JPH06101661B2 - Surface acoustic wave filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a surface acoustic wave filter (Surface Acoustic Wave).
Filter: hereinafter referred to as SAW filter), especially 50 ~
The present invention relates to a SAW filter that requires a sufficient out-of-band attenuation of about 60 dB or more.

[Conventional technology]

Conventionally, a SAW filter used for a communication device or the like has been provided as a structure housed in a metal casing, but its internal structure is configured as shown in FIGS. 5 (a) and 5 (b). ing. That is, the SAW filter package 21 has the fixing screw 22, the input terminal 23, and the output 24 protruding from the surface, and the fixing screw 22 is inserted into the printed circuit board 25 and fastened with the nut 26 to fix the SAW filter package 21.
Is mounted on the printed circuit board 25. In addition, input terminal 23,
Output terminals 24 have impedance matching coils 28 and 2 respectively
9 is connected. The internal structure is housed in a metal casing (not shown), and input / output coils 28 and 29 are connected to the input connector and the output connector provided in the casing.

[Problems to be solved by the invention]

By the way, the insertion loss of the SAW filter as described above is usually about 20 to 40 dB, and when the out-of-band attenuation of about 50 to 60 dB or more is required, the isolation between the input and output sections is about 70 to 100 dB or more. Will be needed.

However, in the conventional SAW filter described above, the SAW filter package 21, the input terminal 23, the output terminal 24 and the coils 28 and 29 connected to these are simply attached to the printed circuit board 25 and the whole is housed in a metal housing. Since this is only a configuration, the input terminal 23, the input part of the coil 28, the output part 24, and the output part of the coil 29 are present in the same cavity, and these coils 28, 29 cause electromagnetic waves between the input and output parts. Interference easily occurs. For this reason, it is difficult to obtain sufficient isolation between the input and output parts, and there is a problem that the out-of-band attenuation cannot be improved as shown by the attenuation characteristics in FIG.

It is an object of the present invention to provide a SAW filter capable of improving the out-of-band attenuation by making the isolation between the input and output sections sufficient.

[Means for solving problems]

The SAW filter of the present invention is a surface acoustic wave filter in which a surface acoustic wave filter package and an impedance matching coil or the like connected to an input / output terminal are mounted on a substrate, and which is internally housed in a metal casing. Is equipped with a partition wall that electromagnetically shields the input / output terminals of the surface acoustic wave filter package and the coils connected to the input and output sections, and a choke coil between the grounds of the input section and the output section. They are connected to each other, and the partition wall enhances the isolation between the input and output portions, and the choke coil prevents leakage around the ground.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 shows the internal structure of one embodiment of the present invention. FIG. 1 (a) is a front view, FIG. 1 (b) is a side view, and FIG. 1 (c) is a bottom view.

In these figures, 1 is the same SAW filter package as before, and a fixing screw 2 is projected at a substantially central position on the front surface thereof, and an input terminal 3 and an output terminal 4 are projected at both side positions thereof. . The SAW filter package 1 is fixedly mounted on the plate 5 by inserting the fixing screw 2 into a through hole of a plate 5 such as a printed circuit board and fastening it with a nut 6. The input / output terminals 3 and 4 are inserted into other through holes of the plate 5. The plate 5 has a shape in which conductive partition walls 7, 7 here are integrally formed between the fixing screw 2 and the input terminal 3 and the output terminal 4, respectively.

Further, coils 8 and 9 for impedance matching are attached to the plate 5 and connected to the input terminal 3 and the output terminal 4, respectively, and a choke coil 10 is attached between the partition walls 7 and 7. The input / output terminals 3 and 4 are connected between the grounds to form the circuit shown in FIG.

Then, as shown in FIGS. 2 (a) and 2 (b), this structural body is housed in a rectangular parallelepiped metal casing 11, and
Tighten the lid 12 with the screw 13 to seal it. At this time, the lid 12 is fixed to each tip of both partition walls 7, 7 of the plate 5 with a screw 13 so that the partition walls 7, 7 electromagnetically shield the input / output terminals 3, 4. The coils 8 and 9 connected to the input / output terminals 3 and 4 are connected to the input connector 14 and the output connector 15, respectively.

Therefore, according to this configuration, the input terminal 3 and the output terminal 4 of the SAW filter package 1 are electromagnetically shielded by the partition walls 7 provided on the plate 4, and thus the input terminal 3 and the output terminal 4 are provided. 4 can suppress or prevent spatial electromagnetic interference, and improve isolation between input and output. Therefore, isolation of 70 to 100 dB or more can be realized, and the amount of out-of-band attenuation can be improved. Further, even when there is a risk that a high-frequency signal leaks between the input and output parts due to a potential difference (ground potential) generated between the grounds of the input part and the output part, while the resistance is sufficiently high for the high-frequency signal, By connecting the choke coil 10 having an impedance characteristic of low resistance to direct current between the grounds of the input section and the output section, the potential difference is made zero and sufficient isolation is obtained for high frequency signal frequencies. It is possible to prevent high frequency signal leakage around the ground. As this choke coil, a coil of about 200 mH is applied in this embodiment.

As a result, the attenuation characteristic of the SAW filter in this embodiment is as shown in FIG. 4, and in the conventional structure shown in FIG.
It can be seen that the out-of-band attenuation at 70 ± 2 MHz was about D / U 40 dB, whereas in the present example, it was improved to D / U 60 dB or more.

〔The invention's effect〕

As described above, according to the present invention, the partition wall is integrally provided on the substrate on which the surface acoustic wave filter package and the impedance matching coil connected to the input / output terminals are mounted. It is possible to electromagnetically shield the input and output parts of the to improve the isolation between them, and also prevent the leakage around the ground caused by the ground potential by the choke coil provided between the grounds of the input part and the output part. It has the effect of achieving sufficient out-of-band attenuation of 50-60 dB or more.

[Brief description of drawings]

FIG. 1 is a view showing the internal structure of an embodiment of the present invention. FIG. 1 (a) is a front view, FIG. 1 (b) is a side view, FIG. 1 (c) is a bottom view, and FIG. 2 is an external view. FIG. 3A is a diagram showing the structure, FIG. 1A is a partially cutaway front view, FIG. 1B is a side view, FIG. 3 is a circuit diagram thereof, and FIG. Is a view showing a conventional internal structure, FIG.
FIG. 6B is a side view, and FIG. 6 is a damping characteristic diagram in the conventional structure. 1 …… SAW filter package, 2 …… Fixing screw, 3
...... Input terminal, 4 ... Output terminal, 5 ... Plate, 6 ...
… Nuts, 7 …… Bulkheads, 8,9 …… Impedance matching coils, 10 …… Choke coils, 11 …… Metal housing, 12
...... Lid, 13 ...... screw, 14 ...... input connector, 15 …… output connector, 21 …… SAW filter package, 22 …… fixing screw, 23 …… input terminal, 24 …… output terminal, 25 …… Printed circuit board, 26 …… Nut, 28,29 …… Coil for impedance matching.

Claims (1)

[Claims] 1. A surface acoustic wave filter in which a surface acoustic wave filter package, an impedance matching coil connected to input / output terminals, etc. are mounted on a substrate, and which is internally housed in a metal casing. Is a partition wall for electromagnetically shielding the input and output terminals of the surface acoustic wave filter package and the coils connected to the input and output sections, respectively, and between the grounds of the input section and the output section. A surface acoustic wave filter characterized in that a choke coil is connected to eliminate a potential difference between an input section and an output section while maintaining isolation for a high frequency signal and prevent a high frequency signal from leaking.