Frequency-independent, self-clocking encoding technique and apparatus

Abstract

A self-clocking encoding technique for synchronous transmission of digital signals, and apparatus therefor. In an exemplary embodiment, the encoding technique utilizes relatively positive and negative pulses of fixed, predetermined duration. For electrical pulses, the point of reference is preferably a zero baseline. At the leading edge LE.sub.i of the i.sup.th bit cell, the value of the i.sup.th bit is encoded as a positive pulse (e.g., 82A) in the case of a logical '1' or a negative pulse (e.g., 82B) in the case of a logical '0'. Further, the next subsequent (i.e., (i+l).sup.th bit has the same value, a pulse (e.g., 82D) of the opposite polarity is injected into the i.sup.th bit cell after the leading edge pulse. Thus, positive and negative pulses alternate and the information content of the encoded signal has no d.c. component; this facilitates a.c. coupling. Further, the encoding technique is bit-rate (i.e., frequency-) independent and usable over a wide range of bit transfer rates. The receiver can synchronously decode the signal if it knows the pulse width; it need not know the sender's transmission rate and indeed, bit transmission rate may even change from one bit cell to the next. For a fiber optic implementation, a non-zero baseline is used. The optical zero output level replaces the electrical negative pulse level, the half-maximum optical output level replaces the electrical zero level and the maximum optical output level replaces the electrically positive pulse.