Inductor devices – Coil or coil turn supports or spacers – Printed circuit-type coil
Reexamination Certificate
2001-05-21
2002-11-19
Mai, Anh (Department: 2832)
Inductor devices
Coil or coil turn supports or spacers
Printed circuit-type coil
C336S223000, C336S232000, C333S026000
Reexamination Certificate
active
06483415
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a balance-to-unibalance transformer (blaun) used in a wireless local network or personal communication, and more specifically to a multi-layer LC resonance balun that can be fabricated as a device in a micro-chip.
BACKGROUND OF THE INVENTION
A balun is a device for converting signals between an unbalanced circuit structure and a balanced circuit structure. The signal of a balanced circuit structure comprises two signal components with same magnitude but 180-degree phase difference. Many analog circuits require balanced inputs and outputs in order to reduce noise and high order harmonics as well as improve the dynamic range of the circuits.
There are several types of baluns that are either active or passive. Passive baluns can be classified as lumped-type, coil-type and distributed-type baluns. A lumped-type balun uses lumped capacitors and inductors to match impedance and generate two balanced signals with same magnitude and 180-degree phase difference. The advantages of a lumped-type balun are small volume and light weight. However, it is not easy to maintain the 180-degree phase difference and the identical magnitude between the two signals.
Coil-type baluns have been widely used in lower frequency and ultra high frequency (UHF) bands. When a coil-type balates is used in higher than the UHF band, it usually has a drawback of having considerable loss. In addition, it has reached the limit of miniaturization and can not be further reduced in size.
Distributed-type baluns can further be classified as 180-degree hybrid and Marchand. A 180-degree hybrid balun has a fairly good frequency response in the microwave frequency band. However, its size often poses a problem when it is used in the radio frequency range between 200 MHz and several GHz. Because a 180-degree hybrid balun comprises a few sections of quarter wave transmission lines, it is difficult to reduce the size. Even if it is manufactured in a meandered way, a significant area is still required. One approach to reducing the size is to use a power divider along with a pair of transmission lines having different length for generating the 180-degree phase difference. Nevertheless, the size is still too large.
As shown in
FIG. 1
, a Marchand balun commonly used in the industry comprises two sections of quarter wave coupled lines. This type of baluns has a fairly large bandwidth. Both phase balance and power distribution of a Marchand balun are reasonably good. However, the transmission lines in a Marchand balun need to be tightly coupled in order to achieve a sufficient bandwidth. Therefore, a Marchand balun is often broadside coupled to reduce its area. It is also fabricated in a meandered way to minimize its size. The balun is commonly seen in an RF application. Using a high dielectric constant material can also reduce the size of a Marchband balun.
U.S. Pat. No. 5,497,137 discloses a chip-type transformer as shown in FIG.
2
. The chip-type transformer comprises a laminate
200
formed by five dielectric substrates
214
a
-
214
e
superimposed one on the other. A ground electrode
216
is formed on a main surface of the first dielectric substrate
214
a
. Another ground electrode
230
is formed on a main surface of the fifth dielectric substrate
214
e
. A connecting electrode
220
is formed on a main surface of the second dielectric substrate
214
b.
There is a first strip line
222
on the third dielectric substrate
214
c
. The first strip line
222
comprises a first spiral portion
224
a
and a second spiral portion
224
b
that are electromagnetically coupled respectively to a second strip line
226
and a third strip line
228
formed on the fourth dielectric substrate
214
d
. The structure of the chip-type balun is broadside coupled and miniaturized by means of a high dielectric constant material. However, its size can not be reduced to a chip size if a low dielectric constant material is used.
SUMMARY OF THE INVENTION
This invention has been made to overcome the above-mentioned drawbacks of conventional baluns. The primary object is to provide a multi-layer balun having an equivalent circuit of an LC resonator. The equivalent circuit comprises at least a section of coupled lines, at least a transmission line and at least a capacitor. By means of the multi-layer structure and meandered coupled lines, the size of the balun of this invention is greatly reduced. In addition, the baluns can be realized with low dielectric constant materials to increase their stability.
According to this invention, the coupled lines of one of the embodied baluns have a symmetric structure with respect to a center geometrically. Both responses of magnitude and phase are well balancing. By adjusting the length of the coupled lines and the capacitance values, the impedance at the balanced output ports can be properly matched.
In a first embodiment, the equivalent circuit of the LC resonance balun comprises two sections of coupled lines connected to a transmission line trimming section and a parallel capacitor. By increasing the capacitance value of the parallel capacitor, the size of the balun can be reduced. Using a multi-layer structure, the capacitor may be fabricated on dielectric layers below or above the coupled lines. A vertically stacked multi-layer structure greatly reduces the size of the balun.
In a second embodiment, the equivalent circuit of the blaun comprises a section of coupled lines connected in parallel with two capacitors. The two ends of coupled lines are connected to an input port and two balanced output ports through transmission lines. The equivalent length of one LC resonator connected to the input port is shorter than a quarter of the wavelength. The equivalent length of the other LC resonator connected to the output ports is shorter than a half of the wavelength.
In the preferred embodiments of this invention, multiple sections of coupled lines can be incorporated. The coupled lines are manufactured with winding lines such as spiral lines, meandered lines, sinusoidal lines or saw-tooth lines. By means of winding lines, the area of the coupled lines is reduced. Multiple capacitors can also be used to increase the capacitance value. Based on the simulation, the balun of this invention shows that in a 200 MHz frequency bandwidth centered at 2.44 GHz, the magnitude difference is less than 2 dB and the 180-degree phase difference is less than 5 degrees at the two balanced ports.
The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.
REFERENCES:
patent: 5061910 (1991-10-01), Bouny
patent: 5455545 (1995-10-01), Garcia
patent: 5497137 (1996-03-01), Fujiki
patent: 5611272 (1997-03-01), Steuer
patent: 5697088 (1997-12-01), Gu
patent: 5886589 (1999-03-01), Mourant
patent: 6150897 (2000-11-01), Nishikawa et al.
patent: 6278340 (2001-08-01), Liu
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