Intel® 820E Chipset

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3.3.3.Crosstalk Theory

AGTL+ signals swing across a smaller voltage range and have a correspondingly smaller noise margin than technologies traditionally used in personal computer designs, so designers using AGTL+ must be more aware of crosstalk than they may have been in previous designs.

Crosstalk is caused through capacitive and inductive coupling between networks. Crosstalk appears as both backward and forward crosstalk. Backward crosstalk creates an induced signal in a victim network that propagates in a direction opposite to that of the aggressor’s signal. Forward crosstalk creates a signal that propagates in the same direction as the aggressor’s signal. On the AGTL+ bus, a driver on the aggressor network is not at the end of the network. Therefore, it sends signals in both directions on the aggressor’s network. Figure 77 shows a driver on the aggressor network and a receiver on the victim network, neither of which is at a network end. The signal propagating in each direction causes crosstalk on the victim network.

Figure 77. Aggressor and Victim Networks

Zo

Victim

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Zo

Signal propagates in both directions on aggressor line.

Aggressor

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aggres_victim

Figure 78. Transmission Line Geometry: (A) Microstrip (B) Stripline

 

 

 

 

 

 

Signal lines

 

Signal lines

 

 

 

 

 

 

 

 

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Dielectric, ε r

Dielectric,

ε r

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AC ground plane

 

 

 

A. Microstrip

 

 

B. Stripline

 

 

 

 

 

 

 

 

 

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Design Guide

 

 

 

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Intel 820E manual Crosstalk Theory, Aggressor and Victim Networks