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

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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.