[SI-LIST] Re: TO define the "Preemphasis"
- From: "Sandor Daranyi" <sandord@xxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 08 Jul 2002 09:39:07 +1000
There is something about that Xilinx text (it can be found at=20
http://www.xilinx.com/publications/products/v2pro/handbook/ug012_glossary.p=
df) which left me thinking.
The thing that puzzles me is that they specifically mention dispersion. No=
w, I understand how pre-ephasis will help in the presence of all the othe=
r effects mentioned, but how can pre-emphasis "magically" counter dispers=
ion?
Could somebody please share his/her insight into this?
Thanks,
Sandor
---
Sandor Daranyi
Senior Design Engineer
Aristocrat Technologies Australia Pty Limited
> -----Original Message-----
> From: DoraBabu - CTD, Chennai. [mailto:dbabu@xxxxxxxxxxxxxxx]
> Sent: Saturday, 6 July 2002 2:27
> To: lincj@xxxxxxxxxxxxxxxxxxx; hpc@xxxxxxxxxx
> Cc: SI_LIST (E-mail)
> Subject: [SI-LIST] Re: TO define the "Preemphasis"
>=20
>=20
>=20
>=20
> Got it from Xilinx Signal Integrity glossary :=20
>=20
> Pre emphasis is magnitude boosting of high frequency spectral=20
> components
> before launching the signal (wave) onto the Transmission=20
> Line. Transmission
> Lines embedded in most standard PCB materials (FR4, Rogers=20
> 43xx, Nelco and
> Rogers) suffer varying degrees of dispersion and loss in the=20
> 1 gigahertz
> spectrum. This is mostly due to conductance losses (leakage=20
> from the copper
> trace to any other conducting structure) and Skin Effect.=20
> Dispersion is a
> phenomenon whereby spectral components travel at different=20
> velocities. The
> waveform looks smeared when it arrives at the receiver.=20
> Both of these "characteristics" play into a diminished and=20
> poorly received
> signal. By boosting the high freq. spectral components, the=20
> magnitude of
> these components can be diminished as the wave travels through the
> Transmission Line, but since it starts out larger than the=20
> lower frequency
> components, the composite signal arrives at the receiver=20
> looking the way it
> was intended.=20
>=20
> Pre Emphasis is done by simply increasing the maximum amplitude of the
> signal for one bit period. If the signal is 1 bit in
> duration, the amplitude
> is allowed to rise to a value which is some percentage
> greater in magnitude.
> At this point, if the signal is to stay at the same logic
> state, the driver
> sends a decreased magnitude signal, or nominal logic level.
> Every time a
> transition occurrs, the greater magnitude level is used. For
> all times after
> this that the same level is to be transmitted, the nominal
> magnitude is
> used.
>
> --Regards
> Dorababu
>
> -----Original Message-----
> From: Miller [mailto:lincj@xxxxxxxxxxxxxxxxxxx]
> Sent: Friday, July 05, 2002 5:38 PM
> To: hpc@xxxxxxxxxx
> Cc: SI_LIST (E-mail)
> Subject: [SI-LIST] Re: TO define the "Preemphasis"
>
>
>
> You can also check xilinx's Multi-Gigahertz Signaling FAQ
> http://www.xilinx.com/xlnx/xil_prodcat_product.jsp?title=3Dsi_gigfaq
>
> Best Regards
>
> Miller Lin
>
>
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