Connectors are devices that are used to connect one PCB board to another. As speeds
increase, connector design becomes increasingly difficult. A good example of a high-speed
connector in a modern digital system is the slot 1 connector used to connect the Pentium III
cartridge processor to the mother-board. Another, more advanced example is the RIMM
(Rambus Inline Memory Module) connector, which is operating at speeds of 800
megatransfers per second.
Since the geometries of connectors are usually complex, it is impossible to accurately
calculate the effective parasitics without the assistance of a two- or a three-dimensional field
solver or measurements. However, the fundamental effects and a basic understanding of
how a connector will affect system performance can be learned early in the design process
by examining a first-order-level model.
In this section we examine the properties important to the design and modeling of high-
speed connectors by concentrating on the fundamental issues. The main topics explored in
this section are connector crosstalk, series parasitics, and return current path inductance.
depicts a conceptual connector that will be used to demonstrate the detrimental
effects on signal integrity.
Figure 5.2: Example of a PCB connector.
5.2.1. Series Inductance
The most fundamental effect of a connector is the addition of a series inductance, which can
be estimated to a first-order level with the use of simple straight-wire formulas. Estimates for
the series inductance of round and rectangular wire, respectively, are [
is the permeability of free space, l the length, r the radius of the wire, and p the
perimeter. It should be noted that the length is the primary contributor to inductance; the
shape of the conductor is not terribly significant as long as the cross-sectional width is small
compared to the length.
A good example of a high-speed connector in a modern digital system is the slot 1 connector used to connect the Pentium III cartridge processor to the mother-board. Series Inductance The most fundamental effect of a connector is the addition of a series inductance, which can be estimated to a first-order level with the use of simple straight-wire formulas.