High performance drive circuits for integrated microLED/CMOS arrays for visible light communication (VLC)

Wireless communication is a form of communication that has been around for over hundreds of years and is the fastest growing segment of the communication industry. Today, wireless communication has become an essential part of almost everyone’s daily life, and the number of users has increased exponentially over the last decade with the introduction of the internet, mobile devices and smart phones. Radio Frequency (RF) transmission is arguably the most popular method of communication and is available worldwide. With the rapid progress in technology and the increase of number of users, the limited RF spectrum is becoming more congested which led to numerous research efforts to find an alternative that can help to alleviate the pending problem. One of the proposed solutions is Visible Light Communication (VLC), which uses visible Light Emitting Diode (LED) for data transmission. In this thesis, three integrated microLED/Complementary Metal Oxide Semiconductor (CMOS) Integrated Circuits (ICs) are presented with the main aim of increasing the data rate of transmission. The first microLED/CMOS IC presented here is the Generation V microLED/CMOS driver which represents the continuation of the earlier work in the HYPIX project, which aimed to develop a microLED/CMOS driver to optically pump an organic polymer laser. A 40x10 pixelarray of Generation V microLED/CMOS driver was thus designed, primarily for optical pumping polymer lasing purposes, but has also demonstrated the ability to perform communication transmission using an On-Off Keying (OOK) modulation scheme. The driver consumes up to 330mA current and produces approximately 12mW of optical power from a single pixel, which is about 3 times higher than its predecessor. The second microLED/CMOS IC is the microLED/CMOS Current Feedback (CCFBK) driver which was designed to facilitate Orthogonal Frequency Division Multiplexing (OFDM) modulation. OFDM is one of the modulation schemes, adopted from the RF domain, that was proposed to be implemented in VLC in order to increase the data transmission rate. To the best of the author’s knowledge, the microLED/CCFBK driver is the first CMOS driver for microLED that was designed to perform analogue modulation for VLC purposes. The driver is characterised and shows the ability to produce up to 3.5mW of optical power with a data transmission rate of up to 486Mbit/s. The microLED/CMOS Optical Feedback (COFBK) driver is the third microLED/CMOS IC presented in this thesis. The driver looks to improve on the performance of the microLED/CCFBK driver. OFDM transmission requires high linearity to ensure low Bit Error Rate (BER) transmission. However, the optical power output of an LED is not, in general, linear with the input voltage signal. The microLED/COFBK driver looks to increase the linearity of the optical power output by integrating a microLED and a photodiode in a single pixel to create a feedback loop. Once again, to the best of the author’s knowledge, the microLED/COFBK driver is the first CMOS driver for microLED which integrates both optical source and sensor in a single pixel to help linearise the optical power output for communication purposes; in this case, VLC. For a similar range of optical power, the microLED/COFBK driver shows a reduction about 5.3% in the degree of non-linearity compared to the microLED/CCFBK driver and produces lower Total Harmonic Distortion (THD). The microLED/COFBK driver showed the potential to increase the data rate by a factor of four over that of microLED/CCFBK driver. The analogue modulated microLED/CMOS ICs described here are the first-generation drivers that have demonstrated the possibilities to increase the data rate using OFDM. A number of possible design improvements have been identified which will enhance future performance and integration with the standard VLC system

Recent Advances in Yttrium Iron Garnet Films: Methodologies, Characterization, Properties, Applications, and Bibliometric Analysis for Future Research Directions

Due to recent advances in communication systems, dielectric and magnetic ceramics (ferrites) are attractive for use in devices. Spinel-type ferrites were the first material utilized in microwave devices; however, yttrium iron garnet (YIG) has low dielectric losses and is exploited in many applications. Owing to its high Faraday rotation, YIG films are utilized in magneto-optical applications. This study intends to examine the research trends and scientific research progress on highly cited papers discussing YIG films published between 2012 and 2022 using a bibliometric method. A comprehensive review of 100 scientific papers about YIG was performed from the Scopus database. The assessment of these highly cited papers was highlighted based on the following factors: publication trends and performance, limitations/research gaps, keywords, sub-fields, methodology journal evaluations, document type evaluation, issues, difficulties, solutions, and applications as well as guiding future YIG research. The majority of publications (99%) comprise experimental analysis, whereas 1% provide a based state-of-the-art overview. Ninety-one percent of articles focused on magnetization characterization. This bibliometric survey indicates that YIG film research is an expanding and developing field. The results of the data analysis can be utilized to improve the researchers’ understanding of YIG research and to encourage additional study in this area

GaN based µLED drive circuit for visible light communication (VLC) with improved linearity using on-chip optical feedback

Solid-state lighting is a rapidly developing field. Visible Light Emitting Diodes (LEDs) are becoming more efficient, have high reliability and can be incorporated into many lighting applications. LED is predicted to become the main source of general illumination due to its high energy efficiency. Such source can also modulate at high speed, thus offering a prospect of illumination and communications simultaneously. Various modulation techniques have been employed such as OOK and OFDM, where the latter has shown ability to transmit into Gb/s region. However, OFDM requires high linearity response from the driver's optical power output. In this paper, we present a drive circuit for GaN μLED which employs on-chip optical feedback technique to suppress non-linearity of the optical power output from the μLED for Visible Light Communication (VLC) with OFDM modulation

Investigating the Performance of Deep Reinforcement Learning-Based MPPT Algorithm under Partial Shading Condition

For renewable energy systems to operate as efficiently and as effectively as possible, maximum power point tracking (MPPT) controllers are essential. They make it possible to precisely and dynamically track the peak output of solar panels or wind turbines, ensuring that the system will be stable and reliable even in the face of changing environmental factors. Recently, more robust algorithms based on deep reinforcement learning (DRL) have been proposed. These DRL-based algorithms optimize the local and global maximum power point (MPP) using deep Q-learning and deep deterministic policy gradient (DDPG). In this study, MATLAB models of a DRL-based MPPT algorithm were developed, tested, and compared to simulation based on two established MPPT algorithms-the Particle Swarm Optimization (PSO), and the Perturb and Observe (P&amp;O). The simulations were conducted under various conditions, including standard test conditions (STC), and partial shading conditions (PSC). Simulation results demonstrate that at STC, both the DRL-based MPPT and PSO algorithm tracks the steady-state power at 0.02 seconds, outperforming the traditional P&amp;O technique of 0.08 seconds. However, the PSO algorithm manages to track 1.18% more power than DRL MPPT at PSC. Despite the limitations of training the DRL, it shows a promising method for addressing MPPT issues under PSC.</p

Effects of argon/nitrogen sputtering gas on the microstructural, crystallographic and piezoelectric properties of AlN thin films

The growth of highly crystalline c-plane AlN 〈002〉 is extremely difficult, entailing high temperature and ultrahigh vacuum condition. In sputtering technique, the addition of nitrogen into argon sputtering gas can significantly assist the formation of AlN 〈002〉 at low temperature. We incorporated purified nitrogen gas and observed the consistent formation of single crystal 〈002〉 AlN thin film layer sputter-deposited on Mo/Si substrate from the AlN ceramic target. Small presence of oxygen content within AlN crystal relates to the preferential growth of AlN 〈002〉. High oxygen content in AlN thin film due to the use of unpurified nitrogen and argon only sputtering gas prefers the formation of AlN 〈100〉. Different AlN crystal structure has shown distinct thin film properties and piezoelectric response. This work provides a method to control the crystal structure of the sputter-deposited AlN thin film layer, either c-plane AlN 〈002〉, a-plane AlN 〈100〉 or polycrystalline AlN