6
Figure 4. Near and far end crosstalk resulting from a step input on an adjacent line
"Long " vs. "Short" Lines
Defining the point at which an interconnect should be treated as a transmission line and hence reflection
analysis applied has no consensus of opinion. A rule of thumb is when the delay from one end to the
other is greater than risetime/2, the line is considered electrically long. If the delay is less than risetime/2,
the line is electrically short. Hence, the following guidelines:
Lumped line: tr/Td >=4
Short line: 4 > tr/Td > 2
Long line: tr/Td <= 2
"Lumped" and "short" lines may always be modeled by lumped circuits. The topic of the next section is to
decide how to best model an electrically "long" line.