VLSI TECHNOLOGY
Microprocessors are essential to many of the products we use every day such as TVs, cars, radios, home appliances and of course, computers. Transistors are the main components of microprocessors.
At their most basic level, transistors may seem simple. But their development actually required many years of painstaking research. Before transistors, computers relied on slow, inefficient vacuum tubes and mechanical switches to process information. In 1958, engineers managed to put two transistors onto a Silicon crystal and create the first integrated circuit, which subsequently led to the first microprocessor.
Upper interconnect layers on anIntel 80486DX2 microprocessor die.
The final step in the development process, starting in the 1980s and continuing through the present, was "very large-scale integration" (VLSI). The development started with hundreds of thousands of transistors in the early 1980s, and continues beyond several billion transistors as of 2007.
Origins of VLSI
• 1959 - Jack St. Claire Kilby (Texas Instruments) - first integrated circuit - 10 components on 9 mm2
• 1959 - Robert Norton Noyce (founder, Fairchild Semiconductor) - improved integrated circuit
• 1968 - Noyce, Gordon E. Moore found Intel
• 1971 - Ted Hoff (Intel) - first microprocessor (4004) - 2300 transistors on 9 mm2
• Since then - continued improvement in technology has allowed for increased performance as predicted by Moore’s Law
DEALING WITH VLSI CIRCUITS
Digital VLSI circuits are predominantly CMOS based. The way normal blocks like latches and gates are implemented is different from what students have seen so far, but the behaviour remains the same. All the miniaturisation involves new things to consider. A lot of thought has to go into actual implementations as well as design. Let us look at some of the factors involved ...
1. Circuit Delays. Large complicated circuits running at very high frequencies have one big problem to tackle - the problem of delays in propagation of signals through gates and wires ... even for areas a few micrometers across! The operation speed is so large that as the delays add up, they can actually become comparable to the clock speeds.
2. Power. Another effect of high operation frequencies is increased consumption of power. This has two-fold effect - devices consume batteries faster, and heat dissipation increases. Coupled with the fact that surface areas have decreased, heat poses a major threat to the stability of the circuit itself.
3. Layout. Laying out the circuit components is task common to all branches of electronics. Whats so special in our case is that there are many possible ways to do this; there can be multiple layers of different materials on the same silicon, there can be different arrangements of the smaller parts for the same component and so on.
The power dissipation and speed in a circuit present a trade-off; if we try to optimise on one, the other is affected. The choice between the two is determined by the way we chose the layout the circuit components. Layout can also affect the fabrication of VLSI chips, making it either easy or difficult to implement the components on the silicon.
DEVELOPMENTS IN THE FIELD OF VLSI
There are a number of directions a person can take in VLSI, and they are all closely related to each other. Together, these developments are going to make possible the visions of embedded systems and ubiquitous computing.
1. Reconfigurable computing:
Reconfigurable computing is a very interesting and pretty recent development in microelectronics. It involves fabricating circuits that can be reprogrammed on the fly! And no, we are not talking about microcontrollers running with EEPROM inside. Reconfigurable computing involves specially fabricated devices called FPGA's, that when programmed act just like normal electronic circuits. They are so designed that by changing or "reprogramming" the connections between numerous sub modules, the FPGA's can be made to behave like any circuit we wish.
This fantastic ability to create modifiable circuits again opens up new possibilities in microelectronics. Consider for example, microprocessors which are partly reconfigurable. We know that running complex programs can benefit greatly if support was built into the hardware itself. We could have a microprocessor that could optimise itself for every task that it tackled! Or then consider a system that is too big to implement on hardware that may be limited by cost, or other constraints. If we use a reconfigurable platform, we could design the system so that parts of it are mapped onto the same hardware, at different times. One could think of many such applications, not the least of which is prototyping - using an FPGA to try out a new design before it is actually fabricated. This can drastically reduce development cycles, and also save some money that would have been spent in fabricating prototype IC's
2. Software Engineers taking over hardware design:
ASIC's provide the path to creating miniature devices that can do a lot of diverse functions. But with the impending boom in this kind of technology, what we need is a large number of people who can design these IC's. This is where we realise that we cross the threshold between a chip designer and a systems designer at a higher level. Does a person designing a chip really need to know every minute detail of the IC manufacturing process? Can there be tools that allow a designer to simply create design specifications that get translated into hardware specifications?
3. The need for hardware compilers:
Before we go further let us look at why we need this kind of technology, that can convert high-level languages into hardware definitions. We see a set of needs which actually lead from one to the other in a series.
A. Rapid development cycles.
The traditional method of designing hardware is a long and winding process, going through many stages with special effort spent in design verification at every stage. This means that the time from drawing board to market, is very long. This proves to be rather undesirable in case of large expanding market, with many competitors trying to grab a share. We need alternatives to cut down on this time so that new ideas reach the market faster, where the first person to get in normally gains a large advantage.
B. Large number of designers.
With embedded systems becoming more and more popular, there is a need for a large number of chip designers, who can churn out chips designed for specific applications. Its impractical to think of training so many people in the intricacies of VLSI design.
C. Specialized training.
A person who wishes to design ASIC's will require extensive training in the field of VLSI design. But we cannot possibly expect to find a large number of people who would wish to undergo such training. Also, the process of training these people will itself entail large investments in time and money. This means there has to be system a which can abstract out all the details of VLSI.
Advanced tools for VLSI design
A VLSI VL82C106 Super I/O chip.
The original business plan was to be a contract wafer fabrication company, but the venture investors wanted the company to develop IC design tools to help fill the foundry.
VLSI became the an early vendor of standard cell (cell-based technology) to the merchant market in the early 80s where the other ASIC-focused company, LSI Logic, was a leader in gate arrays. Prior to VLSI's cell-based offering, the technology had been primarily available only within large vertically integrated companies with semiconductor units such as AT&T and IBM.
VLSI's design tools eventually included not only design entry and simulation but eventually cell-based routing (chip compiler), a datapath compiler, SRAM and ROM compilers, and a state machine compiler. The tools were an integrated design solution for IC design and not just point tools, or more general purpose system tools. A designer could edit transistor-level polygons and/or logic schematics, then run DRC and LVS, extract parasitics from the layout and run Spice simulation, then back-annotate the timing or gate size changes into the logic schematic database. Characterization tools were integrated to generate FrameMaker Data Sheets for Libraries. VLSI eventually spun-off the CAD and Library operation into Compass Design Automation but it never reached IPO before it was purchased by Avanti Corp.
VLSI's physical design tools were critical not only to its ASIC business, but also in setting the bar for the commercial EDA industry. When VLSI and its main ASIC competitor, LSI Logic, were establishing the ASIC industry, commercially-available tools could not deliver the productivity necessary to support the physical design of hundreds of ASIC designs each year without the deployment of a substantial number of layout engineers. The companies' development of automated layout tools was a rational "make because there's nothing to buy" decision. The EDA industry finally caught up in the late 1980s when Tangent Systems released its TanCell and TanGate products. In 1989, Tangent was acquired by Cadence Design Systems (founded in 1988).
Unfortunately, for all VLSI's initial competence in design tools, they were not leaders in semiconductor manufacturing technology. VLSI had not been timely in developing a 1.0 µm manufacturing process as the rest of the industry moved to that geometry in the late 80s. VLSI entered a long-term technology parthership with Hitachi and finally released a 1.0 µm process and cell library (actually more of a 1.2 µm library with a 1.0 µm gate).
VLSI also had an early partnership with PMC, a design group that had been nutured of British Columbia Bell. When PMC wanted to divest its semiconductor intellectual property venture, VLSI's bid was beaten by a creative deal by Sierra Semiconductor. The telecom business unit management at VLSI opted to go it alone. PMC Sierra became one of the most important telecom ASSP vendors.
Scientists and innovations from the 'design technology' part of VLSI found their way to Cadence Design Systems (by way of Redwood Design Automation). Compass Design Automation (VLSI's CAD and Library spin-off) was sold to Avant! Corporation, which itself was acquired by Synopsys.
MOST OF TODAY’S VLSI DESIGNS ARE CLASSIFIED INTO THREE CATEGORIES
1. Analog:
Small transistor count precision circuits such as Amplifiers, Data converters, filters, Phase Locked Loops, Sensors etc.
2. ASICS or Application Specific Integrated Circuits:
Progress in the fabrication of IC's has enabled us to create fast and powerful circuits in smaller and smaller devices. This also means that we can pack a lot more of functionality into the same area. The biggest application of this ability is found in the design of ASIC's. These are IC's that are created for specific purposes - each device is created to do a particular job, and do it well. The most common application area for this is DSP - signal filters, image compression, etc. To go to extremes, consider the fact that the digital wristwatch normally consists of a single IC doing all the time-keeping jobs as well as extra features like games, calendar, etc.
3. SoC or Systems on a chip:
These are highly complex mixed signal circuits (digital and analog all on the same chip). A network processor chip or a wireless radio chip is an example of an SoC.
Global expansion
VLSI maintained operations throughout the USA, and in Britain, France, Germany, Italy, Japan,Singapore and Taiwan. One of its key sites was in Tempe, Arizona, where a family of highly successful chipsets was developed for the IBM PC.
In 1990, VLSI Technology, along with Acorn Computers and Apple Computer were the founding investing partners in ARM Ltd.
Ericsson of Sweden, after many years of fruitful collaboration, was by 1998 VLSI's largest customer, with annual revenue of $120 million. VLSI's datapath compiler (VDP) was the value-added differentiator that opened the door at Ericsson in 1987/8. The silicon revenue and GPM enabled by VDP must make it one of the most successful pieces of customer-configurable, non-memory silicon intellectual property (IP) in the history of the industry. Within the Wireless Products division, based at Sophia-Antipolis in France, VLSI developed a range of algorithms and circuits for the GSM standard and for cordless standards such as the European DECT and the Japanese PHS. Stimulated by its growth and success in the wireless handset IC area, Philips Electronics acquired VLSI in June 1999, for about $1 billion. The former components survive to this day as part of Philips spin-off NXP Semiconductors.
REFRENCES
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Ø Wikipidia.com
Ø Msn.com
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