Complex Pre-emphasis settings

The document does say that one post tap is most popular for post-cursor ISI.

The second post tap is similar to first post tap but with double duration. The document says that the pretap is useful in systems that suffer pre-cursor ISI e.g. in DFE based receivers (DFE can only correct post-cursor ISI).

Thanks for the reply.

really make me very @@ :(

I said double duration not second duration. As you can see in the waveforms of the document. Thus you will have more choice to suit your channel ISI.

DFE receivers are based on Decision Feedback Equalisation and can equalise the post cursor ISI but cannot equalise pre cursor ISI.

Channels distort square waves and thus cause ISI in various forms. For example it may lower the falling edge section (post cursor) or rising edge section(pre cursor). The explanations are analogue related to capacitance, inductance and so on of which I know less than you perhaps.