Patent Publication Number: US-2005130602-A1

Title: [wireless transmitting/receiving circulator circuit]

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims the priority benefit of Taiwan application serial no. 92134784, filed Dec. 10, 2003.  
     BACKGROUND OF INVENTION  
      1. Field of the Invention  
      The present invention relates to a wireless device. More particularly, the present invention relates to a wireless transmitting/receiving circulator circuit.  
      2. Description of the Related Art  
      In the past, communication is achieved by phones using cable connected network system. One major disadvantage of a cable network is that the communicating parties have to be station at fixed locations. In other words, portable communication is impossible using cable connected network system. With the setup of a wireless network such as a global system for mobile communication (GSM), such constraints are being eliminated.  
      In general, a conventional wireless device uses a switching integrated circuit (IC) as a transmission/reception interface so that channels are isolated. However, aside from a high production cost, the switching IC needs to have an external power source to power the circuit and extra external triggering leads to control its operation. Thus, using a switching IC not only increases the current loading of the wireless device but also introduces extra electrical noise during a circuit operation.  
     SUMMARY OF INVENTION  
      Accordingly, one objective of the present invention is to provide a wireless transmitting/receiving circulator circuit for replacing a conventional switching integrated circuit (IC) so that overall production cost and current loading are reduced.  
      To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a wireless transmitting/receiving circulator circuit. The circulator circuit serves as a transmission/reception interface between a wireless device and an antenna such that signals at a first wave band can be received and signals at a second wave band can be transmitted. The circulator circuit comprises a first band-pass filter, a filter and a second band-pass filter. The first band-pass filter is coupled to the receiving end of a wireless device and an antenna for receiving signals from the antenna and filtering the signals to produce a receiving signal. The receiving signal is transmitted to the receiving end of the wireless device. The filter is coupled to the antenna for blocking antenna signals containing the second wave band. The second band-pass filter is coupled to the transmitting end of the wireless device and the filter for receiving signals from the transmitting end and filtering the signals to produce a transmitting signal. The transmitting signal is transmitted via the antenna after passing through the filter.  
      In one embodiment, the first band-pass filter of the wireless transmitting/receiving circulator circuit further comprises a low-pass filter and a high-pass filter. The low-pass filter is coupled to the antenna and the high-pass filter is coupled to the low-pass filter and the receiving end of the wireless device. Furthermore, each of the low-pass filter and the high-pass filter comprises an inductor and a capacitor. One end of the inductor of the low-pass filter is coupled to the antenna while the other end of the inductor of the low-pass filter is coupled to one end of the capacitor of the low-pass filter and one end of the capacitor of the high-pass filter. The other end of the capacitor of the low-pass filter is connected to a ground. The other end of the capacitor of the high-pass filter is coupled to one end of the inductor of the high-pass filter and the receiving end of the wireless device. The other end of the inductor of the high-pass filter is connected to the ground.  
      In one embodiment, the filter of the wireless transmitting/receiving circulator circuit further comprises a capacitor and an inductor. One end of the capacitor is coupled to the antenna while the other end of the capacitor is coupled to one end of the inductor. The other end of the inductor is connected to a ground.  
      In one embodiment, the second band-pass filter of the wireless transmitting/receiving circulator circuit further comprises a low-pass filter and a high-pass filter. The low-pass filter is coupled to the transmitting end of the wireless device. The high-pass filter is coupled to the low-pass filter and the filter. Each of the low-pass filter and the high-pass filter comprises an inductor and a capacitor. One end of the inductor of the low-pass filter is coupled to the transmitting end of the wireless device. The other end of the inductor of the low-pass filter is coupled to one end of the capacitor of the low-pass filter and one end of the capacitor of the high-pass filter. The other end of the capacitor of the low-pass filter is connected to the ground. The other end of the capacitor of the high-pass filter is coupled to one end of the inductor of the high-pass filter. The other end of the inductor of the high-pass filter is connected to the ground.  
      In brief, the present invention provides a wireless transmitting/receiving circulator circuit to serve as a transmission/reception interface between a wireless device and an antenna. The wireless transmitting/receiving circulator circuit is constructed using a few simple passive devices including inductors and capacitor so that overall production cost is reduced and current loading condition is improved.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
      The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The following drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
       FIG. 1  is a circuit diagram of a wireless transmitting/receiving circulator circuit according to one preferred embodiment of this invention. 
    
    
     DETAILED DESCRIPTION  
      Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
       FIG. 1  is a circuit diagram of a wireless transmitting/receiving circulator circuit according to one preferred embodiment of this invention. The wireless transmitting/receiving circulator circuit  100  in  FIG. 1  is a transmission/reception interface between a wireless device (not shown) such as a Global System for Mobile communication (GSM), Code Division Multiple Access (CDMA), Wide-band Code Division Multiple Access (WCDMA) and an antenna  180  for receiving signals at a first wave band and transmitting signals at a second wave band. In this embodiment, the wireless device is assumed to be a GSM system with a transmission waveband between 1710 MHz˜1785 MHz and a reception waveband between 1805 MHz˜1880 MHz.  
      As shown in  FIG. 1 , the wireless transmitting/receiving circulator circuit  100  comprises a first band-pass filter  110 , a high-pass filter  150  and a second band-pass filter  140 . The first band-pass filter  110  further comprises a low-pass filter  130  and a high-pass filter  120  and the second band-pass filter  140  further comprises a low-pass filter  160  and a high-pass filter  170 . Furthermore, the high-pass filter  150  and the high-pass filter  170  may use a common inductor  172  to reduce the number of passive components.  
      The first band-pass filter  110  is coupled to the receiving end of the wireless device and the antenna  180  for receiving signals from the antenna  180  and filtering the signals to produce receiving signals falling within the 1805 MHz˜1880 MHz waveband. Thereafter, the receiving signals are transmitted to the receiving end of the wireless device. The high-pass filter  150  is coupled to the antenna  180  for blocking signals from the antenna  180  falling within the 1710 MHz˜1785 MHz waveband to prevent such signals from transmitting to the transmitting end of the wireless device and lead to interference. In other words, the high-pass filter  150  must have a cutoff frequency greater than 1785 MHz before it can block off signals falling within the 1710 MHz˜1785 MHz waveband. Here, both the high-pass filter  170  and the high-pass filter  150  use the same inductor  172  to reduce the number of passive components. Obviously, a separate inductor may be fitted inside the high-pass filter  150  so that there is no need to share the inductor  172  with the high-pass filter  170  or, alternatively, a low-pass filter may be used. When a low-pass filter is used instead of the high-pass filter  150 , the cutoff frequency of the low-pass filter must be below 1710 MHz in order to block off signals falling within the 1710 MHz 1785 MHz waveband.  
      The second band-pass filter  140  is coupled to the transmitting end of the wireless device and the high-pass filter  150  for receiving signals from the transmitting end and filtering the signals to produce transmitting signals. The transmitting signals are transmitted via the antenna  180  after passing through the high-pass filter  150 .  
      The first band-pass filter  110  comprises a low-pass filter  130  and a high-pass filter  120 . The low-pass filter  130  further comprises an inductor  131  and a capacitor  132  and the high-pass filter  120  further comprises an inductor  122  and a capacitor  121 . One end of the inductor  131  is coupled to the antenna  180  and the other end of the inductor  131  is coupled to one end of the capacitor  132  and one end of the capacitor  121 . The other end of the capacitor  132  is connected to a ground. The other end of the capacitor  121  is coupled to one end of the inductor  122  and the receiving end of the wireless device. The other end of the inductor  122  is connected to the ground.  
      The second band-pass filter  140  comprises a low-pass filter  160  and a high-pass filter  170 . The low-pass filter  160  further comprises an inductor  161  and a capacitor  162  and the high-pass filter  170  further comprises an inductor  172  and a capacitor  171 . Aside from having a capacitor  151 , the high-pass filter  150  also shares the inductor  172  with the high-pass filter  170 . One end of the inductor  161  is coupled to the transmitting end of the wireless device while the other end of the inductor  161  is coupled to one end of the capacitor  162  and one end of the capacitor  171 . The other end of the capacitor  162  is connected to a ground. The other end of the capacitor  171  is coupled to one end of the inductor  172  and one end of the capacitor  151 . The other end of the inductor  172  is connected to the ground. The other end of the capacitor  151  is coupled to the antenna  180 .  
      Although all the filters in the aforementioned wireless transmitting/receiving circulator circuit are assembled using inductors and capacitors, a combination of other passive components such as resistors and capacitors can be used and considered within the scope of the present invention.  
      It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.