MANCHESTER ENCODER-DECODER FOR OPTICAL-DATA COMMUNICATION LINKS

A new encoder-decoder (CODEC) design of a Manchester coding scheme suitable for optical data communication links is presented. The design is simple and uses off-the-shelf digital electronic components and subsystems. The CODEC can be used for high data rate transmissions, typical of optical fiber systems and local area networks. The decoder is insensitive to variations in the clock rates within the range of +/- 33%, whereas the encoder, which is a simple XOR logic gate, is not affected by clock variations. During high-frequency operation (e.g., at 100 MHz), the CODEC can be operated at a wide range of frequencies (from 66.6 to 133.3 MHz) without modification to the CODEC circuitry. Furthermore, the CODEC can be made to operate at any data rate by a simple change of a single capacitor or a single resistor in the decoder circuit. The CODEC was built in the laboratory by using transistor-transistor logic integrated circuits. It was experimentally found that with this decoder the transmitted data, as well as the clock, can be recovered from the Manchester coded signal without being affected by clock variations within the designed range.