Patent Publication Number: US-2005118974-A1

Title: Radio device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a radio device, and more particularly to a radio device capable of accommodating variations in the match condition of an antenna.  
      2. Description of the Background Art  
      A radio device typically includes a transmitter/receiver antenna for communicating with other devices. For efficient transmission/reception, the antenna is matched for the frequency range in which the device is used. If the antenna is sufficiently matched and it is installed in an ideal environment in free space, it will operate in an ideal manner. That is, all of the signal inputted to the antenna will be radiated with no reflected wave coming back toward the circuit side.  
      In practice, however, the antenna maybe in contact with a human body or in proximity to a piece of metal, or the antenna itself may be broken or chipped. In such a case, the antenna will be mismatched, even though the antenna is sufficiently matched under an ideal environment. When transmitting a signal, for example, under such a situation, most of the power of the input signal comes back to the power amplifier in the form of a reflected wave. Then, at the power amplifier, the power being used for amplifying an input signal and the reflected power coming back from the antenna end are superposed on each other. The superposed power is entirely consumed as heat, whereby an abnormal temperature increase occurs at the power amplifier, which may in worst cases break the power amplifier. While the gain, the output power and the current consumption of a power amplifier are determined by the load on the power amplifier, the load on the power amplifier varies following a variation in the match condition of the antenna. Depending on the match condition of the antenna, the current or the output power of the power amplifier may become excessive. If the power in the power amplifier exceeds the withstand power of an element therein, the power amplifier may be broken in worst cases.  
      A conventional approach to this problem is to provide an isolator between the power amplifier and the antenna so as to prevent a variation in the match condition of the antenna from influencing the power amplifier. Another conventional approach is to provide a spare antenna, in addition to a main antenna, in preparation for cases where the main antenna is broken. For example, Japanese Laid-Open Patent Publication No. 9-284169 proposes an antenna selector circuit for switching from a broken antenna to another antenna. The antenna selector circuit will now be described with reference to  FIG. 9 .  
       FIG. 9  illustrates a configuration of the conventional antenna selector circuit. Referring to  FIG. 9 , the antenna selector circuit includes a circulator  102  with three terminals. The feed system is connected to a first terminal  102   a  of the circulator  102 , a main antenna  100  to a second terminal  102   b , and a spare antenna  101  to a third terminal  102   c . In  FIG. 9 , the three terminals of the circulator  102  are designated as the first terminal  102   a , the second terminal  102   b  and the third terminal  102   c  successively in the direction of circulation.  
      Referring to  FIG. 9 , if the main antenna  100  is broken, making the impedance at the second terminal  102   b  infinite, the first terminal  102   a , to which the feed system is connected, is coupled to the third terminal  102   c , to which the spare antenna  101  is connected. Thus, when the main antenna  100  is broken, the power feed connection can be automatically switched to the spare antenna  101  by the antenna selector circuit.  
      With these conventional approaches, however, it is necessary to provide an isolator or a circulator between the power amplifier and the antenna. In other words, these approaches require an additional component to be added to the radio device, thus hindering a reduction in size or cost of the radio device. Moreover, the provision of the additional component between the power amplifier and the antenna increases the loss of transmission power, thus reducing the transmission power or increasing the power consumption.  
     SUMMARY OF THE INVENTION  
      Therefore, an object of the present invention is to provide a radio device, in which the power amplifier can be prevented from being broken, while a reduction in size and cost of the device can be readily made. Another object of the present invention is to provide a radio device, in which the power amplifier can be prevented from being broken, while it is possible to readily suppress a reduction in the transmission power and an increase in the power consumption.  
      The present invention has the following features to attain the objects mentioned above. A first aspect of the present invention is directed to a radio device, including an antenna, a power amplifier, an element, a first connection switch, a match detection section and a control circuit. The power amplifier has an output terminal connected to the antenna, and amplifies a transmitted signal to be radiated through the antenna. The element is connected to the antenna, and is provided for matching the antenna. The element may be, for example, a terminator (see  FIG. 1 ) or a matching element (see  FIG. 2 ). The first connection switch is provided between the antenna and the element. The match detection section detects a variation in a match condition of the antenna. The control circuit closes the first connection switch when a variation in the match condition of the antenna is detected by the match detection section.  
      A second aspect of the present invention is directed to a radio device, including an antenna, a power amplifier, a spare antenna, a first connection switch, a match detection section and a control circuit. The power amplifier has an output terminal connected to the antenna, and amplifies a transmitted signal to be radiated through the antenna. The spare antenna is connected to the power amplifier. The first connection switch is provided between the spare antenna and the power amplifier. The match detection section detects a variation in a match condition of the antenna. The control circuit closes the first connection switch when a variation in the match condition of the antenna is detected by the match detection section.  
      According to the present invention, a variation in the match condition of the antenna, occurring due to a change in the antenna itself or the surrounding environment, is detected based on the amount of reflection or a variation in the current consumption of the power amplifier. If such a variation is detected, the match condition of the antenna itself is changed. Thus, the radio device can prevent the power amplifier from being broken. Moreover, according to the present invention, switches are used for changing the match condition of the antenna. Since the radio device of the present invention uses simple components such as switches, a reduction in size and cost of the device can be readily made.  
      These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  illustrates a radio device according to Embodiment 1 of the present invention;  
       FIG. 2  illustrates a radio device according to Embodiment 2 of the present invention;  
       FIG. 3  illustrates a radio device according to Embodiment 3 of the present invention;  
       FIG. 4  illustrates a radio device according to Embodiment 4 of the present invention;  
       FIG. 5  illustrates a radio device according to Embodiment 5 of the present invention;  
       FIG. 6  illustrates a radio device according to an alternative embodiment of the present invention;  
       FIG. 7  illustrates a radio device according to an alternative embodiment of the present invention;  
       FIG. 8  illustrates a radio device according to an alternative embodiment of the present invention; and  
       FIG. 9  illustrates a configuration of a conventional antenna selector circuit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Embodiment 1  
       FIG. 1  illustrates a radio device according to Embodiment 1 of the present invention. Referring to  FIG. 1 , the radio device includes a receiver circuit  1 , an antenna connection selector switch  2 , a transmitter/receiver antenna  3 , a power amplifier  4 , a reflected wave detection circuit  5 , a control circuit  6  and a terminator  7 . The antenna connection selector switch  2  includes a first terminal  2   a , a second terminal  2   b , a third terminal  2   c , a fourth terminal  2   d , a fifth terminal  2   e  and a sixth terminal  2   f . The receiver circuit  1  is connected to the first terminal  2   a . The transmitter/receiver antenna  3  is connected to the third terminal  2   c . The reflected wave detection circuit  5  is provided between the output terminal of the power amplifier  4  and the second terminal  2   b . The control circuit  6  is provided between the reflected wave detection circuit  5  and the sixth terminal  2   f . The terminator  7  is connected to the fourth terminal  2   d.    
      The antenna connection selector switch  2  includes a first connection switch  2   i  and a second connection switch. The second connection switch includes a first sub-switch  2   g  and a second sub-switch  2   h . The first connection switch  2   i  is provided between the third terminal  2   c  and the fourth terminal  2   d . The first sub-switch  2   g  is provided between the first terminal  2   a  and the third terminal  2   c . The second sub-switch  2   h  is provided between the second terminal  2   b  and the third terminal  2   c.    
      The first and second sub-switches  2   g  and  2   h  are connected to the fifth terminal  2   e . The first and second sub-switches  2   g  and  2   h  are operated based on signals inputted through the fifth terminal  2   e . In Embodiment 1, when the fifth terminal  2   e  is ON, the first sub-switch  2   g  is ON (i.e., closed) and the second sub-switch  2   h  is OFF (i.e., open), whereas when the fifth terminal  2   e  is OFF, the first sub-switch  2   g  is OFF and the second sub-switch  2   h  is ON.  
      The first connection switch  2   i  is connected to the sixth terminal  2   f . The first connection switch  2   i  is operated based on signals inputted through the sixth terminal  2   f . In Embodiment 1, when the sixth terminal  2   f  is ON, the first connection switch  2   i  is ON, whereas when the sixth terminal  2   f  is OFF, the first connection switch  2   i  is OFF.  
      Now, the operation of the radio device having such a configuration as described above will be described. When the radio device receives a signal through the transmitter/receiver antenna  3 , the fifth terminal  2   e  is turned ON, whereas when the radio device transmits a signal through the transmitter/receiver antenna  3 , the fifth terminal  2   e  is turned OFF. In other words, the radio device inputs an ON signal to the fifth terminal  2   e  when receiving a signal and an OFF signal when transmitting a signal. Thus, as the fifth terminal  2   e  is turned ON, the transmitter/receiver antenna  3  and the receiver circuit  1  are connected to each other via the first sub-switch  2   g . As a result, a signal received through the transmitter/receiver antenna  3  (a “received signal”) is inputted to the receiver circuit  1 . As the fifth terminal  2   e  is turned OFF, the reflected wave detection circuit  5  and the transmitter/receiver antenna  3  are connected to each other via the second sub-switch  2   h . Then, a signal to be transmitted (a “transmitted signal”) inputted to the power amplifier  4  is radiated from the transmitter/receiver antenna  3  via the reflected wave detection circuit  5  and the second sub-switch  2   h.    
      In Embodiment 1, the first sub-switch  2   g  and the second sub-switch  2   h  are turned ON and OFF, respectively, when the fifth terminal  2   e  is ON, and OFF and ON, respectively, when the fifth terminal  2   e  is OFF. In other embodiments, the ON/OFF states of these sub-switches as controlled by the fifth terminal  2   e  may be reversed. Specifically, the first sub-switch  2   g  and the second sub-switch  2   h  may be turned ON and OFF, respectively, when the fifth terminal  2   e  is OFF, and OFF and ON, respectively, when the fifth terminal  2   e  is ON.  
      Consider a case where the match condition of the transmitter/receiver antenna  3  varies for some reason. The reason may be the transmitter/receiver antenna  3  being in contact with a human body or in proximity to a piece of metal, or may be the transmitter/receiver antenna  3  itself being broken or chipped, for example. In such a case, not all of the transmitted signal inputted to the power amplifier  4  is radiated through the transmitter/receiver antenna  3 , but some of the transmitted signal is reflected. In the example shown in  FIG. 1 , the reflected wave enters the reflected wave detection circuit  5 . If a reflected wave exceeding a predetermined level is detected, the reflected wave detection circuit  5  outputs to the control circuit  6  a detection signal indicating the detection of a reflected wave. The reflected wave detection circuit  5  detects a variation in the match condition of the transmitter/receiver antenna  3  based on the detection of a reflected wave. If a variation in the match condition of the transmitter/receiver antenna  3  is detected by the reflected wave detection circuit  5 , the control circuit  6  closes the first connection switch  2   i . Thus, when receiving the detection signal, the control circuit  6  turns ON the sixth terminal  2   f . As the sixth terminal  2   f  is turned ON, the first connection switch  2   i  is turned ON, whereby the transmitter/receiver antenna  3  and the terminator  7  are connected to each other, thus terminating the transmitter/receiver antenna  3 . As a result, the transmitter/receiver antenna  3  is matched by the terminator  7 , thereby suppressing a variation in the load on the power amplifier  4  and preventing the power amplifier  4  from being broken.  
      In the example shown in  FIG. 1 , it is preferred that the control circuit  6  keeps the first connection switch  2   i  ON for a predetermined period of time after it stops receiving the detection signal from the reflected wave detection circuit  5 . If the first connection switch  2   i  is turned OFF as soon as the detection signal stops being received from the reflected wave detection circuit  5 , there may be some problems because a reflected wave may occur again immediately after turning OFF the first connection switch  2   i . Specifically, if the control circuit  6  is designed so that the first connection switch  2   i  is turned OFF as soon as the detection signal stops being received, variations in the match condition of the transmitter/receiver antenna  3  and the variation-suppressing operation of terminating the transmitter/receiver antenna  3  will be repeated frequently. Where the radio device performs the signal-transmitting operation and the signal-receiving operation alternately at regular intervals, the predetermined period of time mentioned above may be, for example, the amount of time required to perform the signal-transmitting operation a predetermined number of times. Preferably, the control circuit  6  keeps the first connection switch  2   i  ON also during signal-receiving operations.  
      As described above, in Embodiment 1, when a match condition of the transmitter/receiver antenna  3  varies, the transmitter/receiver antenna  3  is terminated so as to achieve a matched state. Thus, the radio device can prevent the power amplifier  4  from being broken. Moreover, in Embodiment 1, the objective of changing the antenna match condition is realized by the antenna connection selector  2 , which is simply a plurality of switches. Therefore, the radio device of Embodiment 1, having such a simple structure, can be made by using a minimum number of components without requiring a large area.  
      While the first connection switch  2   i  is provided between the second sub-switch  2   h  and the third terminal  2   c  in the example shown in  FIG. 1 , it may be provided between the second sub-switch  2   h  the second terminal  2   b . This similarly applies to alternative embodiments of the present invention, which will be described later.  
     Embodiment 2  
       FIG. 2  illustrates a radio device according to Embodiment 2 of the present invention. The radio device of  FIG. 2  is similar to that shown in  FIG. 1  except that a matching element  8 , instead of the terminator  7 , is connected to the fourth terminal  2   d . In  FIG. 2 , like elements to those shown in  FIG. 1  are given like reference numerals and will not be further described below. Accordingly, the following description of the present embodiment focuses on what is different from Embodiment 1.  
      In Embodiment 2, as in Embodiment 1, the first connection switch  2   i  is turned ON when a reflected wave occurs due to a variation in the match condition of the transmitter/receiver antenna  3 . Then, the transmitter/receiver antenna  3  is connected to the matching element  8  via the first connection switch  2   i . In Embodiment 2, the transmitter/receiver antenna  3  is matched by the matching element  8 , thereby suppressing a variation in the load on the power amplifier  4  and preventing the power amplifier  4  from being broken. For example, the value of the matching element  8  is set so that the match condition of the transmitter/receiver antenna  3  is optimal when the transmitter/receiver antenna  3  is in proximity to a piece of metal. With this radio device, a matched state can be achieved both when the transmitter/receiver antenna  3  is in free space (where it is under an ideal environment) and when it is in proximity to a piece of metal. Thus, the value of the matching element  8  is preferably determined to be an appropriate value in view of a situation or situations expected to cause a variation in the match condition of the transmitter/receiver antenna  3 .  
     Embodiment 3  
       FIG. 3  illustrates a radio device according to Embodiment 3 of the present invention. The radio device of  FIG. 3  is similar to that shown in  FIG. 1  except that a transmitter/receiver spare antenna  9 , instead of the terminator  7 , is connected to the fourth terminal  2   d . In  FIG. 2 , like elements to those shown in  FIG. 1  are given like reference numerals and will not be further described below. Accordingly, the following description of the present embodiment focuses on what is different from Embodiment 1.  
      In Embodiment 3, as in Embodiment 1, the first connection switch  2   i  is turned ON when a reflected wave occurs due to a variation in the match condition of the transmitter/receiver antenna  3 . Then, the transmitter/receiver spare antenna  9  is connected to the reflected wave detection circuit  5  via the first connection switch  2   i . As a result, the transmitted signal is radiated from the matched transmitter/receiver spare antenna  9 , thereby suppressing a variation in the load on the power amplifier  4  and preventing the power amplifier  4  from being broken.  
     Embodiment 4  
       FIG. 4  illustrates a radio device according to Embodiment  4  of the present invention. The radio device of  FIG. 4  is similar to that shown in  FIG. 3  except that the antenna connection selector switch  2  includes a third connection switch  2   j . In  FIG. 4 , like elements to those shown in  FIG. 3  are given like reference numerals and will not be further described below. Accordingly, the following description of the present embodiment focuses on what is different from Embodiment 3.  
      Referring to  FIG. 4 , the third connection switch  2   j  is provided between the third terminal  2   c  and the second sub-switch  2   h . The third connection switch  2   j  is operated based on signals inputted through the sixth terminal  2   f . Specifically, when the sixth terminal  2   f  is ON, the third connection switch  2   j  is OFF, whereas when the sixth terminal  2   f  is OFF, the third connection switch  2   j  is ON.  
      In Embodiment 4, the third connection switch  2   j  is turned OFF when a reflected wave occurs due to a variation in the match condition of the transmitter/receiver antenna  3 . Then, the power amplifier  4  is disconnected from the transmitter/receiver antenna  3  by the third connection switch  2   j . Therefore, even if there occurs a match condition variation or a break such that the transmitter/receiver antenna  3  is shorted, the transmitter/receiver spare antenna  9  is not influenced. Moreover, as in Embodiment 3, the first connection switch  2   i  is turned ON when a reflected wave occurs due to a variation in the match condition of the transmitter/receiver antenna  3 . As a result, the transmitted signal is radiated from the matched transmitter/receiver spare antenna  9 , thereby suppressing a variation in the load on the power amplifier  4  and preventing the power amplifier  4  from being broken.  
     Embodiment 5  
       FIG. 5  illustrates a radio device according to Embodiment 5 of the present invention. The radio device of  FIG. 5  is similar to that shown in  FIG. 1  except that the radio device includes a current detection circuit  10  and a power supply terminal  11 , instead of the reflected wave detection circuit  5 . In  FIG. 5 , like elements to those shown in  FIG. 1  are given like reference numerals and will not be further described below. Accordingly, the following description of the present embodiment focuses on what is different from Embodiment 1.  
      Referring to  FIG. 5 , the current detection circuit  10  is provided between the power supply terminal of the power amplifier  4  and the control circuit  6 . The power supply terminal  11  is connected to the current detection circuit  10 . The power supply terminal  11  supplies power to the power amplifier  4  via the current detection circuit  10 .  
      In Embodiment 5, if the match condition of the transmitter/receiver antenna  3  varies, the load on the power amplifier  4  varies, whereby the current consumption of the power amplifier  4  varies. If there occurs a variation in the current consumption of the power amplifier  4  exceeding a predetermined level, the current detection circuit  10  outputs to the control circuit  6  a detection signal indicating the detection of a variation in the current consumption of the power amplifier  4 . Upon receiving the detection signal, the control circuit  6  turns ON the first connection switch  2   i . Then, the transmitter/receiver antenna  3  and the terminator  7  are connected to each other. Thus, the radio device of Embodiment 5 terminates the transmitter/receiver antenna  3  when the current consumption of the power amplifier  4  varies. As a result, the transmitter/receiver antenna  3  is matched by the terminator  7 , thereby suppressing a variation in the load on the power amplifier  4  and preventing the power amplifier  4  from being broken.  
      As described above, in Embodiment 5, whether or not the match condition of the transmitter/receiver antenna  3  has varied is detected by detecting a variation in the current consumption of the power amplifier  4 . Also in this way, it is possible to terminate the transmitter/receiver antenna  3  according to a variation in the match condition of the transmitter/receiver antenna  3 . While Embodiment 5 is similar to Embodiment 1 except that a variation in the current consumption of the power amplifier  4  is detected, a variation in the current consumption of the power amplifier  4  may be detected also in Embodiments 2 to 4. Specifically, in an alternative embodiment, the matching element  8 , instead of the terminator  7 , may be connected to the fourth terminal  2   d  as illustrated in  FIG. 6 . In another alternative embodiment, the transmitter/receiver spare antenna  9 , instead of the terminator  7 , may be connected to the fourth terminal  2   d  as illustrated in  FIG. 7 . In still another alternative embodiment, the transmitter/receiver spare antenna  9 , instead of the terminator  7 , may be connected to the fourth terminal  2   d , while the antenna connection selector switch  2  includes the third connection switch  2   j , as illustrated in  FIG. 8 . Advantageous effects similar to those of Embodiments 1 to 5 can be obtained also with the configurations illustrated in  FIG. 6  to  FIG. 8 . In the examples shown in  FIG. 5  to  FIG. 8 , as in the example shown in  FIG. 1 , it is preferred that the control circuit  6  keeps the first connection switch  2   i  ON for a predetermined period of time after it stops receiving the detection signal from the current detection circuit  10 .  
      Thus, the radio device of the present invention realizes various objectives, including preventing the power amplifier from being broken, and accommodating variations in the current consumption, the output power, etc., due to a load variation.  
      While the invention has been described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is understood that numerous other modifications and variations can be devised without departing from the scope of the invention.