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Printed Circuit Card Wiring Technique

IP.com Disclosure Number: IPCOM000034821D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 3 page(s) / 172K

Publishing Venue

IBM

Related People

Albu, SM: AUTHOR [+2]

Abstract

In an ideal electronic device cable interconnection the output and input characteristics of a signal through the cable should be identical. However, as a result of capacitive and inductive coupling, crosstalk between different signal lines is always present. The magnitude of crosstalk depends on parameters, such as the signal rise/fall time, current and voltage magnitude, number of parallel signals switching simultaneously, and last but not least, the signal-to-ground return ratio. Theoretically, each signal should have its own ground return, in a 1:1 ratio. In practice, however, many signals share a common ground return practice known as "funnelling".

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Printed Circuit Card Wiring Technique

In an ideal electronic device cable interconnection the output and input characteristics of a signal through the cable should be identical. However, as a result of capacitive and inductive coupling, crosstalk between different signal lines is always present. The magnitude of crosstalk depends on parameters, such as the signal rise/fall time, current and voltage magnitude, number of parallel signals switching simultaneously, and last but not least, the signal-to- ground return ratio. Theoretically, each signal should have its own ground return, in a 1:1 ratio. In practice, however, many signals share a common ground return practice known as "funnelling". A high-speed interconnection system that has signal-to-ground return

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connector contact ratios greater than 1:1 exhibits a noise voltage across the common ground inductance. This noise voltage transfers to all signal lines. Fig. 1 illustrates one end of a cable assembly including connector 1, printed circuit card 2 and controlled impedance cable 3. In this particular example, the connector has 2 rows of 25 contacts. The printed circuit card has two outer signal and one inner ground return planes. The cables have 20 signal and 40 ground return conductors. The function of the printed circuit card is to translate the controlled impedance cable conductors' spacing to the connector contact spacing, gather and redistribute the controlled impedance cable ground returns to the connector, and redistribute the controlled impedance cable signals to the connector.

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This invention is a printed circuit card wiring technique for inductive crosstalk reduction. The tech...