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99-449: A preamplifier , also known as a preamp , is an electronic amplifier that converts a weak electrical signal into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to a power amplifier and a loudspeaker . Without this, the final signal would be noisy or distorted. They are typically used to amplify signals from analog sensors such as microphones and pickups . Because of this,

198-537: A conversation when they are too far apart to be easily heard directly. A telephone converts sound , typically and most efficiently the human voice , into electronic signals that are transmitted via cables and other communication channels to another telephone which reproduces the sound to the receiving user. The term is derived from Ancient Greek : τῆλε , romanized :  tēle , lit.   'far' and φωνή ( phōnē , voice ), together meaning distant voice . In 1876, Alexander Graham Bell

297-514: A ringer or a visual indicator, to announce an incoming telephone call. Telephone calls are initiated most commonly with a keypad or dial, affixed to the telephone, to enter a telephone number , which is the address of the call recipient's telephone in the telecommunications system, but other methods existed in the early history of the telephone. The first telephones were directly connected to each other from one customer's office or residence to another customer's location. Being impractical beyond just

396-408: A speaking tube . In the U.S., a somewhat dated slang term refers to the telephone as "the horn," as in "I couldn't get him on the horn," or "I'll be off the horn in a moment." Early telephones were technically diverse. Some used a water microphone , some had a metal diaphragm that induced current in an electromagnet wound around a permanent magnet, and some were dynamic – their diaphragm vibrated

495-451: A transformer where one winding is used to control the saturation of a magnetic core and hence alter the impedance of the other winding. They have largely fallen out of use due to development in semiconductor amplifiers but are still useful in HVDC control, and in nuclear power control circuitry due to not being affected by radioactivity. Negative resistances can be used as amplifiers, such as

594-646: A transmission line at input and output, especially RF amplifiers , do not fit into this classification approach. Rather than dealing with voltage or current individually, they ideally couple with an input or output impedance matched to the transmission line impedance, that is, match ratios of voltage to current. Many real RF amplifiers come close to this ideal. Although, for a given appropriate source and load impedance, RF amplifiers can be characterized as amplifying voltage or current, they fundamentally are amplifying power. Amplifier properties are given by parameters that include: Amplifiers are described according to

693-406: A vacuum tube or transistor . Negative feedback is a technique used in most modern amplifiers to increase bandwidth, reduce distortion, and control gain. In a negative feedback amplifier part of the output is fed back and added to the input in the opposite phase, subtracting from the input. The main effect is to reduce the overall gain of the system. However, any unwanted signals introduced by

792-690: A bipolar junction transistor can realize common base , common collector or common emitter amplification; a MOSFET can realize common gate , common source or common drain amplification. Each configuration has different characteristics. Vacuum-tube amplifiers (also known as tube amplifiers or valve amplifiers) use a vacuum tube as the active device. While semiconductor amplifiers have largely displaced valve amplifiers for low-power applications, valve amplifiers can be much more cost effective in high power applications such as radar, countermeasures equipment, and communications equipment. Many microwave amplifiers are specially designed valve amplifiers, such as

891-795: A broad spectrum of frequencies; however, they are usually not as tunable as klystrons. Klystrons are specialized linear-beam vacuum-devices, designed to provide high power, widely tunable amplification of millimetre and sub-millimetre waves. Klystrons are designed for large scale operations and despite having a narrower bandwidth than TWTAs, they have the advantage of coherently amplifying a reference signal so its output may be precisely controlled in amplitude, frequency and phase. Solid-state devices such as silicon short channel MOSFETs like double-diffused metal–oxide–semiconductor (DMOS) FETs, GaAs FETs , SiGe and GaAs heterojunction bipolar transistors /HBTs, HEMTs , IMPATT diodes , and others, are used especially at lower microwave frequencies and power levels on

990-490: A coil of wire in the field of a permanent magnet or the coil vibrated the diaphragm. The sound-powered dynamic variants survived in small numbers through the 20th century in military and maritime applications, where its ability to create its own electrical power was crucial. Most, however, used the Edison/Berliner carbon transmitter , which was much louder than the other kinds, even though it required an induction coil which

1089-422: A common battery exchange had a magneto hand-cranked generator to produce a high voltage alternating signal to ring the bells of other telephones on the line and to alert the operator. Some local farming communities that were not connected to the main networks set up barbed wire telephone lines that exploited the existing system of field fences to transmit the signal. In the 1890s a new smaller style of telephone

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1188-485: A few customers, these systems were quickly replaced by manually operated centrally located switchboards . These exchanges were soon connected together, eventually forming an automated, worldwide public switched telephone network . For greater mobility, various radio systems were developed in the mid-20th century for transmission between mobile stations on ships and in automobiles. Hand-held mobile phones were introduced for personal service starting in 1973. In later decades,

1287-408: A higher bandwidth to be achieved than could otherwise be realised even with the same gain stage elements. These nonlinear amplifiers have much higher efficiencies than linear amps, and are used where the power saving justifies the extra complexity. Class-D amplifiers are the main example of this type of amplification. A negative resistance amplifier is a type of regenerative amplifier that can use

1386-479: A home and a shop. Users who wanted the ability to speak to several different locations would need to obtain and set up three or four pairs of telephones. Western Union , already using telegraph exchanges, quickly extended the principle to its telephones in New York City and San Francisco , and Bell was not slow in appreciating the potential. Signalling began in an appropriately primitive manner. The user alerted

1485-561: A large gain, and the output performance of the system (the "closed loop performance ") is defined entirely by the components in the feedback loop. This technique is used particularly with operational amplifiers (op-amps). Non-feedback amplifiers can achieve only about 1% distortion for audio-frequency signals. With negative feedback , distortion can typically be reduced to 0.001%. Noise, even crossover distortion, can be practically eliminated. Negative feedback also compensates for changing temperatures, and degrading or nonlinear components in

1584-576: A new industry comprising many VoIP companies that offer services to consumers and businesses . The reported global VoIP market in October 2021 was $ 85.2 billion with a projection of $ 102.5 billion by 2026. IP telephony uses high-bandwidth Internet connections and specialized customer premises equipment to transmit telephone calls via the Internet, or any modern private data network. The customer equipment may be an analog telephone adapter (ATA) which translates

1683-400: A numeric keypad for dialing, and a display for caller ID . In addition, answering machine function may be built in. The cordless handset contains a rechargeable battery , which the base station recharges when the handset rests in its cradle. Muilt-handset systems generally also have additional charging stands. A cordless telephone typically requires a constant electricity supply to power

1782-591: A satellite phone is that it can be used in such regions where local terrestrial communication infrastructures, such as landline and cellular networks, are not available. Satellite phones are popular on expeditions into remote locations, hunting, fishing, maritime sector, humanitarian missions, business trips, and mining in hard-to-reach areas, where there is no reliable cellular service. Satellite telephones rarely get disrupted by natural disasters on Earth or human actions such as war, so they have proven to be dependable communication tools in emergency situations, when

1881-431: A separate enclosure, called the subscriber set. The dial switch in the base interrupted the line current by repeatedly but very briefly disconnecting the line one to ten times for each digit, and the hook switch (in the center of the circuit diagram) disconnected the line and the transmitter battery while the handset was on the cradle. In the 1930s, telephone sets were developed that combined the bell and induction coil with

1980-465: A separate piece of equipment or an electrical circuit contained within another device. Amplification is fundamental to modern electronics, and amplifiers are widely used in almost all electronic equipment. Amplifiers can be categorized in different ways. One is by the frequency of the electronic signal being amplified. For example, audio amplifiers amplify signals in the audio (sound) range of less than 20 kHz, RF amplifiers amplify frequencies in

2079-445: A signal chain (the output stage) and is the amplifier stage that requires attention to power efficiency. Efficiency considerations lead to the various classes of power amplifiers based on the biasing of the output transistors or tubes: see power amplifier classes below. Audio power amplifiers are typically used to drive loudspeakers . They will often have two output channels and deliver equal power to each. An RF power amplifier

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2178-409: A single chip thereby creating higher scales of integration (such as small-scale, medium-scale and large-scale integration ) in integrated circuits . Many amplifiers commercially available today are based on integrated circuits. For special purposes, other active elements have been used. For example, in the early days of the satellite communication , parametric amplifiers were used. The core circuit

2277-514: A wired interface, such as USB or Lightning connectors. Smartphones, being able to run apps , have vastly expanded functionality compared to previous mobile phones. Having internet access and built in cameras, smartphones have made video calling readily accessible via IP connections. Smartphones also have access to a large number of web services and web apps, giving them functionality similar to traditional computers, although smartphones are often limited by their relatively small screen size and

2376-485: Is derived from the Greek : τῆλε , tēle , "far" and φωνή, phōnē , "voice", together meaning "distant voice". Credit for the invention of the electric telephone is frequently disputed. As with other influential inventions such as radio , television , the light bulb , and the computer , several inventors pioneered experimental work on voice transmission over a wire and improved on each other's ideas. New controversies over

2475-514: Is found in radio transmitter final stages. A servo motor controller amplifies a control voltage to adjust the speed of a motor, or the position of a motorized system. An operational amplifier is an amplifier circuit which typically has very high open loop gain and differential inputs. Op amps have become very widely used as standardized "gain blocks" in circuits due to their versatility; their gain, bandwidth and other characteristics can be controlled by feedback through an external circuit. Though

2574-428: Is limited, usually to within the same building or within a short distance from the base station. Base stations include a radio transceiver which enables full-duplex, outgoing and incoming signals and speech with the handsets. The base station often includes a microphone, audio amplifier , and a loudspeaker to enable hands-free speakerphone conversations, without needing to use a handset. The base station may also have

2673-409: Is most often configured to provide amplification of a voltage applied between base and emitter, and the output signal taken between collector and emitter is inverted, relative to the input. The common collector arrangement applies the input voltage between base and collector, and to take the output voltage between emitter and collector. This causes negative feedback, and the output voltage tends to follow

2772-413: Is said to have a gain of 20 dB might have a voltage gain of 20 dB and an available power gain of much more than 20 dB (power ratio of 100)—yet actually deliver a much lower power gain if, for example, the input is from a 600 Ω microphone and the output connects to a 47  kΩ input socket for a power amplifier. In general, the power amplifier is the last 'amplifier' or actual circuit in

2871-402: Is the device that does the actual amplification. The active device can be a vacuum tube , discrete solid state component, such as a single transistor , or part of an integrated circuit , as in an op-amp . Transistor amplifiers (or solid state amplifiers) are the most common type of amplifier in use today. A transistor is used as the active element. The gain of the amplifier is determined by

2970-539: Is typically a power amplifier (power amp). The preamplifier provides voltage gain (e.g., from 10 mV to 1 V) but no significant current gain. The power amplifier provides the higher current necessary to drive loudspeakers . For these systems, some common sensors are microphones , instrument pickups , and phonographs . Preamplifiers are often integrated into the audio inputs on mixing consoles , DJ mixers , and sound cards . They can also be stand-alone devices. Electronic amplifier An amplifier can be either

3069-611: Is used to boost the signal strength to drive the cable to the main instrument without significantly degrading the signal-to-noise ratio (SNR). The noise performance of a preamplifier is critical. According to Friis's formula , when the gain of the preamplifier is high, the SNR of the final signal is determined by the SNR of the input signal and the noise figure of the preamplifier. Three basic types of preamplifiers are available: In an audio system, they are typically used to amplify signals from analog sensors to line level . The second amplifier

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3168-430: Is useful. Certain signal processing applications use exponential gain amplifiers. Amplifiers are usually designed to function well in a specific application, for example: radio and television transmitters and receivers , high-fidelity ("hi-fi") stereo equipment, microcomputers and other digital equipment, and guitar and other instrument amplifiers . Every amplifier includes at least one active device , such as

3267-475: The Class-D amplifier . In principle, an amplifier is an electrical two-port network that produces a signal at the output port that is a replica of the signal applied to the input port, but increased in magnitude. The input port can be idealized as either being a voltage input, which takes no current, with the output proportional to the voltage across the port; or a current input, with no voltage across it, in which

3366-655: The Earth instead of terrestrial cell sites , as cellphones do. Therefore, they can work in most geographic locations on the Earth's surface, as long as open sky and the line-of-sight between the phone and the satellite is provided. Depending on the architecture of a particular system, coverage may include the entire Earth or only specific regions. Satellite phones provide similar functionality to terrestrial mobile telephones; voice calling , text messaging , and low-bandwidth Internet access are supported through most systems. The advantage of

3465-603: The Internet , giving rise to the field of Internet Protocol (IP) telephony, also known as voice over Internet Protocol (VoIP). VoIP has proven to be a disruptive technology that is rapidly replacing traditional telephone network infrastructure. By January 2005, up to 10% of telephone subscribers in Japan and South Korea had switched to this digital telephone service. A January 2005 Newsweek article suggested that Internet telephony may be "the next big thing." The technology has spawned

3564-471: The bipolar junction transistor (BJT) in 1948. They were followed by the invention of the metal–oxide–semiconductor field-effect transistor (MOSFET) by Mohamed M. Atalla and Dawon Kahng at Bell Labs in 1959. Due to MOSFET scaling , the ability to scale down to increasingly small sizes, the MOSFET has since become the most widely used amplifier. The replacement of bulky electron tubes with transistors during

3663-412: The klystron , gyrotron , traveling wave tube , and crossed-field amplifier , and these microwave valves provide much greater single-device power output at microwave frequencies than solid-state devices. Vacuum tubes remain in use in some high end audio equipment, as well as in musical instrument amplifiers , due to a preference for " tube sound ". Magnetic amplifiers are devices somewhat similar to

3762-441: The radio frequency range between 20 kHz and 300 GHz, and servo amplifiers and instrumentation amplifiers may work with very low frequencies down to direct current. Amplifiers can also be categorized by their physical placement in the signal chain ; a preamplifier may precede other signal processing stages, for example, while a power amplifier is usually used after other amplifier stages to provide enough output power for

3861-514: The tunnel diode amplifier. A power amplifier is an amplifier designed primarily to increase the power available to a load . In practice, amplifier power gain depends on the source and load impedances , as well as the inherent voltage and current gain. A radio frequency (RF) amplifier design typically optimizes impedances for power transfer, while audio and instrumentation amplifier designs normally optimize input and output impedance for least loading and highest signal integrity. An amplifier that

3960-415: The 1960s and 1970s created a revolution in electronics, making possible a large class of portable electronic devices, such as the transistor radio developed in 1954. Today, use of vacuum tubes is limited to some high power applications, such as radio transmitters , as well as some musical instrument and high-end audiophile amplifiers. Beginning in the 1970s, more and more transistors were connected on

4059-491: The 1960s–1970s when transistors replaced them. Today, most amplifiers use transistors, but vacuum tubes continue to be used in some applications. The development of audio communication technology in form of the telephone , first patented in 1876, created the need to increase the amplitude of electrical signals to extend the transmission of signals over increasingly long distances. In telegraphy , this problem had been solved with intermediate devices at stations that replenished

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4158-655: The 1990s, mobile phones have gained other features which are not directly related to their primary function as telephones. These include text messaging, calendars, alarm clocks, personal schedulers, cameras, music players, games and later, internet access and smartphone functionality. Nearly all mobile phones have the ability to send text messages to other users via the SMS (Short Message Service) protocol. The multimedia messaging service (MMS) protocol enables users to send and receive multimedia content, such as photos, audio files and video files. As their functionality has increased over

4257-493: The advent of smartphones, mobile phone manufacturers have also included consumer electronics companies, such as Apple , Samsung and Xiaomi . As of 2022, most mobile phones are smartphones, being a combination of a mobile phone and a personal computing device in the same unit. Most smartphones are primarily operated using a graphical user interface and a touch screen. Many phones have a secondary voice user interface, such as Siri on Apple iPhones , which can operate many of

4356-451: The amplifier specifications and size requirements microwave amplifiers can be realised as monolithically integrated, integrated as modules or based on discrete parts or any combination of those. The maser is a non-electronic microwave amplifier. Instrument amplifiers are a range of audio power amplifiers used to increase the sound level of musical instruments, for example guitars, during performances. An amplifier's tone mainly comes from

4455-447: The amplifier, such as distortion are also fed back. Since they are not part of the original input, they are added to the input in opposite phase, subtracting them from the input. In this way, negative feedback also reduces nonlinearity, distortion and other errors introduced by the amplifier. Large amounts of negative feedback can reduce errors to the point that the response of the amplifier itself becomes almost irrelevant as long as it has

4554-451: The analog cellular system evolved into digital networks with greater capability and lower cost. Convergence in communication services has provided a broad spectrum of capabilities in cell phones, including mobile computing, giving rise to the smartphone , the dominant type of telephone in the world today. Before the development of the electric telephone, the term telephone was applied to other inventions, and not all early researchers of

4653-401: The assistance of a telephone operator. What turned out to be the most popular and longest-lasting physical style of telephone was introduced in the early 20th century, including Bell's 202-type desk set. A carbon granule transmitter and electromagnetic receiver were united in a single molded plastic handle, which when not in use was secured in a cradle in the base unit. The circuit diagram of

4752-526: The base station and charger units by means of a DC transformer which plugs into a wall AC power outlet. A mobile phone or cellphone or hand phone is a handheld telephone which connects via radio transmissions to a cellular telephone network . The cellular network consists of a network of ground based transmitter/receiver stations with antennas – which are usually located on towers or on buildings – and infrastructure connecting to land-based telephone lines. Analog cellular networks first appeared in 1979, with

4851-404: The bell, induction coil, battery and magneto were in a separate bell box or " ringer box ". In phones connected to common battery exchanges, the ringer box was installed under a desk, or other out-of-the-way place, since it did not need a battery or magneto. Cradle designs were also used at this time, having a handle with the receiver and transmitter attached, now called a handset , separate from

4950-409: The capacity, quality, and cost of the network. Integrated Services Digital Network (ISDN) was launched in the 1980's, providing businesses and consumers with access to digital telephony services such as data, voice, video , and fax services. The development of digital data communications methods made it possible to digitize voice and transmit it as real-time data across computer networks and

5049-669: The components in the feedback loop. Negative feedback can be applied at each stage of an amplifier to stabilize the operating point of active devices against minor changes in power-supply voltage or device characteristics. Some feedback, positive or negative, is unavoidable and often undesirable—introduced, for example, by parasitic elements , such as inherent capacitance between input and output of devices such as transistors, and capacitive coupling of external wiring. Excessive frequency-dependent positive feedback can produce parasitic oscillation and turn an amplifier into an oscillator . All amplifiers include some form of active device: this

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5148-470: The cradle base that housed the magneto crank and other parts. They were larger than the "candlestick" and more popular. Disadvantages of single-wire operation such as crosstalk and hum from nearby AC power wires had already led to the use of twisted pairs and, for long-distance telephones, four-wire circuits . Users at the beginning of the 20th century did not place long-distance calls from their own telephones but made an appointment and were connected with

5247-525: The desk set, obviating a separate ringer box. The rotary dial becoming commonplace in the 1930s in many areas enabled customer-dialed service, but some magneto systems remained even into the 1960s. After World War II, the telephone networks saw rapid expansion and more efficient telephone sets, such as the model 500 telephone in the United States, were developed that permitted larger local networks centered around central offices. A breakthrough new technology

5346-420: The device's functions, as well as enabling users to use spoken commands to interact with the internet. Typically alphanumeric text input is accomplished via an on-screen virtual keyboard, although some smartphones have a small physical keyboard. Smartphones offer the ability to access internet data through the cellular network and via wi-fi, and usually allow direct connectivity to other devices via Bluetooth or

5445-407: The dissipated energy by operating a signal recorder and transmitter back-to-back, forming a relay , so that a local energy source at each intermediate station powered the next leg of transmission. For duplex transmission, i.e. sending and receiving in both directions, bi-directional relay repeaters were developed starting with the work of C. F. Varley for telegraphic transmission. Duplex transmission

5544-409: The distortion levels to be greatly reduced, at the cost of lower gain. Other advances in the theory of amplification were made by Harry Nyquist and Hendrik Wade Bode . The vacuum tube was virtually the only amplifying device, other than specialized power devices such as the magnetic amplifier and amplidyne , for 40 years. Power control circuitry used magnetic amplifiers until the latter half of

5643-402: The earliest Strowger switch automatic exchanges had seven wires, one for the knife switch , one for each telegraph key , one for the bell, one for the push-button and two for speaking. Large wall telephones in the early 20th century usually incorporated the bell, and separate bell boxes for desk phones dwindled away in the middle of the century. Rural and other telephones that were not on

5742-457: The electrical device used the term. Perhaps the earliest use of the word for a communications system was the telephon created by Gottfried Huth in 1796. Huth proposed an alternative to the optical telegraph of Claude Chappe in which the operators in the signaling towers would shout to each other by means of what he called "speaking tubes", but would now be called giant megaphones . A communication device for sailing vessels, called telephone ,

5841-449: The feedback between the transistor's source and gate to transform a capacitive impedance on the transistor's source to a negative resistance on its gate. Compared to other types of amplifiers, a negative resistance amplifier will require only a tiny amount of power to achieve very high gain, maintaining a good noise figure at the same time. Video amplifiers are designed to process video signals and have varying bandwidths depending on whether

5940-475: The final use of the signal. The first practical electrical device which could amplify was the triode vacuum tube , invented in 1906 by Lee De Forest , which led to the first amplifiers around 1912. Today most amplifiers use transistors . The first practical prominent device that could amplify was the triode vacuum tube , invented in 1906 by Lee De Forest , which led to the first amplifiers around 1912. Vacuum tubes were used in almost all amplifiers until

6039-525: The first computers . For 50 years virtually all consumer electronic devices used vacuum tubes. Early tube amplifiers often had positive feedback ( regeneration ), which could increase gain but also make the amplifier unstable and prone to oscillation. Much of the mathematical theory of amplifiers was developed at Bell Telephone Laboratories during the 1920s to 1940s. Distortion levels in early amplifiers were high, usually around 5%, until 1934, when Harold Black developed negative feedback ; this allowed

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6138-715: The first amplifiers around 1912. Since the only previous device which was widely used to strengthen a signal was the relay used in telegraph systems, the amplifying vacuum tube was first called an electron relay . The terms amplifier and amplification , derived from the Latin amplificare , ( to enlarge or expand ), were first used for this new capability around 1915 when triodes became widespread. The amplifying vacuum tube revolutionized electrical technology. It made possible long-distance telephone lines, public address systems , radio broadcasting , talking motion pictures , practical audio recording , radar , television , and

6237-524: The first digital cellular networks appearing in the early 1990s. Mobile phones require a SIM card to be inserted into the phone. The SIM card is a small PVC card containing a small integrated circuit which stores the user's international mobile subscriber identity (IMSI) number and its related key, which are used to identify and authenticate subscribers to the cellular network. Mobile phones generally incorporate an LCD or OLED display, with some types, such as smartphones, having touch screens. Since

6336-469: The four types of dependent source used in linear analysis, as shown in the figure, namely: Each type of amplifier in its ideal form has an ideal input and output resistance that is the same as that of the corresponding dependent source: In real amplifiers the ideal impedances are not possible to achieve, but these ideal elements can be used to construct equivalent circuits of real amplifiers by adding impedances (resistance, capacitance and inductance) to

6435-446: The gain stage, but any change or nonlinearity in the components in the feedback loop will affect the output. Indeed, the ability of the feedback loop to define the output is used to make active filter circuits . Another advantage of negative feedback is that it extends the bandwidth of the amplifier. The concept of feedback is used in operational amplifiers to precisely define gain, bandwidth, and other parameters entirely based on

6534-427: The input and output. For any particular circuit, a small-signal analysis is often used to find the actual impedance. A small-signal AC test current I x is applied to the input or output node, all external sources are set to AC zero, and the corresponding alternating voltage V x across the test current source determines the impedance seen at that node as R = V x / I x . Amplifiers designed to attach to

6633-447: The input voltage. This arrangement is also used as the input presents a high impedance and does not load the signal source, though the voltage amplification is less than one. The common-collector circuit is, therefore, better known as an emitter follower, source follower, or cathode follower. Telephone A telephone , colloquially referred to as a phone , is a telecommunications device that permits two or more users to conduct

6732-518: The issue still arise from time to time. Charles Bourseul , Antonio Meucci , Johann Philipp Reis , Alexander Graham Bell , and Elisha Gray , amongst others, have all been credited with the invention of the telephone. Alexander Graham Bell was the first to be awarded a patent for the electric telephone by the United States Patent and Trademark Office (USPTO) in March 1876. Before Bell's patent,

6831-412: The model 202 shows the direct connection of the transmitter to the line, while the receiver was inductively coupled. In local battery configurations, when the local loop was too long to provide sufficient current from the exchange, the transmitter was powered by a local battery and inductively coupled, while the receiver was included in the local loop. The coupling transformer and the ringer were mounted in

6930-554: The order and amount in which it applies EQ and distortion. One set of classifications for amplifiers is based on which device terminal is common to both the input and the output circuit. In the case of bipolar junction transistors , the three classes are common emitter, common base, and common collector. For field-effect transistors , the corresponding configurations are common source, common gate, and common drain; for vacuum tubes , common cathode, common grid, and common plate. The common emitter (or common source, common cathode, etc.)

7029-508: The order of watts specifically in applications like portable RF terminals/ cell phones and access points where size and efficiency are the drivers. New materials like gallium nitride ( GaN ) or GaN on silicon or on silicon carbide /SiC are emerging in HEMT transistors and applications where improved efficiency, wide bandwidth, operation roughly from few to few tens of GHz with output power of few watts to few hundred of watts are needed. Depending on

7128-468: The other end, or the exchange operator , by whistling into the transmitter. Exchange operation soon resulted in telephones being equipped with a bell in a ringer box , first operated over a second wire, and later over the same wire, but with a condenser ( capacitor ) in series with the bell coil to allow the AC ringer signal through while still blocking DC (keeping the phone " on hook "). Telephones connected to

7227-447: The output is proportional to the current through the port. The output port can be idealized as being either a dependent voltage source , with zero source resistance and its output voltage dependent on the input; or a dependent current source , with infinite source resistance and the output current dependent on the input. Combinations of these choices lead to four types of ideal amplifiers. In idealized form they are represented by each of

7326-414: The outputs of which are summed by the same transmission line. The transmission line is a balanced type with the input at one end and on one side only of the balanced transmission line and the output at the opposite end is also the opposite side of the balanced transmission line. The gain of each stage adds linearly to the output rather than multiplies one on the other as in a cascade configuration. This allows

7425-413: The preamplifier is often placed close to the sensor to reduce the effects of noise and interference . An ideal preamp will be linear (have a constant gain through its operating range), have high input impedance (requiring only a minimal amount of current to sense the input signal) and a low output impedance (when current is drawn from the output there is minimal change in the output voltage). It

7524-571: The properties of the transistor itself as well as the circuit it is contained within. Common active devices in transistor amplifiers include bipolar junction transistors (BJTs) and metal oxide semiconductor field-effect transistors (MOSFETs). Applications are numerous. Some common examples are audio amplifiers in a home stereo or public address system , RF high power generation for semiconductor equipment, to RF and microwave applications such as radio transmitters. Transistor-based amplification can be realized using various configurations: for example

7623-422: The properties of their inputs, their outputs, and how they relate. All amplifiers have gain, a multiplication factor that relates the magnitude of some property of the output signal to a property of the input signal. The gain may be specified as the ratio of output voltage to input voltage ( voltage gain ), output power to input power ( power gain ), or some combination of current, voltage, and power. In many cases

7722-410: The property of the output that varies is dependent on the same property of the input, making the gain unitless (though often expressed in decibels (dB)). Most amplifiers are designed to be linear. That is, they provide constant gain for any normal input level and output signal. If an amplifier's gain is not linear, the output signal can become distorted . There are, however, cases where variable gain

7821-426: The service location to the emergency services when an emergency telephone number is called. A cordless telephone or portable telephone consists of a base station unit and one or more portable cordless handsets . The base station connects to a telephone line, or provides service by voice over IP (VOIP). The handset communicates with the base station via radio frequency signals. A handset's operational range

7920-453: The signals of a conventional analog telephone; an IP Phone , a dedicated standalone device; or a computer softphone application, utilizing the microphone and headset devices of a personal computer or smartphone. While traditional analog telephones are typically powered from the central office through the telephone line, digital telephones require a local power supply. Internet-based digital service also requires special provisions to provide

8019-510: The size of their keyboards. Typically, smartphones feature such tools as cameras, media players, web browsers, email clients, interactive maps, satellite navigation and a variety of sensors, such as a compass , accelerometers and GPS receivers . In addition to voice calls, smartphone users commonly communicate using a wide variety of messaging formats, including SMS, MMS, email, and various proprietary messaging services, such as iMessage and various social media platforms. In 2002, only 10% of

8118-458: The telephone transmitted sound in a way that was similar to the telegraph. This method used vibrations and circuits to send electrical pulses, but was missing key features. Bell found that this method produced a sound through intermittent currents, but in order for the telephone to work a fluctuating current reproduced sounds the best. The fluctuating currents became the basis for the working telephone, creating Bell's patent. That first patent by Bell

8217-418: The term today commonly applies to integrated circuits, the original operational amplifier design used valves, and later designs used discrete transistor circuits. A fully differential amplifier is similar to the operational amplifier, but also has differential outputs. These are usually constructed using BJTs or FETs . These use balanced transmission lines to separate individual single stage amplifiers,

8316-448: The turn of the century it was found that negative resistance mercury lamps could amplify, and were also tried in repeaters, with little success. The development of thermionic valves which began around 1902, provided an entirely electronic method of amplifying signals. The first practical version of such devices was the Audion triode , invented in 1906 by Lee De Forest , which led to

8415-508: The twentieth century when power semiconductor devices became more economical, with higher operating speeds. The old Shreeve electroacoustic carbon repeaters were used in adjustable amplifiers in telephone subscriber sets for the hearing impaired until the transistor provided smaller and higher quality amplifiers in the 1950s. The first working transistor was a point-contact transistor invented by John Bardeen and Walter Brattain in 1947 at Bell Labs , where William Shockley later invented

8514-438: The user alternately listening and speaking (or rather, shouting) into the same hole. Sometimes the instruments were operated in pairs at each end, making conversation more convenient but also more expensive. At first, the benefits of a telephone exchange were not exploited. Instead, telephones were leased in pairs to a subscriber , who had to arrange for a telegraph contractor to construct a line between them, for example, between

8613-462: The video signal is for SDTV, EDTV, HDTV 720p or 1080i/p etc. The specification of the bandwidth itself depends on what kind of filter is used—and at which point ( −1 dB or −3 dB for example) the bandwidth is measured. Certain requirements for step response and overshoot are necessary for an acceptable TV image. Traveling wave tube amplifiers (TWTAs) are used for high power amplification at low microwave frequencies. They typically can amplify across

8712-522: The voice at a distant location. The receiver and transmitter are usually built into a handset which is held up to the ear and mouth during conversation. The transmitter converts the sound waves to electrical signals which are sent through the telecommunications system to the receiving telephone, which converts the signals into audible sound in the receiver or sometimes a loudspeaker . Telephones permit transmission in both directions simultaneously. Most telephones also contain an alerting feature, such as

8811-456: The world's population used mobile phones and by 2005 that percentage had risen to 46%. By the end of 2009, there were a total of nearly 6 billion mobile and fixed-line telephone subscribers worldwide. This included 1.26 billion fixed-line subscribers and 4.6 billion mobile subscribers. A satellite telephone, or satphone, is a type of mobile phone that connects to other phones or the telephone network by radio link through satellites orbiting

8910-517: The years, many types of mobile phone, notably smartphones, require an operating system to run. Popular mobile phone operating systems in the past have included Symbian , Palm OS , BlackBerry OS and mobile phone versions of Windows . As of 2022, the most used operating systems are Google's Android and Apple's iOS . Before the era of smartphones, mobile phones were generally manufactured by companies specializing in telecommunications equipment, such as Nokia , Motorola , and Ericsson . Since

9009-461: Was a diode whose capacitance was changed by an RF signal created locally. Under certain conditions, this RF signal provided energy that was modulated by the extremely weak satellite signal received at the earth station. Advances in digital electronics since the late 20th century provided new alternatives to the conventional linear-gain amplifiers by using digital switching to vary the pulse-shape of fixed amplitude signals, resulting in devices such as

9108-457: Was an impedance matching transformer to make it compatible with the impedance of the line. The Edison patents kept the Bell monopoly viable into the 20th century, by which time the network was more important than the instrument. Early telephones were locally powered, using either a dynamic transmitter or by the powering of a transmitter with a local battery. One of the jobs of outside plant personnel

9207-520: Was essential for telephony and the problem was not satisfactorily solved until 1904, when H. E. Shreeve of the American Telephone and Telegraph Company improved existing attempts at constructing a telephone repeater consisting of back-to-back carbon-granule transmitter and electrodynamic receiver pairs. The Shreeve repeater was first tested on a line between Boston and Amesbury, MA, and more refined devices remained in service for some time. After

9306-436: Was introduced, packaged in three parts. The transmitter stood on a stand, known as a " candlestick " for its shape. When not in use, the receiver hung on a hook with a switch in it, known as a "switchhook". Previous telephones required the user to operate a separate switch to connect either the voice or the bell. With the new kind, the user was less likely to leave the phone "off the hook". In phones connected to magneto exchanges,

9405-529: Was invented by Captain John Taylor in 1844. This instrument used four air horns to communicate with vessels in foggy weather. Johann Philipp Reis used the term in reference to his invention, commonly known as the Reis telephone , in c. 1860. His device appears to be the first device based on the conversion of sound into electrical impulses. The term telephone was adopted into the vocabulary of many languages. It

9504-492: Was the master patent of the telephone, from which other patents for electric telephone devices and features flowed. In 1876, shortly after Bell's patent application, Hungarian engineer Tivadar Puskás proposed the telephone switch, which allowed for the formation of telephone exchanges , and eventually networks. In the United Kingdom, the blower is used as a slang term for a telephone. The term came from navy slang for

9603-426: Was the first to be granted a United States patent for a device that produced clearly intelligible replication of the human voice at a second device. This instrument was further developed by many others, and became rapidly indispensable in business , government , and in households . The essential elements of a telephone are a microphone ( transmitter ) to speak into and an earphone ( receiver ) which reproduces

9702-591: Was the introduction of Touch-Tone signaling using push-button telephones by American Telephone & Telegraph Company (AT&T) in 1963. The invention of the transistor in 1947 dramatically changed the technology used in telephone systems and in the long-distance transmission networks, over the next several decades. With the development of stored program control and MOS integrated circuits for electronic switching systems , and new transmission technologies such as pulse-code modulation (PCM), telephony gradually evolved towards digital telephony , which improved

9801-423: Was to visit each telephone periodically to inspect the battery. During the 20th century, telephones powered from the telephone exchange over the same wires that carried the voice signals became common. Early telephones used a single wire for the subscriber's line, with ground return used to complete the circuit (as used in telegraphs ). The earliest dynamic telephones also had only one port opening for sound, with

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