A New PhaseLocked Loop Timing Recovery Method for Digital Regenerators

Timing can be extracted at low cost from a random baseband digital data signal by locking a local oscillator to the reshaped bit streac. To avoid use of a very stable oscillator, a narrowband phase-locked loop is forced to synchronize to the scrambled but otherise unrestricted data by means of an auxiliary frequency sensitive loop. The novel comparator vhich can measure the phase and frequency difference between a local oscillator and a random data signal is described. The method is simple to implement even at high frequency, synchronizes rapidly, and has excellent acquisition and jitter control performance when operated in a cascade of regenerators. A loop with an acquisition range of greater than ±20 percent of the data rate and 0.1 percent noise bandvidth has been demonstrated.