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 adequate 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.