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Amplification | Physics | Research Starters | EBSCO Research Back Browse Subject Areas Copy URL Copy URL Amplification Amplification is the process of enhancing a signal's strength while preserving its original integrity, regardless of the type of signal, whether electrical, optical, thermal, or mechanical. The key characteristic of amplification is that both the input and output signals maintain the same form; if they differ, the process is termed transduction. Amplifiers can significantly increase signal power, requiring an active element like a transistor to achieve this gain. The gain of an amplifier, which is the output signal strength relative to the input, is a crucial factor, along with bandwidth, which indicates the frequency range an amplifier can effectively handle. Historically, the invention of the vacuum tube in 1907 marked the beginning of electronic amplification, later revolutionized by the development of the transistor in 1948. Amplification technologies are foundational in various applications, including telecommunications, audio systems, and industrial controls. They ensure the fidelity of signals, mitigating issues such as noise and distortion, which can affect performance. Overall, amplification plays a vital role in modern technology, influencing everything from everyday devices to complex systems. Authored By : Ashok, S. 1 of 3 Authored By : Ashok, S. Published In : 2022 2 of 3 Published In : 2022 Related Topics : Charges and currents ; Electrons ; Capacitors ; Inductors ; Lee de Forest ; Semiconductors ; Transistors ; Frequency ; Photon Charges and currents ; Electrons ; Capacitors ; Inductors ; Lee de Forest ; Semiconductors ; Transistors ; Frequency ; Photon 3 of 3 On This Page Full Article Full Article Amplification Type of physical science: Electromagnetism, Electrical circuits, Classical physics Field of study: Electromagnetism Amplification is the process of enhancing the power of a signal while maintaining its essential integrity against internal and external influences such as noise and distortion. A strict definition of amplification entails that the form of the signal—electrical, optical, thermal, acoustical, magnetic, mechanical, hydraulic—be the same at both the input and output. If the forms differ, the process is referred to as transduction. Overview "Amplification" refers to the process of enhancing the strength of any physical quantity, such as the tiny voltage generated by a microphone, or the small control current that ignites the engines of a propulsion system, or the feeble light of a twinkling star as it hits the human eye. What is being amplified is an input signal, the amplified version of which then constitutes an output signal. When the physical system carrying out the amplification process involves input and output signals that are in the same form, such as current , voltage, displacement, or light, the system is said to be an "amplifier." If the signals differ—for example, the input may be the current flowing through a loudspeaker, while the output is sound—then the system is referred to as a "transducer." A transducer at the source or signal-generation end serves as a "sensor," while the output transducer is called an "actuator." In between the sensor and the actuator, most physical systems incorporate an amplifier to magnify the signal. This demarcation between an amplifier and a transducer also helps one specify for an amplifier a dimensionless "gain" or "amplification factor," which is defined as the ratio of output-signal strength to input-signal strength. Devices or systems that are distinguished as amplifiers must also cause an overall increase in signal power (energy per unit time) or energy from input to output—that is, the ratio of output power to input power, or "power gain," must be greater than unity. This stipulation is essential in defining true amplification, since it is possible to obtain a gain in one element of the signal (current or displacement) at the expense of a complementary element (voltage or force). An electrical transformer increases either the current or voltage, but not the product of the two (which represents electrical power); hence, a transformer is not an amplifier. In a similar vein, the fabled Archimedian lever that can lift the world is also not an amplifier. The excess signal power is not created by the amplifier but is simply drawn from a local energy source, or "bias," powering the amplifier. Note that the energy source need not always be external; it is now possible to integrate the elements of an electrochemical battery within a silicon-chip amplifier. Thus, a necessary but not sufficient condition of amplification is the presence of an energy source, or "pump," in the system in addition to the signals. The signal-conversion part of a system, as noted earlier, is readily handled by sensors and actuators at the input and output ends, so all that is needed is a "generic" amplifier in between to satisfy the overall system specifications. The question is, what physical entity is chosen to carry out this amplification—for example, mechanical displacement, fluid flow, light, or electrical current? The electron , the flow of which constitutes electric current, is the preeminent choice for two reasons: It has an extremely low mass, and it has a (negative) charge. The low mass means that the electron has low inertia and so will respond to extremely fast (or high-frequency) signals, while its charge implies that a simple voltage source or battery is all that is needed to act as a pump. The dominance of "electronics" in amplification essentially arises from these two facets—enormous speed and ease of control. In contrast, a "fluidic" system of amplification would entail a bulky hydraulic pump with complex sets of valves; even more important, such a system could handle only slowly varying signals. Incidentally, photons (quanta of light) can in principle operate at even higher speeds than electrons, but such photonic amplification systems lack the simplicity and versatility of electronic amplifiers. In view of the above discussion, it may be seen that a complete measure of an amplifier cannot simply be its gain, since speed is also equally important. The maximum frequency that may be handled by an amplifier without a drop in its response or gain is called the "bandwidth"; the bandwidth (measured in hertz) is on the order of the inverse of the switching (off-to-on or on-to-off) time of the signal. According to communication theory, for example, the signal bandwidth is a direct measure of the amount of information transmitted or processed. Thus, a true figure of merit for an amplifier is the "gain-bandwidth product," which then forms a basis for comparing the performance of different systems. An electrical circuit composed solely of "passive" circuit elements—resistors (which impede current flow), capacitors (which store charge), and inductors (which store magnetic field)—cannot be an amplifier, or an "active circuit," since the power gain in such a circuit will always be less than unity. Instead, an "active device" such as a transistor or the nearly extinct vacuum tube is needed to create an electronic amplifier. The ability to amplify signals is of surprisingly recent vintage; it was only in 1907 that Lee de Forest invented the vacuum triode, the first electronic amplifying device. It consisted of an evacuated tube with a heated cathode that emits electrons, an anode with a positive voltage to collect the negatively charged electrons, and a wire mesh called a "control grid" in between the two. By letting the input signal control the (retarding) voltage applied to the grid (just as a sluice gate would control water flow in a channel), a much larger anode current is controlled, thereby causing signal amplification. This seemingly simple device and its variations ushered in the electronic age, with rapid developments in radio, radar, telemetry, industrial control, avionics, and early computing. Vacuum-based electronics remained supreme for nearly six decades, despite strong limitations such as bulkiness, the need for vacuums and high-supply voltages, high operating temperatures, and low reliability. The first challenge to the vacuum tube occurred in 1948, when a group of scientists studying the newly discovered solids known as semiconductors came upon an amplifier that seemed to eliminate all the disadvantages of the vacuum device. While studying the properties of the semiconductor germanium, John Bardeen, Walter Brattain, and William Shockley, working at Bell Labs in Murray Hill, New Jersey, discovered the "transistor" effect. Their transistor is also a three-terminal device with an "emitter" (of electrons), a "base" (into which the electrons are injected by the input signal) and a "collector" (which collects most of the injected electrons). Amplification occurs in a transistor because the (electron) current is transferred from a low-resistance emitter-base input circuit to a high-resistance collector-base output circuit. (The term "transistor" is derived from "transfer resistor.") Unlike in a vacuum amplifier, in a transistor the electrons never leave the solid material; thus, transistorized devices became known as "solid-state" devices. The transistor turned out to be a revolutionary invention that won the 1956 Nobel Prize in Physics for its inventors. It was soon realized that the semiconductor silicon (apart from being abundant, as its source is common sand) had more attractive properties than germanium, and silicon became the preferred material for use in solid-state technology. An important consequence of the transistor was the miniaturization of many electronic systems, which resulted in a mushrooming of new applications—in computing and telecommunications in particular—that had previously been thought impossible. Also, the early, so-called bipolar transistor was soon eclipsed by the Metal-Oxide-Semiconductor Field Effect T