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 MHz 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 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 (20-30V), which offer the highest speed, cannot be used in the converter. In this paper, 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 previously proposed multilevel converters, thus reducing the switching losses and, consequently, increasing the efficiency. In order to experimentally validate the proposed topology, a 73W prototype with a switching frequency of 8MHz was built. The efficiency is 94% and 81.7% at peak output power and at one-tenth of peak output power, respectively.

Visible Light Communication (VLC) is a wireless communication technology that uses visible light to transmit information. The most extended implementation of a VLC transmitter employs a DC-DC power converter that biases the High-Brightness LEDs (HB-LEDs), and a Linear Power Amplifier (LPA) that reproduces the communication signal. Unfortunately, the power efficiency of LPAs is very low, thus reducing the overall system efficiency and requiring huge cooling systems to extract the heat. In this work, the use of Class D Switching-Mode Power Amplifiers (SMPAs) is explored in order to overcome that limitation. It is important to note that this SMPA is widely used for different applications, such as audio and RF power amplifiers. Therefore, there are a lot of versions of a Class D SMPA depending on the topology used for the implementation and the modulation strategy used to control the switches. Hence, this work aims to identify, adapt and explain in detail the best approach for implementing a Class D SMPA for VLC. In order to validate the proposed idea, a power-efficient VLC transmitter intended for short-range and low-speed applications was built and evaluated.

No abstract

No abstract