JPH07170108A - Band pass filter with dielectric resonator - Google Patents

Abstract

PURPOSE:To reduce the cost of the band pass filter using plural dielectric resonators. CONSTITUTION:Plural capacitors 4, 5, 6, 7 are connected sequentially in series between a signal input terminal 19a and an output terminal 23a. Dielectric resonators 1, 2, 3 having the same resonance frequency are connected respectively between the capacitors 4-7 and ground. A capacitor 8 is connected between the dielectric resonator 2 in the middle and ground. A new resonance circuit is formed by the capacitor 8 and the dielectric resonator 2 in the middle. The resonance frequency of the new resonance circuit is lower than the resonance frequency of the dielectric resonators 1, 3 of the input and output stages.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bandpass filter having a plurality of TEM mode dielectric resonators.

[0002]

2. Description of the Related Art One end of an input coupling capacitor or an inductance is connected to a signal input terminal, an input stage dielectric resonator is connected between the other end and ground, and the output of this input stage dielectric resonator is connected. A dielectric filter having a configuration in which a plurality of dielectric resonators are sequentially connected in series to each other via mutual coupling capacitors or inductances, and the output terminals are coupled to the output stage dielectric resonators via output coupling capacitors or inductances. Is used in circuits in the radio frequency band of mobile phones and the like. In a multi-stage dielectric filter in which three or more dielectric resonators are combined, in order to make the passband width close to ideal, the dielectric frequency between these dielectric resonators is higher than the resonance frequency of the dielectric resonators in the input and output stages. Set the resonance frequency of the resonator low.

[0003]

By the way, in order to construct a dielectric filter having three or more stages as described above, it is necessary to prepare a plurality of dielectric resonators having different resonance frequencies. However, since the resonant frequency of the dielectric resonator changes depending on the length of the dielectric resonator, it is necessary to prepare a plurality of dielectric resonators having different lengths, and the dielectric filter is inevitably used. Became expensive. Further, since a plurality of types of dielectric resonators are combined, a defect occurs due to a combination error.

Therefore, an object of the present invention is to reduce the cost of a bandpass filter using a dielectric resonator.

[0005]

In order to achieve the above object, the present invention provides four or more capacitors connected in series in sequence between a signal input terminal and a signal output terminal, and the four or more capacitors. A bandpass filter comprising three or more dielectric resonators connected between capacitors and ground, wherein the three or more dielectric resonators have substantially the same resonance frequency, No capacitors are connected between the dielectric resonators on both sides of the three or more dielectric resonators arranged on the input terminal side and the output terminal side and the ground, or a capacitor having a predetermined capacitance value is provided. A bandpass having a dielectric resonator that is connected, and a capacitor having a value larger than the predetermined value is connected between an inner dielectric resonator arranged between the dielectric resonators on both sides and a ground. Involved in the filter It is intended. As described in claim 2, the capacitor between the signal input terminal and the signal output terminal of claim 1 can be replaced with an inductance. Further, as described in claims 3 and 4, both the capacitor and the inductance can be connected in series between the signal input terminal and the signal output terminal. In the above invention, the capacitor connected between the dielectric resonator and the ground means a capacitor having individual electrodes, a storage capacitance, or a combination thereof.

[0006]

According to the invention of each claim, it is possible to make the resonance frequencies of a plurality of dielectric resonators the same. That is, a bandpass filter having the same characteristics as the conventional one can be obtained by forming a bandpass filter with a plurality of dielectric resonators having the same specifications. Therefore, the cost of the bandpass filter can be reduced. In the inventions of claims 1 to 3, even if a plurality of dielectric resonators having the same resonance frequency are used, by connecting a capacitor between the inner dielectric resonator and the ground. A new LC resonance circuit is formed by the combination of this capacitor and the inner dielectric resonator, and this resonance circuit operates in the same way as the inner dielectric resonator having a low resonance frequency, and has the same frequency characteristic as the conventional one. A bandpass filter can be provided. Further, in the invention of claim 4, a new resonance circuit is formed by the capacitors added with the dielectric resonance on both sides.

[0007]

First Embodiment Next, a bandpass filter having a TEM mode dielectric resonator according to an embodiment of the present invention will be described with reference to FIGS.

As shown in FIG. 1, this bandpass filter includes first, second and third dielectric resonators 1, 2, 3 and
It is composed of first, second, third, fourth and fifth capacitors (capacitance) 4, 5, 6, 7, 8 and a circuit board 9, which are connected as shown in FIG. .

The first to third dielectric resonators 1 to 3 of FIG. 1 have the same specifications, and as shown in FIG.
Cylindrical dielectric 10 and inner conductor 1 formed in resonance hole 11
2 and one end face 13 of the dielectric 10 connected to this
A connection conductor 15 led out to the outer peripheral surface 14 through the outer conductor 16, an outer conductor 16 formed on the outer peripheral surface 14, and a short-circuit conductor that connects the inner conductor 12 and the outer conductor 16 at the other end surface 17 of the dielectric 10. 18 and. The inner conductor 12, the connection conductor 15, the outer conductor 16, and the short-circuit conductor 18 are conductor layers made of a silver paste baking layer or a copper plating layer. In this embodiment, the resonance frequency f0 of the first to third dielectric resonators 1 to 3 is 93.
It is 9.9 MHz. Further, as is well known, the first to third dielectric resonators can be equivalently shown by a parallel circuit of the capacitance C and the inductance L of FIG.

In order to form the filter circuit shown in FIG. 4, the insulating circuit board 9 shown in FIG. 1 has an input terminal conductor layer 19, first, second and third connection conductor layers 20, 21, and 22, The output terminal conductor layer 23, the main ground conductor layer 24, and the sub-ground conductor layer 25 are provided. The input and output terminal conductor layers 19 and 23 extend to the back surface of the substrate 9 through the grooves 26 and 27, and the main ground conductor layer 24 extends to the back surface of the substrate 9 through the grooves 28 and 29 to form the sub ground. Conductor layer 25 is groove 3
0 to the rear surface of the substrate 9 to extend the main ground conductor layer 2
4 is connected.

The outer conductors 16 of the first to third dielectric resonators 1 to 3 are fixed to the main ground conductor layer 24 by solder (not shown), and the connecting conductors 15 are the first to third conductors on the substrate 9. Are fixed to the connection conductor layers 20 to 22 by solder (not shown). The first capacitor 4 in the input stage includes the input terminal conductor layer 19 and the first
The second capacitor 5 is fixed to the connecting conductor layer 20 of the first and second connecting conductor layers 2 by soldering (not shown).
0, 21, the third capacitor 6 is soldered between the second and third connecting conductor layers 21, 22 (not shown).
And the fourth capacitor 7 is connected to the third connection conductor layer 2
2 and the output terminal conductor layer 23 are fixed by solder (not shown), and the fifth capacitor 8 is soldered (not shown) between the second connection conductor layer 21 and the sub-ground conductor layer 25. Is stuck by. In addition, in FIG. 1, in order to simplify the illustration, the conductors 15 and 16 of the dielectric resonators 1 to 3 and the substrate 9 are illustrated.
The respective conductor layers 19 to 25 are shown with the thickness omitted.
The input and output conductor layers 19 and 23 of FIG. 1 correspond to the input and output terminals 19a and 23a of FIG. 4, and the main and sub-ground conductor layers 24 and 25 correspond to the ground terminals 24a and 25a of FIG.

The capacitance value C of each of the first to fourth capacitors 4 to 7
1 to C5 are 1.8 pF and 0.6 pF as shown in FIG.
F, 0.6 pF, 1.8 pF, and the sum of the capacitance of the fifth capacitor 8 and the storage capacitance between the connection conductor layer 22 and the ground conductor layer 24 extending to the back surface of the substrate 9 is 0. It is 82 pF.

FIG. 5 shows the frequency characteristics of the bandpass filter shown in FIGS. This frequency characteristic is the same as that of a conventional bandpass filter. That is, the fifth capacitor 8 is omitted from the circuit of FIG. 4, and the resonance frequency of the second dielectric resonator 2 is replaced by the resonance frequency of the first and third dielectric resonators 1 and 3 (939.9 MHz). 4), the same frequency characteristic as that of a typical conventional bandpass filter with 917.2 MHz, which is lower than that of FIG. Therefore, in the circuit of FIG. 4, it is possible to obtain the same characteristic as the conventional one by using the three dielectric resonators 1 to 3 having the same configuration and the same characteristic. Cost reduction can be achieved by commonality.

Next, the reason why the circuit of FIG. 3 can obtain the same characteristics as the conventional one will be described. Since the third capacitor 8 is connected between the second dielectric resonator 2 and the ground,
It is connected in parallel to the second dielectric resonator 2. By the way, the dielectric resonator 2 has its resonance frequency f0.
In the frequency region lower than (939.9 MHz), it functions as an inductance. Since the frequency of the pass band of the band pass filter is lower than the resonance frequency f0 of the dielectric resonator 2 as is clear from FIG. 5, the dielectric resonator 2 in the pass band has an equivalent inductance as shown in FIG. This inductance and the additional capacitor 8 form a new LC parallel resonance circuit. The resonance frequency of this new LC parallel resonance circuit is the same as the above-mentioned resonance frequency (917.2 MHz) of the central dielectric resonator of the conventional three-stage bandpass filter, and as a result, the circuit characteristics of FIG. The circuit characteristics are the same.

[0015]

[Second Embodiment] A three-stage bandpass filter according to a second embodiment shown in FIG. 7 will be described below. However, in FIG. 7, parts that are substantially the same as those in FIG. 1 are assigned the same reference numerals and explanations thereof are omitted.

The basic structure of the bandpass filter of FIG. 7 is the same as that of FIG. 1, but the first to fifth capacitors 4 to 8 are not composed of individual components as shown in FIG. 9 and the conductor layers 19 to 23 and 25. The equivalent circuit of FIG. 7 can be shown in FIG. 4 as in FIG. That is, the first capacitor 4 in FIG. 4 is formed by the input terminal conductor layer 19 and the first connection conductor layer 20 facing each other with the dielectric substrate 9 in between, and the second capacitor 5 includes the first and second capacitors. Of the connecting conductor layers 20 and 21 of the second and third connecting conductor layers 21 and 22 are formed by facing each other on the surface of the substrate 9.
The fourth capacitor 7 is formed by facing the third connecting conductor layer 22 and the output terminal conductor layer 23 with the substrate 9 interposed therebetween, and the fifth capacitor 8 is formed by facing the third connecting conductor layer 22 and the output terminal conductor layer 23. The connection conductor layer 21 and the sub-ground conductor layer 25 are formed on the surface of the substrate 9 so as to face each other.

If the filter is constructed as shown in FIG. 7, no individual parts are used, so that the cost can be reduced.
Of course, this second embodiment also has the same effect as the first embodiment.

[0018]

[Third Embodiment] A four-stage bandpass filter according to the third embodiment will be described with reference to FIG. However, in FIG. 8 and later-described FIGS. 9 and 10, the same parts as those in FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted.

The input-stage dielectric resonator 1, the output-stage dielectric resonator 3, and the inner dielectric resonators 2a and 2b shown in FIG. 8 all have substantially the same structure and have a resonance frequency of 941.0 MHz. Have. Five capacitors 4, 5, 31, 6, 7 are sequentially connected in series between the input terminal 19a and the output terminal 23a. Each capacitor 4, 5, 31,
Four dielectric resonators 1, 2a, 2b, 3 are connected between each other and the ground terminal 24a. Capacitors 8a and 8b are respectively connected between the two inner dielectric resonators 2a and 2b and the ground.

The capacitance of each capacitor in FIG. 8 is as follows. The capacitance C1 of the capacitor 4 is 1.9 pF, the capacitance C2 of the capacitor 5 is 0.71 pF, and the capacitance C of the capacitor 31.
6 is 0.56 pF and the capacitance C3 of the capacitor 6 is 0.71
pF, the capacitance C4 of the capacitor 7 is 1.9 pF, and the capacitances C5a and C5d of the capacitors 8a and 8b are 0.92 pF, respectively.
Is.

Also in the circuit of FIG. 8, a new LC resonance circuit is formed by the combination of the inner dielectric resonators 2a and 2b and the capacitors 8a and 8b for the same reason as in the first embodiment. Resonance frequency is about 9
Dielectric resonators 1, 2a, 2b at 15.6 MHz,
It becomes lower than the resonance frequency of 3. As a result, the bandpass filter of FIG.
, And has substantially the same frequency characteristic as a conventional bandpass filter in which the resonance frequencies of the two inner dielectric resonators 2a and 2b are 915.6 MHz. Therefore, FIG.
The band-pass filter of 1 has the same effect as that of the first embodiment.

[0022]

[Fourth Embodiment] FIG. 9 shows a bandpass filter having five stages. In this embodiment, capacitors 4, 5, 31a, 31b, 6, and 7 are sequentially connected in series between the input terminal 19a and the output terminal 23a, and these capacitors are connected to each other and the ground terminal 2a.
4a and the same configuration and the same resonance frequency (943.2M
Hz) four dielectric resonators 1, 2a, 2b, 2c, 3
Are connected respectively. Further, a capacitor 8 is provided between the inner three dielectric resonators 2a, 2b, 2c and the ground.
a, 8b, and 8c are respectively connected.

In FIG. 9, the capacitors 4 and 7 have a capacitance of 1.9 pF and the capacitors 5 and 6 have a capacitance of 0.72 pF.
F, capacitors 31a and 31b have a capacitance of 0.55 pF,
The capacitors 8a and 8c have a capacitance of 0.92 pF, and the capacitor 8b has a capacitance of 1.09 pF.

The dielectric resonator 2a and the capacitor 8a shown in FIG.
, A new resonance circuit having a resonance frequency of 917.6 MHz is formed, and a combination of the dielectric resonator 2b and the capacitor 8b results in a resonance frequency of 913.0 MHz.
A new resonance circuit of MHz is formed, and the dielectric resonator 2c
The resonance frequency 9
A new resonant circuit of 17.6 MHz is formed. As a result, the bandpass filter of FIG. 9 omits the capacitors 8a, 8b and 8c of FIG. 9 and the dielectric resonators 2a and 2a.
b and 2c, resonance frequency 917.6MHz, 913.0M
It has the same characteristics as the conventional bandpass filter corresponding to the one replaced with the dielectric resonator of Hz and 917.6 MHz. Therefore, the same working effect as that of the first embodiment can be obtained according to the fourth embodiment.

[0025]

[Fifth Embodiment] FIG. 10 shows capacitors 4, 5, 6, and 7 of the bandpass filter of FIG.
A bandpass filter having a configuration in which 5, 16, and 17 are replaced is shown. Also in this embodiment, three dielectric resonators 1,
2 and 3 have the same length and the same resonance frequency (819.4).
MHz). The first, second, third and fourth inductances between the input terminal 19a and the output terminal 23a are 3.8nH, 16.2nH, 16.2nH,
It is 3.8 nH. The capacitor 18 connected between the second dielectric resonator 2 and the ground according to the present invention is 0.82 pF including the storage capacitance.

The frequency characteristics of the bandpass filter of FIG. 10 are as shown in FIG. This frequency characteristic is shown in FIG.
The circuit has the same characteristics as those of the conventional bandpass filter corresponding to a circuit in which the capacitor 18 is omitted and the second dielectric resonator 2 has a resonance frequency of 802.1 MHz.
Therefore, the same effect as that of the first embodiment can be obtained by the fifth embodiment.

[0027]

[Sixth Embodiment] FIG. 12 shows a bandpass filter in which capacitors 5 and 6 of the bandpass filter shown in FIG. Also in this embodiment, the three dielectric resonators 1, 2 and 3 have the same length and the same resonance frequency (881.5 MHz). Input stage capacitor 4 connected to input terminal 19a
And the output-stage capacitor 7 connected to the output terminal 23a has a capacitance value of 4.3 pF, respectively, and the first stage between them.
And the second inductances 15 and 16 each have a value of 14.2 nH. According to the present invention, the capacitor 18 connected between the second dielectric resonator 2 and the ground is
It is 4.5 pF including stray capacitance.

The frequency characteristics of the bandpass filter of FIG. 12 are as shown in FIG. This frequency characteristic is shown in FIG.
The circuit has the same characteristics as those of the conventional bandpass filter corresponding to the circuit in which the capacitor 18 is omitted and the second dielectric resonator 2 has a resonance frequency of 795.6 MHz.
Therefore, the same effect as that of the first embodiment can be obtained by the sixth embodiment.

[0029]

[Seventh Embodiment] FIG. 14 shows a bandpass filter having a configuration in which the capacitors 4 and 7 of the bandpass filter of FIG. Also in this embodiment, the three dielectric resonators 1, 2 and 3 have the same length and the same resonance frequency (987.5 MHz). The input stage inductance 14 connected to the input terminal 19a and the output stage inductance 17 connected to the output terminal 23a each have a value of 7.2 nH, and two capacitors 5 and 6 connected in series between them. Is 2.0
Each has a capacitance value of pF. In this embodiment, capacitors 18a and 18b of 2.8 pF including a stray capacitance are respectively connected between the first and third dielectric resonators 1 and 3 and the ground. However, no capacitor is connected between the second dielectric resonator 2 arranged between the dielectric resonators 1 and 3 on both sides and the ground. The capacitance value of the stray capacitance between the dielectric resonator 2 and the ground is of course smaller than 2.8 pF.

The frequency characteristics of the bandpass filter of FIG. 14 are as shown in FIG. This frequency characteristic is shown in FIG.
Of the first and third dielectric resonators 1 and 3 at the resonance frequency 884.
This is the same as the characteristic of the conventional bandpass filter corresponding to the one with 2 MHz. Therefore, the same effect as that of the first embodiment can be obtained by the seventh embodiment.

[0031]

MODIFICATION The present invention is not limited to the above-mentioned embodiments, and the following modifications are possible. (1) Each of the capacitors in the circuits of FIGS. 8, 9, 12 and 13 is composed of an individual capacitor as in the first embodiment, but the same circuit board 9 as in FIG. Can be configured using. Further, each of the capacitors of the first to seventh embodiments can be composed of electrodes embedded in a common multilayer substrate. (2) In FIG. 4, FIG. 8, FIG. 9, FIG. 10 and FIG. 12, between the dielectric resonators 1 and 3 on both sides and the ground, the dielectric resonators 2 or 2a, 2b or 2a to 2c on the inner side are provided. It is possible to connect a capacitor having a smaller capacity than the capacitor 8 or 8a, 8b or 8a to 8c added to, or provide stray capacitance. In addition, the capacitor 1 is placed between the dielectric resonator 2 and the ground on the inner side of FIG.
Capacitors (or storage capacitors) having a smaller capacity than 8a and 18b can be connected. (3) Inductance 1 of FIGS. 10 and 12
4, 15, 16, and 17 can be configured by strip lines. (4) The capacitors 4, 5, 6, 7, 31 of FIG. 9 can be replaced with inductances. Further, the circuits of FIGS. 12 and 14 can be modified into circuits of four or more dielectric resonators as shown in FIGS. 8 and 9. (5) The dielectric resonators 1 to 4 can have a rectangular cross section.

[Brief description of drawings]

FIG. 1 is a perspective view showing a bandpass filter according to a first embodiment.

2 is a cross-sectional view of the dielectric resonator of FIG.

3 is an equivalent circuit diagram of the dielectric resonator of FIG.

FIG. 4 is a circuit diagram showing the bandpass filter of FIG.

5 is a frequency characteristic diagram of the bandpass filter of FIG.

FIG. 6 is a diagram showing a combined resonance circuit of the second dielectric resonator and the fifth capacitor of FIG.

FIG. 7 is a perspective view showing a bandpass filter according to a second embodiment.

FIG. 8 is a circuit diagram showing a four-stage bandpass filter according to a third embodiment.

FIG. 9 is a circuit diagram showing a 5-stage bandpass filter according to a fourth embodiment.

FIG. 10 is a circuit diagram showing a bandpass filter according to a fifth embodiment.

11 is a frequency characteristic diagram of the bandpass filter of FIG.

FIG. 12 is a circuit diagram showing a bandpass filter according to a sixth embodiment.

13 is a frequency characteristic diagram of the bandpass filter of FIG.

FIG. 14 is a circuit diagram showing a bandpass filter according to a seventh embodiment.

15 is a frequency characteristic diagram of the bandpass filter of FIG.

[Explanation of symbols]

 1, 2, 3 Dielectric resonators 4, 5, 6, 7, 8 Capacitors

Claims (4)

[Claims] 1. A capacitor comprising four or more capacitors serially connected in series between a signal input terminal and a signal output terminal;
In a bandpass filter composed of three or more dielectric resonators connected between one or more capacitors and the ground, the three or more dielectric resonators have substantially the same resonance frequency. A capacitor is not connected between the dielectric resonators on both sides of the three or more dielectric resonators arranged on the input terminal side and the output terminal side and the ground, or has a predetermined capacitance value. And a capacitor having a value larger than the predetermined capacitance value is connected between the inner dielectric resonator arranged between the dielectric resonators on both sides and the ground. Band-pass filter having a dielectric resonator. 2. The four or more inductances serially connected in series between the signal input terminal and the signal output terminal, and the three inductances connected between the four or more inductances and the ground. In the bandpass filter including the above dielectric resonator, the three or more dielectric resonators have substantially the same resonance frequency, and the input terminal side of the three or more dielectric resonators A capacitor is not connected between the dielectric resonators on both sides of the output terminal and the ground, or a capacitor having a predetermined capacitance value is connected, and the capacitors are arranged between the dielectric resonators on both sides. A bandpass filter having a dielectric resonator, wherein a capacitor having a value larger than the predetermined capacitance value is connected between the inner dielectric resonator and the ground. 3. An input stage capacitor, a plurality of inductances, and an output stage capacitor are sequentially connected in series between a signal input terminal and a signal output terminal, and one end of a series circuit of the input stage capacitor and the plurality of inductances. Dielectric resonance between the connection point of the plurality of inductances and the ground, and between the connection point of the other end of the series circuit and the output stage capacitor and the ground. In a bandpass filter having a configuration in which resonators are connected, the plurality of dielectric resonators have substantially the same resonance frequency, and the dielectric resonators are arranged on an input terminal side and an output terminal side of the dielectric resonators. No capacitor is connected between the dielectric resonators on both sides and the ground, or a capacitor having a predetermined capacitance value is connected between the dielectric resonators on both sides. Bandpass filter having a dielectric resonator in which the capacitor of a predetermined capacitance value is large values is characterized in that connected between the location has been inside the dielectric resonator and the ground. 4. An input stage inductance, a plurality of capacitors, and an output stage inductance are sequentially connected in series between a signal input terminal and a signal output terminal, and one end of a series circuit of the input stage inductance and the plurality of capacitors is connected. Dielectric resonance between the connection point of the capacitor and the ground, between the interconnection point of the plurality of capacitors and the ground, and between the connection point of the other end of the series circuit and the output stage inductance and the ground. In a bandpass filter having a configuration in which resonators are connected, the plurality of dielectric resonators have substantially the same resonance frequency, and the dielectric resonators are arranged on an input terminal side and an output terminal side of the dielectric resonators. A capacitor having a predetermined capacitance value is connected between the dielectric resonators on both sides of the dielectric resonator and the inner dielectric resonator arranged between the dielectric resonators on both sides. Bandpass filter having a dielectric resonator, wherein the or not connected capacitor predetermined capacitance value capacitors even smaller is connected between the lands.