JP4325424B2 - Surface acoustic wave filter device - Google Patents

Description

  The present invention relates to a surface acoustic wave filter device formed by connecting a plurality of end surface reflection type resonator type surface acoustic wave filters, and more specifically, at least one longitudinally coupled end surface reflection type resonator type multimode filter, and at least The present invention relates to a surface acoustic wave filter device formed by cascading one laterally coupled end face reflection type resonator type multimode filter.

  Conventionally, various surface acoustic wave filter devices in which a plurality of end surface reflection type surface acoustic wave filters are connected have been proposed. For example, Patent Document 1 listed below discloses a laterally coupled end face reflection type resonator type multimode filter (hereinafter abbreviated as a laterally coupled filter), a longitudinally coupled end face reflection type resonator type multimode filter on at least one piezoelectric substrate. A surface acoustic wave filter device is disclosed in which a horizontal coupling filter (hereinafter abbreviated as a longitudinal coupling filter) and a lateral coupling filter are arranged in this order in a direction orthogonal to the surface wave propagation direction. Here, a pair of opposing end faces of the piezoelectric substrate are reflection end faces that reflect surface waves.

  In this specification, the distance between the center of the second electrode finger from one end in the surface wave propagation direction of the IDT in the end face reflection type surface wave filter and the end face closer to the electrode finger is the end face position, The distance between the centers of the electrode fingers having the same potential is expressed as an electrode finger pitch.

In the surface acoustic wave device described in Patent Document 1, the end face position of the longitudinally coupled filter is 0.5λ ₁ (where λ ₁ is the electrode finger pitch of the IDT in the longitudinally coupled filter), and the end face position of the laterally coupled filter is 0. 5λ ₂ (λ ₂ is the electrode finger pitch of the IDT in the lateral coupling filter), and λ ₂ was larger than λ ₁ .

  On the other hand, as described above, for example, a surface acoustic wave filter device shown in FIG. 10 is known as a surface acoustic wave device in which a longitudinal coupling filter and a lateral coupling filter are cascade-connected. The surface acoustic wave filter device 101 is configured using a single piezoelectric substrate 102 having a rectangular plate shape. The piezoelectric substrate 102 has a pair of end faces 102a and 102b facing each other.

  By forming electrodes on the piezoelectric substrate 102, the longitudinal coupling filter 103, the lateral coupling filter 104, and the longitudinal coupling filter 105 are arranged in a direction orthogonal to the surface wave propagation direction. The vertical coupling filter 103 has a structure in which IDTs 103a and 103b are arranged at a predetermined IDT interval. The lateral coupling filter 104 has a structure in which the IDTs 104a and 104b are arranged in parallel in a direction orthogonal to the surface wave propagation direction. The longitudinal coupling filter 105 has a structure in which IDTs 105a and 105b are arranged in the surface wave propagation direction with an IDT interval.

  Each of the longitudinal coupling filters 103 and 105 and the lateral coupling filter 104 is an end face reflection type surface wave filter using the end faces 102a and 102b as end faces for reflecting surface waves.

FIG. 11 is a diagram showing the frequency characteristics of the end surface reflection type surface acoustic wave filter device 101 shown in FIG. Here, the electrode finger pitch λ ₁ in the vertical coupling filters 103 and 105 is 44.82 μm, and the electrode finger pitch λ ₂ in the horizontal coupling filter 104 is 45.10 μm. The total number of electrode fingers of each IDT in the vertical coupling filters 103 and 105 is 50 pairs, and the number of electrode fingers of each IDT in the horizontal coupling filter 104 is 50 pairs. Further, the IDT interval in the longitudinal coupling filters 103 and 105 is set to 0.31λ ₁ . The end face positions of the vertical coupling filters 103 and 105 are 0.5λ ₁ , and the end face position of the horizontal coupling filter 104 is 0.58λ ₂ .
Japanese Patent No. 3289673

In the surface acoustic wave filter device described in Patent Document 1, the end face position of the longitudinal coupling filter is 0.5λ ₁ , the end face position of the lateral coupling filter is 0.5λ ₂ , and the electrode finger pitch λ 2 is the electrode finger pitch λ. It was bigger than _one . Therefore, the center frequency of the lateral coupling filter has to be lower than the center frequency of the longitudinal coupling filter. Therefore, there is a problem that ripples are generated in the passband.

  In addition, it is difficult to increase the steepness in the cascade connection with only the vertical coupling filter. In addition, the out-of-band attenuation cannot be increased with the cascade connection of only the lateral coupling filters.

  As shown in FIG. 10, in the surface acoustic wave filter device 101 in which the longitudinal coupling filters 103 and 105 are used at the input end and the output end, and the lateral coupling filter 104 is connected therebetween, the same degree as the lateral coupling filter 104 is obtained. The out-of-band attenuation can be improved while ensuring the low loss and the steepness of the filter characteristics. In addition, there is an advantage that a balanced input and / or output type filter, which has been difficult when only the lateral coupling filter is used, can be easily configured. That is, when the balanced signal terminal is configured using only the lateral coupling filter, a method of separating the common bus bar portion of the coupling portion into two portions or a method of dividing the input / output IDT into two portions has been used. However, the former method has a problem that the electrode at the coupling portion becomes thin, patterning becomes difficult, and the electrode becomes thin, resulting in an increase in electrical resistance. The latter method has a problem that the impedance is quadrupled due to the division and a desired impedance cannot be obtained.

  However, also in the surface acoustic wave filter device 101, in the configuration in which the end face reflection type longitudinal coupling filter and lateral coupling filter are cascade-connected using one piezoelectric substrate, the longitudinal coupling filters 103 and 105 and the lateral coupling filter 104 are connected. The center frequency has to be shifted, and therefore it is difficult to obtain good filter characteristics.

  An object of the present invention is to use a pair of opposing end surfaces of one piezoelectric substrate as reflection end surfaces in view of the above-described state of the prior art, and at least one longitudinally coupled filter on the one piezoelectric substrate, A surface acoustic wave filter device comprising at least one lateral coupling filter and cascaded, wherein the center frequency of the longitudinal coupling filter and the center frequency of the lateral coupling filter are matched, It is an object of the present invention to provide a surface acoustic wave filter device that can effectively improve the external attenuation and enhance the steepness of filter characteristics.

  Another object of the present invention is not only to increase out-of-band attenuation and steepness of filter characteristics, but also in a surface acoustic wave filter device having a configuration in which a longitudinal coupling filter and a lateral coupling filter are connected in cascade. An object of the present invention is to provide a surface acoustic wave filter device that can easily realize a balanced input and / or output type configuration without causing an increase in electrical resistance and an increase in impedance.

A surface acoustic wave filter device according to the present invention includes at least one longitudinally coupled end surface reflection type resonator type multimode filter (longitudinal coupling filter) and at least one laterally coupled end surface reflection type resonator type multimode filter (laterally coupled filter). Are connected in cascade, and the longitudinal coupling filter and the lateral coupling filter are arranged on the same piezoelectric substrate in a direction orthogonal to the surface wave propagation direction, and the longitudinal coupling filter and the lateral coupling filter are When each has at least one IDT and the end face position is the distance between the center and the end face of the second electrode finger from the end of the IDT, the end face position in the longitudinal coupling filter is 0.5λ ₁ (however, , lambda _1, the vertical coupling being other than the electrode finger pitch) of the IDT of the filter, and the position of the end face of the transversely coupled filter 0.5 [lambda ₂ (where, lambda _2, the horizontal The other end face of the longitudinally coupled filter and laterally coupled filter adjacent to each other in the direction orthogonal to the surface wave propagation direction cuts the piezoelectric substrate at a time. It is formed and is flush.

  In the surface acoustic wave filter device according to the present invention, the center frequencies of the longitudinal coupling filter and the lateral coupling filter coincide with each other.

  In a specific aspect of the surface acoustic wave filter device according to the present invention, an intersection of an end surface position dependency curve of the center frequency of the longitudinally coupled filter and an end surface position dependency curve of the center frequency of the laterally coupled filter is Each end face position of the longitudinal coupling filter and the lateral coupling filter is set.

In another specific aspect of the surface acoustic wave filter device according to the present invention, the electrode finger pitch λ ₁ of the longitudinally coupled filter is equal to the electrode finger pitch λ ₂ of the laterally coupled filter.

In still another specific aspect of the surface acoustic wave filter device according to the present invention, the electrode finger pitch λ ₁ of the longitudinally coupled filter is different from the electrode finger pitch λ ₂ of the laterally coupled filter.

In still another specific aspect of the surface acoustic wave filter device according to the present invention, the end face position of the longitudinally coupled filter is 0.51λ ₁ or more and 0.60λ ₁ or less, and the end face position of the laterally coupled filter is 0.58λ. ₂ or more and 0.85λ ₂ or less.

  In still another specific aspect of the surface acoustic wave filter device according to the present invention, in the configuration in which the longitudinal coupling filter and the lateral coupling filter are cascaded, one of the input / output terminals of the longitudinal coupling filter is a balanced signal terminal. Has been.

  In yet another specific aspect of the surface acoustic wave filter device according to the present invention, an end face position a of the longitudinally coupled end face reflection type resonator multimode filter satisfies x−0.1 ≦ a ≦ x + 0.1, The end face position b of the laterally coupled end face reflection type resonator multimode filter satisfies y−0.1 ≦ b ≦ y + 0.1, and x and y satisfy the following expressions (1) and (2). ing.

D ₂ (y−0.5) + V ₂ / λ ₂ = D ₁ (x−0.5) + V ₁ / λ ₁ (1)
2yλ ₂ + N ₂ λ ₂ = 2xλ ₁ + N ₁ λ ₁ + Gλ ₁ (2)
Where λ _{1 is} the electrode finger pitch (μm) of the longitudinal coupling filter, V _{1 is} the substrate sound speed (m / second) when designing the longitudinal coupling filter, and D _{1 is} the change rate of the center frequency depending on the end face position of the longitudinal coupling filter (MHz). / Λ), N ₁ : Logarithm of longitudinal coupling filter, G: Center distance (λ ₁ ) between adjacent electrode fingers in the IDT-IDT gap which is the coupling length of the longitudinal coupling filter, λ ₂ : Electrode finger of lateral coupling filter Pitch (μm), V ₂ : sound velocity (m / sec) of substrate when designing lateral coupling filter, D ₂ : rate of change of center frequency depending on end face position of lateral coupling filter (MHz / λ), N ₂ : lateral coupling filter Preferably, the end face position a of the longitudinal coupling filter is in the range of x−0.05 ≦ a ≦ x + 0.05, and the end face position b of the horizontal coupling filter is y−0.05 ≦ b ≦ y + 0.05. Is in range.

In the surface acoustic wave filter device according to the present invention, at least one longitudinally coupled filter and at least one laterally coupled filter are cascade-connected on a piezoelectric substrate, and the longitudinally coupled filter and the laterally coupled filter are not connected. reflection end surface, in the surface acoustic wave filter device which is constituted by the end faces mutually pair of opposed identical piezoelectric substrate, an end surface position of the longitudinally coupled filter are other than 0.5 [lambda _1, the end surface position of the transversely coupled filter 0.5 [lambda ₂ except a are, each one end face of the longitudinally coupled filter and transversely coupled filters adjacent in a direction orthogonal to the surface wave propagation direction, are formed by cutting the piezoelectric substrate at a time, And it is considered to be the same. Accordingly, since the end face position can be set to other than 0.5λ _{1 in the} longitudinal coupling filter, the center frequency of the longitudinal coupling filter and the center frequency of the lateral coupling filter can be made equal by setting λ ₁ = λ ₂ . Therefore, it is possible to effectively increase the attenuation amount outside the band and improve the steepness of the filter characteristics.

  In the surface acoustic wave filter device according to the present invention, the intersection between the end face position dependency curve of the center frequency of the longitudinally coupled filter and the end face position dependency curve of the center frequency of the laterally coupled filter is the longitudinally coupled filter and laterally coupled filter. The vertical coupling filter and the horizontal coupling filter are configured so as to be at the respective end face positions.

  Therefore, the center frequency of the longitudinal coupling filter and the center frequency of the lateral coupling filter can be easily matched, and good out-of-band attenuation and steepness of filter characteristics can be improved according to the present invention.

In the surface acoustic wave filter device according to the present invention, when the electrode finger pitch λ ₁ of the longitudinal coupling filter is equal to the electrode finger pitch λ ₂ of the lateral coupling filter, the center frequency of the longitudinal coupling filter is set to be higher than that of the lateral coupling filter. Can be easily matched. However, in the present invention, an electrode finger pitch lambda ₁ longitudinally coupled filter may be different from the electrode finger pitch lambda ₂ of transversely coupled filter, also in this case, the control of the end face position, the longitudinally coupled filter The center frequency can be matched with the center frequency of the lateral coupling filter.

In the surface acoustic wave filter device according to the present invention, the end face position of the longitudinal coupling filter is 0.51λ ₁ or more and 0.60λ ₁ or less, and the end face position of the lateral coupling filter is 0.58λ ₂ or more, 0.85λ _2. If it is below, the out-of-band attenuation can be increased to 45 dB or more.

  In the surface acoustic wave filter device according to the present invention, in the configuration in which the longitudinal coupling filter and the lateral coupling filter are cascaded, when one of the input / output terminals of the longitudinal coupling filter is a balanced signal terminal, Since there is no need for a laterally coupled filter electrode structure, a balanced input and / or output type surface acoustic wave filter device can be easily provided.

  That is, the present invention provides a balanced input and / or output type surface acoustic wave filter device in which expansion of out-of-band attenuation and steepness of filter characteristics are enhanced according to the present invention without causing an increase in electrical resistance or impedance. can do.

  In the surface acoustic wave filter device according to the present invention, the end face position a of the longitudinally coupled filter is in the range of x−0.1 ≦ a ≦ x + 0.1, and the end face position b of the laterally coupled filter is y−0.1. If it is in the range of ≦ b ≦ y + 0.1 and x and y are configured to satisfy the above-mentioned formulas (1) and (2), the center frequencies of the longitudinal coupling filter and the lateral coupling filter are matched. Since the range of the end face position that can be set can be set, the in-band ripple is small and the filter can have a steep characteristic.

  In particular, the end face position a of the longitudinally coupled end face reflection type resonator type multimode filter is in the range of x−0.05 ≦ a ≦ x + 0.05, and the end face position b of the laterally coupled end face reflection type resonator type multimode filter. Is in the range of y−0.05 ≦ b ≦ y + 0.05, the end face position range in which the center frequencies of the longitudinal coupling filter and the lateral coupling filter can be matched can be accurately set. Is smaller and a filter having a steep characteristic can be obtained.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention.

In this specification, the total pitch is the distance between the center of the second electrode finger from one end of the IDT and the center of the second electrode finger from the other end in the lateral coupling filter. is a value obtained by adding the lambda _2. On the other hand, in the longitudinal coupling filter, the center of the second electrode finger from the end surface near the IDT of the IDT and the second electrode finger from the end surface of the second IDT on the IDT side are arranged. Is a value obtained by adding λ ₁ to the distance from the center of

FIG. 1 is a plan view showing a surface acoustic wave filter device according to a first embodiment of the present invention. In the surface acoustic wave filter device 1, a piezoelectric substrate 2 on a rectangular plate is used. In this embodiment, the piezoelectric substrate 2 is made of a lead zirconate titanate ceramic. However, the piezoelectric substrate 2 may be made of not only piezoelectric ceramics but also a piezoelectric single crystal such as LiNbO ₃ or LiTaO ₃ .

  By forming a plurality of electrode structures on the piezoelectric substrate 2, the longitudinal coupling filter 3, the lateral coupling filter 4, and the longitudinal coupling filter 5 are configured in this order in a direction orthogonal to the surface wave propagation direction. The longitudinal coupling filter 3, the lateral coupling filter 4, and the longitudinal coupling filter 5 are connected in cascade.

  The longitudinally coupled filter 3 has a first IDT 6 and a second IDT 7 arranged along the surface wave propagation direction. The first IDT 6 includes comb electrodes 6a and 6b. The comb electrodes 6a and 6b are balanced input terminals.

  The second IDT 7 has comb electrodes 7a and 7b. The comb-tooth electrode 7 a is connected to the ground potential, and the comb-tooth electrode 7 b is connected to the lateral coupling filter 4.

  In the present embodiment, the lateral coupling filter 4 has first and second IDTs 9 and 10 arranged in a direction orthogonal to the surface wave propagation direction. The IDT 9 is electrically connected to the comb electrode 7 b of the longitudinal coupling filter 3. The IDTs 9 and 10 are laterally coupled, and one end of the IDT 10 is connected to the longitudinally coupled filter 5. The longitudinal coupling filter 5 includes first and second IDTs 11 and 12. The IDT 11 includes comb-tooth electrodes 11a and 11b, and the comb-tooth electrode 11a is electrically connected to the IDT 10. The comb electrode 11b is connected to the ground potential. The second IDT 12 includes comb electrodes 12a and 12b. The comb-tooth electrodes 12a and 12b constitute balanced output terminals. Therefore, the surface acoustic wave filter device 1 has a balanced input signal terminal and a balanced output signal terminal.

  In this embodiment, the longitudinal coupling filter 3, the lateral coupling filter 4, and the longitudinal coupling filter 5 are configured using an electrode material made of Al. Specifically, the longitudinal coupling filters 3 and 5 and the lateral coupling filter 4 are configured as follows.

(Vertical coupling filter 3)
The number of electrode fingers of the first IDT 6 = 21 pairs, the number of electrode fingers of the second IDT 7 = 29 pairs, the electrode finger crossing width at the IDTs 6 and 7 = 5.0λ ₁ , the IDT interval (adjacent electrodes of the IDTs 6 and 7 (Distance between finger centers) = 0.31λ ₁ , λ ₁ = 44.82 μm
(Horizontal coupling filter 4)
Crossing width of electrode fingers at IDTs 9 and 10 = 1.34λ ₂ , coupling length with IDTs 9 and 10 = 0.3λ ₂ , λ ₂ = 44.82 μm
(Vertical coupling filter 5)
The number of electrode fingers of the _first IDT 11 = 29 pairs, the number of electrode fingers of the second IDT 12 = 21 pairs, the electrode finger crossing width of the IDTs 11 and ₁₂ = 5.0λ ₁ , the IDT interval (the interval between the IDTs 11 and 12 = 0.31λ ₁ , λ ₁ = 44.82 μm
As described above, in this embodiment, the electrode finger pitch λ ₁ of the IDT in the vertical coupling filters 3 and 5 and the electrode finger pitch λ ₂ of the IDT in the horizontal coupling filter 4 are made equal.

The total pitch in the longitudinal coupling filters 3 and 5 and the lateral coupling filter 4 calculated from the above λ ₁ and λ ₂ and the logarithm of the electrode finger of the IDT is as follows.

Total pitch in the longitudinal coupling filters 3 and 5 = 2254.8942 μm, total pitch in the lateral coupling filter 4 = 2241 μm
Therefore, the total pitch in the horizontal coupling filter 4 is 13.8942 μm smaller than the total pitch in the vertical coupling filters 3 and 5. For this reason, the outermost electrode fingers of the IDTs 9 and 10 in the horizontal coupling filter 4 are positioned about 6.9 μm inside compared to the outermost electrode fingers of the vertical coupling filters 3 and 5.

As described above, in this embodiment, the electrode finger pitch λ _{1 of} the longitudinal coupling filters 3 and 5 is equal to the electrode finger pitch λ ₂ of the lateral coupling filter 4, and therefore the end face position of the longitudinal coupling filters 3 and 5 is Compared with the end face position of the lateral coupling filter 4, the distance between IDT and IDT is shortened. Since λ ₁ = λ ₂ , assuming that λ ₁ = λ ₂ = λ, for example, when the end face position of the lateral coupling filter is 0.725λ, the end face positions of the longitudinal coupling filters 3 and 5 are the longitudinal coupling filter 3. , 5 is 0.31λ, so that 0.725λ−0.31λ / 2 = 0.57λ.

  In the present embodiment, the dicing position of the piezoelectric substrate 2 is adjusted so that the center frequency of the longitudinal coupling filters 3 and 5 and the center frequency of the lateral coupling filter 4 coincide. That is, the piezoelectric substrate 2 is diced, the end face 2a or the end face 2b is cut by one cutting, and the positions of the cut end faces 2a and 2b are controlled, whereby the center frequencies of the longitudinally coupled filters 3 and 5; The center frequency of the lateral coupling filter 4 is matched. As described above, dicing may be performed so as to control the end face position in the longitudinal coupling filters 3 and 5.

  In addition, the inventor of the present application has found that the center frequency changes at the end face position in the surface acoustic wave filter device, the longitudinal coupling filter, and the lateral coupling filter, and the rate of change differs between the longitudinal coupling filter and the lateral coupling filter. . This will be described with reference to FIG.

  A curve connecting points indicated by □ in FIG. 2 is a curve indicating the end surface position dependency of the center frequency of one longitudinally coupled filter 3 used in the present embodiment, and the point indicated by Δ is The connected curve is a curve showing the dependence of the center frequency of the lateral coupling filter 4 on the end face position. 2 is a scale of the end face position of the horizontal coupling filter 4. The horizontal axis in FIG. That is, it can be seen that, in both the longitudinal coupling filter 3 and the lateral coupling filter 4, the center frequency changes when the end face position changes. Then, it can be seen that the curve connecting the points indicated by □ intersects the curve connecting the points indicated by Δ at the end face position 0.725λ of the lateral coupling filter 4. That is, it can be seen that when the end face position is 0.725λ, the center frequencies of the longitudinal coupling filter and the lateral coupling filter match. Accordingly, the end surfaces of the longitudinally coupled filters 3 and 5 and the laterally coupled filter 4 may be cut out from the piezoelectric substrate 2 so that the end surface position of the laterally coupled filter 4 is 0.725λ.

  A curve connecting points indicated by ◆ in FIG. 2 is a diagram showing a change in the center frequency when the end face position of the lateral coupling filter is changed in the surface acoustic wave filter device of the above embodiment. Also in the curve connecting the points indicated by ◆, when the end face position of the lateral coupling filter 4 is 0.725λ, the center frequency is 0.725λ of the end face position in the case of the longitudinal coupling filter alone and the lateral coupling filter alone. It turns out that it is the same as the case.

  FIG. 3 is a diagram showing the relationship between the end face position and the 3 dB bandwidth. The 3 dB bandwidth refers to the width of the pass band with an attenuation of 3 dB or less. In FIG. 3, the change in the bandwidth of 3 dB when the curve connecting the points indicated by □ is the vertical coupling filter alone, and the result when the curve connecting the points indicated by Δ is the horizontal coupling filter alone. The curve connecting the points indicated by ♦ indicates the result when a surface acoustic wave filter device having a three-stage configuration is configured according to the above embodiment.

  As is clear from FIG. 3, the end face position dependency curve of the bandwidth of the lateral coupling filter and the end face position dependency curve of the bandwidth of the filter of the first embodiment in which the longitudinal coupling filter and the lateral coupling filter are connected in cascade are as follows. There is a range of end face positions where the bandwidth of this cascade connection filter is larger than the bandwidth of the lateral coupling filter, and the end face position 0.725λ where the center frequencies of the longitudinal coupling filter and the lateral coupling filter coincide is this It can be seen that it falls within the range. Within this range, the end face position range is a preferred range of end face positions because a wider bandwidth is obtained with a filter in which a longitudinally coupled filter and a laterally coupled filter are cascade-connected than with one laterally coupled filter.

  If the end face of the piezoelectric substrate is cut out so that the end face position of the lateral coupling filter 4 becomes 0.725λ as described above, the center frequencies of the longitudinal coupling filters 3 and 5 and the lateral coupling filter 4 coincide with each other. It can be seen that good filter characteristics are obtained.

  This will be described with reference to FIG.

  FIG. 4 shows the filter waveform when the end face positions of the longitudinally coupled filters 3 and 5 and the laterally coupled filter 4 are 0.725λ according to the above embodiment, and the end face position is 0.78λ. Each filter waveform when 0.69λ and 0.65λ are set. Note that any end face position is the end face position of the horizontal coupling filter 4, but the end face position of the vertical coupling filter can be expressed based on the end face position of the horizontal coupling filter. That is, as described above, when the end face position of the lateral coupling filter is 0.725λ, the end face position of the vertical coupling filter is 0.57λ.

  As can be seen from FIG. 4, when the position of the end face of the lateral coupling filter is 0.725λ, a good filter waveform with little ripple can be obtained.

  That is, in the present embodiment, the end face position of the lateral coupling filter that is the intersection of the end face position dependency curve of the center frequency of the longitudinal coupling filters 3 and 5 and the end face position dependency curve of the center frequency of the lateral coupling filter 4 is employed. It can be seen that a good filter waveform with little ripple can be obtained.

  In the present embodiment, the two end faces of the surface acoustic wave filter element are reflection end faces. However, the reflection end face that is cut halfway in the thickness direction from the surface of the substrate may be formed inside the element end face separately from the element end face. Good. In this way, it is possible to prevent the end face from being damaged by the suction collet when the element is die-bonded to the package.

Next, in the surface acoustic wave filter device 1, the electrode finger pitch lambda ₁ longitudinally coupled filter 3, 5, with the exception that was different from the electrode finger pitch lambda ₂ of the lateral coupling filter 4, the surface acoustic wave filter Various surface acoustic wave filter devices were produced in the same manner as the device 1. Here, five types of surface acoustic wave filter devices were produced in which the ratio of λ ₂ / λ ₁ was changed to 0.992, 0.996, 1.0, 1.004, and 1.008. And the end surface position in the horizontal coupling filter of the produced surface acoustic wave filter apparatus was further varied, and the characteristics were evaluated.

FIG. 5 shows that λ ₂ / λ ₁ is 0.992 (A1), 0.996 (A2), 1.0 (A3), 1.004 (A4), and 1.008 (A5) as described above. It is a figure which shows the relationship between the end surface position of the horizontal coupling filter in each surface acoustic wave filter apparatus, and 3 dB bandwidth.

From FIG. 5, when λ ₂ / λ ₁ changes, the end face position where the bandwidth becomes wider also changes. This indicates that the optimum end face position changes by changing λ ₂ / λ ₁ .

In FIG. 6, the total number of electrode fingers of the longitudinal coupling filter and lateral coupling filter is changed from 50 pairs to 33 pairs, or λ ₂ / λ ₁ is 0.992 (B1), 0. Each surface acoustic wave filter device of 996 (B2), 1.0 (B3), 1.004 (B4), and 1.008 (B5) is manufactured, and the end face position of the lateral coupling filter is changed to change the characteristics. The measurement results are shown. The vertical axis in FIG. 6 indicates the 3 dB bandwidth, and the horizontal axis indicates the end face position.

As is apparent from FIG. 6, even when the longitudinal coupling filters 3 and 5 and the lateral coupling filter 4 having a total number of electrode fingers of 33 pairs are used, the bandwidth becomes wider as λ ₂ / λ ₁ changes. The end face position also changes. This indicates that the optimum end face position changes by changing λ ₂ / λ ₁ .

  FIG. 7 shows a band when the position of the end face of the lateral coupling filter in the surface acoustic wave filter device using the longitudinal coupling filters 3 and 5 and the lateral coupling filter 4 having 33 pairs of total electrode fingers is changed. It is a figure which shows the change of external attenuation amount. Note that B1 to B5 in FIG. 7 have the same meanings as B1 to B5 in FIG.

It varies depending apparent to lambda ₂ / lambda ₁ value from 7, in the case of lambda ₂ / lambda ₁ is any value, by selecting the end face position, it can greatly improve the out-of-band attenuation I understand. It will be described below that there is a preferable end face position range in which the end face position at which this large out-of-band attenuation is obtained matches the end face position in FIG. 6 where the 3 dB bandwidth can be widened.

For example, in the case of B3 in FIG. 6, the end face position of the lateral coupling filter is 0.65λ _{2 to} 0.67λ ₂ , and a wide bandwidth of the cascaded surface wave filter can be obtained. When the end face position of the lateral coupling filter is 0.65λ _{2 to} 0.67λ ₂ , a large out-of-band attenuation of 45 to 60 dB is obtained in the cascaded surface wave filter as shown in FIG. However, as is clear from FIG. 7, it can be seen that when the dicing position is shifted in the direction of decreasing the end face position, the out-of-band attenuation is rapidly deteriorated. Further, since the end face position of the longitudinal coupling is 0.48 to 0.50, it is easy to break. Accordingly, the B3 without the position of the end face of the transversely coupled filter 0.61λ ₂ ~0.66λ ₂ as B4. In B4, the bandwidth is as wide as 550 kHz or more, and the out-of-band attenuation is 60 dB or more. Even if the dicing position is shifted in the direction of decreasing the end face position, the out-of-band attenuation amount does not deteriorate rapidly, and a stable attenuation amount can be obtained. Here, the position of the end face of the transversely coupled filter is reduced from 0.65λ ₂ ~0.67λ ₂ to 0.61λ ₂ ~0.66λ _2, the pitch of the longitudinally coupled filter as it, the transversely coupled filter Since the pitch is increased, λ ₂ / λ ₁ = 1.004, and as a result, the end face position where the frequency matches is changed.

As an incidental effect, when λ ₂ / λ ₁ = 1.004, the end face position of the lateral coupling filter is 0.61λ _{2 to} 0.66λ ₂ , and the end face position of the longitudinal coupling filter is 0.51λ corresponding to this. _{1 to} 0.56λ ₁ , and the electrode finger width on the end face is increased. Therefore, there is no fear of disconnection of the end face electrode fingers due to chipping, and characteristic fluctuations are less likely to occur.

FIG. 8 is a diagram showing the end face position at which a characteristic with a small ripple is obtained when λ ₂ / λ ₁ is changed. In order to obtain a small ripple characteristic, the bandwidth of the entire surface acoustic wave filter device in which two longitudinally coupled filters and one laterally coupled filter are cascade-connected becomes wider than the bandwidth of one laterally coupled filter. is required. That is, good characteristics can be obtained when the band of the horizontal coupling filter is included in the band of the vertical coupling filter. Furthermore, if the center frequency of the longitudinally coupled filter and the center frequency of the laterally coupled filter are matched, more excellent characteristics can be obtained.

  In particular, the center value of the end face position range in which the center frequencies of the longitudinal coupling filter and the lateral coupling filter can be matched can be set by the following formulas (1) and (2), thereby reducing the in-band ripple. A filter having a steep characteristic can be easily obtained.

D ₂ (y−0.5) + V ₂ / λ ₂ = D ₁ (x−0.5) + V ₁ / λ ₁ (1)
2yλ ₂ + N ₂ λ ₂ = 2xλ ₁ + N ₁ λ ₁ + Gλ ₁ (2)
Where λ _{1 is} the electrode finger pitch (μm) of the longitudinal coupling filter, V _{1 is} the substrate sound speed (m / second) when designing the longitudinal coupling filter, and D _{1 is} the change rate of the center frequency depending on the end face position of the longitudinal coupling filter (MHz). / Λ), N ₁ : logarithm of longitudinal coupling filter, G: distance between electrode finger centers adjacent to IDT-IDT gap which is coupling length of longitudinal coupling filter (λ ₁ ), λ ₂ : electrode finger of lateral coupling filter Pitch (μm), V ₂ : sound velocity (m / sec) of substrate when designing lateral coupling filter, D ₂ : rate of change of center frequency depending on end face position of lateral coupling filter (MHz / λ), N ₂ : lateral coupling filter Logarithm of

  FIG. 9 is a diagram showing attenuation frequency characteristics of the first surface acoustic wave filter device according to the first embodiment. For comparison, FIG. 9 also shows the filter characteristics when the vertical coupling filter 3 is cascaded in three stages and the filter characteristics when the horizontal coupling filter is cascaded in three stages.

  As is clear from FIG. 9, the surface acoustic wave filter device of the above embodiment has a wide band and a large out-of-band attenuation compared to a configuration in which three horizontal coupling filters are connected, and three vertical coupling filters are connected. It can be seen that, compared with the surface acoustic wave filter device, the attenuation in the vicinity of the band is large, and good filter characteristics with good steepness can be obtained.

  In the embodiment described above, two longitudinally coupled filters and one laterally coupled filter are cascaded. However, the present invention provides at least one longitudinally coupled filter and at least one laterally coupled filter. Can be applied to various surface acoustic wave filter devices connected in cascade.

1 is a plan view of a surface acoustic wave filter device according to an embodiment of the present invention. The figure which shows the change of each center frequency of a lateral coupling filter, a longitudinal coupling filter, and a three-stage cascade connection type surface acoustic wave filter apparatus when an end surface position is changed. The figure which shows the change of 3 dB bandwidth of the surface acoustic wave filter apparatus of a horizontal coupling filter, a longitudinal coupling filter, and a three-stage cascade connection structure when an end surface position is changed. The figure which shows the filter waveform of the surface acoustic wave filter apparatus at the time of changing an end surface position. Three-stage cascaded surface acoustic wave in which λ ₂ / λ ₁ is 0.992, 0.996, 1.0, 1.004, and 1.008, and the number of electrode fingers of each filter is 50 pairs The figure which shows the relationship between the end surface position of a horizontal coupling filter in a filter apparatus, and 3 dB bandwidth. A three-stage cascaded surface acoustic wave in which λ ₂ / λ ₁ is 0.992, 0.996, 1.0, 1.004, and 1.008, and the number of electrode fingers of each filter is 33 pairs The figure which shows the relationship between the end surface position of a horizontal coupling filter in a filter apparatus, and 3 dB bandwidth. A three-stage cascaded surface acoustic wave in which λ ₂ / λ ₁ is 0.992, 0.996, 1.0, 1.004, and 1.008, and the number of electrode fingers of each filter is 33 pairs The figure which shows the change of the end surface position of a horizontal coupling filter in a filter apparatus, and an attenuation amount (Attenuation amount (dB) in 54 MHz-55.25 MHz)). The figure which shows the range of the end surface position from which a desired characteristic is acquired when (lambda) ₂ / (lambda) ₁ is changed. The surface acoustic wave filter device of the embodiment shown in FIG. 1, a surface acoustic wave filter device in which three longitudinally coupled filters prepared for comparison are cascade-connected, and a surface acoustic wave filter device in which three laterally coupled filters are cascaded. The figure which shows each filter waveform. The top view which shows an example of the conventional surface acoustic wave filter apparatus. The figure which shows an example of the filter waveform of the conventional surface acoustic wave filter apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave filter apparatus 2 ... Piezoelectric substrate 3 ... Longitudinal coupling filter 4 ... Lateral coupling filter 5 ... Longitudinal coupling filter 6, 7 ... IDT
6a, 6b, 7a, 7b ... comb-teeth electrodes 8a, 8b ... input terminals 9, 10 ... IDT
11, 12 ... IDT
11a, 11b, 12a, 12b ... comb electrodes 13, 14 ... output terminals

Claims (9)

At least one longitudinally coupled end face reflection type resonator multimode filter and at least one laterally coupled end face reflection type resonator multimode filter are cascade-connected, and the longitudinally coupled end face reflection type resonator multimode filter is connected And the laterally coupled end face reflection type resonator type multimode filter are arranged on the same piezoelectric substrate in a direction orthogonal to the surface wave propagation direction,
Each of the longitudinally coupled end face reflection type resonator multimode filter and the laterally coupled end face reflection type resonator multimode filter has at least one IDT, and the end face position is the second electrode finger from the end of the IDT. Is the distance between the center and the end face of
The end face position in the longitudinally coupled end face reflection type resonator type multimode filter is other than 0.5λ ₁ (where λ ₁ is the electrode finger pitch in the IDT of the longitudinally coupled end face reflection type resonator type multimode filter). The end face position of the laterally coupled end face reflection type resonator type multimode filter is other than 0.5λ ₂ (where λ ₂ is the electrode finger pitch of the IDT of the laterally coupled end face reflection type resonator type multimode filter). And
One end face of each of the longitudinally coupled end face reflection type resonator multimode filter and the laterally coupled end face reflection type resonator multimode filter adjacent in the direction orthogonal to the surface wave propagation direction cuts the piezoelectric substrate at a time. A surface acoustic wave filter device, characterized in that the surface acoustic wave filter device is made of   2. The surface acoustic wave filter device according to claim 1, wherein center frequencies of the longitudinally coupled end surface reflection type resonator type multimode filter and a laterally coupled end surface reflection type resonator type multimode filter are the same.   The intersection between the end face position dependency curve of the center frequency of the longitudinally coupled end face reflection type resonator type multimode filter and the end face position dependency curve of the center frequency of the laterally coupled end face reflection type resonator type multimode filter is the above-mentioned 3. The surface acoustic wave filter device according to claim 1, wherein each of the end surface positions of the longitudinally coupled end surface reflection type resonator type multimode filter and the laterally coupled end surface reflection type resonator type multimode filter is set. The electrode finger pitch lambda ₁ of the longitudinal coupling end face reflection type resonator type multimode filter, the lateral coupling end face reflection type resonator-type multimode electrode finger pitch lambda ₂ are equal filters, any one of claims 1 to 3 2. A surface acoustic wave filter device according to item 1. Wherein the longitudinal coupling end face reflection type resonator electrode finger pitch lambda ₁ of the multi-mode filter, the electrode finger pitch lambda ₂ of the horizontal coupling edge reflection type resonator type multimode filter is different, of claims 1 to 3 The surface acoustic wave filter device according to claim 1. The end face position of the longitudinally coupled end face reflection type resonator multi-mode filter is 0.51λ ₁ or more and 0.60λ ₁ or less, and the end face position of the laterally coupled end face reflection type resonator multi mode filter is 0.58λ ₂ or more. The surface acoustic wave filter device according to claim 1, wherein the surface acoustic wave filter device is 0.85λ ₂ or less.   In the configuration in which the longitudinally coupled end face reflection type resonator multimode filter and the laterally coupled end face reflection type resonator multimode filter are cascade-connected, input / output terminals of the longitudinally coupled end face reflection type resonator multimode filter are connected. The surface acoustic wave filter device according to any one of claims 1 to 6, wherein one is a balanced signal terminal. The end face position a of the longitudinally coupled end face reflection type resonator type multimode filter is x−0.1 ≦ a ≦ x + 0.1, and the end face position b of the laterally coupled end face reflection type resonator type multimode filter is y−. The elastic surface according to claim 1, wherein 0.1 ≦ b ≦ y + 0.1, and x and y are configured to satisfy the following expressions (1) and (2): Wave filter device.
D ₂ (y−0.5) + V ₂ / λ ₂ = D ₁ (x−0.5) + V ₁ / λ ₁ (1)
2yλ ₂ + N ₂ λ ₂ = 2xλ ₁ + N ₁ λ ₁ + Gλ ₁ (2)
Where λ _{1 is} the electrode finger pitch (μm) of the longitudinally coupled end face reflection type resonator type multimode filter, V _{1 is} the substrate sound velocity (m / second) when designing the longitudinally coupled end face reflection type resonator type multimode filter, D ₁ : Center frequency change rate (MHz / λ) depending on end face position of longitudinally coupled end face reflection type resonator type multimode filter, N ₁ : Logarithm of longitudinally coupled end face reflection type resonator type multimode filter, G: Longitudinal coupling end face Center distance (λ ₁ ) between adjacent electrode fingers in the IDT-IDT gap, which is the coupling length of the reflective resonator type multimode filter, λ ₂ : electrode finger pitch of the laterally coupled end face reflection type multimode filter ( μm), V ₂ : sound velocity of substrate (m / sec) when designing a laterally coupled end face reflection type resonator type multimode filter, D ₂ : center frequency depending on the end face position of the laterally coupled end face reflection type resonator type multimode filter. Rate of change (MHz / ), N _2: lateral coupling end face reflection type resonator type multimode logarithmic filter The end face position a of the longitudinally coupled end face reflection type resonator multimode filter is x−0.05 ≦ a ≦ x + 0.05, and the end face position b of the laterally coupled end face reflection type resonator multimode filter is y−0. The surface acoustic wave filter device according to claim 8, wherein .05 ≦ b ≦ y + 0.05.

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