JPS625714A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To compensate the acoustic impedance and to suppress the radiation of a surface wave by having the same periodic structure as that of an input transducer and arranging an electrode finger string the length of electrode fingers orthogonal in the surface acoustic wave propagation direction differs depending on the position in the propagation path. CONSTITUTION:Acoustic impedance compensation electrode finger strings 37, 38 having 1/8 wavelength width are arranged with a space of 1/8 wavelength respectively from input/output transducers 32, 33 to the propagation path between the input and output transducers 32 and 33. The electrode finger strings 37, 38 have the same periodic structure as that of the input/output transducers 32, 33 and the length of each electrode finger orthogonal in the surface wave propagating direction is made different to suppress the electromagnetic coupling with the input transducer 32. The electrode finger string 37 is connected to be of the same potential as that of the 2nd electrode finger 32b being an electric signal supply terminal of the input transducer 32 and the electrode finger string 38 is grounded similarly as the 1st electrode finger 32a being a grounding terminal of the input transducer 33.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a surface acoustic wave device with improved acoustic reflection spurious.

[Technical background of the invention and its problems]

A surface acoustic wave device is known in which a first comb-shaped electrode and a second comb-shaped electrode are engaged with each other on the surface of a piezoelectric substrate to form a pair of electrode fingers, thereby configuring a surface acoustic wave transducer. There is. As shown in FIG. 4, there is a basic elastic table X-wave device in which an input transducer 2 and an output transducer 3 are arranged on a piezoelectric substrate 1. Input transducer 2 and output transducer 3 are 1/
Split-type first electrode fingers 4 and 5 have electrode fingers with a width of 8 wavelengths arranged two on each side, and electrode fingers with a width of 1/8 wavelength are arranged in the center part i.
The two arranged second electrode fingers 6,7 are interlocked with each other, and the gaps 8, 9 between each electrode finger are set to ⅛ wavelength, which is the same as the width of the electrode fingers 4-7. Because of this input/output quadrangle, the reflection of the surface acoustic wave generated at both ends of each electrode finger is due to the difference in acoustic impedance between the location where the electrode finger is present and the location where the electrode finger is not present. It is known that they cancel each other out.

However, if a surface acoustic wave filter is configured with transducers 2.3 that have a structure in which the synthesized wave of acoustic reflection becomes zero inside, there will be a difference in acoustic impedance in the propagation path of the surface acoustic waves where the input/output transducer 2.3 does not exist. As a result, acoustic reflections occur at both ends of the input and output transducers 2, 3.

Therefore, as a means for removing such acoustic reflections, as shown in FIG. 5, acoustic impedance compensation electrodes 11a having the same shape as the electrode fingers 4 to 7 of the input and output transducers 2 and 3 are provided in the surface acoustic wave propagation path, respectively. A surface acoustic wave device was devised in which llb and 11c are arranged to match the period of the acoustic impedance of the input and output transducers 2 and 3. This surface acoustic wave device was introduced at the 1972 "I.I.I. Ultrasonics Symposium" (IE
EEUl trasonics Symposium
) J, pp. 373-376.

However, when such a means is applied to a surface acoustic wave device having a structure in which the input conductor 21 is apodized, for example, as shown in FIG. 6, the following disadvantages arise. In other words, the surface acoustic wave propagation path between the apodice-type input transducer 21 and the normal-type output transducer 22 is
By arranging the acoustic impedance compensation electrode 23 adjacent to the dummy electrode 24 on the electrical signal supply side of the input quadrature stripe 21, radiation of the surface wave 25 occurs in the area where the two face each other, and the frequency The characteristics will deteriorate significantly. In addition, 26 in the figure is an electrode for acoustic impedance compensation arranged on the right side of the output sensor 22.

[Purpose of the invention]

This invention was made to solve the above problems, and provides a surface acoustic wave device that can improve acoustic reflection at both ends of an input/output transducer and suppress radiation of one surface wave. The purpose is to

[Summary of the invention]

This invention has the same periodic structure as an apodized input transducer and a regular output transducer in which the crossing width of electrode finger pairs is uniform, and the length of the electrode fingers perpendicular to the surface wave propagation direction differs depending on the location. By disposing an electrode finger array including a plurality of points in a propagation path between the above-mentioned input quadrature channels, it is possible to compensate for the acoustic impedance of this propagation path and to suppress the radiation of surface waves.

〔Effect of the invention〕

According to this invention, acoustic reflections in the propagation path between the apodized input transducer and the normal output transducer are eliminated, and surface acoustic wave radiation is achieved by electromagnetic coupling between the input and output transducers and the electrode finger array. can be suppressed, so characteristics can be significantly improved.

[Embodiments of the invention]

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

In Figure 1i, 31 is lithium niobate (LiNbO
,), Lithium oxide (LiTaO3), etc. (7) A piezoelectric substrate formed of a piezoelectric material, and this substrate 3
1, an apodized input transducer 327 in which the intersecting width of the pair of electrode fingers varies depending on the location on the surface acoustic wave propagation surface 1, and a normal output transducer 3 in which the intersecting width of the electrode fingers is uniform.
3 is placed. The input transducer 32 has a split-type first electrode finger 32a with a width of <1/8 wavelength as shown in the figure.
Dummy electrodes 321 and 322 are formed on the left side in the figure by engaging the second electrode fingers 32b and the second electrode fingers 32b. The dummy electrodes 321 and 322 are extended in the direction of the end surface of the piezoelectric substrate 31, and a sound absorbing agent 34 is applied to the ends thereof. In addition, the output sensor 33 is a split-type first electrode finger 33a in which two electrode fingers each having a width of 1/8 wavelength are arranged on the left and right sides.
and a second electrode finger 33b in which two electrode fingers each having a width of 1/8 wavelength are arranged in the center. An acoustic impedance compensating electrode 35 having the same periodic structure as the output transducer 33 is disposed on the propagation path located on the right side of the output transducer 33, and a sound absorbing material 3
6 is applied. The gap between each electrode finger of the input/output transducers 32 and 33 described above is set to 78 wavelengths, which is the same as the electrode width.

On the other hand, in the propagation path between the input and output transducers 32 and 33, acoustic impedance compensation electrode finger arrays 37 and 38 having a width of 1/8 wavelength are arranged with a gap of 1/8 wavelength from the input and output transducers 32 and 33, respectively. ing. The electrode finger arrays 37 and 38 include input and output quadrants, -sa 32,
33, and the lengths of the electrode fingers orthogonal to the surface wave propagation direction are made to be different as shown in the figure so as to suppress electromagnetic coupling with the input quadrature sensor 32. The electrode finger row 37 is connected to have the same potential as the second electrode finger 32b, which is the electrical signal supply terminal of the input quadrature sensor 32, and the electrode finger row 38 is connected to the input quadrature sensor 33.
It is grounded similarly to the first electrode finger 32a, which is the ground side terminal.

Further, the first electrode 33a of the output damper adjacent to the electrode finger row 38 and the acoustic impedance compensation electrode 35 adjacent thereto are also grounded.

In a transformer with such a structure.

For example, among the surface acoustic waves 39a and 39b bidirectionally excited from the input transducer 32, the acoustic impedance of the surface acoustic wave 39a traveling toward the left side in the figure changes greatly in the section until it reaches the sound absorbing material 34. There are no exposed areas, so no acoustic reflection occurs.

On the other hand, the surface acoustic wave 39b traveling toward the output transducer 33 is received by the acoustic impedance compensation electrode arrays 37 and 38 adjacent to the input transducer 32 until it is received by the output transducer 33.
Acoustic reflections originate from
The surface acoustic waves that pass through without being received are absorbed by the adsorbent 36 in the traveling direction.

Therefore, according to such a configuration, since no acoustic reflection occurs within the surface acoustic wave propagation path, spurious noise due to acoustic reflection does not appear in the output signal. Furthermore, by suppressing the electromagnetic coupling between the input and output transducers 32 and 33 and the acoustic impedance compensation electrode finger arrays 37 and 38, surface acoustic wave radiation does not occur in the region facing the input and output transducers 32 and 33. Therefore, frequency characteristics can be improved.

Next, other embodiments of the invention will be described with reference to the drawings.

FIG. 2 shows a modification of the above-mentioned embodiment (FIG. 1), in which an acoustic impedance is applied to the second electrode finger 41b, which is the electrical signal supply terminal of the input voltage sensor 41, and the first electrode finger 41a, which is the ground terminal. Compensating electrode finger arrays 42 and 43 are integrally formed on a pattern so that they have the same potential, and each electrode finger of the input/output transducer 41.33 has the same structure as that shown in FIG. In this embodiment, among the electrode finger rows 42 and 43 for acoustic impedance compensation, the electrode finger at the right end in the empty diagram of the electrode finger row 43 is extended between the electric signal terminal portions of the output transducers 41 and 33, and the piezoelectric material substrate is The structure is designed to suppress direct electromagnetic coupling within.

FIG. 3 shows a modification of the above other embodiment (FIG. 2).
In an input transducer 51 having the same structure as that shown in the figure, the dummy electrode 52 on the electrical signal supply side is separated on a batten and grounded so that no electrical signal is applied.

In this way, bulk waves will not be excited,
Moreover, the shielding effect can be enhanced.

In the other embodiments shown in FIGS. 2 and 3 described above, the acoustic impedance in the surface acoustic wave propagation path changes periodically for every 1/8 wavelength, as in the above embodiment, so acoustic reflection spurious The structure is such that no surface acoustic wave radiation occurs, and no surface acoustic wave radiation occurs.

Note that the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without changing the gist.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the configuration of an embodiment of the present invention, and FIG.
3 and 3 are plan views showing the configurations of other different embodiments of the present invention, and FIGS. 4 to 6 are front views showing the configurations of different conventional surface acoustic wave devices. 31... Piezoelectric substrate 32, 41, 51... Input transducer 32a, 33a, 41a...
Split type first electrode phase: 32t'l, :(3h, 41L) - 21st input finger 32i, 322. ．． 52-...Dami...Military 3
3...Out L1[・AnsG 2-S 34.36...
Sound absorbing agent 35...-tI sound in 1-=G]/Additional addition 1゛River Curse 37
．． 38, 42. 43...7 ￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥t compensate for the impedance path/pass compensation 'I pole finger array 39a, 39b =-・Surface acoustic wave 4
2-way ゛-puζノ~ifzua''-s?1Ij4nI filled-
4th floor Aku 3N Figure 4 Figure 5Vζ1 Figure 6

Claims (3)

[Claims] (1) In a surface acoustic wave device in which an apodice-shaped input transducer and a normal-shaped output transducer with a uniform crossing width of electrode finger pairs are formed on a piezoelectric substrate, there is a propagation path between the input and output transducers. It is characterized by providing an electrode finger array that has the same periodic structure as the input/output transducer along the surface wave propagation direction, and includes locations where the length of the electrode fingers perpendicular to the surface wave propagation direction varies depending on the location. Surface acoustic wave device. (2) The surface acoustic wave device according to claim 1, wherein the electrode finger array is integrally formed with either the input transducer or the output transducer. (3) Set the electrode finger width of the electrode finger row to approximately 1/of the wavelength of the surface acoustic wave.
8. The surface acoustic wave device according to claim 1 or 2, wherein the surface acoustic wave device is set to 8.