JPH04138417A - Back light dimmer - Google Patents

Abstract

PURPOSE:To fix the position of a lateral stripe noise which emits light at the time of dimming, to eliminate the reduction in absolute brightness, and to improve picture quality by synchronizing the phase of a dimmer signal, which performs ON/OFF control over the oscillation voltage of a light emission driving circuit, with the vertical synchronizing signal of a liquid crystal panel driving signal. CONSTITUTION:This device is equipped with a lamp 1 as a lighting device provided on the back surface of a translucent type liquid crystal panel so that an image on the translucent type liquid crystal panel can be viewed by transmission and a lamp driving circuit 2 which drives the lamp 1. Further, the device is equipped with a dimmer signal generating circuit 3 which performs the ON/OFF control over the oscillation output of the lamp driving circuit 2 at certain time intervals and varies the ratio of an oscillation time and a stop time to control the brightness of the lamp 1, and a switch SW. Then the dimmer signal generating circuit 3 inputs the vertical synchronizing signal VD of the 1 liquid crystal panel driving circuit and a DC control signal C/L and outputs the dimmer signal which is in phase with the vertical synchronizing signal VD and has its duty ratio controlled with the DC control signal C/L. Consequently, the disturbance to the liquid crystal panel due to the approach of the lamp itself to the liquid crystal panel is reduced without any decrease in lamp absolute brightness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a backlight dimming device for a liquid crystal display device.

(Prior art) Conventionally, the brightness adjustment of fluorescent tube lighting equipment was performed using fluorescent tubes (hereinafter referred to as
The light is dimmed by changing the drive voltage applied to the lamp (referred to as a lamp) or by intermittent operation of the oscillation time of the drive voltage.

In general, the latter h'' method is used.The oscillation frequency of the dimming signal and drive voltage that performs this dimming is - For boat fishing, the frequency and phase are uncorrelated with the drive frequency of the liquid crystal panel. In particular, during dimming, the disturbance of horizontal striped noise that moves upward or downward on the LCD panel display image becomes noticeable.This horizontal striped noise on the LCD panel display image due to lamp drive is caused by the video signal drive frequency. It is thought that the components of the lamp driving frequency or dimming signal cross 1 within the panel and appear as moving horizontal striped noise on the display screen.

Fig. 4 shows an example of the above-mentioned horizontal stripe noise. When the drive signal to the liquid crystal panel is interfered with by the lamp drive waveform,
As shown in the figure, bright and dark stripes flow across the panel surface.

To reduce this noise, countermeasures will vary depending on which part of the lighting device the noise is interfering with the LCD panel display screen, but the oscillation transformer of the lamp drive circuit crosses into the path of the panel drive signal. There are two possible cases: a case in which the lamp itself causes interference, and a case in which the lamp itself closest to the liquid crystal panel has an effect on the panel.

In the former case, in the case of a set, measures such as shielding the oscillation transformer or moving it away from the liquid crystal panel can be considered. However, in the latter case, it is extremely difficult to countermeasures against interference to the LCD panel caused by the lamp itself (including the reflector and diffuser) coming close to the LCD panel, and currently, the oscillation frequency of the lamp drive circuit is Possible measures include setting an oscillation frequency that has less influence, lowering the lamp drive output voltage, and increasing the distance between the lamp and the liquid crystal panel.

However, there is a limit to setting an oscillation frequency that has little influence, considering temperature drift and the like.

Furthermore, it is very difficult to take measures against harmonics generated by intermittent oscillation during dimming. lowering the lamp drive output voltage,
Increasing the distance between the lamp and the liquid crystal panel is not a preferable direction since either method will reduce the absolute brightness on the surface of the liquid crystal panel.

(Problem to be Solved by the Invention) If the lamp itself has an adverse effect on the liquid crystal panel due to its proximity to the liquid crystal panel as described above, conventionally, a net-like metal shield is sandwiched between the lamp and the liquid crystal panel. This reduces the influence of power lines (stray capacity) emitted from the However, although this method can reduce the effect on the LCD panel, the absolute lamp brightness decreases (
Lamp current leaks into the metal shield, reducing absolute brightness to 15-20
% decrease), which is still not a satisfactory measure.

The present invention has been made in order to eliminate such conventional drawbacks, and it is a backlight adjustment that can reduce the disturbance to the liquid crystal panel caused by the lamp itself approaching the liquid crystal panel without reducing the absolute lamp brightness. The purpose is to provide an optical device.

[Structure of the Invention] (Means for Solving the Problems) The present invention that achieves the above object includes a lighting device provided on the back side of a transmissive liquid crystal panel so that an image of the liquid crystal panel can be seen through the transparent panel, and the lighting device. A drive circuit that causes the device to emit light; and a control circuit that outputs a dimming signal that controls the brightness of the lighting device by turning on and off the oscillation output of the drive circuit at certain time intervals and changing the ratio of the oscillation time to the stop time. In the backlight dimming device equipped with an optical signal generation circuit, the dimming signal generation circuit inputs a vertical synchronization signal of a liquid crystal panel drive signal and a DC control signal, and is synchronized in phase with the vertical synchronization signal and It is characterized by outputting a dimming signal whose duty ratio is controlled by a DC control signal.

(Function) In the present invention, by controlling the light emission drive circuit using a dimming signal whose phase is synchronized with the vertical synchronization signal, the phase of the oscillation output of the light emission drive circuit matches the vertical synchronization signal, and as a result, the liquid crystal display The position of horizontal striped noise appearing on the panel is fixed at the same position, reducing interference with the liquid crystal panel and improving image quality.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a backlight dimming device according to an embodiment of the present invention. This backlight dimming device includes a lamp 1 as an illumination device installed on the back of a liquid crystal panel so that an image on a transmissive liquid crystal panel can be seen through the image, a lamp drive circuit 2 that causes the lamp 1 to emit light, and a lamp drive circuit. The lamp 1 is composed of a dimming signal generating circuit 3 that controls the brightness of the lamp 1 by controlling the oscillation output of the lamp 2 on and off at certain time intervals and changing the ratio between the oscillation time and the stop time, and a switch Sv.

The power source B of the lamp drive circuit 2 is connected via a switch S11. This switch Sy has a vertical synchronizing signal VD separated from the video signal and a DC control signal C/l as inputs.
It is controlled by the output of the dimming signal generation circuit 3 having inputs of .

The dimming signal generation circuit 3 converts the internal oscillation into a vertical synchronization signal V
It has a pulse output (FIG. 2(b)) which is reset (phase synchronizes the dimming signal) at D, and the duty of the dimming signal (T) is reset by the DC control signal C/L.

FF) is controlled and output.

The output oscillation waveform of the lamp drive circuit 2 controlled by this switch Sv is reset when the vertical synchronization signal VD is input to the dimming signal generation circuit 3, and its phase is the same as the vertical synchronization signal VD separated from the video signal. Match.

Figure 2 shows the situation. Here, (a) shows the vertical synchronization signal VD, (b) shows the dimming signal generation circuit output, and (e) shows the lamp drive oscillation output waveform (the dimming signal period of the dimming signal generation circuit 3 is [10IIz). . In the case of the example shown in FIG. 2, the frequency of the output oscillation waveform of the lamp drive circuit 2 is approximately 30
kllz, and the period of the vertical synchronization signal VD (60Hz)
controls the oscillation time of the lamp drive circuit 2. Interference from the lamp system occurs when harmonics of the dimming signal (6Hz) interfere with the horizontal frequency of the panel drive signal. Since both the optical signal frequency and the frequency of the panel drive signal are phase-synchronized, the position of horizontal striped noise appearing on the panel is always fixed at the same position based on the vertical synchronization signal VD.

The oscillation frequency of the lamp drive circuit 2 is usually 30 to 50 kl.
Since it is a self-excited chromatic oscillation of lz, it is difficult to control the oscillation frequency by separate excitation, but with the above configuration, it can be easily controlled.

Further, the dimming signal frequency during dimming is not limited to the above-mentioned 6011Z, but can be set within a range where the lamp 1 can be driven. In the experiment of the present invention, the dimming signal frequency (
Even if the internal oscillation of the dimming signal generation circuit 3 was changed to about 50 oscillations, the same effect as above was obtained, although the number of interference stripes increased.

[Effects of the Invention] As explained above, according to the bank light dimmer of the present invention, the dimmer No. 16 "Part 1" for controlling the oscillation voltage of the light emitting drive circuit on and off is controlled by the IT & product panel drive signal. By performing phase synchronization using a vertical synchronization signal, the position of horizontal striped noise that occurs during dimming is fixed, and image quality is improved without reducing absolute brightness.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram of a backlight dimming device according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram illustrating an example of the operation of the backlight dimming device shown in FIG. 1, and FIG. 3 4 is a signal waveform diagram illustrating another example of the operation of the backlight dimming device, and FIG. 4 is an explanatory diagram illustrating an example of conventional horizontal stripe noise. 1...Lamp 1.2...Lamp drive circuit 2.3...
・Dimmer signal generation circuit 3, SW...switch, VD...
・Vertical synchronization signal, C/1. ...DC control signal. Applicant: Toshiba Corporation

Claims (1)

[Claims] An illumination device is provided on the back of the transmissive liquid crystal panel so that the image of the transmissive liquid crystal panel can be seen through the LCD panel, a light emission drive circuit causes the illumination device to emit light, and an oscillation output of the light emission drive circuit is turned on and off at certain time intervals. A backlight dimming device comprising: a dimming signal generation circuit that outputs a dimming signal that controls the brightness of the lighting device by turning off and changing a ratio between an oscillation time and a stop time; is characterized in that it receives a vertical synchronization signal of a liquid crystal panel drive signal and a DC control signal as input, and outputs a dimming signal whose phase is synchronized with the vertical synchronization signal and whose duty ratio is controlled by the DC control signal. Backlight dimmer.