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.