JPH0637510A - Duplexer - Google Patents

Abstract

PURPOSE:To provide a small-sized duplexer without degrading the frequency characteristic. CONSTITUTION:In the equivalent circuit, an LC resonance circuit 5 on the low frequency pass side and an LC resonance circuit 6 on the high frequency pass side are connected in series between terminals 1 and 2. An antenna 8 is connected to a terminal 3. A coil L3 is connected in parallel to a coil L4 and a capacitor C3 connected in series, and a coil L2 is connected in series to the circuit consisting of coils L3 and L4 and the capacitor C3, thereby constituting the circuit 6. Further, the inductance of the coil 14 is set to >=1/100 inductance of the coil 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a duplexer used for a communication device, a portable radio device, a cordless telephone and the like.

[0002]

2. Description of the Related Art Conventionally, as a duplexer,
A device having the electrical equivalent circuit shown in FIG. 8 is known.
This duplexer has a low frequency pass side LC resonance circuit 55 and a high frequency pass side LC resonance circuit 56 between the terminals 50 and 51.
Are connected in series, and the antenna 5 is connected to the central terminal 52.
8 are connected. The low frequency passage side LC resonance circuit 55 is configured by connecting a capacitor C7 in series to a parallel connection circuit of a coil L6 and a capacitor C6. This circuit 55 has a band pass characteristic having an attenuation pole on the high frequency side.
The high frequency passage side LC resonance circuit 56 is configured by connecting a coil L7 in series to a parallel connection circuit of a coil L8 and a capacitor C8. This circuit 56 has a bandpass characteristic having an attenuation pole on the low frequency side.

9 and 10 show specific examples in which the circuit shown in FIG. 8 is composed of a dielectric substrate and a coil and a capacitor which are patterned on the front and back surfaces thereof. On the surface of the dielectric substrate 60, the spiral coil conductor 61a,
62a, 63a and capacitor electrodes 64a, 65a, 6
6a is formed, and a spiral coil conductor 61 is formed on the back surface.
b, 62b, 63b and capacitor electrodes 64b, 65
b and 66b are formed at predetermined positions. The coil conductors 61a to 63a have through holes 71 and 7 respectively.
The coils L6, L7, and L8 are electrically connected to the coil conductors 61b to 63b through 2, 73. The capacitor electrodes 64a to 66a form capacitors C6, C7 and C8 together with the capacitor electrodes 64b to 66b, respectively.

By the way, normally, the inductance value required for the coils L7 and L8 of the high frequency passage side circuit 56 is large, and the coil conductors 62a, 62b, 63a and 63b are
The number of windings is large. Therefore, the size of the substrate 60 becomes large, which hinders the miniaturization of the duplexer. This will be described using specific numerical values. In the high frequency pass side circuit 56, the frequency fr of the attenuation pole, the center frequency fo of the pass band, the coils L7 and L8, and the capacitor C8 have the relationship shown by the following equation.

Fr = 1 / (2π√ (C8 · L8)) (1) fo = (√ (L7 + L8)) / (2π√ (L7 · L8 · C8)) (2) For example, the capacitor C8 Capacity of 10 pF, 254 MH
When an attenuation pole is provided at z and a central frequency of 380 MHz is passed, the inductance of the coil L7 is 31.7.
nH, the inductance of the coil L8 is 39.3 nH. The smaller the inductance of the coils L7 and L8, the smaller the number of turns and the smaller the size of the substrate 60.

Therefore, an object of the present invention is to provide a small duplexer in which the area occupied by the coil conductor with respect to the substrate is reduced without degrading the frequency characteristics.

[0007]

In order to solve the above problems, a duplexer according to the present invention is an equivalent circuit, which is a duplexer including a low frequency pass side LC resonance circuit and a high frequency pass side LC resonance circuit, The high-frequency passage side LC resonance circuit, a capacitor and a first coil connected in series, a second coil connected in parallel to the circuit composed of the capacitor and the first coil, the capacitor and the first, A third connected in series with a circuit consisting of a second coil
And the first coil has an inductance that is 1/100 or more of the inductance of the second coil.

[0008]

With the above structure, for example, the duplexer of the equivalent circuit shown in FIG. 1 is formed. Even if the inductance of the second coil and the third coil is reduced by the first coil that constitutes the high frequency passage side LC resonance circuit of this duplexer, the predetermined frequency characteristic is maintained.

[0009]

Embodiments of the duplexer according to the present invention will be described below with reference to the accompanying drawings. [First Embodiment, FIGS. 1 to 4] FIG. 1 is an electrical equivalent circuit diagram of the duplexer of the first embodiment. This duplexer has a low-frequency pass side LC resonance circuit 5 and a high-frequency pass side LC resonance circuit 6 connected in series between terminals 1 and 2.
An antenna 8 is connected to the central terminal 3.

The low frequency band side LC resonance circuit 5 includes a capacitor C2 in a parallel connection circuit of a coil L1 and a capacitor C1.
Are connected in series. This circuit 5 has a bandpass characteristic having an attenuation pole on the high frequency side. The high frequency passage side LC resonance circuit 6 includes a coil L4 connected in series.
The coil L3 is connected in parallel to the capacitor C3, and the coil L2 is connected in series to the circuit composed of the coils L3 and L4 and the capacitor C3. Further, the inductance of the coil L4 is set to 1/100 or more of the inductance of the coil L3. This circuit 6 has a bandpass characteristic having an attenuation pole on the low frequency side.

The signal input from the antenna 8 is output from either one of the terminals 1 and 2 depending on its frequency. That is, the signal in the low frequency range input from the antenna 8 is the circuit 5
The signal in the high frequency range that is output from terminal 1 via
It is output from the terminal 2 via. On the contrary, regarding the signal input from the terminal 1, only the low-frequency signal is output from the antenna 8 via the circuit 5, and the signal input from the terminal 2 is the high-frequency signal only via the circuit 6. Is output from.

In the high frequency pass side circuit 6 of this electrical equivalent circuit, the frequency fr of the attenuation pole and the center frequency fo of the pass band are
And the coils L2, L3, L4 and the capacitor C3 have the relationship shown by the following equation. fr = 1 / (2π ・ √ (C3 ・ (L3 + L4))) …… (3) fo = (√ (L2 + L3)) / (2π ・ √ (C3 ・ (L2 ・ L3 + L2 ・ L4 + L3 ・ L4))) …… (4) For example, the capacitance of the capacitor C3 is 10 pF, the coil L4
In the case where the inductor has an attenuation pole at 3.7 nH and 254 MHz and passes through with 380 MHz as the center frequency, the inductance of the coil L2 is 22.7 nH and the inductance of the coil L3 is 35.6 nH. Therefore, the inductance of the coil L2 is about 28% smaller than that of the conventional duplexer, and the inductance of the coil L3 is about 10% smaller. Can be smaller. Moreover, since the inductance of the coil L4 is extremely small, the area occupied by the coil L4 on the substrate can be small. As a result, a small duplexer is obtained.

Next, an example in which the circuit shown in FIG. 1 is concretely constituted by a dielectric substrate and patterned coils and capacitors on the front and back surfaces thereof will be described. As shown in FIGS. 2 and 3, on the surface of the dielectric substrate 10, the spiral coil conductors 11a, 12a, 13a and the capacitor electrode 14 are provided.
a, 15a, 16a are formed, and the spiral coil conductors 11b, 12b, 13b, the coil conductor 17, and the capacitor electrodes 14b, 15b, 16b are formed at predetermined positions on the back surface. The coil conductors 11a to 13a are electrically connected to the coil conductors 11b to 13b through the through holes 18, 19 and 20, respectively, to form the coils L1 and L.
2 and L3. The coil conductor 17 is the coil L4.
Is doing. The capacitor electrodes 14a to 16a together with the capacitor electrodes 14b to 16b respectively form a capacitor C
1, C2, C3. The area of the dielectric substrate 10 is about 18% smaller than the area of the dielectric substrate used in the conventional duplexer. On this dielectric substrate 10,
As shown in FIG. 4, after the lead terminals 23, 24, 25 are attached, the lead resin 23, 24, 25 is coated with the exterior resin material 21 to obtain a product.

[Second Embodiment, FIG. 5 and FIG. 6] A second embodiment will explain a laminated duplexer having a circuit similar to the electrical equivalent circuit shown in FIG. 1 of the first embodiment. In the second embodiment, the same components and parts as those in the first embodiment are designated by the same reference numerals. Coil conductors and capacitor electrodes are formed on the front and back surfaces of the dielectric layer 10 in the same shape as in the first embodiment. However, a part of the capacitor electrode 14a is exposed on the right end face of the layer 10, a part of the capacitor electrode 15a is exposed on the center end face of the layer 10, and a part of the capacitor electrode 16a is exposed on the layer 10. It is exposed on the left end face. This dielectric layer 10 is used as a protective layer 2
It is sandwiched by 7, 28 to form a laminated structure. This laminated structure may be fired later, or fired after forming the external electrodes described below. The external electrodes 30, 31, 32 are formed on both ends and the center of this laminated structure by means of vapor deposition, sputtering, printing or the like. The external electrode 30 is electrically connected to the capacitor electrode 14a, the external electrode 31 is electrically connected to the capacitor electrode 15a, and the external electrode 32 is electrically connected to the capacitor electrode 16a.

The duplexer having the above structure has the same operation and effect as those of the first embodiment. [Third Embodiment, FIG. 7] The third embodiment will explain still another embodiment of the duplexer having a circuit similar to the electrical equivalent circuit shown in FIG. 1 of the first embodiment.

On the surface of the insulating substrate 35 (in this case, the substrate 35 need not be a dielectric substrate), an internal conductor 36,
37, 38, 39, 40, 41 and the coil conductor 42 are formed. This substrate 35 has air-core coils 43, 4
4, 45 and chip capacitors 46, 47, 48 are mounted. The air-core coils 43 to 45 respectively correspond to L1 to L3 of the circuit shown in FIG.
Corresponds to L4. Similarly, chip capacitors 46-48
Corresponds to C1 to C3. The inductance of the coil conductor 42 is 1/100 of the inductance of the air-core coil 45.
It is set above.

The duplexer having the above construction has the same operation and effect as those of the first embodiment. [Other Embodiments] The duplexer according to the present invention is not limited to the above embodiments, and can be variously modified within the scope of the gist thereof.

The low frequency pass side LC resonant circuit and the high frequency pass side LC resonant circuit may be separated physically and physically. Also, not as a duplexer, but at the high frequency side L
The C resonance circuit alone may be used as a bypass filter. In this case, the bypass filter can be downsized.

[0019]

As is apparent from the above description, according to the present invention, the inductance of the second coil and the third coil is reduced by the first coil which constitutes the high frequency passage side LC resonance circuit. Even if the area occupied by the second and third coils on the insulating substrate is reduced, a predetermined frequency characteristic can be maintained. Moreover, since the inductance of the first coil itself is small, the area occupied by the first coil on the insulating substrate can be small. As a result, a small duplexer is obtained.

[Brief description of drawings]

1 to 4 show a first embodiment of a duplexer according to the present invention.

FIG. 1 is an electrical equivalent circuit diagram of the duplexer of the first embodiment.

FIG. 2 is a plan view of a dielectric substrate used in the duplexer of the first embodiment as seen from the front side.

FIG. 3 is a plan view of the dielectric substrate shown in FIG. 2 viewed from the back side.

FIG. 4 is a partially cutaway perspective view of the duplexer.

FIG. 5 is an exploded perspective view showing a second embodiment of the duplexer according to the present invention.

FIG. 6 is a perspective view showing the appearance of the duplexer shown in FIG.

FIG. 7 is a plan view showing a third embodiment of the duplexer according to the present invention. 8 to 10 show a conventional duplexer.

FIG. 8 is an electrical equivalent circuit diagram of a conventional duplexer.

FIG. 9 is a plan view of a dielectric substrate used in a conventional duplexer as seen from the front side.

10 is a plan view of the dielectric substrate shown in FIG. 9 viewed from the back side.

[Explanation of symbols]

 5 ... Low frequency passage side LC resonance circuit 6 ... High frequency passage side LC resonance circuit 10 ... Dielectric substrate 12a, 12b ... Coil conductor (third coil) 13a, 13b ... Coil conductor (second coil) 16a, 16b ... Capacitor electrode 17 ... Coil conductor (first coil) 42 ... Coil conductor (first coil) 44, 45 ... Air core coil 48 ... Chip capacitor L2 ... Third coil L3 ... Second coil L4 … First coil C3… Capacitor

Claims (1)

[Claims] 1. A duplexer having an equivalent circuit including a low frequency pass side LC resonance circuit and a high frequency pass side LC resonance circuit, wherein the high frequency pass side LC resonance circuit includes a capacitor and a first coil connected in series. , Said capacitor and first
A second coil connected in parallel to the circuit composed of the coil, and a third coil connected in series to the circuit composed of the capacitor and the first and second coils, and the first coil Is 1 / the inductance of the second coil
A duplexer having an inductance of 100 or more.