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Harmonic content in class AB or B amplifiers

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2 years 3 months ago #561 by UnknownEditor
UnknownEditor created the topic: Harmonic content in class AB or B amplifiers
Does anyone know of a reference that describes how much harmonic content is in the output of an amplifier? For example, 2F0 and 3F0 are down by how many dBc?

Thanks

Steve

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2 years 3 months ago #563 by jkomiak
jkomiak replied the topic: Harmonic content in class AB or B amplifiers
More complicated than you think. The intrinsic non-linearity of the amplifying device is a strong factor. Also, impedance matching networks are filters. Depends on bandwidth.
Like many power amplifier questions, there are few good books with answers.

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2 years 3 months ago #565 by UnknownEditor
UnknownEditor replied the topic: Harmonic content in class AB or B amplifiers
jkomiak

Thanks for the response! Here is how I look at this in a simplistic way. If an amplifier was truly Class B, it would generate no odd harmonics, according to Fourier analysis of a half sine wave. Further, the second harmonic would be ~7.5 dB below the fundamental. The 4th harmonic would be down 21 dB, etc.

Is this a totally invalid for a real amplifier? That is the part I don't have a good feeling for. If you could recommend a book on this, that would be great.

But is it safe to assume 3F0 content is very low? Like down 30 dB?

Thanks
Steve

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2 years 3 months ago #566 by MMWENGR
MMWENGR replied the topic: Harmonic content in class AB or B amplifiers
Steve,

Steve Cripps in RF Power Amplifiers for Wireless Communications seems to believe that the Fourier transform has some validity for predicting harmonic levels vs conduction angle. In the edition I have it's on pages 46-50. For a conduction angle of 180 degrees (Class B) the 3rd and 5th harmonics are predicted to be 0. Even if the half sine wave is clipped by compression/saturation effects, the even symmetry that leads to only even harmonics being present is maintained, so the odds should still be suppressed. Anything that disturbs the even symmetry will degrade odd harmonic suppression.

David

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