Abstract:
A circuit board connection structure comprises: first and second circuit boards; a connector having first and second insertion openings receiving the first and second circuit boards, respectively, the first and second insertion openings being opposite each other. First and second connection pins are located on inner walls of the first and second insertion openings, respectively. The first and second connection pins are connected to each other in the connector. First and second patterned conductors connectable to the first and second connection pins are respectively located on the first and second circuit boards and connected to the first and second connection pins when inserted in the first and second insertion openings. The transmission path from the first connection pin to the second connection pin is a characteristic-impedance-matched coplanar line.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a circuit board connection structure for connecting two circuit boards by a connector and, more particularly, to a circuit board connection structure for connecting a host-side circuit board and a module-side circuit board in a communication apparatus, an electronic computer, a video display or the like through which mainly a digital signal at about 100 megabits/second or more or an analog signal at about 100 megahertz or more is transmitted, and to a circuit board connection structure for connecting two circuit boards in a single apparatus. 
     2. Background Art 
     In radiofrequency circuits, microstrip lines conductor foil in line form formed on a front surface of a dielectric circuit board having conductor foil formed on its back surface are being used widely. A connector is used to connect two circuit boards on which such microstrip lines are formed (see, for example, Japanese Patent Laid-Open No. 4-51475). 
     SUMMARY OF THE INVENTION 
     The art disclosed in Japanese Patent Laid-Open No. 4-51475 has a problem that a connection portion on the ground side of the connector having an increased length due to a difference between two circuit boards exists as an impedance mismatching point and reduces the signal quality. Also, connecting two circuit boards requires extending patterns of microstrip lines to end portions of the circuit boards. There is a problem that the patterns can separate easily from the end portions of the circuit boards. 
     The present invention has been achieved to solve the above-described problem, and an object of the present invention is to provide a circuit board connection structure capable of improving the quality of signals in communication between circuit boards. Another object of the present invention is to provide a circuit board connection structure capable of preventing separation of a pattern on a circuit board. 
     According to one aspect of the present invention, a circuit board connection structure comprises: a first circuit board; a second circuit board; and a connector having a first insertion opening in which the first circuit board is to be inserted, and a second insertion opening in which the second circuit board is to be inserted, the first and second insertion openings being formed so as to face each other, wherein a first connection pin is formed on an inner wall forming the first insertion opening; a second connection pin is formed on an inner wall forming the second insertion opening; the first connection pin and the second connection pin are connected to each other in the connector; a first patterned conductor to be connected to the first connection pin while being inserted in the first insertion opening is formed on the first circuit board; a second patterned conductor to be connected to the second connection pin while being inserted in the second insertion opening is formed on the second circuit board; and a transmission path from the first connection pin to the second connection pin is a characteristic-impedance-matched coplanar line. 
     The present invention enables improving the signal quality in communication between circuit boards. 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 and 2  are perspective views of a connector according to the first embodiment of the present invention. 
         FIG. 3  is a sectional view showing a state where two circuit boards are connected to each other by using the connector according to the first embodiment of the present invention. 
         FIG. 4  is a plan view showing an end portion of a circuit board according to the first embodiment of the present invention. 
         FIG. 5  is a plan view showing transmission paths on the obverse side of the connector according to the first embodiment of the present invention. 
         FIG. 6  is a plan view showing an end portion of a circuit board according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       FIGS. 1 and 2  are perspective views of a connector according to the first embodiment of the present invention.  FIG. 3  is a sectional view showing a state where two circuit boards are connected to each other by using the connector according to the first embodiment of the present invention. 
     In the connector  11 , a first insertion opening  13  in which the first circuit board  12  is to be inserted and a second insertion opening  15  in which the second circuit board  14  is to be inserted are formed so as to face each other. Circuit board fixing screw holes  16  are also formed in the connector  11 . The second circuit board  14  is inserted in the second insertion opening  15 , and screws (not shown) are inserted in the circuit board fixing screw holes  16  to fix the second circuit board  14 . 
     First obverse-side connection pins  17  are formed on an upper surface of an inner wall forming the first insertion opening  13 , while first reverse-side connection pins  18  are formed on a lower surface of the inner wall forming the first insertion opening  13 . Second obverse-side connection pins  19  are formed on an upper surface of an inner wall forming the second insertion opening  15 , while second reverse-side connection pins  20  are formed on a lower surface of the inner wall forming the second insertion opening  15 . 
     The first obverse-side connection pins  17  and the second obverse-side connection pins  19  are connected to each other in the connector  11  by being slanted at an angle θ. The first reverse-side connection pins  18  and the second reverse-side connection pins  20  are connected to each other by being slanted at an angle θ. Even though the first circuit board  12  and the second circuit board  14  differ in thickness from each other, they can be connected to each other by adjusting angle θ. 
     First obverse-side patterned conductors  21  are formed on an obverse surface of the first circuit board  12 , while first reverse-side patterned conductors  22  are formed on a reverse surface of the first circuit board  12 . Second obverse-side patterned conductors  23  are formed on an obverse surface of the second circuit board  14 , while second reverse-side patterned conductors  24  are formed on a reverse surface of the second circuit board  14 . 
     When the first circuit board  12  is inserted in the first insertion opening  13  of the connector  11 , the first obverse-side patterned conductors  21  and the first obverse-side connection pins  17  are connected to each other and the first reverse-side patterned conductors  22  and the first reverse-side connection pins  18  are connected to each other. Also, when the second circuit board  14  is inserted in the second insertion opening  15  of the connector  11 , the second obverse-side patterned conductors  23  and the second obverse-side connection pins  19  are connected to each other and the second reverse-side patterned conductors  24  and the second reverse-side connection pins  20  are connected to each other. 
     For example, at the time of signal transmission from the first circuit board  12  to the second circuit board  14 , signals are transmitted from the first obverse-side patterned conductors  21  of the first circuit board  12  to the second obverse-side patterned conductors  23  of the second circuit board  14  via the first obverse-side connection pins  17  and the second obverse-side connection pins  19  of the connector  11 . Also, signals are transmitted from the first reverse-side patterned conductors  22  of the first circuit board  12  to the second reverse-side patterned conductors  24  of the second circuit board  14  via the first reverse-side connection pins  18  and the second reverse-side connection pins  20  of the connector  11 . In the case of signal transmission from the second circuit board  14  to the first circuit board  12 , the order of the patterned conductors and the connection pins are reversed with respect to the direction of signal transmission. 
       FIG. 4  is a plan view showing an end portion of a circuit board according to the first embodiment of the present invention. Patterned radiofrequency conductors  26  and patterned ground conductors  27  correspond to the first obverse-side patterned conductors  21  and the first reverse-side patterned conductors  22  of the first circuit board  12  and to the second obverse-side patterned conductors  23  and the second reverse-side patterned conductors  24  of the second circuit board  14 . These patterned conductors on the circuit board are divided into portions in a circuit board pattern region  29  not to be brought into contact with the connection pins of the connector  11 , and portions in a connector contact region  30  to be brought into contact with the connection pins of the connector  11 . 
     The line width and the wiring spacing of the patterned radiofrequency conductors  26  are designed to realize a predetermined characteristic impedance. The patterned ground conductors  27  differ in shape from the patterned radiofrequency conductors  26  and designed to be wide enough to ensure a sufficient power supply capacity. The patterned ground conductors  27  are connected to patterned ground conductors  31  in a circuit board inner layer through ground vias  28 . 
     The patterned radiofrequency conductors  26  in the circuit board pattern region  29  constitute microstrip lines in cooperation with the patterned ground conductors  31  in the circuit board inner layer. The patterned radiofrequency conductors  26  in the connector contact region  30  constitute single-end coplanar lines characteristic-impedance-matched to the microstrip lines in cooperation with the adjacent patterned ground conductors  27 . 
       FIG. 5  is a plan view showing transmission paths on the obverse side of the connector according to the first embodiment of the present invention. A transmission path  32  from one of the first obverse-side connection pins  17  to the corresponding one of the second obverse-side connection pins  19  constitutes a single-end coplanar line characteristic-impedance-matched to the microstrip line in cooperation with a ground path  35  which is adjacent to the transmission path  32 , and which extends from one of ground pins  33  in the first insertion opening  13  to one of ground pins  34  in the second insertion opening  15 . In this way, characteristic impedance matching is achieved with respect to a high-rate signal even in the connector  11 , thereby improving the signal quality in communication between the circuit boards. 
     Since the circuit board  12  and the circuit board  14  are connected by forming the patterned conductors in the connector contact regions  30  of the circuit board  12  and  14  and the transmission paths in the connector  11  as coplanar lines, there is no need to extend the patterned conductors on the circuit boards  12  and  14  to circuit board ends  25 . Therefore the patterned radiofrequency conductors  26  and the patterned ground conductors  27  are formed inside the circuit board ends  25  at a certain distance from the circuit board ends  25 , thus enabling prevention of separation between the patterned radiofrequency conductors  26  and the patterned ground conductors  27 . 
     The patterned radiofrequency conductors  26  are uniform in shape through the connector contact region  30  and the circuit board pattern region  29 . Therefore no impedance mismatch occurs due to a change in patterned shape. 
     The ground vias  28  include vias provided at the circuit board end  25  side of the patterned ground conductors  27 . Therefore, when the connections pins of the connector  11  are brought into contact with the patterned ground conductors  27 , a ground current can be caused to flow to each patterned ground conductor  31  in the circuit board inner layer, i.e., a ground surface facing the patterned radiofrequency conductor  26 , at a position closer to the circuit board end  25 . As a result, the length of the impedance mismatching portion is reduced to improve the signal quality in communication between the circuit boards. 
     As shown in  FIG. 3 , the obverse-side slanting angle θ in the connector  11  and the reverse-side slanting angle θ in the connector  11  may be set equal to each other to equalize the length of the transmission paths from the first obverse-side connection pins  17  to the second obverse-side connection pins  19  and the length of the transmission paths from the first reverse-side connection pins  18  to the second reverse-side connection pins  20  and to thereby eliminate the difference in signal transmission delay time between the obverse side and the reverse side of the circuit boards  12  and  14 . It is not necessarily required that the obverse-side slanting angle and the reverse-side slanting angle in the connector  11  be equal to each other in a case where the difference in signal transmission delay time is allowed to exist, for example, in a case where only low-rate signals are transmitted at either of the obverse side and the reverse side of the circuit boards  12  and  14 . 
     Second Embodiment 
       FIG. 6  is a plan view showing an end portion of a circuit board according to the second embodiment of the present invention. Patterned radiofrequency conductors  26  constitute microstrip lines in the circuit board pattern region  29  and constitute differential coplanar lines in the connector contact region  30 . Also, the transmission paths from the first obverse-side connection pins  17  to the second obverse-side connection pins  19  and the transmission paths from the first reverse-side connection pins  18  to the second reverse-side connection pins  20  are formed as differential coplanar lines. In other respects, the construction of the second embodiment is the same as that of the first embodiment. 
     Differential lines are formed as described above to transmit pairs of opposite-phase signals, i.e., normal-phase signals and opposite-phase signals phase-inverted. The resistance to in-phase noise is thereby increased to further improve the signal quality in communication between the circuit boards. 
     Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. 
     The entire disclosure of a Japanese Patent Application No. 2008-111605, filed on Apr. 22, 2008 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.