Page 26 - DSP Integrated Circuits

1.6 DSP System Design 11

the system design is the system specification. Here we assume that the system spec-
ification has been preceded by a thorough investigation of the intended market, for
example, volume, price, consumer preferences and technical and commercial com-
petition. The specification should also include costs and other constraints due to
marketing and maintenance of the DSP system. It is important to consider all costs
incurred during the entire life of the system.
The design of a complex DSP system
can be partitioned into two major phases:
system design and integrated circuit design,
as illustrated in Figure 1.10. These two
phases are followed by a manufacturing
and testing phase. The design of testable
integrated circuits is a very important topic
and should be considered early on in the
system design phase. However, circuit man-
ufacturing [8] and testing [16] issues will
not be discussed in this book.
A design methodology is the overall
strategy to organize and solve the design
tasks at the different steps of the design
process. It is not possible to invent a com-
prehensive design methodology that
applies well in all cases, but all efficient
methodologies have some common features. Figure 1.10 The main phases in the
design of a DSP system
Generally, the design process is viewed
as the development of a sequence of models
of the system, where each model version is more refined than the previous. The
process continues until all design issues are resolved.
It is necessary due to the high complexity of the design problem to follow a
structured design approach that reduces the complexity. Structured design meth-
ods, which will be further discussed in this chapter, are primarily used to

Q Guarantee that the performance goals are met and
Q Attain a short and predictable design time.

The overall performance goals are typically expressed in terms of subgoals such
as acceptable physical size of the system, chip area of the individual integrated cir-
cuits, power consumption, and number of pins, to name a few. An important goal is to
attain a short and predictable design time so that the product can be placed on the
market within the intended time frame. This implies that the risk of ending up with
a nonworking integrated circuit due to design errors, erroneous interface, unsatisfac-
tory throughput, etc. must be minimized by using a good design method. Other fac-
tors that have a major impact on the design process are the design tools and the
layout style used in the integrated circuit design phase. The degree of automation of
the design process varies widely, from fully automatic to hand-crafted design [14].

1.6.1 Specification And Design Problem Capture

Besides a description of the tasks that the system shall perform, the system speci-
fication should also include requirements on physical size, power consumption,