JPH01276911A - Filter device - Google Patents

Abstract

PURPOSE:To prevent the production of signal-through between the input and output and the mismatching at an input/output terminal from being caused by providing a metallic piece for earthing through the use of a shield case and soldering the piece with the metallic case of an SAW filter. CONSTITUTION:A metallic plate 2 utilizing part of a shield case 1 and a metallic case of an SAW filter 4 are soldered. That is, the metallic plate 2 is formed incorporatedly with the shield case 1 in the same direction as the part of leg inserted to a printed circuit board 5, folded further by 90 deg., the end of the earth metallic plate 2 is arranged so as to nearly in contact with a guard of the metallic case of the SAW filter 4 when each terminal of the SAW filter 4 and the leg of the shield case 1 are inserted respectively to the printed circuit board 5 and the contact part is soldered from the upper part. Thus, excellent grounding is obtained by a simple method.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is used in a video intermediate frequency amplification circuit (hereinafter abbreviated as VIP circuit) of a television receiver, a second intermediate frequency amplification circuit of a satellite broadcasting receiver, etc. The present invention relates to a filter device using a surface acoustic wave filter (hereinafter abbreviated as SAW filter).

BACKGROUND OF THE INVENTION In recent years, advances in electrode formation technology have enabled SAW filters to be mass-produced at high yields and at low cost up to high frequency ranges, and have become easy to use in place of LC filters. Among them, the type of SA enclosed in a metal case
W filters are widely used, and a circuit is formed by inserting them into a hole in a board, printing foil on the back side, dip soldering, etc.

Hereinafter, with reference to the drawings, the following will be described.

A conventional filter device will be explained below. FIG. 2 shows the mounting state of a conventional filter device, as seen from the back side of the board. In Figure 2, 1 is a shield case surrounding the VIF circuit, 2 is a printed foil for grounding,
3 is a SAW filter inserted from the front side, 4 is a VIP circuit IC, and 5 is a 7' lint board.

In the filter device configured as described above, the SAW
The filter 3 has, for example, four terminals; in the figure, A is an input, B and C are outputs, and D is a ground terminal. The outputs of B and C are connected to the balanced input terminal of the VIF IC4. or,
The terminal D is connected to the ground foil 2, and then to the legs of the shield case 1, etc. With such a configuration, the input signal connected to the terminal of A passes through the SAW filter 3 and is sent to I.
It is input to C4.

Problems to be Solved by the Invention However, the above configuration has a problem in that sufficient filter characteristics cannot be obtained.

Figure 3 shows the characteristic diagram of the filter, where the solid line (() indicates SA
This is the original characteristic diagram of the W filter alone, and the broken line (b) shows the characteristic diagram obtained by the configuration method shown in FIG. In the case of (b), ripples occur within the band due to reflection, and outside the band, the attenuation is insufficient, making the signal about 1 odB worse than it should be, resulting in a significant deterioration of the jamming performance.

The reason for this phenomenon is that the filter itself is not sufficiently grounded, resulting in signal through between the input and output.
This is because mismatching occurs at the input/output terminals.

In FIG. 2, the ground terminal of the SAW is connected to the shield case 5 through the ground foil 2, but since the foil is thin and long, its conductor impedance becomes high, making it impossible to obtain sufficient grounding characteristics.

Furthermore, since many circuit components are arranged close together on a printed circuit board, it is impossible to form many thick ground foils, and the above-mentioned problems are unavoidable.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a filter device that can exhibit its original filter characteristics.

Means for Solving the Problems To achieve this object, the filter device of the invention comprises:
It consists of a metal plate using a part of the shield case and the metal case of the SAW filter connected by soldering.

Function: With such a configuration, a good grounding condition can be obtained, so that the original filter characteristics can be obtained.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows a filter device in one embodiment of the present invention.

In Fig. 1, 1 is a shield case, 2 is a metal plate for strengthening the ground formed integrally with the shield case 1, 3 is solder, 4 is a SAW filter with a metal case that serves as a ground terminal, and 6 is a printed circuit board. .

The operation of the filter device configured as described above will be explained below. In Figure 1, (6) is a cross-sectional view of the configuration, (F is a plan view, and (Q is a developed view of the shield case. Form the metal plate 2 integrally with the shield case 1, bend it further 90 degrees, and insert each terminal of the SAW filter 4 and 10 pairs of the shield cases into the printed circuit board 6, as shown in FIG. 1 (G). When this happens, the end of the grounding metal plate 2 is placed so that it is almost in contact with the brim of the metal case of the SAW filter 4, and the contact part is soldered from above as shown in Figure 1 (B). .

According to the embodiments described above, good grounding can be obtained in a simple manner, so that the original in-band and out-of-band characteristics can be obtained.

Effects of the Invention As described above, according to the present invention, original good filter characteristics can be obtained by providing a metal piece for grounding using the shield case and bonding it to the metal case of the SAW filter. It can be done, and its practical effects are great.

In the case of the present invention, the metal pieces are provided in the same direction as the legs of the shield case, so there is less material loss, and there is no hole in the case itself, which occurs when cutting and raising from the side. .

Also, it is possible to solder at the head of the SAW filter, but since the SAW chip and grounding terminal are located at the bottom of the metal case, it is better to ground at the brim. The effect is large, and in that sense, the present device is effective.

[Brief explanation of the drawing]

Fig. 1 is a side view, a plan view, and a developed view of a shield case of a filter device according to an embodiment of the present invention, Fig. 2 is a rear view of a conventional filter device as seen from the back side of the substrate, and Fig. 3 is a SAW filter. FIG. 1...Shield case, 2...Metal plate for ground reinforcement %3...Solder, 4...
SAW filter, 5... Printed circuit board. Name of agent, patent attorney Toshio Nakao and 1 other person f-
-Seal y7-s4---. 5AW74Ag5...-Based on Asin

Claims (1)

[Claims] It is composed of a surface acoustic wave filter having a metal case, a shield case, and a printed circuit board, and the shield case is integrally provided with a metal plate for grounding in the same direction as the foot inserted into the printed circuit board. is bent horizontally,
The terminal of the filter and the insertion foot of the shield case are inserted into the board, the grounding metal plate is placed on the front side of the board, and the tip of the grounding metal plate is connected to the bottom of the filter's metal case. A filter device in which the contact portions are soldered.