What is VLSI ?

VLSI (Very large scale integration) is a process of integrating hundreds or thousands of transistors onto a single silicon semiconductor microchip. In present years, contemporary VLSI technology Complex digital systems can now be realized on a single silicon chip. Designers of Custom systems find this technology, particularly attractive since it allows for significant cost reductions by compressing a large amount of digital logic complexity into a single chip.

The number of uses for integrated circuits (ICs) in high performance computing, telecommunications, image and video processing, and consumer electronics has been growing quickly since the introduction of very large scale integration (VLSI) designs. Silicon CMOS technology has emerged as the fabrication process within the last few years. The quick increase in transistors integrated into a single chip’s circuit illustrates the revolutionary significance of these developments.

VLSI

VLSI stands for Very Large Scale Integration. It signifies the process of producing integrated circuits (ICs) by integrating thousands, millions, or even billions of transistors on a single chip. In VLSI, the technology has allowed progressive growth with composite and secure devices, beginning from microprocessors and chips of memory to processors of digital signal and application specific integrated circuits (ASICs).

The integrated circuits ICs are used in VLSI as a broad range of devices, from fundamental devices to advanced supercomputers. In VLSI design, Designers test and design the electronic integrated circuits at a very limited scale, so generally, it is in the range of 0.1 to 0.01 micrometres.

Design Specification, Architectural Design, RTL Design, Functional Verification, Logic Synthesis and verification, Physical Design and verification, sign-off and Fabrication of ICs are methods that are used in the VLSI design process. The layout of transistors and interconnections needs to be constructed and optimized on the chip, designers use authorized software tools to follow the layout of IC design to conserve the performance, power consumption, efficiency, and manufacturability into account.

VLSI chip

Does VLSI need coding?

Let’s understand the need of VLSI coding with different tools and techniques involved in VLSI:

• Yes, VLSI needs coding because it is used to make different complicated designs that are used in the IC’s which are enhanced in today’s life.
• Some circuits that are needed to make digital designs like simulation tools and verification are involved in the broad range of digital IC design tools.
• To ensure the digital design works properly, designers make use of IC design to test the circuits when devices of IC are fabricated.
• Designers make use of VLSI coding by using programming languages and tools involved in VLSI designing.
• HDLs (Hardware Description languages) such as Verilog and VHDL are involved for use in digital circuits by checking the behavior and functionality of digital devices.
• Some EDA tools like Cadence, Synopsys and Mentor Graphics are involved for the purpose to use in VLSI circuits for simulation the digital design.
• Some verification tools like emulation and simulation are involved for the purpose to make use of testing the functionality of VLSI circuits to make sure that they functions properly when the digital ICs are fabricated.
• In conclusion, VLSI technology involves the high number of transistors and other devices components on a single chip that is used for the design and fabrication.

Y Chart

• Y chart is developed by Gajski Kuhn that he developed a model named as Y chart that is used to checking the digital semiconductor devices.
• Gajski Kuhn Y chart has three domains that has to be put on radial axes.
• Various domains are divided into different areas like levels of abstraction using centered rings.
• The top level named as a outer ring, that explains the chip architecture, and the low levels named as a inner rings, to make the design and implementation in a better way by following techniques:
• The process of high-level synthesis or logical synthesis is involved for making a structural description from a behavioral description.
• The layout synthesis is involved for making a physical description from a structural description.

Gajski Kuhn Y Chart

VLSI Design Process

A VLSI chip goes through several stages of VLSI design, from the chip’s specification to the final product’s fabrication. The following steps are involved in the design process:

VLSI design process

Design Specification

• Some specifications involved in VLSI design are power consumption, performance, and functionality and area of chip that are make used in the design specifications.
• Digital devices has some specifications in VLSI design like abstract description of the architecture that must to be designed.

Architectural Design

• After design specification, the architecture of chip is designed. So, to make the architecture of the design by some requirements of the functionality, performance, or general system requirements.
• In this design, all the connections and functions are specified by the component of the chip.

RTL Design

• Using integrated circuits (ICs), designing of electronic circuits is the Register Transfer Level (RTL) design at a high level description.
• The RTL description of the digital circuit is written in hardware description language (HDL) such as VHDL or Verilog, works as the input. The RTL description expresses the functionality and behavior of the circuit at a high level description.

Functional Verification

• Using simulation tools, It simulates the behavior and functionality of the integrated circuit in unique input cases and to meet the specified requirements by design verification to test the ASIC design.
• Our goal is to make sure that chip functions correctly by ensuring to test the ASIC design by verification so it’s behavior is managed by checking specifications and requirements of functionality of design.

Logic Synthesis

• Logic Synthesis defines the RTL code that transforms into a gate-level netlist by using synthesis tool, which represents the logical architecture of the circuit in terms of standard cells.
• Using HDL (Verilog/VHDL), it produces a gate-level netlist that is a description of logic cells and their interconnections. These tools map the functionality described in the HDL to a set of standard cells or library elements.
• Performance, size, and power consumption of the design are all optimized during the synthesis process.

Logical Verification

• A verification is required to be performed to verify whether the synthesis tool produced the gate-level netlist accurately.
• The output of Logic synthesis are gate-level netlist that is given as input to the Physical design after verification and testing.

Physical Design

• In this step, gate-level netlist is converted into a physical layout. Layout is a representation of an IC in terms of planar geometric shapes which correspond to the patterns of metal-oxide or semiconductor layers that make up the components of the IC. A design tool like Cadence Virtuoso is used to create layouts.
• In physical design step, it is divided into sub-steps such as Partitioning, floorplanning, placement, clock-tree synthesis, routing, timing closure are formed.

Given below are the Steps for Physical Design:

1. Partitioning: It is the process of dividing a system on chip (SoC) into small blocks. As a result, you can effectively manage semiconductor designs as a group of connected functional blocks. The best way to handle semiconductor designs is as related groups of functional blocks.
2. Floorplanning: Floorplanning is a process of placing the various blocks and I/O ports across the chip area based on the design constraints. Floorplanning involves determining the physical layout of the IC on the semiconductor wafer or die.
3. Placement: Placement involves assigning physical locations to the standard cells and other components on the chip according to the floorplan.
4. Clock Tree Synthesis: It is the process of connecting the clocks to all clock pin of sequential circuits by using inverters/buffers in order to balance the skew and to minimize the insertion delay. A single clock source powers each and every clock pin. Clock Tree Synthesis is used to minimize delay and skew.
5. Routing: Once every element is positioned, a detailed and global routing is started to establish connections between all the elements. It involves physically connecting metal traces to macros, standard cells, I/O ports, power, and the clock.
6. Timing Closure: It is the process that determines a chip’s speed by satisfying the timing constraints. For a smoother chip operation, it makes sure that all of the signals arrive at the appropriate time. Timing closure involves ensuring that the circuit meets timing requirements, such as setup and hold times, clock frequency, and maximum propagation delays.

Physical Verification and Sign off

• This stage undergoes 3 steps of physical verification known as sign off checks.
• It helps to check whether the layout is working correctly the way it was designed to.

Given below are the Steps for Physical Verification:

1. Layout v/s Schematic (LVS):It is the process of verifying the layout is compared with the schematic whether their functionality matches or not.
2. Design Rule check (DRC):It is the process of verifying whether the given layout follows the design rules given by the fabrication team. DRC checks implies to physical checks of spacing rules between metals, minimum width rules, etc.
3. Logic equivalence checking (LEC):It is a formal verification technique used in VLSI design to verify that two different representations of a digital circuit, often an RTL description and a gate-level netlist, exhibit functional equivalence.

Fabrication

• Output of Layout is GDS-II (Graphical Data Stream Information Interchange) file produced and used by the semiconductor foundries to fabricate the silicon.
• After physical verification step, the design is ready for fabrication. Tape out is the final result of the design process for ICs before they are sent for manufacturing.
• The Tape out is specifically the point at which the graphic for photo-mask of the circuit is sent to foundry.
• Fabrication process consists of several steps involving wafer growth, epitaxial growth, etching, doping, deposition, and diffusion of various materials on the wafer. One mask is used during every step.

Packaging and Testing

• Each of the wafers contains hundreds of chips. The technique of “scribing and cleaving” is used to divide and package these chips. Chips that don’t pass an electrical test are discarded.
• Every chip is tested and packed to make sure it satisfies all design requirements and operates as intended.

Design and Implementation of VLSI

Let’s discuss the Design and Implementation of VLSI by learning the different aspects of IC design in various fields of digital circuit that comes under the VLSI domain:

Digital VLSI Design

• Transistors, logic gates and other electronic components are made by designing of digital circuits known as Digital VLSI design.
• Microprocessors, memory devices, controllers are the digital devices that comes in digital VLSI domain.

Analog VLSI Design

• Analog devices are involved in the process of processing continuous signals by designing and implementation of the analog circuits.
• Analog VLSI domain includes some devices like digital-to-analog converters (DACs), filters, oscillators, amplifiers, etc.

Mixed-Signal VLSI Design

• In mixed-signal VLSI, both analog and digital VLSI techniques are combined on a single chip.
• Both analog and digital VLSI techniques are combined oftenly in SoCs (System on Chip) so to ensure that both analog and digital devices are needed by complex system that is created for the mixed-signal VLSI.

RF (Radio Frequency) VLSI Design

• RF VLSI design involves the main aim of making the integrated circuits for wireless communication devices such as radios, transceivers, etc.
• For the aspect of applications, it involves the designing of circuits that has increased the efficiency for devices like Bluetooth, RFID, Wi-Fi, etc. that works at radio frequencies.

Low-Power VLSI Design

• Low power VLSI design is used to reduce the power consumption of integrated circuits that used in various applications like Internet of Things, battery operated devices and devices which are energy efficient.
• Some methods that are used to make use of low power VLSI operation are voltage scaling, power gating, clock gating, some devices which are energy efficient.

ASIC (Application-Specific Integrated Circuit) Design

• The process of designing specialized integrated circuits for specific tasks or objectives is known as ASIC design.
• ASICs are suitable for specific applications including image processing, sensor interfaces, cryptographic algorithms, and automotive electronics as they improve performance, power economy, and area usage.

FPGA (Field-Programmable Gate Array) Design

• FPGA involves some digital logic devices which needs to be configured and programming the FPGA design so to make the digital circuits by make use of configured digital logic devices.
• In FPGA design, some specific applications like prototyping, etc. are used for fast growth of FPGA design.

Applications of VLSI Technology

There are several applications for VLSI technology across numerous sectors and firms. These are some important fields in which VLSI is extremely significant.

Applications of VLSI technology

Consumer Electronics

• The creation of smartphones, tablets, gaming consoles, and smartwatches has been made possible by VLSI technology, which has completely changed the industry of consumer electronics.
• These products improve user experiences and productivity with their cutting-edge features, quick processing, and energy-saving technologies.

Automotive Industry

• VLSI technology has transformed vehicle functionality and safety in the automobile industry.
• VLSI chips are used by electronics systems, Engine Control Units (ECUs), and Advanced Driver Assistance Systems (ADAS) to provide functions including real-time vehicle diagnostics, autonomous driving, and object, lane, and sign detection.

Telecommunications

• The telecommunications sector has profited tremendously from VLSI technology. It has made it easier to construct 5G wireless communication, high-speed network infrastructure, and cutting-edge mobile devices.
• To provide dependable and quick data transfer, VLSI-based chips are utilized in network switches, routers, modems, and base stations.

Healthcare

• The development of medical imaging equipment, wearable health monitors, and implanted medical devices has been made possible by VLSI technology, which has had a substantial impact on the healthcare industry.
• Accurate diagnosis, real-time monitoring, and enhanced patient care are all provided by these electronic devices.

The Advantages of VLSI technology

• Compact Size: Traditional circuits are significantly greater than VLSI circuits because of electronic circuits are created to ensure the computation of digital logic circuits.
• Consumes less Power: VLSI circuits are better than Traditional circuits because VLSI circuits are eco-friendly. This is necessary for the battery life saving.
• High performance: By adding the high number of transistors on a chip so to accomplish VLSI circuits are high speeds with they perform complex tasks.
• Cost-Effectiveness: By using VLSI technology, electronic circuits which are complicated that they are executed in large quantity. All the features and various components are implemented on a single chip. Electronic circuits are used and implemented because of their easy accessibility.
• Increased Reliability: Comparing to discrete devices, some short link and better manufacturing capabilities used by VLSI circuits because of their better reliability in terms of errors and failures.

The Disadvantages of VLSI technology

• Inflexible: Once fabricated, it is not easy to be modified and is not flexible.
• High Cost of Development: Design tools, development platforms, and testing equipment must be obtained in large quantities throughout the time-consuming and expensive process of developing VLSI devices. It can be challenging and expensive to alter the design since the circuits are specially designed and cannot be readily modified.
• Manufacturing Challenges: The quality and functionality of the finished product may be impacted by a number of manufacturing difficulties that VLSI devices are susceptible to, including yield loss, variability, and reliability problems.
• Time to Market: Longer time to market for new goods might result from the longer design, verification, and manufacturing cycles associated with VLSI devices.
• Short Product Life Cycle: VLSI design perceives rapid technological innovation, which may result in short product life cycles as new technology and products age quickly.

Conclusion

A crucial component of VLSI design is design flow, which offers an efficient and structured process for creating intricate integrated circuits. Designers can successfully navigate through the many stages of the VLSI design process and ensure the successful production of dependable and high-performing electronic systems by adhering to a clearly defined design flow. The design process needs to change as technology develops to be able to address the opportunities and difficulties of the future and produce creative and effective VLSI designs.

Electronics are revolutionized by the development of VLSI, which combines several transistors into a single chip. It makes gadgets faster, smaller, and more efficient viable. Commonly employed technologies comprise BJT, FET, and CMOS. Applications for VLSI can be found in consumer electronics, automotive, industrial automation, telecommunications, and healthcare. Power consumption and chip complexity are constraints. The research and development of new materials like graphene, embedded memory, and 3D integration are among the upcoming trends. As VLSI technology develops, new opportunities arise across a range of industries.

What is VLSI ? – FAQs

What is VLSI used for?

Millions of transistors are needed for manufacturing electronic components like memory chips and microprocessors, which are the primary uses for VLSI.

Is VLSI digital or analog?

VLSI technology includes both digital and analog design elements. Digital circuits are superior at carrying out intricate calculations and logical processes, but analog circuits are excellent at processing continuous signals precisely.

Which HDLs are utilized in VLSI?

Hardware description languages (HDLs) such as Verilog, System Verilog and VHDL, are used to describe the behavior and functionality of digital circuits.

Why Gate array design in VLSI is usually faster than prototype full-custom design?

Predefined standard cells, or pre-designed and pre-characterized building components like flip-flops, multiplexers, and logic gates, make up gate arrays. Because these standard cells have previously been produced and validated, designers can utilize them as the foundation of their ideas instead of needing to create unique transistor-level designs.

Why clock tree synthesis is done before routing?

Clock tree synthesis is performed before signal routing, to prevent congestion to the clock nets and to obtain an optimal timing skew.