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Wednesday 21 September 2011
Saturday 17 September 2011
EMBEDDED SYSTEM
EMBEDDED SYSTEM
By,
D.GOWRI
II B.Tech , E.C.E.,
e-mail :gowri_btech2005 @ yahoo.co.in
&
Y.SUJALA II B.Tech ,E.C.E.,
MEKAPATI RAJA MOHAN REDDY
INSTITUTE OF TECHNOLOGY AND SCIENCE
MeRITS,
UDAYAGIRI,
NELLORE(dt).
ABSTRACT:
This paper attempts to investigate the approach of embedded systems. The embedded system is a combination of computer hardware, software and perhaps additional mechanical or other
parts, designed to perform a specific function within a given time frame.
KEYWORDS:
Design of embedded systems, embedded software architectures, user interfaces.
INTRODUCTION:
An embedded system is a special-purpose computer system built into a larger device .An embedded-system is typically required to meet very different requirements than a general-purpose personal computer Two major areas of differences are cost and power consumption. Since many embedded systems are produced in the tens of thousands to millions of units range, reducing cost is a major concern. Embedded systems often use a (relatively) slow processor and small memory size to minimize costs.
• Some of the attributes of the coming era:
1. The number of smart devices ( i.e., products with embedded operating systems inside ) will grow exponentially, reaching numbers in the billions.
2. The choice of CPU will be more a matter of cost than technology or a architecture
3. Nearly all devices will have connectivity, whether wired or wireless.
4. Most devices will have the ability to be upgraded or repaired remotely, by downloading new firmware or software.
Most devices will have specific rather than general-purpose functionality, so their users application software will be defined by the manufactures (rather than loaded by their).
This needs to, “minimize cost and maximize specialization”creates the opportunity for embedded systems.
Paper Identification Number : SS-2.5
This peer reviewed paper has been published by the Pentagram Research Centre (p) limited. Responsibility of contents of this paper rests upon the authors and not upon pentagram research center (p) limited. Copies can be obtained from the company for a cost.
Embedded systems are becoming all pervasive. Every microwave has one. A cellular hand phone has two. A luxury Mercedes car has around 40. The latest Boeing 777-302,will have tens of dozens-we’re talking about the ubiquitous microprocessor chips and their associated peripheral devices.
To cite other examples, embedded software allows your washing machine to choose speed according to the type of cloth, gives thinking power to the microwave, acts like a music conductor in the car engine and pushes rocket launchers into space
The embedded system generally comprises topics like real time embedded digital signal processing, microprocessor architecture programming concepts; Real-time Operating System (QXN, RT Linux, V x Works); Micro controllers; Embedded Systems Programming Data Communication Networking, C concepts and linux among others.
START UP:
All embedded systems have start-up code. Usually it disables interrupts, sets of up the electronics, tests the computer (RAM, CPU and software), and then starts the application code. Many embedded systems recover from short-term power failures by skipping the self-tests if the software can prove they were done recently. Restart times under a tenth of a second are common.
“Embedded systems’ has come to mean “micro-controller programming”. With the increasing proliferation of embedded systems, and advances in hardware and software technologies and the blurring of the boundary between them we need a more meaning-ful glimpse into this area. “Embedded systems’ addresses this need and brings out the issues in building modern-embedded systems.
DESIGN OF EMBEDDED SYSTEMS
The electronics usually uses either a microprocessor or a microcontroller some large are old systems use general-purpose mainframe computers are mini computers. Embedded systems design is getting complex, requiring intimate knowledge of both the hardware and software worlds. Cramming all those chips in a square centimetre of silicon real estate is more an art then a science. Getting the software to work with limited memory is often a struggle. Designers embedded systems strive to improve performance, reliability and cost effectiveness. Hardware and software choices are simultaneously considered. This is called co-design.
The goal is to produce an efficient implementation that satisfies-performance and cost requirements on the design the entire system on a chip-the SOC approach. Information appliances can be fabricated from custom SOC silicon .This has been successful in designing cellular hand phones where the high volume usually dictate this design strategy.
CHARACTERISTICS :
Two major areas of differences are cost and power consumption . Since many embedded systems are produced in the tens of thousands to millions of units range, reducing cost is a major concern. Embedded systems often use a (relatively) slow processor and small memory size to minimize costs.
The slowness is not just clock speed. The whole architecture of the computer is often intentionally simplified to lower costs.
For example embedded systems often use peripherals controlled by synchronous serial Interfaces, Which are ten to hundreds of times slower than comparable peripheral used in PCs. Programs on an embedded systems often must run with real time constrains with limited hard ware resources:
Often there is no disk drive, operating system , keyboard or screen. A flash drive may replace rotating media and a small keypad and LCD screen may be used instead of a PCs keyboard and screen.
Firmware is the name for software that is embedded in hardware devices, e.g. in one or more ROM memory IC chips .
PLATFORM:
There are many different CPU architecture used in embedded designs.
This in contrast to the disk top computer marke-t, which as of this writing (2003) is to
limited just a few competing architectures , chieply intel’s x86,and the apple/Motorola/IBM power PC, used in the apple macintosh.
One common configuration for embedded system is the system on a chip, an application specific integrated circuit, for which the CPU was purchased as intellectual property to add to IC’s design.
TOOLS:
Like a typical computer programmer, embedded system, designers use compiler, assembler and debbuger to develop an embedded system.
Those software tools can come from several sources:
Soft-ware companies that specialize in the embedded market. Ported from the GNU software development tolls. Some times, development tools for a personal computer can be used if the embedded process is a close relative to a common PC processors . Embedded system designers also use a few software tools rarely used by typical computer programmers.
Some designers keep a utility program to turn data files into codes, so that they can include any kind of data in a program.Most designers also have utility programs to add a check sum or CRC to a program, so it can check its program data before executing it.
OPERATING SYSTEM:
They often have no operating system or a specialized embedded operating system (often real time operating system), or the programmer is assigned to part one of these to the new system .
EMBEDDED SOFTWARE ARCHITECTURES;
There are severally basical different types of software architectures in common use.
THE CONTROL LOOP:
In this design, the software simply has a loop. The loop calls subroutines. Each subroutine manages apart of the hardware or software. Interrupts generally set flags, or update counters that are read by the rest of the software.
A simple API disables and enables interrupts. Done right, it handles nested calls in Nested subroutines, and restores the preceding interrupt state in the outer most enable. This is one of the simplest methods of creating an exokernel.
Typically, there’s some sort of subroutine in the loop to manage a list of software timers, using a periodic real time interrupt.
When a timer expire, an associated subroutine is run, or flag is set . Any expected hardware event should be backed-up with a software timer . Hardware events fail about ones in a trillion times.
That’s about once a year with modern hardware. With a million mass-produced devices, living out a software timer is a business disaster.
State machines are implemented with a function-pointer per state- machine (in C++, C or assembly any way). A change of state stores a different function into the pointer. The function pointer is executed every time the loop runs.
Many designers recommend reading each IO device once per loop, and storing the result so the logic acts on consistent values.
Any designers prefer to design their state machines to check only one are two things per states. Usually this is a hardware event, and a software timer .
Designers recommand the hierarchical state machines should run the lower-level state Machine before the higher, so the higher run with accurate information.
Complex function like internal combustion control are often handle with multi-dimensional tables.
Instead of complex calculations the code looks up the values. The software can interpolate between entries, to keep the table small and cheap. One major weakness of this system is that it does not guarantee a time to respond to any particular hardware event. Careful coding can easily assure that nothing disables interrupts for long.
Thus interrupt code can run at vary precise timings.Another major weakness of this system is that it can become complex to add few features. Algorithms that take along time to run must be carefully broken down so only a little piece gets done each time through the main loop.
This system’s strength is it’s simplicity, and on small pieces of software the loop is usually so fast that nobody cares that is not predictable.
Another advantage is that system guarantees that a software will run. There is no mysterious operating system to blame for bad behaviour.
USER INTERFACES:
User interfaces for embedded systems vary wildly, and thus deserve some special comment. Designers recommend testing the user interface for usability at the earliest possible instant.
Exactly one person should approve the user interface ideally, this should be a customer, the major distributor or someone directly responsible for selling the system. The decision maker should be able to decide. The problem is that a committee will never make-up its mind, and neither will some people. Not doing in this causes avoidable, expensive delays. A usability test is more important then any number of opinions. A touch-screen or screen-edge buttons also minimize that types of user actions. Another basic trick is to minimize and simplify the type output.
Designs should consider using a status light for each interface plug, or failure condition ,to tell what failed. A cheap variation is to have two light bars with a printed matrix of errors that they select-the user can glue on the labels for the languages that she speaks.
For example, Boeing’s standard test interface is a button and some lights. When you press the button all the lights turn on. When you release the button the lights with failures say on. The labels are in basic english. For another example, look at a small computer printer. You might have one next to your computer. Notice that the lights are labeled with stick-on the labels that can be printed in any language. Really look at it.
Designers use colors. Red means the user can get hurt-think of blood.
Yellow means some thing might be wrong. Green means everything’s OK. Another essential trick is to make any modes absolutely clear on the user’s display.
An interface has modes, they must be reversible in an obvious way.
Most designers prefer the display to respond to the user. The display should change immediately after a user action. If the machine is going to do any thing, it should start within 7 seconds, or give progress reports. If a design needs a screen, many designers use plain text.
APPLICATIONS OF EMBEDDED SYSTEM:
• . Automatic Teller Machine (ATM).
• . Cellular telephones and telephone switches.
• . Computer network Equipment , including router and fire wall.………
• . Computer Printer .
• . Disk drive .
• . Engine controller and antilock break controller for automobiles.
• . Home auto machine products, like thermostat sprinkler, and security monitoring . . systems.
• . Handheld Calculator.
• . Household appliance, including. Microwave oven ,washing machine ,television sets . . DVD players/recorders.
• . Inertial guidance system for air-craft and missile.
• . Medical Equipment.
• . Multi function Wristwatches.
• . Personal digital assistants.
• . Programmable logic control for industrial automation and monitoring.
• . Video game console.
CONCLUSION:
In this paper we had tried to cover the fundamental principles of embedded systems used in modern digital instruments. In modern world the major problem with present desktop system is that they are very bulky in size to they cause severe problem in their decomposition. But as the embedded system does same task with smaller size made then vary useful for electronic instruments and many others. So it’s the most crucial thing which will become the heart of every electronic device in feature.
REFERENCES:
1. http://www.bambooweb.com/articles/e/m/embedded system.html
2. http://www.oranetech.com/
wimax technology paper presentation
THE DAWN OF NEW TECHNICAL ERA
PRESENTED BY
L.GURU KUMAR II ECE
E MAIL:lokkugurukumar@gmail.com
B.SRAVAN KUMAR II ECE
E MAIL:sravan111k@gmail.com
(WIRELESS COMMUNICATIONS)
NBKR INSTITUTE OF SCIENCE AND TECHNOLOGY
VIDYANAGAR
NELLORE
ABSTRACT
WiMAX is an acronym that stands for Worldwide Interoperability for Microwave Access. WiMAX is a wireless metropolitan area network (MAN) technology that can connect IEEE 802.11 (Wi-Fi) hotspots with each other and to other parts of the Internet. It can provide a wireless alternative to cable and DSL for last mile (last km) broadband access. WiMAX is the wireless solution for the next step up in scale, the metropolitan area network (MAN). WiMax does not conflict with Wi-Fi but actually complements it. A WiMax system consists of two parts: A WiMax tower & A WiMax receiver. WiMAX has the potential to do to broadband Internet access what cell phones have done to phone access. Some cellular companies are also evaluating WiMAX as a means of increasing bandwidth for a variety of data-intensive applications. The purpose of this Paper is to highlight and assess the value of WiMAX as the right solution to:
• offers cheap voice calls and high speed internet
• ensures a boost for government security
• extend the currently limited coverage of public LAN (hotspots) to citywide coverage (hot zones) the same technology being usable at home and
on the move,
• blanket metropolitan areas for mobile data-centric
service delivery,
• offer fixed broadband access in urban
and suburban areas where copper quality
is poor or unbundling difficult,
• bridge the digital divide in low-density areas where technical and economic factors make broadband deployment very challenging. In addition to these uses, this paper will highlight other potential applications, such as telephony or an effective point-to-multipoint backhauling solution for operators or enterprises
1.INTRODUCTION
WiMAX is an acronym that stands for Worldwide Interoperability for Microwave Access, a certification mark for products that pass conformity and interoperability tests for the IEEE 802.16 standards.
Products that pass the conformity tests for WiMAX are capable of forming wireless connections between them to permit the carrying of internet packet data. It is similar to Wi-Fi in concept, but has certain improvements that are aimed at improving performance and should permit usage over much greater distances. the WiMAX forum, backed by industry leaders, will encourage the widespread adoption of broadband wireless access by establishing a brand for the technology and pushing interoperability
2. TECHNICAL ADVANTAGES OVER WIFI
Because IEEE 802.16 networks use the same Logical Link Controller (standardized by IEEE 802.2) as other LANs and WANs, it can be both bridged and routed to them.
An important aspect of the IEEE 802.16 is that it defines a MAC layer that supports multiple physical layer (PHY) specifications. This is crucial to allow equipment makers to differentiate their offerings. This is also an important aspect of why WiMAX can be described as a "framework for the evolution of wireless broadband" rather than a static implementation of wireless technologies. Enhancements to current and new technologies and potentially new basic technologies incorporated into the PHY (physical layer) can be used. A converging trend is the use of multi-mode and multi-radio SoCs and system designs that are harmonized through the use of common MAC, system management, roaming, IMS and other levels of the system. WiMAX may be described as a bold attempt at forging many technologies to serve many needs across many spectrums.
The MAC is significantly different from that of Wi-Fi (and ethernet from which Wi-Fi is derived). In Wi-Fi, the MAC uses contention access—all subscriber stations wishing to pass data through an access point are competing for the AP's attention on random basis. This can cause distant nodes from the AP to be repeatedly interrupted by less sensitive, closer nodes, greatly reducing their throughput. By contrast, the 802.16 MAC is a scheduling MAC where the subscriber station only has to compete once (for initial entry into the network). After that it is allocated a time slot by the base station. The time slot can enlarge and constrict, but it remains assigned to the subscriber station meaning that other subscribers are not supposed to use it but take their turn. This scheduling algorithm is stable under overload and oversubscription (unlike 802.11). It is also much more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service by balancing the assignments among the needs of the subscriber stations. A recent addition to the WiMAX standard is underway which will add full capability by enabling WiMAX nodes to simultaneously operate in "subscriber station" and "base station" mode. This will blur that initial distinction and allow for widespread adoption of WiMAX based mesh networks and promises widespread WiMAX adoption. The original WiMAX standard, IEEE 802.16, specifies WiMAX in the 10 to 66 GHz range. 802.16a added support for the 2 to 11 GHz range, of which most parts are already unlicensed internationally and only very few still require domestic licenses. Most business interest will probably be in the 802.16a standard, as opposed to licensed frequencies. The WiMAX specification improves upon many of the limitations of the Wi-Fi standard by providing increased bandwidth and stronger encryption. It also aims to provide connectivity between network endpoints without direct line of sight in some circumstances. The details of performance under non-line of sight (NLOS) circumstances are unclear as they have yet to be demonstrated. It is commonly considered that spectrum under 5-6 GHz is needed to provide reasonable NLOS performance and cost effectiveness for PtM (point to multi-point) deployments.
3. HOW WIMAX WORKS
WIMAX TRANSMITTING TOWER
In practical terms, WiMAX would operate similar to WiFi but at higher speeds, over greater distances and for a greater number of users. WiMAX could potentially erase the suburban and rural blackout areas that currently have no broadband Internet access because phone and cable companies have not yet run the necessary wires to those remote locations.
A WiMAX system consists of two parts:
A WiMAX tower, similar in concept to a cell-phone tower - A single WiMAX tower can provide coverage to a very large area -- as big as 3,000 square miles (~8,000 square km). A WiMAX receiver - The receiver and antenna could be a small box or PCMCIA card, or they could be built into a laptop the way WiFi access is today.
A WiMAX tower station can connect directly to the Internet using a high-bandwidth, wired connection (for example, a T3 line). It can also connect to another WiMAX tower using a line-of-sight, microwave link. This connection to a second tower (often referred to as a backhaul), along with the ability of a single tower to cover up to 3,000 square miles, is what allows WiMAX to provide coverage to remote rural areas. What this points out is that WiMAX actually can provide two forms of wireless service:
• There is the non-line-of-sight, WiFi sort of service, where a small antenna on your computer connects to the tower. In this mode, WiMAX uses a lower frequency range -- 2 GHz to 11 GHz (similar to WiFi). Lower-wavelength transmissions are not as easily disrupted by physical obstructions -- they are better able to diffract, or bend, around obstacles
• There is line-of-sight service, where a fixed dish antenna points straight at the WiMAX tower from a rooftop or pole. The line-of-sight connection is stronger and more stable, so it's able to send a lot of data with fewer errors. Line-of-sight transmissions use higher frequencies, with ranges reaching a possible 66 GHz. At higher frequencies, there is less interference and lots more bandwidth. WiFi-style access will be limited to a 4-to-6 mile radius (perhaps 25 square miles or 65 square km of coverage, which is similar in range to a cell-phone zone). Through the stronger line-of-sight antennas, the WiMAX transmitting station would send data to WiMAX-enabled computers or routers set up within the transmitter's 30-mile radius (2,800 square miles or 9,300 square km of coverage
ssssss4. GLOBAL AREA NETWORK
The final step in the area network scale is the global area network (GAN). The proposal for GAN is IEEE 802.20. A true GAN would work a lot like today's cell phone networks, with users able to travel across the country and still have access to the network the whole time. This network would have enough bandwidth to offer Internet access comparable to cable modem service, but it would be accessible to mobile, always-connected devices like laptops or next-generation cell phones). This is what allows WiMAX to achieve its maximum range.
5. USES FOR WIMAX
WiMAX is a wireless metropolitan area network (MAN) technology that can connect IEEE 802.11 (Wi-Fi) hotspots with each other and to other parts of the Internet and provide a wireless alternative to cable and DSL for last mile (last km) broadband access. IEEE 802.16 provides up to 50 km (31 miles) of linear service area range and allows connectivity between users without a direct line of sight. Note that this should not be taken to mean that users 50 km (31 miles) away without line of sight will have connectivity. Practical
limits
om real world tests seem to be around "3 to 5 miles" (5 to 8 kilometers). The technology has been claimed to provide shared data rates up to 70 Mbit/s, which, according to WiMAX proponents, is enough bandwidth to simultaneously support more than 60 businesses with T1-type connectivity and well over a thousand homes at 1Mbit/s DSL-level connectivity. Real world tests, however, show practical maximum data rates between 500kbit/s and 2 Mbit/s, depending on conditions at a given site.
It is also anticipated that WiMAX will allow interpenetration for broadband service provision of VoIP, video, and Internet access—simultaneously. Most cable and traditional telephone companies are closely examining or actively trial-testing the potential of WiMAX for "last mile" connectivity. This should result in better price points for both home and business customers as competition results from the elimination of the "captive" customer bases both telephone and cable networks traditionally enjoyed. Even in areas without preexisting physical cable or telephone networks, WiMAX could allow access between anyone within range of each other. Home units the size of a paperback book that provide both phone and network connection points are already available and easy to install.
There is also interesting potential for interoperability of WiMAX with legacy cellular networks. WiMAX antennas can "share" a cell tower without compromising the function of cellular arrays already in place. Companies that already lease cell sites in widespread service areas have a unique opportunity to diversify, and often already have the necessary spectrum available to them (i.e. they own the licenses for radio frequencies important to increased speed and/or range of a WiMAX connection). WiMAX antennae may be even connected to an Internet backbone via either a light fiber optics cable or a directional microwave link. Some cellular companies are evaluating WiMAX as a means of increasing bandwidth for a variety of data-intensive applications. In line with these possible applications is the technology's ability to serve as a very high bandwidth "backhaul" for Internet or cellular phone traffic from remote areas back to a backbone. Although the cost-effectiveness of WiMAX in a remote application will be higher, it is definitely not limited to such applications, and may in fact be an answer to expensive urban deployments of T1 backhauls as well. Given developing countries' (such as in Africa) limited wired infrastructure, the costs to install a WiMAX station in conjunction with an existing cellular tower or even as a solitary hub will be diminutive in comparison to developing a wired solution. The wide, flat expanses and low population density of such an area lends itself well to WiMAX and its current diametrical range of 30 miles. For countries that have skipped wired infrastructure as a result of inhibitive costs and unsympathetic geography, WiMAX can enhance wireless infrastructure in an inexpensive, decentralized, deployment-friendly and effective manner
Another application under consideration is gaming. Sony and Microsoft are closely considering the addition of WiMAX as a feature in their next generation game console. This will allow gamers to create ad hoc networks with other players. This may prove to be one of the "killer apps" driving WiMAX adoption: WiFi-like functionality with vastly improved range and greatly reduced network latency and the capability to create ad hoc mesh networks
Think about how you access the Internet today. There are basically three different options:
• Broadband access - In your home, you have either a DSL or cable modem. At the office, your company may be using a T1 or a T3 line.
• WiFi access - In your home, you may have set up a WiFi router that lets you surf the Web while you lounge with your laptop. On the road, you can find WiFi hot spots in restaurants, hotels, coffee shops and libraries.
• Dial-up access - If you are still using dial-up, chances are that either broadband access is not available, or you think that broadband access is too expensive.
The main problems with broadband access are that it is pretty expensive and it doesn't reach all areas. The main problem with WiFi access is that hot spots are very small, so coverage is sparse. What if there were a new technology that solved all of these problems? This new technology would provide:
• The high speed of broadband service
• Wireless rather than wired access, so it would be a lot less expensive than cable or DSL and much easier to extend to suburban and rural areas
• Broad coverage like the cell phone network instead of small WiFi hotspots
This system is actually coming into being right now, and it is called WiMAX. WiMAX is short for Worldwide Interoperability for Microwave Access, and it also goes by the IEEE name 802.16.
WiMAX has the potential to do to broadband Internet access what cell phones have done to phone access. In the same way that many people have given up their "land lines" in favor of cell phones, WiMAX could replace cable and DSL services, providing universal Internet access just about anywhere you go. WiMAX will also be as painless as WiFi -- turning your computer on will automatically connect you to the closest available WiMAX antenna.
6. WHAT CAN WIMAX DO?
WiMAX operates on the same general principles as WiFi -- it sends data from one computer to another via radio signals. A computer (either a desktop or a laptop) equipped with WiMAX would receive data from the WiMAX transmitting station, probably using encrypted data keys to prevent unauthorized users from stealing access.
The fastest WiFi connection can transmit up to 54 megabits per second under optimal conditions. WiMAX should be able to handle up to 70 megabits per second. Even once that 70 megabits is split up between several dozen businesses or a few hundred home users, it will provide at least the equivalent of cable-modem transfer rates to each user.
The biggest difference isn't speed; it's distance. WiMAX outdistances WiFi by miles. WiFi's range is about 100 feet (30 m). WiMAX will blanket a radius of 30 miles (50 km) with wireless access. The increased range is due to the frequencies used and the power of the transmitter. Of course, at that distance, terrain, weather and large buildings will act to reduce the maximum range in some circumstances, but the potential is there to cover huge tracts of land.
7. IEEE 802.16 SPECIFICATIONS
• Range - 30-mile (50-km) radius from base station
• Speed - 70 megabits per second
• Line-of-sight not needed between user and base station
• Frequency bands - 2 to 11 GHz and 10 to 66 GHz (licensed and unlicensed bands)
8. WIMAX COULD BOOST GOVERNMENT SECURITY
In an emergency, communication is crucial for government officials as they try to determine the cause of the problem, find out who may be injured and coordinate rescue efforts or cleanup operations. A gas-line explosion or terrorist attack could sever the cables that connect leaders and officials with their vital information networks.
WiMAX could be used to set up a back-up (or even primary) communications system that would be difficult to destroy with a single, pinpoint attack. A cluster of WiMAX transmitters would be set up in range of a key command center but as far from each other as possible. Each transmitter would be in a bunker hardened against bombs and other attacks. No single attack could destroy all of the transmitters, so the officials in the command center would remain in communication at all timesHere's what would happen if you got WiMAX. An Internet service provider sets up a WiMAX base station 10 miles from your home. You would buy a WiMAX-enabled computer (some of them should be on store shelves in 2005) or upgrade your old computer to add WiMAX capability. You would
receive a special encryption code that would give you access to the base station. The base station would beam data from the Internet to your computer (at speeds potentially higher than today's cable modems), for which you would pay the provider a monthly fee. The cost for this service could be much lower than current high-speed Internet-subscription fees because the provider never had to run cables.
Network scale: The smallest-scale network is a personal area network (PAN). A PAN allows devices to communicate with each other over short distances.
Bluetooth is the best example of a PAN.
The next step up is a local area network (LAN). A LAN allows devices to share information, but is limited to a fairly small central area, such as a company's headquarters, a coffee shop or your house. Many LANs use WiFi to connect the network wirelessly.
WiMAX is the wireless solution for the next step up in scale, the metropolitan area network (MAN). A MAN allows areas the size of cities to be connected.
. If you have a home network, things wouldn't change much. The WiMAX base station would send data to a WiMAX-enabled router, which would then send the data to the different computers on your network. You could even combine WiFi with WiMAX by having the router send the data to the computers via WiFi.
WiMAX doesn't just pose a threat to providers of DSL and cable-modem service. The WiMAX protocol is designed to accommodate several different methods of data transmission, one of which is Voice over Internet Protocol (VoIP). VoIP allows people to make local, long-distance and even international calls through a broadband Internet connection, bypassing phone companies entirely. If WiMAX-compatible computers become very common, the use of VoIP could increase dramatically. Almost anyone with a laptop could make VoIP calls.
9. TECHNICAL ADVANTAGES
WiMax does not conflict with WiFi but actually complements it.
WiMAX is a wireless metropolitan area network (MAN) technology that will connect 802.11(WiFi) hotspots to the Internet and provide a wireless extension to cable and DSL for last mile (last km) broadband access. 802.16 provides up to 50 km (31 miles) of linear service area range andallows users connectivity without a direct line of sight to a base station. The technology also provides shared data rates up to 70 Mbit/s, which, according to WiMax proponents, is enough bandwidth to simultaneously support more than 60 businesses with T1-type connectivity and hundreds of homes at DSL-type connectivity.
An important aspect of the 802.16 is that it defines a MAC layer that supports multiple physical layer (PHY) specifications. This is crucial to allow equipment makers to differentiate their offerings.
10. CONCLUSION
The WiMAX forum, backed by industry leaders, helps the widespread adoption of broadband wireless access by establishing a brand forth technology. Initially, WiMAX will bridge the digital divide, the scope of WiMAX deployment will broaden to cover markets where the low POTS penetration, high DSL unbundling costs, or poor copper quality have acted as a brake on extensive high-speed Internet and voice over broadband. WiMAX will reach its peak by making Portable Internet a reality. When WiMAX chipsets are integrated into laptops and other portable devices, it will provide high-speed data services on the move, extending today's limited coverage of public WLAN to metropolitan areas. Integrated into new generation networks with seamless roaming between various accesses, it will enable endorsers to enjoy an "Always Best Connected" experience. The combination of these capabilities makes WiMAX attractive for a wide diversity of people: fixed operators, mobile operators and wireless ISPs, but also for many vertical markets and local authorities.
11. GLOSSARY
CPE: Customer Premise Equipment
DSL: Digital Subscriber Line
FDD: Frequency Division Duplex
MAC: Media Access Control
MIMO: Multiple-Input-Multiple-Output
NLOS: Non-Line-Of-Sight
OFDMA: Orthogonal Frequency Division Multiplex Access
PLC: Power Line Communications
POTS: Plain Ordinary Telephone System
STC: Space Time Coding
TDD: Time Division Duplex
WLAN: Wireless Local Area Network
WLL: Wireless Local Loop
12. REFERENCES
[1].WiMAX: The Critical Wireless Standard, Blueprint WiFi Report,
October 2003
[2].WiMAX/802.16 and 802.20, ABI Research, Q4 2003
Last Mile Wireless High Speed Market, Skylight Research,
March 2004
[3].Providing Always-on Broadband Access to Underserved Areas,
Alcatel Telecommunication Review (p. 127-132), Q4 2003
[4].WiMAX forum web site: www.wimaxforum.org
[5]. IEEE SPECTRUM.
VLSI seminar topic 2
PRESENTED BY
S.SRIKANTH REDDY Y.MARUTHI
III B.tech III.B.tech
Sri.prince087@gmail.com
St.JOHNS COLLEGE OF ENGINEERING
AND TECHNOLOGY,
YERRAKOTA,
YEMIGANUR,
KURNOOL (Dist),
ANDHRA PRADESH.
ABSTRACT
VLSI fabrication augmented its aggrandizement for its insatiable demand for higher operating speeds and device packing densities. The circuits fabricated on bulk Si wafer could not satisfy these requirements. The present paper seeks to ameliorate this area through Silicon-On-Insulator (SOI) technology. It elucidates a novel technology using atomic layer cleavage, which allows SOI processing to be available for many substrate materials. It also presents various other fabrication methods for SOI technology. Using the same transistor dimensions, SOI’s global dielectric isolation enables IC manufacturers to pack more die on a wafer without direct transistor scaling through reduction in the wafer area needed for the device isolation. The SOI process exploits Nano cleaving, which reduces cost and creates SOI wafers with exceptional material quality and high yield. Nano cleave is highly efficient for chipmakers, relying on standard IC fabrication technologies. This paper encompasses Nano cleave process fabrication steps in a lucid manner. It also accrues major advantages of devices built on SOI wafers.
ABSTRACT
AABSTRACT
A
1. PREAMBLE
Silicon-on-insulator (SOI) technology provides opportunities to increase transistor switching and at the same time to improve performance for low-power, battery-driven electronics. With its ability to increase device density through reduction in isolation area, SOI can postpone the need to shift to smaller scale transistors. SOI can contribute to reduced manufacturing costs by simplifying IC fabrication processes, through the elimi-nation of high-energy implantation for well doping and simplification of device isolation. SOI also provides opportunities beyond conventional semiconductor devices. SOI is a key method for fabricating “Silicon-on-Anything” devices, which have the potential to integrate communications, smart cards, sensors and displays with portable, low-power memory and logic devices, as in Figure 1.
Figure 1. SOI technology enables major performance advances in numerous applications
Using a fully-integrated, proprietary SOI manufacturing process, called NanoCleave, advanced corporations have recently begun production of SOI wafers which offers lower cost and higher wafer quality than earlier generations of SOI fabrication methods.
2. SOI ADVANTAGES
The major advantage of devices built on SOI wafers are:
1) 20 to 30% higher operating speeds compared to similar devices on bulk Si
2). higher device packing density for logic and analog circuits and
3). greatly increased immunity to soft-error events generated by decay products of cosmic
ray showers.
Using the same transistor dimensions, SOI’s global dielectric isolation enables IC manufacturers to pack more die on a wafer without direct transistor scaling, through reduction in the wafer area needed for device isolation, as shown in Figure 2. This increase in the die per wafer yield is especially valuable in logic and I/O-dominated layouts such as in system-on-a-chip (SOC) devices. In addition to speed gains in mainstream applications, the negligible current leakage and lower power requirements of SOI-based chips can dramatically improve the performance of battery-powered communication and computing devices for mobile electronics.
3. SOI: AN EMERGING MARKET FOR GIGAHERTZ-SPEED, LOW POWER DEVICES
The need for lower cost IC devices which operate in the Gigahertz frequency range used for mobile communications is driving the switch to SOI wafers. Broadband communication networks, operating on battery or solar cell power, need the low-power, small die size and global Isolation of SOI designs. The lower cost of Silicon device processing on large area wafers provides a key advantage for SOI over communication and computing devices fabricated with more exotic materials, such as GaAs.
Today’s standard processes fabricate transistors directly onto a bulk silicon wafer surface. These transistors operate at relatively low switching speed because large volumes of semiconductor material require more energy to turn on and off. For SOI-based processes, transistors are built on a thin silicon surface layer isolated from the wafer by a layer of oxide, and chips run 20% to 35% faster because less charge is needed to switch the transistor state. This speed gain is equivalent to the advantage gained by a full generation of device scaling on bulk-Silicon.
4. MAKING SOI A PRODUCTION TECHNOLOGY
Despite its many benefits, SOI’s acceptance has been slowed by the high cost and low production-maturity of first-generation SOI manufacturing methods. These various
methods were complex and often produced wafers of low or variable quality. Currently, there are five methods to produce commercially available SOI, based on either direct oxygen implantation or bonded layer transfer technologies, as shown in Table.
The two commercial ways to fabricate SOI wafers, namely, SIMOX (separation by implantation of oxygen) and BESOI (bonded and etch-back) SOI, are quite expensive because of the long implantation time for the SIMOX process and the need to use two wafers to form a single SOI wafer in BESOI. Recently, a method called SMART-CUT or ion cut was proposed by SOITEC, making use of wafer cleavage after hydrogen implantation and subsequent wafer bonding. This technique is potentially cheaper than the conventional BESOI process because one of the wafers can be recycled. The materials cost of SOI can be further reduced if an alternative way can be found to reduce the time required to implant a high enough dose of oxygen (SPIMOX) or
hydrogen (ion-cutting). Plasma immersion ion implantation (PIII) is a burgeoning technique offering many applications in materials and semiconductor processing. In PIII, the sample is immersed in a plasma shroud from which ions are extracted and accelerated through a high-voltage sheath into the target. The dose rate can be as high as ions cm s which is equivalent to ten monolayers of implanted atoms per second and at least an order of magnitude higher than that of a conventional ion implanter.
Since the entire wafer is implanted simultaneously, the implantation time is independent of wafer size, thereby offering an extremely attractive approach for 300-mm
wafers. The use of PIII to synthesize SOI materials has been investigated, and the results are very encouraging. In spite of the tremendous potential, the development of commercial PIII instrumentation has not caught up. The newest of these technologies, “NanoCleave”, represents a unique, second generation, approach that offers a streamlined process flow and the potential for significantly lower SOI manufacturing costs.
One of the earlier barriers to the use of SOI for mainstream chipmaking was the higher cost of SOI wafers, up to 5 times the cost of bulk silicon wafers. With advanced SOI fabrication technology, such as NanoCleave, the cost of SOI wafers can be substantially reduced. It is expected that the price of 200 mm SOI wafers, which is currently in the range of $500 per wafer, will drop by as much as 40% in the coming year as production volumes and consumption of SOI wafers increase.
5. THE NANOCLEAVE PROCESS
SOI process uses NanoCleave and other novel manufacturing methods that reduce cost and create SOI wafers with exceptional material quality and high yield.
Unlike most other competing technologies, the critical layer transfer and wafer bonding steps are accomplished at room temperature. NanoCleave is highly efficient for chipmakers, relying on standard IC fabrication technologies for most of the process steps, supplemented with fully automated tools for the critical wafer bonding and separation steps. Surface roughness of the finished SOI wafer exhibits RMS roughness below 1nm, which is already within specification for use by most IC processes. As a measure of its process simplicity, this is accomplished without the CMP and post-CMP damage removal steps required in earlier generation bonded SOI wafer fabrication processes.
6. NANOCLEAVE PROCESS FABRICATION STEPS
SOI layer transfer techniques involve creating a dual-layer of device-silicon and an insulator layer) (the Buried OXide or “BOX”) grown on a “donor” wafer and bonded to a “handle” wafer. These silicon and buried oxide layers are then separated (‘cleaved’) from the donor wafer, producing a finished SOI wafer. The NanoCleave process greatly simplifies this layering sequence compared to earlier processes, resulting in the potential for major cost reductions in SOI production, Figure 3.
FIGURE 3. THE NANO CLEAVE PROCESS FLOW
The NanoCleave process includes four main steps:
- A “donor” wafer is formed by forming a high-quality silicon layer (which will become the device layer in the final SOI wafer). A cleave plane situated beneath this layer acts as a guide for the cleave front during the separation process. The silicon layer does not contain the yield-limiting crystal defects and oxygen precipitates present in bulk silicon grown by CZ methods. A thermal oxide is grown on the silicon layer that becomes part of the buried oxide layer in the finished SOI wafer, Figure 4. The thermal oxide growth process produces a buried oxide layer that is free of pinholes and silicon inclusions. The NanoCleave silicon/oxide interface, Figure 5, has the low interface trap and fixed charge densities that are required to control the signal frequency dependence of transistor threshold voltage.
2. The NanoCleave process uses implantation in combination with other proprietary process steps to promote low-energy cleaving along the desired wafer separation plane. A standard beam line implanter is presently used for 200mm production in the SiGen pilot line. However, looking ahead towards the needs of high-volume 200mm and 300 mm SOI wafer production, the implant step can be more cost-effectively performed by Plasma Immersion Ion Implantation (PIII) using tools, such as the SiGen PIII implanter.
3. Plasma treatment of the wafer surfaces enables the donor wafer to be bonded to a bare or oxidized “handle” wafer with a bond interface far stronger than the cleave plane. Because the device silicon layer is separated by the buried oxide layer, a handle wafer
with considerably relaxed electrical and chemical specifications, and therefore lower cost, can be used in this process.
4. Using Controlled Cleave Process (CCP), the donor and handle are separated at room temperature. Using a controlled propagation along a single cleave front, as in Figure 6, this atomic layer cleaving process results in an as-cleaved surface roughness less than 1nm (typically 2-5 Angstroms). This is an order of magnitude smoother than the 80 Angstroms of typical hydrogen-induced thermal cleaving, Figure 7. Such a smooth surface is acceptable for many IC applications with no additional surface polishing.
Figure 7 AFM images of as-cleaved surfaces of NanoCleave and Hydrogen- induced thermal separation methods
The edge of the SOI layer has a smooth and regular character without the need for edge polishing, Figure 8.
7. USING A STANDARD TOOL SET FOR SOI
The fabrication sequence has 20- 40% fewer steps than other bonded wafer SOI fabrication methods and uses widely available IC fabrication tools, such as ion implantation, thermal furnace and wet benches, for most of the process steps. The key wafer bonding and atomic layer cleaving steps are done by fully-automated tools which have been developed to be easily integrated into a high-volume SOI wafer fabrication environment.
8. CONCLUSION
The advances in SOI wafer manufacturing technology are lowering the cost of SOI wafers through a simpler, more cost-effective process flow. The NanoCleave process accomplishes this productivity breakthrough by using conventional semiconductor manufacturing tools for most of the process flow and by accomplishing the wafer bonding and cleaving steps at room temperature. The as-cleaved SOI wafer surface is smooth to sub-nanometer dimensions and can be used directly without any post-cleave mechanical polishing or edge treatment.
REFERENCES:
1. Se-Jeong Park, Jeong-Su Kim, Ramchan Woo, Se-Joong Lee,Kang-Min Lee, Tae- Hum Yang, Jin-Yong Jung and Hoi-Jun Yoo, “A Reconfigurable Multilevel ParallelGraphics Memory with 75GB/s Parallel Cache Replacement Bandwidth”,
Symposium on VLSI Circuits 2001, C21p3, in press, Jun. 2001.
2. Sean P.Cunningham and J. George Shanthikumar, “Empirical Results on the Relationship Between Die Yield and Cycle Time in Semiconductor Wafer Fabrication”, In IEEE Transactions on Semiconductor Manufacturing, 9: 273-277,
1996.
3. J.Kook, et al, “A Low Power Reconfigurable I/O DRAM Macro with Single Bit line Writing Scheme”, 26th European Solid-State Circuits Conference, pp.384-387,Sept., 2000.
4. T. Nishikawa, et al., “A 60 MHz 240 mW MEPG-4 Video-Phone LSI with 16 Mb Embedded DRAM”, ISSCC Digest of Technical Papers, pages 230-231, 2000.
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