Pulsewidth Modulated Three-Level Buck Converter Based on Stacking Switch-Cells for High Power Envelope Tracking Applications

Envelope tracking is a well-known RF technique that alleviates the efficiency problem of linear power amplifiers used in wireless communication transmitters. It consists in varying the supply voltage of the amplifier, which is commonly constant, according to the envelope of the communication signal. Therefore, a switching-mode power converter with a bandwidth of several megahertz is required to perform the fast voltage changes needed for tracking the envelope properly. Another important requirement is that the converter needs to be able to achieve high efficiency not only at peak output power, but also at low output power because it operates in that power range most of the time due to the characteristics of modern communication signals. Taking into account these requirements, the design of the converter is very challenging, especially in the case of base stations, where higher power levels are reached by means of higher voltage levels. As a result, transistors with low breakdown voltages (20-30 V), which offer the highest speed, cannot be used in the converter. In this article, a novel multilevel converter able to use transistors with low breakdown voltages is proposed to alleviate that problem. Moreover, it shows a better switching behavior than the previously proposed multilevel converters, thus reducing the switching losses and, consequently, increasing the efficiency. In order to experimentally validate the proposed topology, a 73-W prototype with a switching frequency of 8 MHz was built. The efficiency is 94% and 81.7% at peak output power and at one-tenth of peak output power, respectively.