A High-Speed LED Driver That Sweeps Out the Remaining Carriers for Visible Light Communications

The modulation speed of light-emitting diodes (LEDs) must be increased to improve the speed, increase the bandwidth, and miniaturize the hardware of visible light communication (VLC) systems. The LED modulation speed is limited by the remaining carriers that remain in the depletion capacitance. In this paper, we evaluate the increase in optical transmission rate for an LED driver for the first time by sweeping out the remaining carriers in a GaN-based LED for VLC system. The driver is fabricated using discrete GaAs FETs and passive elements on a board. An optical transmission experiment is performed. The experimental results demonstrate that the driver increases the maximum error-free bit rate for a NRZ PRBS signal from 69 to 95 Mb/s (38% increase). However, the additional current path for carrier sweep-out increases the power dissipation of the driver. To reduce the power dissipation, we employ a CMOS inverter, in which a PMOS FET sweeps out the carriers. The driver is fabricated using a 0.18-μm CMOS IC process and then implemented in a package. The experimental results demonstrate that this design increased the maximum error-free bit rate from 27.5 to 51.8 Mb/s (88% increase). The maximum bit rate for the packaged driver is 20% higher than that of the driver measured on the wafer.