Abstract:
Disclosed is a transmission output control apparatus for controlling transmitter output power to coincide with a first reference value. The apparatus includes an averaging circuit and a control section. The averaging circuit calculates an average value of said detection value of the output power. The control section outputs a differential signal between the average value and the first reference value as a transmitter output level control signal when the difference between said average value and said first reference value is less than a second reference value. The control section outputs a differential signal between said detection value and the first reference value as a transmitter output level control signal when the difference is equal to or greater than the second reference value.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a transmission output control apparatus and its method and a transmitter using the same and, more particularly, to a transmission output control technique for controlling transmission power in a transmitter.  
         [0003]     2. Description of the Related Art  
         [0004]      FIG. 1  shows an example of a conventional transmission output control apparatus. In  FIG. 1 , a mixer  2  and a synthesizer  5  transform the output of a modulator  1  into an RF signal and supply it to an amplifier  4  via a variable attenuator  3 . The variable attenuator and the amplifier  4  amplify the RF signal to a predetermined transmission output and output it. A directional coupler  8  extracts part of the output of the amplifier  4  and supplies it to a detector  8 . The detector  8  detects the extracted signal. A comparator  9  derives a differential signal between a detection voltage and a first reference voltage  12 . Then, a low-pass filter (LPF)  20  and an error amplifier  6  suppress the variation in the differential signal as well as amplifying it. The error amplifier  6  supplies the output to the variable attenuator  3  as an attenuation amount control voltage. The variable attenuator  3  changes its gain based on the attenuation amount control voltage from the error amplifier  6 . In this manner, the transmission output control apparatus in  FIG. 1  controls such that the transmitter output keeps a fixed level at all times.  
         [0005]      FIG. 2A  shows the output voltage of the modulator in  FIG. 1 . The instantaneous level variation in the output voltage is large. Therefore, even if the LPF  20  performs smoothing of the output of the comparator  9 , it is difficult to sufficiently suppress the variation. Because of this, as shown in  FIG. 2B , the transmitter output level follows the envelope of the modulator output to a certain extent.  
         [0006]     To prevent this, it is conceivable to increase the time constant of the LPF  20 . However, if the time constant of the LPF  20  increases, troubles will occur when it is necessary to change the transmitter output level. In other words, if changing the transmitter output level by changing the first reference voltage, the LPF  20  suppresses the change in output of the comparator  9  accompanying the change in the first reference voltage. Because of this, it takes time for the transmitter output level to reach a predetermined transmission output level after the change. Cases where it is necessary to change the transmitter output level include a case of starting the apparatus and a case of changing the frequency. Further, also when another apparatus is performing an Automatic Transmit Power Control (ATPC), the transmitter changes the output level.  
         [0007]     Japanese Patent Application Laid-Open No. HEI 8-97734 (1996) (document 1) disclose examples of techniques relating to such a transmission power control circuit. The document 1 discloses a transmission power control circuit of a transmitter using both the AM modulation wave and the FM modulation wave. The transmission power control circuit changes the time constant of an LPF according to the type of modulation wave. However, this technique does not sufficiently solve the problem caused by an instantaneous level fluctuation in the transmission signal.  
         [0008]     Japanese Patent Application Laid-Open No. HEI 8-102767 (1996) (document 2) discloses a transmission power control circuit in which the envelope feedback loop in the transmitter controls a transmitter output level such that the baseband modulation signal becomes the same as the envelope of the modulated signal when gain fluctuation of a high frequency power amplifier etc. occurs. This transmission power control circuit outputs modulated waves at a fixed power regardless of the gain fluctuation of the power amplifier. However, it does not sufficiently solve the problem about the instantaneous level change in the transmission signal.  
       SUMMARY OF THE INVENTION  
       [0009]     A first exemplary feature of the invention provides a transmission output control apparatus which suppresses the fluctuation in the transmitter output level against the instantaneous level fluctuation in the transmission signal and, the transmission output level of which quickly converges at the changed transmission output level when changing the transmitter output level.  
         [0010]     According to a first exemplary aspect of the invention, there is provided a transmission output control apparatus for controlling transmitter output power to coincides with a first reference value. The apparatus includes an averaging circuit a control section. The averaging circuit calculates an average value of said detection value of the output power. The control section outputs a differential signal between the average value and the first reference value as a transmitter output level control signal when the difference between said average value and said first reference value is less than a second reference value. The control section outputs a differential signal between said detection value and the first reference value as a transmitter output level control signal when the difference between said average value and said first reference value is equal to or greater than the second reference value.  
         [0011]     The first exemplary aspect of the invention controls, when the difference between the average value of transmitter output and a first reference value is greater than or equal to a second reference value, the transmitter output depending on the difference between a detection level and the first reference value. Further, the first exemplary aspect of the invention controls, when the difference between the average value of the transmitter output and the first reference value is less than the second reference value, the transmitter output depending on the difference between the average value and the first reference value. As a result, the first exemplary aspect of the invention suppresses, the fluctuation in the output level against the instantaneous level fluctuation in the transmission signal on one hand, and reduces the time for the transmitter output level to reach the changed transmission output level, when changing the transmitter output level, on the other. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     In the accompanying drawings:  
         [0013]      FIG. 1  is a block diagram showing the related art;  
         [0014]      FIG. 2A  is a waveform diagram showing an output of a modulator in  FIG. 1 ;  
         [0015]      FIG. 2B  is a waveform diagram showing an output level of a transmitter in  FIG. 1 ;  
         [0016]      FIG. 3  is a block diagram showing an embodiment of the present invention;  
         [0017]      FIG. 4A  is a diagram showing an output of an averaging circuit  11  when not changing the transmitter output level;  
         [0018]      FIG. 4B  is a waveform diagram showing the transmission output level in a first embodiment of the present invention when not changing the transmitter output level;  
         [0019]      FIG. 5A  is a diagram showing a temporal change in the transmission output level in the related art when changing the transmitter output;  
         [0020]      FIG. 5B  is a diagram showing a temporal change in the transmitter output level in the exemplary embodiment of the present invention when changing the transmitter output;  
         [0021]      FIG. 6  is a waveform diagram for explaining effects in another embodiment of the present invention when changing the transmission level;  
         [0022]      FIG. 7  is a block diagrams showing still another embodiment of the present invention; and  
         [0023]      FIG. 8  is a flow chart for explaining a program for causing a computer to operate as a control unit of a transmission power control apparatus.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     The following is described with reference to drawings.  FIG. 3  is a block diagram showing an embodiment of the present invention. In  FIG. 3 , the same components as those in  FIG. 1  have the same reference numbers.  
         [0025]     In  FIG. 3 , a mixer  2  and a synthesizer  5  transform the output of a modulator  1  into an RF signal. A variable attenuator  3  and an amplifier  4  amplify the RF signal to a predetermined transmission output level determined by the output of an error amplifier  6  and output it. A directional coupler  7  supplies part of the output of the amplifier  4  to a detector  8 . This embodiment keeps the transmission output level constant by appropriately varying the attenuation value of the variable attenuator  3 .  
         [0026]     The detector  8  supplies a detection voltage to a first input terminal of a switching unit  10  and an averaging circuit  11 . The averaging circuit averages the detection voltage. Further, it is possible to set the time constant of the averaging circuit to a value longer than that of an LPF  7  in  FIG. 1 . The output of the averaging circuit  11  is supplied to a second input terminal of the switching unit  10 .  
         [0027]     A comparator  9  compares the output of the switching unit  10  and a first reference voltage  12 , and supplies a differential signal to the error amplifier  6  and an absolute value calculation circuit  14 . The absolute value calculation circuit  14  calculates the absolute value of the differential signal.  
         [0028]     A comparator  16  compares the output of the absolute value calculation circuit  14  and a second reference voltage  15 , and supplies the comparison result to a controller  13 . The output of the controller  13  is connected to the switching unit  10 .  
         [0029]     The output of the controller may be supplied to the error amplifier  6  in another exemplary embodiment. Moreover, the controller  13  may receive signal information from the modulator  1 . In  FIG. 1 , the part enclosed by a broken line  19  constitutes a control unit.  
         [0030]     Next, there will be described the operation of a transmission output control circuit in this exemplary embodiment of the present invention.  
         [0031]     The directional coupler  7  supplies part of the power of a transmission signal output from the amplifier  4  to the detector  8 . The detector  8  outputs a detection voltage depending on the supplied transmission signal. As shown in  FIG. 2A , the modulator output is a signal having the envelope and ripple components of the modulation wave.  
         [0032]     The averaging circuit  11  performs smoothing of the detection voltage and forms it into a signal with a small amount of fluctuation (refer to  FIG. 4A ). In the normal state, the switching unit  10  selects the averaging circuit  11  by a direction from the control circuit. At this time, the comparator  9  receives the averaged detection voltage. Additionally, as the averaging circuit, it is possible to use a low-pass filter with a narrow pass band.  
         [0033]     The comparator  9  outputs a differential signal between the averaged detection voltage and the first reference voltage  12 . The error amplifier  6  amplifies the differential signal and controls the gain of the variable attenuator  3 . A loop composed of from the variable attenuator  3  to the error amplifier  6  keeps the transmitter output level constant (refer to  FIG. 4B ). The averaging circuit  11  stabilizes the transmitter output even if the transmission signal is the modulation wave. Without the averaging circuit  11 , the detection voltage is fed back to the variable attenuator as it is, therefore, the transmission output varies depending on the envelope of the modulation wave (refer to  FIG. 2B ).  
         [0034]     Next, there will be described the operation of each part when the transmitter changes its output level.  
         [0035]     The transmitter changes its output level by changing the first reference voltage  12 . As a case where the transmitter changes its output level, there is a case of outputting a specified level intentionally (manually). Further, a transmitter employing the ATPC (Automatic Transmit Power Control) technique as the measures against fading frequently changes its transmission power. Furthermore, also when starting the apparatus (turning the power on) etc., the transmitter changes its transmission power from zero to a predetermined value.  
         [0036]     The absolute value calculation circuit  14  calculates the absolute value of the output of the comparator  9  and supplies it to the comparator  16 . The comparator  16  compares the output of the absolute value calculation circuit and the second reference voltage  15 .  
         [0037]     When the first reference voltage  12  is changed, the output of the absolute value calculation circuit  14  becomes greater because the output of the comparator  9  is the differential signal between the detection signal and the first reference voltage. When the absolute value of the output of the comparator  9  becomes equal to or greater than the second reference voltage  15 , the comparator  16  supplies a high-level signal to the controller  13 .  
         [0038]     In other words, the comparator  16  judges whether or not the error (the output of the comparator  9 ) between the transmitter output level and the first reference voltage is greater than a fixed level (the second reference voltage). When the comparator  16  judges that the error is greater than the fixed level, the controller  13  causes the switching unit  10  to output the output of the detector  8 . As a result, the transmitter output level quickly follows the change in the first reference voltage.  
         [0039]     At this time, it is also possible for the controller  13  to increase the gain of the error amplifier  6 . Due to this, it is possible for the transmitter to more quickly change its output level.  
         [0040]     As shown in  FIG. 4A  and  FIG. 4B , by averaging the detection voltage, it is possible for the transmitter to stabilize its output power. If there is no the averaging circuit, it is not possible for the transmitter to sufficiently suppress the fluctuation in the transmission output. Further, if performing the control of the transmission power by using only the averaged detection voltage, it is not possible for the transmitter to quickly change the output power when changing the transmission power. The present embodiment bypasses the averaging circuit  11  when the absolute value of the output of the comparator  9  becomes equal to or greater than the fixed level (the second reference value). After this, when the absolute value of the output of the comparator  16  becomes less than the fixed level, the controller  13  causes the switching unit to select the output of the averaging circuit  11 . As a result, the control of the transmission power in the present embodiment increases in speed, as shown in  FIG. 5B .  
         [0041]     Further, in another exemplary embodiment, by increasing the gain of the error amplifier  6  also, it is possible to perform control at a higher speed as shown in  FIG. 6 .  
         [0042]     The controller  13  may be supplied with information also from the modulator  1  and the synthesizer  13 . When the signal information from the modulator indicates that the modulation wave is CW (no modulation), the controller  13  may also bypass the averaging circuit  11 . Further, when the information from the synthesizer  5  indicates the change in the transmission frequency, it is made possible for the controller  13  to quickly stabilize the transmission output by setting a bypass for the averaging circuit  11  or an increase in gain of the error amplifier  6 .  
         [0043]     As described above, there is no averaging circuit  11 , the transmission output varies as shown in  FIG. 2A . As shown in  FIG. 4B , averaging of the detection voltage stabilizes the transmission output. However, if the signal is averaged at all times, the change in the transmission output becomes slow in speed as shown in  FIG. 5A . In the present embodiment, when the absolute value of the error voltage, which is the output of the comparator  9 , exceeds the second reference voltage, the change in the transmission power is increased in speed by bypassing the averaging circuit  11  as shown in  FIG. 5B . Therefore, in the present embodiment, stabilization of the transmission output level at the time of input of the modulation wave and the speedy control at the time of the change in the transmission level can coexist.  
         [0044]      FIG. 7  is a block diagram showing a still another exemplary embodiment of the present invention and the same portions as those in  FIG. 3  have the same reference numbers. The present embodiment realizes the function equivalent to that of the transmitter in  FIG. 3  with firmware according to a CPU  19 ′.  
         [0045]     In the present embodiment, an A/D converter  18  transforms the output of the detector  8  into a digital signal and supplies it to the CPU  19 ′. Then a D/A converter  17  transforms the output of the CPU  19 ′ into an analog signal. The output of the D/A converter  17  controls the gain of the attenuator  3 . The CPU  19 ′ realizes the function of a control unit  19  in  FIG. 3 . In the present embodiment, a recording medium (not shown) such as ROM stores the operation already explained with reference to  FIG. 3  as a program beforehand. Then, the CPU  19  reads this program and operates similarly as in the embodiment in  FIG. 3 .  
         [0046]      FIG. 8  shows a flow chart of this program.  
         [0047]     In  FIG. 8 , in step S 1 , the CPU  19 ′ initially sets a parameter (MODE) to “0”. The parameter corresponds to an output signal of the controller  13  in  FIG. 3 .  
         [0048]     In step S 2 , the CPU  19 ′ receives the detection voltage (V) from the A/D converter  8  and calculates the average of the detection voltage (AV) in terms of time.  
         [0049]     Next, the CPU checks the parameter Mode. If mode=1, the process of the CPU proceeds to step S 4 . Otherwise, the processing of the CPU proceeds to step S 5 .  
         [0050]     In step S 4 , the CPU obtains the absolute value of the differential signal between the average value (AV) and the first reference value (R 1 ). Then, judgment is made whether or not the absolute value is equal to or more than the second reference voltage (R 2 ). When the judgment result in step S 4  is “YES”, the process of the CPU  19 ′ proceeds to step S 6  and when not, the process of the CPU  19 ′ proceeds to step S 8 .  
         [0051]     In step S 5 , the CPU obtains the absolute value of the differential signal between the detection level (V) and the first reference value (R 1 ). Then, judgment is made whether or not the absolute value is equal to or more than the second reference voltage (R 2 ). When the judgment result in step S 5  is “YES”, the process of the CPU  19 ′ proceeds to step S 6  and when not, the process of the CPU  19 ′ proceeds to step S 8 .  
         [0052]     In step S 6 , the CPU  19 ′ outputs the differential signal (the detection level—the first reference value) to the D/A converter  17 . In step S 7 , the MODE is set to “1”. When this process ends, the process of the CPU  19 ′ returns to step S 2 . Incidentally, in step S 7 , the CPU  19 ′ may multiply the differential signal by a fixed factor (greater than one).  
         [0053]     In step S 8 , the CPU  19 ′ outputs the differential signal (the average value—the first reference value) to the D/A converter  17 . In step S 9 , the MODE is set to “0”. When this process ends, the process of the CPU  19 ′ returns to step S 2 .  
         [0054]     While this invention has been described in connection with certain exemplary embodiments, it is to be understood that the subject matter encompassed by way of this invention is not be limited to those specific embodiments. On the contrary, it is intended for the subject matter of the invention to include all alternatives, modifications and equivalents as can be included with the sprit and scope of the following claims. Further, the inventor&#39;s intent is to retain all equivalents even if the claims are amended during prosecution.