JPH01128606A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To enough suppress an MEL by arranging a crossing width weighting electrode finger with unequal pitch in a different polarity area between second common electrodes and executing electrode arrangement to suppress a reflected wave near a central frequency in the area between same polarity first and second common electrodes. CONSTITUTION:On a surface acoustic wave substrate 1, an input cord shape electrode 2 and an output interdigital electrode 3 are arranged and in the output cord shape electrode 3, a first common electrode 4 and a second common electrode 5 are provided. Then, in an area 6 between the both common electrodes, the electrode finger, whose width is 1/8 of a surface acoustic wave length (lambda0) of the central frequency, is arranged in an equal interval with the pitch of lambda0/4. In an inside area 7 of the second common electrode 5, the electrode is arranged with the unequal pitch in order to obtain an unsymmetrical frequency characteristic. Thus, even in case of the unequal pitch electrode finger arrangement to have the unsymmetrical frequency characteristic, since the MEL (reflection due to the difference of the characteristic impedance of medium quality) can be enough suppressed, a ripple, etc., in a band can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave device that suppresses reflected waves well and has few ripples in frequency characteristics.

[Conventional technology]

In conventional cross-width weighted electrodes, the reflected waves (hereinafter abbreviated as ΣL) caused by the difference in characteristic impedance regarding surface acoustic wave propagation between the part with the electrode and the part without the electrode are '! "1'-22,
(1974), pp. 960-964, there is a known method of suppression by setting the width of one electrode finger to 178 of the surface acoustic wave wavelength (λ0) of the band center frequency. Problem 3 to be Solved If the frequency characteristics are symmetrical with respect to the band center frequency, the electrode pitch is constant, and the above conventional method is effective.

Also, if the frequency characteristics are asymmetric and the electrode pitch is not constant, the interval between the excitation source positions (impulse generation positions) should be adjusted to λo.
By setting it to /4, i9MIL can be suppressed, but
It's still not enough.

An object of the present invention is to provide a surface acoustic wave device that suppresses the above-mentioned MEL even better.

[Means for solving problems]

In order to solve the above-mentioned problems, in the present invention, in addition to a linear first common electrode (bus bar) connecting the end portions of electrode fingers of the same polarity of the unequal pitch crossing width weighted electrodes, A second common electrode is provided that connects t (between the wrapping line of the weighted difference part and the first common electrode) close to the part, and in the region between the second common electrodes of different polarity, the cross width weighted electrodes are arranged at uneven pitches. Arrange your fingers and place the first one of the same polarity. The area between the second common electrodes (each other K
In order to sufficiently suppress the reflected waves near the center frequency (with upper and lower regions of A polarity), the above-mentioned known techniques (for example, arranging electrode fingers with a width of λo/8 at intervals of λo/4, or There is a gap between electrode fingers in the lower region corresponding to the position of the electrode fingers in the upper region, etc.) (provided that both ends thereof are connected to the first and second common electrodes, respectively). A grid-like) array was performed.

[Effect]

If you take the above measures, 1. Since the reflected wave between the second common electrodes is sufficiently suppressed, the reflected wave is actually only for the remaining electrode portion, and a window (window function) is applied to the impulse response of the reflected wave. The inventors of the present invention discovered that the overall level could be lowered by multiplying the
This is to make the propagation velocity (phase) of the surface waves in that part similar to that in the central part.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a diagram schematically showing a first embodiment of the present invention. An input interdigital electrode 2 and an output interdigital electrode 3 are arranged on the surface acoustic wave substrate 1, and the output interdigital electrode 3 is provided with a first common electrode 4 and a second common electrode 5. In region 6, electrode fingers having a width of 1/8 of the surface acoustic wave wavelength (4) of the center frequency are arranged at equal intervals with a pitch of λ0/4. Note that the second common electrode has a cosine shape (equivalent to having a two-sine window).The inner region 7 of the second common electrode 5 has an unequal pitch in order to obtain asymmetric frequency characteristics. The 〇 broken @S where the electrodes are arranged shows the envelope of the intersection. Input/output interdigital electrodes 2.
A sound absorbing material 9 is coated on both sides of the substrate 3 to prevent surface acoustic waves from being reflected at the end faces of the substrate. The board is rotated 128 degrees Y
Axis cutting, X-axis propagation L1Nb03, number of excitation source pairs of input interdigital electrode 2 is 15, input side aperture length 3000 μm1
The number of pairs of excitation sources (between the second common electrodes) of the output interdigital electrode 3 is 50 pairs, and the maximum aperture length on the output side is 2000 μm.The center frequency is 5.5 μm for the intermediate frequency filter of a television receiver.
It's MHz. FIG. 2 is a diagram schematically showing an example (reference example) of a conventional elastic optical surface wave device for the same purpose as this embodiment.

The symbols in the figure are the same as those in FIG. 1, and the substrate, excitation source logarithm, aperture length, etc. are also the same as in the first embodiment.

FIG. 3 shows an intermediate frequency circuit of a television television using this device.The surface acoustic wave device 11 is connected to the chainer 10,
It extracts one channel and sets the video band and audio signal level. The output is connected via a transformer 12 to an integrated circuit 13 having functions such as preamplification and demodulation. Conventionally, a damping resistor 14 was connected in order to perform matching at the output section of the chip, but in a system using the device of the present invention, the impedance of the surface acoustic wave device is lowered to reduce loss. I decided to remove the resistor 14. Therefore, the input side of the surface acoustic wave device 11 was in a state close to matching, and the reflected wave (RW) determined by the load conditions of the electrodes was about 10 (LB).

On the other hand, when using a conventional surface acoustic wave device (reference example) and attempting to sufficiently mismatch the output side to suppress the reflected waves, we found that due to the MBL described above, waves that were multiplely reflected between the electrodes ( Figure 4 shows the reflected wave () by the output interdigital electrode 3 of the reference example.
The results of measuring the loss of MEIL) are shown.

Approximately 23 dB within the filter band - 1 on the input side
Since it is 0 dB, the total is 35 (LB). FIG. 5 shows the insertion loss-frequency characteristics of the reference example.

The loss is good at 18 dB, but there is an amplitude α5 dB within the band.
p-p, a ripple with a group delay of 100 nsp-p is generated.In contrast, FIG. 6 shows the present invention No. 15j! The results of measuring the loss of reflected waves (MEL) of the output interdigital electrode 5 of the example are shown. Approximately 27 within the filter band (IB,
Overall, there was an improvement effect of 37 (LB and 40).

FIG. 7 shows the insertion loss-frequency characteristics of the filter of the first embodiment @amplitude ripple is α2 aap-p.

The group delay ripple is 60 nsp-p], which is a good characteristic.

FIG. 8 is a diagram schematically showing a second embodiment of the present invention. In this embodiment, the second common electrode 5 is installed along the envelope 8 in a portion away from the input side. FIG. 9 shows the reflected wave loss-frequency characteristics of the output interdigital electrode 3 of the second embodiment. Approximately 30 (LB value was obtained within the band. In the second example, the first
Compared to the embodiment, it is possible to further suppress the LB reflected wave. FIG. 10 is a diagram schematically showing the third embodiment of the present invention. In this embodiment, the second common electrode 5 is The front part of the electrode is also made to match the envelope 8. Figure 11 shows the reflected wave loss at the output interdigital pole 5. Approximately 33αB within the band
A value of 90 was obtained, and an improvement effect of 5 dJ3 was obtained in this embodiment compared to the third embodiment.

FIG. 12 is a diagram schematically showing the fourth embodiment of the present invention.
Using the unidirectional electrode 15 as the output interdigital electrode, -
The layer loss is reduced. Even in this embodiment, where the unidirectional electrode 15 is a grouped unidirectional electrode using a meandering electrode 16, the second common electrode 5 is provided to suppress the MBL component. By using this embodiment, it is possible to suppress MEIL even in a structure where MEIL is likely to occur, such as an uneven pitch type unidirectional electrode.

FIG. 13 is a partially enlarged view of the fifth embodiment of the present invention. In this embodiment, the first. λ in the region 6 sandwiched between the second common electrodes.

・An enlarged view of the upper area on the input interdigital electrode side of the output interdigital electrode 3 is shown at 17, an enlarged view of the lower area is shown at 18, an enlarged view of the upper area on the opposite side is shown at 19, and an enlarged view of the lower area is shown. At each position of OA indicated by 20,
The upper reflected wave and the lower reflected wave are in opposite phase and cancel each other out◎
The reflected waves generated from the upper left end and the lower right end of the remaining part are also canceled out near the center frequency. By using this embodiment, it is possible to obtain a rounding effect in which the reflected wave from the region 6 becomes almost zero within the filter band, and a good reflected wave suppression effect can be obtained, and the electrode width can be widened. It is effective in improving manufacturing yield. In addition, here it is λ. Although we have shown an example using electrode fingers with a width of 74, it is possible to set the electrode finger width to any desired width (eg -0/8) if the upper and lower electrode edges are arranged in opposite phases. Needless to say.

〔Effect of the invention〕

As explained above, according to the present invention, even in the case of an uneven pitch electrode finger arrangement having asymmetric frequency characteristics, it is possible to sufficiently suppress MBL (reflection due to a difference in characteristic impedance of the medium), so that in-band ripples can be suppressed. etc., and is effective in improving filter characteristics.

[Brief explanation of the drawing]

Fig. 1 is a diagram schematically showing the first embodiment of the present invention, Fig. 2 is a diagram schematically showing an example of a conventional surface acoustic wave device (reference example), and the fifth factor is the TV screen using this device. Figure 4 is a frequency characteristic diagram of the reflected wave loss due to the output interdigital electrode on the reference side, the fifth factor is a frequency characteristic diagram of the insertion loss of the reference example, and Figure 6 is the frequency characteristic diagram of the insertion loss of the reference example. 1st! ii! FIG. 7 is a frequency characteristic diagram of the reflected wave loss of the output interdigital electrode of the embodiment. FIG. 7 is a frequency characteristic diagram of the filter insertion loss of the first embodiment. FIG. 8 is a diagram schematically showing the second embodiment of the present invention. The figure is a frequency characteristic diagram of reflected wave loss of the output interdigital electrode of the second embodiment, FIG. 10 is a diagram schematically showing the third embodiment of the present invention, and FIG. 11 is the frequency characteristic diagram of the output interdigital electrode of the third embodiment. A frequency characteristic diagram of reflected wave loss, FIG. 12 is a diagram schematically showing the fourth embodiment of the present invention, and FIG. 13 is a partially enlarged view of the fifth embodiment of the present invention. 1...Surface acoustic wave substrate, 2...Input interdigital electrode,
3... Output interdigital electrode, 4... First common electrode, 5
...Second common electrode, 6...Region between both system conductive electrodes, 7
. . . Inner region of second common electrode, 8. Envelope of intersection, 9. Sound absorbing material, 10. Chena, 11.
・Surface acoustic wave device, 15...Integrated circuit, 15...Unidirectional electrode, 16...Meander electrode〇

Claims (5)

[Claims] 1. A surface acoustic wave device that is mounted on a surface acoustic wave substrate, has output interdigital electrodes arranged, and has at least one interdigitated electrode as an unequal pitch intersecting width weighted electrode with changes in electrode finger intersecting width and electrode finger pitch. In addition to the linear first common electrode that connects the ends of the electrode fingers of the same polarity of the unequal pitch crossing width weighted electrodes, a second common electrode is provided that connects the ends of the electrode fingers of the same polarity near the intersections, In the region between the second common electrodes of different polarities, cross-width weighted electrode fingers are arranged at unequal pitches, and in the region between the first and second common electrodes of the same polarity, a well-known method that sufficiently suppresses reflected waves near the center frequency is used. A surface acoustic wave device characterized by having an electrode finger arrangement including a technique. 2. 2. The surface acoustic wave device according to claim 1, wherein the second common electrode of the unequal pitch crossing width weighted electrode has a portion formed along the electrode finger crossing envelope. 3. The electrode finger width of the region between the first and second common electrodes of the unequal pitch cross width weighted electrode is set to 1/8 of the surface acoustic wave wavelength of the filter characteristic center frequency, and the electrode finger pitch is set to 1/8 of the above wavelength. 4. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is characterized in that: 4. The electrode finger arrangement in the surface acoustic wave propagation direction of the upper region and lower region of mutually different polarity between the first and second common electrodes of the above-mentioned unequal pitch cross width weighted electrode is arranged at the position where the electrode fingers exist in one region and the other. 2. The surface acoustic wave device according to claim 1, wherein gaps between the electrode fingers in the region are arranged to correspond to each other. 5. 2. The surface acoustic wave device according to claim 1, wherein said unequal pitch cross width weighted electrode is a group type unidirectional electrode.