Card cage for an electronic control unit having signal-processing components and high-speed digital components coupled to a common ground plane

In the case of a card cage for an electronic control unit having signal-processing analog and/or digital components, high-speed digital components, as well as components having both signal-processing functional parts, as well as high-speed digital functional parts and power components, which are arranged on a multilayer printed-circuit board and are electroconductively connected to a shared ground plane, the signal-processing components of each module having a shared connection to the common ground plane, the radiated interference from the control unit produced by high-frequency interference currents can be reduced, and high current densities in the ground plane and resultant potential shifts can be prevented from adversely affecting the signal processing, in that the signal-processing components are combined into signal-processing modules having at least one shared function, and the ground connections of all components of such a functional module are routed in each case via conductor connections to a common point of connection conductively connected over the shortest path to the shared ground plane, and the high-speed digital and power components are directly linked to the shared ground plane. By introducing an additional voltage-supply plane, the radiated interference from the control unit is able to be further reduced.

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 directly connected to the analog 
ground plane to be distorted, as well as to propagate through very large 
current loops. These current loops, in turn, because of their antenna 
effect, increase the interference radiated by the control unit. 
SUMMARY OF THE INVENTION 
The present invention makes it possible to avoid radiated interference from 
the control unit produced by high-frequency interference currents and to 
prevent high current densities in the ground plane, which are also 
produced by the power components, from having an adverse effect on the 
signal processing. This is accomplished by providing only one single, 
large-surface ground plane and, first of all, by conductively connecting, 
via a direct path, to this ground plane only the ground connections of the 
high-speed digital components belonging to the bus system. A direct 
connection is understood to be conductively connecting a component to the 
point of connection via the shortest possible path while taking the 
position of other electrical connections and components into 
consideration, without connecting a third component therebetween. In 
contrast to the signal-processing components, the high-speed digital 
components can also be directly linked to the signal-processing components 
via a plurality of conductive connections to the shared ground plane, 
since the interference voltages in the ground plane cannot adversely 
affect the method of functioning of the high-speed digital components. By 
directly connecting high-speed digital and power components to the shared 
ground plane, high-frequency signals fed by the high-speed digital 
components to the power components flow back on the ground plane directly 
underneath the signal line. This is because it is precisely on this path, 
even when it is not designed to be the geometrically shortest path between 
the two components, that the impedance is the lowest. The currents do not 
need to make a circuitous route via an additional ground plane or ground 
line, so that the inductance of the ground connections is significantly 
decreased, and the current-loop surfaces of the interference currents, 
which acted as small antennae, are substantially reduced in size. This 
substantially improves both the radiated interference and the 
irradiation-resistance of the control unit, and further reduces the 
expenditure for interference suppression. Therefore, often the need for 
additional plug capacitors and baffle shields can be eliminated, for 
example, so that the cost of manufacturing the control unit can be 
reduced. 
However, the signal-processing analog and digital components are not simply 
linked, individually and directly, to this ground plane, since otherwise 
their method of functioning would be jeopardized by potential shifts 
caused by locally varying current densities in the ground plane, or by the 
unfavorable ground connection of a filter component, or by overly large 
current-loop surfaces. Even the method of functioning of the 
signal-processing digital components could be adversely affected by 
injected, strong interference signals. Instead, the signal-processing 
analog and digital components, which at least have one shared function, 
are combined in functional modules, and the ground connections of all the 
components of such a functional module are linked via conductor 
connections to a common point of connection (ground reference point). This 
connection point of a functional module is first linked in each case via 
the shortest path to the shared ground plane. As a result, all components 
which belong to a signal-processing functional module, are linked only via 
one connection point to the ground plane. The interference current of a 
high-speed digital component, which is further augmented by power 
components and is discharged via the ground plane, can now merely shift 
the potential at the point of connection common to all components of one 
signal-processing functional module, through which means the potential of 
all individual components of the functional module in question rise or 
fall to the same extent. Thus, no shift in potential takes place between 
the individual components of the functional module, and the interference 
current is prevented from having an adverse effect on the method of 
functioning of the module. 
The point of connection of any one functional module has only one single 
connection to the ground plane. However, it is also possible to design the 
point of connection with a plurality of contacting connections that are 
situated closely together and lead to the common ground plane. It is 
crucial in this case that the contacting connections to the ground plane 
be situated closely enough together to ensure that the points of contact 
have an essentially identical potential, and that no potential difference 
that would adversely affect the method of functioning of the module is 
able to arise between the points of contact with the ground plane. Thus, 
it is conceivable, for example, for the point of connection to have two 
contacts that are spaced apart by only a few millimeters. 
If a signal-processing functional module contains an integrated circuit 
(IC), then it is advantageous to arrange the point of connection of the 
functional module in the direct vicinity of the ground connection of the 
IC, and to integrate the negative connection of a back-up capacitor or 
decoupling capacitor in the point of connection. This is done by linking 
the ground connection of the integrated circuit directly to the negative 
connection of the capacitor, by likewise linking the remaining components 
of the functional module to the negative terminal of the capacitor via 
conductor connections, and by directly connecting the negative terminal of 
the capacitor to the shared ground plane. 
Furthermore, by having a direct conductor connection of the power 
components to the shared ground plane, there is no need for additional 
recesses in the ground plane for a power ground connection. This makes it 
possible to further reduce the high-frequency voltage differences in the 
ground plane. By routing the signal-line and ground-line connections, 
irradiation loops are kept as small as possible, it being possible to 
avoid a signal feed-over when no foreign signal lines, i.e., no signal 
lines belonging to another functional module, are placed near the position 
of a signal-processing functional module. 
In the case of a component having a high-speed digital functional part and 
a signal-processing, analog functional part, e.g., a microcontroller 
having an integrated analog-to-digital converter, the connections of the 
analog-to-digital converter are linked in the same manner as the 
connections of an independent, signal-processing analog functional module, 
separately from the remaining connections of the controller via a point of 
connection allocated to the signal-processing functional part to the 
ground plane. 
A design, in the form of a multilayer printed-circuit board, represents an 
especially advantageous refinement of the card cage. The point of 
connection common to all of the ground connections of the components of 
one functional module is able to be easily realized by the connection 
point that are customary in circuit-board technology, and the ground lines 
can be connected via a plurality of layers of the printed-circuit board to 
the connection point, which substantially increases the available design 
space for arranging the components and the connection lines. 
Also by introducing a voltage-supply plane comprising voltage-supply lines 
and a conductive planar section, the current-loop surfaces and the 
galvanic coupling via the positive voltage supply of a signal-processing 
functional module are also reduced, the individual voltage-supply 
connections of the components of the functional module being connected, in 
the same way as the ground connections, to a point of connection, which, 
in turn, is directly linked to a voltage-supply line running in the 
voltage-supply plane. It is advantageous not to directly connect a 
high-speed digital component having a plurality of voltage-supply 
terminals, e.g., a microprocessor, to the conductive planar section of the 
voltage-supply plane, but rather to first link each voltage-supply 
connection to the positive terminal of a back-up or decoupling capacitor 
placed in the immediate vicinity of the microprocessor, and then to 
directly connect this positive terminal to the conductive planar section. 
To optimize the effect of the back-up or decoupling capacitor, the total 
inductance between the microprocessor connections and the capacitor 
terminals should be kept as low as possible. This is achieved, on the one 
hand, by positioning the back-up or decoupling capacitor in the immediate 
vicinity of the microprocessor's voltage-supply terminal and by linking it 
with the shortest possible connection thereto and, on the other hand, by 
directly connecting the ground connection of the microprocessor and the 
negative terminal of the capacitor in each case to the ground plane. 
To reduce the interference radiated over the connecting leads of the 
control unit, it is advantageous to directly connect the shielded line to 
the shared ground plane. The high-speed digital components should be 
arranged as closely together and as far away from the control unit plug as 
possible.

DETAILED DESCRIPTION 
As illustrated in FIG. 1, a card cage for an electronic control unit 
comprises signal-processing analog components 11, signal-processing 
digital components 12, high-speed digital components 10 and components 13, 
both with high-speed digital functional parts 17, as well as with 
signal-processing functional parts 16, as well as with power components 
14, which are arranged on a card cage designed as a multilayer 
printed-circuit board 1. The connector contacts for signal lines, shielded 
and ground lines, and the connector leads interconnecting the components 
are not shown in FIG. 1. The depicted components can be located both on 
the top side designated as the component side, as well as on the bottom 
side of the card cage designated as the soldered side. In the case of 
multilayer printed-circuit board 1, a one-piece, planar, shared ground 
plane 3 is provided, to which all ground connections of the components are 
electroconductively connected, and vertical, galvanic connections 23, such 
as vias, routed through the multilayer printed-circuit board 1, are 
provided as ground connections to the ground plane 3. 
The ground connections of the high-speed digital components 10 are directly 
conductively connected to ground plane 3. The high-speed digital 
components 10 can also be thereby electroconductively connected via a 
plurality of connections 31 to the shared ground plane 3. Power components 
14 are likewise directly conductively connected via connections 35 to the 
shared ground plane 3. In this instance, the ground connection of a power 
component can also be connected by way of a plurality of vias 23, situated 
closely together, to the shared ground plane. A high-frequency 
interference current having a steep signal edge, which is produced by a 
high-speed digital component 10, such as a microprocessor controlling a 
power component, is transmitted via signal line 25 to power component 14, 
and is amplified by the same, is depleted over the shared ground plane 3, 
as is apparent in FIG. 2, directly beneath signal line 25, making 
current-loop surface area 26 for the interference current very small. 
Because of their small dimensions, these small interference-current loops 
act only as small antennae for emitting radiated interference or for 
receiving irradiated interference. It is expedient to arrange the 
high-speed digital components in an area situated on the card cage farther 
away from the signal-processing functional modules and from the control 
unit plug, in order to further reduce the high-frequency coupling. 
As shown in FIG. 1, the signal-processing, analog components 11 and the 
signal-processing, digital components 12 having at least one shared 
function are combined to form signal-processing functional modules 15, the 
ground connections of the components of each functional module being 
routed via conductor connections 32 to a shared point of connection 20, 
which is conductively connected via a direct path 23 to the shared ground 
plane 3 and, at the same time, the point of connection being a back-up or 
decoupling capacitor 43. Conductor connections 32 of the components and of 
capacitor 43 can thereby be linked via one or also a plurality of layers 
of the multilayer printed-circuit board to point of connection 20 of the 
functional module 15. Through the shared point of connection 20, the same 
electric potential is applied to all ground connections of the components 
of a signal-processing functional module 15, so that the high-frequency 
interference current of a high-speed digital component 10, which is 
depleted over the shared ground plane 3, raises and lowers to the same 
extent the frame potential of all components belonging to the same 
functional module by way of via 23 of point of connection 20, without a 
potential shift occurring between the components of one functional module. 
In this manner, by introducing a point of connection 20 common to all 
components of one functional module, the signal transmission of the 
functional module will no longer be adversely affected by the interference 
current. Alternatively to the exemplary design shown here, it is also 
possible to link the point of connection by way of a plurality of vias 23 
situated closely together to common ground plane 3. It is crucial in this 
case that the points of contact of the vias 23 with the ground plane 3 lie 
closely enough together that no potential difference capable of adversely 
affecting the method of functioning of the module can arise between the 
points of contact. 
FIG. 3 depicts a specific embodiment of the present invention of a 
signal-processing module. Via signal line 50, an analog signal with a 
small voltage is transmitted to component 52 and transformed by said 
component 52 into a digital signal, which is output via signal output line 
55. Linked between voltage-supply terminal 58 and ground connection 57 of 
component 52 is a back-up or decoupling capacitor 43. To avoid irradiation 
loops, ground-line connection 51 of a signal-voltage sensor (not shown) 
runs as closely as possible next to the signal-carrying signal line 50 and 
is linked to ground connection 57 of component 52 at point of connection 
20, together with the back-up or decoupling capacitor 43. All further 
local ground connections 59 of the signal-processing module are linked to 
point of connection 20. Point of connection 20 is directly, conductively 
connected by way of a via 23 to the shared ground plane 3 of the control 
unit. As is apparent from FIG. 3, all ground connections of the 
signal-processing module are linked via point of connection 20 to the same 
potential. 
If, as shown in FIG. 4, a signal-processing functional module 15 contains 
an integrated circuit (IC) 18, then the point of connection of functional 
module 15 is arranged in the immediate vicinity of the ground connection 
of IC 18. As illustrated in FIG. 4, the point of connection comprises 
negative terminal 62 of a back-up or decoupling capacitor 61, which is 
directly linked via a low-inductance connection 63 to the IC's ground 
connection. Negative terminal 62 of capacitor 61 integrated in the point 
of connection is linked by way of a via 23 to the shared ground plane 3. 
The remaining signal-processing components 11 of the functional module are 
likewise linked via conductor connections 64 to negative terminal 62 of 
the capacitor 61. Alternatively to the exemplary design shown here of the 
point of connection, it is also possible to place via 23 directly 
underneath negative terminal 62 of capacitor 61. Another specific 
embodiment of the present invention of the point of connection is 
illustrated in FIG. 5. The IC's ground connection is linked at low 
inductance via a connection 63 to negative terminal 62 of a back-up or 
decoupling capacitor 61. This, in turn, is connected via a monoplane to 
the negative terminals of three input filter capacitors 65 of the IC 18. 
Via 23, which is integrated in the point of connection, is situated in the 
middle underneath the uniplanar connection 67 of the capacitors. The 
ground connections of the other signal-processing components 11 of 
functional module 15 are conductively connected via conductor connections 
64 to surface-area connection 67. 
If a component 13 is comprised both of a signal-processing functional part 
16, as well as of a high-speed digital functional part 17, e.g., of a 
microcontroller having an installed analog-into-digital converter, then, 
as shown in FIG. 1, ground connection 34 of the signal-processing 
functional part 16 is treated as the ground connection of an independent, 
signal-processing functional module and is linked separately from the 
other ground connections 33 of the component via a point of connection 20 
to the shared ground plane 3. Ground connections 33 of the high-speed, 
digital functional part 17 are individually linked, in the manner of 
ground connections 31 of a high-speed digital component 10, directly to 
the shared ground plane 3. 
FIG. 1 depicts a specific embodiment of the card cage where, in addition to 
a shared large-surface ground plane 3, a voltage-supply plane 4 is also 
provided. As shown in FIG. 6, voltage-supply plane 4 is comprised of 
individual voltage-supply lines 7 and of a planar section 6, which is 
linked to a shared voltage stabilizer 5. Voltage stabilizer 5 is linked 
via another line 8 to unit plug 9. Power components 14 are directly, 
conductively connected via connections 40 to voltage-supply lines 7 of 
voltage-supply plane 4. The conductive planar section 6 of voltage-supply 
plane 4 is situated on multilayer printed-circuit board 1 directly above 
or underneath the high-speed digital components 10 and the high-speed, 
digital functional parts 17 of combined components 13. Voltage-supply 
terminals 36 of the high-speed digital components 10 are linked to 
positive terminal 47 of a back-up or decoupling capacitor 45 placed in the 
immediate vicinity of component 10. Connection 36 between the 
voltage-supply terminal of component 10 and positive terminal 47 of the 
capacitor 45 is as short and-flat as possible to keep the total inductance 
as low as possible. Positive terminal 47 of capacitor 45 is directly 
connected to the conductive planar section 6 of voltage-supply plane 4. 
Negative terminal 46 of capacitor 45 and the ground connection of the 
high-speed digital component are each directly connected to the shared 
ground plane 3. 
In the same way as the ground connections, the high-speed digital 
components can be linked via a plurality of connections 36 to planar 
section 6 of voltage-supply plane 4. In the same manner, voltage-supply 
terminals 38 of components 13, which are provided with a high-speed, 
digital functional part 17, are linked to voltage-supply plane 4. 
Components 11 and 12, which are combined to form a signal-processing 
functional module 15, are routed via conductor connections 37 to a shared 
point of connection 21, which is conductively connected over a direct path 
to voltage-supply lines 7 of the shared voltage-supply plane 4. Point of 
connection 21 is also the point of connection of back-up or decoupling 
capacitor 43 to the voltage-supply plane. Conductor connections 37 can 
also be linked via a plurality of layers of the multilayer printed-circuit 
board to the via of connection point 21 of the functional module. In the 
same way as the terminal of a signal-processing module, voltage-supply 
terminal 39 of signal-processing functional part 16 of a combined 
component 13 is connected to a voltage-supply line 7 of voltage-supply 
plane 4.