Hermann,
In the beginning of conditioning SerDes channels, all that was needed at 3
Gbps was one Tx pre-cursor, an Rx CTLE and an Rx one tap DFE. The
pre-cursor tap was a "pre-emphasis", but since the total energy output of
an Tx could not be changed, it had the result of "de-emphasis" of the main
cursor. At 28-56 Gbps the Tx now have 1 or more pre-cursor taps and 2 or
more post-cursor taps and the Rx have ~14 DFE taps. Both the Tx pre-cursor
and post-cursor taps de-emphasize the Tx main cursor tap by doing both
pre-emphasis and post emphasis.
So does pre-distortion mean distorting the main cursor due to distortion
introduced by bits already send out by the Tx or distortion of the signal
based on bits that already have been sent out, and bits that are going to
be sent out.
A nose by any other names still smells.
Walter
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Hermann Ruckerbauer
Sent: Monday, May 11, 2015 2:30 AM
To: weirsi@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: differences between de-emphasis and pre-emphasis
Hello,
I have heard serveral different explanations, but basically all mean the
same thing: Pre-destortion of the signal on the TX -Side (and in my naming
conventions Equalization means the equivalent on the RX side).
Sometimes I have heard De-Emphasis due to reduction of energy below the
nominal (as steve mentined), sometimes Pre-Emphasis for going above the
nominal, sometimes Pre for a Pre-Destortion before the channel.
In my "naming convention" I have a maximum energy available, and I can
only reduce this (so I'm not working with nominal, but with max.
engergy). Especially when talking about Pre-Curssor, Post-Cursor,
Boosting, Multibit Pre-Emphasis I prefer this explanation (similar to what
PCIe-Gen3 is doing).
But I have never seen any "official" explanation / description of this
names (and I would not know which consortium would define an official
naming).
I struggled with this also quite a while when working with this stuff, and
if somebody has a good explanation I'm really interested to learn here too
..
Best Regards
Hermann
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Am 11.05.2015 um 04:55 schrieb steve weir:
It is the difference between increasing energy over the nominal, or
decreasing energy below the nominal. In each case the effect is to
predistort the transmitted data pattern to complement the channel
distortion.
Steve.
On 5/10/2015 7:30 PM, mo han wrote:
Hi experts:
I am solving the sata ISI problem by using emphasis,but I am not very
clear about the differences between de-emphasis and
pre-emphasis，could anyone tell me?
Thanks!
Mo Han
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