JP2004128928A - Surface acoustic wave filter and communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high selectivity surface acoustic waver filter and a communication device with excellent selectivity in the vicinity of a passband (with improved attenuation characteristics in a higher region of the passband). <P>SOLUTION: A surface acoustic wave filtering element 101 including interdigital transducers (IDTs) 104, 105 and 106 provided on a piezoelectric substrate along the propagation direction of surface acoustic waves and a surface acoustic wave filtering element including IDTs 109, 110 and 111 are cascaded, and a surface acoustic wave resonator 103 is connected in series between the two filtering elements 101 and 102. A frequency interval between resonant frequency and anti-resonant frequency in the resonator 103 is specified to be ≥0.65 times and ≤0.98 times the bandwidth in the filtering elements 101 and 102. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface acoustic wave filter device and a communication device, and more particularly, to a high-selectivity surface acoustic wave filter device and a communication device with excellent selectivity near a pass band.
[0002]
[Prior art]
2. Description of the Related Art In recent years, there has been remarkable technological progress in reducing the size and weight of communication devices such as mobile phones. As means for achieving this, not only the number of constituent components has been reduced and the size thereof has been reduced, but also the development of components having a plurality of combined functions has been advanced.
[0003]
Surface acoustic wave filters have come to be widely and generally used as RF filters for mobile phones. In recent years, due to the shortage of frequencies used in mobile phones, carrier frequencies have been complicated and frequency bands have been expanded, and there are many cases where a stop band is very close to a pass band, and a filter with high steepness is required. I have.
[0004]
The prior art discloses a method in which a surface acoustic wave resonator is inserted in series between interstages in a two-stage cascaded surface acoustic wave filter device (see Patent Documents 1 and 2). In this prior art, high selectivity is possible by connecting a surface acoustic wave resonator directly to a connection part in a two-stage cascade configuration.
[0005]
[Patent Document 1]
JP-A-11-298283 (publication date: October 29, 1999)
[0006]
[Patent Document 2]
JP-A-2000-349590 (publication date: December 15, 2000)
[0007]
[Problems to be solved by the invention]
In this conventional technique, when the attenuation on the high frequency side of the surface acoustic wave filter is improved, the pitch of the surface acoustic wave resonator is made smaller than the pitch of the surface acoustic wave filter. If the thickness of the surface acoustic wave resonator is the same as that of the surface acoustic wave resonator, the optimum film thickness of the surface acoustic wave resonator having higher frequency characteristics is smaller than the film thickness of the surface acoustic wave filter. However, since the surface acoustic wave filter and the surface acoustic wave resonator have the same film thickness, the electromechanical coupling coefficient of the surface acoustic wave resonator increases, and the resonance frequency of the surface acoustic wave resonator and the anti-resonance frequency are different. Since the interval becomes large, sufficient selectivity cannot be obtained, and there is a problem that the yield is deteriorated due to a shortage of attenuation in a stop band and a shortage of a margin for manufacturing variation.
[0008]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a high selectivity surface acoustic wave having an excellent selectivity near the pass band (an improved attenuation characteristic on the high band side of the pass band). A filter device and a communication device are provided.
[0009]
[Means for Solving the Problems]
A surface acoustic wave filter device according to the present invention includes a plurality of comb-shaped electrode portions arranged on a piezoelectric substrate along a propagation direction of a surface acoustic wave and is cascaded to solve the above problem. A surface acoustic wave filter device comprising two surface acoustic wave filter elements, wherein at least one surface acoustic wave resonator is connected in series between the two surface acoustic wave filter elements. Is characterized in that the frequency interval between the resonance frequency and the anti-resonance frequency is 0.65 times or more and 0.98 times or less the bandwidth of the two surface acoustic wave filter elements.
[0010]
According to the above configuration, the frequency interval between the resonance frequency and the antiresonance frequency of the surface acoustic wave resonator is set to be 0.65 times or more and 0.98 times or less the bandwidth of the two surface acoustic wave filter elements. As a result, it is possible to obtain a filter characteristic with high selectivity (the attenuation characteristic on the high frequency side of the pass band is improved).
[0011]
Further, in order to solve the above-described problem, the surface acoustic wave filter device of the present invention includes a plurality of comb-shaped electrode portions arranged on the piezoelectric substrate along the propagation direction of the surface acoustic wave and is cascaded. Surface acoustic wave filter comprising two surface acoustic wave filter elements, and two surface acoustic wave filter element portions in which a surface acoustic wave resonator is connected in series between the two surface acoustic wave filter elements An apparatus comprising: an unbalanced signal terminal commonly connected to two surface acoustic wave filter element units; and a balanced signal terminal connected to each of the two surface acoustic wave filter element units. In the surface acoustic wave filter element, a frequency interval between a resonance frequency and an anti-resonance frequency of the surface acoustic wave resonator is 0.65 times or more and 0.98 times or less of the bandwidth of the two surface acoustic wave filter elements. so It is characterized in Rukoto.
[0012]
According to the above configuration, the frequency interval between the resonance frequency and the antiresonance frequency of the surface acoustic wave resonator is set to be 0.65 times or more and 0.98 times or less the bandwidth of the two surface acoustic wave filter elements. As a result, it is possible to obtain a filter characteristic with high selectivity (the attenuation characteristic on the high frequency side of the pass band is improved). Furthermore, a balance-unbalance conversion function can be provided, and input and output can be set to different impedances.
[0013]
In order to set the frequency interval between the resonance frequency and the antiresonance frequency of the surface acoustic wave resonator to 0.65 times or more and 0.98 times or less of the bandwidth of the surface acoustic wave filter element as described above. It is preferable that the surface acoustic wave resonator is thinned and weighted. Furthermore, the thickness of the surface acoustic wave resonator may be smaller than the thickness of the surface acoustic wave filter. Further, a capacitance may be added in parallel to the surface acoustic wave resonator.
[0014]
Further, it is preferable that, in adjacent portions of the comb-shaped electrode portions adjacent to each other of the surface acoustic wave filter element, the grounded electrode fingers located closest to the most adjacent portion of each comb-shaped electrode portion are connected to each other. As a result, the number of grounding electrode pads can be reduced, and the size can be reduced.
[0015]
According to another aspect of the invention, there is provided a communication device including any one of the above-described surface acoustic wave filter devices. According to the above configuration, a filter function can be provided, and in addition, excellent attenuation characteristics outside the pass band and in the vicinity of the pass band are excellent, and particularly, there is an excellent characteristic that the amount of attenuation in the high band side of the pass band is large. However, by providing a surface acoustic wave filter device that can also have an unbalanced-balanced conversion function, it is possible to provide a communication device having a large attenuation on the high passband side.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
[Embodiment 1]
An embodiment of the present invention will be described below with reference to FIGS. In the present embodiment, a surface acoustic wave filter device for an advanced mobile phone service (AMPS) type transmission band filter will be described as an example. The required characteristics of the surface acoustic wave filter device are an insertion loss of 3 dB or less in a pass band (842 MHz to 849 MHz) and an attenuation of 35 dB in a stop band (864 MHz to 894 MHz). Actually, there is a frequency variation due to a temperature change and a variation at the time of manufacturing. Therefore, it is necessary to make the difference between the frequency at which the insertion loss becomes 3 dB and the frequency at which the insertion loss becomes 35 dB higher than the center frequency 12 MHz or less. The difference between the frequency at which the insertion loss is 3 dB on the higher frequency side than the center frequency and the frequency at which the insertion loss is 35 dB is referred to as selectivity.
[0017]
FIG. 1 shows a configuration of a main part of a surface acoustic wave filter device 100 according to the present embodiment. The surface acoustic wave filter device 100 has a configuration in which a first surface acoustic wave filter element 101 and a second surface acoustic wave filter element 102 are cascaded on a piezoelectric substrate (not shown). is there. A surface acoustic wave resonator 103 is connected in series between the first surface acoustic wave filter element 101 and the second surface acoustic wave filter element 102. In other words, the first surface acoustic wave filter element 101 and the second surface acoustic wave filter element 102 are cascade-connected via the surface acoustic wave resonator 103.
[0018]
The first surface acoustic wave filter element 101, the second surface acoustic wave filter element 102, and the surface acoustic wave resonator 103 are formed of, for example, Al electrodes. In the present embodiment, 39 ° YX LiTaO is used as the piezoelectric substrate. ₃ A substrate is used. Further, the present invention is not limited to this substrate. ₃ Substrate, 41 ° YcutX propagation LiNbO ₃ A substrate such as a substrate may be used.
[0019]
The configuration of the first surface acoustic wave filter element 101 is such that IDTs 104 and 106 are formed so as to sandwich a comb-shaped electrode portion (Inter-Digital Transducer, hereinafter referred to as IDT) 105 having a plurality of electrode fingers, and reflectors are provided on both sides thereof. 107 and 108 are formed. The ground-side electrode of the IDT 105 is grounded to IDTs 104 and 106 adjacent to the IDT 105 via electrode fingers.
[0020]
In the configuration of the second surface acoustic wave filter element 102, IDTs 109 and 111 are formed so as to sandwich the IDT 110, and reflectors 112 and 113 are formed on both sides thereof. The ground-side electrode of the IDT 110 is grounded to IDTs 109 and 111 adjacent to the IDT 110 via electrode fingers.
[0021]
The surface acoustic wave resonator 103 has a configuration in which reflectors 115 and 116 are formed so as to sandwich the IDT 114. The IDT 114 is weighted by thinning. Here, the term “thinning” refers to the following. While the original IDT has a structure in which electrode fingers having different electrical polarities are alternately arranged, a surface acoustic wave is excited and received. On the other hand, thinning means that electrode fingers having the same electrical polarity are used. It refers to a structure in which a portion is arranged and a portion that does not receive or receive a surface acoustic wave is provided.
[0022]
Further, in the present embodiment, IDT 105 of first surface acoustic wave filter element 101 is connected to input terminal 117. The IDT 110 of the second surface acoustic wave filter element 102 is connected to the output terminal 118.
[0023]
Here, FIG. 2 is a characteristic diagram showing positions of a resonance frequency (resonance point) and an anti-resonance frequency (anti-resonance point) in the surface acoustic wave filter device 100. Further, FIG. 2 shows the resonance frequency (resonance point) and the anti-resonance frequency (anti-resonance) of the surface acoustic wave filter device of the comparative example in which the thinning weight is not applied to the surface acoustic wave resonator 103 of the surface acoustic wave filter device 100. (Resonant point) is also shown.
[0024]
In the configuration of the surface acoustic wave filter device 100, at the resonance frequency of the surface acoustic wave resonator 103, the impedance of the surface acoustic wave resonator 103 is minimized and does not hinder signal transmission. However, at the anti-resonance frequency of the surface acoustic wave resonator 103, since the impedance of the surface acoustic wave resonator 103 is maximized, no signal is transmitted, and the transmission characteristic becomes an attenuation pole. Therefore, if the resonance frequency (resonance point) of the surface acoustic wave resonator 103 is set within the pass band and the anti-resonance frequency (anti-resonance point) is outside the pass band, the insertion loss of the pass band is not deteriorated. Attenuation poles can be created outside the passband. That is, the resonance point is set so as to be within the pass band of the surface acoustic wave filter device, and the anti-resonance point is set so as to be near the pass band higher side of the surface acoustic wave filter device. Further, as shown in FIG. 2, by applying a thinning weight to the surface acoustic wave resonator 103, the interval between the resonance frequency and the anti-resonance frequency of the surface acoustic wave resonator 103 is changed from 37.3 MHz to 29.5 MHz. Can be reduced to Thus, in the surface acoustic wave filter device 100, an attenuation pole can be formed in the vicinity of the pass band, so that filter characteristics with low loss and high selectivity can be obtained. However, if the interval between the resonance frequency and the anti-resonance frequency of the surface acoustic wave resonator is too small, there is a problem that the ripple deviation in the pass band increases.
[0025]
FIG. 3 shows the ratio γ / BW of the interval γ between the resonance frequency and the anti-resonance frequency of the surface acoustic wave resonator 103 to the bandwidth BW of the surface acoustic wave filter elements 101 and 102, and the pass band of the transmission characteristics. Is obtained by simulation calculation and shows the relationship with the selectivity on the high frequency side. From FIG. 3, if γ / BW is 0.98 or less, the selectivity becomes 12 MHz or less, and desired characteristics can be obtained.
[0026]
FIG. 4 shows the ratio γ / BW of the interval γ between the resonance frequency and the anti-resonance frequency of the surface acoustic wave resonator 103 to the surface acoustic wave filter elements 101 and 102, and the ripple deviation in the pass band in the transmission characteristics. FIG. It is considered that the ripple deviation in the pass band is desirably 1 dB or less. From FIG. 4, when γ / BW is smaller than 0.65, the ripple deviation becomes 1 dB or more, so γ / BW must be 0.65 or more.
[0027]
In the surface acoustic wave filter device 100 of the present embodiment, since the surface acoustic wave resonator 103 is thinned and weighted, the interval γ between the resonance frequency and the anti-resonance frequency of the surface acoustic wave resonator 103 is 29. 5 MHz, and the ratio γ / BW of the first surface acoustic wave filter element 101 and the second surface acoustic wave filter element 102 to the bandwidth of 32.8 MHz is 0.9. Therefore, in the surface acoustic wave filter device 100, the selectivity on the high frequency side is improved, the frequency interval from the insertion loss point of 3.0 dB to the point of 35 dB is 11.5 MHz, and the in-band ripple deviation is reduced. Good filter characteristics of 0.86 dB can be obtained.
[0028]
Further, FIG. 5 shows a comparison of frequency characteristics between the surface acoustic wave filter device 100 of the present embodiment and the surface acoustic wave filter device of the comparative example. In the surface acoustic wave filter device of the comparative example, since the surface acoustic wave resonator is not weighted by thinning, γ / BW is as large as 1.15. It can be seen that the surface acoustic wave filter device 100 of the present embodiment has higher selectivity on the high frequency side than the surface acoustic wave filter device of the comparative example.
[0029]
That is, in the surface acoustic wave filter device 100, the frequency interval between the resonance point and the anti-resonance point of the surface acoustic wave resonator 103 is different from that of the first surface acoustic wave filter element 101 and the second surface acoustic wave filter element 102. By setting the bandwidth to be 0.65 times or more and 0.98 times or less of the bandwidth, it is possible to obtain a filter characteristic with high selectivity (improved attenuation characteristics on the high frequency side of the pass band).
[0030]
Further, according to the above configuration, the ground-side electrodes of the IDTs 105 and 110 in the first surface acoustic wave filter element 101 and the second surface acoustic wave filter element 102 have the IDTs 104 and 106 adjacent to the IDTs 105 and 110, respectively. Since the electrodes 109 and 111 are grounded via the electrode fingers, a grounding pad and the like can be omitted, and the size can be reduced.
[0031]
Further, in the present embodiment, the interval γ between the resonance frequency and the anti-resonance frequency is reduced by applying a thinning weight to the surface acoustic wave resonator 103, but the thickness of the electrode forming the surface acoustic wave resonator is reduced. Thus, γ can be reduced. Further, by adding a capacitance in parallel to the surface acoustic wave resonator 103, the interval γ between the resonance frequency and the anti-resonator frequency can be reduced. Also in these cases, it is possible to obtain high selectivity filter characteristics by setting γ / BW to an appropriate value.
[0032]
[Embodiment 2]
The following will describe another embodiment of the present invention with reference to FIG.
[0033]
FIG. 6 shows a configuration of a main part of a surface acoustic wave filter device 200 according to the present embodiment. The surface acoustic wave filter device 200 has a configuration in which a first surface acoustic wave filter element 201 and a second surface acoustic wave filter element 202 are cascaded on a piezoelectric substrate (not shown). Surface acoustic wave resonators 203 and 204 are connected in series between the first surface acoustic wave filter element 201 and the second surface acoustic wave filter element 202. This will be described in more detail below.
[0034]
The first surface acoustic wave filter element 201, the second surface acoustic wave filter element 202, and the surface acoustic wave resonators 203 and 204 are formed of, for example, Al electrodes. In the present embodiment, 39 ° YX LiTaO is used as the piezoelectric substrate. ₃ A substrate is used. Further, the present invention is not limited to this substrate. ₃ Substrate, 41 ° YcutX propagation LiNbO ₃ A substrate such as a substrate may be used.
[0035]
In the configuration of the first surface acoustic wave filter element 201, IDTs 205 and 207 are formed so as to sandwich the IDT 206, and reflectors 208 and 209 are formed on both sides thereof.
[0036]
In the configuration of the second surface acoustic wave filter element 202, IDTs 210 and 212 are formed so as to sandwich the IDT 211, and reflectors 213 and 214 are formed on both sides thereof.
[0037]
The surface acoustic wave resonators 203 and 204 have a configuration in which reflectors 216 and 219 and reflectors 217 and 220 are formed so as to sandwich the IDTs 215 and 218, respectively. The IDTs 215 and 218 are weighted by thinning.
[0038]
The surface acoustic wave resonator 203 is connected in series between the IDT 205 of the first surface acoustic wave filter element 201 and the IDT 210 of the second surface acoustic wave filter element 202. Further, the surface acoustic wave resonator 218 is connected in series between the IDT 207 of the first surface acoustic wave filter element 201 and the IDT 212 of the second surface acoustic wave filter element 202.
[0039]
In the present embodiment, the IDT 206 of the first surface acoustic wave filter element 201 is connected to the input terminal 221. The IDT 211 of the second surface acoustic wave filter element 202 is connected to the output terminal 222.
[0040]
As described above, the interval γ between the resonance frequency and the anti-resonance frequency can be reduced by applying the thinning weight to the surface acoustic wave resonators 203 and 204, and γ / BW is set to 0 as in the first embodiment. By setting the selectivity and the ripple deviation in the range of 0.65 to 0.98, it is possible to provide a good surface acoustic wave filter device in which the selectivity on the high frequency side is improved.
[0041]
Further, in the present embodiment, the interval γ between the resonance frequency and the anti-resonance frequency is reduced by applying a thinning weight to the surface acoustic wave resonators 203 and 204, but the thickness of the electrode forming the surface acoustic wave resonator is reduced. Γ can be reduced by reducing the thickness. Further, by adding a capacitance in parallel to the surface acoustic wave resonators 203 and 204, the interval γ between the resonance frequency and the anti-resonator frequency can be reduced. Also in these cases, it is possible to obtain high selectivity filter characteristics by setting γ / BW to an appropriate value.
[0042]
[Embodiment 3]
The following will describe still another embodiment of the present invention with reference to FIG.
[0043]
FIG. 7 shows a configuration of a main part of a surface acoustic wave filter device 300 according to the present embodiment. The surface acoustic wave filter device 300 includes a first surface acoustic wave filter element 301, a second surface acoustic wave filter element 302, and a third surface acoustic wave filter element on a piezoelectric substrate (not shown). 303, a fourth surface acoustic wave filter element 304, and surface acoustic wave resonators 305 and 306. In the present embodiment, 39 ° YX LiTaO is used as the piezoelectric substrate. ₃ A substrate is used. Further, the present invention is not limited to this substrate. ₃ Substrate, 41 ° YcutX propagation LiNbO ₃ A substrate such as a substrate may be used.
[0044]
The first surface acoustic wave filter element 301 and the second surface acoustic wave filter element 302 are connected in cascade via a surface acoustic wave resonator 305, and these first surface acoustic wave filter elements 301, The second surface acoustic wave filter element 302 and the surface acoustic wave resonator 305 form a first surface acoustic wave filter element. The first surface acoustic wave filter element has the same configuration as the surface acoustic wave filter device 100 of the first embodiment. That is, the first surface acoustic wave filter element 301, the second surface acoustic wave filter element 302, and the surface acoustic wave resonator 305 are respectively the first surface acoustic wave filter device 100 of the first embodiment. This corresponds to the wave filter element 101, the second surface acoustic wave filter element 102, and the surface acoustic wave resonator 103.
[0045]
Further, the third surface acoustic wave filter element 303 and the fourth surface acoustic wave filter element 304 are cascade-connected via a surface acoustic wave resonator 306, and these third surface acoustic wave filter elements 303 , The fourth surface acoustic wave filter element 304 and the surface acoustic wave resonator 306 form a second surface acoustic wave filter element section. This second surface acoustic wave filter element has substantially the same configuration as surface acoustic wave filter device 100 of the first embodiment. That is, the third surface acoustic wave filter element 303, the fourth surface acoustic wave filter element 304, and the surface acoustic wave resonator 306 are respectively formed by the first surface acoustic wave filter device 100 of the first embodiment. This corresponds to the wave filter element 101, the second surface acoustic wave filter element 102, and the surface acoustic wave resonator 103. However, in the present embodiment, third surface acoustic wave filter element 303 differs from first surface acoustic wave filter element 101 in transmission phase characteristics by approximately 180 degrees. That is, the third surface acoustic wave filter element 303 is different from the first, second, and fourth surface acoustic wave filter elements 301, 302, and 304 in transmission phase characteristics by approximately 180 degrees. As a result, the transmission phase characteristics of the first surface acoustic wave filter element and the second surface acoustic wave filter element are different from each other by approximately 180 degrees.
[0046]
The first surface acoustic wave filter element 301 and the third surface acoustic wave filter element 303 are connected to the input terminal 310 in parallel. The second surface acoustic wave filter element 302 and the fourth surface acoustic wave filter element are connected to output terminals 311 and 312, respectively, in series. That is, the first surface acoustic wave filter element unit and the second surface acoustic wave filter element unit are connected to the input terminal 310 after being shared on one side, and connected to the output terminals 311 and 312 on the other side. ing. This allows the input side to be unbalanced and the output side to be balanced. Further, the impedance of the output terminals 311 and 312 can be approximately four times higher than the impedance of the input terminal 310.
[0047]
As described above, the interval γ between the resonance frequency and the anti-resonance frequency can be reduced by applying the thinning weight to the surface acoustic wave resonators 305 and 306, and by setting γ / BW to an appropriate value, A good surface acoustic wave filter device having improved selectivity on the high frequency side can be provided.
[0048]
Further, in the present embodiment, the interval γ between the resonance frequency and the anti-resonance frequency is reduced by applying a thinning weight to the surface acoustic wave resonators 305 and 306, but the electrode thickness forming the surface acoustic wave resonator is reduced. Γ can be reduced by reducing the thickness. Further, by adding capacitance in parallel to the surface acoustic wave resonators 305 and 306, the interval γ between the resonance frequency and the anti-resonator frequency can be reduced. Also in these cases, as in Embodiment 1, good filter characteristics can be obtained by setting γ / BW in the range of 0.65 to 0.98 to obtain desired selectivity and ripple deviation. Is possible. Furthermore, a balance-unbalance conversion function can be provided, and input and output can be set to different impedances.
[0049]
The present invention is not limited to the embodiments described above, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.
[0050]
Next, a communication device using the surface acoustic wave filter device described in the above embodiment will be described with reference to FIG. The communication device 600 includes an antenna 601, an antenna common unit / RFTop filter 602, an amplifier 603, an Rx interstage filter 604, a mixer 605, a first IF filter 606, a mixer 607, and a second IF filter 608 on the receiver side (Rx side) that performs reception. It comprises a 1st + 2nd local synthesizer 611, a TCXO (temperature compensated crystal oscillator) 612, a divider 613, and a local filter 614.
[0051]
As shown by the double line in FIG. 8, it is preferable to transmit each balanced signal from the Rx interstage filter 604 to the mixer 605 in order to ensure balance.
[0052]
In addition, the communication device 600 shares the antenna 601 and the antenna common unit / RFTop filter 602 as a transceiver side (Tx side) that performs transmission, and also includes a Tx IF filter 621, a mixer 622, a Tx interstage filter 623, and an amplifier. 624, a coupler 625, an isolator 626, and an APC (automatic power control) (automatic output control) 627.
[0053]
The surface acoustic wave filter device described in the present embodiment can be suitably used for the Rx interstage filter 604, the 1st IF filter 606, the TxIF filter 621, and the Tx interstage filter 623.
[0054]
The surface acoustic wave filter device according to the present invention can have a filter function, and further, has excellent attenuation characteristics outside the pass band and in the vicinity of the pass band. It has the characteristics described above. Further, an unbalanced-balanced conversion function can be provided. Therefore, the communication device of the present invention having the surface acoustic wave filter device can improve transmission characteristics.
[0055]
【The invention's effect】
As described above, the surface acoustic wave filter device according to the present invention includes a plurality of comb-shaped electrode portions arranged on the piezoelectric substrate along the propagation direction of the surface acoustic wave, and the two cascade-connected surface acoustic wave devices. A surface acoustic wave filter device having a surface acoustic wave filter element, wherein a surface acoustic wave resonator is connected in series between the two surface acoustic wave filter elements. Is between 0.65 and 0.98 times the bandwidth of the two surface acoustic wave filter elements. This makes it possible to improve the attenuation of the pass band on the high frequency side.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a surface acoustic wave filter device according to one embodiment.
FIG. 2 is a characteristic diagram showing positions of a resonance point and an anti-resonance point in the surface acoustic wave filter device and a surface acoustic wave filter device of a comparative example.
FIG. 3 is a graph showing a relationship between γ / BW and selectivity of a surface acoustic wave resonator in the surface acoustic wave filter device.
FIG. 4 is a graph showing a relationship between γ / BW and a ripple deviation of a surface acoustic wave resonator in the surface acoustic wave filter device.
FIG. 5 is a graph comparing frequency characteristics of the surface acoustic wave filter device and a surface acoustic wave filter device of a comparative example.
FIG. 6 is a schematic configuration diagram of a surface acoustic wave filter device according to another embodiment of the present invention.
FIG. 7 is a schematic configuration diagram of a surface acoustic wave filter device according to still another embodiment of the present invention.
FIG. 8 is a main block diagram of a communication device using the surface acoustic wave filter device according to the embodiment.
[Explanation of symbols]
100 Surface acoustic wave filter device
101 First surface acoustic wave filter element
102 Second surface acoustic wave filter element
103 surface acoustic wave resonator
104, 105, 106 IDT (comb electrode)
109, 110, 111 IDT (comb type electrode part)
107, 108, 112, 113, 115, 116 reflector
300 surface acoustic wave filter device
301 First SAW Filter Element
302 Second surface acoustic wave filter element
303 Third SAW Filter Element
304 Fourth surface acoustic wave filter element
305, 306 surface acoustic wave resonator

Claims (7)

The piezoelectric device includes a plurality of comb-shaped electrode portions arranged on a piezoelectric substrate along a propagation direction of the surface acoustic wave, and two cascade-connected surface acoustic wave filter devices. A surface acoustic wave filter device in which at least one surface acoustic wave resonator is connected in series between
A frequency interval between a resonance frequency and an anti-resonance frequency of the surface acoustic wave resonator is 0.65 times or more and 0.98 times or less of a bandwidth of the two surface acoustic wave filter elements. Surface acoustic wave filter device. The piezoelectric device includes a plurality of comb-shaped electrode portions arranged on a piezoelectric substrate along a propagation direction of the surface acoustic wave, and two cascade-connected surface acoustic wave filter devices. A surface acoustic wave filter device comprising two surface acoustic wave filter element portions in which a surface acoustic wave resonator is connected in series,
An unbalanced signal terminal commonly connected to the two surface acoustic wave filter element units, and a balanced signal terminal connected to each of the two surface acoustic wave filter element units;
In each surface acoustic wave filter element, the frequency interval between the resonance frequency and the antiresonance frequency of the surface acoustic wave resonator is 0.65 times or more of the bandwidth of the two surface acoustic wave filter elements and 0.98 or more. A surface acoustic wave filter device characterized by being no more than twice. The surface acoustic wave filter device according to claim 1, wherein the surface acoustic wave resonator is weighted by thinning. The surface acoustic wave filter device according to any one of claims 1 to 3, wherein a film thickness of the surface acoustic wave resonator is smaller than a film thickness of the two surface acoustic wave filter elements. The surface acoustic wave filter device according to any one of claims 1 to 4, wherein a capacitance is added to the surface acoustic wave resonator in parallel. An adjacent portion of the comb-shaped electrode portions adjacent to each other of the surface acoustic wave filter element, wherein grounded electrode fingers located closer to the nearest portion of each comb-shaped electrode portion are connected to each other. Item 6. The surface acoustic wave filter device according to any one of Items 1 to 5. A communication device comprising the surface acoustic wave filter device according to any one of claims 1 to 6.

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