Patent Publication Number: US-2017373362-A1

Title: Structure of serpentine transmssion line

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 105120201 filed in Taiwan, R.O.C. on Jun. 27, 2016, the entire contents of which are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The disclosure relates to a structure of transmission line, more particularly to a structure of a serpentine transmission line. 
     BACKGROUND 
     High frequency electrical products, computer hardware and software adapted for high speed signals and integrated circuits develop rapidly because the age of high speed digitalized communication comes. Therefore, the demands of operation frequencies and frequency bands of signals are increasing. Moreover, the raise of the transmission speed of signals and the demand of minimization of products make layout densities of circuits increase. As a result, signal integrities are affected during the signal transmissions. 
     SUMMARY 
     In one embodiment, the structure of the serpentine transmission line includes a first transmission line and a second transmission line. The first transmission line includes the first line segment, the second line segment and the third line segment. The second transmission line includes the fourth line segment, the fifth line segment and the sixth line segment. All of the first line segment, the second line segment, the fourth line segment and the fifth line segment extend along a first direction and have a first line width. The third line segment extends along a second direction and is electrically connected to the first line segment and the second line segment. The second direction is perpendicular to the first direction. The sixth line segment extends along the second direction and is electrically connected to the fourth line segment and the fifth line segment. Both the third line segment and the sixth line segment have the second line width. The second line width is greater than the first line width. A projection of the third line segment toward the second direction at least partially overlaps a projection of the sixth line segment toward the second direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present disclosure and wherein: 
         FIG. 1  is a top view of a structure of a serpentine transmission line in one embodiment; 
         FIG. 2  is a top view of the structure of the serpentine transmission line in another embodiment; 
         FIG. 3  is a top view of the structure of the serpentine transmission line in another embodiment; 
         FIG. 4  is a waveform of far-end crosstalk noise in one embodiment; and 
         FIG. 5  is a waveform of reflection frequency domain in one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawings. 
     Please refer to  FIG. 1 .  FIG. 1  is a top view of a structure of a serpentine transmission line in one embodiment. As shown in  FIG. 1 , the structure of the serpentine transmission line  10  includes the first transmission line  11  and the second transmission line  12 . The first transmission line  11  includes the first line segment L 1 , the second line segment L 2  and the third line segment L 3 . The second transmission line includes the fourth line segment L 4 , the fifth line segment L 5  and the sixth line segment L 6 . In an example, the first transmission line  11  and the second transmission line  12  both are microstrip lines disposed on circuit boards and configured to transmit signals. All of the first line segment L 1 , the second line segment L 2 , the fourth line segment L 4  and the fifth line segment L 5  extend along the first direction (the direction of X axis in  FIG. 1 ) and have a first line width W  1 . The third line segment L 3  extends along the second direction (the direction of Y axis in  FIG. 1 ) and is electrically connected to the first line segment L 1  and the second line segment L 2 . The second direction is perpendicular to the first direction. The sixth line segment L 6  extends along the second direction and is electrically connected to the fourth line segment L 4  and the fifth line segment L 5 . Both the third line segment L 3  and the sixth line segment L 6  have the second line width W 2 . The second line width W 2  is greater than the first line width W 1 . A projection of the third line segment L 3  toward the second direction partially overlaps a projection of the sixth line segment L 6  toward the second direction. 
     In the structure of the serpentine transmission line of the present disclosure, through the overlapping part of the projection of the third line segment L 3  and the projection of the sixth line segment L 6  toward the second direction, the first transmission line  11  couples the second transmission line  12  so that the capacitance is increased. Therefore the interference of the far-end crosstalk noise in the second transmission line  12  could be reduced. For example, assume the first transmission line  11  is close to the second transmission line  12 . When the signal is transmitted through the first transmission line  11 , the far-end crosstalk noise will be generated in the second transmission line  12 . At this time, because both the third line segment L 3  and the sixth line segment L 6  have the second line width W 2  and their overlapping part toward the second direction increases the capacitance through the coupling effect, the far-end crosstalk noise in the second transmission line  12  will be reduced. In practice, the distance between the third line segment L 3  and the sixth line segment L 6  is greater than or equal to the minimum size of manufacturing process in the relative field such as 3 mil. The above embodiments indicating the first line width W 1  is one third the second line width W 2  are just for illustrating, and the present disclosure is not limited to the line widths. 
     Please refer to  FIG. 2 .  FIG. 2  is a top view of the structure of the serpentine transmission line in another embodiment. The structure of the embodiment in  FIG. 2  is approximately the same as the structure of the embodiment in  FIG. 1 . The difference between the structure of the embodiment in  FIG. 2  and the structure of the embodiment in  FIG. 1  is the overlapping part between the projection of the third line segment L 3  toward the second direction and the projection of the sixth line segment L 6  toward the second direction. As shown in  FIG. 2 , since the projection of the third line segment L 3  toward the second direction fully overlaps the projection of the sixth line segment L 6  toward the second direction, the effects of coupling in the embodiment of  FIG. 2  are more significant than in the embodiment of  FIG. 1  so that the capacitance is raised and the far-end crosstalk noise is decreased effectively. In another embodiment, both the first transmission line  11  and the second transmission line  12  include a plurality of line segments extending along the second direction, and projections of corresponding ones among the line segments toward the second direction overlap each other so that the capacitance could be raised significantly. Therefore the far-end crosstalk noise is decreased significantly. 
     Please refer to  FIG. 3 .  FIG. 3  is a top view of the structure of the serpentine transmission line in another embodiment. Comparing to the embodiments in  FIG. 1  and  FIG. 2 , the first transmission line  11  in the embodiment in  FIG. 3  further includes the seventh line segment L 7  and the eighth line segment L 8 . The seventh line segment L 7  is electrically connected to the first line segment L 1  and the third line segment L 3 . The eighth line segment L 8  is electrically connected to the second line segment L 2  and the third line segment L 3 . The seventh line segment L 7  has a third line width W 3 , and the eighth line segment L 8  has a fourth line width W 4 . The third line width W 3  and the fourth line width W 4  both are less than the first line width W 1 . 
     In one embodiment, the first transmission line  11  further includes the first connector C 1  respectively connected to the first line segment L 1  and the seventh line segment L 7 . The second connector C 2  is respectively connected to the third line segment L 3  and the seventh line segment L 7 . The third connector C 3  is respectively connected to the third line segment L 3  and the eighth line segment L 8 . The fourth connector C 4  is respectively connected to the second line segment L 2  and the eighth line segment L 8 . All of the first connector C 1 , the second connector C 2 , the third connector C 3  and the fourth connector C 4  are trapezoids. Note that those said connectors having the shapes of trapezoids are configured to smoothly connect line segments having different line widths so that the discontinuities of the transmission line caused by the differences of line widths could be avoided. The present disclosure is not limited to trapezoids. The present disclosure covers any type of shapes smoothly connecting the line segments having different line widths. In one embodiment, the greater the length of the first connector C 1  is, the greater the difference between the first line width W 1  of the first line segment L 1  and the third line width W 3  of the seventh line segment L 7  is. The greater the difference between the first line width W 1  of the second line segment L 2  and the fourth line width W 4  of the eighth line segment L 8  is, the greater the length of the fourth connector C 4  is. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 W1 
                 W3 
                 W4 
                 W5 
                 W6 
               
               
                   
               
               
                  6 (mil) 
                  3 (mil) 
                  3 (mil) 
                  3 (mil) 
                  3 (mil) 
               
               
                   
               
               
                 W2 
                 D1 
                 D2 
                 D3 
                 D4 
               
               
                   
               
               
                 18 (mil) 
                 24 (mil) 
                 24 (mil) 
                 24 (mil) 
                 24 (mil) 
               
               
                   
               
            
           
         
       
     
     In one embodiment, the third line width W 3  of the seventh line segment L 7  is one eighth the length D 1  of the seventh line segment L 7 . The fourth line width W 4  of the eighth line segment L 8  is one eighth the length D 2  of the eighth line segment L 8 . For example, as shown in table  1 , when the length D 1  of the seventh line segment L 7  and the length D 2  of the eighth line segment L 8  both are 24 mil, the third line width W 3  of the seventh line segment L 7  and the fourth line width W 4  of the eighth line segment L 8  both are 3 mil. The unit “mil” refers to a thousandth of an inch. The line widths and the lengths mentioned in the above embodiments are just for illustrating, and the present disclosure is not limited to it. 
     The second transmission line  12  further includes a ninth line segment L 9  and a tenth line segment L 10 . The ninth line segment L 9  is electrically connected to the fourth line segment L 4  and the sixth line segment L 6 . The tenth line segment L 10  is electrically connected to the fifth line segment L 5  and the sixth line segment L 6 . The ninth line segment L 9  has a fifth line width W 5 , and the tenth line segment L 10  has the sixth line width W 6 . The fifth line width W 5  and the sixth line width W 6  both are less than the first line width W 1 . 
     In one embodiment, the second transmission line  12  further includes the fifth connector C 5  respectively connected to the fourth line segment L 4  and the ninth line segment L 9 . The sixth connector C 6  is respectively connected to the sixth line segment L 6  and the ninth line segment L 9 . The seventh connector C 7  is respectively connected to the sixth line segment L 6  and the tenth line segment L 10 . The eighth connector C 8  is respectively connected the fifth line segment L 5  and the tenth line segment L 10 . All of the fifth connector C 5 , the sixth connector C 6 , the seventh connector C 7  and the eighth connector C 8  are trapezoids. In one embodiment, the greater the difference between the first line width W 1  of the fourth line segment L 4  and the fifth line width W 5  of the ninth line segment L 9  is, the greater the length of the fifth connector C 5  is. The greater the difference between the first line width W 1  of the fifth line segment L 5  and the sixth line width W 6  of the tenth line segment L 10  is, the greater the length of the eighth connector C 8  is. 
     In one embodiment, the fifth line width W 5  of the ninth line segment L 9  is one eighth the length D 3  of the ninth line segment L 9 , and the sixth line width W 6  of the tenth line segment L 10  is one eighth the length D 4  of the tenth line segment L 10 . For example, as shown in table 1, when the length D 3  of the ninth line segment L 9  and the length D 4  of the tenth line segment L 10  both are 24 mil, the fifth line width W 5  of the ninth line segment L 9  and the sixth line width W 6  of the tenth line segment L 10  both are 3 mil. The ratios regarding the line widths and the lengths mentioned in the above embodiments are just for illustrating, and the present disclosure is not limited to it. In one embodiment, the first line width W 1  is one third the second line width W 2 . For example, as shown in table 1, if the first line width W 1  is 6 mil, then the second line width W 2  is 18 mil. 
     As previously mentioned, in the embodiment of  FIG. 3 , the projection of the third line segment L 3  toward the second direction fully overlaps the projection of the sixth line segment L 6  toward the second direction so that the coupling effect increases the capacitance and the far-end crosstalk noise is decreased. Nevertheless the increase of the capacitance would make the impedances unmatched. Specifically, the impedances are inversely proportional to the capacitance. Thus, if the inductance is fixed, the impedances will decrease when the capacitance increases so that the impedances are unmatched. The input signal of the transmission line will be affected by reflections when the impedances are unmatched. At this time, the input signal will turn into a standing waveform in the transmission line so that the effective power capacity of the transmission line decreases. Therefore, in one embodiment of the present disclosure, the inductance could be raised by decreasing widths of line segments so that the unmatched impedances are eliminated. 
     For a practical example, in the embodiment of  FIG. 3 , the seventh line segment L 7  of the first transmission line  11  has the third line width W 3 , and the eighth line segment L 8  of the first transmission line  11  has the fourth line width W 4 . The third line width W 3  and the fourth line width W 4  both are less than the first line width W 1 . When the projection of the third line segment L 3  toward the second direction fully overlaps the projection of the sixth line segment L 6  toward the second direction so that the coupling effects increase the capacitance, the inductance will increase through the seventh line segment L 7  having the third line width W 3  and the eighth line segment L 8  having the fourth line width W 4  so that the unmatched impedances of the first transmission line  11  would become matched. The third line width W 3  of the seventh line segment L 7  is the same as the fourth line width W 4  of the eighth line segment L 8 . In another embodiment, the third line width W 3  of the seventh line segment L 7  is different from the fourth line width W 4  of the eighth line segment L 8 . Similarly, the ninth line segment L 9  of the second transmission line  12  has the fifth line width W 5 , and the tenth line segment L 10  of the second transmission line  12  has the sixth line width W 6 . The fifth line width W 5  and the sixth line width W 6  both are less than the first line width W  1 . Through the ninth line segment L 9  having the fifth line width W 5  and the tenth line segment L 10  having the sixth line width W 6 , the inductance is raised so that the impedances of the second transmission line  12  become matched. 
     Please refer to  FIG. 3  and  FIG. 4 .  FIG. 4  is a waveform of far-end crosstalk noise in one embodiment. As shown in  FIG. 4 , a parameter S 41  is configured to indicate the far-end crosstalk noise, and its equation is expressed as: 
     
       
         
           
             
               S 
                
               
                   
               
                
               41 
             
             = 
             
               20 
                
               log 
                
               
                  
                 
                   
                     V 
                      
                     
                         
                     
                      
                     4 
                   
                   
                     V 
                      
                     
                         
                     
                      
                     1 
                   
                 
                  
               
             
           
         
       
     
     A voltage V 1  represents an input signal to the first transmission line  11 , and the voltage V 4  represents a voltage of the far-end crosstalk noise in the second transmission line  12 . As indicated in the above equation, the greater the voltage V 4  is, the greater the parameter S 41  is. The closer the curve is to the top of  FIG. 4 , the greater the far-end crosstalk noise is. As shown in  FIG. 4 , the curve P 1  represents the variance of the parameter S 41  based on a linear structure of a transmission line having the first transmission line  11  and the second transmission line  12  disposed in parallel (without line segments extending along the second direction). The curve P 2  represents the variance of the parameter S 41  based on the structure of the transmission line in the embodiment of  FIG. 3 . As shown in  FIG. 3 , the curve P 2  is below the curve P 1 . In other words, the far-end crosstalk noise of the structure of the transmission line in the embodiment of  FIG. 3  is less than the far-end crosstalk noise of the linear structure of the transmission line having the first transmission line  11  and the second transmission line  12  disposed in parallel. In one embodiment, the structure of the transmission line in the embodiment of  FIG. 3  further includes more line segments extending along the second direction corresponding to a curve (not shown in  FIG. 3  and  FIG. 4 ) below the curve P 2 . In other words, the more line segments extending along the second direction the structure of the transmission line could includes, the more significantly the far-end crosstalk noise could be reduced. 
     Please refer to  FIG. 3  and  FIG. 5 .  FIG. 5  is a waveform of reflection frequency domain in one embodiment. As shown in  FIG. 5 , the parameter Sr 1  represents the reflection of signal in the first transmission line  11 , and its equation is expressed as: 
     
       
         
           
             
               S 
                
               
                   
               
                
               r 
                
               
                   
               
                
               1 
             
             = 
             
               20 
                
               log 
                
               
                  
                 
                   Vr 
                   
                     V 
                      
                     
                         
                     
                      
                     1 
                   
                 
                  
               
             
           
         
       
     
     A voltage V 1  represents a input signal voltage to the first transmission line  11 , and the voltage Vr represents a reflecting signal voltage in the first transmission line  11 . During the signal transmission, the weaker the signal reflection is, the more significantly the impedances could be matched. On the contrast, the stronger the signal reflection is, the more significantly the impedances could be unmatched. As indicated in the above equation, the greater the voltage Vr is, the greater the parameter Sr 1  is. In the other words, the closer the curve could be to the top of  FIG. 5 , the more significantly the impedances could be unmatched. As shown in  FIG. 5 , the curve P 3  represents the variance of parameter Sr 1  based on the structure of the transmission line in the embodiment of  FIG. 2 . The curve P 4  represents the variance of the parameter Sr 1  based on the structure of the transmission line in the embodiment of  FIG. 3 . As shown in  FIG. 5 , the curve P 4  is below the curve P 3 . It means that the signal reflection in the structure of the transmission line in the embodiment of  FIG. 3  is less than the signal reflection in the structure of the transmission line in the embodiment of  FIG. 2 . In the other words, the impedances of the structure of the transmission line in the embodiment of the  FIG. 3  are more matched than the impedances of the structure of the transmission line in the embodiment of the  FIG. 2 . 
     Based on the description above, in the structure of the serpentine transmission line, through the increase of the coupling effects generated by the widths of the line segments extending along the second direction, the capacitance is raised so that the interference of the far-end crosstalk noise is reduced. Through decreasing the widths of the line segments connected to the line segments extending along the second direction, the inductance is raised and the impedances become matched. Therefore the signal integrity is improved during the signal transmissions.