Abstract:
An exemplary antenna switching circuit comprises first, second, third and fourth switches. The first switch is activated by a first control signal for establishing a connection between a first transmit port and an antenna; the second switch is activated by a second control signal for establishing a connection between a second transmit port and the antenna; the third switch is activated by a third control signal for establishing a connection between a first receive port and the antenna; and the fourth switch is activated by the third control signal for establishing a connection between a second receive port and the antenna. With this arrangement, the first receive port and the second receive port are simultaneously connected to the antenna when the third switch and the fourth switch are activated by the third control signal.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is generally in the field of semiconductors. More specifically, the invention is in the field of semiconductor circuits. 
   2. Related Art 
   Mobile phones employing the Global System for Mobile Communication (“GSM”) standard are typically capable of operating in multiple frequency bands. For example, tri-band and quad-band GSM mobile phones are capable of operating in three frequency bands and four frequency bands, respectively, thereby allowing the mobile phone to be used with a variety of service providers, each of which employ a different frequency band. 
   Current tri-band and quad-band GSM mobile phones have five or six transmit and receive ports, respectively, tied to a common antenna. Each of these ports typically has at least one and sometimes two control lines per port. In the case of a tri-band GSM mobile phone, for example, five or six control lines are typically required in order provide the antenna switching function for its five transmit and receive ports. For the quad-band GSM mobile phone, six or seven control lines are typically required in order provide the antenna switching function for its six transmit and receive ports. 
   Presently, however, GSM mobile phone chips provide only three or four control lines for the antenna switching function. Conventionally, decoders are used by known antenna switching circuits to reduce the number of control lines from six or seven lines to three or four lines for interfacing with the GSM mobile phone chip. Such decoders, however, occupy significant device area and undesirably increase device size and manufacturing cost. Moreover, the lines which route signals to and from the decoder further consume additional device area and further increase device size and manufacturing cost. 
   Another disadvantage associated with known antenna switching circuits is the significant DC (battery) current consumed even during standby or “all-off” mode due to the current drawn by known switching circuits through bias resistors connected to the battery. For example, even during standby mode, known antenna switching circuits consume between approximately 10 to 100 microamperes at all times, which is undesirable. 
   Accordingly, there is a strong need in the art for an efficient multiple-band antenna switching circuit. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to an efficient multiple-band antenna switching circuit. In one exemplary embodiment, an antenna switching circuit is capable of coupling a plurality of ports to an antenna, and the antenna switching circuit comprises first, second, third and fourth switches. The first switch is activated by a first control signal for establishing a connection between a first transmit port and the antenna; the second switch is activated by a second control signal for establishing a connection between a second transmit port and the antenna; the third switch is activated by a third control signal for establishing a connection between a first receive port and the antenna; and the fourth switch is activated by the third control signal for establishing a connection between a second receive port and the antenna. With this arrangement, the first receive port and the second receive port are simultaneously connected to the antenna when the third switch and the fourth switch are activated by the third control signal. 
   According to another embodiment of the invention, the antenna switching circuit further comprises a fifth switch and a sixth switch such that the fifth switch is activated by a fourth control signal for establishing a connection between a third receive port and the antenna, and the sixth switch is activated by the fourth control signal for establishing a connection between a fourth receive port and the antenna. According to this particular embodiment, the third receive port and the fourth receive port are simultaneously connected to the antenna when the fifth switch and the sixth switch are activated by the fourth control signal. 
   According to another embodiment of the invention, the antenna switching circuit further comprises a bias resistor connected across the first transmit port and the second transmit port. According to this particular embodiment, the bias resistor supplies a pull-up bias to an inactive one of the first switch and the second switch. 
   According to another embodiment of the invention, the first receive port receives low band signals, and the second receive port receives high band signals. According to yet another embodiment of the invention, the first transmit port transmits high band signals, and the second transmit port transmits low band signals. For example, the low band signals may be configured in accordance with one of an 850 megahertz GSM band and a 900 megahertz GSM band, and the high band signals may be configured in accordance with one of an 1800 megahertz GSM band and a 1900 megahertz GSM band. 
   According to various embodiment of the present invention, antenna switching for multiple-band applications, such as tri-band and quad-band applications, is provided by the antenna switching circuit of the present invention without the need for a decoder, resulting in significant savings in device area consumption and manufacturing cost, while additionally reducing DC (battery) current consumption. 
   Other features and advantages of the present invention will become more readily apparent to those of ordinary skill in the art after reviewing the following detailed description and accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  shows a circuit diagram of an exemplary multiple-band antenna switching circuit according to one embodiment of the present invention. 
       FIG. 1B  shows a circuit diagram of an exemplary multiple-band antenna switching circuit according to another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention is directed to an efficient multiple-band antenna switching circuit. The following description contains specific information pertaining to the implementation of the present invention. One skilled in the art will recognize that the present invention may be implemented in a manner different from that specifically discussed in the present application. Moreover, some of the specific details of the invention are not discussed in order not to obscure the invention. The specific details not described in the present application are within the knowledge of a person of ordinary skill in the art. 
   The drawings in the present application and their accompanying detailed description are directed to merely exemplary embodiments of the invention. To maintain brevity, other embodiments of the invention which use the principles of the present invention are not specifically described in the present application and are not specifically illustrated by the present drawings. 
   Referring to  FIG. 1A , there is shown a circuit diagram depicting exemplary antenna switching circuit  100  according to one embodiment of the present invention. Antenna switching circuit  100  may, for example, be integrated onto a single semiconductor die for use in a mobile phone. Antenna switching circuit  100  may, in certain embodiments, be integrated into a transmit module, which itself may include additional functionality, such as a power amplifier, for example. Also discussed below, due to the particular arrangement of antenna switching circuit  100 , antenna switching for multiple-band applications, such as tri-band and quad-band applications, is provided by antenna switching circuit  100  without the need for a decoder, resulting in significant savings in device area consumption and manufacturing cost. Furthermore, antenna switching circuit  100  achieves these advantages while significantly reducing current consumption, resulting in improved operating efficiency. 
   As shown in  FIG. 1A , antenna switching circuit  100  is coupled to antenna  114  via diplexer  116 . Antenna switching circuit  100  is configured to connect and disconnect a plurality of ports to and from antenna  114  in accordance with control signals received via control ports  144 ,  146 ,  148  and  150 , as discussed more fully below. 
   In the particular embodiment shown in  FIG. 1A , switching circuit  100  is configured to support quad-band operation and comprises four receive ports and two transmit ports. For example, receive port  152  is capable of communicating first receive high band signal (“RXH 1 ”)  102 ; receive port  154  is capable of communicating second receive high band signal (“RXH 2 ”)  104 ; transmit port  156  is capable of communicating first transmit high band signal (“TXH 1 ”)  106  and second transmit high band signal (“TXH 2 ”)  107 ; transmit port  158  is capable of communicating first transmit low band signal (“TXL 1 ”)  109  and second transmit low band signal (“TXL 2 ”)  108 ; receive port  162  is capable of communicating first receive low band signal (“RXL 1 ”)  112 ; and receive port  160  is capable of communicating second receive low band signal (“RXL 2 ”)  110 . By way of illustration, RXH 1   102  and TXH 1   106  may be signals configured in accordance with the 1800 megahertz (“MHz”) GSM band; RXH 2   104  and TXH 2   107  may be signals configured in accordance with the 1900 MHz GSM band; RXL 2   110  and TXL 2   108  may be signals configured in accordance with the 850 MHz GSM band; and RXL 1   112  and TXL 1   109  may be signals configured in accordance with the 900 MHz GSM band. 
   Continuing with  FIG. 1A , antenna switching circuit  100  comprises field-effect transistors (“FETs”)  130 ,  132 ,  134 ,  136 ,  138  and  140  and resistors  164 ,  166 ,  168 ,  170 ,  172 ,  174  and  142 . Antenna switching circuit  100  further comprises control ports  144 ,  146 ,  148  and  150 . Control port  144  is configured to receive first receive control signal (“VRX 1 ”)  118 , and is connected to the gate of FET  130  through resistor  164  and to the gate of FET  136  through resistor  170 . A first source or drain (“S/D”) terminal of FET  130  is coupled to receive port  152 , and a second S/D terminal of FET  130  is coupled to first diplexer line  126 . Similarly, a first S/D terminal of FET  136  is coupled to receive port  162 , and a second S/D terminal of FET  136  is coupled to second diplexer line  128 . 
   Control port  146  is configured to receive second receive control signal (“VRX 2 ”)  120 , and is connected to the gate of FET  132  through resistor  166  and to the gate of FET  138  through resistor  172 . A first S/D terminal of FET  132  is coupled to receive port  154 , and a second S/D terminal of FET  132  is coupled to first diplexer line  126 . A first S/D terminal of FET  138  is coupled to receive port  160 , and a second S/D terminal of FET  138  is coupled to second diplexer line  128 . 
   Control port  148  is configured to receive accept low band control signal (“VTXL”)  122 , and is connected to the gate of FET  140  through resistor  174 . A first S/D terminal of FET  140  is coupled to transmit port  158 , and a second S/D terminal of FET  140  is coupled to second diplexer line  128 . Control port  150  is configured to accept transmit high band control signal (“VTXH”)  124 , and is connected to the gate of FET  134  through resistor  168 . A first S/D terminal of FET  134  is coupled to transmit port  156 , and a second S/D terminal of FET  134  is coupled to first diplexer line  126 . Resistor  142  is connected across transmit ports  156  and  158 . 
   In the exemplary embodiment shown in  FIG. 1A , control signals VRX 1   118 , VRX 2   120 , VTXL  122  and VTXH  124  may be generated by a processor, such as a mobile phone chip, for controlling the FETs  130 ,  132 ,  134 ,  136 ,  138  and  140  and, more particularly, for controlling the connections between ports  152 ,  154 ,  156 ,  158 ,  160  and  162  and antenna  114  via diplexer  116 . As shown in  FIG. 1A , antenna switching circuit  100  only requires four control ports  144 ,  146 ,  148  and  150 . Antenna switching circuit  100  achieves this arrangement, among other things, by employing a single control port, e.g., control port  144 , to enable a connection between antenna  114  and at least one receive port for high band signals, e.g., receive port  152 , and at least one receive port for low band signals, e.g., receive port  162 , at the same time. Since the diplexer is capable of splitting and isolating high and low band signals, coupling receive port  152  for high band signals and receive port  162  for low band signals to diplexer  116  via first diplexer line  126  and second diplexer line  128 , respectively, does not adversely affect reception performance. In a similar manner, control port  146  enables a connection between antenna  114  and a second receive port for high band signals, e.g., receive port  154 , and a second receive port for low band signals, e.g., receive port  160 , at the same time. Thus, only two control ports  144  and  146  are required by antenna switching circuit  100  for selection of one of four receive bands. The present invention&#39;s concept to reduce the number of control lines can also be applied to dual-band and tri-band GSM as well as five-band configurations that include Universal Mobile Telecommunications System (“UMTS”) bands. 
   To illustrate the operation of antenna switching circuit  100  according to one embodiment of the invention, reference is now made to Table 1, which shows exemplary function modes of antenna switching circuit  100  based on control signals VRX 1   118 , VRX 2   120 , VTXL  122  and VTXH  124  received via control ports  144 ,  146 ,  148  and  150 , respectively. 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               Function 
               VRX1 
               VRX2 
               VTXL 
               VTXH 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               Standby 
               0 
               0 
               0 
               0 
             
             
               GSM 1800 or 1900 transmit 
               0 
               0 
               0 
               1 
             
             
               GSM 850 or 900 transmit 
               0 
               0 
               1 
               0 
             
             
               GSM 850 or 1900 receive 
               0 
               1 
               0 
               0 
             
             
               GSM 900 or 1800 receive 
               1 
               0 
               0 
               0 
             
             
                 
             
           
        
       
     
   
   As shown in Table 1, standby mode is enabled when VRX 1   118 , VRX 2   120 , VTXL  122  and VTXH  124  are all zero (0) or “low.” In this mode, no current is drawn by antenna switching circuit  100 . In this mode, the mobile phone is not operating so the current drain is the only relevant operating parameter. 
   In GSM  1800  or  1900  transmit mode, antenna switching circuit  100  enables the transmission of both high band signals TXH 1   106  and TXH 2   107  via transmit port  156 . In this mode, VTXH  124  is one (1) or “high,” activating FET  134  and connecting transmit port  156  to first diplexer line  126  and to antenna  114 . Also during GSM  1800  or  1900  transmit mode, VRX 1   118 , VRX 2   120  and VTXL  122  are low, thereby shutting off FETs  130  and  132  and disconnecting receive ports  152  and  154  from antenna  114 . Furthermore, since resistor  142  is connected across transmit ports  156  and  158 , resistor  142  operates as a pull-up bias resistor along with the logic low signals of VRX 1   118 , VRX 2   120 , and VTXL  122  to inactivate FETs  136 ,  138 , and  140  and disconnect receive ports  160  and  162  and transmit port  158  from antenna  114 . This prevents any stray signals present on transmit port  158  from reaching the antenna during GSM  1800  or  1900  transmit mode. Resistor  142  can, for example, be 20–30 KiloOhms (kΩ). 
   In GSM  850  or  900  transmit mode, antenna switching circuit  100  enables the transmission of both low band signals TXL 1   109  and TXL 2   108  via transmit port  158 . In this mode, VTXL  122  is high, activating FET  140  and connecting transmit port  158  to second diplexer line  128  and to antenna  114 . Also during GSM  850  or  900  transmit mode, VRX 1   118 , VRX 2   120  and VTXH  124  are low, thereby shutting off FETs  136  and  138  and disconnecting receive ports  160  and  162  from antenna  114 . In this mode, resistor  142  operates as a pull-up bias resistor along with the logic low signals of VRX 1   118 , VRX 2   120 , and VTXH  124  to inactivate FETs  130 ,  132 , and  135  and disconnect receive ports  152  and  154  and transmit port  156  from antenna  114 . This prevents any stray signals present on transmit port  156  from reaching the antenna during GSM  850  or  900  transmit mode. 
   In GSM  850  or  1900  receive mode, antenna switching circuit  100  enables the reception of both high band signals RXH 2   104  and low band signals RXL 2   110  via receive ports  154  and  160 , respectively. In this mode VRX 2   120  is high, activating FETs  132  and  138 , and connecting receive port  154  to first diplexer line  126  and to antenna  114 , and further connecting receive port  160  to second diplexer line  128  and to antenna  114 . Also during GSM  850  or  1900  receive mode, VRX 1   118 , VTXL  122  and VTXH  124  are low, thereby shutting off FETs  130 ,  134 ,  136  and  140 , and disconnecting receive ports  152  and  162  and transmit ports  156  and  158  from antenna  114 . 
   In GSM  900  or  1800  receive mode, antenna switching circuit  100  enables the reception of both high band signals RXH 1   102  and low band signals RXL 1   112  via receive ports  152  and  162 , respectively. In this mode VRX 1   118  is high, activating FETs  130  and  136 , and connecting receive port  152  to first diplexer line  126  and to antenna  114 , and further connecting receive port  162  to second diplexer line  128  and to antenna  114 . Also during GSM  900  or  1800  receive mode, VRX 2   120 , VTXL  122  and VTXH  124  are low, thereby shutting off FETs  132 ,  134 ,  138  and  140 , and disconnecting receive ports  154  and  160  and transmit ports  156  and  158  from antenna  114 . 
   Due to the unique arrangement of antenna switching circuit  100  combined with diplexer  116 , only two control ports  144  and  146  are required for selection of one of four receive bands, and only two control ports  148  and  150  are required for selection of one of four transmit bands. Thus, only four control ports, i.e., control ports  144 ,  146 ,  148  and  150 , are required in order to provide switching for receive ports  152 ,  154 ,  160  and  162  and transmit ports  156  and  158 . Advantageously, a decoder is not required by antenna switching circuit  100  to provide the above-discussed switching functionality since control lines for the receive ports are paired together to enable reception of at least one high band frequency with at least one low band frequency. It is further noted that the specific assignments for receive bands may be arbitrarily selected provided one high band frequency is paired with one low band frequency, as described above in conjunction with Table 1. For odd-number band configurations, there is always one unpaired receive path, but the benefit of reducing the number of control lines is maintained. As a benefit of the arrangement of antenna switching circuit  100  which does not require a decoder and its associated route lines, device area consumption, device size, and manufacturing cost are substantially reduced. Moreover as discussed above, current consumption by antenna switching circuit  100  is significantly reduced over prior antenna switching circuits. 
   Referring to  FIG. 1B , there is shown a circuit diagram depicting exemplary antenna switching circuit  190  according to another embodiment of the present invention, wherein like references in antenna switching circuit  190  of  FIG. 1B  and in antenna switching circuit  100  of  FIG. 1A  indicate similar elements. 
   Antenna switching circuit  190  of  FIG. 1B  operates substantially as antenna switching circuit  100  of  FIG. 1A , as described above; however, resistor  142  of antenna switching circuit  100  in  FIG. 1A  has been removed from antenna switching circuit  190  of  FIG. 1B , and bias circuit  178  has been added. Bias circuit  178  comprises resistors  180  and  182  and diodes  184  and  186 . Resistor  182  and diode  186  are optional. In one embodiment, resistor  182  and diode  186  are not used. The cathode of diode  184  is connected through resistor  180  to first diplexer line  126 , and the anode of diode  184  is connected to control port  148 . The cathode of diode  186  is connected through resistor  182  to second diplexer line  128 , and the anode of diode  186  is connected to control port  150 . In this arrangement, bias circuit  178  provides the requisite pull-up bias during transmit mode, wherein one of FETs  140  and  134  is active while the other of FETs  140  and  134  is inactive. 
   For example, during GSM 1800 or 1900 transmit mode, as discussed above in conjunction with Table 1, VTXH  124  is high activating FET  134 , and VRX 1   118 , VRX 2   120  and VTXL  122  are low, shutting off FETS  130 ,  132 ,  136 ,  138  and  140 . The voltage supplied by VTXH  124  is also connected across resistor  182  and diode  186  to supply the requisite pull-up bias to inactive FET  140 . Furthermore, during receive mode, such as GSM 900 or 1800 receive mode shown in Table 1, VRX 1   118  is high activating FETs  130  and  136 , and VRX 2   120 , VTXL  122  and VTXH  124  are low, shutting off FETs  132 ,  134 ,  138  and  140 . During this mode, diodes  184  and  186  prevent current from flowing to the low voltages at control ports  148  and  150 , preventing excessive current consumption during receive mode operation. 
   From the above description of exemplary embodiments of the invention it is manifest that various techniques can be used for implementing the concepts of the present invention without departing from its scope. Moreover, while the invention has been described with specific reference to certain embodiments, a person of ordinary skill in the art would recognize that changes could be made in form and detail without departing from the spirit and the scope of the invention. The described exemplary embodiments are to be considered in all respects as illustrative and not restrictive. It should also be understood that the invention is not limited to the particular exemplary embodiments described herein, but is capable of many rearrangements, modifications, and substitutions without departing from the scope of the invention. 
   Thus, an efficient multiple-band antenna switching circuit has been described.