CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-224597, filed Jul. 25, 2001, the entire contents of which are incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a radio communication apparatus having a circuit for controlling transmission power, and more particularly to a radio communication apparatus having a control circuit for adjusting transmission power to a desired value.  
           [0004]    2. Description of the Related Art  
           [0005]    In a conventional radio communication apparatus having a circuit for controlling transmission power, a comparator  30  compares the output of a detection circuit  29  with a first reference signal (reference  1 ) as shown in FIG. 1. Depending upon whether or not the output voltage of the detection circuit  29  is higher than the voltage of the first reference signal, the output signal of the comparator  30  varies. A change in the output signal is fed back to a variable gain amplifier  23  or variable attenuator.  
           [0006]    If the output voltage of the detection circuit  29  is higher than the voltage of the first reference signal, the comparator  30  outputs a signal for reducing the power of a transmission signal. The output signal is supplied to the variable gain amplifier  23 , where the output signal is controlled so that the gain of the transmission signal will be a negative value. As a result, the power of the transmission signal is reduced.  
           [0007]    On the other hand, if the output voltage of the detection circuit  29  is not higher than the voltage of the first reference signal, the comparator  30  outputs a signal for increasing the power of a transmission signal. The output signal is supplied to the variable gain amplifier  23 , where the output signal is controlled so that the gain of the transmission signal will be a positive value. As a result, the power of the transmission signal is increased.  
           [0008]    The above-described feedback control is executed to enable signal transmission with power having an almost desired range.  
           [0009]    However, if a problem occurs in the detection circuit  29  and hence the circuit  29  outputs a signal of a level lower than a desired voltage level, the gain of the variable gain amplifier  23  is adjusted to a higher value. As a result, signal transmission may be executed with power higher than desired power.  
           [0010]    If the communication mode is, for example, CDMA (Code Division Multiple Access), communications are executed using a common channel between a single base station and a plurality of radio communication apparatuses. Further, the total power of the electric waves the base station can treat is substantially constant. Therefore, if signal transmission is executed with high power between the base station and a certain radio communication apparatus as stated above, the high-power signal will undesirably be a radio-frequency interference signal to communications between other radio communication apparatuses and the base station. In this case, it is very possible that some radio communication apparatuses may be disconnected from the base station.  
           [0011]    Further, if the communication mode is TDMA (Time Division Multiple Access), the transmission power used in a transmission circuit is substantially constant as compared to CDMA. Accordingly, once a transmission circuit has consumed much power, the transmission circuit continues to consume much power. As a result, a radio communication apparatus incorporating the transmission circuit significantly consumes power and hence the battery of the apparatus may soon run out.  
         BRIEF SUMMARY OF THE INVENTION  
         [0012]    It is an object of the invention to provide a radio communication apparatus that inhibits the transmission operation of the apparatus if the radio communication apparatus detects a problem in the detection circuit of the apparatus.  
           [0013]    According to a first aspect of the invention, there is provided a radio communication apparatus comprising:  
           [0014]    a power amplifier configured to amplify power of a transmission signal and output the amplified signal to an antenna;  
           [0015]    a power detector configured to detect power of the amplified signal;  
           [0016]    a first comparator configured to compare the detected power with a first reference signal;  
           [0017]    a power adjuster configured to adjust the power of the transmission signal to a desired power value on the basis of a comparison result of the first comparator;  
           [0018]    a second comparator configured to compare the detected power with a second reference signal; and  
           [0019]    a controller configured to control supply of power to the power amplifier on the basis of a comparison result of the second comparator.  
           [0020]    According to a second aspect of the invention, there is provided a radio communication apparatus comprising:  
           [0021]    a power amplifier configured to amplify power of a transmission signal and output the amplified signal to an antenna;  
           [0022]    a power detector configured to detect power of the amplified signal;  
           [0023]    a first comparator configured to compare the detected power with a first reference signal;  
           [0024]    a power adjuster configured to adjust the power of the transmission signal to a desired power value on the basis of a comparison result of the first comparator;  
           [0025]    a second comparator configured to compare the detected power with a second reference signal; and  
           [0026]    a controller configured to control supply of power to the power adjuster on the basis of a comparison result of the second comparator.  
           [0027]    According to a third aspect of the invention, there is provided a radio communication apparatus comprising:  
           [0028]    a power amplifier configured to amplify power of a transmission signal and output the amplified signal to an antenna;  
           [0029]    a power detector configured to detect power of the amplified signal;  
           [0030]    a first comparator configured to compare the detected power with a first reference signal;  
           [0031]    a power adjuster configured to adjust the power of the transmission signal to a desired power value on the basis of a comparison result of the first comparator;  
           [0032]    a second comparator configured to compare the detected power with a second reference signal; and  
           [0033]    an inhibiting part configured to inhibit supply of the amplified signal to the antenna on the basis of a comparison result of the second comparator.  
           [0034]    According to a fourth aspect of the invention, there is provided a radio communication apparatus comprising:  
           [0035]    a first frequency generator configured to generate a frequency signal having a first preset frequency;  
           [0036]    a modulator configured to modulate a baseband signal on the basis of the frequency signal generated by the first frequency generator;  
           [0037]    a power adjuster configured to adjust the modulated baseband signal to a desired power value;  
           [0038]    a second frequency generator configured to generate a frequency signal having a second preset frequency;  
           [0039]    a frequency converter configured to convert a frequency of the adjusted baseband signal on the basis of the frequency signal generated by the second frequency generator;  
           [0040]    a power amplifier configured to amplify power of the converted signal;  
           [0041]    a power detector configured to detect power of the amplified signal;  
           [0042]    a first comparator configured to compare the detected power with a first reference signal and output a compared result to the power adjuster;  
           [0043]    a second comparator configured to compare the detected power with a second reference signal; and  
           [0044]    an inhibiting part configured to inhibit supply of power to at least one of the first and second frequency generators, the modulator, the power adjuster, the frequency converter and the power amplifier, if the second comparator determines that the detected power is lower than the second reference signal.  
           [0045]    According to a fifth aspect of the invention, there is provided a radio communication apparatus comprising:  
           [0046]    a first frequency generator configured to generate a frequency signal having a first preset frequency;  
           [0047]    a modulator configured to modulate a baseband signal on the basis of the frequency signal generated by the first frequency generator;  
           [0048]    a power adjuster configured to adjust the modulated baseband signal to a desired power value;  
           [0049]    a second frequency generator configured to generate a frequency signal having a second preset frequency;  
           [0050]    a frequency converter configured to convert a frequency of the adjusted baseband signal on the basis of the frequency signal generated by the second frequency generator;  
           [0051]    a power amplifier configured to amplify power of the converted signal;  
           [0052]    a power detector configured to detect power of the amplified signal;  
           [0053]    a first comparator configured to compare the detected power with a first reference signal and output a compared result to the power adjuster;  
           [0054]    a second comparator configured to compare the detected power with a second reference signal; and  
           [0055]    an inhibiting part configured to inhibit supply of power to all of the first and second frequency generators, the modulator, the power adjuster, the frequency converter and the power amplifier, if the second comparator determines that the detected power is lower than the second reference signal.  
           [0056]    Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0057]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.  
         [0058]    [0058]FIG. 1 is a block diagram illustrating the electrical structure of a transmission power control circuit incorporated in a conventional radio unit;  
         [0059]    [0059]FIG. 2 is a block diagram illustrating the entire configuration of a radio communication apparatus, according to the embodiment of the invention, which comprises a radio unit including a transmission power control circuit and a control section;  
         [0060]    [0060]FIG. 3 is a block diagram of a radio communication apparatus according to a first embodiment of the invention, illustrating the electrical configuration of a transmission power control circuit, and electrical connection between the transmission power control circuit and a control section that outputs a control signal for turning on/off predetermined elements incorporated in the transmission power control circuit;  
         [0061]    [0061]FIG. 4 is a graph indicating the relationship between the output voltage of a power amplifier and the output voltage of a detection circuit, assumed that the detection circuit is normal; and  
         [0062]    [0062]FIG. 5 is a block diagram of a radio communication apparatus according to a second embodiment of the invention, illustrating the electrical configuration of a transmission power control circuit, and electrical connection between the transmission power control circuit and a control section that outputs a control signal for turning on/off predetermined elements incorporated in the transmission power control circuit.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0063]    A radio communication apparatus according to embodiments of the invention will be described with reference to the accompanying drawings.  
         [0064]    [0064]FIG. 2 is a block diagram illustrating the electrical structure of a radio communication apparatus, according to the embodiment of the invention, which comprises a radio unit including a transmission power control circuit and a control section.  
         [0065]    The radio communication apparatus has a CDMA radio communication function. In the CDMA mode, communications are executed with the radio communication apparatus synchronized with a base station connected to a public network. Further, a radio unit  12  incorporated in the apparatus employs, for example, QPSK (Quadrature Phase Shift Keying) as the modulation mode.  
         [0066]    A voltage controller  15  controls the gain of an amplifier incorporated in the CDMA radio unit  12  under the control of a control section  13 . As a result of this control, the transmission level of a CDMA signal to be transmitted to the base station is determined.  
         [0067]    A speech codec  18  encodes a transmission speech signal input from a microphone  19  in accordance with a predetermined speech encoding mode and decodes a signal input via the CDMA radio unit  12  and control section  13  into a received signal. The received signal is output through a loudspeaker  20 .  
         [0068]    An image codec  13 - 1  decodes received image data or image data stored in a memory  14 . The resultant image is displayed on a display  17  such as an LCD (Liquid Crystal Display).  
         [0069]    An operation section  16  is a key input section that includes a ten-key pad, a four-direction-key pad and various function keys, etc. The operation section  16  is used for, for example, the scroll of information displayed on the display  17  as well as usual signal reception/transmission or instructions to a destination apparatus.  
         [0070]    The memory  14  is formed of a semiconductor memory such as a RAM (Random Access Memory) or a ROM (Read Only Memory). The memory  14  stores data to be transmitted using CDMA, received data, menu information formed of some of the data, etc.  
         [0071]    The control section  13  controls each section of the radio communication apparatus. Specifically, the control section  13  executes various types of control related to CDMA radio communications or to exchange of information such as a phone directory, mails, schedules, etc.  
         [0072]    The present invention is applicable not only to CDMA but also to TDMA. CDMA and TDMA circuit structures differ in the modulation or demodulation form. Accordingly, in the case of using TDMA, the CDMA radio unit  12  is modified so that the modified radio unit will be compatible with TDMA.  
         [0073]    [0073]FIG. 3 is a block diagram of a radio communication apparatus according to a first embodiment of the invention, illustrating the electrical configuration of a transmission power control circuit, and electrical connection between the transmission power control circuit and a control section that outputs a control signal for turning on/off predetermined elements incorporated in the transmission power control circuit.  
         [0074]    A baseband signal, converted into an analog signal and output from the control section  13 , is input to a modulator  21 . The modulator  21  modulates the baseband signal on the basis of a frequency signal output from a local frequency signal generator  22 .  
         [0075]    The modulated baseband signal is input to a variable gain amplifier  23 , where the modulated baseband signal is amplified to a desired power value. The amplified signal is input to a frequency converter  24 . The frequency converter  24  converts the frequency of the amplified signal on the basis of a frequency signal output from a local frequency signal generator  25 .  
         [0076]    The frequency-converted signal is input to a band-pass filter  26 , where a noise component or an undesired signal component which is not within a transmission band is attenuated. The signal having an undesired component attenuated is input to a power amplifier  27 , where the attenuated signal is amplified to desired transmission power.  
         [0077]    The thus-amplified signal is output to an antenna  11  via a duplexer  28 , where the amplified signal is transmitted.  
         [0078]    Further, the amplified signal as the output of the power amplifier  27  is converted into a direct-current voltage signal by a detection circuit  29 . The detection circuit  29  is provided for detecting the power of the signal output from the power amplifier  27 . The direct-current voltage signal converted by the detection circuit is input to a first comparator  30  and a second comparator  41 .  
         [0079]    The first comparator  30  compares the output voltage of the detection circuit  29  with the voltage of a first reference signal (reference  1 ). A comparator similar to the first comparator  30  is employed in a conventional transmission power control circuit.  
         [0080]    The first reference signal is a direct-current voltage signal having a threshold voltage for determining the output voltage of the first comparator  30 , and is used to determine the power of a transmission signal.  
         [0081]    Specifically, if the output voltage of the detection circuit  29  is higher than the voltage of the first reference signal, the first comparator  30  supplies the variable gain amplifier  23  with a signal for setting the gain of the variable gain amplifier  23  to a negative value. On the other hand, if the output voltage of the detection circuit  29  is not higher than the voltage of the first reference signal, the first comparator  30  supplies the variable gain amplifier  23  with a signal for setting the gain of the variable gain amplifier  23  to a positive value.  
         [0082]    In other words, the power value of a transmission signal is fed back to control the gain of the variable gain amplifier  23  on the basis of the power value of the transmission signal. As a result, the transmission signal can be transmitted from the antenna  11  with a desired transmission power value corresponding to the first reference signal.  
         [0083]    The second comparator  41  compares the output voltage of the detection circuit  29  with the voltage of a second reference signal (reference  2 ). The second reference signal is a direct-current voltage signal having a threshold voltage value for determining the output voltage of the second comparator  41  and is used to inhibit the supply of power to the transmission power control circuit so as to prevent a transmission signal from being transmitted via the antenna  11 .  
         [0084]    Specifically, if the output voltage of the detection circuit  29  is not higher than the voltage of the second reference signal, the second comparator  41  supplies the control section  13  with a signal for inhibiting the supply of power to the transmission power control circuit. On the other hand, if the output voltage of the detection circuit  29  is higher than the voltage of the second reference signal, the second comparator  41  supplies the control section  13  with a signal for continuing the supply of power to the transmission power control circuit.  
         [0085]    Alternatively, if the output voltage of the detection circuit  29  is higher than the voltage of the second reference signal, the supply of power to the transmission power control circuit may be continued without supplying any signal to the control section  13 . Control is executed so that power is continuously supplied to the transmission power control circuit.  
         [0086]    If the output signal of the detection circuit  29  has an extremely low voltage, it is determined that the detection circuit  29  is in an abnormal state, whereby the supply of power to the transmission power control circuit is inhibited on the basis of the output signal of the second comparator  41 .  
         [0087]    Further, a switching circuit  42  for turning on/off a transmission power control signal output from the control section  13  is provided. The switching circuit  42  includes switches  42 - 1 ,  42 - 1 ,  42 - 3 ,  42 - 4 ,  42 - 5  and  42 - 6  for turning on/off the supply of power to the modulator  21 , variable gain amplifier  23 , frequency converter  24 , power amplifier  27  and local frequency signal generators  22  and  25 .  
         [0088]    The switches  42 - 1 ,  42 - 1  and  42 - 3  are connected to a power supply  43 . The switch  42 - 4  is connected to a power supply  44 . The switches  42 - 5  and  42 - 6  are connected to a power supply  45 . These switches are used to supply power to the respective elements and to interrupt the supply of power thereto.  
         [0089]    To inhibit the power supply to the transmission power control circuit, the control section  13  controls the switching circuit  42 . Specifically, when the second comparator  41  has detected an abnormality in the detection circuit  29  as aforementioned, the control section  13  turns off at least one of the switches  42 - 1 ,  42 - 1 ,  42 - 3 ,  42 - 4 ,  42 - 5  and  42 - 6 , with the result that the supply of power to the power amplifier  27  is inhibited, thereby inhibiting the transmission operation of the radio communication apparatus and hence inhibiting the transmission of a signal therefrom. In this case, it is advantageous in light of power saving to turn off the switch  42 - 4 , since the power consumption of the switch  42 - 4  is maximum between the switches.  
         [0090]    Moreover, to reduce the consumption of power to the maximum degree, all the switches  42 - 1 ,  42 - 2 ,  42 - 3 ,  42 - 4 ,  42 - 5  and  42 - 6  are turned off. In this case, all the power to be supplied by the power supplies  43 ,  44  and  45  is saved, and at the same time, the transmission operation of the radio communication apparatus is inhibited.  
         [0091]    Before shipping the product the maker may set which one of the switches should be turned off, or after shipping of the product the service company may set which one of the switches should be turned off.  
         [0092]    If the switches or a switch of the switching circuit  42  is turned off, and no transmission signal is generated by the ratio communication apparatus, a message indicative of this is displayed on the display  17 .  
         [0093]    More specifically, when the control section  13  has received a signal output from the second comparator  41  if the output voltage of the detection circuit  29  is not higher than the voltage of the second reference signal, a message stating, for example, that “Please repair the detection circuit” is displayed on the display  17 . Instead of the message, a mark indicative of the failure of the detection circuit  29  may be displayed. The maker can determine the failure of the detection circuit  29  from the mark.  
         [0094]    As described above, in this embodiment, when a problem has occurred in the detection circuit  29 , the output voltage of the detection circuit  29  is compared with the voltage of the second reference signal used for inhibiting the transmission power. In the prior art, if the output voltage of the detection circuit is low, the transmission signal is transmitted with high power as a result of feedback control. In light of this, in the first embodiment, the second reference signal is used to inhibit the signal transmission in such a case. As described above, the radio communication apparatus according to the first embodiment can detect a problem in the detection circuit  29 , thereby inhibiting its transmission operation.  
         [0095]    [0095]FIG. 4 shows the relationship between the output voltage of a power amplifier and the output voltage of a detection circuit, assumed that the detection circuit is normal.  
         [0096]    If the detection circuit is normal, the output voltage of the power amplifier  27  varies within the range A of from X 1  to X 2  shown in FIG. 4. The output range A results from the feature of CDMA that the transmission power of the radio communication apparatus is varied on the basis of the power of a signal received by the apparatus or an instruction signal output from the base station.  
         [0097]    Furthermore, the transmission power determined from the gain of the power amplifier  27  is adjusted to a desired value by feedback control using the first reference signal. The voltage of the first reference signal is varied on the basis of the power of a received signal or instruction signal from the base station.  
         [0098]    Specifically, if the detection circuit  29  is normal, the voltage of the first reference signal varies within the range B of from Y 1  to Y 2  shown in FIG. 4.  
         [0099]    If, on the other hand, the detection circuit  29  is abnormal, the slope of the straight line in FIG. 4, for example, is small. In this case, even if the output voltage of the power amplifier  27  varies within the range of from X 1  to X 2 , there is a case where the output voltage of the detection circuit  29  is lower than Y 1 .  
         [0100]    Further, the output voltage of the detection circuit  29  also varies in accordance with the voltage of the first reference signal as a result of feedback control. Therefore, the output voltage of the detection circuit  29  also varies within the range B of from Y 1  to Y 2 , shown in FIG. 4, in accordance with the output voltage of the amplifier varying within the range of from X 1  to X 2 .  
         [0101]    Since the voltage of the second reference signal is a reference voltage used for detecting whether the output voltage of the detection circuit  29  is lower than a desired value, the voltage of the second reference signal is set to a value lower than Y 1  shown in FIG. 4, for example, to a value Y ref2  that is the intersection of the reference  2  and the ordinate in FIG. 4. In other words, the voltage of the second reference signal is set to a value lower than the voltage of the first reference signal.  
         [0102]    [0102]FIG. 5 is a block diagram of a radio communication apparatus according to a second embodiment of the invention, illustrating the electrical configuration of a transmission power control circuit, and electrical connection between the transmission power control circuit and a control section that outputs a control signal for turning on/off predetermined elements incorporated in the transmission power control circuit.  
         [0103]    A baseband signal, converted into an analog signal and output from the control section  13 , is input to a modulator  21 . The modulator  21  modulates the baseband signal on the basis of a frequency signal output from a local frequency signal generator  22 .  
         [0104]    The modulated baseband signal is input to a variable gain amplifier  23 , where the modulated baseband signal is amplified to a desired power value. As in the first embodiment, the amplified signal is transmitted from an antenna  11  via a frequency converter  24 , band-pass filter  26 , power amplifier  27  and duplexer  28 .  
         [0105]    In the second embodiment, an analog-to-digital converter  46  and digital-to-analog converter  47  are used in place of the comparators  30  and  41  as employed in the first embodiment. The output signal of the detection circuit  29  is converted into a digital signal by the analog-to-digital converter  46 , and is output to a control section  13 .  
         [0106]    The control section  13  receives a first reference signal as a digital signal for determining the power of a transmission signal and a second reference signal as a digital signal for inhibiting the supply of power to the transmission power control circuit to thereby prevent a transmission signal from being transmitted from the antenna  11 . The control executed using the first and second reference signals is similar to that in the first embodiment.  
         [0107]    The first reference signal is referred to in order to feed back the power of a transmission signal and control the gain of the variable gain amplifier  23  on the basis of the power of the transmission signal. Specifically, a digital signal indicative of the output voltage of the detection circuit  29  is compared with the first reference signal (reference  1 ).  
         [0108]    If the output voltage of the detection circuit  29 , indicated by the digital signal, is higher than the voltage of the first reference signal, the control section  13  supplies, via the digital-to-analog converter  47 , the variable gain amplifier  23  with a signal for setting the gain of the variable gain amplifier  23  to a negative value. On the other hand, if the output voltage of the detection circuit  29 , indicated by the digital signal, is not higher than the voltage of the first reference signal, the control section  13  supplies, via the digital-to-analog converter  47 , supplies the variable gain amplifier  23  with a signal for setting the gain of the variable gain amplifier  23  to a positive value.  
         [0109]    The control section  13  calculates the gain of the variable gain amplifier  23  so that the transmission power will correspond to the first reference signal, thereby supplying a signal for controlling the gain to the digital-to-analog converter  47 . As a result, a signal can be transmitted from the antenna  11  with desired transmission power corresponding to the first reference signal.  
         [0110]    The second reference signal is used to inhibit the supply of power to the transmission power control circuit if the digitally converted output signal of the detection circuit  29  is abnormally low and the detection circuit  29  is determined abnormal.  
         [0111]    Specifically, if the voltage indicated by the digitally converted output signal of the detection circuit  29  is not higher than the voltage indicated by the second reference signal, the control section  13  outputs a signal for inhibiting the supply of power to the transmission power control circuit. On the other hand, if the voltage indicated by the digitally converted output signal of the detection circuit  29  is higher than the voltage indicated by the second reference signal, the control section  13  outputs a signal for continuing the supply of power to the transmission power control circuit.  
         [0112]    Alternatively, if the voltage indicated by the digitally converted output signal of the detection circuit  29  is higher than the voltage indicated by the second reference signal, the supply of power to the transmission power control circuit may be continued without outputting any signal from the control section  13 .  
         [0113]    Further, the second embodiment also employs a switching circuit  42  for turning on/off a transmission power control signal output from the control section  13 . This switching circuit is similar to the circuit of the first embodiment in the configuration and control method of the switching circuit.  
         [0114]    If the switches of the switch circuit  42  are turned off, and no transmission signal is generated by the radio communication apparatus, a message indicating that no transmission signal is generated is displayed on the display  17  as in the first embodiment.  
         [0115]    As described above, in the second embodiment, the first and second reference signals input to the control section  13  are not analog signals having respective voltages as shown in FIG. 4 but digital signals indicative of the voltages.  
         [0116]    However, if the first and second reference signals are digitally converted by an analog-to-digital converter before the first and second reference signals are input to the control section  13 , the same type first and second reference signals may be used in the first and second embodiments.  
         [0117]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
A power amplifier amplifies the power of a transmission signal and outputs the amplified signal to an antenna. A power detector detects the power of the amplified signal. A first comparator compares the detected power with a first reference signal. A power adjuster adjusts the power of the transmission signal to a desired power value on the basis of the comparison result of the first comparator. A second comparator compares the detected power with a second reference signal. A controller controls the supply of power to the power amplifier or the power adjuster on the basis of the comparison result of the second comparator.