JPH08237064A - Transversely coupled dual-mode surface acoustic wave filter - Google Patents

Abstract

(57) [Summary] [PROBLEMS] An object of the present invention is to make it possible to fabricate a laterally coupled dual-mode surface acoustic wave filter having a narrow band of a pass band having good characteristics and high reliability. [Structure] By inserting a capacitance between the cascaded connection of the laterally coupled dual-mode surface acoustic wave filter and the ground,
The object was achieved by lowering the frequencies of the anti-resonance points of the S mode and the A mode of the vibration mode of the surface acoustic wave filter. In addition, the capacitance to be inserted between the connection portion of the transversely coupled dual-mode surface acoustic wave filters connected in cascade and the ground is obtained by arranging the ground electrode near the outside of the common bar of the comb-shaped electrode on the connection portion side. Has been realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for narrowing a pass band in a laterally coupled dual mode surface acoustic wave filter.

[0002]

2. Description of the Related Art Conventionally, a method of narrowing the pass band of a laterally coupled dual-mode surface acoustic wave filter is performed by coarsely coupling the gaps G between the comb-shaped electrodes as shown in FIG. Was common.

[0003]

In the prior art, the method of roughening the coupling of the comb-shaped electrodes by separating the gap G between the comb-shaped electrodes is generally used in general in a specific band (passband / center frequency) of the filter. However, there is a problem in that the insertion loss of the laterally coupled dual-mode surface acoustic wave filter is increased if the value is smaller than 0.6 × 10 ⁻³ . The ratio band is a value obtained by dividing the filter pass band (the width of the point at which the filter is lowered by 3 dB) by the center frequency of the filter.

[0004]

In order to solve the problem, by inserting a capacitance between a cascaded connection portion of a laterally coupled dual mode surface acoustic wave filter and a ground, the S mode of the vibration mode of the surface acoustic wave filter and The problem was solved by lowering the frequency of the anti-resonance point of the A mode. In addition, the capacitance to be inserted between the connection portion of the transversely coupled dual-mode surface acoustic wave filters connected in cascade and the ground is obtained by arranging the ground electrode near the outside of the common bar of the comb-shaped electrode on the connection portion side. Has been realized.

[0005]

FIG. 1 shows a pattern diagram of a laterally coupled dual mode surface acoustic wave filter of the present invention. A first surface acoustic wave element 5 including a comb-shaped electrode 2 and a reflector 3 on the piezoelectric substrate 1;
The second surface acoustic wave elements 6 are connected in cascade.

In order to narrow the pass band of the laterally coupled dual mode surface acoustic wave filter by a conventional means, the gap G between the comb electrodes is increased as shown in FIG. However, this method has a drawback that the insertion loss increases, and the specific bandwidth is 0.6 × 10 ^−3.
The degree is the limit, and the present invention is effective in further reducing the specific band.

FIG. 2 shows the relationship between impedance and frequency when the ratio band is larger than 0.6 × 10 ^-3 . The frequency has good characteristics along with S-mode resonance point (Sor) <S-mode anti-resonance point (Soa) <A-mode resonance point (Aor) <A-mode anti-resonance point (Aoa). In order to narrow the pass band of the filter while maintaining this arrangement, it is necessary to insert a capacitance between the cascade connection 4 of the comb electrodes and the ground. This situation is shown in FIG. 2. Since capacity is added, S
Mode anti-resonance point (Soa) and A-mode anti-resonance point (A
The frequency of oa) decreases, and as a result, the anti-resonance point (Soa) of the S mode and the anti-resonance point (Aoa) of the A mode move to the left as indicated by the arrows, and the pass band of the filter becomes narrow.

A circuit diagram is shown in FIG. The first surface acoustic wave element 5 and the second surface acoustic wave element 6 are connected in cascade. The stray capacitance CS originally exists in the cascade connection 4 between the two elements. In this state, the bandwidth is 0.6
This is the case where it is larger than × 10 ^-3 . Next, the capacitance between the cascade connection 4 of the present invention and the ground is represented by CA. As a result, the frequencies of the S-mode anti-resonance point (Soa) and the A-mode anti-resonance point (Aoa) of both the first surface acoustic wave element 5 and the second surface acoustic wave element 6 are lowered. The pass band of the laterally coupled dual mode surface acoustic wave filter can be narrowed beyond the specific band of 0.6 × 10 ^-3 .

As shown in FIG. 1 in which the first surface acoustic wave element 5 and the second surface acoustic wave element 6 are connected in cascade, the comb-shaped electrodes 2 of the first and second surface acoustic wave elements are formed. Cascade connection 4
The ground electrodes 8 are arranged near the outside (the side where the teeth of the comb are not projected) of the common bar 7 of each comb-shaped electrode 2 connected to each other to form a capacitance with the common bar 7. ing. The value of the capacitance is related to the distance and the distance between the common bar 7 and the ground electrode 8 facing each other. If the distance between the common bar 7 and the ground electrode 8 is long and the distance between them is narrow, the capacitance value increases. On the contrary, if the distance between the common bar 7 and the ground electrode 8 is short, and the distance is wide, the capacitance value decreases. Therefore, it can be set by the arrangement of the common bar 7 and the ground electrode 8.

[0010]

According to the present invention, the capacitance of a desired value can be easily realized by the common bar of the comb-shaped electrodes connected to the cascade connection of the first and second surface acoustic wave devices and the ground electrode arranged in the vicinity thereof. As a result, it becomes possible to easily manufacture a laterally coupled dual-mode surface acoustic wave filter with a narrow insertion band and good characteristics, and a low insertion loss, which not only improves productivity and reliability but also reduces costs. Was also realized.

[Brief description of drawings]

FIG. 1 is a pattern diagram showing an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between impedance and frequency of the filter element of the present invention.

FIG. 3 is a circuit diagram showing an embodiment of the present invention.

FIG. 4 is a diagram showing a conventional band narrowing technique.

FIG. 5 is a pattern diagram showing a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 Comb type electrode 3 Reflector 4 Cascade connection section 5 First surface acoustic wave element 6 Second surface acoustic wave element 7 Common bar 8 Ground electrode

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[Procedure amendment]

[Submission date] March 3, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Transversely coupled dual-mode surface acoustic wave filter

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for narrowing a pass band in a laterally coupled dual mode surface acoustic wave filter.

[0002]

2. Description of the Related Art Conventionally, a method of narrowing the pass band of a laterally coupled dual-mode surface acoustic wave filter is performed by coarsely coupling the gaps G between the comb-shaped electrodes as shown in FIG. Was common.

[0003]

In the prior art, the method of roughening the coupling of the comb-shaped electrodes by separating the gap G between the comb-shaped electrodes is generally used in general in a specific band (passband / center frequency) of the filter. However, there is a problem in that the insertion loss of the laterally coupled dual-mode surface acoustic wave filter is increased if the value is smaller than 0.6 × 10 ⁻³ . The ratio band is a value obtained by dividing the filter pass band (the width of the point at which the filter is lowered by 3 dB) by the center frequency of the filter.

[0004]

In order to solve the problem, by inserting a capacitance between a cascaded connection portion of a laterally coupled dual mode surface acoustic wave filter and a ground, the S mode of the vibration mode of the surface acoustic wave filter and The problem was solved by lowering the frequency of the anti-resonance point of the A mode. In addition, the capacitance to be inserted between the connection portion of the transversely coupled dual-mode surface acoustic wave filters connected in cascade and the ground is obtained by arranging the ground electrode near the outside of the common bar of the comb-shaped electrode on the connection portion side. Has been realized.

[0005]

FIG. 1 shows a pattern diagram of a laterally coupled dual mode surface acoustic wave filter of the present invention. A first surface acoustic wave element 5 including a comb-shaped electrode 2 and a reflector 3 on the piezoelectric substrate 1;
The second surface acoustic wave elements 6 are connected in cascade.

In order to narrow the pass band of the laterally coupled dual mode surface acoustic wave filter by a conventional means, the gap G between the comb electrodes is increased as shown in FIG. However, this method has a drawback that the insertion loss increases, and the specific bandwidth is 0.6 × 10 ^−3.
The degree is the limit, and the present invention is effective in further reducing the specific band.

FIG. 2 shows the relationship between impedance and frequency when the ratio band is larger than 0.6 × 10 ^-3 . The frequency has good characteristics along with S-mode resonance point (Sor) <S-mode anti-resonance point (Soa) <A-mode resonance point (Aor) <A-mode anti-resonance point (Aoa). In order to narrow the pass band of the filter while maintaining this arrangement, it is necessary to insert a capacitance between the cascade connection 4 of the comb electrodes and the ground. This situation is shown in FIG. 2. Since capacity is added, S
Mode anti-resonance point (Soa) and A-mode anti-resonance point (A
The frequency of oa) decreases, and as a result, the anti-resonance point (Soa) of the S mode and the anti-resonance point (Aoa) of the A mode move to the left as indicated by the arrows, and the pass band of the filter becomes narrow.

A circuit diagram is shown in FIG. The first laterally coupled surface acoustic wave element 5 and the second laterally coupled surface acoustic wave element 6 are connected in cascade. The stray capacitance CS originally exists in the cascade connection 4 between the two elements. This state is when the specific band is larger than 0.6 × 10 ⁻³ . Next, the capacitance between the cascade connection 4 of the present invention and the ground is represented by CA. As a result, the first laterally coupled surface acoustic wave element 5 and
Second laterally coupled surface acoustic wave element 6 The frequencies of the anti-resonance point (Soa) of S mode and the anti-resonance point (Aoa) of A mode of both elements decrease, and as a result, the passage of the laterally coupled dual mode surface acoustic wave filter. The band can be narrowed beyond the specific band of 0.6 × 10 ⁻³ .

As shown in the first and second transversely coupled surface acoustic wave elements 5 and 6 in FIG. 1 in which the first and second laterally coupled surface acoustic wave elements 6 are connected in cascade. Each comb-shaped electrode 2 connected to the cascade connection part 4 of the comb-shaped electrode 2 of
The ground electrodes 8 are arranged near the outside of the common bar 7 (on the side where the teeth of the comb are not exposed) to form a capacitance with the common bar 7. The value of the capacitance is related to the distance and the distance between the common bar 7 and the ground electrode 8 facing each other. If the distance between the common bar 7 and the ground electrode 8 is long and the distance between them is narrow, the capacitance value increases. On the contrary, if the distance between the common bar 7 and the ground electrode 8 is short, and the distance is wide, the capacitance value decreases. Therefore, it can be set by the arrangement of the common bar 7 and the ground electrode 8.

[0010]

According to the present invention, the common bar of the comb-shaped electrodes connected to the cascade connection of the first and second laterally coupled surface acoustic wave devices and the ground electrode arranged in the vicinity thereof make it easy to obtain a desired capacitance. Since it is possible to realize, it becomes possible to easily manufacture a laterally coupled dual-mode surface acoustic wave filter with good characteristics by narrowing the pass band, and with low insertion loss, which not only improves productivity and reliability, but also We were able to reduce costs.

[Brief description of drawings]

FIG. 1 is a pattern diagram showing an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between impedance and frequency of the filter element of the present invention.

FIG. 3 is a circuit diagram showing an embodiment of the present invention.

FIG. 4 is a diagram showing a conventional band narrowing technique.

FIG. 5 is a pattern diagram showing a conventional technique.

[Explanation of reference numerals] 1 piezoelectric substrate 2 comb-shaped electrode 3 reflector 4 cascade connection part 5 first laterally coupled surface acoustic wave element 6 second laterally coupled surface acoustic wave element 7 common bar 8 ground electrode

Claims (2)

[Claims] 1. A laterally coupled dual-mode surface acoustic wave filter in which a first surface acoustic wave element and a second surface acoustic wave element each comprising a comb-shaped electrode and a reflector are cascade-connected on a piezoelectric substrate. As means for narrowing the pass band width of the dual mode surface acoustic wave filter, a capacitance is provided between the cascade connection of the first surface acoustic wave element and the second surface acoustic wave element and the ground. Horizontally coupled dual-mode surface acoustic wave filter. 2. A ground electrode is arranged outside a common bar of each comb-shaped electrode on the side connected to the cascade connection of the comb-shaped electrodes of the first and second surface acoustic wave devices. A transversely coupled dual-mode surface acoustic wave filter according to claim 1.