Integrated Circuits: SSI, MSI, LSI, VLSI, ULSI
Case-Study:-
INTEGRATED CIRCUITS: SSI, MSI, LSI, VLSI, ULSI
An integrated circuit is a set of electronic circuits on one small flat piece where the piece is made up of semiconductor material (silicon). Where large number of MOSFETs integrate into a small chip . Then the circuits becomes smaller, faster, and less expensive than those discrete electronic component.
The first integrated circuits was “Small-Scale Integration Circuits” contained only a few transistors numbering in the tens. They have played very important role in the field of development of early computers. SSI was followed by MSI (Medium-Scale integration circuits) where the number of transistors present on the chip was in the range of hundreds. Next development was of LSI (Large Scale Integration circuits) where thousands of transistors were present on the chip and it was around 1970s when the production of the MSI was at its peak level .Next generation is VLSI circuits(Very Large Scale Integration Circuits) where hundreds of thousands of transistors were used, it was the first time when CPU(central processing unit) was built on the single integrated circuit and ‘microprocessor’ term was introduced. In 1994 microprocessor chip was produced containing more than 3 million transistors on it. The next generation of VLSI is known as USLI (ultra scale large integrated circuits)
Why integrated circuits are preferred over the circuits made up of discrete electronics component?
· Compact size : Circuits built using IC’s are smaller compared to that built using the discrete circuit
· Low power consumption: because of smaller size and construction IC’s consume less power compared to traditional circuit
· Lesser weight − ICs weighs lesser than discrete circuits that are used for used for implementing the same function of IC.
· Reduced cost: because of the fabrication technologies and usage of lesser material than discrete circuits , the cost is reduced in the manufacturing process of IC’s.
· Improved operating speeds: because of their lesser power consumption and switching speeds , IC’s operate at improved speed as compared to digital circuits.
· Increased reliability: connections in IC’s are lesser in number as compared to that of digital circuits which results in increased reliability.
Types of integrated circuits:
o Analog integrated circuits: analog IC’s operates over an entire range of the continuous values of signal amplitude. Further there are two types of the analog integrated circuits.
1. Linear Integrated Circuits
2. Radio frequency integrated Circuits
o Digital Integrated Circuits : instead of operating for an entire range of continuous values of the signal amplitude , digital integrated circuits operates only at the few predefined levels.
SSI Circuits (small scale integration circuits)
SSI was developed where transistors numbering in the tens providing a few logic gates was present on the chip. Early developments of the integrated circuits started in 1949 when German engineer Werner Jacobi filed a patent on integrated-circuit-like semiconductor amplifying device showing five transistors on a common substrate in a 3-stage amplifier arrangement.The basic idea behind the IC was to create small ceramic squares , each containing a single miniaturized component
Semiconductor IC’s fabrication includes three key process steps — imaging, deposition and etching. The main process steps are supplemented by doping and cleaning. Silicon is almost always used, but various compound semiconductors are used for specialised applications. The entire manufacturing process, from start to packaged chips ready for shipment, takes six to eight weeks and is performed in highly specialized facilities referred to as fabs. Integrated circuits are composed of many overlapping layers, each defined by photolithography, and normally shown in different colors.
SSI circuits were crucial to early aerospace projects, and aerospace projects helped inspire development of the technology , Both the Minuteman missile and Apollo program needed lightweight digital computers for their inertial guidance systems first,MOS chips were small-scale integration chips for NASA satellites.
· Early 3 and later 5 transistor chipset
3 transistor and later 5 transistor microchip was developed for basic electrical functions. The Plessey SL201 integrated circuit and Philips TAA320 integrated circuit were successful examples from the early 1950s
· The ZN414 integrated circuit
The idea was the production of a cheap and efficient 5 transistor microchip for basic radio set circuit functions. It was first created in 1972 and became very popular with both business and hobbyists around the world. The ZN414 integrated circuit is a successful example of this radio-chip concept from 1972.
MSI Circuits (medium scale integration circuits)
It was the next higher level of IC integration, in which, typically 10 to 1000 transistors making 30 to 300 logic gates per chip are fabricated on a single chip. Medium-scale integration technology was prominent between years 1966 and 1971. This technology is used to make multiplexers, decoders, counters, and registers.
MSI circuits was developed in the early days of mainframe computers.It was the next step in the development of integrated circuits contained hundreds of transistors on each chip. In 1964, Frank Wanlass demonstrated a single-chip 16-bit shift register he designed, with an incredible (at the time) 120 transistors on a single chip.As compared to SSI , MSI devices were attractive economically because while they cost little more to produce than SSI devices. they allowed more complex systems to be produced using smaller circuit boards, less assembly work (because of fewer separate components), and a number of other advantages.
SSI and MSI devices often were manufactured by masks created by hand-cutting Rubylith.LSI devices contain so many transistors, interconnecting wires, and other features that it is considered impossible for a human to check the masks or even do the original design entirely by hand. The engineer depends on computer programs and other hardware aids to do most of this work.
MSI or Medium scale integrated circuits are a set of basic, elementary logic circuits. They are available as ICs (integrated chips) and implement specific,commonly used digital functions such as:
1. Multiplexing and Demultiplexing
2. Encoding and Decoding
MSIs can be used as a stand-alone IC or in combination with other ICs in order to implement combinational circuits in various applications. In this module, you will study many of the common types of MSI devices. For each type, you will start with a brief discussion of its basic operating principle and then introduce specific ICs. Now let’s see how they can be used alone or in combination with other ICs in various applications.
Some of the most widely used MSI circuits:
1. 74283 4-bit adder
2. 74HC283 from Philips
3. 555 timer
4. It was used in the core of the CPU of such computers as the PDP-11 and VAX 11/780
LSI Circuits (large scale integration circuits)
It is the process of integrating or embedding thousands of transistors on a single silicon semiconductor microchip. LSI technology was conceived in the mid-1970s when computer processor microchips were under development.
The term “large scale integration” (LSI) was first used by IBM scientist Rolf Landauer when describing the theoretical concept; that term gave rise to the terms “small-scale integration” (SSI), “medium-scale integration” (MSI), “very-large-scale integration” (VLSI), and “ultra-large-scale integration” (ULSI). Large scale integration (LSI) and application specific integrated circuits (ASICs) are exactly what they say they are: integrated circuits that have been specially designed and tooled to do one very specific job. In other words, miniature worlds of components emulating what otherwise would be put together using quantities of separate components on a printed circuit board.
LSI chips are widely used in applications with specific processing requirements and where parameters such as speed and very low cost are important. Custom designed logic integrated circuits devices result in better performance, lower cost, and sometimes lower power consumption at given speeds. They also have some built in security protection: their operation cannot be easily copied by competitors. Applications are to be found just about everywhere: hand-held organizers, cell-phones, telecommunication equipment, musical instruments, MP3 decoders and telephony receivers. Most commercial network interface chips are nothing but LSI devices specially designed to interface between the network and a microprocessor.
VLSI Circuits (very large scale integration circuits)
Very large scale integration is the process of creating an integrated circuit (IC) by combining millions of MOS transistors onto a single chip.
VLSI began in 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 could perform. An electronic circuit might consist of a CPU, ROM, RAM and other glue logic. VLSI lets IC designers add all of these into one chip. 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 chip in 1960, followed by Kahng in 1961, both noting that the MOS transistor’s ease of fabrication made it useful for integrated circuits. General Microelectronics introduced the first commercial MOS integrated circuit 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 in the 1970s and 1980s, with tens of thousands of MOS transistors on a single chip (later hundreds of thousands, then millions, and now billions).
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 obtained by repetitive arrangement of rectangular macro blocks which can 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 may be achieved by hierarchical nesting.
The Design Process of a VLSI IC
Overall, VLSI IC design incorporates two primary stages or parts:
. Front-End Design: This includes digital design using a hardware description language, for example, Verilog, System Verilog, and VHDL. Furthermore, this stage encompasses design verification via simulation and other verification techniques.
. Back-End Design: This consists of characterization and CMOS library design. Additionally, it involves fault simulation and physical design.
VLSI Technology has advanced rapidly since late 90s. Low cost, high performance Chips designed and fabricated made strong impact in systems development and resulted in applications to diversified fields like computers, communications, entertainment electronics, medicine, and rural necessities. Spreading of Internet globally, making this world as a ‘global village” and rapid strides in mobile communications have a direct bearing on the progress made in VLSI technology. Research work is being done to further develop the technology in new dimensions like Silicon Photonics, Organic semi-conductors, Flexible displays etc. These developments take the technology further close to rural applications and can result in significant improvement in the quality of life in villages. Fibre optic connectivity, hosting of portals with useful information to rural folk, e-governance, energy conservation, wireless sensor networks, Telephone-TV can improve the standard of living in rural areas significantly. VLSI technology directly or indirectly is playing a vital role in this direction.
ULSI Circuits (ultra large scale integration circuits)
Ultra large scale integration, which refers loosely to placing more than about one million circuit elements on a single chip.
ULSI technology was conceived during the late 1980s when superior computer processor microchips, specifically for the Intel 8086 series, were under development. ULSI is a successor to large-scale integration (LSI) and very large-scale integration (VLSI) technologies but is in the same category as VLSI.
ULSI was designed to provide the greatest possible computational power from the smallest form factor of microchip or microprocessor dye. This was achieved by embedding and integrating integrated circuits (IC), which were formed with transistors and logic gates. The close placement and design architecture enabled faster resolution of tasks and processes. However, even though VLSI now contains more than millions of transistors, any IC or microchip with more than one million transistors is considered a ULSI implementation.
The term was coined when the critical dimensions of patterns in the chips hovered in the range of 0.25 micrometers, which have now reduced even further to less than 100nm marking a transition from the micron-scale to nano-scale. At such a scale, various issues which did not affect performance of devices at a higher scale like interconnects (RC delays etc.), conductivity requirements and material properties become very critical and cannot be ignored at any stage.
Intel 486 and the Pentium series of processors were built on ULSI principles.
References:
· https://www.engineersgarage.com/what_is/what-is-ulsi/
· https://www.techopedia.com/definition/2900/ultra-large-scale-integration-ulsi
· https://www.daenotes.com/electronics/devices-circuits/integrated-circuits-ic#sthash.wwrwPihR.dpbs
