JP3436812B2 - Surface acoustic wave converter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave converter usually used as a narrow band filter, and in particular, a reflector is provided outside each of an input electrode and an output electrode. The present invention relates to a surface acoustic wave converter provided. 2. Description of the Related Art Conventionally, this type of surface acoustic wave converter 1 has
For example, as shown in FIG. 4, a piezoelectric substrate 2 in which an input electrode 3 and an output electrode 4 formed in a comb shape are opposed to each other.
On the outer sides of the electrodes 3 and 4, the electrodes 3 and 4
And a pair of reflectors 5 and 5 having a plurality of linear conductors 5a arranged in parallel to and at a constant interval with respect to the comb-teeth portion.
Then, the distance between the linear conductors 5a of the two reflectors 5, 5 is set to be the same so that a strong reflection effect is obtained. For example, the frequency characteristics of the reflection coefficients of the reflectors 5 and 5 are as shown in FIG. 5, and the transfer characteristics of the surface acoustic wave converter 1 are as shown in FIG. As shown in FIG. 5, the surface acoustic wave converter has a large reflection coefficient (substantially equal to "1") and a wide flat band. The effective reflection band by the reflector is widened,
In the transfer characteristic of the surface acoustic wave converter, as shown in a circle A in FIG. 6, a peak due to resonance may occur in an unnecessary pass band. On the other hand, the peak of resonance can be reduced by lowering the reflection efficiency of the reflector, but this increases transmission loss of the surface acoustic wave converter in a necessary pass band. An object of the present invention is to solve the above-mentioned problem, and to reduce the effective frequency range by a reflector to suppress a resonance peak in an unnecessary band, thereby improving the surface acoustic wave conversion with improved transfer characteristics. The purpose is to provide a vessel. [0005] In order to achieve the above object,
Because, the present invention is parallel on a piezoelectric substrate arranged input electrodes and output electrodes formed at intersections electrodes of pectinate shape in parallel to each other, the relative comb teeth of the electrodes on the outside of the electrodes To
In a pair of reflectors set only surface acoustic wave transducer comprising a plurality of linear conductors placed, the linear conductors of one of the reflectors
Place at different intervals as the linear conductors of the reflector other hand
So that the effective reflection band of both reflectors partially overlaps
To provide a surface acoustic wave converter characterized by the following.
It is. In the present invention constructed as described above, the frequency characteristic of the reflection coefficient moves on the frequency axis in accordance with the interval between a plurality of linear conductors in the reflector. Large reflection coefficient (approximately equal to "1")
In addition, the flat frequency band portions are shifted from each other (see the reflection bands R1 and R2 in FIG. 2). Since a flat frequency band having a large total reflection coefficient obtained by integrating both reflection coefficients is an overlapping portion of a large portion having the large both reflection coefficients, the flat frequency band having a large total reflection coefficient is narrowed. Therefore, the resonance peak in a portion other than the frequency band of the overlapping portion is suppressed, and the frequency transfer characteristic of the surface acoustic wave converter can be smoothed without increasing the transmission loss in a narrow bandwidth as required. . An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram schematically showing a surface acoustic wave converter according to the embodiment. The surface acoustic wave converter 10 includes LiNbO3, LiTaO3,
It has a piezoelectric substrate 11 in which a piezoelectric material such as quartz is formed in a rectangular parallelepiped shape. On the substrate 11, an input electrode 12 and an output electrode 13 respectively formed in a comb-shaped cross electrode are parallel to each other.
It is provided in. The input electrode 12 includes a pair of bases 12 a and 12 b arranged in parallel with the longitudinal direction of the piezoelectric substrate 11,
Vertically and alternately arranged from each base 12a, 12b
And a plurality of comb teeth 12c and 12d. Similarly to the input electrode 12, the output electrode 13 also has a pair of bases 13 arranged in parallel to the longitudinal direction of the piezoelectric substrate 11.
a, 13b, and comb teeth portions 13c, 13d, which are composed of a large number of comb teeth and are arranged perpendicularly from the respective base portions 13a, 13b so as to cross each other. [0009] A pair of reflectors 14 and 15 are provided opposite to each other outside the input electrode 12 and the output electrode 13 provided on the piezoelectric substrate 11. The reflector 14 has a rectangular shape composed of a number of linear conductors 14a having the same length and being parallel to the comb-tooth portions 12c, 12d, 13a, 13d, and a pair of connecting conductors 14b connecting both ends of each linear conductor 14a. It is formed in a shape. Similarly to the reflector 14, the reflector 15 is connected to a large number of linear conductors 15a having the same length and being parallel to the comb teeth 12c, 12d, 13a, 13d, and both ends of each linear conductor 15a. And a pair of connecting conductors 15b. However, the reflector 14
Is different from the distance d1 between the linear conductors 14a in the reflector 15 and the distance d2 between the linear conductors 15a in the reflector 15. In the state of use of the surface acoustic wave converter configured as described above, as shown in FIG.
A high-frequency oscillator 21 is connected to the bases 12a and 12b, and a resistor 22 is connected between the bases 13a and 13b of the output electrode 13, so that an output signal is obtained from both ends of the resistor 22. Thereby, the high-frequency electric signal from the high-frequency transmitter 21 is converted into a surface acoustic wave by the input electrode 12 ,
The surface acoustic wave propagates on the piezoelectric substrate 11 to the output electrode 13 and is converted into an electric signal again at the output electrode 13 and output. In this case, the input high-frequency electric signal is converted into a signal having a band-limited and predetermined frequency characteristic by the input electrode 12, the output electrode 13, the reflectors 14, 15, and the like, and is output. Here, the surface acoustic wave converted by the input electrode 12 propagates toward the output electrode 13 and
It is reflected by both reflectors 14,15. As described above, since the distance d1 between the linear conductors 14a and the distance d2 between the linear conductors 15a are different from each other, the reflection coefficients of the two reflectors 14 and 15 are large (almost). The frequency band portion which is equal to "1") and flat is shifted on the frequency axis. Since the frequency band having a large total reflection coefficient obtained by integrating the two reflection coefficients is an overlapping portion of the two reflection coefficients, the frequency band having a large total reflection coefficient is narrowed. Accordingly, the peak due to the resonance of the surface acoustic wave in a portion other than the frequency band of the overlapping portion, that is, in the stop band of the surface acoustic wave converter 10, is suppressed, and the elasticity can be increased without increasing the transmission loss in a narrow bandwidth as required. The frequency transfer characteristics of the surface acoustic wave converter 10 can be smoothed. This is shown by a simulation result using a surface acoustic wave converter 10 having the following specifications. (Specifications) Material of piezoelectric substrate 11: Quartz Intersection length of comb teeth of input electrode 12: 1700 μm Number of comb teeth: 397 Distance between comb teeth (electrode pitch): 15.790 μm Comb teeth of output electrode 13 Intersection length: 1700 μm Number of comb teeth: 397 Distance between comb teeth (electrode pitch): 15.790 μm Length of linear conductor of reflector 14: 1700 μm Number of linear conductors: 300 Distance between linear conductors (electrode pitch): 15.822 μm Linear conductor length of reflector 15: 1700 μm Number of linear conductors: 300 Distance between linear conductors (electrode pitch): 15.735 μm According to the surface acoustic wave converter 10 configured as described above, the reflector The frequency characteristic of the reflection coefficient 14 is substantially “1” in the range of approximately 99.4 to 100.2 MHz as shown by the solid line in FIG. 2, and the effective reflection band of the reflector 14 is The shows R1. On the other hand, the frequency characteristic of the reflection coefficient of the reflector 15 is approximately 100.0 to 10 as indicated by the dashed line in FIG.
It becomes almost “1” in the range of 0.8 MHz, and the reflector 15
Is an effective reflection band R2 shown in FIG. That is, the effective reflection band R2 of the reflector 15 is shifted to the high frequency side by about 0.6 MHz from the reflection band R1 of the reflector 14. As a result, the reflection region R3 in which the reflection coefficients of the two reflectors 14 and 15 are large (substantially equal to "1") is approximately 99.9 to 100.
This is a narrow range of 2 MHz. As described above, since the effective reflection band R3 of the reflector is narrowed, the frequency transfer characteristic of the surface acoustic wave converter 10 is improved as shown in FIG. That is, the resonance peak (in the circle A) existing in the frequency transfer characteristic of the conventional surface acoustic wave converter 10 shown in FIG. 6 has been removed as shown in the circle B in FIG. As a result, according to the above-described embodiment, the frequency transfer characteristics of the surface acoustic wave converter 10 can be made smooth without increasing the transmission loss in a narrow bandwidth as required. In the above embodiment, the reflector 1
Both ends of the plurality of linear conductors 14a and 15a are connected by connecting conductors 14b and 15b, respectively. The connecting conductors 14b and 15b reflect light when quartz or LiTaO3 is used as the piezoelectric substrate 11. The coupling conductors 14b and 15b are unnecessary when the reflection efficiency does not need to be increased so much even if the piezoelectric substrate 11 is made of quartz or LiTaO3. You may make it comprise only a plurality of linear conductors 14a and 15a only. Also, as the piezoelectric substrate 11
When LiNbO3 is used, the reflection efficiency when both ends of the linear conductors 14a and 15a are short-circuited by the connection conductors 14b and 15b and the reflection efficiency when not short-circuited depend on the design specifications of the surface acoustic wave converter 10. Therefore, the connecting conductors 14b and 15b may be appropriately provided or not provided according to the same specification. Further, the size, shape, etc. of each part of the surface acoustic wave converter 10 are not limited to those in the above embodiment.
It can be appropriately changed according to the intended use.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram schematically showing a surface acoustic wave converter according to one embodiment of the present invention. FIG. 2 is a graph showing a frequency characteristic of a reflection coefficient of a reflector of the surface acoustic wave converter. FIG. 3 is a graph showing a frequency transfer characteristic of the surface acoustic wave converter. FIG. 4 is a schematic diagram schematically showing a surface acoustic wave converter according to a conventional example. FIG. 5 is a graph showing a frequency characteristic of a reflection coefficient of a reflector of the surface acoustic wave converter. FIG. 6 is a graph showing a frequency transfer characteristic of the surface acoustic wave converter. [Description of Reference Numerals] 10: surface acoustic wave converter, 11: piezoelectric substrate, 12: input electrode, 12a, 12b: base, 12c, 12d: comb tooth, 13: output electrode, 13a, 13b: base, 13c,
13d: comb tooth portion, 14: reflector, 14a: linear conductor, 1
4b: connecting conductor, 15: reflector, 15a: linear conductor, 1
5b ... connecting conductor.

Continuation of the front page (56) References JP-A-4-265009 (JP, A) JP-A-3-261210 (JP, A) JP-A-8-181561 (JP, A) Jpn. , U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H03H 9/25 H03H 9/145

Claims (1)

(57) to the Claims 1 piezoelectric substrate arranged in parallel with each other the output electrode and the input electrodes formed respectively on the cross electrode of pectinate shape, the electrodes on the outside of the two electrodes the parallel to the comb teeth
In a pair of reflectors set only surface acoustic wave transducer comprising a plurality of linear conductors placed at different intervals of linear conductors of one of the reflectors and the interval of the linear conductors of the reflector other hand Arrange the effective reflection band of both reflectors
A surface acoustic wave converter characterized in that the polymer is partially polymerized .