Amplitude distortion
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Amplitude distortion is distortion occurring in a system, subsystem, or device when the output amplitude is not a linear function of the input amplitude under specified conditions.
Generally, output is a
Forms
When output is not in this portion, two forms of amplitude distortion might arise:
- harmonics of the fundamental frequency of a sine waveinput to a system.
- Intermodulation distortion: 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.
Measurement
Amplitude distortion is measured with the system operating under steady-state conditions with a sinusoidal input
See also
- Audio quality measurement
- Noise measurement
- Headroom