JP2004146671A - Surface-mount common mode noise filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-mount common mode noise filter that suppresses common mode noise without exerting any bad influence upon the high-speed transmission signals at high-speed differential signal transmission through the USB 2.0, IEEE 1394, DVI, etc. <P>SOLUTION: This common mode filter is constituted by winding a pair of wires 1 and 2 having an interline distance (a) around the core section 12 of a drum core 11, and respectively electrically connecting the terminals of the wires 1 and 2 to the electrode sections 14 provided in the flanges 12 of the drum core 11 by providing a winding interval (b) between the wires 1 and 2. The ratio a/R of the interline distance (a) to the diameters (R) of the wires 1 and 2 is adjusted to a/R≥0.5, and the ratio b/R of the winding interval (b) to the diameters (R) of the wires 1 and 2 is adjusted to b/R≥0.5. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a common mode noise filter for suppressing a common mode noise such as a signal line, and particularly to a high speed difference such as USB 2.0, IEEE1394, DVI (used for connection of a liquid crystal display or the like) in a personal computer or the like. The present invention relates to a surface mount type common mode noise filter used for attenuating common mode noise passing through two signal lines in dynamic signal transmission.
[0002]
[Prior art]
Conventionally, as a common mode noise filter of this type, a structure in which a pair of wires is closely wound around a core portion of a magnetic or non-magnetic drum core is generally used. Japanese Patent Application Laid-Open Publication No. HEI 10-163556 discloses a structure in which a pair of parallel wires is integrally wound with an insulating material to form a pair. It should be noted, however, that the wires between the paired wires are arranged considerably closer to each other than the wire diameter.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2002-110428
[Problems to be solved by the invention]
In recent years, high-speed differential transmission such as DVI (TMDS) and IEEE 1394 (S800) has appeared in signal transmission between a personal computer and peripheral devices, and depending on the transmission characteristics of a common mode noise filter, a high frequency component of a transmission signal may be reduced. Since it has an adverse effect such as attenuation, it is difficult to use it for high-speed signals. Considering that the degree of influence on the transmission signal depends on (1) the signal cutoff frequency and (2) the characteristic impedance matching, the characteristic impedance cannot be adjusted according to the application at the signal cutoff frequency of about 1 GHz with the conventional common mode noise filter. Situation and can affect signal quality. For example, the transmission method DVI for connecting a liquid crystal display (LCD) to a personal computer has a resolution of SXGA and a transmission speed of 560 MHz. Therefore, considering the third and fifth harmonics, the third and fifth harmonics are considered. Then, it reaches the GHz band. A common mode noise filter having a frequency band of about 1 GHz (in other words, a signal cutoff frequency of about 1 GHz) attenuates these harmonics and deteriorates waveform quality. In order not to attenuate, it is necessary to extend the pass band (signal cutoff frequency) of the common mode noise filter. Also, it has been difficult to adjust the characteristic impedance according to each application with the conventional wire-wound common mode noise filter.
[0004]
In view of the above, the present invention provides a surface mount type common mode noise filter capable of suppressing common mode noise without adversely affecting a high speed transmission signal in high speed differential signal transmission such as USB2.0, IEEE1394, DVI and the like. The purpose is to provide.
[0005]
Other objects and novel features of the present invention will be clarified in embodiments described later.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a surface mount type common mode noise filter according to the invention of claim 1 of the present application winds a pair of wires having a line distance (a) around a core portion of a magnetic or non-magnetic drum core, A winding interval (b) is provided between the pair of wires, and terminals of the pair of wires are electrically connected to electrode portions provided on a flange portion of the drum core, respectively.
The ratio a / R of the distance between the wires (a) and the diameter (R) of the wire is:
a / R ≧ 0.5
And the ratio b / R of the winding interval (b) and the diameter (R) of the wire is:
b / R ≧ 0.5
It is characterized by being.
[0007]
The surface mount type common mode noise filter according to the invention of claim 2 of the present application is characterized in that, in claim 1, the diameter (R) of the wire is 30 μm ≦ R ≦ 50 μm.
[0008]
A surface-mounted common mode noise filter according to a third aspect of the present invention is characterized in that, in the first or second aspect, a magnetic or non-magnetic plate-like core is fixed between upper surfaces of both flange portions of the drum core.
[0009]
The surface mount type common mode noise filter according to the invention of claim 4 of the present invention is the surface mount type common mode noise filter according to claim 1, 2 or 3, wherein the electrode portions are provided at least on both sides of an outer end face of each flange portion. A wire drawing groove is formed at a position passing between the electrode portions on the upper surface or the lower surface, and the pair of wires are collectively passed through the wire drawing groove, separated and connected to the electrode portions at the both side positions. Features.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a surface mount type common mode noise filter according to the present invention will be described with reference to the drawings.
[0011]
1A and 1B show a first embodiment of a surface mount common mode noise filter according to the present invention. In this drawing, reference numeral 11 denotes a drum core made of a magnetic material (e.g., ferrite) or a non-magnetic material (e.g., a ceramic). Two electrode portions 14 are formed on each square flange portion 13 of the drum core 11 by metal plating, baking of a metal paste, or the like. The electrode portion 14 is formed continuously over the upper surface, the outer end surface, and the lower surface (mounting surface) of both ends of the rectangular flange portion 13.
[0012]
As shown in FIG. 2, a pair of wires (conductor wires) 1 and 2 having a line distance a are wound around the core portion 12 of the drum core 11 at a winding interval b. The ends of the wires 1 and 2 are connected (connected) to the upper surface of the electrode portion 14 at both ends of the rectangular flange portion 13 by thermocompression bonding or the like.
[0013]
After the winding of the wires 1 and 2, a magnetic or non-magnetic plate core 20 is fixed between the upper surfaces of both rectangular flange portions 13 of the drum core 11 with an adhesive or the like. The plate-shaped core 20 is provided so that the upper surface of the product can be flattened so as to be able to be sucked by the suction nozzle of the automatic mounting machine. This also contributes to reduction and improvement of common mode noise suppression characteristics.
[0014]
The distance a between the pair of wires 1 and 2 shown in FIG. 2, the winding interval b when the wires 1 and 2 are considered as a pair, and the diameter R of the wires 1 and 2 and the signal cutoff frequency and characteristic impedance. The relationship is discussed below.
[0015]
First, FIG. 3 shows the definition of the signal cutoff frequency of the common mode noise filter, and the 3 dB attenuation point of the Sdd21 characteristic (attenuation characteristic for the differential mode) is defined as the signal cutoff frequency.
[0016]
To increase the signal cut-off frequency, differential mode inductance (hereinafter, Ld hereinafter) and interline capacitance (hereinafter, C ₁₂₎ it is necessary to suppress the low. _Ld, the cutoff frequency _{C 12} is large low, Ld _Conversely, the cutoff frequency _{C 12} is small tends to be higher. In this embodiment, low Ld, changed the conventional winding method of winding in close contact with two wire rods for C ₁₂ implemented, to have a line-to-line distance a between the two wires 1 and 2, further It is wound at a fixed interval (with a winding interval b). As a result, coupling between the wires 1 and 2 loosen can improve the cutoff frequency by subtracting the C _12. The characteristic impedance can be adjusted by changing the line distance a and the winding interval b relative to the diameters of the wires 1 and 2 within the range permitted by the signal cutoff frequency.
[0017]
FIG. 4A shows the relationship between the a / R and the cutoff frequency when the winding interval b = 20 μm is fixed and the values are in the range of 0 μm ≦ a ≦ 60 μm and 30 μm ≦ R ≦ 50 μm. However, the core section of the drum core 11 (ferrite) has a length of 0.5 mm and a width of 0.8 mm, the plate-shaped core 20 is mounted, and the number of turns is 4 turns. If a / R ≧ 0.5, a cutoff frequency of 2.5 GHz or more can be secured.
[0018]
FIG. 4B shows the relationship between a / R and the characteristic impedance (measurement frequency 500 MHz) under the same conditions of a, b, R, the core, and the number of turns. The characteristic impedance is changed to a desired value by changing a / R. Can be set to In particular, the characteristic impedance can be variably set even in a region where the cut-off frequency is 2.5 GHz or more where a / R ≧ 0.5.
[0019]
FIG. 5A shows the relationship between b / R and the cutoff frequency when the line distance a = 20 μm is fixed and the values are in the range of 0 μm ≦ b ≦ 60 μm and 30 μm ≦ R ≦ 50 μm. However, the core and the number of turns are the same conditions as in FIG. If b / R ≧ 0.5, a cutoff frequency of 2.5 GHz or more can be secured.
[0020]
FIG. 5B shows the relationship between b / R and the characteristic impedance (measurement frequency 500 MHz) under the same conditions of a, b, R, the core and the number of turns, and the characteristic impedance is changed to a desired value by changing b / R. Can be set to In particular, the characteristic impedance can be variably set even in a region where the cutoff frequency is 2.5 GHz or more where b / R ≧ 0.5.
[0021]
Curve A in FIG. 7 is the Sdd21 frequency characteristic in the first embodiment shown in FIG. 1 (where a = 20 μm, b = 60 μm, R = 40 μm, and the differential mode inductance is 14 nH). It indicates that the frequency of 0.5 GHz or more has been secured.
[0022]
According to the first embodiment, the following effects can be obtained.
[0023]
(1) A pair of wires 1 and 2 having a wire distance a are wound around a core portion 12 of a magnetic or non-magnetic drum core 11 and a winding interval b is provided between the pair of wires. 2 are electrically connected to the electrode portions 14 provided on the square flange portion 13 of the drum core 11, respectively. Further, the ratio a / R of the distance a between the wires and the diameter R of the wires 1 and 2 is determined by:
a / R ≧ 0.5
And the ratio b / R of the winding interval b and the diameter R of the wires 1 and 2 is
b / R ≧ 0.5
, A common mode noise filter having a cutoff frequency of 2.5 GHz or more can be realized. Therefore, it can be used without adverse effects on high-speed differential signal transmission paths such as USB 2.0, IEEE 1394, and DVI. Although the diameter R of the wires 1 and 2 is about 20 μm to 200 μm, it is preferable to set the diameter R of the wires 1 and 2 to 50 μm or less in order to secure the number of turns when a micro product is targeted.
[0024]
(2) By fixing the magnetic or non-magnetic plate-shaped core 20 between the upper surfaces of both the rectangular flanges 13 of the magnetic or non-magnetic drum core 11, the upper surface of the product is made a flat surface, and is suctioned by the suction nozzle of the automatic mounting machine. If the magnetic material is used for both the drum core 11 and the plate-shaped core 20, the leakage magnetic flux can be reduced and the common mode noise suppression characteristics can be improved.
[0025]
FIGS. 6A and 6B show a second embodiment of the surface mount type common mode noise filter according to the present invention. In FIG. 6A, the lower surface (mounting surface) 14a of the electrode portion 14 provided on the rectangular flange portion 13 of the drum core 11 is shown facing upward. In this case, a wire-drawing groove 15 is formed which crosses the center of the lower surface 13a of the rectangular flange portion 13 where the lower surface 14a of the electrode portion 14 is located in the axial direction of the winding core, and a pair of wires 1 and 2 is inserted into the wire-drawing groove 15. They are separated from each other by passing them together (preferably pulled out in a state of being adjacent to each other and preferably in a parallel arrangement) and connected to the outer end surface 14b of the electrode portion 14 by thermocompression bonding or the like. The other configuration is the same as that of the above-described first embodiment, and the same or corresponding portions are denoted by the same reference characters and description thereof is omitted.
[0026]
In the second embodiment, the terminal mode of the pair of wires 1 and 2 is devised, so that the inductance in the differential mode can be made lower than in the first embodiment. For example, in the curve A (a = 20 μm, b = 60 μm, R = 40 μm) showing the first embodiment of FIG. 7, the differential mode inductance is 14 nH, but in the second embodiment, Under the same conditions of a, b, and R, the inductance in the differential mode can be reduced to 8 nH (43% reduction). Curve B in FIG. 7 is the Sdd21 frequency characteristic in the second embodiment (where a = 20 μm, b = 60 μm, R = 40 μm, and the differential mode inductance is 8 nH), and the attenuation for the differential signal. It can be seen that the cutoff frequency is higher than that of the curve A.
[0027]
In the second embodiment, the wire drawing groove 15 is formed at the center of the lower surface of the rectangular flange 13, but the wire drawing groove 15 is formed so as to cross the center of the upper surface of the rectangular flange in the axial direction of the core. Alternatively, the wires 1 and 2 may be passed through the wires.
[0028]
In addition, the electrode portion 14 in each embodiment can be configured by attaching a terminal fitting to the rectangular flange portion 13 in addition to metal plating, baking of a metal paste, or the like. The connection process can also be a process such as welding or soldering.
[0029]
Although the embodiments of the present invention have been described above, it will be obvious to those skilled in the art that the present invention is not limited to the embodiments and various modifications and changes can be made within the scope of the claims.
[0030]
【The invention's effect】
As described above, according to the present invention, a surface having a high cutoff frequency and capable of suppressing common mode noise without adversely affecting a high-speed transmission signal in high-speed differential signal transmission such as USB 2.0, IEEE 1394, or DVI. A mounting type common mode noise filter can be realized.
[Brief description of the drawings]
FIG. 1 is a first embodiment of a surface-mounted common mode noise filter according to the present invention, in which (A) is an exploded perspective view and (B) is a side view.
FIG. 2 is a longitudinal sectional view of a drum core and a winding portion according to the first embodiment.
FIG. 3 is a diagram illustrating Sdd21 frequency characteristics of the common mode noise filter and illustrating the definition of a signal cutoff frequency.
FIG. 4 is a diagram showing a distance between a pair of wires 1 and 2 in the first embodiment: a, a winding interval when the wires 1 and 2 are considered as a pair, and a diameter of the wires 1 and 2; 7A is a graph showing a relationship between a / R and transmission characteristics when R is set, and FIG. 7A is a graph showing a relationship between cutoff frequency and a / R, and FIG. 7B is a graph showing a relationship between characteristic impedance and a / R.
5A and 5B show a relationship between b / R and transmission characteristics in the first embodiment, wherein FIG. 5A shows a relationship between cutoff frequency and b / R, and FIG. 5B shows a relationship between characteristic impedance and b / R. It is a graph shown respectively.
FIG. 6 is a second embodiment of the surface mount common mode noise filter according to the present invention, in which (A) is an exploded perspective view in which the bottom side faces upward, and (B) is a side view.
FIG. 7 is an Sdd21 frequency characteristic diagram showing a frequency change of an Sdd21 characteristic in the case of the first and second embodiments.
[Explanation of symbols]
Reference numerals 1 and 2 Wire 11 Drum core 12 Core 13 Square flange 14 Electrode 15 Wire lead-out groove 20 Plate core

Claims (4)

A pair of wires having a wire distance (a) is wound around a core portion of a magnetic or non-magnetic drum core, and a winding interval (b) is provided between the pair of wires. A surface-mounted common mode noise filter electrically connected to an electrode provided on a flange of the drum core,
The ratio a / R of the distance between the wires (a) and the diameter (R) of the wire is:
a / R ≧ 0.5
And the ratio b / R of the winding interval (b) and the diameter (R) of the wire is:
b / R ≧ 0.5
A surface-mounted common mode noise filter characterized by the following. The diameter (R) of the wire is 30 μm ≦ R ≦ 50 μm
The surface mount type common mode noise filter according to claim 1, wherein 3. The surface-mounted common mode noise filter according to claim 1, wherein a magnetic or non-magnetic plate-shaped core is fixed between upper surfaces of both flange portions of the drum core. The electrode portion is provided at both sides of at least the outer end surface of each flange portion, and forms a wire drawing groove at a position passing between the electrode portions on an upper surface or a lower surface of the flange portion, and the pair of wires is 4. The surface-mounted common mode noise filter according to claim 1, wherein the common mode noise filter is connected to the electrode portions at both side positions after being collectively passed through the wire drawing groove.

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