Identification and Measurement of Transmitter Non-Linearities

In this article the effects of non-linearities and other impairments in a direct up-conversion transmitter is investigated. By using simple non-linear models for the non-linearities at baseband and for the power amplifier, a total mathematical model of the transmitter is obtained. From the model it can be seen that both the amplitude and the phase distortion of the transmitter are dependent on both the phase and the envelope of the input signal. The parameters of the non-linear baseband and RF distortion of this model are then identified separately by studying the amplitude and phase distortion of the output signal. The method is verified by measurements and it is found that the identified parameters can be used to accurately re-generate the measured output signal in the sense that all main distortion products, i.e. larger than -60 dBc, of the re-generated signal will be within a dB of the distortion products of the measured signal.