VLSI - Very Large Scale Integration

VLSI - Very Large Scale Integration

Very-large-scale integration (VLSI) is a process of combining thousands of transistors into a single chip. It started in the 1970s with the development of complex semiconductor and communication technologies.

A VLSI device commonly known, is the microcontroller. Before VLSI, most ICs had limited functions. An electronic circuit usually consists of a CPU, ROM, RAM and other peripherals on one board. VLSI lets IC designers add all of these into one chip. Let’s look into the backstory of VLSI development before going into specifics.

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Integrated circuit through the years

The first integrated circuits contained only a few transistors. Early digital circuits containing transistors in tens, provided a few logic gates and early ICs had as few as two transistors. The number of transistors in an IC has increased dramatically since then.

VLSI has many advantages

The increase in density happens through multiple developments. Some of which would be a reduction in size, management in power consumption among others,

Designing a VLSI IC

The design of a VLSI IC consists broadly of 2 parts. Front end design includes digital design using HDLs such as Verilog, VHDL, SystemVerilog and the like. It includes design verification through simulation and other verification techniques. The process includes designing, starting from gates to design for testability. Backend design comprises of CMOS library design and its characterization. It also covers physical design and fault simulation. The entire design procedure follows a step by step approach. The front end design steps would involve,

Problem Specification

It is a high-level representation of the system. The major parameters are performance, functionality, physical dimensions, fabrication technology and design techniques. It has to be a tradeoff between market requirements, the available technology and the economic viability of the design. The end specifications include the size, speed, power and functionality of the VLSI system.

Architecture Definition

Basic specifications like floating point units, which system to use, like reduced instruction set computer (RISC) or complex instruction set computer (CISC), number of ALU’s cache size etc.

Functional Design

Defines the major functional units of the system and hence facilitates the identification of interconnect requirements between units, the physical and electrical specifications of each unit.

Logic Design

Boolean expressions, control flow, word width, register allocation etc. are developed and the outcome are the register transfer level (RTL) description. HDLs implement the RTL description onto a system.

Assembly and Packaging

Each of the wafers contains hundreds of chips. A diamond saw cuts the wafer into single chips separating the single chips. The chips failing electrical tests are discarded, whereas the good ones are sent for packaging. Before packaging, remaining chips are observed under a microscope. The good chips are packaged and rechecked after packaging.