Page 31 - DSP Integrated Circuits

16 Chapter 1 DSP Integrated Circuits

the next higher level in the design hierarchy. This allows internal details to be
hidden, so that they do not obstruct the analysis at the next higher level.
The hierarchy of abstractions can, and should, also be used to reduce the
volume of design data and to provide suitable representations to speed up the
operation of the computer-aided design tools. Note that it may be necessary to
store, retrieve, display, and process several hundred megabytes of data if a
nonhierarchical approach is used.
The top-down approach relies on the designer's experience since the partition-
ing must lead to realizable subsystems. From the manager's point of view, it is
easy to monitor the progress of the project and check it against the time schedule.

Bottom-Up Approach
The classical approach is the so-called bottom-up approach that starts by succes-
sively assembling well-known building blocks into more complex blocks until the
whole system is realized. Emphasis is placed on realizability of the basic building
blocks while communication issues and the overall system performance are less
well handled. The probability of getting a nonworking system due to design errors
is reduced by using tested building blocks, but the probability is high that the per-
formance requirements are not met. The success of this approach depends to a
large extent on the experience of the design team.

Edge-In Approach
Often, a variation of the top-down approach, the so-called edge-in approach, is
adopted. In this approach the system is successively partitioned into parts, start-
ing from the inputs and outputs, and working inwards. Figure 1.16 shown a typi-
cal result of this approach. The process continues until the whole system and its
parts have been partitioned into well-known blocks [5]. The edge-in approach
tends to put emphasis on the interfaces and communications between the blocks,
and it inherently provides good control of the overall performance of the system.

Figure 1.16 Example of edge-in decomposition of a DSP system

Critical Part Approach
Yet another approach is the so-called critical part approach that starts by succes-
sively designing the critical subsystems in descending order. Obviously, this
approach puts emphasis on the feasibility of the design, that is, to meet the perfor-
mance goals. Development costs may be reduced, as in the bottom-up approach, by
using previously designed and proven building blocks.

Meet-In-The-Middle Approach
The aim of a structured design methodology is not only to cope with the high
design complexity, but also to increase design efficiency and the probability of an
error-free design. As mentioned earlier, the complexity is reduced by imposing a