Prototyping Design of Low-Cost Bias-T Circuit Based-on Op-Amp for Visible Light Communication

Abstract

The visible light communication (VLC) exploits the LED as an antenna in which only works on “forward bias” conditions. Therefore, when the VLC has an input signal with minus voltage it will be clipped, and only the positive side is transmitted by LED. If the VLC has an analog signal input with a completely positive amplitude, the LED may exhibit flicker-effect when the input frequency is relatively low to medium. Therefore, the correct method for LED conditioning is by lumping the information signal in the DC area. The “Bias Tee” (Bias-T) is a commercial module that is most commonly applied for LED conditioning with analog input signal characteristics. Although the performance is powerful and significant for transmitting the high-frequency, the cost is relatively inexpensive. Therefore, this study proposes a low-cost Bias-T module for a low bit-rate VLC system. Instead of the Bias-T generally, that uses an inductor and capacitor, this module is built by Op-Amps circuit which consists of 1) buffer Op-Amp as DC input (VDC-OFFSET), 2) variable Pre-Amplifier as signal information input (VINF), 3) summing amplifier to combine these two signals (VINF + VDC-OFFSET) and 4) current amplifier for increasing the high-power LED with no-flicker (stable illumination). The designed Bias-T is built on a discrete component. The evaluations involved three approaches, given the input signal: 1) with a single carrier in sine form, 2) analog signal from digital signal processing (DSP) board, 3) audio signal generated from a personal computer. In summary, the Bias-T works as properly as expected.