JP2005323063A - Branching filter circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a branching filter circuit, capable of obtaining an attenuation amount over a wide band and superior insertion loss characteristics for a pass band. <P>SOLUTION: The branching filter circuit is composed of a first filter connected between first and second ports P1, P2 and the pass frequency band of which is a first frequency band; and a second filter connected between first and third ports P1, P3 the pass frequency band of which is a second frequency band. The first filter is provided with a first inductive element L1 located between the P1 and P2; a first series resonance circuit of a second inductive element L2 and a first capacitive element C1 located between the P2 side of the element L1 and ground; and a parallel resonance circuit of a third inductive element L3 and a second capacitive element C2, located on the P2-side of the element L1. The first series resonance circuit has an attenuation pole in the second frequency band, the parallel resonance circuit has an attenuation pole within a frequency band exceeding twice the first frequency band and lower than thrice the first frequency band; and the resonance frequency of the first series resonance circuit is selected lower than the resonance frequency of the parallel resonance circuit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a demultiplexing circuit used in a mobile communication device such as a cellular phone. Specifically, the demultiplexing circuit is used in a high frequency circuit (front end unit) and demultiplexes high frequency signals of at least two communication systems having different frequencies. The present invention relates to a branching circuit.

In recent years, as one form of mobile communication device, there is a multi-band mobile phone that can make a call using two or more communication systems with a single mobile phone. In this cellular phone, a demultiplexing circuit that demultiplexes a high-frequency signal having a frequency corresponding to each system is required.
As such a branching circuit, there is a branching circuit configured by combining a plurality of filter circuits. Patent Document 1 proposes a multilayer duplexer having a multilayer structure in which a filter circuit is composed of an inductance element and a capacitance element, and each element is formed as an electrode pattern in the multilayer body. FIG. 5 shows an equivalent circuit diagram thereof.
In this laminated duplexer, a patterned electrode is formed inside a laminated body in which insulating layers made of a dielectric are laminated and integrated, and an inductance element and a capacitance element constituted by the patterned electrode are connected in series to form two notches. A circuit (series resonance circuit), a low-pass filter circuit and a first series resonance circuit are arranged between the first port P1 and the second port P2, and between the first port P1 and the third port P3. The high-pass filter circuit and the second series resonance circuit are arranged.
The second series resonance circuit is configured to maximize the insertion loss at the frequency f1, and the first series resonance circuit is configured to maximize the insertion loss at a frequency f2 different from the frequency f1. The microwave signal having the frequency f1 input to the first port P1 is not output to the third port P3, and the microwave signal having the frequency f2 input to the first port P1 is not output to the second port P2. Wave signal distribution can be performed.
JP 2001-119258 A

Currently, it can operate as a mobile communication device in communication systems of multiple frequency bands such as DCS1800 (transmission frequency 1710 to 1785 MHz, reception frequency 1805 to 1880 MHz) and GSM900 (transmission frequency 880 to 915 MHz, reception frequency 925 to 960 MHz). Dual-band mobile phone, DCS1800 and PCS1900 (transmission frequency 1850-1910 MHz, reception frequency 1930-1990 MHz) and triple-band mobile phone that can operate with GSM900, and GSM850 (transmission frequency 824-849 MHz, A quad-band mobile phone to which a system having a reception frequency of 869 to 894 MHz) has been proposed, and this is collectively called a multi-band mobile phone.
The use frequency bands of these communication systems are roughly classified into a communication system using a frequency band of 800 MHz to 1 GHz and a communication system using a relatively high frequency band of 1.5 GHz to 2.4 GHz.

With the recent increase in the number of multi-band mobile phones, it has become necessary for the demultiplexing circuit to demultiplex a plurality of low frequency band communication systems and a plurality of high frequency band communication systems. However, it is difficult for the filter circuit constituting the conventional demultiplexing circuit to secure the attenuation over a wide frequency band including the frequency bands of a plurality of communication systems. For this reason, a desired insertion loss is not obtained in the pass band. There was a problem that it could not be obtained.
Therefore, in the present invention, an attenuation amount can be obtained over a wide band in a demultiplexing circuit that demultiplexes a high-frequency signal corresponding to the communication system, which is used in a multiband cellular phone that enables a call in two or more communication systems. An object of the present invention is to provide a branching circuit that can provide excellent insertion loss characteristics in the passband.

  The present invention is a demultiplexing circuit that demultiplexes high-frequency signals of at least two communication systems having different frequencies, and is connected between a first port and a second port, and the first frequency band is defined as a passing frequency band. And a second filter connected between the first port and the third port and having a second frequency band as a pass frequency band, wherein the first filter includes a first port and a second filter. A first inductance element connected between the first inductance element and a first series resonance circuit provided between the second port side of the first inductance element and the ground and having a second inductance element and a first capacitance element; And a parallel resonant circuit that is disposed on the second port side of the first inductance element and includes a third inductance element and a second capacitance element, wherein the first series resonance circuit is The first resonance circuit has an attenuation pole in a second frequency band, and the parallel resonance circuit has an attenuation pole in a frequency band that is more than twice and less than three times the first frequency band. Is a branching circuit set to a frequency lower than the resonance frequency of the parallel resonance circuit.

  In the present invention, it is preferable that a third capacitance element is disposed between at least one end of the parallel resonant circuit and the ground to constitute a low-pass filter.

  The second filter according to the present invention includes a fourth capacitance element connected between a first port and a third port, a fifth capacitance element connected in series with the fourth capacitance element, and the fourth capacitance element. And a fifth capacitance element, and a second series resonance circuit composed of a fourth inductance element and a sixth capacitance element arranged between the connection point of the first capacitance element and the ground. The second series resonance circuit has a first frequency band. It is preferable to have an attenuation pole inside.

  The demultiplexing circuit of the present invention can obtain attenuation over a wide band and can provide excellent insertion loss characteristics in the passband, so that it is possible to make a call with two or more communication systems, particularly three or more communication systems. Useful for multiband mobile phones.

  FIG. 1 is a diagram showing an equivalent circuit of a branching circuit according to an embodiment of the present invention. The branching circuit is connected between the first port P1 and the second port P2, and includes a first filter having a first frequency band f1 as a pass frequency band, and a first port P1 and a third port P3. And a second filter connected in between and having the second frequency band f2 as a pass frequency band. The first frequency band f1 is on the lower frequency side than the second frequency band f2, and is set to a frequency band that does not overlap each other. The first filter exhibits a large attenuation in the second frequency band (high frequency band) f2, and the second filter exhibits a large attenuation in the first frequency band (low frequency band) f1. .

  The first filter connected between the first port P1 and the second port P2 includes a first inductance element L1 having one end connected to the first port P1, and a second port P2 side of the first inductance element L2. A first series resonant circuit that is disposed between the first inductance element L2 and the first capacitance element C1, and a third inductance element L3 that is disposed on the second port P2 side of the first inductance element L1; The parallel resonance circuit including the second capacitance element C2 is provided, and the first series resonance circuit has an attenuation pole in the second frequency band f2, and is configured to maximize the insertion loss. The parallel resonant circuit is configured to have an attenuation pole in a frequency band that is more than twice the first frequency band f1 and less than three times the resonance frequency of the first series resonance circuit. The frequency is set lower than the resonance frequency. With this configuration, it is possible to obtain a large attenuation over a wide band while reducing loss at the passband frequency due to the parallel resonance circuit.

  The second filter connected between the first port P1 and the third port P3 includes a fourth capacitance element C4 connected between the first port P1 and the third port P3, and the fourth capacitance element C4. A fifth capacitance element C5 connected in series, and a fourth inductance element L4 and a sixth capacitance element C6, which are disposed between the connection point of the fourth capacitance element C4 and the fifth capacitance element C5 and the ground. The second series resonant circuit has an attenuation pole in the first frequency band f1, and is configured to maximize the insertion loss.

  With this configuration, the first frequency band f1 input to the first port P1 appears at the second port P2, but is not output to the third port P3, and is input to the first port P1. The second frequency band f1 appears at the third port P3, but is not output to the second port P2, so that a high-frequency signal can be demultiplexed.

  FIG. 2 shows a branching filter according to another aspect of the present invention, in which a third capacitance element C3 is arranged between one end of a parallel resonant circuit of the first filter and the ground. The third capacitance element C3 further improves the attenuation performance of the high frequency side signal. In the duplexer of FIG. 2, the capacitance element is connected to only one end of the parallel resonant circuit. However, if it is also connected to the other end, the high-frequency signal attenuation performance can be further improved.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
FIG. 3 is a circuit block of a front end portion of a multiband mobile phone including the branching circuit of the present invention, and FIG. 4 is an equivalent circuit thereof. In the present embodiment, a front end unit corresponding to the first to fourth communication systems in which a filter circuit and a switch circuit are arranged in addition to the branching circuit will be described. In the description, the first communication system is GSM850 (transmission frequency 824 to 849 MHz, reception frequency 869 to 894 MHz), the second communication system is GSM900 (transmission frequency 880 to 915 MHz, reception frequency 925 to 960 MHz), the third The communication system is DCS1800 (transmission frequency 1710 to 1785 MHz, reception frequency 1805 to 1880 MHz), and the fourth communication system is PCS1900 (transmission frequency 1850 to 1910 MHz, reception frequency 1930 to 1990 MHz).

The front end unit of the multiband mobile phone shown in FIG. 3 includes a demultiplexing circuit 1, a filter circuit 2, and high-frequency switch circuits 3 and 4, and is connected to the demultiplexing circuit 1 and the antenna ANT. A filter circuit 2 and high-frequency switch circuits 3 and 4 are connected to the subsequent stage of the wave circuit 1. The high-frequency switch circuits 3 and 4 are further connected to transmission / reception circuits (Tx, Rx) of GSM850, GSM900, DCS1800, and PCS1900.
The demultiplexing circuit 1 is composed of a plurality of filter circuits selected from a low-pass filter, a band-pass filter, and a notch filter so that transmission / reception signals of GSM850, GSM900, DCS1800, and PCS1900 do not wrap around each other's signal path. . In the present embodiment, the branching circuit shown in FIG. 2 is used.

The first filter that handles the first frequency band f1 of GSM850 and GSM900 having a relatively low frequency includes the first inductance element L1 connected between the first port P1 and the second port P2, and the first filter A first series resonant circuit that is disposed between the second port P2 side of the inductance element L2 and the ground and includes the second inductance element L2 and the first capacitance element C1, and a second port P2 of the first inductance element L1. The third capacitance element C3 is arranged between the parallel resonance circuit including the third inductance element L3 and the second capacitance element C2 and the one end on the second port P2 side of the parallel resonance circuit and the ground. It is a configuration.
The second filter that handles the second frequency band f2 of the DCS 1800 and PCS 1900 having a relatively high frequency includes a fourth capacitance element C4 connected between the first port P1 and the third port P3, and the fourth filter. A fifth capacitance element C5 connected in series with the capacitance element C4, and a connection point between the fourth capacitance element C4 and the fifth capacitance element C5 and the ground, and a fourth inductance element L4 and a sixth capacitance element. This is a configuration having a second series resonant circuit including C6.

The first series resonance circuit forms an attenuation pole in the second frequency band (1710 MHz to 1990 MHz), and the parallel resonance circuit exceeds 3 times the first frequency band (824 MHz to 960 MHz). An attenuation pole is formed in a frequency band less than (less than 1648 MHz and less than 2880 MHz), and the resonance frequency of the first series resonance circuit is set to be lower than the resonance frequency of the parallel resonance circuit. The second series resonant circuit is configured to have an attenuation pole in the first frequency band (824 MHz to 960 MHz).
With such a configuration, the branching circuit of the present invention can obtain a large attenuation over a wide band, and an excellent insertion loss characteristic can be obtained in the pass band. Therefore, the first circuit input to the first port P1 can be obtained. The frequency band f1 appears at the second port P2 but is not output to the third port P3, and the second frequency band f1 input to the first port P1 appears at the third port P3. Since it is not output to the port P2, a high frequency signal can be demultiplexed. The demultiplexed high-frequency signal is input to the high-frequency switch circuits 3 and 4 disposed in the subsequent stage of the demultiplexing circuit.

The high-frequency switch circuits 3 and 4 are generally configured using switching elements such as diodes and transistors. In general, it is known that when a high-power high-frequency signal is input to a nonlinear device such as a diode or transistor, a harmonic having a frequency that is an integral multiple of the fundamental wave appears.
Also in the front end portion of the multiband portable telephone, harmonics are generated by the high output amplifier included in the transmission circuit Tx, and are superimposed on the transmission signal and input to the high frequency switch circuits 3 and 4. Further, in each of the switch circuits 3 and 4, harmonics are generated by the PIN diode used as a switching element. For this reason, in the front-end part of the conventional multiband mobile phone, a filter circuit is separately connected to the path of each transmission signal so as to remove harmonics generated by the high-power amplifier and the switch circuit. However, in the branching circuit of the present invention, only the high-frequency signal in the first frequency band f1 can be passed and attenuated by the first series resonant circuit and the parallel resonant circuit. The radiated harmonics can be reduced, and leakage of the harmonics to a circuit that handles a high-frequency signal in the second frequency band f2 that is close to or overlaps with the harmonics can be prevented. Furthermore, since it is possible to reduce the filter circuit of the front end part, which has been conventionally required, it contributes to the miniaturization of the multiband mobile phone.

  The demultiplexing circuit of the present invention can obtain attenuation over a wide band and can provide excellent insertion loss characteristics in the passband, so that it is possible to make a call with two or more communication systems, particularly three or more communication systems. Useful for multiband mobile phones.

It is an equivalent circuit of the branching circuit which concerns on one Example of this invention. It is an equivalent circuit of the other branching circuit which concerns on one Example of this invention. It is a circuit block of the front end part of a multiband mobile phone. 4 is an equivalent circuit of a front end portion of a multiband mobile phone using a branching circuit according to an embodiment of the present invention. This is an equivalent circuit of a conventional branching circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Split circuit 2 Filter circuit 3, 4 Switch circuit L1, L2, L3, L4 Inductance element C1, C2, C3, C4, C5, C6 Capacitance element P1 1st port P2 2nd port P3 3rd port Tx Transmission circuit Rx Receiver circuit

2 Diplexer circuit 3, 4 Filter circuit 5, 6 Switch circuit 100 Multilayer substrate L21, L31 First inductance element L20. L30 2nd inductance element C23, C33 1st capacitance element

Claims (3)

A demultiplexing circuit for demultiplexing high-frequency signals of at least two communication systems having different frequencies,
A first filter connected between the first port and the second port and having a first frequency band as a pass frequency band, and connected between the first port and the third port, and having a second frequency band And a second filter as a pass frequency band,
The first filter is disposed between a first inductance element connected between a first port and a second port; a second port side of the first inductance element; and a ground; A first series resonance circuit including a first capacitance element; and a parallel resonance circuit disposed on the second port side of the first inductance element and including a third inductance element and a second capacitance element;
The first series resonant circuit has an attenuation pole in a second frequency band,
The parallel resonant circuit has an attenuation pole in a frequency band that is more than twice the first frequency band and less than three times;
The branching circuit according to claim 1, wherein a resonance frequency of the first series resonance circuit is set to be lower than a resonance frequency of the parallel resonance circuit.   The branching circuit according to claim 1, wherein a third capacitance element is disposed between at least one end of the parallel resonant circuit and the ground. The second filter includes a fourth capacitance element connected between the first port and the third port, a fifth capacitance element connected in series with the fourth capacitance element, the fourth capacitance element, and a fifth capacitance. A second series resonant circuit disposed between a connection point of the capacitance element and the ground and having a fourth inductance element and a sixth capacitance element;
3. The branching circuit according to claim 1, wherein the second series resonant circuit has an attenuation pole in a first frequency band. 4.

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