KR100844218B1 - High-Frequency Transmission Line for filtering Common Mode - Google Patents

Abstract

A high frequency transmission line element is disclosed. The high frequency transmission line element is a high frequency transmission line element for transmitting a balanced signal, that is, a differential mode signal, and includes at least two or more line conductors formed on one surface of the dielectric substrate and extending in the high frequency transmission direction and spaced apart from each other, and a dielectric having a line conductor formed thereon. A ground conductor formed on one surface of the substrate and spaced apart from the track conductor by a predetermined distance, the line facing the ground conductor such that the distance between the line conductor and the ground conductor is divided into a narrow area and a wide area along the high frequency transmission direction. A stepped portion is formed on at least one of one side of the conductor or one side of the ground conductor opposite to the line conductor.

Differential mode, common mode, high frequency transmission line

Description

High-Frequency Transmission Line for Filtering Common Mode

1 is a perspective view of a CPW type high frequency transmission line device according to an embodiment of the present invention.

2A is an equivalent model of the high frequency transmission line device according to the present invention, and FIGS. 2B and 2C are top and rear views of the high frequency transmission line device according to the equivalent model, and FIG. 2D is a view taken along line II in FIG. 2C. It is a cross section.

3A and 3B are graphs showing transmission characteristics of common and differential modes for 2-cell and 3-cell structures, respectively, according to a cutoff frequency of 2 GHz.

4A to 4C are top views illustrating various embodiments of the high frequency transmission line device according to the present invention.

The present invention relates to a high frequency transmission line device, and more particularly, to a high frequency transmission line device for transmitting a balanced mode signal, that is, equal in magnitude and opposite in phase.

Flexible printed circuits (FPCs) are flexible and flexible PCBs compared to conventional printed circuit boards (PCBs) made of a hard insulating material such as epoxy. FPC can be used for three-dimensional three-dimensional wiring, miniaturization and light weight of the product, as well as excellent bending resistance, and is used for data transmission of mobile communication devices such as mobile phones, GPS, displays, and PCs.

In an information device using various radio communication frequencies, a serial data transmission line is applied to an FPC in order to transmit data at high speed by using characteristics of the FPC. For example, in the serial data transmission method for the connection between the main board of the small information communication device and the PC and the internal module, immunity to the noise source is very important for fast and accurate data transmission of high quality and large capacity information. However, if a noise source due to crosstalk or interference between the small ICT / PC signal lines or the internal radiating parts inside the device is present near the serial data transmission line, packet data transmission errors are caused. Moreover, recent portable mobile communication devices are highly integrated to contain many functions and thus do not provide sufficient separation between radiating parts such as internal antennas and other parts and cables. Therefore, the separation distance is very close to (within 5mm), so the influence on the common mode noise (Common Mode Noise) will also be large.

Conventionally, in order to solve this problem, a common mode choke (CMC) device incorporating a high frequency inductor is connected to both ends of a serial data transmission line to block common mode noise. However, the CMC is less that the carrier frequency (f _o) the common-mode noise reduction effect after around 1.8 GHz, so that significantly reduced the difference between the common, differential mode impedance in the vicinity of 1.8 GHz frequency, and also the differential mode (Differential Mode) signal Also increases the insertion loss.

The present invention has been made to solve the above-mentioned problems of the prior art, and common mode signal for the f _o frequency band of an antenna or the like on a serial data transmission line to block high frequency noise sources near or above 1.8 GHz such as a built-in antenna. It is an object of the present invention to provide a high frequency transmission line element capable of cutting off. The high frequency transmission line device according to the present invention uses a maximum reflection condition of Bragg`s condition for the right mode, and maintains transmission characteristics for the differential mode signal, but introduces common mode noise introduced from the outside. Shows blocking characteristics. When the high frequency transmission line device according to the present invention is applied to the existing serial data transmission method, it is possible to ensure more improved transmission characteristics by blocking the high frequency common mode noise introduced.

The high frequency transmission line device according to the present invention is a high frequency transmission line device for transmitting a balanced signal, that is, a differential mode signal, wherein at least two or more line conductors and line conductors formed on one surface of the dielectric substrate and extending in the high frequency transmission direction are spaced apart from each other. A ground conductor formed on one surface of the formed dielectric substrate and spaced apart from the line conductor at a predetermined interval, and having a length of λ _g / 4 when the wavelength of the common mode frequency to be blocked is λ _g , and the line conductor and ground Stepped portions are formed on at least one of the one side of the line conductor facing the ground conductor or one side of the ground conductor facing the line conductor so that the distance between the conductors is divided into a narrow region and a wide region along the high frequency transmission direction.

Here, it is preferable that the stepped portion is formed repeatedly periodically along the high frequency transmission direction. In addition, the ground conductor may include a first ground conductor and a second ground conductor formed on one side of each of the line conductors. In addition, the high frequency transmission line device according to the present invention may include a connecting conductor on the other surface of the dielectric substrate opposite to one surface of the dielectric substrate, in which case both ends of the connecting conductor are connected to the first ground conductor and the second ground conductor via the dielectric substrate. Is preferably connected to each other. In addition, the dielectric substrate may be formed of a flexible material and applied to the FPC.

In addition, the high frequency transmission line device according to the present invention includes at least two or more line conductors formed on one surface of the dielectric substrate and extending in the high frequency transmission direction and spaced apart from each other, and a ground conductor formed spaced apart from the line conductors on the dielectric substrate, When the wavelength of the common mode frequency to be cut is λ _g and has a length of λ _g / 4, an impedance of the common mode to at least one of the line conductor and the ground conductor to remove the common mode noise introduced from the outside. Characterized in that the change portion is formed. In particular, the present invention is applicable to both CPW structures or micro strip structures. In the case where the ground conductor is a CPW structure formed on the same surface of the line conductor and the dielectric substrate, the impedance change unit may include at least one of the distance between the line conductors, the line width of each of the line conductors, or the distance between the line conductor and the ground conductor. It can be formed by changing. In addition, when the ground conductor and the line conductor are respectively microstrip structures facing each other in the dielectric substrate, the impedance change unit may be formed by changing at least one of the distance between the line conductors or the line width of the line conductors.

Hereinafter, with reference to the accompanying drawings will be described preferred embodiments of a high frequency transmission line device capable of performing a common mode cut filter function according to the present invention.

First, FIG. 1 is a perspective view of a high frequency transmission line device according to the present invention. In FIG. 1, reference numeral 10 denotes a dielectric substrate, 20 denotes a line conductor constituting a transmission line, and 30a and 30b denote first and second ground conductors formed on one side of each line conductor. The high frequency transmission line device of FIG. 1 is composed of a CPW (Coplannar Waveguide) structure in which the ground conductor and the line conductor are formed on the same surface of the dielectric substrate. It may be a microstrip structure in which a ground conductor is formed on the other surface opposite to one surface. Here, the ground conductor facing the line conductor 20 such that the distance between the line conductor 20 and the ground conductors 30a and 30b is divided into a narrow region g 'and a wide region g along the high frequency transmission direction. Stepped portions 30c are formed on one side of 30a and 30b.

In the high frequency transmission line element capable of performing the common mode blocking filter function according to the present invention, in order to satisfy the maximum reflection condition of the Bragg condition, the length of each transmission line section is set to λ _g / 4 (λ _g : in-wavelength) period. do. For example, referring to FIG. 2A, which is an equivalent model of a common mode cutoff filter, Zeven in each differential line periodically changes its impedance value, and Zodd blocks common mode noise by maintaining a constant impedance value. The discontinuous structure surface is formed by the stepped portion 30c which is formed by repeating periodically on the ground conductors 30a and 30b, and as the discontinuous structure surface increases, the amount of energy reflection for a specific frequency band corresponding to λ _g / 4 is increased. It becomes bigger.

2B and 2C are top and rear views of the high frequency transmission line device according to the equivalent model of FIG. 2A, and FIG. 2D is a cross-sectional view taken along the line II of FIG. 2C. Here, each of the ground conductors 30a and 30b is connected to each other by a connecting conductor 40 formed on the other surface of the dielectric substrate 10. Reference numeral 40a denotes a via contact formed such that one end of the connection conductor 40 is connected to each of the ground conductors 30a and 30b via the dielectric substrate 10.

The transmission line shape shown in this embodiment was selected by using a Coupled Line Coplanar Waveguide (CLCPW) to increase and adjust the difference of the right mode impedance. In the above structure, the CLCPW portion of Zeven = 206Ω, Zodd = 53Ω is g = 600 µm, s = w = 100 µm, and the CLCPW portion of Zeven = 100Ω, Zodd = 50Ω is g '= 100 µm, s = w = 100 Designed to μm. That is, the differential mode impedance of each line was matched to 100Ω. And it may adjust the block range of the common mode noise by connecting to each transmission line according to λ _g / 4 length of a particular frequency band f _o. The λ _g / 4 length of the 2 GHz band common mode cut-off filter applied to the analysis is 26.1 mm, the length of the serial transmission line is 78.3 mm for the 2-cell, and 130.5 mm for the 3-cell.

On the other hand, it is preferable that the connection conductor 40 of FIG. 2C is located in the area | region where the space | interval between the line conductor 20 and the ground conductors 30a and 30b is narrow (region where g '= 100 micrometer in this embodiment). That is, the connection conductor 40 is preferably disposed in an area where the stepped portion 30c is formed. This is to suppress the radiation loss due to the slot mode resulting from the CLCPW, and furthermore, the connection conductor 40 and the ground conductor ( This is to maximize the area where the via contact 40a between 30a and 30b is to be formed.

In addition, in the high frequency transmission line device according to the present invention, a flexible material such as a polyimide dielectric may be used as the substrate 10 in order to be applied to an FPC, and the line conductor 20 may be formed on one surface of the polyimide substrate 10. ) And ground conductors 30a and 30b are attached, and a connecting conductor 40 is formed on the other surface of the substrate 10, and the connecting conductor 40 is connected to the ground conductors 30a and 30b through the via contact 40a. Connected with. In this way, the conductors are stacked on both sides of the flexible substrate so that the upper conductor is CLCPW, and the lower conductor is used as a connecting conductor. In this embodiment, the cover layer of the high frequency transmission line device is manufactured to have a total thickness of 176 μm. In the case of manufacturing FPC in this way, in particular, the connecting conductor 40 is preferably formed in the stepped portion 30c. It is preferable to form a total of three connecting conductors 40 as in 2c.

The structure analysis of the high frequency transmission line device according to the present embodiment was performed using Ansoft's High-Frequency Structure Simulator (HFSS). After fabrication of the device, the GSGSG (G: Ground, S: Signal) structure was used at both ends of the line to match the pre-mode impedance of each line to 100Ω, and the measurement was performed using the GSGSG pad for on-wafer probe measurement. 150 μm pitch). Through this, a 4-port single ended S-parameter was converted into a differential S-parameter to confirm the result.

3A and 3B show results of transmission characteristics in a common / differential mode of a 2-cell and 3-cell structure according to a cutoff frequency of 2 GHz. First, FIG. 3A shows an analysis result of insertion loss for a common mode. In the case of 2-cell at the cut-off frequency of 2 GHz, the insertion loss is -15dB in the case of 2-cell and -22.5dB in the case of 3-cell. This result is consistent with the increase in the amount of reflection of specific band energy as the discontinuity increases under Bragg conditions.

3b shows the results for insertion loss and return loss for differential mode signals. The insertion loss shows a flat characteristic and excellent pass characteristics over the analyzed frequency band. In addition, the S-parameter results for differential-common mode conversion show negligible mode conversion through this structure. In conclusion, the differential mode insertion loss at tens of MHz to hundreds of MHz, which is used for the actual digital signal transmission, is maintained within -0.5 dB, so that the high frequency common mode noise can be blocked together with the function of the serial data transmission method. have.

Although a preferred embodiment of the present invention has been described so far, those skilled in the art will be able to implement in a modified form without departing from the essential characteristics of the present invention. For example, the high frequency transmission line device according to the present invention includes two or more even-numbered leading conductors, so that the high frequency transmission line device can be applied to both high frequency transmission line devices for the transmission of differential mode signals (that is, balanced signals having the same size and opposite phase). have. In particular, the ground conductor formed on the dielectric substrate spaced apart from the line conductor at predetermined intervals may be a CPW structure formed on the same surface as the line conductor, or, conversely, may be a micro strip structure formed on a surface opposite to the surface on which the line conductor is formed. . However, in order to remove common mode noise introduced from the outside, an impedance change unit for the common mode is formed in at least one of the line conductor and the ground conductor.

In the above-described embodiment, the stepped portion 30c functions as an impedance changing portion, and the impedance changing portion is preferably formed periodically repeatedly along the high frequency transmission direction, and furthermore, the wavelength of the common mode frequency to be blocked is lambda _g. It is more preferable to have a length of λ _g / 4.

4A to 4C illustrate various embodiments in which an impedance change unit is formed in a high frequency transmission line element for balanced signal transmission. For example, as shown in FIG. 4A, the stepped portion 20a may be formed in the line conductor 20 to change the distance between the line conductor 20 and the ground conductor 30 without forming an impedance change portion in the ground conductor. Can be. In addition, as shown in FIG. 4B, the stepped portions 20a and 30c are formed in each of the line conductor 20 and the ground conductor 30 to thereby provide a wide area between the line conductor 20 and the ground conductor 30. It may be divided into a narrow area. Furthermore, as shown in FIG. 4C, the stepped portion 20a may be formed by simply changing the line width of the line conductor 20 without changing the profile of the ground conductor 30.

4A to 4C show examples of a CPW structure. On the contrary, a microstrip structure may be formed by forming a ground conductor on one surface of the dielectric substrate on which the line conductor is formed and on the other surface thereof. have. In this case, the step portion constituting the impedance change portion, either changing the interval (s) between the line conductors or the line width (w) of the line conductors, or the interval (s) between the line conductors and the line width of the line conductors (w) can be formed by varying all of them.

The high frequency transmission line device according to the present invention can effectively block the common mode noise introduced from the outside by using a periodic change to the even mode impedance while maintaining the odd mode impedance. The high frequency transmission line device according to the present invention effectively blocks the common mode noise of the frequency band corresponding to λ _g / 4 by applying Bragg conditions. In particular, the analysis of the three-cell structure, it was confirmed that can effectively block the -20dB common mode in the 1.7 GHz ~ 2.3 GHz band. This noise-blocking characteristic improves data transmission by solving electromagnetic interference problems in information equipment using radio frequency such as high frequency radiating parts such as built-in antenna of highly integrated information communication equipment and EMI (Electromagnetic Interference) by infrared communication in PC. Can be guaranteed.

Embodiments of the present invention described herein are to be considered in descriptive sense only and not for purposes of limitation, and the scope of the present invention is shown in the appended claims rather than the foregoing description, and all differences within the scope are equivalent to the present invention. It should be interpreted as being included.

Claims (12)

A high frequency transmission line element for balanced signal transmission, At least two line conductors formed on one surface of the dielectric substrate and extending in a high frequency transmission direction and spaced apart from each other; A ground conductor formed on the one surface of the dielectric substrate on which the line conductor is formed and spaced apart from the line conductor by a predetermined interval; When the wavelength of the common mode frequency to be cut off is λ _g , the ground conductor has a length of λ _g / 4 and the gap between the line conductor and the ground conductor is divided into a narrow region and a wide region along a high frequency transmission direction. And a stepped portion is formed on at least one of one side of the line conductor opposite to or one side of the ground conductor opposite to the line conductor. The high frequency transmission line device according to claim 1, wherein the stepped portion is formed by being periodically repeated along the high frequency transmission direction. delete The high frequency transmission line device of claim 1 or 2, wherein the ground conductor comprises a first ground conductor and a second ground conductor formed on one side of each of the line conductors. The semiconductor device of claim 4, further comprising a connection conductor formed on the other surface of the dielectric substrate opposite to the one surface of the dielectric substrate, wherein both ends of the connection conductor are respectively connected to the first ground conductor and the second ground conductor via the dielectric substrate. High frequency transmission line element, characterized in that. 6. The high frequency transmission line device according to claim 5, wherein the connection conductor is formed in a region where the gap between the line conductor and the ground conductor is narrow. The high frequency transmission line device of claim 1, wherein the dielectric substrate is formed of a flexible material. A high frequency transmission line element for balanced signal transmission, At least two line conductors formed on one surface of the dielectric substrate and extending in a high frequency transmission direction and spaced apart from each other, A ground conductor formed on the dielectric substrate and spaced apart from the line conductor, When the wavelength of the common mode frequency to be cut is λ _g and has a length of λ _g / 4, an impedance of the common mode to at least one of the line conductor and the ground conductor to remove the common mode noise introduced from the outside. A high frequency transmission line element, characterized in that the change portion is formed. The high frequency transmission line device as claimed in claim 8, wherein the impedance change unit is repeatedly formed along a high frequency transmission direction. delete The ground conductor of claim 8 or 9, wherein the ground conductor is formed on the one surface of the dielectric substrate on which the line conductor is formed, and the impedance change unit is spaced between the line conductors, the line width of each of the line conductors, or the And a high frequency transmission line element formed by changing at least one of a gap between a line conductor and the ground conductor. The ground conductor of claim 8 or 9, wherein the ground conductor is formed on the other surface of the dielectric substrate on which the line conductor is formed, and the impedance change unit is formed of at least one of a gap between the line conductors or a line width of the line conductors. A high frequency transmission line element formed by changing one.

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