Design Hierarchy in VLSI

Designing integrated circuits is a complex process that requires a great deal of planning and attention to detail.

Most of the design process for integrated circuits starts with creating a schematic. This is a simple circuit diagram showing the electrical connections between the components. Once the schematic is complete, it is used to create a layout. This more detailed diagram shows how the components will be physically placed on the chip. The layout is then used to create a final design file that can be sent to the fabrication plant.

Methods For Creating Schematics & Layouts

CMOS

There are several different methods for creating schematics and layouts. The most common one is called CMOS (complementary metal-oxide-semiconductor). In CMOS design, each component is represented by a small block, called a transistor. The schematic and layout are created by connecting these blocks together.

RTL

Another method, called RTL (register transfer level), uses a different representation for the components. In RTL design, each component is represented by a set of mathematical equations. The schematic and layout are created by solving these equations. This method is more difficult to use, but it produces designs that are more accurate.

In order to create a successful design, engineers must follow a specific hierarchy.This hierarchy begins with the system specification and moves on to the abstract high level model, logic synthesis, circuit design, and finally the manufacturing process. Let’s take a closer look at each stage of the design hierarchy.

Design Hierachy in VLSI

Stage 1: System Specification

The first stage of the hierarchy is the system specification. In this stage, engineers must define the purpose of the circuit and what it needs to accomplish. All constraints, such as power consumption and area, must also be taken into account. Once the system specification is complete, engineers can move on to the next stage.

Stage 2: Abstract High Level Model

The second stage is creating an abstract high-level model. In this stage, engineers will develop a model of the system using a hardware description language (HDL). This model will be used to verify that the system meets all the requirements specified in the first stage.

Stage 3: Logic Synthesis

The third stage is logic synthesis. In this stage, engineers will take the HDL model developed in Stage 2 and convert it into a netlist. This netlist will contain all the information necessary to implement the design physically.

Stage 4: Circuit Design

The fourth stage is circuit design. In this stage, engineers will physically represent the design using transistors and other components. They will also consider factors such as power consumption and heat dissipation.

Stage 5: Manufacturing Process

The final stage in the hierarchy is the manufacturing process. In this stage, engineers will prepare the design for fabrication. They will also consider any testability issues that may arise during manufacturing. Once all these stages are complete, the integrated circuit can be successfully produced.

Approaches to design VLSI Circuits

Different approaches to design VLSI circuits include the top-down and bottom-up methodologies.

Top Down Methology

In a top-down approach, the design begins with high level specifications and gradually works its way down to the lower levels of circuit design. Top-down design allows for greater flexibility and adaptability in the design process.

Bottom Up Approach

In a bottom-up approach, the design begins with lower level circuit components and gradually builds up to higher levels of design. This approach is often more efficient and can result in faster design times. However, it may also lead to inflexibility in the design process.

Both top-down and bottom-up approaches have their strengths and weaknesses, and it is up to the designer to decide which methodology will best suit their needs. Ultimately, a successful design often involves a combination of both approaches.

By following a specific hierarchy and metholodogy, engineers can ensure that all aspects of the design are taken into account. The hierarchy begins with specifying the system requirements and moves on through stages such as logic synthesis and circuit design before finally preparing the design for fabrication. By following this process, engineers can create successful designs that meet all specifications.

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