FR3067212B1 - ELECTRONIC DEVICE WITH TREATMENT MODULE ACTING ON A RESONANCE FREQUENCY OF A MASS LOOP - Google Patents

Abstract

An electronic device (DE) comprises an electronic card (CE) provided, on the one hand, with a main zone coupled to an element (EM) defining a reference ground, via a first electrical connection (L1), and to a electrical equipment, via an electric cable (CA) provided with a shield (BC) and in which circulates a parasitic current resonating at a resonant frequency, and, secondly, an auxiliary zone (ZA) containing a separate ground plane (PM) to which this shielding (BC) is connected. This electronic card (CE) also comprises at least one processing module (MT) interconnecting the main (ZP) and auxiliary (ZA) zones and shifting the resonance frequency in a selected frequency band and / or attenuating the intensity parasitic current for this resonance frequency.

Description

The invention relates to electronic devices which comprise an electronic card coupled, on the one hand, to an electrical equipment via an armored electrical cable and, on the other hand, to an electrical equipment via an electric shielded cable and, on the other hand, to an element defining a reference ground via an electrical connection.

Some electronic devices include an electronic card having a main area and an auxiliary area electrically and physically isolated from each other. The main zone is coupled to an element which defines a reference ground, via a first electrical connection, and to an electrical equipment, via an electric cable provided with a shield. The auxiliary zone contains a ground plane to which this shield is connected.

This shielded electrical cable is, for example and not limited to, an LVDS interface ("Low Voltage Differential Signaling" - Low-Voltage Differential Signaling), Ethernet or A2B® ("Automotive Audio Bus®" from the company Analog Device).

As known to those skilled in the art, the shielding of this electrical cable, the first electrical connection, the element defining the reference ground (for example a chassis of a motor vehicle), and a second electrical connection or a parasitic capacitance formed between the electrical equipment and this element together form a so-called ground loop in which circulates a parasitic current that can resonate at at least one resonant frequency.

Due to this parasitic current flowing, the ground loop radiates, which induces electromagnetic disturbances penalizing for certain functions, such as the reception of radio waves. In fact, the parasitic current has a frequency that frequently comes into resonance with a so-called resonance frequency. This resonance frequency varies as a function of the lengths of the shielded electrical cable and the electrical ground connections, the geometrical layout of the shielded electrical cable and the electrical ground connections, and the dimensions and impedance of the ground loop. and therefore certain frequency bands (for example critical for the reception of radio waves) can be more or less impacted from one system to another.

This disadvantage is particularly troublesome when it proves difficult, if not impossible, to modify the environment of electronic equipment, and / or to move electronic equipment, and / or to change the length of the shielded electrical cable and / or the lengths of the electrical connections of mass, and / or to modify the electronic card.

It has certainly been proposed to couple the main and auxiliary areas of the electronic card via a capacitive component, when galvanic isolation is necessary (generally for reasons of electrical safety and not electromagnetic compatibility (or EMC)). But this only serves to block the DC component that can pass through the shielded electrical cable. The invention is therefore particularly intended to improve the situation.

To this end, it proposes an electronic device comprising an electronic card equipped, on the one hand, with a main zone adapted to be coupled to an element defining a reference ground, via a first electrical connection, and to an electrical equipment, via an electric cable provided with a shield and in which circulates a parasitic current resonating at at least one resonant frequency, and, secondly, an auxiliary zone containing a separate ground plane to which it is adapted to be connected this shield.

This electronic device is characterized in that its electronic card also comprises at least one processing module interconnecting the main and auxiliary zones between them and shifting the resonance frequency in a selected frequency band and / or attenuating an intensity of the parasitic current for this resonance frequency.

This offset and / or this attenuation makes it possible (tented) to minimize the electromagnetic disturbances for the frequency band to be protected, and therefore not to (or almost not) penalize the function that uses the latter.

The electronic device according to the invention may comprise other characteristics that can be taken separately or in combination, and in particular: the / each processing module may comprise a resistive component, or an inductive component, or at least two components chosen from a resistive component, an inductive component and a capacitive component and coupled together; the auxiliary zone may comprise a portion interposed between the ground plane and the main zone and comprising second electrical connections distant from each other, defining connection terminals for each component of the processing module and among which at least one is connected to the ground plane. In this case, its electronic card comprises at least a third link interconnecting the portion intercalated with the main zone and defining another connection terminal for one of the components of the processing module; The second and third electrical connections may be printed circuits; it can comprise several processing modules. In this case, only one of these processing modules interconnects the main and auxiliary zones; - his card can be a printed circuit board; it can, for example, constitute a computer (electronic) or a receiver of radio waves. The invention also proposes a vehicle, possibly of automobile type, and comprising an element defining a reference mass, at least one electrical equipment connected to an electric cable provided with a shield and in which circulates a parasitic current having at least one frequency resonance, and at least one electronic device of the type shown above, which is coupled to this electric cable and coupled to this element. Other features and advantages of the invention will appear on examining the detailed description below, and the accompanying drawings, in which: - Figure 1 schematically and functionally illustrates an example of an electronic device according to the invention coupled to an element defining a ground plane and electrical equipment, - Figure 2 schematically illustrates, in a perspective view, a portion of a first embodiment of an electronic device according to the invention which is coupled to the shield of 3 illustrates schematically and functionally, in a view from above, a portion of a second exemplary embodiment of an electronic card of an electronic device according to the invention, - Figure 4 illustrates schematically and functionally, in a view from above, a portion of a third embodiment of an electronic card of a electronic device according to the invention, and - Figure 5 schematically illustrates in a diagram the evolution of the emission level (in dB) of a parasitic current as a function of frequency (in Hz) in the absence a processing module (c1), in the presence of a first example of a processing module (c2), and in the presence of a second example of a processing module (c3). The purpose of the invention is notably to propose an electronic device DE comprising an electronic card CE intended to be coupled to an electrical equipment EE, via a shielded electrical cable CA, and to an element EM defining a reference ground, via a first link L1, and able to act on a parasitic current to reduce as much as possible the electromagnetic disturbances it induces.

In what follows, it is considered, by way of non-limiting example, that the electronic device DE, the EE electrical equipment and the EM element are part of a motor vehicle, such as a car. But the invention is not limited to this application. Indeed, the electronic device DE, the electrical equipment EE and the element EM can be part of any system, including a vehicle (land, sea (or fluvial) or air), an installation (possibly industrial type), a device (possibly for the general public), or a building.

FIG. 1 shows schematically and functionally an example of an electronic device DE according to the invention, coupled to an element EM defining a ground plane and to an electrical equipment EE. For example, when the system is a motor vehicle, the EM element may be a part of the chassis, the electronic device DE may be an electronic calculator or a radio wave receiver, and the EE electrical equipment may be another calculator electronic.

The electronic device DE comprises an electronic card CE coupled, on the one hand, to the electrical equipment EE, via an electric cable CA provided with a shielding BC, and, on the other hand, to the element EM, via a first electrical connection L1. For example, this electronic card CE may be a printed circuit board.

As illustrated in FIG. 2, the electronic card CE is provided with a main zone ZP and an auxiliary zone ZA electrically and physically isolated from each other, but intended to be coupled via a processing module MT described further.

The main zone ZP is coupled via the first electrical connection L1 to the EM element defining the reference ground in order to be placed at a zero reference voltage (0 V), and via the shielded electrical cable CA to the electrical equipment. EE. The first electrical connection L1 may, for example, be an electrical wire provided with an insulating sheath, as in the example illustrated in FIG. 1, or a small metal column provided with screws, as in the example illustrated in FIG. 2.

The auxiliary zone ZA contains a separate ground plane PM to which is connected the shielding BC of the electric cable CA, via a coupling coupling LC, for example welded and / or screwed.

Note that the EE electrical equipment could also be coupled to the EM element via another electrical connection (not shown). But without this other electrical connection, there is still a coupling between the electrical equipment EE and the element EM by at least one parasitic capacitance CP when one is in the presence of a high frequency current, as shown in FIG. figure 1.

The shielding BC of the electric cable CA, the first electrical connection L1, the element EM, the stray capacitance CP and the possible other electrical connection together form a ground loop in which circulates a parasitic current entering into resonance at least one frequency resonance and on which we want to act so that it disturbs as little as possible a frequency band to protect bp.

The electronic card CE also comprises at least one processing module MT which interconnects the main ZP and auxiliary ZA zones and is arranged so as to shift this (each) resonant frequency in a chosen frequency band different from the frequency band to protect bp and / or attenuate the intensity of this parasitic current for this (each) resonance frequency.

Thanks to this shift and / or this attenuation, the electromagnetic disturbances become minimal for the frequency band to be protected bp, and therefore the function that uses the latter (bp) is not, or almost not, penalized. For example, when the function is the reception of radio waves, the quality of reception is not, or almost not, degraded. By way of example, the (each) processing module MT may comprise a resistive component C2, or an inductive component C1, or at least two components Cj chosen from a resistive component C2 (j = 2), an inductive component C1 ( j = 1) and a capacitive component C3 (j = 3) and coupled together.

In the first example, which is not limited to FIG. 2, the electronic device DE comprises only a processing module MT comprising a resistive component C2 and a capacitive component C3 connected in series and defining an RC circuit.

In the second example shown in non-limiting manner in FIG. 3, the electronic device DE comprises only a processing module MT comprising an inductive component C1.

In the third example, not limited to FIG. 4, the electronic device DE comprises only a processing module MT comprising a resistive component C2, an inductive component C1 and a capacitive component C3 connected in series and defining an RLC circuit.

The processing module MT, which is installed on the electronic card CE and used to act on the (each) resonant frequency, can be determined by the calculation according to the ground loop, and in particular the respective dimensions of its components and each parasitic capacitance CP, and the frequency band to be protected bp. As a variant, this processing module MT can be determined by means of tests carried out in a development phase with different effective combinations of components Cj installed on the electronic card CE (hence the interest of the presence of different modules ( corresponding to different combinations)).

In order to facilitate the installation of the processing module MT on the electronic card CE, the latter (CE) may comprise second L2 and third (s) L3 electrical connections, as shown without limitation in FIGS. 3 and 4. More precisely, the auxiliary zone ZA may comprise a buffer portion PZ interposed between the ground plane PM and the main zone ZP and comprising second electrical connections L2 distant from each other, defining connection terminals for each component Cj of a processing module MT and at least one of which is connected to the ground plane PM, and the electronic card CE may comprise at least one third link L3 interconnecting this portion PZ to the main zone ZP and defining another connection terminal for the one components Cj of this processing module MT.

It will be understood that each component Cj of a processing module MT is soldered to a terminal of at least one of the second electrical connections L2 and that a component Cj of this same processing module MT (possibly the same (Cj) as the aforementioned) is soldered to a terminal of one of the second electrical connections L2 and to a terminal of a third electrical connection L3.

Note that the second L2 and third (s) L3 electrical connections may be printed circuits, although this is not mandatory.

In the second and third examples, which are not limited to FIGS. 3 and 4, the electronic card CE comprises three second electrical connections L2 and two third electrical connections L3. But it could comprise more than or less than three second electrical connections L2 and / or more than or less than two third electrical connections L3.

It will also be noted, although it does not appear in FIGS. 2 to 4, that the electronic device DE may comprise several processing modules MT. In this case, only one of them interconnects the main ZP and auxiliary ZA zones, and therefore each other processing module MT is not used. This option is intended to make it possible to obtain several different offsets and / or attenuations with the same electronic card CE, respectively using the various processing modules MT according to the needs for action in the system under consideration.

FIG. 5 diagrammatically illustrates an evolution diagram of the emission level (in dB) of a parasitic current as a function of frequency (in Hz). Three curves c1 to c3 are present in this diagram. The first curve c1 corresponds to an electronic device of the prior art, that is to say devoid of processing module MT. The second curve c2 corresponds to an electronic device DE, according to the invention, comprising (and using) a processing module MT comprising an inductive component C1 and a capacitive component C3 connected in series and defining an LC circuit. The third curve c3 corresponds to an electronic device DE, according to the invention, comprising (and using) a processing module MT comprising only a resistive component C2, or a resistive component C2 and a capacitive component C3 connected in series and defining a RC circuit.

By comparing the first c1 and second c2 curves it is observed that the resonant frequency of the parasitic current, initially contained in the frequency band to be protected bp (see c1), is shifted to the right outside the latter (bp) thanks to the use of a processing module MT defining an LC circuit (see c2), for the relevant configuration of the system.

Similarly, by comparing the first c1 and third c3 curves it is observed that the resonance frequency of the parasitic current, initially contained in the frequency band to be protected bp (see c1), is both slightly shifted to the right of the latter. (bp) and greatly attenuated by the use of a processing module MT comprising a resistive component C2 or defining an RC circuit (see c3), for the relevant configuration of the system. The invention offers several advantages, among which: the provision of development levers during the validation phases of the systems (such as, for example, vehicles), in order to obtain the electromagnetic compliance initially provided for, the possibility of remedying a nonconformity strongly penalizing a function and discovering it late, even though it is too late to modify the electronic card or that the search and the implementation of a palliative solution would be too expensive and time-consuming.

Claims (9)

An electronic device (DE) comprising an electronic card (CE) provided with i) a main zone (ZP) adapted to be coupled to an element (EM) defining a reference ground, via a first electrical connection (L1), and to an electrical equipment (EE), via an electric cable (CA) provided with a shield (BC) and in which circulates a parasitic current resonating at at least one resonant frequency, and ii) an auxiliary zone (ZA) containing a separate ground plane (PM) and which is adapted to be connected to said shield (BC), characterized in that said electronic card (CE) further comprises at least one processing module (MT) interconnecting them said main (ZP) and auxiliary (ZA) zones and shifting said resonance frequency in a selected frequency band and / or attenuating an intensity of said parasitic current for said resonant frequency. 2. Device according to claim 1, characterized in that said processing module (MT) comprises a resistive component, or an inductive component, or at least two components (Cj) selected from a resistive component, an inductive component and a capacitive component and coupled together. 3. Device according to claim 2, characterized in that said auxiliary zone (ZA) comprises a portion (PZ) interposed between said ground plane (PM) and said main zone (ZP) and comprising second electrical connections (L2) distant each other, defining connection terminals for each component (Cj) of said processing module (MT), and of which at least one is connected to said ground plane (PM), and in that said electronic board ( CE) comprises at least one third link (L3) interconnecting said portion (PZ) to said main zone (ZP) and defining another connection terminal for one of said components (Cj) of said processing module (MT). 4. Device according to claim 3, characterized in that said second (L2) and third (s) (L3) electrical connections are printed circuits. 5. Device according to one of claims 1 to 4, characterized in that it comprises a plurality of processing modules (MT), only one of them interconnecting said main zone (ZP) and auxiliary (ZA) . 6. Device according to one of claims 1 to 5, characterized in that said electronic card (CE) is a printed circuit board. 7. Device according to one of claims 1 to 6, characterized in that it constitutes a calculator or a receiver of radio waves. 8. Vehicle comprising an element (EM) defining a reference ground and at least one electrical equipment (EE) connected to an electric cable (AC) provided with a shield (BC) and in which circulates a parasitic current resonating with at least one resonant frequency, characterized in that it further comprises at least one electronic device (DE) according to one of the preceding claims, which is coupled to said electric cable (CA) and coupled to said element (EM). 9. Vehicle according to claim 8, characterized in that it is automotive type.