JP4803173B2 - Circuit board - Google Patents

Description

  The present invention relates to a circuit board including a ground through which a return current from an electronic circuit passes and whose shape is not constant, and more particularly, an EMI removal filter that removes common mode noise generated due to a change in ground shape. It is related with the circuit board which has this.

  For example, as shown in FIGS. 6A and 6B, the circuit board is mounted on the dielectric substrate (transmission line 1 formed on one main surface (upper surface) of the dielectric substrate (not shown)). The transmission unit 2 and the reception unit 3 respectively connected to both ends of the transmission line 1 and the ground 4 formed on the other main surface (lower surface) of the dielectric substrate so that the return current from the reception unit 3 passes therethrough. And an electronic circuit. In the case of a high-frequency electronic circuit, noise is likely to be generated in the transmission unit 2 that transmits a high-frequency signal, and the noise generated in the transmission unit 2 is received via the transmission line 1 while being superimposed on the high-frequency signal from the transmission unit 2. Noise is radiated into the space by being transmitted to the unit 3 or using the transmission line 1 as an antenna, and electromagnetic interference is generated. Therefore, an EMI removal filter 5 is provided on the transmission line 1, and noise is removed by the EMI removal filter 5. As described in Non-Patent Document 1, the EMI removal filter 5 is generally provided immediately after the receiving unit 3 and suppresses superimposition of noise on a high-frequency signal and emission to space.

  The electronic circuits shown in FIGS. 6A and 6B are configured as differential signal circuits. In the differential signal circuit, the transmission line 1 connecting the transmission unit 2 and the reception unit 3 is composed of two transmission lines 1A and 1B. The high-frequency signals passing through the two transmission lines 1A and 1B are transmitted as signals of the same level with opposite phases. However, in the two transmission lines 1A and 1B, the balance between the high-frequency signals is lost due to variations in impedance, and common mode noise is generated. Therefore, for example, a common mode choke coil 5 is provided immediately after the transmission unit 2 as an EMI removal filter.

"Countermeasures for noise suppression by EMIFIL" (p2-p21) Noise suppression application materials published by Murata Manufacturing Co., Ltd.

  However, on the circuit board, for example, as shown in FIG. 6A, the shape of the ground 4 is not constant, and the shape of the ground 14 suddenly changes from the narrow line portion 4A to the wide widened portion 4B in the course of the return current. When this is changed, this shape change portion (the boundary between the line portion 4A and the widened portion 4B) becomes a common mode noise generation source 6 (see FIG. 6B). Even if the EMI removal filter 5 is provided at a position corresponding to the portion 4B, the common mode noise caused by the shape change of the ground 4 is generated on the receiving unit 3 side from the EMI removal filter 5, so the EMI removal filter 5 causes the common mode noise to be generated. There was a problem that it was difficult to remove noise. In particular, when a high frequency signal of several hundred MHz or higher is used, common mode noise is likely to occur due to a sudden change in the ground shape. In FIG. 6B, the line portion 4A of the ground 4 is indicated by a thin line, and the widened portion 4B is indicated by a thick line.

The present invention has been made to solve the above-described problem, and includes a differential signal circuit having two transmission lines for transmitting a differential signal between a transmitter and a receiver and a ground for passing a return current. When the shape of the ground changes in the middle of the return current (between the receiving unit and the transmitting unit), it is possible to provide a circuit board that can reliably suppress noise generated due to the shape change. It is aimed.

The circuit board according to claim 1 of the present invention includes an electronic circuit having a transmission line for transmitting a signal between the transmitter and the receiver and a ground for passing a return current, and the shape of the ground In the circuit board that changes between the receiving unit and the transmitting unit, the electronic circuit is a differential signal circuit, and among the grounds, the shape of the ground changes and noise due to the shape change occurs. An EMI removal filter is mounted at a position that deviates from the generated shape change portion toward the receiver, and the EMI removal filter is attached to at least two pairs of transmission lines through which a differential signal of the differential signal circuit is transmitted. It is characterized by being connected.

A circuit board according to a second aspect of the present invention is the circuit board according to the first or second aspect, wherein the transmission line includes a connection portion with a cable.

The circuit board according to claim 3 of the present invention is the circuit board according to claim 1 or 2 , wherein the electronic circuit is a differential signal circuit, and the differential signal circuit is used as the EMI removal filter. A trifilar coil is connected to each transmission line through which the differential signal is transmitted and the ground.

A circuit board according to a fourth aspect of the present invention is the circuit board according to any one of the first to third aspects, wherein the width of the ground to which the EMI removal filter is connected is reduced to the EMI removal. The width of the land portion of the filter is the same as that of the filter.

A circuit board according to claim 5 of the present invention is the circuit board according to any one of claims 1 to 3, wherein the width of the ground on which the EMI removal filter is mounted is set to be the EMI removal. It is characterized by being gradually changed in accordance with the width of the land portion of the filter.

According to the present invention, the differential signal circuit having a ground for the passage of the two transmission lines and the return current for transmitting differential signals between the transmitter and receiver, through the shape of the ground by the return current When changing in the middle (between the receiving unit and the transmitting unit), it is possible to provide a circuit board capable of reliably suppressing noise generated due to the shape change in the two transmission lines .

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows one Embodiment of the circuit board of this invention, (a) is the top view, (b) is the circuit diagram. It is a graph which shows the relationship between the frequency of noise, a noise level, and the attachment position of an EMI removal filter. It is a circuit which shows other embodiment of the circuit board of this invention. 4A and 4B are plan views showing a ground to which the EMI removal filter shown in FIG. 3 is connected, in which FIG. 4A is an enlarged view of a main part thereof, and FIG. 4B is a view showing a form different from FIG. It is a circuit diagram which shows other embodiment of the circuit board of this invention. It is a figure which shows an example of the conventional circuit board, (a), (b) is a figure respectively equivalent to (a), (b) of FIG.

Explanation of symbols

10, 10A, 10B Circuit board 11 Transmission line 14 Ground 14A Line part 14B Widened part 15 Common mode choke coil, trifilar coil (EMI removal filter)
151, 152 Common mode choke coil (EMI suppression filter)

  Hereinafter, the present invention will be described based on the embodiment shown in FIGS.

First Embodiment A circuit board 10 according to this embodiment includes a differential signal formed on the upper surface of a dielectric substrate (not shown) for transmitting a high-frequency signal, for example, as shown in FIG. The transmission line 11, the transmission unit 12 and the reception unit 13 connected to both ends of the differential signal transmission line 11 and mounted on the dielectric substrate, and the return current from the reception unit 13 side to the transmission unit 12 side pass. Thus, a differential signal circuit having a ground 14 formed on the lower surface of the dielectric substrate is provided.

  In this embodiment, since the electronic circuit is configured as a differential signal circuit as shown in FIGS. 1A and 1B, the differential signal transmission line 11 connecting the transmission unit 12 and the reception unit 13 is respectively It is comprised by two transmission lines 11A and 11B which transmit a high frequency signal. As shown in the figure, the ground 14 has a narrow line portion 14A extending from the receiving unit 13 side to the transmitting unit 12 side, and a widened portion 14B having a width that suddenly increases from the line unit 14A on the transmitting unit 12 side. And is formed. In FIG. 1B, the line portion 14A of the ground 14 is indicated by a thin line, and the widened portion 14B is indicated by a thick line.

  As shown in FIG. 1 (a), since the shape of the ground 14 changes abruptly between the line portion 14A and the widened portion 14B, the change in potential when the return current passes through the widened portion 14B from the line portion 14A. For example, common mode noise is generated at the boundary between the line portion 14A and the widened portion 14B. Therefore, in the present embodiment, the common mode choke coil 15 as the EMI removal filter is mounted on the dielectric substrate at a position deviated from the boundary between the line portion 14A and the widened portion 14B of the ground 14 toward the receiving portion 13 and differentially mounted. The signal transmission line 11 is connected to each transmission line 11A, 11B.

  In the present embodiment, the common mode choke coil 15 is connected to the transmission lines 11A and 11B of the differential signal transmission line 11 at a position deviated from the boundary between the line part 14A and the widened part 14B of the ground 14 to the receiving part 13 side. Therefore, common mode noise due to the shape change of the ground 14 is generated between the transmitter 12 and the common mode choke coil 15. Therefore, since the common mode noise generated due to the shape change of the ground 14 is superimposed on the high frequency differential signal transmitted from the transmission unit 12 and passes through the common mode choke coil 15, the common mode noise is transmitted to the transmission unit 12. It is removed by the common mode choke coil 15 together with common mode noise caused by the imbalance between the two differential signals.

  As the common mode choke coil 15 is arranged closer to the receiving unit 13 side, the differential signal transmission line 11 from the transmission unit 12 to the common mode choke coil 15 becomes longer. In order to function as an antenna and radiate common mode noise, the common mode choke coil 15 is preferably disposed on the line portion 14A as close to the widened portion 14B as possible. In addition, the arrow shown with the broken line in (b) of FIG. 1 has shown the transmission direction of common mode noise. The same applies to the other drawings.

  In order to verify the noise suppression effect when the common mode choke coil (EMI removal filter) 15 is provided in the line portion 14A of the ground 14, the mounting position of the common mode choke coil with respect to the ground 14 is shown in FIG. Thus, the noise generated in each circuit board 10 was measured using the 3m method in an anechoic chamber, and the measurement results are shown in FIG. Mounting 1 shows the measurement result of this embodiment in which the EMI removal filter 15 is mounted on the line portion 14A of the ground 14 as shown in FIG. 1, and Mounting 2 mounts the EMI removal filter on the boundary between the ground line portion and the widened portion. As shown in FIG. 6, the mounting 3 shows the measurement result when the EMI removal filter 15 is mounted immediately after the transmitter 2 in the widened portion 4B of the ground 4 as shown in FIG. .

  According to the result shown in FIG. 2, the noise level can be remarkably suppressed in the mounting 3 (immediately after the transmission unit 2 in the widened portion 4B) as compared with the case where the EMI removal filter is not mounted. In the case of), it was found that noise can be further suppressed in comparison with the mounting 3 in a wide frequency band, and that noise can be suppressed more than in the mounting 2 (the boundary between the line portion 14A and the widened portion 14B). That is, in the mounting 2, noise generated at the ground shape change portion (boundary portion between the line portion 14 </ b> A and the widened portion 14 </ b> B) cannot be sufficiently removed, and it is more distant from the shape change portion toward the receiving unit 13. It was found that the noise suppression effect is high.

  As described above, according to the present embodiment, the transmission line 11 that transmits the high-frequency differential signal from the transmission unit 12 to the reception unit 13, and the ground 14 that passes the return current from the reception unit 13 to the transmission unit 12. , The transmission direction of the high-frequency differential signal from the portion (boundary between the line portion 14A and the widened portion 14B) where the shape of the ground 14 changes suddenly in the middle of the direction in which the return current passes. Since the common mode choke coil 15 is connected to the differential signal transmission line 11 at a position that is biased toward the receiving unit 13 in the same direction, even if common mode noise occurs due to a change in the shape of the ground 14, this common The mode noise can be removed by the common mode choke coil 15 to suppress the noise.

Second Embodiment Since the circuit board of this embodiment is configured in the same manner as the circuit board 10 of the first embodiment except that the EMI removal filter is different, this embodiment differs from the first embodiment in this embodiment. The same or corresponding parts are denoted by the same reference numerals and will be described with reference to FIG.

  As shown in FIG. 3, the circuit board 10 </ b> A of the present embodiment includes a differential signal circuit including a differential signal transmission line 11, a transmission unit 12, a reception unit 13, a ground 14, and an EMI removal filter 15. In the present embodiment, two first and second common mode choke coils 151 and 152 are used as the EMI removal filter 15. As in the first embodiment, the first and second common mode choke coils 151 and 152 are both dielectric substrates at positions deviating from the boundary between the line portion 14A and the widened portion 14B of the ground 14 toward the receiving portion 13 side. Has been implemented. The first common mode choke coil 151 is connected to one transmission line 11A of the differential signal transmission line 11 and the line portion 14A of the ground 14, and the second common mode choke coil 152 is connected to the other transmission of the differential signal transmission line 11. The line 11B and the ground line 14 are connected to the line part 14A.

  In the present embodiment, the first common mode choke coil 151 is connected to one transmission line 11A of the differential signal transmission line 11 and the line part 14A of the ground 14 in the line part 14A near the receiving part 13 from the widened part 14B of the ground 14. Since they are respectively connected, not only common mode noise superimposed on the differential signal transmitted from the transmission unit 12 through the transmission line 11A but also common mode noise generated due to the shape change of the ground 14 is transmitted to the transmission line 11A. It can be removed at both grounds 14. The second common mode choke coil 152 is connected to the other transmission line 11B of the differential signal line 11 and the line part 14A of the ground 14 in the line part 14A near the receiving part 13 from the widened part 14B of the ground 14. Therefore, not only common mode noise superimposed on the differential signal transmitted from the transmission unit 12 through the transmission line 11B but also common mode noise generated due to the shape change of the ground 14 is transmitted to both the transmission line 11B and the ground 14. Can be removed.

  Further, in the present embodiment, in order to suppress the generation of noise due to the shape change of the ground 14, the terminals (not shown) of the first and second common mode choke coils 151 and 152, the line portion 14 </ b> A of the ground 14, 4 is devised as shown in FIGS. 4A and 4B in accordance with the width of the line portion 14A of the ground 14. That is, in the case of the connection structure shown in FIG. 4A, the land portion 14C, which is the connection portion of the line portion 14A of the ground 14 to each terminal of the first common mode choke coil 151, is substantially the same as the line portion 14A. Are formed to have the same width. Thus, since the width of the land portion 14C is formed substantially the same as the width of the line portion 14A, there is no shape change between the line portion 14A and the land portion 14C, and unnecessary due to the shape change. Generation of noise can be suppressed.

  When the width of the line portion 14A of the ground 14 is wider than the width of the land portion 14C, as shown in FIG. 4B, a tapered portion where the width of the line portion 14A gradually narrows in accordance with the width of the land portion 14C. 14D is provided in the connection part with the land part 14C, and the terminal width of the taper part 14D is made to coincide with the width of the land part 14C. Even if the width of the land portion 14C is narrower than the width of the line portion 14A, the taper portion 14D can suppress a sudden shape change in the portion from the line portion 14A to the land portion 14C, and unnecessary noise caused by this portion can be suppressed. Can be suppressed. Further, when the width of the line portion is narrower than the width of the land portion, a tapered portion whose width gradually increases from the line portion toward the land portion may be provided at the connection portion with the land portion.

  According to this embodiment, in the line portion 14A near the receiving portion 13 from the widened portion 14B of the ground 14, the corresponding terminals of the first and second common mode choke coils 151 are connected to the transmission lines 11A of the differential signal transmission line 11, 11B and the other corresponding terminals of the first and second common mode choke coils 151 and 152 are individually connected to the line portions 14A and 14A of the ground 14, respectively. The common mode noise generated due to the shape change of the ground 14 by the coils 151 and 152 can be reliably removed in both the differential signal transmission line 11 and the ground 14.

  Further, according to the present embodiment, the width of the line portion 14A of the ground 14 is formed substantially the same as the width of the land portion 14C connecting the terminals of the first and second common mode choke coils 151 and 152. Since the width of the line portion 14A does not substantially change in the mounting portions of the first and second common mode choke coils 151 and 152, the occurrence of common mode noise in these portions can be suppressed or prevented. When the width of the line portion 14A of the ground 14 is wider than the land portion 14C of the first and second common mode choke coils 151 and 152, the land portions of the first and second common mode choke coils 151 and 152 are used. Since the tapered portion 14D that gradually narrows the width of the line portion 14A according to the width of 14C is provided, it is possible to suppress or prevent the occurrence of common mode noise in this portion by suppressing a sudden shape change of the ground 14. it can.

Third Embodiment The circuit board of this embodiment is configured in the same manner as the circuit boards 10 and 10A of the first and second embodiments except that the transmission line and the EMI removal filter are different. In the embodiment, the same or corresponding parts as those in the first and second embodiments are denoted by the same reference numerals and described with reference to FIG.

  As shown in FIG. 5, the circuit board 10 </ b> B of this embodiment includes a differential signal circuit including a transmission line 11, a transmission unit 12, a reception unit 13, a ground 14, and an EMI removal filter 15. In this embodiment, the trifilar coil 15 is used as the EMI removal filter 15. As shown in FIG. 5, the trifilar coil 15 includes three coils, that is, first, second, and third coils 15A, 15B, and 15C. The trifilar coil 15 is mounted on a dielectric substrate at a position deviating from the boundary between the line portion 14A and the widened portion 14B of the ground 14 toward the receiving portion 13 side.

That, tri filer coil 15, the first coil 15A is connected to one transmission line 11A of the differential signal transmission line 11, the second coil 15B is connected to the other transmission line 11B of the differential signal transmission line 11, The third coil 15C is connected to the line portion 14A of the ground 14. Therefore, the trifilar coil 15 has substantially the same function as the first and second common mode choke coils 151 and 152 in the second embodiment. The connection structure between the terminal of the third coil 15C and the ground 14 is devised in the same way as in the second embodiment.

  According to the present embodiment, the trifilar coil 15 is connected to both the differential signal transmission line 11 and the line part 14A at a position deviated from the boundary between the line part 14A and the widened part 14B of the ground 14 to the receiving part 13 side. The trifilar coil 15 functions in substantially the same manner as the first and second common mode choke coils 151 and 152 in the second embodiment, and is generated in the common mode caused by the shape change of the ground 14 in the circuit board 10B. The noise can be reliably removed and suppressed by the trifilar coil 15, and the same effect as the first and second embodiments can be expected.

  The present invention is not limited to the above embodiments. In each of the above embodiments, the differential signal circuit having the differential signal transmission line 11 is described as an example of the electronic circuit. However, the present invention is also applied to an electronic circuit having a single-line transmission line other than the differential signal circuit. can do. In this case, the common mode noise generated due to the change in the shape of the ground can be removed and suppressed by connecting the EMI removal filter to both the transmission line and the ground.

  Moreover, although each said embodiment demonstrated the case where a high frequency signal was transmitted from the transmission part 12 to the receiving part 13 via the differential signal transmission track | line 11, this case also when a circuit board has a connection part with a cable. The invention can be applied. That is, if there is a connection part with a cable on the circuit board, this connection part becomes a signal generation source in the circuit board and transmits a high-frequency signal to the reception part. Therefore, a return current from the reception part to the connection part with the cable is generated. If there is a shape change part in the passing ground, common mode noise caused by this part is generated. Therefore, also in this case, the common mode noise generated due to the change in the shape of the ground can be removed and suppressed by taking the same measures as in the above embodiments.

  In each of the above embodiments, a trifiler coil or a common mode choke coil has been described as an example of an EMI removal filter. However, any filter that can remove common mode noise generated based on a change in the shape of the ground. Various types of filters can be used.

  The present invention can be widely used for circuit boards having a ground in which the shape of the ground through which a return current passes is not constant.

Claims (5)

  A circuit board having an electronic circuit having a transmission line for transmitting a signal between a transmission unit and a reception unit and a ground for passing a return current, the shape of the ground changing between the reception unit and the transmission unit In the above, the electronic circuit is a differential signal circuit, and of the ground, the shape of the ground changes and a position where noise is generated due to the shape change is shifted to the receiving unit side. A circuit board, wherein an EMI removal filter is mounted and the EMI removal filter is connected to at least two pairs of transmission lines through which a differential signal of the differential signal circuit is transmitted. The circuit board according to claim 1, wherein the transmission line includes a connection portion with a cable. It said electronic circuit is a differential signal circuit, claims, characterized in that the as EMI filters, connecting the birds filer coil on each transmission line and the ground differential signal of the differential signal circuit is transmitted The circuit board according to claim 1 or 2 . 4. The circuit board according to claim 1 , wherein a width of the ground to which the EMI removal filter is connected is the same as a width of a land portion of the EMI removal filter. 5. The width of the ground in which the EMI filters are mounted, according to any one of claims 1 to 3, characterized in that gradually changed according to the width of the land portion of the EMI filters Circuit board.

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