JP3181158B2 - Composite surface acoustic wave filter and mobile communication device using composite 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 composite surface acoustic wave filter in which a surface acoustic wave filter and a one-terminal type surface acoustic wave resonator are connected, and more particularly, to an RF band low filter suitable for a mobile communication device or the like. The present invention relates to a composite surface acoustic wave filter having an insertion loss and a mobile communication device using the composite surface acoustic wave filter.

[0002]

2. Description of the Related Art A conventional multi-electrode surface acoustic wave filter using a plurality of different thinning electrodes is configured as shown in FIG. 9, for example. In the example of FIG. 9, for example, 36 ° YX
A plurality of different thinned input electrodes 11 a, 11 b, 11 c, 11 d, 11 c, 11 b, on a LiTaO ₃ substrate 13.
Different thinning output electrodes 12a, 12b, 12c, 12b, 12 are respectively provided at positions between the thinning input electrodes 11a and the respective thinning input electrodes.
a are formed, and the input electrodes 11a, 11b, 11c, 11
d, 11c, 11b, 11a are electrically connected in parallel and connected to the input terminal A, and output electrodes 12a, 12b, 12
c, 12b and 12a are electrically connected in parallel and output terminal B
Are connected to the multi-electrode surface acoustic wave filter 10.

FIG. 10 shows an example of frequency amplitude characteristics (calculated values) of the conventional multi-electrode surface acoustic wave filter 10 configured as described above. The frequency amplitude characteristic shown in FIG. 10 shows a case where an inductance element is connected in parallel as a matching circuit to the multi-electrode surface acoustic wave filter 10, and in this example, the attenuation in the stop band near the lower side of the pass band is about Fifteen
dB, and the attenuation in the stop band near the high band side of the pass band is about 25 dB. In the multi-electrode surface acoustic wave filter 10 of this type, a low insertion loss in the pass band can be obtained. The amount of attenuation outside was not sufficient. Further, it has been difficult to sharpen the cutoff characteristic in the frequency amplitude characteristic.

[0004] In order to improve the out-of-band characteristics, it is necessary to use a multi-electrode surface acoustic wave filter in which electrodes are thinned and weighted. However, although the side lobe of the frequency amplitude characteristic when using the multi-electrode surface acoustic wave filter formed by the thinning-out weighted electrodes is suppressed, the trap frequency bandwidth shown in FIG. 10 is widened.

On the other hand, in a ceramic filter or the like, FIG.
As shown in FIG. 1, by connecting the surface acoustic wave resonators 51 to 55 in a ladder type, a frequency amplitude characteristic as shown in FIG. 12 is obtained. Similarly, it is possible to form a filter by connecting the surface acoustic wave resonators in a ladder type as shown in FIG.

However, in such a configuration, the surface acoustic wave resonators 51 and 53 connected in series with the admittance of the surface acoustic wave resonators 52 and 54 connected in parallel are provided.
It is required that the product of the impedance of 55 is 1 or more outside the pass band. Thus, a specific relationship must be established between the surface acoustic wave resonators 51, 53, 55 connected in series and the surface acoustic wave resonators 52, 54 connected in parallel.

[0007]

As described above, in the conventional multi-electrode surface acoustic wave filter, when the electrodes are thinned and weighted in order to suppress the side lobe, the trap frequency bandwidth is widened, and the cutoff characteristic in the frequency amplitude characteristic is reduced. A problem of deterioration occurs.

Further, in order to increase the amount of attenuation in the stop band, a cascade connection of a multi-electrode surface acoustic wave filter has conventionally been performed. According to this method, the attenuation outside the pass band can be increased, but there is a problem that the insertion loss of the pass band also increases.

Further, in the case of a filter constituted by a surface acoustic wave resonator connected in a ladder type, a filter is connected between a surface acoustic wave resonator connected in series and a surface acoustic wave resonator connected in parallel. Must have a predetermined relationship.As a result, in addition to the problem that the amount of attenuation in the stop band distant from the pass band is small, there is a problem that the pass band width and the notch frequency are restricted. In order to achieve a large attenuation outside the band, the insertion loss must be sacrificed, for example, the insertion loss increases.

The present invention utilizes a surface acoustic wave resonator, has no limitations on the pass band width or notch frequency, has a small insertion loss, and reduces the attenuation on the high band side outside the pass band and the low band side outside the pass band. It is an object of the present invention to provide a composite surface acoustic wave filter having an increased frequency amplitude characteristic and a mobile communication device using the composite surface acoustic wave filter.

[0011]

According to the present invention, there is provided a composite surface acoustic wave filter comprising: an input electrode for converting an electric signal to a surface acoustic wave; and an output electrode for converting the converted surface acoustic wave to an electric signal. The resonance frequency of at least one of the input and output sides of the wave filter passes through the surface acoustic wave filter.
At least one or more first surface acoustic wave resonators set to a frequency within a stop band near the lower band side of the band are electrically connected in parallel to the surface acoustic wave filter, and the anti-resonance frequency Is elastic
Around the stop band near the high-pass side of the surface acoustic wave filter.
At least one second surface acoustic wave resonator set to a wave number is electrically connected in series to the surface acoustic wave filter.

[0012]

In the composite surface acoustic wave filter according to the present invention, the surface acoustic wave filter is provided with a plurality of input electrodes electrically connected in parallel, and is separately provided between the input electrodes, and is electrically connected in parallel. It is a multi-electrode surface acoustic wave filter including a plurality of output electrodes.

The composite surface acoustic wave filter according to the present invention is characterized in that the surface acoustic wave filter is a two-port pair type surface acoustic wave resonator filter.

The composite surface acoustic wave filter according to the present invention has a first
And the second surface acoustic wave resonator is a one-port pair type surface acoustic wave resonator.

The composite surface acoustic wave filter according to the present invention has a first
The second surface acoustic wave resonator is configured on the same substrate as the surface acoustic wave filter.

A mobile communication device according to the present invention is characterized in that one of the composite surface acoustic wave filters according to the present invention is used for an antenna duplexer and / or an interstage filter.

[0018]

According to the present invention, there is provided a composite surface acoustic wave filter comprising: an input electrode for converting an electric signal into a surface acoustic wave; and an output electrode for converting the converted surface acoustic wave into an electric signal. at least one of the output side resonant circumferential
Rejection near the low-pass side of the surface acoustic wave filter whose wave number is
At least one or more first frequencies set to frequencies within the band
The surface acoustic wave resonator is electrically connected in parallel to the surface acoustic wave filter, and the anti-resonance frequency is in the pass band of the surface acoustic wave filter.
Since at least one or more second surface acoustic wave resonators set at a frequency in the stop band near the high frequency side is electrically connected in series to the surface acoustic wave filter, the first surface acoustic wave Due to the low impedance near the resonance frequency of the resonator,
The attenuation of the desired band of the surface acoustic wave filter can be increased, and the attenuation of the desired band of the surface acoustic wave filter can be increased by the high impedance near the resonance frequency of the second surface acoustic wave resonator. can, <br/> one or, that the first and second surface acoustic wave resonator is designed to exhibit capacitive in the passband of the surface acoustic wave filter
As a result, it operates as a part of the matching circuit, so that good frequency amplitude characteristics can be obtained and the matching circuit can be simplified. Furthermore, the composite surface acoustic wave filter of the present invention
The first surface acoustic wave resonance
To the center frequency of the surface acoustic wave filter
And the resonance frequency of the second surface acoustic wave resonator is
Approximately match the center frequency of the surface acoustic wave filter
The impedance in the passband of the surface acoustic wave filter.
1st surface acoustic wave resonance without changing the
Frequency of the resonator and anti-resonance of the second surface acoustic wave resonator
Predetermined capacitance at a third stopband frequency other than the frequency
And the third stopband frequency
Operation as part of the matching circuit for
Achieved wave number characteristics and simplified matching circuit
It is.

Furthermore, the composite surface acoustic wave filter of the present invention
Is the resonance frequency of the first surface acoustic wave resonator is set to a frequency within the stop band of the passband low frequency side near the surface acoustic wave filter, and a surface acoustic wave the anti-resonant frequency of the second surface acoustic wave resonator since set to a frequency within the stop band of the band high-frequency side near pass filter, the low impedance at the resonant frequency near the first surface acoustic wave resonator, the cut-off characteristics of the passband low frequency side of the SAW filter Due to the high impedance in the vicinity of the resonance frequency of the second surface acoustic wave resonator, the cutoff characteristic of the surface acoustic wave filter in the higher pass band becomes steeper.

Whether the surface acoustic wave filter is a multi-electrode surface acoustic wave filter or a two-port pair type surface acoustic wave resonator filter, the attenuation of a desired band of the surface acoustic wave filter is similarly performed. The amount is increased to improve the frequency amplitude characteristics. Further, the resonance frequency of the first surface acoustic wave resonator is set to a frequency in a stop band near the lower side of the pass band of the surface acoustic wave filter, and the anti-resonance frequency of the second surface acoustic wave resonator is set to the surface acoustic wave. When the frequency is set in the stop band near the high pass band of the filter, the cutoff characteristics of the low pass band and the high pass band of the surface acoustic wave filter become steep, and the surface acoustic wave filter Is improved.

Also, when the first and second surface acoustic wave resonators are one-port pair type surface acoustic wave resonators, the attenuation of the desired band of the surface acoustic wave filter is similarly increased. Further, the resonance frequency of the first surface acoustic wave resonator is set to a frequency in a stop band near the lower side of the pass band of the surface acoustic wave filter, and the anti-resonance frequency of the second surface acoustic wave resonator is set to the surface acoustic wave. When the frequency is set in the stop band near the high pass band of the filter, the cutoff characteristics of the low pass band and the high pass band are sharp, and the frequency amplitude characteristics of the surface acoustic wave filter are reduced. Be improved.

In a mobile communication device using the composite surface acoustic wave filter of the present invention as an antenna duplexer and / or an interstage filter, the cutoff characteristic of the frequency amplitude characteristic of the composite surface acoustic wave filter is steep. Even if the reception frequency and the transmission frequency are close to each other, the reception signal is not mixed into the transmission side, so that the transmission signal is not mixed into the reception side, and the frequency of the unnecessary band can be effectively attenuated. it can. Furthermore, since the composite surface acoustic wave filter is small, the size of the mobile communication device can be reduced.

[0023]

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

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

In FIG. 1, reference numeral 20 denotes a composite surface acoustic wave filter according to the first embodiment. The composite surface acoustic wave filter 20 according to the first embodiment includes a plurality of different thinned input electrodes 11.
a, 11b, 11c, 11d, 11c, 11b, 11a
And different thinning output electrodes 12a, 12b, 12c, 1 at positions between the thinning input electrodes 11a to 11d.
2b and 12a are formed on the substrate 13, and the input electrodes 11
a, 11b, 11c, 11d, 11c, 11b, 11a
Are electrically connected in parallel, and the output electrodes 12a, 12b, 1
Reference numerals 2c, 12b, and 12a denote a multi-electrode surface acoustic wave filter 10 using a plurality of different thinning electrodes electrically connected in parallel, and a multi-electrode surface acoustic wave filter 10 on the input end A side of the multi-electrode surface acoustic wave filter 10. One-port pair type surface acoustic wave resonator 71 electrically connected in series to surface acoustic wave filter 10
a, a one-terminal pair type surface acoustic wave resonator 71b electrically connected in series to the multi-electrode surface acoustic wave filter 10 on the output end B side of the multi-electrode surface acoustic wave filter 10, A one-port pair type surface acoustic wave resonator 72a electrically connected in parallel to the multi-electrode surface acoustic wave filter 10 on the input end A side of the wave filter 10, and the output end B side of the multi-electrode surface acoustic wave filter 10 And a one-port pair type surface acoustic wave resonator 72b electrically connected in parallel to the multi-electrode surface acoustic wave filter 10, and the one-port pair type surface acoustic wave resonators 71a, 71b, 72a and 72b also have multiple electrodes. It is formed on the substrate 13 together with the input and output electrodes of the surface acoustic wave filter 10.

Here, the multi-electrode surface acoustic wave filter 10 using a plurality of different thinning electrodes is the same as the multi-electrode surface acoustic wave filter 10 shown in FIG. One-terminal pair type surface acoustic wave resonators 71a, 71b, 72a, 72b
Has the same configuration.

One-terminal pair type surface acoustic wave resonators 71a, 71
B, 72a, and 72b are as shown in FIG. 2 if the configuration is shown by taking one one-port pair type surface acoustic wave resonator 71a as an example. The one-terminal pair type surface acoustic wave resonator 71a includes an electrode 74 formed on a substrate 13 and including an electrode finger 75a and an electrode finger 76a.

One-port pair type surface acoustic wave resonators 71a, 71
The impedances of b, 72a, and 72b show resonance characteristics as shown in FIG. One-terminal pair type surface acoustic wave resonator 71
The impedance of a, 71b, 72a, 72b is low near the resonance frequency and high near the anti-resonance frequency.

One terminal pair type surface acoustic wave resonators 71a, 71
In the case where a filter is configured by using only b, 72a, and 72b alone, the one-port pair surface acoustic wave resonator 71a,
Although good attenuation can be obtained at the anti-resonance frequencies of 71b, 72a and 72b, it is difficult to widen the attenuation bandwidth.

However, like the composite surface acoustic wave filter 20, the one-port pair type surface acoustic wave resonators 71a and 71b are separately provided on the input terminal A side and the output terminal B side of the multi-electrode surface acoustic wave filter 10, respectively. When electrically connected in series to the multi-electrode surface acoustic wave filter 10, a stop band is obtained near the anti-resonance frequency due to the high impedance of the one-port pair surface acoustic wave resonators 71a and 71b near the anti-resonance frequency. In addition, since the low impedance of the one-port pair type surface acoustic wave resonators 71a and 71b near the resonance frequency does not cause an increase in insertion loss, the passing insertion loss does not change much.

As in the case of the composite surface acoustic wave filter 20, one-port pair type surface acoustic wave resonators 72a and 72b are separately provided on the input terminal A side and the output terminal B side of the multi-electrode surface acoustic wave filter 10, respectively. When electrically connected in parallel to the multi-electrode surface acoustic wave filter 10, a stop band is obtained near the resonance frequency because of the low impedance near the resonance frequency of the one-port pair surface acoustic wave resonators 72a and 72b, Also, one-terminal pair type surface acoustic wave resonators 72a and 72
The high impedance near the anti-resonance frequency of b does not cause an increase in insertion loss, and the passing insertion loss does not change much.

In the first embodiment, by setting the electrode finger pitch of the one-port pair type surface acoustic wave resonators 71a and 71b, the one-port pair type surface acoustic wave resonators 71a and 71b are set.
1b with a multi-electrode surface acoustic wave filter 10
Set to a frequency in the stopband near the high passband side of
The resonance frequency is set so as to fall within the pass band of the multi-electrode surface acoustic wave filter 10. Similarly, by setting the number of electrodes and the electrode finger pitch of the one-port pair type surface acoustic wave resonators 72a and 72b, the resonance frequency of the one-port pair type surface acoustic wave resonators 72a and 72b can be increased. 10 is set to a frequency within a stop band near the lower side of the pass band, and the anti-resonance frequency is set to fall within the pass band of the multi-electrode surface acoustic wave filter 10.

With this setting, the impedance of the one-port pair surface acoustic wave resonators 71a and 71b is high due to the high impedance near the anti-resonance frequency of the one-port pair surface acoustic wave resonators 71a and 71b. A stop band is obtained near the resonance frequency, and the multi-electrode surface acoustic wave filter 10
, A steep attenuation characteristic is obtained on the high-passband side of the filter, and the one-port pair surface acoustic wave resonators 72a and 72b
, A stop band is obtained near the resonance frequency of the one-port pair type surface acoustic wave resonators 72a and 72b, and the low pass band of the multi-electrode surface acoustic wave filter 10 is obtained. On the side, a steep attenuation characteristic is obtained.

Further, a one-port pair type surface acoustic wave resonator 71
The low impedances near the resonance frequencies a and 71b do not cause an increase in insertion loss in the pass band of the multi-electrode surface acoustic wave filter 10, and the anti-resonance of the one-port pair surface acoustic wave resonators 72a and 72b. Due to the high impedance near the frequency, the insertion loss in the pass band of the multi-electrode surface acoustic wave filter 10 does not increase.

As a result, the multi-electrode surface acoustic wave filter 1
The attenuation characteristic deteriorated due to the electrode weighting of 0 is improved, and the frequency amplitude characteristic of the composite surface acoustic wave filter 20 when an inductance element is connected in parallel as a matching circuit is shown in FIG. The amount of attenuation in the stop band near the high-pass band and the low-pass band of the filter 20 is 35 dB, and the connection of the two one-port surface acoustic wave resonators 71a, 71b, 72a and 72b. As a result, the attenuation in the stop band near the high pass band is improved by about 15 dB, the attenuation in the stop band near the high pass band is improved by about 20 dB, and the trap frequency bandwidth is narrowed and improved. The same amount of attenuation can be obtained as compared with the conventional method in which the multi-electrode surface acoustic wave filters 10 are cascaded.

The one-terminal pair type surface acoustic wave resonator 71
a, 71b, 72a and 72b act as capacitance elements at frequencies other than near the resonance frequency and other than near the anti-resonance frequency. Therefore, the value of the inductance of the inductance element connected in parallel as a matching circuit can be reduced by the capacitance of the one-terminal pair type surface acoustic wave resonators 72a and 72b. As a result,
The shape of the inductance element is also reduced.

Further, the number of electrodes and the pitch of the electrode fingers of the multi-electrode surface acoustic wave filter 10 are set, and a multi-electrode surface acoustic wave filter 10 is connected so that a capacitance element needs to be connected in parallel as a matching circuit. Is designed, the capacitance of the capacitance elements connected in parallel as a matching circuit can be reduced by the capacitance of the one-terminal pair type surface acoustic wave resonators 72a and 72b. Further, by setting the capacitance of the one-port pair type surface acoustic wave resonators 72a and 72b to a predetermined value, a matching circuit separately connected in parallel to the multi-electrode surface acoustic wave filter 10 is not required. it can. Also, when a matching circuit needs to be connected in series, a part or all of the matching circuit can be omitted by the capacitance of the one-port surface acoustic wave resonators 71a and 71b.

When the anti-resonance frequencies of the one-port pair type surface acoustic wave resonators 71a and 71b are set to be the same in the first embodiment, the pass band of the multi-electrode type surface acoustic wave filter 10 is set to the high band side. The notch in the nearby stopband becomes deeper. Also, a one-terminal pair type surface acoustic wave resonator 71a
When the anti-resonance frequency is set slightly shifted by changing the pitch of the electrode fingers of the multi-electrode surface acoustic wave filter 10 and 71b, a large attenuation is obtained in the stop band near the high band side of the pass band. The frequency bandwidth becomes wider.

In the first embodiment described above, when the resonance frequencies of the one-port surface acoustic wave resonators 72a and 72b are set to be the same, the vicinity of the lower pass band side of the multi-electrode surface acoustic wave filter 10 is reduced. The notch in the stop band of is deepened. When the resonance frequency is slightly shifted by changing the pitch of the electrode fingers of the one-port pair type surface acoustic wave resonators 72a and 72b, the pass band of the multi-electrode surface acoustic wave filter 10 is set to the lower side. The frequency bandwidth in which a large amount of attenuation is obtained in a nearby stop band is widened.

Further, since the one-port pair surface acoustic wave resonators 71a, 71b, 72a and 72b and the multi-electrode surface acoustic wave filter 10 are formed on the same substrate 13, the one-port pair type surface acoustic wave filter is formed. Surface acoustic wave resonators 71a, 71b,
72a and 72b and multi-electrode surface acoustic wave filter 10
The stray capacitance due to the connection line with the wire is small. Also, the mutual relationship between the anti-resonance frequencies of the one-port pair type surface acoustic wave resonators 71a and 71b and the cut-off frequency of the multi-electrode surface acoustic wave filter 10 that is desired to be steep in the higher pass band is the same, and One-terminal pair type surface acoustic wave resonators 72a, 7
The mutual relationship between the resonance frequency 2b and the cut-off frequency of the multi-electrode type surface acoustic wave filter 10 which is desired to be sharpened in the lower pass band is the same, and the one-port pair surface acoustic wave resonators 71a, 71b, 72a , 72b have the same frequency and temperature characteristics as those of the multi-electrode surface acoustic wave filter 10, so that the cut-off frequency due to the frequency deviation when the composite surface acoustic wave filter 20 is manufactured and the resonance Frequency deviation between the frequency and the anti-resonance frequency can be reduced. Further, since the chip area does not increase, the cost can be reduced.

A one-terminal pair type surface acoustic wave resonator 71a
The same effect as described above can be obtained even if any one of the steps 71b and 71b is omitted. One-terminal pair type surface acoustic wave resonators 72a and 72
The same effect as described above can be obtained even if any one of b is omitted.

As shown by the broken lines in FIG. 1, the one-port pair surface acoustic wave resonators 71c and 71d are electrically connected in series to the one-port pair surface acoustic wave resonators 71a and 71b, respectively. You may connect. Thus, the one-port pair type surface acoustic wave resonators 71a, 71b, 71
If the anti-resonance frequencies of c and 71d are the same, the notch in the stop band near the higher pass band side of the multi-electrode surface acoustic wave filter 10 is further deepened, and the one-port pair surface acoustic wave resonators 71a and 71b , 71c, and 71d, the anti-resonance frequency is slightly shifted.
The frequency bandwidth in which a large amount of attenuation is obtained in the stop band near the pass band high side of 0 is further widened.

Further, as shown by the broken lines in FIG. 1, the one-port pair type surface acoustic wave resonators 72a, 72
One terminal pair type surface acoustic wave resonators 72c and 72d may be electrically connected in parallel to each of b. In this manner, the one-terminal pair type surface acoustic wave resonators 72a, 72b,
If the resonance frequencies of 72c and 72d are the same, the notch in the stop band near the lower side of the pass band of the multi-electrode surface acoustic wave filter 10 is further deepened, and the one-port pair surface acoustic wave resonators 72a, 72b, If the resonance frequencies of 72c and 72d are slightly shifted, the multi-electrode surface acoustic wave filter 1
The frequency bandwidth in which a large amount of attenuation is obtained in the stopband near the low-passband side of 0 is further widened.

In the first embodiment, the case where the one-port pair type surface acoustic wave resonator 72a is connected in parallel to the input electrode of the multi-electrode surface acoustic wave filter 10 has been described. The one-terminal pair type surface acoustic wave resonator 72b may be connected in parallel to the output electrode of the multi-electrode surface acoustic wave filter 10, but may be connected in parallel to the output terminal OUT. In this case, the same effect as in the first embodiment can be obtained.

Next, a description will be given of a second embodiment of the composite surface acoustic wave filter according to the present invention.

FIG. 5 is a schematic structural view of a second embodiment of the composite surface acoustic wave filter according to the present invention.

In FIG. 5, reference numeral 30 denotes a composite surface acoustic wave filter according to a second embodiment of the present invention. The composite surface acoustic wave filter 30 includes a multi-electrode surface acoustic wave filter 10 formed on a substrate 13 and a one-port pair type surface acoustic wave resonator 71.
a, 71b, 72c, 72e, and a one-terminal pair type surface acoustic wave resonator 71a is electrically connected in series to the multi-electrode surface acoustic wave filter 10 on the input terminal A side of the multi-electrode surface acoustic wave filter 10. , One terminal pair type surface acoustic wave resonator 71
b is electrically connected in series to the multi-electrode surface acoustic wave filter 10 at the output end B side of the multi-electrode surface acoustic wave filter 10, and the one-port pair type surface acoustic wave resonator 72c is a multi-electrode surface acoustic wave filter. The input terminal A of the terminal 10 is electrically connected to the multi-electrode surface acoustic wave filter 10 in parallel, and the one-terminal pair type surface acoustic wave resonator 72e is
0 is electrically connected in parallel at the input terminal IN.
Therefore, in the second embodiment, the one-port pair type surface acoustic wave resonators 71a, 72c, 72e are connected in a π-type,
It is connected between the input terminal IN and the input terminal A of the multi-electrode surface acoustic wave filter 10. Here, the one-port pair type surface acoustic wave resonators 71b, 72c and 72e have the same configuration as the one-port pair type surface acoustic wave resonator 71a shown in FIG.

One-port pair type surface acoustic wave resonators 71a, 71
The impedances of b, 72c and 72e are low near the resonance frequency and high near the anti-resonance frequency as shown in FIG.

The anti-resonance frequency of the one-port pair type surface acoustic wave resonators 71a and 71b is changed by using a multi-electrode surface acoustic wave filter 1.
Zero is set to a frequency in a stop band near the high-pass band side, and the resonance frequency is set to be within the pass band of the multi-electrode surface acoustic wave filter 10. The resonance frequency of the one-port pair type surface acoustic wave resonators 72c and 72e is set to a frequency within a stop band near the lower side of the pass band of the multi-electrode surface acoustic wave filter 10, and the anti-resonance frequency is set to the multi-electrode surface acoustic wave filter. It is set so that it falls within the pass band of the wave filter 10.

With this setting, a high-impedance near the anti-resonance frequency of the one-port pair type surface acoustic wave resonators 71a and 71b allows a stop band to be obtained near the anti-resonance frequency. Type surface acoustic wave filter 1
A sharp attenuation characteristic is obtained on the high band side of pass band 0,
Further, one-port pair type surface acoustic wave resonators 71a and 71a
Since the impedance is low near the resonance frequency b, the insertion loss in the pass band of the multi-electrode surface acoustic wave filter 10 does not increase.

Further, a one-terminal pair type surface acoustic wave resonator 72
Because of the low impedance near the resonance frequency of c and 72e, a stop band is obtained near the resonance frequency, and a steep attenuation characteristic is obtained on the low band side of the pass band of the multi-electrode surface acoustic wave filter 10. Because of the high impedance near the anti-resonance frequency of the one-port pair type surface acoustic wave resonators 72c and 72e, the multi-electrode surface acoustic wave filter 10
Does not cause an increase in insertion loss in the pass band of

When the anti-resonance frequencies of the one-port pair type surface acoustic wave resonators 71a and 71b are set to be the same, and when the anti-resonance frequencies of the one-port pair type surface acoustic wave resonators 71a and 71b are slightly shifted. When the resonance frequencies of the one-port pair type surface acoustic wave resonators 72c and 72e are set to be the same, the one-port pair type surface acoustic wave resonators 72c and 72e
The operation when the resonance frequency of e is slightly shifted is the same as that of the first embodiment.

Accordingly, the attenuation characteristics deteriorated due to the electrode weighting of the multi-electrode surface acoustic wave filter 10 are improved.

In the first and second embodiments of the present invention, the one-port pair type surface acoustic wave resonators 71a to 71d, 7
2a to 72e illustrate the case of the configuration shown in FIG.
With the terminal pair type surface acoustic wave resonator 71a as an example, reflectors 82 and 83 are arranged outside the electrode 74 as shown in FIG.
It is clear that the same effect can be obtained with the terminal pair type surface acoustic wave resonator. One-terminal pair type surface acoustic wave resonator 71b
The same applies to 71d and 72a〜72e.

Next, a description will be given of a third embodiment of the composite surface acoustic wave filter according to the present invention.

FIG. 7 is a schematic structural view of a composite surface acoustic wave filter according to a third embodiment of the present invention.

In FIG. 7, reference numeral 60 denotes a composite surface acoustic wave filter according to a third embodiment of the present invention. The composite surface acoustic wave filter 60 includes an input electrode 41 and an output electrode 42 provided with the input electrode 41 interposed therebetween and electrically connected in parallel.
a two-terminal pair type surface acoustic wave resonator filter 40, comprising reflectors 43a and 43b formed outside the output electrodes 42a and 42b (on the side opposite to the input electrode 41).
A one-port pair type surface acoustic wave resonator 71 electrically connected in series to the two-port pair type surface acoustic wave resonator filter 40 on the input terminal C side of the two-port pair type surface acoustic wave resonator filter 40.
a, the two-terminal pair type surface acoustic wave resonator filter 4 on the input terminal C side of the two-terminal pair type surface acoustic wave resonator filter 40;
And a two-port pair type surface acoustic wave resonator filter 40 electrically connected in parallel to the first and second terminals.
Of the one-port pair surface acoustic wave resonator 71b electrically connected in series to the two-terminal pair surface acoustic wave resonator filter 40 on the output end D side, and the output of the two-port pair surface acoustic wave resonator filter 40 A two-terminal pair surface acoustic wave resonator 72b electrically connected in parallel to the two-terminal pair surface acoustic wave resonator filter 40 on the end D side; Terminal pair type surface acoustic wave resonator 7
1a, 71b, 72a and 72b are formed on the same substrate 13.

Two-terminal pair type surface acoustic wave resonator filter 40
Are substantially similar to those of the multi-electrode surface acoustic wave filter 10.

Therefore, the composite surface acoustic wave filter 60
Also, the one-port pair surface acoustic wave resonators 71a and 71a
By setting the anti-resonance frequency of 1b to a frequency in a stop band near the high-pass side of the two-port SAW resonator filter 40, the one-port SAW resonator 72 is set.
It is easily understood that the frequency amplitude characteristics can be improved by setting the resonance frequencies of a and 72b to a frequency in a stop band near the lower side of the pass band of the two-port SAW resonator filter 40. Let's do it.

In the first to third embodiments, the resonance frequency of the one-port pair type surface acoustic wave resonators 72a to 72e is determined by the multi-electrode surface acoustic wave filter 10 and the two-port pair surface acoustic wave resonance. The case where the frequency is set in the stop band near the lower pass band of the filter 40 has been described. However, the resonance frequency of the one-port pair type surface acoustic wave resonators 72a to 72e is changed to the side lobe on the lower band side of the pass band of the multi-electrode surface acoustic wave filter 10 and the two-port pair surface acoustic wave filter 40. By setting the frequency within the frequency band to be used, the side lobe on the lower side of the pass band is suppressed.

Similarly, a one-terminal pair type surface acoustic wave resonator 71
The description has been given of the case where the anti-resonance frequencies a to 71d are set to frequencies in the stop band near the high-pass side of the multi-electrode surface acoustic wave filter 10 and the two-port pair surface acoustic wave resonator filter 40. However, the one-port pair type surface acoustic wave resonator 7
The multi-electrode surface acoustic wave filter 10, the two-port pair type surface acoustic wave resonator filter 40
By setting the frequency in the frequency band in which the side lobes of the higher pass band exist, the side lobes of the higher pass band are suppressed.

Next, an example of using the composite surface acoustic wave filter of the present invention will be described.

FIG. 8 is a block diagram showing a partial configuration of a mobile communication device using the composite surface acoustic wave filter of the present invention.

In this mobile communication device, the receiving side employs, for example, a double conversion system, and the output from the antenna 90 is band-limited through a band-pass filter 91 constituting an antenna duplexer 110, and an RF amplifier is provided. 9
After amplifying the signal at 2 and suppressing the noise via the band-pass filter 93, the mixer 96 frequency-mixes the frequency with the first local oscillation frequency via the band-pass filter 95 to convert the frequency to a first intermediate frequency signal. The intermediate frequency signal is noise-suppressed by passing through the band-pass filter 97. The noise-removed first intermediate frequency signal is supplied to a first intermediate frequency amplifier 98, amplified, mixed in a mixer 99 with a second local oscillation frequency, and frequency-converted into a second intermediate frequency signal. The frequency signal is noise-suppressed via a band-pass filter 100, supplied to a second intermediate frequency amplifier 101, amplified, demodulated by a demodulator 102, and transmitted to a subsequent stage.

On the transmitting side, the modulator 103 modulates the carrier frequency with an audio signal, the modulated output is amplified by the amplifier 104, and the amplified output is frequency-converted to the transmission frequency by the mixer 105 using the signal of the local oscillation frequency. The excitation signal is amplified by an excitation amplifier 106 and the band-pass filter 107
, And power is amplified by a transmission power amplifier 108 and transmitted from an antenna 90 through a bandpass filter 109 constituting an antenna duplexer 110.

Reference numeral 94 denotes a frequency synthesizer that outputs signals of the first and second local oscillation frequencies and a carrier frequency.

In such a mobile communication device, since the transmission frequency band and the reception frequency band are close to each other, the band-pass filter is required to have a sharp cutoff characteristic and to be downsized. In this case, the antenna duplexer 1
10, band-pass filters 91 and 109,
The band-pass filters 93 and 107 between the stages, and the band-pass filter 95 between the stages when the signal of the local oscillation frequency is injected into the mixer 96 are used as the composite surface acoustic waves according to the first, second, or third embodiment of the present invention. A filter 20, 30, or 60 is used. This use satisfies the steep cut-off characteristics and meets the demand for miniaturization.

It is also effective to use the composite surface acoustic wave filter of the present invention as a filter in antenna duplexer 110 or as a filter between stages.

[0069]

According to the present invention as described above, according to the present invention, electrostatic
Input electrode for converting air signal into surface acoustic wave and converted bullet
Sex surface waves in at least one of the input side or output side of the SAW filter and an output electrode into an electric signal, an electrical one or more first surface acoustic wave resonator to the surface acoustic wave filter , And one or more second surface acoustic wave resonators are electrically connected in series to the surface acoustic wave filter, so that the first surface acoustic wave resonator has a low impedance near the resonance frequency and the second surface acoustic wave resonator has Due to the high impedance near the anti-resonance frequency of the surface acoustic wave resonator,
The attenuation in the desired band of the surface acoustic wave filter can be increased, and the effect of improving the frequency amplitude characteristics can be obtained. Further, the notch frequency can be set by the resonance frequency of the first surface acoustic wave resonator and the anti-resonance frequency of the second surface acoustic wave resonator, and the pass bandwidth can be set by the pass bandwidth of the surface acoustic wave filter, and there is no restriction. . Also, first and second elasticity
The surface acoustic wave resonator is part of the matching circuit of the surface acoustic wave filter.
To obtain good frequency amplitude characteristics
This also has the effect of simplifying the matching circuit.
You.

At least one of the input end side and the output end side of the surface acoustic wave filter has at least one resonance frequency set to a frequency within a stop band near the lower pass band side of the surface acoustic wave filter. At least the first surface acoustic wave resonator is electrically connected to the surface acoustic wave filter in parallel, and the anti-resonance frequency is set to a frequency in a stop band near the pass band higher side of the surface acoustic wave filter. Since one or more second surface acoustic wave resonators are electrically connected in series to the surface acoustic wave filter, low impedance near the resonance frequency of the first surface acoustic wave resonator and anti-resonance of the second surface acoustic wave resonator are provided. Due to high impedance near the frequency, the cutoff characteristics of the high pass band of the surface acoustic wave filter and the cutoff of the low pass band of the surface acoustic wave filter Sex becomes steep, the effect of frequency-amplitude characteristics are improved is obtained.

Further, the pass band width and the insertion loss in the pass band are determined by the surface acoustic wave filter, and the effect is obtained that the pass band is hardly affected by the surface acoustic wave resonators connected in parallel and the surface acoustic wave resonators connected in series. .

The first and second surface acoustic wave resonators can be used in both cases where the surface acoustic wave filter is a multi-electrode surface acoustic wave filter and where the surface acoustic wave filter is a two-port pair type surface acoustic wave resonator filter. Is a one-port pair type surface acoustic wave resonator, the attenuation in the desired band of the surface acoustic wave filter can be increased, and the resonance frequency and anti-resonance frequency of the one-port pair type surface acoustic wave resonator can be elastically adjusted. When set to a frequency in the stop band near the low band side of the pass band of the surface acoustic wave filter and a frequency in the stop band near the high band side, the cut-off characteristics and the pass band of the high pass band of the surface acoustic wave filter are set. The cutoff characteristic on the low band side becomes sharp, and the effect of improving the frequency amplitude characteristic is obtained.

Further, when the matching circuit connected in parallel by the capacitance exhibited by the one-terminal pair type surface acoustic wave resonator is an inductance element, the inductance value may be small,
In the case of a capacitance element, the capacitance is small,
There is an effect that the shapes of the inductance element and the capacitance element are reduced, and the volume as a whole is also reduced.

When the surface acoustic wave filter and the surface acoustic wave resonator are arranged on the same substrate, the chip area is not increased, and the cutoff characteristics of the surface acoustic wave filter of the surface acoustic wave resonator are reduced. Since the reciprocal relationship between the frequency to be sharpened and the resonance frequency of the surface acoustic wave resonator, the anti-resonance frequency is the same, the cut-off frequency due to the deviation of the frequency at the time of manufacture, and the resonance frequency, between the anti-resonance frequency This has the effect of reducing the frequency shift.

In a mobile communication device using the composite surface acoustic wave filter of the present invention as an antenna duplexer and / or an interstage filter, reception is performed because the cutoff characteristic of the frequency amplitude characteristic of the composite surface acoustic wave filter is steep. Even if the frequency and the transmission frequency are close to each other, the reception signal does not mix into the transmission side, so that the transmission signal does not mix into the reception side, and the frequency of the unnecessary band can be effectively attenuated. effective. Further, since the composite surface acoustic wave filter is small, there is an effect that the size of the mobile communication device can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a schematic view showing a configuration of a one-port pair type surface acoustic wave resonator.

FIG. 3 is a frequency amplitude characteristic diagram of a one-port pair type surface acoustic wave resonator.

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

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

FIG. 6 is a schematic diagram showing the configuration of a one-port pair type surface acoustic wave resonator including a reflector.

FIG. 7 is a schematic diagram showing a configuration of a composite surface acoustic wave filter according to a third embodiment of the present invention.

FIG. 8 is a block diagram showing a part of the configuration of a mobile communication device for showing an example of use of the composite surface acoustic wave filter of the present invention.

FIG. 9 is a schematic diagram showing a configuration of a conventional multi-electrode surface acoustic wave filter.

10 is a frequency amplitude characteristic diagram of the multi-electrode surface acoustic wave filter shown in FIG.

FIG. 11 is a schematic diagram showing a configuration of a conventional filter of a ladder type connection.

12 is a frequency amplitude characteristic diagram of the filter shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Multi-electrode surface acoustic wave filter 11a-11d, 41 ... Input electrode 12a-12c, 42a, 42b ... Output electrode 13 ... Substrate 20, 30, 60 ... Composite surface acoustic wave filter 40 ... Two-terminal pair surface acoustic wave Resonator filters 71a-71d, 72a-72e ... one-port pair type surface acoustic wave resonator

Claims (6)

(57) [Claims] 1. A surface acoustic wave filter comprising an input electrode for converting an electric signal into a surface acoustic wave and an output electrode for converting the converted surface acoustic wave into an electric signal, at least one of an input side and an output side has a resonance. Frequency passes through surface acoustic wave filter
At least one or more first surface acoustic wave resonators set to a frequency within a stop band near the lower band side of the band are electrically connected in parallel to the surface acoustic wave filter, and the anti-resonance frequency Is elastic
Around the stop band near the high-pass side of the surface acoustic wave filter.
A composite surface acoustic wave filter characterized in that at least one or more second surface acoustic wave resonators set to a wave number are electrically connected in series to a surface acoustic wave filter. 2. The composite surface acoustic wave filter according to claim 1, wherein the surface acoustic wave filter is provided between a plurality of input electrodes electrically connected in parallel, and between the input electrodes, respectively, and is electrically connected. A composite surface acoustic wave filter comprising a multi-electrode surface acoustic wave filter including a plurality of output electrodes connected in parallel. 3. The composite surface acoustic wave filter according to claim 1, wherein the surface acoustic wave filter is a two-port pair type surface acoustic wave resonator filter. 4. The composite surface acoustic wave filter according to claim 1, wherein said first and second surface acoustic wave resonators are one-port pair type surface acoustic wave resonators. 5. A composite surface acoustic wave filter according to claim 1, wherein said first and second surface acoustic wave resonators are formed on the same substrate as said surface acoustic wave filter. 6. Any of the composite surface acoustic wave filter according to claim 1 to 5, wherein the mobile communication device characterized by using the antenna duplexer and / or interstage filter.