CN100496187C - Transmission line for cross-groove structure - Google Patents

Abstract

A transmission line for a cross-slot structure utilizes the concept of impedance matching to optimize the line length and line width of a part of line segment of the transmission line connected to the cross-slot structure, so that the part of line segment presents capacitive low-impedance characteristic, the impedance matching of a designed frequency point is achieved, and the discontinuous effect caused by the high-impedance characteristic of the electrical property of the transmission line on the cross-slot structure is further improved.

Description

A transmission line for cross-slot structures

technical field

The present invention relates to a transmission line, in particular to a transmission line used in a cross-slot structure.

Background technique

Layout is one of the designs of Printed Circuit Board (PCB). The quality of wiring will directly affect the performance of the entire system, and most high-speed circuit design theories will eventually be realized and verified through wiring. It can be seen that wiring is crucial in high-speed printed circuit board design.

In the design of multilayer printed circuit boards, in order to save costs, fewer layers must be used to complete the wiring of the entire board. Therefore, different voltage levels must be cut on the limited power supply layer. In this way, If the transmission line crosses these different voltage cutting planes, an Oversplit Plane structure is formed.

Please refer to FIG. 1A and FIG. 1B. FIG. 1A is a schematic diagram 10 of an existing transmission line straddling structure, and FIG. 1B is a top view 11 of an existing transmission line straddling structure. As shown in the figure, a printed circuit board 101 has a cut The trench 102 and the transmission line 103 are used to transmit signals and cross the trench 102 , wherein the line width of the transmission line 103 is W. However, since the transmission line 103 across the groove 102 has no signal reference plane, this part of the line segment presents an inductive high-impedance characteristic, resulting in a discontinuity effect in the impedance of the transmission line, that is, a signal occurs when the signal is transmitted to this part of the line segment. reflection. In view of this, the solution in the prior art is to add capacitors on the two split planes so that the current on the transmission line can flow back on the two split planes, so as to reduce the signal reflection phenomenon. However, although this prior art can solve the signal reflection problem, it increases the manufacturing cost and must face the problem of reducing the wiring space due to the increase of capacitance.

Contents of the invention

In order to solve the above-mentioned problems, the present invention discloses a transmission line for crossing the trench structure. The present invention utilizes the concept of impedance matching and uses Smith Chart to adjust the optimal line length and length of a single transmission line according to the expected frequency. Line width, to change the width of the part of the transmission line connected to the cross-slot structure, so that it presents capacitive low impedance characteristics, achieves impedance matching at the design frequency point, and then improves the inductive high impedance of the transmission line on the cross-slot structure The effect of discontinuity caused by the characteristic, and improve the signal reflection loss.

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments, but not as a limitation of the present invention.

Description of drawings

FIG. 1A is a schematic diagram of an existing cross-groove structure;

FIG. 1B is a top view of an existing trench-spanning structure;

FIG. 2A is a schematic diagram of changing the length and width of part of the transmission line according to the present invention;

Fig. 2B is a top view of changing the line length and line width of part of the transmission line according to the present invention;

FIG. 3 is a curve diagram of impedance mismatch compensation and uncompensated reflection loss before compensation by increasing the line width of the transmission line according to the present invention; and

FIG. 4 is a display diagram of compensation for impedance mismatch and uncompensated by increasing the line width of the transmission line according to the present invention.

Among them, reference signs

10 Schematic diagram of the existing cross-trough structure

11 Top view of the existing trench-spanning structure

20 Schematic diagram of changing the line length and line width of the transmission line part of the present invention

21 Top view of changing the line length and line width of the transmission line part of the present invention

30 Curves of Impedance Mismatch Compensation and Uncompensated Reflection Loss by Increasing the Line Width of the Transmission Line in the Present Invention

40 The present invention utilizes increasing the line width of the transmission line to compensate the impedance mismatch and the display before uncompensation

101, 201 Printed circuit boards

102, 202 Groove

103 transmission line

203 first line segment

204 second segment

301 Reflection loss curve of signal after compensation

302 Reflection Loss Curves for Uncompensated Transmission Line Signals

303, 304 resonance points

401 Display of signal after compensation

402 Display of the signal of the uncompensated transmission line

L2 second line length

W line width

W1 first line width

W2 second line width

Detailed ways

The detailed features and advantages of the present invention are described in detail below in the embodiments, the content of which is sufficient to enable any person familiar with the relevant art to understand the technical content of the present invention and implement it accordingly, and according to the content disclosed in this specification, the scope of the patent application and the drawings , anyone skilled in the relevant art can easily understand the related objects and advantages of the present invention.

The present invention uses the concept of impedance matching to change the width of the transmission line so that part of the line segment of the transmission line across the groove of the printed circuit board presents capacitive low-impedance characteristics to achieve impedance matching at the design frequency point, thereby improving the performance of the transmission line. The effect of impedance discontinuity caused by the high impedance characteristic of inductance.

Please refer to FIG. 2A and FIG. 2B. FIG. 2A is a schematic diagram 20 of changing the length and width of a part of a transmission line according to the present invention, and FIG. 2B is a top view 21 of changing a part of a length and a width of a transmission line according to the present invention. In an embodiment, a Smith Chart is used to adjust the optimized line length and line width of a single transmission line according to the expected frequency to achieve impedance matching. For example, the first line segment 203 of the transmission line on the outer layer of the printed circuit board 201 has The first line length L1 (not shown in the figure) and the first line width W1, if the line segment with the same first line width W1 as the first line segment 203 crosses the trench 202, the transmission line above the trench 202 will be the same as the original The designed transmission line exhibits an inductive high-impedance characteristic with impedance mismatch. Therefore, increasing the line width of the transmission line above the trench 202 to overcome the impedance discontinuity is the second line segment 204, which has the second line length L2 and the second line width W2, and the second line segment 204 with increased line width is With the center of the groove 202, it extends to at least one end of the transmission line. According to a specific embodiment of the present invention, for example, the line width of the first line segment 203 is realized by 7 mils (mil; one thousandth of an inch), and the concave The slot 202 has a width of 20 mils, and the second line segment 204 extends 75 mils to both ends of the transmission line to form a line segment with a second line length L2 of 150 mils and a second line width W2 of 14 mils. The length and width of the line segment with increased line width described here are not intended to limit the scope of the present invention. Those skilled in the art can change the first line length L1 and/or the first line length L1 and/or the first line segment 203 of the groove 202 and the transmission line. The line width W1, and then change the second line length L2 and/or the second line width W2 that should be increased by the second line segment 204 of the transmission line above the groove 202, and according to an embodiment of the present invention, this increases the line width of the transmission line to achieve impedance The matching method can be applied to both single-end (Single-End) transmission and differential mode (Differential Mode) transmission circuits.

Please refer to FIG. 3 , which is a graph 30 of the present invention that utilizes the line width compensation of the transmission line 203 to compensate for impedance mismatch and uncompensated reflection loss curve 30, using the Smith chart to obtain the line length and Line width, measure the reflection loss curve 301 of the compensated signal and compare it with the reflection loss curve 302 of the uncompensated transmission line signal, as shown in the figure, two resonance points 303 can be generated at 2GHz and 6.5GHz after compensation , 304, the frequencies near the two resonance points 303, 304 can greatly reduce the reflection loss.

Please refer to FIG. 4 , which is a display diagram 40 of the present invention before compensating for impedance mismatch and uncompensated by increasing the line width of the transmission line 203. Using the Smith chart, the line length and line width of the transmission line with a frequency of 3 GHz are obtained, and the signal after compensation is measured. The display graph 401 of the uncompensated transmission line signal is compared with the display graph 402 of the signal of the uncompensated transmission line. As shown in the figure, the distortion of the display graph 402 of the signal of the uncompensated transmission line is relatively serious.

Certainly, the present invention also can have other multiple embodiments, without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding Changes and deformations should belong to the scope of protection of the appended claims of the present invention.

Claims (4)

1. A transmission line for a cross-slot structure, the cross-slot structure is a slot arranged on a printed circuit board, the transmission line straddles the slot, the transmission line has a first line length and a first line A first line segment of width, characterized in that: The transmission line is configured with a second line segment with a second line length and a second line width above the groove, and the second line segment extends from the corresponding center position of the groove toward at least one end of the transmission line and connects the first line segment: wherein , The second line width is greater than the first line width. 2. The transmission line for a cross-trench structure according to claim 1, which is used for single-ended transmission. 3. The transmission line for a cross-trench structure according to claim 1, which is used for differential mode transmission. 4. The transmission line for a cross-trench structure according to claim 1, the second line length is 150 mils and the second line width is 14 mils.

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