JP2002171103A - Filter trap circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated strip line filter which is made to have sharp attenuation characteristics without deteriorating the pass band of the filter circuit in loss when the notch frequency of a trap circuit is set higher than the filter pass band of the filter circuit. SOLUTION: A filter trap circuit board 9 is composed of a grounding electrode 4 which is formed on the primary surface of a rectangular laminate composed of laminated dielectric layers or between the laminated dielectric layers, a strip line 1, an inductor 3, an input electrode 7a, an output electrode 7b, and an input/output transmission line 2 connected between the electrodes 7a and 7b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a trap circuit board for a filter for improving an attenuation pole characteristic of a filter in frequency characteristics of a laminated strip line filter and a duplexer used as a high-frequency component. Especially TEM (Transverse Electromagnetic
Mode) or a trap circuit board for a filter formed using a quasi-TEM.

[0002]

2. Description of the Related Art Conventionally, a coaxial dielectric filter using a coaxial dielectric resonator and a dielectric layer using a distributed constant circuit as an internal electrode instead of the coaxial dielectric resonator are laminated. Is known. When obtaining an attenuation characteristic at a desired frequency of such a laminated strip line filter, for example,
A method of incorporating a trap circuit connected in series to an input side or an output side of a multilayer strip line filter is often used.

A laminated strip line filter incorporating such a trap circuit is disclosed in Japanese Patent Application Laid-Open No. 8-27450.
It is shown in FIG. Since the structural design of the coupling part of the laminated strip line filter to the strip line forming the trap circuit can be easily performed, a capacitive coupling type electric connection is made electrically in series with the strip line forming the trap circuit. Trap circuits were commonly used.

FIG. 9 shows an example of the capacitively coupled trap circuit board, FIG. 10 shows an equivalent circuit diagram thereof, and FIG. 11B shows the transmission characteristics of the trap circuit board.

As shown in FIG. 9, a conventional trap circuit board 100 is formed with a dielectric block 600 in which dielectric layers 601 to 604 are sequentially laminated, and a ground electrode 400 and a ground electrode 400 are provided on both main surfaces and end surfaces thereof. 401 is formed.
Further, a strip line 200 having one end short-circuited to the ground electrode 401 is formed extending between the dielectric layers 601 and 602 so as to open the other end.
603, the input electrode 301 and the output electrode 302 are connected to each other, and the strip line 200 and the dielectric layer 60 are connected.
An input / output transmission line 300 orthogonal to the input / output line 2 is formed.

As shown in FIG. 10, the strip line 200 constituting the trap circuit board 100 utilizes an inductive region, and a capacitance component 303 formed by the strip line 200 and the input / output transmission line 300 is used. Are connected in series, and the circuit is connected to the input / output transmission line 300.
, A trap circuit having an attenuation pole at the series resonance frequency is obtained. By connecting this trap circuit in series with the filter circuit of the multilayer strip line filter, it is possible to obtain attenuation characteristics in a desired frequency band.

In such a capacitively coupled trap circuit board 100, since the strip line 200 itself forms a resonance circuit using an inductive region, the trap circuit substrate 100 is larger than the attenuation pole of the trap circuit. The parallel resonance frequency of the strip line 200 exists in a high frequency range, and FIG.
As shown in (b), the attenuation characteristic on the high frequency side is steeper than on the low frequency side based on the notch frequency, which is the attenuation pole of the trap circuit.

[0008]

In mobile communication systems in recent years, standards have been determined for effective use of radio waves. For example, CDMA to be adopted in Japan and Europe
According to the standard, the reception band is 2110 to 2170 MHz, the transmission band is 1920 to 1980 MHz, the interval between the pass bands of the transmission and reception filters is 190 MHz, and the transmission band is formed adjacent to the reception band. Therefore, in the receiving filter, a steep attenuation band characteristic is required on the lower side (shoulder side) of the pass band in the adjacent transmission band. Therefore, the above-described trap circuit is connected in series with the filter circuit, and the notch frequency is changed. Is arranged on the lower band side than the pass band of the filter, a steep attenuation characteristic is obtained on the lower band side, and the loss in the pass band of the filter circuit also has a low loss.

On the other hand, in a transmission filter, a steep attenuation characteristic is required on the high band side (right shoulder side) of the pass band. Therefore, the notch frequency of the trap circuit is set higher than the pass band of the filter circuit. Need to be placed. However,
As described above, since the attenuation characteristic on the lower side than the notch frequency of the trap circuit is formed gently, when the notch frequency of the trap circuit is arranged on the higher side than the pass band of the filter circuit, the pass band of the filter However, there is a problem in that a laminated strip line filter having a large loss and a weak attenuation characteristic is obtained.

On the other hand, the capacitively coupled trap circuit board 10
0 means the input / output transmission line 300 and the strip line 200
If a desired trap characteristic is to be obtained in a state where the capacitive coupling to the trap circuit is large, the attenuation characteristic of the trap circuit increases the transmission loss on the low frequency side with respect to the notch frequency. Therefore, when this trap circuit is connected in series with the filter circuit and the notch frequency is arranged higher than the filter pass band, there is a problem that the loss in the pass band of the filter increases.

The present invention has been devised in view of the above problems, and has as its object to provide a steep attenuation characteristic when a notch frequency of a trap circuit is arranged at a higher frequency side than a filter pass band of a filter circuit. It is an object of the present invention to provide a filter trap circuit that does not deteriorate the loss in the pass band of the filter circuit when the filter trap circuit is connected in series.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an earth electrode formed between a main surface of a rectangular laminate having a plurality of dielectric layers or dielectric layers and a ground electrode opposed to the earth electrode. And a filter including a strip line having one end connected to the ground electrode, an inductance connected at an arbitrary position of the strip line, and an input / output line connected to the inductance and connecting between an input electrode and an output electrode. Provide a trap circuit board for use.

According to the configuration of the present invention, the notch frequency of the trap circuit is reduced by forming an inductive coupling type trap circuit in which the strip line and the inductance connected at an arbitrary position are connected by the input / output transmission line. As a reference, the attenuation characteristic on the low frequency side becomes steep and the transmission loss on the low frequency side can be reduced. Thereby, even when the trap circuit of the present invention is connected in series with the filter circuit and the notch frequency of the trap circuit is arranged higher than the filter pass band, the attenuation of the attenuation pole can be reduced without deteriorating the insertion loss in the pass band. Only the characteristics can be improved.

Further, the inductance is formed in the thickness direction of the laminated body, and the input / output transmission line is formed between layers different from the dielectric layer on which the strip line is formed. The output transmission line is arranged via a dielectric layer.

According to the structure of the present invention, a dielectric layer having a sufficient thickness is interposed between the strip line and the input / output transmission line to generate a signal between the strip line and the input / output transmission line. As a result, it is possible to provide a filter trap circuit having a steep low band attenuation characteristic.

Further, the strip line and the input / output transmission line are formed so as to overlap with a dielectric layer interposed therebetween.
A trap circuit board for a filter, wherein a second ground electrode is interposed between the strip line and the input / output transmission line so as to shield an area of the input / output transmission line overlapping the strip line. I do.

According to the structure of the present invention, the unnecessary coupling capacitance is suppressed by forming the second ground electrode so as to shield the area of the input / output line overlapping the strip line, and the inductive coupling is strengthened. With the notch frequency of the trap circuit as a reference, the attenuation characteristic on the low frequency side can be further sharpened.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 show a first embodiment of the present invention. FIG. 1 is a perspective view of a trap circuit board for a filter according to the present invention, FIG. 2 is a longitudinal sectional view at the center, and FIG.

Referring to FIG. 1, a filter trap circuit board 9 of the present invention includes a laminate 8, a strip line 1, an input / output transmission line 2, and an inductance 3.
The laminate 8 is formed by laminating the dielectric layers 6a to 6e in the thickness direction, and is composed of a dielectric ceramic material and an oxide or a low-melting glass material that can be fired at a low temperature. Specifically, as the dielectric ceramic material, for example, BaO—TiO ₂ system, Ca—TiO ₂ system, M
BiO ₄ , CuO, Li ₂ O, B ₂ O _{3 and the} like are examples of oxides for gO-TiO _{2 and the} like to be fired at a low temperature.
The dielectric layers 4a to 4d each have a thickness of 50 to 300 μm.
m. Further, ground electrodes 4a and 4f are formed over substantially the entire area of both main surfaces of the dielectric block 8,
Earth electrodes 4b to 4e are formed on four side surfaces thereof.

The strip line 1 has dielectric layers 4a, 4b
One end is short-circuited to the ground electrode 4c, and the other end is open. Further, an inductance 3 described below is connected to an arbitrary position of the strip line 1. As this arbitrary position, it is preferable to arrange it so as to intersect with the strip line 1.

The input / output transmission line 2 is formed between 6c and 6d, and connects the input electrode 7a and the output electrode 7b. The input / output transmission line 2 is disposed so as to overlap the open end side of the strip line 1 via the dielectric layers 6b and 6c.

The inductance 3 includes a via-hole conductor 5 filled with a conductor in a through hole penetrating to an arbitrary dielectric layer 6d formed in the thickness direction of the multilayer body 8, and dielectric layers 6c and 6
and an L-shaped conductor line 30 between the conductor lines 30.
The other side is connected to the input / output transmission line 2.

Strip line 1, transmission line 2, inductance 3, ground electrode 4, and via hole 5
Is made of a conductive material mainly composed of Ag, Ag-Pd, Cu, or the like.

With the above configuration, the trap circuit board 9
Is a λλ resonator having the other end of the strip line 1 as an open end and the remaining one side as an electrically short-circuited end, and a resonance circuit utilizing capacitive and inductive properties. By connecting the inductive inductance 3 to the position, a trap circuit having a desired notch frequency can be formed. FIG. 11A shows the transmission characteristics of this trap circuit. With reference to the notch frequency of the trap circuit, the shoulder characteristic on the low frequency side has a steeper attenuation characteristic than that on the high frequency side. FIG. 5 shows an equivalent circuit having the above configuration.

A desired filter characteristic can be obtained by connecting the trap circuit board 9 configured as described above to a filter circuit. However, when a dielectric laminated strip line filter is used as a connection method, Although it is configured integrally with the trap circuit board 9 using the same dielectric layer, the present invention is not limited to this.

Next, a second embodiment is shown in FIGS. FIG. 6 is an exploded perspective view of the trap circuit, and FIG. 7 is a perspective view seen from a plane direction. As shown in the drawing, the difference from the first embodiment is that the trap circuit board 90 includes the second ground electrode 4 g and the strip line 1 and the input / output transmission line 2.
Is formed between the dielectric layers 6b and 6c. The shape of the second earth electrode 4g is a polygonal shape having rectangular or square irregularities, and is connected to the earth electrode 4b on the side surface.

The second earth electrode 4g is formed so that the conductor line 30 which is a part of the inductance 3 connected to the input / output transmission line 2 and the central portion of the input / output transmission line 2 are covered with the second earth electrode 4g. Is formed. Earth electrode 4g
Are preferably arranged so as not to be affected by the electromagnetic coupling between the input / output transmission line and the strip line 1. Further, it is necessary to cover at least the portion where the input / output transmission line 2 and the strip line 1 overlap with each other with the second ground electrode 4g, and it is necessary to cover the strip line 1 to such an extent that the electromagnetic field distribution is not largely obstructed. With such an arrangement of the second ground electrode 4g, it is possible to suppress the coupling of the unnecessary stray capacitance generated between the strip line 1, the input / output transmission line 2, and the inductance 3.

In the present invention, dielectric layers 6c and 6c different from dielectric layers 6a to 6e on which strip line 1 is formed.
Although an example is shown in which the input / output transmission line 2 and the inductance 3 are formed between "d" and "d", the present invention is not limited to this, and the same dielectric material having the strip line 1 formed as shown in FIG. A trap circuit board 91 having the inductance 3 and the input / output transmission line formed on the layer 6b may be used. This makes it possible to reduce the thickness in the thickness direction and to suppress the capacitance component.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A filter trap circuit board 9 shown in FIG.
Was prepared. The size of the stack as a constituent: 8 mm × 4 mm × 2 mm strip line length: about 8.0 mm W-CDMA scheme in the frequency band (around 2.0GHz) permittivity 15-25 material Ba0-TiO ₂ based materials Comparative Examples of the ceramic substrate As a result, a trap circuit board shown in FIG. 9 was produced. As the configuration, the size of the laminated body: 8 mm × 4 mm × 2 mm Strip line length: about 8.0 mm Frequency band of W-CDMA system (around 2.0 GHz) Dielectric constant of ceramic substrate 15 to 25 Material Ba0-TiO ₂ material ( Example 1) FIGS. 11A and 11B are diagrams comparing the resonance frequencies of the trap circuit board 9 of the present invention and the trap circuit board 100 of the comparative example. The vertical axis indicates the attenuation (10 dB / d)
iv), and the horizontal axis is frequency (100 MHz / div)
It is.

As can be seen from these results, in the resonance characteristics, in the comparative example, the attenuation characteristics on the high frequency side with respect to the notch frequency are dull, whereas in the present invention, the attenuation characteristics on the high frequency side are steep. ing. (Embodiment 2) FIG. 12A shows an equivalent circuit in which a trap circuit board 9 having the above-described resonance characteristics and a filter are connected, and FIG. 12B shows a trap circuit board 9 of the present invention and a trap of a comparative example. FIG. 12C shows filter characteristics when the circuit boards 100 are connected to filter circuits and used as transmission filters, and FIG. 12C is an enlarged view of the vicinity of the pass band indicated by the dotted line in FIG. The filter circuit to be connected has a center frequency of 1920 MHz and a bandwidth of 60 MHz. As can be understood from FIGS. 12B and 12C, when the filter characteristics are compared, the steepness of the filter on the high frequency side is not sufficient in the comparative example, whereas the shoulder characteristics of sufficient steepness are secured in the present invention. is made of. Example 3 Next, a filter trap circuit board 90 shown in FIG. 6 was manufactured. The size of the laminated body: 8 mm × 4 mm × 2 mm strip line length: about 8.0 mm W-CDMA frequency band scheme (2.0GHz vicinity) of the ceramic substrate of permittivity 15-25 material Ba0-TiO ₂ based materials should be noted that the second The ground electrode is connected to the dielectric layers 6b and 6b as shown in FIG.
c. The conductor line 30 and the input / output transmission line 2 were covered. In particular, the portion where the strip line 1 overlaps the input / output transmission line 2 was covered with a ground electrode.

In FIG. 14, the stray capacitance (coupling capacitance) is changed by changing the area of the portion where the strip line 1 overlaps the input / output transmission line 2, and the pass band loss of the trap circuit is observed. As conditions, the notch frequency of the trap circuit is 2 GHz, the notch attenuation is 21 dB, and the frequency at which the transmission loss on the low frequency side is measured is 1.9 with reference to the notch frequency.
G to 1.99 GHz. As can be seen from this result, it can be understood that the more the strip line 1 overlaps the input / output transmission line 2 and the more stray capacitance increases, the greater the influence on the passband loss.

Next, FIG. 13 shows a result obtained by connecting a filter circuit to the trap circuit board 90 and examining the filter characteristics. (A) shows the filter characteristics of the trap circuit board 90, and (b) shows the filter characteristics of the trap circuit board 9. (C) is an enlarged view of the waveform at the top of the filter pass band. The solid line indicates the filter characteristic with the trap circuit board 90 connected, and the dotted line indicates the filter characteristic with the trap circuit board 9 connected. In this case, the pass band width of the transmission filter was set to 60 MHz.

It can be understood from the above that the filter circuit to which the trap circuit board 90 with the second ground electrode 4g interposed is able to improve the attenuation in the high-pass band by about 2 dB. Further, although the insertion loss in the passband is slight, an improvement of 0.1 dB is observed.

[0034]

As described above, according to the present invention, even when the trap circuit is formed on the higher band side than the pass band of the laminated strip line filter, the insertion loss in the pass band of the filter does not increase. In addition, it is possible to provide a filter trap circuit board having steep attenuation characteristics.

[Brief description of the drawings]

FIG. 1 is a perspective view of a filter trap circuit board according to a first embodiment.

FIG. 2 is a sectional view of a filter trap circuit board according to the first embodiment.

FIG. 3 is a perspective view of the filter trap circuit board according to the first embodiment as viewed from above.

FIG. 4 is an exploded perspective view of a filter trap circuit board according to the first embodiment.

FIG. 5 is an equivalent circuit diagram of a filter trap circuit board according to the first embodiment.

FIG. 6 is an exploded perspective view of a filter trap circuit board according to a second embodiment.

FIG. 7 is a perspective view of the filter trap circuit board according to the second embodiment as viewed from above.

FIG. 8 is an exploded perspective view of a filter trap circuit board according to a third embodiment.

FIG. 9 is an exploded perspective view of a conventional filter trap circuit board.

FIG. 10 is an equivalent circuit diagram of a conventional filter trap circuit board.

11A is a diagram showing the resonance characteristics of a trap circuit board for a filter of the present invention, and FIG. 11B is a diagram showing the resonance characteristics of a trap circuit board for a conventional filter;

FIG. 12A is an equivalent circuit diagram when the trap circuit board 9 of the present invention is connected to a filter circuit, and FIG.
FIG. 4 is a diagram illustrating transmission characteristics when a trap circuit board 9 is connected to a filter circuit, and FIG. 4C is a diagram illustrating filter characteristics when a conventional trap circuit board 100 is connected to a filter circuit.

13A and 13B show filter characteristics when a trap circuit board 90 is connected to a filter circuit, FIG. 13B shows filter characteristics when a trap circuit board 9 is connected to the filter circuit, and FIG. It is a figure which expands and shows the waveform of a part.

FIG. 14 is a diagram showing the relationship between the passband loss and the stray capacitance (coupling capacitance) changed by changing the area of the portion where the strip line of the trap circuit board overlaps the input / output transmission line.

[Explanation of symbols]

 1: strip line 2: input / output transmission line 3: inductance 4: earth electrode 5: via hole conductor 6a to 6e: dielectric layer 7a, 7b: input / output electrode 8: laminated body 9: filter trap circuit board

Claims (3)

[Claims] 1. A strip line in which a ground electrode formed between a main surface or a dielectric layer of a rectangular laminate in which a plurality of dielectric layers are stacked and which faces the ground electrode, and one end of which is connected to the ground electrode. A filter trap circuit board comprising: an inductance connected at an arbitrary position of the strip line; and an input / output transmission line connected to the inductance and connecting between an input electrode and an output electrode. 2. The method according to claim 1, wherein the inductance is formed in a thickness direction of the multilayer body, and the input / output transmission line is formed between a dielectric layer different from the dielectric layer on which the strip line is formed, and is connected to the strip line. 2. The output transmission line is disposed via a dielectric layer.
A trap circuit board for a filter as described in the above. 3. The strip line and the input / output transmission line are formed so as to overlap with a dielectric layer interposed therebetween, and the strip line and the input / output transmission line overlap each other so as to shield an area of the input / output transmission line overlapping the strip line. 2. The trap circuit board for a filter according to claim 1, wherein a second ground electrode is interposed between the input and output transmission lines.