Designing a high-speed light emitting diode driver circuit for visible light communications

LEDs are an essential component in visible light communication systems and need to be modulated for data transmission at the same time of lighting. The modulation speed of LEDs is limited by the remaining carriers that remain in the depletion capacitance when the LEDs turn off. This paper designs a high-speed LED driver that can remove remaining carriers, which shortens the falling time of modulation pulse, and thus improves the modulation speed. The driver is fabricated using three discrete FETs and some resistors and capacitors on a board. One FET is used to control the lighting and extinguishing of a LED and the other two FETs are used to remove remaining carriers. The performance of the driver is demonstrated by driving a blue LED and a near ultraviolet LED respectively. In experiments, the FETs on the board are triggered by a square-wave signal with the frequency of 1 MHz and the optical signals emitted from the LEDs are detected by a photoelectric detector. The experimental results show that this design decreased the falling time from 66 down to 32 ns for the blue LED as well as from 40 down to 26 ns for the near ultraviolet LED, which demonstrates the improvement of the LED modulation speed.