JPH0653772A - Variable frequency surface acoustic wave function element and variable frequency filter - Google Patents

Abstract

PURPOSE:To obtain a variable frequency converter function element and the variable frequency filter by changing the frequency so as to make the imaginary part of the impedance of the surface acoustic wave function element and the filter using an image connection converter zero. CONSTITUTION:As to the method making an imaginary part of an impedance of interdigital electrodes 2, 3 zero at a frequency, a varactor diode 17 whose electric capacitance is changed due to a change in a voltage is employed to insert a proper inductance 18. Thus, the variable frequency conversion function element and the variable frequency filter are obtained. Or no inductance 18 may be employed in a case. Or as the method to make the imaginary part of the impedance of the interdigital electrodes 2, 3 zero, a variable inductance is employed to obtain the variable frequency conversion function element and the variable frequency filter. Various methods such as series connection or parallel connection are considered as the connection method of two interdigital electrodes of the image connection converter and the insertion method of the impedance.

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 functional element using an image connection converter in a functional element having an interdigital electrode structure provided on a piezoelectric substrate, an electrostrictive substrate or a piezoelectric thin film substrate. Also, the present invention relates to a variable frequency converter functional element and a variable frequency filter having a selection characteristic by changing the frequency at which the imaginary part becomes zero.

[0002]

2. Description of the Related Art Interdigital electrode consisting of positive and negative electrodes provided on a piezoelectric substrate, an electrostrictive substrate or a piezoelectric thin film substrate, a functional element and a filter using a surface acoustic wave surface transducer are generally interdigital. Since the frequency characteristic is determined by the period of the electrode, a functional element and a filter having variable frequency characteristics cannot be obtained. On the other hand, Fig. 1, a functional element in which the interdigital transducer 4 provided on the piezoelectric substrate, the electrostrictive substrate, or the piezoelectric thin film substrate 1 generates the surface acoustic wave 6, and the interdigital electrode 5 receives the surface acoustic wave 6. , The interdigital transducers 2 and 3 provided therebetween are shown in FIG. Consider an image connection converter 23 connected as shown in FIG. This image connection converter 2
3 shows that when the imaginary part of the impedance of the interdigital transducer becomes almost zero, the interdigital electrodes having the same real number are connected to each other so that the surface acoustic wave signal received by one of the interdigital electrodes 2 is completely transmitted to the other. Since the interdigital transducer 3 has a characteristic of emitting as a surface acoustic wave, a surface acoustic wave functional element and a filter are obtained by using the frequency characteristic of the emission. In this case, since the frequency at which the imaginary part becomes zero is fixed, a surface acoustic wave functional element and a filter having variable frequency characteristics cannot be obtained.

[0003]

The problem to be solved by the present invention is that a conventional surface acoustic wave filter has a frequency characteristic which is determined by the period of the interdigital transducer, and therefore a surface acoustic wave functional element and a filter with variable frequency can be obtained. What has not existed is to obtain a variable frequency surface acoustic wave functional element and a filter.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a variable frequency surface acoustic wave converter and a filter using a variable frequency image connection converter. That is, in the interdigital electrodes provided on the piezoelectric substrate, the electrostrictive substrate, or the piezoelectric thin film substrate, when the imaginary part of the impedance of the interdigital electrode becomes substantially zero, the interdigital electrodes having the same real part are connected to each other. By doing so, in the surface acoustic wave functional element and the filter using the image connection converter in which the surface acoustic wave signal received by one of the interdigital electrodes is completely emitted as the surface acoustic wave by the other interdigital electrode, the imaginary part is The present invention relates to a variable frequency converter functional element and a variable frequency filter obtained by changing a frequency that becomes zero.

[0005]

Example FIG. By connecting the impedance element 9 as shown in 2, the variable frequency surface acoustic wave converter and the filter can be obtained by setting the imaginary part of the impedance to zero with respect to the change in frequency. In this case, the impedance element 9 may be connected as shown in the figure, or one of the impedance elements 9 may be connected to the ground side.
There is also a method of connecting the above, which is also included in this patent.
Also, Fig. The same applies to the filters of FIGS.
As shown in FIG. 3, as an example of the structure of the image connection converter, an image connection converter having a structure in which internal reflection type unidirectional converters 7 and 8 are connected and an impedance element 9 are used. By taking the imaginary part of the impedance as an example, a frequency-variable surface acoustic wave functional element and a filter can be obtained. As shown in FIG. 4, as the structure of the image connection converter, by using the image connection converter in which the group type unidirectional interdigital electrodes are used and 0 ° phases are connected to each other and 90 ° phases are connected to each other, the frequency of f ₁ is increased. Then, the surface acoustic wave is directed to the right 6
A surface acoustic wave functional element of a two-frequency type using a method in which a frequency of f ₂ is incident from the left side 6b, an imaginary part is almost zero at each frequency, and radiation is performed in the directions of 6a and 6b. And a filter is obtained. Further, by connecting the impedance element 9 and changing the frequency at which the imaginary part becomes zero, a two-frequency variable frequency converter function element and a variable frequency filter can be obtained. Fig. As shown in Fig. 5, as the structure of the image connection converter, the image connection converter having a structure in which the positive and negative electrodes 13 and 14 having different periods are arranged in the propagation direction of the surface acoustic wave is used, and the impedance element 9 is connected to vary the structure. A frequency converter functional element and a variable frequency filter are obtained. Fig. As shown in FIG. 6, as the structure of the image connection converter, the image connection converter having a structure in which positive and negative electrodes having different electrode periods are arranged in a direction perpendicular to the propagation direction of the surface acoustic wave is used to connect the impedance element 9. As a result, a variable frequency converter functional element and a variable frequency filter are obtained. As a method to make the imaginary part of the interdigital transducer zero with respect to the frequency, Fig. 7, a variable frequency converter functional element and a variable frequency filter are obtained by using a varactor diode 17 whose electric capacity changes with a change in voltage and inserting an appropriate inductance 18. In this case, there may be no inductance 18. Further, by using the variable inductance 19 as a method of making the imaginary part of the interdigital transducer zero with respect to the frequency, a variable frequency converter functional element and a variable frequency filter can be obtained. The connection method of the two interdigital electrodes of the image connection converter and the insertion method of the impedance 9 are serial connection,
Various methods such as parallel connection are conceivable, and these are also included in this patent. The image connection converter having the above structure can be applied to a surface acoustic wave resonator, an oscillator, a delay line, etc., and is included in this patent.

[0007]

As an effect of the present invention, it is possible to obtain a variable frequency surface acoustic wave converter and a filter having a narrow bandwidth, which has not been obtained conventionally. Such a filter is useful as a filter for electronic communication, especially for a mobile phone.

[0008]

[Brief description of drawings]

FIG. 1 is a plan view of a filter using an image connection converter and a cross-sectional view through the center of an electrode.

FIG. 2 shows a variable frequency surface acoustic wave functional element and a filter in which an impedance element is connected to an image connection converter.

FIG. 3 shows a variable frequency surface acoustic wave and a filter using a unidirectional converter as an image connection converter.

FIG. 4 shows a variable frequency surface acoustic wave functional element and a filter using group type unidirectional interdigital transducers as an image connection converter.

FIG. 5 shows a variable frequency surface acoustic wave and a filter using distributed interdigital transducers as an image connection converter.

FIG. 6 shows a variable frequency surface acoustic wave functional element and a filter using interdigital transducers having different periods in a direction perpendicular to a propagation direction as an image connection converter.

FIG. 7 shows a variable frequency surface acoustic wave and a filter using a varactor diode as a method of making the imaginary part of the impedance of the image connection converter zero.

FIG. 8 shows a variable frequency surface acoustic wave and a filter using a variable inductance as a method for making the imaginary part of the impedance of the image connection converter zero.

[Explanation of symbols]

1. ... Piezoelectric substrate, 2. … Interdigital electrodes, 3. ... Interdigital electrodes, 23. ... Image connection converter (converter in which 2 and 3 are connected), 4. ... input converter, 5. ... Output converter, 6. …
Surface acoustic wave, 20. ... Direction of propagation of electric signal, 9. ... Inductance element, 7. … Floating electrode unidirectional converter, 8.
… Floating electrode unidirectional converter, 10. ... Group type unidirectional interdigital transducer, 0 ° phase electrode, 11. … Connection electrodes, 1
2. ... 90 ° phase electrode, 6a. ... Propagation direction of surface acoustic wave, 6b. ... Direction of propagation of surface acoustic wave, 13. ... Dispersion type interdigital transducer, 14. ... Dispersive interdigital transducers, 15. …
Variable period interdigital transducer, 16. ... Variable-cycle interdigital transducers, 17. ... Varactor diode, 18. ... inductance, 19. … Variable inductance

Claims (7)

[Claims] 1. A comb-shaped electrode provided on a piezoelectric substrate, an electrostrictive substrate, or a piezoelectric thin film substrate, wherein when the imaginary part of the impedance of the comb-shaped electrode is substantially zero, the real part is the same. By connecting each other,
The frequency at which the imaginary part becomes zero in a surface acoustic wave function element and filter using an image connection converter in which the surface acoustic wave signal received by one of the interdigital transducers is completely emitted as a surface acoustic wave by the other interdigital electrode. A variable frequency converter functional element and a variable frequency filter obtained by changing the. 2. A variable frequency converter functional element and a variable frequency filter using an image connection converter having a unidirectional converter structure as a structure of the image connection converter according to claim 1. 3. A group-type unidirectional interdigital transducer is used as the structure of the image connecting converter as the structure of the image connecting converter according to claim ₁ , wherein f ₁ At the frequency of, the imaginary part becomes almost zero when the surface acoustic wave propagates in the right direction, while at the frequency of f ₂ , when the left direction, the imaginary part becomes almost zero. And a two-frequency variable frequency converter functional element and a variable frequency filter obtained by changing the frequency at which the imaginary part becomes zero. 4. The image connection converter according to claim 1 or 2, wherein the image connection converter has a structure in which positive and negative electrodes having different periods are arranged in a propagation direction of a surface acoustic wave. Variable frequency converter functional element and variable frequency filter. 5. The positive and negative electrodes having different electrode periods are arranged in the direction perpendicular to the propagation direction of the surface acoustic wave as the structure of the image connection converter according to claims 1 and 2. A variable frequency converter functional element and a variable frequency filter using a structural image connection converter. 6. Claims 1 and 2 and 3
In the paragraphs (4), (4) and (5), as a method of making the imaginary part of the interdigital transducer zero with respect to the frequency, a variable frequency converter functional element and a variable frequency converter using a varactor diode whose electric capacitance changes with a change in voltage Frequency filter. 7. Claims 1 and 2 and 3
A variable frequency converter functional element and a variable frequency filter using an inductance as a method for reducing the imaginary number part of the interdigital transducer in terms of frequency, frequency, and frequency.