[SI-LIST] Re: Question about emphasis taps
- From: Walter Katz <wkatz@xxxxxxxxxx>
- To: "Aubrey Sparkman" <asparky@xxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Mon, 2 Dec 2013 21:29:23 -0500 (EST)
Aubrey,
You are correct, the taps before and after the main cursor tap do
emphasize the pre and post cursor, but they have the effect of de-emphasis
of the main cursor tap, which is the result of emphasizing the pre and
post cursor. Traditional DFE Rx equalization can give the same result of
Tx post cursor taps without reducing the energy transferred by the Tx.
There have been significant advances in Rx equalization technology
recently that can also do pre cursor equalization as well.
Walter
-----Original Message-----
From: Aubrey Sparkman [mailto:asparky@xxxxxxxxxxxxxxxxxxxxxxxx]
Sent: Monday, December 02, 2013 7:55 PM
To: wkatz@xxxxxxxxxx
Cc: <yfu@xxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
Subject: Re: [SI-LIST] Re: Question about emphasis taps
Walter,
In my meager experience, I have seen drivers that boost the leading edges
which I call preEmphasis drivers, others that reduce the drive after the
leading edge, which I call deEmphasis drivers and others that do both
which I don't know what to call. My observations apply to the waveform
and the setting of the 1st post tap when compared to the waveform when the
1st post tap is tuned off.
But I agree that you must consider the eye at the output of the receiver.
Aubrey
Sent from my iPhone
> On Dec 2, 2013, at 4:36 PM, Walter Katz <wkatz@xxxxxxxxxx> wrote:
>
> Johnny,
>
> Calculating the optimal Tx taps is not so simple. First, you need to
> remember that these are not emphasis taps, but are actually
> de-emphasis taps. There is a trade-off between opening the eye at the
> Rx input, and the total amount of energy in the main cursor tap. The
> more energy you put into the pre and post cursor taps, the less energy
> in the main cursor taps. To open up the eye at the Rx latch, the
> optimal Tx taps are a function of the capabilities of the Rx
> equalization. The optimal operation of the channel will often not
> correspond to an optimal eye at the input to the Rx.
>
> Walter
>
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of FU, Yejun
> Sent: Monday, December 02, 2013 4:31 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Question about emphasis taps
>
> Hi all:
>
> I am currently working on a high speed differential trace
> characterization up to 28Gbps, the problem is the high insertion loss,
> your signals has degraded just for several inches. So this company
> comes up with this tools to calculate the emphasis taps you can add
> into your PG to compensate the loss and reopen the eye. I was so
> confused by the way how they calculate it, because sometime they won't
> give you the best optimized taps. Any suggestion to full understand the
Pre-emphasis Vs.
> insertion loss?
>
> Thanks
> Yejun(Johnny) Fu|
> yfu@xxxxxxxxx | 3500 Carling Ave.| Ottawa, ON, K2H 8E9, CAN Direct
> +1.613.670.3283
>
>
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