
capacitance

Odd Mode Transmission

Magnetic Field:

Odd mode

Electric Field:

Odd mode

+1
-
1

+1
-
1

Because currents are flowing in opposite directions, the total
inductance is
reduced

by the mutual inductance (Lm)

Drive (I)

Drive (
-
I)

Induced (
-
I
Lm
)

Induced (I
Lm
)

V

-
I

Lm

dt
dI
Lm
L
dt
I
d
Lm
dt
dI
L
V
)
(
)
(

I

19

Crosstalk Overview

Odd Mode Transmission

Derivation of Odd Mode Inductance”

12
11
11
L
L
L
L
L
m
odd

Mutual Inductance:

Consider the circuit:

dt
dI
L
dt
dI
L
V
dt
dI
L
dt
dI
L
V
m
O
m
O
1
2
2
2
1
1

22
11
L
L
L
k
m

L
11

L
22

I
2

I
1

+
V
2
-

+
V
1
-

Since the signals for odd
-
mode switching are always opposite, I
1

=
-
I
2

and

V
1
=
-
V
2
, so that:

dt
dI
L
L
dt
I
d
L
dt
dI
L
V
dt
dI
L
L
dt
I
d
L
dt
dI
L
V
m
O
m
O
m
O
m
O
2
2
2
2
1
1
1
1
)
(
)
(
)
(
)
(

Thus, since L
O

= L
11

= L
22
,

Meaning that the equivalent inductance seen in an odd
-
mode environment

is reduced by the mutual inductance.

20

Crosstalk Overview

Odd Mode Transmission

Derivation of Odd Mode Capacitance”

m
m
g
odd
C
C
C
C
C

11
1
2
Mutual Capacitance:

Consider the circuit:

C
2g

C
1g

C
m

V
2

V
2

C
1g

= C
2g

= C
O

= C
11

C
12

So,

dt
dV
C
dt
dV
C
C
dt
V
V
d
C
dt
dV
C
I
dt
dV
C
dt
dV
C
C
dt
V
V
d
C
dt
dV
C
I
m
m
O
m
O
m
m
O
m
O
1
2
1
2
2
2
2
1
2
1
1
1
)
(
)
(
)
(
)
(

And again, I
1

=
-
I
2

and V
1
=
-
V
2
, so that:

dt
dV
C
C
dt
V
V
d
C
dt
dV
C
I
dt
dV
C
C
dt
V
V
d
C
dt
dV
C
I
m
O
m
O
m
g
m
O
2
2
2
2
2
1
1
1
1
1
1
)
2
(
))
(
(
)
2
(
))
(
(

Thus,

Meaning that the equivalent capacitance for odd mode switching increases.

21

Crosstalk Overview

Odd Mode Transmission

Odd Mode Transmission Characteristics”

Impedance:

Thus the impedance for odd mode behavior is:

)
2
:
(
12
11
12
11
odd
al
differenti
odd
odd
odd
Z
Z
Note
C
C
L
L
C
L
Z

and the propagation delay for odd mode behavior is:

)
)(
(
12
11
12
11
C
C
L
L
C
L
TD
odd
odd
odd

Propagation Delay:

Explain why.

22

Crosstalk Overview

Since the conductors are always at a equal potential, the
effective capacitance is
reduced

by the mutual capacitance

Even Mode Transmission

Because currents are flowing in the same direction, the total
inductance is
increased

by the mutual inductance (Lm)

Drive (I)

Drive (I)

Induced (I
Lm
)

Induced (I
Lm
)

V

I

Lm

dt
dI
Lm
L
dt
I
d
Lm
dt
dI
L
V
)
(
)
(

I

Electric Field:

Even mode

Magnetic Field:

Even mode

+1 +1

+1 +1

23

Crosstalk Overview

Even Mode Transmission

Derivation of even Mode Effective Inductance

12
11
11
L
L
L
L
L
m
even

22
11
L
L
L
k
m

L
11

L
22

I
2

I
1

+
V
2
-

+
V
1
-

Mutual Inductance:

Again, consider the circuit:

Since the signals for even
-
mode switching are always equal and in the same

direction so that I
1

= I
2

and V
1
=
V
2
, so that:

dt
dI
L
dt
dI
L
V
dt
dI
L
dt
dI
L
V
m
O
m
O
1
2
2
2
1
1

dt
dI
L
L
dt
I
d
L
dt
dI
L
V
dt
dI
L
L
dt
I
d
L
dt
dI
L
V
m
O
m
O
m
O
m
O
2
2
2
2
1
1
1
1
)
(
)
(
)
(
)
(

Thus,

Meaning that the equivalent inductance of even mode behavior increases

by the mutual inductance.

24

Crosstalk Overview

Even Mode Transmission

Derivation of even Mode Effective Capacitance

m
even
C
C
C
C

11
0
Mutual Capacitance:

Again, consider the circuit:

C
2g

C
1g

C
m

V
2

V
2

dt
dV
C
dt
V
V
d
C
dt
dV
C
I
dt
dV
C
dt
V
V
d
C
dt
dV
C
I
O
m
O
O
m
O
2
2
2
2
2
1
1
1
1
1
)
(
)
(

Thus,

Meaning that the equivalent capacitance during even mode behavior

decreases.

25

Crosstalk Overview

Even Mode Transmission

Even Mode Transmission Characteristics”

Impedance:

Thus the impedance for even mode behavior is:

12
11
12
11
C
C
L
L
C
L
Z
even
even
even

and the propagation delay for even mode behavior is:

)
)(
(
12
11
12
11
C
C
L
L
C
L
TD
even
even
even

Propagation Delay:

26

Crosstalk Overview

Odd and Even Mode Comparison for
Coupled Microstrips

Input waveforms

Even mode (as seen on line 1)

Odd mode (Line 1)

v
2

v
1

Probe point

Delay difference due to modal velocity differences

Impedance difference

V1

V2

Line 1

Line2

27

Crosstalk Overview

Microstrip vs. Stripline Crosstalk

Crosstalk Induced Velocity Changes

Chapter 2 defined propagation delay as

Chapter 2 also defined an effective dielectric constant that
is used to calculate the delay for a microstrip that accounted
for a portion of the fields fringing through the air and a
portion through the PCB material

This shows that the propagation delay is dependent on the
effective dielectric constant

In a pure dielectric (homogeneous), fields will not fringe
through the air, subsequently, the delay is dependent on the
dielectric constant of the material

c
T
r
pd

28

Crosstalk Overview

Microstrip vs. Stripline Crosstalk

Crosstalk Induced Velocity Changes

Odd and Even mode electric fields in a microstrip
will have different percentages of the total field
fringing through the air which will change the
effective Er

Leads to velocity variations between even and odd

+1 +1

+1
-
1

The effective dielectric constant, and subsequently
the propagation velocity depends on the electric
field patterns

Er=4.2

Er=1.0

Er=4.2

Er=1.0

Microstrip E field patterns

29

Crosstalk Overview

Microstrip vs. Stripline Crosstalk

Crosstalk Induced Velocity Changes

Subsequently, if the transmission line is implemented in a
homogeneous dielectric, the velocity must stay constant
between even and odd mode patterns

If the dielectric is homogeneous (I.e., buried microstrip or
stripline) , the effective dielectric constant will not change
because the electric fields will never fringe through air

+1 +1

+1
-
1

Er=4.2

Er=4.2

Stripline E field patterns

30

Crosstalk Overview

Microstrip vs. Stripline Crosstalk

Crosstalk Induced Noise

The constant velocity in a homogeneous media (such
as a stripline) forces far end crosstalk noise to be
zero

11
12
11
12
11
12
12
11
12
11
11
12
12
11
12
11
12
11
12
11
)
)(
(
)
)(
(
C
C
L
L
C
L
C
L
C
L
C
L
C
C
L
L
C
C
L
L
TD
TD
even
odd

0
2
)
_
(
11
12
11
12

C
C
L
L
T
LC
X
V
stripline
far
Crosstalk
r
input

Since far end crosstalk takes the following form:

Far end crosstalk is zero for a homogeneous Er

31

Crosstalk Overview

Termination Techniques

Pi and T networks

Single resistor terminations described in chapter 2
do not work for coupled lines

3 resistor networks can be designed to terminate
both odd and even modes

T Termination

-
1

R
1

R
2

R
3

+1

Odd Mode

Equivalent

-
1

R
1

R
2

Virtual Ground

in center

+1

Even Mode

Equivalent

+1

R
1

R
2

2R
3

2R
3

odd
Z
R
R

2
1

odd
even
Z
Z
R

2
1
3
32

Crosstalk Overview

Termination Techniques

Pi and T networks

The alternative is a PI termination

PI Termination

+1

Odd Mode

Equivalent

-
1

R
1

R
2

R
3

-
1

½ R
3

½ R
3

+1

Even Mode

Equivalent

+1

R
1

R
2

even
Z
R
R

2
1
odd
even
odd
even
Z
Z
Z
Z
R

2
3
R
1

R
2