Compression point

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The compression point is used for the quantitative description of the non-linear behavior of an active element ( e.g. an amplifier ) e.g. B. in audio components or in high frequency technology . It indicates the greatest amplitude of the input signal at which the distortions caused by non-linearity do not yet exceed a specified level.

The cause of the non-linear behavior is the saturation that occurs in every amplifying component ( transistor , electron tube ) above a certain input amplitude. The designation compression point indicates that the saturation always leads to a smaller, ie "compressed" (compressed) output signal compared to the linear case.


The 1 dB compression point , often referred to as P1dB , is that value of the input amplitude at which the power of the output signal at the fundamental frequency deviates by 1 decibel from the ideal linearly extrapolated characteristic of the component

( and are linear quantities here.)

In data sheets the P1dB is given as input power in dBm . In addition to the 1 dB compression point, you can also use any other compression point, e.g. B. Define P3dB for a deviation of 3 dB.

Calculation of the amplitude

Schematic representation of the P1dB

The characteristic of a non-linear amplifier can be expressed in a Taylor series


In the 1 dB compression point, the following applies

is the amplitude at the 1 dB compression point

The following results are changed:

or logarithmic:


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See also

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