EVM measurements using orthogonal separation at the output of a non-linear amplifier

A method is developed to obtain the error vector magnitude (EVM) of non-linear amplifiers by mean of orthogonalising the output of the amplifier to extract its uncorrelated non-linear terms. This method allows for extraction of in-band distortion power and spectral regrowth power from the measured RF waveforms which provides invaluable insight to the EVM behaviour of the device. From a frequency domain analysis, the EVM is attributed to the in-band distortion power and spectral regrowth power where it is determined that the in-band distortion power contributes more to the EVM degradation. The amplifier used for verification is modelled from Avago's MGA83563 measured amplitude distortion (AM–AM) and phase distortion characteristics (AM–PM). Finally, the relationship between EVM and gain compression characteristic is derived from the proposed orthogonal model.