Psychology Wiki

Amplifiers (apparatus)

Redirected from Amplifier

34,202pages on
this wiki
Add New Page
Talk0 Share

Ad blocker interference detected!




Psychology: Debates · Journals · Psychologists

Generally, an amplifier is any device that will use a small amount of energy to control a larger amount of energy. In popular use, the term today usually refers to an electronic amplifier, often as in audio applications. The relationship of the input to the output of an amplifier — usually expressed as a function of the input frequency — is called the transfer function of the amplifier, and the magnitude of the transfer function is termed the gain.

General characteristics of amplifiers Edit

Most amplifiers can be characterized by a number of parameters.

Gain Edit

The gain is the ratio of output power to input power, and is usually measured in decibels . (When measured in decibels it is logarithmically related to the power ratio: G(dB)=10log(Pout/Pin)).

Output dynamic range Edit

Output dynamic range is the range, usually given in dB, between the smallest and largest useful output levels. Since the lowest useful level is limited by output noise, this is quoted as the amplifier dynamic range.

Bandwidth and rise time Edit

The bandwidth (BW) of an amplifier is usually defined as the difference between the lower and upper half power points. This is therefore also known as the −3 dB BW. Bandwidths for other response tolerances are sometimes quoted (−1 dB, −6 dB etc.).

A full-range audio amplifier will be essentially flat between twenty hertz to about twenty kilohertz (the range of normal human hearing.) In minimalist amplifier design, the amp's usable frequency response needs to extend considerably beyond this (one or more octaves either side) and typically a good minimalist amplifier will have -3 dB points < 10 and > 65 kHz. Professional touring amplifiers often have input and/or output filtering to sharply limit frequency response beyond 20-20 kHz; too much of the amplifier's potential output power would otherwise be wasted on infrasonic and ultrasonic frequencies, and the danger of AM radio interference would increase. Modern switching amplifiers need steep low pass filtering at the output to get rid of high frequency switching noise and harmonics.


Many amplifiers are ultimately slew rate limited (typically by the impedance of a drive current having to overcome capacitive effects at some point in the circuit), which may limit the full power bandwidth to frequencies well below the amplifiers frequency response when dealing with small signals.


Tr * BW = 0.35, where Tr is in seconds and BW is in Hz.

Settling time and aberrations Edit

Time taken for output to settle to within a certain percentage of the final value (say 0.1%). This is usually specified for oscilloscope vertical amplifiers and high accuracy measurement systems.

Slew rate Edit


Noise Edit

This is a measure of how much noise is introduced in the amplification process. Noise is an undesirable but inevitable product of the electronic devices and components. It is measured in either decibels or the peak output voltage produced by the amplifier when no signal is applied.

Efficiency Edit

Efficiency is a measure of how much of the input power is usefully applied to the amplifier's output. Class A amplifiers are very inefficient, in the range of 10–20% with a max efficiency of 25%. Modern Class AB amps are commonly between 35–55% efficient with a theoretical maximum of 78.5%. Commercially available Class D switching amplifiers have reported efficiencies as high as 97%. The efficiency of the amplifier limits the amount of total power output that is usefully available. Note that more efficient amplifiers run much cooler, and often do not need any fans even in multi-kilowatt designs.

Linearity Edit


Some amplifiers are designed to handle this in a controlled way which causes a reduction in gain to take place instead of excessive distortion; the result is a compression effect, which (if the amplifier is an audio amplifier) will sound much less unpleasant to the ear. For these amplifiers, the 1dB compression point is defined as the input power (or output power) where the gain is 1dB less than the small signal gain.

Linearization is an emergent field, and there are many techniques, such us feedforward, predistortion, postdistortion, EER, LINC, CALLUM, cartesian feedback, etc., in order to avoid the undesired effects of the non-linearities.

Electronic amplifiers Edit

Main article: Electronic amplifier

There are many types of electronic amplifiers for different applications.

One common type of amplifier is the electronic amplifier, commonly used in radio and television transmitters and receivers, high-fidelity ("hi-fi") stereo equipment, microcomputers and other electronic digital equipment, and guitar and other instrument amplifiers. Its critical components are active devices, such as vacuum tubes or transistors.

Electronic amplifier classes Edit

Amplifiers are commonly classified by the conduction angle (sometimes known as 'angle of flow') of the input signal through the amplifying device.

Class A
Class B
Class AB
Class C
Class D
Main article: Switching amplifier
Other classes
Power Amplifier

The term "power amplifier" is a relative term with respect to the amount of power delivered to the load and/or sourced by the supply circuit. In general a power amplifier is designated as the last amplifier in a transmission chain and is the amplifier stage that typically requires most attention to power efficiency. For these reasons, a power amplifier is typically any of the above-mentioned classes except Class A.

Vacuum tube (valve) amplifiers Edit

Main article: valve amplifier


Transistor amplifiers Edit

Main article: transistor





Operational amplifiers (op-amps) Edit

Main article: operational amplifier


Fully differential amplifiers (FDA) Edit

Main article: fully differential amplifier


Video amplifiers Edit

These deal with video signals and have bandwidths of about 5 MHz. Certain requirements for step response and overshoot are necessary in order for acceptable TV images to be presented.

Oscilloscope vertical amplifiers Edit


Distributed amplifiersEdit

Main article: Distributed Amplifier


Microwave amplifiers Edit

Travelling wave tube (TWT) amplifiersEdit

Main article: Traveling wave tube



Main article: Klystron


Musical instrument (audio) amplifiersEdit

Main article: instrument amplifier


Other amplifier types Edit

Carbon microphone Edit


Magnetic amplifier Edit

Main article: magnetic amplifier


An Amplidyne or Rototrol is a rotating machine like an electrical generator that provides amplification of electrical signals by the conversion of mechanical energy to electrical energy.

Optical amplifiers Edit

Main article: Optical amplifier

Optical amplifiers amplify light through the process of stimulated emission.

Miscellaneous types Edit



  1. Robert S. Symons (1998). Tubes: Still vital after all these years. IEEE Spectrum 35 (4): 52–63.

See also Edit




Also on Fandom

Random Wiki