JP5326880B2 - Thin film balun - Google Patents

Description

  The present invention relates to a balun (balun transformer) that performs unbalanced-balanced signal conversion, and more particularly to a thin film balun formed by a thin film process that is advantageous for miniaturization and thinning.

  The wireless communication device includes various high frequency elements such as an antenna, a filter, an RF switch, a power amplifier, an RF-IC, and a balun. Among these, resonant elements such as antennas and filters handle unbalanced signals based on the ground potential (perform signal transmission), but RF-ICs that generate and process high-frequency signals are balanced types. Therefore, when the two are electromagnetically connected, a balun that functions as an unbalanced-balanced converter is used.

  Recently, as a balun used in mobile communication devices such as mobile phones and mobile terminals, wireless LAN devices, and the like, further downsizing and thinning are desired. As such a balun, a magnetic coupling is formed by an unbalanced transmission line and a balanced transmission line arranged opposite to each other, one end of the unbalanced transmission line is connected to an unbalanced terminal, and the other end is connected via a capacitor. A device having a configuration connected to a ground terminal (Patent Document 1) has been proposed.

JP 2006-270444 A

  However, in the balun described in Patent Document 1, the capacitor is formed independently of the unbalanced transmission line and the balanced transmission line, and is formed over the entire surface of the substrate in the same manner as the unbalanced transmission line and the balanced transmission line. There is a limit to reducing the thickness.

  In addition, in order to reduce the size and thickness of a thin film balun, the number of turns and the line length of the coil forming the unbalanced transmission line and the balanced transmission line are inevitably reduced, and the shape and opening of the coil are reduced accordingly. Therefore, the Q value of the coil is lowered, and as a result, the insertion loss cannot be reduced (good attenuation characteristics). Therefore, it is difficult to satisfy the required specifications with the configuration such as the chip type balun described in Patent Document 1.

  This invention is made | formed in view of this situation, and it aims at providing the thin film balun which can be reduced in size and thickness, maintaining the various characteristics of the balun requested | required.

  In order to solve the above-mentioned problems, the thin film balun of the present invention is disposed opposite to each of the unbalanced transmission line having the first line part and the second line part, and the first line part and the second line part. And a balanced transmission line having a third line portion and a fourth line portion that are magnetically coupled, an unbalanced terminal connected to the first line portion, and a C component connected to the first line portion. A grounding terminal and a counter electrode connected to the grounding terminal and facing a part of the first line part, wherein the C component is constituted by a part of the first line part and the counter electrode; is there.

  In such a configuration, since the C component introduced into the resonance circuit of the thin film balun is configured using a part of the first line portion constituting the unbalanced transmission line, the C component is introduced. The increase in the number of new layers can be suppressed, and the thin film balun can be reduced in size and thickness. Further, as a result of intensive studies by the inventor, it has been found that even if it is provided as described above, it is possible to adjust the transmission signal balance characteristic while improving the transmission characteristic of the transmission signal.

  Although details of such an action mechanism are still unclear, a part of the first line portion constituting the unbalanced transmission line also serves as an electrode of the capacitor, so that the capacitor is disposed close to the unbalanced transmission line. From this, it is presumed that not only the capacitance C is directly introduced, but also a capacitance such as a stray capacitance occurs between the surrounding line portions and affects the characteristic impedance. However, the action is not limited to this.

  Furthermore, as a result of further earnest studies, the present inventor has found various examples of more suitable counter electrode configurations. That is, as an example, it is useful that the width of one of the second line portion and the fourth line portion is wider than the width of either the first line portion or the third line portion. Was found.

  For example, the thin film balun according to the present invention includes a first coil part and a second coil part, and an unbalanced transmission line having a first coil part and a second coil part. A balanced transmission line having three coil portions and a fourth coil portion; an unbalanced terminal connected to the first coil portion; a ground terminal connected to the first coil portion via a C component; And a counter electrode that is connected to the terminal and faces a part of the first coil part, and the C component is constituted by a part of the first coil part and the counter electrode. Even if it does in this way, the effect | action similar to having mentioned above is show | played.

  Preferably, the counter electrode is opposed to a part of the coil conductor closer to the outer coil conductor than to the inner coil conductor in the first coil portion. Accordingly, the counter electrode can be appropriately separated from the coil opening through which the magnetic flux generated by the magnetic coupling between the second coil portion and the fourth coil portion passes. As a result, the magnetic coupling between the first coil portion and the third coil portion and the magnetic coupling between the second coil portion and the fourth coil portion are maintained in an equivalent state, and the thin film balun resonance circuit is maintained. Since the capacitance is effectively introduced, the balance characteristic can be adjusted while maintaining a high transmission signal passing characteristic. However, the action is not limited to this.

  According to the present invention, a part of the first line portion constituting the unbalanced transmission line and connected to the unbalanced terminal also serves as one electrode of the capacitor, so that the thin film balun is greatly reduced in size and thickness. The balance characteristic can be adjusted, and the insertion loss can be reduced.

It is an equivalent circuit diagram which shows the structure of one Embodiment of the thin film balun of this invention. It is a vertical sectional view showing the configuration of an embodiment of a thin film balun. 2 is a horizontal sectional view of a wiring layer M0 of a thin film balun 1. FIG. 2 is a horizontal sectional view of a wiring layer M1 of a thin film balun 1. FIG. 2 is a horizontal sectional view of a wiring layer M2 of a thin film balun 1. FIG. 2 is a horizontal sectional view of a wiring layer M3 of a thin film balun 1. FIG. It is a horizontal sectional view in wiring layer M0 of thin film balun 1A. It is a horizontal sectional view in wiring layer M0 of thin film balun 1B. It is a graph which shows the evaluation result of a passage characteristic. It is a graph which shows the evaluation result of phase difference. It is a graph which shows the evaluation result of an amplitude difference.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, positional relationships such as up, down, left and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the illustrated ratios. Further, the following embodiments are exemplifications for explaining the present invention, and are not intended to limit the present invention only to the embodiments. Furthermore, the present invention can be variously modified without departing from the gist thereof.

  FIG. 1 is an equivalent circuit diagram showing the configuration of a preferred embodiment according to the thin film balun of the present invention. The thin film balun 1 includes an unbalanced transmission line (unbalanced circuit) UL in which a line portion L1 (first line portion) and a line portion L2 (second line portion) are connected in series, and a line portion L3 (third Line portion) and a line portion L4 (fourth line portion) and a balanced transmission line (balanced circuit) BL connected in series. The line portion L1, the line portion L3, and the line portion L2, the line portion. Magnetic couplings are formed by the portions L4.

  In the thin film balun 1, the other end of the coupling end of the line portion L1 with the line portion L2 is connected to the unbalanced terminal UT, and a capacitor D in which a part of the line portion L1 is a C component (capacitance component) is provided. To the ground terminal G (ground potential). The capacitor D is configured such that an electrode D1 constituted by a part of the line portion L1 and an electrode D2 (counter electrode) connected to the ground terminal G are disposed to face each other through an appropriate dielectric. The other end of the coupling end of the line portion L2 with the line portion L1 is open. Further, the other ends of the coupling portions in the line portion L3 and the line portion L4 are connected to the balanced terminal BT1 and the balanced terminal BT2. Further, the coupling portion between the line portion L3 and the line portion L4 is connected to the ground terminal G.

  The lengths of the line portions L1 to L4 described above vary depending on the specifications of the thin film balun 1, and may be set to be a 1/4 wavelength (λ / 4) resonator circuit of a transmission signal to be converted, for example. it can. The shape of the line portions L1 to L4 can be any shape as long as the magnetic coupling described above is formed. For example, the shape of a spiral shape (coil shape), a meandering shape, a linear shape, a curved shape, or the like. Is mentioned.

  The basic operation of the thin film balun 1 will be described below with reference to FIG. In the thin film balun 1, when an unbalanced signal is input to the unbalanced terminal UT, the unbalanced signal propagates through the line portion L1 and the line portion L2. Then, the line portion L1 and the line portion L3 are magnetically coupled (first magnetic coupling), and the line portion L2 and the line portion L4 are magnetically coupled (second magnetic coupling), whereby the input unbalanced signal is input. Is converted into two balanced signals having a phase difference of 180 ° (π), and these two balanced signals are output from the balanced terminals BT1 and BT2, respectively. Note that the conversion operation from the balanced signal to the unbalanced signal is the reverse of the conversion operation from the unbalanced signal to the balanced signal described above.

  Next, the wiring structure of the thin film balun will be described. FIG. 2 is a vertical sectional view schematically showing the wiring structure of the thin film balun 1. As shown in FIG. 2, wiring layers M0, M1, M2, and M3 are formed in this order from the insulating substrate 100 side such as alumina. For example, the unbalanced transmission line UL described above is formed by the wiring layer M1, and the balanced transmission line BL is formed by the wiring layer M2. Dielectric layers 101 to 105 are formed between the wirings in the same wiring layer and between different wiring layers. For example, the dielectric layer 102 between the wiring layer M0 and the wiring layer M1 in which the capacitor D is formed, and the wiring layer M1 and the wiring layer M2 in which the magnetic coupling between the unbalanced transmission line UL and the balanced transmission line BL is formed. For example, silicon nitride is used for the dielectric layer 104 therebetween. For example, alumina is used as the dielectric layers 101 and 103 in other portions. For example, polyimide is used as the dielectric layer 105. The material of each of these layers is not limited to those described above, and may be not only an inorganic insulator such as silicon nitride, alumina or silica, but also an organic insulator such as polyimide or epoxy resin, which can be appropriately selected. The unbalanced terminal UT, the balanced terminals BT1 and BT2, and the ground terminal G are formed so as to penetrate all the dielectric layers. Thus, the thin film balun 1 is composed of a thin film multilayer structure formed on the insulating substrate 100.

  Next, the patterns of the wiring layers M0, M1, M2, and M3 in one embodiment of the thin film balun will be described in detail. In the following embodiments, coil portions are used as the line portions L1 to L4.

(First embodiment)
3 to 6 are horizontal sectional views schematically showing each wiring layer in the thin film balun 1 of the first embodiment. As shown in FIGS. 3 to 6, unbalanced terminals UT, balanced terminals BT1 and BT2, and a ground terminal G are formed in all the wiring layers M0 to M3, and the terminals UT to BT2 and G are Electrical connection is made between different layers via through holes P. All through holes P shown in FIGS. 3 to 6 are subjected to metal plating for electrically connecting the upper and lower layers. Hereinafter, the configuration of each wiring layer will be described in detail.

  As shown in FIG. 3, in the wiring layer M0 on the insulating substrate 100, the electrode D2 of the capacitor D is formed at a position facing a part of the coil portion C1 of the wiring layer M1. The electrode D2 is connected to the ground terminal G. The electrode D2 of the capacitor D is disposed so as to face the coil conductor 11 in the second row from the bottom of the coil portion C1 in plan view.

  As shown in FIG. 4, the wiring layer M1 includes a coil part C1 (first coil part, first line part) and a coil part C2 (second coil part, second coil) constituting the unbalanced transmission line UL. 2 line portions) are formed adjacent to each other. Each coil part C1, C2 comprises what is corresponded to a 1/4 wavelength ((lambda) / 4) resonator. The outer end portion 11a of the coil conductor 11 constituting the coil portion C1 is connected to the unbalanced terminal UT, and the inner end portion 11b of the coil conductor 11 is connected to the through hole P. On the other hand, the inner end portion 12b of the coil conductor 12 constituting the coil portion C2 is connected to the through hole P, and the outer end portion 12a of the coil conductor 12 is open. A part of the coil conductor 11 on the outer periphery of the coil part C1 also serves as the electrode D1 of the capacitor, and faces the electrode D2 of the wiring layer M0. Further, as shown in FIG. 4, the width of the coil conductor 12 constituting the coil portion C2 is wider than the width of the coil conductor 11 constituting the coil portion C1. This is because, when the capacitor D is inserted so that a part of the coil part C1 also serves as the electrode D1 of the capacitor, the width of the coil conductor 12 is increased compared to the width of the coil conductor 11 by the inventor's earnest research. This is because it was confirmed that excellent pass characteristics and equilibrium characteristics were obtained. However, the width and the number of turns of the coil conductor 12 and the coil conductor 11 are not limited, and the width and the number of turns of the coil conductor 12 and the coil conductor 11 may be the same or different.

  Furthermore, as shown in FIG. 5, the wiring layer M2 includes a coil part C3 (third coil part, third line part) and a coil part C4 (fourth coil part, constituting the balanced transmission line BL). (Fourth line portion) is formed adjacent to each other. Each coil part C3, C4 comprises what is corresponded to a 1/4 wavelength ((lambda) / 4) resonator similarly to coil part C1, C2. These coil parts C3 and C4 of the balanced transmission line BL are respectively arranged to face the coil parts C1 and C2 of the unbalanced transmission line UL, and are magnetically coupled at the opposed parts to constitute a coupler. The outer end portion 21a of the coil conductor 21 constituting the coil portion C3 is connected to the balanced terminal BT1, and the inner end portion 21b of the coil conductor 21 is connected to the through hole P. On the other hand, the outer end 22a of the coil conductor 22 constituting the coil portion C4 is connected to the balanced terminal BT2, and the inner end 22b of the coil conductor 22 is connected to the through hole P. Moreover, as shown in FIG. 5, the width | variety of the coil conductor 22 which comprises the coil part C4 is wider than the width | variety of the coil conductor 21 which comprises the coil part C3. In the same manner as described above, when the capacitor D is inserted so that a part of the coil portion C1 also serves as the electrode D1 of the capacitor by the intensive research of the present inventor, the width of the coil conductor 21 is compared. This is because it has been confirmed that excellent passage characteristics and equilibrium characteristics can be obtained by increasing the width of the coil conductor 22. However, the width and the number of turns of the coil conductor 22 and the coil conductor 21 are not limited, and the width and the number of turns of the coil conductor 22 and the coil conductor 21 may be the same or different.

  Then, as shown in FIG. 6, in the wiring layer M3, a wiring 31 for connecting the coil part C3 and the coil part C4 to the ground terminal G and a wiring 32 for connecting the coil part C1 and the coil part C2 are provided. Is formed. The wiring 31 is a branch wiring formed so as to connect the two through holes P and the ground terminal G. The wiring 31 is connected to the end portion 21b of the coil conductor 21 and the end portion 22b of the coil conductor 22 formed in the wiring layer M2 through two through holes P. On the other hand, the wiring 32 is connected to the end portion 11b of the coil conductor 11 and the end portion 12b of the coil conductor 12 formed in the wiring layer M1 through the through hole P.

  As described above, in the present embodiment, two coil portions C1 and C2 constituting the unbalanced transmission line are formed in the wiring layer M1 which is one layer, and balanced in the wiring layer M2 which is another layer adjacent thereto. Two coil portions C3 and C4 constituting the transmission line are formed, and the coil portions C1 and C2 are connected to a wiring layer M3 which is another layer opposite to the wiring layer M1 adjacent to the wiring layer M2. The wiring 32 and the wiring 31 that connects the coil portions C3 and C4 are formed, and the coil conductor 11 in the coil portion C1 is formed on the wiring layer M0 on the opposite side of the wiring layer M2 adjacent to the wiring layer M1. A thin film balun 1 constituting an equivalent circuit shown in FIG. 1 is obtained by a multilayer wiring structure in which an electrode D2 for constituting a capacitor D is formed opposite to a part of the capacitor D.

(1A embodiment)
FIG. 7 is a horizontal sectional view schematically showing the wiring layer M0 in the thin film balun 1A of the first embodiment A according to the present invention. The configuration other than the wiring layer M0 is the same as that of the first embodiment. In the thin film balun 1A shown in FIG. 7, the electrode D2 of the capacitor D is arranged so as to face the third row of coil conductors 11 from the bottom of the coil portion C2 in plan view.

(1B embodiment)
FIG. 8 is a horizontal sectional view schematically showing the wiring layer M0 in the thin film balun 1B of the first embodiment according to the present invention. The configuration other than the wiring layer M0 is the same as that of the first embodiment. The thin film balun 1B shown in FIG. 8 is obtained by shortening the length of the electrode D2 of the capacitor D of the thin film balun 1A of the first embodiment.

(Characteristic evaluation)
With respect to the thin film baluns 1, 1 </ b> A, 1 </ b> B of each embodiment described above, the passage characteristics (insertion loss) and the balance characteristics (balance signal phase difference and amplitude difference) were obtained by simulation. The evaluation target frequency (resonance frequency fr) of the transmission signal was set to 2400 to 2500 MHz. 9 is a diagram showing the evaluation result of the pass characteristics, FIG. 10 is a diagram showing the evaluation result of the phase difference, and FIG. 11 is a diagram showing the evaluation result of the amplitude difference. In each figure, curves E1, E1A, E1B show the evaluation results of the thin film baluns 1, 1A, 1B, respectively. A curve R shows an evaluation result of a thin film balun (comparative example) having the same structure except that the capacitor D is not provided.

  The pass characteristic indicates how much the signal is allowed to pass without being lost in the evaluation target frequency region, and 0 dB is an ideal pass characteristic in the evaluation target frequency region. The pass characteristic of each thin film balun was evaluated by setting the attenuation in the frequency range to be evaluated to 1 dB or less. Further, since the phase difference is a phase difference between two balanced signals output from the balanced terminal BT1 and the balanced terminal BT2, 180 deg is a more ideal phase balance. The phase balance of each thin film balun was evaluated with the target specification being a phase difference of 170 deg or more and less than 190 deg in the evaluation target frequency range. Further, since the amplitude difference is an amplitude difference between two balanced signals output from the balanced terminal BT1 and the balanced terminal BT2, 0 dB is a more ideal output balance. The amplitude difference of the thin film balun was evaluated by setting the amplitude difference in the evaluation target frequency range to be -1 dB or more and 1 dB or less.

  From these results, it was confirmed that the thin film baluns E1, E1A, E1B of the respective embodiments maintained excellent characteristics in terms of pass characteristics and phase balance. In particular, these thin-film baluns E1, E1A, E1B have been confirmed to have superior pass characteristics compared to the thin-film balun R that does not include a capacitor. did. This numerical value is a large numerical value as an improved value of the passing characteristics while satisfying the demand for a small and low profile. It was confirmed that the phase balance and the amplitude balance can be adjusted by the arrangement of the electrode D2 of the capacitor D. Among these, in the thin film balun 1 in which the electrode D2 is opposed to a part of the coil conductor closer to the outer coil conductor than to the inner coil conductor in the coil portion C2, the pass characteristics, the phase balance, and the amplitude balance are It was confirmed that it was the best in terms of quality.

  In addition, as above-mentioned, this invention is not limited to said each embodiment, A various deformation | transformation is possible in the limit which does not change the summary. For example, the arrangement of the unbalanced terminal UT, the balanced terminals BT1 and BT2, and the ground terminal G is not limited to the illustrated position. Further, the multilayer wiring structure constituting the thin film balun may be less than the number of layers shown or more than the number of layers shown. Furthermore, it is of course possible to have a structure in which the order of the wiring layers on the insulating substrate 100 is reversed. Furthermore, various coil arrangements can be employed without departing from the scope of the present invention.

  According to the thin film balun of the present invention, various characteristics of the balun required by constituting part of the unbalanced transmission line and part of the first line portion connected to the unbalanced terminal also serving as one electrode of the capacitor. In particular, wireless communication devices, devices, modules, and systems that are required to be small and thin, as well as equipment provided with them, and also widely applied to their manufacture. It is possible.

  DESCRIPTION OF SYMBOLS 1-1B ... Thin film balun based on this invention, 11, 12, 21, 22 ... Coil conductor, 11a, 11b, 12a, 12b, 21a, 21b, 22a, 22b ... End part, 31, 32 ... Wiring, M0, M1 , M2, M3 ... wiring layer, C1 ... coil part (first coil part, first line part), C2 ... coil part (second coil part, second line part), C3 ... coil part (first 3 coil part, 3rd line part), C4 ... coil part (4th coil part, 4th line part), D ... capacitor (C component, capacitive component), D1 ... electrode, D2 ... electrode (opposite) Electrode), G ... ground terminal (ground potential), L1 ... line part (first line part), L2 ... line part (second line part), L3 ... line part (third line part), L4 ... Line part (fourth line part), P ... through hole, UL ... unbalanced transmission line (unbalanced circuit), BL ... balanced transmission Line (balancing circuit), UT ... unbalanced terminal, BT1 ... balanced terminals (a first balanced terminal), BT2 ... balanced terminal (second balanced terminals).

Claims (1)

An unbalanced transmission line having a first coil portion and a second coil portion;
A balanced transmission line having a third coil portion and a fourth coil portion that are arranged opposite to each other and magnetically coupled to each of the first coil portion and the second coil portion;
An unbalanced terminal connected to the first coil portion;
A ground terminal connected to the first coil portion via a C component;
A counter electrode connected to the ground terminal and facing a part of the first coil portion;
With
The C component is constituted by a part of the first coil part and the counter electrode ,
The counter electrode is opposed to a part of the coil conductor closer to the outer coil conductor than the inner coil conductor in the first coil portion.
Thin film balun.

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