What Is VLSI? Definition, Process And Basic Concepts

VLSI or Very Large Scale Integration is the method of building an integrated circuit. In this method, thousands of transistors are combined into a single chip. This method began in 1970, and during that time, communication technologies and complex semiconductors were being developed.  

After the introduction of VLSI, the applications of IC has increased in telecommunication, video processing, controls, computing, etc., and it is expected, there will be rapid growth in the VLSI market as, according to reports, this market is going to reach USD81.09 billion by 2029. In this article, we will talk about what is VLSI, its meaning, basics, job prospects, and more.

What is VLSI in Computer?

VLSI is the method of integrating several transistors into a single silicon semiconductor microchip. VLSI has replaced or is the successor to small-scale, medium-scale, and large-scale integration. The VLSI design included post and pre-synthesis, verification, simulation, register transfer language coding, closure, wafer processing, etc. Over the years, millions of transistors can be put on a single chip as manufacturing technology improves. This results in a more complex and extensive system into a single chip, also known as System-on-Chip (SoC). Taking a VLSI design course can enhance your career scope as this field is developing vastly and opening new career opportunities.

Also Read: VLSI Design Flow

Very Large-Scale Integration (VLSI) Design Process

Now you know what is VLSI design, it is time to look at the VLSI design process. The process of VLSI design is a continuous cycle consisting of some steps such as functional design, logic design, etc. The design process is then checked for accuracy by simulation, and if there are errors at any stage, then that stage is repeated to rectify the error. The VLSI design process includes the following steps:

System Specification

During this step, the cost, performance, architecture, and how the system will communicate are determined. 

Architectural Design

It is vital that the basic architecture of the design must meet the specification of the system. The design engineers design the layout of the system. The architectural design integrates mixed and analog signals, power requirements, external and internal communication, etc.

Functional Design

Functional design is also known as behavioral design, and this step consists of improving the specification of the required design. This step aims to produce an architectural design that can deliver high performance within the cost requirements.

Logic Design

In this step, the desired design structure is added to the behavioral representation. Logic minimization, testability, and performance enhancement are the main specifications considered in this step. This step also considers the problems associated with error detection, test vector generation, and error correction. Numerous logic synthesis tools have been created to automate the logic creation process.

Circuit Design

This step includes replacing the desired design logic blocks with electronic circuits. These electronic circuits consist of electronic devices such as transistors, capacitors, and resistors. At this stage, the circuit simulation also takes place; this is used to know the electronic circuit behavior in branch circuits and node voltages.

Physical Design

At this stage, the layout of the desired system is finished, and all the components are placed in the circuit. The physical design controls the correctness of the chip. 

Fabrication

After the desired design is finalized and checked, it is sent for manufacturing. The design is transferred to the different layers with the help of the photolithographic method. The integrated circuit is then manufactured on silicon wafers. The diameter of these wafers ranges from 200 mm to 300 mm. 

Packaging and Testing

After fabrication, the chips are packed. They can be packed in Ball grid arrays, pin grid arrays, dual-in line packaged, etc. The desired design is packaged, sealed, and then sent to the clients or the users. 

Basic Concepts of VLSI

When understanding what is VLSI design and its basics, it is crucial that you are familiar with some of its concepts:

Stick Diagram in VLSI

A stick diagram is a diagram that depicts the transistor cell. It uses lines or sticks to represent the conductors and devices. It is vital to define the metalization and the direction of the power supply, input, output, and ground to design the architecture of the circuit. 

The importance of stick diagram in VLSI:

• It is an easy way to record the layer information and topography.
• It uses color codes to represent the different layers of information. 
• One can see the positioning of the components easily.
• It helps in route and layout planning. 

Antenna Effect in VLSI

The antenna effect is the charge-collecting effect in the VLSI, and it does not refer to the antenna device. During the plasma etching process, a large amount of charge gets induced. The antenna effect can harm the MOS transistors’ gate oxide during fabrication. This process, also known as the plasma-generated gate oxide, can cause problems with yield and dependability when MOS integrated circuits are produced.

Clock Gating in VLSI

The capacitive load and the switching activity influence the dynamic power of the circuit. The clock elements are one of the most used switching elements in VLSI designs. In fact, in some of the designs, the clock-switching power can contribute 50 percent of the total power. Since power is a vital aspect, taking steps to reduce it is essential. Clock gating helps in saving the dynamic power of the clock elements. The idea behind the clock gating is that it stops the clock of the sequential elements, whose data is not toggling. It is a technique to turn off the clock of certain parts which are not needed. 

Crosstalk in VLSI

Crosstalk in VLSI refers to the electronic phenomenon that happens when a signal transmitted through a channel or a circuit of a transmission system creates an undesirable impact in another channel or circuit. The main cause of the crosstalk is the unwanted conductive coupling, inductive or capacitive, between channels and circuits. It is a significant problem in audio electronics, wireless communication, cabling, and other communication systems.

Floorplanning in VLSI

Floorplanning is a crucial stage in designing the Very Large-Scale Integration as it is a vital means to control the complexity of the circuit design. Since the circuit design complexity is increasing with technological advancement, floorplanning is becoming essential. It involves determining a chip’s shape, size, and location, estimating the chip area and wiring congestion, and providing the groundwork for the layout. 

Synthesis in VLSI

Synthesis is the process of turning the code into a circuit. When it comes to logic gates, synthesis is translating the abstract design into a properly implemented chip. Synthesis is crucial for chip designers as it lets them visualize how the design will appear after its manufacture. The designers can validate and report the factors and make the changes if there is a need for any. 

Advantages of VLSI Technology

The main benefits of VLSI technology are:

• It increases the device’s cost-effectiveness.
• It reduces the circuit size.
• It requires less power as compared to the discrete components.
• It enhances the performance in terms of operating speed.
• It increases the reliability of the devices.
• It encourages miniaturization, and there is a need for less space.

Applications and Job Prospects in VLSI

All modern devices, including mobile phones, anti-lock brake systems, embedded processors, personal computers, electronic medical systems, etc., use VLSI circuits. It goes without saying that the VLSI is meeting the needs of electronic systems and devices. There is a growing demand for compact and functional devices, and VLSI is bringing this improvement to the electronics field. 

Here are the various job roles in the VLSI field: 

• ASIC Verification Engineer: The ASIC verification engineers are experts in control of the physical design of complex digital circuits like ASICs and SoCs or sub-blocks.
• Physical Design Engineer:  The role of the physical design engineer is to design the layout of the chip’s analog and digital circuitry. They work on ADCs, oscillators, power management, PLLs, etc. 
• RF Engineer: RF engineers are responsible for ensuring that the designs they have worked on comply with the standards and requirements. 
• Embedded System Software trainer: The trainer is focused on imparting the practical and theory in data structures, C programming, microcontrollers, device drivers, network protocols, etc. 

Conclusion

In today’s time, there is a demand for portability, miniaturization, functionality, reliability, etc. VLSI technology is the best way to meet these demands and will continue to drive the advancement in the electronics field. Also, to understand the VLSI basics detail, it is recommended to take an online course that covers what is VLSI design, VLSI tools, HDL, etc., and become an expert VLSI engineer. 

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