Crosstalk. Overview and Modes. Overview. What is Crosstalk? Crosstalk Induced Noise Effect of crosstalk on transmission line parameters Crosstalk Trends Design Guidelines and Rules of Thumb. Crosstalk Induced Noise. Key Topics: Mutual Inductance and capacitance Coupled noise
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Crosstalk
Overview and Modes
Crosstalk Overview
Crosstalk Overview
Mutual Inductance and Capacitance
Mutual Inductance, Lm
Mutual Capacitance, Cm
Zo
Zo
Zo
Zo
far
far
Cm
Lm
near
Zs
near
Zs
Zo
Zo
Crosstalk Overview
Mutual Inductance and Capacitance “Mechanism of coupling”
Crosstalk Overview
Crosstalk Induced Noise“Coupled Currents”
Zo
Zo
Zo
Zo
far
far
ICm
ILm
Lm
near
near
Zs
Zs
Zo
Zo
Crosstalk Overview
Crosstalk Induced Noise“Voltage Profile of Coupled Noise”
Zo
Zo
Far End
Driven Line
Un-driven Line
“victim”
Zs
Near End
Driver
Zo
Crosstalk Overview
Time = 0
Near end crosstalk pulse at T=0 (Inear)
~Tr
V
Near end
crosstalk
Zo
TD
Far end crosstalk pulse at T=0 (Ifar)
~Tr
Time= 1/2 TD
2TD
V
Zo
far end
crosstalk
Zo
Time= TD
Far end of current
terminated at T=TD
V
Zo
Zo
Time = 2TD
Near end current
terminated at T=2TD
V
Zo
Zo
Graphical Explanation
Crosstalk Overview
Zo
Zo
Far End
Driven Line
Un-driven Line
“victim”
Zs
Near End
Driver
Zo
Crosstalk Equations
TD
Terminated Victim
A
B
Tr
~Tr
Tr
TD
2TD
Far End
Open Victim
Zo
Far End
Driven Line
Un-driven Line
“victim”
A
B
C
Zs
Near End
Driver
~Tr
Zo
~Tr
Tr
Crosstalk Overview
2TD
Crosstalk Equations
TD
Near End Open Victim
Zo
Zo
Far End
C
A
Driven Line
B
Un-driven Line
“victim”
Tr
Tr
Tr
Zs
Near End
2TD
Driver
3TD
Crosstalk Overview
Creating a Crosstalk Model“Equivalent Circuit”
C12
Line 2
Line 1
C1G
C2G
L11(N)
L11(2)
L11(1)
Line 1
C1G(1)
C1G(N)
C1G(2)
K1
K1
K1
C12(n)
C12(2)
C12(1)
Line 2
L22(N)
L22(2)
L22(1)
C2G(1)
C2G(N)
C2G(2)
Crosstalk Overview
Creating a Crosstalk Model“Transmission Line Matrices”
Inductance Matrix =
Crosstalk Overview
Creating a Crosstalk Model“Transmission Line Matrices”
Capacitance Matrix =
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:
v
R1
R2
Crosstalk Overview
200mV/div
100ps/div
Example (cont.)
Near end crosstalk voltage amplitude (from slide 12):
Far end crosstalk voltage amplitude (slide 12):
The propagation delay of the 2 inch line is:
Thus,
Crosstalk Overview
Crosstalk Overview
Even Mode
Odd Mode
Odd and Even Transmission Modes
Crosstalk Overview
Odd Mode Transmission
+1 -1
Electric Field:
Odd mode
Magnetic Field:
Odd mode
+1 -1
V
Drive (I)
I
Induced (-ILm)
Lm
Induced (ILm)
Drive (-I)
-I
Crosstalk Overview
Odd Mode Transmission“Derivation of Odd Mode Inductance”
L11
I1
Mutual Inductance:
Consider the circuit:
+ V1 -
I2
+ V2 -
L22
Since the signals for odd-mode switching are always opposite, I1 = -I2 and
V1 = -V2, so that:
Thus, since LO= L11 = L22,
Meaning that the equivalent inductance seen in an odd-mode environment
is reduced by the mutual inductance.
Crosstalk Overview
Odd Mode Transmission“Derivation of Odd Mode Capacitance”
V2
Mutual Capacitance:
Consider the circuit:
C1g
Cm
V2
C1g = C2g= CO = C11– C12
C2g
So,
And again, I1 = -I2 and V1 = -V2, so that:
Thus,
Meaning that the equivalent capacitance for odd mode switching increases.
Crosstalk Overview
Odd Mode Transmission“Odd Mode Transmission Characteristics”
Impedance:
Thus the impedance for odd mode behavior is:
Explain why.
Propagation Delay:
and the propagation delay for odd mode behavior is:
Crosstalk Overview
Even Mode Transmission
Electric Field:
Even mode
+1 +1
+1 +1
Magnetic Field:
Even mode
V
Drive (I)
I
Induced (ILm)
Lm
Induced (ILm)
Drive (I)
I
Crosstalk Overview
Even Mode TransmissionDerivation of even Mode Effective Inductance
L11
Mutual Inductance:
Again, consider the circuit:
I1
+ V1 -
I2
+ V2 -
L22
Since the signals for even-mode switching are always equal and in the same
direction so that I1 = I2 and V1 = V2, so that:
Thus,
Meaning that the equivalent inductance of even mode behavior increases
by the mutual inductance.
Crosstalk Overview
Even Mode TransmissionDerivation of even Mode Effective Capacitance
V2
Mutual Capacitance:
Again, consider the circuit:
C1g
Cm
V2
C2g
Thus,
Meaning that the equivalent capacitance during even mode behavior
decreases.
Crosstalk Overview
Even Mode Transmission“Even Mode Transmission Characteristics”
Impedance:
Thus the impedance for even mode behavior is:
Propagation Delay:
and the propagation delay for even mode behavior is:
Crosstalk Overview
Odd and Even Mode Comparison for Coupled Microstrips
Even mode (as seen on line 1)
Input waveforms
Impedance difference
V1
Odd mode (Line 1)
Probe point
Line 1
Line2
v1
v2
V2
Delay difference due to modal velocity differences
Crosstalk Overview
Microstrip vs. Stripline CrosstalkCrosstalk Induced Velocity Changes
Crosstalk Overview
Microstrip vs. Stripline CrosstalkCrosstalk Induced Velocity Changes
Microstrip E field patterns
+1 -1
+1 +1
Er=1.0
Er=1.0
Er=4.2
Er=4.2
Crosstalk Overview
+1 -1
+1 +1
Er=4.2
Er=4.2
Microstrip vs. Stripline CrosstalkCrosstalk Induced Velocity Changes
Stripline E field patterns
Crosstalk Overview
Microstrip vs. Stripline CrosstalkCrosstalk Induced Noise
Crosstalk Overview
+1
R1
Odd Mode
Equivalent
-1
R2
R1
R3
Virtual Ground
in center
R2
2R3
+1
Even Mode
Equivalent
R1
-1
+1
2R3
R2
Termination TechniquesPi and T networks
T Termination
Crosstalk Overview
Termination TechniquesPi and T networks
PI Termination
R1
R1
+1
½ R3
Odd Mode
Equivalent
R3
-1
½ R3
R2
R2
-1
+1
R1
Even Mode
Equivalent
+1
R2
Crosstalk Overview