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COMBINING RADIO FREQUENCY ABSORBER AND DIELECTRIC MATERIALS AS A STRUCTURE TO REDUCE ELECTROMAGNETIC INTERFERENCE EMANATING FROM A TEN GIGABIT PER SECOND PHYSICAL LAYER CHIP

IP.com Disclosure Number: IPCOM000216278D
Publication Date: 2012-Mar-27
Document File: 8 page(s) / 667K

Publishing Venue

The IP.com Prior Art Database

Related People

Diaco Davari: AUTHOR [+8]

Abstract

Existing ten gigabit per second (10G) physical layer chips cause electromagnetic interference (EMI) harmonics above class-A limits at 5, 10 and 20 gigahertz. The EMI problems are primarily attributed to the physical layer chips themselves, as heat sinks can radiate effectively when power supplied to the chip is turned on. There are several approaches to reducing the EMI problems attributed to physical layer chips. For example, reducing the height of heat sink fins could re-tune the harmonics but may not reduce emissions at all harmonics. Grounding the heat sink to a printed circuit board metal may reduce some emissions from the physical chip, but not enough to make the six dB of margin below the class-A limit. Multiple grounding techniques violate high speed routing, and thus cannot be used to reduce the EMI problems. Thin EMI absorber flex material, however, with adhesives may be attached on a top side of the printed circuit board layout covering areas around the physical layer chip to reduce emissions. In particular, a radio frequency (RF) absorber is used to collapse unintentional RF energy into heat without reflecting or refracting EMI energy.

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Page 01 of 8

 COMBINING RADIO FREQUENCY ABSORBER AND DIELECTRIC MATERIALS AS A STRUCTURE TO REDUCE ELECTROMAGNETIC INTERFERENCE EMANATING FROM A TEN GIGABIT PER SECOND PHYSICAL LAYER CHIP

AUTHORS:

Diaco Davari

George Curtis

Jeffrey Evans

Alpesh Bhobe

Xiaoxia Zhou

Nandu Kulkarni

Mike Sapozhnikov Zhenggang Cheng

CISCO SYSTEMS, INC.

ABSTRACT

    Existing ten gigabit per second (10G) physical layer chips cause electromagnetic interference (EMI) harmonics above class-A limits at 5, 10 and 20 gigahertz. The EMI problems are primarily attributed to the physical layer chips themselves, as heat sinks can radiate effectively when power supplied to the chip is turned on. There are several approaches to reducing the EMI problems attributed to physical layer chips. For example, reducing the height of heat sink fins could re-tune the harmonics but may not reduce emissions at all harmonics. Grounding the heat sink to a printed circuit board metal may reduce some emissions from the physical chip, but not enough to make the six dB of margin below the class-A limit. Multiple grounding techniques violate high speed routing, and thus cannot be used to reduce the EMI problems. Thin EMI absorber flex material, however, with adhesives may be attached on a top side of the printed circuit board layout covering areas around the physical layer chip to reduce emissions. In particular, a radio frequency (RF) absorber is used to collapse unintentional RF energy into heat without reflecting or refracting EMI energy.

1

Copyright 2012 Cisco Systems, Inc.


Page 02 of 8

DETAILED DESCRIPTION


Radio frequency (RF) absorbers are used to reduce electromagnetic interference (EMI)

problems for ten gigabit per second (10G) physical layer chips. The RF absorbers consist of EMI absorbers at areas around the physical layer chip. For example, as shown in FIG. 1, below, microwave absorbing material (rubber) may be used as the RF absorbers. RF absorbers are made of lossy materials that absorb the RF energy and convert this energy to imperceptible heat energy.

FIG. 1


The RF absorber may be limited to two vertical strips on the left and right of the physical

layer chip, utilizing adhesives to secure the absorbers in place under the physical layer chip heat sink.

    The RF absorber and dielectric material combination is formed by a ten millimeter solid...