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A method and procedure for dynamic signal amplitude adjustment in high speed serial systems

IP.com Disclosure Number: IPCOM000041590D
Original Publication Date: 2005-Feb-02
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 386K

Publishing Venue

IBM

Abstract

A method and procedure is devised to dynamically adjust signal amplitude in a high speed serial system. Typical systems only provide for static amplitude adjustment, i.e. pre-emphasis. This method can account for and accommodate signal degradation on a real time basis, resulting in a robust and reliable high speed serial interface.

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A method and procedure for dynamic signal amplitude adjustment in high speed serial systems

High speed serial interfaces such as Fibre Channel (FC) are plagued by signal degradation in interconnecting copper cables, resulting in limited cable lengths and/or limited speed of operation. Unexpected or unknown signal losses can ultimately cause operational failures. Such negative electrical signal effects can be caused by many factors, including long cable lengths, low quality cables, aging and environmental conditions such as temperature and mechanical stress. This reduction in signal amplitude is often referred to as "Eye Opening Closure" . See figure 1 as an example of an Eye Opening.

Figure 1

The smaller the signal amplitude, the smaller the eye opening, thereby, reducing the ability to transmit data without failures. This results in a higher Bit Error Rate. For new FC switched architectures, high speed differential signals are transmitted between two FC nodes, each node having a transmit signal and a receive signal (also known as a link). A new and fairly typical FC topology is one in which two separate FC switches intercommunicate via a cascading or trunking scheme using interconnecting cable such as in figure 2.

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Figure 2

Cluster 0

Cluster 1

Device Adapter

Device Adapter

0

Enclosure 1

 20 port FC Switch

 20 port FC Switch

15

FC trunk ports

Enclosure 2

0

 20 port FC Switch

 20 port FC Switch

15

0

Enclosure N

 20 port FC Switch

 20 port FC Switch

15

New FC technologies provide for "selective pre-emphasis" which allows for amplitude adjustment of independently transmitted FC signals. Standard methods for maximizing Eye Openings employ static techniques whereby prede...