[SI-LIST] Re: Pre-emphasis Vs De-emphasis
- From: "Ray Anderson" <ray.anderson@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 14 Jun 2006 16:36:24 -0700
Real simply, pre-emphasis and de-emphasis are techniques used to
compensate for the frequency dependent losses in transmission channels.
Most channels have a falling amplitude response as frequency increases
due to skin effect, dielectric losses, dispersion and the like. In order
to compensate for these effects a signal may be pre-distorted to
emphasize the higher frequency components such that the composite effect
of the pre-distortion and the channel characteristics approximates a
flat response with respect to frequency.
One may pre-distort a signal by emphasizing the high frequency
components or by de-emphasizing the low frequency components. The net
effect in either case is that the relative amplitude of the higher
frequency components of the signal are increased compared to the lower
frequency components.
If one increases the HF components by inducing overshoot of the signal
edges it is thought by some to increase the potential for EMI
generation. Also increasing the signal amplitude on the edges may cause
a violation of the signaling protocol's maximum voltage levels. An
alternative is to de-emphasize the LF components.
Perhaps some of the list members who are currently working with these
issues can provide a more comprehensive answer.
Regards,
-Ray
Raymond Anderson
Senior Signal Integrity Staff Engineer
Product Technology Department
Advanced Package R&D
Xilinx Inc.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Babid A
Sent: Wednesday, June 14, 2006 4:21 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Pre-emphasis Vs De-emphasis
Hi,
=20
What is the difference between pre-emphasis and de-emphasis? Why is
that some chips have de-emphasis instead of pre-emphasis?=20
=20
Is there any document explaining these two topics in detail
(differences, description etc)?
=20
-Thanks
=20
=20
=20
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