Optimized photoelectric receiver to enhance modulation bandwidth of visible light communication system

In the visible light communication (VLC) system which combines lighting and communication functions, the 3-dB modulation bandwidth is mainly limited by the light-emitting diode (LED) suffered high-frequency response attenuation. An optimized photoelectric receiver was proposed to enhance the 3-dB modulation bandwidth. The frequency response of the photoelectric receiver was derived. Theoretical analysis predicted that a gain peak would appear in the high-frequency response of the photoelectric receiver. The value of the gain and the frequency point of the gain peak can be adjusted by selecting appropriate values of feedback resistor and capacitor. Then, the measurement platform of 3-dB modulation bandwidth for blue-LED VLC system was established. Experimental measurements demonstrated that the photoelectric receiver with proper sets of feedback resistor and capacitor can compensate the high-frequency response attenuation of a normal LED. The 3-dB modulation bandwidth obtains 56% enhancement if the photoelectric receiver was replaced from a commercial one to our optimized design. In order to further expand the 3-dB modulation bandwidth, an equalization circuit consists of two-stage transistor amplifier and an emitter-follower was introduced to suppress the low-frequency response. The 3-dB modulation bandwidth for the VLC system with our optimized photoelectric receiver can be expanded to 241 or 281 MHz, while the circuit was, respectively, arranged as pre-equalization or post-equalization.