A simple CMI encoder and a generalized approach to designing similar state machines

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