Patent Publication Number: US-8976011-B2

Title: Circuit board structure

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a circuit board structure for a low noise block down-converter, and more particularly, to a circuit board structure capable of transmitting two radio-frequency signals across each other. 
     2. Description of the Prior Art 
     A satellite communication receiver may include a dish reflector and an LNBF (Low Noise Block Down-converter with Feedhorn). The LNBF is used for gathering satellite signals reflected by the dish reflector and converting the satellite signals into intermediate signals, and then transmitting the intermediate signals to a backend satellite signal processor for signal processing, thereby enabling the playing of satellite television programs. 
     Please refer to  FIG. 1 , which is a structural circuit diagram of a conventional LNB (Low Noise Block down-converter)  10 . The LNB  10  has a function of outputting dual signals for two users. The LNB  10  includes LNAs (Low Noise Amplifiers)  101 - 112 , power dividers  121 - 124 , filters  131  and  132 , mixers  141  and  142 , oscillators  151 - 154  and a cross structure  160 . Connection relations between the elements comprised in the LNB  10  are shown in  FIG. 1 . 
     In operation, when the satellite signals are received by the LNB  10 , the satellite signals may be separated into an RF (Radio-Frequency) signal SV and an RF signal SH according to different polarizations, wherein the RF signal SV is vertically polarized and the RF signal SH is horizontally polarized. Operating voltages of the LNB  10  may be switched to control the elements comprised in the LNB  10  to perform signal processing on the RF signals SV and SH. The operating voltages for respectively processing the RF signals SV and SH are 13 volts and 18 volts. As the RF signal SV entered the LNB  10 , the RF signal SV may be amplified by the LNAs  101  and  102  for two levels of signal amplification first, power divided by the power divider  121 , and then part of the RF signal SV is amplified by the LNA  103  and the rest of RF signal SV is transmitted to the LNA  109  to be amplified by the LNA  109 . Output terminals of the LNAs  103  and  104  may be coupled together to synthesize the RF signals SV and SH into a synthesized RF signal SVH 1 , the RF signal SVH 1  may be amplified by the LNA  105 , filtered by the filter  131 , and mixed with a local oscillate signal L 1  or L 2  by the mixer  141 , so that the RF signal SVH 1  may be down converted into an IF (Intermediate Frequency) signal S 1 . 
     Likewise, as the RF signal SH enters the LNB  10 , the RF signal SH may be amplified by the LNAs  107  and  108  for two levels of signal amplification first, power divided by the power divider  123 , and then part of the RF signal SH is amplified by the LNA  110  and the rest of RF signal SH is transmitted to the LNA  104  to be amplified by the LNA  104 . Output terminals of the LNAs  109  and  110  may be coupled together to synthesize the RF signals SV and SH into a synthesized RF signal SVH 2 , the RF signal SVH 2  may be amplified by the LNA  111 , filtered by the filter  132 , mixed with a local oscillating signal L 1  or L 2  by the mixer  142 , so that the RF signal SVH 2  may be down converted into an IF signal S 2 . 
     In such a structure, the LNB  10  may control operations of the oscillators  151 - 154  to respectively generate the local oscillating signals L 1  and L 2 . Or, the LNB  10  may further control the power dividers  122  and  124  to adjust signal intensities of the local oscillating signals L 1  and L 2 , so as to generate the IF signals S 1  and S 2  having different operating frequencies. For example, the following equations are down-conversion formulas of the LNB  10  for a Ku operating band: (Unit:GHz)
 
 SV/SH (10.7−12.75)− L 1(9.75)= S 1(0.95−3.0)
 
 SV/SH (10.7−12.75)− L 2(10.6)= S 2(0.1−2.15)
 
     Please refer to  FIG. 2 , which is an appearance diagram of the LNB  10 . The LNB  10  includes circuit boards  11  and  12 , spacers  13  and  14 , a housing  15 , output ports P 1  and P 2  and a plurality of thru pins  16 . The circuit boards  11  and  12  are respectively disposed on two sides of the housing  15 , the circuit boards  11  and  12  may be disposed with circuits or elements shown in  FIG. 1  for performing signal process. The spacers  13  and  14  are respectively disposed on the circuit board  11  and  12  for covering the circuit boards  11  and  12 . The thru pins  16  may penetrate through the circuit boards  11  and  12  and the housing  15  for transmitting signals flowing between the circuit boards  11  and  12 . The output ports P 1  and P 2  are coupled to the circuit board  11  for respectively outputting the IF signals S 1  and S 2  to the backend satellite signal processor (not shown in  FIG. 2 ). 
     However, since operating frequencies of the satellite signals, i.e. the RF signals SV and SH and the IF signals S 1  and S 2  are high, a return loss and an insertion loss of the RF signals SV and SH may be increased in the structure shown in  FIG. 2 . Specifically, a characteristic impedance of the thru pins  16  may be different from characteristic impedances of the circuit boards  11  and  12 , and thus the RF signals SV and SH may flow across discontinuous impedances between the thru pins  16  and the circuit boards  11  and  12 , which may increase the return loss and the insertion loss of the RF signals SV and SH. 
     Moreover, an isolation between any two thru pins  16  may be low, which may cause the RF signal flowing on the two thru pins  16  to interfere with each other by coupling or radiation, i.e. signal crosstalk. For example, except for the RF signals SV and SH, other signals such as the IF signals S 1  and S 2  and the local oscillating signals L 1  and L 2  may be viewed as a noise source and radiated by the thru pins  16  due to signal reflection or signal leak. In  FIG. 1 , assume the mixer  141  utilizes the local oscillating signal L 2  generated by the oscillator  152  to mix with the RF signal SVH 1 . However, the local oscillating signal L 1  generated by the oscillator  153  flows from the mixer  142 , the filter  132 , the LNAs  111  and  109  to the LNAs  104  and  105  at the cross structure  160  by coupling, and goes flowing to the filter  131  and finally the mixer  141 . In such a situation, the IF signal S 1  generated by the LNB  10  may include noises generated by mixing the local oscillating signal L 1  with the local oscillating signal L 2 . The noise may be described as the following equation: (Unit:GHz)
 
 L 1(10.6)− L 2(9.75)=0.85
 
     To eliminate the frequency 0.85 GHz and its harmonic frequency 1.7 GHz, an additional filter may be required or a change in the specification of the filter  131 , which may increase a difficulty to design the LNB  10  and a production cost as well. 
     On the other hand, for a production process, it may take a lot of work or time to assemble the thru pins. Besides, two circuit boards and two spacers may increase a weight of the LNB  10 , which not only increases the production cost and also increases a difficulty for installing a satellite television system. Therefore, there is a need to improve the prior art. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a circuit board structure for a low noise block down-converter for transmitting two radio-frequency signals across each other and improve the above mentioned problem. 
     The present invention discloses a circuit board structure for a low noise block down-converter, and used for transmitting a first radio-frequency signal and a second radio-frequency signal across each other, including a first substrate including a first wire for transmitting the first radio-frequency signal, a first grounded wire formed in parallel to one side of the first wire, two ends of the first grounded wire are respectively electrically connected to a first via and a second via, and a second grounded wire formed in parallel to another side of the first wire, two ends of the second grounded wire are respectively electrically connected to a third via and a fourth via, and a second substrate electrically connected to the first substrate, and including a second wire for transmitting the second radio-frequency signal, a third wire formed on one side of the second wire, and electrically connected to one end of the first wire by a fifth via to transmit the first radio-frequency signal, and a fourth wire formed on another side of the second wire, and electrically connected to another end of the first wire by a sixth via to transmit the first radio-frequency signal, wherein the third wire and the fourth wire are indirectly connected to each other, and the first, second, third, fourth, fifth and sixth vias penetrate the first substrate and the second substrate. 
     The present invention further discloses a low noise block down-converter, including a circuit board structure for a low noise block down-converter, and used for transmitting a first radio-frequency signal and a second radio-frequency signal across each other, including a first substrate including a first wire for transmitting the first radio-frequency signal, a first grounded wire formed in parallel to one side of the first wire, two ends of the first grounded wire are respectively electrically connected to a first via and a second via, and a second grounded wire formed in parallel to another side of the first wire, two ends of the second grounded wire are respectively electrically connected to a third via and a fourth via, and a second substrate electrically connected to the first substrate, and including a second wire for transmitting the second radio-frequency signal, a third wire formed on one side of the second wire, and electrically connected to one end of the first wire by a fifth via to transmit the first radio-frequency signal, and a fourth wire formed on another side of the second wire, and electrically connected to another end of the first wire by a sixth via to transmit the first radio-frequency signal, and a housing for covering the circuit board structure, wherein the third wire and the fourth wire are indirectly connected to each other, and the first, second, third, fourth, fifth and sixth vias penetrate the first substrate and the second substrate. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural circuit diagram of a conventional LNB. 
         FIG. 2  is an appearance diagram of the LNB shown in  FIG. 1 . 
         FIG. 3A  to  FIG. 3C  are respectively a perspective view, a bottom view and a top view of a circuit board structure according to an embodiment of the present invention. 
         FIG. 4A  to  FIG. 4C  are schematic diagrams of simulations of insertion losses, isolations and return losses of the circuit board structure shown in  FIG. 3 . 
         FIG. 5A  is an appearance diagram of an LNB according to an embodiment of the present invention. 
         FIG. 5B  is part of the appearance diagram of the LNB shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 3A  to  FIG. 3C , which are a perspective view, a bottom view and a top view of a circuit board structure  30  according to an embodiment of the present invention, respectively. The circuit board structure  30  may be utilized in the cross structure  160  of the LNB  10  shown in  FIG. 1  for transmitting the RF signals SV and SH across each other. The circuit board structure  30  includes a plurality of vias H 1 -H 6 , a first substrate  31  and a second substrate  32 . The first substrate  31  includes a first surface  311 , a second surface  312 , a first wire L 1 , a first grounded wire G 1  and a second grounded wire G 2 . The second substrate includes a first surface  321 , a second surface  322 , a second wire L 2 , a third wire L 3  and a fourth wire L 4 . 
     In detail, the first wire L 1  is used for transmitting the RF signal SV. The first grounded wire G 1  is formed paralleled to one side of the first wire L 1 , two ends of the first grounded wire G 1  are respectively electrically connected to the via H 3  and the via H 4 . The second grounded wire G 2  is formed paralleled to another side of the first wire L 1 , two ends of the second grounded wire G 2  are respectively electrically connected to the via H 5  and the via H 6 . The first wire L 1 , the first grounded wire G 1  and the second grounded wire G 2  are formed on the first surface  311 . The first grounded wire G 1  is electrically connected to a ground (not shown in  FIG. 3A ) of the second substrate  32  by the via H 3  and the via H 4 , the second grounded wire G 2  is electrically connected to the ground of the second substrate  32  by the via H 5  and the via H 6 . The second wire L 2  is used for transmitting the RF signal SH. The third wire L 3  is formed on one side of the second wire L 2 , and electrically connected to one end of the first wire L 1  by the via H 1  to transmit the RF signal SV. The fourth wire L 4  may be formed on another side of the second wire L 2 , and electrically connected to another end of the first wire L 1  by the via H 2  to transmit the RF signal SV. The second wire L 2 , the third wire L 3  and the fourth wire L 4  may be formed on the second surface  322  of the second substrate  32 . 
     In other words, in the cross structure  160 , a signal path from a node B to a node C may be regarded as the second wire L 2  of the circuit board structure  30 , and a signal path from a node A to a node D may be regarded as the third wire L 3 , the first wire L 1  and the fourth wire L 4  of the circuit board structure  30 . Since the third wire L 3  and the fourth wire L 4  are indirectly connected to each other, two ends of the first wire L 1  may be connected between the third and fourth wires L 3  and L 4  by the vias H 1  and H 2 , such that the circuit board structure  30  may be able to transmit the RF signal SV (the nodes A to C) and RF signal SH (the nodes B to D) across each other. 
     As a result, the vias H 1 -H 6  may be substituted for the thru pins  16  shown in  FIG. 2 , the vias H 1 -H 6  may penetrate through the first substrate  31  and the second substrate  32 , the vias H 1  and H 2  may be viewed as signal transmission lines between the first substrate  31  and the second substrate  32  to transmit the RF signal SV. When the RF signal SV is transmitted from the second substrate  32  to the first substrate  31 , the vias H 3 -H 6  and the first and second grounded wires G 1  and G 2  may be viewed as a reference ground of the RF signal SV, such that the RF signal SV may reference a continuous ground even though the RF signal SV is flowing between two layers, which may uniform impedances and decrease return losses of the signal transmission lines for transmitting the RF signal SV. Moreover, the circuit board structure  30  may be designed according to CoPlanar Waveguide principles, so that a designer may adjust a wire width and a dielectric coefficient of the substrate to design a proper transmission line and ensure a uniform and continuous characteristic impedance of the transmission line. In production, the first substrate  31  can be electrically connected to second substrate  32  by a surface mount technology. The second substrate  32  may be viewed as a mother board, and the first substrate  31  may be viewed as a daughter board. The first and second substrates  31  and  32  may be made of a same raw substrate to have a same dielectric coefficient, which may save a cost for producing circuit boards, time and labor for assembling the thru pins  16 , as well as ensure a stability of production. 
     Please refer to  FIG. 3B , a spacer  33  may be disposed on the second surface  322  of the second substrate  32  to enhance isolations and mitigate the electromagnetic radiations between the second wire L 2 , the third wire L 3  and the fourth wire L 4 . The spacer  33  includes separation units  331  and  332 . The separation unit  331  may be formed between the second wire L 2  and the third wire L 3 , electrically connected to one end of the first grounded wire G 1  by the via H 3 , and electrically connected to one end of the second grounded wire G 2  by the via H 5 . The separation unit  332  may be formed between the second wire L 2  and the fourth wire L 4 , electrically connected to another end of the first grounded wire G 1  by the via H 4 , and electrically connected to another end of the second grounded wire G 2  by the via H 6 . The separation units  331  and  332  have a height HT, e.g. 2 mm, such that the separation unit  331  and  332  may be able to shield or block the electromagnetic radiations between the RF signals SH and SV. As a result, the separation units  331  and  332  may be used for shielding or blocking the electromagnetic radiations between the RF signal SV and the RF signal SH to prevent the RF signal SV and RF signal SH from interfering with each other. 
     Please refer to  FIG. 3C , a grounded area GND may be formed on the second surface  312  of the first substrate  31 . The grounded area GND may be electrically connected to the separation units  331  and  332  (not shown in  FIG. 3C ) by the vias H 3 -H 6 . Besides, the grounded area GND, which may be viewed as a ground of the second substrate  32 , may be formed on the first surface  321  of the second substrate  32 , and electrically connected to the separation units  331  and  332  by the vias H 3 -H 6 . In other words, as long as the grounded area GND is electrically connected to the vias H 3 -H 6 , the grounded area GND may shield or block the electromagnetic radiations between the RF signals SV and RF signal SH. 
     Please refer to  FIG. 4A  to  FIG. 4C , which are schematic diagrams of simulations of insertion losses, isolations and return losses of the circuit board structure  30 . In  FIG. 4A , the insertions loss between nodes A and C, which is a signal route of the RF signal SV, is denoted with a solid line, the insertions loss between nodes B and D, which is a signal route of the RF signal SH, is denoted with a dashed line. Table 1 includes measurement data shown in  FIG. 4A : 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Frequency 
                 A-C 
                   
                 B-D 
                   
               
            
           
           
               
               
               
               
               
            
               
                 (GHz) 
                 dB 
                 % 
                 dB 
                 % 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 10.7 
                 −0.33 
                 93 
                 −0.26 
                 94 
               
               
                 12.75 
                 −0.91 
                 81 
                 −0.41 
                 91 
               
               
                   
               
            
           
         
       
     
     As can be seen from Table 1, the circuit board structure  30  has low insertion losses in the operating frequency band 10.7-12.75 GHz. There is at least 81% of the RF signal SV may pass through the circuit board structure  30 , and there is at least 91% of the RF signal SH may pass through the circuit board structure  30 . 
     In  FIG. 4B , the isolation between the nodes B-A is denoted with a solid line, the isolation between the nodes A-D is denoted with a dashed line, the isolation between the nodes C-D is denoted with a dotted line. Table 2 includes measurement data shown in  FIG. 4B : 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Frequency (GHz) 
                 B-A (dB) 
                 A-D (dB) 
                 C-D (dB) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 10.7 
                 −50.0 
                 −43.2 
                 −45.2 
               
               
                   
                 12.75 
                 −38.7 
                 −39.2 
                 −35.2 
               
               
                   
                   
               
            
           
         
       
     
     As can be seen from Table 2, the circuit board structure  30  has high isolations in the operating frequency band 10.7-12.75 GHz. The values of isolation between the nodes B-A, A-D, C-D are all less than −35.2 dB, which indicates there are less than 0.03% signals flowing between the nodes B-A, A-D, C-D. 
     In  FIG. 4C , the return loss of the node A is denoted with a solid line, the return loss of the node B is denoted with a dashed line, the return loss of the node C is denoted with a dotted line, the return loss of the node D is denoted with a bold-faced line. The return losses of the node C at frequencies 10.7 GHz and 12.75 GHz are respectively −13.2 dB and −14.2 dB, which indicates there are 4.7% and 3.8% of the RF signal reflected at the node C. The return losses of the nodes A, B and D are less than the return loss of the node C. 
     Please refer to  FIG. 5A  and  FIG. 5B .  FIG. 5A  is an appearance diagram of an LNB  50  according to an embodiment of the present invention.  FIG. 5B  is part of the appearance diagram of the LNB  50 . As shown in  FIG. 5A , the LNB  50  includes a circuit board  51 , a spacer  53  and a housing  55 . A circuit board structure  30  may be formed on the circuit board  51 , the circuit board  51  may be disposed between the housing  55  and the spacer  53  to cover the circuit board structure  30 . 
     Noticeably, as shown in  FIG. 5B , a slot area  56  may be formed on the housing  55  for containing the first substrate  31  of the circuit board structure  30 . There is a slot height DT, e.g. 1.1 mm, of the slot area  56 , such that the housing  55  may shield or block electromagnetic radiations from the RF signals SV and SH. 
     To sum up, compared with the traditional LNB  10  shown in  FIG. 2 , the LNB  50  of the present invention may be realized by one circuit board  51  and one spacer  53 , which may save the cost for producing circuit boards, time and labor for assembling the thru pins  16 , as well as ensure the stability of production. A weight and a volume of the LNB  50  may be lighter and smaller than a weight and a volume of the LNB  10  shown in  FIG. 2 , which may improve a convenience for installing a television satellite system. Besides, the circuit board structure  30  is designed according to CoPlanar Waveguide principle, a designer may adjust a wire width and a dielectric coefficient of the substrate to design a proper transmission line and ensure the insertion loss, the return loss and the isolation. The housing and the spacer may enhance an ability of the LNB  50  to shield or block the electromagnetic radiation of the RF signal, mitigate the coupling effect or crosstalk between the RF signals to improve an SNR (Signal-to-Noise Ratio) of the LNB. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.