JPH10233647A - Surface acoustic wave filter and transducer used for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a waveform of a pass characteristic of the surface acoustic wave filter symmetrical, to reduce effectively out-band spurious radiation and to obtain a suitable characteristic in the case of designing the surface acoustic wave filter with a steep frequency characteristic. SOLUTION: Let a wavelength of a basic surface acoustic wave stimulated by input side transducer 2 be λ1 and let a wavelength of a basic surface acoustic wave stimulated by output side transducer 4 be λ2 , then the surface acoustic wave filter is configured in a relation of λ1 ≠λ2 so that a center frequency of the surface acoustic wave stimulated by input side transducer 2 is in matching with a center frequency of the surface acoustic wave stimulated by the output transducer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface acoustic wave filter device, and more particularly to a surface acoustic wave filter device suitable for a CDMA communication system. Further, the present invention relates to a converter suitable for the surface acoustic wave filter device.

[0002]

2. Description of the Related Art With the development of digital communication systems, various communication systems have been proposed. Such communication methods include, for example, an FDMA (frequency division multiple access) method and a TDMA (time division multiple access) method. FDMA
In the scheme, the frequency band is divided and these are assigned to the respective radio stations. In contrast, in the TDMA scheme, the time band is divided and these are assigned to the respective radio stations.

Further, a CDMA (code division multiple access) system has recently been proposed. This CDMA system has high utility because a large number of channels can be secured by using signals superimposed on frequency and time, and its development is strongly demanded. The surface acoustic wave filter device used in the CDMA system is required to have a specific filter characteristic, and the characteristic is summarized as follows. (1) Satisfies insertion loss of 10 dB or less. (2) A frequency characteristic with small phase distortion can be obtained. (3) T. of 30 dB or more. T. E. FIG. (triple Transit Ec
ho) Satisfy the attenuation level.

In order to satisfy these characteristics, the surface acoustic wave filter device disclosed in Japanese Patent Application Laid-Open No. Hei 8-213870 by the present inventor uses one of an input converter and an output converter in one direction. And a bi-directional converter. As described above, by appropriately combining the bidirectional converter having the apodized electrode structure and the unidirectional converter using the excitation effect and the reflection effect, the characteristics of the bidirectional converter can be utilized for the frequency characteristics. Insertion loss and T.I. T. E. FIG. As for the attenuation level, the characteristics of the one-way converter are utilized so that the insertion loss, T.T. T. E. FIG. A surface acoustic wave filter device that satisfies all attenuation levels and frequency characteristics can be realized.

[0005]

In such a surface acoustic wave filter device, the waveform of the pass characteristic of the surface acoustic wave filter device becomes asymmetric, and the out-of-band spurious cannot be effectively reduced. Not preferred for the device. Further, in such a surface acoustic wave filter device, it is not preferable to design a surface acoustic wave filter device having sharp frequency characteristics.

A first object of the present invention is to provide a surface acoustic wave in which one of an input-side converter and an output-side converter is constituted by a unidirectional converter and the other is constituted by a bidirectional converter. In a filter device, a surface acoustic wave filter suitable for designing a surface acoustic wave filter device having a symmetrical waveform of a surface acoustic wave pass characteristic, effectively reducing out-of-band spurs, and having a steep frequency characteristic. It is to provide a device.

A second object of the present invention is to provide a surface acoustic wave filter device in which first and second unidirectional transducers are respectively disposed on both sides of a surface acoustic wave propagation axis of a bidirectional transducer. Provided is a surface acoustic wave filter device which makes the waveform of the pass characteristic of a surface wave symmetrical, effectively reduces out-of-band spurious, and is suitable for designing a surface acoustic wave filter device having a sharp frequency characteristic. It is.

A third object of the present invention is to provide a bidirectional converter portion having a bidirectional electrode structure for exciting a surface acoustic wave in both directions of a surface acoustic wave propagation axis, and one of the propagation directions of the surface acoustic wave. With a unidirectional transducer part that has a unidirectional electrode structure that excites surface acoustic waves only in the direction of, and makes the waveform of the pass characteristics of surface acoustic waves symmetrical and effectively reduces out-of-band spurious. Another object of the present invention is to provide a converter suitable for designing a surface acoustic wave filter device having a steep frequency characteristic.

A fourth object of the present invention is to provide a bidirectional transducer portion having a bidirectional electrode structure for exciting a surface acoustic wave in both directions of the surface acoustic wave propagation axis and one of the surface acoustic wave propagation directions. A surface acoustic wave filter device comprising a transducer having a unidirectional transducer portion having a unidirectional electrode structure for exciting a surface acoustic wave in only one direction, and a surface acoustic wave filter device comprising a unidirectional transducer. The present invention is to provide a surface acoustic wave filter device which is suitable for designing a surface acoustic wave filter device having a symmetrical waveform, effectively reducing out-of-band spurious, and having steep frequency characteristics.

[0010]

According to a first aspect of the present invention, there is provided a surface acoustic wave filter device comprising: a piezoelectric substrate; an input-side converter formed on the piezoelectric substrate; A surface acoustic wave filter device comprising an output-side converter for converting the converted surface acoustic wave, wherein one of the input-side converter and the output-side converter is configured as a one-way converter, and Is composed of a bidirectional converter and λ ₁
Where λ ₁ is the propagation wavelength of the basic surface acoustic wave excited by the one-way converter and λ ₂ is the propagation wavelength of the basic surface acoustic wave excited by the bidirectional converter, λ ₁ ≠ λ
It is characterized in that it is configured to be ₂ .

The inventor of the present invention has studied the reason why the waveform of the pass characteristic of the surface acoustic wave transmission device becomes asymmetric and the out-of-band spurious cannot be effectively reduced. As a result, in the surface acoustic wave filter device, the unidirectional converter is used. It has been confirmed that the center frequency of these transducers is shifted because the propagation speed of the surface acoustic wave excited by the transducer is different from the propagation velocity of the surface acoustic wave excited by the bidirectional converter.

As conventionally known, if the propagation velocity, wavelength and center frequency of a basic surface acoustic wave are V, λ and f,

## EQU1 ## There is a relationship of V = fλ. Therefore, when the pitch of the electrode fingers of the unidirectional converter and the pitch of the electrode fingers of the bidirectional converter are both λ, that is, the wavelength of the surface acoustic wave excited by the unidirectional converter and the bidirectional conversion If the speed of the surface acoustic wave excited by the unidirectional converter is different from the speed of the surface acoustic wave excited by the bidirectional converter, if the wavelength of the surface acoustic wave excited by the transducer is the same, The center frequency of the surface acoustic wave excited by the one-way converter is shifted from the center frequency of the surface acoustic wave excited by the two-way converter.

The present inventor has studied the reason why the speed of the surface acoustic wave excited by the one-way converter in the above-mentioned surface acoustic wave filter device is different from the speed of the surface acoustic wave excited by the two-way converter. The propagation speed of the surface acoustic wave is different between the portion of the surface area of the piezoelectric substrate where the electrode fingers are provided and the portion of the surface area of the piezoelectric substrate where the electrode fingers are not provided. Has been confirmed to be different. That is, the velocity of the surface acoustic wave propagating in the portion of the surface area of the piezoelectric substrate on which the electrode finger is provided is increased by the elastic surface wave propagating in the portion of the surface area of the piezoelectric substrate on which the electrode finger is not provided. Slower than the speed of the waves. Therefore, as the ratio of the portion of the surface area of the piezoelectric substrate on which the electrode fingers are provided to the entire surface area of the piezoelectric substrate in the propagation direction of the surface acoustic wave increases, the surface acoustic wave propagating through the transducer increases. Speed slows down.

In the above-described surface acoustic wave filter device, the ratio of the portion where the electrode fingers are provided in the surface area of the piezoelectric substrate to the entire surface area of the piezoelectric substrate in the direction of propagation of the surface acoustic wave is one direction. The sex converter side and the bidirectional converter side are different. For example, when a floating electrode type converter is used as the one-way converter and an apodized type converter is used as the two-way converter, the electrode finger width of the one-way converter is usually λ / 12. And the width of the electrode fingers of the bidirectional converter is all set to λ / 8. Therefore, the sum of the electrode finger widths of the unidirectional converter per 1λ is λ
/ 3, the sum of the electrode finger widths of the bidirectional converter per 1λ is λ / 2, and the sum of the electrode finger widths on the bidirectional converter side is wider. The propagation speed of the surface acoustic wave excited by the converter is lower than the propagation speed of the surface acoustic wave excited by the one-way converter.

The present inventor has set out the following in order to solve the above problems.
That is, in order to make the center frequency of the surface acoustic wave excited by the one-way transducer coincide with the center frequency of the surface acoustic wave excited by the two-way transducer, The propagation wavelength λ ₁ of the surface wave is made different from the propagation wavelength λ ₂ of the basic surface acoustic wave excited by the bidirectional converter. More specifically, assuming that the propagation speed of the surface acoustic wave propagating in the one-way converter is v1 and the propagation speed of the surface acoustic wave propagating in the bidirectional converter is v2, the surface wave is excited by the one-way converter. In order to match the center frequency of the surface acoustic wave excited by the bidirectional converter to the center frequency of the surface acoustic wave excited by the bidirectional converter, Between the wavelength λ ₁ and the wavelength λ _{2 of the} surface acoustic wave excited by the bidirectional converter,

## EQU2 ## It is necessary to set λ ₁ and λ ₂ so as to have a relationship of λ ₁ = v1λ ₂ / v2.

As described above, in a surface acoustic wave filter device in which one of the input-side converter and the output-side converter is constituted by a one-way converter and the other is constituted by a bidirectional converter, Since the center frequency of the surface acoustic wave excited by the one-way transducer and the center frequency of the surface acoustic wave excited by the two-way transducer can be matched, the conventional surface acoustic wave can be maintained while maintaining the conventional advantages. It is also suitable for designing a surface acoustic wave filter device having a symmetrical waveform of the pass characteristic of the wave filter device, effectively reducing out-of-band spurious, and having a sharp frequency characteristic.

According to a second aspect of the present invention, there is provided a surface acoustic wave filter device according to the first aspect of the present invention, wherein the one-way converter uses λ ₁ as a propagation wavelength of a basic surface acoustic wave excited by the one-way converter. , are periodically formed in lambda ₁ pitch periodically formed in the positive electrode width direction of propagation of the surface acoustic wave has a plurality of electrode fingers of approximately lambda _1/12, likewise lambda ₁ pitch, the width of the propagation direction of the surface acoustic wave has electrode fingers of approximately λ _1/12, a negative electrode the electrode fingers are respectively positioned with a center-to-center distance between the positive electrode and the electrode fingers lambda _1/2, the positive is disposed between the electrode fingers and negative electrode electrode fingers of the electrode, the width direction of propagation of the surface acoustic wave has electrode fingers of approximately lambda _1/12,
Short the electrode fingers, which is located in lambda _1/12 deflection in the opposite direction from the intermediate position to the propagation direction or this surface acoustic wave between the electrode fingers of the electrode fingers of the adjacent positive electrodes negative electrodes comprising a mold floating electrode, the bidirectional converter, in the case of a fundamental surface acoustic wave propagation wavelength of being excited lambda ₂ by the bidirectional converter, arranged with center-to-center distance of lambda _2/4 and a positive electrode width direction of propagation of the surface acoustic wave is periodically formed two electrode fingers set a lambda _2/8 at lambda ₂ pitches, as well lambda
Located with a center-to-center distance of _2/4, is formed of two electrode fingers set the width of the propagation direction of the surface acoustic wave is lambda _2/8 periodically at a pitch of lambda, the set of the electrode fingers it is characterized in that it comprises a negative electrode respectively positioned with a pair and lambda _2/2 of the distance between the centers of adjacent electrode fingers of the positive electrode.

As a floating electrode type unidirectional converter, a positive electrode
Propagation of surface acoustic waves on each electrode plate of pole, negative electrode and floating electrode
The width in the direction₁Λ set to / 8₁/ 8 type unidirectional change
And the width of the surface acoustic wave in the propagation direction of the₁/
Λ set to 12 ₁/ 12 type unidirectional converter
You. λ₁In the case of a / 8 type unidirectional converter, the floating electrode
The range in which the electrode finger can be displaced is too narrow,
The arrangement pitch of each of the positive, negative and floating electrodes
The width of the electrode finger (ie, λ₁/ 8) or an integer multiple of this
Cannot be set. As a result, the bidirectional converter and
When combined, the reflection effect of the floating electrode is effectively used.
And therefore insertion loss and G.I. D. T. Face
Cannot be expected to improve the characteristics.

[0019] In contrast, the positive electrode, negative electrode and the case of unidirectional transducer of lambda _1/12-inch and the width is set to lambda _1/12 of each electrode finger of the floating electrode, all of the electrodes of each electrode Finger λ ₁
/ 12 or an integer multiple thereof, and the reflection effect of the floating electrode can be effectively utilized. As a result, when combined with a bidirectional converter, insertion loss, G.I. D. T. Frequency characteristics and T.V. T.
E. FIG. Can be realized.

Next, a bidirectional converter will be considered.
As bidirectional converter, there is a transducer the width of each electrode finger of the positive electrode and the negative electrode was set to λ _2/4. This converter is
It is extremely useful to consider the excitation efficiency. However, since the pitch between each end of the electrode fingers is lambda _2/4, in phase reflected waves from each other generated at each edge of the electrode fingers, as a result, there arises a large ripple than 1 dB. Therefore, when combined with a one-way converter, the frequency characteristics cannot be satisfied.

Further, from each case the width of the electrode fingers of the bidirectional converter as defined in lambda _2/8, the excitation efficiency because the area of the electrode fingers is smaller than lambda _2/4 type lambda _2/4-inch Also decrease. In addition, since the phases of the reflected waves generated at the edges of the electrode fingers are shifted from each other, ripples occur in the frequency characteristics. Therefore, when combined with a unidirectional converter, satisfactory characteristics regarding insertion loss and frequency characteristics cannot be obtained.

[0022] In contrast, both of the two electrode fingers as a pair, the positive electrode and the negative electrode of the electrode fingers is constituted by two electrode finger pairs lambda _2/8-split width of lambda _2/8 for tropism transducer, the area of the electrode fingers is the same as lambda _2/4-inch, high excitation efficiency. In addition, since the reflected waves generated at the electrode finger edges are only reflected waves whose phases are inverted from each other, an extremely good frequency characteristic without ripple can be obtained.

[0023] Thus, by combining the bi-directional converter with the lambda _2/8-split electrode structure as lambda _1/12 type unidirectional transducer, insertion loss, frequency characteristic and T. T. E. FIG. The inherent disadvantages of each converter with respect to the attenuation level are complemented by each other, and as a result, a surface acoustic wave filter device having excellent characteristics can be realized.

According to a third aspect of the present invention, there is provided the surface acoustic wave filter device according to the present invention, wherein the one-way converter uses λ ₁ as a propagation wavelength of a basic surface acoustic wave excited by the one-way converter. and a width in the propagation direction of the surface acoustic wave lambda _1/8
And 3 [lambda] _1/8 electrode fingers pairs of electrode fingers positioned with a center-to-center distance of the 3 [lambda] _1/8 of a first electrode and periodically formed in lambda ₁ pitch, the width in the propagation direction of the surface acoustic wave comprises but a plurality of electrode fingers of lambda _1/8, and periodically formed in lambda ₁ pitch so as to be positioned with a pair and the distance of lambda _1/2 wherein each of the electrode fingers adjacent to the second electrode the bidirectional converter, in the case of a fundamental surface acoustic wave propagation wavelength of being excited lambda ₂ by the bidirectional converter, and arranged with center-to-center distance of lambda _2/4, the surface acoustic wave the width of the propagation direction periodically is formed two electrode fingers set a lambda _2/8 at a pitch of lambda, the set is the positive electrode of the adjacent electrode fingers pairs and lambda / 2 of the electrode fingers And a negative electrode located at a distance from the center.

[0025] Thus, with the configuration in which the width in the propagation direction of the electrode fingers and the surface acoustic wave is a width in the propagation direction of the surface acoustic wave lambda _1/8 is combined with the electrode fingers is 3 [lambda] _1/8 However, the surface acoustic wave incident on the one-way transducer is reflected due to the mismatch of acoustic impedance at the edge of each electrode finger, and the phase of the resultant vector is exactly opposite to the phase of the electrically reflected wave. Therefore, the combined reflected wave can be made zero, and the reflected wave can be eliminated without sacrificing insertion loss.

A surface acoustic wave filter device according to a fourth aspect of the present invention is characterized in that the one-way converter has a regular electrode structure and the two-way converter has a weighted electrode structure. Things.

In this case, the unidirectional converter has a regular electrode structure in which the dimensions of the electrode fingers in the direction orthogonal to the direction of propagation of the surface acoustic wave are set to be the same, and the electrode structure is not weighted. , On the other hand, bidirectional converters have a weighted electrode structure. To set the out-of-band attenuation characteristic large, it is necessary to weight the converter.
Here, if the electrode structure of the one-way converter is weighted, the frequency characteristics deteriorate. In particular, if the short-circuit type floating electrode type one-way converter has a weighted electrode structure, the connection portion connecting the electrode fingers of the short-circuit type floating electrode is located in the excitation region, and undesired reflection at this portion is caused. Since a wave is generated or a propagation velocity difference occurs in the excited surface acoustic wave, a strong ripple is generated. Based on such recognition, the one-way converter has a normal electrode structure, and the bidirectional converter is weighted. With such a configuration, characteristics without ripples can be obtained.

According to a fifth aspect of the present invention, in the surface acoustic wave filter device according to the fifth aspect, the weighting electrode structure of the bidirectional converter is configured such that a length of each electrode finger in a direction orthogonal to a propagation direction of the surface acoustic wave is a surface acoustic wave. It is characterized by being constituted by an apotize method which changes sequentially along the wave propagation direction.

As a weighting method, a thinning method of thinning out electrode fingers at a desired pitch and a Baribic method are known.
However, in these methods, a phase shift occurs in the reflected wave at the electrode finger, which causes a ripple. On the other hand, in the apotize method, the length of the electrode finger in the direction orthogonal to the direction of propagation of the surface acoustic wave is sequentially changed, so that the occurrence of ripple due to phase shift is prevented and frequency characteristics without ripple are obtained. Can be.

A surface acoustic wave filter device according to a sixth aspect of the present invention is characterized in that the piezoelectric substrate is a quartz substrate, a lithium tantalate substrate or a lithium borate substrate.

As the piezoelectric substrate of the surface acoustic wave filter device, a lithium niobate substrate, a quartz substrate, a lithium tantalate substrate, a lithium borate substrate or the like is usually used. Among these substrates, the lithium niobate substrate has a relatively large electromechanical coupling coefficient (K ² ), and thus has an advantage that good conversion characteristics can be obtained. However, there is a drawback in that there is a problem in temperature characteristics, that is, there is a drawback that a change in a bandwidth with respect to a temperature change is large, and the filter has been used only as a filter for a wide band. For this reason,
As a conventional narrow band filter, only a resonance type filter device has been used. However, it has been strongly pointed out that the resonant filter has a large GDT due to its structure. On the other hand, the surface acoustic wave filter device having the floating electrode type or the dirt type converter effectively utilizes the asymmetric structure of the electrodes, so that the insertion loss and the GDT can be significantly reduced. Therefore, if the asymmetric internal reflection type electrode structure is applied to a piezoelectric substrate having excellent temperature characteristics, a surface acoustic wave filter device which is excellent in GDT and insertion loss and has a very small change in a normal band with respect to a temperature change is realized. Therefore, even when configured as a narrow band filter, a surface acoustic wave filter device having extremely good filter characteristics can be realized.

In view of such circumstances, according to the surface acoustic wave filter device of the present invention, the temperature characteristic with respect to frequency is extremely small, the electromechanical coupling coefficient is at least one digit smaller than that of the lithium niobate substrate, and A piezoelectric substrate having a reflection coefficient by an electrode finger having a positive reflection coefficient with respect to a short-circuit type floating electrode is used. In the present invention, as such a piezoelectric substrate, a quartz substrate having an electromechanical coupling coefficient of 0.14%,
A lithium tantalate substrate having an electromechanical coupling coefficient of 0.64% or a lithium borate substrate having an electromechanical coupling coefficient of 1.0% is used. Since the frequency variation of these substrates with respect to a temperature change is very small, if any of these substrates is used as the piezoelectric substrate, the change of the pass frequency band with respect to the temperature characteristic can be maintained in a small range. However, since quartz, lithium tantalate, and lithium borate have small electromechanical coupling coefficients, if an existing converter is formed as it is, it cannot be realized from the viewpoint of insertion loss.

As a result of a detailed study of the insertion loss of the quartz substrate, the lithium tantalate substrate and the lithium borate substrate, it was found that the sign of the reflection coefficient of the floating electrode had a large effect on the insertion loss. . In the case of a quartz substrate, a lithium tantalate substrate, and a lithium borate substrate, the short-circuit type floating electrode has a larger reflection coefficient than the open type floating electrode. Therefore, it is preferable to use a short-circuit type floating electrode as the floating electrode. With this configuration, even when a quartz substrate having a small electromechanical coupling coefficient is used, the insertion loss can be suppressed to an extremely small range,
As a result, a wideband surface acoustic wave filter device having excellent temperature characteristics and low loss can be realized. Also,
Even when a converter having a dirt-type electrode structure is used as the one-way converter, a broadband surface acoustic wave filter device having similarly excellent temperature characteristics and low loss can be realized.

Since a quartz substrate has a very small frequency change with respect to a temperature change, if a quartz substrate is used as the piezoelectric substrate, the change in the pass frequency band due to the temperature change can be maintained in a very small range. However, quartz has a small electromechanical coupling and cannot be put to practical use from the viewpoint of insertion loss if an existing converter is formed as it is. As a result of a detailed study of the insertion loss of the quartz substrate by the present inventor, it was found that the sign of the reflection coefficient of the floating electrode strongly affected the insertion loss. In the case of a quartz substrate, the short-circuit type floating electrode has a larger reflection coefficient than the open type floating electrode. Therefore, it is preferable to use a short-circuit type floating electrode as the floating electrode. With such a configuration, even when a quartz substrate having a small electromechanical coupling coefficient is used, the insertion loss can be suppressed to an extremely small range. As a result, a broadband surface acoustic wave filter device having excellent temperature characteristics and low loss is obtained. Can be realized. In addition, even when a converter having a dart-type electrode structure is used as the one-way converter,
Similarly, a wideband surface acoustic wave filter device having excellent temperature characteristics and low loss can be realized.

The lithium tantalate substrate has almost the same electromechanical coupling coefficient and reflection characteristics as the quartz substrate, and can be used in the same manner as the quartz substrate. Further, the insertion loss of the lithium borate substrate can be further improved, and it can be used in the same manner as the quartz substrate.

According to the present invention, there is provided a surface acoustic wave filter device comprising: a piezoelectric substrate; a bidirectional converter formed on the piezoelectric substrate; and a surface acoustic wave of the bidirectional converter. A first and a second respectively disposed on both sides of the propagation axis
Wherein the bidirectional converter is an input converter, the first and second unidirectional converters are output converters, and the bidirectional converter is Is the output-side converter, the first and second one-way converters are the input-side converters, and λ ₃ is the propagation wavelength of the basic surface acoustic wave excited by the one-way converter. When λ ₄ is the propagation wavelength of the basic surface acoustic wave excited by the bidirectional converter, λ ₃ ≠ λ ₄ .

In the surface acoustic wave filter device having the first and second unidirectional converters disposed on both sides of the propagation axis of the surface acoustic wave of the bidirectional converter, the first and second unidirectional converters are also provided for the above reason. Since the center frequency of the surface acoustic wave excited by the one-way transducer and the center frequency of the surface acoustic wave excited by the two-way transducer can be matched, the conventional surface acoustic wave can be maintained while maintaining the conventional advantages. It is also suitable for designing a surface acoustic wave filter device having a symmetrical waveform of the pass characteristic of the wave filter device, effectively reducing out-of-band spurious, and having a sharp frequency characteristic.

According to the surface acoustic wave filter device of the present invention, the first and second one-way converters preferably include:
in case of a fundamental surface acoustic wave propagation wavelength of excited to lambda ₃ by the unidirectional transducer is periodically formed in lambda ₃ pitch, the width of the propagation direction of the surface acoustic wave is approximately lambda _3/12 Similarly, a positive electrode having a plurality of electrode fingers is formed periodically at a pitch of λ, and has a width of approximately λ ₃ /
Has 12 electrode fingers of, between the negative electrode respectively positioned with a distance between centers of the electrode fingers and lambda _3/2 of the electrode fingers is the positive electrode, the electrode fingers of the positive electrode the electrode finger and the negative electrode disposed, the width of the propagation direction of the surface acoustic wave has a substantially lambda _3/12 electrode fingers of each electrode finger, from the intermediate position between the electrode fingers of the electrode fingers of the adjacent positive electrodes negative electrodes comprising a short-circuit type floating electrodes positioned to lambda _3/12 deflection in a direction opposite to the propagation direction or this surface acoustic wave, the bidirectional converter, lambda
When the propagation wavelength of the fundamental surface acoustic wave excited by the bidirectional converter _4, lambda _4/4 of arranged with a center distance, the width of the propagation direction of surface acoustic waves in the lambda _4/8 a positive electrode which is periodically formed in a certain two pairs of lambda ₄ pitches of the electrode fingers, similarly positioned with a distance between the centers of the lambda _4/4, the width of the propagation direction of the surface acoustic wave is lambda _4/8 periodically formed two electrode fingers pairs is at lambda ₄ pitches, respectively located with a pair and the distance between the centers of the lambda _4/2 of electrode fingers each set of electrode fingers adjacent said positive electrode And a negative electrode.

[0039] In this case, the above reasons, lambda _4/8 bidirectional transducer having a split type electrode structure lambda ₃ /
When combined with a 12-type unidirectional converter, insertion loss,
Frequency characteristics and T.V. T. E. FIG. The inherent disadvantages of each transducer with respect to the attenuation level are complemented by each other,
A surface acoustic wave filter device having excellent characteristics can be realized.

According to a ninth aspect of the present invention, in the surface acoustic wave filter device, the first and second one-way converters include:
If the lambda ₃ to the fundamental surface acoustic wave propagation wavelength of excited by the unidirectional transducer, a width lambda _1/8 in the propagation direction of a surface acoustic wave and 3 [lambda] _3/8 of the electrode fingers 3 [lambda] ₃ / 8 pairs of electrode fingers positioned with a center-to-center distance of the first electrode formed periodically at lambda ₃ pitch, the width in the propagation direction of the surface acoustic wave a plurality of electrode fingers of lambda _3/8, was set and periodically formed in lambda ₃ pitches so as to be positioned with a distance of lambda _3/2 wherein each of the electrode fingers adjacent, comprising a second electrode, the bidirectional converter, lambda ₄ a wherein when the propagation wavelength of the fundamental surface acoustic wave excited by bidirectional converter, and arranged with center-to-center distance of lambda _4/4, the width of the propagation direction of the surface acoustic wave is λ _4/8 2 Λ ₄
A positive electrode which is periodically formed at a pitch of, likewise lambda _4/4
Of located with a center-to-center distance, it is periodically formed two electrode fingers set the width of the propagation direction of the surface acoustic wave is lambda _4/8 in lambda ₄ pitches, each set of electrode fingers the positive it is characterized in that it comprises a negative electrode respectively positioned with a distance between centers set and lambda _4/2 adjacent electrode fingers of the electrode.

[0041] Thus, with the configuration in which the width in the propagation direction of the electrode fingers and the surface acoustic wave is a width in the propagation direction of a surface acoustic wave lambda _3/8 is combined with the electrode fingers is 3 [lambda] _3/8 For the above reasons, the reflected wave can be eliminated without sacrificing the insertion loss.

According to a tenth aspect of the present invention, in the surface acoustic wave filter device, the one-way converter has a normal electrode structure, and the two-way converter has a weighted electrode structure. Things.

For the above reason, the unidirectional converter has a normal-type electrode structure and the bidirectional converter is weighted, whereby characteristics without ripple can be obtained.

According to a eleventh aspect of the present invention, in the surface acoustic wave filter device according to the eleventh aspect of the present invention, the weighting electrode structure of the bidirectional converter is such that the length of each electrode finger in the direction orthogonal to the propagation direction of the surface acoustic wave is a surface acoustic wave. It is characterized by being constituted by an apotize method which changes sequentially along the wave propagation direction.

For the above-mentioned reasons, by using the apotizing method as the weighting method, it is possible to prevent the occurrence of ripple due to the phase shift and to obtain a ripple-free frequency characteristic.

A twelfth surface acoustic wave filter device according to the present invention is characterized in that the piezoelectric substrate is a quartz substrate, a lithium tantalate substrate or a lithium borate substrate.

For the above reason, by using a quartz substrate, a lithium tantalate substrate or a lithium borate substrate as the piezoelectric substrate, a surface acoustic wave filter device having excellent temperature characteristics and low loss can be realized.

The converter according to claim 13 according to the present invention comprises:
A transducer for a surface acoustic wave filter device, comprising a piezoelectric substrate and a bidirectional electrode structure formed on the piezoelectric substrate and configured to excite a surface acoustic wave in both directions of a surface acoustic wave propagation axis. A directional transducer portion, and a unidirectional transducer portion having a unidirectional electrode structure for exciting the surface acoustic wave in only one of the propagation directions of the surface acoustic wave. a directional transducer portion, with the propagation axis of the transducer section are coupled integrally to match each other, the fundamental surface acoustic wave propagation wavelength of excited the lambda ₅ in the unidirectional transducer When λ ₆ is the propagation wavelength of the basic surface acoustic wave excited by the bidirectional converter,
It is characterized in that is configured as a λ ₅ ≠ λ _6.

A bidirectional transducer portion having a bidirectional electrode structure for exciting the surface acoustic wave in both directions of the surface acoustic wave propagation axis, and exciting the surface acoustic wave only in one of the propagation directions of the surface acoustic wave. Also in a converter comprising a unidirectional converter part having a unidirectional electrode structure, for the above reasons,
When the center frequency of the surface acoustic wave excited by the one-way transducer part and the center frequency of the surface acoustic wave excited by the bidirectional transducer part can be matched, when used in combination with other transducers In addition, while maintaining the traditional advantages,
It is also suitable for designing a surface acoustic wave filter device that makes the waveform of the pass characteristic of the surface acoustic wave filter device symmetric, effectively reduces out-of-band spurious, and has a sharp frequency characteristic.

The converter according to claim 14 according to the present invention comprises:
The unidirectional converter portion, when λ ₅ is the propagation wavelength of the basic surface acoustic wave excited by the unidirectional converter,
periodically formed in lambda ₅ pitch periodically formed in the positive electrode width direction of propagation of the surface acoustic wave has a plurality of electrode fingers of approximately lambda _5/12, likewise lambda ₅ pitch, elastic the width of the propagation direction of the surface wave has a substantially lambda _5/12 electrode fingers of the negative electrode each electrode fingers respectively positioned with a center-to-center distance between the positive electrode and the electrode finger lambda _5/2, the positive electrode of being disposed between the electrode fingers of the electrode finger and the negative electrode, the width direction of propagation of the surface acoustic wave has electrode fingers of approximately lambda _5/12, each electrode finger,
A short-circuited floating electrodes positioned to lambda _5/12 deflection in a direction opposite to the propagation direction or this surface acoustic wave from the intermediate position between the electrode fingers of the adjacent positive electrodes of the electrode finger and the negative electrode comprising the bidirectional converter portion, when the fundamental surface acoustic wave propagation wavelength of excited the lambda ₆ in the bidirectional transducer portion, and arranged with center-to-center distance of lambda _6/4, the elastic a positive electrode width direction of propagation of the surface wave is periodically formed two electrode fingers set a lambda _6/8 at a pitch of lambda _6, similarly lambda ₆
/ 4 located with a center-to-center distance, is formed of two electrode fingers set the width of the propagation direction of the surface acoustic wave is lambda _6/8 periodically at a pitch of lambda _6, pairs of the electrode fingers it is characterized in that it comprises a negative electrode respectively positioned with a distance between centers of pairs and lambda _6/2 adjacent electrode fingers of the positive electrode.

[0051] Also in this case, the above reasons, the bidirectional transducer portion having a lambda _6/8 split type electrode structure lambda
_When combined with the 5/12 type unidirectional converter, the insertion loss, frequency characteristics and T.V. T. E. FIG. The inherent disadvantages of each converter part with respect to the attenuation level are complemented by one another, so that a converter with excellent properties can be realized.

According to a fifteenth aspect of the present invention, there is provided a converter comprising:
The unidirectional converter portion and the bidirectional converter portion are weighted such that the length of each electrode finger in the direction orthogonal to the surface acoustic wave propagation direction changes sequentially along the surface acoustic wave propagation direction. It is characterized by the following.

For the above reason, by applying weight to the one-way converter part and the two-way converter part, it is possible to obtain a ripple-free characteristic.

The converter according to claim 16 according to the present invention comprises:
The length in the direction orthogonal to the propagation direction of the surface acoustic wave of the electrode finger of the one-way converter portion is the maximum length in the direction orthogonal to the direction of propagation of the surface acoustic wave of the electrode finger in the bidirectional converter portion. It is characterized by being longer.

For the above reasons, by using the apotizing method as the weighting method, it is possible to prevent the occurrence of ripple due to the phase shift and to obtain a ripple-free frequency characteristic.

The converter according to claim 17 according to the present invention comprises:
The piezoelectric substrate is a quartz substrate, a lithium tantalate substrate or a lithium borate substrate.

For the above-mentioned reasons, when a quartz substrate, a lithium tantalate substrate or a lithium borate substrate is used as the piezoelectric substrate, when used in combination with another converter, it has excellent temperature characteristics and a low-loss surface acoustic wave. A filter device can be realized.

The surface acoustic wave filter device according to claim 18 of the present invention provides a piezoelectric substrate, an input transducer formed on the piezoelectric substrate, and a surface acoustic wave excited by the input transducer. An output-side converter for converting, the one of the input-side converter or the output-side converter, the unidirectionality to excite the surface acoustic wave only in one direction of the propagation axis of the surface acoustic wave A bidirectional transducer part having a bidirectional electrode structure for exciting the surface acoustic wave in both directions of the surface acoustic wave propagation axis, and one of the propagation directions of the surface acoustic wave. A unidirectional transducer portion having a unidirectional electrode structure that excites a surface acoustic wave only in the direction of, and the two-way transducer portion and the one-way transducer portion are connected to the propagation axis of these transducer portions. Are joined together to match each other Composed of exchangers are excited lambda ₈ with a fundamental surface acoustic wave propagation wavelength of excited the lambda ₇ in the unidirectional transducer and unidirectional transducer portion by the bidirectional transducer portion When the propagation wavelength of the basic surface acoustic wave is set, λ ₇ ≠ λ ₈ .

A bidirectional transducer portion having a bidirectional electrode structure for exciting the surface acoustic wave in both directions of the surface acoustic wave propagation axis and a surface acoustic wave for exciting the surface acoustic wave only in one of the propagation directions of the surface acoustic wave. In a surface acoustic wave filter device comprising a transducer having a unidirectional transducer portion having a directional electrode structure, and a unidirectional transducer, the unidirectional transducer portion side and the unidirectional Since the center frequency of the surface acoustic wave excited on the bidirectional converter side and the frequency of the surface acoustic wave excited on the converter side can be matched, the conventional surface acoustic wave filter can be maintained. It is also suitable for designing a surface acoustic wave filter device that makes the waveform of the pass characteristic of the device symmetric, effectively reduces out-of-band spurious, and has a sharp frequency characteristic.

A surface acoustic wave according to claim 19 according to the present invention.
The filter device includes the one-way converter and the one-way converter.
The converter part is λ₇The one-way converter and the one
Propagation wavelength of fundamental surface acoustic wave excited by directional transducer
And λ ₇It is formed periodically at a pitch of
The width in the propagation direction of the surface wave is approximately λ₇With / 12 electrode fingers
Positive electrode, and λ₇Periodically formed at a pitch of
The width in the propagation direction of the surface acoustic wave is approximately λ₇/ 12 electrode fingers
Each electrode finger is the same as the electrode finger of the positive electrode.₇Center of / 2
A negative electrode positioned at a distance between the
A surface acoustic wave is placed between the electrode finger and the negative electrode finger.
Is approximately λ in the propagation direction₇/ 12 electrode fingers, each electrode
The pole finger is positioned between the adjacent positive and negative electrode fingers.
Direction of propagation of surface acoustic waves from the intermediate position between
Λ in pairwise direction₇/ 12 short-circuited floating electrode
Wherein the bidirectional converter portion has λ₈The both
Propagation wavelength of fundamental surface acoustic wave excited by directional transducer
And λ₈弾 with a center distance of / 4
The width of the surface acoustic wave in the propagation direction is λ₈/ 8 two electrode fingers
Set of λ₈Same as the positive electrode periodically formed at the pitch of
To λ₈Of the surface acoustic wave
The width in the seeding direction is λ₈/ 8 is a pair of two electrode fingers₈of
Are formed periodically at a pitch, and each pair of electrode fingers is
Pair of adjacent electrode fingers and λ₈/ 2 distance between centers
Characterized by having a negative electrode located at each position
It is.

[0061] In this case, the above reasons, the bidirectional converter having a lambda _8/8 split type electrode structure lambda ₇ /
When combined with a 12-type unidirectional converter, insertion loss,
Frequency characteristics and T.V. T. E. FIG. The inherent disadvantages of each transducer with respect to the attenuation level are complemented by each other,
A surface acoustic wave filter device having excellent characteristics can be realized.

According to a twentieth aspect of the present invention, in the surface acoustic wave filter device according to the twelfth aspect, the one-way converter portion and the two-way converter portion have a length in a direction orthogonal to a propagation direction of the surface acoustic wave of each electrode finger. Are weighted so as to sequentially change along the propagation direction of the surface acoustic wave.

For the above reasons, by applying weight to the one-way converter part and the two-way converter part, it is possible to obtain a ripple-free characteristic.

According to a twenty-first aspect of the present invention, in the surface acoustic wave filter device according to the twenty-first aspect, a length of the one-way converter portion in a direction orthogonal to a propagation direction of the surface acoustic wave of the electrode finger is set to the two-way converter. It is characterized in that it is longer than the maximum length in the direction orthogonal to the direction of propagation of the surface acoustic waves of the electrode fingers of the part.

For the above-mentioned reason, by using the apotizing method as the weighting method, it is possible to prevent the occurrence of ripple due to the phase shift and to obtain a frequency characteristic without ripple.

A surface acoustic wave filter device according to a twenty-second aspect of the present invention is characterized in that the piezoelectric substrate is a quartz substrate, a lithium tantalate substrate or a lithium borate substrate.

For the above reasons, by using a quartz substrate, a lithium tantalate substrate or a lithium borate substrate as the piezoelectric substrate, a surface acoustic wave filter device having excellent temperature characteristics and low loss can be realized.

[0068]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a surface acoustic wave filter device according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagrammatic plan view of a first embodiment of a surface acoustic wave filter device according to the present invention. In the present embodiment,
A rectangular quartz substrate 1 is used as the piezoelectric substrate. Since the crystal substrate has a small change in the bandwidth with respect to the temperature change, the change in the pass frequency band due to the temperature change can be maintained in a minute range. On the surface of the quartz substrate 1, the input-side converter 2, the shield electrode 3, and the output-side converter 4 are formed along the propagation axis of the surface acoustic wave.

The input-side converter 2 is a one-way converter, and the one-way converter is a short-circuit type in which the positive electrode 5 and the negative electrode 6 are arranged between the electrode fingers of the positive electrode 5 and the negative electrode 6. It is composed of the floating electrode 7. In this embodiment, these positive electrode 5, a width of the electrode fingers in the propagation direction of the surface acoustic wave in the negative electrode 6 and the short-circuit type floating electrode 7 is set to λ _1/12. Here, λ ₁ is the wavelength of the basic surface acoustic wave excited by the input-side converter 2.

The electrode fingers of the positive electrode 5 and the negative electrode 6 are formed at a pitch of λ ₁ , respectively, and the center distance between the electrode finger of the positive electrode 5 and the adjacent electrode finger of the negative electrode 6 is λ ₁ / Set to 2. Moreover, short-circuited floating electrodes 7 of the electrode fingers, the positive electrode from the intermediate between the electrode fingers and the electrode fingers of the negative electrode 6 of the 5, lambda _1/12 on the upstream side in the propagation direction of a surface acoustic wave adjacent thereto The one-way characteristic based on the asymmetric structure of the electrode is enhanced.

The number of pairs of the positive electrode 5 and the negative electrode 6 of the input side converter 2 is set to, for example, 40 pairs. This logarithm can be appropriately set to an optimum condition according to the required filter characteristics.

In the present embodiment, in the input-side converter 2, the short-circuit type floating electrode 7 is arranged at an intermediate position between the electrode finger of the positive electrode 5 and the electrode finger of the negative electrode 6 adjacent thereto. By significantly deviating to further enhance the one-way propagation based on the asymmetric structure, the insertion loss of the surface acoustic wave filter device is reduced.

The output converter 4 is connected to the positive electrode 8 and the negative electrode 9.
It was constituted by a two-way converter periodically plural sets formed split electrode structure a pair of lambda ₂ of the pitch of the two electrode fingers arranged with a center distance of λ _2/4, the electrode fingers of the positive electrode 8 set so as to be positioned respectively with a center distance set of electrode fingers of the negative electrode 9 pairs and lambda _2/2 of the. Where λ
_2, the wavelength of the fundamental surface acoustic wave excited by the output side transducer 4.

In this embodiment, the positive electrode 8 and the negative electrode 8
The width of the electrode finger of the electrode 9 is λ _Two/ 8. in this way
By configuring, the distance between the electrode fingers adjacent to each other is
All λ_Two/ 8. Electrode pair of output side converter 4
The number is set, for example, to 300 pairs.

The output-side converter 4 is weighted by the apodizing method, and the width of the intersection between the electrode finger of the positive electrode 8 and the electrode finger of the negative electrode 9, that is, the opening length is determined by the propagation of the surface acoustic wave. It changes along the direction.

When a unidirectional converter is used as the input converter 2 and a bidirectional converter is used as the output converter 3, when the signals to be filtered are input to the terminals 10 and 11, The surface acoustic wave excited by the converter 2 propagates in almost one direction, that is, in the direction of the output converter 4, is converted into an electric signal by the output converter 4 through the shield electrode 3, and is filtered from the terminals 12 and 13. The output signal is output. The frequency characteristics of the signals obtained from the terminals 12 and 13 are characteristics obtained by multiplying the characteristics of the unidirectional converter and the characteristics of the bidirectional converter. Therefore, by combining the unidirectional converter and the bidirectional converter in the transversal type surface acoustic wave filter device, the good characteristics of the bidirectional converter are utilized for the frequency characteristics, and the insertion loss and the T . T. E. FIG. As for the level, it is possible to realize a surface acoustic wave filter device utilizing the unique characteristics of the one-way converter. As a result, frequency characteristics, insertion loss and T.V. T. A surface acoustic wave filter device that satisfies all the requirements of the E level can be realized.

The operation of this embodiment will be described. In the present embodiment, assuming that the propagation speed of the surface acoustic wave excited by the input-side converter 2 and the propagation speed of the surface acoustic wave excited by the output-side converter 4 are v1 and v2, respectively.

The propagation wavelengths λ ₁ and λ ₂ are set so that the relationship of λ ₁ = v1λ ₂ / v2 (1) is established. As described above, assuming that the center frequency of the surface acoustic wave excited by the input-side converter 2 is f1,

## EQU4 ## The relationship of v1 = f1λ ₁ (2) is established. Similarly, if the center frequency of the surface acoustic wave excited by the output-side converter 4 is f2,

The relationship of v2 = f2λ ₂ (3) holds.

From equation (2), the center frequency f1 is

F1 = v1 / λ ₁ (4) Similarly, from equation (3), the center frequency f2 is

F2 = v2 / λ ₂ (5) Substituting equation (1) into equation (4) gives

F1 = v2 / λ ₂ (6), which coincides with the center frequency f2. In this way, the propagation wavelength λ ₁ of the surface acoustic wave excited by the input-side converter 2 is changed so that the relation of the expression (1) is established. Since the center frequency f1 of the surface acoustic wave excited by the input-side converter 2 and the center frequency f2 of the surface acoustic wave excited by the output-side converter can be matched by making the wavelength λ ₂ different. While maintaining the conventional advantages, it is also possible to design a surface acoustic wave filter device having a symmetrical pass characteristic waveform of the surface acoustic wave filter device, effectively reducing out-of-band spurious, and having a sharp frequency characteristic. It becomes suitable.

FIG. 2 is a diagrammatic plan view of a surface acoustic wave filter device according to a second embodiment of the present invention. In the present embodiment, the input-side converter 2
2, the shield electrode 23, and the output-side converter 24 are sequentially formed along the propagation axis of the surface acoustic wave.

The input converter 22 is a one-way converter,
The unidirectional transducer, when the propagation wavelength of the fundamental surface acoustic wave which is excited with lambda ₁ in the input-side transducer 22, the width in the surface acoustic wave propagation direction of the electrode fingers 25a of lambda _1/8 lambda
Were arranged with the distance between the centers of _1, the positive electrode 25 as a second electrode, a width in the surface acoustic wave propagation direction lambda _1/8
And 3 [lambda] _1/8 of the electrode fingers 26a and 26b 3λ _1/8
Of the set of electrode fingers arranged with a center-to-center distance it was periodically formed in lambda ₁ pitch, is composed of a negative electrode 26 as a first electrode. The center distance between the electrode finger 25a of the positive electrode 25 and the electrode finger 26a of the adjacent negative electrode 26 is 3λ.
It is set to _1/4. The output converter 24 has the same structure as the output converter 4 of FIG. 1 including the positive electrode 28 and the negative electrode 29.

By combining the electrode finger 26a with the electrode finger 26b whose width in the direction of propagation of the surface acoustic wave is three times that of the electrode finger 26a, when the input-side converter 26 is used as a one-way converter, When signals are input to 30 and 31, the excited surface acoustic waves are reflected due to the mismatch of the acoustic impedance of each electrode finger, but the phase of the resultant vector is exactly opposite to the phase of the electrically reflected wave. Therefore, the combined reflected wave can be made zero, and the reflected wave can be eliminated without technically controlling the insertion loss of the surface acoustic wave filter device.

The operation of this embodiment will be described. Also in the present embodiment, the propagation wavelength λ _{1 of the} surface acoustic wave excited by the input-side converter 22 is satisfied so that the relationship of Expression (1) holds.
Is different from the propagation wavelength λ _{2 of the} surface acoustic wave excited by the output-side converter 24, so that the center frequency f1 of the surface acoustic wave excited by the input-side converter 22 and the output side converter are excited. Since the center frequency f2 of the surface acoustic wave can be made to match, the waveform of the pass characteristic of the surface acoustic wave filter device is symmetrical while maintaining the conventional advantages, and the out-of-band spurious is effectively reduced, and It is also suitable for designing a surface acoustic wave filter device having a steep frequency characteristic.

FIG. 3 is a diagrammatic plan view of a surface acoustic wave filter device according to a third embodiment of the present invention. In the present embodiment, the input-side converter 42
And the first output-side converter 43 and the second
Are arranged on the output side. As the input-side converter 42, a bidirectional converter having a positive electrode 45 and a negative electrode 46 and having the same structure as the bidirectional converter shown in FIGS. 1 and 2 is used. In this embodiment, the propagation wavelength of the surface acoustic wave excited by the first output-side converter 43 and the second output-side converter 44 is set to λ _3, and the input-side converter 42
Let λ _{4 be} the propagation wavelength of the surface acoustic wave excited by.

As the output converters 43 and 44,
A one-way converter as shown in FIG. 1 having a positive electrode 47 and a negative electrode 48 and a positive electrode 49 and a negative electrode 50 is used. Floating electrode of the first output-side transducer 43, being displaced by lambda _3/12 to the left with respect to the propagation direction, that FIG surface acoustic wave of the surface acoustic wave filter device, the second output-side transducer 44 floating electrodes is offset by lambda _3/12 to the right with respect to FIG.

The input converter 42 and the output converter 43
And 44 are, for example, 300 pairs, 40 pairs, and 40 pairs, respectively.

The surface acoustic wave excited by the input-side converter 42 propagates to the first output-side converter 43 and the second output-side converter 44 with the same amount of energy, and the first output-side The electric signal is converted by the converter 43 and the second output converter 44. With such a configuration, all surface acoustic waves excited by the bidirectional converter 42 on the input side can be effectively used, and as a result, insertion loss can be further reduced.

The operation of this embodiment will be described. Also in the present embodiment, the propagation velocity of the surface acoustic wave excited by the first output-side converter 43 and the second output-side converter 44 is represented by v
3, and assuming that the propagation speed of the surface acoustic wave excited by the input-side converter 42 is v4, as in the first and second embodiments,

The propagation wavelength λ ₄ of the surface acoustic wave excited by the input-side converter 42 is determined by the first output-side converter 4 so that the following relationship holds: λ ₃ = v3λ ₄ / v4 (6)
By making the propagation wavelength λ _{3 of the} surface acoustic wave excited by the third and second output-side converters 44 different, the center frequency of the surface acoustic wave excited by the input-side converter 42 and the first output-side conversion Since the center frequency of the surface acoustic wave excited by the filter 43 and the second output-side converter 44 can be matched, the waveform of the pass characteristic of the surface acoustic wave filter device is symmetrical while maintaining the conventional advantages. It is also suitable for designing a surface acoustic wave filter device that effectively reduces out-of-band spurious and has a sharp frequency characteristic.

FIG. 4 is a diagrammatic plan view of a surface acoustic wave filter device according to a fourth embodiment of the present invention. In this embodiment, the input-side converter 52
And the first output-side converter 53 and the second
Are arranged on the output side. As the input-side converter 52, a bidirectional converter having a positive electrode 55 and a negative electrode 56 and having the same structure as the bidirectional converter shown in FIGS. 1 and 2 is used. Also in this embodiment, the propagation wavelength of the surface acoustic wave excited by the first output converter 53 and the second output converter 54 is set to λ _3, and the input converter 52
Let λ _{4 be} the propagation wavelength of the surface acoustic wave excited by.

Further, as the output side converters 53 and 54,
A one-way converter having a positive electrode 57 and a negative electrode 58 and a positive electrode 59 and a negative electrode 60 as shown in FIG. 2 is used. The width of the positive electrode 57 of the first output-side converter 53 in the propagation direction of the surface acoustic wave of the surface acoustic wave filter device, that is, to the left in the drawing, is λ ₃ /
8 and 3 [lambda] _3/8 pairs of electrode fingers of constructed by arranged with center-to-center distance of 3 [lambda] _3/8, the positive electrode 59 of the second output-side transducer 54, the surface acoustic wave of the surface acoustic wave filter device on the right side with respect to the propagation direction, that figure, configured by a set of electrode fingers of the width in the propagation direction of a surface acoustic wave is lambda _3/8 and 3 [lambda] _3/8 was arranged with center-to-center distance of 3 [lambda] _3/8.

Also in this case, similarly to the third embodiment, the input converter 52 and the output converters 53 and 54 are provided.
Are, for example, 300 pairs, 40 pairs, and 40 pairs, respectively.

In this case, as in the third embodiment, all surface acoustic waves excited by the bidirectional converter 52 on the input side can be effectively used, and as a result, insertion loss can be reduced. It can be further reduced.

The operation of this embodiment will be described. Also in the present embodiment, the propagation wavelength λ _{4 of the} surface acoustic wave excited by the input-side converter 52 is satisfied so that the relationship of Expression (6) holds.
With the first output converter 53 and the second output converter 5
By different propagation wavelength lambda ₃ of the surface acoustic waves excited by 4, the input-side transducer 52 and the center frequency of the surface acoustic waves excited first output transducer 53 and the second output converter Since the center frequency of the surface acoustic wave excited by the filter 54 can be matched, the pass characteristic of the surface acoustic wave filter device can be made symmetrical and the out-of-band spurious can be effectively reduced while maintaining the conventional advantages. Reduce and
It is also suitable for designing a surface acoustic wave filter device having a steep frequency characteristic.

FIG. 5 is a schematic plan view of an embodiment of a surface acoustic wave converter according to the present invention. This surface acoustic wave converter includes a quartz substrate 61 and interdigital first and second bidirectional converter portions 62a formed on the quartz substrate 61 such that the propagation axes of the surface acoustic waves coincide with each other. And 62b and a one-way transducer section 63. These first and second bidirectional converter portions 62a and 62b
Is basically the same as the electrode structure of the bidirectional converter shown in FIGS. 1 and 2, and the unidirectional converter portion 63 is basically the same as the electrode structure of the unidirectional converter shown in FIG. It is. In this embodiment, the propagation wavelength of the surface acoustic waves excited by the unidirectional transducer portion 63 with a lambda _5, is excited by the first and second bidirectional converter section 62a and 62b Let the propagation wavelength of the surface acoustic wave be λ ₆ .

[0094] The first bidirectional transducer portion 62a is a two electrode fingers pairs arranged distance between the centers in the lambda _6/4 lambda
_A plurality of positive electrodes 64a periodically formed at a pitch of ₆ ;
Similarly the two electrode fingers pairs arranged with a center distance of lambda _6/4 periodically formed at a pitch of lambda _6, each set of electrode fingers of the positive electrode of the electrode fingers pairs and lambda _6/2 And negative electrodes 65a located at a distance from the center. The width in the propagation direction of the surface acoustic wave of the electrode fingers and lambda _6/8. The electrode finger of the electrode finger 64a and the negative electrode 65a facing the electrode finger
Are weighted along the propagation direction of the surface acoustic wave.

The second bidirectional electrode portion 62b has a wavelength λ ₆ /
A pair of two electrode fingers arranged at a center distance of 4 is λ ₆
And a plurality of pairs of positive electrodes 64b periodically formed at a pitch of λ ₆ and two pairs of electrode fingers similarly arranged at a center distance of λ 6/4 at a pitch of λ _6. comprising a negative electrode 65b of the set of fingers are positioned respectively with a distance between centers of the electrode fingers pairs and lambda _6/2 positive electrode 64b. The width in the propagation direction of the surface acoustic wave of the electrode fingers and lambda _6/8, a cross width of the electrode fingers of the positive electrode 64b and the electrode finger of the negative electrode 65b facing the electrode fingers, the propagation direction of the surface acoustic wave Is weighted along.

The one-way converter section 63 includes a positive electrode 64c.
And the negative electrode 65c, and the positive electrode 64c and the negative electrode 6
5c and a short-circuit type floating electrode 66 disposed between the electrode fingers. The one-way converter portion 63 is positioned so as to be adjacent to the portion of the electrode finger of the first bidirectional converter portion 62a and the electrode finger of the second bidirectional converter portion 62b having the maximum crossing width. It is arranged between one bidirectional converter part 62a and the second bidirectional converter part 62b. Further, the opening length of the one-way converter portion 63 is made larger than the maximum opening length of the first bidirectional converter portion 62a and the second bidirectional converter portion 62b.

The operation of the present embodiment will be described. Also in the present embodiment, the propagation speed of the surface acoustic wave excited by the one-way converter portion 63 is set to v5, and the surface acoustic wave excited by the first and second bidirectional converter portions 62a and 62b. Assuming that the propagation speed of v is v6, as in the first to fourth embodiments,

## EQU10 ## The propagation wavelength λ ₅ of the surface acoustic wave excited by the one-way converter section 63 is set so that the relationship of λ ₅ = v5λ ₆ / v6 (7) is satisfied. By making the propagation wavelength λ _{6 of the} surface acoustic wave excited by the directional converter portions 62 a and 62 b different from the center frequency of the surface acoustic wave excited by the unidirectional converter portion 63, Bidirectional converter portions 62a and 62b
The center frequency of the surface acoustic wave excited by the above can be matched, so that the waveform of the pass characteristic of the surface acoustic wave filter device is symmetrical and the out-of-band spurious is effectively reduced while maintaining the conventional advantages. It is also suitable for designing a surface acoustic wave filter device having steep frequency characteristics.

FIG. 6 is a diagrammatic plan view of a fifth embodiment of the surface acoustic wave filter device according to the present invention. In the present embodiment, one of the converters of the surface acoustic wave filter device is a converter shown in FIG. In the present embodiment, the one-way converter shown in FIG. 1 is formed on the substrate 71 as the output-side converter 72, and the bidirectional converter shown in FIG. 5 is used as the input-side converter 73. In this embodiment, the propagation wavelength of the surface acoustic waves excited by the unidirectional transducer portion of the input-side transducer 72 and the output-side transducer 73 with a lambda _7, both of the output side transducer 73 The propagation wavelength of the surface acoustic wave excited by the directional converter is λ ₈ . The input converter 73 has a positive electrode 74 and a negative electrode 75, and the output converter 72 has a positive electrode 76 and a negative electrode 77.

The converter shown in FIG. 5 can be used as an input-side converter and an output-side converter in accordance with the direction of deviation of the electrode finger of the short-circuit type floating electrode. That is, when the electrode fingers of the short-circuited floating electrodes in the propagation direction of the surface acoustic wave is lambda _7/12 deflection is used as output transducers. When used as an input-side transducer contrast causes the direction lambda _7/12 deflection opposite to the propagation direction of the surface acoustic wave.

The operation of the present embodiment will be described. Also in the present embodiment, the propagation wavelength λ ₇ of the surface acoustic wave excited by the one-way converter portion of the output-side converter 72 and the input-side converter 73 is set so that the relationship of Expression (7) holds. By making the propagation wavelength λ _{8 of the} surface acoustic wave excited in the bidirectional converter portion of the input converter 73 different from that of the output converter 7,
2 and the center frequency of the surface acoustic wave excited by the one-way transducer portion of the input-side converter 73 matches the center frequency of the surface acoustic wave excited by the bidirectional converter portion of the output-side converter 73 Therefore, while maintaining the advantages of the related art, the waveform of the pass characteristic of the surface acoustic wave filter device is symmetrical, and the out-of-band spurious is effectively reduced, and
It is also suitable for designing a surface acoustic wave filter device having a steep frequency characteristic.

The present invention is not limited to the above embodiment, and many modifications and variations are possible. For example, in the first to fifth embodiments of the surface acoustic wave filter device and the embodiment of the converter, a quartz substrate is used as the piezoelectric substrate. Lithium tantalate substrates and lithium borate substrates having a coupling coefficient and reflection characteristics can also be used.

In the first to fourth embodiments, a one-way converter is used as an input-side converter and a bidirectional converter is used as an output-side converter. It is also possible to use a one-way converter as an output converter by using a sex converter.

In the second and fourth embodiments, the negative electrode is used as the first electrode and the positive electrode is used as the second electrode. However, the positive electrode is used as the first electrode.
A negative electrode can be used as the second electrode. First
In the third and fifth embodiments, the positive electrode can be used as the negative electrode while the negative electrode can be used as the positive electrode.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a first embodiment of a surface acoustic wave filter device according to the present invention.

FIG. 2 is a schematic plan view of a surface acoustic wave filter device according to a second embodiment of the present invention.

FIG. 3 is a schematic plan view of a surface acoustic wave filter device according to a third embodiment of the present invention.

FIG. 4 is a schematic plan view of a surface acoustic wave filter device according to a fourth embodiment of the present invention.

FIG. 5 is a schematic plan view of an embodiment of a surface acoustic wave converter according to the present invention.

FIG. 6 is a diagrammatic plan view of a fifth embodiment of the surface acoustic wave filter device according to the present invention.

[Description of Signs] 1,21,41,51,61,71 Quartz substrate 2,2
2, 42, 52, 73 input side converter 3, 23 shield electrode 4, 24, 43, 44, 53, 54, 72 output side converter 5, 8, 25, 28, 45, 47, 49,
55, 57, 59, 64a, 64b, 64c, 74, 7
6 Positive electrode 6, 9, 26, 29, 46, 48, 50,
56, 58, 60, 65a, 65b, 65c, 75, 7
7 Negative electrode 7,66 Short-circuit type floating electrode 10,11,
12, 13, 30, 31, 32, 33 terminals 25a,
26a, 26b Electrode finger 62a, 62b Bidirectional converter part 63 Unidirectional converter part

Claims (22)

[Claims] 1. A surface acoustic wave comprising a piezoelectric substrate, an input transducer formed on the piezoelectric substrate, and an output transducer for converting a surface acoustic wave excited by the input transducer. In the filter device, one of the input-side converter and the output-side converter is configured by a one-way converter, the other is configured by a bidirectional converter, and λ ₁ is the one-way converter. When λ ₂ is the propagation wavelength of the basic surface acoustic wave excited by the bidirectional converter and λ ₂ is the propagation wavelength of the basic surface acoustic wave excited by the above, λ ₁ ≠ λ ₂ A surface acoustic wave filter device. 2. The method according to claim ₁ , wherein the one-way converter is formed periodically at a pitch of λ ₁ when λ ₁ is a propagation wavelength of a basic surface acoustic wave excited by the one-way converter. a positive electrode width direction of propagation of the surface wave has a plurality of electrode fingers of approximately lambda _1/12, likewise periodically formed in lambda ₁ pitch,
The width of the propagation direction of the surface acoustic wave has electrode fingers of approximately λ _1/12, a negative electrode the electrode fingers are respectively positioned with a center-to-center distance between the positive electrode and the electrode fingers lambda _1/2, the positive is disposed between the electrode fingers and negative electrode electrode fingers of the electrode, the width direction of propagation of the surface acoustic wave has electrode fingers of approximately lambda _1/12, the electrode fingers of the adjacent positive electrode electrode finger and comprising a short-circuit type floating electrodes positioned to lambda _1/12 deflection in a direction opposite to the electrode fingers of the negative electrode from the intermediate position to the propagation direction or this surface acoustic wave between said bidirectional converter vessel is, lambda when the propagation wavelength of the fundamental surface acoustic wave excited by ₂ the bidirectional converter, and arranged with center-to-center distance of lambda _2/4, the width of the propagation direction of the surface acoustic wave is lambda _2/8 is two of the electrode finger pairs λ
A positive electrode periodically formed at a pitch of ₂ and a λ ₂ /
Located with a center distance of 4, it is periodically formed at a pitch of two electrode fingers set the width of the propagation direction of the surface acoustic wave is lambda _2/8 lambda, each pair of electrode fingers the positive the surface acoustic wave filter device according to claim 1, wherein that it comprises the negative electrode respectively positioned with a pair and the distance between the centers of lambda _2/2 of the adjacent electrode fingers of the electrode. 3. The method according to claim ₁ , wherein the one-way converter has a width in the propagation direction of the surface acoustic wave of λ ₁ / λ ₁ where λ ₁ is a propagation wavelength of a basic surface acoustic wave excited by the one-way converter. 8 and a first electrode the electrode fingers of the 3 [lambda] _1/8 is a set of electrode fingers located with a center-to-center distance of 3 [lambda] _1/8, and periodically formed in lambda ₁ pitch, in the propagation direction of the surface acoustic wave Width is λ
_1/8 of a plurality of electrode fingers, and periodically formed in lambda ₁ pitch so as to be positioned with a pair and the distance of lambda _1/2 wherein each of the electrode fingers adjacent a second electrode comprises the bidirectional converter, in the case of a fundamental surface acoustic wave propagation wavelength of being excited lambda ₂ by the bidirectional converter, and arranged with center-to-center distance of lambda _2/4, the propagation direction of the surface acoustic wave Is λ
Two electrode fingers set a _2/8 are periodically formed at a pitch of lambda, respectively located with a distance between centers of pairs and lambda / 2 of the electrode fingers each set of electrode fingers adjacent said positive electrode 2. The surface acoustic wave filter device according to claim 1, further comprising a negative electrode. 4. The device according to claim 1, wherein the one-way converter has a normal electrode structure, and the two-way converter has a weighted electrode structure. Surface acoustic wave filter device. 5. The weighted electrode structure of the bidirectional converter is constituted by an apotizing method in which the length of each electrode finger in a direction orthogonal to the direction of propagation of the surface acoustic wave sequentially changes along the direction of propagation of the surface acoustic wave. 5. The method according to claim 4, wherein
The surface acoustic wave filter device as described in the above. 6. The surface acoustic wave filter device according to claim 1, wherein the piezoelectric substrate is a quartz substrate, a lithium tantalate substrate, or a lithium borate substrate. 7. A piezoelectric substrate, a bidirectional transducer formed on the piezoelectric substrate, and first and second bidirectional transducers disposed on both sides of a surface acoustic wave propagation axis of the bidirectional transducer. Wherein the bidirectional converter is an input converter, the first and second unidirectional converters are output converters, and the bidirectional converter is Is the output-side converter, the first and second one-way converters are the input-side converters, and λ ₃ is the propagation wavelength of the basic surface acoustic wave excited by the one-way converter. with lambda ₄ if was a fundamental surface acoustic wave propagation wavelength of excited by the bidirectional converter, λ ₃ ≠ λ ₄ and the surface acoustic wave filter device being characterized in that configured to be. 8. The method according to claim 8, wherein said first and second one-way converters are λ
When the propagation wavelength of the fundamental surface acoustic wave excited by ₃ wherein unidirectional transducer periodically formed in lambda ₃ pitches, in the propagation direction of the surface acoustic wave width is approximately lambda _3/12 a positive electrode having a plurality of electrode fingers, formed periodically at a pitch of similarly lambda, the width of the propagation direction of the surface acoustic wave is approximately lambda _3/1
And two electrode fingers, each electrode finger being the same as the electrode finger of the positive electrode.
A negative electrode disposed respectively with a distance between the _3/2 of the center,
Wherein disposed between the electrode fingers of the positive electrode of the electrode finger and the negative electrode, the width direction of propagation of the surface acoustic wave has a substantially lambda _3/12 electrode fingers of each electrode finger, the adjacent positive electrode comprising a short-circuit type floating electrodes positioned to lambda _3/12 deflection in the opposite direction to this propagation direction or of the surface acoustic wave from the intermediate position between the electrode fingers of the electrode finger and the negative electrode, the bidirectional Sex converter is λ ₄
When was the fundamental surface acoustic wave propagation wavelength of excited by the bidirectional converter, and arranged with center-to-center distance of lambda _4/4, the width of the propagation direction of the surface acoustic wave is lambda _4/8 a positive electrode of two electrode fingers pairs were periodically formed in lambda ₄ pitches similarly situated with a center distance of lambda _4/4, the width of the propagation direction of surface acoustic waves in the lambda _4/8 negative in two of the electrode fingers pairs are periodically formed in lambda ₄ pitches, respectively located with a pair and the distance between the centers of the lambda _4/2 of electrode fingers each set of electrode fingers adjacent said positive electrode The surface acoustic wave filter device according to claim 7, comprising an electrode. 9. The method according to claim 1, wherein the first and second one-way converters are λ
_{When 3} was the propagation wavelength of the fundamental surface acoustic wave excited by the unidirectional transducer, a width lambda _1/8 in the propagation direction of a surface acoustic wave and 3 [lambda] _3/8 of the electrode fingers 3 [lambda] _3/8 a set of center-electrode fingers positioned with a distance, a first electrode formed periodically at lambda ₃ pitch, the width in the propagation direction of the surface acoustic wave a plurality of electrode fingers of lambda _3/8, adjacent wherein formed in lambda ₃ pitches so as to be positioned with a set and a distance of lambda _3/2 respective electrode fingers periodically to, comprising a second electrode, said bidirectional converter, said lambda ₄ Assuming that the propagation wavelength of the basic surface acoustic wave excited by the bidirectional converter is λ _{4/4, the} distance between the centers is λ _{4/4, and} the width of the surface acoustic wave in the propagation direction is λ 4/8. Λ ₄
A positive electrode which is periodically formed at a pitch of, likewise lambda _4/4
Of located with a center-to-center distance, it is periodically formed two electrode fingers set the width of the propagation direction of the surface acoustic wave is lambda _4/8 in lambda ₄ pitches, each set of electrode fingers the positive the surface acoustic wave filter device according to claim 7, characterized in that comprises a negative electrode respectively positioned with a pair and the distance between the centers of the lambda _4/2 adjacent electrode fingers of the electrode. 10. The device according to claim 7, wherein the one-way converter has a normal electrode structure, and the two-way converter has a weighted electrode structure. Surface acoustic wave filter device. 11. The weighting electrode structure of the bidirectional converter is constituted by an apotizing method in which the length of each electrode finger in the direction orthogonal to the direction of propagation of surface acoustic waves changes sequentially along the direction of propagation of surface acoustic waves. 2. The method according to claim 1, wherein
0 surface acoustic wave filter device. 12. The surface acoustic wave filter device according to claim 8, wherein the piezoelectric substrate is a quartz substrate, a lithium tantalate substrate, or a lithium borate substrate. 13. A transducer for a surface acoustic wave filter device, comprising: a piezoelectric substrate; and a bidirectional filter formed on the piezoelectric substrate and exciting the surface acoustic wave in both directions of a propagation axis of the surface acoustic wave. A bidirectional transducer portion having an electrode structure, and a unidirectional transducer portion having a unidirectional electrode structure for exciting the surface acoustic wave only in one of the propagation directions of the surface acoustic wave. a transducer portion and a unidirectional transducer portion, these transducer section of the propagation bonded integrally to the axis coincide with each other, of the fundamental surface acoustic wave excited the lambda ₅ in the unidirectional transducer If the lambda ₆ with a propagated wave has a fundamental surface acoustic wave propagation wavelength of excited by the bidirectional converter, transducer, characterized by being configured such that λ ₅ ≠ λ _6. 14. The unidirectional transducer portion, when the fundamental surface acoustic wave propagation wavelength of excited the lambda ₅ in the unidirectional transducer portion periodically formed at a pitch of lambda ₅ ,
A positive electrode width direction of propagation of the surface acoustic wave has a substantially lambda _5/12 a plurality of electrode fingers of similarly formed cyclically at a pitch of lambda _{5, 5} substantially the width of the propagation direction of a surface acoustic wave lambda / 12
It has electrode fingers, the electrode fingers and lambda ₅ of the electrode fingers is the positive electrode
/ 2 arranged between a negative electrode located at a center-to-center distance and an electrode finger of the positive electrode and an electrode finger of the negative electrode,
The width of the propagation direction of the surface acoustic wave has electrode fingers of approximately lambda _5/12, the electrode fingers is, from an intermediate position between the electrode fingers of the electrode fingers of the adjacent positive electrodes negative electrodes of the surface acoustic wave comprising a short-circuit type floating electrodes positioned to lambda _5/12 deflection in a direction opposite to the propagation direction or this, the bidirectional converter portion, lambda ₆
The when said bidirectional converter part propagation wavelength of a fundamental surface acoustic wave excited, arranged with a center distance of lambda _6/4, the width of the propagation direction of a surface acoustic wave is lambda _6/8 Some 2
A positive electrode which is periodically formed a number of electrode fingers set at a pitch of lambda _6, similarly positioned with a distance between centers of lambda _6/4, the width of the propagation direction of the surface acoustic wave is lambda _6/8 two electrode fingers pairs are periodically formed at a pitch of lambda _6, the negative electrode respectively positioned with a distance between centers set and lambda _6/2 of electrode fingers each set of electrode fingers adjacent said positive electrode 14. The converter according to claim 13, comprising: 15. The one-way converter part and the two-way converter part, wherein the length of each electrode finger in the direction orthogonal to the surface acoustic wave propagation direction changes sequentially along the surface acoustic wave propagation direction. The converter according to claim 13, wherein weighting is performed to perform the conversion. 16. The length of a direction orthogonal to the propagation direction of the surface acoustic wave of the electrode finger of the one-way converter portion is orthogonal to the propagation direction of the surface acoustic wave of the electrode finger of the bidirectional converter portion. 16. The converter according to claim 15, wherein the length is longer than a maximum length in a direction in which the light beam travels. 17. The converter according to claim 13, wherein the piezoelectric substrate is a quartz substrate, a lithium tantalate substrate, or a lithium borate substrate. 18. An input device comprising: a piezoelectric substrate; an input converter formed on the piezoelectric substrate; and an output converter for converting a surface acoustic wave excited by the input converter. One of the converter or the output converter,
It consists of a unidirectional transducer that excites surface acoustic waves only in one direction of the surface acoustic wave propagation axis, and the other transducer is a bidirectional transducer that excites surface acoustic waves in both directions of the surface acoustic wave propagation axis. A bidirectional transducer portion having an electrode structure, and a unidirectional transducer portion having a unidirectional electrode structure for exciting the surface acoustic wave only in one of the propagation directions of the surface acoustic wave. The converter part and the one-way converter part are constituted by converters integrally connected such that the propagation axes of these converter parts coincide with each other, and λ _{7 is set} to the one-way converter and the one-way converter. If λ ₈ is the propagation wavelength of the basic surface acoustic wave excited by the bidirectional transducer section and λ ₈ is the propagation wavelength of the basic surface acoustic wave excited by the sexual transducer section, then λ ₇ ≠ λ ₈ Surface acoustic wave filter device characterized by having such a configuration. 19. The one-way converter and the one-way converter portion, wherein λ ₇ is the propagation wavelength of a fundamental surface acoustic wave excited by the one-way converter and the one-way converter portion. when, it is periodically formed at a pitch of lambda _7, periodically formed in the positive electrode width direction of propagation of surface acoustic waves having electrode fingers of approximately lambda _7/12, likewise lambda ₇ pitch , a negative electrode width of the propagation direction of the surface acoustic wave has a substantially lambda ₇ / twelve electrode fingers of each located each electrode fingers with a center-to-center distance between the positive electrode and the electrode finger lambda _7/2, wherein is disposed between the electrode fingers of the positive electrode of the electrode finger and the negative electrode, the width direction of propagation of the surface acoustic wave has electrode fingers of approximately lambda _7/12, the electrode fingers of the adjacent positive electrode electrode lambda _7/12 displaced in the opposite direction to this propagation direction or of the surface acoustic wave from the intermediate position between the electrode fingers of the finger and the negative electrode Comprising a short-circuit type floating electrodes positioned Te, if the bidirectional converter portion, and a fundamental surface acoustic wave propagation wavelength of excited the lambda ₈ in the bidirectional transducer portion, lambda _8/4 the place with a center-to-center distance, the positive electrode width direction of propagation of the surface acoustic wave is periodically formed two electrode fingers set a lambda _8/8 at a pitch of lambda _8, similarly lambda ₈ / located with a center distance of 4, are periodically formed two electrode fingers set the width of the propagation direction of the surface acoustic wave is lambda _8/8 at a pitch of lambda _8, set of said respective electrode fingers the surface acoustic wave filter device according to claim 18, wherein in that it comprises a negative electrode respectively positioned with a distance between centers of pairs and lambda _8/2 adjacent electrode fingers of the positive electrode. 20. The one-way converter and the two-way converter, wherein the length of each electrode finger in a direction orthogonal to the direction of propagation of the surface acoustic wave sequentially changes along the direction of propagation of the surface acoustic wave. 20. The surface acoustic wave filter device according to claim 18, wherein weighting is performed so as to perform the following. 21. A length of a direction orthogonal to a propagation direction of the surface acoustic wave of the electrode finger of the one-way converter portion is orthogonal to a propagation direction of the surface acoustic wave of the electrode finger of the bidirectional converter portion. 21. A length longer than the maximum length in the direction of movement.
The surface acoustic wave filter device as described in the above. 22. A surface acoustic wave filter device according to claim 18, wherein said piezoelectric substrate is a quartz substrate, a lithium tantalate substrate or a lithium borate substrate.