JP2011139324A - Method, device and program for preventing beat disturbance in am radio broadcast - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain display of a liquid crystal panel well while preventing beat disturbance in receiving AM radio. <P>SOLUTION: The method for preventing beat disturbance in a radio receiver including a liquid crystal panel for displaying video based on a video signal, a backlight for illuminating the liquid crystal panel, a dimming circuit for controlling and dimming the backlight, and a video signal processing circuit for outputting the video signal, and capable of executing a plurality of operation modes including an AM radio broadcast mode includes steps of: detecting selection of the AM radio broadcast mode; and changing a duty ratio of a backlight drive pulse output from the dimming circuit to the backlight; wherein, when the selection of the AM radio broadcast mode is detected, the duty ratio of the backlight drive pulse is changed so that the backlight becomes dark relative to the time before the AM radio broadcast mode is selected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radio receiver, and more particularly, in a radio receiver equipped with a liquid crystal panel, beat disturbance caused by the operation of an illumination circuit for a backlight of the liquid crystal panel when receiving an AM radio broadcast. This is to improve the sensitivity deterioration due to.

  Conventionally, a vehicle-mounted device mounted on a vehicle or the like is provided with a receiving unit for receiving radio waves of AM / FM radio broadcasting. In addition, the vehicle-mounted device estimates, for example, the position of the vehicle by using a positioning solution by a GPS (Global Positioning System) receiver and a positioning solution by a dead reckoning sensor such as a vehicle speed sensor or a gyro sensor. Is equipped with a car navigation function that performs route matching using map matching, a function to receive VICS information, a function to perform ETC data communication, a function to view satellite broadcasts, etc. Are being executed simultaneously.

  Different noise frequencies are generated from various devices in the vehicle-mounted device according to the operation. These noise frequencies cause a decrease in reception sensitivity when receiving radio waves of AM / FM radio broadcasting and terrestrial digital broadcasting. One source of noise is a backlight of a liquid crystal panel. A cold cathode tube (CCFL) or LED is used for the backlight. In a cold cathode tube, mercury and a rare gas are enclosed in a glass tube, and ultraviolet rays generated in a positive column of glow discharge are converted into visible light by a phosphor. The cold cathode fluorescent lamp has been improved in lamp efficiency and brightness by improving the cathode material, optimizing the operating temperature, lengthening, and narrowing the tube. As the light guide plate becomes thinner, the cold cathode tube becomes thinner, and a very thin cold cathode tube having a diameter of several millimeters has been rapidly spread in recent years with the development of the light guide plate. The light emission principle of a cold cathode tube is basically the same as that of an ordinary fluorescent tube (hot cathode tube). However, since the electrode does not have a filament, the structure is simple and the electrode can be made small.

  The cold-cathode tube is driven by an inverter circuit which is a dimming circuit. Since this circuit is a high-voltage circuit, it becomes a large noise source when receiving AM radio broadcasts. As countermeasures against this noise, conventionally, the inverter circuit is covered with a shield member such as a shield case or a filter is interposed in the power supply line to reduce the noise level. However, it is not preferable to provide a shield member or a filter because it is contrary to cost reduction and size reduction. Further, since the oscillation frequency of the inverter circuit is several tens kHz and the output amplitude of the transformer in the inverter circuit is several hundred volts, the output level (energy) of harmonics generated from the inverter circuit is high. Therefore, the harmonics from the inverter circuit cannot be completely removed even if the above-described noise countermeasures are taken. In addition, this harmonic may match the reception frequency of the AM radio band. When a radio station receives a broadcast of a radio station having the same frequency as this harmonic, the harmonic jumps into the radio tuner or antenna circuit, or from various wiring patterns such as a power supply system or ground (GND) system of the board. There is a possibility that beat interference will occur due to wraparound interference and AM radio broadcast reception sensitivity will decrease.

  As an example, considering the band of European AM radio broadcasting, the oscillation frequency of the CCFL inverter circuit is 63 kHz. At this time, in the long wave (153 to 279 kHz; inter-station step: 3 kHz), beat interference occurs when a broadcast having the same frequency as the third harmonic (189 kHz) and the fourth harmonic (252 kHz) is received. Further, in the medium wave (531 to 1602 kHz; inter-station step: 9 kHz), beat disturbance occurs when receiving a broadcast having the same frequency as each harmonic from the 9th harmonic (567 kHz) to the 25th harmonic (1575 kHz). appear.

  As a configuration for removing these noise frequencies, an apparatus disclosed in Patent Document 1 has been proposed. In this device, a filter for removing noise frequency corresponding to each device in the vehicle-mounted device is provided. The filter is switched between valid and invalid according to the operation and stop of each device, and the noise present in the received radio wave is removed. By removing and performing signal processing, the reception sensitivity of a desired radio wave is improved.

JP 2007-258805 A

  However, when removing the noise associated with driving the backlight of the liquid crystal panel using the conventional noise removal or noise reduction configuration as described above, a process for selecting an appropriate filter for noise removal or in-vehicle equipment There is a problem that a plurality of processes such as switching on / off of a filter in accordance with on / off of other devices must be performed, and components for noise removal become complicated.

  The present invention has been made in view of the above circumstances. An object of the present invention is to remove noise generated by driving a backlight of a liquid crystal panel with a simple configuration in a radio receiver.

  A method of avoiding beat interference in a radio receiver according to an embodiment of the present invention includes a liquid crystal panel that displays video based on a video signal, a backlight that illuminates the liquid crystal panel, and a dimming control that controls the backlight. A method of avoiding beat interference in a radio receiver capable of executing a plurality of operation modes including an AM radio broadcast mode, comprising an optical circuit and a video signal processing circuit for outputting the video signal, A step of detecting selection, and a step of changing a duty ratio of a backlight drive pulse output from the dimming circuit to the backlight. When the selection of the AM radio broadcast mode is detected, the backlight The duty ratio of the backlight drive pulse is changed so that it is darker than before the selection of the broadcast mode is detected. That is, when the radio receiver mode is switched to the AM radio broadcast mode, the harmonics generated from the transformer of the dimming circuit that drives the backlight do not become a noise source in the reception of the AM radio broadcast. By changing the background color of the liquid crystal panel so that the user does not feel uncomfortable or uncomfortable by changing the duty ratio while changing the duty ratio, the AM radio broadcast can be received and played well. Thus, the display state of the liquid crystal panel can be maintained satisfactorily.

  The image signal processing circuit further includes a step of changing the background color of the liquid crystal panel, and when the selection of the AM radio broadcast mode is detected, the background color of the liquid crystal panel is changed. And when changing the background color of a liquid crystal panel, the brightness of the preset background color is made high. Alternatively, when changing the background color of the liquid crystal panel, the hue of the preset background color is changed. In this way, when switching to AM radio broadcast reception, it is possible to prevent the user from feeling uncomfortable or uncomfortable with the display on the liquid crystal panel by using these background color changing methods.

  Preferably, the method further includes a step of detecting selection switching to a mode other than the AM radio broadcast mode, and when the selection switching from the AM radio broadcast mode to a mode other than the AM radio broadcast mode is detected, the backlight is connected to the AM radio broadcast mode. The duty ratio of the backlight drive pulse is changed again so that the brightness is the same as before the selection of the radio broadcast mode is detected. Therefore, not only when switching to AM radio broadcasting but also when switching from AM radio broadcasting to another type of mode, it is possible to prevent the user from feeling uncomfortable or uncomfortable with the display on the liquid crystal panel. . Further, when the selection switching from the AM radio broadcast mode to a mode other than the AM radio broadcast mode is detected, the background color of the liquid crystal panel is changed again. When the background color of the liquid crystal panel is changed again, the brightness of the background color of the liquid crystal panel is lowered. Alternatively, when the background color of the liquid crystal panel is changed again, the hue of the background color of the liquid crystal panel is changed.

  A radio receiver according to an embodiment of the present invention includes a liquid crystal panel that displays video based on a video signal, a backlight that illuminates the liquid crystal panel, a dimming circuit that performs dimming control on the backlight, A radio receiver comprising a video signal processing circuit for outputting the video signal and capable of executing a plurality of operation modes including an AM radio broadcast mode, wherein the contrast of the liquid crystal panel is detected when selection of the AM radio broadcast mode is detected. The duty ratio of the backlight drive pulse output from the dimming circuit to the backlight is changed so as to be lower than before the selection of the AM radio broadcast mode is detected. When the selection of the AM radio broadcast mode is detected, the background color of the liquid crystal panel is further changed. Further, when selection switching from the AM radio broadcast mode to a mode other than the AM radio broadcast mode is detected, the backlight drive pulse is set so that the backlight has the same brightness as before the selection of the AM radio broadcast mode is detected. Change the duty ratio again. Further, when selection switching from the AM radio broadcast mode to a mode other than the AM radio broadcast mode is detected, the background color of the liquid crystal panel is further changed.

  Furthermore, a program for avoiding beat disturbance in a radio receiver according to an embodiment of the present invention includes a liquid crystal panel that displays video based on a video signal, a backlight that illuminates the liquid crystal panel, and the backlight. A program for avoiding beat disturbance in a radio receiver capable of executing a plurality of operation modes including an AM radio broadcast mode, comprising a dimming circuit for dimming control and a video signal processing circuit for outputting the video signal And detecting the AM radio broadcast mode selection, changing the duty ratio of the backlight drive pulse output from the dimming circuit to the backlight, and detecting the AM radio broadcast mode selection, Backlight drive pulse so that the light is darker than before detecting the selection of the AM radio broadcast mode And a step of changing the duty ratio. The image signal processing circuit further includes a step of changing the background color of the liquid crystal panel, and when the selection of the AM radio broadcast mode is detected, the background color of the liquid crystal panel is changed. Further, the method further includes a step of detecting selection switching to a mode other than the AM radio broadcast mode, and when the selection switching from the AM radio broadcast mode to a mode other than the AM radio broadcast mode is detected, the backlight transmits the AM radio. The duty ratio of the backlight drive pulse is changed again so that the brightness is the same as before the selection of the broadcast mode is detected. Further, when the selection switching from the AM radio broadcast mode to a mode other than the AM radio broadcast mode is detected, the background color of the liquid crystal panel is changed again.

  According to the radio receiver of the present invention, reception and reproduction can be performed satisfactorily without causing beat disturbance when receiving AM radio broadcasts.

FIG. 1 is a block diagram showing an outline of a radio receiver according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a radio receiver according to an embodiment of the present invention. FIG. 3 is a flowchart showing a process in the radio receiver beat avoidance avoiding method according to the embodiment of the present invention.

  Hereinafter, the structure of a radio receiver according to an embodiment of the present invention will be described with reference to the drawings. In addition, the same code | symbol shall be attached | subjected when showing the same member over several figures. In the figure, only blocks related to reception of AM radio broadcasts are shown in the present embodiment, and blocks and descriptions necessary for reception of other types of broadcasts are omitted.

  FIG. 1 is a block diagram showing an outline of a radio receiver 100 in the present embodiment. The radio receiver 100 includes a main body unit 1 and a panel unit 5. In the main unit 1, the radio wave of the desired station received from the antenna circuit 4 is sent to the radio tuner 3. In the radio tuner 3, the AM modulation wave signal of the desired station is amplified by the amplifier circuit, and then the local oscillation signal output from the local oscillator is mixed by the mixing circuit to convert it to an intermediate frequency signal. Specifically, the mixing circuit outputs an intermediate frequency signal based on the frequency of the amplified AM modulated wave signal output from the amplifier circuit and the frequency of the local oscillation signal output from the local oscillator. Subsequently, a frequency component included in the occupied frequency band of the modulated wave signal is extracted from the input intermediate frequency signal by an intermediate frequency amplifier circuit having an intermediate frequency filter in the preceding stage and the subsequent stage. The intermediate frequency signal amplified by the intermediate frequency amplifier circuit is subjected to AM detection processing in the AM detection circuit, and an audio signal is extracted. The extracted audio signal is amplified by an amplifier and then output from a speaker or the like. Note that the radio tuner 3 operates to receive a broadcast from a desired station based on an instruction from the master microcomputer 2. The master microcomputer 2 receives an operation related to a user's desired station from the operation unit 16.

  The master microcomputer 2 executes control of each unit in the radio receiver 100, and includes a ROM (Read-Only Memory) that stores a control program and the like, and a RAM (Random) that temporarily stores calculation data and the like. -Access Memory) and other storage means. In addition to the accessory power source connected to the battery via the key switch, the master microcomputer 2 is electrically connected to a backup power source directly connected to the vehicle battery, and the backup power source while the accessory power source is off. It is possible to operate by being supplied with power.

  The panel unit 5 of the radio receiver 100 includes an inverter circuit 6, a backlight 10, a video signal processing circuit 11, a liquid crystal panel 15, and an operation unit 16. The inverter circuit 6 is a light control circuit that performs light control using pulse width modulation (PWM) that changes the light amount by changing the light emission time (pulse signal width) by the pulse signal, and according to the control signal from the master microcomputer 2. To generate a pulse width modulation signal. The tube current in which the duty ratio is set according to the dimming control by PWM is applied to the backlight 10 so that the luminance control is performed. That is, the luminance of the backlight 10 is controlled by changing the duty ratio, and the contrast in the liquid crystal panel 15 is controlled. A control signal for dimming control from the master microcomputer 2 is sent to the controller circuit 7. The controller circuit 7 controls the duty ratio of the output pulse to the gate of the FET (Field-Effect Transistor) 8 based on the received control signal. The transformer 9 boosts the output pulse whose duty ratio is controlled by the FET 8 to a high voltage AC voltage for lighting the backlight 10, and applies the boosted high voltage AC voltage to the backlight 10 as a backlight driving pulse. Output as.

  The backlight 10 has a cold cathode tube as a light source. In addition, the light source has a reflecting mirror that reflects the light emitted from the light source, and a light guide plate that makes the reflected light a uniform surface light source. Furthermore, it has a reflective film that reflects light from the light guide plate toward the liquid crystal panel 15 and a diffusion film that diffuses light emitted from the light guide plate toward the liquid crystal panel 15.

  The transmittance of each pixel in the liquid crystal panel 15 changes according to the state of each corresponding liquid crystal molecule. For this reason, when the liquid crystal panel 15 is illuminated by the light emitted from the diffusion film of the backlight 10, a bright portion and a dark portion are formed on the screen of the liquid crystal panel 15 due to the difference in transmittance of each pixel. Graphic and character information can be displayed on the screen by such a combination of bright and dark portions.

  The graphic and character information displayed on the screen of the liquid crystal panel 15 is controlled by the video signal processing circuit 11. The video signal processing circuit 11 includes a flash ROM 12, an OSD (On-Screen Display) 13, and a video signal processing unit 14. The OSD 13 generates a composite signal by superimposing graphic and character information displayed on the liquid crystal panel 15 on the video signal under the control of the master microcomputer 2. The graphic and character information superimposed on the video signal includes, for example, the reception frequency of the broadcast station selected by the radio tuner 3 and the content data acquired from the broadcast signal. Further, the OSD 13 reads various information stored in the flash ROM 12, for example, data such as a menu screen (GUI: Graphical User Interface) for the user to operate various settings of the radio receiver 100, and superimposes the data on the video signal. You can also. Furthermore, the OSD 13 also changes and adjusts the background color and the character color such as graphics and character information displayed on the liquid crystal panel 15 according to the control of the master microcomputer 2.

  A signal output from the OSD 13 is input to the video signal processing unit 14. The video signal processing unit 14 performs a drawing process corresponding to the display area of the liquid crystal panel 15 on the composite signal received from the OSD 13 according to the control signal sent from the master microcomputer 2, and displays the processed signal on the liquid crystal panel 15. To do.

  In FIG. 2, the schematic diagram of the radio receiver 100 in this embodiment is shown. The master microcomputer 2, the radio tuner 3, and the antenna circuit 4 of the main body 1 are respectively disposed on the main body substrate 18. The main body substrate 18 is connected to the panel substrate 17 of the panel unit 5 by a connection cable 16. An inverter circuit 6 and a video signal processing circuit 11 are disposed on the panel unit substrate 17. The panel board 17 is connected to the backlight 10 and the liquid crystal panel 15 by another connection cable 16.

  Next, a method for avoiding beat interference of the radio receiver 100 in the present embodiment will be described. FIG. 3 shows a flowchart of processing when the radio receiver 100 receives AM radio broadcast. First, when the user operates the operation unit 16 to select the AM radio broadcast mode and the master microcomputer 2 receives the operation signal, the process proceeds to step S101. In step S <b> 101, the master microcomputer 2 transmits a control signal for reducing the duty ratio of the output pulse output from the controller circuit 7 to the gate of the FET 8 to the controller circuit 7 of the inverter circuit 6. When the duty ratio of the output pulse output to the gate of the FET 8 is reduced by the controller circuit 7 based on the control signal received from the master microcomputer 2, the duty ratio of the backlight drive pulse from the transformer 9 to the backlight 10 is reduced. As a result, harmonic energy generated from the transformer 9 is reduced. Therefore, it is possible to reduce beat disturbance caused by harmonics when receiving the AM radio broadcast by the radio tuner 3 and the antenna circuit 4.

  As the duty ratio of the backlight drive pulse output from the transformer 9 to the backlight 10 decreases, the brightness of the illumination light of the backlight 10 also decreases, and the image displayed on the liquid crystal panel 15 also becomes dark overall. End up. If the display on the liquid crystal panel 15 is left as it is, there is a possibility that the user feels uncomfortable or uncomfortable or misunderstands that a device failure has occurred. In step S103, the video signal processing circuit 11 changes the background color displayed on the liquid crystal panel 15 under the control of the master microcomputer 2. In the present embodiment, as one method for changing the background color, the background color is changed to a background color that is difficult for the user to notice when the display on the liquid crystal panel 15 becomes dark. That is, the brightness of the background color is increased by the amount that the display on the liquid crystal panel 15 becomes dark. For example, the background color is set as the background color after the AM radio broadcast mode is selected by performing correction to approach white on the color palette. Alternatively, a new background color can be set by designating a color completely different from the background color before the AM radio broadcast mode is selected. That is, the hue of the background color is changed. For example, as described above, if the background color displayed on the liquid crystal panel 15 before selecting the AM radio broadcast mode is a gray color, a brown color or a white color is selected as the background color after the AM radio broadcast mode is selected. It can also be specified.

  When changing the background color, a control signal is output from the master microcomputer 2 to the OSD 13. Based on the received control signal, the OSD 13 accesses the flash ROM 12 and reads out color data for changing the current background color before selecting the AM radio broadcast mode to the background color after selecting the AM radio broadcast mode. The OSD 13 performs background image data processing based on the read data, performs RGB color conversion, and sends the result to the video signal processing unit 14. The video signal processing unit 14 processes the received background image data, and displays the changed background image on the liquid crystal panel 15. As described above, the display color of the liquid crystal panel 15 becomes dark by changing the background color so that it is close to the background color before selecting the AM radio broadcast mode or by changing the background color to another background color. And the possibility of giving the user discomfort or the like can be avoided.

  After changing the background color, the process proceeds to step S105, where the radio tuner 3 and the antenna circuit 4 receive and reproduce the AM radio broadcast. As described above, since harmonics generated from the transformer 9 of the inverter circuit 6 are suppressed, good reception and reproduction can be performed without worrying about the influence of beat interference. Subsequently, the process proceeds to step S107, and it is determined whether or not the user has operated the operation unit 16 to perform an operation for switching the type of broadcast to be received, such as FM radio or digital television broadcast. Then, step S107 is repeated until the user performs an operation of switching the broadcast type. When the user switches the broadcast type from the operation unit 16, the process proceeds to step S109. In step S109, it is determined whether another type of broadcast reception is selected from the AM radio broadcast. If the user selects the AM radio broadcast mode again while performing the operation of switching the broadcast type, the process returns to step S107 in order to continue receiving and playing back the AM radio broadcast, and the user performs an operation of switching the broadcast type again. Step S107 is repeated until it is done. If the user selects a type of broadcast other than AM radio broadcast in step S109, the process proceeds to step S111.

  In step S111, since it is not necessary to consider the influence of the harmonics generated from the transformer 9 on the reception of the AM radio broadcast, the controller circuit 7 outputs to the gate of the FET 8 based on the control of the master microcomputer 2. Processing to increase the duty ratio of the pulse and return it to the original value is performed. By increasing the duty ratio, the backlight 10 returns from the dark state. In step S113, the background color displayed on the liquid crystal panel 15 is changed to the original color. Here, when the background color after the AM radio broadcast selection is changed in step S103, when the process of increasing the brightness of the background color is performed, the process of decreasing the brightness of the background color is performed in step S113. As a result, the brightness of the background color does not change greatly when switching from AM radio broadcasting to another broadcasting, and it is possible to prevent the user from feeling uncomfortable or uncomfortable. If the process of changing the hue of the background color is performed in step S103, the background color corresponding to the type of broadcast to be switched is changed in step S113. Thus, since the background color is changed according to the broadcast type every time the broadcast type is switched, the change of the background color does not become unnatural and does not give a sense of incongruity or discomfort. In any of the background color changes, the user can perform an operation without worrying about a background color defect.

  By performing the above processing in the radio receiver 100, even when receiving AM radio broadcasts, it is possible to avoid beat disturbance caused by harmonics generated from the transformer 9 of the inverter circuit 6 and to perform good AM radio broadcasts. While performing reception and reproduction, the display on the liquid crystal panel 15 can be adjusted so as not to give the user a sense of discomfort or discomfort.

  In the above description, it is assumed that the background is other than black. However, if the background is black, the background color display is not affected even if the backlight 10 becomes dark, and it is necessary to change the background color. Absent. Therefore, when black is used as the background color, it is possible to prevent the user from feeling uncomfortable or uncomfortable with the display on the liquid crystal panel 15 by performing a process of making the displayed character color close to white. . In the above description, a cold cathode tube is assumed as the backlight 10, but an LED may be used instead of the cold cathode tube. When the LED is used, the LED driver circuit is used as a dimming circuit to drive the LED, and the LED driver circuit is controlled by the master microcomputer. As in the case of the cold cathode tube, the effect of the present invention can be achieved by reducing the duty ratio of the output from the LED driver circuit.

  Furthermore, in the above description, it is assumed that the background color is changed when the currently executed mode is switched from AM radio broadcast to another broadcast. However, as modes other than AM radio broadcast, CD, DVD, A mode in which processing other than broadcast reception, such as VTR, is also targeted, and the background color may be changed even when the selection is switched from AM radio broadcast reception to these modes.

DESCRIPTION OF SYMBOLS 1 Main-body part 2 Master microcomputer 3 Radio tuner 4 Antenna circuit 5 Panel part 6 Inverter circuit 9 Transformer 10 Backlight 11 Video signal processing circuit 15 Liquid crystal panel

Claims (16)

A liquid crystal panel that displays video based on the video signal, a backlight that illuminates the liquid crystal panel, a dimming circuit that performs dimming control on the backlight, and a video signal processing circuit that outputs the video signal; A method for avoiding beat disturbance in a radio receiver capable of executing a plurality of operation modes including an AM radio broadcast mode,
Detecting a selection of an AM radio broadcast mode;
Changing the duty ratio of the backlight drive pulse output from the dimming circuit to the backlight, and
When the selection of the AM radio broadcast mode is detected, the duty ratio of the backlight drive pulse is changed so that the backlight is darker than before the selection of the AM radio broadcast mode is detected.
A method for avoiding beat disturbance in a radio receiver. A step of changing a background color of the liquid crystal panel by the video signal processing circuit;
When the selection of the AM radio broadcast mode is detected, the background color of the liquid crystal panel is changed.
The method for avoiding beat disturbance in the radio receiver according to claim 1.   3. The method of avoiding beat disturbance in a radio receiver according to claim 2, wherein when the background color of the liquid crystal panel is changed, the brightness of the preset background color is increased.   3. The method of avoiding beat disturbance in a radio receiver according to claim 2, wherein when a background color of the liquid crystal panel is changed, a hue of a background color set in advance is changed. Detecting the selection of a mode other than the AM radio broadcast mode;
When the selection switching from the AM radio broadcast mode to a mode other than the AM radio broadcast mode is detected, the backlight drive pulse is set so that the backlight has the same brightness as that before the selection of the AM radio broadcast mode is detected. Change the duty ratio again,
The method of avoiding beat disturbance in the radio receiver according to any one of claims 2 to 4, characterized in that   The beat interference in the radio receiver according to claim 5, wherein the background color of the liquid crystal panel is changed again when selection switching from an AM radio broadcast mode to a mode other than the AM radio broadcast mode is detected. Workaround method.   7. The method of avoiding beat disturbance in a radio receiver according to claim 6, wherein the brightness of the background color of the liquid crystal panel is lowered when the background color of the liquid crystal panel is changed again.   7. The method of avoiding beat disturbance in a radio receiver according to claim 6, wherein the hue of the background color of the liquid crystal panel is changed when the background color of the liquid crystal panel is changed again. A liquid crystal panel that displays video based on the video signal, a backlight that illuminates the liquid crystal panel, a dimming circuit that performs dimming control on the backlight, and a video signal processing circuit that outputs the video signal; A radio receiver capable of executing a plurality of operation modes including an AM radio broadcast mode,
When the selection of the AM radio broadcast mode is detected, the duty of the backlight drive pulse output from the dimming circuit to the backlight so that the contrast of the liquid crystal panel is lower than before the detection of the AM radio broadcast mode is detected. Change the ratio,
A radio receiver characterized by that.   10. The radio receiver according to claim 9, wherein when a selection of an AM radio broadcast mode is detected, a background color of the liquid crystal panel is further changed.   When the selection switching from the AM radio broadcast mode to a mode other than the AM radio broadcast mode is detected, the backlight drive pulse is set so that the backlight has the same brightness as that before the selection of the AM radio broadcast mode is detected. The radio receiver according to claim 9 or 10, wherein the duty ratio is changed again.   The radio receiver according to claim 11, wherein when a selection switching from an AM radio broadcast mode to a mode other than the AM radio broadcast mode is detected, the background color of the liquid crystal panel is further changed. A liquid crystal panel that displays video based on the video signal, a backlight that illuminates the liquid crystal panel, a dimming circuit that performs dimming control on the backlight, and a video signal processing circuit that outputs the video signal; A program for avoiding beat disturbance in a radio receiver capable of executing a plurality of operation modes including an AM radio broadcast mode,
Detecting a selection of an AM radio broadcast mode;
Changing a duty ratio of a backlight drive pulse output from the dimming circuit to the backlight;
Changing the duty ratio of the backlight drive pulse so that the backlight is darker than before detecting the selection of the AM radio broadcast mode when the selection of the AM radio broadcast mode is detected.
A program characterized by that. A step of changing a background color of the liquid crystal panel by the video signal processing circuit;
When the selection of the AM radio broadcast mode is detected, the background color of the liquid crystal panel is changed.
The program according to claim 13. A step of detecting selection switching to a mode other than the AM radio broadcast mode;
When the selection switching from the AM radio broadcast mode to a mode other than the AM radio broadcast mode is detected, the backlight drive pulse is set so that the backlight has the same brightness as that before the selection of the AM radio broadcast mode is detected. Change the duty ratio again,
The program according to claim 13 or 14, wherein   16. The program according to claim 15, wherein when the selection switching from the AM radio broadcast mode to a mode other than the AM radio broadcast mode is detected, the background color of the liquid crystal panel is changed again.

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