JP2006074838A - Surface acoustic wave high-frequency filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave high-frequency filter which decreases an insertion loss and simultaneously obtains a high attenuation amount out of bands. <P>SOLUTION: A surface acoustic wave high-frequency filter of the present invention is comprised of surface acoustic wave resonators 52-54 with input/output terminals connected in series to signal lines and surface acoustic wave resonators 38-40 with one side of input/output terminals being connected to said signal lines and another side being grounded. The surface acoustic wave resonator 52 comprises inter-digital electrode surface acoustic wave transducers 8, 9 connected in series, the surface acoustic wave resonator 53 comprises inter-digital electrode surface acoustic wave transducers 10, 11 connected in series, and the surface acoustic wave resonator 54 comprises inter-digital surface acoustic wave transducers 12, 13 connected in series. The impedance of each of the surface acoustic wave resonators 52-54 connected in series to the signal lines has four-fold impedance in comparison with the impedance of the surface acoustic wave resonators 38-40 connected in parallel to the signal lines. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface acoustic wave high frequency filter.

  With the rapid spread of automobiles and mobile phones in recent years, the need for surface acoustic wave high-frequency filters has increased as small and high-performance high-frequency filters, and transversal filters that are already a type of surface acoustic wave high-frequency filters are already in practical use. It has become.

  However, as a further characteristic improvement problem, it is desired to reduce the loss and make the matching circuit unnecessary. Therefore, a resonator type filter has been attracting attention. Various methods of configuring the resonator type filter are considered. Here, a ladder type surface acoustic wave high frequency filter (for example, see Patent Document 1), which is one of them, will be described.

  FIG. 11 is a circuit diagram of a conventional surface acoustic wave high frequency filter, and FIG. 12 is an equivalent circuit diagram thereof. In the figure, reference numerals 107 to 109 denote surface acoustic wave resonators connected in parallel to the signal lines, and reference numerals 110 to 112 denote surface acoustic wave resonators connected in series to the signal lines. The first surface acoustic wave resonators 107 and 110 form a first filter functional unit, the surface acoustic wave resonators 108 and 111 form a second filter functional unit, and the surface acoustic wave resonators 109 and 112 form a first filter functional unit. Three filter functional units are formed. The surface acoustic wave resonators 107 to 112 are two-terminal resonators having double resonance characteristics. In the figure, reference numerals 50 and 51 denote input / output terminals of the surface acoustic wave high frequency filter.

FIG. 13 is a graph showing idealized frequency characteristics of the surface acoustic wave resonator. For simplicity of explanation, the impedance is assumed to be pure reactance here, and that of the resonators 110 to 112 connected in series is indicated as X ₁ , and that of the resonators 107 to 109 connected in parallel is indicated as X ₂ .

  Now, since each resonator has a double resonance characteristic, its impedance has two resonance frequencies of 0 and infinity. A frequency at which the impedance becomes 0 is called a resonance frequency or resonance point, and a frequency at which the impedance becomes infinite is called an anti-resonance frequency or anti-resonance point.

When the resonance points of the resonators 110 to 112 coincide with the antiresonance points of the resonators 107 to 109, the resonators 110 to 112 are turned on and the resonators 107 to 109 are turned off in the vicinity of the frequency. Therefore, it becomes a pass band. On the other hand, since the resonators 110 to 112 are turned off at the antiresonance point, an attenuation pole is generated on the higher frequency side than the pass band. Further, since the resonators 107 to 109 are turned on at the resonance point, an attenuation pole is generated even at a lower frequency side than the pass band.
Japanese Patent Laid-Open No. 4-81823

  However, with the conventional surface acoustic wave high-frequency filter, it is impossible to secure a high out-of-band attenuation, as is apparent from the frequency characteristics of FIG. On the other hand, if an attempt is made to obtain a high out-of-band attenuation, the insertion loss increases.

  The solution is to compare the frequency characteristics of the impedance of the resonator connected in series with the signal line with the frequency characteristics of the impedance of the resonator connected in parallel to the signal line, It is effective to make the frequency steep while maintaining the frequency difference.

  As a method of making the impedance characteristic steep, for example, there is a method of reducing the electrode index of the saddle-shaped electrode surface acoustic wave converter. However, this method is not suitable for the above purpose because the impedance change occurs unintentionally on the low frequency side and the high frequency side, and the frequencies of the resonance point and the antiresonance point change.

  There is also a method for reducing the crossing width of electrode fingers (see Japanese Patent Laid-Open No. 4-81823). However, if the crossing width of the electrode fingers is reduced to about a fraction of the original, there are factors that are difficult to calculate, such as stray capacitance at the end surfaces of the electrode fingers and the interaction between the electrode surface wave and the electrode finger connection electrode. It cannot be ignored, and the frequency difference between the resonance point and the anti-resonance point also changes.

  In view of the above circumstances, the present invention compares the frequency characteristic of the impedance of a resonator connected in series with a signal line with the frequency characteristic of the impedance of a resonator connected in parallel to the signal line, The purpose is to make it steep while keeping the frequency difference at the anti-resonance point.

  In order to solve the above problems, a surface acoustic wave high-frequency filter according to the present invention includes a first surface acoustic wave resonator in which an input / output terminal is connected in series to a signal line, and an input / output terminal connected to the signal line. A surface acoustic wave high frequency filter comprising a filter functional unit comprising a second surface acoustic wave resonator having one connected and the other grounded, wherein the first surface acoustic wave resonator includes a saddle electrode elastic surface. It is characterized by having two or more wave converters in series.

  The surface acoustic wave high frequency filter of the present invention includes a first surface acoustic wave resonator in which an input / output terminal is connected in series to a signal line, and one of the input / output terminals is connected to the signal line and the other is grounded. In the surface acoustic wave high-frequency filter comprising a filter functional unit including the second surface acoustic wave resonator formed, the second surface acoustic wave resonator includes two or more saddle electrode surface acoustic wave transducers. It is characterized by having parallel.

  Further, in the above configuration, two or more filter function units may be provided in series.

  In the first configuration, the impedance of the surface acoustic wave resonator including the two saddle-shaped electrode surface acoustic wave transducers in series is shown in FIG. This is twice that of a single one (shown by the solid line).

  That is, if the impedance of a resonator having only one saddle-shaped surface acoustic wave transducer is Z1 (f), the impedance of resonance Z2 (f) having two saddle-shaped electrode surface acoustic wave transducers in series is shown. Is expressed by the following equation.

  As described above, the frequency characteristic of the impedance of the first surface acoustic wave resonator maintains the frequency difference between the resonance point and the antiresonance point as compared with the frequency characteristic of the impedance of the second surface acoustic wave resonator. It becomes steep. Therefore, it is possible to reduce the insertion loss and obtain a high attenuation amount outside the band.

  Further, in the second configuration, the impedance of the surface acoustic wave resonator provided with two saddle-shaped electrode surface acoustic wave transducers in parallel is shown in FIG. It is half that of a single vessel (shown by the solid line).

  That is, assuming that the impedance of a resonator having only one saddle-shaped surface acoustic wave transducer is Z1 (f), the impedance of resonance Z3 (f) having two saddle-shaped electrode surface acoustic wave transducers in parallel is provided. Is expressed by the following equation.

  Therefore, even if the frequency characteristic of the impedance of the first surface acoustic wave resonator remains as it is, the gradient becomes steep in comparison with the impedance of the second surface acoustic wave resonator, so that the insertion loss can be reduced and at the same time out of band. In this case, it is possible to ensure a high attenuation.

  As described above, according to the present invention, the frequency characteristic of the impedance of the resonator connected in series to the signal line is compared with the frequency characteristic of the impedance of the resonator connected in parallel to the signal line. Since the frequency difference between the point and the anti-resonance point can be maintained steep, it is possible to satisfy both the low insertion loss and the high out-of-band attenuation at the same time.

  Hereinafter, the present invention will be described with reference to the drawings showing embodiments thereof.

Example 1
FIG. 1 shows a schematic plan view of a surface acoustic wave high-frequency filter, and FIG. 2 shows an equivalent circuit diagram thereof.

  The surface acoustic wave high-frequency filter includes a first filter functional unit including surface acoustic wave resonators 38 and 52, a second filter functional unit including surface acoustic wave resonators 39 and 53, and a surface acoustic wave resonator 40. , 54 are connected in series to a third filter function unit. The first to third filter functional units are formed on the piezoelectric substrate 1 made of lithium tantalate.

  Each of the surface acoustic wave resonators 52, 53, 54 includes input / output terminals, and these input / output terminals are connected in series to a signal line. On the other hand, the surface acoustic wave resonators 38, 39, and 40 have one of their input / output terminals connected to the signal line and the other grounded. In the figure, 50 is an input terminal in the surface acoustic wave high frequency filter, and 51 is an output terminal.

  The above-described surface acoustic wave resonators 38 to 40 connected in parallel are each one saddle-shaped electrode surface acoustic wave transducer 2, 3, 4 and a pair of strip-type ladder reflectors 14, 15, 16 sandwiching it. , 17, 18, 19.

  On the other hand, in the surface acoustic wave resonators 52 to 54 connected in series to the signal line, the surface acoustic wave resonator 52 includes saddle-shaped electrode surface acoustic wave converters 8 and 9 connected in series, and includes surface acoustic waves. The resonator 53 includes saddle electrode surface acoustic wave converters 10 and 11 connected in series, and the surface acoustic wave resonator 54 includes saddle electrode surface acoustic wave converters 12 and 13 connected in series. . A pair of strip-type ladder reflectors 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, and 37 are provided so as to sandwich the saddle electrode surface acoustic wave transducers 8 to 13. It has been.

  That is, the surface acoustic wave resonator 52 includes surface acoustic wave resonators 44 and 45 connected in series, and the surface acoustic wave resonator 53 includes surface acoustic wave resonators 46 and 47 connected in series. The wave resonator 54 includes surface acoustic wave resonators 48 and 49 connected in series.

  The above-mentioned saddle-shaped electrode surface acoustic wave transducers 2 to 4 and 8 to 13 all have 100 electrode indexes. However, the crossing width of the electrode fingers in the saddle-shaped electrode surface acoustic wave transducers 2 to 4 is 200 μm, and the crossing width of the electrode fingers in the saddle-shaped electrode surface acoustic wave transducers 8 to 13 is 100 μm.

  The strip ladder reflectors 14-19 and 26-37 all have 180 electrode indexes.

  According to the above configuration, the impedance of the surface acoustic wave resonators 52 to 54 connected in series to the signal line is compared with the impedance of the surface acoustic wave resonators 38 to 40 connected in parallel to the signal line. It has 4 times the impedance and its frequency characteristics become steep. This is because each of the surface acoustic wave resonators 52 to 54 includes two saddle-shaped electrode surface acoustic wave transducers 44, 45, 46, 47, 48, and 49 in series, and these saddle-shaped electrode elasticities. This is because the crossing width of the electrode fingers in the surface acoustic wave converter is half the crossing width of the electrode fingers in the surface acoustic wave resonators 38 to 40.

  As described above, the slope of the impedance characteristic becomes steep without moving the resonance point and the anti-resonance point, so that the insertion loss can be reduced and at the same time a high attenuation can be obtained outside the band.

  FIG. 3 is a graph showing frequency characteristics of the surface acoustic wave high-frequency filter having the above structure. Compared with the graph of FIG. 14 showing the frequency characteristics of the conventional structure of FIG. 11, it can be seen that the out-of-band attenuation is greater than 20 dB.

(Example 2)
Hereinafter, another embodiment of the present invention will be described with reference to FIGS.

  In the surface acoustic wave high-frequency filter of the present embodiment, a pair of strip-type ladder reflectors are provided in each of the two saddle-shaped surface acoustic wave transducers in the surface acoustic wave resonator connected in series to the signal line in the first embodiment. In contrast to this, in this embodiment, as shown in FIG. 4, two saddle-shaped electrode surface acoustic wave transducers 5a, 5a and 5b in surface acoustic wave resonators 52, 53, 54 connected in series to signal lines are provided. 5b, 6a, 6b, 7a, 7b is configured to share a pair of strip ladder reflectors 20, 21, 22, 23, 24, 25, respectively. FIG. 5 is an enlarged schematic plan view showing one of the surface acoustic wave resonators connected in series to the signal line.

  The electrode index in each of the two saddle-shaped surface acoustic wave transducers 5a, 5b, 6a, 6b, 7a, 7b is 100, and the crossing width is set to 100 μm. The strip ladder reflectors 20, 21, 22, 23, 34, and 25 all have 180 electrode indexes.

  Also in the surface acoustic wave high-frequency filter having the above-described configuration, a structure in which two bowl-shaped electrode surface acoustic wave transducers are connected in series as in the first embodiment is obtained. Therefore, the slope of the impedance characteristic becomes steep without moving the resonance point and the anti-resonance point, and the insertion loss can be reduced, and at the same time, a high attenuation can be secured outside the band. In addition, since the strip-type ladder reflector is shared, the space for forming the surface acoustic wave resonator is reduced, and the surface acoustic wave high-frequency filter can be downsized.

(Example 3)
Another embodiment of the present embodiment will be described with reference to FIGS.

  FIG. 6 is a schematic plan view of the surface acoustic wave high-frequency filter, and FIG. 7 is an equivalent circuit diagram thereof.

  The surface acoustic wave high-frequency filter includes a first filter functional unit including surface acoustic wave resonators 82 and 85, a second filter functional unit including surface acoustic wave resonators 83 and 86, and a surface acoustic wave resonator 84. , 87 are connected in series with a third filter functional unit.

  Each of the surface acoustic wave resonators 85, 86, 87 includes an input / output terminal, and these input / output terminals are connected in series to a signal line. On the other hand, the surface acoustic wave resonators 82, 83, 84 have one of their input / output terminals connected to the signal line and the other grounded.

  The above-described surface acoustic wave resonators 85 to 87 connected in series are each one saddle-shaped electrode surface acoustic wave transducer 64, 65, 66 and a pair of strip-type ladder reflectors 76, 77, 78 sandwiching it. , 79, 80, 81.

  On the other hand, in the surface acoustic wave resonators 82 to 84 connected in parallel to the signal lines, the surface acoustic wave resonator 82 includes saddle-shaped electrode surface acoustic wave converters 58 and 59 connected in parallel, and the surface acoustic wave resonators are provided. The resonator 83 includes saddle electrode surface acoustic wave transducers 60 and 61 connected in parallel, and the surface acoustic wave resonator 84 includes saddle electrode surface acoustic wave transducers 62 and 63 connected in series. .

  Strip ladder reflectors 68, 67, 69 are formed between and on the side of the saddle-shaped surface acoustic wave transducers 58, 59, and between and on the side of the saddle-shaped electrode surface acoustic wave transducers 60, 61. Strip-type ladder-like reflectors 71, 70, 72 are formed on one side, and strip-type ladder-like reflectors 74, 73, 75 are formed between and on the sides of the saddle-shaped surface acoustic wave transducers 62, 63. ing.

  That is, the surface acoustic wave resonators 82 to 84 connected in parallel to the signal line are not simply formed by connecting two surface acoustic wave resonators in parallel. The surface acoustic wave high-frequency filter is miniaturized by using three strip-type ladder reflectors. FIG. 8 is an enlarged view of one of the surface acoustic wave resonators connected in parallel to the signal line.

  All of the electrode indices of the saddle-shaped electrode surface acoustic wave transducers 58 to 66 are 100. However, the cross width of the saddle electrode surface acoustic wave transducers 58 to 63 is 200 μm, and the cross width of the saddle electrode surface acoustic wave transducers 64 to 66 is 100 μm.

  The strip ladder reflectors 67 to 81 all have 180 electrode indexes.

  According to the above configuration, the surface acoustic wave resonators 82 to 84 connected in parallel to the signal line include two or more saddle-shaped electrode surface acoustic wave transducers in parallel, and the crossing width is 2 Therefore, the impedances of the resonators 82 to 84 are ¼ or less compared with those having one saddle electrode surface acoustic wave transducer.

  Therefore, even if the frequency characteristics of the impedances of the surface acoustic wave resonators 85 to 87 connected in series to the signal lines remain as they are, the gradient becomes steep in comparison with the impedances of the surface acoustic wave resonators 82 to 84 connected in parallel. .

  As a result, like the first and second embodiments, the insertion loss can be reduced, and at the same time, a high attenuation can be secured outside the band.

  FIG. 9 is a graph showing frequency characteristics of the surface acoustic wave high-frequency filter having the above structure. Compared with the graph of FIG. 14 showing the frequency characteristics of the conventional structure of FIG. 11, it can be seen that the out-of-band attenuation is greater than 20 dB.

  In the above embodiment, the surface acoustic wave resonator includes two saddle-shaped electrode surface acoustic wave transducers. The first surface acoustic wave resonator includes two or more saddle electrode surface acoustic wave transducers in series, and the second surface acoustic wave resonator includes two saddle electrode surface acoustic wave transducers. The above configuration may be provided in parallel.

1 is a schematic plan view of a surface acoustic wave high-frequency filter of the present invention. FIG. 2 is an equivalent circuit diagram of the surface acoustic wave high frequency filter of FIG. 1. It is a frequency characteristic figure of the surface acoustic wave high frequency filter of FIG. It is a typical top view of the surface acoustic wave high frequency filter of other examples of the present invention. FIG. 5 is a schematic plan view showing one of the surface acoustic wave resonators connected in series to a signal line in the surface acoustic wave high frequency filter of FIG. 4 in an enlarged manner. It is a typical circuit diagram of the surface acoustic wave high frequency filter of other examples of the present invention. FIG. 7 is an equivalent circuit diagram of the surface acoustic wave high frequency filter of FIG. 6. FIG. 7 is a schematic plan view showing one of the surface acoustic wave resonators connected in parallel to signal lines in the surface acoustic wave high frequency filter of FIG. 6 in an enlarged manner. FIG. 7 is a frequency characteristic diagram of the surface acoustic wave high frequency filter of FIG. 6. Frequency characteristics of impedance of a surface acoustic wave resonator (dotted line) having two saddle-shaped electrode surface acoustic wave converters in series, and a surface acoustic wave resonator having two saddle-shaped electrode surface acoustic wave transducers in parallel It is a graph which each shows the frequency characteristic of the impedance of the impedance of (one-dot chain line), and the impedance frequency characteristic of the surface acoustic wave resonator (solid line) provided with one saddle-shaped electrode surface acoustic wave converter. It is a typical top view of the conventional surface acoustic wave high frequency filter. FIG. 12 is an equivalent circuit diagram of the surface acoustic wave high frequency filter of FIG. 11. It is a frequency characteristic diagram of reactance of an ideal double resonance type surface acoustic wave resonator used for a surface acoustic wave high frequency filter. FIG. 12 is a frequency characteristic diagram of the surface acoustic wave high frequency filter of FIG. 11.

Explanation of symbols

1 Lithium tantalate substrate 2-4, 8-13, 58-66 Saddle electrode surface acoustic wave converter 14-37, 67-81 Strip-type ladder reflector 38-40, 82-84 Connected in parallel to signal lines Surface acoustic wave resonators 52 to 54, 85 to 87 Surface acoustic wave resonators connected in series to signal lines

Claims (1)

A surface acoustic wave high-frequency filter having a plurality of filter functional units each including a first surface acoustic wave resonator connected in series to a signal line and a second surface acoustic wave resonator connected in parallel to the signal line. There,
The filter functional unit that is first connected to the input terminal of the surface acoustic wave high-frequency filter among the plurality of filter functional units is the input without passing through the surface acoustic wave resonator connected in parallel to the signal line. Connected to the terminal,
Within the filter functional unit that is initially connected, from the input terminal side, two or more hook-shaped surface acoustic wave converters connected in series and a pair of reflectors sandwiching the hook-shaped surface acoustic wave converter A surface acoustic wave high-frequency filter, wherein the first surface acoustic wave resonator including the series arm surface acoustic wave resonator and the second surface acoustic wave resonator are connected in order.

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