Wave transmission lines and networks – Plural channel systems
Patent
1995-09-20
1997-07-29
Gensler, Paul
Wave transmission lines and networks
Plural channel systems
333246, 361788, 439 85, H01R 2368
Patent
active
056525532
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
This concerns signal transmission of digital signals in computing installations having rapid communication via a backplane common to a plurality of subassemblies.
2. Prior Art
Computing installations are constructed as a rule from subassemblies which exchange data with one another. These subassemblies are arranged in pluggable fashion on a carrier board and the contacts of the various plug connectors are connected to one another in each case. Hence, a multiplicity of parallel lines is produced via which in each case correspondingly many data can be transmitted during one transmission operation. Apart from these data lines, there are control lines, ground lines and power supply lines.
For the transmission, an asymmetrical drive is often used in which one data line is used per logic signal and is switched with reference to a common ground. In particular, electronic switches are used which connect a potential provided on the data line to a ground line. In the process, because of the inductances and capacitances, slow edges or even oscillations occur on the signal lines during switching on or switching off. This effect can be avoided if the signal lines are terminated with their characteristic impedance. For systems of low speed, a common plug contact for the ground connection of many signal lines is used. Since in this case, via the one or the few ground contacts, considerably higher high-frequency currents flow than via the many signal contacts, interference occurs. One known measure in high-speed applications is therefore the use of one ground contact per signal contact. This solution is ruled out if, for reasons of compatibility, a standardized contact allocation must be used in which the number of ground contacts is fixed.
In the publication DE 38 38 486 A1, a method for producing circuit substrates is specified in which signal lines are located between grounded shields.
In the publication EP 0 414 546 A2, a backplane is specified in which signal lines are arranged between layers for signal ground and voltage supply.
SUMMARY OF THE INVENTION
It is the object of the invention to operate modules on a backplane in such a way that, in spite of asymmetrical operation and a number of signal ground contacts which differs from the number of signal contacts, a high signal speed is possible.
The invention is based on the consideration that, in addition to the plug contacts, which are overloaded in terms of high frequencies, for the signal ground, a considerable number of plug contacts are available for the power supply, these are not loaded in terms of high frequencies and can therefore serve for relieving the contacts for signal ground.
A first solution consists in using the contacts of the voltage supply as an additional high-frequency path, via capacitors. For this purpose, a high-frequency connection must be provided by means of capacitors from the voltage supply to the signal ground to the same extent on the module and the backplane. This requires a number of capacitors which are equal to the product of the number of plug locations and the number of power supply contacts. In this case, these capacitors must be connected with low inductance to the plug contacts, that is to say must be fitted directly alongside them.
As a result of extensive trials, an improved solution could be found in which no capacitors are necessary on the backplane. For this purpose, the voltage supply on the backplane must be implemented in a manner which is equivalent in terms of high frequencies to the signal ground.
This can be achieved if the signal lines have the same characteristic impedance with reference to the signal ground as with reference to the voltage supply. For this purpose, two embodiments could be determined. In the case of a first embodiment, the conductor tracks in a multilayer printed circuit board for signal ground and voltage supply have the same layout and lie in adjacent planes. In this arrangement, the voltage supply is laid in an outer plane and the signal groun
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patent: 3992686 (1976-11-01), Canning
patent: 5027089 (1991-06-01), Henke
patent: 5278524 (1994-01-01), Mullen
Texas Instruments: The TTL Data Book, vol. 2, 1985, pp. 5-24 through 5-41 no month.
TTL-Kochbuch, Muenchen 1975, pp. 259-261 no month.
C.M. Wintzer, Surface Mount Technologies Application Specific IC, International Conf. Jun. 1988, pp. 70-71.
B.C. Wadell, Transmission Line Design Handbook, Artech House, Inc., 1991, pp, 126-129 no month.
J. Fouladian et al, Generalized Analytical Equations for Strip Transmission Lines, Microwave Journal, Nov. 1989, pp. 165-168.
Gensler Paul
Siemens Nixdorf Informationssysteme Aktiengesellschaft
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