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<p class="0abstract">Visible Light Communication (VLC) as one of wireless technology must be able to offer a good capability as mobile communication system. The signal will be faded when the distance and angle of LED to photo-detector become higher at a certain distance. Other problem at VLC system is light interference noise which is caused by flicker effect from other light sources such as incandescent, fluorescent, DC-lamp (i.e. flashlight) and the sunlight. Each of lights have specific carried signal characteristics and it can influences the VLC system. In this paper we offer design of mobile VLC system based on analog domain. We use Automatic Gain Controller (AGC) circuit using commercially available IC and it will be placed at analog front-end receiver side. AGC can self-adjust its gain according to the input signal amplitude.  We also design analog filter to eliminate all interferences noise spectrum which is existed under 50 KHz. We design both circuits, analog filter and AGC in VLC receiver system with low-cost. The test data are obtained through the simulation and achieved good results in ideal condition.</p>

Analog Front-End (AFE) is a part of physical layer (PHY) at Visible Light Communications (VLC) system which has important things to transmit and receive the data. This research is a preliminary study in designing AFE transceiver which consists of LED driver and Trans-impedance Amplifier (TIA). The results are used as advanced reference design of AFE system and also to determine the modulations range (analog as well as digital). The design verification is based on data transmission which generated by signal generator. Square wave signal is used as digital modulation representative, and sinusoid signal as analog modulation representatitive. The range of VLC channels is about 50 cm with 0 o angle. The result shows that digital modulation bandwidth is about 1 KHz to 10 KHz frequency, and analog modulation bandwidth is from 200 KHz to 600 KHz. We also find a significant impact by adding 1 pF capacitor to reduce noise gain. Furthermore, color filter testing is performed to investigate the design performance. Intisari-Analog Front-End (AFE) merupakan bagian dari physical layer pada sistem Visible Light Communications (VLC) yang memiliki peran penting dalam transmisi dan menerima data. Makalah ini merupakan studi awal dalam perancangan transceiver AFE yang terdiri atas driver LED dan Transimpedance Amplifier (TIA). Hasil pengujian dipergunakan sebagai referensi untuk mendesain AFE yang lebih kompleks dan sebagai acuan dalam penentuan range masing-masing modulasi. Verifikasi rancangan dilakukan dengan cara mentransmisikan data berupa sinyal yang dibangkitkan oleh signal generator, dengan sinyal kotak sebagai representasi dari modulasi digital dan sinyal sinus sebagai representasi modulasi sinyal analog. Jarak kanal adalah 50 cm dengan sudut elevasi 0 o. Hasil menunjukkan bahwa bandwidth modulasi digital adalah dari 1 KHz sampai dengan 10 KHz, sedangkan pada modulasi analog adalah dari 200 KHz sampai dengan 600 KHz. Hasil verifikasi lain adalah dengan menggunakan filter warna untuk mengetahui unjuk kerja rancangan serta pengaruh penambahan kapasitor untuk mengkompensasi noise gain.

VLC is a complex system with lots of challenges in its implementation. One of its problems is noise that originated from internal and external sources (sunlight, artificial light, etc). Internal noise is originated from active components of analog front-end (AFE) circuit, which will be discussed in this paper, especially on the trans-impedance amplifier (TIA) domain. The noise characteristics of AFE circuit in VLC system has been analyzed using the variety of available commercial Op Amp and different types of the photodiode (Si, Si-PIN, Si APD). The approach of this research is based on analytical calculus and simulation using MATLAB®. The results of this research show that the main factor that affecting the noise is en, the feedback resistor (Rf), and junction capacitor in the photodiode (Cj). Besides that, the design concept of multi channel TIA (8 channel) using IC Op Amp, with consideration of pin number of each Op Amp, supply needs, the initial value of Rf, converter to 8-DIP and feedback capacitor (Cf) channel, also discussed in this paper.

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