WO1998000914A1 - Surface acoustic wave device - Google Patents

Abstract

First and second acoustic wave filters (103 and 104) which are so connected in parallel that the phases of their electric signals output to first and second output terminals (102a and 102b) may be different from each other by substantially 180° and which have slightly different passbands. They are formed on a piezoelectric substrate between an input terminal (101) and the output terminals (102a and 102b). The acoustic wave filters (103 and 104) thus connected in one stage have small input-output impedances in the passband. The chip size of the device is small. The device has excellent frequency characteristics which are nearly equivalent to those of acoustic wave filters connected in series in two stages.

Description

 Specification

 Surface acoustic wave device

Technical field

 The present invention relates to a surface acoustic wave device, and more particularly to a surface acoustic wave filter. Background art

A surface acoustic wave device converts an electric signal into a surface acoustic wave by means of a comb-shaped electrode (IDT _: Interdigital Transducer) provided on a piezoelectric substrate, and converts the surface acoustic wave propagating on the piezoelectric substrate. It is also a device that receives by IDT provided on the piezoelectric substrate and uses the frequency characteristics related to the conversion between electric signals and surface acoustic waves.

 In recent years, surface acoustic wave devices such as surface acoustic wave filters have been widely used due to their advantages of being thin and compact, such as mobile phones. Among them, the intermediate frequency (IF) stage (approximately 240 MHz) of the mobile phone system in Japan (PHS: Persona 1H andy-phone System), which has just recently become popular, is about 0.1 A surface acoustic wave filter with steep out-of-band attenuation characteristics with a fractional bandwidth of about% is required.

In such applications, relatively electromechanical coupling coefficient k ² in linear coefficient of the frequency temperature characteristic 0 is as large as about 1%, and the reflection coefficient of the elastic sheet surface wave is approximately 3% per one I DT Large 45 ° X-cut Z-propagating LB 0 substrate

(45 ° X—ZLB0: Japanese Patent Application Laid-Open No. 60-25901) is expected to be used. With this LB 0 substrate, using a quartz substrate (the frequency temperature characteristics of the linear coefficient ^{= 0, k 2 = 0. 15} %, the reflection coefficient = 0.7% of the surface acoustic wave per one IDT) Surface acoustic wave element There is an advantage that the surface acoustic wave device can be downsized.

 One example of a conventional surface acoustic wave device using the LB0 substrate will be described with reference to FIGS.

 FIG. 18 is a diagram schematically showing an electrode pattern of a surface acoustic wave device 900 provided on a 45 ° X cut Z-propagating LB0 substrate as a piezoelectric substrate and disposed on the substrate. .

 This surface acoustic wave device 900 is configured by connecting four stages of surface acoustic wave filters 901 to 904 each including one excitation IDT, two reception IDTs, and two reflection electrodes. The surface acoustic wave filter 901 has an excitation IDT 911, which is located at the center, and reception IDTs 91, 931, which are arranged on both sides thereof. Are located. The elastic surface wave filters 902 to 904 have the same configuration.

 In this surface acoustic wave device, the electric signal is input to the excitation IDT 911 of the surface acoustic wave filter 90 1. Here, the electric signal is converted to a surface acoustic wave, propagates to both sides of the excitation IDT 911, and is converted again to an electric signal at the reception IDTs 921, 931. The reception IDT 921 of the surface acoustic wave filter 901 and the excitation IDT 922 of the surface acoustic wave filter 902, as well as the reception IDT 91 and the excitation IDT 932, are electrically connected. The electric signal output from the surface acoustic wave filter 901 is excited by the surface acoustic wave filter 902, and is converted again to surface acoustic waves by the IDTs 922 and 932, and is transmitted to the IDT 912 to receive the IDT. It is output as an electrical signal from 9 12.

 In Fig. 18, the surface acoustic wave filters 903 and 904 are a repetition of the surface acoustic wave filters 901 and 902, and the overall configuration is such that the surface acoustic wave filters are connected in series in four stages. .

1 9 to the excitation I DT of 20.5 pairs, receiving I DT 8 pairs and 3 the incoming received IDT distance and _{λ (λ = V / f n} ; v s is the phase velocity of the surface acoustic wave, Is the center frequency at which the surface acoustic wave filter operates), the distance between the receiving IDT and the reflecting electrode is 0.375 λ, the number of reflecting electrodes is 120, the excitation IDT, the receiving IDT and the length of the reflecting electrode (aperture ) Is 0.72 mm, and the input-output termination impedance is 400 Ω. The frequency characteristics obtained by the simulation are shown. Here, a surface acoustic wave filter with a passband of about 300 KHz and large attenuation is obtained.

 In the surface acoustic wave filters exemplified in FIGS. 18 and 19, the aperture of one surface acoustic wave filter is as large as 0.72 mm, and the chip size is the bonding pad width for wire bonding ( Includes about 0.15 mm square), it is about 2.5 mm X 4.1 mm square even if it is small, and there is a problem that it becomes large.

 Also, in an actual surface acoustic wave filter, there is a problem that the electric resistance increases due to the long electrode length, and the loss as a surface acoustic wave filter increases.

 If the aperture is wider, higher-order transverse mode spurs such as the third and fifth harmonics are generated as shown in Fig. 19, and the surface acoustic wave filter There is a problem that characteristics are deteriorated. To suppress this lateral mode spur, the excitation IDT and the reception ID are weighted, and the excitation distribution of the surface acoustic wave in the direction perpendicular to the surface acoustic wave propagation direction is biased toward the center of the IDT. However, in this method, the impedance of the surface acoustic wave filter is high, and there is a problem that the aperture must be set wider to lower the impedance.

The present invention has been made to solve such a problem. That is, an object of the present invention is to provide a surface acoustic wave device having a wide pass frequency band, excellent cutoff characteristics, and low impedance. Also, at the same time An object of the present invention is to provide a surface acoustic wave device which can be downsized in size and is particularly suitable for mobile communication and portable information equipment.

 The present invention aims to provide a surface acoustic wave device having a small insertion loss.

 Another object of the present invention is to provide an elastic surface acoustic wave device having small transverse mode spurious characteristics and excellent out-of-band characteristics. Disclosure of the invention

 The present invention has the following configuration in order to solve the above-mentioned problems.

 The surface acoustic wave device according to the present invention comprises: a two-port piezoelectric substrate having a center frequency fl disposed between a first input terminal and a first output terminal on the piezoelectric substrate. A first surface acoustic wave filter of I DT (Inter Digital Transducer), and disposed in parallel with the first surface acoustic wave filter between the first input terminal and the first output terminal. A 2 port 3 IDT second surface acoustic wave filter having a center frequency f 2 slightly different from the center frequency fl, wherein the first surface acoustic wave filter and the second The surface acoustic wave filter includes: a phase of a signal output from the first input terminal to the first output terminal via the first surface acoustic wave filter; and a second surface acoustic wave filter. And the phase of the signal output to the first output terminal via It is characterized by being arranged at an angle of 80 °.

 The first surface acoustic wave filter and the second surface acoustic wave filter excite surface acoustic waves having a phase substantially different by 180 ° with respect to a signal input to the first input terminal. You may do so.

For example, the first surface acoustic wave filter is connected to the first input terminal. A first excitation IDT that excites a first surface acoustic wave by an electric signal input to the first input terminal; and a first excitation IDT disposed on both sides of the first excitation IDT. A first reception IDT and a second reception IDT that receive a surface acoustic wave and convert it into an electric ft signal, and wherein the second surface acoustic wave filter is connected to the first input terminal. A second excitation IDT that excites a second surface acoustic wave having a 180 ° phase difference from the first surface acoustic wave by an electric signal input to the first input terminal; and A third reception IDT and a fourth reception IDT that are provided on both sides of the excitation IDT and receive the second surface acoustic wave and convert it into an electric signal may be provided.

 The first surface acoustic wave filter and the second surface acoustic wave filter excite a surface acoustic wave having substantially the same phase with respect to a signal input to the first input terminal. Alternatively, the surface acoustic wave may be converted into an electric signal so that the phase is substantially different by 180 °.

 For example, the first surface acoustic wave filter is connected to the first input terminal, and the first surface acoustic wave filter excites the first surface acoustic wave by an electric signal input to the first input terminal. 1 excitation IDT, and a first reception IDT and a second reception IDT that are disposed on both sides of the first excitation IDT and receive the first surface acoustic wave and convert it into an electric signal. The second surface acoustic wave filter is connected to the first input terminal, and excites the first surface acoustic wave with an electric signal input to the first input terminal. An IDT, disposed on both sides of the second excitation IDT, receiving the first surface acoustic wave, and having a phase of substantially 180 ° with the first reception IDT and the second reception IDT. A third receiving IDT and a fourth receiving IDT for converting into different electrical signals. You may.

The piezoelectric substrate is an electromechanical coupling unit for surface acoustic waves propagating on the substrate. It is preferable to use one having a number k ² of about 1% and a reflection coefficient of the surface acoustic wave per IDT of about 3% or more.

 For example, as the piezoelectric substrate, for example, lithium tetraborate may be used.

 Further, as will be described in detail later, it is preferable that the first center frequency and the second center frequency are different from each other by about 0.10% to about 0.18%.

 Further, the cross width of the comb tooth-shaped electrodes constituting each IDT may be set to be about 10 times or less the arrangement period of the comb tooth-shaped electrodes. Thereby, higher-order transverse mode spurious can be suppressed.

 Such a surface acoustic wave device of the present invention in which the first surface acoustic wave filter having slightly different center frequencies and the second surface acoustic wave filter are connected in anti-phase parallel, has the same piezoelectric property. A plurality of stages may be cascaded on a substrate.

The surface acoustic wave device of the present invention having such a configuration is provided with a piezoelectric substrate, and disposed on the piezoelectric substrate between a first input terminal, a first output terminal, and a second output terminal. A first SAW filter of a two-port 3 IDT having a center frequency f 1, and the first SAW filter disposed between the first input terminal, the first output terminal, and the second output terminal. A 2 port 3 IDT second surface acoustic wave filter having a center frequency f 2 slightly different from the center frequency fl, disposed in parallel with the surface acoustic wave filter of A third surface acoustic wave filter of a 2-port 3 IDT having a center frequency f 1 and disposed between a second output terminal and a third output terminal; the first output terminal and the third output terminal; Between the second output terminal and the third output terminal in parallel with the third surface acoustic wave filter. Is set, the two-port 3 ID fourth SAW Fuiruku and the ingredients of Τ having the center frequency I 2 Wherein the first surface acoustic wave filter and the second surface acoustic wave filter are connected to the first output terminal via the first input terminal via the first surface acoustic wave filter. And the phase of the signal output to the first output terminal via the second surface acoustic wave filter is substantially different by 180 °. The third surface acoustic wave filter and the fourth surface acoustic wave filter are connected to the first output terminal and the second output terminal via the third surface acoustic wave filter. The phase of the signal output to the third output terminal is substantially 180 ° different from the phase of the signal output to the third output terminal via the fourth surface acoustic wave filter. It is characterized by being arranged as follows.

 That is, the first-stage filter is constituted by the first surface acoustic wave filter and the second surface acoustic wave filter, and the second-stage filter is constituted by the third surface acoustic wave filter and the fourth surface acoustic wave filter. These two filters are cascaded on the same piezoelectric substrate.

The first-stage filter and the second-stage filter may or may not have the same configuration. For example, the first-stage filter employs a configuration in which surface acoustic waves of the opposite phase are excited to receive in-phase, and the second stage filter excites surface acoustic waves of the same phase to receive in the opposite phase. A configuration may be adopted. For example, a first input terminal, a first excitation IDT connected to the first input terminal, and exciting a first surface acoustic wave by an electric signal input to the first input terminal; and A first receiving IDT and a second receiving IDT that are disposed on both sides of the first excitation IDT and receive the first surface acoustic wave and convert the same into an electric signal; The first surface acoustic wave filter is connected to the first input terminal and the electric signal input to the first input terminal has a phase of substantially 180 ° with the first surface acoustic wave. A second excitation IDT that excites a different second surface acoustic wave of The first center frequency, which is provided on both sides of the second excitation IDT and includes a third reception IDT and a fourth reception IDT that receive the second surface acoustic wave and convert it into an electric signal; A second surface acoustic wave filter having a second center frequency slightly different from the first surface ID, a first output terminal connected in parallel with the first reception IDT and the third reception IDT, and the second A second output terminal connected in parallel to the reception IDT and the fourth reception IDT, a second input terminal connected to the first output terminal, and a third connection connected to the second output terminal An input terminal, connected to the second input terminal, a third excitation IDT for exciting a third surface acoustic wave by an electric signal input to the input terminal, and connected to the third input terminal. A fourth excitation for exciting the third surface acoustic wave by an electric signal input to the input terminal. An IDT, and a fifth reception IDT that is provided between the third excitation IDT and the fourth excitation IDT and receives the third surface acoustic wave and converts it into an electric signal. The third surface acoustic wave filter having a first center frequency is connected to the second input terminal, and the third surface acoustic wave is excited by an electric signal input to the input terminal. The fifth excitation IDT, the sixth excitation IDT connected to the third input terminal, and exciting a fourth surface acoustic wave by an electric signal input to the input terminal; and the fifth excitation IDT. A sixth reception IDT disposed between the excitation IDT and the sixth excitation IDT, the sixth reception IDT receiving a fourth surface acoustic wave and converting the same into an electric signal; A fourth surface acoustic wave filter, a third reception IDT connected in parallel with the fifth reception IDT and the sixth reception IDT, An output terminal may be provided.

That is, the surface acoustic wave device of the present invention comprises: a piezoelectric substrate; a piezoelectric substrate formed on the piezoelectric substrate; a first input terminal and a first output terminal; and a first input terminal and a second output terminal. Signal input from the first input terminal The signal having the first center frequency is interpolated in parallel so that the phases of the signals output to the first and second output terminals are different from each other by 180 ° with respect to the phase of / 212. A first surface acoustic wave filter and a second surface acoustic wave filter having a second center frequency slightly different from the first center frequency.

 Further, a surface acoustic wave device according to the present invention includes a piezoelectric substrate, formed on the piezoelectric substrate, between a first input terminal and a first output terminal, and between a first input terminal and a second output terminal. Between the first and second output terminals with respect to the phase of the signal input from the first input terminal so that the phases of the signals output from the first and second output terminals differ from each other by 180 °. A first surface acoustic wave filter having a first center frequency and a second surface acoustic wave filter having a second center frequency slightly different from the first center frequency, formed on the piezoelectric substrate. Between the second input terminal and the third output terminal and between the third input terminal and the third output terminal with respect to the phase of the signal input from the second and third input terminals. In parallel so that the phases of the signals output to the third output terminal differ by 180 ° from each other. A third surface acoustic wave filter having a first center frequency, and a fourth surface acoustic wave filter having a second center frequency, between a first output terminal and a second human terminal, and Connection means for electrically connecting between the second output terminal and the third input terminal.

 Also, the surface acoustic wave device of the present invention is connected in parallel with a piezoelectric substrate so that the phases of electric signals formed on the piezoelectric substrate and output to the output terminals are different from each other by 180 ° between the input and output terminals. A first surface acoustic wave filter and a second surface acoustic wave filter having slightly different pass frequency bands.

As described above, as the piezoelectric substrate constituting the surface acoustic wave device of the present invention, It is preferable to use four-layered lithium Li ₂ B _{4 7} . The elastic surface wave device of the present invention can obtain a greater effect by using lithium tetraborate Li ₂ B 0 _?. Similar effects can be obtained by using a piezoelectric substrate material other than lithium tetraborate that has an electromechanical coupling coefficient of about 1% and a surface acoustic wave reflection coefficient per IDT of about 3% or more. Can be.

 In the case of lithium tetraborate, when the cutout angle and the direction of surface acoustic wave propagation from a single crystal of lithium tetraborate are displayed as (90 ° + ci, 90 ° 13, 90 ° + 7), α = + 38 ° to ten 52. , / 8 = —5. It should be set in the range of + 5 ° and 7 = —10 ° to + 10 °. Further, it is preferable that the intersecting width of the comb-teeth-shaped electrode pairs that face each other and constitute each ID is 10 times or less the period of the comb-teeth-shaped electrodes.

 In order to suppress the occurrence of lateral mode spurious, it is preferable that the first center frequency and the second center frequency are set to be different from each other by 0.10 to 0.18%. When connecting the surface acoustic wave filter pairs connected in anti-parallel parallel connection in more stages, the surface acoustic wave filter pairs that constitute each stage are resilient so that their center frequencies differ by 0.10 to 0.18%. What is necessary is just to make it consist of surface wave filters. For example, a third surface acoustic wave filter having a first center frequency and a fourth surface acoustic wave filter having a center frequency different from the third surface acoustic wave filter by 0.10 to 0.18% are provided by a surface acoustic wave filter. An evening pair may be formed.

As described above, the surface acoustic wave device according to the present invention connects the first surface acoustic wave filter and the second surface acoustic wave The signal phase between the input and output of the filter and the second surface acoustic wave filter is changed by 180 °, and the center frequencies of the first surface acoustic wave filter and the second surface acoustic wave filter are slightly different. Thus, the impedance in the pass frequency band of the surface acoustic wave device is reduced, and the attenuation of the stop band is secured. Further, the surface acoustic wave element can be downsized.

 That is, the surface acoustic wave device of the present invention reverses the first surface acoustic wave filter having the first center frequency and the second surface acoustic wave filter having the second center frequency between the input and output terminals. They are connected in parallel.

The first center frequency f ₁ and the Ri second center frequency f 0. 1 0 to 0. Are shifted approximately 1-8%. Here, the center frequency fi is f,. = V, where I is the pitch of the comb-like electrode composing the surface acoustic wave filter, and V is the phase velocity of the surface acoustic wave propagating through the piezoelectric substrate. It is assumed to be displayed in Z.

 S 1

Then, in the surface acoustic wave device of the present invention, the first surface acoustic wave filter having the center frequency f and the _second surface acoustic wave filter having the center frequency f ₂ are provided between the input terminal and the output terminal. The phase of the signal output from the input terminal is different from the phase of the signal input from the input terminal by 180 °, that is, they are interpolated in anti-phase parallel.

 FIG. 1 is a diagram schematically showing one example of an electrode pattern constituting a surface acoustic wave device of the present invention.

The surface acoustic wave device 100 illustrated in FIG. 1 has a conductive pattern including an IDT formed on a piezoelectric substrate, and includes a first input terminal 101 and a first output terminal 102. a and a second output terminal 102 b between the first surface acoustic wave filter 103 having a center frequency f. and the second surface acoustic wave filter 110 having a center frequency f ₂ . And are connected in anti-phase parallel.

FIG. 2 shows a first surface acoustic wave filter 103 a and a second surface acoustic wave filter 1 in a surface acoustic wave device 100 a having the same configuration as the surface acoustic wave device 100 illustrated in FIG. FIG. 4 is a diagram schematically showing one example of anti-phase parallel connection with 04a. The first surface acoustic wave filter 103a is connected to an input terminal 101 to excite a surface acoustic wave formed, and a first excitation IDT 11 1 and this first excitation IDT 11 1 1 A first reception IDT 112 and a second reception IDT 113 that receive a surface acoustic wave and that are formed in a plane-symmetric pattern so as to sandwich the first and second reception IDTs 113 and 113. Of two reflective electrodes 114 arranged to form a cavity with the excitation IDT 111, the first reception IDT 112, and the second reception IDT 113 interposed. Have been.

 The second surface acoustic wave filter 104a has the same configuration. In other words, the second surface acoustic wave filter 104a sandwiches the second excitation IDT 121 that excites a surface acoustic wave formed by being connected to the input terminal 101 and the second excitation IDT 121. A third receiving IDT 122 and a fourth receiving IDT 123 that receive a surface acoustic wave and are formed in a plane-symmetric pattern as described above, and a second excitation IDT further outside these receiving IDTs. 121, and two reflective electrodes 124 disposed so as to form a cavity with the third reception IDT 122 and the fourth reception IDT 123 interposed therebetween. The first excitation IDT 121 of the first surface acoustic wave filter 103 a and the second excitation IDT 121 of the second surface acoustic wave filter 104 a are connected in parallel to the input terminal 101. The IDTs are connected, and each of the IDTs is composed of a pair of comb-toothed electrodes facing each other. Then, one of the comb-like electrodes 1 1 1 a constituting the first excitation I DT 1 1 1 of the first surface acoustic wave filter 103 a is connected to the input terminal 101, and the other is The comb-shaped electrode is connected to the reference potential side 111b.

On the other hand, in the second excitation IDT 121, the comb-shaped electrode 121b corresponding to the comb-shaped electrode 111b connected to the reference potential side of the first excitation IDT 111 is connected to the input terminal 101. And the first excitation I DT 11 1 A comb-like electrode 121a corresponding to the comb-like electrode 111a connected to the input terminal 101 of JP97 / 02212 is connected to the reference potential side. By connecting the first excitation IDT 1 11 1 and the second excitation IDT 121 in this way, the surface acoustic wave excited by the first excitation IDT 1 11 1 and the second excitation IDT 121 are connected to each other. As a result, the surface acoustic wave whose phase is shifted by 180 ° is excited.

 On the other hand, the first reception IDT 112 and the second reception IDT 113 of the first surface acoustic wave filter 103a are also the third reception IDT 122 and the second reception IDT 112 of the second surface acoustic wave filter. The four reception IDTs 123 also include a pair of comb-tooth electrodes facing each other.

 The first reception IDT 12 of the first surface acoustic wave filter 103a and the third reception IDT 122 of the second surface acoustic wave filter are formed in a plane-symmetric pattern, and the comb-shaped electrode 112a And the comb-shaped electrode 122b are connected to the first output terminal 102a. Each of the comb-like electrodes 112b and 122a is connected to a reference potential.

 In addition, the second reception IDT 113 of the first surface acoustic wave filter 103a and the fourth reception IDT 123 of the second surface acoustic wave filter 104a are also formed in a plane symmetric pattern. The comb-shaped electrode 113a and the comb-shaped electrode 123b are connected to the second output terminal 102b. The comb-shaped electrode 113b and the comb-shaped electrode 123a are each connected to a reference potential.

 Therefore, the reception I DT 112 of the first surface acoustic wave filter 103a,

Between 113 and the receiving IDTs 122 and 123 of the second surface acoustic wave filter 104a, the propagated surface acoustic waves are converted into electric signals without any phase shift.

In other words, the first output terminal 102a and the second output terminal 102b output the signal phase passing through the first surface acoustic wave filter 103a and the signal phase passing through the second surface acoustic wave filter 104a. 180 degrees from the signal phase It will be output as an electric signal in the state where it was turned off.

 In the first surface acoustic wave filter 103a and the second surface acoustic wave filter 104a that are connected in anti-parallel and parallel as illustrated in FIG. 2, the phase is determined by the first excitation IDT and the second excitation IDT. A surface acoustic wave shifted by 180 ° will be excited.

 The method of connecting the first surface acoustic wave filter and the second surface acoustic wave filter in anti-phase parallel connection is not limited to the connection illustrated in FIG. 2 .For example, in the case of the excitation IDT, the in-phase surface acoustic waves are excited. The phase may be shifted when the surface acoustic waves are received by the reception IDTs of the first surface acoustic wave filter and the second surface acoustic wave filter.

 FIG. 3 is a diagram schematically illustrating an example of anti-phase parallel connection of the first surface acoustic wave filter 103a and the second surface acoustic wave filter 104b in the surface acoustic wave device 100b. . In the first surface acoustic wave filter 103a and the second surface acoustic wave filter 104b of the surface acoustic wave device 100b, the excitation IDT excites the same phase surface acoustic wave, and the received IDT The connection is such that the phases are shifted.

 The first surface acoustic wave filter 103a of the surface acoustic wave device 100b has the same configuration as that of the above-described first surface acoustic wave filter 103a. The second surface acoustic wave filter 104b is connected to the input terminal 101 to excite a formed surface acoustic wave, and the second excitation IDT 131 is symmetric with respect to the second excitation IDT 131. A third reception IDT 132 and a fourth reception IDT 133 for receiving the surface acoustic wave formed in a pattern, and further outside these reception IDTs, a second excitation IDT 131, a third And two reflective electrodes 134 disposed so as to form a cavity with the receiving IDT 132 and the fourth receiving IDT 133 interposed therebetween.

Ό o The first excitation I DT lll of the first surface acoustic wave filter 103a and the second excitation I DT 131 of the second surface acoustic wave filter 104b are connected in parallel to the input terminal 101. , And each is composed of a pair of comb-shaped electrodes opposed to a plane symmetric pattern. One of the comb-shaped electrodes 111 a constituting the first excitation IDTll of the first surface acoustic wave filter 103 a is connected to the input terminal 101, and the other comb-shaped electrode is connected to the reference terminal. Connected to potential side 1 1 1 b.

 Also in the second excitation IDT 131, the comb-shaped electrode 131b corresponding to the comb-shaped electrode 1 11a connected to the input terminal 101 of the first excitation IDT 1 11 1 is connected to the input terminal 101. The comb-shaped electrode 131a corresponding to the comb-shaped electrode 111b connected to the reference potential side of the first excitation IDTll is connected to the reference potential side.

 By connecting the first excitation I DT I 11 and the second excitation I DT 1 31 in this way, unlike the anti-parallel parallel connection illustrated in FIG. 2, the first excitation I DT Ill The SAW having the same phase is excited by the second excitation IDT 131 and the second excitation.

 On the other hand, the first reception IDT 12 and the second reception IDT 113 of the first surface acoustic wave filter 103 are also the third reception IDT 132 and the fourth reception IDT 132 of the second surface acoustic wave filter. IDT 133 is also composed of a pair of comb-shaped electrodes facing each other.

 The first reception IDTI 12 of the first surface acoustic wave filter 103a and the third reception IDT 132 of the second surface acoustic wave filter are formed in the same pattern, and have a comb-shaped electrode. 112a and the comb-shaped electrode 132b are connected to the first output terminal 102a.

That is, the comb tooth-shaped electrode 132b corresponding to the comb-shaped electrode 112b connected to the reference potential of the first reception IDTI 12 is connected to the first output terminal 102a. The comb-shaped electrode 132a corresponding to the comb-shaped electrode 112a connected to the first output terminal 102a of the first reception IDT 112 is connected to the reference potential. I have.

 The second reception IDT 113 of the first surface acoustic wave filter 103a and the fourth reception IDT 133 of the second surface acoustic wave filter 104b are similarly connected.

 The second reception IDT 133 of the first surface acoustic wave filter 103a and the fourth reception IDT 133 of the second surface acoustic wave filter 104b are similarly connected.

 That is, a comb-like electrode 133b corresponding to the comb-like electrode 113b connected to the reference potential of the second reception IDT 113 is connected to the first output terminal 102b, A comb-shaped electrode 133a corresponding to the comb-shaped electrode 113a connected to the first output terminal 102b of the second reception IDT 113 is connected to the reference potential.

 Therefore, in the first surface acoustic wave filter 103a and the second surface acoustic wave filter 104b, the in-phase surface acoustic waves excited by the first excitation IDT 111 and the second excitation IDT 131 are used. The wave has a phase of 180 at the receiving IDT. It will be converted to an electrical signal in a shifted state o

 That is, the first output terminal 102a and the second output terminal 102b are connected to the phase of the signal passing through the first surface acoustic wave filter 103a and the second output terminal 102b through the second surface acoustic wave filter 104b. The signals are output as electrical signals 180 ° out of phase with each other.

FIG. 4 is a diagram schematically showing one example of a surface acoustic wave device 100 in which a first surface acoustic wave filter 103a and a second surface acoustic wave finolator 104c are connected in anti-phase parallel. The first surface acoustic wave of this surface acoustic wave device 100 c In the filter 103a and the second surface acoustic wave filter 104c, as in the case of the surface acoustic wave device 100b, the excitation IDT excites the same surface acoustic wave and shifts the phase by the reception IDT. It has become. While the surface acoustic wave device 100b illustrated in FIG. 3 is shifted in phase by connection of the reception IDT, the surface acoustic wave device 10b illustrated in FIG.

At 0c, the phase is shifted depending on the location of the receive IDT.

 The first surface acoustic wave filter 103a of the surface acoustic wave device 100c has the same configuration as the first surface acoustic wave filters 103a and 103b described above.

 The second surface acoustic wave filter 104c has a second excitation IDT 131 connected to the input terminal 101 to excite a formed surface acoustic wave, and a surface sandwiching the second excitation IDT 131. A third reception IDT 142 and a fourth reception IDT 143 that receive a surface acoustic wave formed in a symmetric pattern, and further outside these reception IDTs, a second excitation IDT 131 and a third The receiving IDT 142 and the fourth receiving IDT 143 are sandwiched between two reflective electrodes 144 arranged to form a cavity.

 The connection between the first excitation I DT 111 of the first surface acoustic wave filter 103a and the second excitation IDT 131 of the second surface acoustic wave filter 104c is performed using the surface acoustic wave illustrated in FIG. It is connected in the same way as the connection between the excitation IDT 111 of the wave device 100 b and the excitation IDT 121. That is, the first excitation

The 1 DT 111 and the second excitation IDT 131 are connected in parallel to the input terminal 101, and are each formed of a pair of comb-shaped electrodes opposed to a plane symmetric pattern. The first surface acoustic wave filter 103a is connected to the input terminal 101 constituting the first excitation IDT 111 of the 103a. The comb-shaped electrode 131b corresponding to the comb-shaped electrode 111b is connected to the input terminal 101, and the other comb-shaped electrode constituting the first excitation IDT is connected to the reference potential side. A comb-shaped electrode 131a corresponding to 111b is connected to the reference potential side.

 By connecting the first excitation I DT I 11 and the second excitation I DT 131 in this manner, the first excitation ID T 111 and the second excitation I DT 131 are connected in the same manner as the anti-phase parallel connection illustrated in FIG. Surface acoustic waves having the same phase are excited by the excitation IDT 131.

 On the other hand, the first reception IDT 112 and the second reception IDT 113 of the first surface acoustic wave filter 103a are also the third reception IDT 142 and the fourth reception IDT 142 of the second surface acoustic wave filter. As described above, the reception IDT 143 includes a pair of comb-shaped electrodes facing each other.

 In the surface acoustic wave device 100c, a first reception IDT 112 of the first surface acoustic wave filter 103a, a third reception IDT 142 of the second surface acoustic wave filter 104c, Are formed in a plane-symmetric pattern, but are arranged at different distances from the excitation IDT.

That is, the propagation distance of the surface acoustic wave between the first excitation IDT 111 of the first surface acoustic wave filter 103a and the first and second reception IDTs 112, 113 is 1 ^ Then, the propagation distance L _n of the surface acoustic wave between the second excitation I DT 131 of the second surface acoustic wave filter 104c and the third and fourth reception I DTs 142 and 143 is larger than d. It is arranged to be longer by λ / 2. Of course, it may be arranged to be shorter by two.

Then, the comb-shaped electrode 112a of the first reception IDT 112 and the comb tooth-shaped electrode 142b of the third reception IDT are connected to the first output terminal 102a, The first receiving IDT 1 12 has a comb toothbrush electrode 112 b and the third receiving „

 PCT / JP 7/02212

The IDT comb-shaped electrode 142a is connected to the reference potential. That is, the comb-like electrode 142b corresponding to the comb-like electrode 112b connected to the reference potential of the first reception IDT 112 is connected to the first output terminal 102a, A comb-shaped electrode 142a corresponding to the comb-shaped electrode 112a connected to the first output terminal 102a of the reception IDT 112 is connected to the reference potential.

 The second reception IDT 113 of the first surface acoustic wave filter 103a and the fourth reception IDT 143 of the second surface acoustic wave filter 104c are similarly connected. That is, the comb-shaped electrode 113a and the comb-shaped electrode 143b are connected to the second output terminal 102b, and the comb-shaped electrode 113b and the comb-shaped electrode 143a are connected to the reference potential. It is connected to the.

 Therefore, in the surface acoustic wave device illustrated in FIG. 4, similarly to the surface acoustic wave device illustrated in FIG. 3, the same surface acoustic wave device excited by the first excitation IDT 111 and the second excitation IDT 131 is used. The SAW in phase will be converted to an electrical signal with the phase shifted by 180 ° at the receiving IDT.

 That is, the phase of the signal passing through the first surface acoustic wave filter 103a and the signal passing through the second surface acoustic wave filter 104c are applied to the first output terminal 102a and the second output terminal 102b. Are output as electric signals in a state where they are 180 ° out of phase with each other.

 The surface acoustic wave device of the present invention illustrated in FIGS. 1 to 4 is a device in which a first surface acoustic wave filter and a second surface acoustic wave filter having slightly different center frequencies are connected in anti-phase parallel connection. However, a pair of surface acoustic wave filters connected in anti-phase parallel may be connected in multiple stages.

FIG. 5 is a diagram schematically illustrating an example of an electrode pattern of a surface acoustic wave device 500 in which image electrodes are connected in two stages by taking the electrode pattern illustrated in FIG. 1 as one stage. The surface acoustic wave device 500 illustrated in FIG. 5 is mounted on a piezoelectric substrate. A conductor pattern including an IDT is formed at the center frequency f ₁ between the input terminal 101 and the first output terminal 102 a and the second output terminal 102 b. A first surface acoustic wave filter 103 and a _second surface acoustic wave filter 104 having a center frequency of ί2 are connected in anti-phase parallel.

Similarly, also between the second input terminal 1 0 5 a and the third input terminal 1 0 5 b and the third output terminal 1 0 6, the third surface acoustic wave off I the center frequency I ₁ and Le evening 1 0 7, and the fourth surface acoustic wave fill evening 1 0 8 center frequency I ₂ are opposite phase parallel connection.

And between the first output terminal 102a and the second input terminal 105a, and between the second output terminal 102b and the third input terminal 102b. They are electrically connected by connection means 109a and 109b, respectively. Here, the third surface acoustic wave filter 1 0 7 fourth SAW Fi Le motor 1 0 8, the center frequency is f, SIZE is f _2, if is reverse-phase parallel connection Bayoi.

 For example, a first surface acoustic wave filter as illustrated in FIG. 2 is a first stage in which a first surface acoustic wave filter 103 and a second surface acoustic wave filter 104 are connected in anti-phase parallel. The third surface acoustic wave filter 107 and the fourth surface acoustic wave filter 108 are composed of 10 3 a and the second surface acoustic wave filter 104 a, The second connected stage may also be constituted by the first surface acoustic wave filter 103a and the second surface acoustic wave filter 104a as illustrated in FIG.

The first stage is composed of a first surface acoustic wave filter 103a and a second surface acoustic wave filter 104a as illustrated in FIG. 2, and a surface acoustic wave filter 107 and The second stage in which the fourth surface acoustic wave filter 108 is connected in anti-parallel parallel is a first surface acoustic wave filter 103a and a second surface acoustic wave filter 10 as illustrated in FIG. 4b. P97 / 02212 Further, the first stage is composed of a first surface acoustic wave filter 103a and a second surface acoustic wave filter 104a as illustrated in FIG. The second stage where the filter 107 and the fourth surface acoustic wave filter 108 are connected in anti-phase parallel is the first surface acoustic wave filter 103a and the second surface The surface acoustic wave filter 104c of the above may be used.

 Further, the first stage is composed of a first surface acoustic wave filter 103a and a second surface acoustic wave filter 104b as illustrated in FIG. The second stage in which the filter 107 and the fourth surface acoustic wave filter 108 are connected in anti-phase parallel is the first surface acoustic wave filter 103 a and the second surface It may be constituted by a surface acoustic wave filter 104c.

 The surface acoustic wave filter pairs at each stage connected in the image in this manner have center frequencies f i and f. And if they are connected in anti-phase parallel, they need not be the same pattern.

 According to the surface acoustic wave device of the present invention, the first surface acoustic wave filter and the second surface acoustic wave filter are connected in anti-phase parallel with each other having slightly different pass frequency bands, so that the pass frequency band Inside, the first surface acoustic wave filter and the second surface acoustic wave filter operate in parallel, so that the impedance is reduced to about half.

 Further, since the signal phase is different by 180 ° outside the pass frequency band, the signal of the first surface acoustic wave filter and the signal of the second surface acoustic wave filter cancel each other, so that the amount of attenuation is secured. . In particular, by connecting a pair of surface acoustic wave filters connected in anti-phase parallel connection in more stages, sufficient attenuation is secured and the out-of-band characteristics are greatly improved.

Therefore, compared to the conventional 4-stage surface acoustic wave filter, The chip of the surface acoustic wave device can be reduced in size. Also, since the aperture of the surface acoustic wave filter can be narrowed, it is possible to prevent the occurrence of transverse mode 'spurs, and it is not necessary to weight the incoming and outgoing IDTs, thus further increasing the aperture. Can be prevented. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a diagram schematically showing an example of the configuration of the surface acoustic wave device according to the present invention; FIG. 2 is a diagram illustrating a first surface acoustic wave filter and a second surface acoustic wave device in the surface acoustic wave device according to the present invention. Fig. 3 is a diagram schematically showing one example of anti-phase parallel connection with a wave filter;

 FIG. 3 is a diagram schematically showing another example of the anti-parallel parallel connection of the first surface acoustic wave filter and the second surface acoustic wave filter in the surface acoustic wave device of the present invention;

 FIG. 4 is a diagram schematically showing another example of anti-phase parallel connection of the first surface acoustic wave filter and the second surface acoustic wave filter in the surface acoustic wave device of the present invention;

 FIG. 5 is a diagram schematically showing another example of the configuration of the surface acoustic wave device according to the present invention;

 FIG. 6 is a diagram schematically showing an example in which two pairs of surface acoustic wave filter pairs connected in anti-phase parallel are connected in two stages in the surface acoustic wave device of the present invention;

 FIG. 7 is a diagram schematically showing a signal propagation state in the surface acoustic wave device of the present invention illustrated in FIG. 6;

 FIG. 8 is a diagram showing a frequency characteristic of the surface acoustic wave device of the present invention; FIG. 9 is a diagram showing a frequency characteristic of the surface acoustic wave device of the present invention (two-stage antiphase parallel connection);

FIG. 10 shows a surface acoustic wave filter of the surface acoustic wave device of the present invention illustrated in FIG. FIG. 7 is a diagram showing a change in frequency characteristics when a frequency difference between a pair of filters is set to a parameter;

 FIG. 11 is a diagram showing the relationship between the frequency bandwidth of the 3 dB reduction of the surface acoustic wave device of the present invention exemplified in FIG. 6 and the frequency difference of the pair of surface acoustic wave filters connected in anti-parallel. ;

 FIG. 12 is a diagram showing the relationship between the logarithm of IDT between stages and the frequency characteristic of the surface acoustic wave device of the present invention illustrated in FIG. 6;

 FIG. 13 is a diagram showing the relationship between the logarithm of the IDT between the stages of the surface acoustic wave device of the present invention illustrated in FIG. 6 and the frequency bandwidth of 3 dB reduction;

 Figure 14 is a diagram showing the relationship between the stray capacitance of the wiring connecting a plurality of pairs of surface acoustic wave filter pairs and the frequency bandwidth of 4 dB reduction;

 FIG. 15 is a diagram showing the results of analyzing the occurrence level of transverse mode spurs in the surface acoustic wave device of the present invention;

 Figure 16 shows the 45 ° X-cut Z-propagation LB0 substrate of each next-order lateral mode for the width of the aperture of the surface acoustic wave filter with the center frequency f set to 244 MHz (λ = 14.O jum). FIG. 17 is a diagram showing a frequency dispersion characteristic; FIG. 17 shows a first excitation I DT, a second excitation I DT, a fifth reception I DT, 6 is a diagram showing frequency characteristics when the logarithm of the received IDT 6 is set to 45.5 pairs and the aperture is set to 8.9 pairs;

 FIG. 18 is a diagram schematically showing an example of an electrode pattern of a conventional surface acoustic wave device; and

FIG. 19 is a diagram illustrating frequency characteristics of the conventional surface acoustic wave device illustrated in FIG. BEST MODE FOR CARRYING OUT THE INVENTION Example 1

 FIG. 6 is a diagram schematically showing one example of an electrode pattern of the surface acoustic wave device of the present invention.

 The surface acoustic wave device 600 is placed on a piezoelectric substrate composed of LB 0 of 45 ° X cut Z propagation so that the input and output signal phases are substantially 180 ° out of phase with each other. The first surface acoustic wave filter and the second surface acoustic wave filter connected in parallel are image-connected in two stages. The operating frequencies of the surface acoustic wave filter pairs connected in antiphase and parallel constituting each stage are shifted from each other by about 0.10-0.18%.

The first-stage surface acoustic wave filter pair was connected in anti-phase parallel between the first input terminal 61, the first output terminal 60a, and the second output terminal 602. It comprises a first surface acoustic wave filter 603 having a center frequency f e and a second surface acoustic wave filter 604 having a center frequency f ₂ . Here, as in the case of the surface acoustic wave filter pair illustrated in FIG. A surface acoustic wave filter pair that excites a phase-shifted surface acoustic wave is used.

The surface acoustic wave filter pair in the second stage has the same configuration as the surface acoustic wave filter pair in the first stage, but the input terminal and the output terminal are connected in reverse. Sunawa Chi, a second input terminal 6 0 5 a and the third input terminal 6 0 5 b and the third output terminal 6 0 6 a third center frequency I ₁ which is reverse phase connected in parallel between the And a _second surface acoustic wave filter 608 having a center frequency of ί2. Here, the electrode pattern shape of the second-stage surface acoustic wave filter pair is formed in the same shape as the electrode pattern shape of the first-stage surface acoustic wave filter pair. That is, the first surface acoustic wave filter 603 and the third surface acoustic wave filter 607 are formed in the same shape, and the second surface acoustic wave filter 604 and the fourth surface acoustic wave Wave filter 6 0 12

8 is formed in the same shape.

 The first surface acoustic wave filter 603 has a first excitation IDT 611 that excites a surface acoustic wave formed in contact with the input terminal 601, and a first excitation IDT 611 that sandwiches the first excitation IDT 611. A first reception IDT 612 and a second reception IDT 613 for receiving a surface acoustic wave formed in a plane-symmetric pattern, and further outside these reception IDTs 612 and 613, a first excitation I DT 611, two reception electrodes 614 arranged to form a cavity so as to operate as a resonator with the first reception I DT 612 and the second reception I DT 613 interposed therebetween. It is composed of

 The second surface acoustic wave filter 604 also has a second excitation I DT 621 that excites a surface acoustic wave formed by being connected to the input terminal 601, and a second excitation I DT 621 that sandwiches the second excitation I DT 621. A third reception I DT 622 and a fourth reception I DT 623 for receiving a surface acoustic wave formed in a plane symmetric pattern, and a second excitation I DT from further outside of these reception I DTs 622 and 623 And a pair of reflective electrodes 624 arranged to form a cavity so as to operate as a resonator with the third receiving IDT 622 and the fourth receiving IDT 623 interposed therebetween. ing. The first surface acoustic wave filter 603 and the second surface acoustic wave filter 604 are designed so that their operating frequencies are slightly different, for example, by changing the pitch of the IDT comb-shaped electrodes. It is arranged.

 The first surface acoustic wave filter 603 and the second surface acoustic wave filter 604 are connected in anti-phase parallel by the same connection method as the surface acoustic wave device 100a illustrated in FIG.

That is, the first excitation IDT 603 of the first surface acoustic wave filter 603 and the second excitation IDT 621 of the second surface acoustic wave filter are connected in parallel to the input terminal. And a pair of comb teeth that face each other It is composed of electrodes. Then, the second surface acoustic wave filter corresponding to the comb-shaped electrode connected to the input terminal 601 among the comb-shaped electrodes constituting the first excitation IDT 611 of the first surface acoustic wave filter 603 The comb-shaped electrode of the second excitation IDT 621 of 604 is connected to the reference potential side. On the other hand, of the comb-shaped electrodes constituting the first excitation IDT 611 of the first surface acoustic wave filter 603, the second elastic waves corresponding to the comb-shaped electrodes connected to the reference potential. The comb-shaped electrode of the second excitation IDT 621 of the surface wave filter 604 is connected to the input terminal 601.

 By connecting the first excitation I DT 611 and the second excitation I DT 621 in this manner, the first surface acoustic wave filter 603 and the second surface acoustic wave The phase of the surface wave is substantially shifted by 180 °.

 On the other hand, as described above, the phase of the surface acoustic wave propagated by the reception IDT is not shifted between the first surface acoustic wave filter 603 and the second surface acoustic wave filter 604.

 Accordingly, the first output terminal 602a and the second output terminal 602b provide the phase of the signal passing through the first surface acoustic wave filter 603 and the phase of the signal passing through the second elastic surface wave filter 604, respectively. Is output as an electric signal in a state of being substantially 180 ° shifted from each other.

 Next, a second-stage surface acoustic wave filter pair constituting the surface acoustic wave device 600 illustrated in FIG. 6 will be described.

The third surface acoustic wave filter 607 is connected to a third input terminal 605a for exciting a surface acoustic wave formed by being connected to the second input terminal 605a, and to a third input terminal 605b. A fourth excitation I DT 632 that excites the formed surface acoustic wave, and a surface acoustic wave formed to be sandwiched between the third excitation I DT 631 and the fourth excitation I DT 632 are received. Fifth recipient The signal I DT 633 and the third excitation I DT 631 and the fourth excitation I DT 632 and the fifth reception IDT 633 are sandwiched from outside the excitation I DT 631 and 632 to operate as a resonator. And two reflective electrodes 634 arranged to form a cavity. Further, between the first output terminal 602a and the second input terminal 605a, for example, a wiring 609a made of a conductive thin film formed on the same substrate as the first to fourth surface acoustic wave filters is provided. Are electrically connected to each other. The second output terminal 602b and the third input terminal 605b are similarly connected by the wiring 609b.

 A fourth surface acoustic wave filter 608 is also connected to a fifth input terminal 605b for exciting a surface acoustic wave formed by connecting to the second input terminal 605a and a third input terminal 605b. The sixth excitation IDT 642 that excites the formed surface acoustic wave, and the surface acoustic wave formed so as to be sandwiched between the fifth excitation IDT 641 and the sixth excitation IDT 642 The sixth receiving IDT 643 to operate as a resonator with the fifth excitation IDT 641, the sixth excitation IDT 642, and the sixth reception IDT 643 sandwiched between them. And two reflective electrodes 644 arranged in such a way that

 As described above, in the surface acoustic wave element 600 illustrated in FIG. 6, the shape of the electrode pattern forming the pair of surface acoustic wave filters in the second stage is the same as that in the first stage, and the input / output terminals are reversed. Therefore, the phase of the excited surface acoustic wave does not shift between the pair of surface acoustic wave filters. On the other hand, in the third surface acoustic wave filter 607 and the fourth surface acoustic wave filter 608, the phase of the surface acoustic wave propagated in the reception IDT is substantially shifted by 180 °.

Therefore, at the third output terminal 606, the third surface acoustic wave The phase of the signal passing through the filter 607 and the phase of the signal passing through the fourth surface acoustic wave filter 608 are output as electric signals while being substantially 180 ° apart from each other.

 In the surface acoustic wave device of the present invention illustrated in FIG. 6, the surface acoustic wave filter pair in the first stage and the surface acoustic wave filter pair in the second stage are formed in the same shape. The shape of the second step may be changed (see Figs. 2 to 4). Example 2

 Here, signal propagation by the surface acoustic wave device of the present invention illustrated in FIG. 6 will be described.

 In the surface acoustic wave device 600, the electric signal input from the input terminal 601 is applied to the first excitation IDT 61 1 of the first surface acoustic wave filter, and the second excitation of the second elastic surface wave filter 604. Excitation is input to IDT 621 and converted to elastic surface waves. As described above, in the surface acoustic wave device 600 illustrated in FIG. 6, the first excitation IDT and the second excitation IDT 621 excite surface acoustic waves whose phases are substantially shifted by 180 °. .

 The surface acoustic wave excited by the first excitation IDT 611 propagates to both sides, and is converted again into an electric signal by the first reception IDT 612 and the second reception IDT 613.

The surface acoustic wave excited by the second excitation IDT 612 also propagates to both sides, and is converted again into an electric signal by the third reception IDT 622 and the fourth reception IDT 623. In the reception IDT of the first surface acoustic wave filter 603 and the second surface acoustic wave filter 604, the phase does not shift when the received surface acoustic wave is converted into an electric signal. Therefore, the first output terminal 602a and the second output terminal 602b have the first elasticity. A signal passing through the surface acoustic wave filter 603 and a signal passing through the second surface acoustic wave filter 604 substantially 180 ° out of phase with this signal are output.

 The signal output to the first output terminal 602a is input to the second input terminal 605a of the pair of surface acoustic wave filters in the second stage through the wiring 609a. Similarly, the signal output to the second output terminal 602 b is input to the third input terminal 605 b of the second-stage surface acoustic wave filter pair via the wiring 609 b.

 The electric signals input from the second input terminal 605 a and the third input terminal 605 b to the third surface acoustic wave filter 607 and the fourth surface acoustic wave filter The excitation I DT 63 1, the fourth excitation I DT 63 2, the fifth excitation IDT 64 1, and the sixth excitation I DT 642 are converted into surface acoustic waves again. The phases of the surface acoustic waves to be excited do not shift between the third surface acoustic wave filter 607 and the fourth surface acoustic wave filter 608 constituting the second surface acoustic wave filter pair.

 The surface acoustic waves excited by the third excitation I DT 631 and the fourth excitation I DT 632 are received by the fifth reception I DT 633, and the fifth excitation I DT 64 1 and the sixth The surface acoustic wave excited by the excitation I DT 642 is received by the sixth reception I DT 643. At this time, the propagated surface acoustic wave is converted into an electric signal by the fifth reception IDT 633 and the sixth reception IDT 643 with their phases substantially shifted by 180 ° from each other. Then, it is output to the third output terminal 606.

 FIG. 5 is a diagram schematically showing a signal propagation state of the surface acoustic wave device 600 of the present invention.

In the surface acoustic wave device 600 illustrated in FIG. 6, the pair of surface acoustic wave filters in the first stage and the pair of surface acoustic wave filters in the second stage are opposite in phase as illustrated in FIG. Although row connection was adopted, the configuration of the surface acoustic wave filter pair at each stage should have a slightly shifted center frequency, and if connected in anti-phase parallel, use anti-phase parallel connection other than that shown in Fig. 2. Can be. For example, the first-stage surface acoustic wave filter pair and the second-stage surface acoustic wave filter pair may be appropriately combined with the anti-phase parallel connection illustrated in FIGS. 2 to 4.

 When the anti-parallel parallel connection as illustrated in Fig. 3 or Fig. 4 is adopted for the second-stage surface acoustic wave filter pair, surface acoustic waves excited by the third excitation IDT 631 and the fourth excitation IDT 632 And the surface acoustic waves excited by the fifth excitation IDT 641 and the sixth excitation IDT 642 are substantially 180 ° out of phase with each other. The phase is not shifted by the 6 reception IDT 643. Example 3

Hereinafter, the frequency characteristics of the surface acoustic wave device according to the present invention will be described. In the surface acoustic wave device 600 illustrated in FIG. 6, the center frequency fi (about 244 MHz) of the first surface acoustic wave filter 603, the center frequency f of the second surface acoustic wave filter 604, and the third the center frequency I ₁ of the surface acoustic wave fill evening 607 and the center frequency f ₂ of the second surface acoustic wave filter 608, Δ f = f. It is set to differ by one f 異 な る = 0.3 MHz.

 The frequency characteristics of this surface acoustic wave device will be described with reference to FIGS. FIG. 8 is a diagram showing the frequency characteristics of the surface acoustic wave device of the present invention having the configuration illustrated in FIG. 2 or FIG. 6 (first stage).

Here, the first excitation I DT 611, the second excitation I DT 622, the fifth reception I DT 633, and the sixth reception I DT 643 are 20.5 pairs, and the first reception I DT 612, the second Receiving IDT 613, third receiving IDT 622, PC leak 2 4th receive IDT 6 2 3, 3rd excitation IDT 6 3 1, 4th excitation IDT

8 pairs of 6 32, fifth excitation I D T 64 1, and sixth excitation I D T 64 2 were used.

 The distance between the excitation I D T and the reception I D T of each surface acoustic wave filter is set to 3λ (λ = ν / f .; v is the phase velocity of the surface acoustic wave, and f.

 The center frequency at which the S1S1 surface wave filter operates), the distance between the receiving IDT and the reflective electrode was 0.375, and the number of reflective electrodes was 120.

 In addition, the length of the excitation IDT, the reception IDT, and the reflection electrode (aperture) was set to 0.12 mm, and the input / output termination impedance was set to 400 Ω. Also, the center frequencies of the first surface acoustic wave filter and the second surface acoustic wave filter are set to be different from each other by 0.3 MHz.

 Figure 8 compares the frequency characteristics 800 of a single-stage surface acoustic wave filter pair connected in anti-phase parallel with those of the first surface acoustic wave filter 6 The characteristic 8002 of the second surface acoustic wave filter 604 alone is also shown.

 Also, the phase difference 804 generated by the first surface acoustic wave filter 603 and the second surface acoustic wave filter 604 connected in anti-phase parallel is also shown.

 The phase difference between the surface acoustic wave filter pair composed of the first surface acoustic wave filter 603 and the second surface acoustic wave filter 604 is near the passing frequency band of the surface acoustic wave filter. It can be seen that the phase difference is 110 ° to 140 °, but in the stop band it is almost out of phase (essentially 180 ° phase difference).

Therefore, in a single-stage SAW filter pair, a pass frequency band in which the pass frequency bands of the first SAW filter and the second SAW filter overlap is obtained, and at the same time, in the stop band, The signals of the first surface acoustic wave filter and the second surface acoustic wave filter cancel each other to obtain a sufficient attenuation. Can be

Figure 9 shows a first-stage SAW filter pair consisting of a first SAW filter 603 and a second SAW filter 604 connected in anti-phase parallel, and anti-phase parallel connection. This is obtained when the second surface acoustic wave filter pair consisting of the third surface acoustic wave filter 607 and the fourth surface acoustic wave filter 608 is image-connected. FIG. 4 is a diagram showing frequency characteristics obtained. Center frequency difference of the surface acoustic wave filter pair constituting each stage is 0. 3 MH _Z.

 For comparison, the figure also shows the frequency characteristics of a single-stage surface acoustic wave filter pair connected in anti-parallel and parallel. This one-stage frequency characteristic corresponds to the frequency characteristic of the surface acoustic wave device illustrated in FIG. This frequency characteristic corresponds to the frequency characteristic obtained when the first surface acoustic wave filter and the second surface acoustic wave filter are connected in two stages in series.

 In the surface acoustic wave device according to the present invention, the first surface acoustic wave filter and the second surface acoustic wave filter are connected in anti-parallel parallel with each other having slightly different pass frequency bands. In the frequency band, the impedance can be reduced to about half by operating the first surface acoustic wave filter and the second surface acoustic wave filter in parallel. In addition, since the signal phase substantially differs by 180 ° outside the pass frequency band, the signal of the first surface acoustic wave filter and the signal of the second surface acoustic wave filter cancel each other, so that the attenuation is caused. Can be secured.

 A single-stage SAW filter connected in anti-parallel and parallel is substantially equivalent to a two-stage connected SAW filter, especially a pair of anti-parallel connected SAW filters. Furthermore, it can be seen that by connecting in multiple stages, the amount of attenuation outside the pass frequency band is further increased, and the out-of-band characteristics are greatly improved.

Furthermore, the surface acoustic wave device of the present invention has two Since the surface acoustic wave filters of CT / JP97 / 02212 are connected in parallel, the input / output impedance of the surface acoustic wave filter can be reduced, and as a result, the chip size of the surface acoustic wave filter can be reduced. Can be. In particular, the size of the surface of the surface acoustic wave filter in the direction of the aperture can be reduced to about half. This is a particularly significant advantage in areas where chip size reduction is required, such as in mobile communications, as well as suppressing lateral mode and spurious, lowering the electrode resistance of the IDT and reducing loss. Can be reduced. This also means that the frequency characteristics are much better for the same chip size.

 The chip size of the surface acoustic wave device shown in Fig. 9, including the bonding pad, is approximately 2.8 mm x 3.0 mm square.For example, the conventional series four-stage surface acoustic wave filter device shown in Fig. 18 Compared to, the size can be significantly reduced. Example 4

 Next, preferable conditions for connecting a pair of surface acoustic wave filter pairs in anti-phase parallel connection will be described.

 FIG. 10 shows the frequency difference between the surface acoustic wave filter and the surface acoustic wave device (two-stage configuration of the surface acoustic wave filter pair connected in anti-parallel connection) of the present invention described with reference to FIG. This figure shows the change in the frequency characteristics of the surface acoustic wave device when it is changed over time.

 Fig. 11 is a plot of the frequency bandwidth of 3 dB reduction against the frequency difference of a pair of surface acoustic wave filters connected in antiphase in order to characterize the frequency characteristics of this surface acoustic wave device. is there.

As can be seen from FIGS. 10 and 11, the surface acoustic wave device of the present invention increases its pass frequency as the frequency difference between the pair of elastic surface wave filters increases. Several bandwidth increases. However, if the frequency difference is too wide, ripples appear in the passband and the passband decreases again.

 The frequency difference between the pair of surface acoustic wave filters that can be substantially used from Fig. 11 is in the range of 0.25 to 0.45 MHz for a surface acoustic wave filter with a center frequency of 244 MHz, that is, the center frequency. It is preferable to set the frequency difference standardized in the range of 0.10 to 0.18%. Example 5

 FIG. 12 shows the inter-stage IDT constituting the surface acoustic wave device (two-stage configuration of the anti-phase parallel connection surface acoustic wave filter pair) of the present invention illustrated in FIG. 6, that is, the first surface acoustic wave filter 603, and FIG. The first reception I DT 612, the second reception I DT 614, and the third reception I DT 622 of the second surface acoustic wave filter 604, the third surface acoustic wave filter 607, and the fourth surface acoustic wave filter 608. The fourth receiving I DT 623, the third exciting I DT 631, the fourth exciting I DT 632, the fifth exciting I DT 641, and the sixth exciting I DT 64 2 are used as parameters. This figure shows the change in the frequency characteristics of the surface acoustic wave filter when it is changed.

 FIG. 13 shows a configuration of a surface acoustic wave filter pair in which a 3 dB lower bandwidth is connected in anti-phase parallel to characterize the frequency characteristics of the surface acoustic wave device. Receive IDT 614, Third Receive IDT 622, Fourth Receive IDT 623, Third Excitation IDT 631, Fourth Excitation IDT 632, Fifth Excitation IDT 641, and Sixth Excitation It is the figure which plotted with respect to the logarithm of IDT642.

As can be seen from FIG. 12, the surface acoustic wave device of the present invention has a first reception IDT 612, a second reception IDT 614, a third reception IDT 622, and a fourth reception IDT 622. As the logarithm of the reception I DT623, the third excitation I DT631, the fourth excitation I DT 632, the fifth excitation I DT 641 and the sixth excitation I DT 642 increases, the pass frequency bandwidth increases. However, when the logarithm exceeds 9 pairs, ripples appear in the passband and the bandwidth decreases again. Therefore, it is preferable to set the logarithm of these IDTs to 9 or less.

 On the other hand, as can be seen from Fig. 13, the 3 dB bandwidth increases as the logarithm of the IDT increases, but when the logarithm exceeds 8 pairs, the 3 dB bandwidth decreases again. . Therefore, for example, to secure a bandwidth of 0.35 MHz or more as a 3 dB bandwidth, it is preferable to set the logarithm of these IDTs to 5 to 8 pairs. With this logarithm, ripples appear in the passband and the bandwidth does not decrease. Example 6

 FIG. 14 is a diagram showing the relationship between the stray capacitance of wiring connecting a plurality of stages of surface acoustic wave filter pairs and the frequency bandwidth of 4 dB reduction.

For example, if the stray capacitance formed by the interstage connection is 1.5 pF, it can be seen that the logarithm of the IDT should be 10 pairs or more to secure a bandwidth of 0.35 MHz or more. . Also, for example, if the stray capacitance formed by the interstage connection is 2.5 pF, the number of IDTs should be 13 or more to secure a bandwidth of 0.35 MHz or more. You can see that. As described above, in the surface acoustic wave device of the present invention, a sufficient bandwidth can be ensured by optimizing the logarithm of the IDT even when a floating capacitance is formed by interstage connection. Example 7 Next, means for suppressing the transverse mode and spurious in the surface acoustic wave device of the present invention will be described.

 FIG. 15 is a diagram showing the results of analysis of the occurrence level of lateral mode spurious in the surface acoustic wave device of the present invention (two-stage configuration of anti-phase parallel connection surface acoustic wave filter). The frequency difference is 0.3 MHz, the first and second surface acoustic wave filter excitation IDT, the third and fourth surface acoustic wave filter reception IDT is 20.5 pairs, and the aperture width is 25. 7λ (where S is the electrode arrangement period).

 In Fig. 15, 1 st represents the signal component of the basic transverse mode (the same as in Fig. 9), and 3rd and 5th represent the signal components of the third and fifth transverse modes, respectively. As is clear from Fig. 15, the higher-order transverse mode spur degrades the out-of-band characteristics of the surface acoustic wave filter. Figure 16 shows the frequency dispersion of each lateral mode of the LB0 substrate of 45 ° Xcut Z propagation with respect to the width of the aperture of the surface acoustic wave filter with the center frequency set to 244 MHz (λ = 14.0 m). It is a figure showing a characteristic. When the width of the aperture is set to 25.7 λ in the surface acoustic wave device illustrated in FIG. 6, high order transverse mode spurs up to the fifth order are generated.

 If the aperture is set to 10 λ or less, the higher-order transverse modes of the third and higher orders will be higher than the power-off frequency, and the transverse modes will not occur.

FIG. 17 shows the first excitation I DT 611, the second excitation I DT 621, the second excitation I DT 611 in the surface acoustic wave device of the present invention exemplified in FIG. FIG. 18 is a diagram illustrating frequency characteristics when the logarithm of the fifth reception IDT 633 and the sixth reception IDT 643 is set to 45.5 pairs and the aperture is set to 8.9 λ. As in Fig. 9, the first excitation I DT 61 1 Frequency characteristics when the logarithm of the excitation IDT 621, the fifth reception IDT 633, and the sixth reception IDT 643 are set to 20.5 pairs are also shown for comparison. The surface acoustic wave device in which the logarithm of the first excitation I DT 61 1, the second excitation I DT 621, the fifth reception IDT 633, and the sixth reception I DT 643 is set to 45.5 pairs, Even if DT is set to 20.5 pairs, it is clear that the characteristics in the pass frequency band are hardly impaired. Industrial applicability

 According to the surface acoustic wave device of the present invention, by connecting two surface acoustic wave filters having slightly different center frequencies in anti-phase parallel connection, the bandwidth of the pass frequency band as the surface acoustic wave filter can be expanded. it can.

 Further, the surface acoustic wave device of the present invention is characterized in that the first surface acoustic wave filter and the second surface acoustic wave filter are connected in anti-phase parallel with slightly different pass frequency bands, so that the pass Within the band, the impedance can be reduced to about half by operating the first surface acoustic wave filter and the second surface acoustic wave filter in parallel.

Further, since the signal phase is different by 180 ° outside the pass frequency band, the signal of the first surface acoustic wave filter and the signal of the second surface acoustic wave filter cancel each other, so that the amount of attenuation can be secured. In particular, more to connect the surface acoustic wave filter of a pair of reverse-phase parallel connection further in multiple stages, sufficient attenuation can be secured, it is monkey in the out-of-band characteristics are improved greatly ₀

Therefore, when compared with the conventional serial four-stage surface acoustic wave filter device, the chip of the surface acoustic wave device can be downsized. Therefore, in applications where chip size reduction is required, such as in mobile communications, This is a particularly suitable surface acoustic wave device.

 In addition, since the aperture of the surface acoustic wave filter can be reduced by miniaturization, the occurrence of lateral mode spurious can be prevented, and the electrode resistance of the IDT can be reduced to reduce the loss. Also, the occurrence of lateral mode spurious can be suppressed, and the out-of-band characteristics can be improved. Furthermore, there is no need to weight incoming and outgoing IDTs, and further increase in aperture can be prevented.

Claims

The scope of the claims

1. a piezoelectric substrate;

 A two-port 3IDT first surface acoustic wave filter having a center frequency f1 and disposed between the first input terminal and the first output terminal on the piezoelectric substrate;

 2 having a center frequency ί 2 slightly different from the center frequency fl, disposed in parallel with the first surface acoustic wave filter between the first input terminal and the first output terminal. A second surface acoustic wave filter of port 3 ID Τ,

 The first surface acoustic wave filter and the second surface acoustic wave filter may include a signal output from the first input terminal to the first output terminal via the first surface acoustic wave filter. And a phase of a signal output to the first output terminal via the second surface acoustic wave filter is substantially different by 180 °. Surface acoustic wave device.

 2. The surface acoustic wave device according to claim 1, wherein the first surface acoustic wave filter and the second surface acoustic wave filter have a phase with respect to a signal input to the first input terminal. It is characterized by exciting substantially different surface acoustic waves by 180 °.

3. The surface acoustic wave device according to any one of claims 1 and 2, wherein the first surface acoustic wave filter is connected to the first input terminal, and is input to the first input terminal. A first excitation IDT that excites a first surface acoustic wave by the applied electric signal, and disposed on both sides of the first excitation IDT to receive and convert the first surface acoustic wave into an electric signal A first receiving ID Τ and a second receiving IDT, The second surface acoustic wave filter is connected to the first input terminal, and has a 180 ° phase difference from the first surface acoustic wave due to an electric signal input to the first input terminal. A second excitation ID for exciting the second surface acoustic wave, and a third reception IDT arranged on both sides of the second excitation IDT for receiving the second surface acoustic wave and converting it into an electric signal And a fourth reception IDT.

 4. The surface acoustic wave device according to claim 1, wherein the first surface acoustic wave filter and the second surface acoustic wave filter substantially correspond to a signal input to the first input terminal. In addition, a surface acoustic wave having the same phase is excited, and the surface acoustic wave is converted into an electric signal so that the phase is substantially different by 180 °.

 5. The surface acoustic wave filter according to any one of claims 1 to 4,

 The first surface acoustic wave filter is connected to the first input terminal, and the first excitation IDT that excites the first surface acoustic wave by an electric signal input to the first input terminal. A first reception IDT and a second reception IDT that are disposed on both sides of the first excitation IDT and receive the first surface acoustic wave and convert the same into an electric signal,

 The second surface acoustic wave filter is connected to the first input terminal, and the second excitation IDT that excites the first surface acoustic wave by an electric signal input to the first input terminal. The first and second receiving IDTs are disposed on both sides of the second excitation IDT, and receive the first surface acoustic wave so that the phases thereof are substantially different by 180 ° from the first and second receiving IDTs. A third reception IDT and a fourth reception IDT that convert the signal into a simple electrical signal.

6. The surface acoustic wave device according to any one of claims 1 to 5, Wherein the piezoelectric substrate is the electromechanical coupling coefficient k ² of the surface acoustic wave propagating on this substrate is about 1%, the reflection coefficient of the surface acoustic wave per one IDT is about 3% or more And

 7. The surface acoustic wave device according to any one of claims 1 to 6, wherein the piezoelectric substrate is made of lithium tetraborate.

 8. The surface acoustic wave device according to any one of claims 1 to 7, wherein the first center frequency and the second center frequency are different from about 0.10% to about 0.18%. It is characterized by the following.

 9. The surface acoustic wave device according to any one of claims 1 to 8, wherein the intersecting width of the comb-shaped electrodes constituting each IDT is about 10 times the arrangement period of the comb-shaped electrodes. It is characterized by the following.

 10. A surface acoustic wave device comprising a plurality of cascade-connected surface acoustic wave filters according to claim 1 on the piezoelectric substrate.

 1 1. Piezoelectric substrate,

 A first elastic surface of a two-port 3 ID having a center frequency ί1 and disposed between a first input terminal, a first output terminal, and a second output terminal on the piezoelectric substrate. With the wave film,

 A center slightly different from the center frequency f 1, disposed between the first input terminal and the first output terminal and the second output terminal in parallel with the first surface acoustic wave filter; A second surface acoustic wave filter of a 2-port 3 IDT having a frequency f 2,

 A third elastic surface wave filter of a 2-port 3 IDT having a center frequency f 1 and disposed between the first output terminal, the second output terminal, and the third output terminal; ,

The center frequency disposed between the first output terminal, the second output terminal, and the third output terminal in parallel with the third surface acoustic wave filter; A 2 port 3 IDT fourth surface acoustic wave filter having a number f 2,

 The first surface acoustic wave filter and the second surface acoustic wave filter may include a signal output from the first input terminal to the first output terminal via the first surface acoustic wave filter. A phase and a phase of a signal output to the first output terminal via the second surface acoustic wave filter are arranged so as to be substantially 180 ° different from each other;

 The third surface acoustic wave filter and the fourth surface acoustic wave filter are configured to output the third output from the first output terminal and the second output terminal via the third surface acoustic wave filter. The phase of the signal output to the terminal and the phase of the signal output to the third output terminal via the fourth surface acoustic wave filter are substantially different by 180 °. Surface acoustic wave device characterized by the fact that:

 1 2. In a surface acoustic wave device in which an IDT is formed on a piezoelectric substrate, a first input terminal;

 A first excitation IDT that is connected to the first input terminal and excites a first surface acoustic wave by an electric signal input to the first input terminal, and is disposed on both sides of the first excitation IDT. A first surface acoustic wave filter having a first center frequency, comprising: a first reception IDT and a second reception IDT that receive the first surface acoustic wave and convert it to an electric signal; ,

A second surface acoustic wave, which is connected to the first input terminal and has a phase substantially 180 ° different from that of the first surface acoustic wave, is generated by an electric signal input to the first input terminal. A second excitation IDT to be excited; a third reception IDT and a fourth reception IDT disposed on both sides of the second excitation IDT to receive the second surface acoustic wave and convert it into an electric signal. A second elastic surface having a second center frequency slightly different from said first center frequency Wave filters and

 A first output terminal connected in parallel with the first reception IDT and the third reception IDT;

 A second output terminal connected in parallel with the second reception IDT and the fourth reception IDT;

 A second input terminal connected to the first output terminal;

 A third input terminal connected to the second output terminal,

 A third excitation IDT that is connected to the second input terminal, excites a third surface acoustic wave by an electric signal input to the input terminal, and is connected to the third input terminal; A fourth excitation IDT that excites the third surface acoustic wave by an electric signal input to the third excitation IDT, the fourth excitation IDT being disposed between the third excitation IDT and the fourth excitation IDT, A third reception surface acoustic wave filter having the first center frequency, comprising: a fifth reception IDT that receives a surface wave and converts it into an electric signal;

 A fifth excitation IDT that is connected to the second input terminal, excites the third surface acoustic wave by an electric signal input to the input terminal, and is connected to the third input terminal; A sixth excitation IDT that excites a fourth surface acoustic wave by an electric signal input to a terminal; and a fourth excitation IDT disposed between the fifth excitation IDT and the sixth excitation IDT. A fourth surface acoustic wave filter having the second center frequency, comprising: a sixth reception IDT that receives a surface wave and converts it into an electric signal;

 A third output terminal connected in parallel with the fifth reception IDT and the sixth reception IDT;

A surface acoustic wave device comprising:

13. The surface acoustic wave device according to claim 11, wherein the piezoelectric substrate is an electromechanical device of a surface acoustic wave propagating on the substrate. Coupling coefficient k ² is about 1%, and wherein the reflection coefficient of the surface acoustic wave per one I DT is about 3% or more.

 14. The surface acoustic wave device according to any one of claims 11 to 13, wherein the piezoelectric substrate is made of lithium tetraborate.

15. The surface acoustic wave device according to any one of claims 11 to 14, wherein the first center frequency and the second center frequency are about 0.10% to about 0.18%. It is different.

 16. The surface acoustic wave device according to any one of claims 11 to 15, wherein an intersecting width of the comb-shaped electrodes constituting each of the IDTs is equal to a period of arrangement of the comb-shaped electrodes. It is characterized by being about 10 times or less.