Patent Publication Number: US-2011050365-A1

Title: Signal transmission apparatus

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to signal transmission apparatuses, and particularly to a signal transmission apparatus used in a signal receiver or a signal transceiver of a wireless transmission system. 
     2. Description of Related Art 
     Wireless transmissions are widely used in communications and networks. Consequently, electronic devices can be moved freely without limitations of wires when transmitting signals. In a wireless transmission system, a signal for transmission is modulated by a high frequency carrier in a signal transceiver to generate a radio frequency signal. The radio frequency signal is transmitted to a signal receiver via air, and is demodulated into the signal for transmission in the signal receiver. However, bad signal quality may be induced if the signal transceiver and the signal receiver of the wireless transmission system are improperly designed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded, isometric view of a signal transmission apparatus according to an embodiment of the present disclosure, wherein the signal transmission apparatus includes a band pass filter. 
         FIG. 2  is a simulation graph of insertion loss of the band pass filter of the signal transmission apparatus of  FIG. 1 . 
         FIG. 3  is a simulation graph of return loss of the band pass filter of the signal transmission apparatus of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an exemplary embodiment of a signal transmission apparatus  10  is positioned in a printed circuit board, and used in a signal receiver or a signal transceiver to transmit signals. The signal transmission apparatus  10  includes a first ground layer  100 , a second ground layer  200 , a band pass filter  300 , a first insulation layer  400 , a second insulation layer  500 , and a third insulation layer  600 . The first ground layer  100  is parallel to the second ground layer  200 , and sandwiched between the first insulation layer  400  and the second insulation layer  500 . The second ground layer  200  is sandwiched between the second insulation layer  500  and the third insulation layer  600 . The first insulation layer  400  insulates the first ground layer  100  from external environment. The second insulation layer  500  insulates the first ground layer  100  from the second ground layer  200 . The third insulation layer  600  insulates the second ground layer  200  from external environment. The band pass filter  300  includes a first transmission line  310  positioned in a void  110  defined in the first ground layer  100 , and a second transmission line  320  positioned in a void  210  defined in the second ground layer  200 . In one embodiment, each of the first ground layer  100  and the second ground layer  200  is made of conductive material, such as copper. The void  110  and the first transmission line  310  are formed by etching the conductive material of the first ground layer  100 . The void  210  and the second transmission line  320  are formed by etching the conductive material of the second ground layer  200 . Each of the first insulation layer  400 , the second insulation layer  500 , and the third insulation layer  600  may be made of glass fiber epoxy resin (FR-4) material. 
     The first transmission line  310  includes a first coil  312  with a plurality of turns spirally extending in the same plane to form a spiral path, a first gasket  314  located in the center of the first coil  312  and acting as the beginning of the first coil  312 , and a first signal terminal  316  extending from extremity of the first coil  312  along a first direction. The second transmission line  320  includes a second coil  322  with a plurality of turns spirally extending in the same plane to form a spiral path, a second gasket  324  located in the center of the second coil  322  and acting as the beginning of the second coil  322 , and a second signal terminal  326  extending from extremity of the second coil  322  along a second direction opposite to the first direction. The void  110  includes a central area  112 , and two slots  114  and  116  respectively extending from two opposite edges of the first ground layer  100  to the central area  112 . The void  210  includes a central area  212 , and two slots  214  and  216  respectively extending from two opposite edges of the second ground layer  200  to the central area  212 . The voids  110  and  210  have similar shapes, and a projection of the void  110  on the second ground layer  200  completely overlaps the void  210 . The first transmission line  310  and the second transmission line  320  have similar shapes. A projection of a geometric center of the first gasket  314  on the second ground layer  200  completely overlaps a geometric center the second gasket  324 . The first signal terminal  316  and the second signal terminal  326  extending along opposite directions, are used for transmitting and receiving signals. A projection of the first signal terminal  316  on the second ground layer  200  is within the slot  214  of the second ground layer  200 , and a projection of the second signal terminal  326  on the first ground layer  100  is within the slot  116  of the first ground layer  100 . 
     Filtering characteristics of the band pass filter  300  depend on the number of turns of the first and second coils  312  and  322 , line width and line spacing of the spiral path of the first and second coils  312  and  322 , areas of the first and second gaskets  314  and  324 , and a distance between the first ground layer  100  and the second ground layer  200 . Further details of factors that affect the filtering characteristics of the band pass filter  300  will be explained in further detail below. The number of turns of the first and second coils  312  and  322 , and the line width and line spacing of spiral path of the first and second coils  312  and  322  mainly affect inductance effect of the band pass filter  300 , thereby affect bandwidth responded by the band pass filter  300  and drifting of center frequency of the band pass filter  300 . The more turns of the first and second coils  312  and  322 , and the narrower line width and the shorter line spacing of spiral path of the first and second coils  312  and  322 , the stronger inductance effect of the band pass filter  300 , the wider bandwidth responded by the band pass filter  300 , and the center frequency of the band pass filter  300  drifting to lower frequency. The areas of the first and second gaskets  314  and  324  mainly affect bandwidth responded by the band pass filter  300  and insertion loss of the band pass filter  300 . The larger areas of the first and second gaskets  314  and  324 , the wider bandwidth responded by the band pass filter  300 , and the less insertion loss of the band pass filter  300 . The distance between the first ground layer  100  and the second ground layer  200  mainly affects capacitance effect of the band pass filter  300 . The shorter distance between the first ground layer  100  and the second ground layer  200 , the stronger capacitance effect of the band pass filter  300 . 
     In one embodiment, the first coil  312  and the second coil  322  have the same number of turns, the same line width and the same line spacing, the turns of the first coil  312  circularly spiral in the first ground layer  100 , and the turns of the second coil  322  circularly spiral in the second ground layer  200 . Each of the first gasket  314  and the second gasket  324  is a circular gasket, and the geometric center of each of the first gasket  314  and the second gasket  324  is a center of the circular gasket. Each of the central areas  112  and  212  is a circular hollow area. The slots  114  and  116  are parallel to each other and tangent to the central area  112 . The slots  214  and  216  are parallel to each other and tangent to the central area  212 . 
     Referring to  FIGS. 2 and 3 , in one embodiment, parameters of the band pass filter  300  are as follows: the number of turns of each of the first coil  312  and the second coil  322  is about N=4; the line width of spiral path of each of the first coil  312  and the second coil  322  is about W=4 mils; the line spacing of spiral path of each of the first coil  312  and the second coil  322  is about S=4 mils; radius of each of the first gasket  314  and the second gasket  324  is about R=8 mils; the distance between the first ground layer  100  and the second ground layer  200  is about D=2 mils. The band pass filter  300  can be simulated using a simulation software according to the above-mentioned parameters, in order to obtain a graph of an insertion loss of the band pass filter  300  (shown in  FIG. 2 ) and a graph of return loss of the band pass filter  300  (shown in  FIG. 3 ). 
     In  FIG. 2 , the abscissa is a frequency F of a signal transmitted through the band pass filter  300 , the ordinate is an insertion loss IL of the signal, and the more the ordinate of the graph closing to zero, the better performance of the band pass filter  300 . In  FIG. 3 , the abscissa is a frequency F of a signal transmitted through the band pass filter  300 , the ordinate is a return loss RL of the signal, and the smaller the ordinate of the graph, the better performance of the band pass filter  300 . It can be seen in  FIGS. 2 and 3  that a desired performance of the band pass filter  300  is achieved in a frequency band from 2.25 gigahertz (GHZ) to 3.85 GHZ, since the corresponding insertion loss values are close to zero and the corresponding return loss values are less than −10 decibels (dB). In other embodiments, the number of turns, the line width and line spacing of the first and second coils  312  and  322 , the shape of the first and second coils  312  and  322 , the first and second gaskets  314  and  324  and the voids  110  and  210 , and the distance between the first ground layer  100  and the second ground layer  200 , can be adjusted according to actual needs. Additionally, the signal transmission apparatus  10  not only can be used in wireless transmission devices, such as wireless network card and access point, but also can be used in wired transmission devices. Furthermore, according to employing the band pass filter  300 , the signal transmission apparatus  10  has filtering function, therefore, quality of signals transmitted through the signal transmission apparatus  10  is improved. 
     The foregoing description of the exemplary embodiments of the disclosure has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Many modifications and variations are possible in light of the above everything. The embodiments were chosen and described in order to explain the principles of the disclosure and their practical application so as to enable others of ordinary skill in the art to utilize the disclosure and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those of ordinary skills in the art to which the present disclosure pertains without departing from its spirit and scope. Accordingly, the scope of the present disclosure is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.