JP3476299B2 - Double mode surface acoustic wave resonator filter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a surface acoustic wave resonator filter used in mobile communication equipment and the like, and particularly used for some digital communication mobile communication equipment, and has a communication bandwidth of a specific bandwidth. The surface acoustic wave resonator filter is about 0.05 to 0.25%.

[0002]

As a surface acoustic wave resonator filter utilizing multiple modes formed on a piezoelectric substrate, a laterally coupled surface acoustic wave in which a standing wave generated in a direction perpendicular to the propagation direction of the surface acoustic wave is coupled. There is known a resonator filter and a longitudinally coupled surface acoustic wave resonator filter in which standing waves generated in parallel to the propagation direction of surface acoustic waves are coupled.

Transversely coupled multimode surface acoustic wave resonator filters are first described in Thiersten and Smith.
Reported by (Tiersten, Smythe, "Guided Acous
tic Surface Wave Filters ", IEEE Ultrasonics Symposi
um Proceedings 1975, pp. 293-294). Figure 7 (a) shows
It is the figure which showed typically the basic structure of the lateral coupling multimode surface acoustic wave resonator filter, and the standing wave excited. A high frequency signal applied to the input interdigital transducer 3 (hereinafter, interdigital transducer is abbreviated as IDT) is converted into a surface acoustic wave. Surface acoustic waves (hereinafter abbreviated as SAW) between the metallic and non-metallic parts on the piezoelectric substrate.
Since the propagation velocities of the SAW are different, the propagation velocity of the surface acoustic wave changes between the non-metal region and the region where the IDT or metal is formed, and the standing wave is perpendicular to the surface acoustic wave propagation direction (parallel to the IDT). Occurs. As the standing wave, a standing wave 11 in the symmetric mode and a standing wave 12 in the anti-symmetric mode are excited.

On the other hand, a so-called longitudinally coupled multimode surface acoustic wave resonator filter in which standing waves excited in a direction parallel to the propagation direction (longitudinal direction) of the surface acoustic wave are coupled is also known.
(For example, Tanaka, Morita, Ono, Nakazawa, 15th EM Symposium, pages 9 to 15 (1986)). For example, as shown in FIG. 8A, a surface acoustic wave resonator having an input IDT 3 (output IDT 4), a connection IDT 5, and a grating reflector 6 (hereinafter abbreviated as a reflector) on both sides thereof is connected. Busbar 7 for connection ID
A vertical dual mode surface acoustic wave resonator filter having a 2IDT structure in which T5s are cascaded in two stages, as shown in FIG. 8 (b).
Input IDT3 (output IDT4), connection IDT5 on both sides,
Further, there is a vertical double-mode surface acoustic wave resonator filter of a 3IDT structure in which connecting surface IDTs having reflectors 6 on both sides thereof are connected in cascade by connecting IDTs 5 facing each other by connecting busbars 7. In the case of a longitudinally coupled multi-mode surface acoustic wave resonator filter, the standing wave is a fundamental zero-order symmetric mode, a first-order antisymmetric mode, a second-order symmetric mode in the surface acoustic wave propagation direction.
It is known that ... are sequentially excited, and the standing wave modes to be coupled differ depending on the electrode structure.

FIG. 7B schematically shows a surface acoustic wave resonator filter having a 2IDT structure, which is an example of a basic configuration of a longitudinally coupled multimode surface acoustic wave resonator filter, and a standing wave to be excited. Is. Multiple IDTs (input IDT3 and output I
It is a surface acoustic wave resonator filter having a DT 4) and a pair of reflectors 6 arranged outside them. in this case,
A zero-order symmetric mode standing wave 13 and a first-order anti-symmetric mode standing wave 14 are excited.

These laterally-coupled or longitudinally-coupled multimode surface acoustic wave resonator filters adjust the total number of pairs of comb-shaped electrodes and the like to match the input and output impedances, thereby coupling and passing these two resonance modes. It forms a band (hereinafter referred to as a dual-mode surface acoustic wave resonator filter).

In consideration of these standing waves, the input IDT 3
Input terminal 1, 1 ', output terminal 2,
If 2'is provided and a 4-terminal configuration is adopted, the equivalent circuit can be represented as shown in FIG. Letting fs and fa be the resonance frequencies of the standing wave of the symmetric mode and the standing wave of the antisymmetric mode, respectively, L ₁ and C ₁ are the first resonance frequencies on the high pass band side.
Equivalent inductance and capacitance that give (resonance frequency fs generated by the standing wave of the symmetric mode). Also,
L ₂ and C ₂ are an equivalent inductance and an equivalent capacitance that give a second resonance frequency (resonance frequency fa generated by the standing wave of the antisymmetric mode) on the lower side of the pass band. Further, the transformer 21 is inserted in the circuit and is 1: -1 means that the phase of the standing wave in the antisymmetric mode is inverted.
FIG. 10 is an equivalent circuit conversion of the circuit of FIG.
The relationship between the resonance frequency fs and fa of each resonance mode is
fs> fa.

FIG. 11 shows an example of the pass characteristics of a longitudinally coupled dual mode surface acoustic wave resonator filter having a 2IDT structure as shown in FIG. 8 (a). A 45 ° rotation X-cut Z-propagation lithium tetraborate substrate (hereinafter, lithium tetraborate substrate is abbreviated as LBO substrate) is used as a piezoelectric substrate, and a small surface acoustic wave resonator filter having a specific bandwidth of about 0.3 to 0.5% is provided. Has been obtained.

[0009]

By the way, a system having a pass bandwidth of 0.05 to 0.25% in a specific bandwidth has been developed and put into practical use for some digital mobile communication devices. Therefore, a surface acoustic wave resonator filter having a specific bandwidth of about 0.05 to 0.25% is required. Further, there is a strong demand for downsizing in mobile communication devices, and the surface acoustic wave resonator filter is no exception.

As mentioned above, lithium tetraborate (Li ₂ B ₄
O ₇ ) The typical bandwidth of the longitudinally coupled dual-mode surface acoustic wave resonator filter fabricated on the substrate is 0.3-0.5%.
It is a degree. As means for narrowing the pass band width of the longitudinally coupled dual mode surface acoustic wave resonator filter, the
Increasing the IDT logarithm of the IDT (output IDT) and the connection IDT can be mentioned. However, increasing the IDT logarithm increases the amplitude ripple and delay time ripple in the passband,
There is a problem that the flatness of the amplitude characteristic and the group delay time characteristic cannot be satisfied.

On the other hand, as a surface acoustic wave resonator filter manufactured on a quartz substrate, a longitudinally coupled double mode filter, a laterally coupled double mode filter and the like have been put into practical use, but in order to obtain desired characteristics, an IDT is required. It is necessary to increase the logarithm. Therefore, there is a problem that the package size becomes large and it is difficult to cope with the recent demand for miniaturization of mobile communication devices.

An object of the present invention is to provide a longitudinally coupled double mode surface acoustic wave resonator filter which has a narrow pass band width of 0.05 to 0.25% as a specific bandwidth and a remarkably small package size, which has been difficult to realize conventionally. To provide.

[0013]

In order to improve the attenuation characteristic of the surface acoustic wave resonator filter near the pass band, it is considered that forming an attenuation pole near the pass band is an effective means. As a method of forming an attenuation pole in a surface acoustic wave resonator filter, as shown in Japanese Patent Publication No. 59-48565, a surface acoustic wave resonator filter in which surface acoustic wave resonators of 2IDT structure are electrically connected is used. A method is known in which a reactance element is connected in parallel to the series arm impedance displayed by the equivalent circuit of 1 to generate an attenuation pole in the frequency response. Although the surface acoustic wave resonator constituting the surface acoustic wave resonator filter in this embodiment has one resonance point, the reactance elements of different polarities are coupled to the two surface acoustic resonators electrically connected to each other. It is considered that when this is done, a total of two attenuation poles can be formed on the low-pass side and high-pass side of the passband. In the surface acoustic wave resonator filter shown in Japanese Examined Patent Publication No. 59-48565, since there is only one resonance mode that constitutes the pass band, the attenuation pole generated by connecting the reactance element is the surface acoustic wave resonator. There is one for each stage, and therefore, two attenuation poles are generated due to the two-stage configuration.

As one of the configurations of the piezoelectric bulk vibrator, there is known one in which an electromechanical conversion function is added to two mechanical resonators mechanically coupled by a coupling element.
An equivalent circuit of this piezoelectric bulk vibrator is shown in FIG. With this configuration, the polarity of the piezoelectric element is selected so that phase inversion occurs between the input terminals 1 and 1'and the output terminals 2 and 2 ', and the capacitance between the input and output terminals is set.
It is known that by connecting Cb, one attenuation pole is generated on each of the low band side and the high band side of the pass band.

That is, by connecting a capacitance Cb between the terminals 1-2 of the equivalent circuit of the surface acoustic wave resonator filter shown in FIG. 9 (FIG. 2), the attenuation poles are provided on the low frequency side and high frequency side of the resonance frequency. Can be generated, and the amount of attenuation near the pass band can be improved. This method is widely used to secure the amount of attenuation in the vestigial sidebands of television receivers.

Therefore, the present inventors have paid attention to the fact that the electrically equivalent circuit of the longitudinally coupled double-mode surface acoustic wave resonator filter can be expressed similarly to the electrically equivalent circuit of the piezoelectric bulk oscillator, and the piezoelectric bulk oscillator. We wondered if an attenuation pole could be formed in the vicinity of the pass band by connecting a capacitance with the same configuration as in. That is, the input ID for the longitudinally coupled dual-mode surface acoustic wave resonator of the conventional structure shown in FIG.
The electrode on the voltage application side of T3 and output IDT4 or connection IDT
The present invention was conceived in consideration of connecting a capacitance between the electrode 5 and the electrode on the voltage output side.

[0017]

That is, the present invention provides two resonance modes in which a piezoelectric substrate and at least two sets of interdigital transducers on the piezoelectric substrate are arranged close to each other along the traveling direction of the surface acoustic wave and reflectors are arranged on both sides thereof. In a dual-mode surface acoustic wave resonator filter in which surface acoustic wave resonators utilizing the above are cascade-connected, the interdigital transducer is composed of a pair of comb-shaped electrodes that are mutually inserted, and at least one step of the surface acoustic wave is used. At least two sets of interdigital transducers of the wave resonator have one comb-shaped electrode connected to a reference potential, and the other comb-shaped electrode commonly connected via a capacitance. It is a resonator filter, and the combination of the capacitance value and the electrode structure of the surface acoustic wave resonator is different in each stage. A double mode SAW resonator filter, wherein the door. In addition, the interdigital transducer comb-shaped electrode connected to the next-stage surface acoustic wave resonator and the interdigital transducer comb-shaped electrode connected to the preceding surface acoustic wave resonator of each surface acoustic wave resonator are A dual-mode surface acoustic wave resonator filter, which is commonly connected via an electrostatic capacitance. Furthermore, the double mode surface acoustic wave resonator filter is characterized in that a capacitance is connected to the connection portion of the surface acoustic wave resonator and is grounded.

With the above-mentioned structure, the out-of-band suppression amount can be improved, and the double-mode surface acoustic wave resonator filter having the pass bandwidth of 0.05 to 0.25% in the specific bandwidth can be obtained. .

A piezoelectric substrate, an input interdigital transducer connected to an input terminal on the piezoelectric substrate, and two sets of interdigital transducers of a connecting interdigital transducer are arranged close to each other along the traveling direction of the surface acoustic wave, and An energy confinement type first surface acoustic wave resonator using two resonance modes with reflectors arranged on both sides thereof, and two sets of a connection interdigital transducer and an output interdigital transducer connected to an output terminal. An interdigital transducer and an energy confinement type second surface acoustic wave resonator utilizing two resonance modes in which an interdigital transducer is closely arranged along the traveling direction of the surface acoustic wave and reflectors are arranged on both sides thereof. Interdigital transducer for connecting each surface acoustic wave resonator In a dual-mode surface acoustic wave resonator filter that is connected in a gas cascade, each of the interdigital transducers is composed of a pair of comb-shaped electrodes that are interleaved with each other, and is connected to the input terminal of the input interdigital transducer. The electrode and the comb-shaped electrode electrically connected to the interdigital transducer for connecting the second surface acoustic wave resonator of the first surface acoustic wave resonator are connected via a capacitance. It is a dual-mode surface acoustic wave resonator filter characterized by being connected. Furthermore, the double mode surface acoustic wave resonator filter is characterized in that a capacitance is connected to the connection portion of the surface acoustic wave resonator and is grounded. With the above-mentioned configuration, a double-mode surface acoustic wave resonator filter having a good pass band width of 0.05 to 0.25% in the specific band width, which has a good out-of-band suppression amount at frequencies far from the pass band width, is provided. Obtainable.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Capacitance is provided between an electrode on the voltage application side of an IDT and an electrode on the voltage output side of another IDT of a surface acoustic wave resonator constituting a double mode surface acoustic wave resonator filter. By connecting them, attenuation poles are formed on the low-pass side and the high-pass side of the pass band to improve the out-of-band suppression amount.

The principle of the longitudinally coupled double mode surface acoustic wave resonator filter according to the present invention will be described.

An equivalent circuit of the double mode surface acoustic wave resonator filter constituting the longitudinally coupled double mode surface acoustic wave resonator filter can be represented as shown in FIG. L ₁ and C ₁ are an equivalent inductance and an equivalent capacitance representing the first resonance, and the resonance angular frequency ω ₁ is given by ω ₁ ² = 1 / (L ₁ × C ₁ ) (Equation 1). L ₂ and C ₂ are an equivalent inductance and an equivalent capacitance representing the second resonance, and the resonance angular frequency ω ₂ is given by ω ₂ ² = 1 / (L ₂ × C ₂ ) (Equation 2). In addition, the resonance mode that gives ω ₂ is represented by using the transformer 21 because the phase is inverted. These ω ₁ and ω ₂ form a pass band.

When a capacitance is connected in parallel to the impedance arm composed of the equivalent inductance and the equivalent capacitance,
Due to the parallel resonance, an anti-resonance frequency is generated on the low band side or the high band side of the pass band, and this appears as an attenuation pole in the pass characteristic of the surface acoustic wave resonator filter. FIG. 2 shows an equivalent circuit in which a capacitance Cb is connected between terminals 1-2 of the circuit of FIG.

When the electrostatic capacitance Cb is connected in parallel to the series impedance composed of the equivalent inductance L ₁ and the equivalent capacitance C ₁ , the antiresonance angular frequency ω _a1 is ω _a1 ² = (C ₁ + Cb) / (L ₁ × C ₁ × Cb)> ω ₁ ² (Equation 3), and an attenuation pole is formed on the resonance angular frequency ω _{1, that} is, on the high frequency side of the pass band.

On the other hand, the equivalent inductance L ₂ and the equivalent capacitance
Capacitance Cb in parallel with the series impedance composed of C ₂
, The anti-resonance angular frequency ω _a2 becomes ω _a2 ² = (Cb-C ₂ ) / (L ₂ × C ₂ × Cb) <ω ₂ ² (Equation 4) because phase inversion occurs. An attenuation pole is formed on the resonance angular frequency ω _{2, that} is, on the low frequency side of the pass band.

Since the value of the electrostatic capacitance Cb depends on the characteristic impedance of the surface acoustic wave resonator filter, it is set according to its electrode structure and required characteristics. Depending on the value of capacitance,
The frequency at which the attenuation pole is generated can be changed, and the out-of-band suppression amount can be adjusted. This is also possible by changing the resonance frequency of the surface acoustic wave resonator.

Further, by selecting a surface acoustic wave resonator which constitutes a longitudinally coupled dual mode surface acoustic wave resonator filter coupled with a capacitance, the number of attenuation poles to be formed can be adjusted, and the band width can be adjusted. The amount of external suppression can be improved.

When a capacitance is coupled to the one-stage surface acoustic wave resonator, two attenuation poles are generated. Therefore, all the surface acoustic wave resonator filters in which the N-stage surface acoustic wave resonators are vertically connected are used. When a capacitance is connected to the surface acoustic wave resonator, depending on the combination of the capacitance value of the surface acoustic wave resonator's electrode structure and the capacitance to be connected, N in the low side of the pass band and high in the high side It is possible to form N attenuation poles, a maximum of 2N in total. Therefore, by varying the frequencies of the attenuation poles generated on the low band side or the high band side of the pass band, it is possible to secure a certain amount of attenuation or more in a certain range of frequencies. For example, in the case of a two-stage longitudinally-connected longitudinally coupled dual-mode surface acoustic wave resonator filter in which a capacitance Cb is connected to each of the two-stage surface acoustic wave resonators, the resonance of the first-stage surface acoustic wave resonator Frequency and resonance frequency of the second-stage surface acoustic wave resonator and capacitance Cb1 connected to the first-stage surface acoustic wave resonator
By adjusting the value of the electrostatic capacitance Cb2 connected to the 2nd stage surface acoustic wave resonator, there are 4 attenuations, 2 on the low band side and 2 on the high band side of the pass band with different frequencies. A pole is formed
(It can be confirmed from Formula 3 and Formula 4).

In the case of a two-stage cascaded surface acoustic wave resonator filter, the electrode on the voltage input side of the input IDT of the surface acoustic wave resonator of only the first stage among the surface acoustic wave resonators. When the electrode on the voltage output side of the connection IDT is connected via a capacitance, the amount of feedthrough that occurs between the input terminal and the output terminal is reduced, so that the out-of-band suppression level has a capacitance of each stage. Is better than the case of connecting.

The electrostatic capacitance is formed by forming a comb-shaped electrode for the electrostatic capacitance at a position where it does not interfere with the surface acoustic wave excited by the surface acoustic wave resonator, or by providing the package with the electrostatic capacitance. . Capacitance can be formed on the substrate while keeping the package size small.

Further, the out-of-band suppression amount can be further improved by forming an electrostatic capacitance on the connecting bus bar of the surface acoustic wave resonators that are cascade-connected in multiple stages and grounding the electrostatic capacitance.

[0033]

【Example】

Example 1 A vertical double mode surface acoustic wave resonator filter as shown in FIG. 1 was produced on a 45 ° rotating X cut Z propagating lithium tetraborate substrate. One input IDT 3 having an input terminal 6, one connection IDT 5 and reflectors 6 on both sides thereof.
2nd stage surface acoustic wave in which one output IDT 4 and one connecting IDT 5 having a first stage surface acoustic wave resonator and output terminals 7 and reflectors 6 arranged on both sides thereof are arranged. A resonator was formed, and the connecting IDTs 5 of these surface acoustic wave resonators were connected by a connecting bus bar 7. The input terminal 6 of the input IDT 3 of the first-stage surface acoustic wave resonator and the connecting bus bar 7 of the connecting IDT 5 are connected via a capacitance Cb1, and the second-stage surface acoustic wave resonance is connected. Similarly, the connection bus bar 7 of the child IDT 5 and the output terminal 7 of the output IDT 4 were also connected via the electrostatic capacitance Cb2. In addition, a capacitance Cd was connected to the connecting bus bar 7 and grounded.

The pattern of the comb-shaped electrodes was formed by vacuum-depositing an aluminum metal film, forming a resist pattern by a well-known photolithography technique, and then etching the aluminum metal film. In addition, the comb-shaped electrode is of a so-called normal type in which the overlapping lengths of the paired electrode fingers are substantially equal. The input IDT 3 (output IDT 4) has 44.5 comb electrode pairs, and the connecting IDT 5 has 40 comb electrode pairs.
Five pairs, the aperture length is 9.3λ, the number of reflectors is 70, the comb electrode period is 0.985λ, the reflector period is λ, and the metallization ratio is 0.5. The terminating impedance was 250Ω and matched. That is, the surface acoustic wave resonator is a so-called energy trapping type in which the comb-shaped electrode period is made slightly smaller than the reflector period and excellent resonance characteristics (high Q value) can be achieved. Capacitance
Cb1, Cb2, and Cd were 0.1 pF, 0.1 pF, and 0.8 pF, respectively, and were formed by interdigital electrodes.

FIG. 3 is a diagram showing the frequency response of the dual mode surface acoustic wave resonator filter according to the present invention. The pass bandwidth was 0.22% in terms of specific bandwidth. Here, the value of the specific bandwidth is based on the standardized frequency obtained by standardizing the frequency at the center frequency. Attenuation poles are on the low frequency side (normalized frequency is near 0.997) and high frequency side (normalized frequency is near 1.00035) in the passband
You can see that they are formed one by one. S _{21 in} FIG. 3 is a parameter representing the insertion loss.

FIG. 4 shows electrostatic capacitance Cb1 = Cb2 = Cb connected to the two-stage surface acoustic wave resonators of the longitudinally coupled dual mode surface acoustic wave resonator filter of FIG. 0.1p
It is a figure showing the frequency response when changing to F, 0.2pF, 0.3pF, and 0.4pF. It can be seen that as the value of Cb is increased, the frequencies of the attenuation poles formed on the low band side and the high band side of the pass band approach the pass band.

FIG. 5 is a diagram showing the frequency response when the values of the longitudinally coupled dual mode surface acoustic wave resonator filter of FIG. 1 and the capacitances Cb1 = 0.3 pF and Cb2 = 0.1 pF are varied. . Since the value of the capacitance to be connected is changed between the surface acoustic wave resonator in the first stage and the surface acoustic wave resonator in the second stage, the attenuation pole is on the lower side of the passband (normalized frequencies 0.997 and 0.9975). It can be seen that two each are formed on the high frequency side (near) and on the high frequency side (normalized frequencies around 1.002 and 1.035). The outer damping pole is formed of Cb2 and the inner damping pole is formed of Cb1.

Example 2 A vertical double mode surface acoustic wave resonator filter as shown in FIG. 1 was produced on a 45 ° rotating X cut Z propagating lithium tetraborate substrate. One input IDT 3 having an input terminal 6, one connection IDT 5 and a first stage surface acoustic wave resonator having reflectors 6 arranged on both sides thereof and one output IDT 4 having an output terminal 7. And one IDT for connection
5 and a second-stage surface acoustic wave resonator in which reflectors 6 are arranged on both sides thereof for connecting these surface acoustic wave resonators.
The IDTs 5 were connected to each other by the connecting bus bar 7. The input terminal 6 of the input IDT 3 of the first-stage surface acoustic wave resonator and the connecting bus bar 7 of the connecting IDT 5 were connected via a capacitance Cb1. IDT for connecting the second stage surface acoustic wave resonator
No capacitance Cb2 was connected between the connecting bus bar 7 of 5 and the output terminal 7 of the output IDT 4. Capacitance Cb1 = 0.
The electrode structure was the same as in Example 1 with 3 pF.

The pass bandwidth of this filter is a specific bandwidth of 0.
It was 22%. The frequency response is shown in FIG. In addition, the results of Example 1 when Cb1 = Cb2 = 0.1pF are shown in FIG. 6 (b), and the results of Example 1 when Cb1 = 0.3pF and Cb2 = 0.1pF are shown in FIG. 6 (c). In the case of the vertical double-mode surface acoustic wave resonator filter of FIG. 6 (a), the attenuation poles are located on the low band side and the high band side of the pass band.
They are formed one by one, and since the capacitance Cb2 is not connected, the amount of suppression outside the band can be large. In the configuration of FIG. 6C, since the capacitances Cb1 and Cb2 are changed, two attenuation poles are formed on the low band side and the high band side of the pass band. In this case, this is a particularly effective means when it is desired to secure a certain amount of attenuation or more in a certain frequency range near the pass band.

(Comparative Example) A vertical double-mode surface acoustic wave resonator filter as shown in FIG. 8A was produced on a 45 ° rotating X-cut Z-propagating lithium tetraborate substrate. Input terminal 6
1 input IDT 3 having 1 and 1 connection IDT 5 and 1 output IDT 4 having 1st stage surface acoustic wave resonator having output terminals 7 and a 1st stage surface acoustic wave resonator having reflectors 6 arranged on both sides thereof and 1 The connecting IDT 5 and the second-stage surface acoustic wave resonator in which the reflectors 6 are arranged on both sides of the connecting IDT 5 are formed, and the connecting IDTs 5 of these surface acoustic wave resonators are connected by the connecting bus bar 7.
Input IDT3, output IDT4, connection IDT5, reflector 6,
The structure of the connecting bus bar 7 is similar to that of the embodiment.

FIG. 11 is a diagram showing the frequency response of the dual mode surface acoustic wave resonator filter according to the comparative example. The pass bandwidth was about 0.3 to 0.5% in terms of specific bandwidth. It can be seen that the attenuation characteristic is poor in the vicinity of the pass band as compared with the example.

In the embodiment, the electrostatic capacitances Cb1 and Cb2 are adjusted, but the pass band width is controlled by the electrostatic capacitance Cd connected to the connecting bus bar of the front and rear surface acoustic wave resonators connected in a multistage cascade. It is also possible. The capacitance Cd connected to the connecting bus bar can improve the attenuation characteristic in the vicinity of the pass band without providing it.

In the embodiment, the piezoelectric substrate is rotated by 45 °.
An X-cut Z-propagating lithium tetraborate substrate has been described. However, it has good temperature characteristics and a large electromechanical coupling coefficient of 40 °.
Needless to say, it can be applied to other piezoelectric substrates such as a ~ 45 ° rotation X-cut Z-propagation lithium tetraborate substrate, a quartz substrate, a LiNbO ₃ substrate, and a LiTaO ₃ substrate.

[0044]

By constructing the dual mode surface acoustic wave resonator filter as described above, it becomes possible to generate an attenuation pole near the pass band and to easily control the pass band width. It is possible to provide a dual-mode surface acoustic wave resonator filter suitable for a communication system in which the pass bandwidth which cannot be applied is 0.05 to 0.25% in specific bandwidth.

Japanese Patent Laid-Open No. 55-3307 discloses a dual mode surface acoustic wave resonator composed of two IDTs (no reflector outside the IDT). 2 in Figure 11 of the specification
It is disclosed that by inserting a stray capacitance or a specific capacitance between bus ID electrodes of each IDT electrode, an attenuation pole is formed in the vicinity of the pass band and the cutoff characteristic becomes steep. However, the surface acoustic wave resonator of the present invention is not
There are reflectors on both outer sides of T, and the structure of the surface acoustic wave resonator is different. Therefore, in JP-A-55-3307, unlike the surface acoustic wave of the present application, excellent resonance characteristics cannot be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an example of a dual mode surface acoustic wave resonator filter of the present invention.

FIG. 2 is a diagram showing an equivalent circuit of a surface acoustic wave resonator filter according to the present invention.

FIG. 3 is a diagram showing a frequency response of a dual mode surface acoustic wave resonator filter (Cb1 = Cb2) of an example.

FIG. 4 is a diagram showing a frequency response when the value of the electrostatic capacitance Cb is changed in the dual mode surface acoustic wave resonator filter of the example.

FIG. 5 is a diagram showing a frequency response of a dual mode surface acoustic wave resonator filter (Cb1 ≠ Cb2) of the example.

FIG. 6 is a diagram showing the frequency response of the dual mode surface acoustic wave resonator filter of the example, in which (a) is Cb1 = 0.3 pF (C
b2 = 0pF), (b) Cb1 = Cb2 = 0.1pF, (c) Cb1 = 0.3p
It is the frequency response when the capacitance of F and Cb2 = 0.1pF.

FIG. 7A is a schematic diagram showing the configuration and standing wave distribution of an example of a conventional laterally coupled multimode surface acoustic wave resonator filter. FIG. 2B is a schematic diagram showing the configuration and standing wave distribution of an example of a conventional longitudinally coupled dual mode surface acoustic wave resonator filter. It is a figure which shows the structure of the conventional vertical double mode surface acoustic wave resonator filter.

8A and 8B are diagrams showing an example of the configuration of a conventional vertical double-mode surface acoustic wave resonator filter.

FIG. 9 is a diagram showing an equivalent circuit of a conventional dual mode surface acoustic wave resonator filter.

10 is a diagram showing another equivalent circuit of a conventional dual mode surface acoustic wave resonator filter obtained by equivalently converting the circuit of FIG.

FIG. 11 is a diagram showing a frequency response of a vertical double-mode surface acoustic wave resonator filter manufactured on a lithium tetraborate substrate of a comparative example (conventional).

FIG. 12 is a diagram showing an equivalent circuit of an example of a piezoelectric bulk vibrator.

[Explanation of symbols]

1, 1'Input terminal 2, 2'Output terminal 3 Input IDT 4 Output IDT 5 Connection IDT 6 Reflector 7 Connection busbar 8 Input terminal 9 Output terminal Cb, Cb1, Cb2, Cd Capacitance 10a, 10b , 10c Interdigital transducer (IDT) 11 Standing wave of symmetric mode 12 Standing wave of antisymmetric mode 13 Standing wave of 0th symmetric mode 14 Standing wave of 1st order antisymmetric mode 21 Transformer

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Claims (4)

(57) [Claims] 1. A piezoelectric substrate, and at least two on the piezoelectric substrate.
A pair of interdigital transducers and a pair of interdigital transducers are arranged close to each other in the traveling direction of a surface acoustic wave, and a surface acoustic wave resonator utilizing two resonance modes, in which reflectors are arranged on both sides of the surface acoustic wave, is connected in multiple stages in a dual mode elasticity. A surface acoustic wave resonator filter , wherein the interdigital transducer is composed of a pair of comb-shaped electrodes that are interleaved with each other, and one interdigital transducer of at least two sets of at least one stage of the surface acoustic wave resonator. In a dual-mode surface acoustic wave resonator filter , the electrodes are connected to a reference potential, and the other comb-shaped electrodes are commonly connected via an electrostatic capacitance. Pair with child electrode structure
A double module characterized in that the matching is different at each stage.
Surface acoustic wave resonator filter. 2. A method according to claim 1 Symbol, characterized in that grounded it connects the capacitance to the connection portion of the SAW resonator
Double mode SAW resonator filter of the mounting. 3. A piezoelectric substrate, an input interdigital transducer connected to an input terminal on the piezoelectric substrate, and two sets of interdigital transducers, which are an interdigital transducer for connection, are arranged close to each other along a traveling direction of a surface acoustic wave. And an energy confinement type first surface acoustic wave resonator using two resonance modes in which reflectors are arranged on both sides, and an interdigital transducer for connection and an interdigital transducer for output connected to the output terminal. A pair of interdigital transducers and a second surface acoustic wave resonator of an energy confinement type utilizing two resonance modes in which a pair of interdigital transducers are closely arranged along the traveling direction of the surface acoustic wave and reflectors are arranged on both sides thereof. The interdigital transducer for connecting each surface acoustic wave resonator. In a dual-mode surface acoustic wave resonator filter that is connected in a gas cascade, each of the interdigital transducers is composed of a pair of comb-shaped electrodes that are interleaved with each other, and is connected to the input terminal of the input interdigital transducer. The electrode and the comb-shaped electrode electrically connected to the interdigital transducer for connecting the second surface acoustic wave resonator of the first surface acoustic wave resonator are connected via a capacitance. A dual mode surface acoustic wave resonator filter characterized by being connected. Claim 3 Symbol, characterized in that grounded it connects the capacitance to the connection portion of the SAW resonator
Double mode SAW resonator filter of the mounting.