Patent Publication Number: US-2012032755-A1

Title: Delay line structure

Description:
This application claims the benefits of the Taiwan Patent Application Serial NO. 099125912 filed on Aug. 4, 2010, the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a delay line structure, and more particularly to a serpentine delay line structure with grounding guard traces. 
     2. Description of the Prior Art 
     Signal synchronizing is always a concern when it comes to the high speed digital signal. Usually the requirement of synchronizing signals is met by increasing delay time with a delay line. 
     To save space, the delay line is usually bent. There are various delay lines, among which a serpentine delay line is very common. Referring to  FIG. 1 ,  FIG. 1  illustrates a delay line structure in prior art. A serpentine delay line  11  is bent repeatedly and arranged on a substrate  100 . 
     However, bending the delay line forms several coupling line segments in the delay line itself, also generates crosstalk noise disturbance and further affects a signal waveform received, which leads to misinterpretation on a voltage level of a digital signal. As a result, in prior art, a guard trace with both ends connecting to the ground is utilized for decreasing the crosstalk noise. Referring to  FIG. 2 ,  FIG. 2  is a schematic view showing a guard trace with both ends connecting to the ground being applied to a serpentine delay line in prior art. The serpentine delay line  11  is bent repeatedly and arranged on the substrate  100 , and therefore a coupling area H 1  opening toward a first direction S 1  and a coupling area H 2  opening toward a direction opposite to the first direction S 1  are formed. A guard trace  12  and a guard trace  13  are inserted in the coupling area H 1  and coupling area H 2  separately. Moreover, two ends of the guard trace  12  are electrically connected to a grounding layer of the substrate  100  by a via  121  and via  122  while two ends of the guard trace  13  are electrically connected to the grounding layer of the substrate  100  by a via  131  and via  132 . 
     Although the guard trace  12  and  13  can efficiently decrease the crosstalk noise of the serpentine delay line  11 , the coupling area H 1  and H 2  must be large enough for the via  122  and  132  to be disposed inside the serpentine delay line  11 , which is difficult to process. That is why, downsizing a structure for the serpentine delay line  11  is still a difficulty. Meanwhile, since the guard trace  12  and  13  with two ends connecting to the ground can merely be utilized in a structure of microstrip line, the utilization is still limited. 
     SUMMARY OF THE INVENTION 
     A delay line structure is provided according to the present invention. The delay line structure does not need the installation of via inside the serpentine delay line and effectively reduces the crosstalk noise disturbance in the serpentine delay line. 
     A delay line structure is disposed on a substrate. The substrate includes a grounding layer and a layout layer, wherein the grounding layer includes a grounding circuit. The delay line structure accordingly includes a serpentine delay line, at least a first grounding guard trace and at least a second grounding guard trace. 
     The serpentine delay line is disposed in the layout layer in a manner of extending from an input end to an out put end in serpentine so as to form at least a first coupling area having a first opening toward a first direction and at least a second coupling area having a second opening toward a second direction opposite to the first direction. 
     The first grounding guard trace is disposed in the layout layer in a manner of extending from the first opening toward the first coupling area, having an interval between the first grounding guard trace and the serpentine delay line, wherein an end of the first grounding guard trace close to the first opening is electrically connected to the grounding circuit through a first via. 
     The second grounding guard trace is disposed in the layout layer in a manner of extending from the second opening toward the second coupling area, having an internal between the second grounding guard trace and the serpentine delay line, wherein an end of the second grounding guard trace close to the second opening is electrically connected to the grounding circuit through a second via. 
     According to an embodiment of the present invention, an end of the first grounding guard trace is electrically connected to the first via, and the end is positioned outside the first opening; an end of the second grounding guard trace is electrically connected to the second via, and the end is positioned outside the second opening. 
     According to an embodiment of the present invention, the serpentine delay line includes a strip line. 
     When compared with the delay line in prior art, which is not installed with grounding guard traces, the present invention avoids the crosstalk noise disturbance by means of the first grounding guard trace and the second grounding guard trace connecting to the ground with an end. When compared with the serpentine delay line having a guard trace with both ends connecting to the ground in prior art, since there is no need to install the via inside the serpentine delay line according to an embodiment of the present invention, the problem of being unable to downsize the serpentine delay line is easily solved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of this invention will become more apparent in the following detailed description of the preferred embodiments of this invention, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a delay line structure in prior art; 
         FIG. 2  is a schematic view showing a guard trace with both ends connecting to the ground being applied to a serpentine delay line in prior art; 
         FIG. 3  is the upper view illustrating an embodiment of a serpentine delay line structure according to the present invention having grounding guard trace; 
         FIG. 4  shows a cross-sectional view of the strip line of the serpentine delay line according to an embodiment of the present invention taken along the A-A line in  FIG. 3 ; 
         FIG. 5  is a measure figure showing the time domain transmit of various transmission lines employed in the serpentine delay line structure of the present invention; 
         FIG. 6  is an output eye diagram of a serpentine delay line without being installed with ground guard trace in prior art; and 
         FIG. 7  is an output eye diagram of a serpentine delay line of an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention relates to a delay line structure, and more particularly to a serpentine delay line structure with grounding guard traces. In the following description, numerous details are set forth in order to provide a thorough understanding of the present invention. It will be appreciated by one skilled in the art that variations of these specific details are possible while still achieving the results of the present invention. In other instance, well-known components are not described in detail in order not to unnecessarily obscure the present invention. 
     Referring to  FIG. 3  and  FIG. 4 , wherein  FIG. 3  is the upper view of an embodiment of a serpentine delay line structure having grounding guard trace according to of the present invention while;  FIG. 4  shows the cross-sectional view of a strip line of the serpentine delay line according to the present invention taken along the A-A line in  FIG. 3 . A delay line structure is disposed on a substrate  300 . The substrate  300  includes a grounding layer  32  and a layout layer  31 , wherein the grounding layer  32  includes a grounding circuit  33 . The delay line structure accordingly includes a serpentine delay line  21 , at least a first grounding guard trace  22  and at least a second grounding guard trace  23 . 
     The serpentine delay line  21  is disposed in the layout layer  31  in a manner of extending from an input end  211  to an out put end  212  in serpentine so as to form at least a first coupling area H 3  having a first opening O 1  toward a first direction S 1  and at least a second coupling area H 4  having a second opening O 2  toward a direction opposite to the first direction S 1 , wherein the length and times of serpentine of the serpentine delay line  21  vary on the demand of signal delay time; the number of first coupling area H 3  can be the same as or different from the number of the second coupling area H 4 . 
     The first grounding guard trace  22  is disposed in the layout layer  31  in a manner of extending from the first opening O 1  toward the first coupling area H 3 , having an interval (not shown) between the first grounding guard trace  22  and the serpentine delay line  21 , wherein an end (not shown) of the first grounding guard trace  22  close to the first opening O 1  is electrically connected to the grounding circuit  33  through a first via  221 , wherein according to an embodiment of the present invention, an end of the first grounding guard trace  22  is electrically connected to the first via  221 , and the end is positioned outside the first opening O 1 . 
     The second grounding guard trace  23  is disposed in the layout layer  31  in a manner of extending from the second opening O 2  toward the second coupling area H 4 , having an internal between the second grounding guard trace  23  and the serpentine delay line  21 , wherein an end of the second grounding guard trace  23  close to the second opening O 2  is electrically connected to the grounding circuit  33  through a second via  231 , wherein according to an embodiment of the present invention, an end of the second grounding guard trace  23  is electrically connected to the second via  231 , and the end is positioned outside the second opening O 2 . 
     Moreover, the delay line structure of the present invention is applied to various kinds of substrate  300 . For example, the substrate  300  may include materials having a plurality of dielectric constants and the substrate  300  may include materials having a single dielectric constant. The layout layer  31  is disposed inside the substrate  300 . According to an embodiment of the present invention, the serpentine delay line  32  includes a strip line as it is shown in  FIG. 4 , and the upper side and lower side of the substrate  300  respectfully includes grounding circuit  33  and  33 ′. When at least one of the grounding circuit  33  and  33 ′ is electrically connected by the via  221 , the effect of ground guard is reached. 
     Referring to  FIG. 5 ,  FIG. 5  is a measure figure showing the time domain transmit of various transmission lines. It is obvious that the waveform measured by a straight transmission line is an ideal square wave signal. On the contrary, the waveform measured by a serpentine delay line without being installed with ground guard trace shows ups and downs, which is very different from the square wave signal. The waveform measured by the serpentine delay line of an embodiment of the present invention is very close to the ideal square wave signal. In other words, the delay line structure of the present invention can effectively reduce the disturbance of crosstalk noise. 
     Referring to  FIG. 6  and  FIG. 7 , wherein  FIG. 6  is an output eye diagram of a serpentine delay line without being installed with ground guard trace in prior art while  FIG. 7  is an output eye diagram of a serpentine delay line of an embodiment of the present invention. The abovementioned two eye diagrams are measured with an electronic measurement and simulation software, Advanced Design System (ADS) 2006, of the company of Agilent Technologies, Taipei, Taiwan. It is clear that the output eye diagram of a serpentine delay line of an embodiment of the present invention has better signal integrity than the output eye diagram of a serpentine delay line without being installed with ground guard trace in prior art. 
     In conclusion, when compared with the delay line in prior art, which is not installed with grounding guard traces, the present invention avoids the crosstalk noise disturbance by means of the first grounding guard trace and the second grounding guard trace connecting to the ground with an end. When compared with the serpentine delay line having a guard trace with both ends connecting to the ground in prior art, since there is no need to install the via inside the serpentine delay line of the present invention, the problem of being unable to downsize the serpentine delay line is easily solved. Meanwhile, since a strip line structure can also applied in an embodiment of the present invention, it is more flexible for manufacturing. 
     While the present invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be without departing from the spirit and scope of the present invention.