JP2002135083A - Surface acoustic wave filter - Google Patents

Abstract

(57) [Problem] To provide a broadband resonator type surface acoustic wave filter. SOLUTION: A two-terminal-pair 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 is provided. The two surface acoustic wave resonators are connected side by side, and the two two-port surface acoustic wave resonators are connected in phase and connected to each other, and connected in opposite phases to form a resonator type surface acoustic wave filter.

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, and more particularly, to a surface acoustic wave filter (hereinafter referred to as a "surface acoustic wave filter") constructed by connecting two 2-port surface acoustic wave resonators each having three IDT electrodes in parallel. , SAW 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. 6 shows JP-A-61-142812 and JP-A-62-4.
FIG. 3 is a plan view showing a configuration of a resonator-type SAW filter disclosed in Japanese Patent No. 3204 and connected in parallel with different resonance frequencies of a two-terminal surface acoustic wave resonator having two IDT electrodes. 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, 55 are arranged on both sides thereof. Then, the two-terminal pair surface acoustic wave resonator A (resonance frequency f1a)
To form Here, as shown in FIG.
Reference numerals 2 and 53 denote 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.
And one of the interdigital electrodes forming the IDT electrode 53 is 5
3a, the other one is 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. 6, 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-like electrode 52b, and the comb-like 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 when 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 charges opposite thereto are connected to the input IN2. Further, a comb-shaped electrode 53a that generates charges of the same polarity as the comb-shaped electrode 52a and a comb-shaped electrode 57b that generates charges of the opposite polarity to the comb-shaped electrode 56a are connected to form an output OUT1, and the output OUT1 is formed. And a comb electrode 57a that generates a charge having the same polarity as that of the comb electrode 56a.
T2. That is, if two 2-port surface acoustic wave resonators having different resonance frequencies are connected in parallel such that the phase shift amounts between the input and output terminals are 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. By appropriately terminating the lattice type circuit, a filter having a pass bandwidth proportional to the difference between the resonance frequencies f1a and f1b of the two-port surface acoustic wave resonators A and B can be obtained.

FIG. 7 schematically shows the frequency spectra of the two-port surface acoustic wave resonators A and B shown in FIG. 6 in the vicinity of these resonances, and shows only the main vibration and the higher-order secondary mode. I'm drawing. Two-terminal pair surface acoustic wave resonators A and B
Has almost the same electrode structure except for the phase relationship,
The shapes of the main vibration and the spectrum of the higher-order second-order mode are almost the same. The bandpass filter is formed using the resonance frequencies f1a and f1b of the main vibrations of the two-port surface acoustic wave resonators A and B, respectively. The resonance frequency f2 of the higher-order second mode of the wave resonator B exists in the pass band, and this becomes ripple.

FIG. 8 shows that a 42 基板 YX LiTa film is formed on a piezoelectric substrate.
The electrode period of O ₃ and IDT electrodes 52 and 53 is set to λ _A by 1.86 μ.
m, the electrode period λ _B of the IDT electrodes 56 and 57 is 1.80 μm,
The number of DT electrodes 52, 53, 56, 57 is 18 pairs, their intersection width is 93 μm, and the reflectors 54, 55, 58,
Both the number of 59 was 100 and the aluminum electrode thickness was 0.17
This is a filter characteristic in the case of μm, and is far from an ideal bandpass filter.

[0007]

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, it is difficult to set the frequency f2 of the higher-order secondary mode excited on the lower frequency side of the main resonance f1b of the two-port surface acoustic wave resonator B having a high main resonance frequency to an arbitrary value. There is a problem that there is a limit in widening the pass bandwidth of the SAW filter due to mode resonance. The present invention has been made to solve the above problem, and has as its object to provide a wide band SAW filter.

[0008]

According to a first aspect of the present invention, there is provided a surface acoustic wave filter according to the present invention, wherein a surface acoustic wave filter is formed on a main surface of a piezoelectric substrate along a propagation direction of a surface acoustic wave.
Two IDT electrodes are arranged close to each other and grating reflectors are arranged on both sides of the IDT electrodes. Two 2-terminal surface acoustic wave resonators are arranged side by side on the piezoelectric substrate at different frequencies, and the two 2-terminals are arranged. A surface acoustic wave filter characterized in that a surface acoustic wave resonator is connected in-phase to be an input and connected to an opposite phase to be output. The invention according to claim 2 is the surface acoustic wave filter according to claim 1, wherein at least one of the input and output of the surface acoustic wave filter is a balanced connection. The invention according to claim 3 is the surface acoustic wave filter according to claim 1 or 2, wherein a center IDT electrode among the three IDT electrodes is of a two-part series connection type. Claim 4
The invention described in the above is a surface acoustic wave filter according to any one of claims 1 to 3, wherein a plurality of the surface acoustic wave filters are connected in cascade.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1 shows the S according to the present invention.
FIG. 2 is a plan view showing the configuration of the AW filter, and illustrates a piezoelectric substrate 1;
The three IDT electrodes 2, 3, and 4 are arranged close to each other along the propagation direction of the surface acoustic wave on the principal surface of the substrate, and the reflectors 5 and 6 are arranged on both sides of the three IDT electrodes. (Hereinafter referred to as a two-port SAW resonator) C. Further, the same piezoelectric substrate 1 is arranged in parallel with the two-terminal SAW resonator C.
IDT electrodes 2 ′, 3 ′, 4 ′ are disposed close to each other, and reflectors 5 ′, 6 ′ are disposed on both sides of the IDT electrodes 2 ′, 3 ′, 4 ′. The SAW resonator D is formed. Here, the IDT electrode 2,
3, 4 and 2 ', 3' and 4 'each comprise a pair of comb-shaped electrodes having a plurality of electrode fingers interposed therebetween, and a two-terminal pair S
The electrode period of the IDT electrodes 2, 3, 4 forming the AW resonator C is λc, the period of the reflectors 5, 6 is λ′c, the intersection width is Wc, and a two-port SAW resonator D is formed. IDT to do
The electrode period of the electrodes 2 ′, 3 ′, 4 ′ is λd, the reflectors 5, 6
Is set to λ'd, and the intersection width is set to Wd. And
The IDT electrodes 3 and 3 'at the center are connected to each other at the center of the piezoelectric substrate 1 to form an input terminal IN.
With respect to the piezoelectric substrate 1 of the T electrodes 2, 4 and 2 ', 4', the comb-shaped electrodes closer to the periphery are connected to form an output terminal OUT. The other comb electrodes of the IDT electrodes 3, 3 'and the other comb electrodes of the IDT electrodes 2, 4, 2', 4 'are grounded to form a resonator type SAW filter.

A feature of the present invention is that the two-port SAW resonators C and D are connected to three IDT electrodes 2, 3, 4 (2 ', 3',
4 ') are formed close to each other, one of the IDT electrodes 3 (3') at the center is an input terminal, and I
Since each of the DT electrodes 2 and 4 (2 ′, 4 ′) is connected to one of the comb-shaped electrodes to form an output terminal, a higher even-order mode excited on the lower frequency side of the main vibration, for example, a second-order mode Since the charges cancel each other and cannot be excited, the broadband SA
This is suitable for constituting a W filter.

FIG. 2 shows the frequency spectrum of each of the two-terminal SAW resonators C and D of the resonator type SAW filter shown in FIG.
Since there is no spurious between the resonance frequency f1c of the two-port SAW resonator C and the resonance frequency f1d of the two-port SAW resonator D, as shown in the lower part of FIG. Will be done.

FIG. 3 is an electrode pattern diagram showing the configuration of a second embodiment according to the present invention.
11 and 12 are arranged close to each other, and reflectors 13 and
14 is similar to the example of FIG.
At the moment when the charge excited by the comb electrodes 10a and 11a of the electrodes 10 and 11 is (+), the charge excited by the electrodes 10b and 11b becomes (-). However, the polarity of the electrode finger of the IDT electrode 12 is configured so that the (-) charge is excited on the comb electrode 12a of the IDT electrode 12 and the (+) charge is excited on the comb electrode 12b. A two-terminal SAW resonator E is formed. Further, in the two-port SAW resonator F, the two-port SAW resonator E is arranged point-symmetrically with respect to the center of the two-port SAW resonators E and F. Then, the IDT electrodes 11, 1
1 'is connected to a comb-shaped electrode near the center of the substrate to be an input IN, and IDT electrodes 10, 10' and 12, 12 'are connected to comb-shaped electrodes near the center of the substrate to output OUT1,
OUT2, an input unbalanced-output balanced type filter can be configured. The comb-shaped electrodes of the IDT electrodes 10, 12 and 10 ', 12' on the outer side of the substrate are connected to each other, and the comb-shaped electrodes of the IDT electrodes 11, 11 'on the outer side of the substrate are grounded.

With the above configuration, the phase relationship between the input and the output can be controlled to 0 ° and 180 °. That is, the phase of the output IDT electrode 10 differs from the input of the IDT electrode 11 by 180 °,
The phase of the electrode 12 becomes 0 °. As described above, by changing the connection order of the electrode fingers, the input IN and the output OUT2 have the same phase and the output OUT1 has a 180 ° phase difference, thereby realizing an input unbalanced-output balanced type SAW filter. Can be.

FIG. 4 is an electrode pattern diagram showing the configuration of a third embodiment according to the present invention. The SAW filter comprises SAW resonators S2 and S3 connected in series to both outputs of the SAW filter shown in FIG. Filter. SAW resonators S2, S3
By setting the anti-resonance frequency to a frequency that requires a large amount of attenuation, the amount of attenuation at that frequency can be greatly improved.

FIG. 5 is an electrode pattern diagram showing the configuration of a fourth embodiment according to the present invention. The configuration of the center IDT electrode 21 (21 ') is different from that of the second embodiment shown in FIG. different. That is, the IDT electrode 21 (21 ') is of a two-part series connection type. With such a configuration, not only can the input and output be balanced, but also the input impedance can be quadrupled, which means that the impedance of the connected IC circuit can be reduced from 200Ω to several hundreds. It can be said that this configuration is suitable for Ω.

[0016]

Since the present invention is constructed as described above, a broadband resonator type SAW according to the first aspect of the present invention is provided.
A filter can be configured. According to the second aspect of the present invention, it is possible to constitute a balanced filter which is a broadband filter required for a cellular phone or the like, and one of the input and output is a balanced type. According to the third aspect of the invention, the terminal impedance can be reduced. According to the fourth aspect of the present invention, it is possible to cope with a demand for 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 showing respective frequency spectra of two two-port SAW resonators having different frequencies from each other and filter characteristics of a resonator type SAW filter configured.

FIG. 3 is a plan view showing a configuration of a second resonator type SAW filter according to the present invention.

FIG. 4 is a plan view showing a configuration of a third resonator type SAW filter according to the present invention.

FIG. 5 is a plan view showing a configuration of a fourth resonator type SAW filter according to the present invention.

FIG. 6 is a diagram showing a configuration of a conventional resonator-type SAW filter in which two two-terminal surface acoustic wave resonators are connected in parallel.

FIG. 7 is a diagram illustrating a frequency spectrum of a conventional resonator-type SAW filter and filter characteristics of the resonator-type SAW filter configured.

FIG. 8 shows transmission characteristics of a SAW filter configured using the electrode patterns of FIG. FIG. 9 is a diagram illustrating the attenuation characteristics of an improved conventional SAW filter.

[Explanation of symbols]

1. Piezoelectric substrate IDT electrode: 2, 3, 4, 2 ', 3', 4 ', 10,
11, 12, 10 ', 11', 12 ', 20, 21, 2
2, 20 ', 21', 22 'grating reflectors, 5, 6, 5', 6 ', 13,
14, 13 ', 14', 23, 24, 23 ', 24' C, D, a two-port pair surface wave resonator having three IDT electrodes λ _c , λ _{d, an} electrode period λ ' _c , lambda _'d · · grating reflector of the period of double d · · central center distance W between the relative facing electrode fingers of the IDT electrode and the opposite sides of the IDT electrode _C, W _D · · crossing width f1c, f1d · · 2 terminal Resonance frequency of surface acoustic wave resonator S1, S2, S3.

Claims (4)

[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. Are arranged side by side on the piezoelectric substrate at different frequencies, and the two two-terminal pair surface acoustic wave resonators are connected in the same phase as an input, and connected in the opposite phase as an output. Surface acoustic wave filter. 2. The surface acoustic wave filter according to claim 1, wherein at least one of the input and output of the surface acoustic wave filter is a balanced connection. 3. A central ID among the three IDT electrodes.
3. The surface acoustic wave filter according to claim 1, wherein the T electrode is of a two-part series connection type. 4. A surface acoustic wave filter according to claim 1, wherein a plurality of said surface acoustic wave filters are connected in cascade.