Adapting Techniques to Improve Efficiency in Radio Frequency Power Amplifiers for Visible Light Communications

Abstract

It is well known that modern wireless communications systems need linear, wide bandwidth, efficient Radio Frequency Power Amplifiers (RFPAs). However, conventional configurations of RFPAs based on Class A, Class B, and Class AB exhibit extremely low efficiencies when they manage signals with a high Peak-to-Average Power Ratio (PAPR). Traditionally, a number of techniques have been proposed either to achieve linearity in the case of efficient Switching-Mode RFPAs or to improve the efficiency of linear RFPAs. There are two categories in the application of aforementioned techniques. First, techniques based on the use of Switching-Mode DC–DC converters with a very-fast-output response (faster than 1 µs). Second, techniques based on the interaction of several RFPAs. The current expansion of these techniques is mainly due to their application in cellphone networks, but they can also be applied in other promising wireless communications systems such as Visible Light Communication (VLC). The main contribution of this paper is to show how Envelope Tracking (ET), Envelope and Elimination (EER), Outphasing, and Doherty techniques can be helpful in developing more efficient VLC transmitters capable of reaching high bit-rates (higher than 1 Mbps) by using advance modulation schemes. Finally, two examples based on the application of the Outphasing technique and the use of a Linear-Assisted Envelope Amplifier (EA) to VLC are presented and experimentally verified.

Latest Developments in LED Drivers

“…The final two papers, [12] and [13], introduce novel solutions to a new trend in LED drivers: VLC. The need for VLC-LED drivers derives from the fact that the RF spectrum is limited and expensive.…”

“…A 120 W experimental prototype is tested, achieving bit rates of 10 kbps. Finally, [13] presents a set of solutions for VLC-LED drivers based on the adaptation of traditional solutions either to improve efficiency or linearize RF power amplifiers (RFPAs) for VLC. Experimental prototypes demonstrate that the adaptation of the outphasing technique and the linear-assisted technique, using Class-E RFPAs, is found to be very interesting in order to efficiently reproduce more complex modulation schemes (e.g., quadrature amplitude modulation, QAM, and phase-shift keying, PSK).…”

On the Use of Class D Switching-Mode Power Amplifiers in Visible Light Communication Transmitters

“…Therefore, the LPA of the VLC driver shown in Figure 1 could be replaced by a SMPA in order to alleviate the power efficiency problem. In this sense, previous works explored the use of Class E SMPAs [14], [15]. Unfortunately, that SMPA class is not able to modulate the amplitude of the communication carrier and, consequently, that approach only allows us to reproduce phase-modulated schemes.…”

“…Moreover, the Class E SMPA suffers from high voltage stresses across the switches and low slew-rates. In this sense, the use of a LPA that linearly assists the Class E SMPA was proposed to increase the slew-rate [14]. However, that LPA also damages the power efficiency and increases the complexity of the VLC driver.…”