Virtex-5 的I/O怎么实现1.25 Gb/s的LVDS输出？

&nbsp;Virtex-5&nbsp;的I/O怎么实现1.25&nbsp;Gb/s的LVDS输出？<br /><br />Virtex-5&nbsp;数据手册上说<br />Extremely&nbsp;high-performance&nbsp;<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-&nbsp;Up&nbsp;to&nbsp;800&nbsp;Mb/s&nbsp;HSTL&nbsp;and&nbsp;SSTL&nbsp;(on&nbsp;all&nbsp;single-ended&nbsp;I/Os)<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-&nbsp;Up&nbsp;to&nbsp;1.25&nbsp;Gb/s&nbsp;LVDS&nbsp;(on&nbsp;all&nbsp;differential&nbsp;I/O&nbsp;pairs&nbsp;)<br /><br />但是Virtex-5内部时钟最大也才支持550MHz,&nbsp;即使是差分，怎么实现1.25G,&nbsp;这里面有什么技术问题，请那位兄弟解答一下。&nbsp;Thanks<br />

实际时钟只有300多MHz