Buck derived converters based on gallium nitride devices for Envelope Tracking applications

Envelope tracking (ET) is a technique designed to enhance the efficiency of radio frequency power amplifiers (RF PA). It is based on providing the voltage to the RF PA with variations that mimic the shape of the envelope of the communication signal that the RF PA is processing. As the bandwidth of these signals can be around several megahertz, the switching frequency of the switching mode power supply designed for ET applications has to be very high. The good switching characteristics of Gallium Nitride devices makes them suitable for this application. This paper presents two multiphase converters to be used as envelope modulators in envelope tracking application

Reproducing single-carrier digital modulation schemes for VLC by controlling the first switching harmonic of the dc-dc power converter output voltage ripple

A DC-DC power converter based on a two-phase synchronous buck converter that reproduces single-carrier digital modulation schemes by controlling the first switching harmonic of the output voltage ripple is presented in this work. The DC-DC power converter carries out both the lighting and the transmission functionalities of Visible Light Communication (VLC) transmitters. Control of both the amplitude and the phase of sinusoidal currents injected towards High-Brightness LEDs (HB-LEDs) enables the use of efficient modulation schemes such as Quadrature Amplitude Modulation (QAM), Carrier-less Amplitude and Phase modulation (CAP), Amplitude-Shift Keying (ASK) and Phase-Shift Keying (PSK). These modulation schemes achieve higher spectral efficiency (i.e. more data can be transmitted using the same bandwidth) than previously proposed modulation schemes performed by VLC transmitters based on the use of DC-DC power converters. To the author's knowledge, the ratio between the bit rate achieved and the switching frequency of the DC-DC power converter presented in this paper is the highest that can be found in literatur

A linear assisted switching envelope amplifier for a UHF polar transmitter

Spectrally efficient wireless communication standards impose stringent linearity specifications, which would require traditional IQ transmitters to operate with back-offed and power inefficient linear RF power amplifiers (PAs). In order to overcome such a significant limitation, alternative architectures have been proposed, as those based on the envelope elimination and restoration technique. An example of the application of this technique is the polar transmitter. In this paper, a UHF polar transmitter is presented, combining switching and linear stages in the envelope amplifier as to achieve both wide bandwidth and high efficiency, when drain modulating a GaN HEMT Class E RF PA. Several tests, using EDGE, TETRA, and WCDMA standards have been performed with good results.This work was supported by the Spanish Ministries MICINN and MINECO through the FEDER cofunded Project TEC2011-29126-C03-01, Consolider Project CSD2008-00068, Consolider Project RUECSD2009-00046, and Project DPI2010-21110-C02-01

Efficient Visible Light Communication Transmitters Based on Switching-Mode dc-dc Converters

Visible light communication (VLC) based on solid-state lighting (SSL) is a promising option either to supplement or to substitute existing radio frequency (RF) wireless communication in indoor environments. VLC systems take advantage of the fast modulation of the visible light that light emitting diodes (LEDs) enable. The switching-mode dc-to-dc converter (SMCdc-dc) must be the cornerstone of the LED driver of VLC transmitters in order to incorporate the communication functionality into LED lighting, keeping high power efficiency. However, the new requirements related to the communication, especially the high bandwidth that the LED driver must achieve, converts the design of the SMCdc-dc into a very challenging task. In this work, three different methods for achieving such a high bandwidth with an SMCdc-dc are presented: increasing the order of the SMCdc-dc output filter, increasing the number of voltage inputs, and increasing the number of phases. These three strategies are combinable and the optimum design depends on the particular VLC application, which determines the requirements of the VLC transmitter. As an example, an experimental VLC transmitter based on a two-phase buck converter with a fourth-order output filter will demonstrate that a bandwidth of several hundred kilohertz (kHz) can be achieved with output power levels close to 10Wand power efficiencies between 85% and 90%. In conclusion, the design strategy presented allows us to incorporate VLC into SSL, achieving high bit rates without damaging the power efficiency of LED lightin

On the Role of Power Electronics in Visible Light Communication

The continuous demand of increasing data rates provided by wireless communication systems is contributing to saturating the RF spectrum. Visible Light Communication (VLC) systems aim to alleviate this congestion by using the visible light spectrum. These systems have been proposed to make use of High-Brightness LEDs (HB-LEDs) not only for lighting, but also for transmitting information by rapidly changing the intensity of the emitted light. A critical issue is that VLC requires a fast HB-LED driver in order to reproduce the target light intensity waveforms, which can include components of several MHz. Consequently, the HB-LED drivers proposed to date are based on the use of an RF Power Amplifier (RFPA). These devices provide the required speed, but suffer from very high power losses. To overcome this drawback, different solutions based on the use of fast-response DC/DC converters are presented in this paper. Several DC/DC converters, either to be used instead of an RFPA or to help an RFPA to achieve high efficiency, are thus analysed. The proposed HB-LED drivers enable the implementation of VLC transmitters without sacrificing one of the most important advantages of HB-LED lighting, namely its high power efficienc

Design of a Two-Phase buck converter with fourth-order output filter for envelope amplifiers of limited bandwidth

The use of techniques such as envelope tracking (ET) and envelope elimination and restoration (EER) can improve the efficiency of radio frequency power amplifiers (RFPA). In both cases, high-bandwidth DC/DC converters called envelope amplifiers (EA) are used to modulate the supply voltage of the RFPA. This paper addresses the analysis and design of a modified two-phase Buck converter optimized to operate as EA. The effects of multiphase operation on the tracking capabilities are analyzed. The use of a fourth-order output filter is proposed to increase the attenuation of the harmonics generated by the PWM operation, thus allowing a reduction of the ratio between the switching frequency and the converter bandwidth. The design of the output filter is addressed considering envelope tracking accuracy and distortion caused by the side bands arising from the nonlinear modulation process. Finally, the proposed analysis and design methods are supported by simulation results, as well as demonstrated by experiments obtained using two 100-W, 10-MHz, two-phase Buck EAs capable of accurately tracking a 1.5-MHz bandwidth OFDM signal

Power-Efficient VLC Transmitter Able to Reproduce Multi-Carrier Modulation Schemes by Using the Output Voltage Ripple of the HB-LED Driver

2018 IEEE 19th Workshop on Control and Modeling for Power Electronics (COMPEL), 25-28 junio, Padua (Italia)Visible Light Communication (VLC) consists in using High-Brightness LEDs (HB-LEDs) not only for lighting, but also for transmitting information by changing the light intensity rapidly. One of the most important problems of VLC is that the HB-LED drivers that have been proposed for achieving the highest bit rates offer low power efficiency. The reason is that since these HB-LED drivers must be able to reproduce fast current waveforms, the use of Linear Power Amplifiers (LPAs) has been adopted, which damages the power efficiency of HB-LED lighting. To the author’s knowledge, there is only one approach reported in the literature that is able to reproduce the most recommended modulation schemes by using a power efficient HB-LED driver. However, since it is based on the use of pulse-width modulated dc-dc power converters, the required switching frequency is between 3 and 6 times higher than the maximum frequency of the communication signal. As a result, the approach suffers from high switching losses when the highest bandwidths are addressed. A method for reproducing the most recommended modulation schemes by modulating both the amplitude and the phase of the output voltage ripple is presented in this work. The major benefits are the high efficiency, the simplicity and the lower switching frequency required for the implementatio

Power Efficient VLC Transmitter Based on Pulse-Width Modulated DC-DC Converters and the Split of the Power

Visible Light Communication (VLC) has gained relevance during the last years. It consists in using High-Brightness LEDs (HB-LEDs) both for lighting and for transmitting information changing the light intensity rapidly. However, there are some bottlenecks that are slowing down the deployment of this technology. One of the most important problems is that the HB-LED drivers proposed for addressing high data rates in VLC achieve poor power efficiency. Since these HB-LED drivers must be able to reproduce fast current waveforms, the use of Linear Power Amplifiers (LPAs) has been adopted, which clearly damages the power efficiency of HB-LED lighting. In order to alleviate this problem, a HB-LED driver made up of two DC-DC power converters is presented in this work. One of them is responsible for performing the communication functionality by operating at high switching frequency (10 MHz), whereas the second converter fulfills the illumination functionality by ensuring a certain biasing point. The split of the power allows us to minimize the power delivered by the fast-response DC-DC power converter, which suffers from high switching losses. Thus, the overall efficiency can be maximized for each particular communication scenario and for scenarios with changing condition

Taking advantage of the sum of the light in outphasing technique for visible light communication transmitter

Visible Light Communication (VLC) takes advantage of the widespread use of the LEDs, and by modifying the driver stage, the LEDs are capable of lighting and transmitting information. One of the main drawbacks is the low power efficiency due to the modification of the LED driver stage in order to add the communication capability. Most of the research work related to VLC is towards the communication task, whereas there is a limited work about the improvement on the power efficiency. This paper proposes a high efficiency LED driver for VLC working as a transmitter based on the outphasing technique. This technique is used also in RF communications and increases the efficiency of the amplifiers. The proposed transmitter is made up of two switching-mode power amplifiers that reproduce the signals required for the outphasing technique and a DC/DC converter that biases the LEDs. The proposal exploits the light and, instead of being added electrically, the signals are added in their light form, which leads to a reduction in the complexity of the design. As experimental results, a transmitter was built of two Class E amplifiers reproducing a 16-QAM modulation, achieving a signal-generation efficiency of 78% and an overall efficiency of 92

Design of a Linear-Assisted VLC-LED Transmitter Based on Summing the Light

45th Annual Conference of the IEEE Industrial Electronics Society (IES), Lisboa, 2019A high efficiency linear-assisted Visible Light Communication (VLC) LED driver working as a transmitter is presented in this work. A linear-assisted transmitter is based on the idea of using a high efficiency but bandwidth limited circuitry which delivers most of the power and a low efficiency but fast linear amplifier (linear assistance) which corrects the distortion of the signal. The presented solution takes advantage of the light in a VLC system by summing the contribution of the linear amplifier in light instead of electrically, which leads to a electrical isolation between both stages and a reduction of the complexity comparing to the traditional approach used in Envelope Tracking (ET) and Envelope Elimination and Restoration (EER) techniques. As experimental results, the design of a linear-assisted Class E amplifier delivering a 16-PSK phase digital modulation with a 1 MHz carrier is presented. On one hand, the Class E amplifier delivers most of the power (92% of the signal power) at high efficiency (81%) and, on the other hand, the linear amplifier only delivers the error signal at lower efficiency. The efficiency of the signal circuitry is up to 75% and the efficiency of the whole system considering the signal and the LED biasing circuitry is up to 85