JPH09246911A - Resonator type surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the ripple of the low frequency end of the passing band of a filter by turning parallel arm SAW resonators to the resonators whose weighting ratio is higher than a specified %, turning serial arm SAW resonators to the resonators of a normal type and constituting the resonance type SAW filter of multi-stage ladder type constitution. SOLUTION: The serial arm SAW resonators 36 electrically serially connected between a first input terminal 28 and a first output terminal 32 are inserted and the parallel arm SAW resonators 38 are inserted between the connection points of the respective terminals of the resonators 36 and a common line 102 connected between a second input terminal 30 and a second output terminal 34. The parallel arm SAW resonators 38 for constituting this resonator type SAW filter of ladder type circuit constitution are turned to the resonators for which weighting is executed to 50% or more of an electrode number and the serial arm SAW resonators 36 are turned to normal type SAW resonators. Thus, the ripple by a high-order mode generated at the low frequency end of the passing band is suppressed, the loss of the passing band is lowered further and flatter passing band characteristics are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonator type surface acoustic wave filter.

[0002]

2. Description of the Related Art A surface acoustic wave (hereinafter referred to as SAW) resonator is a comb-shaped electrode (IDT [Interdigital transduce] provided on a piezoelectric substrate.
Also called r]. Hereinafter, it may be abbreviated as IDT. ) Is a device for performing electro-acoustic wave conversion.

Here, the interdigital electrode is an electrode formed by arranging metal films called electrode fingers, which are vapor-deposited on a piezoelectric substrate, in parallel in a comb-teeth shape and are electrically connected to each other. Say that. The surface acoustic wave resonator has two interdigital electrodes facing each other on the same piezoelectric substrate, and the interdigital electrodes of the interdigital electrodes are parallel and are separated from each other without making electrical contact with each other. Then, the structure is arranged so as to intersect with each other. The transmission characteristics of the SAW resonator are the size, the interval, and the crossing length of each electrode finger (the length of the portion (intersection portion) where adjacent electrode fingers cross and overlap each other when viewed from the direction perpendicular to the length direction of the electrode fingers). S.)).

In addition to the above-mentioned IDT, the SAW resonator may include grating reflectors provided on both sides of the IDT. Here, the grating reflector is composed of metal patterns in which metal films (also referred to as reflective strips) are formed in parallel with each other at a constant pitch on a piezoelectric substrate, and each metal film is a SAW propagation direction. Are aligned in the direction perpendicular to. Thus, the SAW resonator is
A high frequency electric signal is applied between the input terminal and the output terminal to excite the SAW by the IDT, and the excited SAW is reflected by the elastic / electrical perturbation effect by the grating reflector and fixed between the two grating reflectors. This is a device that utilizes the resonance phenomenon that forms standing waves.

A SAW filter constructed by using a plurality of SAW resonators is called a resonator type SAW filter, and is characterized in that it is small in size, light in weight and can be used without adjustment, and in its manufacturing process, Since the photolithography technology used in the conventional semiconductor fine processing technology can be used, mass productivity is also excellent. Further, as one mode of this resonator type SAW filter, there is a ladder type circuit configuration type. In addition to the above-mentioned features, this ladder-type circuit configuration type resonator SAW filter has features such as low loss, high attenuation, narrow band, and no matching circuit in principle. Conventionally, for example, as a resonator type SAW filter of a ladder type circuit configuration type, there is one disclosed in Document 1 "Science Technical Report US95-25, EMD95-21, CPM95-35 (1995), p39". In addition, reference 2 "16th EM Symposium Proceedings (1987) pp.27-32" and reference 3 "Surface wave devices and their applications, edited by Japan Electronic Materials Industry Association, Nikkan Kogyo Shimbun (1978)" show elastic surfaces. Various technologies related to wave devices, such as weighting by the apodization method (p.3
9, p.174) is disclosed.

[0006]

However, the above-mentioned resonator type SAW filter has the following problems.

First, a resonator type SA of ladder type circuit configuration type.
The transmission characteristics of the W filter will be described. Figure 1 shows SA
It is a top view which shows the structure of a W resonator. On the upper surface of the piezoelectric substrate 10, an IDT (comb-shaped electrode) 14 is provided, which is configured by arranging a plurality of electrode fingers 12 alternately in parallel in a comb shape. The IDT 14 includes electrode terminals 16a and 16b in two electrically separated electrode regions, for example, using the electrode terminal 16a as an input terminal,
The electrode terminal 16b is used as an output terminal. IDT
On both sides of 14 are grating reflectors 18a and 1
8b is a direction in which the longitudinal direction of the reflective strip (metal film) 20 constituting these grating reflectors is perpendicular to the SAW propagation direction (the direction indicated by the arrow p in FIG. 1), that is, the longitudinal direction of the reflective strip 20 is the electrode. They are arranged on the piezoelectric substrate 10 so as to be parallel to the longitudinal direction of the finger 12.

If the wavelength of the excited SAW is λ, then I
The electrode finger 12 of the DT 14 and the grating reflector 18a
And the reflecting strips 20 of 18b are both arranged at a pitch of λ / 2. Further, the distance between the IDT 14 and the grating reflector 18a and between the IDT 14 and the grating reflector 18b is also set to λ / 2, respectively. In addition, the reflecting strips 20 forming the grating reflectors 18a and 18b are each usually 10% in order to make the reflectance of the SAW in the grating reflectors 18a and 18b substantially 100%.
It is formed so as to have 0 or more.

FIG. 2 is a circuit diagram showing an equivalent circuit of this SAW resonator. In general, the SAW resonator, as shown in the figure, is connected in series between the input terminal 24a (corresponding to the electrode terminal 16a) and the output terminal 24b (corresponding to the electrode terminal 16b) as in the case of a normal vibrator. An electrostatic capacitance C ₀ which is represented by an RCL series circuit 22 to which a resistor R, a capacitor C and a coil L are connected, and which is formed in parallel with the RCL series circuit 22 and which forms an IDT 14 called a braking capacitance between the electrode fingers 12 constituting the IDT Is connected to the circuit.

The reactance characteristic of the equivalent circuit of this SAW resonator is shown in FIG. FIG. 3 is a graph showing frequency on the horizontal axis and reactance on the vertical axis. The reactance characteristic shown in FIG. 3 is represented by the curve 26 and the curve 2
There are two frequencies (resonance frequency f _r and anti-resonance frequency f _a ) at which the reactance becomes zero, that is, the intersection between 6 and the frequency axis, which is a so-called double resonance characteristic. Therefore,
A bandpass filter can be configured by assembling a ladder circuit using this SAW filter.

FIG. 4 is a circuit diagram showing a structure of a resonator type SAW filter having a one-stage ladder type circuit structure using a SAW resonator. The resonator type SAW filter having the one-stage ladder type circuit configuration composed of two SAW resonators has a first input terminal 2
Four terminals, namely, 8, a second input terminal 30, a first output terminal 32, and a second output terminal 34 are provided. First input terminal 2
The SAW resonator 36 connected between the 8 and the first output terminal 32 is called a series arm SAW resonator. Further, between the first output terminal 32 and the second output terminal 34, that is, between the second input terminals 30 (the second input terminal 30 and the second output terminal 3
4 has a common potential. ) Connected to the SAW resonator 38 is called a parallel arm SAW resonator.

Next, the resonator type S of this one-stage ladder type circuit configuration
The characteristics of the AW filter will be described. The upper diagram of FIG. 5 shows the SAW resonator 36 constituting this resonator type SAW filter.
6 is a graph showing the reactance characteristics of the resonators 38 and 38, and the lower diagram of FIG. 5 is a graph showing the transmission characteristics of the resonator type SAW filter. In the graph of the reactance characteristics of FIG. 5, the horizontal axis represents frequency and the vertical axis represents reactance. Further, the horizontal axis of the graph of the transmission characteristics of FIG. 5 shows the frequency, and the vertical axis shows the attenuation amount S _21.
Took and showed.

The reactance characteristic of the series arm SAW resonator 36 is shown by a curve 40 shown in FIG. The reactance characteristic of the parallel arm SAW resonator 38 is shown by the curve 42 shown in FIG. The frequencies f ₁ and f ₂ respectively represent the resonance frequency and the anti-resonance frequency of the series arm SAW resonator 36, and the frequencies f ₃ and f
Reference numeral ₄ represents the resonance frequency and the anti-resonance frequency of the parallel arm SAW resonator 38, respectively. The series arm SAW resonator 36 and the parallel arm SAW resonator 38 have a frequency f ₁
And f ₄ are designed to be substantially equal to each other. If the resonators 36 and 38 are designed and constructed in this manner, as is apparent from the circuit network theory, the S ₂₁ transmission characteristic shown by the curve 44 in the lower diagram of FIG. realizable. According to the S ₂₁ transmission characteristic represented by the curve 44, the transmission band has a pass band 46 having a frequency f ₁ (= f ₄ ) as a center frequency (a frequency region in a range indicated by a diagonal line group 46 in the figure) Also, the pass band 46
Attenuation regions 48 (frequency regions within the range indicated by the shaded group 48 in the figure) and 50 (frequency regions within the range indicated by the shaded group 50 in the figure) are provided on the lower frequency side and the higher frequency side than the pass band 46, respectively. ing.

FIG. 6 shows a resonator type SA having a multi-stage ladder type circuit configuration.
It is an example of a circuit diagram showing a configuration of a W filter. The resonator-type SAW filter having the multi-stage ladder circuit configuration is the same as the resonator-type SAW filter having the configuration described with reference to FIG.
In the configuration, the first output terminal 32 and the second output terminal 34 of another resonator type SAW filter are sequentially connected to the input terminal 30.

FIG. 7 is a graph showing the S ₂₁ transmission characteristic of the resonator type SAW filter having the multi-stage ladder circuit structure. The horizontal axis shows frequency and the vertical axis shows S ₂₁ transmission characteristics. In FIG. 7, curves 52, 54 and 56 are respectively one stage and three.
5 shows S ₂₁ transmission characteristics of a resonator type SAW filter having a stage and a 5-stage ladder type circuit configuration. As shown in FIG. 7, it is convenient that the attenuation amounts in the attenuation regions 48 and 50 increase as the number of stages increases, but at the same time, the bandwidth of the pass band 46 narrows and the insertion loss increases as the number of stages increases. Therefore, it is necessary to consider these matters when determining the number of stages.

As described above, the resonator type SA of the ladder type circuit configuration type
Although the transmission characteristic of the W filter has been described, the transmission characteristic of FIG. 7 is in an ideal state, and actually, due to various causes, ripples occur in the transmission characteristic as shown in FIG. FIG. 8 shows a resonator type S having a multi-stage ladder circuit configuration.
6 is a graph used to explain an actual S ₂₁ transmission characteristic of an AW filter. Four ripples are formed in the curve 76 showing the S ₂₁ transmission characteristic of this SAW filter. First,
In the pass band 46, ripples 78 and 80 are formed near the boundaries with the attenuation regions 48 and 50, respectively. Further, in the attenuation region 50, ripples 82 are formed on the low frequency side and ripples 84 are formed on the high frequency side. Of these ripples, the ripple 78 is generated by the influence of the wave of the higher-order mode excited in the parallel arm SAW resonator 38. Further, the ripple 80 is generated due to the influence of the wave of the higher mode excited in the series arm SAW resonator 36. The ripple 82 is generated by the influence of SSBW (Surface Skimming Bulk Wave) excited in the parallel arm SAW resonator 38. Furthermore, Ripple 84
Is the SSB excited in the series arm SAW resonator 36.
It is caused by the influence of W.

Here, the SSBW is a bulk wave propagating in the vicinity of the surface of an elastic body (corresponding to the piezoelectric substrate 10 constituting the configuration examples of FIGS. 1, 4 and 6) (SS).
BW mainly occurs when the basic mode is pseudo SAW. ). The ripples 82 and 84 generated by this spurious mode are generated by designing such that the ratio between the film thickness of the electrode fingers forming the IDT and the wavelength of the excited SAW becomes an appropriate value. Since the frequency position can be moved, these ripples can be moved to the attenuation band 50 side outside the pass band 46, so that the transmission characteristics of the pass band are not affected.

In addition, the grating reflector which constitutes the SAW resonator electrically changes the propagation velocity of the propagated SAW.
The elastic perturbation effect causes the SAW energy to be slower than that at the free surface, so that the SAW energy is trapped inside the grating reflector. Thus, the grating reflector acts as a waveguide. At this time, in the conventional normal type SAW resonator, since the crossing length of the electrode fingers is constant, the wave of the higher mode is excited. Since the generated higher-order mode wave generally has a higher phase velocity than the fundamental mode wave, the higher-order mode resonance appears as a sub-resonance on the high frequency side of the fundamental mode. Therefore, as described above, in the transmission characteristic of the resonator type SAW filter of the ladder type circuit configuration composed of this SAW resonator, small ripples are formed at both frequency ends of the pass band, and the insertion loss of the pass band. There was a problem that was increased. Especially,
The influence of the higher-order modes of the parallel arm SAW resonator is large, as shown in FIG.
As shown by the transmission characteristic of No. 1, there is a problem that the insertion loss on the low frequency side in the pass band is larger than that on the high frequency side, and a flat pass band characteristic cannot be obtained.

The transmission characteristics (FIG. 8) of the resonator type SAW filter described above are not particularly mentioned, but the normal type SAW filter is used.
The characteristics of the resonator type SAW filter formed by using the resonator are described. Here, the normal type SAW filter is one in which the crossing lengths of the respective electrode fingers forming the IDT are all equal (the structure shown in FIG. 1). On the other hand, there is a SAW resonator having a configuration in which the crossing length of each electrode finger of the IDT forming the SAW resonator is changed according to a certain rule and weighted. Such a weighting method is called an apodization method, and the IDT weighted in this way is called an apodization electrode. This apodization method has been conventionally known as a method for suppressing higher-order mode waves (Reference 2).

In FIG. 9A, a rhombus-shaped weighting is applied to all the electrode fingers constituting the IDT, and the rhombus-weighted structure is 100% (the electrode fingers constituting the IDT are within a rectangular region). However, the SAW resonator having a structure in which the intersecting portions of the electrode fingers are formed in a rhombus whose apex is the center point of each side of the rectangular region is shown in a plan view. . The piezoelectric substrate 10 shown in FIG.
The IDT 58 (I that constitutes the SAW resonator provided above is
The DT 58 includes electrode terminals 16a and 16b. ) Shows not only the electrode fingers that actually contribute to the excitation of SAW, but also the electrode fingers called dummy electrodes. Excitation area 6 surrounded by a dotted line q in the figure
The electrode fingers within 0 (the area inside the diamond) are the actual SA.
Electrode fingers that contribute to the excitation of W, and are dotted lines r ₁ , r ₂ , r
The electrode fingers in the respective dummy regions 62 surrounded by ₃ and r ₄ (the region which is the quadrangular region and excludes the region inside the rhombus) are dummy electrodes. Further, from a functional viewpoint, when the IDT is weighted in this way, even in the case of the same electrode finger, the region of the electrode finger is in which region (dotted lines q, r ₁ , r ₂ , r ₃ and r ₃ and r). _The area surrounded by ₄ ) is divided into a SAW excitation portion and a dummy electrode portion. The electrode fingers and the dummy electrodes are arranged at a constant pitch (adjacent intervals are λ / 2).

Here, the dummy electrode does not serve as an excitation source for the SAW but serves as a reflector for the SAW. Therefore, by providing an appropriate number of dummy electrodes, it is possible to construct a SAW resonator having a structure that does not require a grating reflector which is normally required. For example, FIG. 9B is an enlarged view of the area surrounded by the solid line s in FIG. 9A. Solid line s
Four electrode fingers 12 are included in the area surrounded by. In the figure, the SAW excitation electrodes 64a, 66 and 68a are the electrode fingers 12 included in the excitation region 60 above the dotted line q.
Or a portion thereof, the dummy electrodes 64b, 70 and 68b are the electrode fingers 12 or portions thereof included in the lower side of the dummy region 62 from the dotted line r _4. SAW excitation electrode 6
The SAW 72 generated from 4a is the SAW excitation electrode 64a.
Is reflected by the dummy electrodes 70 and 68b, etc., which are separated by an integral multiple of λ / 2. Further, the SAW 74 generated from the SAW excitation electrode 66 is λ / 2 from the SAW excitation electrode 66.
Is reflected by the dummy electrode 68b and the like which are separated by an integral multiple of.

Therefore, after all, when such weighting is performed, the area of the SAW excitation source becomes smaller toward the both ends of the resonator, so that the SA emitted from the both ends of the resonator is radiated to the outside.
W energy decreases. Further, by providing the dummy electrode, it is possible to further reduce the external radiation of the SAW. Therefore, the SAW resonator having such a configuration does not need a grating reflector or can be configured with a small number of reflective strips.

As described above with reference to the drawings, the ID
If a ladder circuit is assembled using a SAW resonator in which T is weighted, a resonator type SAW filter exhibiting transmission characteristics in which ripples in the pass band are suppressed can be configured. However, in the past, there have been reports on what shape the weighting should be given, but there is no specific report as to what proportion of the number of electrode fingers constituting the IDT should be weighted. It was Therefore, it cannot be said that the conventional resonator type SAW has sufficient transmission characteristics, and there is room for improvement.

Therefore, there has been a demand for the appearance of a resonator type SAW filter exhibiting good transmission characteristics in the pass band, and the present invention provides this resonator type SAW filter.

[0025]

According to a resonator type surface acoustic wave filter (hereinafter referred to as a resonator type SAW filter) of the present invention, a plurality of electrode fingers are arranged in parallel and alternately. A surface acoustic wave resonator (hereinafter, referred to as SAW resonator) having interdigital electrodes (hereinafter, referred to as IDTs) obtained by weighting the crossing lengths of the electrode fingers according to the apodization method in parallel arms SAW. In a resonator type SAW filter which is arranged as a resonator or a series arm SAW resonator on a piezoelectric substrate so as to form a multi-stage ladder circuit, the parallel arm SAW resonator is used for 50% or more of the electrode fingers. With the weighted resonator,
The serial arm SAW resonator is a normal type SAW resonator.

As described above, by weighting the crossing lengths of the electrode fingers forming the IDT with the above proportion based on the apodization method, the higher-order mode that causes ripples in the pass band of the transmission characteristic. Since it is possible to reduce the occurrence of the SAW wave, the resonator type SAW filter exhibiting excellent transmission characteristics can be obtained.

Further, according to another resonator type SAW filter of the present invention, a plurality of electrode fingers are arranged in parallel and alternately, and a crossing length of these electrode fingers is weighted according to the apodization method. SAW with IDT
A resonator type SAW filter in which a resonator is arranged as a parallel arm SAW resonator or a series arm SAW resonator to form a multi-stage ladder circuit on a piezoelectric substrate.
The AW resonator is a normal type SAW resonator, and the series arm SA is
The W resonator is a resonator in which the weight is applied to 30 to 80% of the number of electrode fingers.

As described above, by weighting the crossing lengths of the electrode fingers forming the IDT in the above ratio based on the apodization method, the higher-order mode that causes ripples in the pass band of the transmission characteristics. Since it is possible to reduce the occurrence of the SAW wave, the resonator type SAW filter exhibiting excellent transmission characteristics can be obtained.

Further, according to another resonator type SAW filter of the present invention, a plurality of electrode fingers are arranged in parallel and alternately, and a crossing length of these electrode fingers is given weighting according to the apodization method. SA with IDT
In a resonator type SAW filter in which a W resonator is arranged as a parallel arm SAW resonator or a series arm SAW resonator so as to form a multi-stage ladder circuit on a piezoelectric substrate, the parallel arm SAW resonator has the number of electrode fingers. 50% or more of the resonators are weighted as described above, and the series-arm SAW resonator is the resonator weighted as 30-80% of the number of electrode fingers.

As described above, by weighting the crossing lengths of the electrode fingers forming the IDT in the above ratio based on the apodization method, the higher-order mode that causes ripples in the pass band of the transmission characteristics. Since it is possible to reduce the occurrence of the SAW wave, the resonator type SAW filter exhibiting excellent transmission characteristics can be obtained.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Incidentally, the drawings are schematically shown to the extent that the size, shape and arrangement of the structure of the present invention can be understood, and the numerical conditions described below are merely examples. It is not limited to the embodiment.

[First Embodiment] FIG. 10 is a plan view for explaining the structure of a SAW resonator constituting the resonator type SAW filter of this configuration example. Electrode fingers 12 are alternately arranged in parallel on the upper surface of the piezoelectric substrate 10.
A T (blind electrode) 86 is formed. IDT86
The electrode terminal 16 in the two electrode regions that are electrically separated.
a and 16b are provided, and the electrode terminal 16a is used as an input terminal and the electrode terminal 16b is used as an output terminal, for example. Grating reflectors 18a and 18b are provided on both sides of the IDT 86, and reflective strips (metal films) 20 constituting these grating reflectors 20 are provided.
The longitudinal direction of the reflective strip 20 is perpendicular to the SAW propagation direction (the direction indicated by arrow p in FIG. 10).
Are aligned and provided on the piezoelectric substrate 10 so as to be parallel to the electrode fingers 12.

If the wavelength of the excited SAW is λ, then the electrode fingers 12 constituting the IDT 86 and the reflecting strips 20 of the grating reflectors 18a and 18b are both arranged at a pitch of λ / 2. And IDT8
6 and the grating reflector 18a, and the IDT86
The distance between the grating reflector 18b and the grating reflector 18b is also set to λ / 2. In addition, the reflecting strip 2 which constitutes the grating reflectors 18a and 18b
0 is provided for each of the grating reflectors 18a and 18b so that the reflectance of the SAW is substantially 100% and the SAWs are multiply propagated between the two grating reflectors 18a and 18b to cause resonance.

Next, the IDT 86 of this configuration example has an ID weighted by 50% according to the apodization method.
It is T. The electrode fingers in the excitation regions 88 and 90 surrounded by the dotted lines q ₁ or q ₂ in the figure are SAW excitation electrodes that contribute to the actual excitation of SAW, and the dotted lines r ₁ , r ₂ ,
a respective dummy region 92 surrounded by r ₃ and r ₄ ,
The electrode fingers 12 in 94, 96 and 98 are dummy electrodes. In addition, a rectangular regular area 10 surrounded by a dotted line t
The electrode fingers 12 within 0 are not weighted.
As described above, the SAW excitation electrodes and the dummy electrodes are arranged at a constant pitch (adjacent intervals are λ / 2). As shown in FIG. 10, in this configuration example, triangular weights that are left-right symmetric are attached to the respective quarter regions of the entire IDT 86 from both grating reflectors 18a and 18b of the IDT 86. It is as a structure. Therefore, the electrode finger 1 in the region 100 which is the central region of the IDT and occupies half of the entire IDT 86.
2 is not weighted, and the crossing length of each electrode finger 12 in this region is constant. In this embodiment, such a structure is referred to as having a rhombic shape weighted by 50%.

In this SAW resonator configuration example, only one example of a SAW resonator having a weighted IDT is shown, and the weighting ratio is not limited to the above-mentioned 50%, and will be described later. As described above, in the first embodiment, it may be 50% or more. In the description of the structure of the SAW resonator, only the weighting method has been described. What is important is, in a resonator type SAW filter having a ladder circuit structure, what ratio is given to each SAW resonator forming the filter. Whether to give weighting.

Here, the weighting ratio means the ratio of the number of weighted electrode fingers to the number of all electrode fingers forming the IDT. Further, in this embodiment, the weighting shape is a rhombus, but the weighting shape is not limited to this but may be another shape if the shape is based on the apodization method. For example, weighting may be added so that the crossing length of the electrode fingers changes in a sine wave shape. Further, it is not necessary that the shape of the weighted region is bilaterally symmetric, and the position of this region is also shown in FIG.
It is not necessary to be at a position where a normal region is formed in the center as in the configuration example of.

Further, in this configuration example, the number of the reflecting strips 20 of each of the grating reflectors 18a and 18b is set to 50 when the weighting ratio is 50%, but it is not particularly limited to this number. This is because it is sufficient if the number is the minimum number in the range of 0 to 50. Normally, the number of reflective strips of the grating reflector that constitutes the SAW resonator is required to be 100 or more, but it is possible to create such a small number by using the ID of the SAW resonator of this configuration example.
This is because the electrode finger 12 of T86 is weighted based on the apodization method, and the dummy electrode is provided. Therefore, the larger the value of the weighting ratio, the more the number of reflection splits of the grating reflector can be reduced.

Further, in this configuration example, as the materials of the electrode fingers 12 constituting the IDT 86 and the reflecting strips 20 constituting the grating reflectors 18a and 18b,
Aluminum or an aluminum alloy containing several% of copper or silicon (Si) is used. As the material of the electrode fingers 12 and the reflection strip 20, a metal material having a small specific gravity is used in order to reduce the load against the vibration of the SAW, as in the conventional case. Further, gold is used for the electrode terminals 16a and 16b to facilitate bonding.

Further, in the SAW resonator of this configuration example, the electrode fingers 12, the reflecting strips 20, the electrode terminals 16a and 16b are deposited on the piezoelectric substrate 10, and the deposited metal films are patterned by using the photolithography technique. Since it is formed through steps, it can be formed by a conventional semiconductor manufacturing technique. Such advantages are also applicable to the resonator type SAW filter formed by using the SAW resonator of this configuration.

A resonator type SAW filter having a ladder circuit configuration is constructed by using the SAW resonator of this configuration example described above. FIG. 11 shows the resonance type SA of the first embodiment.
It is an example of a circuit diagram showing a configuration of a W filter. In this configuration example, the series arm SAW resonator 36 electrically connected in series between the first input terminal 28 and the first output terminal 32 has a connection point of each terminal of the series arm SAW resonator 36,
The parallel arm SAW resonator 38 is inserted and connected between the common line 102 connected between the second input terminal 30 and the second output terminal 34. In the first embodiment, the parallel arm SAW resonator 38 forming the resonator type SAW filter of the ladder circuit structure is a resonator in which 50% or more of the electrode fingers are weighted, and the series arm is used. The SAW resonator 36 is a normal type SAW resonator.

Next, the characteristics of the configuration of the first embodiment will be described first with reference to FIGS. 12 to 16. 12 to 16 are graphs showing measurement results of S ₂₁ transmission characteristics and S ₁₁ reflection characteristics of a circuit in which one SAW resonator is connected in parallel. In the circuit used for this measurement, only one SAW resonator of this configuration example described above is connected between the first input terminal 28 and the second input terminal 30, and the SAW resonator between the first input terminal 28 and the second input terminal 30 is connected. by applying an electrical signal to, S ₂₁ in FIG. 12 the state of a circuit constructed (circuit a first input terminal 28 and a second input terminal 30 as the first output terminal 32 and the second output terminal 34 as each transmission Shown on the side of the characteristic). The transmission characteristics of such a circuit are shown in FIGS. 12 to 16 (A), and the reflection characteristics are shown in FIGS. 12 to 16 (B), and the weighting ratio of this SAW resonator is 0%. 33
%, 50%, 83%, 100%, and the measurement results are shown in each figure. The graph of S ₂₁ transmission characteristics is
Input electric signal frequency is 100MHz on the horizontal axis
The scale is shown for each MHz, and the attenuation amount S ₂₁ is shown for each 5 dB in dB on the vertical axis. The S ₁₁ reflection characteristics are shown on the Smith chart. Also, FIG.
Table 1 shows the relationship between the value of the attenuation amount [dB] of the marker M3 and the weighting ratio [%] shown in the S ₂₁ transmission characteristics of FIGS.

The SAW resonator of this configuration example is the piezoelectric substrate 1
0 is a 36 ° rotated Y plate LiTaO ₃ substrate, and this SAW
When a resonator type SAW filter having a ladder circuit configuration is formed using a resonator, a pass band width of 25 MHz and 800 M
The size of the electrode finger 12 was determined to be in the Hz band. Further, in order to prevent the spurious of SSBW from being formed in the pass band, the ratio H / λ between the film thickness H of the electrode finger 12 and the wavelength λ of the excited SAW is designed and configured to be 0.08 or more. Furthermore, in the structure of the IDT 86 of this configuration example, 120 pairs of electrode fingers have a maximum crossing length of 100 μm, and the capacitance C ₀ of the IDT 86 is 4.80 pF.

[0043]

[Table 1]

Each S ₂₁ shown in FIG. 12 to FIG.
In both graphs of the transmission characteristic and the S ₁₁ reflection characteristic, the marker M1 represents the resonance frequency, and the marker M2 represents the spurious of the higher order mode. Further, the marker M3 is located on the higher frequency side by 20 MHz than the marker M1 of the resonance frequency, and this marker M3 is used when a SAW resonator is configured in a ladder circuit to form a resonator type SAW filter in the 800 MHz band. Shows the frequency position corresponding to the low frequency end of the pass band. When the diamond weighting ratio becomes 50% or more (FIGS. 14 to 16), another higher-order mode occurs at the position of the marker M4 in addition to the higher-order mode of the marker M2. Since the frequency position of the higher order mode of the marker M4 is a position shifted from the pass band of the filter to the low frequency side, the pass band is not affected by the higher order mode.

As is clear from the graphs shown in FIGS. 12 to 16, in particular the S ₁₁ reflection characteristic by the Smith chart, the discontinuity (dent) of the marker M2 is eliminated as the diamond weighting ratio increases. The weighting ratio is 50% or more (Figs. 14 to 16)
Then, it can be seen that the influence of the higher-order modes is almost eliminated. Therefore, it can be seen that the high-order mode spurious of the marker M2 is suppressed by applying the diamond weighting. At the same time, the weighting ratio is 0% to 10%.
According to increase to 0%, as is clear in the S ₂₁ transmission characteristic, -1.94D loss in the marker M3
It is understood that B (FIG. 12 (A)) is reduced to −0.52 dB (FIG. 16 (A)) to realize low loss.

FIG. 17A shows an S of a resonator type SAW filter in which a SAW resonator having a normal type, that is, a weighting ratio of 0% is used as a series arm and a parallel arm SAW resonator to form a ladder circuit. Fig. 1 shows a graph of ₂₁ transmission characteristics.
7 (B) is S with 100% weighting.
Normal type SAW using AW resonator as parallel arm resonator
S ₂₁ of the resonator type SAW filter according to the first embodiment in which the resonator is used as a series arm SAW resonator to form a ladder circuit.
A graph of transmission characteristics is shown. The measurement results of both graphs (A) and (B) of FIG. 17 are obtained by using an 800 MHz band resonator type SAW filter.
AW filter intended electrostatic capacitance C ₀ is configured with series arm SAW resonator 5.76PF, the capacitance C ₀ is a ladder type circuit 5 stages Te than in the parallel arm SAW resonator 1.44pF Is. In both graphs (A) and (B) of FIG. 17, the horizontal axis represents the input electric signal frequency in MHz units and the range of 200 MHz is graduated in 20 MHz, and the vertical axis represents the attenuation amount S ₂₁ in dB units. The scale is shown at 10 dB.

Markers M5 and M6 in the graphs of FIGS. 17A and 17B indicate the low frequency end and the high frequency end of the pass band, respectively. In the graph in FIG. 17A, the attenuation amount of the marker M5 is −2.01 dB, and the attenuation amount of the marker M6 is −1.81 dB. In the graph of FIG. 17B, the attenuation amount of the marker M5 is -1.71 dB, and the attenuation amount of the marker M6 is -1.87 dB. Comparing FIG. 17A showing the characteristic of the conventional configuration example with FIG. 17B showing the characteristic of the configuration example of the first embodiment, the parallel arm SAW is shown.
By changing the weight ratio of the resonator from the normal type to 100%, the insertion loss at the low frequency end of the pass band indicated by the marker M5 is -2.01 dB to-.
The characteristic is improved to 1.71 dB, and the characteristic of the pass band from the marker M5 to the marker M6 shows a flatter characteristic. Therefore, it is understood that the ripple due to the higher-order mode indicated by the marker M5 in the pass band of the resonator type SAW filter is suppressed and the loss is reduced.

As is clear from the above description, in the resonator type SAW filter in which the SAW resonator is composed of the multi-stage ladder circuit, the normal type resonator as the series arm SAW resonator and 50% or more as the parallel arm SAW resonator. By using a resonator with a weighted ratio of, it is possible to suppress ripples due to higher-order modes that occur at the low-frequency end of the passband, and further reduce the loss in the passband and achieve a flatter pass. Band characteristics can be obtained. As described above, the rhombus weighting of the parallel arm SAW resonator is 50%.
If the SAW resonators applied in the above proportions are used, this SA
The reflection split of the W resonator grating reflector is 0.
Since it is possible to complete the process with about 50 filters, the size of the chip that constitutes the SAW filter can be reduced.

In the resonator type SAW filter of the first embodiment described above, the parallel arm SAW resonators used in the multi-stage ladder circuit structure are all weighted at the same ratio. However, the weighting ratio may be 50% or more, and it is not necessary to set the weighting ratios of all the parallel arm SAW resonators to the same value. In this way, the same effect can be obtained even if the weighting ratios of the parallel arm SAW resonators constituting the resonator type SAW filter are different.

[Second Embodiment] FIG. 18 is an example of a circuit diagram for explaining the configuration of a resonator type SAW filter according to a second embodiment. This configuration example shows the first input terminal 2
8 and the first output terminal 32, the series arm SAW resonator 36 electrically connected in series, the connection point of each terminal of these series arm SAW resonator 36, the second input terminal 30 and the second output. The parallel arm SAW resonator 38 is inserted and connected between the common line 102 connected between the terminals 34.

In the second embodiment, the parallel arm SA that constitutes the resonator type SAW filter of the ladder type circuit configuration is used.
The W resonator 38 is a normal type SAW resonator, and the series arm SAW
The resonator 36 is a resonator in which 30 to 80% of the number of electrode fingers is weighted. Further, since the structure and standard of each SAW resonator are the same as those of the configuration example of the first embodiment, description thereof will be omitted. However, series arm SA
The reflection strips of the grating reflectors provided on both sides of the IDT of the W resonator 36 are provided more than in the case of the configuration example of the first embodiment, and the number is about 50 to 80 in order to prevent SAW leakage. . Even so, normally, the number of reflective strips of the grating reflector that constitutes the SAW resonator is required to be 100 or more, so it is smaller than that case, and the size of the chip in which the SAW filter is configured should be reduced accordingly. You can

Next, the characteristics of the configuration of the second embodiment will be described first with reference to FIGS. 19 to 23. 19 to 23 are graphs showing measurement results of S ₂₁ transmission characteristics and S ₁₁ reflection characteristics of a circuit in which one SAW resonator is connected in series. In the circuit used for this measurement, only one SAW resonator of the above-described configuration example is connected between the first input terminal 28 and the first output terminal 32, and the circuit between the first input terminal 28 and the second input terminal 30 is connected. 19 and a circuit configured to extract an output signal from the first output terminal 32 and the second output terminal 34 (S _{21 in} FIG. 19).
The state of the circuit is shown on the horizontal side of the transmission characteristic graph. ). The transmission characteristics of this circuit are shown in FIGS. 19 to 23 (A), and the reflection characteristics are shown in FIGS. 19 to 23 (B), and the weighting ratio of this SAW resonator is 0%, 3
The results measured by changing the values to 3%, 50%, 83% and 100% are shown in each figure. In the graph of the S ₂₁ transmission characteristic, the horizontal axis shows the input electric signal frequency in the range of 100 MHz in steps of 10 MHz, and the vertical axis shows the attenuation S ₂₁ in dB units in steps of 5 dB. Indicated. Also, S ₁₁
The reflection characteristics are shown on the Smith chart. still,
Marker M3 shown in the S ₂₁ transmission characteristics of FIGS. 19 to 23
Table 2 shows the relationship between the value of the attenuation [dB] and the weighting ratio [%].

The SAW resonator of this configuration example is the piezoelectric substrate 1
0 is a 36 ° rotated Y plate LiTaO ₃ substrate, and this SAW
When a resonator type SAW filter having a ladder circuit configuration is formed using a resonator, a pass band width of 25 MHz and 800 M
The size of the electrode finger 12 was determined to be in the Hz band. Further, in order to prevent the spurious of SSBW from being formed in the pass band, the ratio H / λ between the film thickness H of the electrode finger 12 and the wavelength λ of the excited SAW is designed and configured to be 0.08 or more. Furthermore, in the structure of the IDT 86 of this configuration example, 120 pairs of electrode fingers have a maximum crossing length of 100 μm, and the capacitance C ₀ of the IDT 86 is 4.80 pF.

[0054]

[Table 2]

Each S ₂₁ shown in FIG. 19 to FIG.
In both graphs of the transmission characteristic and the S ₁₁ reflection characteristic, the marker M1 represents the anti-resonance frequency, and the marker M2 represents the spurious of the higher order mode. Further, the marker M3 is located on the lower frequency side by 20 MHz than the marker M1 of the resonance frequency, and this marker M3 is a resonator type SAW filter in the 800 MHz band when the SAW resonator is formed in a ladder circuit. Shows the frequency position corresponding to the high frequency end of the pass band.

Here, when the diamond weighting ratio is set higher than 80% (FIGS. 22 and 23), another higher-order mode is generated at the position of the marker M4 in addition to the higher-order mode of the marker M2. Since the frequency position of the higher order mode of the marker M4 is near the center of the pass band when the filter is constructed, the higher order mode adversely affects the pass band. Further, as can be seen from Table 2, when the weighting ratio is set to be greater than 80%, the loss of the marker M3 increases due to the spurious effect indicated by the marker M4. Therefore, it is not possible to use a SAW resonator having a rhombic weighting greater than 80% as a series arm SAW resonator having a multi-stage ladder circuit configuration.

As is clear from the graphs shown in FIGS. 19 to 23, particularly the S ₁₁ reflection characteristic by the Smith chart, the discontinuous portion (dented portion) of the marker M2 is eliminated as the diamond weighting ratio increases. ing. This effect is most pronounced in the weighting ratio range of 30 to 50% (FIGS. 20 and 21),
Therefore, it is sufficiently predicted that it appears well in the range of 30 to 80%, and it can be seen that the influence of the higher-order modes is almost eliminated in the range of 30 to 80%. Therefore, it can be seen that the higher-order mode spurious of the marker M2 is suppressed by performing the diamond weighting of this ratio. Therefore, if the SAW resonator weighted at a rate of 30 to 80% is used as a series arm SAW resonator to configure a resonator type SAW filter having a ladder circuit configuration,
It is possible to suppress the ripple generated at the high frequency end in the pass band of the filter due to the higher order mode of the marker M2.

As is clear from the above description, in the resonator type SAW filter in which the SAW resonator has a multi-stage ladder circuit structure, a resonator having a weight of 30 to 80% as a series arm SAW resonator, By using a normal type resonator as the parallel arm SAW resonator, it is possible to suppress the ripple due to the higher-order mode generated at the high frequency end of the pass band, and further reduce the loss of the pass band. .

In the resonator type SAW filter of the second embodiment described above, the series arm SAW resonators used in the multi-stage ladder circuit configuration are all weighted at the same ratio. However, the weighting ratio may be 30 to 80%, and it is not necessary to set the weighting ratios of all the series arm SAW resonators to the same value.
In this way, the same effect can be obtained even if the weighting ratios of the series arm SAW resonators constituting the resonator type SAW filter are different.

[Third Embodiment] FIG. 24 is an example of a circuit diagram for explaining the configuration of a resonator type SAW filter according to a third embodiment. This configuration example shows the first input terminal 2
8 and the first output terminal 32, the series arm SAW resonator 36 electrically connected in series, the connection point of each terminal of these series arm SAW resonator 36, the second input terminal 30 and the second output. The parallel arm SAW resonator 38 is inserted and connected between the common line 102 connected between the terminals 34.

In the third embodiment, the parallel arm SA which constitutes the resonator type SAW filter of the ladder type circuit structure is formed.
The W resonator 38 is a resonator weighted to 50% or more of the number of electrode fingers, and the series arm SAW resonator 36 is a resonator weighted to 30 to 80% of the number of electrode fingers. Further, since the structure and standard of each SAW resonator are the same as those of the configuration examples of the first and second embodiments, description thereof will be omitted. However, the number of reflective strips of the grating reflectors provided on both sides of the IDT of the parallel arm SAW resonator 38 is about 0 to 50, and the number of reflective strips of the grating reflectors provided on both sides of the IDT of the series arm SAW resonator 36 is about 50 to 50. The number is about 80.

Next, the characteristics of the configuration of the third embodiment will be described. First, as described in the first embodiment, when the resonator type SAW filter having the ladder type circuit configuration is assembled, the parallel arm SAW resonator 38 has five electrode fingers.
By using the resonator weighted to 0% or more, it is possible to suppress the ripple due to the higher mode generated at the low frequency end of the pass band of the filter. Further, as described in the second embodiment, when the resonator type SAW filter having the ladder circuit configuration is assembled, the series arm SAW is
By using, as the resonator 36, a resonator in which 30 to 80% of the number of electrode fingers is weighted, it is possible to suppress the ripple due to the higher-order mode generated at the high frequency end of the pass band of the filter. Therefore, the above-mentioned third
As described in the description of the structure of the above embodiment, when the resonator type SAW filter having the ladder type circuit configuration is assembled, the parallel arm SA is
As the W resonator 38, a resonator in which 50% or more of the number of electrode fingers is weighted is used, and the series arm SAW resonator 3 is used.
By using a resonator weighted to 30 to 80% of the number of electrode fingers as 6, the ripple due to the higher-order mode generated at the low frequency end of the pass band of the filter and the high frequency end of the pass band of the filter. It is possible to simultaneously suppress the ripple due to the higher-order mode that occurs in 1).

Therefore, according to the configuration example of the third embodiment, it is possible to suppress the ripple due to the higher-order mode generated at the low frequency end and the high frequency end of the pass band of the filter, and to further improve the pass band. Of low loss, and the first
As described in the above embodiment, a flatter pass band characteristic can be obtained. Further, as described in the first and second embodiments, when the SAW resonator having rhombus weighting at a ratio of 50% or more is used as the parallel arm SAW resonator, the grating reflector of the SAW resonator is Only about 50 reflection splits are required, and the series arm S
If a SAW resonator with rhombic weighting of 30 to 80% is used as the AW resonator, the grating reflector of the SAW resonator can have about 50 to 80 reflection splits. It also leads to miniaturization of the chips that are configured.

In the resonator type SAW filter of the third embodiment described above, it is not necessary to use the parallel arm SAW resonators used in the multi-stage ladder type circuit structure, which are all weighted at the same ratio. However, the weighting ratio may be 50% or more. In this way, the same effect can be obtained even if the weighting ratios of the parallel arm SAW resonators constituting the resonator type SAW filter are different. Further, it is not necessary that all the series arm SAW resonators are weighted at the same rate, and the weighting rate may be 30 to 80%. In this way, the same effect can be obtained even if the weighting ratios of the series arm SAW resonators constituting the resonator type SAW filter are different.

[0065]

According to the resonator type SAW filter of the present invention, the parallel arm SAW resonator has a weighting ratio of 50% based on the apodization method with respect to the crossing length of the electrode fingers constituting the IDT. The resonator described above is used, and the series arm S
By configuring a resonator type SAW filter having a multi-stage ladder circuit configuration using the AW resonator as a normal type resonator, ripples at the low frequency end of the pass band of the filter can be suppressed, and low loss and A resonator type SAW filter having a flattened pass band and exhibiting good transmission characteristics can be obtained.

According to the resonator type SAW filter of the present invention, the parallel arm SAW resonator is a normal type resonator,
The resonator arm SAW having a multi-stage ladder circuit structure is used as the resonator in which the weight of the serial arm SAW resonator is set to 30 to 80% based on the apodization method with respect to the crossing length of the electrode fingers forming the IDT. By configuring the filter,
The ripple at the high frequency end of the pass band of the filter can be suppressed, and the pass band has a low loss.
A resonator type SAW filter exhibiting good transmission characteristics can be obtained.

Further, according to the resonator type SAW filter of the present invention, the parallel arm SAW resonator has a weighting ratio of 50% based on the apodization method with respect to the crossing length of the electrode fingers forming the IDT. In the above-described resonator, the series arm SAW resonator is a multi-stage ladder type resonator in which the weighting ratio applied based on the apodization method is 30 to 80% with respect to the crossing length of the electrode fingers forming the IDT. By configuring the resonator type SAW filter having the circuit configuration, it is possible to suppress the ripple at the low frequency end and the high frequency end of the pass band of the filter, and also to have a low loss and flattened pass band. A resonator type SAW filter exhibiting good transmission characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a SAW resonator.

FIG. 2 is a diagram showing an equivalent circuit of a SAW resonator.

FIG. 3 is a diagram showing reactance characteristics of a SAW resonator.

FIG. 4 is a diagram showing a configuration of a resonator type SAW filter having a one-stage ladder type circuit configuration.

FIG. 5 is a diagram showing reactance characteristics of a SAW resonator and transmission characteristics of a resonator type SAW filter.

FIG. 6 is a diagram showing a configuration of a resonator type SAW filter having a multi-stage ladder circuit configuration.

FIG. 7 is a diagram showing ideal transmission characteristics of a resonator type SAW filter.

FIG. 8 is a diagram showing actual transmission characteristics of a resonator type SAW filter.

9A is a plan view showing a configuration of a SAW resonator with 100% weighting, and FIG. 9B is an enlarged view of a main part of FIG. 9A.

FIG. 10 is a diagram showing a configuration of a SAW resonator with a weight of 50%.

FIG. 11 is a diagram showing a configuration of a resonator type SAW filter according to the first embodiment.

FIG. 12A is a transmission characteristic of the first embodiment,
FIG. 6B is a diagram showing the reflection characteristic of the first embodiment.

13A is a diagram showing transmission characteristics of the first embodiment following FIG. 12, and FIG. 13B is a diagram showing reflection characteristics of the first embodiment following FIG.

14A is a diagram showing a transmission characteristic of the first embodiment following FIG. 13, and FIG. 14B is a diagram showing a reflection characteristic of the first embodiment following FIG.

15A is a diagram showing transmission characteristics of the first embodiment following FIG. 14, and FIG. 15B is a diagram showing reflection characteristics of the first embodiment following FIG.

16A is a diagram showing a transmission characteristic of the first embodiment following FIG. 15, and FIG. 16B is a diagram showing a reflection characteristic of the first embodiment following FIG.

17A is a diagram showing the transmission characteristic of the conventional configuration example, and FIG. 17B is a diagram showing the transmission characteristic of the configuration example of the first embodiment.

FIG. 18 is a diagram showing a configuration of a resonator type SAW filter according to a second embodiment.

FIG. 19A is a transmission characteristic of the second embodiment,
FIG. 6B is a diagram showing the reflection characteristic of the second embodiment.

20A is a diagram showing the transmission characteristic of the second embodiment following FIG. 19, and FIG. 20B is a diagram showing the reflection characteristic of the second embodiment following FIG.

21A is a diagram showing the transmission characteristic of the second embodiment following FIG. 20, and FIG. 21B is a diagram showing the reflection characteristic of the second embodiment following FIG.

22A is a diagram showing the transmission characteristic of the second embodiment following FIG. 21, and FIG. 22B is a diagram showing the reflection characteristic of the second embodiment following FIG. 21.

23A is a diagram showing the transmission characteristic of the second embodiment following FIG. 22, and FIG. 23B is a diagram showing the reflection characteristic of the second embodiment following FIG.

FIG. 24 is a diagram showing a configuration of a resonator type SAW filter according to a third embodiment.

[Explanation of symbols]

10: Piezoelectric substrate 12: Electrode fingers 14, 58, 86: IDT 16a, 16b: Electrode terminal 18a, 18b: Grating reflector 20: Reflecting strip 22: RCL series circuit 24a: Input terminal 24b: Output terminal 26, 40, 42 , 44, 52, 54, 56, 76: Curve 28: First input terminal 30: Second input terminal 32: First output terminal 34: Second output terminal 36: Series arm SAW resonator 38: Parallel arm SAW resonator 46: Pass band 48, 50: Attenuation region 60, 88, 90: Excitation region 62, 92, 94, 96, 98: Dummy region 64a, 66, 68a: SAW excitation electrode 64b, 68b, 70: Dummy electrode 72, 74 : SAW 78, 80, 82, 84: Ripple 100: Normal area 102: Common line

Claims (3)

[Claims] 1. A surface acoustic wave resonator having interdigital transducers in which a plurality of electrode fingers are arranged in parallel and alternately and a crossing length of these electrode fingers is weighted according to the apodization method. A resonator-type surface acoustic wave filter, which is arranged as a multi-step ladder type circuit on a piezoelectric substrate as an arm surface acoustic wave resonator or a series arm surface acoustic wave resonator, wherein the parallel arm surface acoustic wave resonator is 50% of the number of electrode fingers
A resonator-type surface acoustic wave filter, characterized in that the above-mentioned weighted resonator is used and the series arm surface acoustic wave resonator is a normal type surface acoustic wave resonator. 2. A surface acoustic wave resonator having interdigital transducers in which a plurality of electrode fingers are arranged in parallel and alternately and weighting according to the apodization method is applied to a crossing length of these electrode fingers in parallel. A resonator-type surface acoustic wave filter, which is arranged as a multi-stage ladder circuit on a piezoelectric substrate as an arm surface acoustic wave resonator or a series arm surface acoustic wave resonator, wherein the parallel arm surface acoustic wave resonator is a normal surface acoustic wave resonator. Resonator type surface acoustic wave resonator, wherein the series arm surface acoustic wave resonator is a resonator in which the weight is applied to 30 to 80% of the number of electrode fingers. . 3. A surface acoustic wave resonator having interdigital transducers in which a plurality of electrode fingers are arranged in parallel and alternately and a weight according to the apodization method is applied to a crossing length of these electrode fingers in parallel. A resonator-type surface acoustic wave filter, which is arranged as a multi-step ladder type circuit on a piezoelectric substrate as an arm surface acoustic wave resonator or a series arm surface acoustic wave resonator, wherein the parallel arm surface acoustic wave resonator is 50% of the number of electrode fingers
For the above weighted resonator, the series arm surface acoustic wave resonator is 30 to 80% of the number of electrode fingers.
A resonator type surface acoustic wave filter, characterized in that the resonator is weighted with respect to.