JP7627610B2 - Balun transformer - Google Patents

Description

The present invention relates to a balun transformer, and in particular to a chip-type balun transformer with a structure in which multiple coil patterns are coaxially stacked.

Normally, transmission lines connected to antennas and the like are unbalanced transmission lines, while transmission lines connected to high-frequency circuits such as semiconductor ICs are balanced transmission lines. For this reason, when connecting an unbalanced transmission line to a balanced transmission line, a balun transformer is inserted between them to convert between unbalanced signals and balanced transmission lines. Here, an unbalanced signal refers to a single-ended signal based on a fixed potential (e.g., ground potential), and a balanced signal refers to a differential signal. Patent Document 1 discloses a chip-type balun transformer with a structure in which multiple coil patterns are stacked coaxially.

Japanese Patent Application Publication No. 9-260146

However, with the balun transformer described in Patent Document 1, it was difficult to increase the magnetic coupling between the primary and secondary windings.

Therefore, the present invention aims to provide a balun transformer with enhanced magnetic coupling between the primary winding and the secondary winding.

The balun transformer according to the present invention comprises first to fourth terminal electrodes, first and third coil patterns connected in parallel between the first and second terminal electrodes, and second and fourth coil patterns connected in parallel between the third and fourth terminal electrodes, and is characterized in that the first, second, third and fourth coil patterns are coaxially stacked in this order.

According to the present invention, the first and third coil patterns that form the primary winding and are connected in parallel to each other, and the second and fourth coil patterns that form the secondary winding and are connected in parallel to each other are alternately stacked, thereby making it possible to increase the magnetic coupling between the primary winding and the secondary winding.

The balun transformer according to the present invention may further include fifth and seventh coil patterns connected in parallel to each other and in series to the first and third coil patterns, and sixth and eighth coil patterns connected in parallel to each other and in series to the second and fourth coil patterns, and the fifth, sixth, seventh and eighth coil patterns may be stacked coaxially in this order. This makes it possible to secure a larger number of turns.

In this case, the outer circumferential ends of the first and third coil patterns may be commonly connected to the first terminal electrode, the outer circumferential ends of the second and fourth coil patterns may be commonly connected to the third terminal electrode, the outer circumferential ends of the fifth and seventh coil patterns may be commonly connected to the second terminal electrode, the outer circumferential ends of the sixth and eighth coil patterns may be commonly connected to the fourth terminal electrode, the inner circumferential ends of the first and third coil patterns may be commonly connected to the inner circumferential ends of the fifth and seventh coil patterns, and the inner circumferential ends of the second and fourth coil patterns may be commonly connected to the inner circumferential ends of the sixth and eighth coil patterns. This makes it easy to connect the terminal electrodes and the coil patterns.

The balun transformer according to the present invention further includes a fifth coil pattern connected in series to the first and third coil patterns and a sixth coil pattern connected in series to the second and fourth coil patterns, the outer circumferential ends of the first and third coil patterns are commonly connected to the first terminal electrode, the outer circumferential ends of the second and fourth coil patterns are commonly connected to the third terminal electrode, the outer circumferential end of the fifth coil pattern is connected to the second terminal electrode, the outer circumferential end of the sixth coil pattern is connected to the fourth terminal electrode, the inner circumferential ends of the first and third coil patterns are commonly connected to the inner circumferential end of the fifth coil pattern, the inner circumferential ends of the second and fourth coil patterns are commonly connected to the inner circumferential end of the sixth coil pattern, and the pattern width of the fifth and sixth coil patterns may be wider than the pattern width of the first to fourth coil patterns. This makes it easy to adjust the number of turns and reduces the difference in current density of the current flowing through each coil pattern.

In this way, according to the present invention, it is possible to provide a balun transformer with enhanced magnetic coupling between the primary winding and the secondary winding.

FIG. 1 is a schematic perspective view for explaining the structure of a balun transformer 1 according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view for explaining the structure of the balun transformer 1. As shown in FIG. FIG. 3 is a schematic plan view for explaining the pattern shapes of the conductor layers L1, L3, L5, and L7. FIG. 4 is a schematic plan view for explaining the pattern shapes of the conductor layers L2, L4, L6, and L8. FIG. 5 is an equivalent circuit diagram of the balun transformer 1. FIG. 6 is a graph showing the relationship between frequency and coupling coefficient. FIG. 7 is a graph showing the relationship between frequency and insertion loss. FIG. 8 is a schematic perspective view for explaining the structure of a balun transformer 2 according to a second embodiment of the present invention. FIG. 9 is a schematic cross-sectional view for explaining the structure of the balun transformer 2. As shown in FIG. FIG. 10 is a schematic plan view for explaining the pattern shapes of the conductor layers L1, L3, and L5. FIG. 11 is a schematic plan view for explaining the pattern shapes of the conductor layers L2, L4, and L6. FIG. 12 is an equivalent circuit diagram of the balun transformer 2.

A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

First Embodiment
Fig. 1 is a schematic perspective view for explaining the structure of a balun transformer 1 according to a first embodiment of the present invention, and Fig. 2 is a schematic cross-sectional view for explaining the structure of the balun transformer 1.

As shown in Figs. 1 and 2, the balun transformer 1 according to the first embodiment includes eight conductor layers L1 to L8 stacked in this order, a magnetic base body 3 in which the conductor layers L1 to L8 are embedded, and terminal electrodes E1 to E4. The conductor layers L1 to L8 each have coil patterns 10, 20, 30, 40, 50, 60, 70, and 80, and are covered with an insulating resin layer 4. The conductor layers L1 to L8 are embedded in the magnetic base body 3 via the insulating resin layer 4. Four terminal electrodes E1 to E4 are exposed from the magnetic base body 3. The magnetic base body 3 is a composite member containing a metal magnetic filler made of iron (Fe) or a permalloy-based material and a resin binder, and forms a magnetic path for magnetic flux generated by passing a current through the coil patterns 10, 20, 30, 40, 50, 60, 70, and 80. It is preferable to use a liquid or powdered epoxy resin as the resin binder.

The terminal electrodes E1 and E2 are used, for example, as primary side terminals (unbalanced signal terminals), and the terminal electrodes E3 and E4 are used, for example, as secondary side terminals (balanced signal terminals). In this case, one of the terminal electrodes E1 and E2 constituting the unbalanced signal terminal is connected to an unbalanced transmission line, and the other is connected to the ground wiring. The terminal electrodes E3 and E4 are connected to a pair of balanced transmission lines.

Coil patterns 10, 30, 50, and 70 arranged on conductor layers L1, L3, L5, and L7 are connected between terminal electrode E1 and terminal electrode E2. Coil patterns 20, 40, 60, and 80 arranged on conductor layers L2, L4, L6, and L8 are connected between terminal electrode E3 and terminal electrode E4.

Figure 3 is a schematic plan view illustrating the pattern shapes of conductor layers L1, L3, L5, and L7.

As shown in FIG. 3, the coil patterns 10 and 30 included in the conductor layers L1 and L3 have their outer ends 11 and 31 commonly connected to the terminal electrode E1. The coil patterns 50 and 70 included in the conductor layers L5 and L7 have their outer ends 51 and 71 commonly connected to the terminal electrode E2. The inner ends 12, 32, 52, and 72 of the coil patterns 10, 30, 50, and 70 included in the conductor layers L1, L3, L5, and L7 are short-circuited. The coil patterns 10 and 30 are wound counterclockwise (left-handed) from the outer ends 11 and 31 toward the inner ends 12 and 32, and the coil patterns 50 and 70 are wound clockwise (right-handed) from the outer ends 51 and 71 toward the inner ends 52 and 72. The relay patterns 33, 53, 73 included in the conductor layers L3, L5, L7 are independent of the coil patterns 30, 50, 70, and are connected to the inner ends 22, 42, 62, 82 of the coil patterns 20, 40, 60, 80 described below. The dummy pattern 13 provided on the conductor layer L1 is provided to prevent steps in this area on the upper conductor layers L2 to L8.

Figure 4 is a schematic plan view illustrating the pattern shapes of conductor layers L2, L4, L6, and L8.

As shown in FIG. 4, the coil patterns 20 and 40 included in the conductor layers L2 and L4 have their outer ends 21 and 41 connected in common to the terminal electrode E3. The coil patterns 60 and 80 included in the conductor layers L6 and L8 have their outer ends 61 and 81 connected in common to the terminal electrode E4. The inner ends 22, 42, 62, and 82 of the coil patterns 20, 40, 60, and 80 included in the conductor layers L2, L4, L6, and L8 are short-circuited. The coil patterns 20 and 40 are wound clockwise (right-handed) from the outer ends 21 and 41 toward the inner ends 22 and 42, and the coil patterns 60 and 80 are wound counterclockwise (left-handed) from the outer ends 61 and 81 toward the inner ends 62 and 82. The relay patterns 23, 43, and 63 included in the conductor layers L2, L4, and L6 are independent of the coil patterns 20, 40, and 60, and are connected to the inner ends 12, 32, 52, and 72 of the coil patterns 10, 30, 50, and 70.

The balun transformer 1 according to this embodiment has the coil patterns 10, 30, 50, 70 and the coil patterns 20, 40, 60, 80 having the above-mentioned structure stacked alternately in a coaxial manner. Therefore, as shown in the equivalent circuit diagram of FIG. 5, the parallel-connected coil patterns 10, 30 and the parallel-connected coil patterns 50, 70 are connected in series between the terminal electrodes E1 and E2, and the parallel-connected coil patterns 20, 40 and the parallel-connected coil patterns 60, 80 are connected in series between the terminal electrodes E3 and E4. Here, the number of turns of each of the coil patterns 10, 30, 50, 70 is 4.5 turns, so a total of 9 turns of coils are connected between the terminal electrodes E1 and E2. Similarly, the number of turns of each of the coil patterns 20, 40, 60, 80 is 4.5 turns, so a total of 9 turns of coils are connected between the terminal electrodes E3 and E4.

Figure 6 is a graph showing the relationship between frequency and coupling coefficient, and Figure 7 is a graph showing the relationship between frequency and insertion loss, where in both cases, symbol A indicates the characteristics of the balun transformer 1 according to this embodiment, and symbol B indicates the characteristics of a general balun transformer. A general balun transformer has coil patterns 10, 30, 50, and 70 all connected in series, and coil patterns 20, 40, 60, and 70 all connected in series, and the total number of turns in the coil patterns is adjusted to 9 turns to match the inductance value with the balun transformer 1 according to this embodiment.

As shown in Figures 6 and 7, the balun transformer 1 according to this embodiment has a higher coupling coefficient and a lower insertion loss, especially in the high frequency range, compared to a typical balun transformer.

In this way, in the balun transformer 1 according to this embodiment, the parallel-connected coil patterns 10, 30 and the parallel-connected coil patterns 20, 40 are stacked coaxially in this order, and the parallel-connected coil patterns 50, 70 and the parallel-connected coil patterns 60, 80 are stacked coaxially in this order, making it possible to enhance the magnetic coupling between the coil patterns 10, 30, 50, 70 that constitute the primary winding and the coil patterns 20, 40, 60, 70 that constitute the secondary winding.

In addition, since the terminal electrodes E1 to E4 are all connected to the outer periphery of the corresponding coil patterns, it is easy to connect the coil patterns to the terminal electrodes E1 to E4.

Second Embodiment
Fig. 8 is a schematic perspective view for explaining the structure of a balun transformer 2 according to a second embodiment of the present invention, and Fig. 9 is a schematic cross-sectional view for explaining the structure of the balun transformer 2.

As shown in Figures 8 and 9, the balun transformer 2 according to the second embodiment includes six conductor layers L1 to L6 stacked in this order, a magnetic base body 3 in which the conductor layers L1 to L6 are embedded, and terminal electrodes E1 to E4. The configuration of the conductor layers L1 to L4 is the same as that of the balun transformer 1 according to the first embodiment, and the configuration of the conductor layers L5 and L6 is different from that of the balun transformer 1 according to the first embodiment. Coil patterns 10, 30, and 50 arranged on the conductor layers L1, L3, and L5 are connected between the terminal electrodes E1 and E2. Coil patterns 20, 40, and 60 arranged on the conductor layers L2, L4, and L6 are connected between the terminal electrodes E3 and E4. The other basic configuration is the same as that of the balun transformer 1 according to the first embodiment, so the same elements are given the same reference numerals and a duplicated description is omitted.

Figure 10 is a schematic plan view illustrating the pattern shapes of conductor layers L1, L3, and L5.

As shown in FIG. 10, the pattern shapes of the coil patterns 10 and 30 included in the conductor layers L1 and L3 are the same as those of the balun transformer 1 according to the first embodiment. The coil pattern 50 included in the conductor layer L5 has an outer peripheral end 51 connected to the terminal electrode E2 and an inner peripheral end 52 commonly connected to the inner peripheral ends 12 and 32 of the coil patterns 10 and 30.

Figure 11 is a schematic plan view illustrating the pattern shapes of conductor layers L2, L4, and L6.

As shown in FIG. 11, the pattern shapes of the coil patterns 20 and 40 included in the conductor layers L2 and L4 are the same as those of the balun transformer 1 according to the first embodiment. The coil pattern 60 included in the conductor layer L6 has an outer peripheral end 61 connected to the terminal electrode E4 and an inner peripheral end 62 commonly connected to the inner peripheral ends 22 and 42 of the coil patterns 20 and 40.

The balun transformer 2 according to this embodiment has the coil patterns 10, 30, 50 and the coil patterns 20, 40, 60 having the above-mentioned structure stacked alternately in a coaxial manner. Therefore, as shown in the equivalent circuit diagram of FIG. 12, the parallel-connected coil patterns 10, 30 and the coil pattern 50 are connected in series between the terminal electrodes E1 and E2, and the parallel-connected coil patterns 20, 40 and the coil pattern 60 are connected in series between the terminal electrodes E3 and E4. Here, the number of turns of each of the coil patterns 10 and 30 is 4.5 turns, and the number of turns of the coil pattern 50 is 2.5 turns, so that a total of 7 turns of coils are connected between the terminal electrodes E1 and E2. Similarly, the number of turns of each of the coil patterns 20 and 40 is 4.5 turns, and the number of turns of the coil pattern 60 is 2.5 turns, so that a total of 7 turns of coils are connected between the terminal electrodes E3 and E4.

As illustrated in this embodiment, the balun transformer according to the present invention may have a mixture of coil patterns that are connected in parallel and coil patterns that are not connected in parallel. This allows the total number of layers to be reduced and the total number of turns to be easily adjusted. Moreover, in this embodiment, the radial pattern width of the coil patterns 50 and 60 is wider than the radial pattern width of the coil patterns 10, 20, 30, and 40, and is approximately twice as wide. This makes it possible to reduce the difference in current density of the current flowing through each coil pattern. Furthermore, when the coil patterns constituting the primary winding and the coil patterns constituting the secondary winding each have a three-layer structure as in this embodiment, it is difficult to make the total number of turns of the primary winding and the secondary winding an odd number in a typical balun transformer, but in this embodiment, the total number of turns of the primary winding and the secondary winding can be any number.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention, and it goes without saying that these are also included within the scope of the present invention.

For example, in the balun transformer 1 according to the first embodiment, two coil patterns located on different conductor layers are connected in parallel, but three or more coil patterns located on different conductor layers may be connected in parallel.

In addition, in the balun transformers 1 and 2 according to the first and second embodiments, the number of turns in the primary winding and the secondary winding are equal, but this is not essential to the present invention.

1, 2 Balun transformer 3 Magnetic body 4 Insulating resin layer 10, 20, 30, 40, 50, 60, 70, 80 Coil pattern 11, 21, 31, 41, 51, 61, 71, 81 Outer periphery 12, 22, 32, 42, 52, 62, 72, 82 Inner periphery 13 Dummy pattern 23, 33, 43, 53, 63, 73 Relay pattern E1 to E4 Terminal electrodes L1 to L8 Conductor layer

Claims (2)

First to fourth terminal electrodes;
first and third coil patterns connected in parallel ;
second and fourth coil patterns connected in parallel ;
fifth and seventh coil patterns connected in parallel;
sixth and eighth coil patterns connected in parallel;
the first and third coil patterns and the fifth and seventh coil patterns are connected in series between the first terminal electrode and the second terminal electrode;
the second and fourth coil patterns and the sixth and eighth coil patterns are connected in series between the third terminal electrode and the fourth terminal electrode,
A balun transformer, wherein the first, second, third , fourth , fifth, sixth, seventh and eighth coil patterns are coaxially stacked in this order. outer circumferential ends of the first and third coil patterns are commonly connected to the first terminal electrode,
outer circumferential ends of the second and fourth coil patterns are commonly connected to the third terminal electrode,
outer circumferential ends of the fifth and seventh coil patterns are commonly connected to the second terminal electrode,
outer circumferential ends of the sixth and eighth coil patterns are commonly connected to the fourth terminal electrode,
the first and third coil patterns have their inner circumferential ends connected in common to the inner circumferential ends of the fifth and seventh coil patterns;
2. The balun transformer according to claim 1 , wherein inner peripheral ends of the second and fourth coil patterns are commonly connected to inner peripheral ends of the sixth and eighth coil patterns.

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