مرکز منطقه ای اطلاع رساني علوم و فناوري - Pulse Shared Optical Modem with Multiple LEDs

Abstract :

In this study, a MODEM is designed to communicate optically in the free space. Multiple LEDs are used as light emitter at the transmitter and a photodiode is used as a photo detector at the receiver end. In many available applications photo detector sensitivity has been increased to increase communication distance. In this application LED’s radiant power have been increased rather than photo detector sensitivity. LEDs radiant power can be increased in pulsed high current operation. In this application it is possible to flow LED current pulses which have a few amperes amplitude. Photodiode has been used in photoconductive mode. Beside of increasing communication distance the background noise effect has been decreased by driving LEDs with pulsed high currents. The data pulse duration is very long to drive LEDs directly with them. LEDs must be driven with narrow pulses which have been produced at the suitable moments of data pulses. In the design that made here, suitable modulation (and demodulation) methods and suitable circuit techniques are used to handle high radiation power and to realize higher data communication speeds. The circuit technique based on driving different LEDs one by one with serial successive data pulses.