JP4969193B2 - Duplexer - Google Patents

Description

  The present invention relates to a duplexer in which surface acoustic wave elements for transmission and reception are mounted on a wiring board.

  In recent years, with the development of mobile communication systems, mobile communication devices such as mobile phones and portable information terminals have rapidly spread, and because of the demand for miniaturization and high performance of these devices, components used in these devices However, miniaturization and high performance are required.

  In mobile phones, two types of analog and digital wireless communication systems are used, and the frequencies used range from 800 to 1000 MHz and 1.5 to 2.0 GHz. In these mobile communication devices, a duplexer is used as a component in an RF unit that branches and generates signals transmitted and received through an antenna.

  As an example of the duplexer, a surface acoustic wave element in which an IDT electrode, an input / output electrode and a ground electrode are formed on one main surface of a piezoelectric substrate, and a surface on which an IDT electrode or the like is formed on a wiring substrate made of ceramics or the like A duplexer is known that is mounted and fixed by a flip chip mounting method with a cap placed on a wiring board and sealed (see, for example, Patent Document 1).

  On the other hand, on the lower surface of the wiring board of the high-frequency module equipped with the duplexer, a common ground as a potential reference surface is a reception signal output terminal in a top view for the purpose of stabilizing the high-frequency signal and forming a transmission line structure. It is disclosed that it is provided so as to face a side other than the side along the edge of the wiring board (see, for example, Patent Document 2).

  Here, an important characteristic of the duplexer is an isolation characteristic between the transmission wiring and the reception wiring. This is evaluated as the signal strength leaking to the reception wiring side in the transmission frequency band or the signal strength leaking to the transmission wiring side in the reception frequency band, and the strength of these leakage signals must be less than a predetermined level. In general, the level required in the transmission frequency band is stricter than the level required in the reception frequency band.

  In order to achieve good isolation characteristics, it is indispensable to sufficiently secure the out-of-band attenuation of the surface acoustic wave element, and in particular, the attenuation in the transmission frequency band of the surface acoustic wave element for reception, which has strict requirements. It is necessary to secure a sufficient amount.

It is generally known that the amount of attenuation is adjusted by the characteristics of the resonator constituting the surface acoustic wave element or by an inductance component such as a ground wiring connecting the ground electrode of the surface acoustic wave element and the common ground. It has been.
WO2002 / 005424 publication JP 2005-223582 A

  However, along with downsizing and higher frequency, there are cases where sufficient isolation characteristics cannot always be obtained only by the adjustment described above.

  In the operating state of the duplexer, the common ground cannot maintain a stable potential state, and the potential value varies depending on the location and time. The potential fluctuation forms a standing wave of a certain mode (depending on the structure of the wiring board and the characteristics of the surface acoustic wave device) and has a spatial spread. When the fluctuation (spread) of the potential of the common ground reaches the reception signal output terminal, the potential of the reception signal output terminal also changes. When the potential of the reception signal output terminal fluctuates, it means that energy is propagated, and this results in a decrease in isolation characteristics.

  Such fluctuations in the potential of the common ground are weak compared to the input signal. However, such weak fluctuations in potential affect the attenuation level of −50 dB or less required for the duplexer. It will exert.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a duplexer having good isolation characteristics.

The present invention includes a wiring board in which transmission signal input wiring, reception signal output wiring and ground wiring are provided, a surface acoustic wave element for transmission and a surface acoustic wave element for reception mounted on the upper surface of the wiring board, A reception signal output terminal provided along an edge of the wiring substrate on a lower surface of the wiring substrate, and electrically connected to an output electrode of the surface acoustic wave element for reception via the reception signal output wiring; and the wiring Provided on the lower surface or inside of the substrate so as to face a side other than the side along the edge of the wiring substrate in the reception signal output terminal in a top view, and the surface acoustic wave element for transmission is provided via the ground wiring has and a common ground that is electrically connected to the ground electrode and the ground electrode of the reception surface acoustic wave element, the common ground, the edge of the wiring board of the reception signal output terminal Different sides to each other that sides facing other than sides along is provided inside the wiring substrate, than the connection portion between the reception signal output terminal in a top view and the reception signal output wire of the wiring substrate The connection wiring arranged on the edge side is electrically connected on the edge side of the wiring board with respect to the connection portion between the reception signal output terminal and the reception signal output wiring in a top view. It is a branching filter.

  Here, it is preferable that the different sides of the common ground are electrically connected by the connection wiring in the vicinity of the edge of the wiring board. Further, the different sides of the common ground facing each other across the reception signal output terminal in a top view are electrically connected by the connection wiring arranged along the edge of the wiring board. It is preferable.

  According to the present invention, it is possible to suppress the fluctuation of the potential of the common ground provided to face the side other than the side along the edge of the wiring board in the reception signal output terminal in a top view, and the fluctuation is caused by the fluctuation of the potential. Propagation of the potential wave to the reception signal output terminal can be suppressed. That is, a duplexer with good isolation characteristics can be obtained.

An embodiment of the duplexer of the present invention will be described.
FIG. 1 is an explanatory view showing an embodiment of the duplexer of the present invention, and FIG. 2 is a plan perspective view of the duplexer shown in FIG.

  The duplexer of the present invention shown in FIG. 1 has a configuration in which a surface acoustic wave element for transmission 21 and a surface acoustic wave element for reception 22 are face-down mounted (flip chip mounted) on the upper surface of a wiring board 1.

  The surface acoustic wave element 21 for transmission and the surface acoustic wave element 22 for reception are formed of, for example, a lithium tantalate single crystal, a lanthanum-gallium-niobium single crystal having a langasite type crystal structure, a lithium tetraborate single crystal, or the like. A surface acoustic wave (SAW) element in which an IDT electrode, an input electrode, an output electrode, and a ground electrode are formed of silver, copper, or the like on the surface of a piezoelectric substrate. In this embodiment, the transmitting surface acoustic wave element 21 and the receiving surface acoustic wave element 22 are formed separately, but they may be formed integrally. Further, the mounting method is not limited to flip chip mounting, and may be mounting by wire bonding, for example, and the mounting method of the surface acoustic wave element for transmission 21 and the surface acoustic wave element for reception 22 is not particularly limited.

  The wiring board 1 is made of, for example, an insulating base made of a plurality of insulating layers made of a dielectric material such as LTCC or alumina, and the surface (upper surface and lower surface) or inside of the insulating base is made of silver, copper, tungsten, molybdenum, or the like. Various formed wirings (for example, matching circuit and inductance adjusting wiring) are included.

  Specifically, an input pad and an output pad (not shown) corresponding to the input electrode and the output electrode (not shown) of the surface acoustic wave element 21 for transmission and the surface acoustic wave element 22 for reception are formed on the upper surface of the wiring board 1. Are formed, and ground pads 11 and 12 are formed corresponding to the respective ground electrodes 211 and 221. The corresponding input electrode and input pad, output electrode and output pad, and ground electrode and ground pad are connected by soldering.

  In addition, a transmission signal input wiring (not shown) for transmitting a transmission signal to an input electrode (not shown) of the surface acoustic wave element 21 for transmission inside the wiring substrate 1 and an output electrode (not shown) of the surface acoustic wave element 22 for reception. A reception signal output wiring 13 for transmitting a reception signal from (not) and a ground wiring 14 connected to the ground electrodes 211 and 221 of the respective surface acoustic wave elements.

  Further, a reception signal output terminal 15 electrically connected to the output electrode of the surface acoustic wave element for reception 22 via the reception signal output wiring 13 is provided on the lower surface of the wiring board 1, and also via the ground wiring 14. A common ground 16 electrically connected to each of the ground electrodes of the surface acoustic wave element 21 for transmission and the surface acoustic wave element 22 for reception is provided.

  The wiring board is finally mounted on the external circuit board, and the reception signal output terminal 15 serves as an electrode for sending a reception signal to a reception system circuit formed on the external circuit board. The reception signal output terminal 15 is provided along the edge of the wiring board 1. The reception signal output terminal 15 and the common ground 16 are separated by a U-shaped slit, and the common ground 16 has a side other than the side along the edge of the wiring board 1 in the reception signal output terminal 15 in a top view. It is provided so as to face each other. This structure has a transmission line shape just like a coplanar line with the common ground 16 located on both sides of the reception signal output terminal 15 and the reception signal output terminal 15 (positions facing each other across the reception signal output terminal 15). The received signal is sent in the direction toward the peripheral side of the wiring board 1 inside the external circuit board.

  Here, in the operating state of the branching filter, in order to prevent the fluctuation of the potential of the common ground 16 from propagating to the reception signal output terminal 15 to deteriorate the isolation characteristic, In the common ground 16, different sides facing different sides of the reception signal output terminal 15 are provided inside the wiring board 1, and the connection between the reception signal output terminal 15 and the reception signal output wiring 13 is viewed from above. It is important that the connection wiring 17 arranged on the edge side of the wiring board 1 is electrically connected to the part.

  In the form shown in FIG. 1 and FIG. 2, the connection wiring 17 in which different sides of the common ground 16 facing each other with the reception signal output terminal 15 in the top view are arranged along the edge of the wiring board 1. Are electrically connected.

  Although the reception signal output wiring 13 is composed of a conductor layer and a via hole conductor, the portion directly connected to the reception signal output terminal 15 is often composed of a via hole conductor. Therefore, as shown in FIG. 2, the connection wiring 17 is closer to the edge of the wiring board 1 than the connection portion between the reception signal output terminal 15 and the reception signal output wiring 13 in a top view so as not to contact the reception signal output wiring 13. Is arranged. In addition, the potentials of the different sides of the common ground 16 may be greatly different as approaching the edge of the wiring board 1 when viewed from above, so that the reception signal output terminal 15 and the reception signal output wiring are viewed from above. Different side portions of the common ground 16 are electrically connected to each other by the connection wiring 17 on the edge side of the wiring board 1 with respect to the connection portion with the wiring 13. Thereby, the fluctuation of the potential can be suppressed and the isolation can be improved. If it is connected on the inner side of the reception signal output wiring 13 in a top view, the effect cannot be expected. In particular, the different sides of the common ground 16 are electrically connected by the connection wiring 17 in the vicinity of the edge of the wiring board 1 because it is located on the most exit side in the direction in which the received signal is sent. preferable.

  The connection wiring 17 is composed of a via hole conductor 171 and a connection conductor layer 172, and a portion directly connected to one edge and the other edge of the common ground 16 serves as a via hole conductor 171. The conductor 171 is connected inside the wiring substrate 1 by the connection conductor layer 172.

  In the form shown in FIGS. 1 and 2, different sides of the common ground 16 facing different sides of the reception signal output terminal 15 are opposed to each other across the reception signal output terminal 15 in a top view. It means different sides. Different sides of the common ground 16 facing each other across the reception signal output terminal 15 in top view are electrically connected by connection wirings 17 arranged along the edge of the wiring board 1.

  In this way, different sides of the common ground 16 facing each other across the reception signal output terminal 15 in top view are connected by the connection wiring 17 on the peripheral side of the reception signal output wiring 13. The impedance of the space near the reception signal output electrode 15 changes. As a result, the standing wave mode of the electromagnetic field due to the potential fluctuation of the common ground 16 changes. As a result, it is possible to design the reception signal output terminal 15 so that a portion having a large standing wave amplitude does not appear, and to suppress leakage of energy to the reception signal output electrode.

Here, the reception filter characteristic and the isolation characteristic will be compared between the structure of the present invention and the conventional structure.
FIG. 3 shows the reception filter characteristics and isolation characteristics of the structure of the present invention (a structure in which different sides of the common ground 16 facing each other across the reception signal output terminal 15 are connected by the connection wiring 17). Results are shown. Specifically, the structure shown in FIG. 1 is formed by forming a wiring conductor (received signal output terminal, common ground, received signal input wiring, etc.) made of copper on an insulating base made of LTCC having a dielectric constant of about 4.5. The width of the reception signal output terminal is 600 μm, the distance between the reception signal output terminal and the common ground (slit width) is 200 μm, the height of the connection conductor layer in the connection wiring is 50 μm, and the width is 200 μm. The connection position is in the vicinity of the periphery of the wiring board. According to FIG. 3, in the structure of the present invention, the attenuation rate of the reception filter waveform and the isolation waveform exceeds −50 dB in the transmission signal band 1850 to 1910 MHz. Here, the isolation waveform refers to a waveform that shows the frequency characteristics of the rate at which the transmission signal leaks to the reception signal output terminal 15. This isolation waveform behaves to some extent in accordance with the reception filter waveform, and if the reception filter characteristic is improved, the isolation characteristic is improved accordingly.

  On the other hand, FIG. 4 shows the results of measuring the reception filter characteristics and the isolation characteristics for a conventional structure without connection wiring. According to FIG. 4, the conventional structure has an attenuation factor of about -45 dB in the transmission signal band of 1850 to 1910 MHz. That is, it can be seen that the structure of the present invention is improved by 10 dB or more on average as compared with the conventional structure.

Next, the results of studying the height and width of the connection conductor layer 172 in the connection wiring 17 will be described.
FIG. 5 shows a case where the height of the connection conductor layer 172 in the connection wiring 17 is changed when the common ground 16 together with the reception signal output terminal 15 is provided on the lower surface of the wiring board 1 as shown in FIG. 3 is a graph showing the reception filter characteristics of the surface acoustic wave element 22. When the connection wiring 17 does not connect one edge separated from the other edge by the reception signal output terminal 15 when viewed from the vertical direction of the common ground 16 (when there is no connection wiring), the level is less than −40 dB. On the other hand, when the connection wiring 17 is used, an improvement of about 5 to 10 dB is observed. From the result of FIG. 5, it can be seen that the closer the distance between the connection conductor layer 172 and the reception signal output terminal 15 is, the better the reception filter characteristic is. Similarly, it can be seen that the isolation characteristics are better when the distance between the connection conductor layer 172 and the reception signal output terminal 15 is shorter.

  FIG. 6 shows the reception of the surface acoustic wave element 22 for reception when the width of the connection conductor layer 172 in the connection wiring 17 is changed when the common ground 16 together with the reception signal output terminal 15 is provided on the lower surface of the wiring board 1. It is the graph which showed the filter characteristic. As can be seen from FIG. 6, when the width of the connection conductor layer 172 becomes too large, the electromagnetic coupling with the reception signal output terminal 15 and the surrounding wiring increases, and the reception filter characteristics deteriorate. Similarly, it can be seen that the isolation characteristic also decreases when the width of the connection conductor layer 172 becomes too large. Therefore, the width of the connection conductor layer 172 is preferably narrow, and this width is preferably 200 μm or less.

  Although the common ground 16 shown in FIG. 1 is provided on the lower surface of the wiring board 1, the common ground 16 faces a side other than the side along the edge of the wiring board 1 in the reception signal output terminal 15 in a top view. As long as it is provided, it may be provided inside the wiring board 1 as shown in FIG. In this case, the connection wiring 17 may be composed of a via-hole conductor 171 and a connection conductor layer 172 as shown in FIG. 7, but the connection conductor layer 172 is formed in the same layer as the common ground 16. Also good.

  Further, when the reception signal output terminal 15 is positioned at the corner of the wiring board 1 in a top view, the reception signal output terminal 15 and the common ground 16 are separated by an L-shaped slit as shown in FIG. The different sides facing the different sides of the reception signal output terminal 15 in the top view of the ground 16 are such that the ends of the different sides coincide (intersect), and the connection wiring 17 is a wiring board. A structure provided along the corner is adopted.

It is a schematic sectional drawing of one Embodiment of the splitter of this invention. FIG. 2 is a plan perspective view of the duplexer shown in FIG. 1. It is the graph which showed the receiving filter characteristic and isolation characteristic of the duplexer of this invention. It is the graph which showed the receiving filter characteristic and isolation characteristic of the splitter of the conventional structure which has no connection wiring which connects a common ground. 3 is a graph showing reception filter characteristics when the height of connection wiring in the duplexer shown in FIG. 1 is changed. 3 is a graph showing reception filter characteristics when the width of connection wiring in the duplexer shown in FIG. 1 is changed. It is a schematic sectional drawing of other embodiment of the splitter of this invention. It is a plane perspective view of further another embodiment of the duplexer of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Wiring board 11, 12 ... Ground pad 13 ... Reception signal output wiring 14 ... Ground wiring 15 ... Reception signal output terminal 16 ... Common ground 17 ... Connection wiring 171, ..Via-hole conductor 172... Connection conductor layer 21... Surface acoustic wave element for transmission 22... Surface acoustic wave elements for reception 211 and 221.

Claims (3)

A wiring board in which transmission signal input wiring, reception signal output wiring and ground wiring are provided; a surface acoustic wave element for transmission and a surface acoustic wave element for reception mounted on the upper surface of the wiring board;
A reception signal output terminal provided along the edge of the wiring substrate on the lower surface of the wiring substrate, and electrically connected to an output electrode of the surface acoustic wave element for reception via the reception signal output wiring;
The surface acoustic wave for transmission is provided on the lower surface or inside of the wiring substrate so as to face a side other than the side along the edge of the wiring substrate at the reception signal output terminal in a top view. A common ground electrically connected to each of the ground electrode of the element and the ground electrode of the surface acoustic wave element for reception,
In the common ground, different side portions of the reception signal output terminal that are opposed to sides other than the side along the edge of the wiring substrate are provided inside the wiring substrate, and the reception signal is viewed from above. by than the connection portion between the output terminal receiving the signal output lines disposed on the edge side of the wiring substrate connection wiring, the than the connecting portion between the reception signal output terminal and the reception signal output line viewed from the top A duplexer characterized in that it is electrically connected on the edge side of the wiring board .   2. The duplexer according to claim 1, wherein the different sides of the common ground are electrically connected by the connection wiring in the vicinity of the edge of the wiring board.   The different side portions of the common ground facing each other across the reception signal output terminal in a top view are electrically connected by the connection wiring arranged along the edge of the wiring board. The duplexer according to claim 2.

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