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Among other goals, multilevel burst-mode radio frequency (RF) transmitters have to achieve two main objectives: high efficiency, and good transmission signal quality. Both of these goals depend, to a large extent, on the driving signal modulator, which can, for example, be a digital pulse-width modulator. However, conventional digital pulse-width modulation (PWM) contains aliasing distortion that prevents achieving satisfying transmission signal quality.In this paper, an aliasing-free digital multilevel PWM method is introduced that allows for achieving good transmission signal quality, while at the same time offering the potential of reaching a coding efficiency of 100%. The mathematical equations for aliasing-free digital PWM are extended in a way that makes them suitable for the use in multilevel burst-mode RF transmitters. It is then shown how the aliasing-free multilevel PWM method can be used to achieve 100% coding efficiency. Simulations demonstrate the performance capabilities of the proposed PWM method.

Pulse-width modulators (PWMs) are implemented in wire less transmitters to utilize highly efficient switched-mode power amplifiers (SMPAs) such as Class-D,E,F,J amplifiers. This paper gives the analytical expressions for the natural-sampling trailing-edge PWM (TE-NPWM) signals with input signals bounded by [0, 1J. Such PWM modulators can be incorporated in a polar architecture. Important relations of polar modulated PWM signals are analyzed in detail by exploiting the results of the analysis. The image problem is illustrated when a baseband PWM signal is modulated to the passband with the phase-modulated carrier. A properly designed lowpass filter can be used to reduce the image distortions, but increases the total design costs. It further introduces extra delay and has the possible drawback of reducing the overall efficiency.Based on the spectral analysis, two alternative approaches are proposed to show how the image distortions can be reduced without a lowpass filter.The performance of the presented approaches for the image reduction is demonstrated through numerical simulations.