Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus access regulation
Patent
1997-08-27
1999-10-12
Sheikh, Ayaz R.
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus access regulation
361600, 361679, 361748, 361794, G06I 1300, H02B 100, H05K 500, H05K 100
Patent
active
059648546
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention is directed to a card cage for an electronic control unit having signal-processing analog and/or digital components, and high-speed digital components.
Background Information
"High-speed" digital components differ from signal-processing digital components by operating frequency and by associated conducted interference in the area of current and voltage supply or current and voltage discharge. Numbered among the high-speed digital components are, in addition to the microprocessor and the microcontroller, all digital components which belong to a bus system and are connected to an address, data, bus control, or chip select line of a microprocessor or microcontroller (such as an EPROM), RAM and address latch, and which transmit data at frequencies greater than one MHZ.
Besides the signal-processing and the high-speed digital components, a card cage of this type also has components with both high-speed, digital functional parts and signal-processing functional parts. The card cage of this type also has power components, which are mounted on the card cage and, which, e.g., can be a printed-circuit board, together with printed connections for the voltage supply and ground, and connector contacts for signal lines, shielded and ground lines. In this instance, the printed connections can also be designed in a plurality of superposed planes. To avoid a disruptive potential gradient in the ground lines, which can adversely affect the functioning of individual components, it has proven to be advantageous for the ground connections to be electrically connected in a ground plane over a large surface.
In spite of this advantageous configuration, strong power currents discharging via the ground connections of individual components can lead to potential shifts and to significant current densities in the ground plane. This entails the serious drawback that when there are high current densities in the ground plane, small, analog signal voltages are afflicted with unacceptable errors. Moreover, the ground connection of analog, signal-processing, and high-speed digital components on a shared ground plane brings about an undesired high-frequency coupling, which is emitted, above all, via the ground connection or the ground connections of the control unit.
For this reason, there are design approaches, whereby ground planes, which are isolated from each other, are allocated to the high-speed digital components, on the one hand, and to the signal-processing components, on the other hand, analog components being exclusively provided as signal-processing components, and the two isolated ground planes being joined, in each case separately from one another, via conductor connections to a third ground plane. The European Patent No. 0 429 695 discloses an electronic control unit for controlling functions of a motor vehicle. Its ground plane is so conceived for the high-speed digital components that, except for a conductive connection to a shared ground base plate, which also includes the ground connection of the control unit, it is isolated from a ground plane that is allocated to the signal-processing analog components and includes the ground connection for signal and shielded lines. As a result, the high-frequency coupling between the ground plane allocated to the signal-processing analog components and the ground plane allocated to the high-speed digital components is reduced, which, in turn, has a positive effect on the interference radiated via the connecting leads of the control unit.
There is an inherent drawback to this design approach that has to be considered, however. Namely, in spite of the separate design of the two ground planes, which deplete the high current densities produced by the power components and the high-frequency interference currents produced by the high-speed digital components, potential shifts are produced in the analog ground plane connected thereto. This can cause small signals from the signal-processing analog components direc
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Roozenbeek Herman
Tepass Bernd
Jean Frantz Blanchard
Robert & Bosch GmbH
Sheikh Ayaz R.
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