Balun built in multiple ceramic layers

A balance-to-unbalance transformer (10), comprising an input terminal (11), a first output terminal (12), a second output terminal (13), a first circuit line comprising at least two capacitors (C1, C2) in parallel with each other and a first inductor L1 in series with the capacitors (C1, C2), wherein one electrode of each of the capacitors (C1, C2) are grounded, and a second circuit line comprising at least two capacitors (C3, C4) in series with each other and a second inductor (L2) in parallel with the capacitors (C3, C4), wherein one end of the second inductor (L2) is grounded. One end of the first circuit line and one end of the second circuit line are connected in parallel with the input terminal (11), and the other ends of the first and second circuit lines are the first and second output terminal, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a balance-to-unbalance (Balun) transformer, and, more particularly, to a Balun built in multiple ceramic layers.

2. Description of the Related Art

In terms of the technology of wireless network communication, a balance-to-unbalance (Balun) transformer is a crucial component, which is provided between a balanced circuit and an unbalanced circuit for transforming signals.

Conventionally, the Balun transformer is composed of microstrips or windings. However, if the conventional Balun transformer is used in applications with a radio frequency of several hundreds MHz or several GHz, the size of the Balun transformer and the weight thereof will be too enormous to be practically incorporated in such applications.

Thus, there is a need for a Balun transformer with reduced size and weight.

BRIEF SUMMARY OF THE INVENTION

In view of the above, it is thus an object of the present invention to provide a balance-to-unbalance (Balun) transformer structure. According to a first preferred embodiment of the present invention, the Balun transformer structure comprises an input terminal, a first output terminal, a second output terminal, a first circuit line, which comprises at least two capacitors in parallel with each other and a first inductor in series with the capacitors, wherein one electrode of each of the capacitors are grounded, and a second circuit line, which comprises at least two capacitors in series with each other and a second inductor in parallel with the capacitors, wherein one end of the second inductor is grounded. In more detail, one end of the first circuit line and one end of the second circuit line are connected in parallel with the input terminal, and the other ends of the first and second circuit lines are the first and second output terminals, respectively.

Preferably, the input terminal is provided for inputting an unbalanced signal and each of the first and second output terminals are provided for outputting a balanced signal, and the power of the outputted balanced signal is one half of the power of the inputted unbalanced signal according to the first preferred embodiment of the present invention.

Preferably, the unbalanced signal is a positive quarter-wavelength and the balanced signal is a negative quarter-wavelength according to the first preferred embodiment of the present invention.

Still, it is another object of the present invention to provide a Balun transformer built in multiple ceramic layers. According to a second preferred embodiment of the present invention, the Balun transformer built in multiple ceramic layers comprises an input terminal, a first output terminal, a second output terminal, at least four ceramic layers, wherein all the input terminal and the first and second output terminals are positioned on one outer surface of a laminated structure of the ceramic layers, at least five patterned metal layers provided for a plurality of capacitance electrodes of first to fourth capacitors, a plurality of wiring lines provided for first and second inductors, and a plurality of via holes provided for electrically connecting the capacitance electrodes and the first and second inductors located between respective metal layers, so as to constitute the Balun transformer, wherein the first and second capacitors in parallel with each other are series connected with the first inductor, one electrode of each of the first and second capacitors are grounded, the third and fourth capacitors in series with each other are parallel connected with the second inductor, and one end of the second inductor is grounded. In more detail, one end of the first capacitor and one end of the third capacitor are connected in parallel with the input terminal, and the other ends of the second and fourth capacitors are the first and second output terminals, respectively.

Preferably, the respective dielectric constants of the ceramic layers are within a range of 7 to 8 according to the second preferred embodiment of the present invention.

Preferably, the input terminal is provided for inputting an unbalanced signal and each of the first and second output terminals is provided for outputting a balanced signal, and the power of the outputted balanced signal is one half of the power of the inputted unbalanced signal according to the second preferred embodiment of the present invention.

Preferably, the unbalanced signal is a positive quarter-wavelength and the balanced signal is a negative quarter-wavelength according to the second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Please refer toFIG. 1, illustrating a circuit diagram of a Balun transformer according to the first preferred embodiment of the present invention.

As illustrated inFIG. 1, a Balun transformer structure10comprises an input terminal11, first and second output terminals12,13, a first circuit line, which comprises at least two capacitors C1, C2in parallel with each other and a first inductor L1in series with the capacitors C1, C2, wherein one electrode of each of the capacitors C1, C2are grounded, and a second circuit line, which comprises at least two capacitors C3, C4in series with each other and a second inductor L2in parallel with the capacitors C3, C4, wherein one end of the second inductor L2is grounded. Preferably, one end of the first circuit line and one end of the second circuit line are connected in parallel with the input terminal11, and the other ends of the first and second circuit lines are the first and second output terminals12,13, respectively.

It is to be noted that the input terminal11is provided for inputting an unbalanced signal and each of the first and second output terminals12,13is provided for outputting a balanced signal, and, preferably, the power of the outputted balanced signal is one half of the power of the inputted unbalanced signal according to the first preferred embodiment of the present invention.

It is preferred that the unbalanced signal is a positive quarter-wavelength and the balanced signal is a negative quarter-wavelength according to the first preferred embodiment of the present invention.

For enabling a reduction in the volume of the Balun transformer10according to the first preferred embodiment of the present invention, a Balun transformer10built in multiple ceramic layers are illustrated inFIGS. 2A and 2Baccording to the second preferred embodiment of the present invention.

As illustrated inFIGS. 2A and 2B, the Balun transformer10built in multiple ceramic layers comprises an input terminal11, first and second output terminals12,13, at least four ceramic layers21to24, wherein all the input terminal11and the first and second output terminals12,13are positioned on one outer surface of a laminated structure of the ceramic layers21to24, at least five patterned metal layers provided for a plurality of capacitance electrodes31of first to fourth capacitors C1, C2, C3and C4, a plurality of wiring lines33provided for first and second inductors L1and L2, and a plurality of via holes32provided for electrically connecting the capacitance electrodes31and the first and second inductors L1and L2located between respective metal layers, so as to constitute the Balun transformer10.

It is to be noted that the first and second capacitors C1and C2in parallel with each other are series connected with the first inductor L1, and one electrode of each of the first and second capacitors C1and C2are grounded. In addition, the third and fourth capacitors C3and C4in series with each other are parallel connected with the second inductor L2, and one end of the second inductor L2is grounded. In more detail, one end of the first capacitor C1and one end of the third capacitor C3are connected in parallel with the input terminal11, and the other end of the second and fourth capacitors C2and C4are the first and second output terminals12,13, respectively.

It is preferred that the respective dielectric constants of the ceramic layers21to24are within a range of 7 to 8 according to the second preferred embodiment of the present invention.

Similar to the first preferred embodiment, the input terminal11is provided for inputting an unbalanced signal and each of the first and second output terminals12,13is provided for outputting a balanced signal, and, preferably, the power of the outputted balanced signal is one half of the power of the inputted unbalanced signal according to the second preferred embodiment of the present invention.

Preferably, the unbalanced signal is a positive quarter-wavelength and the balanced signal is a negative quarter-wavelength according to the first preferred embodiment of the present invention.