Data are symbols. Information occurs when symbols are used to refer to something.
Raw data refers to a collection of numbers, characters, images or other outputs
Metadata is "data about other data".
knowledge piece of information in a particular field.
Information is a message received and understood. It is a quality of a message from a sender to one or more receivers.
A communication system consists of three basic parts, namely, the sender, the channel, and the receiver.
The sender and receiver have to have at least a fundamental set of codes in common, in order for them to communicate successfully.
Electrical communication systems are designed to send messages or information from a source that generates the messages to one or more destinations.A transducer is usually required to convert the output of a source into an electrical signal that is suitable for transmission.The heart of the communication system consists of three basic parts, namely, the transmitter, the channel, and the receiver.
The Transmitter (sender).—The transmitter converts the electrical signal into a form that is suitable for transmission through the physical channel or transmission medium.In general, the transmitter performs the matching of the message signal to the channel by a process called modulation and may also include coding.. In general carrier modulation such as AM, FM, and PM is performed at the transmitter.In addition to modulation, other functions that are usually performed at the transmitter are filtering of the information-bearing signal, amplification of the modulated signal, and in the case of wireless transmission, radiation of the signal by means of a transmitting antenna.
The Channel.—The communications channel is the physical medium that is used to send the signal from the transmitter to the receiver.It may be a pair of wires, a coaxial cable, or a radio wave or laser beam. Whatever the physical medium for signal transmission, the essential feature is that the transmitted signal is corrupted in a random manner by a variety of possible mechanisms. Every channel introduces some amount of transmission loss or attenuation(fading), distorsion, interference and noise (thermal noise, man-made noise and atmospheric noise). So, the signal power progressively decreases with increasing distance.
The Receiver.—It operates on the output signal from the channel in preparation for delivery to the transducer at the destination. Receiver operations include amplification to compensate for transmission loss. These also include demodulation and decoding to reverse the signal procession performed at the transmitter. Filtering is another important function at the receiver.
This is a one-way or simplex (SX) transmission. Two way communication of course requires a transmitter and receiver at each end. A full-duplex (FDX) system has a channel that allows simultaneous transmission in both directions. A half-duplex (HDX) system allows transmission in either direction but not at the same time.
Message is defined as the physical manifestation of information as produced by the source
There are two distinct message categories:
An analog message is a physical quantity that varies with time usually in a smooth and continuous fashion.
Examples of analog messages are: the acoustic pressure produced when you speak, the angular position of an aircraft gyro, the light intensity at some point in a television image.
A digital message is an ordered sequence of symbols selected from a finite set of discrete elements.
Examples of digital messages are: letters printed on this page, listing of hourly temperature readings , the keys you press at a computer terminal.
Whether the message is analog or digital, it needs to be converted into an electrical signal.
Analog signal which is a continuous-time signal waveform.
Digital signal which is discrete in time and has a finite number of output characters.
They can be transmitted directly (base band) or via carrier modulation or digital modulation over the communication channel.
There are some potential advantages to transmitting an analog signal by means of digital modulation. The most important reason is that signal fidelity is better controlled through digital transmission than analog transmission. In particular, digital transmission allows us to regenerate the digital signal in long-distance transmission, thus eliminating effects of noise at each regeneration point. Another reason is that the analog message signal may be highly redundant. With digital processing, redundancy may be removed prior to modulation, thus conserving channel bandwidth.
Yet a third reason may be that digital communication systems are often cheaper to implement. An improved security of message. A common format for encoding different kinds of message signals.
In a digital communication system, the messages produced by the source are usually converted into a sequence of binary digits. The process of efficiently (little or no redundancy) converting the output of either an analog or a digital source into a sequence of binary digits is called source encoding or data compression.
Then the information sequence is passed to the channel encoder which introduce some redundancy which can be used at the receiver to overcome the effects of noise and interference encountered in the transmission of the signal through the channel.
The binary sequence is passed to the digital modulator, which serves as the interface to the communications channel.
The digital modulator map the binary information sequence into signal waveforms.
The digital demodulator reduces each waveform to a single number that represents an estimate of the transmitted data symbol.
The channel capacity is defined as: the maximum rate of reliable (error-free) information transmission through the channel.
C = B log2(1+S/N)
where C is the channel capacity, B is the channel bandwidth in hertz, S is the signal power and N is the noise power in watts or volts2, so the signal-to-noise ratio here is expressed as a power ratio, not in decibels (dB); signal-to-noise ratio SNR=10 log(Ps/Pn)
If the information rate, R is equal to or less than the channel capacity, C, then there is, in principle, a coding technique which enables transmission over the noisy channel with no errors. The inverse of this is that if R > C, then the probability of error is close to 1 for every symbol.
The channel capacity, C, increases as the available bandwidth increases and as the signal to noise ratio increases (improves).
In earlier times, the most widely used form of communication was a system based on the transmission of a continuous-wave (CW) signal. With this system, the signal was interrupted periodically (Morse code) to produce a coded message.
The literal meaning of the modulation is "to change". In modulation, some characteristic of carrier wave is changed in accordance with the intensity (i.e., amplitude, frequency, phase) of the signal. The resultant wave is called modulated wave or radio wave and contains the information signal.
Modulation is extremely necessary in communication systems due to the following reasons:
Practical Antenna Length (L)
When free space is the communication channel, antennas radiate and receiver the signal. Theory shows that the antennas operate effective only when their dimensions are of the order of the magnitude of wavelength of the signal being transmitted.
One desirable feature of radio transmission is that it should be carried without wires (i.e.,) radiated into space.
The energy of a wave depends upon its frequency. The greater the frequency of the wave, the greater is the energy possessed by it.
We can have three different types of analog modulation.
Amplitude of Modulation
The amplitude of the carrier wave is varied (change) in accordance with the modulating wave.
In AM the two side-band lie on either side of the carrier frequency called the upper side band frequency (USB) and the lower side-band frequency (LSB).
The ratio of change of amplitude of carrier wave to the amplitude of normal carrier wave is called the modulation factor and determines the strength and quality of the transmitted signal. If the carrier is over-modulated, distortion will occur during reception.
Disadvantages of Amplitude Modulation
In amplitude modulation, the sidebands contain the signal. The power in the sidebands is the only useful power. The power carrier by the side bands is only 33.3% even when there is 100% modulation. Clearly, the useful power is small. So, the amplitude modulation has low efficiency.
Different types of atmospheric and other electrical disturbance are reproduced in amplitude modulation receivers. This makes the reception noisy.
Small Operating Range
Due to small useful power the messages cannot be transmitted over large distance. So, the transmitter based on amplitude modulation has small range.
Reproduction is not of High Fidelity
For high fidelity reception, the audio frequencies from 20Hz to 20000Hz must be reproduced. This requires a bandwidth + 20000Hz. The bandwidth actually assigned for AM transmission is 20000Hz. This is done to keep the interference from adjacent broadcasting stations to a minimum. Thus, the highest modulating frequency is 10000Hz. This is not sufficient to reproduce music properly. Thus, the reproduction is not of high fidelity.
The frequency of the carrier wave is varied(change) in accordance with the modulating wave
In frequency modulation, the deviation of the carrier frequency from its average value is proportional to the instantaneous amplitude of the modulating signals. When the signal voltage is zero, the carrier frequency is unchanged.
When the signal approaches its positive peaks, the carrier frequency is increased to maximum . However, during the negative peaks of signals, the carrier frequency is reduced to minimum.
Need for Frequency Modulation
1 Various electrical machines and noises cause amplitude disturbance in the transmission of amplitude-modulated wave. This makes the reception noisy. So, there is a need for different type of modulation, which can reduce the noise factor. Frequency modulation (FM) was proposed as a means of improving the signals-to-noise ratio of a radio system.
2 Fidelity or audio quality of amplitude-modulated transmission is poor. This types of transmission is also not good for musical programmes. There is a need to eliminate amplitude-sensitive noise. This is possible if we eliminate amplitude variations. In other words, there is a need to keep the amplitude of the carrier constant.
The phase angle q of the carrier wave is varied according to the modulating wave. The common name for "phase modulation" and "frequency modulation" is "angle modulation".
The digital transmission of analog signals involves pulse modulation.
In amplitude modulation and frequency modulation, the modulation was done by sinusoidal signals. In pulse modulation, short pulses may do the modulation of a radio-frequency carrier.
Most pulse systems are based on sampling of the information signal amplitude at periodic intervals, usually about twice the maximum frequency present.
Pulse Amplitude Modulation (PAM).Pulse Position Modulation (PPM).Pulse Duration Modulation (PDM).Pulse-Code Modulation (PCM).
Wave is the displacement of energy propagating along a medium.
The wavelength is the total distance traveled by the wave in one full cycle.
The period is the amount of time it takes to complete one cycle.
The frequency is the number of cycles the wave completes in a given time, and is the inverse of the period. The frequency times the wavelength is the velocity of the wave.
The amplitude of a wave is the maximum displacement from the equilibrium position.
The velocity of a wave is only affected by the properties of the medium. It is not possible to increase the speed of a wave by increasing its wavelength.
There are three types of waves:
- Mechanical waves require a material medium to travel (air, water, ropes). These waves are divided into three different types.
Water waves and Rayleigh surface waves are an example of waves that involve a combination of both longitudinal and transverse motions.
- Transverse waves cause the medium to move perpendicular to the direction of the wave.
- Longitudinal waves cause the medium to move parallel to the direction of the wave.
- Surface waves are both transverse waves and longitudinal waves mixed in one medium.
- Electromagnetic waves do not require a medium to travel (light, radio).
- Matter waves are produced by electrons and particles.
Electromagnetic waves are formed when an electric field couples with a magnetic field.
The magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave.
The electromagnetic (EM) spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared, optical, ultraviolet, X-rays, and gamma-rays.
Radio waves.They carry signals for your radio, television and cellular phones.
Microwaves are the waves which heat our food in a microwave oven (They will cook your popcorn in just a few minutes!). They are used in remote sensing, the doppler radar used in weather forecasts.They can transmit information like telephone calls and computer data.
The cosmic microwave background radiation, which fills the entire Universe, is believed to be a clue to Big Bang's beginning.
Infrared light. Far infrared waves are thermal.Special lamps that emit thermal infrared waves are often used in fast food restaurants. Near infrared waves are the ones used by your TV's. remote control.
Snakes like rattlesnakes can detect warm blooded animals in IR.
Visible light waves.We see these waves as the colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light.
Colours of the rainbow are red, orange, yellow, green, blue, indigo, violet.
Cones in our eyes are receivers for these tiny visible light waves.
Ultraviolet (UV) light. Scientists have divided the ultraviolet into three regions: the near ultraviolet (NUV), the far ultraviolet (FUV), and the extreme ultraviolet (EUV).The UV from our sun are responsible for causing our sunburns. Most of the ultraviolet waves from the Sun are blocked from entering by various gases like Ozone. Some insects, like bumblebees, can see them.
X-rays. Your doctor uses them to look at your bones and your dentist to look at your teeth.
Gamma-rays are generated by radioactive atoms and in nuclear explosions. Gamma-rays can kill living cells, a fact which medicine uses to its advantage, using gamma-rays to kill cancerous cells.
Radio waves empectrum
|ELF|| Extremely Low Frequency|| -3kHz |
|VLF|| Very Low Frequency|| 3KHz-30KHz |
|LF|| Low Frequency|| 30KHz-300KHz |
|MF|| Medium Frequency|| 300KHz-3MHz|
|HF|| High Frequency|| 3MHz-30MHz |
|VHF|| Very High Frequency|| 30MHz-300MHz |
|UHF|| Ultra High Frequency|| 300MHz-3GHz |
|SHF|| Super High Frequency|| 3GHz-30GHz |
|EHF|| Extremely High Frecuency|| 30GHz-300GHz |
Sound consists of compression waves in some material—usually air.Sound can also be created by vibrating an object in a liquid such as water or in a solid such as iron.
Infrasound is transmitted with a frequency that is too low (less than 16 hertz) to be heard by a human. One major feature of infrasound is that it can travel great distances and go around objects smaller than its wavelength.
Elephants have been known to communicate with other elephants that are many miles away with these low frequency sounds that humans cannot hear. Earthquakes also vibrate in low frequencies with long wavelengths.
The speed of sound in air at room temperature is about 344 meters/second.
Audio frequencies are those in the range of 20 Hz to 20,000 Hz that humans can hear.
Ultrasound is sound with a frequency greater than the upper limit of human hearing.
The very simplest working telephone only contains three parts and they are all simple:
A switch to connect and disconnect the phone from the network. It connects when you lift the handset.
A speaker.A microphone Any "real" phone contains a device to block the sound of your own voice from reaching your ear. A modern telephone also includes a bell so it can ring and a touch-tone keypad and frequency generator.
The telephone network starts in your house. A pair of copper wires runs from a box at the road to a box (often called an entrance bridge) at your house. From there, the pair of wires is connected to each phone jack in your house.
Along the road runs a thick cable packed with 100 or more copper pairs. Depending on where you are located, this thick cable will run directly to the phone company's switch in your area or it will run to a box that acts as a digital concentrator.
The concentrator digitizes your voice at a sample rate of 8,000 samples per second and 8-bit resolution. It then combines your voice with dozens of others and sends them all down a single wire (usually a coax cable or a fiber-optic cable) to the phone company office. Either way, your line connects into a line card at the switch so you can hear the dial tone when you pick up your phone.
If you are calling someone connected to the same office, then the switch simply creates a loop between your phone and the phone of the person you called. If it's a long-distance call, then your voice is digitized and combined with millions of other voices on the long-distance network. Your voice normally travels over a fiber-optic line to the office of the receiving party, but it may also be transmitted by satellite or by microwave towers.
When you pick up the phone, the switch senses the completion of your loop and it plays a dial tone sound so you know that the switch and your phone are working.
You then dial the number using a touch-tone keypad. The different dialing sounds are made of pairs of tones.
If the number is busy, you hear a busy signal that is made up of two tones, with a cycle of one-half second on and one-half second off.
In order to allow more long-distance calls to be transmitted, the frequencies transmitted are limited to a bandwidth of about 3,000 hertz. All of the frequencies in your voice below 400 hertz and above 3,400 hertz are eliminated.
Cordless telephones or portable telephone
A cordless telephone is basically a combination telephone and radio transmitter/receiver. A cordless phone has two major parts: base and handset.
The base is attached to the phone jack through a standard phone wire connection. The base receives the incoming call through the phone line, converts it to an FM radio signal and then broadcasts that signal.
The handset receives the radio signal from the base, converts it to an electrical signal and sends that signal to the speaker, where it is converted into the sound you hear. When you talk, the handset broadcasts your voice through a second FM radio signal back to the base. The base receives your voice signal, converts it to an electrical signal and sends that signal through the phone line to the other party.
The base and handset operate on a frequency pair that allows you to talk and listen at the same time, called duplex frequency.
Mobile phone, mobile or cell phone, handphone with a cell phone, you can talk to anyone on the planet from just about anywhere.
Depending on the cell-phone model, you can: Store contact information. Make task or to-do lists. Keep track of appointments and set reminders. Use the built-in calculator for simple math. Send or receive e-mail .Get information (news, entertainment, stock quotes) from the Internet. Play games. Watch TV. Send text messages. Integrate other devices such as PDAs, MP3 players and GPS receivers.
The genius of the cellular system is the division of a city into small cells. This allows extensive frequency reuse across a city, so that millions of people can use cell phones simultaneously.
A cell phone is a full-duplex device. That means that you use one frequency for talking and a second, separate frequency for listening. Both people on the call can talk at once.
Cell phones operate within cells, and they can switch cells as they move around. Cells give cell phones incredible range. Someone using a cell phone can drive hundreds of miles and maintain a conversation the entire time because of the cellular approach.
The carrier chops up the city into cells. Cells are normally thought of as hexagons on a big hexagonal grid.Because cell phones and base stations use low-power transmitters, the same frequencies can be reused in non-adjacent cells.
When you first power up the phone, it listens for an SID (System Identification Code) on the control channel. The control channel is a special frequency that the phone and base station use to talk to one another about things like call setup and channel changing. If the phone cannot find any control channels to listen to, it knows it is out of range and displays a "no service" message.
When it receives the SID, the phone compares it to the SID programmed into the phone. If the SIDs match, the phone knows that the cell it is communicating with is part of its home system.
Along with the SID, the phone also transmits a registration request, and the MTSO keeps track of your phone's location in a database -- this way, the MTSO (Mobile Telephone Switching Office) knows which cell you are in when it wants to ring your phone.
The MTSO gets the call, and it tries to find you. It looks in its database to see which cell you are in.
The MTSO picks a frequency pair that your phone will use in that cell to take the call.
The MTSO communicates with your phone over the control channel to tell it which frequencies to use, and once your phone and the tower switch on those frequencies, the call is connected. Now, you are talking by two way radio to a friend.
As you move toward the edge of your cell, your cell's base station notes that your signal strength is diminishing.
Meanwhile, the base station in the cell you are moving toward sees your phone's signal strength increasing. The two base stations coordinate with each other through the MTSO , and at some point, your phone gets a signal on a control channel telling it to change frequencies. This hand off switches your phone to the new cell.
Analog Cell Phones are the firt generation (1G) of cellular technology (in 1983).
Digital cell phones are the second generation (2G) of cellular technology. 3G stands for "third generation". 3G technology is intended for the true multimedia cell phone and features increased bandwidth and transfer rates to accommodate Web-based applications and phone-based audio and video files.
If you take a basic digital cell phone apart, you find that it contains just a few individual parts:
An amazing circuit board containing the brains of the phone (microprocessor, rom and flash memory). An antenna. A liquid crystal display (LCD). A keyboard. A microphone. A speaker. A battery
This type of phone communicates directly with an artificial satellite, which in turn relays calls to a base station or another satellite phone. Their use is typically limited to people in remote areas where no mobile phone coverage exists, such as mountain climbers, mariners in the open sea, and news reporters at disaster sites.
This type of phone delivers or receives calls over internet, LAN or WAN networks using VoIP. Additionally, some cellular mobile phones include the ability to place VoIP calls over cellular high speed data networks and/or wireless internet.
Any radio setup has two parts: the transmitter and the receiver
The transmitter takes some sort of message (it could be the sound of someone's voice, pictures for a TV set, data for a radio modem or whatever), encodes it onto a sine wave and transmits it with radio waves. The receiver receives the radio waves and decodes the message from the sine wave it receives. Both the transmitter and receiver use antennas to radiate and capture the radio signal.
Your AM radio receiver needs an antenna to help it pick the transmitter's radio waves out of the air. An AM antenna is simply a wire or a metal stick that increases the amount of metal the transmitter's waves can interact with.
Your radio receiver needs a tuner. The antenna will receive thousands of sine waves. The job of a tuner is to separate one sine wave from the thousands of radio signals that the antenna receives.
Tuners work using a principle called resonance. That is, tuners resonate at, and amplify, one particular frequency and ignore all the others.
Now the radio has to extract the voice out of that sine wave. This is done with a part of the radio called a detector or demodulator. In the case of an AM radio, the detector is made with an electronic component called a diode. A diode allows current to flow through in one direction but not the other, so it clips off one side of the wave.
The radio next amplifies the clipped signal and sends it to the speakers (or a headphone). The amplifier is made of one or more transistors.
TVs in use today rely on devices known as the cathode ray tube, LCDs, plasma or OLED to display their images.
Cathode ray tube, or CRT
The "cathode" is a heated filament. The heated filament is in a vacuum created inside a glass "tube." The "ray" is a stream of electrons that naturally pour off a heated cathode into the vacuum.
Electrons are negative. The anode is positive, so it attracts the electrons pouring off the cathode. In a TV's cathode ray tube, the stream of electrons is focused by a focusing anode into a tight beam and then accelerated by an accelerating anode. This tight, high-speed beam of electrons flies through the vacuum in the tube and hits the flat screen at the other end of the tube. This screen is coated with phosphor, which glows when struck by the beam.
A color TV screen differs from a black-and-white screen in three ways:
There are three electron beams that move simultaneously across the screen. They are named the red, green and blue beams.
The screen is not coated with a single sheet of phosphor as in a black-and-white TV. Instead, the screen is coated with red, green and blue phosphors arranged in dots or stripes.
On the inside of the tube, very close to the phosphor coating, there is a thin metal screen called a shadow mask. This mask is perforated with very small holes that are aligned with the phosphor dots (or stripes) on the screen.
DTV or HDTV (high-definition TV). DTV uses MPEG-2 (Moving Pictures Experts Group 2) encoding just like the satellite systems do, but digital TV allows a variety of new, larger screen formats.
A digital TV decodes the MPEG-2 signal and displays it just like a computer monitor does, giving it incredible resolution and stability. There is also a wide range of set-top boxes that can decode the digital signal and convert it to analog to display it on a normal TV.
TFT LCD (Thin Film Transistor Liquid Crystal Display) has a sandwich-like structure with liquid crystal filled between two glass plates.
TFT Glass has as many TFTs as the number of pixels displayed, while a Color Filter Glass has color filter which Nematic liquid crystal is a translucent liquid that changes the polarity of light waves passing through it. The word “nematic” comes from the Greek word for thread, and describes the thread-like formations that can form in the liquid crystal. Nematic liquid crystal is frequently used in liquid-crystal displays (LCD) screens such as those on digital watches.
In creating an LCD screen, two polarized pieces of glass are used, one with a thin filter of nematic liquid crystal.
The glass is then hooked to two electrodes that can provide electrical charges. By running controlled charges through the glass, the nematic liquid crystal will twist and untwist, allowing only the electrically requested areas of light to go through. Screens using twisted nematic liquid crystal are common features in modern technology, used in laptops and digital clocks and watches.
A plasma TV uses small gas plasma cells that charge electric voltage in order to create light and a clear image picture. Basically, every picture element that comes from a plasma TV is a small light source in and of itself.
One of the main differences between a plasma TV and an LCD TV is LCD panels do not generate light. They either filter or decrease the light by a source of backlighting in order to
Projection TVs are available in two main configurations -- front projection and rear projection.Rear-projection systems look more like traditional televisions.
Reflective displays types include digital light processing (DLP) and liquid crystal on silicon (LCoS).
Organic light-emitting diodes (OLEDs).
An OLED is a solid-state semiconductor device. OLEDs can have either two layers or three layers of organic material; in the latter design, the third layer helps transport electrons from the cathode to the emissive layer.
An OLED consists of the following parts:
Substrate (clear plastic, glass, foil) - The substrate supports the OLED.
Anode (transparent) - The anode removes electrons (adds electron "holes") when a current flows through the device.
Organic layers - These layers are made of organic molecules or polymers.
Conducting layer - This layer is made of organic plastic molecules that transport "holes" from the anode. One conducting polymer used in OLEDs is polyaniline.
Emissive layer - This layer is made of organic plastic molecules (different ones from the conducting layer) that transport electrons from the cathode; this is where light is made. One polymer used in the emissive layer is polyfluorene.
Cathode (may or may not be transparent depending on the type of OLED) - The cathode injects electrons when a current flows through the device.
They have to convert light into electrons.
The first TV cameras used rather large tubes( iconoscope -late 1930's,orthicon-vidicon -late 1940's-,plumbicon)
a television camera pickup tube of high sensitivity in which the image is focused on a thin, transparent metal film backed with a layer of photoconductive material that is scanned with a low-velocity electron beam.
UK colour system (PAL).
Light enters via the lens on the left and is split into three paths by mirrors and semi-transparent mirrors.
The light in each path passes through a colour filter.
Red, blue and green filters are used.
The coloured images are focused on the faces of the three colour tubes which scan the images.
Each tube gives a signal out, proportional to the amount of colour.
This gives a luminance (brightness) signal.
The luminance signal is labelled Ey, and is used by black and white receivers.
The colour signals are known as Er, Eg, and Eb.
The red and blue signals are converted into two new signals called the red and blue colour difference signals. They are (Er - Ey) and (Eb - Ey).
These two signals are modulated onto a "sub carrier" at 4.43 MHz which becomes the chrominance (colour) signal.
The luminance, chrominance and sync signals are combined and are then used to amplitude modulate a carrier in the UHF band.
An associated sound signal frequency modulates a second carrier, which is 6 MHz apart from the vision carrier.
Parts of a vidicon:
Imaging lens -->glass faceplate-->photoconductive target-->grid-->grids-->cathode and heater
horizontal and vertical deflection coils and alignment coil.
They use image sensors like CCD (charge-coupled device) and CMOS (complimentary metal-oxide semiconductor). -early 1990's-
The next step is to read the value (accumulated charge) of each cell in the image. In a CCD device, the charge is actually transported across the chip and read at one corner of the array. An analog-to-digital converter turns each pixel's value into a digital value. In most CMOS devices, there are several transistors at each pixel that amplify and move the charge using more traditional wires.
TDM Time Division Multiplexing.
FDM Frequency Division Multiplexing.
Common analog modulation techniques are:
- Amplitude modulation (AM) (here the amplitude of the modulated signal is varied)
- Double-sideband modulation (DSB)
- Double-sideband modulation with unsuppressed carrier (DSB-WC)
- Double-sideband suppressed-carrier transmission (DSB-SC)
- Double-sideband reduced carrier transmission (DSB-RC)
- Single-sideband modulation (SSB, or SSB-AM)
- SSB with carrier (SSB-WC)
- SSB suppressed carrier modulation (SSB-SC)
- Vestigial sideband modulation (VSB, or VSB-AM)
- Quadrature amplitude modulation (QAM)
- Angle modulation
- Frequency modulation (FM) (here the frequency of the modulated signal is varied)
- WBFM Wide Band FM
- NBFM Narrow band FM
- Phase modulation (PM) (here the phase shift of the modulated signal is varied)
These are the most fundamental digital modulation techniques:
- Phase Shift Keying (PSK), a finite number of phases are used.
- Frequency Shift Keying (FSK), a finite number of frequencies are used.
- Amplitude Shift Keying (ASK), a finite number of amplitudes are used.
- Quadrature Amplitude Modulation(QAM), a finite number of at least two phases, and at least two amplitudes are used.
Pulse modulation methods:
- Analog-over-analog methods:
- Pulse-amplitude modulation (PAM)
- Pulse-width modulation (PWM)
- Pulse-position modulation (PPM)
- Analog-over-digital methods:
- Pulse-code modulation (PCM)
- Differential PCM (DPCM)
- Adaptive DPCM (ADPCM)
- Delta modulation (DM or ?-modulation)
- Sigma-delta modulation (??)
- Continuously variable slope delta modulation (CVSDM), also called Adaptive-delta modulation (ADM)
- Pulse-density modulation (PDM)