JP2002359541A - Resonator-type surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wideband resonator-type surface acoustic wave filter. SOLUTION: Two pieces of pair-terminal surface acoustic wave resonators, each of which is constituted by arranging three IDT electrodes closely in the direction of propagation of surface acoustic waves on the main surface of a piezoelectric substrate and arranging grating reflectors on both sides of them, are arranged side by side; the outermost electrode finger in the IDT electrode at the center of the above one pair-terminal surface wave resonator is made wider than others; and also the above two pair-terminal surface acoustic wave resonators are connected in the same phase to make input and are connected in reverse phase form an output, thus a resonator-type surface acoustic wave filter is constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonator type surface acoustic wave filter (hereinafter, referred to as a SAW filter) formed by connecting two 2-port pair surface acoustic resonators in parallel, and more particularly to a SAW filter having a wide band. Regarding filters.

[0002]

2. Description of the Related Art In recent years, surface acoustic wave filters have been widely used in the field of communications, and have been used particularly in portable telephones and the like because of their excellent characteristics such as high performance, small size, and mass productivity.
FIG. 9 shows JP-A-61-142812 and JP-A-62-4.
FIG. 3 is a plan view illustrating a configuration of a resonator type SAW filter disclosed in Japanese Patent Publication No. 3204, in which two 2-port surface acoustic wave resonators having different resonance frequencies are connected in parallel to form a SAW filter. . Two IDT electrodes 52, 53 are arranged on the main surface of the piezoelectric substrate 51 along the propagation direction of the surface wave, and grating reflectors (hereinafter, referred to as reflectors) 54, 5 are provided on both sides thereof.
5 to form a two-terminal pair surface acoustic wave resonator A (resonance frequency f1a). The IDT electrodes 52 and 53 are each composed of a pair of comb-shaped electrodes having a plurality of electrode fingers interposed therebetween, one of the comb-shaped electrodes forming the IDT electrode 52 is denoted by 52a, and the other is denoted by 52b.
One of the interdigital electrodes forming the electrode 53 is denoted by 53a, and the other is denoted by 53b.

Further, parallel to the two-terminal pair surface acoustic wave resonator A, IDT electrodes 56, 5
7 and reflectors 58 and 59 on both sides thereof to form a two-terminal pair surface acoustic wave resonator B (resonance frequency f1b). One of the comb electrodes forming the IDT electrode 56 is 56
a, the other one is 56b, one comb-shaped electrode forming the IDT electrode 57 is 57a, and the other is 57b.

In FIG. 9, the center distance between the innermost electrode fingers of the IDT electrodes 52 and 53 is λ / 2 of the wavelength λ to be excited,
Alternatively, it is set to (2n + 1) λ / 2 (n = 0, 1, 2,...), And the two-terminal pair surface acoustic wave resonator A has a resonance frequency f1
In the state of being excited at a, for example, the comb-shaped electrode 52
When the moment when a positive electric charge is generated on a is captured, a negative electric charge is generated on the comb-shaped electrode 52b, and the comb-shaped electrode 5
A positive charge is generated on 3a and a negative charge is generated on the comb electrode 53b. Similarly, the center distance between the innermost electrode fingers of the IDT electrodes 56 and 57 is λ ′ / 2 or (2n + 1) λ ′ / 2 (n =
0, 1,...), And excited at the resonance frequency f1b of the two-terminal surface acoustic wave resonator B, at the moment positive charges are generated on the comb-shaped electrodes 56a and 57a, Negative charges are excited on the comb electrodes 56b and 57b. First, the comb-shaped electrodes 52a and 5
The input IN1 is connected to the same potential as that of the input electrode 6a, and the comb-shaped electrodes 52b and 56b that generate the opposite charges are connected to the input IN2. Further, a comb-shaped electrode 53a which generates charges of the same polarity as the comb-shaped electrode 52a and a comb-shaped electrode 57b which generates charges of the opposite polarity to the comb-shaped electrode 56a are connected to form an output OUT1, and the output OUT1 is inverted. And a comb electrode 57a that generates a charge having the same polarity as that of the comb electrode 56a.
T2. That is, two 2-port surface acoustic wave resonators having different resonance frequencies are connected in parallel such that the phase shift between the input and output terminals is different from each other by (2n + 1) π (n = 0, 1, 2,...). It is well known that the series arm is converted into a lattice-type circuit having a resonance frequency f1b and the lattice arm having a resonance frequency f1a. Then, by appropriately terminating the lattice type circuit, a filter having a pass bandwidth proportional to the difference between the respective resonance frequencies f1a and f1b of the two-port SAW resonators A and B can be obtained.

FIG. 10 schematically shows the frequency spectrum of the two-port surface acoustic wave resonators A and B shown in FIG. 9 in the vicinity of these resonances, and shows only the main vibration and the higher-order secondary mode. I'm drawing. 2-terminal pair surface acoustic wave resonator A,
Since B has almost the same electrode structure except for the phase relationship, the spectrums of the main vibration and the higher-order second-order mode have almost the same shape. In order to configure the bandpass filter, it is configured using the resonance frequencies f1a and f1b of the main vibrations of the two-terminal pair surface acoustic wave resonators A and B, respectively.
Higher order 2 of the two-terminal pair surface acoustic wave resonator B on the higher frequency side
The resonance frequency f2 of the next mode exists in the pass band, and this results in ripple.

FIG. 11 shows that a 42 基板 YX LiTaO film is formed on a piezoelectric substrate.
_3. The electrode period of the IDT electrodes 52 and 53 is λ _A 1.86 μm,
The electrode period λ _B of the IDT electrodes 56 and 57 is 1.80 μm,
The number of electrodes 52, 53, 56, and 57 is 18 pairs, their intersection width is 93 μm, and the reflectors 54, 55, 58, and 59 are used.
Are 100 and the thickness of the aluminum electrode is 0.17 μm, which is far from an ideal bandpass filter.

Therefore, the two-terminal pair surface acoustic wave resonator B
The resonance frequency f2 of the next mode is changed to the two-port SAW resonator A.
In order to shift to a lower frequency region than the resonance frequency f1a of FIG.
The electrode pattern of the two-terminal surface acoustic wave resonator A 'shown in FIG.
The two-port SAW resonator A shown in FIG.
Pattern of the IDT electrodes 56 and 57 of the surface acoustic wave resonator B '
Changed to the IDT electrodes 60 and 61 shown in FIG.
Is known. That is, the ID of the IDT electrode 60
The width of the electrode finger adjacent to the T electrode 61 is 0.25λ. _BOnly wide
0.5λ_BIt was. Thus, the electrode finger width
Is expanded, as shown schematically in FIG.
Is substantially the same as the resonance frequency f2 of the
Only 1b moves to the high frequency side, and the frequency of f1b and f2
It is known that the intervals increase. Therefore, the desired band
In order to obtain a resonator type SAW filter having a width, the frequency f1
a and f1b may be set appropriately. FIG.
Using the electrode pattern shown in the figure, 42 ゜ Y-XL
iTaO₃Of the IDT electrodes 52, 53 and 60, 61
Each intersection width W_A, W_BAre both 112 μm and IDT electrode 5
2, 53, 60, 60 have 18 pairs of logarithms, and the reflector 54,
55, 58, 59, 100 each, IDT electrode 5
2, 53 and the electrode period λ of each of 60 and 61_A, Λ_B
Are 1.86 μm together and the reflectors 54, 55 and 58, 59
2 times of each period λ '_A, Λ '_B1.86μm, Al
The filter is constructed with the minium electrode film thickness of 0.17μm.
FIG. As shown in FIG.
The over-bandwidth was found to be around 57MHz.

[0008]

The pass band width is determined in a conventional SAW filter in which two terminal-pair surface acoustic wave resonators using two IDT electrodes are connected in parallel. Thus, the frequency difference between the main resonance frequency f1a of the two-port surface acoustic wave resonator A and the main resonance frequency f1b of the two-port surface acoustic wave resonator B can be arbitrarily set. However, the frequency interval between the main resonance frequency f1b of the two-port SAW resonator B and the frequency f2 of the higher-order secondary mode excited on the lower frequency side cannot be set to an arbitrary value, but has an upper limit. There is a drawback in that there is a limit to widening the pass band width of the filter. For example, the latest WC that is expected to spread in the future
80MHz bandwidth required in DMA communication system
There is a problem that it is difficult to realize the above SAW filter by this configuration. The present invention has been made to solve the above problems, and has as its object to provide a wide band SAW filter.

[0009]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
And a resonator type surface acoustic wave filter according to the present invention.
The described invention is directed to the propagation direction of the surface wave on the main surface of the piezoelectric substrate.
Along with three IDT electrodes
2-port bullet with grating reflectors on both sides
Two surface acoustic wave resonators with different frequencies from each other
And connecting the two two-terminal surface acoustic wave resonators in phase.
A surface acoustic wave filter that is used as input and connected in reverse phase as output
The two-terminal pair surface acoustic wave resonator having a high frequency.
The terminal period of the IDT electrode of the two-port surface acoustic wave resonator is λ._D
And the phase of the center IDT electrode and the IDT electrodes on both sides
The center distance d between the facing electrode fingers is nλ_D/ 2 <d <(n +
1) λ_D/ 2 (n = 0, 1, 2, ...)
Resonator type surface acoustic wave filter characterized by setting
It is. According to a second aspect of the present invention, the two two-port bullets
High frequency two-port surface acoustic wave resonator
The electrode period of the_D, Twice the period of the reflector, λ '_D,frequency
The electrode period of the low-number two-port surface acoustic wave resonator is λ_C,
Λ 'is twice the period of the reflector _CAnd λ_D≤λ_CAnd λ '_D≤λ '_C 2. The method according to claim 1, wherein
This is the resonator type surface acoustic wave filter described above. Claim 3
The invention according to claim 1, wherein the input or output of the surface acoustic wave filter
Claims characterized in that at least one of the components is a balanced type.
Item 3. A surface acoustic wave filter according to Item 1 or 2. Claim 4
The described invention is directed to the input of the surface acoustic wave filter or
One terminal pair surface acoustic wave resonator for at least one of the output terminals
4. The method according to claim 1, wherein
This is a resonator type surface acoustic wave filter. Claim 5
Akira constitutes the two two-port SAW resonators.
A grating electrode is placed between each of the three IDT electrodes.
5. The resonator according to claim 1, wherein said resonator is arranged.
Type surface acoustic wave filter. The invention according to claim 6 is
It is characterized in that a plurality of the surface acoustic wave filters are connected in cascade.
6. The surface acoustic wave filter according to claim 1, wherein:
You.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1 is a plan view showing a configuration of a resonator type SAW filter according to the present invention, in which three IDT electrodes 2, 3, and 4 are arranged on a main surface of a piezoelectric substrate 1 along a propagation direction of a surface wave. In addition, the reflectors 5 and 6 are arranged on both sides thereof to form a two-terminal pair surface acoustic wave resonator (hereinafter, referred to as a two-terminal pair SAW resonator) C. Further, three IDT electrodes 2 ', 3', 4 'are arranged close to each other on the same piezoelectric substrate 1 in parallel with the two-port SAW resonator C, and reflectors 5', 6 'are arranged on both sides thereof. Thus, a two-port SAW resonator D having a higher resonance frequency than the two-port SAW resonator C is formed. Here, the IDT electrodes 2, 3, 4 and 2 ', 3', 4 'are formed of a pair of comb-shaped electrodes having a plurality of electrodes interposed between each other,
The electrode period of the IDT electrodes 2, 3, 4 is λc, and the reflectors 5, 6
Λ'c, the width of the intersection is Wc, the electrode period of the IDT electrodes 2 ′, 3 ′, 4 ′ is λd, and the period of the reflector is 2
Let the double be λ'd and the intersection width be Wd.

As shown in FIG. 1, a central IDT electrode 3,
Comb-shaped electrodes near the center of the 3 'piezoelectric substrate 1 are connected to each other to form an input terminal IN, and comb-shaped electrodes near the periphery of the piezoelectric substrates 1 of the IDT electrodes 2, 4 and 2', 4 'on both sides are connected to each other. This is used as the output terminal OUT. IDT electrode 3,
3 'each other comb-shaped electrode, IDT electrodes 2, 4
And the other respective comb electrodes of 2 'and 4' are grounded to form a SAW filter. The center IDT electrodes 3 and 3 'are mirror-inverted about the dashed line, and the IDT electrodes 2, 4 and 2', 4 'on both sides are mirror-inverted about the dashed line, and each is 180 °. It is an inverted pattern. Thus, the IDT electrodes 2, 3, 4, and 2 ', 3', 4 'are formed and the central IDT
The input side is connected in phase by connecting the comb-shaped electrodes of the electrodes near the center of the piezoelectric substrate 1 to the input terminals, while the piezoelectric substrates 1 of the IDT electrodes 2, 4, and 2 ', 4' on both sides are connected.
Are connected to the output terminal, the output sides are connected in opposite phases. In this embodiment, the IDT electrodes 2 ′ and 4 ′ on both sides are respectively located at the center I.
Of the comb-shaped electrodes that move closer to the DT electrode 3 'and are not connected to the output terminal OUT, the electrode fingers that are close to the central IDT electrode are deleted. Further, the outermost side of one of the comb-shaped electrodes constituting the central IDT electrode 3 '(not connected to the input IN) becomes wider as the electrode fingers of the IDT electrodes 2' and 4 'are deleted.

A feature of the present invention is that first, the two-port SAW resonators C and D are connected to three IDT electrodes 2, 3, 4 (2 ',
3 ', 4') are arranged close to each other, one of the IDT electrodes 3 (3 ') at the center is an input terminal, and the ID electrodes on both sides are ID terminals.
Since one of the T-shaped electrodes 2 and 4 (2 ′, 4 ′) is connected as an output terminal, a higher even-order mode excited on the low frequency side of the main vibration, for example, the second mode is A wide-band SAW filter is realized by utilizing the phenomenon that the charge is canceled out and cannot be excited. Second, of the two-port SAW resonators C and D constituting the resonator type SAW filter of FIG. 1, the center IDT electrode 3 'and the IDT electrodes 2' on both sides of the high-frequency 2-port SAW resonator D are arranged. , 4 ′, the center distance d between the electrode fingers facing each other is nλ _D
/ 2 <d <(n + 1) λ _D / 2 (n = 0, 1, 2,.
・). Therefore, the IDT at the center of the two-port SAW resonator D as shown in FIG.
The two electrode fingers arranged on both outermost sides of the electrode were formed so as to have a wider width. From the frequency relationship between the two two-port SAW resonators C and D, it is natural that λ _D ≦ λ _C and λ ′ _D ≦ λ ′ _C.

As shown in FIG. 1, IDT electrodes 2, 3, 4 and 2 ', 42 ゜ YX LiTaO ₃ were used for the piezoelectric substrate 1.
Each of the intersection widths W _C and W _D of 3 ′ and 4 ′ is 111 μm,
The IDT electrodes 2, 4 and 2 ', 4' each have a logarithm of 10.5 pairs,
15 pairs of IDT electrodes 3 and 3 ′, reflectors 5, 6,
The number of 5 'and 6' is 100 each, and the IDT electrodes 2, 3, and 4
Each of the electrode periods λ _C and λ _D of 2 ′, 3 ′ and 4 ′ is 1.85 μm, and the respective periods λ ′ _C and λ ′ _D of the reflectors 5, 6 and 5 ′ and 6 ′ are twice as large. The frequency spectrum of each of the two-terminal SAW resonators C and D is 1.86 μm, the width of the electrode finger placed on the outermost side of the IDT electrode 3 ′ is 0.5λ _D , and the thickness of the aluminum electrode is 0.17 μm. FIG. 2 schematically shows the characteristics of the resonator type SAW filter formed at the lower end.

As is apparent from FIG. 2, the resonance frequency f3 of the higher-order tertiary mode excited by the higher-frequency two-port SAW resonator D is equal to the lower-frequency two-port SAW resonator D.
It can be seen that the excitation is sufficiently lower than the main resonance frequency f1c of the resonator C and does not affect the pass bandwidth formed by the resonance frequencies f1c and f1d. FIG. 3 shows filter characteristics when the resonator type SAW filter shown in FIG. 1 is prototyped using the above-described various constants, and FIG. 4 shows an enlarged view of the passband. As can be seen from the figure, the pass bandwidth of 3 dB is 81.3 MHz, which is significantly larger than the conventional one shown in FIG.

FIG. 5 shows that the electrode period λ _C of the two-port SAW resonator C is set to 1.87 μm to increase the width of the pass band.
AW 1.85 The electrode period lambda _D of the resonator D, crossing width W _C, W _D
Were set to 126 μm and the terminating resistance was set to 50Ω. As a result, although the flatness of the pass band is slightly inferior, 3
The pass bandwidth in dB could be extended to about 90 MHz.

FIG. 6 is an electrode pattern diagram showing a configuration of a second embodiment according to the present invention, which is a configuration of an input unbalanced-output balanced type SAW filter. As in FIG. 1, the two-port SAW resonators C and D are formed,
The input terminals IN are formed by connecting the comb-shaped electrodes near the center of the IDT electrodes 3 and 3 ′, and the output terminals are formed by the I terminals on both sides.
The output OUT1 is connected by connecting the comb-shaped electrodes of the DT electrodes 2 and 4 near the periphery of the piezoelectric substrate 1, and the output OUT2 is connected by connecting the comb-shaped electrodes of the IDT electrodes 2 'and 4' near the periphery of the piezoelectric substrate 1.
The output terminal has a balanced configuration. FIG.
As shown in (1), when configuring a balanced SAW filter, the total number of electrode fingers of the comb electrode connected to the balanced terminal OUT1 is equal to the total number of electrode fingers of the comb electrode connected to OUT2. It is desirable to set.

FIG. 7 is an electrode pattern diagram showing the configuration of the third embodiment according to the present invention. The output terminal of the SAW filter of the present invention shown in FIG.
(Referred to as AW resonator) S1 is connected in series. Here, by setting the anti-resonance frequency of the SAW resonator S1 to the attenuation pole of the filter, an attenuation pole is formed at the frequency. For example, a large amount of attenuation is required to remove spurious components. It is particularly effective when doing so.

FIG. 8 is an electrode pattern diagram showing a configuration of a fourth embodiment according to the present invention, in which three IDT electrodes 2, 3, forming a two-terminal SAW resonator of a resonator type SAW filter. 4 (2 ′, 3 ′, 4 ′), the gratings G1, G2 (G′1, G′2) are inserted respectively, and the two-port SAW resonator C ′ (two-terminal SAW resonator) is inserted. D '), and these are connected in parallel to form a SAW filter. With such a configuration, the pass bandwidth can be adjusted by adjusting the pitch of the gratings G1, G2 (G'1, G'2).

In the above description, 42 基板 YX LiTaO was applied to the piezoelectric substrate.
₃ has been described with reference, that the present invention is applicable to other cutting angles, also other piezoelectric substrate such as lithium niobate, lithium tetraborate, can of course be applied to a langasite or the like. Further, in the above description, one filter is used as a filter. However, it is needless to say that a plurality of filters according to the present invention may be connected in parallel or cascaded.

[0020]

According to the present invention, the W-CDMA system is constructed as described above.
A wide-band resonator-type surface acoustic wave filter that satisfies the above standard can be configured. According to the third aspect of the present invention, it is possible to configure a balanced and wide-band resonator type SAW filter required for a mobile phone or the like. According to the fourth aspect of the present invention, it is possible to increase the attenuation at a desired frequency by connecting the one-terminal surface acoustic wave resonator in series. In the invention according to claim 5, three IDs
Placing a grating between each of the T allows the bandwidth of the filter to be adjusted. According to the invention described in claim 6, it is possible to respond to a request that requires a high attenuation.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of a resonator type SAW filter according to the present invention.

FIG. 2 is a diagram schematically illustrating frequency spectra C and D of two 2-port SAW resonators constituting a resonator type SAW filter according to the present invention, and filter characteristics configured.

FIG. 3 is a diagram illustrating an attenuation characteristic of the resonator type SAW filter illustrated in FIG. 1;

FIG. 4 is a diagram showing passband characteristics of the resonator type SAW filter shown in FIG. 1;

FIG. 5 is a diagram illustrating passband characteristics of a resonator type SAW filter according to a second embodiment.

FIG. 6 is a diagram illustrating an electrode pattern of a resonator type SAW filter according to a third embodiment.

FIG. 7 is a diagram showing an electrode pattern of a resonator type SAW filter according to a fourth embodiment.

FIG. 8 is a diagram showing an electrode pattern of a resonator type SAW filter according to a fifth embodiment.

FIG. 9 is a diagram showing the configuration of a conventional resonator-type SAW filter in which two two-port surface acoustic wave resonators are connected in parallel.

FIG. 10 shows a configuration 2 of a conventional resonator type SAW filter.
Frequency spectra A and B of the terminal-to-surface acoustic wave resonator;
It is a figure which shows the filter comprised by it typically.

FIG. 11 is a diagram illustrating transmission characteristics of a resonator type SAW filter configured using the electrode patterns of FIG. 9;

FIG. 12 is a diagram showing a configuration of an improved conventional resonator type SAW filter.

FIG. 13 shows a frequency spectrum A ′ of a two-port surface acoustic wave resonator constituting an improved resonator type SAW filter;
It is a figure which shows B 'and the filter comprised by it typically.

FIG. 14 is a diagram showing the attenuation characteristics of an improved conventional resonator type SAW filter.

[Explanation of symbols]

1. Piezoelectric substrate IDT electrode 2, 3, 4, 2 ', 3', 4 'Grating reflector 5, 6, 5, 5', 6 'C, D 2 terminal pair surface acoustic wave resonator λ _c , λ _d ··· electrode period λ ' _c , λ' _d · · twice the period of the grating reflector d · · · center spacing W _C , W between electrode fingers facing the center IDT electrode and the IDT electrodes on both sides _D · · crossing width f1c, f1d · · 2-port surface wave resonance frequency S1 · · 1-port surface wave resonator of the second mode of resonance frequency f2 · · 2-port surface wave resonator resonator

Claims (6)

[Claims] 1. A two-terminal surface acoustic wave resonator comprising three IDT electrodes arranged close to each other on a main surface of a piezoelectric substrate along a propagation direction of a surface acoustic wave and grating reflectors arranged on both sides thereof. A surface acoustic wave filter in which the two two-terminal pair surface acoustic wave resonators are connected in phase and used as an input, and connected in the opposite phase and output as an output. The period of the IDT electrode of the high-frequency two-terminal pair surface acoustic wave resonator among the terminal-pair surface acoustic wave resonators is λ _D
, The center distance d between the electrode fingers facing the center IDT electrode and the IDT electrodes on both sides is nλ _D / 2 <d <(n + 1) λ _D / 2 (n = 0, 1, 2)
・ ・) A resonator type surface acoustic wave filter characterized by satisfying the following conditions. 2. An electrode period of a two-terminal surface acoustic wave resonator having a high frequency among the two two-port surface acoustic wave resonators is λ.
_D , twice the period of the reflector is λ ′ _D , the electrode period of the low-frequency two-port surface acoustic wave resonator is λ _C , and the period of the reflector is 2
2. The resonator type surface acoustic wave filter according to claim 1, wherein, when the double is λ ′ _C , λ _D ≦ λ _C and λ ′ _D ≦ λ ′ _C are satisfied. 3. 3. The surface acoustic wave filter according to claim 1, wherein at least one of an input and an output of the surface acoustic wave filter is of a balanced type. 4. The resonator type surface acoustic wave according to claim 1, wherein a one-terminal surface acoustic wave resonator is connected in series to at least one of input or output terminals of said surface acoustic wave filter. filter. 5. The resonator-type surface acoustic wave device according to claim 1, wherein a grating electrode is arranged between each of the three IDT electrodes constituting the two two-port surface acoustic wave resonators. Wave filter. 6. A surface acoustic wave filter according to claim 1, wherein a plurality of said surface acoustic wave filters are connected in cascade.