distortion


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distortion,

in electronics, undesired change in an electric signal waveform as it passes from the input to the output of some system or device. In an audio system, distortion results in poor reproduction of recorded or transmitted sound. In passing through an electronic device, the amplitude of an input signal may be changed. For example, any voltage that is applied to an amplifier may be increased by a factor of 10. Amplitude distortion occurs when this factor is not the same for all input voltages. Frequency distortion occurs when the amplitudes of the different frequency components of an input signal are changed by a factor that is not the same for all frequencies. Phase distortion occurs when there is a phase shift between a system's output- and its input-signal components. It occurs because the time of propagation through a system can vary with frequency. Intermodulation distortion, also known as cross modulation, results from the mixing of signals in a non-linear system; the output will contain the sums and differences of the input signals' harmonics. Some kinds of distortion are subjectively more objectionable than others.

distortion

(field distortion) An aberration of a lens or mirror in which the image has a distorted shape as a result of nonuniform lateral magnification over the field of view. In barrel distortion the magnification decreases toward the edge of the field; in pincushion distortion there is greater magnification at the edge.

Distortion

 

an image defect in optical systems that causes the disruption of the geometric similarity between the object and its image; one of the aberrations of optical systems. Distortion arises as a result of the fact that the linear magnification of various parts of the image is different. A characteristic example of the distortions generated by the system involving distortion is the image of a square shown in Figure 1. A pincushion, or positive, distortion is shown on the left; a barrel, or negative, distortion is shown on the right. Distortion does not affect the sharpness of the image. The distortion of an optical system is quantitatively characterized by the so-called relative distortion v = (β/β0) - 1, where β0 is the linear magnification of the ideal system without distortion and β is the actual magnification. The relative distortion is expressed in percent.

Figure 1

Distortion is particularly undesirable in photographic lenses used in geodesy or photogrammetry. The quantity v is about 0.5 percent in good photographic lenses. Distortion is –0.01 percent in lenses used for aerial photography. In some cases (symmetrical photographic lenses or telescopes), distortion may be eliminated.

distortion

[di′stȯr·shən]
(electronics)
Any undesired change in the waveform of an electric signal passing through a circuit or other transmission medium.
(engineering)
In general, the extent to which a system fails to accurately reproduce the characteristics of an input signal at its output.
(engineering acoustics)
Any undesired change in the waveform of a sound wave.
(optics)
A type of aberration in which there is variation in magnification with the distance from the axis of an optical system, so that images are not geometrically similar to their objects.

Distortion (electronic circuits)

The behavior of an electrical device or communications system whose output is not identical in form to the input signal. In a distortionless communications system, freedom from distortion implies that the output must be proportional to a delayed version of the input, requiring a constant-amplitude response and a phase characteristic that is a linear function of frequency.

In practice, all electrical systems will produce some degree of distortion. The art of design is to see that such distortion is maintained within acceptable bounds, while the signal is otherwise modified in the desired fashion. In general, distortion can be grouped into four forms: amplitude (nonlinear), frequency, phase, and cross modulation.

Amplitude distortion

All electronic systems are inherently nonlinear unless the input signal is maintained at an incrementally small level. Once the signal level is increased, the effects of device nonlinearities become apparent as distorted output waveforms. Such distortion reduces the output voltage capability of operational amplifiers and limits the power available from power amplifiers. Amplitude distortion may be reduced in amplifier stages by the application of negative feedback. See Amplifier, Feedback circuit, Operational amplifier

Frequency distortion

No practical device or system is capable of providing constant gain over an infinite frequency band. Hence, any nonsinusoidal input signal will encounter distortion since its various sinusoidal components will undergo unequal degrees of amplification. The effects of such distortion can be minimized by designing transmission systems with a limited region of constant gain. Thus, in high-fidelity systems, the amplifier response is made wide enough to capture all the harmonic components to which the human ear is sensitive.

Phase distortion

Since the time of propagation through a system varies with frequency, the output may differ in form from the input signal, even though the same frequency components exist. This can easily be demonstrated by noting the difference between the addition of two in-phase sine waves and two whose phase relationship differs by several degrees. In digital systems, such changes can be significant enough to cause timing problems. Hence, the phase-frequency response must be made linear to obtain distortionless transmission. See Equalizer

Cross modulation

Sometimes referred to as intermodulation, this occurs because of the nonlinear nature of device characteristics. Thus, if two or more sinusoidal inputs are applied to a transistor, the output will contain not only the fundamentals but also signal harmonics, sums and differences of harmonics, and various sum or difference components of fundamental and harmonic components. While these effects are generally undesirable, they may be utilized to advantage in amplitude modulation and diode detection (demodulation). See Amplitude-modulation detector, Amplitude modulator

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