Abstract:
A signal processing circuit is disclosed, comprising a first node for coupling with a first antenna, a second node for coupling with a second antenna, a third node for receiving a first signal from a transmitting circuit, a fourth node for coupling with a receiving circuit, a signal dividing circuit, a phase shifting circuit, and a signal combining circuit. The signal dividing circuit divides the first signal into a second signal and a third signal, and transmits the second signal to the first antenna. The phase shifting circuit shifts the phase of the third signal to generate a fourth signal for canceling at least part of a coupled signal between the third node and the fourth node. The signal combining circuit combines the fourth signal and a fifth signal received from the second antenna, and transmits the combined signal to the receiving circuit.

Description:
BACKGROUND 
       [0001]    The present disclosure generally relates to a signal processing circuit, and more particularly, to a signal processing circuit utilized in a multiple-antenna device. 
         [0002]    In wireless communications, the utilization of multiple antennas may effectively enhance the system performance. The antennas may be used to provide the antenna diversity, the multiple-input-multiple-output (MIMO) function, etc. For example, IEEE 802.11n devices and long-term-evolution (LTE) devices have utilized multiple antennas for providing the MIMO function. 
         [0003]    The utilization of multiple antennas, however, may also bring side effects. For example, the signals transmitted from one antenna may be coupled with another antenna and act as noise or interference in the receiving circuit. The coupled signals, therefore, degrade the system performance. 
         [0004]    In some devices, the distance between the antennas is increased for reducing the coupling effect. In other applications, isolators may also be used to reduce the coupling effect. As the dimensions of the electronic devices keep shrinking and more elements are built in, the coupling effect becomes even more severe and deteriorates the system performance. Increasing the distance between the electronic elements is not always possible because of the limited physical space of the electronic device. On the other hand, isolators also take a lot of space and are therefore not feasible in many applications. Moreover, isolators often possess a limited bandwidth and may not provide satisfactory isolation. 
       SUMMARY 
       [0005]    In view of the foregoing, it is appreciated that a substantial need exists for the device and method for reducing the coupling effect in the multiple-antenna devices to mitigate the problems mentioned above. 
         [0006]    An example embodiment of a signal processing circuit, comprising: a first node for coupling with a first antenna; a second node for coupling with a second antenna; a third node for receiving a first signal from a transmitting circuit; a signal dividing circuit, coupled with the first node and the third node, for dividing the first signal into a second signal and a third signal and transmitting the second signal to the first antenna; a phase shifting circuit, coupled with the signal dividing circuit, for shifting the phase of the third signal to generate a fourth signal; and a signal combining circuit, coupled with the phase shifting circuit and the second node, for combining the fourth signal and a fifth signal received from the second antenna, wherein the fourth signal cancels at least part of a coupled signal coupled between the third node and the fourth node. 
         [0007]    An example embodiment of a communication method, comprising: dividing a first signal into a second signal and a third signal; transmitting the second signal to a first antenna; shifting the phase of the third signal to generate a fourth signal; receiving a fifth signal from a second antenna; combining the fourth signal and the fifth signal; and canceling at least part of a coupled signal coupled between the first antenna and the second antenna with the fourth signal. 
         [0008]    An example embodiment of a communication device, comprising: a first node for coupling with a first antenna; a second node for coupling with a second antenna; a third node for coupling with a transmitting circuit; a fourth node for coupling with a receiving circuit; and a signal processing means, coupled with the first, the second, the third, and the fourth nodes, for receiving a first signal from the transmitting circuit, dividing the first signal into a second signal and a third signal, transmitting the second signal to the first antenna, shifting the phase of the third signal to generate a fourth signal, combining the fourth signal and a fifth signal received from the second antenna, and transmitting the combined signal to the receiving circuit, wherein the fourth signal cancels at least part of a coupled signal coupled between the third node and the fourth node. 
         [0009]    It is understood that both the foregoing general descriptions and the following detailed descriptions are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows a simplified block diagram of an example multiple-antenna communication device; 
           [0011]      FIG. 2  shows a simplified block diagram of an example signal dividing circuit in  FIG. 1 ; 
           [0012]      FIG. 3  shows a simplified block diagram of another example signal dividing circuit in  FIG. 1 ; and 
           [0013]      FIG. 4  shows a simplified block diagram of still another example signal dividing circuit in  FIG. 1 , all arranged in accordance with at least some embodiments of the present disclosure described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Reference will be made in detail to exemplary embodiments of the disclosure, which are illustrated in the accompanying drawings. The same reference numbers may be used throughout the drawings to refer to the same or like parts or operations. 
         [0015]    Certain terms are used throughout the description and the following claims to refer to particular components. As one skilled in the art will appreciate, a component may be referred to as different names. This disclosure does not intend to distinguish between components that differ in name but not in function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to” The phrase “coupled with” is intended to compass any indirect or direct connection. Accordingly, if this disclosure mentioned that a first device is coupled with a second device, it means that the first device may be directly or indirectly connected to the second device through an electrical connection, wireless communications, optical communications, or other signal connections with/without other intermediate device or connection means. 
         [0016]      FIG. 1  shows a simplified block diagram of an example multiple-antennas communication device  100 . The communication device  100  comprises antennas  120  and  140 , a signal processing circuit  160 , a transmitting circuit  170 , and a receiving circuit  190 . The signal processing circuit  160  comprises a signal dividing circuit  162 , a phase shifting circuit  164 , and a signal combining circuit  166 . Other components and connections are omitted for conciseness. 
         [0017]    The antennas  120  and  140  may be realized with any appropriate type of antennas, for example, dipole antennas, printed circuit antennas, non-planar antennas, and antenna arrays. The circuits  160 ,  162 ,  164 ,  166 ,  170 , and  190  may be realized with discrete circuits, integrated circuits, processors, specific hardware, software, the collaboration of hardware and software, and/or other possible means. 
         [0018]    The antennas  120  and  140  may be used to transmit and/or receive signals jointly or separately. The transmitting circuit  170  is used to generate signals for trans-mission and the receiving circuit  190  is used to process the received signals. 
         [0019]    As shown in  FIG. 1 , the communication device  100  transmits the signal St and receives the signal Sr through the antennas  120  and  140 , respectively. The transmitting circuit  170  transmits the signal S 0  to the signal diving circuit  162 . Besides, a coupled signal Sc represents the component of the signal S 0  coupled from the transmitting circuit  170  to the receiving circuit  190 . The coupled signal Sc is illustrated for easier comprehension only. In reality, the signal S 0  may be coupled from the antenna  120  to the antenna  140 , through the common ground between the transmitting circuit  170  and the receiving circuit  190 , or other possible coupling paths between the transmitting circuit  170  and the receiving circuit  190 . 
         [0020]    The signal diving circuit  162  receives the signal S 0  from the transmitting circuit  170  and divides it into the signals St and S 1 . In this embodiment, the signals St and S 1  are attenuated signals of the signal S 0 . The signal St is transmitted to the antenna  120 . The signal S 1  has substantially the same amplitude as the coupled signal Sc, and is transmitted to the phase shifting circuit  164 . The phase shifting circuit  164  receives the signal S 1  and shifts the phase of the signal S 1  to generate a signal S 2 , which has substantially the same amplitude and a phase difference of approximate 180 degrees with respect to the coupled signal Sc. In another embodiment, the signals St and S 1  may be respectively configured to have the same amplitude, the attenuated amplitude, or the amplified amplitude with respect to the signal S 0 . 
         [0021]    The antenna  140  receives the signal Sr and transmits it to the signal combining circuit  166 . The signal combing circuit  166  combines the signal Sr and the signal S 2  to generate a signal S 3 , which is transmitted to the receiving circuit  190 . The receiving circuit  190  effectively receives the coupled signal Sc and the signal S 3  (which comprises the signal S 2  and the signal Sr). Because the signal S 2  and the coupled signal Sc have substantially the same amplitude and a phase difference of approximate 180 degrees, the signal S 2  may reduce or eliminate the influence of the coupled signal Sc. The receiving circuit  190  may, therefore, process the received signal Sr and achieve a better performance. 
         [0022]    In one embodiment, the phase shifting circuit  164  is realized with one or more resistor-capacitor circuits for generating the required phase shift. In another embodiment, the phase shifting circuit  164  may also be realized with one or more trans-mission lines of appropriate lengths, or circuits with passive and/or active components. 
         [0023]    In one embodiment, the signal combining circuit  166  wires the signal S 2  and the signal Sr for generating the combined signal S 3 . In another embodiment, the signal combining circuit  166  converts the signals S 2  and/or Sr into appropriate forms, e.g., into voltage form or current format, and generates the combined signal S 3 . 
         [0024]    In one embodiment, the magnitude of the coupled signal Sc and the phase difference of the coupled signal Sc and the signal S 0  may be measured in low interference or interference-free laboratories and/or estimated by software simulations. The measurement or simulation results of the magnitude of the coupled signal Sc and the phase difference of the coupled signal Sc and the signal S 0  may be used to configure the signals dividing circuit  162  and/or the phase shifting circuit  164  for generating the signal S 2 , which has substantially the same magnitude and a phase difference of approximate 135 to 225 degrees with respect to the coupled signal Sc. The coupling effect of the coupled signal Sc may be reduced or eliminated by the signal S 2 . In another embodiment, the signal S 2  may be configured to have substantially the same magnitude and a phase difference of 180 degrees with respect to the coupled signal Sc. 
         [0025]    In yet another embodiment, the communication device  100  transmits signals through the antenna  140  and receives signals through the antenna  120 . The transmitting circuit  170  is coupled with the antenna  140  for transmitting the signal St and the receiving circuit  190  is coupled with the antenna  120  for receiving the signal Sr. 
         [0026]    In still another embodiment, there are multiple coupling paths between the transmitting signal  170  and the receiving signal  190 . The signal processing circuit  160  and/or other signal processing circuits of the communication device  100  may be configured according to the measurement or simulation results of the magnitude of the coupled signal Sc and the phase difference between the coupled signal Sc and the signal S 0  for reducing or eliminating the influence of the coupled signals between the transmitting circuit  170  and the receiving signal  190 . For example, to reduce the influence of the coupled signals from two coupling paths, the signal processing circuit  160  may generate corresponding signals for canceling the coupled signals from the two coupling paths. In further another embodiment, multiple signal processing circuits may be used to generate corresponding signals for canceling the coupled signals Sc and therefore for reducing or eliminating the influence of the coupled signal Sc on the receiving circuit  190 . 
         [0027]      FIG. 2  shows a simplified block diagram of an example signal dividing circuit  162  in  FIG. 1 . In this embodiment, the signal dividing circuit  162  comprises a Wilkinson power divider circuit. The signal dividing circuit  162  comprises capacitors  211 ,  212  and  213 , inductors  221  and  222 , and a resistor  231 . The signal dividing circuit  162  is coupled with the transmitting circuit  170 , the antenna  120 , and the phase shifting circuit  164  for receiving and transmitting signals, respectively. 
         [0028]    In one embodiment, the magnitude of the coupled signal Sc is approximately 1/√2 of the magnitude of the signal S 0 . The signal dividing circuit  162  may be configured as an equally splitting Wilkinson power divider, which divides the signal S 0  into two substantially equal magnitude signals St and S 1 . For example, the communication device  100  transmits and receives signals at approximately 2.4 GHz. The capacitors  211 ,  212 , and  213  of the signal dividing circuit  162 , i.e., the equally splitting Wilkinson power divider, are configured to be approximately 1.9 pF, 1 pF, and 1 pF, respectively. The inductors  214  and  215  are configured to be approximately 4.6 nH. The resistor  216  is configured to be approximately 100 ohm. The signal dividing circuit  162  may, therefore, generate two substantially equal magnitude signals St and S 1 . 
         [0029]    In another embodiment, the magnitude of the coupled signal Sc is less than 1/√2 of the magnitude of the signal S 0 . The signal dividing circuit  162  may be configured as an unequally splitting Wilkinson power divider, which divides the signal S 0  into the signals St and S 1 . In this embodiment, the magnitude of the signals St and S 1  are not equal. In some preferred embodiments, the signal dividing circuit  162  is configured so that the magnitude of the signal S 1  is between 1/√2 and 1/100 of the magnitude of the signal S 0 . 
         [0030]      FIG. 3  shows a simplified block diagram of another example signal dividing circuit  162  in  FIG. 1 . In this embodiment, the signal dividing circuit  162  comprises a directional coupler circuit for dividing the signal S 0  into the signals St and S 1 . The signal dividing circuit  162  comprises six capacitors  311 - 316 , inductors  321  and  322 , and a resistor  331 . 
         [0031]      FIG. 4  shows a simplified block diagram of still another example signal dividing circuit  162  in  FIG. 1 . In this embodiment, the signal dividing circuit  162  comprises a hybrid coupler circuit for dividing the signal S 0  into the signals St and S 1 . The signal dividing circuit  162  comprises six capacitors  411 - 416 , four inductors  421 - 424 , and a resistor  431 . 
         [0032]    The figures and embodiments are illustrative only and not intended to limit the scope of the present invention. For example, the circuit  162 ,  164 ,  166 ,  170 , and/or  190  may be realized with one or more circuits. The communication device  100  may comprise more antennas and circuits. 
         [0033]    In the above embodiments, the values of the elements in the signal dividing circuit  162  may be configured according to different design considerations, for example, the magnitude of the coupled signal Sc, the frequency band and the bandwidth of the transmitting signals and the receiving signals, and/or the required bandwidth of the signal dividing circuit  162 . 
         [0034]    As shown in the aforementioned descriptions, the signal processing circuit  160  may be realized with passive elements, for example, resistors, capacitors, and/or inductors, and therefore only occupies a small space. Moreover, by appropriately configuring the values of the passive elements, the characteristics of the signal processing circuit  160  may be easily adjusted according to the magnitude of the coupled signals, the required bandwidth, and other design parameters. Besides, the signal processing circuit  160  and other decoupling approaches, e.g., isolators and increasing the distance of antennas, may be jointly implemented in the electronic devices to achieve a better system performance. 
         [0035]    Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and embodiments be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.