JP3248231B2 - Surface acoustic wave transducer and surface acoustic wave device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a surface acoustic wave (Surface
Acoustic Wave (abbreviated as SAW) relates to a transducer and a surface acoustic wave device, particularly a high-performance and small-sized SAW filter, resonator, or the like used for a wireless communication device or the like.

[0002]

2. Description of the Related Art Conventionally, in a SAW device, particularly in a filter or the like, for example, a proceeding of eye lens is used.
E-i-67, Vol. 129, tribute 1979 (Proc.
IEEE, vol. 67, p. 129, 1979).
It has been the mainstream to implement a filter characteristic by introducing a weighting method called apodization or a weighting method called thinning into input and output transducers formed on a substrate through which an AW can propagate.

[0003]

In a filter having the structure of the prior art, S which is excited in both directions from a transducer is used.
Since only one side of the AW is used, the loss in the pass band of the filter is large, and the loss in a typical intermediate frequency filter of a television reaches 15 to 20 dB.

In recent years, especially in mobile radios for mobile communication represented by automobile telephones and the like, radio terminals have been downsized from portable to more pocketable terminals. In the future, a fountain pen-shaped ultra-small terminal is expected to be realized, and the need for a small device is great. In addition, demands for devices to be used with such miniaturization of wireless terminals are extremely severe. Although the surface acoustic wave device is considered to be the device that most contributes to miniaturization, it has not been used in practice because of problems such as loss as described above.
In mobile communication, a conventional analog system is shifting to a digital system.
Since signals are transmitted by tiple access (time division multiplexing), the bandwidth per channel is increased by about one digit compared to the analog system.
In the intermediate frequency band (300 MHz or less), it is necessary to extract a signal for each channel with a filter. However, it is extremely difficult for a SAW filter to cope with a wide band of the intermediate frequency band filter.

[0005] For the above reasons, current radio terminal filters mainly use a filter having a combination of inductance and capacitance. However, this filter is bulky and requires many adjustments. Therefore, there is a problem about miniaturization and non-adjustment of the entire radio terminal.

An object of the present invention is to provide a surface acoustic wave transducer and a surface acoustic wave device capable of realizing a low-loss SAW filter or a wideband filter in order to solve this problem.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to reflect an SAW into a transducer using an electrode finger whose minimum electrode finger width has a minimum width of 1/16 of the wavelength λ _O of the SAW. This can be achieved by providing a part having the function of a reflector, and independently realizing the function of the excitation part of the transducer and the function of the reflector within one wavelength.

More specifically, in a substrate that propagates a surface acoustic wave and a surface acoustic wave transducer having electrodes formed on the substrate, the basic unit of the transducer is determined by the width of the excitation portion and the width of the excitation portion. The sum of the width of the part that has the function of a surface acoustic wave reflector and the width of the surface acoustic wave is one wavelength λ _O, and the basic unit is repeatedly arranged many times in the direction of surface acoustic wave propagation. The minimum electrode finger width can be achieved by forming an electrode finger having a minimum width of 1/16 of the wavelength of the surface acoustic wave at the portion having the function of the reflector. Here, the wavelength λ _O of the SAW is the wavelength of a surface acoustic wave that can propagate at the center frequency of the device.

[0009]

The operation of the present invention will be described with reference to FIG. Considering the center of the basic unit of the transducer, that is, the area indicated by L in the symmetrical figure, the following can be understood. λ _O
/ 8 excitation electrode finger, and λ _O / 8 space on both sides
There is an earth electrode finger of λ _O / 16 through the ground. In such a configuration, the lines of electric force run symmetrically in the section of L as shown in the figure, so that the SAW having the same amplitude and
Can be excited. Therefore, in designing a filter or the like, the transducer has a width L around each excitation electrode finger.
The SAW excitation region may be designed to exist periodically, and the conventional design method can be applied in exactly the same manner.

Next, considering the outside of the region L, the following can be understood. L left the lambda _O / 4 of authors - scan electrode, on the right lambda _O / 4 of space - scan is arranged. That is,
The SAW excited by L propagates out of L, but the propagation conditions are different between left and right. This different propagation region is an SA of width L.
One SAW reflector exists on both sides of the W excitation region and forms a periodic structure as a whole transducer.

The operation as a reflector will be described in detail with reference to FIG. One section of the periodic structure shown by using a broken line in FIG. Assuming a SAW incident from the right side,
Since the SAW is reflected at the edge of each electrode finger, reflected waves are generated from each edge. In LiNbO ₃ , LiTaO ₃ , quartz, and the like, which are often used as a SAW piezoelectric substrate, the phase relationship of the reflected waves is as shown in FIG. 2B. That is, the SA of the transducer
The reflection SAWs reflected from the W excitation area L cancel each other out when the sum of all of them is taken, and becomes zero as a whole. Therefore, it can be seen that the area L is not related to reflection. Further, it can be seen that the reflection SAW reflected at the end of the region L is equal in both amplitude and phase, and the sum is a reflected wave whose amplitude is doubled.

In a piezoelectric substrate or the like, the SAW excited in the SAW excitation region L and the above-mentioned reflected wave have almost the same phase, and therefore are added in a direction in which the amplitude increases.

On the other hand, assuming a SAW incident from the left side, a reflected wave similar to the above occurs at the edge of the electrode finger. The totally reflected waves from within the SAW excitation region L cancel each other out and become zero as a whole, similarly to the case where the waves are incident from the right side. When the amplitude and the phase are illustrated in the same manner as in FIG. 2B, it can be seen that the reflected wave corresponding to + in FIG. 2B has a reversed phase relationship with the case of FIG. 2B. That is, the phase of the SAW excited in the SAW excitation area L and the phase of the reflected wave are almost reversed, and the sum of the two is the excitation SA.
It acts in the direction of decreasing the amplitude of W. More specifically,
By using an electrode finger having a width 1/16 of the wavelength of the SAW for the transducer, the SAW can be excited or received at the center of the excitation electrode finger in the same manner as the conventional transducer for the excitation or reception of the SAW. You can receive. Further, by using an electrode finger having a width of 1/16 of the wavelength, the reflection electrode finger reflects the SAW independently of the excitation electrode finger, and has the same phase in the positive direction as the SAW excited by the excitation electrode finger. In the negative direction, the signals can be added in opposite phases. Therefore, the transducer has directionality, and low loss of a device such as a SAW filter can be achieved. Furthermore, a desired frequency characteristic can be realized by introducing weighting to these transducers or electrically connecting two or more sets.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to specific embodiments.

Embodiment 1 A SAW transducer according to Embodiment 1 of the present invention will be described with reference to FIG. SAW having an exciting electrode finger having a wavelength of λ _O and a width of l ₃ , which can be propagated at the center frequency of the device.
It is a transducer. FIG. 1A shows an electrode pattern formed on a substrate that propagates a surface acoustic wave. As shown in the figure, the left side of the width l ₂ of the excitation electrode fingers of width l ₃ space -
An earth electrode finger of width l ₁ through the space, and a space of width l _{4 on} the right side
A width l ₅ through the scan - scan electrode fingers and the width l ₆ space - as a basic unit a pattern arranged to scan, the basic unit is formed by repeating a number of times in the propagation direction of the surface acoustic wave . Here, l ₁ = 5λ _O / 16, l ₂ = λ _O / 8, l ₃ = λ _O / 8,
Let l ₄ = λ _O / 8, l ₅ = λ _O / 16, and l ₆ = λ _O / 4.

Since the transducer shown in FIG. 1A has a periodic structure, a phenomenon similar to the phenomenon described with reference to FIG. 2 in the section of the operation occurs in each section. Therefore, such a transducer excites a large SAW to the right when used for excitation, and has a directionality with good reception efficiency for a SAW incident from the right when used for reception. It becomes a transducer with.

According to the results of computer simulations and basic experiments, the directionality of this unidirectional transducer is 30.
A value on the order of dB is feasible. Therefore, as shown later, by using the unidirectional transducer having the structure shown in FIG. 1A, a low-loss and very high-performance SAW filter or the like, which cannot be realized conventionally, can be realized.

In the above description, LiNb is used as the piezoelectric substrate.
The case where O ₃ , LiTaO ₃ , quartz, or the like is used has been described. However, very specific examples are, for example, LiNbO ₃
However, in the case of 128 DEG Y-cut X propagation, when the thickness of the aluminum electrode forming the transducer is increased, the SAW reflection coefficient at the electrode edge is inverted in phase from the case where the aluminum electrode is thin. In this case, a unidirectional transducer can be realized in the same manner.
As shown in FIG. 1B, it is necessary to make the structure shown in FIG. It has been confirmed by simulation and basic experiments that the same unidirectionality can be obtained in the structure of FIG. 1B using LiNbO ₃ .

FIGS. 3A and 4A show a method of constructing a transducer which is relatively similar to the structure of the present invention. FIG.
The configuration of (a) is based on IEICE Transactions (C), Vo
l. J69-C, p. 1297, 1986, and the configuration of FIG.
Of 1990 III Ultrasonics Symposium 37 (Proc. Of
1990 Ultrasonics Symposi
um, p. 37). These transducers have a function as a unidirectional transducer as in the structure of the present invention. However, as a result of the inventor's detailed studies in simulations and basic experiments, the following points were found to be inferior to those of the present invention shown in FIG.

In the configuration of FIG. 3A, about 3λ _O / 3 is provided on the left side of the excitation electrode finger having a width of about λ _O / 8 via a space of about λ _O / 8.
8 A - scan electrode fingers, the right to about lambda _O / 8 space - through the scan of about lambda _O / 8 A - scan electrode fingers about lambda _O / 8 of space - basic unit pattern arranged to scan And a transducer that repeats many times in the propagation direction of the surface acoustic wave. FIG. 2 (b)
FIG. 3B shows the relationship between the amplitude and the phase of the SAW reflected from the electrode finger edge in the same manner as described in FIG. That is, the sum of the reflected waves of-cancels each other, but the phases of the remaining waves are not equal to each other. That is, their sum does not double in amplitude as in the present invention. Therefore, the transducer of FIG. 3 has a weak unidirectional function as compared with the present invention, and it has been found that it is difficult to realize a very low-loss filter or the like.

The structure shown in FIG. 4A has an earth electrode finger of about λ _O / 4 via a space of about 3λ _O / 16 on the left side of the excitation electrode finger having a width of about λ _O / 8. about lambda _O / 8 of space on the right - through the scan of about lambda _O / 8 a - scan electrode fingers and about 3 [lambda] _O / 16 of space - a pattern arranged to scan a basic unit, the propagation direction of a surface acoustic wave Is a transducer that repeats many times. Reflection SA from the electrode finger edge as in the description of FIG.
FIG. 4B shows the relationship between the amplitude and the phase of W. That is, the sum of the reflected waves of-cancels each other, and the remaining waves have the same amplitude and the same phase, and the sum of these becomes a reflected wave of twice the amplitude as in the case of the present invention. is there. However, in the configuration shown in FIG. 4A, the width of the space existing on both sides of the excitation electrode finger having a width of about λ _O / 8 is asymmetric. That is, the left side is 3λ _O / 1
6. The right side is λ _O / 8. Therefore, as shown in the figure, the lines of electric force running from the excitation electrode finger to the left and right earth electrode fingers are:
It becomes left-right asymmetric. It has been found that the SAW excited left and right by the asymmetrical lines of electric force have different amplitudes and phases. As a result of computer simulations and basic experiments, the combination of electrode fingers and reflective electrode fingers that asymmetrically excite the SAW in this way has the same phase in the positive direction as the excited SAW and the opposite phase in the negative direction. It turned out that the ideal addition which becomes a phase is not realized. The transducer having such a structure has a weak unidirectional function similarly to the structure shown in FIG. 3A, and it is difficult to realize a very low-loss filter or the like.

In contrast to the conventional structure described above, the structure of the present invention shown in FIG.
The area as a reflector that reflects the AW is completely independent, and a transducer having an ideal unidirectional function can be realized. One of the features of the present invention is to use a ground electrode finger having a width of about λ _O / 16. In general, when the electrode finger becomes thinner, a problem occurs in the process of forming the electrode finger, particularly as the frequency increases. However, the progress of the semiconductor process is remarkable at present, and the process of the SAW device is relatively simple. Therefore, forming a fine electrode finger by using a semiconductor device has almost no problem. Therefore, the structure of the present invention is superior to the conventional structure in terms of function as described above, and can be said to be substantially equivalent to the conventional structure with respect to the formation of the fine electrode fingers.

As described above, the feature of the present invention is that SA
That is, the region L for exciting W and the region as a reflector for reflecting SAW are completely independently separated. That is, in the region L in which the SAW is excited, the SAW is reflected at the edge of each electrode finger, but the sum of the totally reflected waves in the L cancels each other and becomes zero. Based on such an idea, it is considered that the structure of the present invention does not necessarily need to be the structure of FIG. In particular, it is sufficient that the region L basically has a configuration in which the totally reflected waves cancel each other. Embodiment 2 FIG. 5A shows an embodiment of another SAW transducer. In particular, when the electrode finger having a width of about λ _O / 16 is widened to form an electrode finger, disconnection or the like in a process is minimized. Of the spaces l ₂ , l ₄ and l ₆ , l ₆ is fixed at about λ _O / 4, and l ₂ and l ₄ are narrowed to increase the width of the other electrode fingers. That is, l ₁ is 5λ _O / 1
6 + Δ1, l ₂ is λ _O / 8−Δ1-Δ2, l ₃ is λ _O / 8 +
Δ2 + Δ3, l ₄ is λ _O / 8−Δ3-Δ4, l ₅ is λ _O / 1
6 + Δ4, l ₆ is about λ _O / 4, and Δ4 is appropriately selected from Δ1. Δ1 to Δ4 are 0 ≦ Δ1 to Δ4 ≦
Although the value is λ _O / 16, there is an infinite number of conditions under which the sum of the totally reflected waves in the excitation region L of the SAW becomes almost zero. As an example, FIG. 5 shows the amplitude and phase of the reflected wave from the edge of each electrode finger when Δ1 = Δ2 = Δ3 = Δ4 = λ _O / 32.
It is shown in (b). As in the case of FIG. 2B, the sum of the reflected waves is zero, and it can be seen that the configuration of FIG. 5A can realize a unidirectional function completely equivalent to that of FIG. It is obvious that the present invention also includes the configuration of FIG.

The first and second embodiments have been described with respect to the transducer having a very ideal unidirectional function. Next, means for realizing the frequency characteristics required by a filter or the like using the transducer of the present invention will be described. Generally, in a low-loss filter, a weighting method for changing the crossing width of the excitation electrode finger, which is called apotization, cannot be applied to realize the frequency characteristics. First, I
E-i Transaction Microwave Theory and Technique, Volume 33, Item 510, 198
5 years (IEEE Trans. Microwave
Theoryand Tech. , MTT-33,5
10, 1985. ) Has the same function as Apotize,
We proposed a weighting method that has no loss due to weighting in principle (hereinafter referred to as phase weighting method).

Although the frequency characteristics that can be realized are limited, thinning weighting is also known as weighting without weight loss. The following shows that both weighting methods can be applied to the transducer of the present invention without any problem.

Embodiment 3 FIG. 6 shows an example in which phase weighting is introduced into the transducer of FIG. FIG. 6 shows an example in which a reflector having a space of about λo / 4 and an earth electrode finger is further introduced into a portion where the excitation electrode finger does not exist. As described above, by introducing the reflection electrode finger into a portion where the excitation electrode finger does not exist, both the weighting effect and the unidirectional effect of the reflector can be expected. Embodiment 4 FIG. 7 shows an example in which thinning-out weighting is introduced into the transducer of FIG. In the same manner as in the third embodiment, a reflector having a space of about λo / 4 and a ground electrode finger is introduced into a thinned portion having no excitation electrode finger to thereby reduce the weighting effect of the thin film. Both unidirectional effects can be expected.

Fifth Embodiment FIG. 8 shows a fifth embodiment of the present invention in which a SAW filter device is formed using the transducer shown in FIG.
A set of transducers is arranged so that the directions face each other, one of which is input and the other is output. The phase weighting of FIG. 6 and the thinning weighting of FIG. 7 are introduced as necessary. In order to further reduce the loss, a configuration in which reflectors are further introduced on both sides of the filter as shown in FIG. 7 can be considered.

Embodiment 6 FIG. 9 shows another embodiment of the present invention. In this example, two sets of filters of the fifth embodiment are used, and one of the transducers of each filter is electrically connected. If necessary, electrical connection is made via a matching circuit as shown in FIG. Alternatively, two sets may be formed on a single chip, the intermediate terminals may be once taken out of the chip, and a matching circuit may be provided outside. In the configuration of FIG. 9, the matching circuit can be easily realized by a simple series inductance or a parallel inductance. In general, by adopting the configuration shown in FIG. 9, the out-of-band attenuation can secure a value twice or more that of the configuration shown in FIG. This is explained as follows.

The matching circuit introduced between the electrically connected transducers does not match the impedance of the transducer with a pure resistance such as a power supply or a load resistor, but rather uses a similar transducer. A circuit to match the impedance of the In such a matching circuit, impedance matching is realized in the pass band of the filter, but acts outside the pass band to increase the impedance mismatch. This means that the filter attenuation increases outside the pass band.

The increase in the amount of attenuation is very important depending on the use of the filter of the present invention. One application of the present filter is considered to be an intermediate frequency filter for digital mobile communication, which has been receiving attention in recent years. In general,
In the intermediate frequency filter, the loss is small and the image
In the frequency range, an attenuation of about 80 dB is required. As means for realizing such an extremely large amount of attenuation, FIG.
Is a very important configuration.

Embodiment 7 FIG. 10 shows another embodiment of the present invention. The pair of transducers shown in FIG. 1 arranged so as to face each other is electrically connected in parallel or in series to serve as an input or output. Further, a third transducer is introduced between the filters, and this is an output or input filter. In a configuration in which, for example, an input transducer is arranged on both sides as shown in FIG.
Since the AW enters and the leakage of the SAW occurs only from the input transducer and not from the output transducer, the loss can be further reduced as compared with the configuration of FIG. In FIG. 10, the width of the excitation electrode finger of the third transducer is different from that of the left and right unidirectional transducers. Generally, since the third transducer does not require directivity, it is sufficient to introduce a transducer having high excitation efficiency and which is most easy to synthesize frequency characteristics. The width of the excitation electrode finger of such a transducer,
The repetition pitch of the electrodes and the
It is usually different from sa. In addition, as in FIGS. 6 and 7, a unidirectional transformer is used for synthesizing necessary frequency characteristics.
At the same time as introducing phase weighting or thinning-out weighting to a transducer, phase weighting or thinning-out weighting can also be introduced to a transducer having no third directionality. Eighth Embodiment FIG. 11 shows a filter configuration in which the output transducer of FIG. 10 is electrically connected, similarly to the sixth embodiment. Also, an example is shown in which connection is made via an electrical matching circuit. By performing such a connection, a high out-of-band attenuation can be ensured as described above.

Embodiment 9 FIG. 12 shows an embodiment of a SAW resonator. When a pair of directional transducers are electrically connected in parallel or in series to form a two-terminal element, the SAW excited from the left and right toward the center forms a standing wave to form one resonator. Becomes Further, as shown in FIG. 12, such a resonator introduces a third transducer having no directivity between a pair of transducers having directivity, and forms a third transformer. It can also be realized by electrically connecting them in parallel or in series including a transducer. In this case, Example 8
Similarly, the third transducer comprises left and right transducers.
The width of the excitation electrode fingers and the electrode repetition pitch may be different from those of the left and right unidirectional transducers.

Embodiment 10 FIG. 13 shows an embodiment of a filter in which the SAW resonator of Embodiment 9 is combined. In the filter of this embodiment, a pair of SAW resonators shown in FIG. 12 are formed on the same piezoelectric substrate, and are electrically and independently of each other as input and output resonators. When a pair of resonators are arranged close to each other as shown in FIG. 13, the SAW leaked from the input resonator reaches the output resonator and excites the oscillation of the SAW again in the output resonator. The above phenomenon appears within a limited frequency range in which the input / output resonator enters a resonance state. That is, since the transmission of energy from the input resonator to the output resonator is also performed within a very limited frequency range, a filter having a relatively narrow band and very steep frequency characteristics can be realized.

The coupling between the input resonator and the output resonator can be more physically described as follows. That is, when the resonator is in a resonance state, the portion where the electrode fingers are present becomes an equivalent waveguide, and the vibration energy of the SAW concentrates on the waveguide. Outward from the waveguide, the distribution is such that the amplitude of the vibration attenuates exponentially. Such an energy distribution is called an intrinsic mode distribution of the waveguide.

When a pair of resonators are arranged close to each other as shown in FIG. 13, there are equivalently two waveguides, and the SAW vibrations are mutually coupled between the waveguides. This is called mode coupling between waveguides. As a result of the combination, 2
An amplitude distribution (mode distribution) of vibration inherent to the waveguide is generated. These are two distributions, an even mode and an odd mode, with respect to the center line of the two waveguides, as shown in FIG.

The input resonator is brought into a resonance state due to the incident energy, and this state is evenmode and odd.
It is represented by the superposition of the modes. Each mode independently propagates through the waveguide, but since the propagation speeds are different from each other, it behaves as if the energy of vibration is alternately exchanged between the input resonator and the output resonator along the waveguide. . As a result, it is possible to realize a very steep frequency characteristic having a pass band only in a certain narrow frequency range where the resonator is in a resonance state.

Next, specific experimental results will be shown. FIG.
9 shows the frequency characteristics of the filter of the sixth embodiment. As the piezoelectric substrate, ST cut quartz was used. The loss is about 4 dB, and broadband frequency characteristics are obtained. FIG. 15 shows frequency characteristics of the filter of the eighth embodiment. Similarly, ST cut quartz crystal was used for the piezoelectric substrate. The loss is about 3.5dB,
Broadband frequency characteristics are obtained. 14 and 15, an attenuation of about 80 dB is obtained at the image frequency and the like. This can be used as an intermediate frequency filter or the like for digital mobile communication.

[0038]

As described above, the surface acoustic wave device is said to be the device most contributing to the miniaturization of mobile radio communication devices and the like, but there are many problems to be solved in terms of performance, and the device has not been widely adopted. In particular, in the future digital mobile communication, since the bandwidth per channel is increased by about one digit, very high performance is required for the intermediate frequency filter and the like. In order to replace these filters, which were conventionally realized by a combination of a coil and a capacitor and had a very large volume, with a SAW filter, the proposal of a filter having a new structure has been awaited. The present invention answers these requests.

In addition to being able to be used as a wide band intermediate frequency filter, etc., it will contribute to further miniaturization and weight reduction of the radio terminal by integrating with an intermediate frequency amplifier, a mixer and the like in the future. is there.

[Brief description of the drawings]

FIG. 1 is an electrode pattern of a SAW transducer according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating the operation of the present invention.

FIG. 3 is an electrode pattern of a conventional SAW transducer.

FIG. 4 is an electrode pattern of a conventional SAW transducer.

FIG. 5 is an electrode pattern of a SAW transducer according to a second embodiment of the present invention.

FIG. 6 is a block diagram of a third embodiment of the present invention in which phase weighting is introduced;
It is an electrode pattern of an AW transducer.

FIG. 7 is an electrode pattern of a SAW transducer in which thinning weight is introduced according to a fourth embodiment of the present invention.

FIG. 8 is an electrode pattern of a SAW filter and the like according to a fifth embodiment of the present invention.

FIG. 9 is an electrode pattern of a SAW filter or the like according to a sixth embodiment of the present invention.

FIG. 10 is an electrode pattern of a SAW filter according to a seventh embodiment of the present invention.

FIG. 11 is an electrode pattern of a SAW filter according to an eighth embodiment of the present invention.

FIG. 12 is an electrode pattern of a SAW resonator according to a ninth embodiment of the present invention.

FIG. 13 is an electrode pattern of a SAW filter according to a tenth embodiment of the present invention.

FIG. 14 is a diagram illustrating frequency characteristics of a SAW filter according to a sixth embodiment of the present invention.

FIG. 15 is a diagram illustrating frequency characteristics of a SAW filter according to an eighth embodiment of the present invention.

[Explanation of symbols]

1: input terminal, 2: earth terminal, 3: output terminal, 4,
5: electrical connection terminals, 6, 6-1, 6-2, 6-3,
6-4, 9-1, 9-2, 12-1, 12-2, 16:
Excitation electrode fingers, 7, 7-1, 7-2, 7-3, 7-4,
8, 8-1, 8-2, 8-3, 8-4, 10-1, 10
-2, 11-1, 11-2, 13-1, 13-2, 14
-1, 14-2, 17: earth electrode finger, 15: reflector.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-132208 (JP, A) JP-A-1-252015 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03H 9/145 H03H 9/64

Claims (5)

(57) [Claims] 1. A surface acoustic wave transducer having a substrate that propagates a surface acoustic wave and an electrode formed on the substrate, wherein the basic unit of the transducer that is repeatedly arranged in the direction of propagation of the surface acoustic wave is: is configured such that the wave lambda ₀ of the surface acoustic wave, the planar shape of the electrode corresponding to the base unit, lambda wide lambda _0/8 or more ₀
/ 4 or less wide to the left or right side of the excitation electrode fingers lambda _0/8
Width 5λ through the following first space _0/16 or more 3
lambda _0/8 has the first earth electrode fingers positioned below, and the first width lambda _0/8 following the first space on the side opposite to the ground electrode fingers with respect to the excitation electrode fingers located width lambda _0/16 or more lambda _0/8 following the second ground electrode fingers through the second space of the same width, the second and the earth electrode the excitation electrode fingers to fingers SAW transducers third space width lambda _0/4 on the opposite side has a shape located. 2. A surface acoustic wave transducer comprising the first and second surface acoustic wave transducers according to claim 1 , wherein the first and second surface acoustic wave transducers face each other. A surface acoustic wave filter arranged and one of which functions as an input transducer and the other functions as an output transducer. 3. A having a first and second surface acoustic wave filter having first and second surface acoustic wave transducer consisting of a surface acoustic wave transducer according to claim 1,
The second surface acoustic wave transducers of the first and second surface acoustic wave filters are electrically connected to each other, one of the first surface acoustic wave transducers serves as an input transducer, and the other serves as an input transducer. A surface acoustic wave filter characterized by acting as an output transducer. 4. A surface acoustic wave transducer comprising the surface acoustic wave transducer according to claim 1 , wherein the first and second surface acoustic wave transducers face each other. And a third surface acoustic wave transducer disposed between the first and second surface acoustic wave transducers, and electrically connected in parallel or in series. A surface acoustic wave filter characterized in that one of the second surface acoustic wave transducer and the third surface acoustic wave transducer functions as an input transducer, and the other functions as an output transducer. 5. A surface acoustic wave transducer comprising the first and second surface acoustic wave transducers according to claim 1 , wherein the first and second surface acoustic wave transducers face each other. Are arranged and electrically connected in parallel or in series, and further comprise first and second surface acoustic wave transducers arranged between the first and second surface acoustic wave transducers. The surface acoustic wave filter of the first, the third surface acoustic wave transducer of each of the first and second surface acoustic wave filters are electrically connected, the first surface acoustic wave filter of the first The first and second surface acoustic wave transducers are electrically connected in parallel or in series to constitute one of an input or output transducer, SAW filter the first and second surface acoustic wave transducer sexual SAW filter, characterized in that constitutes the other input or output transducer are electrically connected in parallel or in series.