In our own reflection abstraction is a throwing off of useless baggage for the sake of more easily handling the knowledge which is to be compared, and has therefore to be turned about in all directionsâ¦
—Arthur Schopenhauer, The World as Will and Idea (translated from the German by R. B. Haldane and J. Kemp), 1909VLSI design flow often starts with an RTL model and goes through a sequence of logical and physical design processes. Finally, we obtain a layout typically represented in the GDS format.
In this chapter, we briefly explain the tasks involved in transforming an RTL model into GDS. We will describe these tasks in detail in the subsequent chapters.
ABSTRACTION IN VLSI DESIGN FLOW
We can represent a design in several ways. For example, we can describe it as an algorithm, RTL model, connection of logic gates, and layout. These descriptions differ in (a) the level of abstraction and (b) the design view or the design domain.
Abstraction: Abstraction means hiding lower-level details in a description. For example, an algorithm does not contain the timing information of a design, while an RTL model typically describes the flow of data at different clock cycles. Therefore, an algorithm is a more abstract description than an RTL model.
View: A view refers to the aspect of a design that we capture in the description. It can be a design's behavior, structure, or physical form. For example, we can describe a design by an algorithm (behavioral view), the connection of logic gates (structural view), or the layout (physical view).
Gajski-Kuhn's Y-chart
We can depict different abstract representations of a design and visualize their transformations using Gajski-Kuhn's Y-chart, shown in Figure 4.1 [1–3].
The concentric circles show different levels of abstraction. As we move from an outer circle to an inner one, the abstraction level decreases, and more details get added to a design. For example, the abstraction decreases as a design evolves as follows: system specification → algorithm → RTL specification → Boolean equation → differential equation.
The three different views of a design are shown on three axes forming a “Y”: behavioral, structural, and physical. The behavior describes the functionality, the structure describes the interconnections, and the physical design view describes the components’ shape, size, and location.