JP2773590B2 - Low-pass filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pass filter, and more particularly to a high-frequency low-pass filter having a coil electrode used as an inductor.

[0002]

2. Description of the Related Art FIG. 6 is a perspective view showing an example of a conventional high-frequency low-pass filter. The low-pass filter 1 shown in FIG. A ground electrode 3 is formed on one entire main surface of the dielectric substrate 2. Dielectric substrate 2
In the center of the other main surface, two coil electrodes 4a and 4b serving as first and second inductors are formed. Further, on the other main surface of the dielectric substrate 2, a first capacitor electrode 5a constituting a part of the first capacitor and an input electrode 6a serving as an input terminal extend from one end of one coil electrode 4a. A second capacitor electrode 5b formed and constituting a part of the second capacitor is connected to one coil electrode 4a.
The third capacitor electrode 5c, which is formed to extend from one end of the other coil electrode 4b and one end of the other coil electrode 4b, and constitutes a part of the third capacitor, and the output electrode 6b serving as an output terminal are connected to the other coil electrode 4b. It is formed to extend from the other end.

FIG. 7 is a perspective view showing another example of a conventional high-frequency low-pass filter. The low-pass filter 1 shown in FIG. 7 is different from the low-pass filter 1 shown in FIG.
Three chip capacitors 7 instead of one capacitor electrode
a, 7b and 7c are used.

A low-pass filter 1 shown in FIGS. 6 and 7
Have the equivalent circuits shown in FIG. That is, each of the low-pass filters 1 shown in FIGS. 6 and 7 has an input terminal IN and an output terminal OUT. Between the input terminal IN and the output terminal OUT, the first and second
Inductor L ₁ and L ₂ are connected in series. Further, the input terminal IN is grounded via a _first capacitor C1, the connection point of the _first and _second inductors L1 and L2 is grounded via a _second capacitor C2, and the output terminal OUT is Grounded via a _third capacitor C3.

[0005]

In the conventional examples shown in FIGS. 6 and 7, when the stray capacitance between the ground electrode and the coil electrode increases, the inductive impedance between both ends of the coil electrode decreases, It is difficult to reduce the size and reduce the frequency.

Further, in the conventional examples shown in FIGS. 6 and 7, when the stray capacitance between the ground electrode and the coil electrode increases, the frequency at which the impedance between both ends of the coil electrode reverses to capacitive decreases. Higher frequency becomes difficult.

In the conventional example shown in FIGS. 6 and 7,
In each case, an unnecessary pass band is generated due to resonance at a frequency that is an integral multiple of a half wavelength of the line length of the coil electrode, and good spurious characteristics cannot be obtained.

Therefore, a main object of the present invention is to provide a low-pass filter having good spurious characteristics.

[0009]

According to the present invention, there is provided a coil electrode used as an inductor, a capacitor electrode connected to the coil electrode, and formed between the coil electrode and the capacitor electrode and connected in parallel to the inductor. A low-pass filter including a capacitor, wherein a parallel resonance frequency of the inductor and the capacitor is substantially matched to a frequency of a half wavelength of the line length of the coil electrode.

[0010]

Since the parallel resonance frequency of the inductor and the capacitor is approximately equal to the frequency of a half wavelength of the line length of the coil electrode, the resonance at a frequency that is an integral multiple of the half wavelength of the line length of the coil electrode is achieved. Unnecessary passing areas are suppressed.
Therefore, spurious characteristics are improved.

[0011]

According to the present invention, a low-pass filter having good spurious characteristics can be obtained. In the low-pass filter according to the present invention, since the coil electrode is used as the inductor and the capacitor electrode is used,
It can be formed in a stacked type, so that downsizing is possible and it can be manufactured as a surface mount component.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0013]

FIG. 1 is a perspective view showing an embodiment of the present invention.

The laminated body 11 includes a first dielectric layer 12, as shown in FIG. On the first dielectric layer 12, a ground electrode 14 is formed on almost the entire surface. Earth electrode 1
Four lead terminals 16a, 16b, 16c, 16d, 16e, and 16f are formed from 4 toward the end of the first dielectric layer 12. Two extraction terminals 16a and 16
“b” is formed toward one end of the first dielectric layer 12 and is formed at an interval from each other. The other two lead-out terminals 16c and 16d are formed toward the other end of the first dielectric layer 12, and are formed at positions near the center thereof. The other lead terminals 16e and 16f are formed toward the other facing end of the first dielectric layer 12, respectively.

On the ground electrode 14, the second dielectric layer 1
8 are stacked. On the second dielectric layer 18, the first, second, and third capacitors constituting a part of the first, second, and third capacitors are provided.
And third capacitor electrodes 20, 22, and 24 are formed. The second capacitor electrode 22 is formed near one end of the second dielectric layer 18 and substantially near the center. Further, the first and third capacitor electrodes 20 and 24 are formed on both sides near the other end of the second dielectric layer 18 with a space therebetween. The first to third capacitor electrodes 20 to 24 are formed so as to face the ground electrode 14. Further, from the second capacitor electrode 22 toward one end of the second dielectric layer 18, two connection terminals 22 a
And 22b are formed. These connection terminals 22a and 22b are formed close to each other near the center on one end side of the second dielectric layer 18. Further, the connection terminals 20a and 24a extend from the first and third capacitor electrodes 20 and 24 toward the other end of the second dielectric layer 18.
Are formed respectively. These connection terminals 20a and 24a are formed spaced apart from each other.

On the first to third capacitor electrodes 20 to 24, a third dielectric layer 26 is laminated. On the third dielectric layer 26, first and second coil electrodes 28 and 30 used as first and second inductors are formed. First and second coil electrodes 28 and 30
Are formed as meander lines meandering from one end to the other end of the third dielectric layer 26, respectively. In this case, in order to form a capacitor for parallel resonance with the inductor by the first coil electrode 28, a part of the first coil electrode 28 is connected to the first and second capacitor electrodes 20.
And 22 are formed. Furthermore, the second
In order to form a capacitor for parallel resonance with the inductor by the coil electrode 30 of the second embodiment, a part of the second coil electrode 30 is partially connected to the second and third capacitor electrodes 22 and 2.
4. One end 28a of the first coil electrode 28 is formed at a position corresponding to the connection terminal 22a of the second capacitor electrode 22, and the other end 28b
Is formed at a position corresponding to the connection terminal 20a of the first capacitor electrode 20. Further, one end 30a of the second coil electrode 30 is connected to the connection terminal 2 of the second capacitor electrode 22.
The other end 30b is formed at a position corresponding to the connection terminal 24a of the third capacitor electrode 24.

First and second coil electrodes 28 and 3
A fourth dielectric layer 32 is stacked on the zero. On almost the entire surface of the fourth dielectric layer 32, a shield electrode 36 is formed.
Is formed. From the shield electrode 36 to the fourth dielectric layer 3
Toward the end of the two, six lead-out terminals 36a, 36b,
36c, 36d, 36e and 36f are formed. 2
The four lead terminals 36a and 36b are connected to the fourth dielectric layer 3
2 are formed toward one end side and are formed at an interval from each other. Another two extraction terminals 36c and 36d are:
The fourth dielectric layer 32 is formed toward the other end side, and is formed at a position close to the center thereof. Further, a fifth dielectric layer 38 is laminated on the shield electrode 36.
The other two lead terminals 36e and 36f are formed toward the other opposing ends of the fourth dielectric layer 32, respectively.

As shown in FIG. 1, ten external electrodes 40a, 40b, 40c,
40d, 40e, 40f, 40g, 40h, 40i and 40j are formed. These external electrodes 40a-40
j, four external electrodes 40 a to 40 d are
And four other external electrodes 40e to 40e
h is formed on the other end of the multilayer body 11, and the other two external electrodes 40i and 40j are formed on the other facing end side of the multilayer body 11. These external electrodes 40a to 40j
The stacked body 11 is formed so as to reach the lower surface from the upper surface via the side surface.

External electrodes 40a, 40d, 40f, 40
g, 40i and 40j are connected to the extraction terminals 16a, 16b, 16c, 16d, 16e and 16f of the ground electrode 14, respectively. At the same time, the external electrodes 40a, 40
d, 40f, 40g, 40i and 40j are lead terminals 36a, 36b, 36c,
36d, 36e and 36f. The external electrode 40 b is connected to one end 28 a of the first coil electrode 28 and the connection terminal 22 a of the second capacitor electrode 22. Further, the external electrode 40e is connected to the first coil electrode 2
8 and the connection terminal 20 a of the first capacitor electrode 20. Further, the external electrode 40c is connected to one end 30a of the second coil electrode 30 and the connection terminal 22b of the second capacitor electrode 22. Further, the external electrode 40h is connected to the other end 30b of the second coil electrode 30.
And the connection terminal 24a of the third capacitor electrode 24.

This high-frequency low-pass filter 10
For example, it is formed by applying an electrode paste in the shape of each electrode and each terminal on a dielectric ceramic green sheet, laminating and firing. At this time, the number of ceramic green sheets to be laminated is adjusted according to the thickness of each dielectric layer. To form the external electrode,
The electrode paste may be applied and fired integrally before firing the laminate, or the electrode paste may be applied and fired after firing the laminate.

This high-frequency low-pass filter 10
As shown in FIG. 3, the first and second inductors L ₁ and L ₂ and the first, second and third capacitors C ₁ , C 2
₂ and C ₃ have an equivalent circuit connected in π-type.
Note that inductors L ₁₁ , L ₁₂ and L ₁₃ formed by the ground electrode 14 and the like are formed between the first to third capacitors C ₁ , C ₂ and C ₃ and the ground potential, respectively.

Furthermore, the low-pass filter 10 for the high frequency, the first inductor L ₁ and capacitor C ₁₁ for parallel resonance in parallel are connected, a capacitor C ₁₂ for parallel resonance in parallel with the second inductor L ₂ Is connected.

[0023] In this case, one of the capacitance of the capacitor C ₁₁ for parallel resonance, the parallel resonance frequency of the first inductor L ₁ and capacitor C ₁₁ is first inductor L ₁ (first coil electrode 28) Is selected so as to substantially coincide with the frequency of a half wavelength of the line length of. Further, the capacitance of the capacitor C ₁₂ for the other parallel resonance, the second inductor L ₂
And the parallel resonance frequency of the capacitor C ₁₂ is chosen to substantially match the line frequency of the half wavelength of the length of the second inductor L ₂ (the second coil electrode 30).

Therefore, in the high-frequency low-pass filter 10, the first and second coil electrodes 28 and 3
An unnecessary pass band due to resonance at a frequency that is an integral multiple of a half wavelength of the line length of 0 is suppressed, and the spurious characteristics are good.

In this embodiment, the capacitance of one of the parallel resonance capacitors C ₁₁ is the third dielectric layer 2.
6 and the area of the first and second capacitor electrodes 20 and 22 facing the first coil electrode 28 can be adjusted. In this case, if the thickness of the third dielectric layer 26 is reduced, its capacitance increases. In addition, if the facing area between the first and second capacitor electrodes 20 and 22 and the first coil electrode 28 is increased, the capacitance is increased. Further, in order to change the facing area of the electrodes, the shape or the forming position of the electrodes may be changed. Similarly, the capacitance of the other parallel resonance capacitor C ₁₂ depends on the thickness of the third dielectric layer 26 and the second and third capacitor electrodes 22 and 24.
It can be adjusted by changing the area where the second coil electrode 30 faces the second coil electrode 30.

As an experimental example, each of this embodiment and a comparative example in which each parallel resonance frequency in this embodiment is made not to coincide with an integral multiple of a half wavelength of the line length of each inductor will be described. , The amount of attenuation with respect to frequency and the return loss were measured. FIGS. 4 and 5 show frequency characteristics of the example and the comparative example, respectively.

As is clear from the graphs shown in FIGS. 4 and 5, the comparative example has an unnecessary pass band at about 6.8 GHz which deteriorates spurious characteristics, but the embodiment suppresses such unnecessary pass band. It can be seen that the spurious characteristics are improved.

As described above, by making the parallel resonance frequency of the inductor and the capacitor substantially equal to the frequency of 1/2 wavelength of the line length of the coil electrode, the parallel resonance frequency of the inductor electrode and the capacitor is an integral multiple of 1/2 wavelength of the line length of the coil electrode. It can be seen that the unnecessary pass band due to the resonance at the frequency is suppressed, and the spurious characteristics are improved.

In the above-described embodiment, each of the capacitor electrodes 20, 22, and 24 functions as a notch filter at a frequency corresponding to １ ／ wavelength of each length, and an attenuation pole is generated at each frequency. Therefore, if these frequencies are set to integral multiples of the cutoff frequency, the amount of attenuation at harmonics of the cutoff frequency can be further increased.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is an exploded perspective view of the laminate of the embodiment shown in FIG.

FIG. 3 is an equivalent circuit diagram of the embodiment shown in FIG.

FIG. 4 is a graph showing frequency characteristics of the embodiment shown in FIG.

FIG. 5 is a graph showing frequency characteristics of a comparative example.

FIG. 6 is a perspective view showing an example of a conventional high-frequency low-pass filter.

FIG. 7 is a perspective view showing another example of a conventional high-frequency low-pass filter.

8 is an equivalent circuit diagram of the conventional example shown in FIGS. 6 and 7. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Low-pass filter 11 Laminated body 12 1st dielectric layer 14 Earth electrode 18 2nd dielectric layer 20 1st capacitor electrode 22 2nd capacitor electrode 24 3rd capacitor electrode 26 3rd dielectric layer 28th 1st coil electrode 30 2nd coil electrode 32 4th dielectric layer 36 Shield electrode 38 5th dielectric layer

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01F 15/00 H01P 1/20 H01P 1/203 H01P 1/212 H03H 7/01 H03H 7/075

Claims (1)

(57) [Claims] A coil electrode used as an inductor; a capacitor electrode connected to the coil electrode; and a coil electrode formed between the coil electrode and the capacitor electrode;
A low-pass filter including a capacitor connected in parallel to the inductor, wherein a parallel resonance frequency of the inductor and the capacitor is substantially equal to a frequency of a half wavelength of a line length of the coil electrode.