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Tuning the 8255x Controller’s Equalizer for Capacitor-Coupled Applications

Application Note (AP-435) Revision 1.1 November 2005 Revision History Revision 1.1 1.0 Revision Date Nov 2005 Jan 2002 Initial Release Initial Release (Confidential) Description Information in this document is provided in connection with Intel products. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Intel's Terms and Conditions of Sale for such products, Intel assumes no liability whatsoever, and Intel disclaims any express or implied warranty, relating to sale and/or use of Intel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. Intel products are not intended for use in medical, life saving, or life sustaining applications. Intel may make changes to specifications and product descriptions at any time, without notice. Designers must not rely on the absence or characteristics of any features or instructions marked "reserved" or "undefined." Intel reserves these for future definition and shall have no responsibility whatsoever for conflicts or incompatibilities arising from future changes to them. The 8255x Controllers may contain design defects or errors known as errata which may cause the product to deviate from published specifications. Current characterized errata are available on request. Contact your local Intel sales office or your distributor to obtain the latest specifications and before placing your product order. Copies of documents which have an ordering number and are referenced in this document, or other Intel literature may be obtained by calling 1-800- 548-4725 or by visiting Intel's Web site at http://www.intel.com. Intel® is a trademark or registered trademark of Intel Corporation or its subsidaries in the United States and other countries. Copyright © 2005, Intel Corporation. All rights reserved. * Other product and corporate names may be trademarks of other companies and are used only for explanation and to the owners’ benefit without intent to infringe. Application Note (AP-435) Tuning the 8255x Controller’s Equalizer 1.0 Introduction The adaptive equalizer is a key circuit block within the 8255x controller PHY unit. Its job is to restore the distorted MLT-3 signal received at the end of the wire to a waveform that can be used to reliably extract the 125 MHz clock and decode the data. Equalization is a three-step process based on voltage, phase, and bit error detection. Normally, the equalizer performs adaptation on a received signal that traversed a length of balanced CAT5 cable and passed through two magnetics modules along the way. The equalizer is optimized to amplify this specific signal for a range of cable lengths from zero to 100 meters. Equalizer adaptation occurs every time the PHY attempts to establish link. When the 8255x controller is used in a point-to-point or backplane application, the differential pairs are typically connected to a link partner through circuit board traces and AC coupling capacitors instead of through magnetics modules and CAT5 cables. With capacitive coupling, “looks” like a high pass filter instead of the low pass filter presented by transformer-based Read the full Tuning the 8255x Controller’s Equalizer for Capacitor-Coupled Applications.

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