请教BC6的时钟参数

在CSR的BC6中有对时钟的参数要求，其中有个参数是Edge jitter[/COLOR]要小于15ps，这个Edge jitter是什么意思?对应的物理意义是什么?
请高手帮忙解答一下[upload=jpg]UploadFile/2009-3/09321@3721RD_bt clk.JPG[/upload]

The phisical meaning is the timing refer to the zero crossing point, it will impact the timing sequence and the sampling point accuracy.