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Amplitude, Frequency and Phase Distortion

  • Signal distortion can be of three types. They are Amplitude, Frequency and Phase Distortion

    1. Amplitude distortion.

    Amplitude distortion is due to the nonlinearity of the devices used in the system. The wave shape changes resulting in the generation of harmonics. Hence amplitude distortion is also sometimes referred as the harmonic distortion.

    2. Frequency distortion.

    Frequency distortion is one in which the gain of the system vanes with frequency of the applied input voltage. This is primarily caused by the presence of reactive elements m the system.

    3. Phase distortion.

    Phase distortion is the phase shift between the output and input of the system. It is related to the time of transmission through the amplifier in accordance with the relation:

    Phase shift (lag) in radians = ωγ + nπ

    where γ is called the time delay in seconds and ω is 2π times the frequency, and n is an integer which will be odd if the system has an inherent tendency to reverse the phase of all components of the applied voltage. It will be even if there is no tendency for phase reversal. It is to be noted here that the phase shift of 180° given by an amplifier is not termed as distortion as any signal undergoes this inversion.

    Harmonic distortion present in the output of an audio generator can be measured, using distortion factor meter. It measures the R.M.S. harmonic distortion, represented by a ratio of the amplitude of the harmonic to that of the fundamental frequency, expressed as a percentage. Then harmonic distortion is represented as :

    D2 = B2/B1, D3 = B3/B1, D4 = B4/B1

    Where Dn (n = 2, 3, 4, ...) represents the distortion of the nth harmonic, Bn is the amplitude of the nth harmonic and B1 is the amplitude of the fundamental.

    The total harmonic distortion or distortion factor is defined as :

    D = (D22 + D32 + D42+………..)


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