Introduction to VLSI Design Flow

Earlier, we discussed dividing the RTL to GDS implementation flow into two stages: logic synthesis and physical design. In part II of this book, we discussed logic synthesis. In this part of the book, we will discuss physical design.

Physical design involves transforming a netlist into a layout. It takes a design from the structural domain to the physical domain. The primary task of physical design is to decide the location of each design element and make their interconnections. During this process, we must ensure that the functionality of a design at the layout level is the same as that delivered by the given netlist. Furthermore, design metrics, such as yield, performance, power, and reliability, must be acceptable. Therefore, physical design implementation and verification are critical in a design flow.

In this part of the book, we will discuss each major physical design task in separate chapters. In Chapter 24 (“Basic Concepts for Physical Design”), we will explain some concepts needed for understanding physical design tasks. In Chapters 25-28, we will discuss essential physical design tasks: chip planning, placement, clock tree synthesis, and routing. In Chapter 29 (“Physical Verification and Signoff”), we will discuss physical verification tasks, including parasitic extraction and signoff. Finally, in Chapter 30 (“Post-silicon Validation”), we will explain the validation tasks performed on the first few fabricated chip samples.

It is worthy to point out that the primary objective of these chapters is to explain essential concepts and principles governing physical design. We have attempted to provide explanations not based on any specific physical design tool or proprietary data format. Therefore, readers can apply these concepts to any tool they choose for physical design, and the learning of these chapters can be relevant despite changes in tools and technology.

In the following chapters, we will also explain some popular algorithms that accomplish physical design tasks. The primary motivation for discussing these algorithms is to illustrate physical design challenges and present a few approaches to tackle them. However, note that we do not analyze these algorithms rigorously in this book. Therefore, readers who are interested in the implementation details of physical design tools should refer to standard textbooks on physical design algorithms such as [1–4].