Intel: Anodes Crosstalk Overview

clappergappawpawΠολεοδομικά Έργα

16 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

47 εμφανίσεις

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