Abstract:
A device for enhancing electromagnetic susceptibility comprises a first bridge. The first bridge is near to a first trace of a differential pair routing and electrically connects an RF grounding with an analog grounding. The RF grounding and the analog grounding are separated. The differential pair routing transmits signals between an RF circuit and an analog circuit. The first trace of the differential pair routing is closer to an antenna coupled to the RF grounding than a second trace of the differential pair routing. The RF circuit is coupled to the RF grounding, and the analog circuit is coupled to the analog grounding.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims priority of Taiwan Patent Application No. 101100137, filed on Jan. 3, 2012, the entirety of which is incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to wireless communication device and more particularly to a wireless communication device having separated groundings. 
         [0004]    2. Description of the Related Art 
         [0005]    For system-level layout design, good grounding is important. Generally, in order to suppress noise, the simplest and most effective way is to separate groundings with different properties, for example, groundings for analog and digital portions of circuitry. On the other hand, for signal trace routing, in order to avoid being influenced by EMI (Electromagnetic Interference), a differential architecture is a commonly used structure to improve EMS (Electromagnetic Susceptibility) of a system. For antenna design engineers, enhancing the efficiency of antennas is an important task. However, too much radiation power sometimes causes trouble to the system. For example, enhancing the antenna efficiency may result in enhancing EMI noise owing to radiation or conduction. 
         [0006]      FIG. 1(   a ) shows a top view of a wireless communication device  10 . An RF (Radio Frequency) grounding  120  and an analog grounding  130  are provided on a printed circuit board  100 . There&#39;s a moat  110  between the RF grounding  120  and the analog grounding  130 , so the RF grounding  120  and the analog grounding  130  are separated groundings.  FIG. 1(   a ) only shows a portion of the wireless communication device  10 . An on-board antenna, such as a printed inverted-F antenna  140 , is provided on the printed circuit board  100  and coupled to the RF grounding  120 .  FIG. 1(   b ) is a partial enlarged view of  FIG. 1(   a ). Differential pair routings  150  and  160  used to transmit signals are wiring devices with two traces. Parts of the differential pair routings  150  and  160  are in the same layer as the RF grounding  120  and the analog grounding  130 . Other parts of the differential pair routings  150  and  160  enter other layers by drilling so as to connect with circuits or other modules on the other layers, such as an RF module. The on-board antenna on the circuit board induces strong edge current. When increasing the efficiency of antennas, the current density becomes larger on the groundings. The current energy, especially the current energy along the edges of groundings, couples the conductive EMI energy to the differential pair routings  150  and  160  via stray capacitance between groundings and differential pair routings. In the differential pair routing  150 , the trace  150 - a,  which is closer to the antenna  140 , has more EMI noise than the other trace  150 - b,  and thus magnitudes of EMI noise on two traces of the differential pair routing  150  are unequal. A colored figure in  FIG. 5  is a simulation diagram of current density of the wireless communication device in  FIG. 1(   a ) and  FIG. 1(   b ). The left part of the colored figure in  FIG. 5  corresponds to the structure in  FIG. 1(   a ) and the right part of the colored figure in  FIG. 5  corresponds to the structure in  FIG. 1(   b ). As shown in right part of the colored figure in  FIG. 5 , red parts representing higher current density are drawn near the trace  150 - a,  which is closer to the antenna  140  in the differential pair routing. Orange parts representing second high current density are drawn near the other trace  150 - b.  Therefore, higher current density is distributed in the trace  150 - a,  which is closer to the antenna  140  in the differential pair routing, than in the other trace  150 - b.  Furthermore, as shown in  FIG. 2 , simulated voltage response between trances of the differential pair routing has bigger fluctuations, and hence the EMI noise can&#39;t be diminished effectively through differential pair routings. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    In view of this, a bridge is arranged near to a differential pair routing to reduce EMI noise of the differential pair routing and hence improve immunity against EMI. 
         [0008]    In one embodiment, the invention provides a device for enhancing electromagnetic susceptibility, comprising: a first bridge, arranged near to a first trace of a differential pair routing and electrically connecting a radio frequency (RF) grounding with a analog grounding, wherein the RF grounding and the analog grounding are separated, the differential pair routing transmits signals between an RF circuit and an analog circuit, the first trace of the differential pair routing is closer to an antenna coupled to the RF grounding than a second trace of the differential pair routing, the RF circuit is coupled to the RF grounding, and the analog circuit is coupled to the analog grounding. 
         [0009]    In another embodiment, the invention provides a grounding device for enhancing electromagnetic susceptibility, comprising: an RF grounding; an analog grounding, separated from the RF grounding; and a first bridge, arranged near to a first trace of a differential pair routing and electrically connecting the RF grounding with the analog grounding, wherein the differential pair routing transmits signals between an RF circuit and an analog circuit, the first trace of the differential pair routing is closer to an antenna coupled to the RF grounding than a second trace of the differential pair routing, the RF circuit is coupled to the RF grounding, and the analog circuit is coupled to the analog grounding. 
         [0010]    In still another embodiment, the invention provides a wireless communication device, comprising: a circuit board, wherein a layer of the circuit board comprises an RF grounding and an analog grounding, the RF grounding and the analog grounding are separated, the RF grounding is coupled to an RF circuit, and the analog grounding is coupled to an analog circuit; an antenna, arranged on the circuit board and coupled to the RF grounding; a differential pair routing, transmitting signals between the RF circuit and the analog circuit and comprising a first trace and a second trace, wherein the first trace is closer to the antenna than the second trace; and a first bridge, arranged near to the first trace of the differential pair routing and electrically connecting the RF grounding with the analog grounding. 
         [0011]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0013]      FIG. 1(   a ) shows a top view of a wireless communication device in prior art; 
           [0014]      FIG. 1(   b ) is a partial enlarged view of  FIG. 1(   a ); 
           [0015]      FIG. 2  shows a simulation diagram of voltage response of a differential pair routing of the wireless communication device in prior art; 
           [0016]      FIG. 3(   a ) shows a top view of a wireless communication device according to an embodiment of the invention; 
           [0017]      FIG. 3(   b ) is a partial enlarged view of  FIG. 3(   a ); 
           [0018]      FIG. 4  shows a simulation diagram of voltage response of a differential pair routing of the wireless communication device according to an embodiment of the invention; 
           [0019]      FIG. 5  is a colored simulation diagram of current density of the wireless communication device in  FIG. 1(   a ) and  FIG. 1(   b ); and 
           [0020]      FIG. 6  is a colored simulation diagram of current density of the wireless communication device in  FIG. 3(   a ) and  FIG. 3(   b ). 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0022]      FIG. 3(   a ) shows a top view of a wireless communication device  30  according to an embodiment of the invention.  FIG. 3(   a ) only shows a portion of the wireless communication device  30 . The wireless communication device  30  comprises a printed circuit board  300  having an RF grounding  320  and an analog grounding  330 . There is a moat  310  between the RF grounding  320  and the analog grounding  330 , and hence the RF grounding  320  and the analog grounding  330  are separated groundings. In an example, the RF grounding  320  and the analog grounding  330  are metal layers. The RF grounding  320  is coupled to an RF module (not shown) for processing RF signals. The analog grounding  330  is coupled to an analog module (not shown) for processing analog signals. A printed inverted-F antenna  340  is arranged on the printed circuit board  300  and coupled to the RF grounding  320 .  FIG. 3(   b ) is a partial enlarged view of  FIG. 3(   a ). Differential pair routings  350  and  360  used to transmit signals are wiring devices with two traces. As shown in  FIG. 3(   b ), parts of the differential pair routings  350  and  360  are in the same layer as the RF grounding  320  and the analog grounding  330 , and other parts of the differential pair routings  350  and  360  enter other layers by drilling so as to connect with circuits or other modules on the other layers, such as an input port for analog signals in an RF module. The wireless communication device  30  further comprises bridges  370  and  380 . Bridges  370  and  380  are arranged on two sides of the differential pair routing  350 , respectively, and near to (but not connected to) the differential pair routing  350 . In other words, bridges  370  and  380  are arranged near to two traces  350 - a  and  350 - b  of the differential pair routing  350 , respectively. Bridges  370  and  380 , respectively arranged on two sides of the differential pair routing  350 , connect the RF grounding  320  with the analog grounding  330  and conduct strong edge current on edges of groundings, and hence the edge current is not easy to flow near to the differential pair routing. Therefore, EMI is reduced, and influence of EMI on transmitting signals is reduced remarkably so as to enhance EMS. 
         [0023]    As described above, bridges  370  and  380  are devices for enhancing EMS. The bridge  370  is arranged near to the trace  350 - a  of the differential pair routing  350  and connects the RF grounding  320  with the analog grounding  330  separated from the RF grounding  320 . The bridge  380  is arranged near to the trace  350 - b  of the differential pair routing  350  and connects the RF grounding  320  with the analog grounding  330  separated from the RF grounding  320 . The trace  350 - a  is closer to the antenna  340  than the trace  350 - b.    
         [0024]      FIG. 6  is a colored simulation diagram of current density of the wireless communication device in  FIG. 3(   a ) and  FIG. 3(   b ). The left part of the colored figure in  FIG. 6  corresponds to the structure in  FIG. 3(   a ) and the right part of the colored figure in  FIG. 6  corresponds to the structure in  FIG. 3(   b ). As shown in right part of the colored figure in  FIG. 6 , the red parts represent higher current density masses on the bridge  370  of  FIG. 3(   b ). Because the bridge conducts the strong edge current, the current density is mainly distributed on the bridge  370  which is closer to the printed inversed-F antenna  340 . Therefore, as shown in right part of the colored figure in  FIG. 6 , the simulation result of current density on the differential pair routing  350  is uniformly green. Hence, unlike the differential pair routing  150  having higher current density distributed on the trace  150 - a  than the trace  150 - b,  current density on the differential pair routing  350  is much more uniform than that on the differential pair routing  150  of the colored figure in  FIG. 5 . 
         [0025]      FIG. 4  shows a simulation diagram of voltage response of the differential pair routing of the wireless communication device  30  in  FIG. 3(   a ). The simulation simulates the voltage difference between the differential pair routings as time steps go on. The unit of time steps is a nanosecond (ns). As shown in  FIG. 4 , the fluctuation of voltage response in  FIG. 4  is much less than that in  FIG. 2 . 
         [0026]    In the embodiment, bridges are arranged on two sides of the differential pair routing  350 , and thus the RF grounding  320 , the analog grounding  250  and bridges  370  and  380 , which are all conductive materials, surround (but not contact with) the differential pair routing  350  to prevent EMI from being coupled to the differential pair routing  350 , and thus EMI on signals transmitted by the differential pair routing  350  is effectively diminished. In another embodiment, only the side of the differential pair routing  350  which is closer to the printed inverted-F antenna  340  has a bridge, that is, the bridge  370 . In other words, the bridge is arranged near to the trace  350 - a  of the differential pair routing  350 . Note that bridges  370  and  380  don&#39;t have to be in the same layer as the RF grounding  320  and the analog grounding  330 . Bridges  370  and  380  are arranged near to the differential pair routing  350 . When the bridges  370  and  380  are in the same layer as the RF grounding  320  and the analog grounding  330 , printed circuit technology may be used to form the bridges  370  and  380 . When the bridges  370  and  380  are not in the same layer as the RF grounding  320  and the analog grounding  330 , the bridges  370  and  380  are connectors with conductive material to connect the RF grounding  320  with the analog grounding  330 . 
         [0027]    As described above, arranging bridges on two sides of the differential pair routing and near to the differential pair routing effectively diminishes EMI as shown from the colored simulation diagram in  FIG. 5  and  FIG. 4 . 
         [0028]    Though above embodiments are illustrated with an example of the RF module and the analog module, a person skilled in the art is able to apply the invention to an RF circuit and an analog circuit. 
         [0029]    In the specification, simulated results of  FIG. 2 ,  FIG. 4 ,  FIG. 5 ,  FIG. 6  are simulated by a 3D EM simulator GEMS of 2COMU. 
         [0030]    The wireless communication device in the embodiments of the invention is especially applied to a wireless communication device performing wireless communication and analog signal processing at the same time, such as a two-way voice communication device. 
         [0031]    Embodiments of the invention especially applies to wireless communication devices implementing wireless communication and processing analog signals at the same time, such as a two-way voice communication device, like a wireless intercom device. 
         [0032]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.