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Method for T-topology impedance control

IP.com Disclosure Number: IPCOM000007986D
Publication Date: 2002-May-09
Document File: 2 page(s) / 38K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for T-topology impedance control. Benefits include improved performance and improved signal quality.

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Method for T-topology impedance control

Disclosed is a method for T-topology impedance control. Benefits include improved performance and improved signal quality.

Description

              The disclosed method uses even-mode switching to alleviate the impedance discontinuities that occur in T topologies. By always having the nearest neighbor switch in even mode and controlling the space between them, the impedance before and after the T can be controlled while maintaining high-volume printed circuit board (PCB) manufacturing rules.

              Keys to the disclosed method include:

§         Guard trace before the T reduces the impedance of that section of transmission line.

§         After the T, the transmission lines are placed closer together, and the guard trace is removed.

              This approach increases the impedance of the post-T transmission line and minimizes the impedance discontinuity.

Advantages

              The disclosed method uses the effects of even mode switching to help alleviate the impedance discontinuity that occurs in T topologies. The transmission lines after the T have half the impedance of the transmission line before the T, causing reflections and degradation of the signal integrity. The disclosed method increases the impedance after the T to reduce these reflections and improve signal integrity.

              The disclosed method works best for signals that are unidirectional, such as command signals (clock enable) for double data rate (DDR) that are only driven from the memory controller hub and always have a complement. T...