Digital design is entering a new realm. Bus speeds have increased to a point where high-
frequency phenomena that previously had second- or third-order effects on system
performance have become first order. Many of these numerous high-speed issues have
never needed to be considered in digital design of times past. Subsequently, modern high-
speed design not only requires the engineer to continuously break new ground on a
technical level, but it also requires the engineer to account for significantly more variables.
Since the complexity of a design increases dramatically with the number of variables, new
methodologies must be introduced to produce a robust design. The methodologies
introduced in this chapter show how to systematically reduce a problem with an otherwise
intractable amount of variables to a solvable problem.
Many previous designs have used the route--simulate--route method. This old methodology
requires the layout engineer to route the board prior to any simulation. The routed board is
then extracted and simulated. When timing and/or signal integrity errors are encountered,
the design engineer determines the necessary corrections, the layout is modified, and the
loop begins all over again. The problem with the old methodology is that it takes a significant
amount of time to converge and often does not provide a thorough understanding of the
solution space. Even when a solution is determined, there may not be an understanding of
why the solution worked. A more efficient method of design process would entail a structured
procedure to ensure that all variables are accounted for in the pre-layout design. If this is
done correctly, a working layout will be produced on the first pass and then the board
extraction and simulation process is used only to double check the design.
The methodologies introduced in this section concentrate on efficiently producing high-speed
bus designs for high-volume manufacturing purposes. Additionally, it outlines proven
strategies that have been developed to handle the large number of variables that must be
accounted for in these designs. Some of the highest-performance digital designs on the
market today have been developed using these or a variation of the methodologies in this
chapter. Finally, in this section we introduce a specific design flow that allows the engineer to
proceed from the initial specifications to a working bus design with minimal layout iteration.
This methodology will produce robust digital designs, improve time to market, and increase
the efficiency of the designer.
Chapter 9: Design Methodologies OVERVIEW Digital design is entering a new realm. Since the complexity of a design increases dramatically with the number of variables, new methodologies must be introduced to produce a robust design. Finally, in this section we introduce a specific design flow that allows the engineer to proceed from the initial specifications to a working bus design with minimal layout iteration.