Description

The invention relates to a coupling structure for a galvanically separating transmission of a high frequency signal and a corresponding inverter. The structure is adapted to be particularly used within a multilayer printed circuit board (PCB).

It has become a technical commodity to implement communication options within electronic devices. This way, remote monitoring or control of such electronic devices has become viable. Advantageously, wireless communication solutions are used to minimize installation effort for the communication. It is known to implement a radio transmission such as Bluetooth, WLAN, ZigBee or alike for exchange of data between a sending and a receiving unit.

A coupling structure for the transmission of radio signals within a PCB is for example disclosed in the document US2010/0245202.

A specific requirement for the transmission of signals within a device is generated, if a galvanic separation between the signal line as well as the reference potential line of an antenna relative to its sending or receiving unit is requested, as it is common for instance in photovoltaic inverters. A known option to provide such a separation by a capacitor may in this case not be viable, since such capacitors requiring a isolation voltage rating of sometimes significantly exceeding 5kV are often not available, too expensive, or they tend to excessively attenuate the high frequency transmission signal.

Therefore, it is an object of the invention to provide a coupling structure for transmitting a high frequency signal under galvanic separation between an antenna and a sending or receving unit that is cost-effective and at the same time ensures a high transmission quality. A coupling structure with the features of independent claim 1 solves this problem. Embodiments of the invention are described in the dependent claims 2 to 10. A communicaton structure comprising the inventive coupling structure and an inverter with such a communication structure is claimed in the claims 1 1 and 12, with embodiments of the inverter described in dependent claims 13 and 14.

According to the invention, a coupling structure for a galvanically separating transmission of a high frequency signal between an antenna and a sending/receiving unit comprises a first reference plate arranged in a first metal layer of a multilayer printed circuit board, and a second reference plate arranged in a second metal layer of the multilayer printed circuit board. The first reference plate is or may be connected to a reference potential terminal of the sending/receiving unit and the second reference plate is or may be connected to a reference potential terminal of the antenna. The coupling structure further comprises a first metal line connected to a signal terminal of the sending/receiving unit and arranged in a third metal layer of a multilayer printed circuit board, and a second metal line connected to a signal terminal of the antenna and arranged in a fourth metal layer of a multilayer printed circuit board. The third and fourth metal layers are interposed between the first and the second metal layer. In a projection perpendicular to the plane of the multilayer printed circuit board, the first reference plate and the second reference plate form a complementary arrangement with a boundary line. The first metal line and the second metal line form a ring structure in this projection, wherein the ring structure comprises a first ring segment and a second ring segment with the first metal line and the second metal line running in parallel to each other in the first and second ring segment. In a third ring segment and a fourth ring segment, each arranged at both ends between the first and second ring segment, the ring structure is solely formed by the first metal line and by the second metal line, respectively. An end of the first metal line and an end of the second metal line are each located at the boundary line within the projection.

The coupling structure described allows for a low loss transmission of high frequency signals, wherein the signal potential as well as the reference potential are galvanically separated. The various conductor potentials are located on different layers of a multilayer printed circuit board, so that leakage path lengths do not need to be regarded. Accordingly, the coupling structure becomes particularly compact and requires little area on the PCB. At the same time, even large potential differences of several kilovolts, for example 5kV or even more than 6kV, as rated within photovoltaic inverters, are insulated from each other reliably.

In a projection, the coupling structure may comprise a round shape, such as a circle or an ellipse, or a rectangular shape. A mixture of both with a number of corners and roundings is as well contemplated.

Preferably, the second and/or third metal layer may be arranged between the first and fourth metal layers comprising the reference potential plates. Particularly advantageous is an arrangement of the second metal layer between the first and the third metal layer. This results in a effective coupling between the signal carrying lines.

In an embodiment of the invention, the width of the metal lines is varied within the ring structure relative to the connecting segment of the ring structure. Preferably, the width of the metal line within the ring structure is increased relative to the connecting structure. In addition, the width of the metal lines within the ring structure may be varied, for example the width may vary between ring segments such as a width within the first and second ring segment being larger than a width in the third and fourth ring segment. Preferably, the length and width of each ring segment is selected to provide a constructive interference of the signal

components transmitted within the first and second ring segment. All these measures are suitable to improve the transmission quality of the signals within the selected frequency range.

Frequency ranges for the high frequency signal of particular technical interest are between 2 and 3 GHz, and between 5.5 and 6.5 GHz. These frequency ranges are approved for radio transmission of data signals.

As further aspects of the inventions, communication structures are provided comprising an antenna, a sending/receiving unit and the aforementioned coupling structure. The coupling structure couples the antenna to the sending/receiving unit with galvanic separation. At the same time, transmission of signals between the antenna and the sending/receiving unit is possible. The communication structure may form part of an inverter, in particular a photovoltaic inverter, and provides wireless communication via radio transmission protocols such as Bluetooth, WLAN, and ZigBee.

In the following, embodiments of the invention are illustrated and explained by means of figures showing:

Fig. 1 an inverter with a communication structure according to the invention,

Fig. 2 a top view of a coupling structure according to the invention in a partly covered view of components of the coupling structure

Fig. 3 a cross section through the coupling structure along a line ΙΙ-ΙΓ of Fig. 2,

Fig. 4 a top view of a variant of the coupling structure according to the

invention with a circular ring structure in a partly covered view,

Fig. 5 a top view of a variant of the coupling structure according to the

invention with a rectangular ring structure in a partly covered view,

Fig. 6 three detailed views of variants of metal line arrangements of a coupling structure according to the invention with variations of line widths, and

Fig. 7 a variant of a coupling structure without a ring structure.

The figures are considered as an illustration of aspects of the invention. Type, form and arrangement of the elementes are merely an example for realizing the inventive teaching, and are not meant to limit the invention to the embodiments shown. Terms such as "above", "below", left", right" and similar expressions are related to the position within the figures and shall support easier understanding of the description. Therefore, these terms are not essential features of a claimed apparatus, which may as well comprise other orientations of the elements. The invention shall only be limited by the wording of the claims.

Fig. 1 shows an inverter 1 that may in particular be a solar inverter. The inverter 1 comprises a sending/receiving unit 40 that is connected to a coupling structure 50 by two conductors. A signal terminal 41 of the sending/receiving unit 40 is connected to a first terminal 51 of the coupling structure 50, while a reference potential terminal 42 is connected to a second terminal 52 of the coupling structure 50 and to a reference potential 60.

The coupling structure 50 is further connected to an antenna 30, wherein a signal terminal 31 of the antenna 30 is connected to a third terminal 53 of the coupling structure 50, and a reference potential terminal 32 of the antenna 30 is connected to a fourth terminal 54 of the coupling structure 50. Optionally, the reference potential terminal 32 may be connected to a housing 10 of the inverter 1 , as shown. The housing 10 may be connected to a ground potential 70. The components mentioned may form parts of a communication structure 20 of the inverter 1 .

Further components of the inverter 1 , such as a connected solar generator or a grid connection, are not shown to simplify the illustration. In such an application, the reference potential 60 differs from a ground potential 70 during operation of the inverter 1 by several 100 volts, e.g. by 600 V to 1000 V. In such a case, the coupling structure 50 is required to ensure a galvanic separation up to a voltage exceeding the operation voltage by factors. For instance, safety regulations require a galvanic separation under the given circumstance up to a voltage of 6000 V, with sufficiently low attenuation of a high frequency signal to be transmitted. Such a regulation currently cannot be met by a coupling structure just consisting of a single capacitor. Furthermore, such a capacitor or capacitors would require significant space, since a sufficient leakage path length for a reliable isolation of the capacitor electrodes is to be provided.

Fig. 2 shows a top view of a coupling structure according to the invention, formed as a metal structure within a mutli layer PCB. The top view corresponds to a projection to the plane of the PCB, wherein the components shown are distributed among a plurality of metal layers of the PCB. In Fig. 2a, the full arrangment with partially overlapping components of the coupling structure 50 is shown, while Fig. 2b and Fig. 2c each only show a part of the components to illustrate how the components overlap. Therefore, Fig. 2a forms a superposition of both Figs. 2b and 2c. A first reference plate 200 as part of a first metal layer of a multilayer PCB extends to a boundary line 250. This boundary line 250 also forms a boundary of a second reference plae 210 of a different metal layer of the multilayer PCB, wherein the second reference plate 210 extends to a side of the boundary line 250 opposite to the first reference plate 200. Accordingly, the first and second reference plates 200, 210 form a complementary arrangement, wherein the reference plates do not overlap in a top view, but form a complementary coverage of the coupling structure 50. The metal layers of the first and second reference plates 200, 210 are advantageously selected as outer metal layers of the multilayer PCB.

Fig. 2c also shows in addition to the reference plate 200 a first metal line 220 comprising a connecting segment 221 and a coupling section 222. The reference plate 200 and the first metal line 220 are formed within different metal layers of the PCB and jointly form a wave guide for a high frequency signal entering or leaving the coupling structure 50. For this purpose, the connecting segment 221 may be connected via the terminal 51 to the signal terminal 41 , and the reference plate 200 may be connected via the terminal 52 to the reference potential terminal 42 of the sending/receiving unit 40 of Fig. 1 . The coupling section 222 has a hook shape, such that a part of the coupling section 222 overlaps with the reference plate 200, but extends across the boundary line 250, and returns back to the boundary line 250 over two corners.

Fig. 2b shows a second metal Iine230 with a connecting segment 231 and a coupling section 232 and a reference plate 210. The reference plate 210 and the second metal line 230 are formed within further, different metal layers of the PCB and jointly form a wave guide for a high frequency signal entering or leaving the coupling structure 50. For this purpose, the connecting segment 231 may be connected via the terminal 53 to the signal terminal 31 , and the reference plate 210 may be connected via the terminal 54 to the reference potential terminal 32 of the antenna 30 of Fig. 1 . The shape of the coupling section 232 corresponds to a shape of the coupling section 222, rotated by 180°, and also ends at the boundary line 250.

As shown in Fig. 2a, the coupling sections 222, 232 are laterally arranged relative to each other so as to form a rectangular ring structure 240, divided in four ring segments 241 , 242, 243, 244. In a first ring segment 241 and a second ring segment 242, both coupling sections 222, 232 overlap, while in a third ring segment 243 the ring structure 240 is only formed by the coupling section 232, and in a fourth ring segment 244 the ring structure 240 is only formed by the coupling section 222. The third and fourth ring segments 243, 244 are arranged between the first ring segment 241 and the second ring segment 242 on both sides.

Preferably, the metal lines 220, 230 are formed such that the shape of one of the metal lines can be transformed into the shape of the other metal line by rotation by 180° around a center point of the coupling structure 240. This way, the structure provides comparable transmission properties for both transmission directions.

The connection segment 221 of the first metal line 220 comprises a lower width as compared to the coupling section 222, thereby providing a step in the wave impedance of the wave guide formed by the metal line 220 and the reference plate 200 at the changeover from the connecting segment 221 to the coupling section 222. A further step of the wave impedance along the wave guide occurs at the crossing of the first metal line 220 over the boundary line 250 due to the end of the reference plate 200. Respective steps of the wave impedance occur within the wave guide formed by the second metal line 230 and the reference plate 210. It may be contemplated to effect steps of the wave impedance by an increase of the metal line width at the changeover between the connection segment 221 and the coupling section 222 instead of a reduction as described above. The choice of an optimum width depends inter alia on the properties and dimension of the PCB substrate.

By the steps of the wave impedance at the location of the changeover between ring segments a transformation of wave modes of the high frequency signal into other wave modes is caused, such that the signal is at least partially transferred from one wave guide to the other wave guide. Adjustment of the phase orientation of the signal components transferred at the respective step locations for constructive interference may be achieved by selecting appropriate dimensions of the ring structure 240. This way, reflection and transmission properties of the coupling structure may be optimized for the operation frequency band of the coupling structure, for example 2.4-2.5 GHz). These properties may be adjusted with the following, non-exclusive list of parameters:

- Thickness and material of the metal layers

- Distance between the metal layers and kind of dielectric material between the metal layers

- Width and length of the metal lines 220, 230 within the respective ring segments

- Length of the overlap 260 of the metal lines 220, 230 over the boundary line 250, in this example half of the length of the ring structure 240, and width 270 of the ring structure 240.

The selection of one tenth of the wave length λ of the operation frequency for the width 270 is preferred, and a length of the overlap 260 of λ/13.5.

An example set of parameters for a coupling structure 50 with an operation frequency band of 2.4-2.5 GHz is given in the following table:

To better illustrate the arrangement of the components of the coupling structure 50, Fig. 3 shows a cross section of the coupling structure of Fig. 2a along the line ΙΙ-Ι . The reference plate 200 is part of an upper metal layer, the reference plate 210 is part of a lower metal layer. These metal layers may be outer metal layers of a multilayer PCB 300 and disposed at an outer surface thereof. However, further metal layers may as well be disposed over, respectively under the reference plates 200, 210. The upper and/or lower metal layer, as well as other metal layers referred to in the following description, may comprise copper or any other metal or metal alloy used within PCBs.

Between the metal layers of the reference plates 200, 210, two further metal layers are arranged, wherein one metal layer facing the lower reference plate 210 and separated therefrom by a layer of insulating material comprises the second metal line 230. The second metal line 230 forms a wave guide in combination with the reference plate 210. The second metal line 230 reaches over the reference plate 210 ending at the boundary line 250 by an overlap 260 within the cross section II- ΙΓ, and forms part of the third ring segment 243. Other than shown in Fig. 3, the second metal line 230 may run over its full length or just sectionally within a plane having a smaller distance to the plane of the reference plate 200 compared to a distance to the plane of the reference plate 210. Accordingly, the first metal line 220 may run over its full length or just sectionally within a plane having a smaller distance to the plane of the reference plate 210 compared to a distance to the plane of the reference plate 200.

The first metal line 220 shown in Fig. 2a or Fig. 2c, respectively, is included in the cross section 11— 11 ' only as a coupling section 222 extending from the boundary line 250 as the end of the reference plate 200 by a further overlap 260 into the adjacent region. This determines the dimension of the first ring segment 241 , where the two metal lines 220, 230 run in parallel with electrical separation by a further layer of insulating material of the PCB 300. The thickness of this further layer is selected to provide the desired voltage rating of the galvanic separation within the coupling structure 50. The course of the remaining parts of the first metal line 220, not shown, results from a reference to the Figs. 2a and 2c.

Fig. 4 shows an alternative embodiment of a coupling structure 50 according to the invention, wherein only the course of the first metal line 220 and the second metal line 230 is shown. The coupling structure 50 comprises a circular ring structure 240, wherein again the ring segments 241 and 243 are formed by parts of the two metal lines 220, 230 running in parallel. The ring segment 243 is only formed by the second metal line 230, while the ring segment 244 is only formed by the first metal line 220. Here again, the coupling properties may be adjusted to the operation frequency by the selection of the length of the individual ring segments 241 , 242, 243, 244. Other round shapes of the ring structure 240, such as for example an ellipse shape, or as well arbitrarily corrugated or angled courses of the metal lines 220, 230, may be contemplated, wherein shapes, in which the course of the first metal line 220 may be transformed into the course of the second metal line by a rotation by 180° around a point located on the boundary line 250 are preferred.

To illustrate the course of the metal lines 220 and 230, two inserts of Fig. 4 show only one of the metal lines (Fig. 4b for metal line 223, Fig. 4c for metal line 220). Put on top of each other, the structure of Fig. 4a is yielded.

Fig. 5a shows a coupling structure 50 according to the invention that differs from the structure of Fig. 2 in that the connection of the metal line 220 to the ring structure 240 is provided between the first ring segment 241 and the third ring segment 243. Accordingly, the second metal line 230 is connected at the opposite side of the ring structure 240. The resulting courses of the two metal lines 220 and 230 is shown in the Figs. 5b and 5c.

Fig. 6 shows further embodiments of a design of a metal line. Only one metal line is shown, while the other metal line may be complemented with one of the embodiments accordingly to form the full ring structure 240. As already stated, it is preferred to use the same of the disclosed designs for both metal lines to yield a coupling structure 50 with rotation symmetry of the metal lines 220, 230.

Instead of an abrupt end of the metal line, the left portion of Fig. 6 shows a gradual decrease of the line width, in particular a stepwise decrease. The width may however as well decrease continuously. The region of line width decrease may extend over a full ring segment or just a part of it.

The middle portion of Fig. 6 shows a so called„hammer-head" design of a metal line. At the end of the metal line a region exists with an increased line width. The right portion of Fig. 6 shows another variant of a ring structure 240 with individual line width for each of the ring segments 241, 242, 243, 244. The transmission properties of the ring structure 240 may be adjusted to the specific requirements of an application by the selection of the line width. It may be preferred to select different line width for both metal lines overlapping within the first ring segment 241 and the third ring segment 243 to achieve a desired transmission characteristics. The line width within the first ring segment 241 and within the third ring segment 243 may be selected to differ from each other for that purpose.

Although not shown, a variation of the line width within the transition region between ring segments is also possible to achieve optimum transmission properties for high frequency signals for a specific application.

A further variant of a coupling structure 50 without a ring structure is shown in Fig. 7. The upper portion of Fig. 7 shows a top view of the coupling structure 50, while the lower portion of Fig. 7 shows a cross section along line I II— 111 ^* _ Here again, the reference plates 200, 210 form a complementary arrangement within the coupling structure region. The first metal line 220 runs in parallel to the reference plate 200 and extends across the boundary line 250 between the reference plates 200 and 210 by an overlap 260. Accordingly, the second metal line 230 runs in parallel to the reference plate 210 and extends across the boundary line 250 between the reference plates 200 and 210 by an overlap 260. In the region of the overlaps 260, both metal lines 220, 230 run in parallel to each other and overlap to constitute coupling sections 222, 232.

The invention is not limited to the embodiments shown, but may be modified and complemented in various ways. In particular, it is possible to combine the mentioned features in other ways as explicitly described and to add known methods or components to achieve a cost effective and reliable signal

transmission within an inverter, while ensuring a galvanic separation of signal and reference potentials, thereby providing an inverter with improved operational safety at low cost. Bezugszeichenliste

1 Inverter

10 Housing

20 Communication structure 30 Antenna

31 Signal terminal

32 Reference potential terminal 40 Sending/receiving unit 41 Signal terminal

42 Reference potential terminal 50 Coupling structure

51 -54 Terminal

60 Reference potential

70 Ground potential

200, 210 Reference potential plate 220,230 Metal line

221 , 231 Connecting segment 222, 232 Coupling section

240 Ring structure

241 , 242, 243, 244 Ring segment

250 Boundary line

260 Overlap

270 Width of the ring strcture

300 Printed circuit board