Digital Quadrature Mixing of Lowpass Sigma-Delta Modulators for Switch-mode Power Amplifiers
Finnerty, Keith and Dooley, John and Farrell, Ronan (2011) Digital Quadrature Mixing of Lowpass Sigma-Delta Modulators for Switch-mode Power Amplifiers. In: European Conference on Circuit Theory and Design (ECCTD 2011), 29th-31st August 2011, Linkoping, Sweden.
In this paper a phase compensation technique for the digital upconversion of a quadrature signal for amplification with switch mode power amplifiers is proposed. When a digital signal generator is used to generate the complex envelope signal care must be taken to compensate for the phase skew between the two paths. If phase compensation is not implemented an image caused by up converting the complex envelope of the modulation signal is created. By compensating for phase skew between the I and Q signal paths it is possible to remove this image signal and enable the transmission of multi carrier signals. As a direct result of this technique there is a reduction in the filtering effort at the output of the power amplifier to meet spectral mask requirements.
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