JPH07106912A - Multiplex electrode type surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To provide a multiplex surface acoustic wave filter which reduces the ripples within a pass band and can serve as an excellent high frequency element. CONSTITUTION:Two or more comb-line input electrodes 1a and one or more comb-line output electrodes 2a are provided on the same transmission line formed on a piezoelectric substrate to transmit and receive the surface acoustic waves with each other. Then a pair of strip type comb-line reflectors 3 and 3' are places to hold those electrode groups 1a... and 2a... between them. In such a constitution of a multiplex electrode type surface acoustic wave filter, the reflector 3 is connected to the ground and the reflector 3' is opened respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-electrode surface acoustic wave filter.

[0002]

2. Description of the Related Art FIGS. 7 and 8 show a conventional multi-electrode type surface acoustic wave filter. In the figure, 1 is an input unit and 2 is an output unit. Two or more comb-shaped input electrodes 1a are formed in the input section 1, and one or more comb-shaped output electrodes 2a are formed in the output section 2. The comb-shaped input / output electrodes 1a and 2a are alternately arranged on the same propagation path.

A pair of strip type reflectors 3, 3'or reflectors 4, 4'are provided on the outermost side of the comb type input / output electrode group for the purpose of reducing insertion loss. Reflectors 3 and 3'are comb type (open strip type)
And a reflector 3 extending from the conductor portions 3a, 3a (3a ', 3a') arranged opposite to each other, which constitute each reflector 3 (3 ').
.. (3b '...) are formed so as not to contact the conductor portions 3a (3a') facing each other. On the other hand, the pair of reflectors 4 and 4'is a ladder type (short strip type).
And a reflector 4 extending from opposing conductor portions 4a, 4a (4a ', 4a') constituting each reflector 4 (4 ').
.. (4b '...) are formed so as to contact the conductor portions 4a (4a') facing each other.

In the conventional multi-electrode type surface acoustic wave filter, the conductor portions 3a and 3a 'of the reflectors 3 and 3', which face each other, are connected to the ground, and the reflectors 3a and 3a 'are connected to the ground. Both of the conductors 4a and 4a 'have a structure in which the conductor portions 4a and 4a' on one side facing each other are connected to the ground.

By the way, the multi-electrode surface acoustic wave filter provided with the above-mentioned ladder type reflectors 4 and 4'has the drawback that ripples exist in the frequency characteristics. On the other hand, it is known that the multi-electrode surface acoustic wave filter including the conventional comb-shaped reflectors 3 and 3'can reduce the ripple generated by the influence of the reflector to some extent.

[0006]

However, a multi-electrode type surface acoustic wave filter using the comb-shaped reflectors 3 and 3'is also
The ripple generated in the pass band was about 1 dB, and it could not be said that the stability was satisfied as a high frequency element.

In view of the above circumstances, it is an object of the present invention to provide a multi-electrode type surface acoustic wave filter that reduces ripples in the pass band and is excellent as a high frequency element.

[0008]

In order to solve the above problems, a multi-electrode surface acoustic wave filter of the present invention has two or more comb-shaped input electrodes for transmitting and receiving surface acoustic waves to and from each other on a piezoelectric substrate. A multi-electrode surface acoustic wave filter in which one or more comb-shaped output electrodes are arranged on the same propagation path, and a pair of strip-shaped comb-shaped reflectors are provided on the outermost side so as to sandwich the input / output electrode group. It is characterized in that one of the pair of comb-shaped reflectors sandwiching the input / output electrode group is connected to the ground and the other is open.

Further, in the above structure, the number of reflectors of the comb-shaped reflector is -30% or more of the minimum number of electrode fingers of the comb-shaped input electrode.

[0010]

According to the above structure, the ripple in the pass band can be reduced as compared with the conventional structure in which both the pair of comb-shaped reflectors are connected to the ground.

Further, the insertion loss can be suppressed low by setting the number of reflectors of the comb-shaped reflector to -30% or more of the minimum number of electrode fingers in the comb-shaped input electrode.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing its embodiments. For convenience of explanation, the same parts as those of the conventional example are designated by the same reference numerals.

FIG. 1 is a schematic plan view of a multi-electrode surface acoustic wave filter of this embodiment. In the figure, 1 is an input unit and 2 is an output unit. The input section 1 has two or more comb-shaped input electrodes 1a, and the output section 2 has one or more comb-shaped output electrodes 2a.
a is formed, and the comb-shaped input electrodes 1a and the comb-shaped output electrodes 2a are alternately arranged on the same propagation path. Also, 7
Is a bonding pad and is connected to ground.

A pair of strip-shaped comb-shaped reflectors 3, 3'are provided on the outermost sides of the comb-shaped input / output electrode groups 1a, 2a, ... For the purpose of reducing insertion loss.

The pair of comb-shaped reflectors 3 and 3'includes the conductor portions 3a, which are opposed to each other and constitute the comb-shaped reflectors 3 (3 ').
3a (3a ', 3a'), and the conductor portions 3a, 3a
Reflectors 3b ... (3b ') extending from (3a', 3a ')
Are formed so as not to contact the conductor portion 3a (3a ') opposite thereto.

In the multi-electrode type surface acoustic wave filter of this embodiment, only the comb-shaped reflector 3 on the left side in the figure is grounded.
Connected to. Specifically, one conductor portion 3a of the conductor portions 3a, 3a facing each other in the comb-shaped reflector 3 is opened, but the other conductor portion 3a is connected to the ground 8.

On the other hand, the comb-shaped reflector 3'on the right side of the drawing is open. That is, both of the conductor portions 3a 'and 3a' facing each other in the comb-shaped reflector 3'are opened.

In FIG. 1 described above, only the comb-shaped reflector 3 on the left side of the drawing is grounded, but as shown in FIG. 2, only the comb-shaped reflector 3'on the right side of the drawing is grounded. It's okay.

Next, the characteristics of the multi-electrode surface acoustic wave filter will be described.

FIG. 3 is a graph showing the pass characteristics of the multi-electrode surface acoustic wave filter of the above embodiment. Further, the graphs of FIGS. 4 and 5 are shown for the purpose of comparing the characteristics. FIG. 4 is a pass characteristic of the multi-electrode surface acoustic wave filter having the conventional configuration of FIG. 7, and FIG. 5 is a pass characteristic of the configuration of FIG. 7 when neither of the comb reflectors is grounded. . In addition,
The filter has a center frequency of 836 MHz and a bandwidth of 25
It is based on the MHz specifications.

As can be seen from these figures, the insertion loss of both the multi-electrode surface acoustic wave filter of this embodiment and the conventional filter is 2.9 dB, which is almost the same.

However, as is clear from the comparison between FIG. 3 and FIG. 4, the pass characteristics of the multi-electrode surface acoustic wave filter of this embodiment have a ripple in the pass band of about 0.3 dB as compared with the conventional configuration. Will be reduced. Therefore,
The ripple in the pass band is 0.7 dB or less,
The characteristics required as a high frequency filter will be satisfied.

On the other hand, in the case of FIG. 5, as in the case of this embodiment, the ripple in the pass band is about 0.7 dB, which can be said to be almost the same as that of the multi-electrode surface acoustic wave filter of this embodiment. However, it can be said that the multi-electrode surface acoustic wave filter of this embodiment is superior because the waveform droop exists on the low frequency side of the pass band. It is considered that the above-mentioned drooling of the waveform is caused by potential instability due to the fact that the reflector has no ground.

By the way, FIG. 6 is a graph showing the relationship between the insertion loss and the ratio of the number of reflectors of the comb reflector 3 to the minimum number of electrode fingers of the comb input electrode 1a. The above ratio is calculated by setting the minimum number of electrode fingers of the comb-shaped input electrode 1a as M _i and the number of reflectors of the comb-shaped reflector as M _r , and then 100.
It is calculated as (M _r −M _i ) / M _i . As can be seen from this graph, in order to keep the insertion loss within -3.0 dB, the above ratio needs to be -30% or more. Therefore, in the multi-electrode surface acoustic wave filter of the present embodiment, the number of reflectors of the comb-shaped reflectors 3 and 3'is set to -30% or more of the minimum number of electrode fingers in the comb-shaped input electrode 1a, Insertion loss is suppressed.

[0025]

As described above, according to the present invention, the in-band ripple due to the influence of the reflector can be reduced without increasing the insertion loss.

[Brief description of drawings]

FIG. 1 is a schematic plan view of a multi-electrode surface acoustic wave filter of the present invention.

FIG. 2 is a schematic plan view of a multi-electrode surface acoustic wave filter of the present invention.

FIG. 3 is a graph showing pass characteristics of the multi-electrode surface acoustic wave filter of the present invention.

FIG. 4 is a graph showing pass characteristics of a conventional multi-electrode surface acoustic wave filter having a comb-shaped reflector (a type in which both comb-shaped reflectors are grounded).

FIG. 5 is a graph showing a pass characteristic in the case of a conventional multi-electrode surface acoustic wave filter having a comb-shaped reflector in which both the comb-shaped reflectors are not grounded.

FIG. 6 is a graph showing the relationship between the insertion loss and the ratio of the number of reflectors to the minimum number of input electrodes.

FIG. 7 is a schematic plan view of a multi-electrode surface acoustic wave filter having a conventional comb-shaped reflector (a type in which both comb-shaped reflectors are grounded).

FIG. 8 is a schematic plan view of a multi-electrode surface acoustic wave filter having a conventional ladder-type reflector (a type in which both the ladder-type reflectors are grounded).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input part 1a Comb type input electrode 2 Output part 2a Comb type output electrode 3,3 'Comb type reflector 3a, 3a' Conductor part 3b, 3b 'Reflector 8 Ground

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Kaburagi 2-18, Keihanhondori, Moriguchi-shi, Osaka Within Sanyo Electric Co., Ltd. (72) Yusuke Takahashi 2--18, Keihanhondori, Moriguchi, Osaka Sanyo Denki Co., Ltd. (72) Inventor Isao Kiyose 2-18 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Inventor Kenichi Shibata, 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. A piezoelectric substrate is provided with two or more comb-shaped input electrodes and one or more comb-shaped output electrodes, which transmit and receive surface acoustic waves to each other, on the same propagation path, and sandwich the input / output electrode group. Thus, in the multi-electrode surface acoustic wave filter having the pair of strip-shaped comb-shaped reflectors provided on the outermost side, one of the pair of comb-shaped reflectors sandwiching the input / output electrode group is connected to the ground,
The other is an open surface type multi-electrode surface acoustic wave filter. 2. The multi-electrode type according to claim 1, wherein the number of reflectors of the comb-shaped reflector is -30% or more of the minimum number of electrode fingers in the comb-shaped input electrode. Surface acoustic wave filter.