M. Gadringer, W. Bösch, G. Magerl:
"Phase Dependent Distortion in Direct Conversion Transmitters";
IEEE Transactions on Microwave Theory and Techniques,
The impairments and nonlinear (NL) distortion generated by the analog quadrature modulator in a direct conversion transmitter affect the performance of a transmission system. These effects cause input signal dependent gain variations at the lowpass equivalent I/Q-modulator output. The aim of this paper is to analytically derive the relationship between the mean transmitter gain and the tone phases of single- or two-tone excitation signals. This relationship is separately evaluated for the different distortion sources in the direct conversion transmitter. It will be shown that only two-tone signals with frequencies symmetrical to CD are able to excite these phase-dependent gain variations. Additionally, the conditions for the presence of the distortion mechnisms are highlighted. Using measurements of an experimental transmitter setup, the validity of the derived results is shown. The presence of phase-dependent gain changes were also measured when applying a DC-symmetric multi-tone signal.
Erstellt aus der Publikationsdatenbank der Technischen Universitšt Wien.