Page 41 - DSP Integrated Circuits

26 Chapter 1 DSP Integrated Circuits

the models belong to the same domain. The transformations needed to derive the
VLSI implementation are therefore not straightforward.
Experience gained from both software and hardware projects indicates that it
is important that all members of a design team share a common view of, not only
the design goals, but also of the design process [12]. Without such a common view
severe communication and coordination difficulties may arise in the design process.

1.7.1 System Design Methodology
Integrated circuit design, also called VLSI design, is the process of transforming
the structural description of the logic circuitry into a detailed physical layout. This
process is complex and error prone. It is therefore mandatory to adhere to a highly
structured design methodology for the integrated circuit design phase.

1.7.2 Technical Feasibility

One of the first steps in the design of a DSP system is a feasibility study of the
whole project. The question is, can the project, given economic and technical con-
straints, be finished within the available time frame? If the project is feasible, the
next step is to determine a more detailed plan for the whole project. This section
deals primarily with the technical feasibility of the VLSI circuit. The economic and
time aspects depend largely on the previous experience of the design team, the
available CAD tools, and the circuit library. The technical feasibility study of the
system generally involves many different issues:

SYSTEM-RELATED
Partitioning into cabinets, boards, and circuits
Mixed digital and analog circuits on the same chip
Clock frequencies
Power dissipation and cooling
Circuit area and packaging
I/O interface

CIRCUIT-RELATED
External
Interchip propagation delay
Data transfer frequencies
Input protection
Loads that have to be driven, including expected PCB runs
Available input drivers
Drive capacity for output buffers
Restrictions on pin-outs
Internal
Clock frequencies
Data transfer frequencies and distances
Critical timing paths
Noncritical timing paths
Power dissipation and cooling