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VLSI Full Form - Very Large Scale Integration

 Very Large-Scale Integration

Very Large-Scale Integration

  • Very Large-Scale Integration (VLSI) is that the process of making an integrated circuit ( IC ) by combining many MOS transistors onto one chip.
  • VLSI began within the 1970s when MOS integrated circuit chips were widely adopted, enabling complex semiconductor and telecommunication technologies to be developed.
  • The microprocessor and memory chips are VLSI devices. Before the introduction of VLSI technology, most ICs had a limited set of functions they might perform.
  • An electronic circuit might contain a CPU, ROM , RAM and other glue logic. VLSI lets IC designers add all of those into one chip.

History of VLSI

  • Very large-scale integration was made possible with the wide adoption of the MOS transistor, originally invented by Mohamed M. Atalla and Dawon Kahng at Bell Labs in 1959. Atalla first proposed the concept of the MOS integrated circuit contribute 1960, followed by Kahng in 1961, both noting that the MOS transistor's simple fabrication made it useful for integrated circuits.
  • General Microelectronics introduced the primary commercial MOS microcircuit in 1964.In the early 1970s, MOS integrated circuit technology allowed the integration of more than 10,000 transistors in a single chip.
  • This paved the way for VLSI within the 1970s and 1980s, with tens of thousands of MOS transistors on one chip (later many thousands, then millions, and now billions).
  • The first semiconductor chips held two transistors each. Subsequent advances added more transistors, and as a consequence, more individual functions or systems were integrated over time.
  • The primary integrated circuits held only a couple of devices, perhaps as many as ten diodes, transistors, resistors and capacitors, making it possible to fabricate one or more logic gates on one device.
  • Now known retrospectively as small-scale integration (SSI), improvements in technique led to devices with many logic gates, referred to as medium-scale integration (MSI). Further improvements led to large-scale integration (LSI), i.e. systems with a minimum of thousand logic gates.
  • Current technology has moved far past this mark and today's microprocessors have many gates and billions of individual transistors.
  • At just one occasion, there was an attempt to call and calibrate various levels of large-scale integration above VLSI. Terms like ultra-large-scale integration (ULSI) were used. But the large number of gates and transistors available on common devices has rendered such fine distinctions moot. Terms suggesting greater than VLSI levels of integration are not any longer in widespread use.
  • In 2008, billion-transistor processors became commercially available. This became more commonplace as semiconductor fabrication advanced from the then-current generation of 65 nm processes.
  • Current designs, unlike the earliest devices, use extensive design automation and automatic logic synthesis to get out the transistors, enabling higher levels of complexity within the resulting logic functionality.
  • Certain high-performance logic blocks just like the SRAM (static random-access memory) cell, are still designed by hand to make sure the very best efficiency.

Structured design

  • Structured VLSI design is a modular methodology originated by Carver Mead and Lynn Conway for saving microchip area by minimizing the interconnect fabrics area.
  • This is often obtained by repetitive arrangement of rectangular macro blocks which may be interconnected using wiring by abutment. An example is partitioning the layout of an adder into a row of equal bit slices cells. In complex designs this structuring could also be achieved by hierarchical nesting.
  • Structured VLSI design had been popular within the early 1980s, but lost its popularity later due to the appearance of placement and routing tools wasting tons of area by routing, which is tolerated due to the progress of Moore's Law.
  • When introducing the hardware description language KARL within the mid' 1970s, Reiner Hartenstein coined the term "structured VLSI design" (originally as "structured LSI design"), echoing Edsger Dijkstra's structured programming approach by procedure nesting to avoid chaotic spaghetti-structured program

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