JP2002217670A - Balun transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in that an insertion loss is low at a frequency higher than a given frequency and noises with frequency higher than a working frequency band is also produced. SOLUTION: The balun transformer includes first and second lines connected in series between an unbalanced terminal and a dummy terminal, a third line joined electromagnetically to the first line and connected between a first balanced terminal and the ground, and a fourth line electromagnetically joined to the second line and connected to a second balanced terminal. A first parallel circuit made up of a first inductor and a first capacitor connected in parallel is connected between an input/output terminal and the unbalanced terminal. A second parallel circuit made up of a second inductor and a second capacitor connected in parallel is connected between one end of the first parallel circuit and the ground. As a result, noise removing performance other than the working frequency band can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device such as a mobile communication device, and more particularly, to an impedance converter for converting transmission line impedance, and a signal of a balanced transmission line and a signal of an unbalanced transmission line. The present invention relates to a balun transformer used for a signal converter, a phase converter, and the like for converting a signal into a signal, and removes an unnecessary signal to improve characteristics.

[0002]

2. Description of the Related Art A conventional balun transformer is electromagnetically coupled to a first line, a second line, and a first line which are connected in series between an unbalance terminal and a dummy terminal. A third line connected between the ground and a fourth line electromagnetically coupled to the second line and connected between the balancing terminal and the ground.
There is a so-called marchand type balun transformer equipped with a railway line. FIG. 5 shows a structure in which these four lines are constituted by strip lines or coaxial lines.
1 and a dummy terminal 52, a line S9 and a line S10 each having a length of λ / 4 are connected in series, and a line S11 having a length of λ / 4 is connected between the balancing terminal 53 and the ground.
A line S12 having a length of / 4 is connected between the balancing terminal 54 and the ground. And the track S9 and the track S
11 are electromagnetically coupled, and the line S10 and the line S12 are electromagnetically coupled. Since such a balun transformer is constituted by distributed constants, it is necessary to make the length of λ / 4 of a frequency band using four lines, and the shape of the balun transformer becomes large.

FIG. 6 shows the above-mentioned four lines formed by a coil wound around a core or a coil pattern formed in an insulator layer to make lumped constants.
A line S13 and a line S14 each formed by an inductor are connected in series between the dummy terminal 62 and the dummy terminal 62, and a line S15 formed by the inductor is connected to the balancing terminal 63.
Line S1 formed by an inductor between
6 are connected between the balance terminal 64 and the ground.
Then, the line S13 and the line S15 are electromagnetically coupled,
The line S14 and the line S16 are electromagnetically coupled.

[0004]

Electronic devices using this type of balun transformer include two types of frequency band signals in one band so as not to interfere with each other, as in a dual-band mobile communication device. Remove the signal in the band
If you need to remove one signal in the other band,
2. Description of the Related Art Some receivers such as radios and televisions need to remove noise having a frequency twice or half the frequency used in order to prevent image interference. However, the conventional balun transformer has a low insertion loss at a frequency higher than a predetermined frequency as shown by 71 in FIG. 7 and also outputs noise at a frequency higher than the operating frequency band. There was a problem that it could not be used.

An object of the present invention is to provide a balun transformer capable of improving the noise removal capability outside the frequency band used.

[0006]

According to the present invention, a first line, a second line, and a first line, which are connected in series between an unbalance terminal and a dummy terminal, are electromagnetically coupled to the first line. Balun transformer having a third line connected between the balance terminal and the ground, and a fourth line electromagnetically coupled to the second line and connected between the second balance terminal and the ground. At
A first parallel circuit in which a first inductor and a first capacitor are connected in parallel is connected between an input / output terminal and an unbalanced terminal, and a second parallel circuit is connected between one end of the first parallel circuit and ground. A second parallel circuit in which the inductor and the second capacitor are connected in parallel is connected.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A balun transformer according to the present invention is electromagnetically coupled to a first line, a second line, and a first line connected in series between an unbalanced terminal and a dummy terminal. A third line connected between the first balancing terminal and the ground, and a second line electromagnetically coupled to the second line;
And a fourth line connected between the balance terminal and the ground. A parallel resonance circuit in which an inductor and a capacitor are connected in parallel is connected between the unbalanced terminal and the input / output terminal. A parallel resonance circuit in which an inductor and a capacitor are connected in parallel is connected between one end of the parallel resonance circuit and the ground. Therefore, in the balun transformer of the present invention, a notch filter is formed on the unbalanced end side by the two parallel resonance circuits, and the notch filter is used outside the used frequency band of the insertion loss characteristic, particularly, about twice or about the used frequency band. An attenuation pole is formed at half the frequency.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A balun transformer according to the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram showing a balun transformer according to a first embodiment of the present invention, wherein 11 denotes an unbalanced terminal, 12 denotes a dummy terminal, and 13 and 14 denote balanced terminals. The line S1 and the line S2 are connected in series between the unbalance terminal 11 and the dummy terminal 12. Balance terminal 13
The line S3 is connected between the ground and the ground. A line S4 is connected between the balancing terminal 14 and the ground. And
The line S1 and the line S3 are electromagnetically coupled, and the line S2 and the line S4 are electromagnetically coupled. An inductor L1 and a capacitor C1 are provided between the unbalanced terminal 11 and the input / output terminal 15.
Are connected in parallel. A parallel resonance circuit in which an inductor L2 and a capacitor C2 are connected in parallel is connected between one end of the parallel resonance circuit on the unbalanced terminal side and the ground. The resonance frequencies of the two parallel resonance circuits are set such that an attenuation pole is formed at a frequency at which noise whose insertion loss characteristic is to be removed exists (for example, a frequency approximately twice as large as a used frequency band). C3 indicates a capacitor for impedance matching. In this balun transformer, an unbalanced transmission line is connected to the input / output terminal 15 and balanced transmission lines are connected to the balancing terminals 13 and 14. The signal input from the input / output terminal 15 is input to the line S1 and the line S2 via a notch filter formed by two parallel resonance circuits.
3 and from the line S2 to the line S4. The signal transmitted to the line S3 and the line S4 is the balance terminal 1
It is output from 3 and 14. Further, the signal input from the balancing terminal is transmitted from the line S3 and the line S4 to the line S1 respectively.
And transmitted to S2. The signals transmitted to the lines S1 and S2 are combined and output from the input / output terminal 15 via a notch filter formed by two parallel resonance circuits.

The lines S1 to S4 of the balun transformer having such a circuit configuration are formed by a coil pattern formed in a laminate by laminating an insulator layer and a conductor layer. In addition, the inductor and the capacitor of the parallel resonance circuit may be composed of separate discrete components,
It may be constituted by a laminated component in which two parallel resonance circuits are integrally formed, or may be constituted integrally with the lines S1 to S4 in a laminated body in which an insulator layer and a conductor layer are laminated.

In such a balun transformer, the line S
1, the inductance value of S2 is 20 nH, and the lines S3, S
4, the inductance value of the inductor L1 is 12 nH, the inductance value of the inductor L1 is 4 nH, and the capacitance of the capacitor C1 is 2 pH.
F, the inductance value of the inductor L2 is set to 10 nH, the capacitance of the capacitor C2 is set to 2.3 pF, and the capacitance of the capacitor C3 is set to 2 pF. When the load was connected, characteristics as shown in FIG. 2 were obtained. In addition,
2, the horizontal axis represents frequency, the vertical axis represents attenuation, 21 represents insertion loss characteristics, and 22 represents reflection loss characteristics. This balun transformer has a frequency range of 925 to 960M.
At 1.3 Hz, the insertion loss is 1.34 dB or less, and an attenuation pole is formed at a frequency approximately twice the used frequency band of the insertion loss characteristic by the notch filter composed of two parallel resonance circuits. 45d
B or more. This is because the insertion loss of the frequency band approximately twice as large as the frequency band used in the conventional balun transformer is 6 dB at the maximum, so that the balun transformer of the present invention has a noise removal capability of the frequency band approximately twice as large as the frequency band used. It has been greatly improved.

FIG. 3 is a circuit diagram showing a second embodiment of the balun transformer of the present invention. The line S5 and the line S6 are connected in series between the unbalance terminal 31 and the dummy terminal 32. The line S7 electromagnetically coupled to the line S5 is connected between the balancing terminal 33 and the ground. A line S8 electromagnetically coupled to the line S6 is connected between the balancing terminal 14 and the ground. A parallel resonance circuit in which an inductor L3 and a capacitor C4 are connected in parallel is connected between the unbalanced terminal 31 and the input / output terminal 35. A parallel resonance circuit in which an inductor L4 and a capacitor C5 are connected in parallel is connected between one end of the parallel resonance circuit on the input / output terminal side and the ground. The resonance frequencies of the two parallel resonance circuits are set such that an attenuation pole is formed at a frequency at which noise whose insertion loss characteristic is to be removed exists (for example, a frequency approximately 1/2 times the frequency band used). L5 indicates an impedance matching inductor, and C6 indicates an impedance matching capacitor. In this balun transformer, an unbalanced transmission line is connected to an input / output terminal 35, and balanced transmission lines are connected to balancing terminals 33 and 34.

The lines S5 to S6 of the balun transformer having such a circuit configuration are constituted by a coil pattern formed in a laminate by laminating an insulator layer and a conductor layer. In addition, the inductor and the capacitor of the parallel resonance circuit may be composed of separate discrete components,
It may be constituted by a laminated component in which two parallel resonance circuits are integrally formed, or may be constituted integrally with the lines S5 to S6 in a laminated body in which an insulator and a conductor layer are laminated.

In such a balun transformer, the line S
5, the inductance value of S6 is 13 nH, and the lines S7, S
8, the inductance value of the inductor L3 is 6.7 nH, the capacitance value of the capacitor C4 is 4
pF, the inductance value of the inductor L4 was set to 4 nH, the capacitance of the capacitor C5 was set to 2 pF, the inductance value of the inductor L5 was set to 3 nH, and the capacitance of the capacitor C6 was set to 3 pF. When a load of 25Ω was connected to terminals 33 and 34,
The characteristics as shown in FIG. 4 were obtained. In FIG. 4, the horizontal axis represents frequency, the vertical axis represents attenuation, and 41 represents insertion loss characteristics.
Reference numeral 2 denotes the characteristic of the return loss. This balun transformer has an insertion loss of 1.7 dB or less in a used frequency band of 1805 to 1990 MHz, and has a notch filter including two parallel resonance circuits to attenuate the attenuation pole to a frequency approximately half the used frequency band of the insertion loss characteristic. Is formed 925
At ~ 1100 MHz, the insertion loss was 20.37 dB or more. This is because the insertion loss of the frequency band about 1/2 times the used frequency band in the conventional balun transformer is 6 dB at the maximum, so that the balun transformer of the present invention has a frequency band about 1/2 times the used frequency band. The noise removal capability has been greatly improved.

Although the embodiments of the balun transformer of the present invention have been described above, the present invention is not limited to these embodiments. For example, grounded second parallel circuits may be connected to both ends of the first parallel circuit connected between the input / output terminal and the unbalanced terminal. In addition, the first to fourth
May be formed by a strip line or a coaxial line, or may be formed by a winding wound around a core. Further, in the first embodiment, an inductor and a capacitor may be connected between a pair of balancing terminals as in the second embodiment. Still further, in the second embodiment,
As in the first embodiment, only a capacitor may be connected between a pair of balancing terminals.

[0015]

As described above, according to the balun transformer of the present invention, the first line, the second line, and the first line connected in series between the unbalanced terminal and the dummy terminal are electromagnetically connected. A third line coupled and connected between the first balancing terminal and ground; and a fourth line electromagnetically coupled to the second line and connected between the second balancing terminal and ground. And a first inductor and a first capacitor connected in parallel.
A second parallel circuit in which a second inductor and a second capacitor are connected in parallel between one end of the first parallel circuit and the ground. Is connected, an attenuation pole can be formed at a frequency at which noise whose insertion loss characteristic is to be removed exists.
Therefore, the balun transformer of the present invention can improve the noise removal capability outside the frequency band used.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a balun transformer according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram of a first example of the balun transformer of the present invention.

FIG. 3 is a circuit diagram showing a second embodiment of the balun transformer of the present invention.

FIG. 4 is a characteristic diagram of a balun transformer according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram of a conventional balun transformer.

FIG. 6 is a circuit diagram of a conventional balun transformer.

FIG. 7 is a characteristic diagram of a conventional balun transformer.

[Explanation of symbols]

 11 Unbalanced terminal 13, 14 Balanced terminal

Claims (3)

[Claims] 1. A first line and a second line connected in series between an unbalance terminal and a dummy terminal, electromagnetically coupled to the first line, and connected between the first balance terminal and the ground. And a third line connected to the second line and electromagnetically coupled to the second line,
In a balun transformer provided with a fourth line connected between a second balancing terminal and a ground, a first parallel circuit in which a first inductor and a first capacitor are connected in parallel comprises an input / output terminal and an input / output terminal. A second parallel circuit connected between the unbalanced terminals and one end of the first parallel circuit and ground;
A second parallel circuit in which the inductor and the second capacitor are connected in parallel. 2. The balun transformer according to claim 1, wherein one end of said second parallel circuit is connected between said first parallel circuit and said unbalanced terminal. 3. The balun transformer according to claim 1, wherein one end of said second parallel circuit is connected between said input / output terminal and said first parallel circuit.