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This paper presents two tools for feedforward correction in transmitter chains in software-defined radio. The methods presume that the radio configuration already has a gate array and a mixer juxtaposed with one another. Programming is added in the gate array to affect preconditioning of the signals presented to in-phase and quadrature channels of a hybrid mixer so as to correct and enhance the analog RF performance of the mixer. The first of the methods comprises a realization with off-the-shelf components of feedback of the RF output of the mixer. Spectrum analysis in the gate array allows separation and cancellation of the unwanted difference-frequency sideband in the mixer's output. The second tool is a feedforward correction of imperfect performance of a hybrid mixer. The correction parameters are determined through sideband reduction via the feedback scheme in the first method. It is shown that the correction scheme performs well even for very large deviations from the ideal in the mixer parameters. As a consequence, the scheme may be used to extend the operating band of the gate-array/mixer combination to extreme bandwidths-approaching 200%.
Microwave Theory and Techniques, IEEE Transactions on (Volume:57 , Issue: 3 )
Date of Publication: March 2009