Community hub
Recent from talks
Contribute something to knowledge base
Content stats: 0 posts, 0 articles, 0 media, 0 notes
Members stats: 0 subscribers, 0 contributors, 0 moderators, 0 supporters
Subscribers
Supporters
Contributors
Moderators
Hub AI
Design closure AI simulator
(@Design closure_simulator)
Hub AI
Design closure AI simulator
(@Design closure_simulator)
Design closure
Design Closure is a part of the digital electronic design automation workflow by which an integrated circuit (i.e. VLSI) design is modified from its initial description to meet a growing list of design constraints and objectives.
Every step in the IC design (such as static timing analysis, placement, routing, and so on) is already complex and often forms its own field of study. This article, however, looks at the overall design closure process, which takes a chip from its initial design state to the final form in which all of its design constraints are met.
Every chip starts off as someone’s idea of a good thing: "If we can make a part that performs function X, we will all be rich!" Once the concept is established, someone from marketing says "To make this chip profitably, it must cost $C and run at frequency F." Someone from manufacturing says "To meet this chip’s targets, it must have a yield of Y%." Someone from packaging says “It must fit in the P package and dissipate no more than W watts.” Eventually, the team generates an extensive list of all the constraints and objectives they must meet to manufacture a product that can be sold profitably. The management then forms a design team, which consists of chip architects, logic designers, functional verification engineers, physical designers, and timing engineers, and assigns them to create a chip to the specifications.
The distinction between constraints and objectives is straightforward: a constraint is a design target that must be met for the design to be successful. For example, a chip may be required to run at a specific frequency so it can interface with other components in a system. In contrast, an objective is a design target where more (or less) is better. For example, yield is generally an objective, which is maximized to lower manufacturing cost. For the purposes of design closure, the distinction between constraints and objectives is not important; this article uses the words interchangeably.
Designing a chip used to be a much simpler task. In the early days of VLSI, a chip consisted of a few thousand logic circuits that performed a simple function at speeds of a few MHz. Design closure was simple: if all of the necessary circuits and wires "fit", the chip would perform the desired function.
Modern design closure has grown orders of magnitude more complex. Modern logic chips can have tens to hundreds of millions of logic elements switching at speeds of several GHz. This improvement has been driven by Moore’s law of scaling of technology, and has introduced many new design considerations. As a result, a modern VLSI designer must consider the performance of a chip against a list of dozens of design constraints and objectives including performance, power, signal integrity, reliability, and yield. In response to this growing list of constraints, the design closure flow has evolved from a simple linear list of tasks to a very complex, highly iterative flow such as the following simplified ASIC design flow:
The purpose of the flow is to take a design from concept phase to working chip. The complexity of the flow is a direct result of the addition and evolution of the list of design closure constraints. To understand this evolution it is important to understand the life cycle of a design constraint. In general, design constraints influence the design flow via the following five-stage evolution:
A good example of this evolution can be found in the signal integrity constraint. In the mid-1990s (180 nm node), industry visionaries were describing the impending dangers of coupling noise long before chips were failing. By the mid-late 1990s, noise problems were cropping up in advanced microprocessor designs. By 2000, automated noise analysis tools were available and were used to guide manual fix-up. The total number of noise problems identified by the analysis tools identified by the flow quickly became too many to correct manually. In response, CAD companies developed the noise avoidance flows that are currently in use in the industry.
Design closure
Design Closure is a part of the digital electronic design automation workflow by which an integrated circuit (i.e. VLSI) design is modified from its initial description to meet a growing list of design constraints and objectives.
Every step in the IC design (such as static timing analysis, placement, routing, and so on) is already complex and often forms its own field of study. This article, however, looks at the overall design closure process, which takes a chip from its initial design state to the final form in which all of its design constraints are met.
Every chip starts off as someone’s idea of a good thing: "If we can make a part that performs function X, we will all be rich!" Once the concept is established, someone from marketing says "To make this chip profitably, it must cost $C and run at frequency F." Someone from manufacturing says "To meet this chip’s targets, it must have a yield of Y%." Someone from packaging says “It must fit in the P package and dissipate no more than W watts.” Eventually, the team generates an extensive list of all the constraints and objectives they must meet to manufacture a product that can be sold profitably. The management then forms a design team, which consists of chip architects, logic designers, functional verification engineers, physical designers, and timing engineers, and assigns them to create a chip to the specifications.
The distinction between constraints and objectives is straightforward: a constraint is a design target that must be met for the design to be successful. For example, a chip may be required to run at a specific frequency so it can interface with other components in a system. In contrast, an objective is a design target where more (or less) is better. For example, yield is generally an objective, which is maximized to lower manufacturing cost. For the purposes of design closure, the distinction between constraints and objectives is not important; this article uses the words interchangeably.
Designing a chip used to be a much simpler task. In the early days of VLSI, a chip consisted of a few thousand logic circuits that performed a simple function at speeds of a few MHz. Design closure was simple: if all of the necessary circuits and wires "fit", the chip would perform the desired function.
Modern design closure has grown orders of magnitude more complex. Modern logic chips can have tens to hundreds of millions of logic elements switching at speeds of several GHz. This improvement has been driven by Moore’s law of scaling of technology, and has introduced many new design considerations. As a result, a modern VLSI designer must consider the performance of a chip against a list of dozens of design constraints and objectives including performance, power, signal integrity, reliability, and yield. In response to this growing list of constraints, the design closure flow has evolved from a simple linear list of tasks to a very complex, highly iterative flow such as the following simplified ASIC design flow:
The purpose of the flow is to take a design from concept phase to working chip. The complexity of the flow is a direct result of the addition and evolution of the list of design closure constraints. To understand this evolution it is important to understand the life cycle of a design constraint. In general, design constraints influence the design flow via the following five-stage evolution:
A good example of this evolution can be found in the signal integrity constraint. In the mid-1990s (180 nm node), industry visionaries were describing the impending dangers of coupling noise long before chips were failing. By the mid-late 1990s, noise problems were cropping up in advanced microprocessor designs. By 2000, automated noise analysis tools were available and were used to guide manual fix-up. The total number of noise problems identified by the analysis tools identified by the flow quickly became too many to correct manually. In response, CAD companies developed the noise avoidance flows that are currently in use in the industry.