JPH03278606A - Surface acoustic wave resonator and communication equipment using the same - Google Patents

Abstract

PURPOSE:To eliminate disturbance in a reflecting wave from each electrode finger and to suppress a side lobe by adjusting a space width of an electrode finger extraction part of an extract system weighting reflector by a specific space width. CONSTITUTION:An interdigital electrode 2 and a grating reflector electrode 3 are formed on a piezoelectric substrate 1 and quantization weighting in a way of a cosine function is applied to the grating reflector electrode 3 to suppress the reflection other than a stop band. Then the electrode extracted from the grating reflector electrode 3 has a space length being a same space length as the electrode width in addition to a space length to correct a phase lag due to the energy storage effect. Thus, the disturbance in the phase of a reflecting wave is corrected to make the phases of reflecting waves from each electrode finger are made coincident and the excellent reflecting characteristic suppressing a side lobe is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave resonator in which the phases of reflected waves from each electrode finger of a reflector electrode are matched to sufficiently suppress side lobes.

[Conventional technology]

Regarding the improvement of the characteristics of the grating reflector electrode of a surface acoustic wave resonator, conventionally, IE Transactions on Sonics and Ultrasonics, S.U. 26 (1979) (WILLIAM
J, TANSKI “SAW Re5onators
UtilizingWithdrawal Weight
ted Reflectors"IEEE TRANS
ACTTONS ON 5ONIC8ANDULTR
ASONIC3, VOL, 5U-26°NO, 6, NO
VEMBER 1, 979pp, 404-410) describes two-electrode finger extraction type weighting. As described herein, in order to suppress the sidelobes of the reflection characteristics of the grating reflector electrode, weighting such that the reflectance gradually decreases is effective.

[Problem to be solved by the invention]

As in the above-mentioned paper, in order to suppress the sidelobes of the reflection characteristics of the grating reflector electrode, a conventional technique has been used to extract the electrode so that the reflectance gradually decreases. However, this does not take into consideration the fact that by removing the electrodes, the phase delay due to the energy storage effect in the electrodes that existed before the electrodes were removed is eliminated, and the reflected waves at each electrode do not have the same phase. Therefore, there was a problem that the reflection characteristics deteriorated.

The present invention solves the above problems and provides a surface acoustic wave resonator in which weighting is performed using an electrode finger extraction method, and the reflected waves from each electrode finger are aligned in phase, and side lobes are sufficiently controlled. The purpose is to

[Means to solve the problem]

In order to achieve the above object, the present invention provides at least one interdigital electrode on a piezoelectric substrate, and in order to reflect the surface acoustic waves excited by the interdigital electrode, at least one reflective electrode is provided on the piezoelectric substrate. In the surface acoustic wave resonator in which the reflector electrode is arranged, the reflector electrode is a sampling type weighted reflector in which a part of the group of electrode fingers arranged periodically is extracted, and the space of the electrode finger extraction part (piezoelectric (Referring to the exposed part of the substrate surface where no electrode fingers are formed on the physical substrate) compared to before the electrode fingers are removed, the width of the space is equal to the phase delay that would have occurred due to the energy accumulation effect of the electrode fingers if the electrode fingers had not been removed. I decided to postpone it.

In addition, when performing sampling method weighting by replacing the solid electrode fingers of the reflector electrode with non-reflective split electrode fingers, the space width corresponding to the increase in the electrode index and the increase in phase delay due to the energy storage effect However, I decided to shorten the space width there. .

Furthermore, when sampling method weighting is performed by replacing the electrode fingers of the reflector electrodes with electrode fingers that are wider than the periodically arranged electrode fingers, the electrode index decreases compared to the conventional method, which is due to the energy storage effect. We decided to increase the space width by the space width equivalent to the decrease in phase delay.

[Effect]

In the present invention, when the sampling method weighting is performed as described above, the space width is adjusted by the space width corresponding to the phase delay caused by the energy accumulation effect of the extracted electrode finger, and the phase disturbance is corrected. The phases of the reflected waves from the electrode fingers were aligned. Therefore, there is no disturbance in the reflected waves from each electrode finger, a reflection characteristic in which the reflectance gradually decreases is obtained, and side lobes can be sufficiently suppressed. Further, the frequency characteristics of a resonator using this reflector electrode have good characteristics with suppressed side lobes. Even if a split electrode finger structure or a broad electrode finger structure is used instead of removing the electrode fingers, the same effect can be obtained by correcting the phase of the reflected wave from each electrode using the above method, following the weighting of the electrode finger removal method. It will be done.

Embodiment C] FIG. 1 is a schematic plan view of an embodiment of the present invention. An ST-cut quartz crystal was used as the piezoelectric substrate 1, and an interdigital electrode 2 and a grating reflector electrode 3 were formed on the substrate by photolithography.

Here, aluminum is used as the electrode material, and the film thickness is 300 mm.
nm, aperture length 300 μm, and electrode width 2.8 pm [7].

The grating reflector electrode 3 is quantized and weighted using a cosine function as described in the paper by William J. Tanski (WILLIAM J. TANSKI) to suppress reflections outside the stop band.

The number of grating reflector electrodes 3 before extraction is 30.
When the number of electrodes is 0, the removed electrode portion has a space length equal to the electrode width, plus a space length S for correcting the phase delay due to the energy storage effect B. However, the space length S corresponds to one electrode finger and is determined by the following formula.

S=B・λ/π B=cl+c2・H+c3・H” H=h/λ λ: Surface acoustic wave wavelength h: Electrode film thickness cl, c2.c3: Substrate material constant Considering the energy storage effect at the electrode finger end The reflection characteristics of the conventional grating reflector electrode 3 and the frequency characteristics of the resonator are shown in FIG. 2, and those of the embodiment of the present invention are shown in FIG. The broken line shows the frequency characteristic of the reflection of the reflector electrode.From now on, in this example, sidelobe suppression outside the stop band is better than in the conventional example, and in terms of frequency characteristics, sidelobe suppression is also improved. It can also be seen that the loss at the peak frequency of the resonator has also improved.

Although we have shown a method of removing the electrode fingers of the grating reflector electrode 3 in order to gradually reduce the reflectance, other methods that can achieve the same effect include split electrode fingers that do not cause reflection, or conventional periodic electrode fingers. It is also possible to replace the electrode fingers with broad electrode fingers whose width is wider than the width of the electrode fingers arranged in the . FIG. 4 illustrates these various imprinted grating reflector electrode structures. In the split type, in which split electrode fingers are placed instead of removing electrode fingers, the number of electrode fingers increases compared to conventional methods, so in order to match the reflected wave phase,
It is necessary to shorten the space length by an amount corresponding to the increased space length. With the broad type, where the electrode index is reduced by using broad electrode fingers, the phase delay due to the energy storage effect is reduced compared to the conventional method, so in order to match the reflected wave phase, the space length is reduced by the space length corresponding to the reduced amount. It needs to be longer. Similar effects can be obtained in either case.

FIG. 5 is a schematic plan view of a narrow band filter in which resonators of the present invention are connected in series. Note that the symbols in the figure are the same as in FIG. 1. By using the weighted grating reflector 3, spurious signals outside the band can be sufficiently suppressed.

Figure 6 shows the SAW of a single super pager circuit.
This is an example in which the narrow band filter of the present invention as shown in FIG. 5 is used as a filter. In the figure, 4 is a high frequency crucible;
5 is SAW filter, 6 is local oscillator, 7 is 455kl
(Z filter, 8 is an intermediate frequency amplifier. By using the narrow band filter of the present invention, the circuit can be simplified and the set can be made smaller.

〔Effect of the invention〕

As explained above, according to the present invention, the disturbance in the phase of the reflected wave that has conventionally occurred when weighting the grating reflector electrode with electrode fingers removed is corrected, and the phase of the reflected wave from each electrode finger is corrected. As a result, good reflection characteristics with side lobes sufficiently suppressed can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of an embodiment of the present invention, FIG. 2 is a diagram of the reflection characteristics of a conventional grating reflector electrode and frequency characteristics of a resonator, and FIG. 3 is a diagram of reflection characteristics and resonance of an embodiment of the present invention. FIG. 4 is a diagram of the structure of weighted grating reflector electrodes using various electrode finger extraction methods, and FIG. 5 is a schematic plan view of a narrowband filter in which resonators of the present invention are connected in series. 1... Piezoelectric substrate 2... Interdigital electrode 3... Grating reflector electrode 5... SAW filter.

Claims (5)

[Claims] 1. A surface acoustic wave resonator in which at least one or more interdigital electrodes are provided on a piezoelectric substrate, and at least one or more reflector electrodes are arranged to reflect surface acoustic waves excited by the interdigital electrodes, The reflector electrode is a pull-out type weighted reflector in which a part of a group of electrode fingers arranged periodically is extracted, and the space width of the electrode finger pull-out part is equal to the energy of the electrode finger when the electrode finger is not pulled out. A surface acoustic wave resonator characterized in that the space width is extended from before extraction by the space width corresponding to the phase delay caused by the accumulation effect. 2. When the solid electrode fingers of the reflector electrode are replaced with non-reflective split electrode fingers and sampling method weighting is performed, the space width corresponding to the increase in the electrode index and the increase in the phase delay due to the energy storage effect is The surface acoustic wave resonator according to claim 1, characterized in that the space width is shortened. 3. When sampling method weighting is performed by replacing the electrode fingers of the reflector electrode with electrode fingers that are wider than the periodically arranged electrode fingers, the electrode index is reduced compared to the conventional method, and the phase delay due to the energy storage effect is reduced. 2. The surface acoustic wave resonator according to claim 1, wherein the space width is increased by the space width corresponding to the width of the surface acoustic wave resonator. 4. A surface acoustic wave resonator comprising a plurality of surface acoustic wave resonators according to claim 1 connected in series. 5. A communication device using the surface acoustic wave resonator according to any one of claims 1 to 4.