JP2888739B2 - 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, and more particularly, to a surface acoustic wave filter having a low loss in an RF band used in mobile communication.

[0002]

2. Description of the Related Art As shown in FIG. 7, a conventional two-port pair type surface acoustic wave resonator filter 20 has an input electrode 21 and an output electrode 22 electrically connected in parallel with the input electrode 21 interposed therebetween.
a, 22b, and reflectors 23a, 23b disposed outside each of the output electrodes 22a, 22b, and these are formed on the same substrate. FIG. 8 shows a calculation result of the frequency characteristics of the two-port pair type surface acoustic wave resonator filter 20. FIG. 8 shows an example of the frequency characteristic of the two-terminal pair type surface acoustic wave resonator filter 20 in which the substrate is 64y-xLiN
This is a calculation example when bO3 is used, the number of input electrode finger pairs is 18.5, the number of output electrode finger pairs is 12.5, and the aperture length is about 60λ. Here, λ is the wavelength of the input signal.

[0003] The two-port pair type surface acoustic wave resonator filter 20 described above can realize low loss characteristics.
The attenuation characteristic in a frequency band away from the pass band is good. However, in this structure, a large level side lobe essentially occurs on the high frequency side near the pass band.

Normally, in order to improve this disadvantage, as shown in FIG. 9, a two-port pair type surface acoustic wave resonator filter 40 is used.
To the input electrode 21 and the output electrodes 22a and 22 shown in FIG.
b, a two-terminal pair type surface acoustic wave resonator filter 20 composed of reflectors 23a and 23b,
1. A large number of out-of-band attenuations are obtained by cascade connection such as cascade connection by providing a two-terminal pair surface acoustic wave resonator filter 30 composed of output electrodes 32a, 32b and reflectors 33a, 33b on the same substrate. Have gained.

Further, as shown in FIG. 10, another conventional two-terminal pair type surface acoustic wave resonator filter 50 includes an input electrode 51, an output electrode 52, and a reflector 53a disposed outside the input electrode 51. And a reflector 53b disposed outside the output electrode 52, which are formed on the same substrate. The frequency characteristics of the two-port SAW resonator filter 50 are as shown in FIG. In this two-port pair type surface acoustic wave resonator filter 50, basically, the two-port pair type surface acoustic wave resonator filter 20 shown in FIG.
As in the case of the above, the attenuation characteristic on the high frequency side near the pass band is not good. Two-port pair type surface acoustic wave resonator filter 5 of this example
In the case of 0, x-112yLiTaO3 is used as the substrate, and the number of input electrode finger pairs is 50, the number of output electrode finger pairs is 50, and the number of reflectors is 100.

[0006]

However, according to the two-port pair type surface acoustic wave resonator filter 40 described above,
The out-of-band characteristic is a two-port pair type surface acoustic wave resonator filter 20.
Can be obtained, but the insertion loss also doubles. Further, when the amount of attenuation is insufficient, the number of cascade connection stages is increased to three stages and four stages. As described above, in the two-port pair type surface acoustic wave resonator filter, there is no method for suppressing the limited side lobe generated on the high frequency side near the pass band. There was a problem that it was necessary to connect.

That is, in the case of a two-port pair type surface acoustic wave resonator filter, the attenuation on the high frequency side near the pass band is good even though the attenuation characteristics on the high frequency side near the pass band are good. There is a problem that it is necessary to cascade another two-port pair type surface acoustic wave resonator filter only to secure the amount.

The present invention provides a surface acoustic wave filter in which the level of a side lobe on a high frequency side near a pass band, which is essentially generated in a two-port pair type surface acoustic wave resonator filter, is reduced by a simple configuration. The purpose is to do.

[0009]

A surface acoustic wave filter according to the present invention has a two-terminal pair type surface acoustic wave resonator filter having an input electrode and an output electrode and having a reflector disposed on the outermost side. 1 is disposed on at least one side of an input electrode or an output electrode of a two-terminal pair type surface acoustic wave resonator filter.
And one or more one-port pair surface acoustic wave resonators, wherein the anti-resonance frequency of the one-port pair surface acoustic wave resonator is higher than the pass band of the two-port pair surface acoustic wave filter. And the one-port pair type surface acoustic wave resonator and the two-terminal pair type surface acoustic wave filter are electrically connected in series.

A surface acoustic wave filter according to the present invention has a two-terminal pair type surface acoustic wave filter having an input electrode and an output electrode and having a reflector disposed on the outermost side, and the two-terminal pair type surface acoustic wave filter. At least one of an input electrode and an output electrode of a wave resonator filter, and one or more one-port pair surface acoustic wave resonators, wherein an anti-resonance frequency of the one-port pair surface acoustic wave resonator is provided. Is set to a frequency lower than the pass band of the two-port pair surface acoustic wave filter, and the one-port pair surface acoustic wave resonator, the two-port pair surface acoustic wave filter, Are electrically connected in series.

[0011]

The surface acoustic wave filter according to the present invention is characterized in that the anti-resonance frequencies of the one-port pair type surface acoustic wave resonator are different from each other.

[0013]

According to the surface acoustic wave filter of the present invention, the anti-resonance frequency of the one-port pair type surface acoustic wave resonator is set to a higher frequency (lower side) of the pass band of the two-port pair type surface acoustic wave resonator filter. And at least one of the one or more electrodes is provided on at least one side of the input electrode or the output electrode of the two-port pair type surface acoustic wave resonator filter.
Since the terminal pair type surface acoustic wave resonator is electrically connected in series, the impedance near the anti-resonance frequency of the one terminal pair type surface acoustic wave resonator is high and higher than the pass band of the two terminal pair type surface acoustic wave resonator filter. The attenuation on the band side (low band side) is increased, and the level of the side lobe on the high band side (low band side) is lower than the pass band inherent in the two-port pair type surface acoustic wave resonator filter. And the frequency characteristics are improved.

[0014]

According to the surface acoustic wave filter of the present invention, since the anti-resonance frequencies of the one-port pair type surface acoustic wave resonator are different from each other, even if the frequency range of the side lobe is wide,
That level is reduced.

[0016]

The present invention will be described below with reference to examples.

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

Reference numeral 1 denotes a surface acoustic wave filter according to one embodiment of the present invention. The surface acoustic wave filter 1 includes an input electrode 3,
A two-terminal pair type surface acoustic wave resonator filter including output electrodes 4a and 4b disposed on both sides of the input electrode 3, a reflector 5a disposed outside the output electrode 4a, and a reflector 5b disposed outside the output electrode 4b. 2, a one-port pair type surface acoustic wave resonator 7a disposed on the signal input end side of the two-port pair type surface acoustic wave resonator filter 2, and a signal output end side of the two-port pair type surface acoustic wave resonator filter 2 And a one-terminal pair type surface acoustic wave resonator 7a is electrically connected in series to a signal input terminal of the two-port pair type surface acoustic wave resonator filter 2. And one-port pair surface acoustic wave resonator 7
An input signal is supplied to the signal input terminal of the two-terminal pair type surface acoustic wave resonator filter 2 via a.
The terminal pair type surface acoustic wave resonator 7b is electrically connected in series to output an output signal via the one terminal pair type surface acoustic wave resonator 7b, and the two terminal pair type surface acoustic wave resonance is performed. The filter 2, the one-terminal pair type surface acoustic wave resonators 7a and 7b are formed on the same substrate.

On the other hand, the input impedance of the one-port SAW resonator as shown in FIG. 2 shows resonance characteristics as shown in FIG. By electrically connecting the one-port pair surface acoustic wave resonators 7a and 7b in series, a stop band can be obtained near the anti-resonance frequency.

Here, the one-port pair type surface acoustic wave resonator 7
The anti-resonance frequencies of a and 7b are normalized frequencies, which are respectively set to the high-frequency side fa and fb near the pass band of the two-port pair type surface acoustic wave resonator filter 2.

That is, the frequency characteristics of the two-port pair type surface acoustic wave resonator filter 2 exhibit the same frequency characteristics as the frequency characteristics shown in FIG. The resonance frequency is a normalized frequency fa, fb
, The level of the side lobe occurring on the high frequency side near the pass band of the two-port pair type surface acoustic wave resonator filter 2 is greatly reduced. The frequency characteristics of the wave filter 1 are as shown in FIG. 4, and the insertion loss is hardly increased.

As described above, in the surface acoustic wave filter 1 of this embodiment, the one-port pair type surface acoustic wave resonators 7a and 7b are connected to the signal input terminal and the signal output terminal of the two-port pair type surface acoustic wave resonator filter 2. By cascading each of them, the side lobes on the high frequency side near the pass band, which occur in the conventional two-port pair type surface acoustic wave resonator filter 20 shown in the prior art, are reduced over the entire region, and the level thereof is reduced. And sufficient attenuation characteristics can be obtained.

In this case, the one-terminal pair type surface acoustic wave resonators 7a and 7b act as a capacitance at frequencies other than the vicinity of the resonance frequency and the anti-resonance frequency, and make the capacitance value relatively small. By setting large,
It is possible to prevent the impedance in the pass band of the two-terminal pair type surface acoustic wave resonator filter 2 from changing. Further, setting this capacitance value to an appropriate value is equivalent to the fact that the capacitance elements are electrically connected in series in the pass band of the two-terminal pair type surface acoustic wave resonator. That is, this can be used as a matching circuit element. Therefore, the degree of freedom in designing the two-terminal pair type surface acoustic wave resonator filter 2 is increased.

Actually, even in the present embodiment, the two-port pair type surface acoustic wave resonator filter 20 shown in FIG. 7, which was designed without a matching circuit in the 50Ω system, has the one-port pair type surface acoustic wave resonator 7a. , 7b, the frequency characteristic shown in FIG. 4 is obtained.

Next, another embodiment of the present invention will be described.

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

Reference numeral 9 denotes a surface acoustic wave filter according to another embodiment. The surface acoustic wave filter 9 includes a two-terminal pair type surface acoustic wave resonator including an input electrode 3, an output electrode 4, a reflector 5a disposed outside the input electrode 3, and a reflector 5b disposed outside the output electrode 4. A one-port pair type surface acoustic wave resonator 8a is electrically connected in series to a signal input terminal of the filter 10 and a two-port pair type surface acoustic wave resonator filter 10 to form a one-port pair type surface acoustic wave resonator 8a. An input signal is supplied through the filter, and a one-port pair surface acoustic wave resonator 8b is electrically connected in series to a signal output terminal of the two-port pair surface acoustic wave resonator filter 10,
Further, a one-port pair type surface acoustic wave resonator 8c is electrically connected in series to a signal output terminal of the one-port pair type surface acoustic wave resonator 8b, and an output signal is output via the one-port pair type surface acoustic wave resonator 8c. And a two-port pair surface acoustic wave resonator filter 10 and one-port pair surface acoustic wave resonators 8a, 8b and 8c are formed on the same substrate.

Here, the one-port pair type surface acoustic wave resonator 8
The antiresonant frequencies of a, 8b and 8c are normalized frequencies,
The frequencies fa, fb, and fc on the high frequency side near the pass band of the two-terminal pair type surface acoustic wave resonator filter 10 are set separately.

That is, the two-port pair type surface acoustic wave resonator filter 10 is a two-port pair type surface acoustic wave resonator filter 50.
The frequency characteristics are the same as the frequency characteristics shown in FIG. 11, but the anti-resonance frequencies of the one-port pair surface acoustic wave resonators 8a, 8b, 8c are normalized frequencies fa. , Fb, and fc, the level of the side lobe generated on the high frequency side near the pass band of the two-port pair type surface acoustic wave resonator filter 10 is greatly reduced. The frequency characteristic of the surface acoustic wave filter 9 according to the embodiment is as shown in FIG. 6, and the insertion loss hardly increases.

In this case, since the attenuation characteristic on the high frequency side near the pass band of the two-port pair type surface acoustic wave resonator filter 10 is not good, that is, the generation range of the side lobe is wide, the Surface wave resonators 8a, 8b and 8
c were used. The frequency characteristic shown in FIG. 11 is an example of the frequency characteristic in the case where the surface acoustic wave resonator filter 50 does not have a matching circuit. It is obtained by connecting.

[0031]

In the above-described embodiment and the other embodiments, the two-port surface acoustic wave filter and the one-port surface acoustic wave resonator are formed on the same substrate. The degree of freedom in design can be increased by making the substrate of the terminal-pair type surface acoustic wave resonator filter different from the substrate of the one-port pair type surface acoustic wave resonator.

Further, in the above-described embodiment and the other embodiments, the one-port pair surface acoustic wave resonators are configured to have different anti-resonance frequencies, and electrically connected to the two-port pair surface acoustic wave filter. Although they are connected in series, they can be made to have high impedance by configuring them with the same anti-resonance frequency and electrically connecting them in series to a two-port pair type surface acoustic wave resonator filter. The degree increases.

Further, in the above-described embodiment and the other embodiments, a plurality of one-port pair surface acoustic wave resonators are used.
Although the case where the terminal pair type surface acoustic wave resonator filter is electrically connected in series is shown, one one terminal pair type surface acoustic wave resonator is electrically connected in series to the two terminal pair type surface acoustic wave resonator filter. However, when the frequency range of the side lobe existing on the high frequency side near the pass band is narrow, the level of the side lobe can be reduced, which is effective.

In the above-described embodiment and the other embodiments, the one-port pair surface acoustic wave resonator is exemplified by the case where it is composed of only electrodes. The same effect can be obtained even with a one-port pair type surface acoustic wave resonator having a reflector disposed outside.

When a side lobe exists on the lower side near the pass band of the two-port pair surface acoustic wave resonator filter, the side lobe having the anti-resonance frequency on the lower side near the pass band is used.
One or more one-port pair surface acoustic wave resonators may be electrically connected in series to the input electrode or output electrode of the two-port pair surface acoustic wave resonator filter.

[0037]

As described above, according to the surface acoustic wave filter of the present invention, the impedance near the anti-resonance frequency of the one-port pair surface acoustic wave resonator is high, and the anti-resonance frequency is two-port pair surface acoustic wave resonator. The one or more one-port pair surface acoustic wave resonators set to a frequency higher than the pass band of the wave resonator filter are connected to at least one of the input electrodes or output electrodes of the two-port pair surface acoustic wave filter. Since it is electrically connected in series to one side, the attenuation on the higher side than the pass band of the two-port pair type surface acoustic wave resonator filter is increased, and
There is an effect that the level of the side lobe on the higher frequency side than the pass band inherent in the terminal pair type surface acoustic wave resonator filter is reduced, and the frequency characteristic is improved.

When there is a side lobe on the low frequency side near the pass band of the two-port pair type surface acoustic wave resonator filter,
One or more one-port pair surface acoustic wave resonators having an anti-resonance frequency on the low frequency side near the pass band are electrically connected in series to an input electrode or an output electrode of a two-port pair surface acoustic wave resonator filter. As a result, the level of the side lobe on the lower side than the pass band of the two-port pair surface acoustic wave resonator filter is reduced, and the frequency characteristics are improved.

[0039]

According to the surface acoustic wave filter of the present invention, 1
Because the anti-resonance frequencies of the terminal-pair surface acoustic wave resonators are different from each other, even if the side lobe frequency range is wide,
There is an effect that the level is reduced.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram of a one-port pair type surface acoustic wave resonator according to an embodiment of the present invention.

FIG. 3 is an input impedance characteristic diagram of a one-port pair type surface acoustic wave resonator.

FIG. 4 is a frequency characteristic diagram of the surface acoustic wave filter according to one embodiment of the present invention.

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

FIG. 6 is a frequency characteristic diagram of a surface acoustic wave filter according to another embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a conventional two-port pair surface acoustic wave resonator filter.

8 is a frequency characteristic diagram of the two-port pair type surface acoustic wave resonator filter shown in FIG.

9 is a schematic configuration diagram in the case where the two-port pair type surface acoustic wave resonator filter shown in FIG. 7 is cascaded.

FIG. 10 is a schematic configuration diagram of another conventional two-port pair type surface acoustic wave resonator filter.

FIG. 11 is a frequency characteristic diagram of the conventional two-port pair surface acoustic wave resonator filter shown in FIG.

[Description of Signs] 1, 9: Surface acoustic wave filter 2, 10: 2-port pair type surface acoustic wave resonator filter 3: Input electrode 4, 4, a, 4b: Output electrode 5a, 5b: Reflector 7a, 7b, 8a -8c: 1-port pair surface acoustic wave resonator

Claims (3)

(57) [Claims] 1. A two-port pair type surface acoustic wave resonator filter having an input electrode and an output electrode and having a reflector disposed on the outermost side, and an input electrode of the two-port pair type surface acoustic wave resonator filter. Or one or more one-port pair surface acoustic wave resonators disposed on at least one side of the output electrode,
An anti-resonance frequency of the one-port pair type surface acoustic wave resonator is set to a frequency higher than a pass band of the two-port pair type surface acoustic wave resonator filter; A surface acoustic wave filter in which a resonator and the two-terminal pair surface acoustic wave resonator filter are electrically connected in series. 2. A two-port pair type surface acoustic wave resonator filter having an input electrode and an output electrode and having a reflector disposed on the outermost side, and an input electrode of the two-terminal pair type surface acoustic wave resonator filter. Or one or more one-port pair surface acoustic wave resonators disposed on at least one side of the output electrode,
An anti-resonance frequency of the one-port pair surface acoustic wave resonator is set to a frequency lower than a pass band of the two-port pair surface acoustic wave resonator filter; A surface acoustic wave filter in which a resonator and the two-terminal pair surface acoustic wave resonator filter are electrically connected in series. 3. The surface acoustic wave filter according to claim 1, wherein the two or more one-port pair surface acoustic wave resonators have different anti-resonance frequencies.