Hardware Modelling Using Verilog

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Lecture 1

Main Objectives Of Learning Verilog

• Learn about the Verilog hardware description language.
• Understand the difference between behavioral and structural design styles.
• Learn to write test benches and analyze simulation results.
• Learn to model combinational and sequential circuits.
• Distinguish between good and bad coding practices.
• Case studies with some complex designs.

VLSI design process

design complexity increasing rapidly

Design complexity in Very Large Scale Integration (VLSI) is increasing rapidly. As technology advances, the number of transistors that can be integrated into a single chip continues to grow, which allows for more advanced and complex electronic systems.

Fabrication Technology is also improving day by day. Since the technology is improving there is also a necessity for CAD tools for designing complex designs. It is also a challenge to manage the area, speed and power consumption for a particular design.

Present Trend

Present trend in vlsi is to have a standardized design flow for every design that we design.

Also the main objective of todays vlsi technology is to emphasize on low power design and Increased performance.

Evolution of ICs

The first integrated circuit (IC) was developed in the late 1950s and early 1960s, and it was a significant milestone in the history of electronics. The first IC was a simple device that contained a few transistors and resistors on a single chip of semiconductor material as shown in the image below.

Since then, IC technology has advanced significantly, and modern ICs are much more complex and capable than their early counterparts. Today's ICs can contain billions of transistors on a single chip, and they can perform a wide range of functions, including digital signal processing, memory storage, and wireless communication. A typical Intel processor IC is shown below .

Moore's Law

Moore's Law is a prediction made by Gordon Moore, the co-founder of Intel, in 1965 that the number of transistors that could be placed on an integrated circuit (IC) would double roughly every two years, while the cost per transistor would decrease.

Moore's Law has been remarkably accurate for over five decades, with the number of transistors on a chip doubling every 18 to 24 months. This has led to a rapid increase in computing power, as more and more transistors can be packed onto a single chip, enabling faster processing speeds and more advanced features.

However, some experts predict that Moore's Law will eventually come to an end, as it becomes increasingly difficult to continue shrinking transistors while maintaining performance and energy efficiency. Nonetheless, the impact of Moore's Law on the development of modern computing cannot be overstated, and it has played a critical role in shaping the world we live in today.

Technologies

CMOS

Complementary Metal Oxide Semiconductor is a type of metal oxide semiconductor field-effect transistor fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions. In the CMOS technology we can reduce the size upto 22nm.

Nano meter technology refers to the minimum feature size means that during the fabrication process of a transistor, how closely can the transistors be placed on a chip to be used for various purposes.

FinFET

The Fin Field Effect Transistor is similar to the traditional CMOS design but the arrangement of the transistors are done vertically rather than making it horizontally. This technology allows to reduce the feature size upto 14nm. Most of the modern chips are manufactured using this FinFET technology.

CAD Tools

What is CAD Tools?

In simple words Computer-Aided Design (CAD) is the use of computers to aid in the creation, modification, analysis, or optimization of complex designs.

The CAD tools used in vlsi are based on Hardware Description Languages[HDLs], which is actually used to describe the hardware design in CAD tool. So a CAD software takes the input in the form of HDL and transforms it into output which is also a HDL, but the output contains more detailed information about the hardware.

Why CAD Tools?

The design of complex modules like processors, we require the help of CAD Tools as it is beyond the capabilities of a human being to carry out design in manual way. Hence we have to depend on CAD Tools

Typical CAD Tool working

• It converts the design that is fed into it using HDL, which is the behavioral level to the Register Transfer Level [RTL]

An RTL describes how data is transformed as it is passed from register to register.

• Next from RTL it converts it to Gate level

Gate level describes the design in terms of logical gates and inter-connection between them

• Next from Gate level to Transistor level

Transistor level is the lowest level (most fundamental level) of design where the design is represented using Nmos and Pmos transistors

• At last it is converted to Layout level

HDLs

VHDL

The VHSIC Hardware Description Language is a hardware description language that can model the behavior and structure of digital systems at multiple levels of abstraction, ranging from the system level down to that of logic gates. VHDL is based on Ada and Pascal languages. VHDL is complex than Verilog. VHDL is not case sensitive language.

VHDL is