JPH04284606A - Filter element - Google Patents

Abstract

PURPOSE:To improve the passing band characteristic of a bandpass filter and to make a filter element small-sized. CONSTITUTION:At a filter element where shunt-arm type bandpass filter circuits which have connected a plurarity of LC resonators in parallel in a capacity coupling manner have been mounted on a multilayer substrate, coils of adjacent LC resonators are coupled magnetically inside the multilayer substrate. For example, a two-turn coil L10 composed of coils 8, 10 and a two-turn coil L11 composed of coils 12, 14 are coupled magnetically. An equivalent LC resonator is formed of the capacity of a coupling capacitor C2 and of a mutual inductance generated between said coils L10, L11; passing band characteristics are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a filter element,
More specifically, the present invention relates to a filter element that is used in a shunt arm type bandpass filter in which a plurality of LC resonators are connected in parallel through capacitive coupling, and in particular, the filter is mounted on a multilayer substrate. [0002] FIG. 4 is a diagram showing an example of a circuit of a conventional band-pass filter, and (A) shows an example of a band-pass filter (
1) and (B) show an example (2) of a bandpass filter. In the figure, L1, L2, L10 to L12 are coils, C1
~C4, C10~C12 are capacitors, IN is an input terminal, and OUT is an output terminal. Conventionally, a shunt arm type bandpass filter in which a plurality of LC resonators are connected in parallel through capacitive coupling has a circuit configuration as shown in FIG. 4(A), for example. [0004] In FIG. 4(A), C10, L10, and C11
and L11, C12, and L12 each constitute an LC resonator (parallel resonant circuit), and these LC resonators are coupled via coupling capacitors C2 and C3, respectively. [0005] Furthermore, an input terminal IN and an output terminal OUT
Coupling capacitors C1 and C4 are also connected to the sides, forming a bandpass filter as a whole. By the way, a band-pass filter as shown in FIG. 4B, for example, has been known as a band-pass filter with improved pass band characteristics. In order to improve the attenuation characteristics outside the passband, this bandpass filter connects coils L1 and L2 in parallel with the coupling capacitors C2 and C3 shown in FIG. It is a circuit in which each LC resonator is connected. [0008] In a bandpass filter having such a circuit configuration, characteristics are improved by creating attenuation poles in the pass band characteristics using the above-mentioned LC resonators L1 C2 and L2 C3. Problems to be Solved by the Invention The conventional devices as described above had the following problems. (1) FIG. 4(B) is an improved version of the bandpass filter shown in FIG. 4(A).
A bandpass filter having the circuit configuration shown in FIG. 1 is known. These improved bandpass filters require an extra coil. For this reason, when a bandpass filter circuit is mounted on a multilayer substrate to form a filter element, the filter element becomes larger due to the additional coils. (2) The bandpass filter before the characteristic improvement shown in FIG. 4(A) has a smaller filter element than the bandpass filter shown in FIG. 4(B) after the characteristic improvement, but the characteristics The passband characteristics are worse than the improved filter. SUMMARY OF THE INVENTION An object of the present invention is to solve these conventional problems, improve the passband characteristics of a bandpass filter, and downsize the filter element. [Means for Solving the Problems] In order to solve the above problems, the filter element of the present invention was constructed as follows. That is, in a filter element in which a circuit of a shunt arm type band-pass filter in which a plurality of LC resonators are connected in parallel by capacitive coupling is mounted on a multilayer substrate, each adjacent LC resonator in the multilayer substrate between the coils,
They are arranged so that they are magnetically coupled, and an equivalent LC resonator can be formed by the mutual inductance generated by the magnetic coupling and the coupling capacitance between each LC resonator. [0016] The filter element having the above structure is used as a band pass filter. During use, only signals within a predetermined frequency band among the signals input to this filter element are passed. In this case, there is magnetic coupling between the coils of adjacent LC resonators, and due to the mutual inductance generated at this time and the capacitance of the coupling capacitor connected between adjacent LC resonators, the equivalent LC A resonator is formed. This equivalent LC resonator creates an attenuation pole outside the passband of the bandpass filter, improving the passband characteristics. [0019] In this way, there is no need to add a new coil in order to improve the passband characteristics. Therefore,
The number of coils mounted on the multilayer board can be reduced, making it possible to reduce the size of the filter element and improve passband characteristics at the same time. [Embodiments] Hereinafter, embodiments of the present invention will be explained based on the drawings. (Description of one embodiment) FIGS. 1 to 3 are views showing one embodiment of the present invention, in which FIG. 1 is an exploded perspective view of a filter element, and FIG. 2 is a sectional view of FIG. 3 is a band pass filter circuit. In the figure, 1 to 6 are dielectric layers, 7, 11, 15
is the GND electrode, 8, 10, 12, 14, 16 are the coils,
9 and 13 are capacitor electrodes, 17 and 18 are connection lines (connection through blind through holes), C10-1,
C10-2, C11-1, C11-2, C1, C2
, C10, C11, C12, C3 are capacitors, L1
0, L11, and L12 are coils, M is mutual inductance, and IN is an input terminal. In this embodiment, the circuit of the bandpass filter mounted on the multilayer substrate is shown in FIG. 3(A). Figure 3 (
In the circuit A), the capacitor C10 and the coil L10, the capacitor C11 and the coil L11, and the capacitor C12 and the coil L12 each constitute an LC resonator (parallel resonant circuit). Capacitors C1 to C4 are each a coupling capacitor. This circuit has N LC resonators (
(N is an arbitrary integer) are connected in parallel, but only a part of the circuit is shown in the figure. [0025] When mounting such a circuit on a multilayer board,
Between the coils of adjacent LC resonators, that is, between the coil L10 and the coil L11, between the coil L11 and the coil L12...
are arranged so as to be magnetically coupled to each other. Using the mutual inductance M caused by this magnetic coupling, the coupling capacitors C2, C3,
An equivalent LC resonant circuit as shown in FIG. 3(B) is formed by capacitors such as C4 and the mutual inductance M. The passband characteristics of the bandpass filter are improved by this equivalent LC resonator (characteristics are improved by forming an attenuation pole). An example of a filter element in which a circuit having the above configuration is mounted on a multilayer substrate will be described below with reference to FIGS. 1 and 2. In this figure, among the circuits shown in FIG. 3(A), C1,
Only the implementation diagram of the portions C2, C10, L10, C11, and L11 is shown. Also, the cross-sectional view along the X-Y line is shown in Figure 2(A).
The sectional view taken along the line ST is shown in FIG. 2(B). As shown in the figure, an input terminal IN is formed as a thick film pattern (thick film printed pattern) on the dielectric layer 1 of the multilayer substrate constituting the filter element. A GND electrode 7 and a coil 8 are integrally provided on the dielectric layer 2 below the dielectric layer 1 using a thick film pattern. A capacitor electrode 9 and a coil 10 are integrally formed in a thick film pattern on the dielectric layer 3 below. Further, on the dielectric layer 4 below, a coil 1 is formed.
2 and the GND electrode 11 are integrally provided. On the dielectric layer 5 below this dielectric layer 4, a capacitor electrode 13 is provided.
and a coil 14 are formed in a thick film pattern, and on the dielectric layer 6 thereunder, a GND electrode 15 and a coil 16 are integrally formed in a thick film pattern. When forming the above thick film pattern, the coils of each layer (thick film coil pattern) are formed at positions facing each other in the stacking direction of the multilayer substrate. This provides an arrangement in which the coils of adjacent LC resonators can be magnetically coupled. In order to adjust the mutual inductance M between the coils, it is also possible to arrange the coils in a staggered arrangement and face each other in the stacking direction. Further, each capacitor electrode and the GND electrode are also formed at positions facing each other in the stacking direction of the multilayer substrate. Among the above-mentioned coils, one end of the coil 8 formed on the dielectric layer 2 (the end not connected to the GND electrode 7) and one end of the coil 10 formed on the dielectric layer 3. (the end not connected to the capacitor electrode 9) is connected by a blind through hole (through hole whose inside is filled with a conductor) (see line 17 indicating connection). [0036] Through this connection between the coils, the coils on both dielectric layers are integrated to form a two-turn coil. This integrated coil is the coil L in Fig. 3(A).
It becomes 10. Also, one end of the coil 12 on the dielectric layer 4 (
(the end not connected to the GND electrode 11) and one end of the coil 14 on the dielectric layer 5 (the end not connected to the capacitor electrode 13) are connected by a blind through hole. (see line 18). With this connection, the coil 12 and the coil 14
are integrated to form a two-turn coil. This integrated coil becomes coil L11 in FIG. 3(A). The coil L10 (coil 8 and coil 10) and the coil L11 (coil 12 and coil 14) are configured to be magnetically coupled. Capacitor electrode and GND on each dielectric layer
A capacitor is formed between each electrode as follows. A capacitor C1 (coupling capacitor) is formed between the input terminal IN and the capacitor electrode 9, and a capacitor C2 (coupling capacitor) is formed between the capacitor electrode 9 and the capacitor electrode 13.
A capacitor C10-1 is formed between the GND electrode 7 and the capacitor electrode 9, and a capacitor C10-1 is formed between the capacitor electrode 9 and the GND electrode 11.
2 is formed. These capacitors C10-1 and C1
0-2 becomes the capacitor C10 in FIG. 3(A). A capacitor C11-1 is formed between the GND electrode 11 and the capacitor electrode 13, and a capacitor C11-1 is formed between the capacitor electrode 13 and the GND electrode 15.
1-2 is formed. These capacitors C11-1 and C11-2 form the capacitor C11 in FIG. 3(A). Note that the coil 1 formed on the dielectric layer 6
6 becomes a part of the coil (coil L12 in FIG. 3) that constitutes the next stage LC resonator. Generally, when N LC resonators are connected in parallel, a thick film pattern similar to that shown in FIG. 1 may be repeatedly formed. If the bandpass filter circuit shown in FIG. 3(A) is mounted on a multilayer substrate as described above, the equivalent circuit will be as shown in FIG. 3(B). As shown in the figure, an equivalent LC resonant circuit is formed by the mutual inductance M generated between the coils of adjacent LC resonant circuits and the capacitance of the coupling capacitor. For example, the mutual inductance M between the coils L10 and L11 and the coupling capacitor C2 form an equivalent LC resonator as shown. The circuit in which this LC resonator is formed has the same configuration as the circuit shown in FIG. 4(B). That is, the bandpass filter in which an LC resonator is formed by the mutual inductance M and the coupling capacitor is a filter with improved passband characteristics (M
(Adjust the characteristics of the LC resonator to be appropriate.) [0048] As explained above, the present invention has the following effects. (1) There is no need to add a new coil to improve the passband characteristics of the bandpass filter. Therefore, the number of coils mounted on the multilayer board can be reduced, and the filter element can be made smaller and the passband characteristics can be improved at the same time. (2) Since the number of coils is small,
Accordingly, the number of manufacturing steps is also reduced. Therefore, the filter element becomes cheaper.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view of a filter element in an embodiment of the present invention.

FIG. 2 is a cross-sectional view of FIG. 1;

FIG. 3 is a circuit diagram of a bandpass filter in an example.

FIG. 4 is a circuit diagram of a conventional bandpass filter.

[Explanation of symbols]

1 to 6 Dielectric layers 7, 11, 15 GND electrodes 8, 10, 12, 14, 16 Coils 9, 13 Capacitor electrodes 17, 18 Connection line IN Input terminal

Claims (1)

[Claims] 1. A filter element in which a circuit of a shunt arm type bandpass filter in which a plurality of LC resonators are connected in parallel through capacitive coupling is mounted on a multilayer substrate, in which coils of adjacent LC resonators are connected in parallel in the multilayer substrate. The two LC resonators are arranged so that they are magnetically coupled, and an equivalent LC resonator can be formed by the mutual inductance (M) generated by the magnetic coupling and the coupling capacitance between each LC resonator. A filter element characterized by: