JP2003179458A - Surface acoustic wave device and communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a longitudinally coupled resonator surface acoustic wave (SAW) device having a balance/unbalance (balun) input/output function and having an improved balance between balance terminals. <P>SOLUTION: Longitudinally coupled SAW filters 8, 14, 17a and 18 are respectively provided on a piezoelectric substrate 30 so as to have the balun input/ output function. An electrode finger positioned at the outermost region of an IDT (interdigital transducer) 23a having the phase which is inverted 180° from the other IDTs to obtain the balun input/output function is thinned, and a dummy electrode finger 23b connected to the ground is provided at the thinned position. <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 more particularly to a surface acoustic wave device also having a balanced-unbalanced conversion function, and a communication device having the same.

[0002]

2. Description of the Related Art In recent years, there have been remarkable technological advances in reducing the size and weight of communication devices such as mobile phones.
As a means to realize this, reduction of each component,
In addition to miniaturization, the development of electronic components that combine multiple functions has progressed.

Against this background, the surface acoustic wave device, which is an electronic component used as a filter in the RF stage, having a balance-unbalance conversion function, that is, a so-called balun function, has been actively studied in recent years. , GSM (Global Sys
tem for Mobile communications) has come to be used mainly.

Several patents relating to the surface acoustic wave device having such a balanced-unbalanced conversion function have been filed. As a surface acoustic wave device having a balanced-unbalanced conversion function by making the input impedance and the output impedance different from each other, for example, as shown in FIG.
The configuration described in Japanese Patent Publication No. 117123 is known. Note that the piezoelectric substrate is omitted in FIG.

In the above-mentioned surface acoustic wave device, the first surface acoustic wave filter 101 and the second surface acoustic wave filter 101 differ in phase of the output signal by 180 degrees on the piezoelectric substrate.
The surface acoustic wave filter 102 of FIG. Accordingly, the surface acoustic wave device can exhibit the balanced-unbalanced conversion function as well as the filter function.

The first surface acoustic wave filter 101 includes three interdigital transducers (inter-digital transducers, hereinafter, I).
(DT) type longitudinally coupled resonator type surface acoustic wave filter 108, and longitudinally coupled resonator type surface acoustic wave filter 108.
On the other hand, a two-stage cascade connection of a 3IDT type longitudinally coupled resonator type surface acoustic wave filter 114, which is mirror-symmetrical with a line of symmetry along the propagation direction of the surface acoustic wave being sandwiched therebetween.

Vertically coupled resonator type surface acoustic wave filter 108
Arranges the IDTs 104, 105 on the left and right of the central IDT 103 (along the propagation direction of the surface acoustic wave), and the reflectors 106, 107 respectively sandwich the IDTs 104, 103, 105 from both the left and right sides. It is arranged. Similarly, in the longitudinally coupled resonator type surface acoustic wave filter 114, the IDTs 110 and 111 are arranged on the left and right of the central IDT 109, respectively.
Reflector 11 so that 0, 108, and 111 are sandwiched.
2, 113 are arranged.

Vertically coupled resonator type surface acoustic wave filter 108
In, the pitches of several electrode fingers (at 115 and 116 in FIG. 17) between the IDT 103 and the IDT 104 and between the IDT 103 and the IDT 105 are made narrower than the pitches of other portions of the IDT (hereinafter, referred to as narrow pitches). Pitch electrode fingers), and the IDT-IDT interval is set to about 0.5 times the wavelength of the IDTs around it, thereby reducing the loss due to the component emitted as a bulk wave. By the way, in FIG. 17, the number of electrode fingers is reduced to simplify the drawing.

The second surface acoustic wave filter 102 is 3I.
DT type longitudinally coupled resonator type surface acoustic wave filter 114
Same as the longitudinally coupled resonator type surface acoustic wave filter 118 and 3
IDT type longitudinally coupled resonator type surface acoustic wave filter 10
The longitudinally coupled resonator type surface acoustic wave filter 117 provided with the IDT 123 in which the direction of the central IDT 103 is inverted and the phase thereof is inverted (that is, about 180 °) with respect to FIG.
It is connected in cascade.

The first and second surface acoustic wave filters 101,
Each of the terminals 119 and 120 on one side of 102 is electrically connected in parallel, and the terminals 121 and 122 on the other side are electrically connected in series, and the unbalanced terminals 131 are connected in series by the terminals connected in parallel. Each balanced terminal 132, 13
Make up three.

In the surface acoustic wave device having a balanced-unbalanced conversion function, an unbalanced terminal 131 and each balanced terminal 132,
The transmission characteristics within the pass band between the respective terminals of 133 are equal in amplitude characteristics and 1 in phase characteristics.
It is required to be inverted by 80 degrees. These characteristics are called the amplitude balance degree and the phase balance degree, respectively.

With regard to the amplitude balance and phase balance, the surface acoustic wave device having the balance-unbalance conversion function is considered as a 3-port device. For example, the unbalanced input terminal is port 1, and each balanced output terminal is When port 2 and port 3 are set, amplitude balance = | A |, A = | 20logS21 | − | 2
0logS31 |, phase balance = | B−180 |, B = | ∠S21−∠S3
1 | is defined. Such a balance degree is ideally set such that the amplitude balance degree is 0 dB and the phase balance degree is 0 degree in the pass band of the filter.

[0013]

However, as shown in FIG.
In order to obtain a surface acoustic wave device having a balanced-to-unbalanced conversion function with such a configuration, in the surface acoustic wave filter 108, the electrode fingers connected to the ground are opposed to each other at the facing portions of the IDTs adjacent to each other. Since the electric charges are not picked up at this portion because they face each other, in the surface acoustic wave filter 117, the IDs that are adjacent to each other.
At the facing portion of T, the electrode finger connected to the ground and the electrode finger connected to the signal terminal face each other, so that charge pickup is performed at this portion.

Therefore, in the above-described conventional art, there is a problem in that the surface acoustic wave filter 108 and the surface acoustic wave filter 117 have different resonance mode intervals, which deteriorates the balance.

[0015]

In order to solve the above-mentioned problems, the surface acoustic wave device of the present invention has an ID on a piezoelectric substrate.
A surface acoustic wave filter having a plurality of Ts is provided for balanced-unbalanced input / output by two or more, and in the surface acoustic wave filter, an IDT whose phase is inverted for balance-unbalanced input / output is provided. It is characterized in that the electrode fingers located in the outermost region are thinned out.

According to the above configuration, by thinning out the electrode fingers located in the outermost region of the IDT whose phase is inverted with respect to the others for balanced-unbalanced input / output, the IDTs adjacent to each other are thinned.
In the facing part of, the electrode fingers connected to the ground are faced to each other, or conversely, the electrode finger connected to the ground and the electrode finger connected to the signal terminal are faced to each other. You can change the presence / absence of surface acoustic wave excitation with your finger.

Therefore, in the above configuration, in two or more surface acoustic wave filters for balanced-unbalanced input / output, the excitation relations of the surface acoustic waves at the facing portions are brought closer to each other and the spacing between resonance modes is increased. The difference can be reduced, and thus the balance can be improved.

In the surface acoustic wave device, it is preferable that the dummy electrode finger is provided at a thinned position and connected to the ground.

In the above-mentioned surface acoustic wave device, it is desirable that the dummy electrode fingers connect the electrode fingers, which are connected to the ground, of the IDTs adjacent to each other.

In the surface acoustic wave device, the surface acoustic wave resonator may be connected to the surface acoustic wave filter in at least one of series and parallel.

In the above-mentioned surface acoustic wave device, it is preferable that the surface acoustic wave filter is a longitudinally coupled type.

In the surface acoustic wave device, the surface acoustic wave filter has three or more IDTs formed on the piezoelectric substrate along the propagation direction of the surface acoustic wave for balanced-unbalanced input / output. By reversing the direction of the first surface acoustic wave filter and the IDT connected to the input side or the output side, which has three or more IDTs formed along the propagation direction of the surface acoustic wave on the piezoelectric substrate. The second surface acoustic wave filter is different from the first surface acoustic wave filter in the transmission phase characteristic by about 180 degrees.
And a surface acoustic wave filter, wherein one terminal of each of the first and second surface acoustic wave filters is electrically connected in parallel, and the other terminal is electrically connected in series and connected in parallel. The terminals may be unbalanced terminals, and the terminals connected in series may be balanced terminals.

In order to solve the above problems, another surface acoustic wave device of the present invention is capable of balanced-unbalanced input / output with two or more surface acoustic wave filters having a plurality of IDTs on a piezoelectric substrate. In each surface acoustic wave filter,
It is characterized in that the number of electrode fingers to which surface acoustic waves are not excited is set to be equal to each other.

According to the above structure, in each surface acoustic wave filter, the number of electrode fingers between which surface acoustic waves are not excited is
Since they are set to have the same number as each other, the excitation relationship of surface acoustic waves in two or more surface acoustic wave filters for balanced-unbalanced input / output is brought closer to each other to reduce the difference in resonance mode. Therefore, the degree of balance can be improved.

In order to solve the above-mentioned problems, a communication device of the present invention is characterized by having any one of the surface acoustic wave devices described above.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION The following will describe each embodiment of the present invention in reference to FIGS. 1 to 16.

First Embodiment of Surface Acoustic Wave Device According to the Present Invention
In the description of the mode, the reception filter for EGSM will be described as an example. In the first embodiment, for example, the first and second surface acoustic wave filters 1 and 2 are formed of aluminum (Al) electrodes on the piezoelectric substrate 30 made of, for example, 40 ± 5 ° YcutX propagation LiTaO _3. There is.

In the configuration of the first embodiment of the present invention, for each configuration having the same function as the configuration of the conventional example, as shown in FIG. 1, each configuration used in the description of the conventional example shown in FIG. The last two digits of the member numbers added to the above are added to omit the basic description thereof. In each of the embodiments, 0 is omitted from the member numbers such as 01. The detailed design is shown below. Crossover width: 25.2 λI ₁ Number of IDTs (in order of 4, 3, 5): 23 (4) / (4) 2
6 (4) / 23 (4) (number of electrode fingers with narrow pitch in parentheses) IDT wavelength λI ₁ : 4.204 μm, λI ₂ : 3.85
4 μm (λI ₁ is the part where the pitch is not narrowed, λI ₂
Is a portion where the pitch is narrowed) Reflector wavelength λR: 4.279 μm Number of reflectors: 90 IDT-IDT interval: Place sandwiched between electrode fingers of wavelength λI ₁ and wavelength λI ₂ : 0.
25λI ₁ + 0.25λI ₂ Location sandwiched between electrode fingers of wavelength λI ₂ : 0.50λI ₂ IDT-reflector spacing: 0.470λR IDTduty: 0.720 reflector duty: 0.55 Electrode film thickness: 0.08λI ₁ is there.

The feature of the first embodiment is that the IDT 23 is inverted in order to make the transmission phase characteristics of the surface acoustic wave filter 17a different from the surface acoustic wave filter 8 by 180 degrees.
One of the electrode fingers located at both ends (outermost region) along the propagation direction of the surface acoustic wave in a and connected to the unbalanced terminal 31 was thinned, and the thinned portion was connected to the ground. The point is that the dummy electrode fingers 23b are provided.

The effects based on such characteristics will be described below. FIG. 2 shows a graph of amplitude balance with respect to frequency change in the configuration of the first embodiment. For comparison, the result of the conventional example of FIG. 17 is also shown in FIG. EGSM-
The frequency range of the pass band in Rx is 925 MHz to 9
It is 60 MHz. The maximum amplitude balance in this range is 1.4 dB in the conventional example, whereas it is 0.6 dB in the first embodiment, and the amplitude balance of 0.8 dB is improved compared to the conventional example.

This effect will be described below. In order to form a pass band in the 3IDT type longitudinally coupled resonator type surface acoustic wave filter as in this embodiment, FIG.
As shown in (3), three resonance modes are used.

FIG. 3A shows frequency characteristics measured by intentionally making the input and output impedances in a mismatched state in order to make the resonance mode easy to understand. The points indicated by A, B, and C are the resonance frequencies of each resonance mode. The intensity distribution of the active current in each resonance mode is shown in FIG. The response in the center of the band corresponding to point B is called the secondary mode,
It is a resonance mode having two nodes in the effective current distribution.

The response with the lowest frequency corresponding to point A is called the 0th-order mode, which is a resonance mode showing no nodes in the effective current intensity distribution. The highest frequency response at point C is the standing wave resonance mode having the peak of the surface acoustic wave intensity distribution in the IDT-IDT interval. This 3
In the resonance mode seen in the center of the band of the two resonance modes and the resonance mode seen in the high band side, the effective current intensity of the surface acoustic wave in the IDT-IDT interval is also large, and the excitation of the surface acoustic wave in this part Very susceptible to the presence or absence of received waves.

Excitation of the surface acoustic wave is performed between the electrode fingers when the electrode fingers having different polarities are adjacent to each other. In Figure 4,
In the case of the conventional example shown in FIG. 17, each surface acoustic wave filter 1
The state of excitation of the surface acoustic wave in the vicinity of the IDTs adjacent to each other in 01 and 102 (regions adjacent to and facing each other, which are surrounded by a circle in FIG. 17) is illustrated. In FIG. 4, only three electrode fingers are shown from the end of the portion where the IDTs are adjacent to each other, and the other electrodes are omitted. IDTs 103, 104, and 105 in FIG.
In 502 and 503, IDTs 123, 124 and 125 are I
It corresponds to DT504, 505, and 506, respectively.
In FIG. 4, the part marked with a circle indicates that the surface acoustic wave is excited, and the part marked with a x indicates that the surface acoustic wave is not excited.

In the case of the conventional example shown in FIG. 17, in the first surface acoustic wave filter 101, the IDTs 103, 104,
Since the outermost electrode fingers of each 105 are connected to the ground, the surface acoustic waves are not excited in the respective IDT-IDT gap portions.

On the other hand, in the second surface acoustic wave filter 102, I at the center of the first surface acoustic wave filter 101.
Since the transmission phase characteristic of the first surface acoustic wave filter 101 is different from that of the first surface acoustic wave filter 101 by about 180 degrees by the central IDT 123 whose direction is inverted, the central IDT 12
The outermost electrode fingers of 3 are connected to the signal terminals, and the outermost electrode fingers of the IDTs 124 and 125 on both sides are connected to the ground.

Therefore, the second surface acoustic wave filter 10
In 2 unlike the case of the first surface acoustic wave filter 101, the surface acoustic wave is excited also in the respective IDT-IDT gap portions, and when comparing the whole surface acoustic wave filter, the first surface acoustic wave Surface wave filter 10
As compared with 1, the second surface acoustic wave filter 102 has two more places where surface acoustic waves are excited. In other words, the first surface acoustic wave filter 101 and the second surface acoustic wave filter 102 differ in the number of places (non-excitation regions) where surface acoustic waves are not excited between adjacent electrode fingers. Was.

Therefore, in the conventional example, the first surface acoustic wave filter 101 and the second surface acoustic wave filter 10 are used.
2 and 3, the distribution of the effective current intensity of the surface acoustic wave in the IDT-IDT interval part is different, and as a result,
Of the two resonance modes, the interval between the resonance mode seen at the center of the band and the resonance mode seen at the high band side is different, and the degree of balance between the balanced terminals 132 and 133 is deteriorated.

Next, FIG. 5 shows the first and second surface acoustic wave filters 1 and 2 in the case of the first embodiment shown in FIG.
7 illustrates the situation of the surface acoustic wave excitation in the vicinity where the IDTs are adjacent to each other (a region portion surrounded by a circle in the drawing, which is adjacent to and faces each other).

Also in FIG. 5, as in the case of FIG.
DT shows only three electrode fingers from the edge of the adjacent part,
Others are omitted.

In the case of the first embodiment, by inverting the direction of the IDT 23a connected to the input side, the second surface acoustic wave filter 1 has a transmission phase characteristic different from that of the second surface acoustic wave filter 1 by about 180 degrees. In the surface wave filter 2, the outermost electrode finger of the IDT 23a connected to the signal terminal on the input side is thinned out, and a dummy electrode 23b is provided at that portion and is connected to the ground.

Therefore, in the second surface acoustic wave filter 2, in one of the IDT-IDT gap portions 40, the electrode fingers connected to the signal terminals and the electrode fingers connected to the ground are alternately arranged, so that the elasticity is increased. Surface waves are excited,
In the other IDT-IDT gap part 41,
Since three electrode fingers connected to the ground are lined up, two portions where surface acoustic waves are not excited occur.

As a result, in the first surface acoustic wave filter 1 and the second surface acoustic wave filter 2, the total number of places where the surface acoustic wave is not excited between the electrode fingers, that is, the surface acoustic wave between the electrode fingers. Since the total number of excited points becomes equal to each other, the difference between the resonance mode intervals becomes smaller than that in the conventional example, and the degree of amplitude balance between the balanced terminals 32 and 33 is improved.

In the first embodiment, the first embodiment in which the 3IDT type longitudinally coupled resonator type surface acoustic wave filters are connected in a two-stage cascade manner is used.
The surface acoustic wave filter 1 and the second surface acoustic wave filter 1 having a transmission phase characteristic different by about 180 degrees from the first surface acoustic wave filter 1 by reversing the direction of the central IDT 23a connected to the input side of the first stage. The surface acoustic wave filter 2 of FIG.
The central IDTs 3 and 23a are connected in parallel to form an unbalanced terminal 31, and the central IDTs 9 and 29 of the second-stage longitudinally coupled resonator type surface acoustic wave filters 14 and 18 are connected in series. In the above description, the configuration in which the balanced terminals 32 and 33 are formed has been described, but the present invention is not limited to this configuration.

The present invention can be applied to any surface acoustic wave filter having a balanced terminal and having an inverted ID.
Thinning out the electrode fingers connected to the signal terminals in the outermost region of T,
The same effect can be obtained by providing a dummy electrode finger connected to the ground at the position where it is thinned out.

For example, as shown in FIG. 6, a first surface acoustic wave filter 1 in which three IDT type longitudinally coupled resonator type surface acoustic wave filters 8 and 14 are connected in a two-stage cascade, and a first surface acoustic wave filter 1 are provided. By transmitting the first surface acoustic wave filter 1 by reversing the direction of the central IDT 29a of the longitudinally coupled resonator type surface acoustic wave filter 18a connected to the output side of the second stage with respect to the surface acoustic wave filter 1. A second surface acoustic wave filter 2a having a different phase characteristic of about 180 degrees is provided, and the central IDTs 3 of the longitudinally coupled resonator type surface acoustic wave filters 8 of the first stage are connected in parallel. Each of the surface acoustic wave filters 1 of the second-stage longitudinally coupled resonator type constitutes the balanced terminal 31.
Even when the central IDTs 9 and 29a of 4 and 18a are connected in series to form the balanced terminals 32 and 33, respectively, the IDT 29a
In the surface acoustic wave device, the outermost electrode fingers connected to the signal terminals may be thinned out and dummy electrode fingers 29b may be provided in the thinned out portions to connect to the ground.

As a result, the state of the surface acoustic wave excitation around the IDT-IDT gap of the output side surface acoustic wave filter (the portion circled in FIG. 6) is as shown in FIG.
In the first surface acoustic wave filter 1 and the second surface acoustic wave filter 2a, the total number of places where surface acoustic waves are not excited between electrode fingers, that is, the total number of places where surface acoustic waves are excited between electrode fingers. Are equal, so each balanced terminal 32,
The amplitude balance between 33 is improved.

Further, instead of the central IDT 29 of the second IDT 3 shown in FIG. 7, as shown in FIG. 8, the transmission phase characteristics are approximated by inverting the directions of the outer IDTs 40a and 41a. Even when different from each other by 180 degrees, the outermost electrode finger of one of the IDTs 40a and 41a whose directions are reversed is thinned out, and a dummy electrode finger 41b is provided at that portion, and the elastic surface is connected to the ground. It may be a wave device.

As a result, the situation of the surface acoustic wave excitation around the IDT-IDT gap of each of the output surface acoustic wave filters 14 and 18b (the portion circled in FIG. 8) is as shown in FIG. In the first surface acoustic wave filter 1 and the second surface acoustic wave filter 2b, the total number of locations where surface acoustic waves are not excited between the electrode fingers, that is, the locations where surface acoustic waves are excited between the electrode fingers are Since the total numbers are equal, the degree of amplitude balance between the balanced terminals 32 and 33 is improved.

Further, as shown in FIG. 10, instead of the 3IDT resonator type surface acoustic wave filter shown in FIG.
Even when the IDT type resonator type surface acoustic wave filter is used, the electrode fingers located on the outermost side of one side of the IDT of the IDT 1101 whose direction is reversed are thinned out, and dummy electrode fingers 1102 are provided in that portion. In the first surface acoustic wave filter 1103 and the second surface acoustic wave filter 1104, which are provided and connected to the ground, the total number of places where surface acoustic waves are not excited between the electrode fingers, that is, the surface acoustic waves between the electrode fingers. Since the total number of points where the waves are excited becomes equal, the degree of amplitude balance between the balanced terminals 32 and 33 is improved.

Next, regarding the second embodiment of the present invention,
A DCS reception filter will be described as an example with reference to FIG. In the second embodiment, for example, 40 ± 5 °
Each surface acoustic wave filter is formed by an Al electrode on a piezoelectric substrate 30 made of YcutX propagation LiTaO ₃ . A comparative example with respect to the second embodiment is shown in FIG.
The configuration of the second embodiment and the configuration of the comparative example are reversed I
It is basically the same except that the outermost electrode finger connected to the signal terminal in the DT is thinned out and a dummy electrode finger connected to the ground is provided at that position. The detailed design is shown below. [Vertical coupling resonator type surface acoustic wave filter 1207, 1
208] Crossover width: 37.12λI ₁ Number of IDTs (in the order of 1204, 1205, 1206):
(4) 19 / (4) 31 (4) / 19 (4) (number of electrode fingers with narrow pitch in parentheses) IDT wavelength λI ₁ : 2.156 μm, λI ₂ : 1.92
6 μm (λI ₁ is the part where the pitch is not narrowed, λI ₂
Is a portion where the pitch is narrowed) Reflector wavelength λR: 2.177 μm Number of reflectors: 150 IDT-IDT interval: Place between electrode fingers of wavelength λI ₁ and wavelength λI ₂ : 0.
25λI ₁ + 0.25λI ₂ Place between electrode fingers of wavelength λI ₂ : 0.50λI ₂ IDT-reflector interval: 0.50λR IDTduty: 0.63 Reflector duty: 0.60 Electrode film thickness: 0.09λI ₁ [ Surface acoustic wave resonator 1202] Crossing width: 14.3 λI Number of IDTs: 241 IDT wavelength (λI) and reflector wavelength (λR):
2.102 μm Number of reflectors: 30 IDT-reflector interval: 0.50λR [SAW resonator 1203] Crossing width: 37.1λI Number of IDTs: 241 IDT wavelength (λI) and reflector wavelength (λR):
2.023 μm Number of reflectors: 30 IDT-reflector interval: 0.50λR.

The feature of the second embodiment is that the ID is inverted in order to make the transmission phase characteristic of the surface acoustic wave filter 1208 different from the surface acoustic wave filter 1207 by 180 degrees.
A dummy electrode finger 1210 located at the end of T1209 and connected to the signal terminal is thinned out and a dummy electrode finger 1210 connected to the ground is provided at that portion.
The point is that the electrode finger on the ground side of the central IDT 1209 is connected to the ground via 10.

Next, the effect of the second embodiment will be described. FIG. 13 shows a graph of amplitude balance with respect to frequency change in the configuration of the second embodiment. As a comparison,
The results of Comparative Example 2 are also shown. The frequency range of the pass band in DCS-Rx is 1805 MHz to 1880 MHz. The maximum amplitude balance in this range is 3.3 in the comparative example.
In contrast to dB, 1.5 dB in the second embodiment.
Then, the 1.8 dB amplitude balance is improved.

This is similar to the case of the first embodiment,
In the comparative example shown in FIG. 12, as shown in FIG. 14, the number of places where surface acoustic waves are excited around the IDTs adjacent to each other (the portion surrounded by circle in FIG. 12) is the first surface acoustic wave filter. Whereas 1301 and the second surface acoustic wave filter 1302 are different, in the case of the second embodiment, as shown in FIG. 15, the periphery where the IDTs are adjacent to each other (the portion circled in FIG. 11). The number of points where surface acoustic waves are excited is the first
Since the surface acoustic wave filter 1207 of FIG. 3 and the second surface acoustic wave filter 1208 are the same, the resonance mode seen in the center of the three resonance modes shown in FIG. This is because the interval of is closer to that of the comparative example and the degree of balance between the balanced terminals 32 and 33 is improved.

As described above, in the present invention, three or more IDTs formed on the piezoelectric substrate along the surface acoustic wave propagation direction.
And a three or more IDs formed on the piezoelectric substrate along the propagation direction of the surface acoustic wave.
And a second surface acoustic wave filter having a transmission phase characteristic different from that of the first surface acoustic wave filter by about 180 degrees by inverting the direction of the IDT connected to the input side or the output side. One terminal of each of the first and second surface acoustic wave filters is electrically connected in parallel, the other terminal is electrically connected in series, and the terminals connected in parallel are an unbalanced terminal and a series terminal. In a surface acoustic wave device in which a balanced terminal is constituted by terminals connected to, by thinning out electrode fingers located on the outermost side of the IDT whose direction is reversed in the second surface acoustic wave filter and connected to the signal terminal, It is possible to realize a surface acoustic wave filter having a balanced-unbalanced conversion function with improved balance between balanced signal terminals.

Next, a communication device using the surface acoustic wave device described in each of the above embodiments will be described with reference to FIG. The communication device 600 is a receiver side (R
x side), an antenna 601, an antenna common part / RF
Top filter 602, amplifier 603, Rx interstage filter 604, mixer 605, 1st IF filter 606,
Mixer 607, 2nd IF filter 608, 1st + 2
nd local synthesizer 611, TCXO (temperat
A ure compensated crystal oscillator 612, a divider 613, and a local filter 614 are provided.

Rx interstage filter 604 to mixer 605
It is preferable to transmit each balanced signal in order to secure balance, as shown by the double line in FIG.

Further, the communication device 600 uses the antenna 601 as the transceiver side (Tx side) for transmission.
And the antenna sharing unit / RFTop filter 602 are shared, and the TxIF filter 621 and the mixer 6 are also provided.
22, Tx interstage filter 623, amplifier 624, coupler 625, isolator 626, APC (automatic powe)
r control (automatic output control) 627.

Then, the above Rx interstage filter 604,
1stIF filter 606, TxIF filter 621,
For the Tx interstage filter 623, the surface acoustic wave device described in the first and second embodiments of the present embodiment described above can be preferably used.

The surface acoustic wave device according to the present invention has an unbalanced-balanced conversion function as well as a filter function, and further,
It has an excellent characteristic that the amplitude characteristic between each balanced signal is closer to the ideal. Therefore, the communication device of the present invention including the surface acoustic wave device can improve the transmission characteristics.

[0061]

As described above, in the surface acoustic wave device of the present invention, two or more surface acoustic wave filters having a plurality of IDTs are provided on the piezoelectric substrate for balanced-unbalanced input / output. In the surface acoustic wave filter, the electrode fingers located in the outermost region of the IDT, whose phase is inverted from the others for balanced-unbalanced input / output, are thinned out.

Therefore, in the above configuration, the excitation relationship of the surface acoustic waves at the facing portion of each IDT in each surface acoustic wave filter can be brought closer to each other to reduce the difference in the spacing of the resonance modes, so that the degree of balance can be improved. It has the effect of being able to improve.

[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 graph showing the degree of amplitude balance between the conventional example and the first embodiment.

3A and 3B are explanatory diagrams showing a frequency relationship of a resonance mode and an active current distribution, FIG. 3A is a graph showing a frequency characteristic of insertion loss, and FIG. 3B is a schematic configuration diagram of a surface acoustic wave device; It is a graph which shows a resonance mode.

FIG. 4 is a schematic configuration diagram showing a situation of surface acoustic wave excitation in the vicinity of IDTs adjacent to each other in a conventional example.

FIG. 5 is a schematic configuration diagram showing a situation of surface acoustic wave excitation in the vicinity of the IDTs adjacent to each other in the first embodiment.

FIG. 6 is a schematic configuration diagram of a surface acoustic wave device according to a modification of the first embodiment.

FIG. 7 is a schematic configuration diagram showing a state of surface acoustic wave excitation in the vicinity of IDTs adjacent to each other in the above modification.

FIG. 8 is a schematic configuration diagram of a surface acoustic wave device according to another modification of the first embodiment.

FIG. 9 is a schematic configuration diagram showing a situation of surface acoustic wave excitation in the vicinity of the IDTs adjacent to each other in the other modification example.

FIG. 10 is a schematic configuration diagram of a surface acoustic wave device according to still another modification of the first embodiment.

FIG. 11 is a schematic configuration diagram of a surface acoustic wave device according to a second embodiment of the invention.

FIG. 12 is a schematic configuration diagram of a surface acoustic wave device of a comparative example with respect to the second embodiment.

FIG. 13 is a graph showing frequency characteristics of amplitude balance between the second embodiment and the comparative example.

FIG. 14 is a schematic configuration diagram showing a situation of surface acoustic wave excitation in the vicinity of adjacent IDTs in the comparative example.

FIG. 15 is a schematic configuration diagram showing a situation of surface acoustic wave excitation in the vicinity of adjacent IDTs in the second embodiment.

FIG. 16 is a circuit block diagram of a main part of a communication device of the present invention.

FIG. 17 is a schematic configuration diagram showing a conventional surface acoustic wave device.

[Explanation of symbols]

8, 14, 17a, 18 Surface acoustic wave filter 23a IDT (comb-shaped electrode part) 23b Dummy electrode finger 30 Piezoelectric substrate

Claims (8)

[Claims] 1. A surface acoustic wave filter having a plurality of comb-shaped electrode portions is provided on a piezoelectric substrate so as to allow balanced-unbalanced input / output by two or more electrodes. A surface acoustic wave device characterized in that electrode fingers located in the outermost region of a comb-shaped electrode portion whose phase is inverted for output are thinned out. 2. A dummy electrode finger is provided in a thinned-out position so as to be connected to the ground.
The surface acoustic wave device described. 3. The surface acoustic wave device according to claim 2, wherein the dummy electrode fingers connect the electrode fingers connected to the ground in the adjacent comb-shaped electrode portions. 4. The surface acoustic wave resonator according to claim 1, wherein a surface acoustic wave resonator is connected to the surface acoustic wave filter in at least one of series and parallel. Surface wave device. 5. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave filter is a longitudinally coupled type. 6. A surface acoustic wave filter having a first and a third comb-shaped electrode portions formed on a piezoelectric substrate along a propagation direction of a surface acoustic wave for balanced-unbalanced input / output. A surface acoustic wave filter and three or more comb-shaped electrode portions formed on the piezoelectric substrate along the propagation direction of the surface acoustic wave. The direction of the comb-shaped electrode portion connected to the input side or the output side is reversed. Therefore, the first surface acoustic wave filter has a second surface acoustic wave filter having a transmission phase characteristic different by about 180 degrees, and one terminal of each of the first and second surface acoustic wave filters is electrically connected. 4. The parallel connection, the other terminal is electrically connected in series, the parallel connection terminals are unbalanced terminals, and the series connection terminals are balanced terminals. 5. The surface acoustic wave device according to any one of items 1 to 5. Place 7. A surface acoustic wave filter having a plurality of comb-shaped electrode portions is provided on a piezoelectric substrate so as to allow balanced / unbalanced input / output by two or more, and the surface acoustic wave in each surface acoustic wave filter is A surface acoustic wave device, wherein the number of electrode fingers that are not excited is set to be the same as each other. 8. A communication device comprising the surface acoustic wave device according to claim 1. Description: