JP2006287782A - Transversal type saw filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transversal type SAW filter in which three IDT electrodes are spaced at predetermined intervals on a piezoelectric substrate, and in which attenuation characteristics are improved without increasing device size. <P>SOLUTION: The IDT electrodes 1-3 are spaced at predetermined intervals along the propagation direction of a SAW on the piezoelectric substrate. The IDT electrode 1 is connected to an input/output terminal 10, the IDT electrodes 2, 3 are connected to each other by a lead electrode 11 and connected to an input/output terminal 12. Then, electromagnetic coupling between the input/output terminals is suppressed by arranging a ground line 13 in a gap between the input/output terminal 10 connected to the IDT electrode 1 and the lead electrode 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a transversal SAW filter in which three IDT electrodes are arranged at predetermined intervals along the propagation direction of a surface acoustic wave (SAW) on a piezoelectric substrate.

  In recent years, SAW filters have been widely used in the communication field, and are often used particularly for mobile phones because they have excellent characteristics such as high performance, small size, and mass productivity. Due to the increasing demand for data communications such as images, IF filters used in mobile phones are required to be small and have high attenuation characteristics. Transversal SAW filters are suitable as filters that satisfy these specifications. .

  FIG. 6 shows a plan view of a conventional transversal SAW filter. An input IDT electrode 102 and an output IDT electrode 103 are arranged on the main surface of the piezoelectric substrate 101 along the SAW propagation direction at a predetermined interval, and an input / output terminal is provided between the IDT electrodes 102 and 103. A shield electrode 104 for shielding the direct wave between them is arranged. The IDT electrodes 102 and 103 are composed of a pair of comb electrodes having a plurality of electrode fingers interleaved with each other, and one comb electrode of the IDT electrode 102 is connected to the input terminal IN and the other comb electrode is It is grounded, and one comb electrode of the IDT electrode 103 is grounded and the other comb electrode is connected to the output terminal OUT. In order to suppress unnecessary reflected waves from the substrate end face, the sound absorbing material 105 is applied to both ends of the piezoelectric substrate 101 in the long side direction (SAW propagation direction).

  In the transversal type SAW filter, the SAW excited by the input IDT electrode 102 propagates equally to the left and right, so that a bidirectional loss of 6 dB occurs when the SAW is picked up by the output IDT electrode 103. It is generally known that it is disadvantageous for reducing the loss.

  In order to avoid the deterioration of the insertion loss due to the bidirectional loss, three IDT electrodes are arranged at predetermined intervals along the SAW propagation direction on the main surface of the piezoelectric substrate in Japanese Patent Application Laid-Open No. 57-129512. A transversal SAW filter was considered. FIG. 7 shows a typical structure of the transversal SAW filter. IDT electrodes 112 and 113 are arranged on both sides of the IDT electrode 111, and one comb electrode of the IDT electrode 111 is connected to the input / output terminal 120. The comb electrodes of the IDT electrodes 112 and 113 are connected to each other by the lead electrode 121 and also to the input / output terminal 122. The other comb-type electrode of the IDT electrodes 111 to 113 is connected to the ground terminal to constitute a transversal SAW filter. In order to prevent direct waves between input and output terminals, shield electrodes 114 are arranged between the IDT electrode 111 and the IDT electrode 112 and between the IDT electrode 111 and the IDT electrode 113. Although not shown, a sound absorbing material or a reflector for absorbing a reflected wave from the end face of the substrate is provided outside the IDT electrodes 112 and 113.

When three IDT electrodes are arranged on a piezoelectric substrate like the transversal SAW filter, the bidirectional loss is reduced to 3 dB, and the insertion loss can be greatly improved compared to the structure of FIG. Is very advantageous.
Japanese Patent Laid-Open No. 57-129512

Incidentally, in the transversal SAW filter of FIG. 7, electromagnetic coupling occurs between the input / output terminal 120 connected to the IDT electrode 111 and the lead electrode 121 and the input / output terminal 122 connected to the IDT electrodes 112 and 113. There was a problem that the attenuation characteristics of the material deteriorated greatly. Further, if the gap between the input / output terminal 120 and the lead electrode 121 is sufficiently separated, the influence of electromagnetic coupling can be reduced. However, the chip size is increased correspondingly, which is disadvantageous for miniaturization.

  In order to solve the above problems, the present invention improves the attenuation characteristics of the transversal SAW filter in which three IDT electrodes are arranged along the SAW propagation direction on the piezoelectric substrate without increasing the device size. The purpose is to do.

  In order to solve the above-mentioned problems, the invention according to claim 1 of the transversal SAW filter according to the present invention is characterized in that three IDT electrodes are arranged at predetermined intervals along the propagation direction of the surface acoustic wave (SAW) on the piezoelectric substrate. In the transversal-type SAW filter arranged at an opening, the IDT electrode arranged at the center is the first IDT electrode, the IDT electrodes arranged on both sides thereof are the second IDT electrode and the third IDT electrode, respectively, and the first IDT Either one of the input or output terminals is connected to one of the comb-shaped electrodes constituting the electrode, and one of the comb-shaped electrodes constituting the second and third IDT electrodes is connected to each other by the lead electrode and also output or input The ground line is arranged in the gap between the terminal connected to one of the comb electrodes of the first IDT electrode and the lead electrode. It is a symptom.

  The invention according to claim 2 is a transversal type SAW filter in which three IDT electrodes are arranged at predetermined intervals along the propagation direction of surface acoustic wave (SAW) on a piezoelectric substrate. The electrode is the first IDT electrode, and the IDT electrodes arranged on both sides thereof are the second IDT electrode and the third IDT electrode, respectively, and one of the comb-shaped electrodes constituting the first IDT electrode is either input or output Are connected, and one of the comb-shaped electrodes constituting the second and third IDT electrodes is connected to each other by a lead electrode and is connected to either the output or input terminal, and the first IDT electrode and the first IDT electrode are connected to each other. The shield electrode is disposed between the two IDT electrodes and between the first IDT electrode and the third IDT electrode, and the shield electrodes are connected to each other by a ground line. It is characterized by disposing the earth line to the gap between the first one of the comb-shaped electrodes in the connected pin and the lead electrodes of the IDT electrode.

  The invention according to claim 3 is the transversal SAW filter according to claim 1 or 2, wherein the distance between the input / output terminal connected to the first IDT electrode and the lead electrode is D, and the width of the ground line is W. In this case, W / D ≧ 0.2.

  According to a fourth aspect of the present invention, in the transversal SAW filter according to any one of the first to third aspects, the other comb electrode and the shield electrode of the first to third IDT electrodes are connected to a common ground terminal. It is characterized by being connected.

  According to a fifth aspect of the present invention, in the transversal SAW filter according to any one of the first to fourth aspects, the input / output terminal is a balanced-balanced termination or an unbalanced-balanced termination.

  According to the first aspect of the present invention, in the transversal SAW filter in which three IDT electrodes are arranged at predetermined intervals along the propagation direction of the surface acoustic wave (SAW) on the piezoelectric substrate, the first By arranging a ground line between the input / output terminal connected to the IDT electrode and the lead electrode connected to the second and third IDT electrodes, electromagnetic coupling between the input / output terminals can be suppressed and the device size can be increased. The attenuation characteristics can be improved without doing so.

  According to the second aspect of the present invention, in the transversal SAW filter in which three IDT electrodes are arranged at predetermined intervals along the propagation direction of the surface acoustic wave (SAW) on the piezoelectric substrate, each IDT electrode An input / output terminal connecting the shield line to the first IDT electrode, and a lead electrode connecting the second and third IDT electrodes; By disposing them between the two, the electromagnetic coupling between the input / output terminals and between the IDT electrodes can be suppressed, and the attenuation characteristics can be further improved without increasing the device size.

  According to the third aspect of the present invention, when the distance between the input / output terminal connected to the first IDT electrode and the lead electrode is D and the width of the ground line is W, W / D ≧ 0.2. preferable.

According to the invention of claim 4, by connecting the first to third IDT electrodes and the shield electrode to a common ground terminal, the number of connection members such as bonding wires or metal bumps can be reduced, The SAW filter can be reduced in size and cost.

  According to the fifth aspect of the present invention, it is possible to provide a balanced-balanced termination or unbalanced-balanced termination transversal SAW filter having good balance and attenuation characteristics.

Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings. FIG. 1 shows a transversal SAW filter according to a first embodiment of the present invention. An IDT electrode 1 and IDT electrodes 2 and 3 are arranged on the piezoelectric substrate on the piezoelectric substrate, and the IDT electrodes 1 to 3 are each composed of a pair of comb-shaped electrodes having a plurality of electrode fingers interleaved with each other. One comb electrode of the electrode 1 is connected to the input / output terminal 10, and one comb electrode of the IDT electrodes 2 and 3 is connected to each other by the lead electrode 11 and also to the input / output terminal 12. Then, the other comb electrode of the IDT electrodes 1 to 3 is connected to the ground terminal 14. Further, shield electrodes 4 and 4 are disposed between the IDT electrode 1 and the IDT electrode 2 and between the IDT electrode 1 and the IDT electrode 3, and are connected to each other by the earth line 13. Although not shown, a sound absorbing material or a reflector for absorbing a reflected wave from the substrate end face is provided outside the IDT electrodes 2 and 3.

As described above, in this embodiment, the shield electrodes 4 and 4 are disposed between the IDT electrode 1 and the IDT electrode 2 and between the IDT electrode 1 and the IDT electrode 3, and the shield electrodes 4 and 4 are grounded. By connecting the line 13 and arranging the earth line between the input / output terminal 10 and the lead terminal 11, electromagnetic coupling between the input / output terminals and between the IDT electrodes was suppressed.

FIG. 2 shows a comparison of the attenuation characteristics when the distance between the input / output terminal 10 and the lead electrode 11 is D and the width of the ground line 13 is W and the W / D is changed in the transversal SAW filter. Is shown. The characteristics indicated by F1 in the figure are filter characteristics when D = 50 μm and W = 10 μm and W / D = 0.2, and the characteristics indicated by F2 are D / 50 μm and W = 30 μm and W / D = 0. The filter characteristics when. Further, the characteristic indicated by F0 indicates the filter characteristic of the conventional example of FIG. 6 in which the ground line for comparison is not provided. In any of the characteristics, the center frequency fo is 40 (MHz), the rotation Y-cut X-propagation LiNbO ₃ substrate is used as the piezoelectric substrate, the IDT electrode 1 has 7 pairs, and the IDT electrodes 2 and 3 have 5 pairs. The crossing width of each IDT electrode is 7λ (λ: period of the IDT electrode).

As shown in FIG. 2, it can be seen that the characteristics F1 and F2 of the present invention in which the ground line is provided have a larger attenuation characteristic in the vicinity of the pass band than the characteristic F0 of the conventional example. Further, F2 with W / D = 0.6 has a larger attenuation characteristic than F1 with W / D = 0.2. By setting W / D ≧ 0.2, the attenuation characteristic is further increased. Confirmed improvement.

FIG. 3 shows a modification of the present embodiment. The difference from FIG. 1 is that the ground terminals 14 connected to the IDT electrodes 1 to 3 and the shield electrodes 4 and 4 are shared. In this structure, since the number of connection members such as bonding wires or metal bumps connected to the ground terminal can be reduced, the SAW filter can be reduced in size and cost.

FIG. 4 shows another modification of the present embodiment. The difference from FIG. 1 is that no shield electrode is arranged in the gap between the IDT electrodes, and the ground line 13 is connected between the input / output terminal 10 and the lead electrode 11. And are arranged independently so as to surround the input / output terminal 10. In this structure, the electromagnetic coupling between the input and output terminals can be suppressed, so that a good attenuation characteristic can be obtained, and the SAW filter can be downsized.

  Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 5 shows a transversal SAW filter according to a second embodiment of the present invention. An IDT electrode 21 and IDT electrodes 22 and 23 are arranged on both sides of the piezoelectric substrate, and the IDT electrodes 21 to 23 are each constituted by a pair of comb-shaped electrodes having a plurality of electrode fingers inserted into each other. The balancing input / output terminal 30 is connected to one comb-shaped electrode of the electrode 21, the balancing input / output terminal 40 is connected to the other comb-shaped electrode, and one of the comb electrodes of the IDT electrodes 22 and 23 is connected to each other by the lead electrode 31. They are connected to each other and connected to the balancing input / output terminal 32, and the other comb electrodes are connected to each other by the lead electrode 41 and also connected to the balancing input / output terminal 42. Further, shield electrodes 24 and 24 are arranged between the IDT electrode 21 and the IDT electrode 22 and between the IDT electrode 21 and the IDT electrode 23, and the shield electrodes are connected to each other by ground lines 33 and 43. The ground line 33 is disposed between the balancing input / output terminal 30 and the lead electrode 31, and the ground line 43 is disposed between the balancing input / output terminal 40 and the lead electrode 41.

In the transversal type SAW filter of this embodiment, the input / output terminals are balanced-balanced terminations, and an earth line is disposed between the input / output terminals and the lead electrodes, thereby suppressing electromagnetic coupling between the input / output terminals. Therefore, a good balance and attenuation characteristics can be realized. Similarly, it goes without saying that the present invention can also be applied to a transversal SAW filter whose input / output terminals are unbalanced-balanced termination.

In the above embodiment, the rotating Y-cut X-propagating LiNbO ₃ is used as the piezoelectric substrate, but the present invention is not limited to this, and other piezoelectric substrates such as quartz, LiTaO ₃ , and LBO may be used. The same effect can be obtained when the electrode fingers of the IDT electrode are weighted or a unidirectional SAW converter is used.

It is a figure explaining the transversal type SAW filter concerning the 1st example of the present invention. In the transversal SAW filter according to the first embodiment of the present invention, a comparison of filter characteristics when W / D is changed is shown. It is a figure explaining the modification of the transversal type SAW filter concerning the 1st example of the present invention. It is a figure explaining another modification of the transversal type SAW filter concerning the 1st example of the present invention. It is a figure explaining the transversal type SAW filter concerning the 2nd example of the present invention. It is a figure explaining the conventional transversal type SAW filter. It is a figure explaining the transversal type SAW filter which has arrange | positioned three IDT electrodes on the conventional piezoelectric substrate.

Explanation of symbols

1, 2, 3, 21, 22, 23: IDT electrode 4, 24: Shield electrode 10, 12: Input / output terminal 11, 31, 41: Lead electrode 13, 33, 43: Earth line 14: Earth terminal 30, 32 , 40, 42: I / O terminals for balancing

Claims (5)

In a transversal SAW filter in which three IDT electrodes are arranged at predetermined intervals along the propagation direction of a surface acoustic wave (SAW) on a piezoelectric substrate,
The IDT electrode arranged in the center is the first IDT electrode, and the IDT electrodes arranged on both sides thereof are the second IDT electrode and the third IDT electrode, respectively, and input to one of the comb electrodes constituting the first IDT electrode Alternatively, one of the output terminals is connected, and one of the comb electrodes constituting the second and third IDT electrodes is connected to each other by a lead electrode and connected to either the output or input terminal,
A transversal type SAW filter, wherein a ground line is arranged in a gap between a terminal connected to one of the comb electrodes of the first IDT electrode and the lead electrode. In a transversal SAW filter in which three IDT electrodes are arranged at predetermined intervals along the propagation direction of a surface acoustic wave (SAW) on a piezoelectric substrate,
The IDT electrode arranged in the center is the first IDT electrode, and the IDT electrodes arranged on both sides thereof are the second IDT electrode and the third IDT electrode, respectively, and input to one of the comb electrodes constituting the first IDT electrode Alternatively, one of the output terminals is connected, and one of the comb electrodes constituting the second and third IDT electrodes is connected to each other by a lead electrode and connected to either the output or input terminal,
A shield electrode is disposed between the first IDT electrode and the second IDT electrode and between the first IDT electrode and the third IDT electrode, and the shield electrodes are connected to each other by a ground line, A transversal SAW filter, characterized in that an earth line is disposed in a gap between a terminal connected to one comb electrode of the first IDT electrode and a lead electrode.   The transversal SAW filter is characterized in that W / D ≧ 0.2 when the distance between the input / output terminal connected to the first IDT electrode and the lead electrode is D and the width of the ground line is W. The transversal SAW filter according to claim 1 or 2.   4. The transversal SAW filter according to claim 1, wherein the other comb electrode and the shield electrode of the first to third IDT electrodes are connected to a common ground terminal. 5. Transversal SAW filter. 5. The transversal SAW filter according to claim 1, wherein the transversal SAW filter has a balanced-balanced termination or an unbalanced-balanced termination as an input / output terminal.

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