JP3532624B2 - Surface acoustic wave filter - Google Patents

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 electrode finger crossing width 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 very narrow, and the specific bandwidth of the realized filter (at the center frequency of the filter is 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 in 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 is increased and the size of the entire circuit is increased, 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 achieve 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 acoustic resonators are arranged in proximity to each other in parallel with the SAW propagation direction to acoustically couple, and one electrode finger and the other electrode finger that constitute the SAW resonator arranged in the center are arranged outside. Inside the IDT electrode that constitutes the SAW resonator
The SAW resonances in which the electrode fingers of the
Placed in the gap between the IDT electrode and the reflector electrode that make up the reflector.
Ground through the electrode pattern made by
Each is connected to the input terminal and the output terminal .

[0011]

[0012] In the above first configuration of the present invention, preferably connected to the plurality cascade by interstage connecting electrode patterns formed on a piezoelectric substrate. Further, in this case, it is preferable to form the electrode pad for bonding to a portion of the connecting electrode pattern between said stages. Further, in this case, it is preferable that the inter-stage connection electrode pattern is grounded via a reactance element formed by the electrode pattern on the same piezoelectric substrate. In this case, it is 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 electrode pattern for the bus bar between the two AW resonators is divided, and one electrode finger and the other electrode finger of the SAW resonator arranged at the center are arranged outside.
The IDT electrode that constitutes the SAW resonator and the reflector electrode
Grounded via the electrode pattern arranged in the gap with the pole, and outside
Constituting one of the SAW resonators arranged in the
Connect the electrode fingers of the electrodes to the balanced input terminals and
IDT electrode constituting the other SAW resonator
The electrode finger of is connected to the balanced output terminal .

[0014] In the above second configuration of the present invention, the line width of the bus bar electrode pattern constituting the IDT electrodes of the SAW resonators arranged on the outer side, the SAW resonator disposed at the center It is preferable to make the line width larger than the line width of the bus bar electrode pattern forming the IDT electrode.

[0015]

Further, 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. Further, in this case, it is preferable to form an electrode pad for bonding on a part of the plurality of inter-step connection electrode patterns. Further, in this case, the inter-stage connection patterns of the plurality of, preferably connected via a reactance element. Further, in this case, grounded one of said interstage connecting electrode pattern of the plurality of, preferably ground connection electrode pattern between the other of said stage via a reactance element. In this case, it is preferable that the reactance element is a spiral inductor formed by an electrode pattern on the same piezoelectric substrate.

A 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 approximately equal to the IDT electrode finger crossing 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. And the periodic structure electrode array are arranged close to each other for acoustic coupling, and the strip line electrodes forming the periodic structure electrode array are connected to each other by bus bar electrodes provided at both ends of the strip line electrodes. it is obtained by grounded electrode.

[0018] In the above third configuration of the present invention, the S of the periodic structure shaped electrode row, is disposed outside
Preferably grounded via the electrode and the bus bar electrode disposed in the gap between the IDT electrode and the reflector electrode of AW resonators. Also, in this case, the front of one placed on the outside
Serial connecting the IDT electrodes constituting the SAW resonators to the balanced type input terminal, it is preferable to connect the IDT electrodes constituting the other of the SAW resonator disposed on the outer side to the balanced output terminal. Furthermore, in this case, it was placed outside
Wherein the IDT electrodes constituting the SAW resonators, the line width of the bus bar electrode pattern on the side adjacent to the periodic structure shaped electrode rows, to be larger than the line width of the bus bar electrode pattern formed on the periodic structure shaped electrode row Is preferred. Also,
In the third 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.

[0019] In the above third configuration of the present invention, the IDT electrode on the side adjacent to the periodic structure shaped electrode row of the SAW resonator, connecting the periodic structure shaped electrode row
It is preferable to integrate the bus bar electrode and ground the periodic structure electrode array.

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

[0033]

[0034]

According to the first configuration of the action The present invention, on the piezoelectric substrate, the SAW resonator provided with the reflector electrodes on both sides of the IDT electrodes, in parallel with three proximity placement and direction of propagation of the SAW acoustic One electrode finger and the other electrode finger that are coupled to each other and that are arranged in the center to form the SAW resonator, and an electrode finger that is arranged outside and that is inside the IDT electrode that forms the SAW resonator.
The SAW resonators arranged outside, respectively.
Electrode disposed in the gap between the IDT electrode and the reflector electrode
Ground through the pattern and input each outer electrode finger
By connecting the terminal and the output terminal, the potential of the SAW resonator arranged in the center can be freely distributed, and the potential is not canceled between the SAW resonators arranged on the outer side. A strong excitation strength can be obtained for the mode as well. 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. Further, since the SAW filter utilizing the three excitation modes can be realized 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. You can also In addition, the IDT electrode that constitutes the SAW resonator
Since there is more freedom in determining the gap between the reflector electrode and the
The gap between the DT electrode and the reflector electrode is appropriately determined and the out-of-band scan is performed.
You can control the purious. The result is better
Out-of-band characteristics can be obtained.

[0035]

Further, in the first configuration of the present invention,
According to a preferred configuration of connecting to the plurality cascade by interstage connecting electrode patterns formed on a piezoelectric substrate,
The out-of-band attenuation amount characteristic is significantly improved, and a better filter characteristic can be obtained. In this case, according to a preferred configuration of forming an electrode pad for bonding to a portion of the connecting electrode pattern between said stages, a good pass characteristics by connecting a matching element of the inductance or the like connected to the electrode patterns interstage When it is obtained, the connection between the inter-stage connection electrode pattern and the external circuit becomes easy. In this case, according to the connection electrode pattern between said stages, a preferred configuration that is grounded via a reactive element formed by an electrode pattern on the same piezoelectric substrate, since the external circuit is not required,
It is possible to reduce the size of the filter circuit. in this case,
Further, according to a preferred configuration of the reactance element is a spiral inductor, it is possible to reduce the size of the reactance element.

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. with splitting the use electrode patterns, one of the electrodes constituting the SAW resonator disposed at the center
The SAW resonance in which the finger and the other electrode finger are arranged outside
Placed in the gap between the IDT electrode and the reflector electrode that make up the reflector.
Grounded through the patterned electrode and placed outside
One of the electrode fingers of the IDT electrode that constitutes the SAW resonator
Connect to the balanced input terminals and place the other
Balance the electrode fingers of the IDT electrodes that compose the SAW resonator
By connecting to the mold output terminal, 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 can be independently wired. Therefore, I which constitutes the SAW filter
Since only the IDT electrode of the SAW resonator arranged in the center of the DT 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, further improving the out-of-band attenuation characteristics of the filter. can do. Also, SA
The gap between the IDT electrode and the reflector electrode that form the W resonator is
Since the degree of freedom to decide increases, the IDT electrode and the reflector electrode
Controlling Out-of-Band Spurious by Properly Gap
You can As a result, obtain better out-of-band characteristics
You can Further, one of the SAWs arranged outside
Connect the IDT electrode that constitutes the resonator to the balanced input terminal
The other SAW resonator arranged outside.
It is a good idea to connect the IDT electrode to the balanced output terminal.
According to the better configuration, use an external circuit such as a balun
Instead, connect a balanced element such as an IC to the front and back of the filter.
Can improve the noise characteristics of the entire circuit.
be able to.

In the second structure of the present invention ,
The line width of the bus bar electrode pattern constituting the IDT electrodes of the SAW resonators arranged on the outer side, larger than the line width of the bus bar electrode pattern constituting the IDT electrodes of the SAW resonator disposed at the center According to the preferable configuration described above, the insertion loss of the filter can be improved. The reason will be described below. Adjacent SAW
The distance G between the comb-shaped electrodes forming the IDT electrode of the resonator is
The degree of coupling between the two SAW resonators is controlled, and the smaller the distance, the greater the degree of coupling between the SAW resonators. However, if this distance G is too small, the line widths W ₁ , W of the bus bar electrodes provided at this portion
_{Since 2} becomes smaller than that, the effect of the electrical resistance loss of the IDT electrode in this portion on the insertion loss of the filter cannot 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. IDTs that make up
It is used to ground the electrode 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, by increasing the line width W ₁ of the bus bar electrode arranged outside by reducing the line width W ₂ of the bus bar electrode arranged in the center, the inter-electrodes between the comb-shaped electrodes forming the IDT electrodes of the adjacent SAW resonators can be 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.

[0039]

In the second structure of the present invention,
According to a preferred configuration of connecting a plurality cascade by interstage connecting electrode pattern of a plurality of which are formed on the piezoelectric substrate, that out-of-band attenuation characteristics are significantly improved, to obtain a more excellent filter characteristic it can. Also in this case,
According to a preferable configuration in which an 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 obtain good pass characteristics. In addition, the connection between the inter-stage connection electrode pattern and the external circuit becomes easy. In this case, among the plurality of stages connected between patterns, according to a preferred configuration of connecting via a reactance element,
Good pass characteristics can be obtained. Also in this case,
While grounded in the interstage connecting electrode pattern of plural, by the preferred configuration of the connecting electrode pattern between the other of said stages is grounded through a reactance element, it is possible to obtain excellent pass characteristics. In this case, further, before
According to a preferred configuration of the serial reactance element is a spiral inductor formed by an electrode pattern on the same piezoelectric substrate, it is possible to reduce the size of the reactance element.

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. The structural electrode rows are arranged close to each other for acoustic coupling, and the stripline electrodes constituting the periodic structural electrode row are connected to each other by bus bar electrodes provided at both ends thereof to ground the stripline electrodes . As a result, 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, if the electrode period is the same, the surface acoustic wave is generated as in the case of the first invention. Propagation is possible. As a result, the band of the SAW filter can be widened. Further, the periodic structure electrode array can have the same structure as the reflector electrode. In addition, in the third configuration of the present invention, the electrode having the periodic structure electrode is disposed in a gap between the IDT electrode and the reflector electrode of the SAW resonator arranged outside, and the bus bar electrode. According to a preferable configuration in which the periodic structure electrodes are electrically isolated from the input / output terminals. As a result, the grounding state of the periodic structure 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, which is different from the case of the second invention. Similarly, the out-of-band attenuation characteristic of the filter can be further improved. In addition, since the degree of freedom for determining the distance between the reflector electrode and the IDT electrode and the periodic structure electrode forming the SAW resonator is increased, the gap 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, the IDT that constitutes one of the SAW resonators arranged outside is further added.
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, an external circuit such as a balun is used. Instead, since balanced elements such as ICs can be connected to the front and rear stages of the filter, the noise characteristics of the entire circuit can be improved. Further, in this case, the line width of the bus bar electrode pattern on the side adjacent to the periodic structure electrode array of the IDT electrodes constituting the SAW resonator arranged on the outside is set to the bus bar formed in the periodic structure electrode array. According to the preferable configuration in which the line width of the electrode pattern for use is made larger, the insertion loss of the filter can be further improved as compared with the case of the second invention. This is because 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 electrode arranged in the center, as compared with the case of the second invention. Since the proportion of the portion is reduced, 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. Further, in the third configuration of the present invention, 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 can be obtained.

In the third structure of the present invention,
An IDT electrode on the side adjacent to the periodic structure shaped electrode row of the SAW resonator, while integrated with the <br/> bus bar electrode connected to the periodic structure shaped electrode array, the periodic structure shaped electrode row According to the preferable configuration of grounding, the first
Although the unbalanced input / output configuration can be achieved as in the case of the invention described above, the bandwidth of the SAW filter can be widened also in this case.

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[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 is a single crystal piezoelectric substrate, and by forming an electrode pattern in the form of a periodic strip line 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 influences 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 in 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 constituting the central SAW resonator are grounded, and the IDT electrodes constituting 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. 4, a plurality of SAW filters 4 are formed on the same piezoelectric substrate 41.
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 is not required, 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 the 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 is also provided.
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. 2, and it is possible to realize the wide band of the SAW filter and 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 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. Further, 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, 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 the present embodiment, as shown in FIG. 7, if a plurality of SAW filters 72, 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 is not required, 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 good 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 deviates to some extent 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.

In this embodiment, the input / output electrode structure of the SAW filter is assumed to be balanced, and the description has been made in comparison with the second embodiment. However, 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 with 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 pass characteristic in the band as indicated 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 both of them overlap each other, so that the change of 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 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 unnecessary radiation due to the routing of the bonding wire and the like. Since it 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 cascade-connected 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 the 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 IDT electrode finger of the SAW resonator filter 152 which is adjacent to the SAW resonator filter 152 is divided into 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 the structure in which the SAW filter of this embodiment is mounted in a surface mounting package, and the parts corresponding to those in FIG. 15 are designated by the same reference numerals. 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 in the case of the fourth embodiment shown in FIG. 13, and the band widening of the SAW filter can be realized. 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.
Further, 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, 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 top of 1 and connecting to a terminal electrode of the surface mounting package 161 by 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 this 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 functions as a matching circuit for the SAW filter, and as a result, an external matching circuit is not required. Therefore, 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 composed of 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 of 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 can be provided between the stages. It is possible to realize the adjustment between the stages of the SAW filter that has to be connected without increasing the electrode area on the piezoelectric substrate 201.

Moreover, since the inductor elements of the reflector electrodes 203 and 206 are 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 stage 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 constituted 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, and the input / output electrodes of the IDT electrodes 222 and 225 are respectively formed. 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 must be formed at positions separated to some extent in order to prevent unnecessary elastic coupling between them. Therefore, as shown in FIG. 22, the above-mentioned 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 filter 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 formed by 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
By trimming the electrode pattern 232 portion of FIG. 23 (b) for 3 etc. and trimming the electrode pattern 233 portion of FIG. 23 (c) for the interdigital capacitor electrodes 174, 204, 224 etc. Each reactance value can be finely adjusted.

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

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 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 also 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. In addition, the IDT electrode and the reflector forming the SAW resonator
Since the degree of freedom for determining the gap with the electrode is increased, the IDT electrode
The gap between the reflector electrode and the reflector
Can be controlled. As a result, better out of band
The characteristics 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 disposed. Can be wired independently. Therefore, among 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 greatly reduced, so that the out-of-band attenuation characteristics of the filter can be further improved. it can. In addition, a SAW resonator is used.
Freedom to determine the gap between the IDT electrode and the reflector electrode
As the degree increases, the gap between the IDT electrode and the reflector electrode is appropriate.
The out-of-band spurious can be controlled according to the above. So
As a result, better out-of-band characteristics can be obtained. It
In addition, one of the SAW resonators arranged outside is configured.
Connect the IDT electrode to the balanced input terminal and place it outside
Of the other SAW resonator that has been generated
The preferred configuration of connecting the poles to the balanced output terminals
If this is the case, the filter can be
Balanced devices such as ICs can be connected in the front and back
Therefore, the noise characteristic of the entire circuit can be 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 of the periodic structure, the SAW filter structure is improved. A wide band can be achieved.

[0128]

[0129]

[0130]

[0131]

[0132]

[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 substrates 12, 13, 14 SAW resonators 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 bus bar 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 characteristic 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 pattern 231 Short circuit electrode pattern

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kozo Murakami 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Kazuki Nishimura, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. In-house (56) Reference JP 5-136651 (JP, A) JP 4-373304 (JP, A) JP 3-222512 (JP, A) JP 2-81511 (JP, A) ) JP-A-59-131213 (JP, A) JP-A-63-285018 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03H 9/64 H03M 9/25

Claims (18)

(57) [Claims] 1. A surface acoustic wave (SAW) resonator having reflector electrodes on both sides of an interdigital transducer (IDT) electrode on a piezoelectric substrate is arranged in close proximity to three SAW resonators in parallel with the SAW propagation direction. One electrode finger and the other electrode , which are coupled to each other and constitute the centrally arranged SAW resonator
A finger and I constituting the SAW resonator arranged outside
The electrode fingers inside the DT electrode were respectively placed outside
The IDT electrode that constitutes the SAW resonator and the reflector electrode
Grounded via the electrode pattern arranged in the gap with the pole, and outside
A surface acoustic wave filter in which the electrode fingers of are connected to the input terminal and the output terminal, respectively . 2. The surface acoustic wave filter according to claim 1, wherein a plurality of inter-stage connection electrode patterns formed on the piezoelectric substrate are connected in cascade. 3. The surface acoustic wave filter according to claim 2 , wherein an electrode pad for bonding is formed on a part of the inter-stage connection electrode pattern. 4. The surface acoustic wave filter according to claim 2 , wherein the inter-stage connection electrode pattern is grounded via a reactance element formed by an electrode pattern on the same piezoelectric substrate. 5. The surface acoustic wave filter according to claim 4 , wherein the reactance element is a spiral inductor. 6. A piezoelectric substrate is provided with three SAW resonators, each having reflector electrodes on both sides of an IDT electrode, arranged close to each other in parallel with the SAW propagation direction to acoustically couple the adjacent SAW resonators.
The electrode pattern for the bus bar between the two AW resonators is divided, and one electrode finger and the other electrode finger of the SAW resonator arranged at the center are arranged outside.
The IDT electrode that constitutes the SAW resonator and the reflector electrode
Grounded via the electrode pattern arranged in the gap with the pole, and outside
Constituting one of the SAW resonators arranged in the
Connect the electrode fingers of the electrodes to the balanced input terminals and
IDT electrode constituting the other SAW resonator
A surface acoustic wave filter in which the electrode fingers of are connected to a balanced output terminal . 7. The I of the SAW resonator arranged on the outside.
7. The surface acoustic wave filter according to claim 6 , wherein the line width of the bus bar electrode pattern forming the DT electrode is larger than the line width of the bus bar electrode pattern forming the IDT electrode of the SAW resonator arranged at the center. . 8. The plurality of inter-stage connection electrode patterns formed on the piezoelectric substrate are connected in cascade.
The surface acoustic wave filter according to item 6 . 9. The surface acoustic wave filter according to claim 8 , wherein an electrode pad for bonding is formed on a part of a plurality of the inter-stage connection electrode patterns. 10. The surface acoustic wave filter according to claim 8 , wherein a plurality of the inter-stage connection patterns are connected to each other via a reactance element. 11. The surface acoustic wave filter according to claim 8 , wherein one of a plurality of the inter-stage connection electrode patterns is grounded and the other of the inter-stage connection electrode patterns is grounded via a reactance element. 12. The surface acoustic wave filter according to claim 10 or 11 wherein the reactive element is a spiral inductor formed by an electrode pattern on the same piezoelectric substrate. 13. A SAW resonator having reflector electrodes on both sides of an IDT electrode is formed on a piezoelectric substrate in parallel with the SAW propagation direction, and the SAW resonator is 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. The resonator and the periodic structure electrode array are arranged close to each other for acoustic coupling, and the strip line electrodes forming the periodic structure electrode array are connected to each other by bus bar electrodes provided at both ends of the strip line electrodes. A surface acoustic wave filter with the line electrode grounded. 14. the periodic structure shaped electrode rows, to claim 13 which is grounded via the electrode and the bus bar electrode disposed in the gap between the IDT electrode arranged the SAW resonator outside said reflector electrodes The surface acoustic wave filter described. 15. An IDT electrode constituting one of the SAW resonators arranged outside is connected to a balanced type input terminal,
The surface acoustic wave filter according to claim 14 , wherein an IDT electrode constituting the other SAW resonator arranged outside is connected to a balanced output terminal. 16. A busbar formed on the periodic structure electrode array by setting a line width of an electrode pattern for a busbar on the side adjacent to the periodic structure electrode array of the IDT electrode constituting the SAW resonator arranged on the outer side. The surface acoustic wave filter according to claim 15 , wherein the line width of the electrode pattern for use is made larger. 17. The surface acoustic wave filter according to claim 13 , wherein a plurality of inter-stage connection electrode patterns formed on the piezoelectric substrate are connected in cascade. 18. The IDT electrode of the SAW resonator on the side adjacent to the periodic structure electrode array and the bus bar electrode connecting the periodic structure electrode array are integrated,
The surface acoustic wave filter according to claim 13 , wherein the periodic structure electrode array is grounded.