JP2009200951A - Rds receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an RDS (radio data system) receiver for improving a PI acquisition rate even in a case where neighboring noise is present. <P>SOLUTION: The RDS receiver 100 includes: an antenna section 110 for receiving an FM broadcast signal; a front end section 120 for converting the FM broadcast signal into an intermediate frequency signal; a variable IF filter section 130, of which the filter bandwidth is variable, for band-limiting the intermediate frequency signal with a predetermined filter bandwidth and outputting a filter output signal; an FM detection section 140 for FM-detecting the filter output signal; an RDS demodulation section 160 for demodulating the FM-detected signal to obtain a PI code of a substitute station; a neignboring noise detection section 150 for extracting the signal of a station adjacent to the substitute station from the FM-detected signal and detecting the neignboring noise value of the signal; and a CPU 190 for varying the filter bandwidth of the variable IF filter section 130 in accordance with the neignboring noise value when the RDS demodulation section 160 obtains the PI code of the substitute station. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an RDS receiver that receives RDS data.

  A radio data system (RDS) is a service that, in FM broadcasting, multiplexes additional information regarding broadcast stations and broadcast contents as RDS data into FM broadcast signals and provides them to the FM broadcast receiving side. As an example of the service, there is a method of displaying the name of a song broadcast on a selected broadcast station on an FM broadcast receiver (hereinafter referred to as “RDS receiver”). In recent years, FM broadcast receivers that can receive RDS data have spread in Europe, the United States, and the like.

  In RDS, the same broadcast content is broadcast in a plurality of frequency bands. For example, even if the reception state of an RDS receiver mounted on a vehicle deteriorates due to the movement of the vehicle, the RDS receiver is a broadcasting station that broadcasts the same broadcast content at a frequency different from the frequency being received (hereinafter “ Search for an alternative broadcasting station with good reception quality from the "alternative station") and switch. At this time, the RDS receiver switches broadcast stations based on the RDS data.

  The RDS data includes an AF (alternative frequency) list that describes the frequency at which the alternative station is broadcast (hereinafter referred to as “alternative frequency”) and the PI (program identification) code of the alternative station. The PI code is a code for identifying a broadcasting station, and the same PI code is assigned to broadcasting stations that broadcast the same broadcast content. The RDS receiver acquires an AF list in advance from the FM broadcast being received, and when the signal reception quality deteriorates, the RDS receiver can switch to an alternative station with good reception quality based on the AF list.

  The RDS receiver performs an AF operation when switching to an alternative station. The AF operation is an operation of searching for an alternative frequency with good signal reception quality from the alternative frequencies described in the AF list and switching to the searched alternative frequency. The AF operation is composed of two processes of “AF check” and “PI check”. “AF check” is a method for detecting whether the electric field strength of an FM broadcast signal transmitted at an alternative frequency is greater than or equal to a threshold, and whether or not RSD data can be acquired from an alternative station. It is a process to confirm. The “PI check” is a process for confirming whether the PI code of the currently receiving broadcast station matches the PI code of the alternative station described in the AF list.

The conventional RDS receiver includes a wideband filter unit having a wide passband and a narrowband filter unit having a narrow passband. A conventional RDS receiver forcibly uses a wideband filter section at the time of PI check (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 6-232737

  However, since the RDS receiver described in Patent Document 1 forcibly uses the wideband filter unit at the time of PI check, there is noise (hereinafter referred to as “adjacent noise”) generated by the broadcast signal of the broadcast station adjacent to the alternative station. In this case, there is a problem that the PI code acquisition rate decreases.

  During the PI check, reception of the FM broadcast signal being received is interrupted. At this time, since the sound is interrupted, it is necessary to complete the PI check in a very short time so that the user does not notice it. If the PI code acquisition rate decreases due to adjacent noise, the PI check will not be completed in a short time. Therefore, in order to complete the PI check in a short time, it is desired to increase the PI code acquisition rate.

  An object of the present invention is to provide an RDS receiver capable of improving the PI code acquisition rate even when adjacent noise exists.

  The present invention provides an antenna unit that receives an FM broadcast signal, a front end unit that converts an FM broadcast signal received by the antenna unit into an intermediate frequency signal, and an intermediate frequency signal output by the front end unit as a predetermined frequency. A variable IF filter unit with a variable filter bandwidth that outputs a filter output signal with a band limited by a filter bandwidth, an FM detection unit that performs FM detection on the filter output signal output by the variable IF filter unit, and the FM An RDS demodulator that demodulates the signal detected by the FM by the detector and obtains the PI code of the alternative station; and a signal of a station adjacent to the alternative station is extracted from the signal that has been FM detected by the FM detector; An adjacent noise detection unit that detects an adjacent noise value of the variable IF filter unit, and a control unit that changes a filter bandwidth of the variable IF filter unit. , When said RDS demodulator acquires the PI code of the alternative station, in response to said adjacent noise value outputted by the adjacent noise detection unit, which is the variable IF filter section RDS receiver to change the filter bandwidth.

  According to the present invention, since the filter bandwidth of the variable IF filter unit is changed according to the adjacent noise value, the PI code acquisition rate can be improved even when adjacent noise exists.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a system configuration diagram showing a configuration of an RDS receiver according to an embodiment of the present invention.

  In FIG. 1, an RDS receiver 100 includes an antenna unit 110, a front end unit 120, a variable IF filter unit 130, an FM detection unit 140, an adjacent noise detection unit 150, an RDS demodulation unit 160, a ROM (read only memory) 170, a RAM (Random access memory) 180, CPU (central processing unit) 190, MPX (multiplex) demodulator 200, mute unit 210, speaker unit 220, display device 230, and operation unit 240.

  The antenna unit 110 receives FM-multiplexed FM broadcast signals.

  The front end unit 120 converts an FM broadcast signal of a broadcast station designated by the user or a predetermined broadcast station, among FM broadcast signals received by the antenna unit 110, into an intermediate frequency (IF) signal. To do.

  The variable IF filter unit 130 band-limits the intermediate frequency signal converted by the front end unit 120 with a predetermined filter bandwidth, and outputs a filter output signal. The filter bandwidth of the variable IF filter unit 130 is variable and is controlled by the CPU 190.

  The FM detection unit 140 performs FM detection on the filter output signal output by the variable IF filter unit 130 and outputs a detection signal. Further, the FM detection unit 140 detects the electric field strength of a detection signal (hereinafter referred to as “desired wave”) in a frequency band broadcast by a predetermined broadcasting station during the AF operation of the RDS receiver 100.

  The adjacent noise detection unit 150 detects the electric field strength of the adjacent noise (hereinafter referred to as “adjacent noise value” as appropriate) from the detection signal output from the FM detection unit 140. Hereinafter, the adjacent noise is not limited to noise due to FM broadcast signals of other adjacent broadcast stations, but refers to noise existing in the vicinity of the desired wave.

  The adjacent noise detection unit 150 includes a bandpass filter (BPF) unit 151 and an electric field strength measurement unit 152. The bandpass filter unit 151 extracts a detection signal in a frequency band (hereinafter referred to as “noise detection band”) that is a target of detection of adjacent noise from the detection signal output by the FM detection unit 140.

  The electric field strength measurement unit 152 measures the electric field strength of the detection signal in the noise detection band, and outputs the measurement result as an adjacent noise value.

  The RDS demodulator 160 performs demodulation and decoding processing for extracting RDS data from the detection signal output from the FM detector 140. The RDS data includes an AF list that lists alternative frequencies and a PI code.

  The ROM 170 stores various control programs executed by the CPU 190 in advance. The CPU 190 controls each unit by reading the control program stored in the ROM 170 into the RAM 180 and executing it. The ROM 170 stores in advance an AF operation selection table, a PI check selection table, and an IF filter selection table. In the AF operation selection table, numerical values serving as determination criteria for selecting whether or not to start the AF operation are described. The PI check selection table describes a numerical value serving as a determination criterion for selecting whether or not to execute the PI check, and the filter bandwidth of the variable IF filter unit 130 when the PI check is executed. The IF filter selection table describes the filter bandwidth of the variable IF filter unit 130 when receiving an FM broadcast signal.

  FIG. 2 is a diagram showing an example of the contents of the AF operation selection table.

  As shown in FIG. 2, the AF operation selection table 310 includes an electric field intensity 311 of a desired wave (hereinafter referred to as “own station desired wave”) of a receiving broadcast station (hereinafter referred to as “own station”), and a local station desired The frequency with which the AF operation is performed is described for each combination with the electric field strength 312 of the adjacent noise of the wave.

  When the electric field strength of the local station desired wave is high and the electric field intensity of the adjacent noise of the local station desired wave is low, the reception quality is good and the necessity of switching to an alternative station is low. On the other hand, when the electric field strength of the local station desired wave is low or when the electric field intensity of the adjacent noise of the local station desired wave is high, the reception quality is bad and the viewing of the broadcast is hindered, so it is necessary to switch to an alternative station. Therefore, in the AF operation selection table 310, the frequency of AF operation is increased as the electric field strength of the local station desired wave is lower and as the electric field intensity of the adjacent noise of the local station desired wave is higher.

  For example, in response to the condition that the electric field intensity 311 of the local station desired wave is less than 20 dBμV (decibel microvolt) and the electric field intensity 312 of the adjacent noise of the local station desired wave is less than 30 dBμV, "300 ms (milliseconds)" is described. This prescribes that the AF operation is executed once every 300 ms when the above condition is satisfied. Further, for example, “0 times” is described in response to the condition that the electric field intensity 311 of the local station desired wave is 50 dBμV or more and the electric field intensity 312 of the adjacent noise of the local station desired wave is less than 30 dBμV. ing. This prescribes that the AF operation need not be executed when the above condition is satisfied. Even though the electric field intensity 311 of the local station desired wave is at the same level, such a different content is that the reception quality of the FM broadcast signal of the local station desired wave is that of the adjacent noise of the local station desired wave. This is because it is easily affected by the electric field strength.

  By determining the frequency of performing the AF operation using the AF operation table 310, the AF operation can be executed at an appropriate frequency according to the reception quality of the desired wave of the own station.

  FIG. 3 is a diagram illustrating an example of the contents of the PI check selection table.

  As shown in FIG. 3, the PI check selection table 320 includes a PI check selection table 320 for each combination of the electric field intensity 321 of the desired wave of the alternative station (hereinafter referred to as “substitute station desired wave”) and the adjacent noise 322 of the alternative station desired wave. Whether or not to execute the check and the filter bandwidth of the variable IF filter unit 130 at the time of the PI check are described.

  When the electric field intensity of the alternative station desired wave is high and the electric field intensity of the adjacent noise of the alternative station desired wave is low, the reception quality of the alternative station desired wave is high. Therefore, the PI check selection table 320 is determined so that the PI check is executed when the electric field strength of the alternative station desired wave is high and the electric field strength of the adjacent noise is low.

  When executing the PI check, when the electric field strength of the adjacent noise of the alternative station desired wave is low, it is desirable to control the variable IF filter unit 130 so that the filter bandwidth is wide. This is because, when noise due to multipath is generated, the electric field drops due to fading, and therefore, the broadband can improve the PI code acquisition rate.

  On the other hand, when the electric field strength of the adjacent noise of the alternative station desired wave is high, if the control is performed so that the filter bandwidth of the variable IF filter unit 130 becomes wide, the influence of the adjacent noise increases, and the PI code acquisition rate decreases. . Therefore, when the electric field strength of the adjacent noise of the alternative station desired wave is high, the PI check selection table 320 is determined so as to have a narrow filter bandwidth in order to remove the adjacent noise.

  In the PI check selection table 320 shown in FIG. 3, narrow band, medium band, and wide band are defined as filter bandwidths at the time of PI check. The narrow band is, for example, a band having a width of ± 60 kHz (kilohertz) with respect to the center frequency of the alternative station desired wave. The middle band is, for example, a band having a width of about ± 80 kHz with respect to the center frequency of the alternative station desired wave. The wide band is, for example, a band having a width of about ± 100 kHz with respect to the center frequency of the alternative station desired wave.

  For example, “◯, broadband” is described corresponding to the condition that the electric field strength 321 of the alternative station desired wave is 50 dBμV or more and the electric field strength 322 of the adjacent noise of the alternative station desired wave is less than 30 dBμV. Yes. This prescribes that when the above condition is satisfied, the PI check is performed in a state where the filter bandwidth of the variable IF filter unit 130 is wide. Further, for example, in response to the condition that the electric field intensity 321 of the alternative station desired wave is 50 dBμV or more and the electric field intensity 322 of the adjacent noise of the alternative station desired wave is 60 dBμV or more, “◯, narrow band” is is described. This prescribes that when the above condition is satisfied, the PI check is performed in a state where the filter bandwidth of the variable IF filter unit 130 is narrow. Although the electric field strength 321 of the alternative station desired wave is the same, such a different content is that when the electric field strength of the adjacent noise of the alternative station desired wave is high, the adjacent noise band is set as a narrow band. This is because the removal rate can improve the PI code acquisition rate.

  By referring to such a PI check selection table 320, it is possible to select whether or not to switch to an alternative station and an appropriate filter bandwidth in accordance with the reception quality of the broadcast wave of the alternative station.

  FIG. 4 is a diagram illustrating an example of the contents of the IF filter selection table.

  When the AF operation is not performed in the IF filter selection table 330 for each combination of the electric field strength 331 of the local station desired wave and the electric field strength 332 of the adjacent noise of the local station desired wave (hereinafter referred to as “normal time”). The filter bandwidth of the variable filter section 130 is described.

  Here, as an example of the filter bandwidth, the narrowest band is defined in addition to the above-described narrow band, medium band, and wide band. The narrowest band is, for example, a band having a width of ± 40 kHz (kilohertz) with respect to the center frequency of the local station desired wave. The narrowest band allows a broadcast wave (hereinafter referred to as “main wave”) in which the audio is broadcast among the desired wave of the own station to pass, but a broadcast wave (hereinafter referred to as “RDS subcarrier”) in which RDS data is multiplexed. Is a band that is not allowed to pass. Note that the filter bandwidth is not limited to the above content, and a different value may be set between the PI check time and the normal time.

  In normal times, when the electric field strength of the adjacent noise of the local station desired wave is low, as described above, it is desirable to control so that the filter bandwidth becomes wide in consideration of the signal multipath and the like. On the other hand, when the electric field strength of the adjacent noise of the local station desired wave is high, if a wideband signal is used, the influence of the adjacent noise is increased, and the reception quality of the FM broadcast signal may be deteriorated. Therefore, the IF filter selection table 330 has a narrow filter bandwidth so that the adjacent noise can be sufficiently removed when the electric field strength of the adjacent noise of the local station desired wave is high in normal times. Determined.

  By referring to such IF filter selection table 330, it is possible to select an appropriate filter bandwidth in accordance with the reception quality of the local station.

  FIG. 5 is a diagram illustrating an example of the contents of the AF list acquired from the RDS data and stored in the RAM 180. The AF list is stored in the RAM 180.

  As shown in FIG. 5, the AF list 340 describes the center frequency 341 of the local station desired wave, the number of alternative frequencies 342, and one or more alternative frequencies. The number of alternative frequencies 342 is the number of alternative frequencies described in the AF list 340, and is hereinafter referred to as “N”. The alternative frequency 343 is the center frequency of the alternative station desired wave. The same PI should be acquired at the center frequency 341 of the desired wave of the own station and the alternative frequency 343.

  By referring to such an AF list 340, it is possible to obtain the alternative frequencies of the desired wave of the local station, the number of the alternative frequencies, and the PIs to be received at the respective alternative frequencies.

  The CPU 190 of FIG. 1 controls each part of the RDS receiver 100 by executing a control program stored in the ROM 170, and controls the entire operation of the RDS receiver 100. In addition, the CPU 190 uses various tables stored in the ROM 170 to determine whether or not to execute the AF operation and what filter bandwidth should be set in the variable IF filter unit 130 at the time of PI check and normal time. Judgment is made by referring to it as appropriate. In particular, the CPU 190 refers to the PI check selection table 320 shown in FIG. 3 during the PI check of the AF operation, and the filter bandwidth of the variable IF filter unit 130 so that the PI code acquisition rate can be improved according to the adjacent noise value. To change.

  The MPX demodulation unit 200 demodulates the detection signal output from the FM detection unit 140, and outputs an L (left) side audio signal and an R (right) side audio signal.

  Under the control of the CPU 190, the mute unit 210 reduces the signal level of the audio signal output from the MPX demodulation unit 200 for a predetermined period described later.

  The speaker unit 220 converts an audio signal input via the mute unit 210 into sound and outputs the sound.

  Based on the RDS data demodulated by RDS demodulator 160, display device 230 displays additional information such as frequency, broadcast station name, broadcast program name, broadcast song name, etc., regarding the FM broadcast signal being received.

  The operation unit 240 accepts user operations on the RDS receiver 100 for designating the frequency of the broadcasting station to be listened to and adjusting the audio output level.

  According to such an RDS receiver 100, the filter bandwidth at the time of PI check is changed according to the adjacent noise value of the desired wave so that the PI code acquisition rate can be improved. Reception of broadcast programs can be continued.

  The RDS receiver 100 controls the variable IF filter 130 (hereinafter referred to as “variable IF filter control”) according to the stage of operation. Specifically, the RDS receiver 100 performs the first variable IF filter control at the AF check, the second variable IF filter control at the PI check, and the third variable IF filter control at the normal time or normal time. I do.

  Here, with respect to the specific contents of the first to third variable IF filter controls, the local desired wave or alternative frequency, adjacent noise, the filter bandwidth of the bandpass filter unit 151, and the filter bandwidth of the variable IF filter unit 130 This will be explained together with the relationship.

  FIG. 6 is a diagram for explaining the contents of the first variable IF filter control. In the figure, the horizontal axis indicates the frequency, and the vertical axis indicates the electric field strength of the signal.

  As shown in FIG. 6, the center frequency of the desired wave 411 is the alternative frequency f1, and the RDS data is broadcast to the bands centering around the two frequencies (f1 + 57 kHz, f1-57 kHz) of plus and minus 57 kHz of the alternative frequency f1. An RDS subcarrier 412 that is a broadcast wave is located. This is the same for other broadcasting stations that can become adjacent noise. For example, when a broadcast wave of an adjacent broadcast station exists at the frequency f2, an adjacent noise (interference wave) 413 centered on the frequency f2 is generated. The adjacent noise 413 due to the RDS subcarrier is also generated in the vicinity of the frequency f2 plus or minus 57 kHz.

  In the first variable IF filter control, the RDS receiver 100 sets the filter bandwidth (frequency characteristics of the filter in the variable IF filter unit 130) 414 of the variable IF filter unit 130 to f1-ΔF0 including the noise detection band. A fixed filter bandwidth is set in which the band up to f1 + ΔF0 is the pass band. Further, the filter bandwidth 415 of the bandpass filter unit 151 is set in advance to a filter bandwidth whose passband is the noise detection band.

  Therefore, as shown in FIG. 6, when the noise detection band is the frequency Fa to the frequency Fb and the frequency f2 is located between the frequency Fa and the frequency Fb, it corresponds to the adjacent noise 413 in the detection signal. The signal component (portion 416) is input to the electric field strength measurement unit 152. Further, when the electric field strength of the adjacent noise 413 is high, the electric field strength of the signal input to the electric field strength measuring unit 152 is also high.

  Usually, the frequency of each broadcasting station is set at a distance of at least 100 kHz. Therefore, it is considered that the adjacent noise that most greatly affects the reception quality of the desired wave is the adjacent noise 413 having the frequency f2 = f1 + 100 kHz. Therefore, if the frequency of the adjacent noise 413 having the frequency f2 = f1 + 100 kHz is set as a noise detection band and ΔF0 = 120 kHz, the adjacent noise 413 that greatly affects the reception quality of the desired wave 411 can be detected. The values of ΔF0, frequency Fa, and frequency Fb are stored in the ROM 170 in advance.

  Thus, in the first variable IF filter control, the adjacent noise value is detected as the electric field strength in the noise detection band. Further, since the filter bandwidth of the variable IF filter unit 130 is fixed, the detection of the electric field strength of the desired wave of the alternative frequency is stably performed, and the radio wave environment of the switching destination candidate is correctly grasped.

  7 to 9 are diagrams for explaining the contents of the second variable IF filter control.

  In the second variable IF filter control, the RDS receiver 100 refers to the PI check selection table 320 shown in FIG. 3, and based on the adjacent noise value detected by the adjacent noise detection unit 150, the wideband described in FIG. , Medium band or narrow band. 7 to 9 respectively correspond to the case where the wide band is selected, the case where the medium band is selected, and the case where the narrow band is selected.

  For example, when the electric field strength of the desired wave 411 of the alternative frequency is 50 dBμV or more and the electric field strength of the adjacent noise of the alternative frequency is less than 30 dBμV, the filter bandwidth 414 of the variable IF filter unit 130 is set to a wide band. The In this case, as shown in FIG. 7, the RDS receiver 100 passes the band of the variable IF filter unit 130 up to f1−ΔF1 to f1 + ΔF1 (here, ΔF1 = 100 kHz) as the passband. To the filter bandwidth. As apparent from FIG. 7, when the electric field strength of adjacent noise is sufficiently low, even if a wide band is selected, the reception quality of the desired wave 411 is hardly deteriorated by the adjacent noise.

  For example, when the electric field strength of the desired wave 411 of the alternative frequency is 50 dBμV or more and the electric field strength of the adjacent noise of the alternative frequency is 30 dBμV or more and less than 60 dBμV, the filter bandwidth 414 of the variable IF filter unit 130 is the middle band Set to In this case, as shown in FIG. 8, the RDS receiver 100 passes the band 414 of the variable IF filter unit 130 up to f1−ΔF2−f1 + ΔF2 (here, ΔF2 = 80 kHz). To the filter bandwidth. As can be seen from FIG. 8, when the adjacent noise 413 exists but the electric field strength is small, the pass band is expanded to the middle band, so that the adjacent noise of the detection signal is secured with the pass band as wide as possible. The electric field strength of the signal component (part 417) corresponding to 413 can be kept low.

  For example, when the electric field strength of the desired wave 411 of the alternative frequency is 50 dBμV or more and the electric field strength of adjacent noise of the alternative frequency is 60 dBμV or more, the filter bandwidth 414 of the variable IF filter unit 130 is set to a narrow band. Is done. In this case, as shown in FIG. 9, the RDS receiver 100 passes the band 414 of the variable IF filter unit 130 up to f1−ΔF3 to f1 + ΔF3 (here, ΔF2 = 60 kHz). To the filter bandwidth. As is clear from FIG. 9, even when the electric field strength of the adjacent noise 413 is high, the pass band is limited to a narrow band, so that the signal component corresponding to the adjacent noise 413 of the detection signal is secured with the pass band as wide as possible. The electric field strength of (part 417) can be kept low.

  As described above, in the second variable IF filter control, the reception bandwidth is deteriorated by the desired wave 411 and the RDS subcarrier 412 due to the adjacent noise by changing the filter bandwidth of the variable IF filter unit 130 according to the adjacent noise value. Can be suppressed.

  10 and 11 are diagrams for explaining the contents of the third variable IF filter control.

  In the third variable IF filter control, the RDS receiver 100 refers to the IF filter selection table 330 shown in FIG. 4 and based on the adjacent noise value detected by the adjacent noise detection unit 150, the wideband described in FIG. , Medium band, narrow band, or narrowest band. 10 and 11 respectively correspond to the case where the wide band is selected and the case where the narrowest band is selected.

  For example, when the electric field strength of the desired wave 411 of the local station is 50 dBμV or more and the electric field strength of the adjacent noise of the local station desired wave is less than 30 dBμV, the filter bandwidth 414 of the variable IF filter unit 130 is wide. Is set. In this case, as shown in FIG. 10, the RDS receiver 100 passes the band from f1−ΔF4 to f1 + ΔF4 (here, ΔF4 = 100 kHz) to the filter bandwidth 414 of the variable IF filter unit 130. To the filter bandwidth. As is clear from FIG. 10, when the electric field strength of adjacent noise is sufficiently low, the reception quality of the desired wave 411 is hardly deteriorated by the adjacent noise even when a wide band is selected.

  For example, when the electric field strength of the desired wave 411 of the alternative frequency is 50 dBμV or more and the electric field strength of the adjacent noise of the alternative frequency is 60 dBμV or more, the filter bandwidth 414 of the variable IF filter unit 130 is set to the narrowest band. Is set. In this case, as shown in FIG. 11, the RDS receiver 100 uses the filter bandwidth 414 of the variable IF filter unit 130 as a passband through a band from f1−ΔF5 to f1 + ΔF5 (here, ΔF5 = 40 kHz). To the filter bandwidth. As is clear from FIG. 11, even when the electric field strength of the adjacent noise 413 is high, the pass band is limited to the narrowest band, so a pass band capable of receiving the desired wave 411 and its RDS subcarrier 412 is secured. In this state, the electric field strength of the signal component (part 417) corresponding to the adjacent noise 413 of the detection signal can be further reduced.

  As described above, in the third variable IF filter control, the deterioration of the reception quality of the desired wave 411 due to the adjacent noise can be further suppressed by changing the filter bandwidth of the variable IF filter unit 130 according to the adjacent noise value. .

  Next, the operation of the RDS receiver 100 having the above configuration will be described.

  FIG. 12 is a flowchart showing an operation flow of the RDS receiver 100.

  First, in step S1100, the CPU 190 determines whether or not an FM broadcast viewing start is instructed by power-on of the own device or a user operation of the operation unit 240, and when the FM broadcast viewing start is instructed (S1100). : YES), CPU 190 advances the process to step S1200. As an initial state, the CPU 190 controls the mute unit 210 so that the signal level of the audio signal becomes zero.

  In step S1200, since the frequency of the FM broadcast signal received last is stored in the ROM 170, the CPU 190 reads out the frequency and sets the read frequency as the desired local wave f0.

  Then, in step S1300, CPU 190 tunes the reception frequency of antenna unit 110 to desired local wave f0.

  In step S1400, the CPU 190 measures the electric field strength of the desired wave of the local station desired wave f0 using the FM detection unit 140, and measures the electric field strength of the adjacent noise of the local station desired wave f0 using the adjacent noise detection unit 150. To do. The CPU 190 stores the measurement result in the RAM 180.

  In step S1500, CPU 190 determines whether to perform an AF operation. Specifically, the CPU 190 refers to the AF operation selection table 310 shown in FIG. 2, and based on the electric field strength of the local station desired wave f0 and the adjacent field electric field strength of the local station desired wave f0 measured in step S1400, It is determined whether or not to execute the AF operation. When executing the AF operation (S1500: YES), the CPU 190 advances the process to step S1600. When the AF operation is not executed (S1500: NO), CPU 190 advances the process to step S1700.

  In step S1600, CPU 190 executes an AF operation. Details of the AF operation will be described later.

  In step S <b> 1700, CPU 190 determines whether or not the FM broadcast viewing end is instructed by the power stop of RDS receiver 100 or the user operation of operation unit 240. If the end of viewing of FM broadcast is not instructed (S1700: NO), the process proceeds to step S1800.

  In step S1800, CPU 190 determines whether or not a change of a broadcasting station to be viewed is instructed by a user operation of operation unit 240 or the like. If the broadcast station change is not instructed (S1800: NO), the process returns to step 1400. If the broadcast station change is instructed (S1800: YES), the process proceeds to step S1900. Thereby, the measurement of the electric field strength and the AF operation as necessary are repeated.

  In step S1900, CPU 190 sets the frequency of the broadcast station instructed as the change destination to a new desired station desired wave f0, and then returns the process to step S1300. Thereby, viewing of the broadcast of the alternative station is started.

  On the other hand, if an instruction to end viewing of FM broadcast is given in step S1700 (S1700: YES), CPU 190 advances the process to step S2000.

  In step S2000, CPU 190 stores the frequency of the FM broadcast signal received last in ROM 170, and ends a series of processing.

  FIG. 13 is a flowchart showing the flow of the AF operation, and corresponds to step S1600 in FIG.

  First, in step 1601, the CPU 190 causes the mute unit 210 to reduce the signal level of the audio signal to a level that the user cannot recognize by hearing, thereby muting the output audio.

  In step S1602, the CPU 190 tries to acquire the AF list of the local station, and determines whether an alternative frequency is described in the acquired AF list. If the AF list of the local station can be acquired and the alternative frequency is described in the acquired AF list (S1602: YES), the CPU 190 advances the process to step S1603. The acquisition of the AF list is performed, for example, when the corresponding AF list is stored in the ROM 170, read from the ROM 170, and when the corresponding AF list is not stored in the ROM 170, the RDS demodulator 160 obtains the AF list from the RDS data. Extraction may be performed. Each time the CPU 190 acquires the AF list from the RDS data, it is desirable to store the acquired AF list in the ROM 170.

  In step S1603, the CPU 190 sets a value “0” to the initial value of the variable L that indicates what number of alternative frequencies in the AF list is to be processed.

  In step S1604, the CPU 190 sets the Lth alternative frequency in the AF list as the alternative frequency f1 to be processed.

  In step S1605, the CPU 190 performs the first variable IF filter control described with reference to FIG. That is, the CPU 190 sets the filter bandwidth of the variable IF filter unit 130 so that the adjacent noise value of the alternative frequency can be detected.

  In step S1606, the CPU 190 tunes the reception frequency of the antenna unit 110 to the alternative frequency f1.

  In step S1607, the CPU 190 measures the electric field strength of the desired wave having the alternative frequency f1, and the adjacent noise detecting unit 150 measures the electric field strength of the adjacent noise having the alternative frequency f1. The CPU 190 stores the measurement result in the RAM 180.

  In step S1608, the CPU 190 performs an AF check that is a determination as to whether or not to switch to the alternative station having the alternative frequency f1. Specifically, the CPU 190 refers to the PI check selection table shown in FIG. 3 and determines whether to perform the PI check based on the electric field strength of the alternative frequency f1 and the adjacent noise electric field strength of the alternative frequency f1 measured in step S1607. Judge whether or not. If the CPU 190 determines not to perform the PI check, that is, determines that switching to reception of the alternative frequency f1 is not performed (S1608: NO), the process proceeds to step S1609.

  In step S1609, the CPU 190 determines whether the variable L exceeds the number N of alternative frequencies described in the AF list, that is, whether there is an unprocessed alternative frequency. If the variable L has not yet exceeded the number N (S1609: NO), the CPU 190 advances the process to step S1610.

  In step S1610, CPU 190 increases variable L by value 1, and then returns the process to step S1604. As a result, while the switching destination is not determined, while the switching destination candidates remain, AF checks are sequentially performed on the alternative frequencies described in the AF list.

  On the other hand, when it is determined to perform the PI check, that is, when it is determined to switch to reception of the alternative frequency f1 (S1608: YES), the CPU 190 advances the process to step S1611.

  In step S <b> 1611, the CPU 190 performs the second variable IF filter control described with reference to FIGS. 7 to 9. That is, CPU 190 sets the filter bandwidth of variable IF filter section 130 according to the adjacent noise value so as to suppress the deterioration of the reception quality of alternative frequency f1 due to the adjacent noise.

  In step S1612, the CPU 190 obtains a PI code from the FM broadcast signal having the alternative frequency f1, and then determines whether or not the obtained PI code matches the PI code of the desired station wave described in the AF list. A PI check is performed. If the PI code cannot be acquired or if the acquired PI code does not match the PI code of the AF list (S1612: NO), the CPU 190 advances the process to step S1609. Thereby, it can transfer to the process to another switching destination candidate. On the other hand, if the PI code can be acquired and the acquired PI code matches the PI code of the AF list (S1612: YES), the CPU 190 advances the process to step S1613.

  In step S1613, the CPU 190 performs the third variable IF filter control described with reference to FIGS. That is, CPU 190 sets the filter bandwidth of variable IF filter section 130 according to the adjacent noise value so as to suppress the deterioration of the reception quality of alternative frequency f1 due to the adjacent noise.

  In step S <b> 1614, the CPU 190 controls the mute unit 210 to increase the signal level of the audio signal to a level that can be recognized by the user.

  On the other hand, when the variable L exceeds the number N of alternative frequencies described in the AF list, that is, when the switching destination is not finally determined (S1609: YES), the CPU 190 advances the process to step S1615.

  In step 1615, the CPU 190 performs the third variable IF filter control on the desired signal of the own station in the same manner as in step 1613. Change so that deterioration of the product can be suppressed.

  Then, in step S1616, CPU 190 retunes the reception frequency of antenna unit 110 to own station desired wave f0, and proceeds to step S1614.

  If the AF list of the own station cannot be acquired, or if an alternative frequency is not described in the acquired AF list (S1602: NO), the CPU 190 proceeds directly to step S1614.

  In this way, the CPU 190 changes the filter bandwidth of the variable IF filter unit 130 so that the PI code acquisition rate can be improved.

  Hereinafter, experimental data indicating that the PI acquisition rate is improved by using the RDS receiver 100 according to the present embodiment will be described.

  FIG. 14 is a diagram illustrating the relationship between the type of adjacent noise, the filter bandwidth of the variable IF filter unit 130, and the PI acquisition rate. In the figure, the horizontal axis indicates the filter bandwidth of the variable IF filter unit 130, and the vertical axis indicates the PI acquisition rate. A line 510 is a PI acquisition rate when there is noise due to multipath. Line 520 is the PI acquisition rate when there is adjacent noise.

  As shown in FIG. 14, when there is multipath noise, the PI acquisition rate increases as the IF filter bandwidth increases. At this time, the filter bandwidth of the variable IF filter unit 130 is set to a wide band (f1 ± ΔF1).

  Also, when there is adjacent noise, the PI acquisition rate becomes higher as the IF filter bandwidth becomes narrower. At this time, the filter bandwidth of the variable IF filter unit 130 is set to a narrow band (f1 ± ΔF3).

  Thus, it can be seen that RDS receiver 100 according to the present embodiment can improve the PI acquisition rate regardless of whether there is multipath noise or adjacent noise.

  As described above, according to the RDS receiver 100 according to the present embodiment, when the RDS data of the alternative station is acquired, the filter bandwidth of the variable IF filter unit 130 according to the adjacent noise value of the alternative frequency Therefore, the PI acquisition rate can be improved even when adjacent noise exists.

  In addition, you may make it detect adjacent noise using a filter output signal instead of a detection signal. Further, the noise detection band may be set on both the high frequency side and the low frequency side of the desired wave.

  The RDS receiver according to the present invention is useful as an RDS receiver that can improve the PI acquisition rate even when adjacent noise exists.

The system block diagram which shows the structure of the RDS receiver which concerns on one embodiment of this invention The figure which shows an example of the content of the AF operation | movement selection table in this Embodiment The figure which shows an example of the content of the PI check selection table in this Embodiment The figure which shows an example of the content of the IF filter selection table in this Embodiment The figure which shows an example of the content of the AF list | wrist in this Embodiment The figure for demonstrating the content of the 1st variable IF filter control in this Embodiment The figure for demonstrating the content of the 2nd variable IF filter control when the wide band in this Embodiment is selected. The figure for demonstrating the content of the 2nd variable IF filter control when the middle band in this Embodiment is selected The figure for demonstrating the content of the 2nd variable IF filter control when the narrow band in this Embodiment is selected. The figure for demonstrating the content of the 3rd variable IF filter control when the wide band in this Embodiment is selected. The figure for demonstrating the content of the 3rd variable IF filter control when the narrowest band in this Embodiment is selected. The flowchart which shows the flow of operation | movement of the RDS receiver in this Embodiment. Flowchart showing the flow of AF operation in the present embodiment The figure which shows the relationship between the filter bandwidth and PI acquisition rate in this Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 RDS receiver 110 Antenna part 120 Front end part 130 Variable IF filter part 140 FM detection part 150 Adjacent noise detection part 151 Band pass filter part 152 Electric field strength measurement part 160 RDS demodulation part 170 ROM
180 RAM
190 CPU
200 MPX Demodulator 210 Mute Unit 220 Speaker Unit 230 Display Device 240 Operation Unit

Claims (5)

An antenna unit for receiving FM broadcast signals;
A front end unit for converting an FM broadcast signal received by the antenna unit into an intermediate frequency signal;
A variable IF filter unit with a variable filter bandwidth, which outputs a filter output signal by limiting the intermediate frequency signal output by the front end unit with a predetermined filter bandwidth;
An FM detector for FM detecting the filter output signal output by the variable IF filter;
An RDS demodulator that demodulates the signal detected by the FM detector and obtains the PI code of the alternative station;
An adjacent noise detection unit that extracts a signal of a station adjacent to an alternative station from the signal detected by the FM detection unit and detects an adjacent noise value of the signal;
A control unit that changes a filter bandwidth of the variable IF filter unit,
The control unit changes the filter bandwidth of the variable IF filter unit according to the adjacent noise value output by the adjacent noise detection unit when the RDS demodulation unit acquires the PI code of the alternative station. RDS receiver characterized.   When the adjacent noise value output from the adjacent noise detection unit is equal to or greater than a predetermined value, the control unit uses a filter bandwidth of the variable IF filter unit as a first filter band including a center frequency of a desired wave of an alternative station When the adjacent noise value output by the adjacent noise detection unit is less than a predetermined value, the filter bandwidth of the variable IF filter unit is a second filter bandwidth wider than the first filter bandwidth. The RDS receiver according to claim 1.   The first filter bandwidth is a filter bandwidth including an intermediate frequency signal to which a PI code of an alternative station is transmitted among the intermediate frequency signals output from the front end unit. 2. The RDS receiver according to 2. An MPX demodulator that demodulates the detection signal output by the FM detector and outputs an audio signal;
A mute unit for muting the audio signal output by the MPX demodulation unit when the RDS demodulation unit obtains the PI code of the alternative station;
The RDS receiver according to claim 1, further comprising a speaker unit that outputs the audio signal as audio. When the adjacent noise detection unit extracts the detection signal of the station adjacent to the alternative station from the detection signal output by the FM detection unit, the control unit sets the filter bandwidth of the variable IF filter unit adjacent to the alternative station. The RDS receiver according to claim 1, wherein the RDS receiver is controlled to a filter bandwidth including an intermediate frequency signal of a station to be operated.

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