GB2300772A

GB2300772A - Reducing interference in an electronic circuit using separate ground planes connected by a capacitor

Info

Publication number: GB2300772A
Application number: GB9609654A
Authority: GB
Inventors: Steffen Gieseler; Klaus Mueller
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1995-05-09
Filing date: 1996-05-09
Publication date: 1996-11-13
Anticipated expiration: 2016-05-09
Also published as: GB9609654D0; GB2300772B; FR2734119B1; DE19516918A1; FR2734119A1; JPH0951181A

Description

2300772 INTERFERENCE SUPPRESSION IN A CONTROL DEVICE The present invention

relates to a control device, especially for the control of functions of a motor vehicle, and has particular reference to interference suppression in such a device.

A control device, in particular for the control of functions of a motor vehicle, which comprises a control circuit wit h digital components for. obtaining a control signal from an input signal and a power circuit with power components for signal output, is known from EP-O 429 695 Al.

High-frequency switching operations in the digital part cause high-frequency interferences which are radiated by way of, in particular, the ground line. For reduction in this radiation, the power circuit on the one hand and the control circuit with a processor, bus and further digital components on the other hand are associated with area] grounds, which are electrically insulated from each other and separately connected with a conducting ground plate of the control device and to which an earth line is also connected.

It is achieved by the spatial separation and electrical insulation of the area] ground - the power ground - associated with the power circuit and the areal ground - the control ground - associated with the control circuit that on the one hand the high current flowing in the power circuit cannot flow by way of the control ground circuit, which would cause ground offsets or potential displacements liable to disturb reliable functioning of the digital components, and on the other hand the high-frequency coupling between the two grounds is substantially reduced.

2 - It is, however, a disadvantage of this circuit that high-frequency disturbances, which arise in spite of the separation of the grounds and which are brought about by the digital components and amplified by the power components of the power circuit, always flow away over the entire power ground and in particular by way of external lines connected to the control device. Consequently, relatively large current loops, which by reason of their aerial effect cause a high interference radiation, result in the case of high-frequency interference currents.

Moreover, it is known from the publication "Machine Design", 6 September 1984, to make the current loops of the high-frequency interferences as small as possible by subdivision of the digital circuit into several small regions for minimisation of high-frequency interference radiation in digital circuits. It is disadvantageous that the subdivision of the circuit into many small regions is very expensive and that the interference current loops cannot be made smaller as desired, since each circuitboard region must have at least the size of one or more components.

It would thus be desirable to so improve a control device, in particular for control of functions in a motor vehicle, that high- frequency interference currents no longer flow over the entire power ground or by way of an external ground connected thereto and that these high-frequency interference currents can in simple manner be attenuated substantially more strongly by comparison with those of known control devices. In particular, highfrequency interference current loops should preferaly be made as small as possible in terms of area.

According to the present invention there is provided a control device comprising a control circuit with digital components for obtaining a control signal from an input signal, a power circuit with power components for a signal output, a first area] ground associated with the control circuit, a second area] ground associated with the power circuit and spatially separated and electrically insulated from the first ground apart from an electrically conductive connection, and at least one capacitance electrically connecting the first and second grounds on the shortest path to form a short-circuit in high-frequency interference current loops.

Such a control device may have the advantage that, due to the electrical connection of the control ground with the power ground by at least one capacitance for the formation of a short-circuit in the highfrequency interference current loops on the shortest path, only very small interference current loops arise by comparison with the current loop which is formed by way of the otherwise existing electrically conductive connection between the control ground and the power ground. These small interference current loops, due to their small size, act only as small aerials in the radiation or reception of interference signals. Consequently, a further appreciable reduction in the radiation or reception of interference signals is achieved. In addition, high-frequency interference currents are prevented from flowing away over the entire power ground by way of the external lines arranged thereat or from cross-coupling to adjacent lines.

It is, for example, advantageous if the control device has a multilayer circuitboard, one layer on which - the ground layer comprises the control ground and the power ground. This appreciably reduces the technical effort for production of the two mutually separate grounds by comparison with known control devices.

Preferably, the control ground is spatially separated from the power ground by a non-conducting gap which is formed on the ground layer-simply as an interruption of the conductive coating.

For the electrically conductive connection of the control ground with the power ground and of the two grounds with an external earth line, a ground star point is preferably arranged on the ground layer. In this manner, no additional lines for interconnection of the grounds are necessary. Such lines could otherwise serve as additional interference sources for radiation of high-frequency interference signals.

In order to structure the interference current loops to be as small as possible, the capacitances are advantageously arranged adjacent to the ground connections of the power components. It is particularly advantageous if a respective capacitance is associated with each power component. In that case, several very small current loops are made possible, which in their turn by reason of their small size exhibit only a very small aerial effect.

Preferably, the capacitances are electrically conductively connected on the lowest resistance path directly with the ground connections of the power components and with the ground connections of the digital components.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is a schematic view of a first control device with a multilayer circuitboard which comprises a control circuit, a power circuit, a control ground and a power ground separated therefrom; and Fig. 2 is a schematic view of a second control device with two multilayer circuitboards which each comprise a power circuit, a control ground and a power ground separated therefrom.

In the described embodiments the intention is that, in a control device, in particular for the control of functions of a motor vehicle, with at least one control circuit having digital components for obtaining a control signal from an input signal, at least one power circuit having power components for signal output, at least one first area] ground (control ground) associated with the control circuit and at least one second area] ground (power ground) which is associated with the power circuit and spatially separate from the control ground and which is electrically insulated from the control ground with exception of an electrically conductive connection, the radiation of high-frequency interferences is to be minimised by structuring the current loops of the high-frequency interference currents to be as small as possible in terms of area by at least one additional electrical connection of the control ground with the power ground by means of capacitances, so that the aerial effect connected with the current loops is as small as possible. 20 In the case of the embodiment of Fig. 1, the control device is constructed as multilayer circuitboard 1 which has a control circuit 2 with digital components 3 and a power circuit 4 with power components 6. The digital components 3, for example microprocessors, storage devices and the like, are arranged in one region 7 of the circuitboard and the power components 6 in another region 8 of the circuitboard.

The control circuit 2 is associated with a first area] ground, i.e. the control ground 9, and the power circuit 4 with a second area] ground, i.e. the power ground 11. The control ground 9 is spatially separate from the power ground 11 and, with the exception of an electrically conductive connection in the form of a ground star point 15, electrically insulated by a non-conducting gap 12. In the case of the embodiment of Fig. 1, the control ground 9 and the power ground 11 are parts of a single ground layer and the gap 12 is simply an interruption of the conductive coating forming this ground layer.

A plug strip 13, one pin 14 of which is connected with at least one external earth line (not illustrated), is connected to the multilayer circuitboard 1 for the connection of external lines. The pin 14, the control ground 9 and the power ground 11 are electrically conductively connected together at the common ground star point 15 formed by the ground layer. In that case, the pin 14 is preferably arranged directly on the ground layer and in contact therewith. Consequently, connecting lines between the control ground 9, the power ground 11 and the pin 14 are superfluous. As is further evident from Fig. 1, the power current path (arrows A) leads past the plug strip 13 to the pin 14 and is conducted away by way of this by the external earth line.

With this arrangement, a high-frequency interference, for example due to a steep signal edge, caused by the digital components 3 can be conducted away by the power components 6, for example power output stages for amplification of the signals, along the current path denoted by the arrows A to the earth 1 ine. A relatively large current loop would result and would act as an effective aerial not only for radiation, but also for reception of interference. The external earth line would act as further aerial.

In order to prevent these large current loops, capacitances 16, which each provide a short-circuit on the shortest path in the highfrequency interference current loops, are arranged adjacent to the power components 6. As a result of these short-circuits, the current path from the source of the interference currents to the sink is reduced substantially, whereby the aerial effect of the interference current loops is reduced appreciably.

Preferably, the capacitances 16 are arranged spatially adjacent to the power components 6 and a respective capacitance 16 is associated with each power component 6. Consequently, the resulting current loops are very small and function only as particularly small aerials.

The capacitances 16 are electrically conductively connected on the lowest resistance path directly with the ground terminals of the power components 6 and with the ground terminals of the digital components 3. They are preferably connected electrically conductively with the terminal legs of the ground terminals of the power components 6 and, for example, with the ground area of the computer core.

The capacitances 16 are preferably ceramic capacitors or film capacitors.

Fig. 2 shows a further embodiment of a control circuit, in particular for the control of functions of a motor vehicle. The embodiment according to Fig. 2 differs from that according to Fig. 1 only by the provision of two multilayer circuitboards 1, which each comprise at least one control circuit 2, at least one power circuit 4 and control grounds 9 and power grounds 11 respectively associated with these. The control ground 9 and power ground 11 of each circuitboard are again separated spatial.ly from each other by an electrically nonconductive gap 12. Each circuitboard 1 also comprises a plug strip 13.

As is evident from Fig. 2, the two circuitboards 1 are connected together by way of a circuitboard connector 17. The power grounds 11 are connected together by way of an earth line 18. One of the circuitboards 1 has the ground star point 15, to which the control grounds 9 and the power grounds 11 of the two circuitboards 1 are connected by a ground terminal pin 14 of one of the plug strips 13. The two circuitboards 1 are preferably mounted in the control device so 10 as to be disposed one above the other.

It is, of course, possible to link more than two multilayer circuitboards 1 together in the described manner.

Claims

1. A control device comprising a control circuit with digital components for obtaining a control signal from an input signal, a power circuit with power components for a signal output, a first area] ground associated with the control circuit, a second area] ground associated with the power circuit and spatially separated and electrically insulated from the first ground apart from an electrically conductive connection, and at least one capacitance electrically connecting t-he first and second grounds on the shortest path to form a shortcircuit in high-frequency interference current loops.

2. A control device as claimed in claim 1, wherein the grounds are spatially separated by an electrically non-conductive gap.

3. A control device as claimed in claim 1 or claim 2, wherein the circuits are arranged on a multilayer circuitboard and the first and second grounds are provided by a layer on the circuitboard.

4. A control device as claimed in claim 3, wherein the first ground, the second ground and a terminal for an external earth line are electrically conductively connected together at a common ground star point on the layer.

5. A control device as claimed in any one of the preceding claims, wherein the capacitance or capacitances is or are arranged spatially adjacent to the power components.

6. A control device as claimed in claim 5, comprising a respective capacitance associated with each power component.

7. A control device as claimed in claim 6, wherein the capacitances are electrically conductively connected directly with ground connections of the power components and with ground connections of the digital components on the path of lowest resistance.

8. A control device substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

9. A control device substantially as hereinbefore described with 10 reference to Fig. 2 of the accompanying drawings.