JPS58130614A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To improve the acoustic reflection at both end parts of input/output transducers, by distributing strip electrodes so as to have coincidence between the acoustic impedance of a transmission line to the travelling direction of a surface acoustic wave and the period of distribution of the acoustic impedance of the input/output transducers. CONSTITUTION:For input and output transducers 31 and 32, electrode fingers 31a and 32a having 5/8 wavelength width and electrode fingers 31b and 32b having 1/8 wavelength width are set with gaps 31c and 32c of 1/8 wavelength width. In addition, strip electrodes 33, 34 and 35 having 5/8 and 1/8 wavelength widths are formed as shown in a diagram. The finger 31b has 1/8 wavelength width, and a strip 33a having 5/8 wavelength width is provided after the finger 31b with a gap 33c having 1/8 wavelength width. Furthermore a strip 33b having 1/8 wavelength width is provided after the strip 33a with a gap 33c. A number of strips of such constitutions are provided, and an absorber 36 of reflected waves on the electrode 33 at a proper position. So is with the electrodes 35 and 34. In such a way, the reflection is avoided at both end parts for the surface acoustic wave.

Description

[Detailed description of the invention] [Technical field of invention] This invention relates to a surface acoustic wave device.

[Technical background of the invention and its problems] A first comb-shaped electrode and a second comb-shaped electrode are interlocked with each other on a piezoelectric substrate to form nine electrode finger pairs, thereby producing a surface acoustic wave transducer. A surface acoustic wave device configured with the following is known. Figure 1 shows the basic structure of this Hinoki transducer. In the figure, the width of the first electrode finger 4, the width of the second electrode finger 50, and the width of the second electrode finger 50 of each of the input and output juicers 2 and 3 formed on the piezoelectric substrate 1 are shown.
The gap 6 between the electrode finger 4 and the second electrode finger 5 has a wavelength of 1/4 of the surface acoustic wave propagating on the piezoelectric substrate 1, respectively. However, with this electrode finger structure, surface acoustic waves are reflected at both ends of each electrode finger 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, and the phase of this reflected wave is There is a problem in that all rounding is in phase, and this appears as spurious in the output signal.

Therefore, when a surface acoustic wave filter is constructed using a transducer having this electrode finger structure, ripples appear in the passband due to the influence of spurious acoustic reflected waves. As a means to eliminate this drawback, 1, US Pat. No. 3,727,155
The comb-shaped electrodes of the transducer can be replaced with split-type electrodes with a wavelength of V88 as described in the specification, or
The structure is a combination of /8 wavelength width electrodes and t/S wavelength width electrodes, and the phase of the acoustic reflected waves at both ends of the electrode finger is reversed.
There are known methods that reduce the composite wave to zero. When a surface acoustic wave filter is configured with such non-reflective electrodes, the composite wave of acoustic reflected waves inside the transducer becomes zero, but this alone still causes the following phenomenon. Ripples occur within the In other words, as mentioned above, acoustic reflection occurs at both ends of the electrode finger because the acoustic impedance is different between the location where the electrode finger is present and the location where the electrode finger is not present, but similarly, the transducer and the surface acoustic wave where the transducer is not present also propagate. Acoustic reflections occur at both ends of the transducer due to the difference in acoustic impedance KA from the transducer.

As a means to eliminate this acoustic reflection, a surface acoustic wave device with a propagation structure between the input and output quadrature transducers 21 and 22 as shown in Fig. 2 was developed in 1972 at IEEE Itrason.
lca8ympoiium Pj 37. )" 376. However, in this structure, acoustic reflection still occurs at the end of the transducer on the sound absorbing material side due to the surface acoustic waves24.25 propagating toward the sound absorbing material, causing spurious noise. In addition, even in a transducer in which the width of the first electrode finger is V8 wavelength and the width of the second electrode finger is V8 wavelength, the propagation path between the input and output quadrant transducers is simply 1/8 wavelength and V8 wavelength. Placing strips with a width of

[Purpose of the invention]

This invention improves the drawbacks of the conventional surface acoustic wave devices described above, and improves the acoustic reflection at both ends of the input and output quadrant transducers even in transducers in which the interdigitated interdigitated electrode fingers have different electrode finger widths. The present invention provides a surface acoustic wave device that can perform

[Summary of the invention]

The present invention is aimed at improving acoustic reflection at both ends of an input/output transducer that constitutes a surface acoustic wave device in which interdigitated interdigitated electrode fingers have different width dimensions. The strip electrodes are distributed in such a way that the acoustic impedance of the propagation path in the hitting direction matches the period of the acoustic impedance distribution of the quadratic transducer, thereby reducing the composite wave of acoustic reflected waves to zero. be.

[@Ming effect]

According to the present invention, it is possible to improve the acoustic reflected waves at both ends of the input/output transducer, so that the effect that spurious noise due to the acoustic reflected waves does not appear in the output signal can be obtained.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.
FIG. 3 shows an embodiment of the present invention, in which a piezoelectric substrate 30
An input transducer 31 and an output transducer 32 are formed thereon.

The output juicer 31 and the output juicer 32 each have first electrode fingers 31m and 3 having a wavelength width of 5A.
2a and the second electrode fingers 31b and 32b of V88 wavelength are 1/
8 wavelengths of sky! 1 31c and 32c are arranged side by side. The surface wave propagation path between the input quadrature juicer 31 on the left side in the figure, the output quadrangle juicer 32 on the right side in the figure, and the input and output quadrature juicers 31 and 32 consists of strips with a 5A wavelength width and a 1/8 wavelength width, respectively. Strip electrodes 33, 34 and 35 are formed. The strip electrode 33 is connected to the inlet juicer 31
In order to improve acoustic reflection at the left end in FIG. That is, first, the input fluid juicer 31
Since the leftmost electrode 1ii31b has an IA wavelength width, a space 1133c of 1/8 wavelength is placed from the leftmost electric finger of Jin.
A 5/8 wave long strip 33 m is arranged.

Further, a strip 33b having a V88 wavelength is arranged with a gap 1133c having a V8 wavelength from the strip 33m having a wavelength width of 5A. 5/8 wavelength book 3311 with such a configuration
A large number of strips of 78 wavelength width 33b are arranged, and 2M
A sound absorbing material 36 is provided on the strip electrode 33 at the appropriate position to absorb unnecessary reflected waves. Similarly, the strip electrodes 35 between the input and output quadrant transducers 31. The distribution is formed in

That is, first, since the width of the rightmost electrode finger 31b of the input quadrature transducer 31 is V8 wavelength, the gap 3 is 1/8 wavelength.
5/8 wavelength width with 5c) IJg 35a,
1/8 wavelength wide strips 35b are arranged periodically in the direction of the output transducer. Since the electrode finger 54b on the left end of the output transducer 54 has a wavelength width of ■A, the empty FJ35c of 1/8 wavelength is used.

Furthermore, the strip electrode 34 on the right side of the output transducer genie t32 is formed to match the period of the acoustic impedance distribution of the output transducer 32. There is. In other words, the rightmost electrode finger 3 of the output reducer
Since the width of the electrode finger 2b is the V8 wavelength, a strip 32a having a width of 5/8 wavelength is arranged with a gap 32c having a width of 1/8 wavelength from the electrode finger 32b, and a gap 32c having a width of 1/8 wavelength.
Strips 32b each having a width of 1/8 wavelength are arranged at intervals of 1/8 wavelength. A sound absorbing material 37 for absorbing unnecessary surface acoustic waves is provided at an appropriate position on the strip electrode 34 made up of such a repeating structure. Note that the IJ knob electrodes 33, 34 and 35 are each grounded.

According to the above structure, first, for the surface acoustic wave generated by the input quadrature transducer 31 and propagating to the left among the nine surface acoustic waves, the acoustic impedance of the electrode finger of the input transducer is located on the left side of the input quadrature transducer 31. Since the IJ tube electrode 33 is provided, which corresponds to the period of the distribution of , there is no reflection of surface acoustic waves at the left end of the input quadrature transducer 31 due to mismatch in acoustic impedance. Also, KFi on the left end of the IJ knob electrode 33
Since the sound absorbing material 36 is formed, the strip electrode 33
Reflection of surface acoustic waves at the left end of is prevented.

Regarding the surface acoustic waves propagating to the right side of the nine quadrant transducer 31, nine strip electrodes 35 are provided between the input and output quadrant transducers 31 and 32, matching the acoustic impedance distribution of the input transducer. Reflection of surface acoustic waves at the right end of is eliminated. Since this strip electrode 35 also matches the acoustic impedance distribution of the output transducer 32, reflection of surface acoustic waves at the left end of the output transducer 32 can also be prevented.

Furthermore, regarding the surface acoustic waves that pass through the output reducer 32 without being converted into electric signals, a strip electrode 34 whose acoustic impedance distribution matches that of the output reducer is provided on the right side of the output reducer 32. Reflection of surface acoustic waves at the right end of the output reducer 32 is eliminated. Also, this strip electrode 34
Since a sound absorbing material 37 is provided on the right end of the strip electrode 3, the surface acoustic waves that have passed through the strip electrode 34
Reflection at the right end of 4 is prevented.

Therefore, according to the present invention, it is possible to realize a surface acoustic wave in which no spurious due to acoustic reflection appears in the output signal.

[Other embodiments of the invention]

Figure 4 shows that the present invention has N pairs of electrode fingers (N=1..2.3...
・It is applied to a surface acoustic wave device equipped with an input/output quadrant transducer with N=2) configuration in Figure 1. , 34m, 35m and 1/8 wavelength width strip 33b.

The arrangement order of 34b and 35b matches the acoustic impedance distribution of the input and output quadrant transducers (it is changed depending on the structure of the input and output quadrant transducers 31 and 32).

FIG. 5 shows a configuration in which the present invention is applied to a surface acoustic wave device in which the phase of the electrically reflected wave that is re-excited due to a mismatch between the phase of the acoustically reflected wave generated within the transducer and the external load is in the opposite phase. show.

The transducer of this type of surface acoustic wave device has the effect of improving unnecessary reflected waves by reducing the magnitude of acoustic reflection and electrical reflection. However, even in this transducer structure, acoustic reflections occur at both ends of the transducer. The transducer is made by interlocking electrode fingers 50b with IA wavelength width and electrode fingers 50b with l wavelength width, and 1/8
It is constructed by interlocking a pair of electrode fingers 50a with a wavelength width and a pair of electrode fingers 50e with a v8 wavelength width. In the input/output quadrant transducer shown in FIG. 5, the acoustic impedance gradually changes in the aperture direction from the center of the transducer, and the electrode finger structure at both ends of the transducer is different from the electrode finger structure at the center. In such a structure, it is important to distribute the acoustic impedance of the surface acoustic wave propagation path so as to be continuous with the period of the acoustic impedance distribution near both ends of the transducer.

FIG. 6 shows the structure of a tap delay line having the transducer of FIG. 5, but similar to the surface acoustic wave device of FIG. 5, the composite wave of unnecessary acoustic reflected waves is made to be zero.

[Brief explanation of the drawing]

Figure 1 shows the basic transducer structure in which the electrode fingers are solid-shaped. Figure 2 shows the propagation path of the surface acoustic wave between the input and output quadrant transducers. FIG. 3 is a diagram showing a conventional surface acoustic wave device in which acoustic reflection is improved by arranging strips of different widths. FIG. 3 is a diagram showing an embodiment of the surface acoustic wave device of the present invention.
The figure shows an example in which the present invention is applied to a surface acoustic wave device having an input/output quadrant transducer structure with N pairs of electrode fingers, and Figure 5 shows an example in which the present invention is applied to a surface acoustic wave device having a different electrode structure. FIG. 6 is a diagram showing an example in which the present invention is applied to a tap delay line transducer. 30... Piezoelectric substrate, 31... Input transducer, 32... Output transducer, 33, 34. 35... Strip electrode, 36, 37...
・Sound absorbing agent.

Claims (2)

[Claims] (1) In a surface acoustic wave device formed by forming a comb-shaped first electrode on a piezoelectric substrate, the acoustic impedance of the propagation path in the traveling direction of the surface acoustic wave on both sides of the transducer is A surface acoustic wave device comprising nine strip electrodes distributed to match the period of acoustic impedance distribution. (2) The surface acoustic wave device according to claim 1, characterized in that the strip electrode wire has a sound absorbing material on the outer side of the electrode wire.