| 摘要 |
PURPOSE:To prevent the deterioration in the quality of transmission of a low- order group signal, by spreading at random a low frequency jitter with stuffing generated at a staff synchronizing device at the transmission side, and suppressing it with a PLL circuit at the receiving side for eliminating jitter. CONSTITUTION:A clock (b) is extracted from an input data signal (a) at a clock extracting circuit 1 and written in a buffer memory 3. The phase of a read clock and a readout clock is compared at a phase comparator 5 via phase information (g) and (h), and when this phase difference is a predetermined value or below, the stuff request signal (g) is transmitted. The signal is inputted to a residual jitter detecting circuit 9 where whether the residual jitter is larger or smaller than the set threshold value is compared, and when larger, a control signal (p) is outputted to operate a random pulse generator 12. The final discriminating point of the presence of the stuff is switched at random at each frame within a suitable range M at a random switching device 11 of the final discriminating point with the information (q) from the random pulse generator 10, allowing to spread the residual jitter of low frequency. |
