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amplifier

amplifier, device that accepts a varying input signal and produces an output signal that varies in the same way as the input but has a larger amplitude. The input signal may be a current, a voltage, a mechanical motion, or any other signal; the output signal is usually of the same nature. The most common types of amplifiers are electronic and have transistors or electron tubes as their principal components. Electronic amplifiers are used in radio and television transmitters and receivers, audio and stereo systems, intercoms, and other consumer electronics devices. Amplifiers in their simplest form are built around a single transistor. In one type of single-transistor amplifier, known as a common-emitter circuit, a varying input voltage is fed to the base of the transistor, and the output appears at the transistor's collector; the ratio of the output voltage to the input voltage is called the voltage gain. For many purposes a single transistor does not provide sufficient gain, or amplification. In a cascade, or multistage, amplifier, the output of the first amplifying device (transistor) is fed as input to the second amplifying device, whose output is fed as input to the third, and so on until an adequate signal amplification has been achieved. In a device such as a radio receiver, several amplifiers boost a weak input signal until it is powerful enough to drive a speaker. Usually, multistage amplifiers are not made of discrete components, but are built as integrated circuits. Another less common group of electronic amplifiers use magnetic devices as their principal components. There are also many kinds of mechanical amplifiers, e.g., the power steering system of an automobile. See operational amplifier.

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amplifier

am·pli·fi·er / ˈampləˌfīər/ • n. an electronic device for increasing the amplitude of electrical signals, used chiefly in sound reproduction. ∎  a device of this kind combined with a loudspeaker, used to amplify electric guitars and other musical instruments.

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amplifier

amplifier. A piece of electrical equipment which ‘amplifies’, i.e. increases, the vol. of sound. Voltage-controlled amplifiers alter the vol. of the input signal. They can be used in electronic music in conjunction with voltage-controlled oscillators and filters and a kbd. to function as a monophonic mus. instr.

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amplifier

amplifier Device for changing the magnitude (size) of a signal, such as voltage or current, but not the way it varies. Amplifiers are used in radio and television transmitters and receivers, and in audio equipment. See also thermionics

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amplifier

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Amplifier

Amplifier

Amplifiers and energy

Efficiency

Cascading amplifiers

Discrete and integrated amplifiers

Resources

An amplifier is a device, usually electronic, that accepts a signal at its input end and produces a more powerful (amplified) version of that signal at its output end. Amplifiers are usually electronic but may utilize hydraulics or magnetic principles.

Amplifiers are usually used when the power of an electrical signal must for any reason be increased. Audio amplifiers can increase the microwatts developed by a microphone to over a million watts of power, as required to fill a stadium during a concert. Satellites use amplifiers to strengthen radio signals so they can be received easily when beamed back to Earth.

Long-distance telephone circuits were made possible when amplifiers magnified power that had been dissipated by the resistance of cross-country phone wires. Amplifiers were also needed to restore lost volume. Undersea telephone cables require amplifiers beneath the sea. Cable-television systems require as many as 100 sophisticated broad-band width amplifiers to serve subscribers.

Amplifiers and energy

Just as a faucet is not the source of the water it dispenses, an amplifier does not create the energy it dispenses. An amplifier draws energy from a device called a power supply, which draws electrical energy from a conventional source such as a power plant or solar cell, and essentially uses that energy to make a more powerful copy of the input signal.

For example, a battery installed in a portable cassette-tape player supplies it with all the energy that will eventually create sounds during the life of that battery. Amplifiers in the tape player make it possible for the program on a compact disc, cassette tape, or a radio signal to dispense the batterys energy at a controlled rate as needed to produce the desired sounds.

Efficiency

No amplifier can be 100% efficient. All amplifiers waste some of the energy supplied to them and introduce some distortion into the signals they process.

Cascading amplifiers

To process an extremely weak signal, an amplifier must be able to magnify data power by a factor of

KEY TERMS

Electron tube Active device based on control of electrons with electric fields.

Feedback Signal fed from output back to an amplifiers input.

Gain Measure of increase in voltage, power, or current.

Loudspeaker Device that converts electrical signals into sound.

Microwatt One-millionth of a watt.

Resistor An electric circuit component that opposes the flow of current.

millions. To achieve this, amplifier stages are frequently connected in series to multiply their gain. Each stage in a chain provides the signal for the following stage, an arrangement called a cascade. The total amplification of a cascade is equal to the product of the individual-stage gains. If each of three amplifiers in a cascade has a voltage gain of 100, the overall voltage gain will equal one million. A 10-micro volt signal processed by this cascade increases to a 10-volt signal.

Discrete and integrated amplifiers

Electronic amplifiers using separate transistors, resistors, and capacitors wired into place one by one are called discrete amplifiers. Discrete amplifiers have been all but superseded by integrated circuits (ICs) for small-signal applications. Vast numbers of transistors and many supporting components are contained on an ICs single silicon crystal chip. Circuit boards now use just a few encapsulated chips in place of the hundreds of individual components once required. An engineer or technician normally does not need to be aware of an ICs internal circuitry, further simplifying their use.

See also Electronics.

Resources

BOOKS

Wolfgang, Larry D. Understanding Basic Electronics (Publication No. 159 of the Radio Amateurs Library). Newington, CT: American Radio Relay League, 2006.

Donald Beaty

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Amplifier

Amplifier

An amplifier is a device, usually electronic, that magnifies information to a more powerful signal at the amplifier's output. Amplifiers are usually based on electronic principles but may utilize hydraulics or magnetics.

Amplifiers are used when the electrical power of a signal must be increased. Audio amplifiers can increase the microwatts developed by a microphone to more than a million watts of power required to fill a stadium during a concert. Satellites use amplifiers to strengthen television and telephone signals so they can be received easily when beamed back to Earth .

Long-distance telephone circuits were made possible when amplifiers magnified power that had been dissipated by the resistance of cross-country phone wires. Amplifiers were also needed to restore lost volume. Undersea telephone cables require amplifiers beneath the sea. Cable-television systems require as many as 100 sophisticated broad-band width amplifiers to serve subscribers.


Amplifiers and energy

Just as a faucet is not the source of the water it dispenses, an amplifier does not create the energy it controls. An amplifier draws on the power of the weak input signal and supplements it with energy provided by a power source, increasing the power of the signal.

A replacement battery installed in a portable cassette-tape player supplies it with all the energy that will eventually create sounds during the life of that battery. The battery contains no information about the music or speech the player will eventually produce. Amplifiers in the tape player make it possible for the program on a compact disc , cassette tape, or a radio signal to dispense the battery's energy at a controlled rate as needed to produce the desired sounds.


Efficiency

No amplifier can be 100% efficient. All amplifiers waste some of the energy supplied to them. For instance, an amplifier's efficiency may be improved, but the result may be increased distortion in the final output.

Cascading amplifiers

To process an extremely weak signal, an amplifier must be able to magnify data power by a factor of millions. To achieve this, amplifier stages are frequently connected in series to multiply their gain. Each stage in a chain provides the signal for the following stage, an arrangement called a cascade. The total amplification of a cascade is equal to the product of the individual-stage gains. If each of three amplifiers in cascade has a voltage gain of 100, the overall voltage gain will equal one million. A 10-micro volt signal processed by this cascade increases to a 10-volt signal.

Discrete and integrated amplifiers

Electronic amplifiers using separate transistors, resistors, and capacitors wired into place one by one are called discrete amplifiers. Discrete amplifiers have been all but superseded by integrated circuits (ICs) for small-signal


applications. Vast numbers of transistors and many supporting components are contained on an IC's single silicon crystal chip. Circuit boards now use just a few encapsulated chips in place of the hundreds of individual components once required. An engineer or technician normally does not need to be aware of an IC's internal circuitry, further simplifying their use.

See also Electronics.


Resources

books

Cannon, Don L. Understanding Solid-State Electronics. 5th ed. SAMS division of Prentice Hall Pub. Co., 1991.


Donald Beaty

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electron tube

—Active device based on control of electrons with electric fields.

Feedback

—Signal fed from output back to an am plifier's input.

Gain

—Measure of increase in voltage, power, or current.

Loudspeaker

—Device that converts electrical signals into sound.

Microwatt

—One-millionth of a watt.

Resistor

—An electric circuit component that opposes the flow of current.

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