JPH0851334A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To obtain a surface acoustic wave filter capable of miniaturization over a wide band and realizing a stable characteristic and balanced input/output. CONSTITUTION:A first SAW resonator consisting of an IDT electrode 52a and reflector electrodes 52b and 52c, a second SAW resonator consisting of an IDT electrode 53a and reflector electrodes 53b and 53c and a third SAW resonator consisting of an IDT electrode 54a and reflector electrodes 54b and 54c are formed on a piezoelectric substrate 51. One electrode finger of the IDT electrode 53a is grounded through an electrode pattern provided in a clearance between the IDT electrode 52a and the reflector electrode 52b. The other electrode finger of the IDT electrode 53a is grounded through an electrode pattern provided in a clearance between the IDT electrode 54a and the reflector electrode 54c. A bus bar electrode of a part where the IDT electrodes are adjacent to each other is made independant electrically.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter used in a high frequency circuit of a wireless device.

[0002]

2. Description of the Related Art Surface acoustic wave (SAW) filters have been widely used as filters for RF and IF stages in transmission / reception circuits of communication equipment. In recent years, with the digitalization of mobile communication, development of digital mobile phones and digital cordless phones has been actively promoted. In the communication systems used for these, since information is given to the phase in addition to the amplitude, it is important that the filter used in the IF stage has not only good amplitude characteristics but also flat group delay deviation characteristics. . Further, since excellent characteristics are required for the selectivity for distinguishing between the signal of the adjacent channel and the desired signal, a steep out-of-band attenuation amount characteristic is required. Furthermore, recently, due to the high density mounting accompanying the miniaturization of the set,
Problems such as coupling and interference between parts due to insufficient ground strength and insufficient shield are being developed, and balanced circuits are being developed in order to suppress the effects.

Conventionally, SA which can be used for IF stage
As a W filter, a transversal type SAW filter and two types of SAW resonator filters of a longitudinal mode coupling resonator type and a transverse mode coupling resonator type are well known.
The transversal type SAW filter has excellent group delay deviation characteristics, but has a large insertion loss and size, and also has poor out-of-band attenuation characteristics. On the other hand, the SAW resonator filter has excellent out-of-band attenuation amount characteristics, small insertion loss and size, but inferior in group delay deviation characteristics as compared with the transversal type. In addition, the longitudinal mode coupled resonator type is characterized in that there is a large spurious near the pass band in the high frequency side.
The transverse mode coupled resonator type is characterized by having a very narrow band pass characteristic. As a conventional IF filter for mobile communication, a transverse mode coupled resonator type SAW filter, which is small and has excellent out-of-band attenuation characteristics, has been often used.

Hereinafter, a conventional transverse mode coupled resonator type SAW is used.
The filter will be described. FIG. 24 is a configuration diagram showing an electrode pattern of a transverse mode coupled resonator type SAW filter in the related art. In FIG. 24, reference numeral 241 is a single crystal piezoelectric substrate, and by forming an electrode pattern on this piezoelectric substrate 241, surface acoustic waves can be excited. 242a is an interdigital transducer (IDT) electrode, and reflector electrodes 242 are provided on both sides of the electrode.
By arranging b and 242c, an energy trap type SAW resonator is formed. A similar SAW resonator is formed by the IDT electrode 243a and the reflector electrodes 243b and 243c. The two resonators are arranged close to each other, and acoustic coupling occurs between them, thereby forming a first-stage SAW resonator filter. Further, the IDT electrode 2 is formed on the piezoelectric substrate 241.
44a, 245a and reflector electrodes 244b, 244c,
245b and 245c allow the second stage SA to be used as described above.
A W resonator filter is constructed. SAW of the above two steps
The resonator filters are electrically connected in cascade by the electrode pattern 246, and thus a multi-stage connection SAW filter is configured.

A multi-stage connection SAW configured as described above
In the filter, the modal frequencies of the two types of surface acoustic waves excited on the piezoelectric substrate are determined by the crossing width of the electrode fingers of the IDT electrode and the distance between two SAW resonators arranged close to each other, and the pass band width of the filter is Set.

[0006]

However, in the multistage SAW filter configured as described above, the achievable bandwidth is extremely narrow, and the realized specific bandwidth (at the center frequency of the filter) The normalized bandwidth) is at most about 0.1%. Further, since the input / output impedance characteristic depends on the dimension of the finger cross width of the IDT electrode, it is difficult to realize an arbitrary impedance. Further, since one side of the electrode fingers of the IDT electrodes 242a and 245a of the input / output stage is grounded, balanced input / output cannot be realized.

Further, in order to correspond to the above-mentioned digitization, (1) widen the pass characteristic to widen the flat band of the group delay deviation characteristic, and (2) enable balanced input / output. Is required. Conventionally, when a wider band is required, an extension coil has been inserted between the stages of the filter and the ground. Further, a matching circuit element is added to the input / output stage in order to connect to the peripheral circuit.

However, in such a structure, since the extension coil and the matching circuit element are provided outside the SAW filter,
There are problems that the number of parts increases and the size of the entire circuit increases, and that variations and couplings of these elements adversely affect the circuit characteristics of the filter, and the input and output are unbalanced.

In order to solve the above-mentioned problems in the prior art, the present invention can realize miniaturization and wide band, stable characteristics, and balanced input / output. An object of the present invention is to provide a surface acoustic wave filter capable of achieving the above.

[0010]

In order to achieve the above object, the first structure of the surface acoustic wave filter according to the present invention is
Interdigital transducer (ID
T) surface acoustic wave (S) with reflector electrodes on both sides of the electrode
AW) Three resonators are acoustically coupled by arranging three resonators close to each other in parallel with the SAW propagation direction, and all the IDT electrodes constituting the SAW resonator arranged at the center are grounded, and the SAW arranged outside the SAW resonator. The IDT electrodes forming the resonator are electrically independent.

In the first structure of the present invention, the IDT electrode forming the SAW resonator arranged at the center and the IDT electrode forming the SAW resonator arranged outside are arranged.
It is preferably grounded via an electrode pattern arranged in the gap between the electrode and the reflector electrode.

Further, in the first configuration of the present invention, it is preferable that a plurality of cascaded connection electrode patterns are formed on the piezoelectric substrate and are connected in cascade. Further, in this case, it is preferable to form an electrode pad for bonding on a part of the inter-stage connection electrode pattern. Further, in this case, it is preferable that the inter-stage connection electrode pattern is grounded via the reactance element formed by the electrode pattern on the same piezoelectric substrate. In this case, it is further preferable that the reactance element is a spiral inductor.

The second structure of the surface acoustic wave filter according to the present invention is such that three SAW resonators having reflector electrodes on both sides of an IDT electrode are provided on a piezoelectric substrate in parallel with the SAW propagation direction. The S adjacent to each other and acoustically coupled to each other are adjacent to each other.
The bus bar electrode pattern between the AW resonators is divided, and all the IDT electrodes constituting the SAW resonator arranged at the center are grounded.

In the second structure of the present invention, I which constitutes one of the SAW resonators arranged outside is I.
It is preferable to connect the DT electrode to the balanced input terminal and connect the IDT electrode forming the other SAW resonator arranged outside to the balanced output terminal. Further, in this case, the line width of the bus bar electrode pattern forming the IDT electrode of the SAW resonator arranged outside is set to the line width of the bus bar electrode pattern forming the IDT electrode of the SAW resonator arranged in the center. It is preferably larger than the width.

In the second structure of the present invention, the IDT electrode forming the SAW resonator arranged in the center is provided in the gap between the IDT electrode and the reflector electrode of the SAW resonator arranged outside. It is preferably grounded through the arranged electrode pattern.

In the second structure of the present invention, it is preferable that a plurality of inter-stage connection electrode patterns formed on the piezoelectric substrate are connected in cascade. Also,
In this case, it is preferable to form an electrode pad for bonding on a part of a plurality of inter-step connection electrode patterns.
Further, in this case, it is preferable that a plurality of inter-stage connection electrode patterns are connected to each other via a reactance element.
Further, in this case, it is preferable that one of the plurality of inter-stage connection electrode patterns is grounded and the other inter-stage connection electrode pattern is grounded via the reactance element. In this case, it is preferable that the reactance element is a spiral inductor formed by the electrode pattern on the same piezoelectric substrate.

The third structure of the surface acoustic wave filter according to the present invention is such that two SAW resonators having reflector electrodes on both sides of an IDT electrode are provided on a piezoelectric substrate in parallel with the SAW propagation direction. And forming the SAW between the SAW resonators.
By arranging strip line electrodes having a length substantially equal to the IDT electrode finger cross width of the resonator in parallel with the SAW resonator at the same electrode period, a periodic structure electrode array is formed and the SAW resonance is formed. The container and the periodic structure electrode array are arranged close to each other and are acoustically coupled.

In the third structure of the present invention, it is preferable that the strip line electrodes forming the periodic structure electrode array are connected to each other by bus bar electrodes provided at both ends thereof. Further, in this case, it is preferable that the periodic structure electrode is grounded via the bus bar electrode and the electrode arranged in the gap between the IDT electrode and the reflector electrode of the SAW resonator arranged outside. Further, in this case, it is preferable that one SAW resonator electrode arranged on the outer side is connected to the balanced type input terminal and the other SAW resonator electrode arranged on the outer side is connected to the balanced type output terminal. . further,
In this case, the line width of the bus bar electrode pattern on the side adjacent to the periodic structure electrode of the IDT electrode constituting the SAW resonator arranged on the outside is set to the bus bar electrode pattern formed on the periodic structure electrode. It is preferable that the width is larger than the track width. Further, in this case, it is preferable that a plurality of cascade-connected electrode patterns formed on the piezoelectric substrate are connected in cascade.

In the third structure of the present invention, the I on the side adjacent to the periodic structure electrode array of the SAW resonator.
It is preferable that the DT electrode and the bus bar electrode that connects the periodic structure electrode array are integrated and that the periodic structure electrode array is grounded. Further, in this case, it is preferable that a plurality of inter-stage connection electrode patterns formed on the piezoelectric substrate be connected in cascade. Further, a fourth structure of the surface acoustic wave filter according to the present invention is such that an IDT is formed on a piezoelectric substrate.
Two SAW resonator filters, in which SAW resonators each having a reflector electrode on both sides of the electrode are closely arranged and acoustically coupled to each other, are formed, and the electrode arrangement of the SAW resonator constituting the first SAW resonator filter is reversed. The SAW resonators constituting the second SAW resonator filter are arranged in phase and the electrodes are arranged in the same phase, and the first SAW resonator filter and the second SAW resonator are arranged in phase.
The W resonator filters are connected in parallel.

In the fourth aspect of the present invention, the first aspect
It is preferable that the high-frequency side excitation frequency of one of the SAW resonator filters and the low-frequency side excitation frequency of the other SAW resonator filter of the second SAW resonator filter and the second SAW resonator filter are matched.

Further, the fifth structure of the surface acoustic wave filter according to the present invention is a SAW resonance in which SAW resonators having reflector electrodes on both sides of an IDT electrode are closely arranged and acoustically coupled on a piezoelectric substrate. Of four SAW resonators, the electrodes of the SAW resonators forming the first and second SAW resonator filters have opposite phases, and the electrodes of the SAW resonators forming the third and fourth SAW resonator filters The arrangement is the same phase, the first SAW resonator filter and the third SAW resonator filter are connected in parallel, and the second SAW resonator filter and the fourth SAW resonator filter are connected in parallel. At the same time, the first and third SAW resonator filters and the second and fourth SAW resonator filters are connected in series by an electrode pattern formed on the piezoelectric substrate.

Further, in the fifth configuration of the present invention, the high-side excitation frequency of one of the SAW resonator filters of the first and third SAW resonator filters and the other SAW resonator filter of the other SAW resonator filter. Of the second and fourth SAW resonator filters, the high-side excitation frequency of one of the second and the fourth SAW resonator filters and the low-frequency of the other SAW resonator filter of the other SAW resonator filter. It is preferable to match the values of the side excitation frequencies.

In addition, in the fifth aspect of the present invention, the first SAW resonator filter and the second SAW resonator filter are arranged next to each other in parallel with the propagation direction of the surface acoustic wave, and the third SAW resonator filter and the third SAW resonator filter are arranged next to each other. SAW resonator filter and 4th
It is preferable to arrange the SAW resonator filter of (1) adjacent to each other in parallel with the propagation direction of the surface acoustic wave.

The sixth structure of the surface acoustic wave filter according to the present invention is a SAW resonator in which a SAW resonator having reflectors on both sides of an IDT electrode is closely arranged and acoustically coupled on a piezoelectric substrate. The resonator filter is configured to divide the bus bar electrode pattern in the central portion of the IDT electrode adjacent to the SAW resonator filter, and the plurality of SAW resonators arranged close to each other have electrically independent bus bars. It is a thing.

Further, in the sixth structure of the present invention, two surface acoustic wave filters are formed on the same piezoelectric substrate, and the electrode arrangement of the SAW resonator constituting the first SAW resonator filter is reversed phase. And the electrode arrangement of the SAW resonator forming the second SAW resonator filter is in phase with the first SAW resonator filter and the second SAW resonator.
It is preferable to connect the W resonator filters in parallel. Further, in this case, the values of the high-side excitation frequency of one of the first and second SAW resonator filters and the low-side excitation frequency of the other SAW resonator filter. Are preferably matched.

A seventh structure of the surface acoustic wave filter according to the present invention is a SAW resonance in which SAW resonators having reflector electrodes on both sides of an IDT electrode are closely arranged and acoustically coupled on a piezoelectric substrate. The central busbar electrode pattern of the filter is divided into four SAW resonator filters to form the first and second SAW resonator filters.
The electrodes of the AW resonator are arranged in reverse phase, and the third and fourth SAs are arranged.
The electrode arrangements of the SAW resonators constituting the W resonator filter are in the same phase, and the first SAW resonator filter and the third SAW resonator filter are the same.
SAW resonator filters are connected in parallel, and the second S
An AW resonator filter and the fourth SAW resonator filter are connected in parallel, and a space between the first and third SAW resonator filters and the second and fourth SAW resonator filters is on the piezoelectric substrate. The electrodes are connected in series by the electrode pattern formed on.

In the seventh structure of the present invention, the high-side excitation frequency of one of the first and third SAW resonator filters and the low SAW resonator filter of the other SAW resonator filter. The values of the band-side excitation frequencies are made to match, and the high-band side excitation frequency of one of the second and fourth SAW resonator filters and the low-band side of the other SAW resonator filter. It is preferable to match the values of the excitation frequencies.

In the eighth structure of the surface acoustic wave filter according to the present invention, the reactance element is formed by utilizing a part of the electrode pattern forming the SAW filter. In addition, in the eighth configuration of the present invention, the IDT
It is preferable that the reactance element is formed by using an electrode and a reflector electrode, and using the reflector electrode. Further, in this case, it is preferable that the reactance element is an inductor formed by connecting the stripline electrodes arranged in parallel and forming the reflector electrode in a substantially zigzag shape. Further, in this case, it is preferable that the reactance element is an inductor formed by bundling a plurality of parallel-arranged stripline electrodes forming a reflector electrode and connecting them in a substantially zigzag shape. Further, in this case, it is preferable that the reactance element is a capacitor formed by connecting strip electrodes arranged in parallel and forming a reflector electrode in an interdigital form.

In the eighth structure of the present invention, it is preferable that the reactance element is used to form the input / output matching circuit. Further, in the eighth configuration of the present invention, it is preferable that the reactance element is used to configure the interstage matching circuit.

Further, in the eighth structure of the present invention, it is preferable that a plurality of SAW resonators having reflector electrodes on both sides of the IDT electrode are arranged close to each other for acoustic coupling. Further, in this case, it is preferable to configure the reactance element by utilizing the reflector electrode.

In the ninth structure of the surface acoustic wave filter according to the present invention, a plurality of SAW resonators having reflector electrodes on both sides of the IDT electrode are closely arranged and acoustically coupled to each other.
Form a plurality of AW resonator filters on the same piezoelectric substrate,
While connecting the SAW resonator filters in cascade,
An input / output matching circuit is configured using a reactance element formed by the electrode pattern on the piezoelectric substrate.

Further, in the ninth aspect of the present invention, it is preferable that the reactance element is constructed by utilizing the reflector electrode. The tenth configuration of the surface acoustic wave filter according to the present invention is the same piezoelectric substrate having a SAW resonator filter in which a plurality of SAW resonators having reflector electrodes on both sides of an IDT electrode are closely arranged and acoustically coupled. A plurality of SAW resonator filters are formed on the upper side, the SAW resonator filters are connected in series, and the connection points are grounded via a reactance element formed by an electrode pattern on the same piezoelectric substrate.

In the tenth structure of the present invention, the reactance element is preferably a spiral inductor. Further, in this case, it is preferable to form the spiral inductor by utilizing the space between the plurality of SAW filters. Further, in this case, it is preferable to provide at least one short-circuit electrode pattern that short-circuits and connects the adjacent winding electrode patterns of the spiral inductor.

[0034]

According to the first structure of the present invention, three SAW resonators having reflector electrodes on both sides of the IDT electrode are arranged close to each other on the piezoelectric substrate in parallel with the SAW propagation direction. All the IDT electrodes composing the SAW resonator arranged in the center are grounded, and the IDT electrodes composing the SAW resonator arranged outside are electrically independent so that they are arranged in the center. Since the potential of the SAW resonators thus arranged can be freely distributed and the potentials are not canceled between the SAW resonators arranged outside, a strong excitation strength can be obtained even for the secondary mode. As a result, a SAW filter using three excitation modes can be realized, and a wider band pass characteristic than a conventional SAW filter using two excitation modes can be obtained without using an external expansion coil or the like. Therefore, the size of the filter circuit can be reduced. In addition, S using three excitation modes in this way
Since the AW filter can be realized, the conventional 2
The out-of-band attenuation gradient characteristic becomes steeper than that of the next SAW filter, and a better selectivity characteristic can be obtained.

Further, in the first configuration of the present invention,
According to a preferable configuration, the IDT electrode forming the SAW resonator arranged in the center is grounded via the electrode pattern arranged in the gap between the IDT electrode forming the SAW resonator arranged outside and the reflector electrode. For example, since the degree of freedom in determining the distance between the IDT electrode and the reflector electrode forming the SAW resonator is increased, the distance between the IDT electrode and the reflector electrode can be appropriately set to suppress the out-of-band spurious.
As a result, better out-of-band characteristics can be obtained.

Further, in the first configuration of the present invention,
According to a preferable configuration in which a plurality of cascaded connection electrode patterns formed on the piezoelectric substrate are connected in cascade, the out-of-band attenuation amount characteristic is significantly improved, and a better filter characteristic can be obtained. Further, in this case, according to a preferable configuration in which an electrode pad for bonding is formed on a part of the inter-stage connection electrode pattern, a matching element such as an inductance is connected to the inter-stage connection electrode pattern to obtain good pass characteristics. In this case, the connection between the inter-stage connection electrode pattern and the external circuit becomes easy. Further, in this case, according to the preferable configuration in which the inter-stage connection electrode pattern is grounded via the reactance element formed by the electrode pattern on the same piezoelectric substrate, an external circuit is not required, so that the filter circuit can be downsized. Can be planned. In this case, further, the reactance element can be downsized according to a preferable configuration in which the reactance element is a spiral inductor.

According to the second structure of the present invention,
On the piezoelectric substrate, three SAW resonators having reflector electrodes on both sides of the IDT electrode are arranged close to each other in parallel with the propagation direction of the SAW and acoustically coupled, and two bus bars between the adjacent SAW resonators. By dividing the electrode pattern for use and grounding all the IDT electrodes constituting the SAW resonator arranged in the center, the bus bar in the central portion of the IDT electrode can be electrically independent, so that it can be arranged outside. All the IDT electrodes of the SAW resonator can be independently wired. Therefore, the ID that constitutes the SAW filter
Of the T electrodes, the IDT of the SAW resonator arranged in the center
Since only the electrode is grounded, this portion can be electrically isolated from the input / output terminal. As a result, the grounding state of the IDT electrode does not directly affect the input / output characteristics of the filter, and the direct achievement of the signal between the input / output terminals is also greatly reduced, so that the out-of-band attenuation characteristic of the filter is further improved. be able to.

In the second structure of the present invention,
IDT that constitutes one SAW resonator arranged outside
According to a preferable configuration in which the electrode is connected to the balanced type input terminal and the IDT electrode constituting the other SAW resonator arranged outside is connected to the balanced type output terminal, it is possible to use an external circuit such as a balun. , IC before and after the filter
Since balanced elements such as can be connected, noise characteristics of the entire circuit can be improved. Further, in this case, the line width of the bus bar electrode pattern forming the IDT electrode of the SAW resonator arranged on the outer side is calculated from the line width of the bus bar electrode pattern forming the IDT electrode of the SAW resonator arranged in the center. According to the preferable configuration in which the filter is also increased, the insertion loss of the filter can be improved. The reason will be described below. The distance G between the comb-shaped electrodes forming the IDT electrodes of the adjacent SAW resonators governs the degree of coupling between the two SAW resonators. The smaller this distance, the greater the degree of coupling between the SAW resonators, resulting in a wider band. Is preferred. However, if this distance G is too small, the line widths W ₁ and W _{2 of the} bus bar electrodes provided in this portion become smaller than that, so that the electrical resistance loss of the IDT electrode in this portion is reduced by the insertion loss of the filter. Can no longer be ignored. Here, the bus bar electrode (line width W ₁ ) arranged outside is directly connected to one of the balanced input / output terminals, but the bus bar electrode (line width W ₂ ) arranged in the center is the SAW resonator in the center. It is used for grounding the IDT electrode that constitutes the element, and is not electrically connected to the input / output terminal. That is, the size of the line width W ₂ of the bus bar electrode arranged in the center has no influence on the insertion loss of the filter. Therefore, if the line width W ₁ of the bus bar electrode arranged in the center is increased and the line width W ₁ of the bus bar electrode arranged outside is increased by the amount corresponding to the decrease of the line width W ₂ of the bus bar electrode arranged in the center, the space between the comb-shaped electrodes forming the IDT electrodes of the adjacent SAW resonators is increased. Since the electrical resistance loss to the input / output terminal can be reduced without changing the size of the distance G, the insertion loss of the filter can be improved.

In the second structure of the present invention,
According to the preferable configuration in which the IDT electrode forming the SAW resonator arranged in the center is grounded via the electrode pattern arranged in the gap between the IDT electrode and the reflector electrode of the SAW resonator arranged outside Since the degree of freedom in determining the distance between the IDT electrode and the reflector electrode forming the SAW resonator is increased, the distance between the IDT electrode and the reflector electrode can be appropriately set to suppress the out-of-band spurious. as a result,
It is possible to obtain better out-of-band characteristics.

In the second structure of the present invention,
According to the preferable configuration in which a plurality of inter-stage connection electrode patterns formed on the piezoelectric substrate are connected in cascade, the out-of-band attenuation amount characteristic is significantly improved, and a better filter characteristic can be obtained. . Further, in this case, according to the preferable configuration in which the electrode pad for bonding is formed on a part of the plurality of inter-stage connection electrode patterns, a matching element such as an inductance is connected to the inter-stage connection electrode pattern to achieve a good passage. When obtaining the characteristics, the connection between the inter-stage connection electrode pattern and the external circuit becomes easy. Also in this case,
According to the preferable configuration in which the plurality of inter-stage connection electrode patterns are connected to each other through the reactance element, good pass characteristics can be obtained. Further, in this case, good pass characteristics can also be obtained by a preferable configuration in which one of the plurality of inter-stage connection electrode patterns is grounded and the other inter-stage connection electrode pattern is grounded via the reactance element. . In this case, further, according to the preferable configuration in which the reactance element is the spiral inductor formed by the electrode pattern on the same piezoelectric substrate, the reactance element can be downsized.

According to the third aspect of the present invention,
Two SAW resonators having reflector electrodes on both sides of an IDT electrode are formed on a piezoelectric substrate in parallel with the SAW propagation direction, and the IDT of the SAW resonator is provided between the SAW resonators.
By arranging stripline electrodes having a length approximately equal to the electrode finger crossing width in parallel with the SAW resonator at the same electrode period, a periodic structured electrode array is formed, and the SAW resonator and the period are arranged. By arranging the structural electrode arrays close to each other and acoustically coupling them, even if the electrode structure in the central SAW resonator is changed from the IDT electrode to the stripline electrode array having the periodic structure, if the electrode period is the same, As in the case of the first aspect, the surface acoustic wave can be propagated. As a result, the band of the SAW filter can be widened. Further, in the third configuration of the present invention, according to a preferable configuration in which the strip line electrodes forming the periodic structure electrode array are connected to each other by the bus bar electrodes provided at both ends thereof, the periodic structure electrode array is formed. The structure can be similar to that of the reflector electrode. Also,
In this case, according to a preferable configuration in which a plurality of cascaded connection electrode patterns formed on the piezoelectric substrate are connected in cascade, the out-of-band attenuation amount characteristic is significantly improved, and a better filter characteristic can be obtained. . Further, in this case, the periodic structure electrode array is connected to the SAW resonator I arranged outside.
According to a preferable configuration in which the electrodes are arranged in the gap between the DT electrode and the reflector electrode and the bus bar electrode is grounded,
The periodic structure electrode can be electrically independent of the input / output terminal. As a result, the grounding state of the periodic structure electrode does not directly affect the input / output characteristics of the filter, and the amount of direct achievement of the signal between the input / output terminals is also greatly reduced, which is the same as the case of the second invention. In addition, the out-of-band attenuation characteristic of the filter can be further improved. In addition, since the degree of freedom in determining the distance between the reflector electrode and the IDT electrode and the periodic structure electrode forming the SAW resonator is increased, the distance between the IDT electrode and the periodic structure electrode and the reflector electrode is appropriately determined. Out-of-band spurious can be suppressed. As a result, better out-of-band characteristics can be obtained. In this case, one SAW resonator electrode arranged on the outside is further connected to the balanced type input terminal, and the other SAW resonator arranged on the outside is connected.
According to the preferable configuration in which the W resonator electrode is connected to the balanced output terminal, a balanced element such as an IC can be connected to the front and rear stages of the filter without using an external circuit such as a balun. The noise characteristic of can be improved. Furthermore, in this case, the SA located outside
A preferable structure in which the line width of the bus bar electrode pattern on the side adjacent to the periodic structure electrode of the IDT electrode forming the W resonator is made larger than the line width of the bus bar electrode pattern formed on the periodic structure electrode. According to this, the insertion loss of the filter can be further improved as compared with the case of the second invention. This is because, compared with the case of the above-mentioned second invention, there is no electrode at a distance G between the comb-shaped electrode forming the IDT electrode of the SAW resonator arranged outside and the periodic structure-shaped electrode arranged in the center. Is reduced, and the line width W ₁ of the bus bar electrode pattern on the side adjacent to the periodic structure electrode of the IDT electrode constituting the SAW resonator arranged outside can be increased by that much. is there.

In the third structure of the present invention,
IDT on the side adjacent to the periodic structure electrode array of the SAW resonator
According to a preferred configuration in which the electrode and the bus bar electrode connecting the periodic structure electrode array are integrated and the periodic structure electrode array is grounded, the unbalanced input / output is performed as in the case of the first invention. Although it can be configured, in this case also, the band of the SAW filter can be widened. Further, in this case, according to a preferable configuration in which a plurality of inter-stage connection electrode patterns formed on the piezoelectric substrate are connected in cascade, the out-of-band attenuation amount characteristic is significantly improved, and a better filter characteristic is obtained. Can be obtained.

According to the fourth aspect of the present invention,
A SAW resonator that forms a first SAW resonator filter by forming two SAW resonator filters that are acoustically coupled by closely disposing SAW resonators having reflector electrodes on both sides of an IDT electrode on a piezoelectric substrate. The electrode arrangement of the vessel is opposite phase, and the second
Of the SAW resonator constituting the SAW resonator filter, the electrodes are arranged in phase with each other, and the first SAW resonator filter and the second SAW resonator filter are connected in parallel, so that the pass characteristics within the band are obtained. The bandwidth can be increased without degrading the bandwidth. The reason will be described below. A single SAW resonator filter has f ₁ and f
_It has two excitation frequencies of ₂ (f ₁ <f ₂ ) or f ₃ and f ₄ (f ₃ <f ₄ ), and their phase relationships are opposite to each other. Therefore, as in the present invention, the electrode arrangement of the SAW resonator forming the first SAW resonator filter is in the opposite phase and the electrode arrangement of the SAW resonator forming the second SAW resonator filter is in the same phase. , The first
By connecting the above SAW resonator filter and the second SAW resonator filter in parallel, the phase relationship between f ₁ and f _{2 and} the phase relationship between f ₃ and f ₄ can be reversed. That is, since the phases of f ₂ and f ₃ can be made in-phase, if the excitation frequencies of f ₂ and f ₃ are matched, the bandwidth can be widened without deteriorating the pass characteristic in the band. .

According to the fifth aspect of the present invention,
On the piezoelectric substrate, four SAW resonator filters, in which SAW resonators having reflector electrodes on both sides of the IDT electrode are closely arranged and acoustically coupled, are formed to form first and second SAW resonator filters. The electrodes of the SAW resonator to be used are arranged in opposite phases, and S constituting the third and fourth SAW resonator filters is formed.
The electrodes of the AW resonator are arranged in phase, the first SAW resonator filter and the third SAW resonator filter are connected in parallel, and the second SAW resonator filter and the fourth SAW resonator filter are connected.
Of the SAW resonator filters are connected in parallel, and an electrode pattern is formed on the piezoelectric substrate between the first and third SAW resonator filters and the second and fourth SAW resonator filters. By connecting in series, the two sets of SAW resonator filters connected in parallel each perform the same operation as in the first aspect of the invention, and by connecting these in series, the out-of-band attenuation of the filter is further increased. Be improved.

In addition, in the fifth configuration of the present invention,
Of the first and third SAW resonator filters, one of the SAW resonator filters has a higher-side excitation frequency and the other SAW resonator filter has a lower-side excitation frequency of the same value, and the second According to a preferable configuration in which the value of the high frequency side excitation frequency of one of the SAW resonator filters and the value of the low frequency side excitation frequency of the other SAW resonator filter is made to coincide with each other, As in the case of the above-mentioned fourth invention, the bandwidth can be widened without deteriorating the in-band pass characteristic.

In addition, in the fifth configuration of the present invention,
The first SAW resonator filter and the second SAW resonator filter are arranged next to each other in parallel with the propagation direction of the surface acoustic wave, and the third SAW resonator filter and the fourth SW resonator filter are arranged.
According to the preferable configuration in which the AW resonator filters are arranged next to each other in parallel with the direction in which the surface acoustic wave propagates, it is possible to remove unnecessary stray capacitance between the cascade-connected multistage SAW filters. No matching circuit between stages is required. As a result, it is possible to reduce the size of the circuit and stabilize the filter characteristics.

According to the sixth aspect of the present invention,
A SAW resonator filter is configured by arranging acoustically coupling SAW resonators having reflector electrodes on both sides of the IDT electrode on a piezoelectric substrate and acoustically coupling them to each other. By dividing the electrode pattern for the bus bar of each part and having a plurality of the SAW resonators arranged close to each other electrically independent, the ground electrodes of the input IDT electrode and the output IDT electrode are independently taken. In addition, it is possible to realize balanced input / output of the SAW filter. As a result, SAW
No need to ground the IDT electrode of the filter, SA
The grounded state of the W electrode does not directly affect the input / output characteristics of the filter, and the direct achievement of the signal between the input / output terminals is also greatly reduced, so that the out-of-band attenuation characteristic of the filter can be improved. Further, it is possible to connect, for example, a balanced element such as an IC including a differential IF amplifier to the front and rear stages of the filter without using an external circuit such as a balun, so that the noise characteristic of the entire circuit is improved. You can also

In the sixth structure of the present invention,
Two surface acoustic wave filters are formed on the same piezoelectric substrate, and the electrode arrangement of the SAW resonator forming the first SAW resonator filter is opposite to that of the SAW resonator forming the second SAW resonator filter. According to a preferable configuration in which the electrodes are arranged in the same phase and the first SAW resonator filter and the second SAW resonator filter are connected in parallel, as in the case of the fourth invention, The bandwidth can be widened without deteriorating the pass characteristic of.

According to the seventh aspect of the present invention,
On a piezoelectric substrate, SAW resonators having reflector electrodes on both sides of an IDT electrode are closely arranged and acoustically coupled to each other, and a central bus bar electrode pattern of a SAW resonator filter is divided into four SAW resonator filters. The electrode arrangements of the SAW resonators that are individually formed and constitute the first and second SAW resonator filters have opposite phases, and the electrode arrangements of the SAW resonators that constitute the third and fourth SAW resonator filters have the same phase. Connecting the first SAW resonator filter and the third SAW resonator filter in parallel, connecting the second SAW resonator filter and the fourth SAW resonator filter in parallel, and Since the first and third SAW resonator filters and the second and fourth SAW resonator filters are connected in series by the electrode pattern formed on the piezoelectric substrate, Connected two pairs of SAW resonator filter are respectively the same operation as in the case of the sixth invention, by which they are cascade-connected, out-of-band attenuation of the filter is further improved.

According to the eighth aspect of the present invention,
Since the reactance element is formed by using a part of the electrode pattern forming the SAW filter, it is not necessary to secure a new electrode area. Therefore, it is possible to realize the above circuit configuration with the same piezoelectric substrate area as the conventional one. You can

In the eighth structure of the present invention,
According to the preferable configuration including the IDT electrode and the reflector electrode and forming the reactance element using the reflector electrode, the variation in the element value is reduced as compared with the case where the external circuit element is used. Therefore, it is possible to stabilize the characteristics of the SAW filter circuit. Further, in this case, the reactance element is preferably an inductor formed by connecting stripline electrodes that are arranged in parallel and form a reflector electrode in a substantially staggered manner, thereby reducing the size of the reactance element. Can be planned. Further, in this case, according to a preferred embodiment, the reactance element is an inductor formed by bundling a plurality of parallel arranged stripline electrodes forming a reflector electrode and connecting the stripline electrodes in a substantially zigzag shape. Since the resistance component of the inductor can be reduced, deterioration of filter characteristics can be prevented. Further, in this case, according to a preferable configuration in which the reactance element is a capacitor formed by connecting the strip electrodes arranged in parallel and forming the reflector electrode in an interdigital form, the reactance is reduced by trimming the electrode pattern. You can fine-tune the value.

In the eighth structure of the present invention,
According to the preferable configuration of forming the input / output matching circuit or the inter-stage matching circuit using the reactance element, the reactance electrode pattern functions as the matching circuit of the SAW filter, and as a result, the external matching circuit is unnecessary. It is possible to reduce the number of parts and downsize the entire circuit.

In the eighth structure of the present invention,
According to a preferable configuration in which a plurality of SAW resonators having reflector electrodes on both sides of the IDT electrode are closely arranged and acoustically coupled, an energy trap SAW resonator filter having a piezoelectric substrate area similar to the conventional one is provided. Can be realized. Further, in this case, according to the preferable configuration in which the reactance element is configured by using the reflector electrode, the variation in the element value can be reduced as compared with the case where the external circuit element is used. It is possible to stabilize the circuit characteristics.

According to the ninth aspect of the present invention,
A plurality of SAW resonator filters having reflector electrodes on both sides of the IDT electrode are closely arranged and acoustically coupled to form a plurality of SAW resonator filters on the same piezoelectric substrate, and the SAW resonator filters are connected in cascade. In addition, since the input / output matching circuit is configured by using the reactance element formed by the electrode pattern on the piezoelectric substrate, it is possible to reduce variation in element value as compared with the case where an external circuit element is used. Therefore, it is possible to stabilize the characteristics of the multi-stage SAW filter circuit.

According to the tenth structure of the present invention, the SAW resonator filter in which a plurality of SAW resonators having reflector electrodes on both sides of the IDT electrode are closely arranged and acoustically coupled is formed on the same piezoelectric substrate. A plurality of SAWs are formed on the top.
By connecting the resonator filters in cascade, and grounding the connection point through the reactance element formed by the electrode pattern on the same piezoelectric substrate, the reactance element formed by the electrode pattern on the piezoelectric substrate is a filter step. Since it acts as a matching element for the inter-stage, the inter-stage adjustment of the SAW filter such as a wide band type transverse mode coupled resonator type SAW filter, which conventionally required to connect an adjusting circuit such as an extension coil between the stages, It can be realized without newly increasing the electrode area on the piezoelectric substrate.

In the tenth structure of the present invention, according to the preferable structure in which the reactance element is a spiral inductor, the reactance element can be downsized. In this case, in addition,
According to the preferable structure in which the space between the W filters is used to form the spiral inductor, it is not necessary to make the piezoelectric substrate larger than in the conventional case, so that the circuit can be downsized. Further, in this case, according to a preferred configuration in which at least one short-circuit electrode pattern for short-circuiting and connecting the adjacent winding electrode patterns of the spiral inductor is provided, the short-circuit electrode pattern is trimmed with a laser or the like to thereby improve the reactance value. Since it can be finely adjusted, it becomes possible to finely adjust the filter characteristics after the SAW filter substrate is mounted on the package.

[0057]

EXAMPLES The present invention will be described in more detail below with reference to examples. (First Embodiment) FIG. 1 is a block diagram showing a first embodiment of a surface acoustic wave filter according to the present invention. In FIG.
Reference numeral 11 denotes a single crystal piezoelectric substrate. By forming an electrode pattern in the form of a periodic structure stripline on the piezoelectric substrate 11, surface acoustic waves can be excited. On the piezoelectric substrate 11, an energy trap type first SAW resonator including an interdigital transducer (IDT) electrode 12a and reflector electrodes 12b and 12c is formed. In addition, on the piezoelectric substrate 11,
A second SAW resonator composed of the IDT electrode 13a and the reflector electrodes 13b and 13c, and a third SW resonator composed of the IDT electrode 14a and the reflector electrodes 14b and 14c.
And an AW resonator. And the above three S
AW resonators are placed close to each other, and IDs of adjacent parts
The T electrode and the reflector electrode are connected by a common bus bar. The electrode fingers outside the IDT electrode 12a are connected to the input terminal, and the electrode fingers outside the IDT electrode 14a are connected to the output terminal. In addition, one electrode finger of the IDT electrode 13a is common to the electrode finger inside the IDT electrode 12a and the common bus bar and the IDT electrode 12a and the reflector electrode 1.
It is grounded through an electrode pattern provided in the gap 2b. The other electrode finger of the IDT electrode 13a is I
The electrode fingers inside the DT electrode 14a are grounded through a common bus bar and an electrode pattern provided in the gap between the IDT electrode 14a and the reflector electrode 14c.

The operation of the surface acoustic wave filter thus configured will be described below. FIG. 2 is an excitation mode distribution diagram of the SAW filter according to the present embodiment, and parts corresponding to those in FIG. 1 are given the same numbers. In FIG. 2, (a) is an electrode configuration diagram of the SAW filter shown in FIG. 1, and acoustic coupling occurs between the SAW resonators 12, 13, and 14 when they are arranged close to each other. As a result, first-order, second-order, and third-order modes having a potential distribution as shown in FIG. 2B are excited. Where 2
The next mode corresponds to a portion where the IDT electrodes of the SAW resonator 13 arranged at the center of the mode distribution node intersect, and the polarities of the potential distribution are switched above and below the IDT electrode. Therefore, if the electrode pattern is configured as shown in FIG. 2A, the excitation intensity of the secondary mode becomes considerably weaker than that of the primary and tertiary modes. Then, the pass band characteristic when the filter is directly connected to 50 Ω at this time has a shape in which the center of the band is depressed as shown in FIG. Therefore, 1
In the case of a wideband design in which the frequency difference between the second-order mode and the third-order mode is standardized at the center frequency and exceeds 0.1%, the band does not become flat even with a matching circuit, and good filter characteristics are obtained. I can't. Therefore, in order to obtain a good filter characteristic in the electrode configuration as shown in FIG. 1, it is necessary to strongly excite the secondary mode and use it for the pass characteristic. To this end, (1) the potential of the SAW resonator 13 arranged in the center can be freely distributed, and
(2) It is necessary that the potential is not canceled between the outer SAW resonators 12 and 14.

In this embodiment, the IDT electrode of the central SAW resonator 13 is grounded on both sides, and I
The DT electrode fingers 21 and 22 are connected to the input terminal and the output terminal, respectively, and are electrically independent (see FIG. 1), and satisfy the above conditions (1) and (2). At this time, the pass band characteristic of the filter directly connected with 50Ω is as shown in FIG. 3B, and a strong excitation intensity can be obtained also in the secondary mode. Therefore, it is possible to realize a SAW filter that uses three excitation modes, and obtain a wider band pass characteristic than a conventional SAW filter that uses two excitation modes.

By the way, the distance between the IDT electrode and the reflector electrode of the SAW resonator affects the strength of the out-of-band spurious, and the spurious can be suppressed by appropriately setting the dimension thereof. In this embodiment, an electrode pattern for grounding the IDT electrode of the SAW resonator arranged at the center is provided in this portion, which increases the degree of freedom in determining the distance between the IDT electrode and the reflector electrode. Therefore, it is possible to suppress out-of-band spurious and obtain better out-of-band characteristics.

Further, the SAW filter in this embodiment uses the three excitation modes, so the filter order is the third order, and the out-of-band attenuation gradient characteristic is higher than that of the conventional SAW filter having the second order. Since it becomes steep, better selectivity characteristics can be obtained.

As described above, according to this embodiment, three SAW resonators are arranged close to each other, all the IDT electrodes forming the central SAW resonator are grounded, and the IDT electrodes forming the outer SAW resonator are grounded. By electrically independent of each other, it is possible to realize a wide band of the SAW filter without using an external expansion coil or the like.

In this embodiment, the SA having a one-stage structure is used.
Although the W filter has been described as an example, as shown in FIG.
If two and 43 are connected in cascade to form a multi-stage SAW filter, the insertion loss slightly increases, but the out-of-band attenuation characteristic is significantly improved, and a better filter characteristic can be obtained.

By the way, the input / output impedance of the SAW filter is governed by the number of IDT electrode pairs of the SAW resonator and cannot be set arbitrarily. Therefore, simply connecting the filters in cascade is preferable because of mismatch at the time of connection. In some cases, it may not be possible to obtain good passage characteristics. In this case, a reactance element such as an inductance may be connected as a matching element to the electrode pattern 44 that is cascade-connected between stages. In this case, if an electrode pad 45 for bonding is provided on the electrode pattern 44, connection with an external circuit becomes easy. Further, if a reactance element such as a spiral inductor is formed on the same piezoelectric substrate 41, and one end is connected to the electrode pattern 44 and the other end is grounded, an external circuit becomes unnecessary, so that the filter circuit can be downsized. You can

In this embodiment, the number of SAW resonators arranged close to each other has been described as three, but the number is not necessarily limited to three, and this number is increased to four or more. It is also possible to configure a SAW filter using a higher-order mode. However, as the number of resonators increases, it becomes difficult to design a filter, and the sensitivity of the matching circuit also increases, which makes it impossible to achieve good filter characteristics. Therefore, it is preferable that the number of SAW resonators arranged closely be three.

(Second Embodiment) FIG. 5 is a constitutional view showing a second embodiment of the surface acoustic wave filter according to the present invention. As shown in FIG. 5, the IDT is formed on the single crystal piezoelectric substrate 51.
A first SAW resonator composed of the electrode 52a and the reflector electrodes 52b and 52c is formed. Further, on the piezoelectric substrate 51, the IDT electrode 53a and the reflector electrode 53 are formed.
a second SAW resonator composed of b and 53c,
A third SAW resonator including the IDT electrode 54a and the reflector electrodes 54b and 54c is formed. The three SAW resonators are arranged close to each other.
Further, one electrode finger of the IDT electrode 53a is grounded via an electrode pattern provided in the gap between the IDT electrode 52a and the reflector electrode 52b. Also, the IDT electrode 53
The other electrode finger of a is the IDT electrode 54a and the reflector electrode 5
It is grounded through an electrode pattern provided in the gap with 4c. The above is the same configuration as the first embodiment shown in FIG.

The difference from the first embodiment is that the busbar electrodes of the adjacent portions of the IDT electrodes constituting the SAW resonator are electrically independent, and the IDT electrode 52a.
Of the IDT electrode 54 connected to the balanced input terminal
This is the point where the electrode finger of a is connected to the balanced output terminal.

The operation of the surface acoustic wave filter thus constructed is basically the same as in the case of the first embodiment shown in FIG. Outer spurious can be suppressed and good out-of-band characteristics can be obtained. Further, in this embodiment, the bus bar at the center of the IDT electrode is electrically independent, so that the IDT electrode 52 of the SAW resonator 52 is
Since a and the IDT electrodes 54a of the SAW resonator 54 can all be independently wired, it is possible to realize balanced input / output of the SAW filter with the terminal configuration shown in FIG.

As described above, according to this embodiment, of the IDT electrodes forming the SAW filter, only the IDT electrode 53a of the central SAW resonator 53 is grounded, and this portion serves as an input / output terminal. Are electrically independent. Therefore, the grounded state of the IDT electrode does not directly affect the input / output characteristics of the filter, and the direct achievement of the signal between the input / output terminals is also greatly reduced, so that the out-of-band attenuation characteristic of the filter is further improved. be able to. Moreover, since balanced elements such as ICs can be connected to the front and rear stages of the filter without using an external circuit such as a balun, the noise characteristics of the entire circuit can be improved.

FIG. 6 shows the IDT electrode 52a in FIG.
An enlarged view of a portion where the IDT electrodes 53a are arranged close to each other is shown.
You Comb forming the IDT electrode 52a and the IDT electrode 53a
The distance G between the electrodes is the connection of the two SAW resonators 52 and 53.
The smaller the distance G, the more the coupling between the resonators.
This is preferable for widening the band because it increases the frequency. However, the distance G is
If it is too small, the bus bar
Width W of poles 61 and 62₁, W_TwoBecomes smaller than that,
The electric resistance loss of the IDT electrode in this part is
Can no longer ignore the effect on insertion loss of
It Here, the bus bar electrode 61 is directly connected to one of the balanced input terminals.
The bus bar electrode 62 is connected to the center SA.
Used to ground the IDT electrode that makes up the W resonator
Are not electrically connected to the input / output terminals.
Yes. That is, the width W of the bus bar electrode 62 _TwoThe size of
It has no effect on the insertion loss of the filter. Therefore,
Width W of bus bar electrode 62_TwoBusbar electrode
61 width W₁Is increased, the size of the distance G is changed.
Without reducing the electrical resistance loss to the input terminals,
The insertion loss of the data can be improved. Also, on the output side,
That is, the IDT electrode 54a and the IDT electrode 53a are placed close to each other.
For the part to be placed, the same configuration as above
Therefore, the same effect can be obtained. Experimentally, S
A 240MHz band filter was constructed on a T crystal substrate.
In the case, when the distance G is one wavelength (about 12 μm), W₁, W
_TwoThe insertion loss is 3.86 when the size of both is 0.25 wavelength.
It becomes dB, but W₁The size of 0.4 wavelength, W_TwoThe size of
If the wavelength is 0.15 wavelength, the insertion loss is 2.83 dB.
It was possible to improve by 1.03 dB.

Also in this embodiment, as shown in FIG. 7, if a plurality of SAW filters 72 and 73 are connected in cascade on the same piezoelectric substrate 71 to form a multi-stage connection SAW filter, the insertion is performed. Although the loss increases a little, the out-of-band attenuation characteristic is significantly improved, and a better filter characteristic can be obtained. However, in this case as well, it may be impossible to obtain good pass characteristics simply by connecting filters in cascade. In this case, as in the first embodiment, a reactance element such as an inductance may be connected as a matching element to the electrode pattern 74 connected in cascade between stages. As a connection method, there is a method of connecting between the balanced electrodes 74, 74, but the same effect can be obtained by connecting between one electrode pattern 74 and the ground and grounding the other electrode pattern 74. . Further, in this case, if an electrode pad 75 for bonding is provided on the electrode pattern 74, connection with an external circuit becomes easy. Further, if a reactance element such as a spiral inductor is formed on the same piezoelectric substrate 71, and one end is connected to the electrode pattern 74 and the other end is grounded, an external circuit becomes unnecessary, so that the filter circuit can be downsized. You can

As described above, by forming the IDT electrodes of the SAW resonators arranged close to each other electrically independently to form a balanced type input / output terminal structure, the same effect as that of the first embodiment can be obtained. While being obtained, its properties can be further improved.

(Third Embodiment) FIG. 8 is a block diagram showing a third embodiment of the surface acoustic wave filter according to the present invention. As shown in FIG. 8, the IDT is formed on the single crystal piezoelectric substrate 81.
A first SAW resonator composed of the electrode 82a and the reflector electrodes 82b and 82c and a third SAW resonator composed of the IDT electrode 84a and the reflector electrodes 84b and 84c are formed. The above is the same configuration as the second embodiment shown in FIG.

The difference from the second embodiment is that the reflector electrode 8
The IDT electrode portion of the second SAW resonator formed in the center with 3b and 83c has the same structure as the reflector electrode,
A stripline electrode array 83a having a periodic structure having a length similar to the electrode finger crossing width of the IDT electrode 53a in FIG.
It is composed of

Similar to the second embodiment, the above three SAWs are used.
The resonators are arranged close to each other, and the bus bar electrodes of the adjacent portions of the IDT electrodes are electrically independent. Also, ID
The electrode finger of the T electrode 82a is connected to the balanced input terminal, and I
The electrode finger of the DT electrode 84a is connected to the balanced output terminal. Furthermore, a stripline electrode array 83 having a periodic structure
a is grounded through an electrode pattern provided in the gap between the IDT electrode 82a and the reflector electrode 82c and an electrode pattern provided in the gap between the IDT electrode 84a and the reflector electrode 84b.

By configuring the surface acoustic wave filter as described above, even if the structure of the electrode 83a in the central SAW resonator is changed from the IDT electrode to the strip line electrode array having the periodic structure, if the electrode period is the same, Surface acoustic waves can propagate in exactly the same way. Therefore, the operation is as shown in FIG.
Is basically the same as the case of the first embodiment shown in FIG.
A wide band of the AW filter can be realized, out-of-band spurious can be suppressed, and excellent out-of-band characteristics can be obtained. Also, as in the second embodiment, the ID
Since the bus bar in the central portion of the T electrode is electrically independent, balanced input / output of the SAW filter can be realized, so that the out-of-band attenuation characteristic of the filter can be improved.

FIG. 9 shows an enlarged view of a portion where the IDT electrode 82a and the strip line electrode array 83a having the periodic structure are arranged in proximity to each other in FIG. Compared with the case of the second embodiment shown in FIG. 6, the ratio of the portion where no electrode exists in G is reduced, and the width W ₁ of the bus bar electrode 91 is compared with the width W ₂ of the bus bar electrode 92 by that much. It is possible to increase it. Therefore, the insertion loss of the filter can be further improved as compared with the case of the second embodiment.

As described above, according to this embodiment, it is possible to obtain the same effect as that of the second embodiment and further improve its characteristics. In this embodiment, as shown in FIG. 8, the IDT electrode 82a and the IDT electrode 84a are arranged in the same phase as each other.
Even when the IDT electrodes 102 and the IDT electrodes 104 shown in FIG. 2 are arranged in opposite phases to each other, similar effects can be obtained although the appearance of out-of-band spurious is slightly different. Further, in FIG. 10, the stripline electrode array 103 having the central periodic structure is grounded only through the electrode pattern on the side of the IDT electrode 104, but even if the symmetry of the upper and lower electrode patterns is slightly shifted in this way. Wiring to the outside can be simplified without significantly affecting the filter characteristics. In FIG. 10, 101 is a piezoelectric substrate.

Also in the present embodiment, if a plurality of SAW filters are connected in cascade to form a multi-stage SAW filter, the out-of-band attenuation amount characteristic is greatly improved and a better filter characteristic can be obtained. You can The cascade connection method at this time is exactly the same as in the case of the second embodiment shown in FIG.

Further, although the present embodiment has been described in comparison with the second embodiment assuming that the input / output electrode configuration of the SAW filter is balanced, as shown in FIG.
It is obvious that the same effect can be obtained even when compared with the first embodiment by forming the portion in which the SAW resonators are arranged close to each other by a common bus bar to have an unbalanced input / output configuration. In FIG. 11, 111 is a single crystal piezoelectric substrate, 112,
Reference numeral 114 is an IDT electrode, and 113 is a strip line electrode array having a periodic structure.

(Fourth Embodiment) FIG. 12 is a constitutional view showing a fourth embodiment of the surface acoustic wave filter according to the present invention.
As shown in FIG. 12, on the single crystal piezoelectric substrate 121,
IDT electrodes 122a and 122b and reflector electrodes 123a,
First composed of 124a, 123b, and 124b
SAW resonator filter is formed, and the phase relationships of the electrode fingers of the IDT electrode 122a and the IDT electrode 122b are opposite to each other. Further, on the same piezoelectric substrate 121, the IDT electrodes 125a and 125b and the reflector electrode 12 are formed.
A second SAW resonator filter composed of 6a, 127a, 126b, 127b is formed.
The phase relationship of the electrode fingers of the T electrode 125a and the IDT electrode 125b is the same. These two SAW resonator filters are electrically connected in parallel by a wiring pattern 128a and an electrode pattern 128b.

The operation of the surface acoustic wave filter thus constructed will be described below. FIG. 13 shows the pass characteristic of the SAW filter in this embodiment when it is directly connected to 50Ω. In FIG. 13A, 131 and 132 are shown in FIG.
2 is a pass characteristic of either the first SAW resonator filter or the second SAW resonator filter shown in FIG. In this way, a single SAW resonator filter has f ₁ and f ₂ (f ₁ <f ₂ ) or f ₃ and f ₄
It has two excitation frequencies of (f ₃ <f ₄ ), and their phase relationships are opposite to each other. As described above, since the first SAW resonator filter has the IDT electrode arrangement of the opposite phase and the second SAW resonator filter has the IDT electrode arrangement of the same phase (FIG. 12), the phases of f ₁ and f ₂ are The relationship and the phase relationship between f ₃ and f ₄ are opposite. That is, the phases of f ₂ and f ₃ are the same. Therefore, if the excitation frequencies of f ₂ and f ₃ are made to coincide with each other, the bandwidth can be widened without deteriorating the in-band pass characteristic as shown by 133 in FIG. 13B.

At this time, it is difficult to actually make f ₂ and f ₃ completely coincide with each other, and some deviation occurs, but f ₂ <
In the case of f ₃ , the pass band characteristic is gradually deteriorated. However, in the case of f ₂ > f ₃ , the peaks of the two overlap and the change in the phase becomes severe, and the group delay deviation characteristic is particularly disturbed. Therefore, when considering the manufacturing deviation of the SAW filter, the peak value should be f ₂ <f ₃
By slightly shifting it to the side, the yield of the filter can be improved.

Further, by forming a part of the parallel connection of the SAW filters by utilizing the electrode pattern on the piezoelectric substrate, it is possible to prevent the stray capacitance of the line and the unnecessary radiation due to the routing of the bonding wires and the like. Therefore, good filter characteristics can be obtained.

As described above, according to the present embodiment, the SAW filters whose IDT electrode fingers are arranged in opposite phase to each other are connected in parallel, and the high-side excitation frequency of one SAW filter and the low SAW filter of the other SAW filter are connected. By matching the band-side excitation frequencies, it is possible to realize a wide band of the SAW multimode filter without using an external expansion coil or the like.

In this embodiment, only one side of the parallel connection is connected using the electrode pattern 128b.
It is also possible to use electrode patterns for all the connection parts. (Fifth Embodiment) FIG. 14 is a constitutional view showing a fifth embodiment of the surface acoustic wave filter according to the present invention. As shown in FIG. 14, SAW resonator filters 142, 143, 144, and 145 are formed on the piezoelectric substrate 141.
The SAW resonator filters 142 and 144 are similar to the first SAW resonator filter in FIG.
The T electrode fingers are arranged in the opposite phase. In addition, the SAW resonator filters 143 and 145 correspond to the second S in FIG.
Similar to the AW resonator filter, the adjacent IDT electrode fingers are arranged in the same phase. Then, the SAW resonator filters 142 and 143 and the SAW resonator filters 144 and 1
45 are connected in parallel by bonding wires 146, 147 and electrode patterns 148a, 148b, 148c, respectively, and these two sets of parallel connection SAW filters are connected in cascade by electrode patterns 148a, 148b. In FIG. 14, reference numeral 149 is an absorber for blocking the propagation of surface acoustic waves of different SAW resonator filters.

When the surface acoustic wave filter is constructed as described above, the two sets of SAW resonator filters connected in parallel operate in the same manner as in the first embodiment, and these are connected in cascade. This further improves the out-of-band attenuation of the filter.

Also in this embodiment, the parallel connection and the cascade connection of the SAW filters are formed by using the electrode pattern on the piezoelectric substrate, so that the stray capacitance of the line and the unnecessary radiation due to the routing of the bonding wires and the like. Since this can be prevented, good filter characteristics can be obtained.

Further, by arranging the SAW filters having the same characteristics so as to be adjacent to each other in parallel with the propagation direction of the surface acoustic wave, it is possible to remove unnecessary stray capacitance between the cascaded SAW filters. As a result, a matching circuit between stages becomes unnecessary. As a result, miniaturization of the circuit can be used, and stable characteristics of the filter can be realized. However, in this case as well, it may be impossible to obtain good pass characteristics simply by connecting filters in cascade. In this case, a reactance element such as an inductance may be connected as a matching element to the electrode patterns 148a, 148b, 148c that are connected in cascade between the stages.

As described above, by connecting the SAW filters connected in parallel in cascade, it is possible to obtain the same effect as that of the fourth embodiment and further improve its characteristics.

In this embodiment, the electrode pattern 1
Although each stage is connected in parallel by 48c, the same effect can be obtained even if the SAW filters of each multi-stage connection are connected in parallel after removing the electrode pattern 148c and connecting the SAW filters in cascade. You can

(Sixth Embodiment) FIG. 15 is a block diagram showing a sixth embodiment of the surface acoustic wave filter according to the present invention.
As shown in FIG. 15, on the single crystal piezoelectric substrate 151,
SAW resonator filters 152 and 153 are formed. In the SAW resonator filter 152, the adjacent IDT electrode fingers are arranged in the opposite phase.
In 53, the adjacent IDT electrode fingers are arranged in the same phase. Then, these two SAW resonator filters 15
The electrodes 2 and 153 are electrically connected in parallel by the electrode patterns 156a and 157a and the wiring pattern 154a. The above is the same configuration as that of the fourth embodiment shown in FIG.

The difference from the fourth embodiment is that the bus bar electrode 158 at the center of the adjacent IDT electrode finger of the SAW resonator filter 152 is divided to form electrically independent electrodes 156b and 157b, respectively. Similarly, the SAW resonator filter 153 is also configured such that the central bus bar electrode is divided.

FIG. 16 shows an example of a structure in which the SAW filter of this embodiment is mounted on a surface mounting package, and the parts corresponding to those of FIG. 15 are designated by the same numbers. In FIG. 16, reference numeral 161 denotes a surface mounting package, on which a piezoelectric substrate 151 having a SAW filter is mounted. Further, 162 is an electrode pad for bonding, and the input terminal electrodes 164a and 164b and the output terminal electrode 165 are respectively formed by the bonding wires 163.
a, 165b, the ground electrode 166, etc.

The operation of the surface acoustic wave filter thus constructed is basically the same as that of the fourth embodiment shown in FIG. 13, and it is possible to realize a wide band of the SAW filter. Furthermore, in this embodiment, the bus bar at the center of the IDT electrode is divided, so that the input I
Since the ground electrodes of the DT electrode portions 154a, 154b and the output IDT electrode portions 155a, 155b can be independently taken, if the wiring shown in 154a, 154b, 155a, 155b is provided, the balanced input / output of the SAW filter can be obtained. Can be realized.

Therefore, according to this embodiment, it is not necessary to ground the IDT electrode of the SAW filter. as a result,
Similarly to the second embodiment, the grounding state of the SAW electrode does not directly affect the input / output characteristics of the filter, and
Since the direct achievement of the signal between the input and output terminals is also greatly reduced,
The out-of-band attenuation characteristic of the filter can be improved.
Moreover, since balanced elements such as ICs can be connected to the front and rear stages of the filter without using an external circuit such as a balun, the noise characteristics of the entire circuit can be improved.

Further, as shown in FIG. 16, the piezoelectric substrate 15
A SAW filter compatible with surface mounting can be easily realized by providing an electrode pad 162 for bonding on the first substrate 1 and connecting it to a terminal electrode of the surface mounting package 161 with a bonding wire. Incidentally, the structure for dividing the bus bar in the central portion of the SAW filter is not limited to the parallel connection type SAW filter shown in the present embodiment, and the structure shown in FIG.
It can also be applied to a conventional SAW filter as shown in FIG.

Further, in the present embodiment, the case where the number of stages of the SAW filter is one has been described in the column.
The present invention can also be applied to a SAW filter having two or more stages connected in multiple stages as shown in the above embodiment.

(Seventh Embodiment) FIG. 17 is a block diagram showing a surface acoustic wave filter according to a seventh embodiment of the present invention.
As shown in FIG. 17, the IDT is formed on the piezoelectric substrate 171.
A first-stage SAW resonator filter formed by the electrode 172 and the reflector electrodes 173 and 174 is formed.
Further, on the piezoelectric substrate 171, the second stage S composed of the IDT electrode 175 and the reflector electrodes 176 and 177 is formed.
An AW resonator filter is formed. And the above 2
The SAW resonator filters of the stages are electrically connected in cascade by the inter-stage electrode pattern 178, whereby a SAW filter of a multi-stage connection is configured. The first-stage and second-stage SAW resonator filters are configured by arranging two energy trap type SAW resonators close to each other and causing acoustic coupling between them.

Each of the reflector electrodes 173 and 176 constitutes a meander line type inductor electrode in which a plurality of strip electrodes are bundled and connected in a substantially zigzag shape. The IDT electrodes 172 and 175 are connected to the input and output sides thereof, respectively. It is connected in parallel between the electrode and ground. Also, the reflector electrode 1
74 and 177 form interdigital capacitor electrodes, which are connected in series to the input / output side electrodes of the IDT electrodes 172 and 175, respectively.

The operation of the surface acoustic wave filter thus constructed will be described below. FIG. 18 is an equivalent circuit diagram of the SAW filter electrode pattern in the present embodiment, and the portions corresponding to those in FIG. 17 are assigned the same numbers. In FIG. 18, 181 is the first stage SAW filter,
Reference numeral 182 denotes a second stage SAW filter.

In FIG. 17, electrode patterns 173, 1
Although 74, 176, and 177 are formed as elastic reflectors of a SAW resonator that constitutes a SAW multimode filter, each electrode is a transmission line, and the electrode patterns 173 and 176 are meander line type inductors. Functioning, the electrode patterns 174, 177 function as interdigital capacitors. Therefore, by connecting these reflector electrodes to the input / output side electrodes of the IDT electrodes 172 and 175 as described above, a matching circuit as shown in FIG. 18 can be constructed.

The reactance electrode pattern thus formed on the piezoelectric substrate 171 acts as a matching circuit for the SAW filter, and as a result, an external matching circuit is unnecessary, so that the number of parts can be reduced and the entire circuit can be made compact. Can be converted. Further, the reactance electrode pattern is SA
Since it is formed using the reflector electrode of the W resonator,
Since it is not necessary to newly secure the electrode area, the above circuit configuration can be realized with the same piezoelectric substrate area as the conventional one.

Further, if the reactance element is constituted by the strip electrode of the reflector, the variation in the element value can be reduced as compared with the case where an external circuit element is used, so that the SAW filter circuit characteristic is stabilized. Can be planned. Furthermore, if the meander line is composed of several reflector strip electrodes per direction (two in each of 173 and 176 in FIG. 17), the resistance component of the inductor can be reduced, so that the filter characteristic It is possible to prevent deterioration. The number of reflector strip electrodes per line may be appropriately determined depending on the required inductance value and the resistance value in that case.

As described above, according to this embodiment, it is possible to realize the SAW filter in which the filter matching circuit is integrated on the piezoelectric substrate 171. In this embodiment, the matching circuit having the configuration in which the inductors are connected in parallel and the capacitors are connected in series has been described as an example, but the present invention is not limited to this configuration, and the circuit configuration is SA.
It can be arbitrarily changed according to the impedance of the W filter.

(Eighth Embodiment) FIG. 19 is a block diagram showing an eighth embodiment of the surface acoustic wave filter according to the present invention.
As shown in FIG. 19, the IDT is formed on the piezoelectric substrate 191.
A first-stage SAW resonator filter composed of the electrode 192 and the reflector electrodes 193 and 194 is formed.
Further, on the piezoelectric substrate 191, the second stage S composed of the IDT electrode 195 and the reflector electrodes 196 and 197.
An AW resonator filter is formed. And the above 2
The SAW resonator filters of the stages are electrically connected in cascade by the inter-stage electrode pattern 198, whereby a SAW filter of multistage connection is configured. The first-stage and second-stage SAW resonator filters are configured by arranging two energy trap type SAW resonators close to each other and causing acoustic coupling between them.

Each of the reflector electrodes 193 and 196 constitutes a meander line type inductor electrode in which a plurality of strip electrodes are bundled and connected in a substantially zigzag shape. A short-circuit electrode is formed at the center of the strip electrode of the reflector electrode 193, and the reflector electrode 196 has a meander line folded back at the center of the strip electrode. Further, the reflector electrodes 194 and 197 form an interdigital capacitor electrode, and the reactance value can be finely adjusted by trimming the electrode pattern. The input / output terminals are taken out from the common bus bar portions at the center of the reflector electrodes 194 and 197, and the electrode discontinuous portions at the center portions of the reflectors are eliminated as much as possible.

In the SAW filter configured as described above, the matching circuit of the input / output stage is formed on the same piezoelectric substrate 191 as in the seventh embodiment, and the common bus bar electrode of the reflector portion is present. By doing so, it is possible to suppress unnecessary coupling between the SAW resonators arranged close to each other, so that it is possible to obtain better filter characteristics.

Also in this embodiment, the circuit configuration can be arbitrarily changed according to the impedance of the SAW filter. (Ninth Embodiment) FIG. 20 is a constitutional view showing a ninth embodiment of the surface acoustic wave filter according to the present invention. As shown in FIG. 20, a first-stage SAW resonator filter including an IDT electrode 202 and reflector electrodes 203 and 204 is formed on a piezoelectric substrate 201. Further, on the piezoelectric substrate 201, the IDT electrode 205 and the reflector electrode 20 are provided.
A second-stage SAW resonator filter constituted by 6 and 207 is formed. The two-stage SAW resonator filters are electrically connected in cascade by the inter-stage electrode pattern 208, whereby multi-stage SAW resonators are connected.
The filter is configured. In addition, the S of the first stage and the second stage
The AW resonator filter is configured by arranging two energy trap type SAW resonators close to each other and causing acoustic coupling therebetween.

The reflector electrodes 203 and 206 constitute meander line type inductor electrodes in which strip electrodes are connected in a substantially zigzag shape, and IDT electrodes 202 and 202, respectively.
It is connected in parallel between the inter-stage electrode pattern 208 of 205 and the ground. In addition, the reflector electrodes 204 and 207 form interdigital capacitor electrodes,
The IDT electrodes 202 and 205 are connected in series to the input / output side electrodes, respectively.

The operation of the surface acoustic wave filter thus constructed will be described below. FIG. 21 is an equivalent circuit diagram of the SAW filter electrode pattern according to the present embodiment, and the portions corresponding to those in FIG. 20 are given the same numbers. In FIG. 21, reference numeral 211 denotes a first stage SAW resonator filter, and 212 denotes a second stage SAW resonator filter.
As is clear from FIG. 21, the reflector electrodes 204, 207
It can be seen that, as in the seventh embodiment, acts as a part of the input / output matching circuit, but the reflector electrodes 203 and 206 act as matching elements between the stages of the filter.

By connecting the inductor element constituted by the reflector electrode between the stages of the filter as described above, a wide band type transverse mode coupled resonator type SAW filter or the like, and an adjusting circuit such as an extension coil or the like is provided between the stages. It is possible to realize the inter-stage adjustment of the SAW filter which has been required to be connected without newly increasing the electrode area on the piezoelectric substrate 201.

Further, since the inductor elements of the reflector electrodes 203 and 206 are respectively connected in parallel with the inter-stage electrode pattern 208, the inductance value can be adjusted by cutting one of the electrode patterns.

As described above, according to the present embodiment, the interstage adjusting circuit of the filter is also integrated on the piezoelectric substrate 201.
An AW filter can be realized. In this embodiment, an inductor is connected in parallel between filter stages,
The matching circuit having a configuration in which capacitors are connected in series to the input / output stages has been described as an example, but the present invention is not necessarily limited to this configuration, and the circuit configuration can be arbitrarily changed according to the impedance of the SAW filter. it can. Further, when the matching circuit element formed by the reflector electrode is insufficient, a reactance electrode pattern may be newly formed on the piezoelectric substrate 201, or an external circuit may be connected.

Further, the reflector electrode pattern in this embodiment can be replaced with the reflector electrode pattern having the common bus bar shown in the eighth embodiment. (Tenth Embodiment) FIG. 22 is a structural diagram showing a tenth embodiment of a surface acoustic wave filter according to the present invention. As shown in FIG. 22, the IDT electrode 22 is formed on the piezoelectric substrate 221.
2 and the reflector electrodes 223 and 224
A stage SAW resonator filter is formed. Further, on the piezoelectric substrate 221, a second stage SAW resonator filter including the IDT electrode 225 and the reflector electrodes 226 and 227 is formed. Then, the above two-stage SA
The W resonator filters are electrically connected in cascade by the inter-stage electrode pattern 228, which allows the multi-stage S-connection.
An AW filter is configured. The SAW resonator filters of the first stage and the second stage are energy trap type 2 filters.
Two SAW resonators are arranged close to each other, and acoustic coupling occurs between them.

Each of the reflector electrodes 223 and 226 constitutes a meander line type inductor electrode in which a plurality of strip electrodes are bundled and connected in a substantially zigzag shape. Is connected in parallel between and. Also, the reflector electrode 22
Reference numerals 4 and 227 constitute interdigital capacitor electrodes, which are connected in series to the input / output electrodes of the IDT electrodes 222 and 225, respectively. The inter-stage electrode pattern 228 is grounded via a spiral inductor electrode pattern 229 newly formed on the piezoelectric substrate 221.

In the surface acoustic wave filter configured as described above, a series capacitor and a parallel inductor circuit are formed in the input / output stage similarly to the equivalent circuit shown in FIG. 18, and a parallel inductor is provided between the SAW filter stages. The circuit configuration is provided with. Therefore, the matching circuit of the input / output stage can be formed on the same piezoelectric substrate 221 as in the seventh embodiment, and the adjusting circuit between stages as described in the ninth embodiment is also the same piezoelectric substrate 221. 221 above.

Further, the first-stage SAW resonator filter and the second-stage SAW resonator filter need to be formed at positions separated to some extent in order to prevent unnecessary elastic coupling between the two. Therefore, as shown in FIG. 22, the spiral inductor electrode pattern 229 can be formed by utilizing the space between the SAW resonator filters.
As a result, it is not necessary to make the piezoelectric substrate 221 larger than the conventional one, so that the circuit can be downsized.

As described above, according to this embodiment, the same effect as that of the seventh embodiment can be obtained, and further, an adjusting circuit is required between the stages of the filters as shown in the ninth embodiment. It can be adapted to the case.

In the present embodiment, a matching circuit having a configuration in which inductors are connected in parallel between filter stages, inductors are connected in parallel in the input / output stage, and capacitors are connected in series is described as an example. However, the configuration is not necessarily limited to this configuration, and the circuit configuration can be arbitrarily changed according to the impedance of the SAW filter. Furthermore, it is also possible to form and use only a part of these reactance elements.

Further, the reflector electrode pattern in this embodiment can be replaced with the reflector electrode pattern having the common bus bar shown in the eighth embodiment. Further, as shown in FIG. 23A, if a short-circuit electrode pattern 231 that short-circuits and connects adjacent winding electrode patterns to each other is formed on the spiral inductor electrode pattern 229 in the present embodiment, the above-mentioned short-circuit electrode pattern can be converted into a laser or the like. Since the reactance value can be finely adjusted by trimming with, the filter characteristics can be finely adjusted after the SAW filter substrate is mounted on the package.

In the seventh, ninth and tenth embodiments,
Meander line type inductor electrodes 173, 203, 22
23 and the like, by trimming the electrode pattern 232 portion of FIG. 23 (b), and for the interdigital capacitor electrodes 174, 204, 224 and the like, trimming the electrode pattern 233 portion of FIG. 23 (c). Each reactance value can be finely adjusted.

In the seventh, eighth, ninth and tenth embodiments, the two-stage cascade connection SAW filter has been described as an example. However, the present invention is applicable to general resonator type SAW filters and multi-electrode type SAW filters. It can be applied to all surface acoustic wave devices including a reflector including a SAW filter.

Further, as the piezoelectric substrate in the present invention, it is preferable to use ST-cut quartz having excellent temperature characteristics, but substrates such as LiTaO ₃ , LiNbO ₃ and Li ₂ B ₄ O ₇ can also be used. Further, as the electrode material, since it is easy to control the electrode film thickness, it is preferable to use aluminum having a relatively low density, but it is also possible to use a gold electrode. Furthermore, the present invention is not limited to surface acoustic waves using Rayleigh waves, but slip waves (SS
It is also applicable to a resonator using BW), pseudo surface acoustic wave (Leaky SAW), or the like.

[0125]

As described above, according to the first structure of the surface acoustic wave filter of the present invention, it is possible to realize a SAW filter utilizing three excitation modes and use an external expansion coil or the like. Without using a SAW filter that uses two conventional excitation modes, a wider band pass characteristic can be obtained, so that the filter circuit can be downsized. In addition, since it is possible to realize a SAW filter using three excitation modes in this way,
The out-of-band attenuation gradient characteristic becomes steeper than that of the conventional second-order SAW filter, and a better selectivity characteristic can be obtained.

Further, according to the second structure of the surface acoustic wave filter of the present invention, the bus bar in the central portion of the IDT electrode can be electrically independent, so that the IDT electrode of the SAW resonator arranged outside is formed. Can be wired independently. Therefore, of the IDT electrodes forming the SAW filter, only the IDT electrode of the SAW resonator arranged at the center is grounded, and this portion can be electrically isolated from the input / output terminal. As a result, ID
The grounding state of the T electrode does not directly affect the input / output characteristics of the filter, and the direct achievement of the signal between the input / output terminals is significantly reduced, so that the out-of-band attenuation characteristic of the filter can be further improved. .

Further, according to the third structure of the surface acoustic wave filter of the present invention, even if the electrode structure in the central SAW resonator is changed from the IDT electrode to the strip line electrode array having the periodic structure, the SAW filter is A wide band can be achieved.

Further, according to the fourth structure of the surface acoustic wave filter of the present invention, the bandwidth can be widened without deteriorating the in-band pass characteristic. Further, according to the fifth structure of the surface acoustic wave filter of the present invention, the two sets of SAW resonator filters connected in parallel each perform the same operation as in the fourth invention, and these are connected in cascade. By doing so, the out-of-band attenuation of the filter is further improved.

According to the sixth structure of the surface acoustic wave filter of the present invention, the input IDT electrode and the output IDT are provided.
The ground electrode of the electrode can be taken independently and S
The balanced input / output of the AW filter becomes possible. as a result,
There is no need to ground the IDT electrode of the SAW filter, the grounding state of the SAW electrode does not directly affect the input / output characteristics of the filter, and the direct achievement of the signal between the input / output terminals is greatly reduced. The out-of-band attenuation characteristic can be improved. Further, since it is possible to connect a balanced type element such as an IC to the front and rear stages of the filter without using an external circuit such as a balun, it is possible to improve the noise characteristic of the entire circuit.

Further, according to the seventh structure of the surface acoustic wave filter of the present invention, the two sets of SAW resonator filters connected in parallel each perform the same operation as in the case of the sixth invention, By connecting these in cascade, the out-of-band attenuation of the filter is further improved.

Further, according to the eighth structure of the surface acoustic wave filter of the present invention, the above circuit structure can be realized with a piezoelectric substrate area which is substantially the same as the conventional one. Further, according to the ninth structure of the surface acoustic wave filter of the present invention, it is possible to reduce variations in element values as compared with the case where an external circuit element is used. Can be stabilized.

Further, according to the tenth structure of the surface acoustic wave filter of the present invention, since the reactance element formed by the electrode pattern on the piezoelectric substrate acts as a matching element with respect to the stage of the filter, it is of a wide band type. Realization of inter-stage adjustment of SAW filters such as transverse mode coupled resonator type SAW filters, which conventionally required connecting adjustment circuits such as extension coils, without increasing the electrode area on the piezoelectric substrate. can do.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a surface acoustic wave filter according to the present invention.

FIG. 2 is an excitation mode distribution diagram of the surface acoustic wave filter according to the first embodiment.

FIG. 3 is a pass band characteristic diagram of the surface acoustic wave filter according to the first embodiment.

FIG. 4 is a configuration diagram showing a multi-stage connection surface acoustic wave filter according to a first embodiment.

FIG. 5 is a configuration diagram showing a second embodiment of the surface acoustic wave filter according to the present invention.

[FIG. 6] I of a surface acoustic wave filter according to a second embodiment.
It is an enlarged view of a portion in which DT electrodes are arranged in proximity.

FIG. 7 is a configuration diagram showing a multi-stage surface acoustic wave filter according to a second embodiment.

FIG. 8 is a constitutional view showing a third embodiment of the elastic surface filter according to the present invention.

FIG. 9 shows I of the surface acoustic wave filter in the third embodiment.
It is an enlarged view of a portion in which DT electrodes are arranged in proximity.

FIG. 10 is a configuration diagram in which the IDT electrodes of the surface acoustic wave filter according to the third embodiment are arranged in reverse phase.

FIG. 11 is a configuration diagram of a surface acoustic wave filter according to a third embodiment in the case of unbalanced input / output.

FIG. 12 is a configuration diagram showing a fourth embodiment of the elastic surface wave filter according to the present invention.

FIG. 13 is a pass band characteristic diagram of a surface acoustic wave filter according to a fourth embodiment.

FIG. 14 is a configuration diagram showing a fifth embodiment of the surface acoustic wave filter according to the present invention.

FIG. 15 is a configuration diagram showing a sixth embodiment of the surface acoustic wave filter according to the present invention.

FIG. 16 is a mounting diagram of a surface acoustic wave filter according to a sixth embodiment in a surface mounting package.

FIG. 17 is a configuration diagram showing a seventh embodiment of the surface acoustic wave filter according to the present invention.

FIG. 18 is an equivalent circuit diagram of a surface acoustic wave filter according to a seventh embodiment.

FIG. 19 is a configuration diagram showing an eighth embodiment of the surface acoustic wave filter according to the present invention.

FIG. 20 is a configuration diagram showing a ninth embodiment of the surface acoustic wave filter according to the present invention.

FIG. 21 is an equivalent circuit diagram of a surface acoustic wave filter according to a ninth embodiment.

FIG. 22 is a configuration diagram showing a tenth embodiment of the surface acoustic wave filter according to the present invention.

FIG. 23 is a configuration diagram of reactance electrode patterns in the seventh, eighth, ninth and tenth embodiments.

FIG. 24 is a configuration diagram showing a surface acoustic wave filter according to a conventional technique.

[Explanation of symbols]

11, 41, 51, 71, 81, 101, 111, 12
1, 141, 151, 171, 191, 201, 221
Piezoelectric substrate 12, 13, 14 SAW resonator 12a, 13a, 14a, 52a, 53a, 54a, 8
2a, 84a, 102, 104, 112, 114, 12
2a, 122b, 125a, 125b, 172, 17
5, 192, 195, 202, 205, 222, 225
IDT electrodes 12b, 12c, 13b, 13c, 14b, 14c, 5
2b, 52c, 53b, 53c, 54b, 54c, 82
b, 82c, 83b, 83c, 84b, 84c, 123
a, 123b, 124a, 124b, 126a, 126
b, 127a, 127b, 173, 174, 176, 1
77, 193, 194, 196, 197, 203, 20
4, 206, 207, 223, 224, 226, 227
Reflector electrodes 21, 22, 156a, 156b, 157a, 157b
IDT electrode fingers 42, 43, 72, 73, 142, 143, 144, 1
45, 152, 153 SAW filters 44, 74, 128b, 148a, 148b, 148
c, 232, 233 Electrode patterns 45, 75, 162 Electrode pads 61, 62, 91, 92, 158 Busbar electrodes 83a, 103, 113 Strip line electrode rows 128a, 146, 147, 154a, 154b, 15 having a periodic structure
5a, 155b Wiring patterns 131, 132, 133 SAW filter pass characteristics 163 Bonding wire 149 Absorber 161 Surface mounting package 164a, 164b Input terminal electrode 165a, 165b Output terminal electrode 166 Ground electrode 178, 198, 208, 228 Inter-stage electrode Patterns 181, 211 First-stage SAW filters 182, 212 Second-stage SAW filters 229 Spiral inductor electrode patterns 231 Short-circuit electrode patterns

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuki Nishimura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (48)

[Claims] 1. A surface acoustic wave (SAW) resonator having reflector electrodes provided on both sides of an interdigital transducer (IDT) electrode on a piezoelectric substrate and arranged in proximity to each other in parallel with the propagation direction of the SAW. A surface acoustic wave filter which is coupled and grounds all the IDT electrodes constituting the SAW resonator arranged at the center and electrically separates the IDT electrodes constituting the SAW resonator arranged outside. 2. The IDT electrode forming the SAW resonator arranged in the center is grounded via an electrode pattern arranged in the gap between the IDT electrode forming the SAW resonator arranged outside and the reflector electrode. The surface acoustic wave filter according to claim 1. 3. The surface acoustic wave filter according to claim 1, wherein a plurality of cascaded connection electrode patterns formed on the piezoelectric substrate are connected in cascade. 4. The surface acoustic wave filter according to claim 3, wherein an electrode pad for bonding is formed on a part of the inter-stage connection electrode pattern. 5. The surface acoustic wave filter according to claim 3, wherein the inter-stage connection electrode pattern is grounded via a reactance element formed by the electrode pattern on the same piezoelectric substrate. 6. The surface acoustic wave filter according to claim 5, wherein the reactance element is a spiral inductor. 7. A piezoelectric substrate is provided with three SAW resonators, each having reflector electrodes on both sides of an IDT electrode, arranged in proximity to each other in parallel with the propagation direction of the SAW to acoustically couple the adjacent SAW resonators.
A surface acoustic wave filter in which an electrode pattern for two bus bars between AW resonators is divided and all IDT electrodes constituting the SAW resonator arranged in the center are grounded. 8. An IDT electrode constituting one SAW resonator arranged outside is connected to a balanced input terminal, and an IDT electrode constituting the other SAW resonator arranged outside is connected to a balanced output terminal. The surface acoustic wave filter according to claim 7, which is connected to. 9. The IDT electrode constituting the SAW resonator arranged in the center is the ID of the SAW resonator arranged outside.
The surface acoustic wave filter according to claim 7, wherein the surface acoustic wave filter is grounded via an electrode pattern arranged in a gap between the T electrode and the reflector electrode. 10. The ID of the SAW resonator arranged outside.
The line width of the electrode pattern for the bus bar forming the T electrode is
9. The surface acoustic wave filter according to claim 8, wherein the surface width is larger than the line width of the bus bar electrode pattern forming the IDT electrode of the SAW resonator arranged in the center. 11. The plurality of inter-stage connection electrode patterns formed on the piezoelectric substrate are connected in cascade.
The surface acoustic wave filter according to. 12. The surface acoustic wave filter according to claim 11, wherein an electrode pad for bonding is formed on a part of a plurality of inter-step connection electrode patterns. 13. The surface acoustic wave filter according to claim 11, wherein a plurality of inter-stage connection electrode patterns are connected to each other through a reactance element. 14. The surface acoustic wave filter according to claim 11, wherein one of the plurality of inter-stage connection electrode patterns is grounded and the other inter-stage connection electrode pattern is grounded via a reactance element. 15. The surface acoustic wave filter according to claim 13, wherein the reactance element is a spiral inductor formed by an electrode pattern on the same piezoelectric substrate. 16. A piezoelectric substrate, on which two SAW resonators having reflector electrodes on both sides of an IDT electrode are formed in parallel with the SAW propagation direction, and the SAW resonators are provided between the SAW resonators.
By forming stripline electrodes having a length approximately equal to the IDT electrode finger cross width of the W resonator in parallel with the SAW resonator at the same electrode period, a periodic structure electrode array is formed and the SAW resonator is formed. A surface acoustic wave filter in which a resonator and the periodic structure electrode array are arranged close to each other and acoustically coupled. 17. The surface acoustic wave filter according to claim 16, wherein the strip line electrodes forming the periodic structure electrode array are connected to each other by bus bar electrodes provided at both ends thereof. 18. The surface acoustic wave according to claim 17, wherein the periodic structure electrode is grounded through an electrode arranged in a gap between the IDT electrode and the reflector electrode of the SAW resonator arranged outside and a bus bar electrode. filter. 19. The SAW resonator electrode arranged on the outer side is connected to a balanced type input terminal, and the other SAW resonator electrode arranged on the outer side is connected to a balanced type output terminal. Surface acoustic wave filter. 20. The bus bar electrode pattern formed on the periodic structure electrode, wherein the line width of the bus bar electrode pattern on the side adjacent to the periodic structure electrode of the IDT electrode constituting the SAW resonator arranged on the outside is formed on the periodic structure electrode. The surface acoustic wave filter according to claim 19, wherein the surface acoustic wave filter has a width larger than the line width. 21. A plurality of cascade-connected electrodes are formed by a plurality of inter-stage connection electrode patterns formed on a piezoelectric substrate.
The surface acoustic wave filter according to item 6. 22. The IDT electrode on the side adjacent to the periodic structure electrode array of the SAW resonator and the bus bar electrode connecting the periodic structure electrode array are integrated, and the periodic structure electrode array is grounded. Item 17. The surface acoustic wave filter according to item 17. 23. The surface acoustic wave filter according to claim 22, wherein a plurality of cascaded connection electrode patterns formed on the piezoelectric substrate are connected in cascade. 24. Two SAW resonator filters, in which SAW resonators having reflector electrodes on both sides of an IDT electrode are closely arranged and acoustically coupled to each other, are formed on a piezoelectric substrate.
The electrode arrangement of the SAW resonator forming the AW resonator filter is set to the opposite phase, and S forming the second SAW resonator filter is formed.
A surface acoustic wave filter in which the electrodes of the AW resonator are arranged in phase and the first SAW resonator filter and the second SAW resonator filter are connected in parallel. 25. The values of the high frequency side excitation frequency of one of the first and second SAW resonator filters and the low frequency side excitation frequency of the other SAW resonator filter match. The surface acoustic wave filter according to claim 24, which is made to operate. 26. First and second SAW resonator filters are formed on a piezoelectric substrate by forming four SAW resonator filters acoustically coupled by closely disposing SAW resonators having reflector electrodes on both sides of an IDT electrode. The electrode arrangements of the SAW resonators forming the resonator filter have opposite phases, the electrode arrangements of the SAW resonators forming the third and fourth SAW resonator filters have the same phase, and the first SAW resonator filter and the A third SAW resonator filter is connected in parallel, the second SAW resonator filter and the fourth SAW resonator filter are connected in parallel, and the first and third SAW resonator filters and the A surface acoustic wave filter in which the second and fourth SAW resonator filters are connected in series by an electrode pattern formed on the piezoelectric substrate. 27. Among the first and third SAW resonator filters, the value of the high frequency side excitation frequency of one of the SAW resonator filters and the value of the low frequency side excitation frequency of the other SAW resonator filter are made to match. And the values of the high-side excitation frequency of one of the SAW resonator filters and the low-side excitation frequency of the other SAW resonator filter of the second and fourth SAW resonator filters are matched. 26. The surface acoustic wave filter according to 26. 28. A first SAW resonator filter and a second SAW resonator filter are arranged next to each other in parallel with a surface acoustic wave propagating direction, and a third SAW resonator filter and a fourth SAW resonance filter are arranged. 27. The surface acoustic wave filter according to claim 26, wherein the container filters are arranged next to each other in parallel with the propagation direction of the surface acoustic wave. 29. A SAW resonator filter is constructed by arranging acoustically coupled SAW resonators having reflectors on both sides of an IDT electrode on a piezoelectric substrate, and adjoining the SAW resonator filter. A surface acoustic wave filter having a busbar in which a plurality of SAW resonators arranged in proximity to each other are divided while dividing a busbar electrode pattern in a central portion of an IDT electrode. 30. Two surface acoustic wave filters are formed on the same piezoelectric substrate, and the electrode arrangement of the SAW resonator forming the first SAW resonator filter is opposite to that of the second SAW resonator filter. 30. The electrodes of the SAW resonators to be arranged are in phase with each other, and the first SAW resonator filter and the second SAW resonator filter are connected in parallel.
The surface acoustic wave filter according to. 31. Among the first and second SAW resonator filters, the value of the high-frequency side excitation frequency of one of the SAW resonator filters and the value of the low-frequency side excitation frequency of the other SAW resonator filter match. The surface acoustic wave filter according to claim 30, wherein the surface acoustic wave filter is used. 32. A central bus bar electrode pattern of a SAW resonator filter in which SAW resonators having reflector electrodes on both sides of an IDT electrode are closely arranged on a piezoelectric substrate and acoustically coupled to each other, and the SAW resonator electrode pattern is divided. Four resonator filters are formed, and the electrode arrangement of the SAW resonators forming the first and second SAW resonator filters is opposite phase, and the third and fourth SW resonators are arranged.
The electrode arrangement of the SAW resonator forming the AW resonator filter is in phase, the first SAW resonator filter and the third SAW resonator filter are connected in parallel, and the second SAW resonator filter and the second SAW resonator filter are connected. A fourth SAW resonator filter is connected in parallel, and the first and third SAWs are connected.
A surface acoustic wave filter in which a resonator filter and the second and fourth SAW resonator filters are connected in series by an electrode pattern formed on the piezoelectric substrate. 33. Of the first and third SAW filters, the value of the high-frequency side excitation frequency of one of the SAW resonator filters and the value of the low-frequency side excitation frequency of the other SAW resonator filter are matched, and 32. The values of the high-side excitation frequency of one of the SAW resonator filters and the low-side excitation frequency of the other SAW resonator filter of the second and fourth SAW resonator filters are matched. The surface acoustic wave filter according to. 34. A surface acoustic wave filter having a reactance element formed by utilizing a part of an electrode pattern constituting a SAW filter. 35. An IDT electrode and a reflector electrode are provided,
The surface acoustic wave filter according to claim 34, wherein a reactance element is formed by using the reflector electrode. 36. The surface acoustic wave filter according to claim 35, wherein the reactance element is an inductor formed by connecting parallel-arranged stripline electrodes forming a reflector electrode in a substantially zigzag shape. 37. The elastic surface according to claim 35, wherein the reactance element is an inductor formed by bundling a plurality of parallel-arranged stripline electrodes forming a reflector electrode and connecting the stripline electrodes in a substantially zigzag shape. Wave filter. 38. The surface acoustic wave filter according to claim 35, wherein the reactance element is a capacitor formed by connecting strip electrodes arranged in parallel and forming a reflector electrode in an interdigital form. 39. The surface acoustic wave filter according to claim 34, wherein an input / output matching circuit is configured using a reactance element. 40. The surface acoustic wave filter according to claim 34, wherein an interstage matching circuit is configured using a reactance element. 41. The surface acoustic wave filter according to claim 34, wherein a plurality of SAW resonators having reflector electrodes on both sides of the IDT electrode are arranged close to each other and acoustically coupled. 42. The surface acoustic wave filter according to claim 41, wherein the reactance element is formed by using a reflector electrode. 43. A plurality of SAW resonator filters acoustically coupled by closely disposing a plurality of SAW resonators having reflector electrodes on both sides of an IDT electrode are formed on the same piezoelectric substrate to form the SAW resonator filter. A surface acoustic wave filter in which input and output matching circuits are configured by using a reactance element formed by an electrode pattern on the piezoelectric substrate while connecting the elements in cascade. 44. The surface acoustic wave filter according to claim 43, wherein the reactance element is formed by using a reflector electrode. 45. A plurality of SAW resonator filters acoustically coupled by closely disposing a plurality of SAW resonators having reflector electrodes on both sides of an IDT electrode are formed on the same piezoelectric substrate to form the SAW resonator filter. A surface acoustic wave filter in which the connection points are connected in cascade, and the connection points are grounded via a reactance element formed by an electrode pattern on the same piezoelectric substrate. 46. The surface acoustic wave filter according to claim 45, wherein the reactance element is a spiral inductor. 47. The spiral inductor is formed by utilizing a space between a plurality of SAW filters.
The surface acoustic wave filter according to. 48. The surface acoustic wave filter according to claim 46, wherein a short-circuit electrode pattern for short-circuiting and connecting between adjacent winding electrode patterns of the spiral inductor is provided at at least one location.