Introduction to VLSI

We no longer have huge computers made of vacuum tubes that take up an entire room, and have the ability to do about 360 multiplications of 10 digit numbers in a second. Modern day computers are smaller, faster, and cheaper and more power efficient. With laptops, tablets and smart phone flooding the markets, the progress every second is obvious. The new domain of computing was ushered in by multiple advancements in electronic miniaturization and the semiconductor transistor by Bardeen in 1947-48, and then the Bipolar Transistor by Shockley in 1949.

Since the invention of the first Integrated Circuit(IC) by Jack Kilby in 1958, our ability to pack more and more transistors onto a single chip has been very rapid. In the early 1960s, low density fabrication processes classified under Small Scale Integration (SSI) in which transistor count was limited to about 10. This rapidly gave way to Medium Scale Integration (MSI) later in the decade, when around 100 transistors could be placed on a single chip. Declining costs of research encouraged private companies to enter the industry in contrast to the earlier years where the main burden was borne by the military. Early 1970s saw the growth of transistor count to about 1000 per chip called the Large Scale Integration (LSI).

By mid-1980, the transistor count on a single chip exceeded 1000 and hence came the age of Very Large Scale Integration or VLSI, which is large scale integration with a single chip of size as small as 50 millimeters square having more than a million transistors and circuits in it. VLSI circuits have opened up a big opportunity to do things that were not possible before. VLSI circuits are everywhere. They are in your computer, your car, your digital camera, mobile phones…the list goes on.

VLSI chiefly comprises of front end design and back end design. While front end design includes digital design using HDL, design verification through simulation and other verification techniques, the design from gates and design for testability, backend design comprises of complementary metal-oxide semiconductor (CMOS) design and its characterization.

The entire VLSI circuit design procedure follows a step by step approach, where each design step is followed by simulation before it's put into the hardware. The main design steps are:

  • Problem Specification
  • Architecture Definition
  • Functional Design
  • Logic Design
  • Circuit Design
  • Physical Design
  • Circuit Partitioning
  • Floor Planning and Placement
  • Routing
  • Layout Compaction
  • Extraction and Verification
  • Packaging

Most VLSI Designs are Classified Into Three Categories:

  • Analog: Small transistor count precision circuits such as Amplifiers, Data converters, filters, Phase Locked Loops, Sensors etc.
  • Application Specific Integrated Circuits (ASICS): Progress in the fabrication of internal circuits has enabled faster and more powerful circuits in smaller and smaller devices. ASICS are created for specific purposes and each device is created to do a particular job, and do it well.
  • Systems on a Chip (SoC): These are highly complex mixed signal circuits, such as a network processor chip or a wireless radio chip.

VLSI has been around for a long time now, but with the fast advances especially in the world of computers, there has been a dramatic proliferation of tools that can be used to design VLSI circuits. Examples are embedded systems, where intelligent devices are put inside everyday objects, and ubiquitous computing where small computing devices proliferate to such an extent that even the shoes you wear may actually do something useful like monitoring your heartbeats.

 

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