JP2004077585A - Method and device for controlling luminance of backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent flickering of a screen in remote control operation. <P>SOLUTION: A backlight is controlled so as to fix a pulse width of a PWM signal to a last value for a fixed time period after a microcomputer 13 detects an input of a remote control signal. Thereby, even when the remote control signal is made incident on a photosensor 17 to detect ambient illuminance, a detected illuminance value based on the incident remote control signal is neglected for a fixed time period and backlight luminance just before the incidence of the remote control signal is maintained. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for controlling the luminance of a backlight, and is particularly suitable for a method and an apparatus for controlling the luminance of a backlight lamp of a liquid crystal display (LCD) according to the ambient illuminance.
[0002]
[Prior art]
Generally, in the LCD, the visibility (visibility) of display contents changes depending on the brightness of the surroundings. For this reason, in an in-vehicle LCD monitor in which the ambient illuminance frequently changes according to the driving situation, the backlight luminance (LCD luminance) of the LCD is controlled to a predetermined value according to the ambient illuminance in order to improve visibility. That is being done. An automatic light control device is used for the automatic adjustment of the LCD brightness.
[0003]
In this automatic light control device, for example, PWM (Pulse Width Modulation) control is performed so that the LCD brightness is most suitable for a certain ambient illuminance. That is, the pulse width of the PWM signal is determined in real time according to the ambient illuminance, and switching control of the backlight drive unit is performed according to the pulse width. Thus, the LCD brightness is linearly adjusted so that the backlight is dark when the ambient illuminance is low and bright when the ambient illuminance is high.
[0004]
In order to automatically adjust the LCD brightness, it is necessary to detect the ambient illuminance, and a photo sensor is used for that purpose. The photo sensor is installed at a predetermined position on a monitor so that the illuminance around the LCD can be detected more accurately. On the other hand, when an infrared remote controller is used to operate a monitor or a navigation device, an infrared sensor for the remote controller must be provided on the monitor.
[0005]
[Problems to be solved by the invention]
The above-mentioned photo sensor and remote control sensor are often installed close to each other due to the configuration of the monitor. In addition, the photo sensor also responds to infrared rays due to its characteristics. Therefore, when the remote controller is operated, the infrared signal emitted from the remote controller is also incident on the photosensor for illuminance detection, and the automatic light control device erroneously determines that the ambient illuminance has become bright. In this case, there is a problem that the screen flickers because the automatic light control device instantaneously controls the backlight.
[0006]
The present invention has been made to solve such a problem, and an object of the present invention is to prevent a disadvantage that a backlight becomes momentarily bright when a remote controller is operated and a screen flickers.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problem, according to the present invention, when an operation signal is input from a remote controller, control is performed so that the luminance of the backlight is fixed for a certain period after that. For example, control is performed so that the pulse width of the PWM signal used for switching control of the voltage applied to the backlight is fixed. According to the present invention configured as described above, even if an operation signal from the remote control is incident on the photosensor for detecting ambient illuminance, an illuminance detection value based on the incident operation signal is ignored for a certain period, and the operation signal is ignored. The backlight luminance immediately before the light is incident is maintained.
[0008]
In another aspect of the present invention, the backlight is controlled to be fixed for a certain period by using a leader pulse of the operation signal as a trigger. When an infrared signal is used as an operation signal of the remote controller, its leader pulse is standardized regardless of a product or a manufacturer. Therefore, by using the reader pulse as a trigger, the generation of the operation signal can be reliably detected regardless of which remote control is used, and the illuminance detection value based on the operation signal is ignored for a certain period. .
[0009]
In another aspect of the present invention, the brightness of the backlight is controlled by using the calculated values of the latest plural pieces of the illuminance data intermittently detected by the photo sensor. When the brightness of the backlight is fixed by using the leader pulse of the operation signal as a trigger as described above, the time until the leader pulse is determined (the time from when the operation signal starts being input until the leader pulse is determined) is: The dimming control of the backlight is performed based on the operation signal input to the photo sensor. On the other hand, even if the illuminance detection value increases in a short time until the leader pulse is determined by performing dimming control using the calculated values (eg, integral values) of the illuminance data of the past several times, It is averaged with other small illuminance detection values and almost ignored.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration example of a liquid crystal display device to which a backlight luminance control device according to the present invention is applied. As shown in FIG. 1, the liquid crystal display device of the present embodiment includes an LCD panel 11, a backlight power supply circuit 12, a microcomputer 13, a table storage unit 14, AD converters 15 and 16, a photo sensor 17, and a remote control sensor 18. It is configured.
[0011]
The photo sensor 17 detects the illuminance around the liquid crystal display device. The AD converter 15 converts an analog voltage corresponding to the ambient illuminance detected by the photo sensor 17 into digital data. By using the photo sensor 17 and the AD converter 15, digital data corresponding to the ambient illuminance is obtained intermittently (for example, every several msec), and the digital data is sequentially supplied to the microcomputer 13.
[0012]
The remote control sensor 18 receives an infrared operation signal (hereinafter, referred to as a remote control signal) emitted from a remote control (not shown). This remote control signal is composed of a leader pulse having a constant width indicating that the signal is a remote control signal, and a command indicating the operation content following the leader pulse. The AD converter 16 converts the analog voltage of the remote control signal incident on the remote control sensor 18 into digital data, and supplies the result to the microcomputer 13.
[0013]
The microcomputer 13 performs PWM control on the voltage applied to the backlight of the liquid crystal display device according to the data of the ambient illuminance supplied from the AD converter 15. That is, the microcomputer 13 variably controls the pulse width of the PWM signal used for switching control of the voltage applied to the backlight according to the ambient illuminance. This controls the brightness of the backlight.
[0014]
For example, the backlight can be brightened by increasing the duty of the PWM signal to extend the ON period of the switching. In addition, the backlight can be darkened by reducing the duty of the PWM signal to shorten the ON period of the switching.
[0015]
The table storage unit 14 stores table information indicating the relationship between the ambient illuminance and the duty of the PWM signal, and is configured by, for example, an EEPROM. The microcomputer 13 refers to the table storage unit 14 based on the data of the ambient illuminance supplied from the AD converter 15, obtains a duty corresponding to the ambient illuminance, and supplies the duty to the backlight power supply circuit 12.
[0016]
The backlight power supply circuit 12 includes a PWM signal generation unit that generates a PWM signal having a duty transmitted from the microcomputer 13, a switch that is turned on / off based on the PWM signal, and a DC power supply that is chopped by a switch to generate a duty cycle of the PWM signal. A DC-AC converter (a so-called inverter) that generates a rectangular wave signal (AC voltage) having the following, and a transformer that drives the backlight of the LCD panel 11 by boosting the AC voltage output from the DC-AC converter. I have.
[0017]
The microcomputer 13 also controls the liquid crystal display device and a navigation device (not shown) to execute the specified command based on a remote control signal supplied from the AD converter 16. Usually, a remote controller (not shown) is operated toward the remote controller sensor 18, but the remote controller sensor 18 is installed near the photo sensor 17 due to the configuration of the liquid crystal display device. Therefore, the remote control signal is also incident on the photo sensor 17.
[0018]
In the present embodiment, the microcomputer 13 controls the backlight brightness to be fixed for a certain period after a remote control signal is input to the remote control sensor 18 (when the microcomputer 13 detects the input of the remote control signal). I do. Specifically, control is performed so that the pulse width of the PWM signal is fixed for a certain period after detecting the leader pulse of the remote control signal.
[0019]
In the above configuration, the microcomputer 13 forms a control unit of the present invention. Further, the microcomputer 13 and the backlight power supply circuit 12 constitute the light control means of the present invention.
[0020]
FIG. 2 is a diagram schematically illustrating an outline of dimming control according to the present embodiment. As shown in FIG. 2, in this embodiment, when the microcomputer 13 recognizes the leader pulse of the remote control signal when the remote control is operated, the pulse width of the PWM signal is fixed to the immediately preceding value for a certain period after that. Control.
[0021]
The fixed period in which the pulse width is fixed is at least the command period or a period slightly longer than the command period, as shown in FIG. The length of the command depends on the operation. The length of the command may differ between remote control manufacturers. Therefore, it is preferable to set a period slightly longer than the maximum length of each command as the above-mentioned fixed period.
[0022]
In this manner, by controlling the PWM output to be fixed for a certain period of time after the input of the remote control signal, even if the remote control signal is incident on the photosensor 17 for detecting the ambient illuminance, the incident remote control signal is controlled. The illuminance detection value that has increased in response to the signal is ignored for a certain period, and the backlight luminance immediately before the remote control signal is input is maintained. As a result, even when the remote control is operated while the ambient illuminance is low and the backlight is dark, it is possible to avoid a malfunction in which the backlight is instantaneously brightened according to the input of the remote control signal, and the backlight can be prevented from malfunctioning. Flickers can be prevented.
[0023]
Also, since the leader pulse of the remote control signal is used as a trigger, it is possible to prevent flickering of the backlight due to the remote control signal, regardless of which remote control is used. That is, the leader pulse of the remote control signal is standardized and is almost the same regardless of the manufacturer. Therefore, by using the leader pulse as a trigger, the input of the remote control signal can be reliably detected by the microcomputer 13 regardless of the remote control of any manufacturer, and malfunction due to the remote control signal can be eliminated. This is effective in a case where a navigation device, an audio device, or the like is provided as an in-vehicle device, and different remote controllers exist for each of them.
[0024]
In the case where the brightness of the backlight is controlled to be fixed by using the leader pulse of the remote control signal as a trigger as described above, the time required to determine the leader pulse (the time until the microcomputer 13 determines the leader pulse) is equal to the PWM signal. The pulse width is variably controlled (see FIG. 2). Therefore, it is erroneously determined that the ambient illuminance is bright based on the reader pulse input to the photo sensor 17, and the backlight may be instantaneously brightened.
[0025]
Therefore, the dimming control is preferably performed as follows. That is, as shown in FIG. 3, the pulse width of the PWM signal is referred to by referring to the table storage unit 14 using the calculated values of the latest plural pieces of the ambient illuminance data intermittently detected by the photo sensor 17 and the AD converter 15. Is variably controlled. For example, PWM control is performed using an integrated value (average value) of data of past several times including the latest illuminance detection data. In this case, the microcomputer 13 executes an integral operation of the illuminance detection data.
[0026]
In this way, even if the illuminance detection value by the photo sensor 17 increases in a short time until the leader pulse is determined, the illuminance detection value is averaged by several small illuminance detection values before the leader pulse is input, and is almost ignored. Will be done. Therefore, the pulse width of the PWM signal does not greatly change during the period required for determining the leader pulse, and flickering of the backlight due to the leader pulse can be effectively prevented.
[0027]
It should be noted that if the integration period is too long, the follow-up of the dimming control when the ambient illuminance really changes becomes worse. Therefore, it is necessary to set the integration period to an appropriate value. For example, although it depends on the detection time interval of the ambient illuminance, it is preferable to integrate data of the past 10 times including the latest illuminance detection data.
[0028]
FIG. 4 is a flowchart illustrating a backlight dimming control method according to the present embodiment. 4, the photo sensor 17 detects the illuminance around the liquid crystal display device and supplies the analog voltage to the AD converter 15 (step S1). The AD converter 15 converts an analog voltage corresponding to the ambient illuminance detected by the photo sensor 17 into digital data, and supplies the result to the microcomputer 13 (Step S2).
[0029]
The microcomputer 13 calculates an integral value using the latest ambient illuminance detection data supplied from the AD converter 15 and the past several ambient illuminance detection data stored in a register (not shown) or the like (step S3). . Then, the duty of the PWM signal according to the integrated value is determined by referring to the table storage unit 14 based on the integrated value (step S4).
[0030]
Next, the microcomputer 13 determines whether or not the pulse width of the PWM signal is currently fixed (step S5). If it is not during the fixed period of the PWM output, it is further determined whether a leader pulse is detected based on the input from the remote control sensor 18 (step S6). If the leader pulse is not detected, the microcomputer 13 variably controls the pulse width of the PWM signal (step S7). That is, by transmitting the duty determined in step S4 to the backlight power supply circuit 12, a PWM signal having the duty is generated.
[0031]
On the other hand, if it is determined in step S5 that the PWM output is in the fixed period, or if a leader pulse is detected in step S6, the microcomputer 13 fixes the pulse width of the PWM signal for a fixed period. (Step S8). That is, the duty determined in step S4 is ignored, and the duty used before the input of the reader pulse is transmitted to the backlight power supply circuit 12 to generate a PWM signal having the duty.
[0032]
The backlight power supply circuit 12 controls the luminance of the backlight by generating a PWM signal having a duty transmitted from the microcomputer 13 and switchingly supplying a DC voltage based on the PWM signal (step S9). Thereafter, the process returns to step S1, and the same process is repeated.
[0033]
As described in detail above, according to the present embodiment, even when the remote control is operated while the ambient illuminance is low and the backlight is dark, it is possible to prevent flickering of the backlight due to the remote control signal.
[0034]
In the above-described embodiment, an example has been described in which the microcomputer 13 determines the duty of the PWM signal and the backlight power supply circuit 12 generates the PWM signal having the duty. However, the microcomputer 13 performs the processing up to the generation of the PWM signal. You may do it.
[0035]
Further, in the above-described embodiment, an example in which the backlight luminance is controlled in multiple stages by PWM control has been described. However, the present invention is similarly applied to the case where the backlight dimming control is performed in two stages of only bright or dark. It is possible to do. In this case, complicated control such as PWM control is unnecessary.
[0036]
In addition, the above-described embodiment is merely an example of the embodiment of the present invention, and the technical scope of the present invention should not be interpreted in a limited manner. That is, the present invention can be embodied in various forms without departing from the spirit or main features thereof.
[0037]
【The invention's effect】
As described above, according to the present invention, the control is performed so that the brightness of the backlight is fixed for a certain period after the operation signal of the remote control is input. Even when the operation signal is incident on the sensor, the backlight luminance can be maintained at the level immediately before the operation signal is incident, and flickering of the backlight due to the input of the operation signal can be prevented.
[0038]
According to another feature of the present invention, the brightness of the backlight is controlled to be fixed by using the leader pulse of the operation signal as a trigger, so that the input of the operation signal can be reliably captured regardless of which remote control is used. To prevent flickering of the backlight.
[0039]
According to another feature of the present invention, the brightness of the backlight is controlled using the calculated values of the latest plurality of illuminance data intermittently detected by the photo sensor, so that until the leader pulse is determined. The large ambient illuminance detected at the time can be ignored, and the flicker of the backlight due to the reader pulse can be effectively prevented.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration example of a liquid crystal display device to which a backlight luminance control device according to the present invention is applied.
FIG. 2 is a diagram schematically illustrating an outline of dimming control according to the present embodiment.
FIG. 3 is a diagram schematically illustrating an outline of dimming control using an integrated value according to the present embodiment.
FIG. 4 is a flowchart illustrating a backlight dimming control method according to the embodiment.
[Explanation of symbols]
Reference Signs List 11 LCD panel 12 Backlight power supply circuit 13 Microcomputer 14 Table storage unit 15, 16 AD converter 17 Photo sensor 18 Remote control sensor

Claims (7)

A backlight brightness control method of detecting the ambient illuminance of the liquid crystal display device with a photo sensor and controlling the brightness of the backlight of the liquid crystal display device according to the detected ambient illuminance,
A backlight brightness control method, characterized in that when an operation signal is input from a remote controller, control is performed such that the brightness of the backlight is fixed for a certain period after that. Controlling the brightness of the backlight by performing PWM control on the driving of the backlight;
2. The backlight brightness control method according to claim 1, wherein when an operation signal is input from the remote controller, control is performed such that a pulse width of the PWM signal is fixed for a certain period after that. The backlight brightness control method according to claim 1, wherein the control is performed such that the brightness of the backlight is fixed for a certain period of time by using a leader pulse of the operation signal as a trigger. 4. The backlight brightness control according to claim 3, wherein the brightness of the backlight is controlled by using the calculated values of the latest plurality of illuminance data intermittently detected by the photo sensor. Method. A photo sensor for detecting the illuminance around the liquid crystal display device;
Dimming means for controlling the brightness of the backlight of the liquid crystal display device according to the ambient illuminance detected by the photo sensor;
Control means for controlling the dimming means so as to keep the brightness of the backlight fixed for a certain period of time when an operation signal is input from a remote control; Control device. 6. The backlight brightness control device according to claim 5, wherein the control means controls the brightness of the backlight to be fixed for a certain period by using a leader pulse of the operation signal as a trigger. The dimming unit includes an arithmetic unit that calculates an integral value for the latest plurality of illuminance data intermittently detected by the photosensor, and controls the luminance of the backlight using the integral value. The backlight brightness control device according to claim 6, characterized in that:

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