In this paper, we present an improvement for LED driver circuit by inserting a threshold voltage on the resistive branch of the conventional RC current-shaping circuit. The proposed method enhances the peaking and carrier sweep-out effects in the LED's active region when the electrical pulse is turned on and off, respectively, thereby the LED modulation rate can be greatly improved. A practical implementation of the transmitter using Schottky diodes to provide the threshold voltage and an off-the-shelf AlGaInP 660 nm RC-LED is reported. We demonstrate an error-free data transmission at the rate of 500 Mbit/s over 20 m step-index POF.
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