JP4213694B2 - Filter element - Google Patents

Description

  The present invention relates to a filter element, and more particularly to a filter element suitable for use in removing common mode noise.

  In recent years, the USB 2.0 standard and the IEEE 1394 standard are widely used as high-speed signal transmission interfaces, and are used in many digital devices such as personal computers and digital cameras. Unlike the single-ended transmission method that has been common for a long time, interfaces such as the USB 2.0 standard and the IEEE 1394 standard adopt a differential signal method that transmits a differential signal using a pair of signal lines.

  The differential transmission system has an excellent feature that not only the radiation electromagnetic field generated from the signal line is small compared to the single-end transmission system, but also that the differential transmission system is less susceptible to external noise. For this reason, it is easy to reduce the amplitude of the signal, and by shortening the rise time and the fall time due to the small amplitude, it becomes possible to perform signal transmission at a higher speed than the single-ended transmission method.

  FIG. 7 is a circuit diagram of a general differential transmission circuit.

  The differential transmission circuit shown in FIG. 7 includes a pair of signal lines 11 and 12, an output buffer 13 that supplies differential signals to the signal lines 11 and 12, and an input buffer that receives differential signals from the signal lines 11 and 12. 14. With this configuration, the input signal IN given to the output buffer 13 is transmitted to the input buffer 14 via the pair of signal lines 11 and 12, and is reproduced as the output signal OUT. Such a differential transmission circuit has a feature that the radiated electromagnetic field generated from the signal lines 11 and 12 is small as described above, but noise common to the signal lines 11 and 12 (common mode noise) is generated. When superposed, a relatively large radiated electromagnetic field is generated. In order to reduce the radiated electromagnetic field generated by the common mode noise, it is effective to insert the common mode filter 20 into the signal lines 11 and 12 as shown in FIG.

The common mode filter 20 has a characteristic that the impedance to the differential component (signal) transmitted through the signal lines 11 and 12 is low and the impedance to the in-phase component (common mode noise) is high. For this reason, by inserting the common mode filter 20 into the signal lines 11 and 12, the common mode noise transmitted through the pair of signal lines 11 and 12 can be blocked without substantially attenuating the differential signal. As the common mode filter 20, for example, an element described in Patent Document 1 is known.
JP 2003-168611 A

  However, since the impedance of the common mode filter with respect to the in-phase component is generally high in the high frequency range and low in the low frequency range, there is a problem that the common mode noise in the low frequency range cannot be sufficiently removed. In order to solve such a problem, it is effective to connect a filter element 30 for bypassing low-frequency common mode noise between the signal lines 11 and 12 and the ground, as shown in FIG.

  As such a filter element 30, a common common mode filter can be used. As shown in FIG. 8, terminal electrodes 31 and 32 normally used as a pair of input terminals are respectively connected to the signal line 11 and the ground. The terminal electrodes 33 and 34 normally connected as a pair of output terminals may be connected to the ground and the signal line 12, respectively. As a result, the frequency characteristic for the in-phase component of the filter element 30 is the same as the frequency characteristic for the differential component of the common mode filter 20, so that a low impedance is obtained in a low frequency range. That is, low-frequency common mode noise can be bypassed to the ground.

  On the other hand, since the frequency characteristic for the differential component of the filter element 30 is the same as the frequency characteristic for the common-mode component of the common mode filter 20, a high impedance is obtained for the differential signal. Therefore, if such a filter element 30 is added, the frequency characteristics of the common mode filter 20 can be complemented and common mode noise can be removed over a wide area without substantially affecting the differential signal. It becomes possible.

  However, in order to use a general common mode filter as the filter element 30 shown in FIG. 8, it is necessary to use a different connection method as described above. However, the pattern will be significantly different from normal. For this reason, problems such as the symmetry of the signal lines 11 and 12 being lost and the occupied area of the wiring pattern on the substrate being increased more than necessary have occurred.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a filter element suitable for use as an element for bypassing low-frequency common mode noise.

A filter element according to one aspect of the present invention is a filter element that is bypass-connected between a pair of symmetrically arranged signal lines that constitute a differential transmission circuit and a ground, and is provided at a core part and both ends thereof. A drum-type core having the first and second flange portions, the first and second terminal electrodes formed on the first flange portion, and the third and second terminals formed on the second flange portion. 4 is wound in a predetermined direction from one end to the other end in the first region of the core part, one end is connected to the first terminal electrode, and the other end is connected to the third terminal electrode. The connected first coil and the second region different from the first region of the core portion are wound from one end to the other end in a direction different from a predetermined direction, and one end is a second terminal It is connected to the electrode, and a second coil whose other end is connected to the fourth terminal electrode, the first and second ends Electrodes are respectively connected to the pair of signal lines, third and fourth terminal electrodes are connected to ground, and wherein the number of turns and the number of turns of the second coil of the first coil is the same.

  Thus, the winding direction of the first coil starting from the first terminal electrode is opposite to the winding direction of the second coil starting from the second terminal electrode. By connecting the first and second terminal electrodes provided on the collar part to a pair of signal lines, and connecting the third and fourth terminal electrodes provided on the second collar part to the ground, a low It can be used as an element that bypasses common mode noise in the region.

  Furthermore, since the first coil and the second coil are respectively wound around different regions of the core part, the first coil and the second coil can be separately wound during manufacturing. It is also possible to increase the degree of freedom of winding work.

  In this case, it is preferable that the moving direction of the winding position from one end of the first coil to the other end and the moving direction of the winding position from one end of the second coil to the other end are the same direction. According to such a configuration, it becomes easy to make the entire length of the first coil equal to the entire length of the second coil, so that the symmetry of the first coil and the second coil can be enhanced. .

A filter element according to another aspect of the present invention is a filter element that constitutes a differential transmission circuit and is bypass-connected between a pair of symmetrically arranged signal lines and a ground. A drum core having first and second collars provided at both ends, first and second terminal electrodes formed on the first collar, and a second core formed on the second collar. The third and fourth terminal electrodes are wound around the core portion in a predetermined direction from one end to the other end, one end is connected to the first terminal electrode, and the other end is connected to the third terminal electrode. The first coil and the winding core portion are wound in a direction different from a predetermined direction along the first coil from one end to the other end, and one end is connected to the second terminal electrode, and a second coil whose other end is connected to the fourth terminal electrode, the first and second terminal electrodes respectively of the pair Line to be connected, the third and fourth terminal electrodes are connected to ground, and wherein the number of turns and the number of turns of the second coil of the first coil is the same.

  Even in such a configuration, the winding direction of the first coil starting from the first terminal electrode is opposite to the winding direction of the second coil starting from the second terminal electrode. The first and second terminal electrodes provided on the first collar are connected to a pair of signal lines, and the third and fourth terminal electrodes provided on the second collar are connected to the ground. Thus, it can be used as an element for bypassing low-frequency common mode noise.

  Further, since the first coil and the second coil are wound in parallel, the first coil and the second coil can be so-called bifilar wound at the time of manufacturing, and the efficiency of the winding work is increased. It is also possible. Further, by performing bifilar winding, the degree of coupling of the windings can be increased, the impedance between the transmission line and the ground can be lowered, and common mode noise can be bypassed to the ground more than in the split winding.

  In the filter element according to the present invention, the number of turns of the first coil and the number of turns of the second coil are preferably the same. According to this, it becomes possible to keep the symmetry of the pair of signal lines connecting the filter elements uniform.

  As described above, the filter element according to the present invention connects the first and second terminal electrodes provided in the first flange part to the pair of signal lines, and the third and second terminals provided in the second flange part. By connecting the terminal electrode 4 to the ground, it can be used as an element for bypassing low-frequency common mode noise. That is, on the substrate on which the filter element according to the present invention is to be mounted, the wiring patterns to be a pair of signal lines are collectively arranged on the first collar side, and the ground pattern is collectively arranged on the second collar side. Therefore, low-frequency common mode noise can be reduced without causing the problem that the symmetry of the pair of signal lines that transmit the differential signal is lost or the occupied area of the wiring pattern on the board is unnecessarily increased. It can be effectively removed.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  [First Embodiment]

  FIG. 1 is a schematic perspective view showing the structure of a filter element 100 according to a preferred first embodiment of the present invention.

  As shown in FIG. 1, the filter element 100 according to the present embodiment includes a drum core 110 and first and second coils 121 and 122. The drum core 110 includes a rod-shaped core portion 130 and first and second flange portions 141 and 142 provided at both ends thereof. First and second terminal electrodes 151 and 152 are formed on the first flange 141, and third and fourth terminal electrodes 153 and 154 are formed on the second flange 142. The material of the drum core 110 is not particularly limited, but it is preferable to use a material having high magnetic permeability, such as ferrite.

  The first and second coils 121 and 122 are wiring members in which the periphery of a conductor such as copper (Cu) is coated with an insulator, and both are wound around the core portion 130 of the drum core 110. More specifically, the first coil 121 is wound around the first region 131 of the core part 130, one end 121 a is connected to the first terminal electrode 151, and the other end 121 b is the first coil 121. 3 terminal electrodes 153. On the other hand, the second coil 122 is wound around the second region 132 of the core 130, one end 122 a is connected to the second terminal electrode 152, and the other end 122 b is the fourth terminal electrode 154. It is connected to the.

  As shown in FIG. 1, the first region 131 of the core portion 130 is a region located on the first flange portion 141 side (left side in FIG. 1) as viewed from the axial center portion 130 a of the core portion 130. Conversely, the second region 132 of the core portion 130 is a region located on the second flange 142 side (the right side of the page in FIG. 1) when viewed from the center portion 130a. Thus, in the present embodiment, the first and second coils 121 and 122 are wound around different regions. Note that the positional relationship between the first region 131 and the second region 132 is not limited to the above-described positional relationship, and may be reversed.

  In the present embodiment, the number of turns of the first coil 121 and the number of turns of the second coil 122 are both four. Of course, in the present invention, the number of turns of the first and second coils 121 and 122 is not limited to this, and may be any number of turns. However, in order to maintain the symmetry of the first and second coils 121 and 122, the number of turns of the first coil 121 and the number of turns of the second coil 122 need to be the same.

Further, when viewed from the arrow A shown in FIG. 1, the first coil 121 is wound clockwise (clockwise) from one end 121a to the other end 121b, and the second coil 122 has one end 122a. Is wound counterclockwise (counterclockwise) toward the other end 122b. As described above, one end 121a of the first coil 121 is connected to the first terminal electrode 151, and one end 122a of the second coil 122 is connected to the second terminal electrode 152, so that the first terminal The winding direction of the first coil 121 starting from the electrode 151 and the winding direction of the second coil 122 starting from the second terminal electrode 152 are opposite to each other.

  FIG. 2 is a circuit diagram showing a usage pattern of the filter element 100 according to the present embodiment.

  The circuit diagram shown in FIG. 2 is substantially the same as the circuit diagram shown in FIG. 8, but the arrangement of the terminal electrodes 151 to 154 provided on the filter element 100 is the normal filter element 30 (FIG. 8), the paired first and second terminal electrodes 151 and 152 are connected to the pair of signal lines 11 and 12, and the paired third and fourth terminal electrodes are 153 and 153, respectively. By connecting to 154 ground, it can be used as a filter that bypasses common mode noise. Here, “to be paired” means terminal electrodes formed on the same collar.

  That is, when a general common mode filter is used, it is necessary to connect the pair of signal lines 11 and 12 to terminal electrodes (more specifically, located on diagonal lines) formed on different flanges. Therefore, as shown in FIG. 3, it is necessary to bypass one of the pair of signal lines 11 and 12 (the signal line 11 in FIG. 3) on the substrate 190. Specifically, the pair of terminal electrodes 31 and 32 provided on the filter element 30 are connected to the signal line 11 and the ground GND, respectively, and the pair of terminal electrodes 33 and 34 are connected to the ground GND and the signal line 12 respectively. Therefore, the signal lines 11 and 12 cannot be arranged symmetrically and in parallel. As a result, the area occupied by the wiring pattern increases, and the signal quality is degraded due to the loss of symmetry.

  On the other hand, if the filter element 100 according to the present embodiment is used, the pair of signal lines 11 and 12 can be laid in parallel on the substrate 190 as shown in FIG. There is no need for detours. Therefore, the occupied area of the wiring pattern on the substrate 190 does not increase more than necessary, and high symmetry can be ensured. As a result, it is possible to simultaneously reduce the size of the entire apparatus and improve the signal quality.

  In the present embodiment, since the first coil 121 and the second coil 122 are wound around different regions 131 and 132 of the core part 130, respectively, the first coil 121 and the second coil 122 are manufactured at the time of manufacture. The coils 122 can be wound separately. Thereby, it is also possible to increase the degree of freedom of the winding work.

  Furthermore, in the filter element 100 according to the present embodiment, the winding position of both the first coil 121 and the second coil 122 moves from the one end 121a, 122a to the other end 121b, 122b, as indicated by the arrow a shown in FIG. It is wound to move in the direction of. According to such a winding method, since it becomes easy to make the total length of the first coil 121 and the total length of the second coil 122 equal, the first coil 121 and the second coil 122 are symmetrical. It is possible to improve the signal quality and contribute to the improvement of the signal quality.

  However, in the present invention, it is not essential to employ the above-described winding method. As illustrated in FIG. 5, the winding position of the first coil 121 increases from one end 121a to the other end 121b. The second coil 122 is wound so as to move in the direction of arrow a shown in FIG. 5, and the winding position moves in the direction of arrow b shown in FIG. 5 as it goes from one end 122 a to the other end 122 b. It may be wound so as to move.

  [Second Embodiment]

  FIG. 6 is a schematic perspective view showing the structure of a filter element 200 according to the second preferred embodiment of the present invention.

  The filter element 200 according to the present embodiment is different from the filter element 100 according to the above-described embodiment in the winding method of the first coil 121 and the second coil 122. Since the other points are the same as those of the filter element 100 according to the above-described embodiment, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 6, in the filter element 200 according to the present embodiment, the first coil 121 and the second coil 122 are not wound in different regions, but are so-called bifilar wound in the same region. . That is, the first coil 121 and the second coil 122 are wound in parallel along each other. However, the connection relationship between the coils 121 and 122 and the terminal electrodes 151 to 154 is the same as that of the filter element 100 according to the above embodiment. That is, one end and the other ends 121a and 121b of the first coil 121 are connected to the first and third terminal electrodes 151 and 153, respectively, and one end and the other ends 122a and 122b of the second coil 122 are respectively connected to the first and second terminal electrodes 151 and 153. The second and fourth terminal electrodes 152 and 154 are connected.

  For this reason, when viewed from the arrow A shown in FIG. 6, the winding direction of the first coil 121 is counterclockwise (counterclockwise) from the one end 121a to the other end 121b. The directions are clockwise (clockwise) from one end 122a to the other end 122b, and are opposite to each other. This is the same as the filter element 100 according to the above embodiment.

  Therefore, the filter element 200 according to the present embodiment has the same function as the filter element 100 according to the above-described embodiment in terms of circuit. However, the filter element 200 according to the present embodiment can wind the first coil 121 and the second coil 122 together at the time of manufacture. Efficiency can be increased.

  Also in this embodiment, the number of turns of the first coil 121 and the number of turns of the second coil 122 are both four, whereby the symmetry of the first and second coils 121 and 122 is maintained. ing.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, the winding directions of the first and second coils 121 and 122 are not particularly limited as long as they are opposite to each other.

1 is a schematic perspective view showing a structure of a filter element 100 according to a preferred first embodiment of the present invention. 4 is a circuit diagram showing a usage pattern of the filter element 100. FIG. It is a figure for demonstrating the wiring pattern on a board | substrate in the case of using a common common mode filter. It is a figure for demonstrating the wiring pattern on a board | substrate in the case of using the filter element 100. FIG. 6 is a schematic perspective view showing a modification of the filter element 100. FIG. It is a schematic perspective view which shows the structure of the filter element 200 by preferable 2nd Embodiment of this invention. It is a circuit diagram of a general differential transmission circuit. It is the figure which added the element 30 which bypasses the low-frequency common mode noise to the circuit of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 12 Signal line 13 Output buffer 14 Input buffer 20 Common mode filter 100, 200 Filter element 110 Drum type core 121 First coil 121a First coil one end 121b First coil other end 122 Second coil 122a One end 122b of the second coil The other end 130 of the second coil 130 The core part 130a The central part 131 in the axial direction of the core part 131 The first area 132 The second area 141 The first collar 142 The second collar 151 First terminal electrode 152 Second terminal electrode 153 Third terminal electrode 154 Fourth terminal electrode 190 Substrate

Claims (3)

A filter element that constitutes a differential transmission circuit and is bypass-connected between a pair of symmetrically arranged signal lines and a ground,
A drum core having a core part and first and second flanges provided at both ends of the core part;
First and second terminal electrodes formed on the first flange;
Third and fourth terminal electrodes formed on the second flange;
In the first region of the core part, it is wound in a predetermined direction from one end to the other end, the one end is connected to the first terminal electrode, and the other end is connected to the third terminal electrode. A first coil formed;
In the second region different from the first region of the core, the wire is wound from one end to the other end in a direction different from the predetermined direction, and the one end is connected to the second terminal electrode. A second coil having the other end connected to the fourth terminal electrode ,
The first and second terminal electrodes are respectively connected to the pair of signal lines, the third and fourth terminal electrodes are connected to the ground, and the number of turns of the first coil and the second coil A filter element having the same number of turns .   The moving direction of the winding position from the one end to the other end of the first coil and the moving direction of the winding position from the one end to the other end of the second coil are the same direction. The filter element according to claim 1. A filter element that constitutes a differential transmission circuit and is bypass-connected between a pair of symmetrically arranged signal lines and a ground,
A drum core having a core part and first and second flanges provided at both ends of the core part;
First and second terminal electrodes formed on the first flange;
Third and fourth terminal electrodes formed on the second flange;
The winding core is wound in a predetermined direction from one end to the other end, the one end is connected to the first terminal electrode, and the other end is connected to the third terminal electrode. Coils,
The winding core portion is wound in a direction different from the predetermined direction along the first coil from one end to the other end, the one end is connected to the second terminal electrode, A second coil having the other end connected to the fourth terminal electrode ,
The first and second terminal electrodes are respectively connected to the pair of signal lines, the third and fourth terminal electrodes are connected to the ground, and the number of turns of the first coil and the second coil A filter element having the same number of turns .

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