JPH01136405A - Filter circuit - Google Patents

Abstract

PURPOSE:To form a filter circuit with an inexpensive cost and small volume by adopting the LC of a tuning element as a fixed part and providing a small hole for tuning to a shield case so as to deform the L mechanically thereby varying the inductance. CONSTITUTION:One terminal of tuning coils L1, L2 is connected to ground and the terminal is connected to ground via capacitors C1, C2 to form a parallel resonance circuit. The two resonance circuits are coupled by an inductive inductance M. The filter is set in the vicinity of a desired frequency by impedances L1, C1, and L2, C2 at first. An adjustment window 2 for L(L1, L2) is provided on a shield case 1. The lower face E of a double-side printed circuit board 3 is enclosed with the shield case 1 by soldering, etc. In the adjustment of the filter frequency, an insulation rod made of a plastic, etc., is inserted from the adjustment window 2 to vary the length of the solenoid tuning coil L for the optimum adjustment. The filter is not limited to two-stage but the filter of one stage - n-stage can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a miniaturized filter circuit having one or multiple stages of tuning elements.

(Prior Art) Conventionally, in this type of filter circuit, a tuned circuit has been formed by varying the inductance L or capacitance C. Figure 4 shows a conventional filter circuit.
In Figure (A), a metal rod or ferrite rod is inserted into a coiled inductance to change L (Ll, L2). FIG. 4(B) uses a variable capacitor c (ct, C2) such as a variable capacitor.

(Problems to be Solved by the Invention) In the conventional filter circuit shown in FIG. 4(A), the variable portion of L is mechanically large.

In (B), the volume was large and the cost was high.

The purpose of the present invention is to overcome the drawbacks of the prior art, have a small volume,
The purpose of the present invention is to provide a filter circuit at a low cost.

(Means for Solving the Problems) The filter circuit of the present invention is a filter circuit consisting of one or more LC tuning elements, in which the LC of the tuning element is fixed, and the L of the tuning circuit is mechanically deformed. A filter that tunes to a predetermined band and frequency is formed by changing the inductance, and a small hole for tuning is provided in the shield case so that the edge of the tuning element can be deformed and adjusted.

(Function) According to the present invention, since the adjustment hole for deforming the coil L is provided in the shield case, even if the LC is of a fixed type, the LC can be adjusted by deforming the coil. As a result, the filter circuit becomes smaller.

(Example) An example of the present invention will be described based on FIGS. 1 to 3.

FIG. 1 is a diagram showing the principle of a filter circuit according to the present invention.

In the figure, Ll and L are tuning coils of the filter.

C1, C, is the tuning capacitor of the filter.

C,, C2 are fixed capacitors, Ll and L are grounded at the - end, and the other end is grounded via C1 and C.
A parallel resonant circuit is formed. The two resonant circuits are coupled by an inductive inductance M. Also T1. T is an input/output terminal, and a predetermined output impedance is provided between each terminal and the ground.

The above filter is initially set near the desired frequency by C1 and L2°C2, but is not perfectly tuned. Here, L 1 gL2 is varied to match the desired frequency.

For this adjustment, the inductance L is changed by changing or changing the length of the solenoid coil.

FIG. 2 is an external view of the filter circuit of the present invention.

A necessary condition for the filter is that it be suitably shielded and hardly susceptible to external influences.

FIG. 3 is an exploded view showing the internal structure of FIG. 2.

The figure satisfies the above two conditions, namely variable inductance and shielding.

In Figures 2 and 3, 1 is a shield case, 2
is the L provided in the shield case 1 (L,.

The adjustment window 3 of Lz) is a double-sided printed circuit board, and the lower surface E is enclosed by the shield case 1 and the soldering board. 4 is the input or output terminal of the filter circuit;
5 is a ground terminal of the shield case 1, and LC is a tuned circuit element. To adjust the filter frequency, an insulating rod made of plastic or the like is inserted through the adjustment window 2, and the length of the solenoid-shaped tuning coil L is changed to obtain the optimum condition.

The above-mentioned filter is not limited to two stages, but a filter having one or more n stages can be formed. At 3rd stage or higher.

The intermediate tuning element is an independent tuning element and is coupled to the input and output circuits with an induction factor M. However, these circuits are not limited to the two-tuned circuits as described above, but can also be applied to various types of filters such as constant type and inductive M type.

In the above embodiment, an adjustment hole is provided on the side of the solenoid coil L, but this means that the adjustment hole is provided on the axis of the coil, and the solenoid coil is not crushed or stretched with a hook-shaped adjustment tool. It is also possible to adjust it as desired.

Next, as can be seen from Fig. 3, the filter circuit of the present invention is shielded by enclosing the shield case and the back side of the printer board by soldering, etc., and the input and output terminals of the filter are connected to the printed board. and the ground terminal, and by providing the ground terminal of the shield case in the same direction.

Like other device components, it can be handled as a solid component, and can be mounted on a main board together with other device components using a solder bath or the like, making it suitable for mass production.

(Effects of the Invention) According to the present invention, a double-sided substrate is used for the substrate of the filter forming portion, and the lower surface is connected to and enclosed by the shielding case, so that a sufficiently good shielding effect can be obtained. In addition, since the printed circuit board's ground plate, input and output terminals, and shield case are pulled out to one side as terminals, they can be handled like other equipment parts and attached to the main board using methods such as a solder bath, making them suitable for mass production. ing. Furthermore, compared to conventional filters, since there are no variable parts, the filter is extremely small and the cost can be reduced, and its practical effects are extremely large.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram of a filter circuit according to an embodiment of the present invention, Fig. 2 is an external view of the same, Fig. 3 is an exploded view showing the internal structure of the same, and Fig. 4 is an explanatory diagram of a conventional filter circuit. . L... Tuning coil, C... Tuning capacitor, M...
...Inductive inductance, T, T2...Input/output terminal, 1...Shield case, 2...Adjustment window, 3...
・Double-sided printed board. 4... Input/output terminal, 5... Earth terminal. Patent applicant: Matsushita Electric Industrial Co., Ltd., Midori Musen Co., Ltd. + +,;'';□11゜ Agent: Kouji Hoshino □-・j Iwagami Noboru - 1+ Commentary. Figure 1 Figure 2

Claims (1)

[Claims] In a filter consisting of one or more LC tuning elements, the LC of the tuning element is fixed, and the inductance is changed by mechanically deforming L of the tuning circuit to form a filter that tunes to a predetermined band and frequency. A filter circuit characterized in that a small adjustment hole is provided in the shield case so that L of the tuning element can be deformed and adjusted.