JP2001292050A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave filter with an excellent characteristic that can attain balanced operation under various impedance values. SOLUTION: In a 3-electrode type interdigital electrode 15 where a 1st interdigital electrode 11 is placed on a piezoelectric substrate 10 and 2nd and 3rd interdigital electrodes 12, 13 are placed at both sides in a surface wave propagation direction, and a reflector electrode 14 is placed at both sides of the electrode 15, the 1st interdigital electrode 11 is split around its middle, electrode fingers 11a, 11b are connected to balance input terminals 16a, 16b of a package, one electrode finger of the 2nd and 3rd interdigital electrodes 12, 13 is connected to an earth terminal 18 of the package, the other is connected to an unbalanced output terminal 17, and splitting the 1st interdigital electrode 11 around its mid-position can increase the impedance of the balanced input terminals 16a, 16b by a multiple of 4 in comparison with that before the splitting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter used for a high-frequency circuit or the like in a wireless communication device.

[0002]

2. Description of the Related Art A conventional longitudinal mode coupling type balanced-unbalanced surface acoustic wave filter will be described below.

FIG. 12 is a top view of a conventional longitudinal mode coupling type surface acoustic wave filter. On the piezoelectric substrate 140, three-electrode-type comb electrodes 141 and 142 (portions surrounded by dotted lines in the drawing) are connected in cascade. The three-electrode-type comb electrodes 141 and 142 are a first comb-shaped electrode 143a, 144a, a second comb-shaped electrode 143b, 144b, and a third comb-shaped electrode 143c, 144, respectively.
c (portions surrounded by dotted lines) and reflector electrodes 145 on both sides thereof are arranged in the surface acoustic wave propagation direction. The first comb-shaped electrode 143a of the three-electrode-type comb electrode 141 has both opposing electrode fingers connected to the balanced input / output terminals 146a and 146b. Is connected to the unbalanced output terminal 147, and the other is connected to the ground terminal 148. The first comb electrode 143a of the three-electrode comb electrode 141, the three-electrode comb electrode 1
A surface wave is excited by applying a voltage between the first comb-shaped electrodes 144a, and a filter characteristic is formed by confining energy between the reflector electrodes 145.

[0004] By forming such a filter, for example, a balanced-unbalanced surface acoustic wave filter having an input and output impedance of 50Ω has been obtained.

[0005]

However, in the conventional surface acoustic wave filter, it is difficult to freely change the impedance at the balanced end, and it is very difficult to cope with various kinds of circuits. However, there is a problem that it is necessary to use a matching circuit outside the device or to use an unbalanced-balanced conversion component.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface acoustic wave filter capable of performing a balanced operation of various impedances without using a matching circuit or an unbalanced-balanced conversion part and having good characteristics. Is what you do.

[0007]

To achieve this object, a surface acoustic wave filter according to the present invention comprises a piezoelectric substrate, a first comb-shaped electrode formed on the piezoelectric substrate, and a first comb-shaped electrode. It has second and third comb-shaped electrodes provided on both sides in the surface wave propagation direction, and a reflector electrode provided so as to sandwich the second and third comb-shaped electrodes, and divides the first comb-shaped electrode. In addition, both opposing electrode fingers are used as an input electrode or an output electrode as balanced input or balanced output, and one of the opposing electrode fingers of the second and third comb electrodes is output when the first comb electrode is an input electrode. When the first comb-shaped electrode is an output electrode, the first comb-shaped electrode is used as an input electrode. The impedance at the balanced end is within a range of 1 to 4 times (excluding 1) the impedance of the first comb-shaped electrode before division. Since it can be set arbitrarily, It is possible to achieve the purpose.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a piezoelectric substrate, a first comb-shaped electrode formed on the piezoelectric substrate, and both sides of the first comb-shaped electrode in the surface wave propagation direction. And a reflector electrode provided so as to sandwich the second and third comb-shaped electrodes.
And the opposing electrode fingers are used as input electrodes or output electrodes for balanced input or balanced output, and one of the opposing electrode fingers of the second and third comb electrodes is connected to the first comb electrode. Output electrode for input electrode,
When the first comb-shaped electrode is an output electrode, the first comb-shaped electrode is a surface acoustic wave filter used as an input electrode, and the impedance of a balanced input or balanced output terminal can be set to a desired value.

According to a second aspect of the present invention, the width of the electrode dividing the first comb-shaped electrode is λ (λ / 2 = the electrode finger width of the first comb-shaped electrode + the electrode of the first comb-shaped electrode. 2. The surface acoustic wave filter according to claim 1, wherein
The surface wave excitation and the energy confinement state of the reflector electrode are improved.

According to a third aspect of the present invention, there is provided a piezoelectric substrate, a first comb-shaped electrode formed on the piezoelectric substrate, and second and second electrodes provided on both sides of the first comb-shaped electrode in the surface wave propagation direction. And a three-electrode-type comb electrode provided with three comb-shaped electrodes and a reflector electrode provided so as to sandwich the second and third comb-shaped electrodes, and cascade-connected to the three-electrode-type comb electrode on the piezoelectric substrate. At least one of the input electrode and the output electrode is a balanced input or a balanced output, and the comb-shaped electrode serving as the balanced input or the balanced output is a divided surface acoustic wave filter, The amount of attenuation is large.

According to a fourth aspect of the present invention, there is provided the surface acoustic wave filter according to the third aspect, wherein both the input electrode and the output electrode are of a balanced type, and the comb-shaped electrodes serving as the input electrode and the output electrode are divided. And the impedance of the balanced output terminal can be set to a desired value.

According to a fifth aspect of the present invention, the width of the electrode dividing the comb-shaped electrode is not more than λ (λ / 2 = the width of the electrode finger of the comb-shaped electrode + the width of the electrode finger gap of the comb-shaped electrode). 3. The surface acoustic wave filter according to 3, wherein the surface acoustic wave excitation and the energy confinement state of the reflector electrode are improved.

According to a sixth aspect of the present invention, the filter connected to the three-electrode type comb electrode is a ladder type filter.
And the attenuation can be flexibly designed.

According to a seventh aspect of the present invention, there is provided a piezoelectric substrate, a first comb-shaped electrode formed on the piezoelectric substrate, and second and second electrodes provided on both sides of the first comb-shaped electrode in the surface wave propagation direction. 3 and a reflector electrode provided so as to sandwich the second and third comb-shaped electrodes. The second and third comb-shaped electrodes are divided and one of the electrode fingers is connected to the input electrode or the other. It is a surface acoustic wave filter that serves as an output electrode and has a balanced input or a balanced output, and can set the impedance of the balanced input or balanced output terminal to a desired value.

According to an eighth aspect of the present invention, the width of the electrode dividing the second and third comb-shaped electrodes is λ (λ / 2 = electrode finger width of the first comb-shaped electrode + the first comb-shaped electrode). The surface acoustic wave filter according to claim 7, wherein the width is not more than the electrode finger gap width of the electrode, and the surface wave excitation and the energy confinement state of the reflector electrode are improved.

According to a ninth aspect of the present invention, when the second and third comb-shaped electrodes are input electrodes, the first comb-shaped electrode is used as an output electrode for balanced output, and the second and third comb-shaped electrodes are used as output electrodes. 8. In the case of an electrode, the surface acoustic wave filter according to claim 7, wherein the first comb-shaped electrode is a parallel input as an input electrode, and the first comb-shaped electrode is also divided. It can be a desired value.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG. 1 is a top view of a surface acoustic wave filter according to Embodiment 1 of the present invention.

Reference numeral 10 denotes a piezoelectric substrate, 11 denotes a first comb-shaped electrode (portion surrounded by a dotted line in the figure), 11a and 11b denote electrode fingers constituting the first comb-shaped electrode 11, 12 denotes a second comb-shaped electrode,
13 is a third comb-shaped electrode, 14 is a reflector electrode, 15 is a three-electrode type comb electrode (portion surrounded by a dotted line in the figure), 16a and 16b
Is a balanced input terminal, 17 is an unbalanced output terminal, and 18 is a ground terminal.

A first comb-shaped electrode 11 on a piezoelectric substrate 10 and second and third comb-shaped electrodes 12 on both sides in the surface wave propagation direction.
In the three-electrode type comb electrode 15 provided with the reflector electrodes 14 on both sides thereof, the first comb-shaped electrode 11 is divided near the center, and the opposing electrode fingers 11a and 11b are separated by the surface acoustic wave. It is connected to the balanced input terminals 16a and 16b of a package (not shown) that houses the filter. One of the opposing electrode fingers of the second and third comb electrodes 12 and 13 is connected to the ground terminal 18 of the package, and the other is connected to the unbalanced output terminal 17.

In this surface acoustic wave filter, if the capacitance of the first comb-shaped electrode 11 before division is C0 and the capacitance of the first comb-shaped electrode 11 after division is C1, C1 ≒ C0 / 4. If the impedance of the first comb-shaped electrode 11 before division is Z0 and the impedance of the first comb-shaped electrode 11 after division is Z1, Z1 ≒ Z0 × 4.

That is, by dividing the first comb-shaped electrode 11 near the center, the impedance of the balanced input terminals 16a and 16b can be increased about four times as much as before the division. If the design of the three-electrode comb electrode 15 before the division of the first comb electrode 11 is 50Ω, the impedance of the balanced input terminals 16a and 16b is 200Ω by dividing the first comb electrode 11. A surface acoustic wave filter having an impedance of the unbalanced output terminal 17 of 50Ω can be obtained.

FIG. 2 shows the characteristics of the surface acoustic wave filter. It can be seen from FIG. 2 that the surface acoustic wave filter of the present embodiment has good characteristics.

In this surface acoustic wave filter, good characteristics are obtained when the balanced input terminals 16a and 16b are used as balanced output terminals and the unbalanced output terminal 17 is used as an unbalanced input terminal.

(Embodiment 2) FIG. 3 is a top view of a surface acoustic wave filter according to Embodiment 2 of the present invention.
Is a piezoelectric substrate, 31 is a first comb-shaped electrode (portion surrounded by a dotted line in the figure), 31a and 31b are electrode fingers, 32 is a second comb-shaped electrode, 33 is a third comb-shaped electrode, 34 is a reflector electrode, 35 is a three-electrode type comb electrode (portion surrounded by a dotted line), 36a, 36b
Is a balanced input terminal, 37 is an unbalanced output terminal, and 38 is a ground terminal. FIG. 4 shows the first comb-shaped electrode 31 shown in FIG.
FIG.

In the second embodiment, as in the first embodiment, a first comb-shaped electrode 31 is formed on a piezoelectric substrate 30 and second and third comb-shaped electrodes 32, 33 are formed on both sides in the surface wave propagation direction.
In a three-electrode comb electrode 35 having reflector electrodes 34 on both sides thereof, the first comb-shaped electrode 31 is divided at an arbitrary position as shown in FIG.
b is connected to the balanced input terminals 36a and 36b of a package (not shown) containing the surface acoustic wave filter. One of the opposing electrode fingers of the second and third comb-shaped electrodes 32 and 33 is connected to the ground terminal 38 of the package, and the other is connected to the unbalanced output terminal 37.

In such a surface acoustic wave filter,
The capacitance of the first comb-shaped electrode 31 before division is C0, and the capacitance of the first comb-shaped electrode 31 after division is C1, and the cross width (a, b) of the electrode fingers 31a, 31b after division as shown in FIG. )When,
Assuming that the ratio of the electrode fingers 31a and 31b before division to the intersection width (c) is n (a / c) and n-1 (b / c), C1 ≒ n
(1−n) × C0. If the impedance of the first comb-shaped electrode 31 before division is Z0 and the impedance of the first comb-shaped electrode 31 after division is Z1, Z1 ≒ Z0 ×
1 / n (1-n).

By dividing the first comb-shaped electrode 31 at an arbitrary position in this manner, the balanced input terminals 36a, 36b
Is 1 to 4 times or less (1
) Can be obtained.

This surface acoustic wave filter also has excellent characteristics similarly to the surface acoustic wave filter shown in the first embodiment.

In this surface acoustic wave filter,
Similar good characteristics are obtained when the balanced input terminals 36a and 36b are used as balanced output terminals and the unbalanced output terminal 37 is used as an unbalanced input terminal.

(Embodiment 3) FIG. 5 is a top view of a surface acoustic wave filter according to Embodiment 3 of the present invention.
Is a piezoelectric substrate, 41 is a three-electrode comb electrode (portion surrounded by a dotted line in the figure), 42 is a filter composed of the same three-electrode comb electrode, and 43 and 43a are first comb electrodes (43 is a portion surrounded by a dotted line). ) And 44 are second comb electrodes, 45 is third comb electrodes, 46 is reflector electrodes, 47a and 47b are electrode fingers, 48
a and 48b are balanced input terminals, 48c is an unbalanced output terminal,
49a, 49b and 49c are ground terminals, and 50 is a split electrode.

On the piezoelectric substrate 40, a three-electrode type comb electrode 41 and a filter 42 are connected in cascade. The three-electrode comb electrode 41 is the first
, And second and third comb-shaped electrodes 44 and 45 arranged on both sides in the surface wave propagation direction, and a reflector electrode 46 is provided on both sides thereof. The first comb-shaped electrode 43 is divided near the center, and the two opposing electrode fingers 47a,
47b is connected to balanced input terminals 48a and 48b of a package (not shown) that accommodates the surface acoustic wave filter.

The filter 4 comprising a three-electrode type comb electrode
2 is composed of first, second, and third comb-shaped electrodes 43a, 44, and 45 and a reflector electrode 46, similarly to the three-electrode-type comb electrode 41. However, unlike the first comb electrode 43, the first comb electrode 43a is not divided. One electrode finger of the first comb-shaped electrode 43a of the filter 42 composed of the three-electrode-type comb electrode is connected to the unbalanced output terminal 48c of the package.
The other electrode finger is connected to a ground terminal 49b.

Further, a three-electrode type comb electrode 41 and a filter 42
Of the second comb-shaped electrode 44 are connected to each other, and the other electrode finger is connected to the ground terminal 49 of the package.
a, 49c. Similarly, the opposing electrode fingers of the three-electrode comb electrode 41 and the third comb electrode 44 of the filter 42 are connected, and the other electrode fingers are connected to the ground terminals 49a and 49c of the package, respectively.

FIG. 6 is a characteristic waveform diagram of the surface acoustic wave filter according to the third embodiment. Impedance is balanced 200
Ω and unbalanced 50 Ω, and it can be seen that the cascade connection of the three-electrode comb electrode 41 and the filter 42 results in a balanced-unbalanced surface acoustic wave filter having an excellent out-of-band attenuation.

Further, by dividing the first comb-shaped electrode 43 at an arbitrary position, the impedance of the balanced input terminals 48a and 48b is increased by 1 to 4 times (excluding 1) as before the division as in the second embodiment. It is also possible to set any value within the range.

FIG. 7 shows a characteristic waveform change in the third embodiment when the width (d) of the divided electrode 50 that divides the opposing electrode fingers 47a and 47b of the first comb-shaped electrode 43 is changed. ing. As can be seen from FIG. 7, it can be confirmed that the spurious in the pass band increases as the width of the split electrode 50 increases. This is because if the width of the split electrode 50 is large, the first comb-shaped electrode 43
The width d of the divided electrode 50 is λ (λ / 2 = comb electrode finger width +
(The width of the comb electrode finger gap).

The surface acoustic wave filter according to the third embodiment has the same good characteristics as the surface acoustic wave filter before the first comb-shaped electrode 43 is divided.

In this surface acoustic wave filter,
Good characteristics are obtained when the balanced input terminals 48a and 48b are used as balanced output terminals and the unbalanced output terminal 48c is used as an unbalanced input terminal.

(Embodiment 4) FIG. 8 is a top view of a surface acoustic wave filter according to Embodiment 4 of the present invention.
Is a piezoelectric substrate, 91 is a first comb-shaped electrode, 92 is a second comb-shaped electrode (portion surrounded by a dotted line in the figure), 92a is an electrode finger, 93
Is a third comb-shaped electrode (portion surrounded by a dotted line in the figure), 93a is an electrode finger, 94 is a reflector electrode, 95 is a three-electrode-type comb electrode (portion surrounded by a dotted line in the diagram), and 96a and 96b are balanced inputs. Terminal, 97 is an unbalanced output terminal, 98a, 98b, 98c are ground terminals, and 99 is a split electrode.

On the piezoelectric substrate 90, the second and third comb electrodes 92 and 93 are provided on both sides of the first comb electrode 91 in the surface wave propagation direction.
Are arranged, and in a three-electrode type comb electrode 95 provided with a reflector electrode 94 on both sides thereof, the second and third comb-shaped electrodes 92,
93 is divided near the center, and the second comb-shaped electrode 92
Electrode finger 92a and the electrode finger 93a of the third comb-shaped electrode 93
Are connected to the balanced input terminals 96b and 96a of a package (not shown) that houses the surface acoustic wave filter. The other electrode fingers of the second and third comb electrodes 92 and 93 are connected to the ground terminals 98b and 98c of the package.
Connected to One electrode finger of the first comb-shaped electrode 91 is connected to the unbalanced output terminal 97 of the package, and the other is connected to the ground terminal 98a.

In this surface acoustic wave filter, the impedance of the balanced input terminals 96a and 96b is about four times as compared with that before dividing the second and third comb-shaped electrodes 92 and 93. That is, by changing the division positions of the second and third comb-shaped electrodes 92 and 93, the impedance of the balanced input terminals 96a and 96b is set to an arbitrary size of 1 to 4 times (excluding 1) before the division. Can be. The width (d) of the divided electrode dividing the second and third comb-shaped electrodes 92 and 93 is limited to the surface wave excited by the second and third comb-shaped electrodes 92 and 93 and the energy of the reflector electrode 94. In order to minimize the effect on the effect, it is desirable that d = λ (λ / 2 = comb electrode finger width + comb electrode finger gap width) or less.

This surface acoustic wave filter has the same good characteristics as the surface acoustic wave filter before the second and third comb electrodes 92 and 93 are divided.

In this surface acoustic wave filter,
Similarly, when the average input terminals 96a and 96b are used as balanced output terminals and the unbalanced output terminal 97 is used as an unbalanced input terminal, good characteristics are obtained.

(Embodiment 5) FIG. 9 is a top view of a surface acoustic wave filter according to Embodiment 5 of the present invention.
0 is a piezoelectric substrate, 101 is a first comb-shaped electrode, and 102 is a second comb-shaped electrode.
(A portion surrounded by a dotted line in the figure), 102a is an electrode finger, 103 is a third comb-shaped electrode (a portion surrounded by a dotted line in the figure), 103a is an electrode finger, 104 is a reflector electrode, 105
Is a three-electrode type comb electrode (portion surrounded by a dotted line in the figure), 106
a and 106b are balanced input terminals, 107 is an unbalanced output terminal, 108a, 108b and 108c are ground terminals,
9 is a split electrode.

On the piezoelectric substrate 100, the first comb-shaped electrode 10
The second and third comb-shaped electrodes 10 on both sides in the direction of propagation of the surface acoustic wave.
2 and 103 and reflector electrodes 104 on both sides thereof.
, The second and third comb-shaped electrodes 102 and 103 are divided at an arbitrary position, and the electrode finger 102 on one side of the opposing electrode finger of the second comb-shaped electrode 102 is provided.
a and the electrode finger 103a on one side of the opposing electrode finger of the third comb-shaped electrode 103 are connected to the balanced input terminals 106b and 106 of a package (not shown) for accommodating the surface acoustic wave filter.
6a. Also, connect the other electrode finger to ground terminal 1
08b, 108c.

Further, one electrode finger of the first comb-shaped electrode 101 is connected to the ground terminal 108a, and the other electrode finger is connected to the unbalanced output terminal 107.

That is, the surface acoustic wave filters of the fifth and fourth embodiments are the second and third comb-shaped electrodes 102, 1
The configuration is the same except that the division position of 03 is different.

As shown in the surface acoustic wave filter shown in FIG.
By dividing the second and third comb electrodes 102 and 103 at arbitrary positions, balanced input terminals 106a and 106b
Of the second and third comb electrodes 102 and 10
3 can be set to any value within the range of 1 to 4 times (excluding 1) the impedance of the balanced input terminal in the surface acoustic wave filter before being divided at an arbitrary position.

Further, the second and third comb-shaped electrodes 102 and 103
The width of the divided electrode 109 for dividing the surface wave is determined by the surface wave excited by the second and third comb-shaped electrodes 102 and 103 and the width of the reflector electrode 1.
In order to minimize the effect of the energy of 04 on the confinement effect, it is desirable to set it to λ (λ / 2 = comb electrode finger width + comb electrode finger gap width) or less.

This surface acoustic wave filter has the same good characteristics as the surface acoustic wave filter before the second and third comb electrodes 102 and 103 are divided.

In this surface acoustic wave filter,
Similarly, when the balanced input terminals 106a and 106b are used as balanced output terminals and the unbalanced output terminal 107 is used as an unbalanced input terminal, good characteristics are obtained.

(Embodiment 6) FIG. 10 is a top view of a surface acoustic wave filter according to Embodiment 6 of the present invention.

Reference numeral 110 denotes a piezoelectric substrate, 111 denotes a first comb-shaped electrode (portion surrounded by a dotted line in the drawing), 111a and 111b denote electrode fingers, 112 denotes a second comb-shaped electrode (portion surrounded by a dotted line in the drawing), 112a Is an electrode finger, 113 is a third comb-shaped electrode (portion surrounded by a dotted line in the drawing), 113a is an electrode finger, 114 is a reflector electrode, 115 is a three-electrode type comb electrode (portion surrounded by a dotted line in the drawing), 116a , 116b are balanced input terminals, 117
Reference numerals a and 117b denote balanced output terminals, 118a and 118b denote ground terminals, and 119 denotes a split electrode.

On the piezoelectric substrate 110, second and third comb-shaped electrodes 112 and 113 are arranged on both sides of the first comb-shaped electrode 111 in the surface wave propagation direction, and a reflector electrode 114 is provided on both sides thereof. In the electrode-type comb electrode 115, one of the electrode fingers 112 facing the second comb-shaped electrode 112.
a and one of the electrode fingers 113a of the opposing electrode fingers of the third comb-shaped electrode 113 are connected to the balanced input terminals 116b and 116 of a package (not shown) containing the surface acoustic wave filter.
a. Also, the second and third comb-shaped electrodes 11
The other electrode fingers of the ground terminals 118a, 11
8b. Further, the first comb-shaped electrode 1
11 in the vicinity of the center, and opposing electrode fingers 111a,
111b is connected to the balanced output terminals 117a and 117 of the package.
b.

With this configuration, the balanced output terminals 117a,
The impedance of 117b can be set to a value that is approximately four times the impedance before the first comb-shaped electrode 111 is divided.

By dividing the first comb-shaped electrode 111 at an arbitrary position, the impedance can be changed within a range of 1 to 4 times (excluding 1) before the division.

This surface acoustic wave filter has the same good characteristics as the surface acoustic wave filter before the second and third comb electrodes 112 and 113 are divided.

In this surface acoustic wave filter,
Similar good characteristics are obtained when the balanced input terminals 116a and 116b are used as balanced output terminals and the balanced output terminals 117a and 117b are used as balanced input terminals.

Although only the first comb electrode 111 is divided in the sixth embodiment, the first comb electrode 111 is divided.
Similarly, when the second and third comb-shaped electrodes 112 and 113 which are connected to the balanced end without being divided are also divided at the center, the impedance is divided at an arbitrary position, approximately four times the impedance before division. Therefore, the impedance before division is 1
It can be set to a value of up to 4 times (excluding 1).

Further, in the sixth embodiment, input,
Since the output is also a balanced end, by dividing all of the first, second and third comb-shaped electrodes 111, 112 and 113,
Balanced input terminals 116a and 116b, balanced output terminal 117
a, 117b can be set to an arbitrary value.

Embodiment 7 FIG. 11 is a top view of a surface acoustic wave filter according to Embodiment 7 of the present invention.
Reference numeral 30 denotes a piezoelectric substrate, 131 denotes a first comb-shaped electrode (portion surrounded by a dotted line in the drawing), 131a and 131b denote electrode fingers, 132 denotes a second comb-shaped electrode (portion surrounded by a dotted line in the drawing), 132a, and 132a.
132b is an electrode finger; 133 is a third comb-shaped electrode (portion surrounded by a dotted line in the figure); 133a and 133b are electrode fingers;
Is a reflector electrode, 135 is a three-electrode comb electrode (portion surrounded by a dotted line in the figure), 136a and 136b are balanced input terminals, 13
6c is an unbalanced output terminal, 137 is a ladder-type filter composed of ladder-type comb electrodes, and 138a and 138b are ground terminals.

On the piezoelectric substrate 130, the first comb-shaped electrode 131 and the second and third comb-shaped electrodes 132, 133 are arranged on both sides in the direction of propagation of the surface wave, and the reflector electrodes 134 are provided on both sides thereof. In the three-electrode electrode 135, the first
Of the comb-shaped electrode 131 in the vicinity of the center, and opposing electrode fingers 131a and 131b are connected to the balanced input terminals 136a and 136a of a package (not shown) containing the surface acoustic wave filter.
136b. Also, one of the electrode fingers 132b, 13 of the second and third comb-shaped electrodes 132, 133
3b is connected to the unbalanced output terminal 136c via the series arm resonator of the ladder type filter 137. The other electrode fingers 132a and 133a of the second and third comb-shaped electrodes are connected to a ground terminal 138a of the package. Further, the parallel arm resonator of the ladder type filter 137 is connected to the ground terminal 138b of the package.

By connecting the ladder-type filter 137 to the three-electrode-type comb electrode 135 in this way, the degree of attenuation of the ladder-type filter 137 can be flexibly designed, and as shown in the third embodiment, The surface acoustic wave filter has more desired filter characteristics than the filter having the sub-type comb electrode. Further, this surface acoustic wave filter has good characteristics similarly to the surface acoustic wave filter before the second and third comb-shaped electrodes 112 and 113 are divided.

Further, in the seventh embodiment, the first comb-shaped electrode 131 is divided near the center.
The impedance can be set within a range of four times (excluding 1).

Furthermore, in this surface acoustic wave filter, similarly good characteristics are obtained when the balanced input terminals 136a and 136b are used as balanced output terminals and the unbalanced output terminal 136c is used as an unbalanced input terminal. .

[0067]

As described above, according to the present invention, a surface acoustic wave filter having a desired value of the impedance of the balanced input terminal or the balanced output terminal can be obtained, and the matching matching with the peripheral circuit can be easily performed.

[Brief description of the drawings]

FIG. 1 is a top view of a surface acoustic wave filter according to Embodiment 1 of the present invention.

FIG. 2 is a frequency characteristic curve diagram of the surface acoustic wave filter shown in FIG.

FIG. 3 is a top view of a surface acoustic wave filter according to Embodiment 2 of the present invention.

FIG. 4 is an enlarged top view of a main part of the surface acoustic wave filter shown in FIG. 3;

FIG. 5 is a top view of a surface acoustic wave filter according to Embodiment 3 of the present invention.

6 is a frequency characteristic curve diagram of the surface acoustic wave filter shown in FIG.

FIG. 7 is a frequency characteristic curve diagram when the width of a divided electrode that divides the first comb-shaped electrode of the surface acoustic wave filter shown in FIG. 5 is changed.

FIG. 8 is a top view of a surface acoustic wave filter according to Embodiment 4 of the present invention.

FIG. 9 is a top view of a surface acoustic wave filter according to Embodiment 5 of the present invention.

FIG. 10 is a top view of a surface acoustic wave filter according to Embodiment 6 of the present invention.

FIG. 11 is a top view of a surface acoustic wave filter according to Embodiment 7 of the present invention.

FIG. 12 is a top view of a conventional surface acoustic wave filter.

[Explanation of symbols]

 Reference Signs List 10 piezoelectric substrate 11 first comb-shaped electrode 11a electrode finger 11b electrode finger 12 second comb-shaped electrode 13 third comb-shaped electrode 14 reflector electrode 15 three-electrode-type comb electrode 16a balanced input terminal 16b balanced input terminal 17 unbalanced output terminal 18 ground terminal 30 piezoelectric substrate 31 first comb electrode 31a electrode finger 31b electrode finger 32 second comb electrode 33 third comb electrode 34 reflector electrode 35 three-electrode comb electrode 36a balanced input terminal 36b balanced input terminal 37 non Balanced output terminal 38 Ground terminal 40 Piezoelectric substrate 41 Three-electrode-type comb electrode 42 Filter 43 First comb-shaped electrode 43a First comb-shaped electrode 44 Second comb-shaped electrode 45 Third comb-shaped electrode 46 Reflector electrode 47a Electrode finger 47b Electrode Finger 48a Balanced input terminal 48b Balanced input terminal 48c Unbalanced output terminal 49a Earth terminal 49b Terminal 49c ground terminal 50 split electrode 90 piezoelectric substrate 91 first comb electrode 92 second comb electrode 92a electrode finger 93 third comb electrode 93a electrode finger 94 reflector electrode 95 three electrode comb electrode 96a balanced input terminal 96b Balanced input terminal 97 Unbalanced output terminal 98a Ground terminal 98b Ground terminal 98c Ground terminal 99 Split electrode 100 Piezoelectric substrate 101 First comb electrode 102 Second comb electrode 102a Electrode finger 103 Third comb electrode 103a Electrode finger 104 Reflector Electrode 105 Three-electrode type comb electrode 106a Balanced input terminal 106b Balanced input terminal 107 Unbalanced output terminal 108a Earth terminal 108b Earth terminal 108c Earth terminal 109 Split electrode 110 Piezoelectric substrate 111 First comb electrode 111a Electrode finger 111b Electrode finger 112 Second Comb-shaped electricity 112a Electrode finger 113 Third comb electrode 113a Electrode finger 114 Reflector electrode 115 Three-electrode comb electrode 116a Balanced input terminal 116b Balanced input terminal 117a Balanced output terminal 117b Balanced output terminal 118a Earth terminal 118b Ground terminal 119 Divided electrode 130 Piezoelectric substrate 131 first comb-shaped electrode 131a electrode finger 131b electrode finger 132 second comb-shaped electrode 132a electrode finger 132b electrode finger 133 third comb-shaped electrode 133a electrode finger 133b electrode finger 134 reflector electrode 135 three-electrode comb electrode 136a balanced input terminal 136b Balanced input terminal 136c Unbalanced output terminal 137 Ladder type filter 138a Earth terminal 138b Earth terminal

 ──────────────────────────────────────────────────の Continuing on the front page (72) Kazuo Ikeda 1006 Kazuma Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Akio Tsunekawa 1006 Kadoma Kadoma, Kadoma City, Osaka Pref. F term (reference) 5J097 AA11 AA14 BB02 BB11 CC02 DD04

Claims (9)

[Claims] 1. A piezoelectric substrate, a first comb-shaped electrode formed on the piezoelectric substrate, and second and third comb-shaped electrodes provided on both sides of the first comb-shaped electrode in a surface wave propagation direction. Second,
A reflector electrode provided so as to sandwich a third comb-shaped electrode, wherein the first comb-shaped electrode is divided, and both opposing electrode fingers are used as an input electrode or an output electrode to be a balanced input or a balanced output; A surface acoustic wave filter in which one of the opposing electrode fingers of the third comb-shaped electrode is an output electrode when the first comb-shaped electrode is an input electrode, and the input electrode when the first comb-shaped electrode is an output electrode. 2. The width of an electrode dividing the first comb-shaped electrode is
λ (λ / 2 = the electrode finger width of the first comb-shaped electrode + the first
2. The surface acoustic wave filter according to claim 1, wherein the width is not more than the electrode finger gap width of the comb-shaped electrode. 3. A piezoelectric substrate, a first comb-shaped electrode formed on the piezoelectric substrate, and second and third comb-shaped electrodes provided on both sides of the first comb-shaped electrode in a surface wave propagation direction. Second,
A three-electrode comb electrode including a reflector electrode provided so as to sandwich the third comb electrode, and a filter cascade-connected to the three-electrode comb electrode on the piezoelectric substrate; At least one of the electrodes has a balanced input or a balanced output, and the comb-shaped electrode serving as the balanced input or the balanced output is a divided surface acoustic wave filter. 4. An input electrode and an output electrode are both balanced.
4. The surface acoustic wave filter according to claim 3, wherein the comb-shaped electrode serving as the input electrode and the output electrode is divided. 5. The width of an electrode dividing a comb-shaped electrode is λ (λ
4. The surface acoustic wave filter according to claim 3, wherein the ratio is equal to or less than (/ 2 = electrode finger width of the comb-shaped electrode + electrode finger gap width of the comb-shaped electrode). 6. The surface acoustic wave filter according to claim 3, wherein the filter connected to the three-electrode type comb electrode is a ladder type filter. 7. A piezoelectric substrate, a first comb-shaped electrode formed on the piezoelectric substrate, and second and third comb-shaped electrodes provided on both sides of the first comb-shaped electrode in a surface wave propagation direction. Second,
A reflector electrode provided so as to sandwich the third comb-shaped electrode, the second and third comb-shaped electrodes are divided, and one electrode finger is used as an input electrode or an output electrode, and a balanced input or balanced output is provided. Surface acoustic wave filter. 8. The width of an electrode dividing the second and third comb electrodes is λ (λ / 2 = electrode finger width of the first comb electrode + electrode finger gap width of the first comb electrode). Claim 7 which is
3. The surface acoustic wave filter according to 1. 9. When the second and third comb-shaped electrodes are input electrodes, the first comb-shaped electrode is used as an output electrode to provide balanced output, and when the second and third comb-shaped electrodes are output electrodes, the first comb-shaped electrode is used as an output electrode. 8. The surface acoustic wave filter according to claim 7, wherein said comb-shaped electrode is used as an input electrode for balanced input, and said first comb-shaped electrode is also divided.