Abstract:
A communication device having a structure that utilizes a minimum number of switches to bypass a power amplifier in the communication device is disclosed. The communication device takes advantage of the half-duplex operation of the RF transmitter and receiver in the communication device to minimize the number of switches required to bypass a power amplifier in the communication device.

Description:
RELATED APPLICATION 
   This application claims priority to U.S. Provisional Application Ser. No. 60/407,409 filed Aug. 30, 2002. 

   BACKGROUND 
   The present invention generally relates to wireless communication devices and, more particularly, to bypassing a power amplifier in a wireless communication device communicating with an access point in a local area network (LAN). 
   Wireless communication devices, for example devices using radio frequency signal transmission, generally must comply with regulations limiting, for example, the radio frequency emissions, transmit power, and mode of operation of the devices. Such regulations may be enforced by the Federal Communications Commission (FCC) in the United States, for example, or in Europe by the European Telecommunications Standards Institute (ETSI). Wireless LAN communication networks are subject, for example, to the IEEE 802.11 standard, which includes, for example, 802.11a, 802.11b, and 802.11g standards. The 802.11b standard limits transmit power for wireless LAN communication devices in the United States to 30 decibels relative to one milliwatt (dBm), in Europe, to 20 dBm, and in Japan, to 10 dBm per megaHertz (dBm/MHz). Such wireless LAN communication devices may be described as stations or access points. Stations typically may be found in laptop computers, cell phones, portable modems, or personal digital assistants (PDAs), where they are used for communication with a wired LAN through an access point, which may be generally described as a wireless transmitter/receiver connected into the wired LAN for interfacing the wired LAN to the wireless communication devices. Stations may also communicate with other stations in a peer-to-peer network, without the presence of an access point, described in the IEEE 802.11a, 802.11b or 802.11g standard as “ad-hoc” mode. 
   The 802.11 standard specifies a half-duplex mode of operation for wireless transmitter-receivers, also commonly referred to as “transceivers”, included in wireless LAN communication devices. Half-duplex operation is characterized by the transceiver, at any given time, either transmitting a signal or receiving a signal, but not both. Half-duplex operation is distinguished from full-duplex operation in which the transceiver may simultaneously transmit one signal while receiving a second signal. Half-duplex operation typically requires control by the communication device as to whether the transmitter or the receiver is either operating or has an access to the communication channel. As illustrated by  FIG. 1 , for example, the control over access to the communication channel may be accomplished by switching the connection of the antenna of the wireless communication device between the receiver and the transmitter of the device. 
     FIG. 1  shows an example of a wireless LAN communication device  100  developed in accordance with the IEEE 802.11a, 802.11b or 802.11g standard. The communication device  100  includes an antenna  101  for receiving and transmitting signals. The antenna  101  is connected to an RF filter  103  for filtering jammer signals. The RF filter  103  is coupled to a switch  104  that switches between signal paths  104   a  and  104   b . The switch  104  selects the signal path  104   a  when the communication device  100  is receiving a signal. The received signal is propagated from the switch  104  to a low noise amplifier (LNA)  106  that amplifies the received signal. The output signal of the LNA  106  is processed by an RF receiver  109 . The processed signal is transmitted to a modem  111 . An RF transceiver chip  112  contains the LNA  106 , the RF receiver  109 , a power amplifier  107 , a switch  108  and an RF transmitter  110 . 
   On the other hand, when the communication device  100  transmits a signal, the switch  104  switches to the signal path  104   b  that is connected to a switch  105 . The switch  105  works in conjunction with the switch  108  to bypass the power amplifier  107  when the communication device  100  is transmitting a signal. When the communication device  100  is transmitting a signal, a signal from the RF transmitter  110  is received by the switch  108 , and the switch  108  switches to a signal path  105   a  if the power amplifier  107  is bypassed but switches to a signal path  107   a  if the signal from the RF transmitter  110  needs to be amplified by the power amplifier  107 . The output of the power amplifier  107  is connected to the signal path  105   b . In certain situations, the power amplifier  107  needs to be bypassed because the amplification by the power amplifier  107  may create a signal that interferes with other signals due to the strength of the signal. Such situations may occur if the communication device  100  is close to an access point or a base station. In other situations, the power amplifier  107  is bypassed to conserve battery power. 
   If the signal from the RF transmitter  110  needs to be amplified, the switch  108  switches to the signal path  107   a , and the power amplifier  107  receives the signal and amplifies the signal. The amplified signal is received by the switch  105  through the signal path  105   b.    
   Since the switch  105  may receive and propagate an amplified signal to the switch  104 , the switch  105  must meet certain strict linearity requirements or the amplified signal will become distorted by the switch  105 . In order to meet such strict linearity requirement, the switch  105  cannot be integrated into the RF transceiver chip  112  because the switch  105  may require different fabrication process (such as a GaAs process as opposed to the SiGe process used for the RF tranceiver chip  112 ). Since the switch  105  is external to the RF transceiver chip  112  and requires a different fabrication process from the RF transceiver  112 , the fabrication of the switch  105  incurs extra costs and extra board space. 
   SUMMARY 
   This disclosure is directed to a communication device having a structure that utilizes a minimum number of switches to bypass a power amplifier in the communication device. 
   In one embodiment, a communication device takes advantage of the half-duplex operation of the communication device to minimize the number of switches required to bypass a power amplifier in the communication device. The communication device bypasses the power amplifier while transmitting a signal by using a switch coupled to the power amplifier to direct the signal to a receiver path instead of a transmitter path. Since the receiver path is not used while transmitting a signal, the signal is able to bypass the power amplifier without being corrupted. The signal is then directed to a switch located outside of an RF transceiver in the communication device. The switch located outside of the RF transceiver then directs the signal to an antenna for transmission. 
   Various embodiments may be implemented in a communication device in software, hardware, firmware, or any combination thereof. If implemented in software, the techniques may be embodied in a computer readable medium comprising instructions that cause the wireless device to perform the techniques. Additional details of various embodiments are set forth in the accompanying drawings and the description below. Other features, objects and advantages will become apparent from the description and drawings, and from the claims 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of one example of a wireless communication device that operates in half-duplex mode. 
       FIG. 2  is a diagram of a wireless LAN, having access to a wired LAN, in accordance with an embodiment of the present invention. 
       FIG. 3  is a block diagram of an exemplary wireless communication device according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   One example of wireless communication devices that could benefit from the application of an embodiment the present invention is wireless local area network (LAN) communication devices that may typically be found in laptop computers, cell phones, portable modems, or personal digital assistants (PDAs), where they are used for communication in a wireless LAN subject to the IEEE 802.11a, 802.11b or 802.11g standard or for communication with a wired LAN through an access point subject to the IEEE 802.11a, 802.11b or 802.11g standard. For example,  FIG. 2  shows a wireless LAN  200  comprising wireless communication devices  202 , where at least one of the wireless communication devices  202 , for example, a wireless communication device  204 , may include a power amplifier bypass according to an embodiment of the present invention as more fully described below. As illustrated in  FIG. 2 , the communication device  204  may be included in a laptop computer  205 , for example, providing wireless communication between the laptop computer  205  and the wireless LAN  200 . 
   The wireless LAN  200  may operate in ad hoc mode, as described above, so that, for example, the wireless communication devices  202  operate in a peer-to-peer network, without the presence of an access point, or the wireless LAN  200  may be connected through one or more access points  206  to a wired LAN  208 . The access points  206 , for example, may provide wireless communication according to the IEEE 802.11a, 802.11b or 802.11g standard between the wireless LAN  200  and wired LAN  208 . The wired LAN  208  may be used, for example, to connect various devices, such as network printer  210 , personal computer  212 , and file server  214  as known in the art. The wired LAN  208  may also be used, for example, to connect the various devices, such as network printer  210 , personal computer  212 , and file server  214 , to the access points  206  and thereby to the wireless LAN  200 . One or more access points, for example, the access point  216 , may include power amplifier bypass in accordance with an embodiment of the present invention. 
   Certain embodiments of the present invention may operate in accordance to the 802.11 standards, and other embodiments may operate in accordance to other wireless communication standards that support half-duplex mode of operation. 
     FIG. 3  illustrates a wireless LAN communication device  300  in accordance with an embodiment of the present invention. The communication device  300  operates in accordance to a half-duplex mode of operation. The communication device  300  includes an antenna  301  for receiving and transmitting signals. The antenna  301  is coupled to an RF filter  303  for filtering jammer signals. The RF filter  303  is coupled to a switch  304  that switches between signal paths  304   a  and  304   b . A first terminal  304 ( i ) of the switch  304  is coupled to the RF filter  303 , a second terminal  304 ( ii ) is coupled to the signal path  304   a , and the third terminal  304 ( iii ) is coupled to the signal path  304   b . The switch  304  switches between the second terminal  304 ( ii ) and the third terminal  304 ( iii ) to connect to the first terminal  304 ( i ). 
   A modem  320  commands the switch  304  to select the signal path  304   a  when the communication device  300  is receiving a signal. The signal path  304   a  forms a part of the receiver path used to propagate signals received at the antenna  301  to an RF receiver  312 . The switch  304  is coupled to an RF transceiver IC  310  that includes a low noise amplifier (LNA)  311 , the RF receiver  312 , an RF transmitter  315 , a switch  314  and a power amplifier  313 . In certain embodiments of the present invention, the power amplifier  313  may be located outside of the RF transceiver IC  310 . The received signal is transmitted from the switch  304  to the low noise amplifier (LNA)  311  that amplifies the received signal. The output signal of the LNA  311  is processed by the RF receiver  312 . The RF receiver  312  downconverts the received RF signal from the LNA  311  to a baseband signal. The RF receiver  312  also filters out any noise or unnecessary signals. The RF receiver  312  outputs a baseband signal to the modem  320  for further processing. During the receiving mode, the modem  320  turns off the RF transmitter  315  and the power amplifier  313 . 
   When the communication device  300  is transmitting a signal, the modem outputs a baseband signal to the RF transmitter  315 . The RF transmitter  315  upconverts the received baseband signal to an RF signal (i.e., a transmitting RF signal). The RF transmitter  315  outputs the transmitting RF signal to a switch  314 . A first terminal  314 ( i ) of the switch  314  is coupled to the RF transmitter  315 , a second terminal  314 ( ii ) is coupled to a signal path  314   a , and the third terminal  314 ( iii ) is coupled to a signal path  314   b . The switch  314  switches between the second terminal  314 ( ii ) and the third terminal  314 ( iii ) to connect to the first terminal  314 ( i ). The switch  314  switches between the signal paths  314   a  and  314   b  depending on whether the power amplifier  313  is to be bypassed or not. The modem  320  may decide to bypass the power amplifier  313  if the amplification by the power amplifier  313  may create an overly strong signal that may interfere with other signals in the LAN. Such situation may arise if the communication device  300  is too close to an access point. The modem  320  also may decide to bypass the power amplifier  313  if the battery power needs to be conserved. 
   If the modem  320  decides to bypass the power amplifier  313 , the modem  320  commands the switch  314  to select the signal path  314   a  that is connected to the signal path  304   a . Thus, if the power amplifier  313  is bypassed, the signal from the switch  314  travels down the signal path  314   a  and into the switch  304  through the signal path  304   a . Thus, the communication device  300  uses a part of the receiver path (i.e., the signal path  304   a  ) to bypass the power amplifier  313 . The communication device  300  is able to use the signal path  304   a  to bypass the power amplifier  313  because of the half-duplex mode of operation. The signal from the switch  314  does not proceed into the LNA  311  because the modem  320  turns off the LNA  311  and the RF receiver  312  when the communication device is transmitting a signal. When the LNA  311  is turned off, the input impedance into the LNA  311  is nearly infinite, so the signal from the switch  314  will not travel into the LNA  311 . The modem  320  commands the switch  304  to select the signal path  304   a  when the power amplifier  313  is to be bypassed. The signal is then transmitted to the RF filter  303  and then to the antenna  301  for transmission. 
   If the modem  320  decides not to bypass the power amplifier  313 , the switch  314  selects the signal path  314   b , and the signal from the RF transmitter  315  is received by the power amplifier  313  that amplifies the signal in accordance with a command from the modem  320 . The output of the power amplifier  313  is received by the switch  304  that selects the signal path  304   b  to receive the signal from the power amplifier  313 . The signal is then propagated to the antenna  301  through the RF filter  303 , as explained above. 
   The above structure allows the communication device  300  to bypass a power amplifier with one less switch than the structure shown in  FIG. 1 . The communication device  300  uses the switches  314  and  304  to bypass the power amplifier  313  and does not require another additional switch outside of the RF transceiver  310  to bypass the power amplifier  313 . By using one less switch than the structure shown in  FIG. 1 , the communication device  300  uses less board space and saves costs. 
   It is to be understood that even though various embodiments and advantages of the present invention have been set forth in the foregoing description, the above disclosure is illustrative only, and changes may be made in detail, yet remain within the broad principles of the invention. Therefore, the present invention is to be limited only by the appended claims.