TREA

Marchand Balun With Air Bridge

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Information

  • Patent Application
  • 20070285189
  • Publication Number
    20070285189
  • Date Filed
    June 08, 2006
    19 years ago
  • Date Published
    December 13, 2007
    18 years ago
Information
Abstract
The present invention provides a microwave and millimeter-wave balun. This balun is different from the conventional planar Marchand balun by using three edge-coupled lines instead of two edge-coupled lines and adding a pair of broadside coupled-lines. The broadside couple-lines are achieved by stacking two lines fully overlapped; the upper line is implemented using air-bridges to cross over the bottom line. By combining three edge-coupled-lines and broadside coupled-line, it will make the Marchand balun have a higher coupling coefficient and increase the operation bandwidth. The microwave monolithic integrated circuit (MMIC) mixer based on this invention can provide compact size compared to conventional ones.
Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be apparent to those skilled in the art by reading the following detailed description of a preferred embodiment thereof, with reference to the attached drawings, in which:



FIG. 1 is a schematic view of a conventional Marchand balun;



FIG. 2 is a schematic view of another conventional Marchand balun;



FIG. 3 is a schematic view of another conventional Marchand balun;



FIG. 4 is a schematic view of the Marchand balun according to the present invention;



FIG. 5 is a cross-sectional view of the Marchand balun according to the present invention;



FIG. 6
a is a curve diagram of simulation and measurement result of insertion loss in a preferred embodiment of the present invention;



FIG. 6
b is a diagram showing difference in amplitude and in phase of balanced signals in a preferred embodiment of the present invention;



FIG. 7 is a curve diagram showing measured relationship between conversion loss and LO driving power in a preferred embodiment of the present invention;



FIG. 8 is a curve diagram showing simulation and measurement result of conversion loss and LO operating frequency in a preferred embodiment of the present invention; and



FIG. 9 is a curve diagram showing measurement result of LO-to-RF isolation in a preferred embodiment of the present invention.





DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT


FIG. 4 is a schematic top view of an embodiment of the Marchand balun according to the present invention. As shown in FIG. 4, the Marchand balun 400 contains two edge-coupled-line set 402 each having three coupled lines and a plurality of air bridges 410. Each edge-coupled-line set 402 contains a first coupled line 404, a second coupled line 406 and a third coupled line 408. The number of the air bridges 410 is a design parameter and can be different in different embodiments. For the present embodiment, six air bridges are adopted.


In the present embodiment as shown in FIG. 4, the third coupled line 408 is used for receiving and processing input signal.


In a preferred embodiment of the present invention, the third coupled line 408 can be, but is not limited to, a parallel edge-coupled line of ¼ wavelength in length.


The first coupled line 404 is parallel disposed to a side of the third coupled line 408 and is electrically connected to ground. The first coupled line 404 is also a parallel edge-coupled line of ¼ wavelength in length.


The second coupled line 406 is parallel disposed to the other side of the third coupled line 408 and is electrically connected to ground. The second coupled line 406 is also a parallel edge-coupled line of ¼ wavelength in length.


The first coupled line 404 and the second coupled line 406 are electrically coupled by the air bridges 410. As such, a balanced signal is provided from the second coupled line 406 from the processed input signal. The ratio of the length of the air bridges 410 to the total length of the first coupled line 404 and the second coupled line 406 is greater than 50%.


In a preferred embodiment of the present invention, the air bridges 410 are made of a metallic material.



FIG. 5 is a cross-sectional view of the Marchand balun of FIG. 4. As shown in FIG. 5, the air bridge 502 (i.e., the air bridge 410 of FIG. 4) is disposed across a metal stub 504 (i.e., the third coupled line 408 of FIG. 4).


By the standard air bridge manufacturing process, the maximal width of the air bridge 502 is 20 μm. Therefore, a long air bridge can be replaced by a number of short air bridges 502. Moreover, the using of three edge-coupled lines, i.e. the first coupled line 404, the second coupled line 406, and the third coupled line 408, increases coupling coefficient and widens operation bandwidth of the Marchand balun 400 according to the present invention.


The Marchand balun with air bridges according to the present invention is preferred to contain two symmetric edge-coupled-line sets, each containing three edge-coupled lines.


By achieving wider operation bandwidth as described, the central frequency of the Marchand balun 400 according to the present invention can be increased so as to reduce chip size.


In a preferred embodiment according to the present invention, the input signal is microwave or millimeter-wave signal.


In an embodiment according to the present invention, the air bridges can be integrated into a standard manufacturing process of monolithic microwave integrated circuit (MMIC) to produce a MMIC mixer. The MMIC mixer, under experiment, shows a high performance which suffers less than 10 dB conversion loss for 50-78 GHz with a compact size as small as 0.57×0.52 mm2, much smaller than conventional circuits.


To apply the microwave and millimeter wave baluns of the present invention, the microwave circuit (including MMIC) usually has a multi-layered structure.



FIG. 6
a and FIG. 6b are small signal data analysis diagrams measured by Anritsu 37397A vector analyzer at 65 GHz of an embodiment of the present invention. In the measurement, three-port S-parameters are extracted from two port measurement by a port reduction method. FIG. 6a shows the simulation and measurement curves of insertion loss according to the present invention. FIG. 6b shows the differences in amplitude and in phase of the balanced signals according to the present invention. As illustrated, the Marchand balun 400 has better performance at the amplitude difference 1 dB and phase difference 12 degree within 40-65 GHz band.


Spectrum analyzer and microwave power meter can also be used to measure the performance of a wideband MMIC mixer according to the present invention. The measurement is limited to 41-78 GHz due to the constraints of the W-band high-power source. For the mixer, the local oscillator (LO) is driven by signal generator with power amplifier. The radio frequency (RF) signal is provided by the Agilent 8510C network analyzer capable of millimeter scale measurement.



FIG. 7 is a diagram showing the measured relationship between the conversion loss and the LO driving power. As shown in FIG. 7, the conversion loss is greater than the LO driving power at 77 GHz, which means using 12.5 dBm LO power to drive the mixer is acceptable for achieving low power loss. FIG. 8 is a curve diagram showing the simulation and measurement result of conversion loss and LO frequency of an embodiment of the present invention. In the present invention, the mixer has 7-10 dB conversion loss when LO driving power is 12.5 dBm and the center frequency is fixed at 1 GHz.



FIG. 9 is a curve diagram showing measurement result of the relationship between LO and RF isolation. As shown in FIG. 9, RF isolation is greater than 20 dB within 50 to 78 GHz.


Table 1 is a summary the performances of conventional millimeter-wave passive MMIC mixers. Present invention has a smallest chip size with competitive performance and wide bandwidth.















TABLE 1







Frequency
Conversion
Design
Manufacturing
Chip size



(GHz)
loss (dB)
topology
process
(mm2)





















L. Verweyen
75–88
6.8–10 
Singly balanced
GaAs
1.6 × 2.4


et al. (1998)


diode mixer
MESFET


K. Kamozaki
76.6
9.5
Singly balanced
0.15 μm GaAs
1.2 × 1.4


et al. (1997)


diode mixer
HEMT


T. N. Trinh et
  50–103.5
11.6 ± 2.8
Singly balanced
0.15 μm GaAs
1.2 × 1.2


al. (1987)


resistive mixer
HEMT


A. R. Barnes
 88–100
8
Single-ended
0.1 μm InP
1.175 × 1.1 


et al. (2002)


resistive mixer
HEMT


A. R. Barnes
 75–105
10–12
Singly balanced
0.1 μm InP
1.8 × 1.1


et al. (2002)


resistive mixer
HEMT


Y. Mimino et
52–64
12–14
Singly balanced
0.15 μm GaAs
1.18 × 1.2 


al. (2002)


resistive mixer
HEMT


H. J. Siweris
74–76
10
Single-device
0.13 μm GaAs
0.7 × 0.8


et al. (2003)


balanced mixer
HEMT


M. Kimishima
56–72
10.6
Singly balanced
0.15 μm GaAs
1.8 × 2  


et al. (2001)


resistive mixer
HEMT


M. Kimishima
72–84
10.6
Singly balanced
0.15 μm GaAs
1.8 × 2.4


et al. (2001)


resistive mixer
HEMT


Present
46–78
 7–10
Singly balanced
0.15 μm GaAs
0.57 × 0.52


invention


diode mixer
HEMT









According to the above description, the Marchand balun of the present invention has following advantages:

    • (1) the Marchand balun of the present invention has wider operation bandwidth than conventional Marchand balun in the same chip size which allows the present invention to be applied for more different types of systems; or the present invention has smaller size than conventional Marchand balun at the same center frequency which can reduce the manufacturing cost; and
    • (2) the present invention can be applied to MMICs, which conforms to the current industry trend, and the present invention can be applied to chip using silicon substrate in the future, which conforms to the cost reduction strategy.


Although the present invention has been described with reference to the preferred embodiment thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.

Claims
  • 1. A Marchand balun, comprising: an edge-coupled-line set, comprising: a first coupled line electrically coupled to ground;a second coupled line is substantially parallel disposed to one side of the first coupled line and electrically coupled to ground;a third coupled line is substantially parallel disposed between the first coupled line and the second coupled line for receiving and processing a input signal; anda plurality of air bridges electrically coupled to the first coupled line and to the second coupled line as transmission lines between the first coupled line and to the second coupled line;wherein, the air bridges have total length longer than one half of total length of the first and the second coupled lines.
  • 2. The Marchand balun as claimed in claim 1, wherein the air bridges are made of a metallic material.
  • 3. The Marchand balun as claimed in claim 1, wherein the air bridges are electrically coupled between the first coupled line and the second coupled line for coupling the processed input signal to the second coupled line as a balanced output signal.
  • 4. The Marchand balun as claimed in claim 1, wherein the first coupled line is a parallel edge-coupled line of ¼ wavelength in length.
  • 5. The Marchand balun as claimed in claim 1, wherein the second coupled line is a parallel edge-coupled line of ¼ wavelength in length.
  • 6. The Marchand balun as claimed in claim 1, wherein the third coupled line is a parallel edge-coupled line of ¼ wavelength in length.
  • 7. The Marchand balun as claimed in claim 1, wherein the input signal is a microwave signal.
  • 8. The Marchand balun as claimed in claim 1, wherein the input signal is a millimeter-wave signal.
  • 9. The Marchand balun as claimed in claim 1, wherein the Marchand balun comprises two symmetric sets of said edge-coupled-line sets.