JPH0652853B2 - Electrode structure of reflector type high frequency narrow band multiple mode filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is a multimode method utilizing surface acoustic waves (hereinafter referred to as SAW) or slip waves (hereinafter referred to as SSBW).
The present invention relates to an electrode structure of a filter.

(Prior Art) Several types of SAW multimode filters have been proposed in the past, but the basic form thereof is that a set of SAW resonators 2 and 3 are provided on a piezoelectric substrate 1 as shown in FIG. By placing adjacent SAWs in parallel along the propagation direction of the excited SAWs, acoustic coupling is generated between the excited SAWs, and the resulting two symmetric and antisymmetric frequencies are used to filter the filter. It is to be composed.

Therefore, the inventors of the present application experimentally studied the acoustic coupling generation condition between the resonators 2 and 3 arranged close to each other. According to the result, the acoustic coupling generation condition is as follows. Electrode finger cross width w and common bus bar 4 for both electrodes
It was found that the value depends on the width g between the electrode finger ends which sandwiches the distance, and in particular that the value of g is at most about three times the surface wave length excited.

Under such conditions, the width of the common bus bar 4 needs to be set to about 20 μm assuming that the piezoelectric substrate 1 is a rotating Y-cut crystal and g is one wavelength at a center frequency of 100 MHz.

This means that not only the lead wire cannot be directly bonded to the common bus bar 4, but if the number of electrode finger pairs is increased to 400 to 800 in order to raise the Q of the both resonators sufficiently, the common bus bar 4 It means that the ohmic loss of the filter is increased, and as a result, the loss of the filter itself is increased.

As a solution to this problem, the same applicant has already filed Japanese Patent Application No. 57-131855.
In "Reflector type high frequency narrow band multimode filter electrode structure", the number of electrode finger pairs of both resonators is made as small as possible in order to reduce ohmic loss caused by the extremely thin common bus bar. Instead, it is a so-called reflector type that has reflectors at both ends to compensate for the drop in Q,
An electrode structure of a multi-mode filter using a SAW or SSBW in which the bus bars of both resonators including the common bus bar are integrated with a part or all of the reflector is provided.

However, even with this method, when the number of electrode finger pairs of the interdigital transducer IDT increases and the length of the common busbar increases, the Q of the resonator deteriorates due to the sheet resistance of the common busbar of the IDT, and as a filter. However, there is a drawback that the insertion loss increases.

(Object of the Invention) The present invention relates to an improvement of the above-mentioned invention by the same applicant, and an object thereof is to provide an electrode structure of a multimode filter in which the sheet resistance of a common bus bar is further reduced.

(Summary of the Invention) Therefore, in the present invention, a ground pattern for connecting the common bus bar and the ground point is provided at the central portion of the IDT electrode or at a plurality of substantially equal points.

(Examples) Hereinafter, the present invention will be described in detail based on illustrated examples.

Before that, the invention relating to the same applicant will be briefly described with reference to FIGS. 5 and 6 in order to facilitate understanding of the invention.

That is, in FIG. 5, 5 and 6 are IDTs formed in parallel on the piezoelectric substrate 1, and the common bus bar 7 crosses the gratings of the reflectors 8 and 9 provided at both ends of the electrodes 5 and 6, respectively. Thus, the grating is extended and connected to these, and is grounded via either one or both of the bus bars 10 and 11 which connect them in parallel on both sides of the grating.

By doing so, the width of the common bus bar 7 is extremely small only in the width corresponding to the widths of the interdigital transducer electrodes 5 and 6, and the other widths are equivalent to being extremely large. The ohmic loss of the common bus bar 7, which is the ground wire of the filter, can be suppressed to a minimum, and as a result, the filter loss can also be minimized.

Further, since the connecting portion of the electrode of the common bus bar 7 with the lead terminal can be directly wire-bonded to the bus bar 10, 11 of the reflector 8 and / or 9, a land for connection with the lead terminal is specially provided. There is no need to provide it.

When this idea is applied to the busbars 12 or 13 to be connected to the hot terminals of the pair of interdigital transducer electrodes 5 and 6, respectively, the reflector 9 is divided at appropriate places as shown in FIG. On the other hand, the bus bar 14 is connected to the extension of the bus bar 12 of the interdigital transducer electrode 5. Further, the common bus bar 7 is configured to be connected only to the other grating 15 of the divided reflector 9.

By doing so, it is possible to concentrate all of the lead connecting portions of each electrode on one edge of the piezoelectric substrate 1 forming these electrodes and reflectors, and therefore, the wiring for using the filter becomes easy.

However, even with such a method, as the length of the IDT increases, the ohmic cross of the common bus bar increases during this period, as described above. FIG. 1 is an electrode structure diagram showing an embodiment of a dual mode filter according to the present invention.

This drawing is an example in which the present invention is applied to the conventional structure shown in FIG. 5, and the same reference numerals indicate the same parts.

In this embodiment, the IDT 6 is divided into two at the center, and the ground pattern 17 connected to the common bus bar 7 is inserted between the hot terminals 16 and 16 'of the IDT 6 which are also divided into two. At this time, the divided hot terminals 16 and 16 'are connected by wire bonding, or terminals are provided on the respective electrodes for external connection.

With this structure, the central portion of the common busbar having an extremely small width is grounded, so that the IDT of the common busbar is grounded via the reflectors 8 and 9 at both ends thereof.
It can be easily understood that it is effective in reducing the oscillating loss in the section and making the ground potential of the section uniform.

FIG. 2 shows an example in which the present invention is applied to the one shown in FIG. 6, but since it is the same as the embodiment shown in FIG. 1, its explanation is omitted.

Further, the present invention is not limited to the above-mentioned example, but may be modified as follows.

FIG. 3 shows a modified embodiment of the present invention, in which two ground patterns are added to the common bus bar of the IDT.

That is, one of the input / output IDT 6 and this hot terminal electrode 18
Both and are approximately equally divided into three, and a common bus bar 7 is provided between them.
The ground patterns 19 and 19 'connected to each other are positioned, and the three divided hot terminal electrodes 18, 18' and 18 "are connected to each other by wire bonding. The other ends of the ground patterns 19 and 19 'are hot terminal electrodes. It is configured to be connected by an external pattern and grounded.

By grounding the common bus bar of the IDT at a plurality of points in this manner, it is effective in reducing the ohmic cross of the common bus bar when the IDT electrode width is relatively large and making the ground potential of the portion uniform.

In each of the embodiments described above, the case in which only one of the IDTs arranged in parallel is divided and the ground pattern is inserted is shown, but the present invention is not limited to this, and both the IDTs are provided with the above-mentioned ground pattern. It will be obvious that it is good.

The gap between the electrode fingers of the interdigital transducer electrode and the grating of the reflector or the gap between the divided gratings of the reflectors is set so as not to disturb the uniformity of the propagation and reflection of the excited surface wave. Long one
It goes without saying that the interval should be an integral multiple of / 4.

Although only the SAW filter has been described above, the present invention is not limited to this, and any wave that can be excited by the interdigital transducer electrode, for example, S wave, can be used.
It is obvious that it can be applied to a filter using SBW, Love wave, SH wave, or Brustein-Gourier Shimizu wave.

(Effects of the Invention) Since the present invention is configured as described above, the common bus bar of the interdigital transducer electrodes of a multimode filter using SAW or SSBW having a reflector has an extremely small cross-sectional area. In particular, it has a particularly remarkable effect in suppressing the loss of the filter.

[Brief description of drawings]

FIG. 1 is an electrode structure diagram showing an embodiment of a dual mode filter according to the present invention, FIG. 2 is an electrode structure diagram of a dual mode filter showing another embodiment of the present invention, and FIG. FIG. 4 is an electrode structure diagram of a dual mode filter showing a modified embodiment of the invention.
FIG. 5, FIG. 5 and FIG. 6 are electrode structure diagrams of a conventional filter. 1 ... Piezoelectric substrate, 5 and 6 ... Input / output IDT, 7 ... Common bus bar, 8 and 9 ... Reflector, 13, 13 ', 1
6, 16 ', 18, 18', 18 "... I divided into each
DT hot terminal electrode, 17, 19, 19 '... Ground pattern.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takefumi Kurosaki 753 Otani, Samukawa-cho, Takaza-gun, Kanagawa Prefecture Toyo Communication Equipment Co., Ltd. Examiner Masaaki Suzuki

Claims (1)

[Claims] 1. Two interdigital transducer electrodes are arranged in parallel and close to each other on a piezoelectric substrate to share a bus bar on each adjacent side, and the electrodes are provided at both ends of the interdigital transducer electrode. In a SAW multimode filter of the type in which a reflector of the SAW excited by the electrodes is arranged to cause acoustic coupling between the SAWs excited by the respective electrodes, the interdigital transducer electrode is provided at the central portion thereof. Alternatively, the reflector type high frequency narrow band multimode filter is characterized in that it is divided at a plurality of substantially equal points and an earth pattern extending from a common bus bar is arranged between the divided interdigital transducer electrodes. Electrode structure.