Digital Design Process

Prerequisite – Introduction to Digital Systems

Computer Added Design (CAD) tools are introduced in the process due to its increased size and complexity in current trends. Designers want to standardize the design procedure, starting from the design idea to get the design implemented then so called design flow.

New CAD tools are based on Hardware Description Language (HDL) to improve the process. HDLs provide formats for representing the outputs of various design steps. An HDL based Design Automation (DA) tool transforms for its HDL input into an HDL, which contains more hardware information.

Representation :

Behavioral Representation :
It describes how a particular design should respond to a given set of inputs. Behavior may be specified by:

• Boolean equations
• Tables of input and output values
• Algorithm written in standard high level computer language or in special hardware description language.

An n-bit Adder is a good example of Behavioral representation.

Structural Representation :
It specifies how components are interconnected to perform a certain function or achieve a designated hardware. In general, the description is a list of modules and their interconnects – often called netlist.

At the Structural level, the level of abstraction are:

• The module level
• The gate level
• The switch level

Physical Representation :
In an IC process, the lowest level of physical specification is the photo-mask information required by the various processing steps in the fabrication process. At the module level, the physical layout for the 4 bit Adder may be defined by a rectangle or polygon that specifies the outer boundary of all the geometry for the Adder, set of submodules and collection of inputs.