JPS6261413A - Shield pattern for multi-stage connection saw multiplex mode filter - Google Patents

Abstract

PURPOSE:To improve the filter characteristic and its attenuation characteristic especially by overlapping the shield pattern arranged between sections while taking the connection pattern as the boundary. CONSTITUTION:The surface of a piezoelectric substrate 1 is provided with two sections of SAW duplicated mode filters arranged in parallel where a couple of IDT electrodes 2, 2' and reflectors 3, 3' arranged at both sides arranged nearly in parallel and they are connected electrically by a step shape connection pattern 6. Then shield patterns 7, 7' are arranged between the sections and both the patterns are formed so as to be overlapped between the IDT electrodes while taking the connection pattern 6 as a boundary and they are connected with bus bar of the reflectors 3, 3' to be grounded from the other bus bar via the grating of the reflector. Thus, the direct transmission wave between the IDT electrodes constituting the two sections is blocked nearly completely and the filter characteristic, especially its attenuation characteristic is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a structure of a shield pattern in a FisAW multimode filter, particularly a multistage cascaded SAW multimode filter.

(Prior Art) The inventors of the present application have been researching and developing a so-called SAW multimode filter that utilizes the acoustic coupling of SAW excited to each SAW resonator by arranging multiple SAW resonators in parallel and close to each other. However, in order to improve the filter characteristics, especially its cut-off characteristics and guaranteed attenuation, the SAW multimode filter is made into a multi-mode filter, and the required number of SAW multimode filters are connected in cascade on a single piezoelectric substrate to form a multi-stage SAW. It is often necessary to construct multiple i1 mode filters.

In such a case, a shield pattern 7f as shown in FIG. 2, for example, has been conventionally provided between each sector 7117 in order to prevent direct waves from reaching the sector 7117 and maintain a good filter guaranteed attenuation amount.

That is, a pair of interdigital transducer electrodes (hereinafter referred to as IDT electrodes) 2.2' and reflectors 3.3"i disposed on both sides of these electrodes are arranged in parallel and close to each other on the piezoelectric substrate 1 to form a so-called SAW dual mode filter. A two-stage cascade-connected 5AW dual-mode filter is constructed by cascading two sections of this section.At this time, a shield pattern 4 is placed on the surface of the piezoelectric substrate between the two sections to prevent direct waves between the sections. .4't-forming, these are integrated with the busbars of the reflectors 3', 3', . Ta.

However, as is clear from this figure, the shield pattern with such a configuration separates at the connection pattern 5 for electrical connection, resulting in direct waves between the sections. Since it is difficult to completely block the filter, there is a drawback that fully satisfactory filter characteristics cannot be obtained.

(Object of the Invention) The present invention has been made in view of the above-mentioned defects of the shield pattern in conventional multi-stage connected SAW multimode filters, and improves the filter characteristics by improving the shape of the shield pattern. In particular, the overall purpose is to improve its damping characteristics.

(Summary of the Invention) In order to achieve the above object, the shield pattern according to the present invention basically has the following configuration.

That is, in the multi-stage connection SAW multiplex mode, the connection pattern for electrically connecting each section constituting the filter is completely overlapped with the shield pattern placed between each section with the connection butter as a boundary. I'll go.

(Embodiments of the Invention) The present invention will be described below in detail based on embodiments shown in the drawings.

FIG. 1 is a plan view showing the structure of a two-stage connected SAW dual mode filter according to the present invention.

In this figure, a pair of IDT electrodes 2 are on the surface of the piezoelectric substrate 1,
2' and reflectors 3' and 3' on both sides of the SAW dual mode filter, which are arranged in parallel and close together.
They are arranged in parallel and electrically connected by a stepped connection pattern 6.

There is a shield pattern 7.7' between each section.
These two patterns are formed so as to overlap between the IDT electrode portions with the connection pattern 6 as a boundary, and are connected to the bus bars of the reflectors 3' and 3' respectively, and are connected to the other through the grating of the reflector. It is configured to be grounded from the bus bar.

By forming the shield pattern in this way, the direct waves between the IDT electrode parts constituting the two sets of sections are completely blocked, and the filter characteristics, especially its attenuation characteristics, are as good as those of the conventional one shown in the second factor. Compared to that, it is improved by about 5 dB (However, the center frequency is 28 using an ST cut crystal substrate)
It is a 0MHz filter and is an IDT [in the case of 300 vs. 9 reflector gratings, 300 on the left and right sides].

According to a series of experiments that led to the present invention, the shield putter 77.7' is connected to the reflector 3 as shown in FIG.
There is almost no change in the characteristics even if the reflector 3 is electrically connected to one of the reflectors 3 and 3 as shown in Figure 4.
', 3' were grounded completely independently, and 90,000 obtained even better results in completely improving the attenuation characteristics of the filter. The reason for this is that the shield pattern generates nine currents in the reflector 3.
3"i, the distance to the grounding point will be large, and the reflector 3.3' must also serve as the grounding wire for each sector 1, so the electric current 11 from the shield pattern is
This is thought to be due to the fact that tatami mats have some kind of negative effect.

However, as shown in Figure 4, it is obvious that separating the shield pattern from each sector of the multi-stage connected filter increases the number of grounding wires, which directly leads to a decrease in reliability and an increase in the number of wire bonding steps. The appropriateness of implementation should be determined by taking into account the specifications.

Although the basic shape of the shield putter 7 according to the present invention has been described above, the present invention is not necessarily limited to the patterns shown in FIGS.
As shown in the figure, the IDT electrode portions 2, 2' of each sector, /
Exactly the same effect can be obtained even if the connection patterns 8 are formed to run diagonally with respect to their center lines, and shield patterns 9.9t- are provided along the patterns on both sides of the connection patterns. Needless to say, it will probably happen.

That is, the shield pattern can be of any shape as long as it extends overlappingly from both sides of the electrical connection pattern of each sector 1 as a boundary and can block direct waves between each sector. It is possible.

Furthermore, in order to simplify the drawing, only the configuration of a 5AW dual-mode filter with two-stage cascade connection has been described; however, if necessary, a multi-stage connection of three or more stages may be performed, and three or more SAW multi-mode filters may be used as each section. It will be obvious to those skilled in the art that the idea of the present invention can be applied to any case.

(Effects of the Invention) Since the shield pattern of the multi-stage connected SAW multi-mode filter according to the present invention is configured as explained above, it is possible to completely prevent direct transmission between the sections constituting the multi-stage connected filter. Therefore, it has a remarkable effect on improving the characteristics of the filter, especially the guaranteed attenuation amount.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of a shield pattern in a two-stage cascade-connected SAW dual-mode filter according to the present invention, and FIG. 2 is an example of a conventional two-stage cascade-connected 5AW dual-mode filter. FIGS. 3 to 5 are plan views showing different embodiments of the present invention. 1...Piezoelectric substrate, 2.2'...
......IDT electrode, 5, 6 and 8...-
・・・・・・Butter y for each sexy connection, 4.7 and 9・・・・・・・・・ Shield putter/. Patent issue filed Toyo Tsushinki Co., Ltd. 2'2 2nd G Atsushi 3 Figure No. 4

Claims (1)

[Claims] A plurality of interdigital transducer electrodes are arranged in parallel and close to each other on a single piezoelectric substrate, and a SAW multimode filter that utilizes the acoustic coupling of the SAW excited to the interdigital transducer is made into a -section and these are divided into the required number of sections. Cascading multi-stage connection SA
In the W multi-mode filter, shield patterns that are divided and extended between each section on both sides of a connection pattern that interconnects these sections are overlapped with each other along the interdigital transducer electrodes of each section. A multi-stage connection SA characterized by
Shield pattern of W multimode filter.