Fast dynamic response multilevel converter for voltage tracking applications

The envelope tracking technique is used to increment the efficiency of modern radiofrequency trans­mitters. It is based on supplying the linear radiofrequency power amplifier of the transmitter with a time-varying voltage that tracks the envelope of the information signal being transmitted. These systems require a converter capable of varying its output voltage very fast and a control system able to acquire the envelope reference signal and generate the adecquate control signals. This paper presents a digitally-controlled multilevel buck converter suitable to supply radiofrequency power amplifiers: it achieves high efficiency, low output voltage ripple and high tracking bandwidth. An hybrid pulse-width modulation system implemented in a FPGA generates the appropriate control pulses for the transistors, which are drived from an especial floating driver scheme. The proposed system is tested using a resistive load that simulates the amplifier behaviour, and it is demonstrated that it is able to track an arbitrary envelope signal.

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