JP2003188674A - Surface acoustic wave device and communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device for improving spurious characteristics without deteriorating in-band characteristics and a communication device having it. <P>SOLUTION: A plurality of interdigital electrode parts 2, 1 and 3 formed along a propagation direction of an elastic surface wave are provided on a piezoelectric substrate 10, respectively. Reflectors 4 and 5 sandwiching each interdigital electrode part 2, 1 and 3 from the sides along the propagation direction are provided, respectively. At least one of a pitch and an electrode width in at least one of each reflector 4 and 5 is changed in the reflector. <P>COPYRIGHT: (C)2003,JPO

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 device having a filter function and excellent transmission characteristics, and a communication device having the same.

[0002]

2. Description of the Related Art Surface acoustic wave devices are widely used as bandpass filters in the RF stage in communication devices such as mobile phones. Performances required of the bandpass filter include low loss and wide band in the pass band and high attenuation outside the pass band.

The above-mentioned surface acoustic wave device is called a comb-shaped electrode portion (a comb-shaped electrode or an interdigital transducer) having a plurality of electrode fingers crossing each other, and is hereinafter referred to as ID.
T) are provided along the propagation direction of the surface acoustic wave, and reflectors are provided on both sides of each IDT along the propagation direction.

In such a surface acoustic wave device, saw-tooth spurs appear outside the pass band on the low frequency side near the pass band. Therefore, it is difficult to secure a sufficient amount of attenuation in this band.

This spurious is caused by each I of the surface acoustic wave device.
This is because the reflection response of each reflector provided on both sides of DT is not zero on the low frequency side near the pass band outside the pass band.

As a countermeasure against this, Japanese Patent Laid-Open No. 11-31764
Japanese Patent Publication No. 3 discloses a configuration in which the pitch of each reflector of the surface acoustic wave device is changed between left and right. In the above configuration, when the pitch is changed, the reflection response of each of the left and right reflectors is frequency-shifted between each other.Therefore, by designing so that the peaks and valleys of the spurious part caused by each reflector cancel each other, the attenuation (Spurious) can be improved.

[0007]

In the configuration described in the above-mentioned prior art publication, by changing the pitch of each reflector between the left and right as described above, spurious on the low frequency side near the pass band outside the pass band is generated. Although it can be improved, when the pitch of each reflector is changed uniformly between left and right, the frequency band in which the reflectance of surface acoustic waves that can form a pass band is high, so-called stop band, is also frequency-shifted.

Therefore, the stopbands of the left and right reflectors are also displaced (shifted) from each other, and only the overlapping portions of the stopbands have a frequency band capable of forming a passband. As a result, the above-mentioned conventional technique has a problem that the pass band is narrowed.

It is an object of the present invention to provide a surface acoustic wave device capable of improving the amount of attenuation outside the pass band by attenuating only the spurious portion while maintaining the pass band width substantially, and a communication device using the same. Is.

[0010]

In order to solve the above-mentioned problems, a surface acoustic wave device of the present invention includes a plurality of IDTs formed on a piezoelectric substrate along the surface acoustic wave propagation direction.
A surface acoustic wave element having a reflector sandwiching the IDT from both sides along the propagation direction, wherein at least one of a pitch and an electrode width in at least one of the reflectors is within the reflector. It is characterized by changing.

According to the above configuration, the difference between the pass band and the outside of the pass band can be more clearly provided by having a plurality of IDTs, and by having each of the above reflectors,
The generated surface acoustic waves can be efficiently converted into electric energy and insertion loss can be reduced.

Moreover, in the above structure, since at least one of the pitch and the electrode width in at least one of the reflectors is changed in the reflector, it is outside the pass band, particularly in the low band from the pass band. It is possible to reduce the spurious noise on the side, increase the amount of attenuation outside the pass band, and suppress narrowing of the pass band.

In the surface acoustic wave device, at least one of the pitch and the electrode width in each of the reflectors changes in the reflector, and the changes in the reflectors are different from each other. Good.

In the surface acoustic wave device, a plurality of surface acoustic wave elements may be connected.

In order to solve the above problems, another surface acoustic wave device of the present invention propagates the plurality of IDTs formed on the piezoelectric substrate along the surface acoustic wave propagation direction. A surface acoustic wave device in which two or more surface acoustic wave elements each having a reflector sandwiched from both sides along the direction are cascade-connected to each other, wherein a pitch and an electrode in at least one reflector of the surface acoustic wave elements. At least one of the widths is changed in the reflector.

Also in the above configuration, as described above, it is possible to reduce spurious, increase the amount of attenuation outside the pass band, and suppress narrowing of the pass band.

Further, in the above structure, even if at least one of the pitch and the electrode width in at least one of the surface acoustic wave devices is changed in the reflector, the changed pitch of the reflector and the electrode width are changed. At least one of the electrode widths can be provided with a portion that matches the pitch or electrode width of another reflector, and the matching portion can maintain the pass band and suppress the narrowing of the pass band.

In the above surface acoustic wave device, it is preferable that the reflectors sandwiching the IDT from both sides along the propagation direction have the same pitch in the vicinity of the side facing the adjacent IDTs.

According to the above structure, in each of the reflectors sandwiching the IDT, the pass band can be maintained by providing the portions having the same pitch or electrode width in the vicinity of the adjacent IDTs. On the other hand, spurious can be reduced by providing different pitch portions in each of the reflectors.

In the surface acoustic wave device, at least one of the surface acoustic wave elements may have a reflector.
The pitch may be constant and the electrode width may be changed within the reflector.

In the surface acoustic wave device, both the pitch and the electrode width of at least one of the surface acoustic wave elements may be changed in the reflector.

In the surface acoustic wave device, at least one of the surface acoustic wave elements may be a reflector.
The electrode width may be constant and the pitch may vary within the reflector.

In the surface acoustic wave device, the respective reflectors are provided so that the pitch becomes smaller from the outer side toward the central part, and even if the degree of pitch change is set to be different from each other. Good.

In the surface acoustic wave device, each of the reflectors is provided so that the pitch thereof gradually increases from the outer side toward the central portion, and the degree of pitch change is set to be different from each other. Good.

The surface acoustic wave device may have an unbalanced-balanced conversion function. A communication device of the present invention is characterized by having any one of the surface acoustic wave devices described above.

According to the above structure, the spurious characteristic is improved and the surface acoustic wave device in which the narrowing of the pass band is suppressed is provided, so that the communication characteristic can be improved.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Each embodiment of the surface acoustic wave device of the present invention will be described below with reference to FIGS. 1 to 12.

In the first embodiment of the surface acoustic wave device of the present invention, as shown in FIG. 1, 40 ± 5 ° YcutX
A plurality of, for example, three input / output IDTs 2, 1, 3 are provided in this order on a piezoelectric substrate 10 made of propagation LiTaO ₃ or the like along a propagation direction of a surface acoustic wave (hereinafter abbreviated as SAW). Further, the above-mentioned input / output IDTs 2,
Two reflectors 4 and 5 sandwiching 1 and 3 from both left and right sides (from the direction along the SAW propagation direction) are provided. The input / output IDT 1 is connected to the input / output terminal 6. The input / output IDTs 2 and 3 are connected to the input / output terminal 7.

The IDT is formed of a metal thin film such as aluminum, and the input electric signal (AC) is S
Converted to AW (surface acoustic wave) and propagated on the piezoelectric substrate,
It functions as a SAW conversion unit that converts the propagated SAW into an electric signal and outputs the electric signal. The reflector has a function of reflecting the propagated SAW in the incoming direction.

In such an IDT, the length and width of each comb-shaped electrode finger, the distance between the comb-shaped electrode fingers that cross each other, and the inter-face length in the intricate state between the comb-shaped electrode fingers are set. The signal conversion characteristics and the pass band can be set by setting the cross widths shown. Also,
In the reflector, the reflection characteristics can be set by adjusting the width and interval of each reflector electrode finger.

Then, in the surface acoustic wave device of the first embodiment, at least one of the two reflectors 4 and 5, for example, the reflector 5 is provided so that the pitch becomes gradually smaller from the outer side toward the central portion. It is used (chirp type). Also,
In the reflector 5, the IDTs (adjacent IDTs)
3 is preferably set to be equal to the pitch 41 from the center of the reflector 4 (near the portion facing the adjacent IDT 2).

The reflectors 4 and 5 are set such that the duty ratio of the reflector electrode fingers is constant and the number of reflector electrode fingers is equal to each other. The reflectors 4 are provided so that their pitches are also equal along the SAW propagation direction. Other design parameters of the surface acoustic wave device are shown in Table 1 below.

[0033]

[Table 1]

On the other hand, as a conventional surface acoustic wave device for comparison, as shown in FIG. 2, instead of the reflector 5, the pitch is uniformly changed with respect to the other reflector 4. The surface acoustic wave device manufactured in the same manner as the surface acoustic wave device of the first embodiment except that the reflector 8 was used was used.

Next, the operation and effect of the surface acoustic wave device of the first embodiment will be described. As in the first embodiment, the pitch is changed in one reflector 5 along the SAW propagation direction, more preferably sequentially, so that the surface acoustic wave device according to the first embodiment is changed. Then
Since the extreme values are shifted between the left and right reflectors 4 and 5, the spurious is attenuated.

FIG. 3 shows frequency characteristics of insertion loss in a surface acoustic wave device (without pitch change) in which the pitches of the left and right reflectors are equal to each other. Further, FIG. 4 shows frequency characteristics of insertion loss in the surface acoustic wave device of the first embodiment. From FIGS. 3 and 4, it can be seen that in the surface acoustic wave device of the first embodiment, spurious is attenuated outside the pass band, particularly on the low band side from the pass band.

Further, the reflection coefficient of the surface acoustic wave device according to the first embodiment changes as shown in FIG. The pitch ratio shown in FIGS. 5 and 7 is the ratio of the minimum pitch to the maximum pitch in the reflector 5. 5 (c) shows no pitch change, and FIG. 5 (b) shows pitch change (1) (pitch ratio 0.9
94) and FIG. 5 (a) show a pitch change (2) (pitch ratio 0.
981).

On the other hand, in the above-mentioned conventional surface acoustic wave device, when the pitch of the reflector 8 is set so as to obtain the spurious attenuation level (FIG. 6) at the same level as above, the reflection coefficient is measured as shown in FIG. Became. 7A to 7C are shown in FIG.
(A) to (c) of FIG. Here, the results of comparing the shifts of the respective stop bands in FIG. 5 and FIG. 7 are shown in Table 2 (the unit of numerical values in Table 2 is MHz).

[0039]

[Table 2]

As is clear from Table 2, the deviation from the state without pitch change is smaller in the first embodiment of the present invention than in the conventional example and is advantageous for widening the band. As a result, in the first embodiment of the present invention, it is possible to suppress the narrowing of the pass band while maintaining the amount of attenuation outside the pass band (particularly on the low frequency side), and maintain a wide pass band width.

In the above, the pitch of the reflectors 5 is set to SA.
Although an example in which the width is increased from the center toward the outer side along the propagation direction of W has been described, substantially the same effect can be obtained by decreasing the size on the contrary. Further, when the pitch 51 from the center of the reflector 5 and the pitch 41 from the center of the reflector 4 are set to be equal to each other, the displacement of the pass band becomes smaller.

By the way, in the conventional example shown in FIG. 2, by changing the pitch of the reflector 4 and the reflector 8, the spurious outside the pass band outside the pass band can be attenuated. Because even the band is canceled,
It could not be used for a filter that requires a wide band.

On the other hand, in the first embodiment of the present invention, by using a reflector whose pitch is internally changed like the reflector 5, as shown in FIGS. 4 and 5, the pass band is reduced. It is possible to cancel spurious outside the pass band while suppressing. Therefore, the surface acoustic wave device according to the first embodiment of the present invention can be used for a filter or the like which requires a wide band.

Next, a surface acoustic wave device according to a second embodiment of the present invention will be described with reference to FIG. In the surface acoustic wave device, the surface acoustic wave element 11 having three IDTs and the surface acoustic wave element 12 having three IDTs are provided in parallel with each other.

Surface acoustic wave element 11 and surface acoustic wave element 1
It is set to have a phase difference of 180 degrees with respect to 2. A terminal 6 is connected to each IDT in the center of each surface acoustic wave element 11, 12. On the other hand, the terminal 9 is connected to each IDT outside the surface acoustic wave element 11, and the surface acoustic wave element 12 is connected.
The other terminal 9 is connected to each IDT outside. As a result, the surface acoustic wave device has an unbalanced-balanced conversion function. Terminal 6 is the unbalanced side and each terminal 9 is the balanced side.

In the surface acoustic wave device,
Although the respective reflectors 14 of the surface acoustic wave element 11 are set at equal pitches, the respective reflectors 16 of the surface acoustic wave element 12 are arranged.
Are set such that the pitch becomes gradually smaller toward the central portion (each IDT sandwiched therebetween).

In such a surface acoustic wave device, the unbalanced-
By having a balance conversion function and changing the pitch in each reflector 16, the narrowing of the pass band is reduced as in the first embodiment, while spurious outside the pass band is canceled. Can be suppressed.

Also in the above-mentioned surface acoustic wave device, the reflector 1
An example was given in which the pitch of 6 was sequentially increased from the center toward the outside along the SAW propagation direction, but conversely the same effect can be obtained by decreasing it sequentially. Further, as in the first embodiment, the displacement of the pass band becomes smaller when the pitch from the center of the reflector 16 and the pitch from the center of the reflector 14 are set to be equal to each other. Therefore, it is preferable.

Further, each reflector 16 sandwiching each IDT therebetween.
Passes through the center of the central IDT of each of the above IDTs, and SA
It is desirable that the symmetry axis is an imaginary line that is orthogonal to the W propagation direction.

Next, a surface acoustic wave device according to a third embodiment of the present invention will be described with reference to FIG. In the surface acoustic wave device, the surface acoustic wave elements 11, 11, 22, 32 having three IDTs are provided in a multi-stage cascade connection.

The surface acoustic wave elements 11 and 22 are in phase with each other and connected in parallel, while the surface acoustic wave elements 1 are connected in parallel.
Phases 1 and 32 are 180 degrees out of phase with each other and are connected in parallel. The surface acoustic wave elements 11 and 22 having the same phase with each other and the surface acoustic wave elements 11 and 32 having phases different from each other by 180 degrees are cascade-connected in two stages.
As a result, the surface acoustic wave device has an unbalanced-balanced conversion function.

In the surface acoustic wave device,
The respective reflectors 14 of the surface acoustic wave element 11 are set at equal pitches, but the respective reflectors 16 of the surface acoustic wave elements 22 and 32 are directed toward the central portion (each IDT sandwiched therebetween). The pitch is set to be gradually smaller.

In such a surface acoustic wave device, the unbalance-
By having a balance conversion function and changing the pitch in each reflector 16, the narrowing of the pass band is reduced as in the first embodiment, while spurious outside the pass band is canceled. Can be suppressed.

Also in the above surface acoustic wave device, the reflector 1
An example was given in which the pitch of 6 was sequentially increased from the center toward the outside along the SAW propagation direction, but conversely the same effect can be obtained by decreasing it sequentially. Further, as in the first embodiment, the displacement of the pass band becomes smaller when the pitch from the center of the reflector 16 and the pitch from the center of the reflector 14 are set to be equal to each other. Therefore, it is preferable.

In each of the above embodiments, the pitch of the reflectors is changed internally, but the reflector electrode finger width (duty ratio, electrode width) of the reflectors may be changed internally. Alternatively, both the pitch and the width of the reflector electrode finger may be internally changed. Furthermore, in each of the above-described embodiments, the example in which the pitch is sequentially changed is described, but the pitch is internally changed at a relative ratio of (5, 5, 3, 3, 1), which is more widely separated. Good.

As a modification of the present invention, as shown in FIG. 10, even in the two-stage surface acoustic wave device, at least one of the reflectors 5 has a pitch (electrode width is also acceptable).
By internally changing, the spurious can be reduced while maintaining the pass band, and the transmission characteristic (increasing the amount of attenuation) outside the pass band can be improved.

As another modification of the present invention, FIG.
1 has an unbalanced-balanced conversion function,
Even in the surface acoustic wave device having the one-stage structure, by changing the pitch (electrode width is also acceptable) inside at least one of the reflectors 5 inside, the spurious can be reduced while maintaining the pass band, and the spurious can be kept outside the pass band. The transmission characteristics (increased attenuation) can be improved.

Next, the communication device 100 equipped with the surface acoustic wave device of the present invention will be described with reference to FIG. The communication device 100 includes an antenna 101, an antenna common unit / as a receiver side (Rx side) for receiving.
RFTop filter 102, amplifier 103, Rx interstage filter 104, mixer 105, 1stIF filter 10
6, mixer 107, second IF filter 108, 1st
+ 2nd local synthesizer 111, TCXO (temp
An erature compensated crystal oscillator 112, a divider 113, and a local filter 114 are provided. It is preferable to transmit each balanced signal from the Rx interstage filter 104 to the mixer 105 in order to secure balance, as shown by the double line in FIG.

Further, the communication device 100 uses the antenna 101 as a transceiver side (Tx side) for transmission.
And the antenna sharing unit / RFTop filter 102 are shared, and the TxIF filter 121 and the mixer 12 are also provided.
2, Tx interstage filter 123, amplifier 124, coupler 1
25, isolator 126, APC (automatic power
control (automatic output control) 127.

Then, the antenna common part / RFTop
Filter 102, Rx interstage filter 104, 1stIF
Filter 106, 2ndIF filter 108, TxIF
For the filter 121, the surface acoustic wave device described in each of the above-described embodiments can be preferably used.

Therefore, in the above communication device, the surface acoustic wave device used is multifunctionalized and downsized, and further has excellent transmission characteristics (pass band is wide band, large attenuation outside pass band). As a result, it is possible to achieve a good transmission and reception function as well as downsizing.

[0062]

As described above, the surface acoustic wave device of the present invention includes the surface acoustic wave element having the IDT and each reflector, and the pitch and electrode width in at least one of the reflectors. At least one of the two is changing in the reflector.

Therefore, in the above structure, by changing at least one of the pitch and the electrode width in at least one of the reflectors in the reflector,
The effect that the spurious characteristics outside the pass band can be improved while reducing the deterioration of the in-band characteristics.

In the surface acoustic wave device, the ID
In each reflector that sandwiches T from both sides along the propagation direction,
The pitch near the side facing each adjacent IDT is
It is preferable that they are the same as each other.

According to the above structure, in each of the reflectors sandwiching the IDT, a part where the pitch or the electrode width is partly the same,
By providing the IDTs near each adjacent IDT, the pass band can be more reliably maintained, while providing at least one of the pitch and the electrode width, which are different from each other in each of the above reflectors, stabilizes the spurious reduction. There is an effect that can be realized.

[Brief description of drawings]

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

FIG. 2 is a schematic configuration diagram of a conventional surface acoustic wave device.

FIG. 3 is a graph showing a frequency characteristic of insertion loss in a surface acoustic wave device with no pitch change.

FIG. 4 is a graph showing a frequency characteristic of insertion loss in the surface acoustic wave device according to the first embodiment of the present invention.

FIG. 5 is a graph showing a change in pass band due to a pitch change in the first embodiment, where (a) is a pitch change (2).
, (B) shows pitch change (1), and (c) shows no pitch change.

FIG. 6 is a graph showing frequency characteristics of insertion loss in a surface acoustic wave device of a conventional surface acoustic wave device.

FIG. 7 is a graph showing a change in pass band due to a pitch change of a conventional surface acoustic wave device, (a) showing a pitch change (2)
, (B) shows pitch change (1), and (c) shows no pitch change.

FIG. 8 is a schematic configuration diagram of a surface acoustic wave device according to a second embodiment of the present invention.

FIG. 9 is a schematic configuration diagram of a surface acoustic wave device according to a third embodiment of the present invention.

FIG. 10 is a schematic configuration diagram showing a modification of the surface acoustic wave device.

FIG. 11 is a schematic configuration diagram showing another modification of the surface acoustic wave device.

FIG. 12 is a circuit block diagram of a main part of a communication device of the present invention.

[Explanation of symbols]

1, 2, 3 IDT (comb type electrode part) 4,5 reflector

Claims (12)

[Claims] 1. A piezoelectric substrate having a plurality of comb-shaped electrode portions formed along the propagation direction of surface acoustic waves, and a reflector sandwiching the comb-shaped electrode portions from both sides along the propagation direction. A surface acoustic wave device comprising a surface acoustic wave element, wherein at least one of a pitch and an electrode width of at least one of the reflectors is changed in the reflector. 2. At least one of a pitch and an electrode width in each of the reflectors changes in each of the reflectors, and changes in each of the reflectors are different from each other. The surface acoustic wave device according to claim 1. 3. The surface acoustic wave device according to claim 1, wherein a plurality of the surface acoustic wave elements are connected to each other. 4. A piezoelectric substrate having a plurality of comb-shaped electrode portions formed along a surface acoustic wave propagation direction, and a reflector sandwiching the comb-shaped electrode portions from both sides along the propagation direction. In a surface acoustic wave device in which two or more surface acoustic wave elements are connected in cascade, at least one of a pitch and an electrode width in at least one reflector in each of the surface acoustic wave elements is within the reflector. A surface acoustic wave device characterized by being changed. 5. In each of the reflectors sandwiching the comb-shaped electrode portion from both sides in the propagation direction, the pitches in the vicinity of the sides facing the adjacent comb-shaped electrode portions are the same. The surface acoustic wave device according to any one of claims 1 to 4. 6. At least one of the surface acoustic wave devices has a constant pitch and an electrode width of at least one reflector.
6. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device changes within the reflector. 7. The surface acoustic wave device according to claim 1, wherein at least one of the surface acoustic wave devices has both a pitch and an electrode width changed within the reflector. The surface acoustic wave device according to any one of claims. 8. The electrode width and pitch of at least one of the surface acoustic wave elements are constant,
6. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device changes within the reflector. 9. The reflectors are provided so that the pitch thereof becomes smaller from the outer side toward the central part, and the degree of change in pitch is set to be different from each other. Item 7. The surface acoustic wave device according to any one of items 1 to 5. 10. The reflectors are provided so that the pitch increases from the outer side toward the central portion, and the degree of pitch change is set to be different from each other. Any one of items 1 to 5
The surface acoustic wave device according to item. 11. The surface acoustic wave device according to claim 1, which has an unbalanced-balanced conversion function. 12. A communication device comprising the surface acoustic wave device according to claim 1. Description: