Abstract
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.
© 2013 IEEE
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