Generalized-and efficient techniques for the design of CMI and other encoders

The coded mark inversion (CMI) line code is becoming popular for wide-band fiber-optic systems. The advantages of the CMI include DC balance and guaranteed transition density, which simplifies timing recovery. Previous CMI encoder implementations typically relied on a mixture of digital, analog, and delay-line techniques. The encoders proposed are digital state machines that allow elegant, accurate, and efficient implementation with gate arrays or discrete logic components. A general approach is then discussed for designing state machines of the type described here. Such state machines may be used to implement other codes, such as Manchester, RZ, and BnZS codes.