ac,dc参数各起什么作用？

这两天在看SSTL_2接口规范，对其中关于ac，dc参数的解释不是很明确。想请教一下，给个更详细的解释！谢谢！

2 Supply voltage and logic input levels
The standard defines both ac and dc input signal values. Making this distinction is important for the design of high gain, differential, receivers that are required. The ac values are chosen to indicate the levels at which the receiver must meet its timing specifications. The dc values are chosen such that the final logic state is unambiguously defined, that is once the receiver input has crossed this value, the receiver will change to and maintain the new logic state. The reason for this approach is that many input wave-forms will include a certain amount of “ringing”. The system designer can be sure that the device will switch state a certain amount of time after the input has crossed ac threshold and not switch back as long as the input stays beyond the dc threshold. The relationship of the different levels is shown in figure 1. An example of ringing is illustrated in the dotted wave-form.

[求助]ac,dc参数各起什么作用?

顶起来

难道没有TX能够指点一二吗?

捞起来：）

AC值是时序参数测量的基准，DC值是逻辑电平判别的基准。

其實已經寫的很明白, 若要說白話一點, ac的規範, 用來定義暫態的部分, 以計算 timing margin;而dc的規範,則是規範在logic H/L時;因為信號的ringing會改變信號的H/L值,以致 receiver 誤判其邏輯值,所以可用來決定 noise margin.

谢谢