Integrated Transceiver Design for Visible Light Communication System
LEDs, as energy-efficient solid-state lighting devices, will replace conventional incandescent and fluorescent light bulbs in the next few years, resulting in tremendous energy savings. In addition to high lighting efficiency, LED bulbs have other advantages over traditional light sources including long life expectancy, easy maintenance and environmental friendly. Uniquely, LEDs can be switched on/off at very high speed without flickering to human eyes, which means the light can be modulated to realize visible light communications (VLC) while lighting. However, almost all reported VLC systems are based on discrete PCB board electronics that are needed to drive the LEDs and process the signals. While discrete and PCB electronics based VLC systems demonstrated the feasibility and capability, the fundamental problem arise in terms of the system size, performance, reliability and costs.
This thesis proposed the first reported Manchester modulation based transceiver integrated circuit (IC) for LED-based VLC system, including voltage & current reference generation, LED-based transmitter, optical receiver, Manchester encoding & decoding circuitry, digital control and full chip ESD protection. Before the integrated solution for VLC, discrete and PCB electronics based VLC system was at first built and demonstrated. The link performance, especially the noise performance, was studied at to provide initial guideline to the next step of integrated transceiver design. However, challenges arise in all aspects of integrating various electronics on a single chip and are mostly addressed in this thesis. Super high accuracy Bandgap structure with trimming and curvature correction was proposed to provide precise voltage and current source to the whole transceiver. Chopper modulation was further introduced to reduce the Opamp offset effect and low frequency noise. For the lighting LED-based transmitter, pre-equalization was employed to boost the modulation bandwidth of LED. At the receiver side, two important optical receiver structures, including singe photodiode and imaging receiver, was discussed and compared. The principles of Manchester encoding and decoding were then investigated and designed, from the perspective of both system level and IC design level. In addition, the transceiver features I2C programming interface. Last but not the least, full chip ESD protection was designed for this transceiver implemented in 0.18ìm BCDMOS technology while field-dispensable ESD concept was proposed and verified for ultra-high speed IC implemented in 28nm CMOS technology.