Generation of Digital Modulation for Optical Communication Using Tunable Active-R Oscillator

Abstract

This paper describes the design of an active-R biphase oscillator using a pair of matched Operational Amplifier (OA) and a few resistors. The frequency of oscillation of such oscillator is tunable by a resistor (R0). The oscillator can be readily extended to the digitally tunable version by replacing the tuner resistor with a Binary Weighted Switched Resistor Array (BWSRA). The digitally tunable oscillator can also be hooked up with microprocessor using CMOS CD 4066 switches. Generation of BFSK/BPSK wave modulations have then been considered using this oscillator. Subsequently, the BFSK/BPSK. modulations are used to excite 4N25 Optoisolator. The received BFSK/BPSK signals from the Optoisolator are in full conformity with the corresponding transmitted ones. Experimental results are included.