One of the causes of intersymbol interference is what is known as multipath propagation in which a wireless signal from a transmitter reaches the receiver via many different paths. The causes of this include reflection (for instance, the signal may bounce off buildings) Lenovo S10-2 Battery 5200mAh ,
refraction (such as through the foliage of a tree) and atmospheric effects such as atmospheric ducting and ionospheric reflection. Since all of these paths are different lengths - plus some of these effects will also slow the signal down - this results in the different versions of the signal arriving at different times Lenovo Y730 Battery 5200mAh .
This delay means that part or all of a given symbol will be spread into the subsequent symbols, thereby interfering with the correct detection of those symbols. Additionally, the various paths often distort the amplitude and/orphase of the signal thereby causing further interference with the received signal Lenovo Y710 Battery 5200mAh .
Another cause of intersymbol interference is the transmission of a signal through a bandlimited channel, i.e., one where the frequency response is zero above a certain frequency (the cutoff frequency) Lenovo Y530 Battery 5200mAh .
Passing a signal through such a channel results in the removal of frequency components above this cutoff frequency; in addition, the amplitude of the frequency components below the cutoff frequency may also be attenuated by the channel.
This filtering of the transmitted signal affects the shape of the pulse that arrives at the receiver Lenovo Y510 Battery 5200mAh .
The effects of filtering a rectangular pulse; not only change the shape of the pulse within the first symbol period, but it is also spread out over the subsequent symbol periods. When a message is transmitted through such a channel, the spread pulse of each individual symbol will interfere with following symbols Lenovo S10-3 Battery 5200mAh .
As opposed to multipath propagation, bandlimited channels are present in both wired and wireless communications. The limitation is often imposed by the desire to operate multiple independent signals through the same area/cable; due to this, each system is typically allocated a piece of the total bandwidth available Lenovo G450 Battery 5200mAh .
For wireless systems, they may be allocated a slice of the electromagnetic spectrum to transmit in (for example, FM radio is often broadcast in the 87.5 MHz - 108 MHz range). This allocation is usually administered by a government agency; in the case of the United Statesthis is the Federal Communications Commission (FCC) Lenovo E30 Battery 5200mAh .
In a wired system, such as an optical fiber cable, the allocation will be decided by the owner of the cable.
The bandlimiting can also be due to the physical properties of the medium - for instance, the cable being used in a wired system may have a cutoff frequency above which practically none of the transmitted signal will propagate Lenovo E40 Battery 5200mAh .
Communication systems that transmit data over bandlimited channels usually implement pulse shaping to avoid interference caused by the bandwidth limitation. If the channel frequency response is flat and the shaping filter has a finite bandwidh, it is possible to communicate with no ISI at all Lenovo E50 Battery 5200mAh .
Often the channel response is not known beforehand, and an adaptive equalizer is used to compensate the frequency response.
Effects on eye patterns
One way to study ISI in a PCM or data transmission system experimentally is to apply the received wave to the vertical deflection plates of an oscilloscope and to apply a sawtooth wave at the transmitted symbol rate R Lenovo G460 Battery 5200mAh ,
1/T to the horizontal deflection plates . The resulting display is called an eye pattern because of its resemblance to the human eye for binary waves. The interior region of the eye pattern is called the eye opening. An eye pattern provides a great deal of information about the performance of the pertinent system Lenovo Y460 Battery 5200mAh .
- The width of the eye opening defines the time interval over which the received wave can be sampled without error from ISI. It is apparent that the preferred time for sampling is the instant of time at which the eye is open widest Lenovo Y450 Battery 5200mAh .
- The sensitivity of the system to timing error is determined by the rate of closure of the eye as the sampling time is varied.
- The height of the eye opening, at a specified sampling time, defines the margin over noise.
An eye pattern, which overlays many samples of a signal, can give a graphical representation of the signal characteristics Lenovo N200 Battery 5200mAh .
The first image below is the eye pattern for a binary phase-shift keying (PSK) system in which a one is represented by an amplitude of -1 and a zero by an amplitude of +1. The current sampling time is at the center of the image and the previous and next sampling times are at the edges of the image Lenovo T410 Battery 5200mAh .
The various transitions from one sampling time to another (such as one-to-zero, one-to-one and so forth) can clearly be seen on the diagram.
The noise margin - the amount of noise required to cause the receiver to get an error - is given by the distance between the signal and the zero amplitude point at the sampling time Lenovo T510 Battery 5200mAh ;
in other words, the further from zero at the sampling time the signal is the better. For the signal to be correctly interpreted, it must be sampled somewhere between the two points where the zero-to-one and one-to-zero transitions cross. Again, the further apart these points are the better Lenovo SL410 Battery 5200mAh ,
as this means the signal will be less sensitive to errors in the timing of the samples at the receiver.
The effects of ISI are shown in the second image which is an eye pattern of the same system when operating over a multipath channelLenovo SL510 Battery 5200mAh .
The effects of receiving delayed and distorted versions of the signal can be seen in the loss of definition of the signal transitions. It also reduces both the noise margin and the window in which the signal can be sampled, which shows that the performance of the system will be worse (i.e. it will have a greater bit error ratio) Lenovo C100 Battery 5200mAh .
There are several techniques in telecommunication and data storage that try to work around the problem of intersymbol interference.
- Design systems such that the impulse response is short enough that very little energy from one symbol smears into the next symbol Lenovo T400S Battery 5200mAh .
- Separate symbols in time with guard periods.
- Apply an equalizer at the receiver, that, broadly speaking, attempts to undo the effect of the channel by applying an inverse filter Lenovo Y430 Battery 5200mAh .
- Apply a sequence detector at the receiver, that attempts to estimate the sequence of transmitted symbols using the Viterbi algorithm Ibm ThinkPad G40 Battery 5200mAh .
Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using apseudorandom sequence known to both transmitter and receiver. It is utilized as a multiple access method in the frequency-hopping code division multiple access(FH-CDMA) scheme Ibm ThinkPad X200T Battery 5200mAh.
A spread-spectrum transmission offers three main advantages over a fixed-frequency transmission:
- Spread-spectrum signals are highly resistant to narrowband interference. The process of re-collecting a spread signal spreads out the interfering signal, causing it to recede into the background Apple A1280 battery 5200mAh .
- Spread-spectrum signals are difficult to intercept. An FHSS signal simply appears as an increase in the background noise to a narrowband receiver. An eavesdropper would only be able to intercept the transmission if the pseudorandom sequence was known Apple A1281 battery 5200mAh .
- Spread-spectrum transmissions can share a frequency band with many types of conventional transmissions with minimal interference. The spread-spectrum signals add minimal noise to the narrow-frequency communications, and vice versa. As a result, bandwidth can be utilized more efficiently Samsung R522 battery 5200mAh .
Spread-spectrum signals are highly resistant to deliberate jamming, unless the adversary has knowledge of the spreading characteristics. Military radios use cryptographic techniques to generate the channel sequence under the control of a secret Transmission Security Key (TRANSEC) that the sender and receiver share in advance Samsung P467 battery 5200mAh .
By itself, frequency hopping provides only limited protection against eavesdropping and jamming. To get around this weakness most modern military frequency hopping radios often employ separate encryption devices such as the KY-57. U.S. military radios that use frequency hopping include the JTIDS/MIDS family, HAVE QUICK and SINCGARS Hp Pavilion dm3 Battery 5400mAh .
Since the Federal Communications Commission (FCC) amended rules to allow frequency hopping spread spectrum systems in the unregulated 2.4 GHz band, many consumer devices in that band have employed various spread-spectrum modes Hp Pavilion dm4 Battery 5200mAh .
Some walkie-talkies that employ frequency-hopping spread spectrum technology have been developed for unlicensed use on the 900 MHz band. Several such radios are marketed under the nameeXtreme Radio Service (eXRS). Despite the name's similarity to the FRS allocation, the system is a proprietary design Hp Pavilion cq62 Battery 5200mAh ,
rather than an official U.S. Federal Communications Commission (FCC) allocated service.
The overall bandwidth required for frequency hopping is much wider than that required to transmit the same information using only one carrier frequency Hp Pavilion cq42 Battery 5200mAh .
However, because transmission occurs only on a small portion of this bandwidth at any given time, the effective interference bandwidth is really the same. Whilst providing no extra protection against wideband thermal noise, the frequency-hopping approach does reduce the degradation caused by narrowband interferers Hp Pavilion cq72 Battery 5200mAh .
One of the challenges of frequency-hopping systems is to synchronize the transmitter and receiver. One approach is to have a guarantee that the transmitter will use all the channels in a fixed period of time. The receiver can then find the transmitter by picking a random channel and listening for valid data on that channel Hp cq20 Battery 2600mAh .
The transmitter's data is identified by a special sequence of data that is unlikely to occur over the segment of data for this channel and the segment can have a checksum for integrity and further identification. The transmitter and receiver can use fixed tables of channel sequences so that once synchronized they can maintain communication by following the table Hp 2230 Battery 2600mAh .
On each channel segment, the transmitter can send its current location in the table.
In the US, FCC part 15 on unlicensed system in the 900 MHz and 2.4 GHz bands permits more power than non-spread spectrum systems. Both frequency hopping and direct sequence systems can transmit at 1 Watt Dell Inspiron Mini 12 battery 7800mAh .
The limit is increased from 1 milliwatt to 1 watt or a thousand times increase. The Federal Communications Commission (FCC) prescribes a minimum number of channels and a maximum dwell time for each channel.
In a real multipoint radio system, space allows multiple transmissions on the same frequency to be possible using multiple radios in a geographic area Dell XPS M1730 battery 7800mAh .
This creates the possibility of system data rates that are higher than the Shannon limit for a single channel. Spread spectrum systems do not violate the Shannon limit. Spread spectrum systems rely on excess signal to noise ratios for sharing of spectrum. This property is also seen in MIMO and DSSS systems Dell XPS M2010 battery 7800mAh .
Beam steering and directional antennas also facilitate increased system performance by providing isolation between remote radios.
Perhaps the earliest mention of frequency hopping in the open literature is in radio pioneer Johannes Zenneck's book Wireless Telegraphy (German, 1908, English translation McGraw Hill, 1915) Dell Studio XPS 1340 battery 5200mAh/7800mAh ,
although Zenneck himself states that Telefunken had already tried it.
The German military made limited use of frequency hopping for communication between fixed command points in World War I to prevent eavesdropping by British forces, who did not have the technology to follow the sequence Dell Inspiron 9100 battery 7800mAh .
A Polish engineer, Leonard Danilewicz, came up with the idea in 1929. Several other patents were taken out in the 1930s, including one by Willem Broertjes (U.S. Patent 1,869,659, issued Aug. 2, 1932).
During World War II, the US Army Signal Corps was inventing a communication system called SIGSALY, which incorporated spread spectrum in a single frequency context Dell Inspiron N4010 battery 5200mAh .
However, SIGSALY was a top-secret communications system, so its existence did not become known until the 1980s.
The most celebrated invention of frequency hopping was that of actress Hedy Lamarr and composer George Antheil, who in 1942 received U.S. Patent 2,292,387 for their "Secret Communications System Dell Inspiron N3610 battery 5200mAh .
" This early version of frequency hopping used a piano-roll to change between 88 frequencies, and was intended to make radio-guided torpedoes harder for enemies to detect or to jam. The patent was rediscovered in the 1950s during patent searches when private companies independently developed Code Division Multiple Access Dell Inspiron N5010 battery 5200mAh ,
a civilian form of spread-spectrum.
Variations of FHSS
Adaptive Frequency-hopping spread spectrum (AFH) (as used in Bluetooth) improves resistance to radio frequency interference by avoiding using crowded frequencies in the hopping sequence Dell Inspiron N7010 battery 5200mAh .
This sort of adaptive transmission is easier to implement with FHSS than with DSSS.
The key idea behind AFH is to use only the “good” frequencies, by avoiding the "bad" frequency channels—perhaps those "bad" frequency channels are experiencing frequency selective fading Dell Inspiron 1464 battery 5200mAh ,
or perhaps some third party is trying to communicate on those bands, or perhaps those bands are being actively jammed. Therefore, AFH should be complemented by a mechanism for detecting good/bad channels.
However, if the radio frequency interference is itself dynamic, then the strategy of “bad channel removal”, applied in AFH might not work well Dell Inspiron 1564 battery 5200mAh .
For example, if there are several colocated frequency-hopping networks (as Bluetooth Piconet), then they are mutually interfering and the strategy of AFH fails to avoid this interference.
In this case, there is a need to use strategies for dynamic adaptation of the frequency hopping pattern Dell Inspiron 1764 battery 5200mAh .
Such a situation can often happen in the scenarios that use unlicensed spectrum.
In addition, dynamic radio frequency interference is expected to occur in the scenarios related to cognitive radio, where the networks and the devices should exhibit frequency-agile operation Dell Inspiron 1320 battery 5200mAh .
Chirp modulation can be seen as a form of frequency-hopping that simply scans through the available frequencies in consecutive order.
The GSM cellular system uses frequency hopping, as a form of frequency interleaving, in view to avoid that two phone calls in adjacent cells constantly interfere with each other Dell Inspiron 1320n battery 5200mAh .
However, this is not considered as spread spectrum, since the two phonecalls within the same cell never use the same frequency.
In digital recording, the analog signal of video or sound is converted into a stream of discrete numbers, representing the changes in chroma and luminancevalues (video) or air pressure (audio) through time Dell Vostro 1710 battery 5200mAh ,
thus making an abstract template for the original sound or moving image.
Beginning in the 1980s, music that was recorded, mixed and mastered digitally was often labelled using the SPARS code to describe which processes were analog and which were digital Dell Vostro 1720 battery 5200mAh .
- In 1937, British scientist Alec Reeves files the first patent describing Pulse-code modulation.
- In 1943, Bell Telephone Laboratories develops the first digital scrambled speech transmission system, SIGSALY Dell Studio XPS 1640 battery 5200mAh .
- In 1957, Max Mathews of Bell develops the process to digitally record sound via computer.
- In 1967, the first digital tape recorder is invented . A 12-bit 30 kHz stereo device using a compander (similar to DBX Noise Reduction) to extend the dynamic range Dell Vostro A840 battery 5200mAh .
- In the 1970s[when?], Thomas Stockham makes the first digital audio recordings using standard computer equipment and develops a digital audio recorder of his own design, the first of its kind to be offered commercially (through Stockham's Soundstream company) Dell Vostro A860 battery 5200mAh .
- In 1970, James Russell patents the first digital-to-optical recording and playback system, which would later lead to the Compact Disc.
- In 1972, Denon invents the first 8-track reel to reel digital recorder Dell Studio 1535 battery 5200mAh/7800mAh .
- In 1978, Sound 80 Records of Minneapolis records "Flim and the BB's" (S80-DLR-102) directly to digital before pressing the vinyl LP. The mastering engineer is Bob Berglund. The recording system is a 3M Digital Audio Mastering System.
- In 1979, the first digital Compact Disc prototype was created as a compromise between sound quality and size of the mediumDell Studio 1735 battery 5200mAh/7800mAh .
- In 1979, the first digitally recorded album of popular music Bop 'Til You Drop by guitarist Ry Cooder is released by Warner Bros. Records. The album was recorded in Los Angeles on a 32-track digital machine built by the 3M corporation Dell Vostro 1310 battery 5200mAh .
- In 1982, the first digital compact discs are marketed, and New England Digital offers the Sample-to-Disk option on the Synclavier, the first commercial hard disk recording system.
- In 1990, digital radio begins in Canada, using the L-Band Dell Latitude E6400 battery,10400mAh/7800mAh .
- In 1996 DVD players begin selling in Japan.
- In 2010 HEDA (Harmonically Enhanced Digital Audio) technology is incorporated within Protools Heat and Universal Audio's Studer A800.
- The analog signal is transmitted from the input device to an analog-to-digital converter (ADC) Dell Latitude E6400 Battery,10400mAh/7800mAh .
- The ADC converts this signal to a series of binary numbers. The quantity of numbers produced per second is called the sample rate.
- These numbers are stored onto recording media such as magnetic tape or hard drive or optical drive Dell Latitude E6400 Battery,10400mAh/7800mAh .
- The sequence of numbers is transmitted from storage into a digital-to-analog converter (DAC), which converts the numbers back to an analog signal.
- This signal amplified and transmitted to the loudspeakers or video screen Dell Latitude E6500 battery,10400mAh/7800mAh.
Getting the bits recorded
Even after getting the signal converted to bits, it is still difficult to record: the hardest part is finding a scheme that can record the bits fast enough to keep up with the signal. For example, to record two channels of audio at 44.1 kHz sample rate with a 16 bit word size, the recording software has to handle 1,411,200 bits per second Dell Latitude E6500 battery,10400mAh/7800mAh .
Techniques to record to commercial media
For digital cassettes, the read/write head moves as well as the tape in order to maintain a high enough speed to keep the bits at a manageable size.
For CDs or DVDs, a laser is used to burn microscopic holes into the dye layer of the medium Dell Latitude E6500 battery,10400mAh/7800mAh .
A weaker laser is used to read these signals. This works because the metallic substrate of the disc is reflective, and the unburned dye prevents reflection while the holes in the dye permit it, allowing digital data to be represented Dell Latitude E6500 battery,10400mAh/7800mAh .
The number of bits used to represent a single audio wave (the word size) directly affects the achievable noise level of a signal recorded with added dither, or the distortion of an undithered signal. Increasing a sample's word length by one bit doubles its possible values HP Pavilion DV6-1210SA battery - 5200mAh/8800mAh ,
likewise increasing the potential accuracy of each sample and the fidelity of the recording to the original. 24-bit recording is generally considered a current practical limit as this word length allows a signal-to-noise ratio exceeding that of most analog circuitry, which by necessity must be used in at least two points in the recording/playback chain HP Pavilion DV7 battery - 7200mAh .
The sample rate is even more important a consideration than the word size. If the sample rate is too low, the sampled signal cannot be reconstructed to the original sound signal. Hence the output will be different from the input Ibm THINKPAD X200 Battery 8800mAh .
The process of under sampling results in aliasing whereby the high frequency components of the sound wave are represented as being lower than they should be. This causes the output wave shape to be severely altered.
To overcome aliasing, the sound signal (or other signal) must be sampled at a rate at least twice that of the highest frequency component in the signal Ibm THINKPAD X200 Battery 8800mAh .
This is known as the Nyquist-Shannon sampling theorem.
For recording music-quality audio the following PCM sampling rates are the most common:
When making a recording, experienced audio recording and mastering engineers will normally do a master recording at a higher sampling rate (i.e. 88.2, 96, 176.4 or 192 kHz) and then do any editing or mixing at that same higher frequency Ibm THINKPAD X200 Battery 8800mAh .
High resolution PCM recordings have been released on DVD-Audio (also known as DVD-A), DAD (Digital Audio Disc—which utilizes the stereo PCM audio tracks of a regular DVD), DualDisc (utilizing the DVD-Audio layer), or Blu-ray (Profile 3.0 is the Blu-ray audio standard, although as of mid-2009 it is unclear whether this will ever really be used as an audio-only format) SONY VAIO VGN-FW21E Battery .
In addition it is nowadays also possible and common to release a high resolution recording directly as either an uncompressed WAV or lossless compressed FLAC file (usually at 24 bits) without down-converting it .
However if a CD (the CD Red Book standard is 44.1 kHz 16 bit) is to be made from a recording, then doing the initial recording using a sampling rate of 44.1 kHz is obviously one approach Asus M52N Battery .
Another approach that is usually preferred is to use a higher sample rate and then downsample to the final format's sample rate. This is usually done as part of the mastering process. One advantage to the latter approach is that way a high resolution recording can be released, as well as a CD and/or lossy compressed file such as mp3—all from the same master recording Dell Latitude E6400 ATG Battery .
One of the key challenges of the cognitive radio based wireless networks, such as IEEE 802.22 wireless regional area networks (WRAN) , is to address two apparently conflicting requirements: assuring Quality of Services (QoS) satisfaction for services provided by the cognitive radio networks SONY VAIO VGN-FW21J Battery ,
while providing reliable spectrum sensing for guaranteeing licensed user protection. To perform reliable sensing, in the basic operation mode on a single frequency band (the so called “listenbefore-talk” mode) one has to allocate Quiet Times, in which no data transmission is permitted SONY VAIO VGN-FW21L Battery .
Such periodic interruption of data transmission could impair the QoS of cognitive radio systems.
This issue is addressed by an alternative operation mode proposed in IEEE 802.22 called Dynamic Frequency Hopping (DFH) where data transmission of the WRAN systems are performed in parallel with spectrum sensing without any interruption SONY VAIO VGN-FW21M Battery .
A digital native is a young person who was born during or after the general introduction of digital technology, and through interacting with digital technology from an early age, has a greater understanding of its concepts. Alternatively, this term can describe people born in the latter 1970s or later SONY VAIO VGN-FW21Z Battery ,
as the Digital Age began at that time; but in most cases the term focuses on people who grew up with 21st century modern technology.
Other popular discourse identifies a digital natives as a person who understands the value of digital technology and uses this to seek out opportunities for implementing it with a view to make an impact SONY VAIO VGN-FW25T/B Battery .
This term has been used in several different contexts, such as education (Bennett, Maton & Kervin 2008) (in association with the term New Millennium Learners (OECD 2008)). A digital immigrant is an individual who was born before the existence of digital technology and adopted it to some extent later in their life SONY VAIO VGN-FW26T/B Battery .
As Dr. Ofer Zur and Azzia Zur discuss (in 2009), not all digital immigrants are technologically inept, as they fall into a number of categories; Avoiders, Reluctant Adopters and Eager Adopters. Avoiders may only have a minimal amount of technology involved in their lives and households (Ex. A landline phone and a television) SONY VAIO VGN-FW27/B Battery .
Reluctant Adopters often see ways that technology might be needed in their lives, but they try to avoid it when possible (Ex. Letters instead of email, rotary telephones). Eager Adopters have enthusiasm or a talent for technology that makes them very similar to Digital Natives. Similarly, not all digital natives are comfortable with technology SONY VAIO VGN-FW27/W Battery .
Marc Prensky coined the term digital native in his work Digital Natives, Digital Immigrants published in 2001. In his seminal article, he assigns it to a new group of students enrolling in educational establishments. The term draws an analogy to a country's natives, for whom the local religion rSONY VAIO VGN-FW31ZJ Battery ,
language, and folkways are natural and indigenous, compared with immigrants to a country who often are expected to adapt and begin to adopt the region's customs. Prensky refers to accents employed by digital immigrants, such as printing documents rather than commenting on screen or printing out emails to save as a hard copy SONY VAIO VGN-FW27T/H Battery .
Digital immigrants are said to have a "thick accent" when operating in the digital world in distinctly pre-digital ways, for instance, calling people into a room to see a webpage instead of sending them the URL. A digital native might refer to their new "camera"; but a digital immigrant might refer to their new "digital camera" SONY VAIO VGN-FW29/B Battery .
The analogy of the digital native was also used by Josh Spear and Aaron Dignan (Spear's business partner in the Manhattan-based agency Undercurrent) who talked about people who were "born digital", first appearing in a series of presentations given by Josh Spear in 2007 SONY VAIO VGN-FW290JRB Battery .
First, at Google's Zeitgeist Europe Conference in May 2007. A different version of this presentation was delivered again in December 2007 at the United Kingdom at the Internet Advertising Bureau Engage 2007 Conference. A Digital Native research project is being run jointly by the Berkman Centre for Internet & Society SONY VAIO VGN-FW290JTB Battery
at Harvard Law School and the Research Center for Information Law at the University of St. Gallen in Switzerland. A collaborative research project is being run by Hivos, Netherlands and the Bangalore based Centre for Internet and Society SONY VAIO VGN-FW290JTH Battery .
Gartner presented on the term at their May, 2007 IT Expo (Emerging Trends) Symposium in Barcelona and, more recently, Gartner referenced Prensky's work, specifically the 18 areas of change comprising the Work Style of Digital Natives, in their "IT-Based Collaboration and Social Networks Accelerate R&D" research paper published on January 22, 2008 SONY VAIO VGN-FW33G/E1 Battery .
Conflicts between generations
Due to the obvious divide set between digital natives and digital immigrants, sometimes both generations are forced to meet which commonly results in conflicting ideologies of digital technology SONY VAIO VGN-FW33G/W Battery .
The everyday regime of worklife is becoming more technologically advanced with improved computers in offices, more complicated machinery in industry etc. With technology moving so fast it is hard for digital immigrants to keep up.
This creates conflicts among older supervisors and managers with the increasingly younger workforce SONY VAIO VGN-FW33GW Battery .
Similarly, parents clash with their children at home over gaming, texting, YouTube, Facebook and other Internet technology issues. What many digital immigrants miss is that digital natives grew up with technology, and it is how they connect with their friends, perform research, and feel at home Dell XPS M1210 Battery) http://www.hdd-shop.co.uk .
Young people are not "addicts" or "bad" simply for using the tools of the world they grow up in. In their 2011 article, Dr. Ofer Zur and Azzia Zur discuss the issue of generation clashes at home, school and the workplace.
Education, as Marc Prensky states, is the single largest problem facing the digital world as our Digital Immigrant instructors Dell KM958 battery ,
who speak an outdated language (that of the pre-digital age), are struggling to teach a population that speaks an entirely new language. Immigrants suffer complications in teaching natives how to understand an environment which is "native" to them and foreign to Immigrants Dell Studio 1555 battery .
Prensky's own preference to this problem is to invent computer games to teach digital natives the lessons they need to learn, no matter how serious. This ideology has already been introduced to a number of serious practicalities. For example, piloting an Unmanned Aerial Vehicle (UAV) Sony VGP-BPS13 battery
in the army consists of someone sitting in front of a computer screen issuing commands to the UAV via a hand-held controller which resembles (in detail) the model of controllers that are used to play games on an Xbox 360 game console. (Jodie C Spreadbury, Army Recruiting and Training Division) Sony VGP-BPS13/B battery .
Not everyone agrees with the language and underlying connotations of the digital native. It suggests a familiarity with technology that not all children and young adults who would be considered digital natives have, though some instead have an awkwardness with technology that not all digital immigrants have Sony VGP-BPS13/S battery .
In its application, the concept of the digital native preferences those who grow up with technology as having a special status, ignoring the significant difference between familiarity and creative application. Like animals to their natural habitat, those who were raised in a digital world naturally develop a keen perception and understanding of their surroundings Sony VGP-BPS13A/B battery .
The term digital immigrant overlooks the fact that many people born before the digital age were the inventors, designers, developers and first users of digital technology and in this sense could be regarded as the original 'natives'. To confuse the prolific (and arguably superficial) Sony VGP-BPS13B/B battery
use of digital technology by current adolescents as deep knowledge and understanding is potentially misleading and unhelpful to the discourse. The term also discounts the broader and more holistic knowledge, experience and understandings that older generations may have about digital technologies and their potential place in society Sony VGP-BPL9 battery .
Crucially, there is debate over whether there is any adequate evidence for claims made about digital natives and their implications for education. Bennett, Maton & Kervin (2008), for example, critically review the research evidence and describe some accounts of digital natives having an academic form of a moral panic Sony VGP-BPS13B/B battery .
Using such a terminology is rather a sign of unfamiliarity and exoticism in relation to digital culture. Of course, nobody is "born digital"; as with any cultural technology, such as reading and writing, it is matter of access to education and experience .
It considers that all youths are digital natives in the modern age Sony VGP-BPL15 battery .
However, this is not the case. It is primarily based on cultural differences and not by age. According to Henry Jenkins (2007), "Part of the challenge of this research is to understand the dynamics of who exactly is, and who is not, a digital native, and what that means Dell Inspiron E1505 battery .
" There are underlying conflicts on the definition of the term "digital natives" and it is wrong to say that all modern age youths are placed in that particular category or that all older adults can be described as digital immigrants.
The formulation of digital native is also challenged by researchers looking at emerging technology landscapes HP Pavilion dv6000 Battery .
The current discourse concentrates largely on developed technology geographies and has a particular bias towards white, liberal, middle-class youth who have the privilege of access to technology. Nishant Shah (2009) says, "It is necessary to promote research that grasps that not all Digital Natives are equal HP Pavilion dv8000 battery .
Each context will have certain norms by which digital nativity is understood and experienced. Dismantling the universal Digital Native and considering contextualised Digital Native identities might also help us move away from speaking of the Digital Native as a necessarily HP PAVILION DV6000 Battery, 8800mAh
elite power-user of technology and understand the identity as a point of departure from earlier technology-mediated identities within those contexts." He also suggests that one way of understanding digital natives is to look at how they use digital technologies to engage with their immediate environments and initiate processes of social and personal change HP PAVILION DV8000 Battery, 8800mAh .
The information age, also commonly known as the computer age or information era, is an idea that the current age will be characterized by the ability of individuals to transfer information freely, and to have instant access to knowledge that would have been difficult or impossible to find previously SONY VAIO VGN-FZ Battery .
The idea is linked to the concept of a digital age or digital revolution, and carries the ramifications of a shift from traditionalindustry that the industrial revolution brought through industrialization, to an economy based on the manipulation of information HP Pavilion DV6000 battery - 8800mAh .
Commonly seen as an outflow from the space age, capitalizing on the computer microminiaturization advances of that effort, with a fuzzy transition spanning from the advent of the personal computer in the late 1970s to the internet reaching a critical mass in the early 1990s, and the adoption of such technology by the public in the two decades after 1990 HP Pavilion DV8000 battery - 7800mAh .
The Information Age has allowed rapid global communications and networking to shape modern society.
The Internet was conceived as a fail-proof network that could connect computers together and be resistant to any one point of failure; the Internet cannot be totally destroyed in one event HP Pavilion DV6000 battery - 8800mAh ,
and if large areas are disabled, the information is easily rerouted. It was created mainly by DARPA; its initial software applications were e-mail and computer file transfer.
Though the Internet itself has existed since 1969 HP Pavilion DV8000 battery - 6600mAh ,
it was with the invention of the World Wide Web in 1989 by British scientist Tim Berners-Lee and its implementation in 1991 that the Internet truly became a global network. Today the Internet has become the ultimate platform for accelerating the flow of information and is, today SONY VAIO VGN-FZ18 Battery ,
the fastest-growing form of media, and is pushing many, if not most, other forms of media into obsolescence.
The proliferation of the smaller and less expensive personal computers and improvements in computing power by the early 1980s resulted in a sudden access to and ability to share and store information for more and more workers SONY VAIO VGN-FZ21E Battery.
Connectivity between computers within companies led to the ability of workers at different levels to access greater amounts of information.
In the 1990s, the spread of the Internet caused a sudden leap in access to and ability to share information in businesses, at home and around the globe SONY VAIO VGN-FW31J Battery 10400mAh .
Technology was developing so quickly, that a computer costing $3,000.00 in 1997, only cost $2000.00 two years later and the same caliber of machine cost only $1000.00 the following year.
Concurrently during the 1980s and 1990s in the United States, Canada, Australia, New Zealand, and Western Europe SONY VAIO VGN-FW31J Battery 10400mAh ,
there was a steady trend away from people holding Industrial Age manufacturing jobs. An increasing number of people held jobs as clerks in stores, office workers, teachers, nurses, etc. The industrial world was shifting into a service economy SONY VAIO VGN-FW21E Battery .
Eventually, Information and Communication Technology—computers, computerized machinery, fiber optics, communication satellites, Internet, and other ICT tools—became a significant part of the economy. Microcomputers were developed and many business and industries were greatly changed by ICT SONY VAIO VGN-NR11S/S Battery .
Nicholas Negroponte captured the essence of these changes in his 1995 book, Being Digital. His book discusses similarities and differences between products made of atoms and products made of bits. In essence, one can very cheaply and quickly make a copy of a product made of bits SONY VAIO VGN-NR11M/S Battery ,
and ship it across the country or around the world both quickly and at very low cost.
The term has been noted as identifying an era when "ideas about the computer, the internet, or digital resources seem to influence policy decisions more than social concerns about access, privacy or preservation SONY VAIO VGN-NR11Z/S Battery ."
Thus, the term "Information Age" is often applied in relation to the use of cell phones, digital music, high definition television, digital cameras, the Internet, cable TV, and other items that have come into common use in the past 30 years .
The impact on jobs and income distribution
The information age has impacted the workforce in several ways SONY VAIO VGN-NR11Z/T Battery .
First, it has created a situation in which workers who perform tasks which are easily automated are being forced to find work which involves tasks that are not easily automated. Second, workers are being to forced to compete in a global job market. This creates problems for workers in industrial societies Sony VAIO VGN-FZ21E Battery .
Jobs traditionally associated with the middle class (assembly line workers, data processors, foremen, and supervisors) are beginning to disappear, either through outsourcing or automation. Individuals who lose their jobs must either move up, joining a group of “mind workers” Sony VAIO VGN-FW21E Battery
(engineers, attorneys, scientists, professors, executives, journalists, consultants), or settle for low-skill, low-wage service jobs.
The “mind workers” form about 20% of the workforce. They are able to compete successfully in the world market and command high wages Sony VAIO VGN-NR11S/S Battery .
Conversely, production workers and service workers in industrialized nations are unable to compete with workers in developing countries and either lose their jobs through outsourcing or are forced to accept wage cuts. In addition, the internet makes it possible for workers in developing countries to provide in-person services and compete directly with their counterparts in other nationsSony VAIO VGN-NR11Z/S Battery .
This has had several major consequences:
- Growing income inequality in industrial countries
The polarization of jobs into relatively high-skill, high wage jobs and low-skill, low-wage jobs has led to a growing disparity between incomes of the rich and poor Sony VAIO VGN-NR11M/S Battery .
The United States seems to have been more impacted than most countries; income inequality started to rise in the late 1970,’s, however the rate of increase rose sharply in the 21st century. Income inequality in the United States has now reached a level comparable to that found in South America Sony VAIO VGN-NR11Z/T Battery .
- Increased opportunity in developing countries
Workers in developing countries have a competitive advantage which translates into increased opportunities and higher wages. The full impact on the workforce in developing countries is complex; there are downsides. (see discussion in section on globalization)SONY VAIO VGN-FZ180E Battery .
- The globalization of the workforce
In the past, the economic fate of workers was tied to the fate of national economies. For example, workers in the United States were once well paid in comparison to the workers in other countries SONY VAIO VGN-FZ220E Battery .
With the advent of the information age and improvements in communication, this is no longer the case. Because workers are forced to compete in a global job market, wages are less dependent on the success or failure of individual economies SONY VAIO VGN-FZ340E Battery .
Automation, productivity, and job loss
There is another way in which the information age has impacted the workforce: automation and computerization have resulted in higher productivity coupled with net job loss. In the United States for example, from Jan 1972 to August 2010, the number of people employed in manufacturing jobs fell from 17,500,000 to 11,500,000 while manufacturing value rose 270% SONY VAIO VGN-FZ430E Battery .
It initially appeared that job loss in the industrial sector might be partially offset by the rapid growth of jobs in the IT sector. However after the recession of March 2001, the number of jobs in the IT sector dropped sharply and continued to drop until 2003. Even the IT sector is not immune to this problem SONY VAIO VGN-FZ460E Battery .
The rise of information-intensive industry and "the new entrepreneurialism"
Industry is becoming more information-intensive and less labor and capital-intensive (see Information industry). This trend has important implications for the workforce SONY VAIO VGN-FZ480E Battery ;
workers are becoming increasingly productive as the value of their labor decreases. However, there are also important implications for capitalism itself; not only is the value of labor decreased, the value of capital is also diminished. In the classical model, investments in human capital and financial capital are important predictors of the performance of a new venture SONY VAIO VGN-FZ4000 Battery .
However, as demonstrated by Mark Zuckerberg andFacebook, it now seems possible for a group of relatively inexperienced people with limited capital to succeed on a large scale.
Interpreting technology: "the medium is the message"
The information age has changed us profoundly SONY VAIO VGN-FZ31E Battery .
It has changed our culture, it has changed our language, and it has even changed the way we think. However, before investigating these ideas further, it is necessary to consider the question of interpretation; how are we to understand the implications of technology SONY VAIO VGN-FZ31B Battery ?
- The relationship between mind and technology
There are many theories which suggest how to interpret technology. Most of these theories involve the relationship between technology and society; prompting questions about agency and determinism SONY VAIO VGN-FZ31J Battery .
The school of thought that Thorstein Veblen called “technological determinism” interprets technology as a force largely beyond our control that shapes our history and culture. The implication that our tools somehow control us led to a reaction; in the instrumentalist view, technology is interpreted as a means to an end SONY VAIO VGN-FZ31M Battery .
James Carey, in Communication as Culture writes: “Technology is technology, it is a means for communication and transportation over space, and nothing more.”
A recent book by Nicholas Carr, The Shallows: What the Internet is Doing to Our Brains, suggests a problem with the both the determinist and instrumentalist positions SONY VAIO VGN-FZ31Z Battery ;
they all view technology as something apart from mind. Carr points out that technology can actually affect the way the brain is wired. For example, experiments have shown that the brains of literate and illiterate individuals differ in many ways. Literacy not only affects how we understand language SONY VAIO VGN-FZ38M Battery ,
it also affects how we process visual signals, how we reason, and how we form memories.
The changes in our brain brought about by technology are, in a sense, irreversible. The brain is plastic; when we develop new patterns of thought, the brain forms new structures of neural connections SONY VGP-BPS8 Battery .
The old neural loops do not stick around; they are reused by the brain in different ways. This does not mean that we can’t relearn old habits; it simply means that the longer we use new patterns of thought, the harder is to go back. In Carr’s words, “plastic does not mean elastic.” SONY VGP-BPS13/S Battery .
Cognitive science has shown us we can no longer view technology as something separate from mind. The relationship of mind and tec
- Marshal McLuhan and his theory of extensions
Marshal McLuhan, in Understanding Media: The Extensions of Man,suggested that technological innovations should be understood, not in terms of their content, but in terms of how they change society SONY VGP-BPS13B/B Battery .
His famous one-liner “the medium is the message” should be understood this way. He explored this idea metaphorically by suggesting that media act as extensions of the human body. For example, the automobile could be viewed as an extension of the feet; it allows man to travel places in the same manner as the feet, only faster and with less effort SONY VGP-BPS13A/S Battery .
According to McLuhan, most people understand this intuitively, however they tend not to realize that every extension implies an amputation. The development of the automobile reduces the need for a walking culture, which in turn influences the development of society as a whole SONY VGP-BPS13AS Battery .
McLuhan also warns us of the dangers of over-extending technology. When a medium like the automobile becomes over-extended, the resulting amputations (carbon emissions, obesity.) may outweigh the benefits of getting places faster.
According to McLuhan, when we create a new technology, we are changing ourselves; something has been amputated Dell Inspiron 1320n Battery .
When a technology becomes over extended, it is not possible to simply go back. For example, when the automobile becomes over-extended, we cannot go back to a walking culture because we have forgotten how to walk. McLuhan states that "every process pushed far enough tends to reverse or flip suddenly" Dell Studio 1450 Battery ,
but this flip is never a literal return to the past, instead it involves a qualitative change, something radically new that seeks to recover something that has been lost. In McLuhan’s words, “we use the new to do the old.”
A Hall effect sensor is a transducer that varies its output voltage in response to changes in magnetic field Dell Studio 1457 Battery .
Hall sensors are used for proximity switching, positioning, speed detection, and current sensing applications.
In its simplest form, the sensor operates as an analogue transducer, directly returning a voltage. With a known magnetic field, its distance from the Hall plate can be determined Dell Latitude D610 Battery .
Using groups of sensors, the relative position of the magnet can be deduced.
Electricity carried through a conductor will produce a magnetic field that varies with current, and a Hall sensor can be used to measure the current without interrupting the circuit Toshiba NB100 Battery .
Typically, the sensor is integrated with a wound core or permanent magnet that surrounds the conductor to be measured.
Frequently, a Hall sensor is combined with circuitry that allows the device to act in a digital (on/off) mode, and may be called a switch in this configuration Toshiba Satellite M65 battery .
Commonly seen in industrial applications such as the pictured pneumatic cylinder, they are also used in consumer equipment; for example some computer printers use them to detect missing paper and open covers. When high reliability is required, they are used in keyboards Toshiba Satellite M60 battery .
Hall sensors are commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing, tachometers and anti-lock braking systems. They are used in brushless DC electric motors to detect the position of the permanent magnet Dell Latitude D830 Battery .
In the pictured wheel with two equally spaced magnets, the voltage from the sensor will peak twice for each revolution. This arrangement is commonly used to regulate the speed of disc drives.
A hall probe contains an indium compound crystal such as indium antimonide, mounted on an aluminum backing plate, and encapsulated in the probe head Dell Latitude D620 Battery .
The plane of the crystal is perpendicular to the probe handle. Connecting leads from the crystal are brought down through the handle to the circuit box.
When the Hall Probe is held so that the magnetic field lines are passing at right angles through the sensor of the probe, the meter gives a reading of the value of magnetic flux density (B) Dell Inspiron Mini 10 Battery .
A current is passed through the crystal which, when placed in a magnetic field has a “Hall Effect” voltage developed across it. The Hall Effect is seen when a conductor is passed through a uniform magnetic field. The natural electron drift of the charge carriers causes the magnetic field to apply a Lorentz force Sony VGN-FW11S Battery
(the force exerted on a charged particle in an electromagnetic field) to these charge carriers. The result is what is seen as a charge separation, with a build up of either positive or negative charges on the bottom or on the top of the plate. The crystal measures 5 mm square Sony VGN-FW11M Battery .
The probe handle, being made of a non-ferrous material, has no disturbing effect on the field.
A Hall Probe is enough to measure the Earth's magnetic field. It must be held so that the Earth's field lines are passing directly through it. It is then rotated quickly so the field lines pass through the sensor in the opposite direction Sony VGN-FW139E/H battery .
The change in the flux density reading is double the Earth's magnetic flux density. A hall probe must first be calibrated against a known value of magnetic field strength. For a solenoid the hall probe is placed in the center.
Hall Effect Sensor Interface
Hall effect sensor may require analog circuitry to be interfaced to microprocessors Dell Latitude E5400 Battery .
These interfaces may include input diagnostics, fault protection for transient conditions, and short/open circuit detection. It may also provide and monitor the current to the hall effect sensor itself. There are precision IC products available to handle these featuresDell Latitude E4200 Battery .
A current sensor is a device that detects electrical current (AC or DC) in a wire, and generates a signal proportional to it.
The sensed current and the output signal can be:
- AC current input,
- analog output, which duplicates the wave shape of the sensed current Dell Inspiron 300M Battery
- bipolar output, which duplicates the wave shape of the sensed current
- unipolar output, which is proportional to the average or RMS value of the sensed current
- DC current input Dell Studio 1737 battery ,
- unipolar, with a unipolar output, which duplicates the wave shape of the sensed current
- digital output, which switches when the sensed current exceeds a certain threshold Dell Inspiron E1505 battery
Analogue electronics (or analog in American English) are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two different levels. The term "analogue" describes the proportional relationship between a signal and a voltage or current that represents the signal Dell RM791 battery .
The word analogue is derived from the Greek word ???????? (analogos) meaning "proportional".
An analogue signal uses some attribute of the medium to convey the signal's information Toshiba Satellite P10 Battery .
For example, an aneroid barometer uses the angular position of a needle as the signal to convey the information of changes in atmospheric pressure. Electrical signals may represent information by changing their voltage, current, frequency, or total charge Acer Aspire One battery 10400mAh .
Information is converted from some other physical form (such as sound, light, temperature, pressure, position) to an electrical signal by a transducer which converts one type of energy into another (e.g. a microphone).
The signals take any value from a given range, and each unique signal value represents different information SONY VGN-FZ210CE Battery .
Any change in the signal is meaningful, and each level of the signal represents a different level of the phenomenon that it represents. For example, suppose the signal is being used to represent temperature, with one volt representing one degree Celsius. In such a system 10 volts would represent 10 degrees, and 10.1 volts would represent 10.1 degrees Dell Precision M70 Battery .
Another method of conveying an analogue signal is to use modulation. In this, some base carrier signal has one of its properties altered: amplitude modulation (AM) involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation (FM) changes the frequency Toshiba Satellite L305 Battery .
Other techniques, such as phase modulation or changing the phase of the carrier signal, are also used.
In an analogue sound recording, the variation in pressure of a sound striking a microphone creates a corresponding variation in the current passing through it or voltage across it Toshiba Satellite T4900 Battery .
An increase in the volume of the sound causes the fluctuation of the current or voltage to increase proportionally while keeping the same waveform or shape.
Mechanical, pneumatic, hydraulic and other systems may also use analogue signals Toshiba PA3399U-2BRS battery .
Analogue systems invariably include noise; that is, random disturbances or variations, some caused by the random thermal vibrations of atomic particles. Since all variations of an analogue signal are significant, any disturbance is equivalent to a change in the original signal and so appears as noise Sony VGP-BPS10 battery 10400mAh .
As the signal is copied and re-copied, or transmitted over long distances, these random variations become more significant and lead to signal degradation. Other sources of noise may include external electrical signals or poorly designed components. These disturbances are reduced by shielding, and using low-noise amplifiers (LNA) Sony VGP-BPS9 battery 10400mAh .
Analogue vs. digital electronics
Since the information is encoded differently in analogue and digital electronics, the way they process a signal is consequently different. All operations that can be performed on an analogue signal such as amplification, filtering, limiting, and others, can also be duplicated in the digital domain Sony VGP-BPS11 battery 10400mAh .
Every digital circuit is also an analogue circuit, in that the behaviour of any digital circuit can be explained using the rules of analogue circuits.
The first electronic devices invented and mass produced were analogue Sony VGP-BPS22 battery 10400mAh .
The use of microelectronics has reduced the cost of digital techniques and now make digital methods feasible and cost-effective such as in the field of human-machine communication by voice.
The main differences between analogue and digital electronics are listed below Sony VGP-BPL8 battery 10400mAh :
Because of the way information is encoded in analogue circuits, they are much more susceptible to noise than digital circuits, since a small change in the signal can represent a significant change in the information present in the signal and can cause the information present to be lost Sony VGP-BPS14 battery 10400mAh .
Since digital signals take on one of only two different values, a disturbance would have to be about one-half the magnitude of the digital signal to cause an error; this property of digital circuits can be exploited to make signal processing noise-resistant Sony VGP-BPS21 battery 10400mAh .
In digital electronics, because the information is quantized, as long as the signal stays inside a range of values, it represents the same information. Digital circuits use this principle to regenerate the signal at each logic gate, lessening or removing noise Toshiba Satellite A200 Battery .
A number of factors affect how precise a signal is, mainly the noise present in the original signal and the noise added by processing. See signal-to-noise ratio. Fundamental physical limits such as theshot noise in components limits the resolution of analogue signalsToshiba Satellite 1200 Battery .
In digital electronics additional precision is obtained by using additional digits to represent the signal; the practical limit in the number of digits is determined by the performance of the analogue-to-digital converter (ADC), since digital operations can usually be performed without loss of precision Toshiba Satellite M300 Battery .
The ADC takes an analogue signal and changes into a series of binary numbers. The ADC may be used in simple digital display devices e. g. thermometers, light meters but it may also be used in digital sound recording and in data acquisition. However, a digital-to-analogue converter (DAC) is used to change a digital signal to an analogue signal SONY VGP-BPS13A/Q Battery .
A DAC takes a series of binary numbers and converts it to an analogue signal. It is common to find a DAC in the gain-control system of an op-amp which in turn may be used to control digital amplifiers and filters.
Analogue circuits are harder to design, requiring more skill, than comparable digital systems SONY VGP-BPS13A/Q Battery .
This is one of the main reasons why digital systems have become more common than analogue devices. An analogue circuit must be designed by hand, and the process is much less automated than for digital systems. However, if a digital electronic device is to interact with the real world, it will always need an analogue interface SONY VGP-BPS13B/Q Battery .
For example, every digital radio receiver has an analogue preamplifier as the first stage in the receive chain.
An analog or analogue signal is any continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal SONY VGP-BPS13B/Q Battery .
It differs from a digital signal in terms of small fluctuations in the signal which are meaningful. Analog is usually thought of in an electrical context; however, mechanical, pneumatic,hydraulic, and other systems may also convey analog signals.
An analog signal uses some property of the medium to convey the signal's information SONY VGP-BPS13/Q Battery .
For example, an aneroid barometer uses rotary position as the signal to convey pressure information. Electrically, the property most commonly used is voltage followed closely by frequency, current, and charge.
Any information may be conveyed by an analog signal SONY VGP-BPS13/Q Battery ;
often such a signal is a measured response to changes in physical phenomena, such as sound, light, temperature, position, or pressure, and is achieved using a transducer.
For example, in sound recording SONY VGP-BPS21A/B Battery ,
fluctuations in air pressure (that is to say, sound) strike the diaphragm of a microphone which induces corresponding fluctuations in the current produced by a coil in an electromagnetic microphone, or the voltage produced by a condensor microphone. The voltage or the current is said to be an "analog" of the sound SONY VGP-BPS21/S Battery .
An analog signal has a theoretically infinite resolution. In practice an analog signal is subject to noise and a finite slew rate. Therefore, both analog and digital systems are subject to limitations in resolution and bandwidth. As analog systems become more complex SONY VGP-BPS21B Battery ,
effects such as non-linearity and noise ultimately degrade analog resolution to such an extent that the performance of digital systems may surpass it. Similarly, as digital systems become more complex, errors can occur in the digital data stream SONY VGP-BPS21A Battery .
A comparable performing digital system is more complex and requires more bandwidth than its analog counterpart.In analog systems, it is difficult to detect when such degradation occurs. However, in digital systems, degradation can not only be detected but corrected as well SONY VGP-BPS21 Battery .
The main advantage is the fine definition of the analog signal which has the potential for an infinite amount of signal resolution. Compared to digital signals, analog signals are of higher density.
Another advantage with analog signals is that their processing may be achieved more simply than with the digital equivalent Sony VGP-BPS21A/B Battery .
An analog signal may be processed directly by analog components, though some processes aren't available except in digital form.
The primary disadvantage of analog signaling is that any system has noise – i.e., random unwanted variation Sony VGP-BPS21/S Battery .
As the signal is copied and re-copied, or transmitted over long distances, these apparently random variations become dominant. Electrically, these losses can be diminished by shielding, good connections, and several cable types such as coaxial or twisted pair.
The effects of noise create signal loss and distortion Sony VGP-BPS21A Battery .
This is impossible to recover, since amplifying the signal to recover attenuated parts of the signal amplifies the noise (distortion/interference) as well. Even if the resolution of an analog signal is higher than a comparable digital signal, the difference can be overshadowed by the noise in the signal Sony VGP-BPS21 Battery .
Most of the analog systems also suffer from generation loss.
Another method of conveying an analog signal is to use modulation. In this, some base signal (e.g., a sinusoidal carrier wave) has one of its properties modulated Sony Vaio PCG-5G2L Battery :
amplitude modulation involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation changes the frequency. Other techniques, such as changing the phase of the base signal also work.
Analog circuits do not involve quantisation of information into digital format Sony Vaio PCG-5G3L Battery .
The concept being measured over the circuit, whether sound, light, pressure, temperature, or an exceeded limit, remains from end to end.
See digital for a discussion of digital vs. analog Sony Vaio PCG-5J1L Battery.
Sources: Parts of an earlier version of this article were originally taken from Federal Standard 1037C in support of MIL-STD-188.
An analog chip is a set of miniature electronic analog circuits formed on a single piece of semiconductor material.
The circuits in analog chips operate with voltage and current varying in a continuous fashion Sony Vaio PCG-5K2L Battery ;
in contrast, digital chips only use and create voltages or currents at discrete levels, with no intermediate values. Analog chips often have passive elements (Inductor/Capacitors/Resistors) built into them, whereas most digital chips typically do not.
Many modern analog chips contain digital logic elements also Sony Vaio PCG-5J2L Battery
-- either to replace some analog functions, or to allow the chip to communicate with a microprocessor. For this reason and since logic is commonly implemented using CMOS technology, these chips use BiCMOS processes by companies such as Freescale (Freescale Analog products), Texas Instruments, STMicroelectronics and others Sony Vaio PCG-5K1L Battery .
The death of pure analog chips has been proclaimed regularly, however the field continues to grow and prosper. Some examples of long-lived and well-known analog chips are the 741 op-amp which was the original internally compensated opamp, and the 555 timer. The popular 555 timer was invented by Hans Camenzind in the 1970s Sony Vaio PCG-6S2L Battery .
Power supply chips are also considered to be analog chips, but their main purpose is to produce a well-regulated output voltage supply for other chips in the system. Since all electronic systems require electrical power, power supply ICs PMICs are important elements of those systems Sony Vaio PCG-6S3L Battery .
Important basic building blocks of analog chip design include:
- current sources
- current mirrors
- differential amplifier
- bandgap references. Sony Vaio PCG-6V1L Battery
All the above circuit building blocks can be implemented in bipolar as well as MOS technology. MOS Bandgap references use lateral (poor) bipolar transistors for their functioning.
People who have specialized in this field include Bob Widlar, Bob Pease, Hans R. Camenzind, George Erdi, and Barry Gilbert among others Sony Vaio PCG-6W1L Battery .
Analog verification is a methodology for performing functional verification on analog, mixed-signal and RF integrated circuits and systems on chip. Discussion of analog verification began in 2005 when it started to become recognized that the analog portion of large mixed-signal chips had gottenSony Vaio PCG-6W2L Battery
so complex that a significant and ever increasing number of these chips were being designed with functional errors in the analog portion that prevented them from operating correctly.
Analog verification is built on the idea that transistor level simulation will always be too slow to provide adequate functional verification Sony Vaio PCG-6W3L Battery .
Instead, it is necessary to build simple and efficient models of the blocks that make up the analog portion of the design and use those to verify the design. Those models are typically written in Verilog or Verilog-AMS, but could also be written in VHDL or VHDL-AMS. However, simply using a simple functional model is not sufficient Sony Vaio PCG-7111L Battery .
It is also necessary to build a comprehensive self-checking testbench, that thoroughly exercises the design and compare its response against a previously written specification for the design. Furthermore, this testbench should be applied in turn to both the model and the design Sony Vaio PCG-7112L Battery .
In this case, the design is represented with a transistor-level schematic. If both the model and the design pass all tests, and if the testbench is comprehensive, then this confirms that the model is consistent with the design and that the design is consistent with the specification Sony Vaio PCG-7113L Battery .
Applying a comprehensive testbench to an entire analog functional unit such as an audio codec, power management unit, serdes, or RF transceiver, represented at the transistor level is impractical. So instead, the verification proceeds hierarchically. One first builds simple models and testbenches for individual blocks Sony Vaio PCG-7133L Battery .
The block-level testbenches are used to confirm that models match the implementation of the blocks and that the implementation matches the block-level specification. Then testbenches are built for the entire analog functional unit, and applied to the top-level schematic of that unit with the blocks represented with their now verified models Sony Vaio PCG-7Z2L Battery .
To further improve the tests, one can perform mixed-level simulation, where the testbench for the functional unit is applied with one or two blocks at the transistor level, and all others at the model level.
Radio Data System, or RDS, is a communications protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts Sony Vaio PCG-8Y1L Battery .
RDS standardises several types of information transmitted, including time, station identification and programme information .
Radio Broadcast Data System (RBDS) is the official name used for the U.S. version of RDS. The two standards are only slightly different Sony Vaio PCG-8Y2L Battery .
The standard began as a project of the European Broadcasting Union (EBU), but has since become an international standard of the International Electrotechnical Commission (IEC).
Both carry data at 1,187.5 bits per second on a 57 kHz subcarrier, so there are exactly 48 cycles of subcarrier during every data bitSony Vaio PCG-8Z1L Battery .
The RBDS/RDS subcarrier was set to the third harmonic of the 19 kHz FM stereo pilot tone to minimize interference and intermodulation between the data signal, the stereo pilot and the 38 kHz DSB-SC stereo difference signal. (The stereo difference signal extends up to 38 kHz + 15 kHz = 53 kHz, leaving 4 kHz for the lower sideband of the RDS signal Sony Vaio PCG-8Z2L Battery .)
The data are sent with error correction. RDS defines many features including how private (in-house) or other undefined features can be "packaged" in unused program groups.
RDS was inspired by the development of the Autofahrer-Rundfunk-Informationssystem (ARI) in Germany by the Institut für Rundfunktechnik (IRT) and the radio manufacturer Blaupunkt SONY VAIO VGN-FW31J Battery .
ARI used a 57 kHz subcarrier to indicate the presence of traffic information in an FM radio broadcast.
The EBU Technical Committee launched a project at its 1974 Paris meeting to develop a technology with similar purposes to ARI SONY VAIO VGN-FW31E Battery ,
but which was more flexible and which would enable automated retuning of a receiver where a broadcast network transmitted the same radio programme on a number of different frequencies. The modulation system was based on that used in a Swedish paging system and the baseband coding was a new design SONY VAIO VGN-FW31B Battery ,
mainly developed by the British Broadcasting Corporation (BBC) and the IRT. The EBU issued the first RDS specification in 1984.
Enhancements to the alternative frequencies functionality were added to the standard and it was subsequently published as a European Committee for Electrotechnical Standardization (CENELEC) standard in 1990 SONY VAIO VGN-FW31M Battery .
In 1992 the US National Radio Systems Committee issued the North American version of the RDS standard, called the Radio Broadcast Data System. The CENELEC standard was updated in 1992 with the addition of Traffic Message Channel and in 1998 with Open Data Applications and, in 2000, RDS was published worldwide as IEC standard 62106 SONY VAIO VGN-FW31Z Battery .
In addition, RDS is being proposed as the data transmission protocol in California's pioneering "Programmable Communicating Thermostat" (PCT) program SONY VAIO VGN-FW38M Battery .
The proposed technology would allow electricity consumers exposed to “time-based pricing” for electricity to respond to an RDS signal containing price information when their retail electricity price changed during periods of high wholesale electricity costs or abnormally high demand that threatened the stability of the electricity grid SONY VAIO VGN-AW41JF Battery .
The PCT could then automate any actions that the consumer had pre-programmed the device to take. For example, if the price of electricity went up on a hot afternoon because of extremely high demand, the consumer could preset the PCT to raise their air conditioner cooling set point by a few degrees in order to reduce their overall electricity consumption and bill SONY VAIO VGN-AW41JF/H Battery .
The technology could be extended to other home electricity consuming devices such as water heaters, clothes dryers, dishwashers, swimming pool pumps, etc. allowing consumers under time-based pricing for electricity significant automatic control over their electricity consumption during periods when the price of electricity is naturally higher than normal SONY VAIO VGN-AW41MF Battery .
The goal is to give consumers a choice between paying more for high value peak electricity, or reducing their lowest value loads at those times. Such voluntary “demand response” behavior could significantly reduce the price of electricity during non-peak periods because of reduced need for infrequently used peaking power plants SONY VAIO VGN-AW41MF/H Battery ,
and also reduce the chances of blackouts during emergency events when the electricity grid is stressed or damaged.
RDS subcarrier use for the control of peak power has been in development in Australia since early 2000. ETSA the South Australia Electricity Trust and Saab Systems Australia, a local South Australian company SONY VAIO VGN-FW30B Battery ,
pioneered the idea after Saab engineer Trent Ryan developed the idea in late 1999 and brought it to Saab for further refinement.
Companies such as ST Microelectronics, Silicon Labs in Austin, Texas and NXP Semiconductors (formerly Philips) offer single chip solutions that are found in these devices SONY VAIO VGN-FW50B Battery .
The Silicon Labs part supports PS, RT, PTY, TMC, and all other RDS types in a single 3x3 mm chip and its intended purpose is portable usage (such as mobile phones and MP3 players). NXP also has solutions in this field, and has some automotive chips.
The Digital Revolution is the change from analog mechanical and electronic technology to digital technology that has taken place since c. 1980 and continues to the present day SONY VAIO VGN-FW51B/W Battery .
Implicitly, the term also refers to the sweeping changes brought about by digital computing and communicationtechnology during the latter half of the 20th century. Analogous to the Agricultural Revolution and Industrial Revolution, the Digital Revolution marked the beginning of the Information Age SONY VAIO VGN-FW51MF Battery .
Central to this revolution is the mass production and widespread use of digital logic circuits, and its derived technologies, including the computer, digitalcellular phone, and fax machine.
A digital signal is a physical signal that is a representation of a sequence of discrete values (a quantified discrete-time signal) SONY VAIO VGN-FW51MF/H Battery ,
for example of arbitrary bit stream, or of a digitized (sampled and analog-to-digital converted) analog signal. The term digital signal can refer to
- a continuous-time waveform signal used in any form of digital communication SONY VAIO VGN-FW51ZF Battery
- a pulse train signal that switches between a discrete number of voltage levels or levels of light intensity, also known as a a line coded signal, for example a signal found in digital electronics or inserial communications using digital baseband transmissionin, or a pulse code modulation (PCM) representation of a digitized analog signal SONY VAIO VGN-FW51ZF/H Battery .
A signal that is generated by means of a digital modulation method (digital passband transmission), produced by a modem, is in the first case considered as a digital signal, and in the second case as converted to an analog signal SONY VAIO VGN-FW52JB Battery .
Waveforms in digital systems
In computer architecture and other digital systems, a waveform that switches between two voltage levels representing the two states of a Booleanvalue (0 and 1) is referred to as a digital signal, even though it is an analog voltage waveform, since it is interpreted in terms of only two levels SONY VAIO VGN-FW54FB Battery .
The clock signal is a special digital signal that is used to synchronize digital circuits. The image shown can be considered the waveform of a clock signal. Logic changes are triggered either by the rising edge or the falling edge.
The given diagram is an example of the practical pulse and therefore we have introduced two new terms that are SONY VAIO VGN-FW70DB Battery :
- Rising edge: the transition from a low voltage (level 1 in the diagram) to a high voltage (level 2).
- Falling edge: the transition from a high voltage to a low one.
Although in a highly simplified and idealised model of a digital circuit we may wish for these transitions to occur instantaneouslySONY VAIO VGN-FW71DB/W Battery ,
no real world circuit is purely resistive and therefore no circuit can instantly change voltage levels. This means that during a short, finite transition time the output may not properly reflect the input, and indeed may not correspond to either a logically high or low voltage SONY VAIO VGN-FW72JGB Battery .
Logic voltage levels
The two states of a wire are usually represented by some measurement of an electrical property: Voltage is the most common, but current is used in some logic families. A threshold is designed for each logic family. When below that threshold, the wire is "low," when above "high SONY VAIO VGN-FW73JGB Battery .
" Digital circuits establish a "no man's area" or "exclusion zone" that is wider than the tolerances of the components. The circuits avoid that area, in order to avoid indeterminate results.
It is usual to allow some tolerance in the voltage levels used; for example, 0 to 2 volts might represent logic 0, and 3 to 5 volts logic 1 SONY VAIO VGN-FW74FB Battery .
A voltage of 2 to 3 volts would be invalid, and occur only in a fault condition or during a logic level transition. However, few logic circuits can detect such a condition and most devices will interpret the signal simply as high or low in an undefined or device-specific manner SONY VAIO VGN-FW81HS Battery .
Some logic devices incorporate schmitt trigger inputs whose behaviour is much better defined in the threshold region, and have increased resilience to small variations in the input voltage.
The levels represent the binary integers or logic levels of 0 and 1 SONY VAIO VGN-FW81NS Battery .
In active-high logic, "low" represents binary 0 and "high" represents binary 1. Active-low logic uses the reverse representation.
In telecommunication, intersymbol interference (ISI) is a form of distortion of a signal in which one symbol interferes with subsequent symbols SONY VAIO VGN-FW81S Battery .
This is an unwanted phenomenon as the previous symbols have similar effect as noise, thus making the communication less reliable. ISI is usually caused by multipath propagation or the inherent non-linear frequency response of a channel causing successive symbols to "blur" together SONY VAIO VGN-FW82DS Battery .
The presence of ISI in the system introduces errors in the decision device at the receiver output. Therefore, in the design of the transmitting and receiving filters, the objective is to minimize the effects of ISI, and thereby deliver the digital data to its destination with the smallest error rate possible SONY VAIO VGN-FW82JS Battery .
Ways to fight intersymbol interference include adaptive equalization and error correcting codes.
Content and implementation
The following information fields are normally contained in the RDS data SONY VAIO VGN-FW82XS Battery :
- AF (alternative frequencies)
- This allows a receiver to re-tune to a different frequency providing the same station when the first signal becomes too weak (e.g., when moving out of range). This is often utilized in car stereo systems SONY VAIO VGN-FW83DS Battery .
- CT (clock time)
- Can synchronize a clock in the receiver or the main clock in a car. Due to transmission vagaries, CT can only be accurate to within 100 ms of UTC.
- EON (enhanced other networks) SONY VAIO VGN-FW83JS Battery
- Allows the receiver to monitor other networks or stations for traffic programmes, and automatically temporarily tune into that station.
- PI (programme identification)
- This is the unique code that identifies the station. Every station receives a specific code with a country prefix SONY VAIO VGN-FW83XS Battery .
- In the US, PI is determined by applying a formula to the station's call sign.
- PS (programme service)
- This is simply an eight-character static display that represents the call letters or station identity name SONY VAIO VGN-FW90NS Battery .
- Most RDS capable receivers display this information and, if the station is stored in the receiver's presets, will cache this information with the frequency and other details associated with that preset.
- PTY (programme type)
- This coding of up to 31 pre-defined programme types SONY VAIO VGN-FW37J/B Battery
- (e.g., in Europe: PTY1 News, PTY6 Drama, PTY11 Rock music) allows users to find similar programming by genre. PTY31 seems to be reserved for emergency announcements in the event of natural disasters or other major calamities SONY VAIO VGN-FW37J Battery .
- REG (regional)
- This is mainly used in countries where national broadcasters run "region-specific" programming such as regional opt-outs on some of their transmitters. This functionality allows the user to "lock-down" the set to their current region or let the radio tune into other region-specific programming as they move into the other region SONY VAIO VGN-FW378J/B Battery .
- RT (radio text)
- This function allows a radio station to transmit a 64-character free-form textual information that can be either static e.g. station slogans or in sync with the programming such as the title and artist of the currently playing song SONY VAIO VGN-FW378DH Battery .
- TA, TP (traffic announcement, traffic programme)
- The receiver can often be set to pay special attention to this flag and, for example, stop the tape/pause the CD or retune to receive a traffic bulletin SONY VAIO VGN-FW378J/B Battery .
- The TP flag is used to allow the user to find only those stations that regularly broadcast traffic bulletins whereas the TA flag is used to stop the tape or raise the volume during a traffic bulletin SONY VAIO VGN-FW37J Battery .
- TMC (Traffic Message Channel)
- Digitally encoded traffic information. Not all RDS equipment supports this. Often available for Automotive navigation systems. In many countries only encrypted data is broadcast, and so a subscription and appropriate decoder is required to use SONY VAIO VGN-FW41E/H Battery SONY VAIO VGN-FW41J/H Battery SONY VAIO VGN-FW41M/H Battery SONY VAIO VGN-FWZJ/H Battery