Abstract: Apparatus for use in a fiber optic transmission system having a variable bit rate and a variable duty cycle. The system senses data bit transmissions of bi-phase encoded data, and provides a restored clock frequency corresponding to a clock encoded in the bi-phase data. Midbit zero data transmissions are distinguished from the transitions denoting the beginning and end of a data pulse to define the pulse duty cycle. A logic circuit transfers operation between high speed and low speed modes of operation.

Abstract: A synchronous counter operating from a fixed frequency time base senses the data rate of an incoming bit stream and provides a time base synchronized with the incoming data. Detection of the data rate is accomplished in real time without software or user intervention. A two-stage counter, clocked by a crystal oscillator, is triggered by transitions of bi-phase data pulses. The circuit automatically shifts the frequency of operation to conform to the incoming data rate and returns to the high speed mode upon the cessation of low speed data rates.

Abstract: A synchronous decoder for recovering a train of binary data encoded in a biphase format and decoding into NRZ format. Encoded data is sampled during the first half of a bit period and the second half of a bit period and stored respectively into two storage elements. The stored data is combined and applied to a third storage element at the beginning of the next bit period. The state of the third storage element is responsive to the sequentially applied combined signals in the train of data and thereby produces a pulsed output encoded in NRZ format.