JPS5937724A - Surface acoustic wave resonator type filter - Google Patents

Abstract

PURPOSE:To realize loss reduction and band narrowing by a larger peak used as a passing band and the suppression of a smaller peak as an unnecessary wave, by providing different numbers of electrode fingers constituting an input and an output converter respectively, and providing both converters with the same effective passing band. CONSTITUTION:An input reed screen type converter 53 and an output reed screen type converter 54 are provided on a piezoelectric substrate 50. A reed screen type electrode 53 has N1 couples of electrode fingers at finger intervals L1 and a reed screen type electrode 54 has N2 (=N1) at finger intervals L2 (=L1). Both electrodes have the same resonance frequency by setting N1>N2 and L1>L2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resonator filter using surface acoustic waves.

As a narrowband filter using surface acoustic waves, there is a device in which a pair of interdigital m-poles are arranged facing each other on a piezoelectric substrate.

In such a narrow band filter, by increasing the number of pairs of electrode fingers, the propagation of surface acoustic waves other than the center frequency determined by the electrode finger spacing is suppressed, and the amplitude characteristic becomes narrow band.

However, an increase in the number of pairs of electrode fingers causes an increase in loss due to defects such as disconnections and short circuits that occur during fabrication, and minute causes of acoustic propagation loss on the surface (for example, dirt, scratches, protrusions, etc.). Therefore, in order to realize a narrow band filter with a smaller number of pairs of electrode fingers, there is a resonator type filter that actively utilizes internal reflection of busy interdigital electrodes. FIG. 1 shows a plan view of such a conventional resonator filter.

In the figure, the upper pressure formed on the piezoelectric substrate 10 and the input/output interdigital electrodes 13 and 14 have an internal impedance of 1.
1 and a high frequency power source 12 having a load impedance 15
are connected to each. The electrode fingers of the interdigital electrodes 13 and 14 have a single structure. In general, the electrode finger portion of the interdigital electrode becomes a discontinuous portion of the acoustic impedance due to surface acoustic wave activity due to the presence or absence of electrodes due to *i additive effect or piezoelectric reaction, so the surface acoustic wave reflection t
-p occurs, but the interdigital 'wL pole is within one wavelength as shown in Figure 2 [#'i in the case of a single structure with one pair of electrode fingers, the reflection elasticity generated at the end of each electrode finger Surface waves are in phase and overlap. Therefore, in such a single electrode structure, as the number of electrode pairs increases, each interdigital electrode strongly exhibits the characteristics of not only an electric/acoustic transducer but also a single surface wave resonator. (7) The amplitude characteristics of the interdigital electrodes are narrower than the band determined by the logarithm of the electrode fingers.If interdigital electrodes with such resonator properties are placed close to each other, one A part of the surface acoustic wave resonating in the interdigital electrode propagates to the other interdigital M, pole.Therefore, when the two interdigital electrodes are used as an input/output converter, it can be used as a filter. As a result of the product of the width characteristics of the two n-shaped electrodes, a narrow band filter is realized.

By the way, the disadvantage of the example shown in FIG. 1 is that since the interdigital electrodes also have resonance characteristics, unnecessary peaks appear near the center frequency, deteriorating the out-of-band attenuation.

This will be discussed in detail below. A resonator filter with a 21 mm pole configuration operates as a transversal filter that does not include the effects of multiple reflections between interdigital electrodes. In this case, the frequency characteristics are as follows.

The voltage VL applied to the load on the output side is 5lnx 11 vt, --Vn () where the input side voltage is Vn, the number of electrodes is N1, the angular frequency is ω, and the center angular frequency is ωO () Therefore, such multiple reflections are not included. Even in this case, as the number of pairs of electrode fingers increases, the band becomes narrower. If the interdigital electrode has a single structure, the influence of multiple reflections will appear as the electrode finger width is increased, and the lower end frequency in the band when the resonance of one interdigital electrode itself does not include the influence of multiple reflections. seen in In addition, when the two interdigital electrodes are arranged to face each other so that the interval between them is an odd multiple of 1/2 the wavelength of the surface wave, the resonance of the interdigital electrodes themselves and 1/(
Resonance occurs between the two interdigital electrodes. In this case, resonance appears at frequencies at both ends of the band of the interdigital electrode itself. Therefore, when the two interdigital electrodes are used as an input/output converter, the common characteristics of the filter are the resonance of the input/output interdigital electrodes themselves and the resonance between the interdigital electrodes.
It depends on the severity of the individual's co-girlfriend.

At the lower end frequency in the band when the effects of multiple reflections are not included, three resonances occur: the resonance of the interdigital electrode itself and the resonance between the interdigital electrodes, and a sharp dog beak can be seen in the radiation characteristics. On the other hand, at the upper end frequency within the band, only resonance between the interdigital electrodes occurs, and a small peak is seen in the vibration characteristics. An example of iI calculation in this upstream case is the Journal of the Acoustical Society of Japan, Vol. 33, No. 10 (
1977), p. 557, by Deshiro Koyama et al. [
A two-terminal pair surface acoustic wave co-sensor using a multi-pair IDT''

Here, calculation examples of insertion loss when the number of electrode finger pairs is 100 and 300 are shown in Figures 3 and 4, respectively.◇According to this calculation example, when the number of electrode finger pairs is large, the resonance characteristics As explained above, it can be seen that peaks of different sizes appear within the busy band.◇The large peaks are actually used as passbands. On the other hand, the smaller peak is an unnecessary wave near the passband. Also, these large and small peaks are ′FIL
As the number of pole pairs increases, the larger peak used as the passband increases significantly, and at the same time the band becomes narrower. However, the smaller peaks, which are unnecessary waves, also increase.

Therefore, as described above, in the known examples, progress toward narrowing the band and reducing loss leads to deterioration of out-of-band attenuation.

In a surface acoustic wave resonator type filter having an input and output N-shaped transducer on the pressure Jrt1 substrate, the electrode fingers constituting the input and output transducer tubes are The feature is that the logarithms are different from each other, and the spacing between the electrode fingers in the front of the button is adjusted so that the effective passbands of the input and output interdigital transducers coincide, and the larger peak used as the passband The present invention provides a resonator filter '5C which simultaneously achieves low loss and narrow band and suppression of smaller peaks, which are unnecessary waves.

Next, the present invention will be explained with reference to the drawings. Fifth
The figure is a plan view showing an embodiment of the surface acoustic wave resonator type filter according to the present invention, in which an input transducer 53 and an output transducer 54 are provided on a piezoelectric substrate 50. .

Here, the interdigital electrode 53 has a number of electrode finger pairs of Nl and an electrode spacing of Ll. On the other hand, the interdigital electrode 54 has a number of electrode finger pairs of Nl (''; I, t ), 11T, and an electrode spacing of Ll.

('=L+). Input/output blind type ■, pole 53゜5
4, the relationship between the number of pairs of electrode fingers is Nl ) N t , and M
The L electrode finger spacing relationship is Lt > Lt. In the frequency characteristic of the interdigital electrode 530, since the number of electrode finger pairs is larger than the number of electrode finger pairs of the interdigital electrode 54 when Nl>teeth, the bandwidth is small when multiple reflections are not included.

On the other hand, the frequency characteristics of the interdigital electrode 540 have a small number of electrode finger pairs (the iF bandwidth is large. Therefore, if the electrode finger spacing of both interdigital electrodes is set to the same value, resonance of the interdigital electrode itself occurs at the lower end frequency of the band). Since their respective bandwidths are different, their resonance frequencies do not match.

Therefore, in this embodiment, the n-shaped electrode 54 has a small number of pairs of electrode fingers.
The electrode finger spacing is selected so that the resonance frequencies of the two interdigital electrodes themselves match.

Rimashi interdigital electrode 540, pole finger spacing ■J! I'm sorry
The electrode finger spacing I,1 of the shaped electrode 53 is also made smaller.

By arranging the interdigital electrodes 53 and 54 close to each other, which have the relationship between the number of pairs of electrode fingers and the electrode finger spacing, the resonance between the interdigital electrodes is suppressed. Electricity is generated only at the same frequency as the resonance of the interdigital ML pole itself, which coincides at the lower end frequency in each of the n bands.

On the other hand, since the number of electrodes N1 is greater than N, the upper end frequency V in the band of the n-shaped electrode is different between the two interdigital electrodes. Resonance cannot occur. Therefore, the filter characteristics of both interdigital electrodes are limited to various peaks that appear due to the resonance of the n-shaped electrode itself and the resonance between the interdigital electrodes, and small peaks that are unnecessary waves as in the conventional example. There are no mines.

For the above reasons, the resonator original filter with this configuration achieves lower loss and narrower band by increasing the larger peak used as the passband, and suppresses the smaller peak, which is unnecessary waves, at the same time. Ru.

As a specific example, the number of pairs of electrode fingers is 150 on a 36° rotated Y-cut zI propagation crystal substrate, the number of pairs of electrode fingers is 100 pairs, and the number of pairs of electrode fingers is 150 pairs, the electrode finger spacing is 0.79 μm, and the electrode finger spacing is 0.78 μm. In the case of an n-type conductor, the Al film thickness is 30
0A, the intersecting width is 69.37'm.

FIG. 7 is a plan view showing another embodiment of the surface acoustic wave resonator type filter according to the present invention, in which two interdigital electrodes 73° 75 are attached to the soil of the piezoelectric substrate 70 on both sides 1c of the central interdigital electrode 74. This is what was placed.

Here, it is a three-electrode system in which the central blind 1 is used as a transducer (74t) and the human power converter, and the two blind-shaped electrodes on both sides are connected in parallel with buttons to form one output converter.

With the above configuration, the number of pole fingers of each interdigital transducer is determined so that the bandwidth of the input transducer excluding multiple reflections is smaller than that of the output transducer.

Furthermore, the interdigital electrodes 73 and 75 constituting the output converter have equal electrode finger spacing, and the interdigital spacing of the K interdigital electrodes 73 and 75 is adjusted so that the resonant frequencies of each of the interdigital transducer electrodes match. Select the electrode finger spacing of the IL-shaped electrode 74.

However, in this example, the bandwidth when multiple reflections are not included is small. 74ON pole finger spacing [
1 of 73,75! The distance between the electrode fingers is increased.

Due to the structure having the relationship between the number of electrode finger pairs and the electrode finger spacing as described above, the resonance of the interdigital electrode itself and the resonance between the interdigital electrodes resonate together for the same reason as the embodiment shown in FIG. Low loss and narrow band due to the large peak that appears, and suppression of small peaks that are unnecessary waves are simultaneously achieved.A specific example is a 360 rotation Y force, 200 pairs of electrode fingers on the z1 propagation crystal substrate, and an electrode. There are 75 pairs of electrode fingers on both sides of the central n-shaped electrode with a finger spacing of 0.79 μm, and the electrode finger spacing is Q and 76 mm, and the At film thickness is 300 μm.
X, the intersection width is 693 μm.Although the embodiments of the present invention have been described above, it goes without saying that the surface acoustic waves used in the present invention can be applied to the case of S H wave history surface waves.

[Brief explanation of drawings]

Figure 1 is a plan view showing a conventional resonator filter;
The figure is a plan view showing the single structure of the interdigital electrode.
FIGS. 3 and 4 are calculation examples of insertion loss when the number of electrode finger pairs of an n-shaped electrode on an 8T cut crystal substrate is set to ioo and 300, respectively. In both cases, the electrode metal is aluminum and the center frequency fO is 157.4MH
z, film thickness is 0.2574m, electrode finger period is 2o/Jm
, the intersecting width is 0.45 mm. FIG. 5 shows a first embodiment according to the present invention; 12 is a piezoelectric substrate; 12 is a high-frequency power source; 11 is an internal impedance of the high-frequency power source; 15 is a load impedance; 13, 14, 5
3, 54, 73, 74.75 are interdigital electrodes for input/output conversion. (MH=t) O 5 Illustration Lo mouth/jl Liquid number (CrHz) O 7 Mouth 6n 75B/ruθ 1
．． Otsu 2/! I Maki (CrH2) Procedural Amendment (Voluntary) 5B, 11.24 Director General of the Patent Office 1, Indication of Case 1981 Patent Application No. 1484
No. 18 No. 3, Relationship with the case of the person making the amendment Applicant: 33-1 Shiba 5-chome, Minato-ku, Tokyo (423) NEC Corporation Representative: Tadahiro Sekimoto 4, Agent: 108 Shiba 5-chome, Minato-ku, Tokyo No. 37 No. 8 Sumitomo Sanda Building 5, Claims column of the specification to be amended, Detailed explanation of the invention column 6 of the specification, Contents of amendment 1, Claims of the specification as attached. Correct. 2. In the third line of page 5 of the specification, "1/2 wavelength" is corrected to "1/2 wavelength." 3. In the 15th line of page 7 of the specification, "(kiL1)" is corrected to "(kiN1)". 4. On page 8, line 8 of the specification, the phrase "this implementation" is amended to read "this example." 22 people B1 Physician Susumu Uchihara J1, J9,1
, 7'2, Claims A surface acoustic wave resonator type filter comprising input and output interdigital transducers on a piezoelectric substrate, wherein the effective passbands of the output interdigital transducers are mutually A surface acoustic wave resonator type filter, characterized in that the intervals between the electrode fingers are adjusted so as to match each other.

Claims (1)

[Scope of Claims] In a surface acoustic wave resonator type filter comprising input and output interdigital transducers on a piezoelectric substrate, the input and output transducers constitute the input and output transducers. The number of pairs of electrode fingers is different from each other, and the effective passbands of the input and output interdigital transducers are mutually different.