The concept of a circuit’s three domains, namely its behavioral, structural, and geometrical/physical views, was initially introduced by Gajski and Kuhn in what is known as the Gajski-Kuhn Y-Chart. This chart is named the “Y-chart” because it has three arms, resembling the letter Y.
In this model, the “hierarchy” dimension of the 3D model is aligned with concentric abstraction levels, forming the three axes of the Y-chart. Each of these axes represents a distinct design perspective or domain, describing various attributes that characterize the element under design. Together, these views provide a comprehensive description of the design subject.
Also known as behavioral description, this view describes all aspects of the design subject’s behavior. It encompasses the operations performed by the element being designed and its dynamic response. Equations, functions, and algorithms are integral parts of the behavioral view.
Referred to as structural description, this view defines the logical structure or the abstract implementation of the design subject. It represents the topographical configuration of components and their connections. Block diagrams and symbols for components, like CPUs and memory chips, are utilized in this view.
Known as geometrical/physical realization, this view details how the design object is physically implemented. It provides the precise geometrical layout and configuration of all components and their connectivity architectures. The physical view deals with the actual physical objects used in the construction.
In each of these three views, the design is documented at different degrees of abstraction, characterized by abstraction levels or design levels. The Y-chart encompasses five abstraction levels, moving from the outermost circle to the innermost circle:
System (Architectural) Level: At this level, the global properties of an electronic system are specified. Behavioral descriptions include block diagrams representing signals and their transient responses, while structural descriptions involve block symbols for components like CPUs and memory chips.
Algorithmic Level: Concurrent algorithms, such as signals, loops, variables, and assignments, are defined at this level. The structural view may include blocks like Arithmetic Logic Units (ALUs).
Functional Block Level (Register Transfer): This level offers a more detailed abstraction where interactions between communicating registers and logic units are described. Data structures and data flows are defined, and the geometrical view involves floorplan design.
Logical Level: In the behavioral perspective, Boolean equations describe this level. The structural view includes gates and flip-flops, while the geometrical view uses standard cells to describe the logical level.
Circuit Level: The innermost level is modeled using mathematical differential equations. This represents the actual hardware level and includes components like transistors and capacitors, extending down to crystal lattices.
The Y-chart serves as a valuable tool for illustrating physical design terms related to synthesis and generators on the left side, as well as individual design steps on the right side, as depicted in Figure 4.10. It complements the concept of hierarchy within the 3D design space, allowing for separate hierarchies in each of the three domains or views. In the Y-chart, an abstraction level is determined based on the modeling concept relevant to the specific domain or view, while the 3D model’s hierarchy embodies the composition and decomposition concept within that domain’s branch of the Y-chart.
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