A high speed LED driver for visible light communications with drawing out remaining carriers by a CMOS inverter

Attention has been drawn to visible light communication systems that communicate by modulating light and illumination. To improve the speed, increase the bandwidth, and miniaturize the hardware of these systems, it is important to improve the transmission speed of the light-emitting diodes (LEDs) they use. However, LED transmission speed is greatly restricted by carriers that remain in junction capacity. To address this issue, we propose an LED driver with a CMOS inverter that uses a PMOS as a carrier drawing-out part. This circuit is practical because it is fabricated on a chip. Furthermore, the added carrier drawing-out part consumes hardly any extra power because it requires no additional drain current path. The driver was fabricated with a 0.18-μm CMOS process and its performance was measured in an optical data transmission experiment. Results showed that it decreases the fall time of optical waveforms from 63.0 to 12.5 ns and increases the error-free bit rate for an NRZ PRBS signal from 19.5 to 43.1 Mb/s.