Multilevel converter for Envelope Tracking in RF power amplifiers

Envelope Tracking techniques are used to increase the efficiency of modern radiofrequency transmitters. These techniques are based on varying the supply voltage of the amplifiers according to the envelope of the signal being transmitted, thus maximizing their efficiency. Converters suitable for Envelope Tracking applications must provide high tracking bandwidths, along with low output voltage ripple. This paper presents a power supply for Envelope Tracking applications based on a multilevel topology: it targets relatively low voltage systems (12-28 volt range) and medium to high power applications (> 50 W peak power). It uses several input voltages to generate a multilevel square waveform which can be easily filtered; it achieves low output voltage ripple, high tracking bandwidths, high efficiency and high output power capabilities. This paper first analyzes its steady-state behaviour; then, a design procedure is provided, along with guidelines for appropriate implementation of the proposed system. A three-level prototype was built to test the system, and its performance is shown in the experimental results section. Finally, conclusions are stated.