Electronic CADD - Very Large Scale Integration

VLSI stands for "Very Large Scale Integration". This is the field which involves packing more and more logic devices into smaller and smaller areas. Circuits that would have taken board full of space can now be put into a small space few millimeters across! This has opened up a big opportunity to do things that were not possible before.

The development of microelectronics spans a time which is even lesser than the average life expectancy of a human, and yet it has seen as many as four generations. Early 60's saw the 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 in the late 60's when around 100 transistors could be placed on a single chip. By mid eighties, the transistor count on a single chip had already exceeded 1000 and hence came the age of Very Large Scale Integration or VLSI.

VLSI circuits are everywhere; your computer, your car, your brand new state-of-the-art digital camera, the cell-phones etc. Obeying Moore's law, the capability of an IC has increased exponentially over the years, in terms of computation power, utilisation of available area, yield. The combined effect of these two advances is that people can now put diverse functionality into the IC's, opening up new frontiers. 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!

Integrated Circuits:
Digital logic is implemented using transistors in integrated circuits containing many gates.

1. Small-Scale integrated circuits (ssI) contain 10 gates or less.
2. Medium-Scale integrated circuits (MSI) contain 10-100 gates.
3. Large-Scale integrated circuits (LSI) contain up to 104 gates.
4. Very large-scale integrated circuits (VLSI) contain >104 gates.

Improvements in manufacturing lead to ever smaller transistors allowing more per chip.
1. 107 gates/chip now posssible; doubles every 18 months or so

Variety of logic families.
1. TTL - transistor-transistor logic
2. CMOS - complementary metal - Oxide semiconductor
3. ECL - Emitter-coupled logic
4. GaAs-Gallium arsenic

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