Amplitude distortion is
distortion
In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...
occurring in a
system
A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its open system (systems theory), environment, is described by its boundaries, str ...
, subsystem, or device when the output amplitude is not a linear function of the input amplitude under specified conditions.
Generally, output is a
linear
In mathematics, the term ''linear'' is used in two distinct senses for two different properties:
* linearity of a '' function'' (or '' mapping'');
* linearity of a '' polynomial''.
An example of a linear function is the function defined by f(x) ...
function of input only for a fixed portion of the transfer characteristics. In this region, I
c=βI
b where Ic is collector current and Ib is base current, following
linear
In mathematics, the term ''linear'' is used in two distinct senses for two different properties:
* linearity of a '' function'' (or '' mapping'');
* linearity of a '' polynomial''.
An example of a linear function is the function defined by f(x) ...
relation y=mx.
When output is not in this portion, two forms of amplitude distortion might arise
#
Harmonic distortion
In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...
: The creation of
harmonics
In physics, acoustics, and telecommunications, a harmonic is a sinusoidal wave with a frequency that is a positive integer multiple of the ''fundamental frequency'' of a periodic signal. The fundamental frequency is also called the ''1st harm ...
of the
fundamental frequency
The fundamental frequency, often referred to simply as the ''fundamental'' (abbreviated as 0 or 1 ), is defined as the lowest frequency of a Periodic signal, periodic waveform. In music, the fundamental is the musical pitch (music), pitch of a n ...
of a
sine wave
A sine wave, sinusoidal wave, or sinusoid (symbol: ∿) is a periodic function, periodic wave whose waveform (shape) is the trigonometric function, trigonometric sine, sine function. In mechanics, as a linear motion over time, this is ''simple ...
input to a system.
#
Intermodulation distortion
Intermodulation (IM) or intermodulation distortion (IMD) is the amplitude modulation of signals containing two or more different frequencies, caused by nonlinearities or time variance in a system. The intermodulation between frequency compo ...
: This form of distortion occurs when two sine waves of frequencies ''X'' and ''Y'' are present at the input, resulting in the creation of several other frequency components, whose frequencies include (X+Y), (X-Y), (2X-Y), (2Y-X), and generally (mX ± nY) for integer m and n. Generally the size of the unwanted output falls rapidly as m and n increase.
Due to the additional outputs, this form of distortion is definitely unwanted in audio, radio and telecommunication amplifiers, and it occurs for more than two waves as well.
In a narrowband system such as a radio communication system, unwanted outputs such as X-Y and 2X+Y will be remote from the wanted band and so be ignored by the system. In contrast, 2X-Y and 2Y-X will be close to the wanted signals. These so-called third order distortion products (third order as m+n = 3) tend to dominate the non-linear distortion of narrowband systems.
Amplitude distortion is measured with the system operating under steady-state conditions with a sinusoidal input
signal
A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology.
In ...
. When other frequencies are present, the term ''"amplitude"'' refers to that of the fundamental only.
See also
*
Audio quality measurement
Audio system measurements are used to quantify audio system performance. These measurements are made for several purposes. Designers take measurements to specify the performance of a piece of equipment. Maintenance engineers make them to ens ...
*
Noise measurement In acoustics, noise measurement can be for the purpose of measuring environmental noise or measuring noise in the workplace. Applications include monitoring of construction sites, aircraft noise, road traffic noise, entertainment venues and neighb ...
*
Headroom
References
{{Reflist
External links
Arcane Radio Trivia amplitude distortion article w/ examplesRF article with trigonometry
Electrical parameters