统计预测法与同步数字系列基群时钟同步恢复

同步数字系列 ( SDH)指针调整给支路时钟带来了幅度很大的低频抖动 ,一般的时钟同步恢复方法 (如简单的模拟或数字锁相环 )已无法将其滤除 ,为恢复 SDH中基群时钟同步 ,提出了一种新的全数字化方法——统计预测法。该方法通过对一个统计周期内欲平滑时钟与参考时钟的差异的统计 ,在下一个周期内预测出支路时钟。从该方法的原理、抖动性能的分析以及给出的计算仿真结果和实验测试结果可知 ,该方法可以有效地平滑由于指针调整和码速调整产生的很大的相位跃变 ,恢复的时钟抖动很小 ,有很好的抖动转移特性和很大的捕捉范围 ,且不需要锁相环 ,系统便于集成 ,有利于设备的小型化。

Counting forecast and regeneration of the 2.048 MHz clock in the SDH equipment

The large magnitude low frequency jitter from SDH pointer adjustments are difficult to be reduced using ordinary methods such as general analog or digital phase locked loops. A novel digital desynchronizer technique was developed to regenerate the 2.048 MHz clock in the SDH equipment. By counting the difference between the write clock and a reference clock, the speed of the read clock can be forecasted. The operating principles, the jitter performance analysis and experiment results are given to show that the recovered clock has little output jitter and this technique has better jitter transfer characteristics and a wider catching range. Moreover, this technique is completely digital and can be integrated.