JP4956057B2 - Differential impedance matching printed wiring board - Google Patents

Description

  The present invention relates to a printed wiring board capable of matching differential impedance, and in particular, differential impedance matching printing excellent in suppressing fluctuation of differential impedance and reducing signal reflection in an opening of a differential transmission line. It relates to a wiring board.

  2. Description of the Related Art In recent years, various electric devices have been enhanced in functionality from communication devices such as mobile phones to home appliances. Along with these higher functions, higher speed and higher frequency response in printed wiring boards are required, and differential transmission lines are often used as transmission lines used in printed wiring boards.

  In order to make the differential transmission function effectively, it is important to control the differential impedance with high accuracy and to match the termination resistance. Therefore, it is important to keep the width and the distance between the pair wirings constant for the paired wirings that perform differential transmission.

  Until now, many techniques have been disclosed regarding the pair wiring for performing the differential transmission.

  For example, in Patent Document 1 described later, even when a via is provided in a pair of differential transmission lines, the problem is provided on a substrate with the object of suppressing a shift in impedance and preventing the collapse of a signal waveform. A pair of differential transmission lines, a pair of vias provided in the substrate in a direction perpendicular to the extending direction of the differential transmission lines, and a pair of differential transmission lines In a circuit board comprising a pair of connection lines each extending toward a corresponding pair of vias, the shape of the pair of connection lines in plan view is symmetrical with respect to the center line of the pair of differential transmission lines A technique to be solved by providing is disclosed.

  Further, in Patent Document 2 described later, by devising the pattern layout, the noise caused by the generation of the differential signal line and the clock line can be reduced without using dedicated parts necessary for noise countermeasures, and the development man-hours can be reduced. In order to provide a printed circuit board capable of reducing the number of the printed circuit boards, the problem is solved by using a differential signal circuit or the like on a printed circuit board on which a wiring pattern of signal lines that operate differentially is formed. The book patterns are laid out in parallel and close to each other. The other signal lines are laid out at a position as far as possible from the differential signal lines. In addition, using a multilayer board, placing differential signal lines in the power supply layer suppresses unwanted radiation noise, prevents crosstalk, and avoids further multilayering of the board, making the wiring pattern thinner. A technique for solving the problem by preventing the problem is disclosed.

  However, in the actual circuit pattern, there has been a problem that the differential impedance greatly fluctuates due to the connection with the pad or the terminating resistor at the end of the transmission line or the connection with the connector of the differential transmission characteristic evaluation circuit. . The problem will be described with reference to FIG.

  In the differential transmission line 61 through which the differential signal is transmitted from the input end A1 and the input end A2 to the output end B1 and the output end B2 via the line space 62, a resistor is provided ahead of the output end B1 and the output end B2. When a component such as this is connected, the interval between the wirings of the differential transmission line 61 must be opened with the line opening 63 as a base point in accordance with the shape of the component.

  In such a case, the differential impedance varies greatly and is affected by signal reflection. Further, the influence of the signal reflection here may cause a malfunction of an IC or the like mounted on the printed wiring board.

  Further, the influence of the signal reflection here is a significant influence in the environment of high-speed transmission or high-frequency signal, and is a problem because the change in differential impedance becomes large in the printed wiring board processed with fine wiring. .

The above-mentioned problems are caused by the fact that the printed wiring board is required to be high-speed and high-frequency compatible, and in electronic devices that will be miniaturized and speeded up in the future, differential impedance control is required to be controlled with higher accuracy. In the background, it is a problem to be solved.
JP 2006-032513 A JP 2001-267701 A

  Based on the above background, the problem to be solved by the present invention is to suppress differential impedance fluctuations and reduce signal reflection at the line opening where the differential transmission line expands as components are mounted. It is an object of the present invention to provide a differential impedance matching printed wiring board which is advantageous in making it.

  The inventor has made various studies in order to solve the above problems. As a result, when there is a line expansion region in which the differential transmission line expands in the output end direction of the pair of differential transmission lines, the feedback current passes through the feedback current space along the line expansion region. It has been found that extremely good results can be obtained by arranging the patterns, and the present invention has been completed.

That is, according to the present invention, a pair of differential transmission lines (1a) and (1b) is provided, and the differential transmission lines (1a) are arranged in the direction of the output ends B1 and B2 of the differential transmission lines (1a) and (1b). , (1b) in the printed wiring board provided with the line expansion region (3) , another conductor wiring is provided via the feedback current space (5) along the line expansion region (3). Is a single floating island-like feedback current pattern (7) that is not electrically connected to the differential transmission line (1a), (1b) inside or / and outside the differential. The above problems are solved by an impedance matching printed wiring board.

  Further, the present invention provides a differential impedance matching printed wiring board characterized in that the width of the feedback current space 5 is the same space width as the line space 2 between the pair of differential transmission lines 1a and 1b. It solves the above problems.

  The present invention also provides a differential impedance matching printed wiring board characterized in that the width of the feedback current space 5 is narrower than the line space 2 between the pair of differential transmission lines 1a and 1b. It solves the above problems.

  In addition, the present invention solves the above problems by a differential impedance matching printed wiring board, wherein the line opening angle of the line opening 3 is less than 90 degrees.

  In addition, the present invention solves the above problems by a differential impedance matching printed wiring board, wherein the feedback current pattern 7 is in the form of a single floating island that is not electrically connected to other conductor wiring. .

  ADVANTAGE OF THE INVENTION According to this invention, in the printed wiring board which has a differential transmission line, the fluctuation | variation of differential impedance can be suppressed and signal reflection can be reduced in the line opening part which a differential transmission line spreads.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 shows a first embodiment of a differential impedance matching printed wiring board according to the present invention.

(First embodiment)
In the structure shown in FIG. 1, a pair of differential transmission lines, that is, a differential transmission line 1a and a differential transmission line 1b are arranged in parallel via a line space 2 serving as a gap. In this manner, by arranging the pair of differential transmission lines 1a and 1b in parallel via the line space 2, the differential impedance between the pair of differential transmission lines 1a and 1b can be matched.

  In the differential transmission line 1a and the differential transmission line 1b in which the differential signal is transmitted from the input terminal A1 and the input terminal A2 to the output terminal B1 and the output terminal B2 through the line space 2, the output terminal B1 and the output terminal In many cases, a component mounting pad, a terminal resistor, or the like is provided at the tip of B2, and when the component is connected, a pair of differential transmission lines 1a with the line opening 3a as a base point according to the shape of the component. , 1b is provided, and a line expansion region 3 is provided. In such a case, a signal reflection failure occurs near the line opening 3a, and the differential impedance varies greatly.

  Therefore, in the present invention, the feedback current pattern 7 is provided via the feedback current space 5 so as to follow the opening shape of the line expansion region 3 in the direction of the output ends B1 and B2 of the differential transmission lines 1a and 1b. It has been. Thereby, the fluctuation of the differential impedance is reduced by suppressing the reflection of the signal.

  Here, the features of the feedback current pattern 7 and the feedback current space 5 will be described. The feedback current pattern 7 is provided in a shape that follows the opening shape of the line expansion region 3. As an example, as shown in FIG. 1, the feedback current pattern 7 is made into a solid conductor shape, and the inner opening is formed inside the pair of differential transmission lines 1 a and 1 b in the line expansion region 3. The feedback current pattern 7 is arranged through the feedback current space 5 so as to follow the angle.

  The feedback current pattern 7 has a single floating island shape that is not electrically connected to other conductor wiring. This is because a single floating island that is not electrically connected is used as a feedback current path for the differential transmission lines 1a and 1b.

  By adopting such a structure, a feedback current path is provided for the differential transmission lines 1a and 1b, and a coupling capacity lost due to an increase in the wiring interval can be compensated. As a result, it is possible to suppress differential impedance fluctuations that occur in the differential transmission lines 1a and 1b, particularly in the vicinity of the line opening 3a, and to reduce signal reflection.

  In the design of the feedback current space 5, the same width as the line space 2 between the pair of differential transmission lines 1 a and 1 b arranged in parallel or the feedback current space 5 is narrower than the line space 2. Is desirable.

  For example, when the width of the line space 2 is 50 μm, the width of the feedback current space 5 is preferably narrower than 50 μm to 50 μm.

  This is because when the reflection of the electric signal is taken into consideration, it is preferable that the width of the feedback current space 5 is the same as the width of the line space 2 as a structure having the least signal reflection. On the other hand, when the width of the feedback current space 5 is wider than the width of the line space 2, the coupling capacitance is lost due to the widening of the wiring interval. Therefore, the feedback current space 5 is preferably narrower than the line space 2.

  Also in the circuit formation method of the printed wiring board, the width of the feedback current space 5 is the same as that of the line space 2 or the feedback current space 5 is narrower than the line space 2. Considering this, it is preferable because a circuit can be easily formed.

  FIG. 2 shows a second embodiment of the differential impedance matching printed wiring board of the present invention.

(Second embodiment)
The feedback current pattern 7 has a shape that follows the opening shape of the line expansion region 3 in the direction of the output ends B1 and B2 of the differential transmission lines 1a and 1b, and is provided via the feedback current space 5 to thereby provide a signal. Is suppressed, and fluctuations in differential impedance are reduced. Therefore, the arrangement of the feedback current pattern 7 may be the structure shown in FIG.

  That is, it is shaped so as to follow the opening shape of the line expansion region 3 in the direction of the output ends B1 and B2 of the differential transmission lines 1a and 1b, and electrically with other conductor wirings via the feedback current space 5. A feedback current pattern 7a may be provided outside the pair of differential transmission lines 1a and 1b in the line expansion region 3 in a single floating island shape that is not connected, or inside the pair of differential transmission lines 1a and 1b. A feedback current pattern 7b may be provided.

  Even in such a structure shown in FIG. 2, the feedback current pattern 7 has a shape that follows the opening shape of the line expansion region 3 in the direction of the output ends B1 and B2 of the differential transmission lines 1a and 1b. This is because the reflection of the signal generated in the vicinity of the line opening 3a can be reduced and the differential impedance can be matched.

  The feedback current pattern 7a provided outside the pair of differential transmission lines 1a and 1b in the line expansion region 3 and the feedback current pattern 7b provided inside the pair of differential transmission lines 1a and 1b. Either may be sufficient, and the structure provided with both may be sufficient.

  FIG. 3 shows the line opening angle 8 of the line expanding region 3 in the differential impedance matching printed wiring board of the present invention.

  The reason for designing the printed wiring board provided with the line opening angle 8 is that the differential signal is transmitted from the input terminal A1 and the input terminal A2 to the output terminal B1 and the output terminal B2 via the line space 2. In the transmission lines 1a and 1b, when a component such as a resistor is connected to the tip of the output end B1 and the output end B2, the distance between the wirings of the differential transmission lines 1a and 1b is increased according to the shape of the component. This is because the situation becomes unavoidable.

  That is, the line opening angle 8 differs depending on the design of the printed wiring board and the shape of the components mounted on the printed wiring board. Therefore, if the line opening angle 8 is less than 90 degrees, an arbitrary angle is used in an actual printed wiring board.

  In view of such a background, in the present invention, it is possible to cope by setting the line opening angle 8 to less than 90 degrees.

  For example, when the line opening angle 8 is 30 degrees to less than 90 degrees, the structure as shown in FIG. 1 is used, and the inside of the pair of differential transmission lines 1a and 1b in the line opening 3 A feedback current pattern 7 is arranged through a feedback current space 5 so as to be along the line expansion region 3.

  On the other hand, when the line opening angle 8 is less than 30 degrees, it is difficult to provide the feedback current pattern 7 inside the pair of differential transmission lines 1a and 1b in the line expansion region 3 as shown in FIG. Therefore, as shown in FIG. 2, this can be dealt with by providing a feedback current pattern 7a outside the pair of differential transmission lines 1a and 1b in the line expansion region 3.

  The above 30 degree notation is an example, and if a fine circuit forming method represented by an additive method of a printed wiring board is used, the inside of the differential transmission lines 1a and 1b in the line expansion region 3 and The feedback current pattern 7 can be provided at a desired outside position.

(Test example)
The differential impedance matching printed wiring board of the present invention has less signal reflection at the line opening of the differential transmission line, and is advantageous when matching the differential impedance. Here, as a test example, in order to clarify the electric characteristics in the present invention, a comparison test with respect to the characteristic of the differential impedance was performed with the conventional technique.

  As a test method, a model in both the structure of the present invention shown in FIG. 1 and the structure of the prior art shown in FIG. 6 is prepared using an electromagnetic field analysis simulator (MW-Studio) manufactured by CST. The comparison of transmission characteristics was examined by non-stationary analysis.

  FIG. 4 shows the differential impedance characteristic in the differential impedance matching printed wiring board of the present invention. The measurement results are shown with the vertical axis representing differential impedance [Zdiff (unit: Ω)] and the horizontal axis representing time (unit: s). Here, 100Ω was set as the evaluation method of the differential impedance characteristic, and actual measurement for the setting was recorded.

  As a result, with respect to the setting of 100Ω, the measured differential impedance was 102Ω at the maximum, so that signal reflection was suppressed and the differential impedance could be matched.

  On the other hand, for the purpose of clarifying the difference from the prior art, a model in the structure of the prior art shown in FIG. 6 is prepared in the same manner as the test method, and comparison of transmission characteristics is examined by non-stationary analysis, The results are shown in FIG.

  As a result, with respect to the setting of 100Ω, the measured differential impedance was 130Ω or more, and the result that the signal reflection was not suppressed and the structure was not suitable for matching the differential impedance was obtained.

  From the results shown in FIG. 4 and FIG. 5, the differential impedance matching printed wiring board according to the present invention is provided with the feedback current pattern 7 for the pair of differential transmission lines 1a and 1b. The coupling capacitance lost in the vicinity of the line opening can be compensated, and as a result, the fluctuation of the differential impedance can be suppressed and the signal reflection can be reduced.

  In the future, since higher speed and narrower pitch of printed wiring boards will be required, this variation in differential impedance will not be negligible, and there is a high possibility that malfunction due to signal reflection will become apparent. Therefore, the structure of the differential impedance matching printed wiring board of the present invention is important.

The schematic explanatory drawing which shows 1st Embodiment of this invention printed wiring board. The model explanatory drawing which shows 2nd Embodiment of this invention printed wiring board. Model explanatory drawing which shows the track | line opening angle in this invention printed wiring board. The graph which shows the differential impedance characteristic of this invention printed wiring board. The graph which shows the differential impedance characteristic of the conventional printed wiring board. Model explanatory drawing which shows a conventional printed wiring board.

Explanation of symbols

1a, 1b: differential transmission line 2: line space 3: line expansion region 3a: line opening 5: feedback current space 7, 7a, 7b: feedback current pattern 8: line opening angle 61: differential transmission line 62: Track space 63: Track opening

Claims (4)

A pair of differential transmission lines (1a), (1b) is provided, and differential transmission lines (1a), (1b) are provided in the direction of the output ends B1, B2 of the differential transmission lines (1a), (1b). In the printed wiring board provided with the line expanding area (3) that expands , the other conductor wiring is electrically connected to the printed wiring board via the feedback current space (5) along the line expanding area (3). A differential impedance matching printed wiring board characterized in that an unconnected floating island-shaped feedback current pattern (7) is arranged inside or / and outside a pair of differential transmission lines (1a), (1b) .   The width of the feedback current space (5) is the same space width as the line space (2) between the pair of differential transmission lines (1a), (1b). Differential impedance matching printed wiring board.   The width of the feedback current space (5) is a space width narrower than a line space (2) between the pair of differential transmission lines (1a) and (1b). Differential impedance matching printed wiring board.   The differential impedance matching printed wiring board according to any one of claims 1 to 3, wherein a line opening angle of the line opening (3) is less than 90 degrees.

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