Abstract:
An FM receiver which can be used by being switched between stereophonic and monophonic, and comprises detecting unit for detecting a received signal, two routes over which a detected signal is transmitted to an output buffer, and a switching unit for selecting either one of the two routes. The two routes consist of a route passing through a stereophonic demodulator unit and a route bypassing the stereophonic demodulator unit; and the switching unit selects either one of the two routes based on a control signal indicating the selection of either one of stereophonic and monophonic, and, when the route bypassing the stereophonic demodulator unit is selected, turns off power supply to the stereophonic demodulator unit based on the above control signal.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an FM receiver in which electric power consumption can be reduced. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventionally, in an FM receiver as shown in  FIG. 1 , FM radio waves are received by an antenna unit (not shown), prescribed detection processes are conducted in an FM detector unit  51 , and stereophonic demodulation processes are conducted in a stereophonic demodulator unit  52  comprising a stereophonic demodulator circuit, a 38 kHz stereophonic generator circuit and a pilot signal detector circuit. Then, a signal which has been subject to the stereophonic demodulation is output as audio information via an output buffer  53 . 
         [0003]    The FM receiver as above is used by being switched between stereophonic and monophonic. However, even when monophonic output is produced, signals are transmitted through the stereophonic demodulator unit, accordingly, electric power is consumed by the stereophonic demodulator unit in vain. 
         [0004]    As for a method of efficiently reducing electric power consumption, a receiver is disclosed in the Patent Document 1 below, for example, in which receiving operations are continued for a prescribed time period from a reception start time to a reception end time when a reception start time of signals is known in advance. 
         [0005]    In this receiver, a power source is turned on around the above reception start time, signals are generated which only activate necessary units in accordance with respective stages of reception operations until the reception is completed, and electric power can be supplied to units which need electric power in respective stages based on the above signals, so that electric power consumption is reduced. 
         [0006]    Patent Document 1: Japanese Patent Application Publication No. 10-70500 “Receiver” 
         [0007]    However, the technique in the above Patent Document 1 can only be applied when information such as a reception start time, a reception end time or the like is known in advance, and it is impossible to reduce electric power consumption by directly applying this technique to an FM receiver in which switching can be conducted between stereophonic and monophonic. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an object of the present invention to provide an FM receiver which can be used by being switched between stereophonic and monophonic, in which electric power consumption can be reduced. 
         [0009]    An FM receiver according to an aspect of the present invention is an FM receiver which can be used by being switched between stereophonic and monophonic, comprising detecting unit for detecting a received signal, switching unit for selecting either one of a route via a stereophonic demodulator unit and a route bypassing the stereophonic demodulator unit upon transmitting the detected signal to an output buffer, based on a control signal indicating the selection of either one of the stereophonic and the monophonic, in which electric power supply to the stereophonic demodulator unit is turned off based on the control signal when the route bypassing the stereophonic demodulator unit is selected. 
         [0010]    Based on the above, when the monophonic mode is selected, the route bypassing the stereophonic demodulator unit is selected, and also, electric power supply to the stereophonic demodulator unit which is not used is turned off, accordingly, electric power consumption is reduced. 
         [0011]    The above switching between the stereophonic and monophonic can be conducted in accordance with an external switching instruction provided by a user. 
         [0012]    Also, the above comparison between stereophonic and monophonic can be conducted by further comprising comparison unit for comparing a strength of the received signal with a reference value, and the switching unit can select the route via the stereophonic demodulator unit when the received signal is higher than the reference value, and/or select the route bypassing the stereophonic demodulator unit when the received signal is equal to or lower than the reference value, based on an output signal of the comparison unit. 
         [0013]    In both of the above cases, the stereophonic demodulator unit turns off electric power supply to the stereophonic demodulator unit when the route via the stereophonic demodulator unit is selected, based on the switching instruction provided by the user or the output signal of the comparison unit. 
         [0014]    Also, when the switches are arranged after a branch of the route via the stereophonic demodulator unit and the route bypassing the stereophonic demodulator unit and close to the branch, and also, are arranged before a joining point of the route via the stereophonic demodulator unit and the route bypassing the stereophonic demodulator unit and close to the joining point, the number of circuit portions (sections) over which unnecessary propagation of signals occurs can be reduced so that factors deteriorating the stability of operation of the circuit can be reduced. 
         [0015]    According to the FM receiver of the present invention, when a monophonic mode is selected, the route bypassing the stereophonic demodulator unit is selected and also, electric power supply to the stereophonic demodulator unit which is not used is turned off so that electric power consumption is reduced. 
         [0016]    Also, when the switches are arranged after a branch into the route via the stereophonic demodulator unit and the route bypassing the stereophonic demodulator unit and close to the branch, and also, are arranged before a joining point of the route via the stereophonic demodulator unit and the route bypassing the stereophonic demodulator unit and close to the joining point, the number of circuit portions (sections) over which unnecessary propagation of signals occurs can be reduced so that factors deteriorating the stability of operation of the circuit can be reduced. 
         [0017]    Also, in the FM receiver according to the present invention, because the stereophonic demodulator unit is bypassed by selecting routes between the case of outputting monophonic audio and the case of outputting stereophonic audio, accordingly, deterioration in signals when the monophonic output is desired is reduced so that audio quality can be improved, compared to the case where the monophonic audio and the stereophonic audio are output via the same route, i.e., the case of a conventional example without the route selection. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIG. 1  is a block diagram for showing an example of a configuration of a conventional FM receiver; 
           [0019]      FIG. 2  is a block diagram for showing a configuration of an FM receiver according to the present embodiment; 
           [0020]      FIG. 3  is a block diagram for showing an alternative of the FM receiver according to the present embodiment; 
           [0021]      FIG. 4A  shows a specific circuit configuration of one of switches  13   b  and  17   b  in  FIG. 3 ; 
           [0022]      FIG. 4B  shows a specific circuit configuration of one of switches  13   a  and  17   a  in  FIG. 3 ; 
           [0023]      FIG. 5  is a first diagram for showing a circuit configuration of a principal unit related to electric power supply to a stereophonic demodulator unit; 
           [0024]      FIG. 6  is a second diagram for showing a circuit configuration of a principal unit related to electric power supply to the stereophonic demodulator unit; 
           [0025]      FIG. 7  is a block diagram for showing a second alternative of the FM receiver according to the present embodiment; 
           [0026]      FIG. 8A  is a diagram for explaining positions at which switches are arranged, and shows the case where the switches are arranged only at a point close to a branch on the route via the stereophonic demodulator unit and at a point close to the branch on the route bypassing the stereophonic demodulator unit; and 
           [0027]      FIG. 8B  is a diagram for explaining positions at which switches are arranged, and shows the case where the switches are arranged at points respectively close to both of the branch and the joining point on the route via the stereophonic demodulator unit and the route bypassing the stereophonic demodulator unit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Hereinafter, embodiments of the present invention will be explained in detail by referring to the drawings. 
         [0029]      FIG. 2  is a block diagram for showing a configuration of an FM receiver according to the present embodiment. Additionally, at least some of the components in  FIG. 2 , for example switches  13  and  17 , a stereophonic demodulator unit  15 , a route  1  and a route  2 , are mounted on a semiconductor integrated circuit substrate which is produced by a CMOS process that can form a P-channel MOS transistor and an N-channel MOS transistor. 
         [0030]    In  FIG. 2 , the FM receiver according to the present embodiment comprises an FM detector unit  11 , the switches  13  and  17 , the stereophonic demodulator unit  15  and an output buffer  19 . 
         [0031]    Hereinafter, operations of the FM receiver will be explained. 
         [0032]    First, FM radio waves are received by an antenna (not shown), and a detection process is conducted by an FM detector unit  11 . A switch  13  provided at a later stage of the FM detector unit  11  selectively switches between a route  1  and a route  2  in the figure based on an instruction of a user of the FM receiver such as pressing of buttons on a surface of the receiver. The above route  2  is a route via the stereophonic demodulator unit  15 , and the route  1  is a route which bypasses the stereophonic demodulator unit  15 . 
         [0033]    Audio which is to be output via the output buffer  19  based on the above instruction by the user is switched from stereophonic output to monophonic output, or conversely, from monophonic output to stereophonic output. This instruction of the user is input to the switch  13 , the stereophonic demodulator unit  15  and the switch  17  as a power enable signal specifying whether the stereophonic output is conducted or the monophonic output is conducted. 
         [0034]    When a user does not need the stereophonic output such as in a case where it is desired that the receiver is used for a long time based on electric power supplied by a battery, or reception conditions are bad, the user provides an instruction to switch to a monophonic mode, and a route of a detected signal is switched from a route  2  via the stereophonic demodulator unit  15  to a route  1  bypassing the stereophonic demodulator unit  15  in accordance with a power enable signal specifying contents of the instruction. When the route bypassing the stereophonic demodulator unit  15  is selected, electric power supply to the stereophonic modulator unit  15  is turned off in accordance with the above power enable signal so that reduced electric power consumption is realized. 
         [0035]    Additionally, when the user provides an instruction to switch to a stereophonic mode, the route of the detected signal is switched from the route  1  bypassing the stereophonic demodulator unit  15  to the route  2  via the stereophonic demodulator unit  15  in accordance with a power enable signal specifying contents of the instruction. When the route via the stereophonic demodulator unit  15  is selected, electric power supply to the stereophonic modulator unit  15  is turned on in accordance with the above power enable signal. 
         [0036]      FIG. 3  is a block diagram for showing an alternative of the FM receiver according to the present embodiment. 
         [0037]    In this alternative embodiment, the switching which has been conducted based on the instruction provided by the user in the first embodiment is automatically conducted based on the strength of a received signal. 
         [0038]    In  FIG. 3 , in the FM receiver, information specifying reception strength of the received signal such as, for example, an RSSI voltage, is output by a limiter  21 , and the output information is input to one input of a 2-input comparator  22 . To the other input of the comparator  22 , a reference value (reference voltage) is input, and the above RSSI voltage and the reference voltage are compared by the comparator  22 . A comparison result signal SW specifying the comparison result is output by the comparator  22 , and the comparison result signal SW and an inverted signal thereof are input to switches  13   a ,  13   b ,  17   a ,  17   b  and the stereophonic demodulator unit  15  via an inverter  23  provided at a later stage to the comparator  22 . Additionally, in the present alternative embodiment, when the above value specifying the reception strength is lower than the reference value, switching is conducted to a monophonic mode. 
         [0039]      FIG. 4A  and  FIG. 4B  are circuit diagrams for showing specific configurations of the switches.  FIG. 4A  shows the following switches  13   b  and  17   b  and  FIG. 4B  shows the following switches  13   a  and  17   a  respectively. 
         [0040]      FIG. 4A  specifically shows circuit configurations of the switches  13   b  and  17   b . The above switches each comprise two control terminals for inputting the comparison result signal SW and the inverted signal thereof. And, switching of whether or not a signal of an input (in) side is allowed to pass to an output (out) side is conducted in accordance with values input to the control terminals. Because the switches  13   b  and  17   b  are provided on a route via the stereophonic demodulator circuit, the configuration in the figure assumes the case in which the comparison result signal SW of the comparator  22  is set to “H” and accordingly, the inverted signal thereof is set to “L” when the reception strength is higher than the reference value. With the comparison result signal SW and the inverted signal thereof as above, the switches  13   b  and  17   b  in  FIG. 3  are turned on (become continuous) and the switches  13   a  and  17   a  are turned off (become discontinuous), and the signal passes on the route via the stereophonic demodulator unit  15 . 
         [0041]      FIG. 4B  specifically shows circuit configurations of the switches  13   a  and  17   a . The above switches each comprise two control terminals for inputting the comparison result signal SW and the inverted signal thereof. And, switching of whether or not a signal on an input (in) side is allowed to pass to an output (out) side is conducted in accordance with values input to the control terminals. Because the switches  13   a  and  17   a  are provided on a route bypassing the stereophonic demodulator circuit, the configuration in the figure assumes the case in which the comparison result signal SW of the comparator  22  is set to “L” and accordingly, the inverted signal thereof is set to “H” when the reception strength is equal to or lower than the reference value. With the comparison result signal SW and the inverted signal thereof as above, the switches  13   a  and  17   a  in  FIG. 3  are turned on (become continuous) and the switches  13   b  and  17   b  are turned off (become discontinuous), and the signal passes on the route bypassing the stereophonic demodulator unit  15 . 
         [0042]    Additionally, as the switches  13  and  17 , semiconductor switching elements such as MOS transistors or the like, as shown in  FIG. 4A  or  4 B can be employed, however, other types of switches such as mechanical switches for example can also be employed. 
         [0043]      FIG. 5  is a first diagram for showing a circuit configuration of a principal unit related to electric power supply to the stereophonic demodulator unit. 
         [0044]    In  FIG. 5 , the principal unit related to the electric power supply to the stereophonic demodulator unit comprises, together with a main power supply  31 , a first transistor group consisting of transistors  32 ,  33  and  34 , and a second transistor group consisting of transistors  36 ,  37  and  38 . As shown, the transistors  32 ,  33  and  34  are P-channel transistors, and are provided on a first direct current electrical potential side (VDD side). The transistors  36 ,  37  and  38  are N-channel transistors, and are provided on a second direct current electrical potential side (ground side). Additionally, the comparison result signal SW and the inverted signal of the comparison result signal SW are applied respectively to a gate of the transistor  32  and a gate of the transistor  36 . 
         [0045]    Hereinafter, a control upon turning off electric power supply in the principal unit in the above configuration will be explained. 
         [0046]    In  FIG. 5 , when the inverted signal of “H” of the comparison result signal SW is applied to the gate of the transistor  36  provided on the second direct current electrical potential side (ground side) in the case when the above comparison result signal SW is “L”, the transistor  36  is turned ON (continuous) because the transistor  36  is an N-channel transistor, and referring to the above second direct current electrical potential, “L” is applied to the gate of the transistor  37 , which is the other of the transistors forming a differential pair with the above transistor  36  and which is provided on the same second direct current electrical potential side and/or to the gate of the transistor  38  provided on the same second direct current electrical potential side. As a result, the transistor  37  and the transistor  38  are turned off (discontinuous). 
         [0047]    Also, when a comparison result signal SW “L” is applied to a gate of the transistor  32  provided on the first direct current electrical potential side (VDD side), the transistor  32  is turned ON because the transistor  32  is a P-channel transistor, and referring to the above first direct current electrical potential, “H” is applied to the gate of the transistor  33 , which is the other of the transistors forming a differential pair with the above transistor  32  and which is provided on the same first direct current electrical potential side and/or to a gate of the transistor  34  provided on the same first direct current electrical potential side. As a result, the transistor  33  and the transistor  34  are turned off (discontinuous). In the figure, the transistor  34  constitutes a first stage of a multistage transistor circuit for example, and by turning off this transistor  34 , electric current is prevented from flowing through subsequent circuit portions so that electric power consumption can be reduced. 
         [0048]    Additionally, in the stereophonic demodulator unit in  FIG. 5 , the switching regarding on and off of the electric power supply to the stereophonic demodulator unit is conducted by inputting both the comparison result signal SW and the inverted signal thereof. However, it is also possible to conduct switching regarding on and off of the electric power supply based on either one of the above signals. A configuration example of such a stereophonic demodulator unit is shown in  FIG. 6 . 
         [0049]    In  FIG. 6 , when the inverted signal “H” of the comparison result signal SW is applied to a gate of the transistor  46  provided on the second direct current electrical potential side (ground side) in the case when the comparison result signal SW is “L”, the transistor  46  is turned ON (continuous) because the transistor  46  is an N-channel transistor, and referring to the above second direct current electrical potential, “L” is applied to the gate of the transistor  47  which is the other of the transistors forming a differential pair with the above transistor  46  and which is provided on the same second direct current electrical potential side and/or to a gate of the transistor  48  provided on the same second direct current electrical potential side. As a result, the transistor  47  and the transistor  48  are turned off (discontinuous). In the figure, the transistor  48  constitutes a first stage of a multistage transistor circuit for example, and by turning off this transistor  48 , electric current is prevented from flowing through subsequent circuit portions so that electric power consumption can be reduced. 
         [0050]    The circuit configuration of the stereophonic demodulator units in  FIG. 5  and  FIG. 6  are examples. In these configurations, by providing signals to the upstream transistors constituting multiple stages (the transistors  32  and  36  in  FIG. 5 , the transistor  46  in  FIG. 6 ), causing these transistors to be continuous, the transistor which is the other of the transistors forming each differential pair with the transistor (the transistors  33  and  37  in  FIG. 5 , the transistor  47  in  FIG. 6 ) can be turned off. 
         [0051]    As above, in the present embodiment, when the route bypassing the stereophonic demodulator unit is selected, electric power supply to the stereophonic demodulator unit is turned off, accordingly, electric power consumption can be reduced. 
         [0052]    Additionally, as a configuration of the stereophonic demodulator unit, an arbitrary configuration that allows switching between ON and OFF of electric power supply by a control of the FM receiver according to the present invention can be employed besides those shown in  FIG. 5  and  FIG. 6 . 
         [0053]      FIG. 7  is a block diagram for showing a second alternative of the FM receiver according to the present embodiment. In this second alternative embodiment, the switch can respond to a MUTE instruction provided by a user. 
         [0054]    In  FIG. 7 , in the FM receiver, information specifying reception strength of the received signal such as, for example, an RSSI voltage, is output by the limiter  21 , and the output information is input to one input of the 2-input comparator  22 . To the other input of the comparator  22 , a reference value (reference voltage) is input, and the above RSSI voltage and the reference voltage are compared by the comparator  22 . The comparison result signal SW specifying the comparison result is output by the comparator  22 , and is input via one of inputs (terminals) of a 2-input and 4-output selector  24  provided at a later stage than the comparator  22 . To the other input (terminal) of the selector  24 , a signal (MUTE signal) specifying a MUTE instruction (an instruction not to output audio) provided by a user is input. 
         [0055]    The selector  24  receives the above two inputs, generates output signals as below and transfers them to the respective switches and stereophonic demodulator unit. 
         [0000]    1. A→L, B→L regardless of the value of the comparison result signal SW, when the MUTE signal is ON (MUTE instruction is provided)
 
2. A→H, B→L when the MUTE signal is OFF and the comparison result signal SW specifies monophonic
 
3. A→L, B→H when the MUTE signal is OFF and the comparison result signal SW specifies stereophonic
 
         [0056]    Hereinafter, respective cases will be explained. 
         [0057]    When the MUTE instruction is provided by a user, signals of A→L and B→L are output by the above selector  24 . As a result, to the control terminals of the switches  13   a  and  17   a  are input the signal A (L) and the inverted signal (H) of the signal A, and the switches  13   a  and  17   a  are turned off. Also, to the control terminals of the switches  13   b  and  17   b  are input the signal B (L) and the inverted signal (H) of the signal B, and the switches  13   b  and  17   b  are turned off. Also, to the stereophonic demodulator unit  15  is input the signal B (L), and the inverted signal (H) of the signal B, and thereby, electric power supply to the stereophonic demodulator unit  15  is cut. As above, when the MUTE instruction is provided, the switches  13   b  and  17   b  on the route via the stereo demodulator unit  15  and the switches  13   a  and  17   a  on the route bypassing the stereophonic demodulator unit  15  are turned off and also, electric power supply to the stereophonic demodulator unit  15  is turned off. 
         [0058]    When the MUTE instruction is not provided and an instruction to switch to a monophonic mode is provided (or automatic switching to a monophonic mode occurs), signals of A→H and B→L are output from the above selector  24 . As a result, to the control terminals of the switches  13   a  and  17   a  are input the signal A (H) and the inverted signal (L) of the signal A, and the switches  13   a  and  17   a  are turned on. Also, to the control terminals of the switches  13   b  and  17   b  are input the signal B (L) and the inverted signal (H) of the signal B, and the switches  13   b  and  17   b  are turned off. Also, to the stereophonic demodulator unit  15  is input the signal B (L), and the inverted signal (H) of the signal B, and thereby, electric power supply to the stereophonic demodulator unit is cut. As above, when the instruction to switch to a monophonic mode is provided (or automatic switching to a monophonic mode occurs), the switches  13   b  and  17   b  on the route via the stereophonic demodulator unit  15  are turned off, and the switches  13   a  and  17   a  on the route bypassing the stereophonic demodulator unit  15  are turned on, and also, electric power supply to the stereophonic demodulator unit  15  is turned off. 
         [0059]    When the MUTE instruction is not provided and an instruction to switch to a stereophonic mode is provided (or automatic switching to a stereophonic mode occurs), signals of A→L and B→H are output from the above selector  24 . As a result, to the control terminals of the switches  13   a  and  17   a  are input the signal A (L) and the inverted signal (H) of the signal A, and the switches  13   a  and  17   a  are turned off. Also, to the control terminals of the switches  13   b  and  17   b  are input the signal B (H) and the inverted signal (L) of the signal B, and the switches  13   b  and  17   b  are turned on. Also, to the stereophonic demodulator unit  15  is input the signal B (H), and the inverted signal (L) of the signal B, and thereby, electric power supply is turned on. As above, when the instruction to switch to a stereophonic mode is provided (or automatic switching to a stereophonic mode occurs), the switches  13   b  and  17   b  on the route via the stereophonic demodulator unit  15  are turned on, and the switches  13   a  and  17   a  on the route bypassing the stereophonic demodulator unit  15  are turned off, and also, electric power supply to the stereophonic demodulator unit  15  is turned on. 
         [0060]    Additionally, in  FIG. 7 , switching between stereophonic and monophonic is automatically conducted based on a determination of the comparator, however, it is needless to mention that even when the switching between stereophonic and monophonic is conducted based on an instruction of a user, the switch can be similarly constituted with an added MUTE function. 
         [0061]    Additionally, in the above explanation, the switches are arranged after a branch into a route via the stereophonic demodulator unit and a route bypassing the stereophonic demodulator unit and before a joining point of the above two routes, however, the switch may be arranged either after a branch or before a joining point. However, it is desirable that the switches are arranged at both a point which is after the branch and which is as close to the branch as possible, or a point which is before the joining point and which is as close to the joining point as possible. 
         [0062]      FIG. 8A  and  FIG. 8B  are diagrams for explaining positions at which the switches are arranged.  FIG. 8A  shows the case where the switches are arranged only at a point close to a branch on the route via the stereophonic demodulator unit and at a point close to the branch on the route bypassing the stereophonic demodulator unit.  FIG. 8B  shows the case where the switches are arranged at points close to both the branch and the joining point respectively on the above two routes. 
         [0063]    In  FIG. 8A , a detected signal S 1  is branched into a signal S 2  and a signal S 3  at a branching point P 1 . In the figure, the case where the route via the stereophonic demodulator unit is selected is assumed, therefore, the signal S 3  reaches a joining point P 2  via the switch  13   b  and the stereophonic demodulator unit  15 . At the joining point P 2 , the signal S 3  is branched into a signal S 4  transmitted to an output buffer provided at a later stage and into a signal S 5  propagating along the route for a monophonic signal in the backward direction. The above propagation of the signal S 5  in the backward direction along the route for the monophonic direction further causes propagation along the same route in the forward direction because the switch  13   a  in an off state functions as a barrier, which can be a factor in causing deterioration of the stability of operation of the circuit. Generally, a section over which the signal S 2  and signal S 5  in the figure propagate i.e., the section denoted by X and the section denoted by Y (section X+Y) are subject to the occurrence of propagation of unnecessary signals as above. Additionally, as is obvious from the above explanation, the length of the section X+Y over which the above unnecessary signal propagates basically does not change in the case where a switch is arranged at one point on each route. 
         [0064]    Meanwhile, when the switches  13   a ,  13   b ,  17   a  and  17   b  are respectively arranged after the branching point P 1  and before the joining point P 2 , the detected signal S 1  is branched into the signal S 2  and the signal S 3  at the branching point P 1 . The signal S 3  reaches the joining point P 2  via the switch  13   b , the stereophonic demodulator unit  15  and the switch  17   b . At the joining point P 2 , the signal S 3  is branched into the signal S 4  transmitted to the output buffer provided at a later stage, and into the signal S 5  which propagates along the route for the monophonic signal in the backward direction. The sum X+Y of sections over which unnecessary signals propagate in the circuit is greatly reduced compared to the configuration shown in  FIG. 8A , and the above factor deteriorating the stability of the operation of the circuit, is reduced in proportion to the amount the above sum is reduced. Additionally, in this regard, it is desirable that the positions after the branch at which the switches  13   a  and  13   b  are arranged are as close to the branch as possible, as long as necessary requirements regarding design are satisfied. Additionally, it is desirable that the positions before the joining point at which the switches  17   a  and  17   b  are arranged are as close to the joining point as possible, as long as necessary requirements regarding design are satisfied. 
         [0065]    Additionally, in the FM receiver according to the present embodiment, routes are selected between the case of outputting monophonic audio and the case of outputting stereophonic audio, accordingly, deterioration in signals when the monophonic output is desired is reduced so that audio quality can be improved compared to the case where the monophonic audio and the stereophonic audio are output via the same route, i.e., as in the case of the conventional example without the route selection. This is because the stereophonic demodulator unit is bypassed upon the monophonic output and thereby deterioration in signals that occurs when the signals are transmitted through the stereophonic demodulator unit is suppressed. 
       APPLICABILITY TO INDUSTRIES 
       [0066]    The present invention can be applied to an FM receiver in which switching between stereophonic and monophonic can be conducted.