[SI-LIST] Re: pre-cursor post-cursor
- From: "T.K. Jeon" <tkjeon@xxxxxxxxxxx>
- To: Kihong Joshua Kim <joshuakh@xxxxxxxxx>
- Date: Wed, 13 Jun 2012 17:23:37 -0700
Hello Joshua,
Good to hear from you and thanks for the compliment.
I just noticed you are at Silicon Image. Are you working in the Bay Area now?
Best Regards,
TK
From: Kihong Joshua Kim [mailto:joshuakh@xxxxxxxxx]
Sent: Wednesday, June 13, 2012 9:45 AM
To: T.K. Jeon
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] pre-cursor post-cursor
Hi T.K.,
(Been a long time!)
Thanks for the comprehensive answer WITH kind illustration.
It should also be a good record for other people who needs similar help.
Best,
Joshua Kihong Kim
Architect, Silicon Image Inc.
On Tue, Jun 12, 2012 at 8:17 PM, T.K. Jeon
<tkjeon@xxxxxxxxxxx<mailto:tkjeon@xxxxxxxxxxx>> wrote:
Hi Joshua,
You can see apparently both the pre-cursors and the post-cursors from a pulse
response out of lossy channels.(Indeed, if you have a scope with
differentiating function, you can try it out using a step signal like a long
0's and long 1's or you can extract it from s-parameters). The pre-emphasis you
are familiar with is to cancel post cursors and is implemented by subtracting
the replica signal, which is DELAYED by 1 bit with a certain weighting value,
from the main signal.
Let's say you have data stream like 1 -1 1 1 1 -1 -1 -1 -1 1, and your tap
value is 0.2. The 1 bit delayed version should be:
Main: 1 -1 1 1 1 -1 -1 -1 -1 1
Post: 0.2 -0.2 0.2 0.2 0.2 -0.2 -0.2 -0.2 -0.2 0.2
You will get the data shown below that has the first transition bit emphasized
after subtracting.
Dout: -1.2 1.2 0.8 0.8 -1.2 -0.8 -0.8 -0.8 1.2
On the other hand, pre-cursor is canceled by delaying MAIN signal instated of
the replica signal. Thus, if your tap value for the pre-cursor is 0.2 with the
same data, the signal will be:
Pre : 0.2 -0.2 0.2 0.2 0.2 -0.2 -0.2 -0.2 -0.2 0.2
Main: 1 -1 1 1 1 -1 -1 -1 -1 1
The 'Pre' signal in the example above is just a replica of data that is
ADVANCED by 1 bit.
After the subtraction, the output is going to have the last transition bit
emphasized like following
Dout: 1.2 -1.2 0.8 0.8 1.2 -0.8 -0.8 -0.8 -1.2
The good news for using this kind of FIR filter is it cancels out most of ISI,
but the bad news is it enhances noise too much.
Hope this helps.
Best Regards,
TK
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx<mailto:si-list-bounce@xxxxxxxxxxxxx>
[mailto:si-list-bounce@xxxxxxxxxxxxx<mailto:si-list-bounce@xxxxxxxxxxxxx>] On
Behalf Of Kihong Joshua Kim
Sent: Tuesday, June 12, 2012 10:39 AM
To: si-list@xxxxxxxxxxxxx<mailto:si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] pre-cursor post-cursor
Dear SI-lister,
I am reading Xilinx GTX manual for evaluation purpose.
Anyone can help the definition for pre-cursor and post-cursor in time and
amplitude to calculate? Hopefully in conjunction with pre-emphasis which I
have know for long.
Regards,
Joshua Kihong Kim
Architect, Silicon Image
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