JPH08186468A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE: To easily control the band width of the pass band by making the transmission characteristic of a surface acoustic wave device symmetrical to eliminate the peak. CONSTITUTION: An input electrode 12 provided With base parts 12a and 12b and a comb tooth part 12c consisting of many linear conductors 12c1 and 12d1 and an output electrode 13 provided with base parts 13a and 13b and comb tooth parts 12c and 12d consisting of many linear conductors 13c1 and 13d1 are arranged on a piezoelectric substrate 11 so as to face each other. Linear conductors 12c1, 12d1, 13c1, and 13d1 are divided in the lengthwise direction. A pair of reflectors 14 and 15 are provided on the outsides of the input electrode 12 and the output electrode 13 so as to face each other. Phases of surface acoustic waves reflected between divided linear conductors 12c1 and 12d1 are shifted from each other and are cancelled by each other to prevent the reflection of surface acoustic waves in input and output electrodes 12 and 13. Consequently, reflected waves of surface acoustic waves are controlled by only reflectors 14 and 15 to make the frequency transmission characteristic of the surface acoustic wave device symmetrical with the pass band as the center.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device used as a resonance type filter, and more particularly to a surface acoustic wave device having a reflector provided outside each of an input electrode and an output electrode.

[0002]

2. Description of the Related Art Conventionally, a surface acoustic wave device 1 of this type is provided with an input electrode 3 and an output electrode 4 facing each other on a piezoelectric substrate 2, as shown in FIG. The input electrode 3 includes a linear base portion 3a facing each other and a comb tooth portion 3b composed of a large number of linear conductors extending inward from the linear base portion 3a alternately in parallel with each other at regular intervals. It is configured. The output electrode 4 also includes linear base portions 4a facing each other, and comb-teeth portions 4b formed of a large number of linear conductors extending inward from the linear base portions 4a alternately in parallel with each other at regular intervals. It is configured. A plurality of linear conductors 5a are provided outside the input electrode 3 and the output electrode 4 on the piezoelectric substrate 2 in parallel with the comb teeth 3b, 4b and at a constant interval substantially equal to the input / output electrodes 3, 4. And a pair of reflectors 5 and 5, respectively.

In this surface acoustic wave device 1, the surface acoustic waves reflected by the reflectors 5 and 5 are confined between the input and output electrodes 3 and 4 as shown by W1 in FIG. 3 to reduce the transmission loss. It has the characteristics of Further, in this surface acoustic wave device 1, since the spacing and width of the linear conductors of the comb tooth portions 3b and 4b are substantially the same as the spacing and width of the linear conductor 5a of the reflectors 5 and 5, the input / output electrodes Also in 3 and 4, Fig. 3
As shown in W2 of the above, the surface acoustic wave was reflected. Therefore, various resonance modes occur in the surface acoustic wave device 1,
By utilizing this, the pass band of the electric signal could be widened.

[0004]

By the way, the transfer characteristics of the surface acoustic wave device 1 are as follows.
4 also reflects, so the pass band B is asymmetrical as shown in FIG. Therefore, even if an attempt is made to increase this when sufficient attenuation cannot be obtained in the stop band near the pass band B, it is not possible to remove unnecessary signals by utilizing the symmetry of the transfer characteristic, and the stop band It is not possible to improve the transfer characteristics by increasing the amount of attenuation sufficiently. Further, there is a problem that a peak P occurs due to resonance between the input / output electrodes 3 and 4 in the high frequency side stop band, the phase change at the peak frequency becomes large, and the circuit operation becomes unstable. Further, the surface acoustic wave device 1 uses various resonance modes to form a pass band, and these resonance modes influence each other, so that the characteristics are complicated, and therefore, the bandwidth is set to an arbitrary value. It is difficult to design the value.

The present invention is intended to solve the above-mentioned problems, and makes the passband of the transfer characteristic symmetrical so as to eliminate the peak in the transfer characteristic due to resonance between the input and output electrodes, thereby controlling the bandwidth of the passband. An object is to provide an easy surface acoustic wave device.

[0006]

In order to achieve the above object, a structural feature of the present invention is that a pair of base portions facing each other and a base portion of the same pair are alternately turned inward from the base portion and are opposed to each other. An input electrode and an output electrode each having a comb tooth portion formed of a large number of linear conductors extending in parallel are arranged in parallel, and on the outside of each of the input electrode and the output electrode on the piezoelectric substrate. In a surface acoustic wave device, each of which is provided with a pair of reflectors made of a plurality of linear conductors provided in parallel to the comb tooth portion and at regular intervals, each linear conductor of the comb tooth portion is divided in the longitudinal direction. There is something I did.

[0007]

In the present invention configured as described above, the linear conductor of the comb tooth portion is divided in the longitudinal direction, so that the elasticity reflected between the divided linear conductors. It is possible to prevent the surface acoustic waves from being reflected by the input / output electrodes by offsetting the phase of the surface waves and canceling each other. Therefore, the phase change of the output signal due to the reflection by the input / output electrodes can be reduced, and the circuit using the surface acoustic wave device can be stabilized. Also, since the reflection of surface acoustic waves at the input / output electrodes is prevented from occurring only at the reflectors on both sides, the transfer characteristics of the surface acoustic wave device are symmetrical with respect to the pass band. Therefore, it becomes possible to remove the unnecessary signal in the stop band by using this symmetry.

Further, since this surface acoustic wave device forms the pass band by using only the resonance mode between the reflectors, it is possible to utilize many higher order modes by increasing the distance between the reflectors. Therefore, the maximum pass band can be widened. Further, by adjusting the distance between the reflectors, the pass band width can be designed to an arbitrary value.
As a result, when designing a resonance filter using this surface acoustic wave device, the degree of freedom in design is increased and the design is facilitated.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing a surface acoustic wave device according to the embodiment.

The surface acoustic wave device 10 includes a piezoelectric substrate 11 in which a piezoelectric material such as LiNbO3, LiTaO3, and quartz is formed into a rectangular parallelepiped shape. On the piezoelectric substrate 11, an input electrode 12 and an output electrode 13 formed in a comb shape are provided so as to face each other. The input electrode 12 includes a pair of bases 12a and 12b extending parallel to the long side direction of the piezoelectric substrate 11 and a large number of lines extending vertically and alternately from the bases 12a and 12b at equal intervals. It is composed of comb-tooth portions 12c and 12d composed of conductors 12c1 and 12d1.
Each of the linear conductors 12c1 and 12d1 is divided into two along the longitudinal direction at the central position, and is composed of a pair of divided linear conductors arranged in parallel with each other at a predetermined interval.

These large numbers of divided linear conductors have a space or width between them which will be described later.
When the distance and the width are equal to 4a and 15a (for example, 1/4 wavelength of the surface acoustic wave to be passed through the surface acoustic wave device 10), the reflection is increased. Each of the linear conductors 14a and 15a of 14 and 15
Different from the spacing or width of the. In this example,
The intervals and widths of a large number of divided linear conductors are set to values slightly deviated from half of the intervals and widths of the linear conductors 14a and 15a of the reflectors 14 and 15. However, if the intervals and widths are different, it is particularly about half. No need to set. However, the intervals and widths of the large number of divided linear conductors are set to values near 1/8 wavelength of the surface acoustic wave to be passed through the surface acoustic wave device 10 due to problems in exciting or receiving the surface acoustic wave. Is desirable.

Similarly to the input electrode 12, the output electrode 13 also has
A comb tooth portion 13 including a pair of base portions 13a and 13b and a large number of linear conductors 13c1 and 13d1 extending vertically and alternately from the base portions 13a and 13b at equal intervals.
c, 13d. Each linear conductor 13c
Each of 1 and 13d1 is also divided into two along the longitudinal direction at the central position, and is composed of a pair of divided linear conductors that are arranged in parallel with each other at a predetermined interval. The intervals and widths of these many divided linear conductors are the same as in the case of the input electrode 12.

A pair of reflectors 14 and 15 are provided on the outside of the input electrode 12 and the output electrode 13 on the piezoelectric substrate 11 so as to face each other. The reflector 14 is provided for each comb tooth portion 1.
It is formed in a rectangular shape by a plurality of linear conductors 14a arranged parallel to 2c, 12d, 13c and 13d at equal intervals and a connecting conductor 14b connecting both ends of each linear conductor 14a. Similarly to the reflector 14, the reflector 15 also has a rectangular shape with a plurality of linear conductors 15a parallel to the comb teeth 12c, 12d, 13c, 13d and a connecting conductor 15b connecting both ends of each linear conductor 15a. Is formed in. The intervals and widths of the linear conductors 14a and 15a of the reflectors 14 and 15 are equal to each other, and are set to ¼ wavelength of the surface acoustic wave to be passed through the surface acoustic wave device 10.

When the surface acoustic wave device configured as described above is in use, as shown in FIG. 1, a high frequency oscillator 21 is connected to the base 12a of the input electrode 12 and a resistor 22 is connected to the base 13a of the output electrode 13. Connected and base 12
b and 13b are grounded so that an output signal is obtained from both ends of the resistor 22. As a result, the high frequency electric signal from the high frequency oscillator 21 is converted into a surface acoustic wave by the input electrode 12, the surface acoustic wave is propagated to the output electrode 13 and is converted into an electric signal again by the output electrode 13 and output. It 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 12, the output electrode 13, the reflectors 14 and 15 and the like, and then output.

Here, the surface acoustic wave converted by the input electrode 12 propagates toward the output electrode 13 as shown by W1 in FIG. 1 and reaches both reflectors 14 and 15,
It is reflected by both reflectors 14 and 15. However, in the input electrode 12 and the output electrode 13, as shown by W2 in FIG. 1, since the linear conductors 12c1, 12d1, 13c1, 13d1 of the comb tooth portions 12c, 12d, 13c, 13d are divided, Each linear conductor 12c1, 12d1, 13c
Since the phase of the reflected wave reflected by each of the divided linear conductors obtained by dividing 1 and 13d1 is offset and the reflected wave is canceled, the reflection of the surface acoustic wave at the input electrode 12 and the output electrode 13 is prevented. Therefore, since the reflection of the surface acoustic wave occurs only in the reflectors 14 and 15 on both sides, the frequency transfer characteristic of the surface acoustic wave device 10 is symmetrical about the pass band.

When this is shown using the simulation result of the surface acoustic wave device 10 according to the specifications of Table 1 below, the frequency transfer characteristic of the device 10 is as shown in FIG.

[0017]

[Table 1] Material of the piezoelectric substrate 11: Crossing length of comb teeth of the crystal input electrode 12: 1700 μm Number of comb teeth: 310 Distance between each divided linear conductor: 3.9 μm Width of each divided linear conductor: 3 .9 μm Crossing length of comb teeth of output electrode 13: 1700 μm Number of comb teeth: 310 Distance between each divided linear conductor: 3.9 μm Width of each divided linear conductor: 3.9 μm Linear conductor of reflector 14 Length: 1700 μm Number of linear conductors: 300 Distance between each linear conductor: 7.9 μm Width of each linear conductor: 7.9 μm Linear conductor length of reflector 15: 1700 μm Number of linear conductors: 300 Between each linear conductor Distance: 7.9 μm Width of each linear conductor: 7.9 μm As can be seen from the frequency characteristics of FIG. 2, in the surface acoustic wave device 10 according to the present embodiment, the reflection due to the input electrode 12 and the output electrode 13 causes Of the output signal The phase change can be reduced and the circuit using the surface acoustic wave device 10 can be stabilized. Further, by preventing the reflection of the surface acoustic wave at the input electrode 12 and the output electrode 13, the reflection of the surface acoustic wave occurs only at the reflectors 14 and 15 on both sides, so that the surface acoustic wave device 10 has a frequency transfer characteristic. It becomes symmetrical about the pass band, and it becomes possible to remove unnecessary signals in the stop band by using this symmetry.

Further, since the surface acoustic wave device 10 forms the pass band by using only the resonance mode between the reflectors, by increasing the distance between the reflectors 14 and 15, many higher order modes can be obtained. Can be used, and thus the maximum passband can be widened. Furthermore, the reflectors 14, 1
The bandwidth of the pass band can be designed to an arbitrary value by adjusting the distance between the five. As a result, in designing a resonance filter using the surface acoustic wave device 10, the degree of freedom in design is increased and the design is simplified.

In the above embodiment, the reflector 1
Although both ends of the plurality of linear conductors 14a and 15a of 4 and 15 are connected by the connecting conductors 14b and 15b, respectively, the connecting conductors 14b and 15b are reflections when quartz or LiTaO3 is used as the piezoelectric substrate 11. This is used to increase the efficiency. Even if the piezoelectric substrate 11 is made of quartz or LiTaO3 and the reflection efficiency does not need to be increased so much, the connecting conductors 14b and 15b are unnecessary and the reflectors 14 and 15 are used. You may make it comprised only with the some linear conductor 14a, 15a. In addition, 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 connecting conductors 14b and 15b and the reflection efficiency when not short-circuited are determined according to the design specifications of the surface acoustic wave device 10. Since it changes, it is preferable to appropriately provide or not provide the connecting conductors 14b and 15b according to the same specifications.

Further, the size, shape, etc. of each part of the surface acoustic wave device 10 are not limited to those in the above embodiment,
It can be appropriately changed depending on the intended use.

[Brief description of drawings]

FIG. 1 is a schematic diagram schematically showing a surface acoustic wave device according to an embodiment of the present invention.

FIG. 2 is a graph showing frequency transfer characteristics of the surface acoustic wave device.

FIG. 3 is a schematic diagram schematically showing a surface acoustic wave device according to a conventional example.

FIG. 4 is a graph showing frequency transfer characteristics of the surface acoustic wave device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Surface acoustic wave device, 11 ... Piezoelectric substrate, 12 ... Input electrodes, 12a, 12b ... Base part, 12c, 12d ... Comb tooth part,
12c1, 12d1 ... Linear conductor, 13 ... Output electrode, 13
a, 13b ... Base portion, 13c, 13d ... Comb tooth portion, 13c
1, 13d1 ... Linear conductor, 14 ... Reflector, 14a ... Linear conductor, 14b ... Connection conductor, 15 ... Reflector, 15a ... Linear conductor, 15b ... Connection conductor.

Claims (1)

[Claims] 1. A piezoelectric substrate is provided with a pair of base portions facing each other and a comb-tooth portion formed of a plurality of linear conductors extending inward alternately and in parallel from the same pair of base portions. And a plurality of linear conductors provided on the outside of the input electrode and the output electrode on the piezoelectric substrate in parallel with the comb teeth and at regular intervals. A surface acoustic wave device having a pair of reflectors, wherein each linear conductor of the comb tooth portion is divided in the longitudinal direction.