Patent Publication Number: US-2005143030-A1

Title: Receiving apparatus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a receiving apparatus for receiving radio waves including an analog sound modulated wave signal and a digital sound modulated wave signal. The use of the invention is not limited to the receiving apparatus.  
      2. Description of the Related Art  
      In recent years, digitization of radio broadcasting using ground waves is being promoted as digital radio broadcasting using a satellite develops, and a radio receiver adapted to the digital broadcasting using ground waves is being spread. A digital signal is added to the existing analog radio waves transmitted from a broadcast station, and the radio receiver can receive the same broadcast program by both the analog radio waves and the digital signal.  
       FIG. 1  shows an RF device of the radio receiver. As shown in  FIG. 1 , the RF device  100  of the radio receiver has, like normal radio receiver of only the analog system, an antenna  101 , an attenuator  102  for attenuating an RF signal input from the antenna  101 , a band pass filter  103  for regulating a band of the RF signal attenuated by the attenuator  102 , an amplifier  104  for amplifying the RF signal output from the band pass filter  103 , a band pass filter  105  for regulating a band of the RF signal amplified by the amplifier  104 , a voltage controlled oscillator  106 , a mixer  107  for mixing the RF signal output from the band pass filter  105  and an oscillation signal of the voltage controlled oscillator  106 , there by generating an IF signal, and an AGC circuit  108  for controlling an attenuation amount of the attenuator  102  on the basis of the output from the band pass filter  105  or mixer  107  and controlling the gain of the amplifier  104 .  
      The attenuator  102  used in the RF device  100  attenuates the level difference between the antenna input level at which IM (Inter-Modulation) interference occurs and the maximum antenna input level from the broadcast station. As the attenuator  102 , an attenuator which obtains an attenuation amount by an impedance division ratio using a direct current resistance value when a forward current is passed by using a pin-diode or the like or an attenuator using a dual-gate type FET having a gate dedicated to adjust the gain for an RF amplifier is often used.  
      As such a radio receiver, an OFDM receiver is disclosed in which a distortion caused by improper control that occurs when the power ratio of each of carriers of an OFDM becomes excessive, for example, in a DAB mobile receiver is suppressed. The OFDM receiver calculates the center frequency of an OFDM modulated wave, that is, the power in the center point of an FFT in a demodulator. A signal of the calculated value is transmitted as a control signal to an AGC amplifier for the IF stage and the like via a time constant circuit. The AGC amplifier for the IF stage or the like amplifies an output from a mixer in the second stage with respect to a control signal of a predetermined value or a larger value from the time constant circuit and outputs the amplified signal to an AGC block of the IF stage. As a result, an output of an attenuator is suppressed (refer to, for example, Japanese Patent Application Laid-open No. 11-46151).  
     SUMMARY OF THE INVENTION  
      However, in the conventional technique, demodulation of an analog signal and a digital signal is switched according to BER (Bit Error Rate) obtained at the time of demodulating a digital signal. Therefore, in the case where the field intensity of an RF signal input by receiving an analog modulated wave is high to such a degree that IM interference occurs, that is, in the case where an RF signal is excessively input, if the BER is high, demodulation of a digital modulated wave is switched to demodulation of an analog modulated wave. It causes one problem such that the reception quality deteriorates and the sound quality deteriorates.  
      On the other hand, in the case where the attenuator for suppressing excessive input of the RF signal is provided as in the conventional technique, the number of parts increases and it causes one problem such that the size and weight of the radio receiver cannot be reduced. Further, one problem also occurs such that the price of the radio receiver increases.  
      The invention according to the present invention relates to a receiving apparatus comprising: 
          a receiving device which receives a radio wave including at least an analog sound modulated wave signal and a digital sound modulated wave signal;     an analog demodulating device which demodulates the analog sound modulated wave signal received by said receiving device;     a digital demodulating device which demodulates the digital sound modulated wave signal received by said receiving device;     a determining device which determines whether a reception level of said radio wave is equal to or higher than a predetermined level or not on the basis of a radio frequency signal obtained by receiving said radio wave by said receiving device;     a selecting device which selects either said analog demodulating device or said digital demodulating device on the basis of a result of determination made by said determining device; and     a sound output device which outputs sound on the basis of the sound demodulated signal obtained from the demodulating device selected by said selecting device.        

    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram showing the hardware configuration of an RF device of a conventional radio receiver.  
       FIG. 2  is a frequency characteristic diagram of a radio wave received by a receiving apparatus according to an embodiment of the invention.  
       FIG. 3  is a front view schematically showing the receiving apparatus according to the embodiment of the invention.  
       FIG. 4  is a block diagram showing a functional configuration of the receiving apparatus according to the embodiment of the invention.  
       FIG. 5  is a block diagram showing a hardware configuration of a first example of the receiving apparatus according to the embodiment.  
       FIG. 6  is a flowchart showing the procedure in the first example of the receiving apparatus according to the embodiment.  
       FIG. 7  is a block diagram showing a hardware configuration of a second example of the receiving apparatus according to the embodiment.  
       FIG. 8  is a flowchart showing a procedure in the second example of the receiving apparatus according to the embodiment.  
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION  
      A preferred embodiment of a receiving apparatus according to the invention will be described in detail hereinbelow with reference to the appended drawings. First, frequency characteristics of a radio wave received by the receiving apparatus according to the embodiment of the invention will be described.  FIG. 2  is a frequency characteristic diagram of a radio wave received by the receiving apparatus according to the embodiment of the invention. The vertical axis of the characteristic diagram indicates signal level and the horizontal axis thereof indicates frequency. The radio wave includes an analog sound modulated wave signal fa and a digital sound modulated wave signal fd and is transmitted from an arbitrary broadcast station. The analog sound modulated wave signal fa is, for example, a sound signal such as an FM wave or AM wave. The digital modulated wave signal fd includes, for example, a digital sound modulated wave signal which is the same sound data as the analog sound modulated wave signal fa and also a digital character/image modulated wave signal such as character data or still image data such as the name of a broadcast station, frequency, program name, title of a music piece, time, weather, news, advertisement, or the like.  
      The receiving apparatus according to the embodiment of the invention will be schematically shown.  FIG. 3  is a front view schematically showing the receiving apparatus according to the embodiment of the invention. As shown in  FIG. 3 , a receiving apparatus  300  has, for example, a display such as a liquid crystal display  301 . By demodulating the digital character/image modulated wave signal, characters or a still image of the name of a broadcast station, frequency, program name, title of a music piece, time, weather, news, advertisement, or the like can be displayed on the liquid crystal display  301 .  
      The functional configuration of the receiving apparatus according to the embodiment of the invention will now be described.  FIG. 4  is a block diagram showing the functional configuration of the receiving apparatus  300  according to the embodiment of the invention. The receiving apparatus  300  is constructed by a receiving device  401 , an intermediate frequency signal separating device  402 , an analog demodulating device  403 , a digital demodulating device  404 , a determining device  405 , a selecting device  406 , and an output device  407 .  
      The receiving device  401  receives a radio wave including an analog sound modulated wave signal, a digital sound modulated wave signal, and a digital character/image modulated wave signal and generates an intermediate frequency signal. Concretely, the receiving device  401  has a radio wave receiving device  411 , an amplifying device  412 , an intermediate frequency signal generating device  413 , a gain control device  414 , and a gain detecting device  415 . The radio wave receiving device  411  receives the radio wave including the analog modulated wave signal, digital modulated wave signal, and digital character/image modulated wave signal. The amplifying device  412  amplifies a radio frequency signal obtained by receiving a radio wave by the radio wave receiving device  411 .  
      The intermediate frequency signal generating device  413  generates an intermediate frequency signal from the radio frequency signal amplified by the amplifying device  412 . The gain control device  414  controls the gain of the radio frequency signal amplified by the amplifying device  412  on the basis of an output received from the radio wave receiving device  411 , amplifying device  412 , or intermediate frequency signal generating device  413 . The gain detecting device  415  detects whether or not the gain of the radio frequency signal is a predetermined gain or higher by the gain control device  414 . When it is detected that the gain of the radio frequency signal is equal to or higher than the predetermined gain, the receiving device  401  excessively receives the radio frequency signal. On the other hand, when it is detected that the gain of the radio frequency signal is less than the predetermined gain, the receiving device  401  stably receives the radio frequency signal.  
      The intermediate frequency signal separating device  402  separates the analog modulated wave signal and the digital modulated wave signal (refer to  FIG. 1 ) included in the intermediate frequency signal output from the intermediate frequency signal generating device  413 , outputs the analog modulated wave signal to the analog demodulating device  403 , and outputs the digital modulated wave signal to the digital demodulated device  404 . The analog demodulating device  403  demodulates the analog sound modulated wave signal separated by the intermediate frequency signal separating device  402 . The digital demodulating device  404  demodulates the digital sound modulated wave signal and the digital character/image modulated wave signal separated by the intermediate frequency signal separating device  402 .  
      The determining device  405  determines whether the level of the received radio wave is equal to or higher than the predetermined level or not on the basis of the radio frequency signal obtained by receiving the radio wave by the receiving device  401 . As an example of the determining process of the determining device  405 , an intermediate frequency signal generated by the intermediate frequency signal generating device  413  in the receiving device  401  is used and whether the signal level of the intermediate frequency signal is equal to the predetermined signal level or not can be determined. When it is determined that the signal level of the intermediate frequency signal is equal to or higher than the predetermined signal level, it can be determined that a desired wave is received.  
      As an example of the determining process of the determining device  405 , a gain level detected by the gain detecting device  415  is used and whether the gain level is equal to or higher than the predetermined level can be determined. When it is determined that the gain level is equal to or higher than the predetermined level, it can be determined that the reception level is too high, that is, the input radio frequency signal is excessive. Therefore, by using the signal level of the intermediate frequency signal and the gain level of the gain detecting device  415 , whether the sensitivity of the received radio wave is good or not can be determined.  
      Further, as an example of the determining process of the determining device  405 , the BER (Bit Error Rate) in demodulation by the digital demodulating device  404  is used and whether the BER is equal to or higher than the predetermined rate can be also determined. In such a manner, whether the quality of digital sound output by decoding of the digital demodulating device  404  is good or not can be determined.  
      The selecting device  406  selects either the analog demodulating device  403  or the digital demodulating device  404  on the basis of a result of determination made by the determining device  405 . By the operation, a decoder for generating a sound decoded signal to be output can be determined. The output device  407  has a sound output device  421  and a display device  422 . The sound output device  421  outputs sound on the basis of the sound demodulated signal obtained from the demodulating device ( 403  or  404 ) selected by the selecting device  406 . The display device  422  displays characters or an image on the screen by the character/image demodulated signal obtained by demodulating the digital character/image modulated wave signal by the digital demodulating device  404 .  
      As described above, in the receiving apparatus  300  according to the embodiment, the reception level of a received radio wave is determined by using the signal level of the intermediate frequency signal or the gain level detected by the gain detecting device  415 , and whether the reception sensitivity is good or not can be determined. Therefore, in the case where the signal level of the intermediate frequency signal is equal to or higher than the predetermined signal level or in the case where the gain level is equal to or higher than the predetermined level, the selecting device  406  selects the digital demodulating device  404 . Thus, sound can be output by using the digital sound demodulated signal obtained by demodulation of the digital demodulating device  404  and the user can listen to digital sound of high sensitivity.  
      On the other hand, in the case where the signal level of the intermediate frequency signal is less than the predetermined signal level and in the case where the gain level is less than the predetermined level, the selecting device  406  selects the analog demodulating device  403 . Therefore, in the case where digital sound cannot be output with high sensitivity, sound is output by using the analog sound demodulated signal obtained by demodulation of the analog demodulating device  403 . Consequently, when the analog sound is output, the radio frequency signal is not excessively received always. It is therefore unnecessary to attenuate the radio frequency signal by using an attenuator, so that the attenuator is unnecessary. Thus, the number of parts can be decreased and the size and weight of the receiving apparatus  300  can be reduced. Further, by using the BER, the output sound can be switched depending on the quality of the output sound and the user can listen to digital sound of high sensitivity and high quality.  
     EXAMPLE 1  
      A first example of the receiving apparatus  300  according to the embodiment will be described.  FIG. 5  is a block diagram showing the hardware configuration of the first example of the receiving apparatus  300  according to the embodiment. As shown in  FIG. 5 , the receiving apparatus  300  of the first example has: an antenna  501  for receiving a radio wave including an analog sound modulated wave signal, a digital sound modulated wave signal, and a digital character/image modulated wave signal; and a first band pass filter  502  for regulating the band of the radio frequency signal obtained from the antenna  501 . The antenna  501  and the first band pass filter  502  construct the radio wave receiving device  411  shown in  FIG. 4 .  
      An amplifier  503  amplifies the radio frequency signal output from the first band pass filter  502 . The amplifier  503  is a component of the amplifying device  412  shown in  FIG. 4 . A second band pass filter  504  regulates a band of the radio frequency signal amplified by the amplifier  503  and outputs the resultant to a mixer  506 . A voltage controlled oscillator (VCO)  505  outputs an oscillation signal of a predetermined frequency to the mixer  506 . The mixer  506  mixes the radio frequency signal output from the second band pass filter  504  with the oscillation signal output from the voltage controlled oscillator  505 , thereby generating an intermediate frequency signal. A third band pass filter  507  regulates the intermediate frequency signal output from the mixer  506  to a frequency band of a desired wave. The second band pass filter  504 , voltage controlled oscillator  505 , mixer  506 , and third band pass filter  507  construct the intermediate frequency signal generating device  413  shown in  FIG. 4 .  
      An AGC (Auto Gain Control) circuit  508  controls the gain of the amplifier  503  on the basis of the field intensity obtained from the mixer  506 , first band pass filter  502 , or second band pass filter  504 . The AGC circuit  508  is a component of the gain control device  414  shown in  FIG. 4 . The AGC circuit  508  includes an AGC detecting circuit  509 . In the AGC detecting circuit  509 , a threshold voltage for detecting whether the field intensity obtained from the mixer  506 , first band pass filter  502 , or second band pass filter  504  is equal to or higher than a predetermined level or not is set. The field intensity equal to or higher than the threshold voltage is detected as an AGC voltage. In such a manner, excessive input of the radio frequency signal caused by interference of an interfering wave to a received wave can be detected. The AGC detecting circuit  509  is a component of the gain detecting device  415  shown in  FIG. 4 .  
      An A/D converter  510  converts an intermediate frequency signal output from the third band pass filter  507  to a digital signal. A digital filter  511  frequency decomposes the digitally converted intermediate frequency signal, outputs the analog modulated wave signal to an analog sound decoder  512 , and outputs the digital modulated wave signal to a digital sound decoder  513  and a character/image decoder  514 . Therefore, intermediate frequency signal is separated. The A/D converter  510  and the digital filter  511  construct the intermediate frequency signal separating device  402  shown in  FIG. 4 .  
      The analog sound decoder  512  receives the analog modulated wave signal separated by the digital filter  511  and demodulates the analog modulated wave signal into an analog sound demodulated signal. The analog sound decoder  512  is a component of the analog demodulating device  403  shown in  FIG. 4 .  
      The digital sound decoder  513  receives the digital sound modulated wave signal included in the digital modulated wave signal separated by the digital filter  511  and demodulates the digital sound modulated wave signal to a digital sound demodulated signal. The character/image decoder  514  receives the digital character/image modulated wave signal included in the digital modulated wave signal separated by the digital filter  511  and demodulates the input digital character/image modulated wave signal to a character/image demodulated signal. The digital sound decoder  513  and the character/image decoder  514  construct the digital demodulating device  404  shown in  FIG. 4 .  
      A determining circuit  515  is constructed by first to third comparators  516  to  518  and a D/A converter  519 . In the first comparator  516 , a predetermined threshold voltage is preset. The first comparator  516  compares the threshold voltage with the signal level of the intermediate frequency signal output from the third band pass filter  507 . The threshold voltage is a value corresponding to reception sensitivity of the intermediate frequency signal, at which digital sound can be properly output.  
      When it is determined that the signal level of the intermediate frequency signal is less than the threshold voltage, the reception sensitivity of the intermediate frequency signal is less than the predetermined sensitivity, and the first comparator  516  outputs a low-level signal to a selecting circuit  520 . On the other hand, when it is determined that the signal level of the intermediate frequency signal is equal to or higher than the threshold voltage, the intermediate frequency signal is equal to or higher than predetermined sensitivity, and the first comparator  516  outputs a high-level signal to the selecting circuit  520 .  
      The second comparator  517  determines whether an AGC voltage is detected by the AGC detecting circuit  509  or not. Concretely, when the AGC voltage is supplied from the AGC detecting circuit  509 , the second comparator  517  outputs a high-level signal to the selecting circuit  520 . When the AGC voltage is not supplied from the AGC detecting circuit  509 , the second comparator  517  outputs a low-level signal to the selecting circuit  520 .  
      The D/A converter  519  converts the BER (Bit Error Rate) detected at the time of the decoding process of the digital sound decoder  513  into an analog signal and inputs the analog signal to the third comparator  518 . In the third comparator  518 , a threshold value for determining whether the BER detected by the digital sound decoder  513  is a permissible level value or not is set.  
      When it is determined that the BER detected by the digital sound decoder  513  is the threshold voltage or higher than the voltage, the BER is equal to or higher than the permissible level, that is, the sound quality of the digital sound is lower than the sound quality of the permissible level, and the third comparator  518  outputs a low-level signal to the selecting circuit  520 . On the other hand, when the BER is determined to be less than the threshold voltage, the BER is less than the permissible level, that is, the sound quality of the digital sound is higher than the sound quality of the permissible level, and the third comparator  518  outputs a high-level signal to the selecting circuit  520 . The determining circuit  515  is a component of the determining device  405  shown in  FIG. 4 .  
      The selecting circuit  520  selects either the digital sound decoder  513  for demodulating the digital sound modulated wave signal or the analog sound decoder  512  for demodulating the analog modulated wave signal on the basis of output signals (high-level signal and low-level signal) output from the first to third comparators  516  to  518  of the determining circuit  515 . Concretely, when the high-level signal is input from any of the first to third comparators  516  to  518 , the selecting circuit  520  connects the digital sound decoder  513  and a D/A converter  521 . On the other hand, when low level signals are received from all of the first to third comparators  516  to  518 , the selecting circuit  520  connects the analog sound decoder  512  and the D/A converter  521 . The selecting circuit  520  is a component of the selecting device  406  shown in  FIG. 4 .  
      The D/A converter  521  is connected to the analog sound decoder  512  or digital sound decoder  513  via the selecting circuit  520  and D/A converts the input analog sound demodulated signal or digital sound demodulated signal. A speaker  522  outputs the analog sound demodulated signal or digital sound demodulated signal output from the D/A converter  521  as sound. The D/A converter  521  and speaker  522  construct the sound outputting device  421  shown in  FIG. 4 .  
      An output I/F (interface)  523  is connected to the character/image decoder  514 . The output I/F  523  is constructed by, concretely, for example, a graphic controller for controlling a whole display  524 , a buffer memory such as a VRAM (Video RAM) for temporarily storing image information which can be immediately displayed, and a control IC for controlling the display  524  on the basis of image data output from the graphic controller. The display  524  is connected to the output I/F  523  and displays character/image data. The display  524  is constructed by, concretely, for example, a liquid crystal display  301  shown in  FIG. 3 , an LED or the like. The output I/F  523  and the display  524  construct the display device  422  shown in  FIG. 4 .  
      The procedure in the receiving apparatus  300  of the first example will now be described.  FIG. 6  is a flowchart showing the procedure of the receiving apparatus  300  of the first example. First, the receiving apparatus  300  receives a radio wave including the analog modulated wave signal, digital modulated wave signal, and digital character/image modulated wave signal (step S 601 ). An intermediate frequency signal is generated by the mixer  506  (step S 602 ) and the AGC voltage is detected by the AGC detecting circuit  509  (step S 603 ).  
      After that, demodulation is performed by the analog sound decoder  512  and digital sound decoder  513  (step S 604 ). In the case where the output of the first comparator  516  is at the low level (L in step S 605 ), the determining process by the second comparator  517  is performed (step S 606 ). When the output of the second comparator  517  is at the low level (L in step S 606 ), the determining process by the third comparator  518  is performed (step S 607 ) When the output of the third comparator  518  is at the low level (L in step S 607 ), the analog sound decoder  512  is selected by the selecting circuit  520  (step S 608 ).  
      On the other hand, when the outputs of the first to third comparators  516  to  518  are at the high level (H in step S 605 , H in step S 606 , and H in step S 607 ), the digital sound decoder  513  is selected by the selecting circuit  520  (step S 609 ). Sound is output by the sound demodulated signal obtained from the selected sound decoder (step S 610 ).  
      In the first example, reception sensitivity of the modulated wave can be determined by the first comparator  516 . By the second comparator  517 , whether or not the radio frequency signal is excessively input because the interference wave is included in the analog modulated wave can be determined. Further, the quality of digital sound data can be determined by the third comparator  518 . Therefore, in the first example, the digital sound data can be output at high sensitivity and high quality with the simple configuration.  
      In the case where the radio frequency signal is excessively input, the digital sound decoder  513  is selected. In other words, when the analog sound decoder  512  is selected, the radio frequency signal is not excessively input. Consequently, without separately providing the receiving device  401  with an attenuator, analog sound can be properly output. Thus, as compared with the normal receiving apparatus  300  for receiving the radio wave including the analog modulated wave signal and the digital modulated wave signal, the number of parts can be decreased and the size and weight of the receiving apparatus  300  can be reduced. As the number of parts is reduced, the inexpensive receiving apparatus  300  can be provided.  
     EXAMPLE 2  
      A second example of the receiving apparatus  300  according to the embodiment will now be described.  FIG. 7  is a block diagram showing the hardware configuration of the second example of the receiving apparatus  300  of the embodiment. The receiving apparatus  300  of the second example executes or stops the demodulating process of the analog sound decoder  512 . The same reference numerals are designated to components which are the same as those of the first example and their description will not be repeated.  
      At the preceding stage of the analog sound decoder  512  in the receiving apparatus  300  of the second example, an internal switch  701  is provided. The internal switch  701  is switched to ON or OFF in accordance with an output of a determining circuit  702  and executes or stops the demodulating process of the analog sound decoder  512 . When the internal switch  701  is ON, the analog sound decoder  512  receives the analog sound modulated wave signal separated by the digital filter  511  and demodulates it to an analog sound demodulated signal. The internal switch  701  is connected to first to third comparators  703  to  705  provided in the determining circuit  702 . The analog sound decoder  512  and the internal switch  701  construct the analog demodulating device  403  shown in  FIG. 4 .  
      The determining circuit  702  is constructed by the first to third comparators  703  to  705  and a D/A converter  706 . In the first comparator  703 , a predetermined threshold voltage is preset. The first comparator  703  compares the threshold voltage with the signal level of an intermediate frequency signal output from the third band pass filter  507 . The threshold voltage is a value corresponding to reception sensitivity at which digital sound can be properly output.  
      In the case where the signal level of the intermediate frequency signal is determined to be less than the threshold voltage, the reception sensitivity of the intermediate frequency signal is less than the predetermined sensitivity, and the first comparator  703  outputs a low-level signal to the selecting circuit  520 . On the other hand, when the signal level of the intermediate frequency signal is determined to be equal to or higher than the threshold voltage, the intermediate frequency signal is equal to or higher than predetermined sensitivity, and the first comparator  703  outputs a high-level signal to the selecting circuit  520 .  
      The second comparator  704  determines whether the AGC voltage is detected by the AGC detecting circuit  509  or not. Concretely, when the AGC voltage is supplied from the AGC detecting circuit  509 , the second comparator  704  outputs a high-level signal to the selecting circuit  520 . When the AGC voltage is not supplied from the AGC detecting circuit  509 , the second comparator  704  outputs a low-level signal to the selecting circuit  520 .  
      The D/A converter  706  converts the BER (Bit Error Rate) detected at the time of the decoding process of the digital sound decoder  513  into an analog signal and inputs the analog signal to the third comparator  705 . In the third comparator  705 , the threshold value for determining whether the BER detected from the digital sound decoder  513  is a value of the permissible level or not is set.  
      In the case where the BER detected from the digital sound decoder  513  is determined to be equal to or higher than the threshold voltage, the BER is equal to or higher than the permissible level, that is, the quality of the digital sound is lower than that of the permissible level, and the third comparator  705  outputs a low-level signal to the selecting circuit  520 . On the other hand, when it is determined that the BER is lower than the threshold voltage, the BER is lower than the permissible level, that is, the quality of the digital sound is higher than that of the permissible level. The third comparator  705  outputs a high-level signal to the selecting circuit  520 . The determining circuit  702  is a component of the determining device  405  shown in  FIG. 4 .  
      The procedure in the receiving apparatus  300  of the second example will now be described.  FIG. 8  is a flowchart showing the procedure of the receiving apparatus  300  of the second example. First, the receiving apparatus  300  receives a radio wave including the analog modulated wave signal, digital modulated wave signal, and digital character/image modulated wave signal (step S 801 ). An intermediate frequency signal is generated from the mixer  506  (step S 802 ) and the AGC voltage is detected by the AGC detecting circuit  509  (step S 803 ).  
      After that, demodulation is performed by the digital sound decoder  513  (step S 804 ). In the case where the output of the first comparator  703  is at the low level (L in step S 805 ), the determining process by the second comparator  704  is performed (step S 806 ). When the output of the second comparator  704  is at the low level (L in step S 806 ), the determining process by the third comparator  705  is performed (step S 807 ). When the output of the third comparator  705  is at the low level (L in step S 807 ), the analog sound decoder  512  is selected by the selecting circuit  520  (step S 808 ).  
      After that, the ON/OFF state of the internal switch  701  is determined (step S 809 ). In the case where the internal switch  701  is OFF (“Yes” in step S 809 ), the internal switch  701  is switched to the ON state (step S 810 ) When it is determined as “No” in step S 810  or S 809  and the internal switch  701  is turned ON, demodulation is performed by the analog sound decoder  512  (step S 811 ).  
      On the other hand, when the outputs of the first to third comparators  703  to  705  are at the high level (H in step S 805 , H in step S 806 , and H in step S 807 ) , the digital sound decoder  513  is selected by the selecting circuit  520  (step S 812 ). After that, the ON/OFF State of the internal switch  701  is determined (step S 813 ). In the case where the internal switch  701  is ON (“Yes” in step S 813 ), the internal switch  701  is switched to the OFF state (step S 814 ). When it is determined as “No” in step S 814  or S 813  and the internal switch  701  is turned OFF, sound is output by the demodulated signal obtained from the selected sound decoder (step S 815 ).  
      In the second example, in a manner similar to the first example, digital sound data can be output with high sensitivity and high quality with the simple configuration. Without separately providing the receiving device  401  with an attenuator, analog sound can be properly output. Thus, in a manner similar to the first example, the number of parts can be decreased and the size and weight of the receiving apparatus  300  can be reduced. By reducing the number of parts, the inexpensive receiving apparatus  300  can be provided.  
      Further, the internal switch  701  is provided at the preceding stage of the analog sound decoder  512  and the ON/OFF state of the internal switch  701  is controlled in accordance with the result of determination of the determining circuit  702 . Consequently, in the case of demodulating the digital sound modulated wave signal, the demodulating process of the analog sound decoder  512  can be stopped and the power can be saved. Thus, for example, in a portable receiving apparatus, drive time by a battery can be increased.  
      In the case where sound information included in the analog modulated wave signal and that included in the digital modulated wave signal are the same in the first and second examples, sound can be output by a demodulated signal of high sensitivity in accordance with the radio wave conditions. Even if the radio wave conditions change, the user can listen to sound of high quality with little influence of noise and the like. Further, in the case where the digital sound modulated wave signal and the character/image modulated wave signal are included in the digital modulated wave signal, irrespective of the results of determination of the determining circuits  515  and  702 , the character/image modulated wave signal is always demodulated and the demodulated signal can be displayed on the display  524 . Therefore, even in the case where the radio wave conditions change and the analog sound decoder  512  is consequently selected, while outputting analog sound by the analog sound demodulated signal, characters/image suitable for the analog sound can be displayed on the display  524 .  
      As described above, in the receiving apparatus  300  according to the embodiment, sound can be output with high sensitivity and high definition by the simple configuration. Since an attenuator is unnecessary, because of decrease in the number of parts, the size and weight can be reduced. Thus, the inexpensive receiving apparatus  300  can be provided. For example, the receiving apparatus  300  according to the embodiment is useful for an HD (High Definition) radio receiver capable of demodulating both digital and analog signals and can be applied to, in particular, a portable radio receiver and an on-vehicle audio set.  
      The invention may be embodied in other specific forms without departing from the spirit thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.  
      The entire disclosure of Japanese Patent Application No. 2003-435496 filed on Dec. 26, 2003 including the specification, claims, drawings and abstract is incorporated herein by reference in its entirety.