JPH0629771A - Surface acoustic wave converter - Google Patents

Abstract

PURPOSE:To prevent each comb tooth(electrode finger) of an an input electrode from being easily disconnected and to improve the group delay characteristic and the amplitude characteristic for frequency. CONSTITUTION:An input electrode 21 which consists of base parts 21a and 21b and electrode fingers 21c and 21d and constitutes a weighting surface acoustic wave converter and an output electrode 22 constituting a normal surface acoustic wave converter are arranged on a piezoelectric substrate 20. Parts of electrode fingers 21c and 21d which do not cross of the input electrode 21 are linearly coated with a sound absorbing material 25 across electrode fingers 21c and 21d, and the edge part of the surface acoustic wave propagation path between the input electrode 21 and the output electrode 22 is coated with a sound absorbing material 26. Thus, unnecessary surface acoustic waves due to multipath reflection or a diffraction phenomenon are absorbed to suppress ripple, undulation, or the like in the group delay characteristic and the amplitude characteristic for frequency. The sound absorbing material 25 increases the strength of parts of electrode fingers 21c and 21d without an influence upon generation of a surface acoustic wave.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention changes the characteristics of an input electric signal and outputs it by once converting the electric signal into a surface acoustic wave and again converting the surface acoustic wave into an electric signal and outputting the electric signal. The present invention relates to a surface acoustic wave converter.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 6, for example, a device of this kind has a comb-teeth-shaped input electrode 11 having different crossing lengths on a piezoelectric substrate 10 and a comb facing the input electrode 11. A tooth-shaped output electrode 12 is provided, and sound absorbing materials 13 and 14 are applied to the outer sides of the input electrode 11 and the output electrode 12, respectively. The high frequency signal from the oscillator 15 is input to the input electrode 11 and output. A resistor 16 connected to the electrode 12 is used to obtain an output signal that is band-limited and has a predetermined frequency characteristic.

[0003]

However, in the above-mentioned conventional device, multiple reflection in the input electrode 11 itself,
There is a problem that ripples and undulations occur in the group delay characteristic and the amplitude characteristic with respect to frequency due to multiple reflection between the input electrode 11 and the output electrode. Further, due to the diffraction phenomenon, there is a problem that ripples, undulations, etc. occur in the group delay characteristic and the amplitude characteristic with respect to the frequency. Further, the comb teeth of the input electrode 11 are often broken during manufacture. The present invention has been made to solve the above problems, and provides a surface acoustic wave converter that prevents each comb tooth of an input electrode from being easily broken and that has good group delay characteristics and amplitude characteristics with respect to frequency. To do.

[0004]

In order to achieve the above-mentioned object, the structural feature of the invention according to claim 1 is that a sound absorbing material is crossed over each comb tooth at the comb tooth portion where the input electrodes do not intersect. It was applied in a linear manner.

Further, the constitutional feature of the invention according to claim 2 is that in the surface acoustic wave converter according to the invention according to claim 1, the propagation path of a surface acoustic wave between an input electrode and an output electrode. The second sound absorbing material is applied to the edge of the.

[0006]

In the invention according to claim 1 configured as described above, the applied sound absorbing material has multiple reflections at the input electrode portion or multiple reflections between the input electrode and the output electrode. Is suppressed, ripples, undulations, etc. in the group delay characteristic and the amplitude characteristic with respect to the frequency can be suppressed to be small. Further, the comb-teeth portion where the input electrodes do not intersect does not contribute to the generation of the surface acoustic wave, and the applied sound absorbing material prevents the breakage of the comb-teeth portion. The sound absorbing material increases the strength of the comb tooth portion without affecting the generation. As a result, according to the invention of claim 1, the group delay characteristic and the amplitude characteristic with respect to the frequency are improved, and the comb teeth of the input electrode are not easily broken.

Further, in the invention according to claim 2 configured as described above, in addition to the above-described action, the second sound absorbing material causes the second sound absorbing material to have ripples, undulations, etc. in the group delay characteristic and the amplitude characteristic with respect to the frequency due to the diffraction phenomenon. To prevent the occurrence of. As a result, according to the invention of claim 2, the group delay characteristic and the amplitude characteristic with respect to frequency are further improved as compared with the invention of claim 1.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view schematically showing a surface acoustic wave converter according to the embodiment. This surface acoustic wave converter is
The piezoelectric substrate 20 has a rectangular parallelepiped shape made of a piezoelectric material such as NbO ₃ , LiTaO ₃ , and quartz. An input electrode 21 and an output electrode 22 are provided on the piezoelectric substrate 20 so as to face each other, and a surface acoustic wave W1 is propagated from the input electrode 21 to the output electrode 22. The input electrode 21 includes a pair of bases 21a and 21b extending in parallel and the bases 21a and 21b.
a plurality of electrode fingers 21c extending vertically from b,
21d, and each electrode finger 2
The weighted surface acoustic wave converter is configured by changing the crossing length between 1c and 21d. The output electrode 22 includes a pair of bases 22a and 22b extending in parallel and the bases 22a and 22b.
A small number of electrode fingers 22c, 2 vertically extending from the
2d and the electrode fingers 21 are formed in a comb shape.
A normal type surface acoustic wave converter is configured with a constant intersection length between c and 21d.

Sound absorbing materials (damper materials) 23 and 24 are applied to the outer sides of the input electrode 21 and the output electrode 22, respectively. Electrode fingers 21c and 2 that do not intersect the input electrode 21
1d, that is, the comb tooth portions, a plurality of linear sound absorbing materials 25, 25 ... Are applied at substantially equal intervals so as to intersect the electrode fingers 21c, 21d, and both ends of each sound absorbing material 25, 25. Are connected to the base portions 21 a and 21 b of the input electrode 21 and the sound absorbing material 23. Further, the input electrode 21 and the output electrode 22
A pair of sound absorbing materials 26, 26 are applied to the edge of the propagation path of the surface acoustic wave between and.

When the surface acoustic wave converter thus constructed is in use, the base portions 21a and 21b of the input electrode 21 are in use.
And a high frequency oscillator 27 is connected to the output electrode 22.
A resistor 28 is connected between the bases 22a and 22b of the so as to obtain an output signal from both ends of the resistor 28. As a result, the high frequency electric signal from the high frequency oscillator 27 is converted into the surface acoustic wave W1 by the input electrode 21, the surface acoustic wave W1 is propagated to the output electrode 22, and is converted into the electric signal again by the same electrode 22. Is output. In this case, the input high frequency signal is converted into a signal having a band-limited and predetermined frequency characteristic by the input electrode 21, the output electrode 22, etc., and then output.

In such an operating state of the surface acoustic wave transducer, the sound absorbing materials 23, 25 and 26 are unnecessary surface acoustic waves W which are output from the input electrode 21 and propagate on the piezoelectric substrate 20.
2, W3 is absorbed, and the sound absorbing material 24 absorbs the unnecessary surface acoustic wave W4 output from the output electrode 22 and propagating on the piezoelectric substrate 20. Particularly, the sound absorbing material 25 is the electrode finger 21 of the input electrode 21.
There is an effect of absorbing unnecessary surface acoustic waves due to multiple reflections of c and 21d, and the sound absorbing material 26 has an effect of absorbing unnecessary surface acoustic waves due to the diffraction phenomenon.

The sound absorbing effect of the sound absorbing materials 25 and 26 will be described with reference to FIGS. 2 to 5. FIG.
24 shows a delay time characteristic with respect to frequency in the case where the sound absorbing materials 25 and 26 are not used (prior art) with 24 provided, and FIG. 3 shows a case where only the sound absorbing material 25 is used in the same state by a broken line (the sound absorbing material 26 The same delay time characteristics (in the case of not using
5 shows the same delay characteristic when 5, 26 are used. According to this, the sound absorbing material 25 suppresses ripples and undulations of the overall delay characteristic, and the sound absorbing material 26 particularly suppresses ripples and undulations of the delay characteristic in the portion surrounded by the one-dot chain line in FIG. I understand. Further, FIG. 4 shows the amplitude characteristics with respect to frequency in the case where the sound absorbing materials 25 and 26 are not used (prior art) with the solid lines provided with solid lines, and the amplitude characteristics are plotted in the vertical direction with broken lines. 5 shows the same amplitude characteristics when the sound absorbing materials 25 and 26 are used in the same state by a solid line, and the amplitude characteristics are shown by a 10 times scale in the vertical direction by a broken line. There is. According to this, it can be understood that the sound absorbing materials 25 and 26 suppress the overall ripple and undulation of the amplitude characteristic.

Further, according to the above-described embodiment, the sound absorbing material 25 is provided at the portion where the electrode fingers 21c and 21d of the input electrode 21 do not intersect, and this portion contributes to the generation of the surface acoustic wave. I haven't. On the other hand, the sound absorbing material 25 enhances the strength of the above-mentioned portion and prevents disconnection during the manufacturing process. Therefore, the sound absorbing material 25 does not affect the generation of surface acoustic waves, and the electrode fingers 21 of the input electrode 21 are not affected.
Since c and 21d are not easily broken, the yield of this surface acoustic wave converter can be improved.

In the above embodiment, the input electrode 2
Since 1 is configured symmetrically so that the portions where the electrode fingers 21c and 21d do not intersect appear symmetrically, the sound absorbing material 25 is provided symmetrically, but the portions where the electrode fingers 21c and 21d do not intersect are not provided symmetrically. When the sound absorbing member 25 is deviated to one side, the sound absorbing material 25 is provided only on the one side, that is, a portion where the electrode fingers 21c and 21d do not intersect.

[Brief description of drawings]

FIG. 1 is a schematic plan view of a surface acoustic wave converter according to an embodiment of the present invention.

FIG. 2 is a characteristic graph of delay time with respect to frequency in the related art.

FIG. 3 shows the delay time characteristics when only the sound absorbing material 25 is used by a broken line, and the sound absorbing material 2 is shown by a solid line.
5 is a graph showing the same delay characteristics when 5, and 26 are used.

FIG. 4 is a graph in which a solid line shows the amplitude characteristic with respect to the frequency in the conventional technique, and a broken line shows the same amplitude characteristic with a scale of 10 in the vertical direction.

FIG. 5 is a graph in which a solid line shows the amplitude characteristics when the sound absorbing materials 25 and 26 are used, and a broken line shows the same amplitude characteristics with a scale of 10 in the vertical direction.

FIG. 6 is a schematic plan view of a conventional surface acoustic wave converter.

[Explanation of symbols]

20 ... Piezoelectric substrate, 21 ... Input electrode, 22 ... Output electrode, 2
3 to 26 ... Sound absorbing material.

Claims (2)

[Claims] 1. A surface acoustic wave converter having a comb-teeth-shaped input electrode having different crossing lengths and a comb-teeth-shaped output electrode opposed to the input electrode on a piezoelectric substrate. A surface acoustic wave converter characterized in that a sound absorbing material is linearly applied so as to intersect the comb teeth at the comb teeth where the electrodes do not intersect. 2. The surface acoustic wave converter according to claim 1, wherein a sound absorbing material is applied to an edge portion of a surface acoustic wave propagation path between the input electrode and the output electrode. Surface wave converter.