JP2004252127A - Liquid crystal display device and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which has superior moving picture characteristics and higher luminance by improving the screen luminance when blinking of a linear lamp is used and deterring blurring when a moving picture is displayed. <P>SOLUTION: Although a tube current I<SB>L1</SB>controlled into a control waveform INV of an inverter supplied in synchronism with frame cycles according to a blinking signal is cut off before as shown by I<SB>L2</SB>, 30 to 60% of a current in an ON period is supplied even in an OFF period to continue discharge. The ON/OFF tube current ratio is set to 30 to 50% for driving. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to a backlight type liquid crystal display device in which an illumination light source is provided on the back of a liquid crystal display panel, and a driving method thereof.
[0002]
[Prior art]
2. Description of the Related Art Liquid crystal display devices are widely used as high-definition color monitors for computers and other information devices, or as display devices for television receivers. A liquid crystal display device basically has a so-called liquid crystal display panel in which a liquid crystal layer is sandwiched between two (a pair of) substrates made of transparent glass or the like, at least one of which is formed on a substrate of the liquid crystal display panel. A method of selectively applying a voltage to the various electrodes for forming a pixel to turn on and off a predetermined pixel, forming the various electrodes and an active element for pixel selection, and selecting the active element to form a predetermined pixel. Are turned on and off.
[0003]
In particular, the latter type of liquid crystal display device is called an active matrix type, and has become the mainstream of the liquid crystal display device because of its contrast performance, high-speed display performance, and the like. An active matrix type liquid crystal display device is a so-called vertical electric field in which an electric field for changing the orientation direction of liquid crystal molecules constituting a liquid crystal layer is applied between an electrode formed on one substrate and an electrode formed on the other substrate. There is known a liquid crystal display device of a so-called lateral electric field system (also referred to as an IPS system) in which a direction of an electric field applied to a liquid crystal layer is set to a direction substantially parallel to a substrate surface.
[0004]
The above-described various liquid crystal display devices include a light source device (generally referred to as a backlight) for illuminating the liquid crystal display panel from the back. The backlight has a side edge type in which a light source (a linear light source such as a cold cathode fluorescent lamp, or a light emitting diode or a diode array, hereinafter referred to as a linear lamp) is provided on a side surface of a light guide plate made of a transparent material, and a liquid crystal. There is known a so-called direct type in which a light source is installed directly below a panel main surface.
[0005]
The liquid crystal display device having such a configuration is being replaced by a cathode ray tube (cathode ray tube: CRT) display due to features such as thinness and low power consumption. Behind this replacement is technological innovation for improving the image quality of liquid crystal display devices. In particular, there has recently been a strong demand for displaying moving images represented by television images, and improvements have been made by liquid crystal materials and driving methods.
[0006]
However, while a CRT is an impulse light emission of a phosphor by scanning of an electron gun, a liquid crystal display device is a hold type light emission using a backlight system using a linear lamp as an illumination light source. Has been difficult. That is, when a moving image is displayed on a display device using a liquid crystal display panel, so-called moving image contour deterioration occurs due to the hold characteristic, and image quality deteriorates. It should be noted that such moving image contour deterioration occurs not only in a display device using a liquid crystal display panel, but also in other types of display devices having a hold characteristic.
[0007]
FIG. 11 is a schematic diagram illustrating a mechanism of occurrence of moving image contour deterioration when a moving image is displayed on a display device having a hold characteristic. Here, a display device using a liquid crystal display panel will be described as an example. 11A shows a case where a black display moving in the direction of arrow A is displayed on a part of the background screen of the liquid crystal display panel LCD, and FIG. 11B shows an enlarged view of the black / white boundary portion. (C) is an explanatory view of the cause of the occurrence of the moving image contour deterioration, and (d) is an enlarged view similar to (b) showing the moving image contour deterioration state. In the figure, a unit square indicates a pixel. In the drawings, the degradation of the outline of a moving image is described as “blurring” or “motion picture blurring”.
[0008]
As shown in (c) in which one line of the black / white boundary portion of FIG. 11 (b) is displayed in chronological order, as the displayed image moves in the direction of arrow A, the line of sight is obliquely lower right in the figure. Move as indicated by the arrow B drawn in. The luminance of the pixels displayed during the movement of the display of one frame is held. Since the luminance is obtained by integrating the luminance of the pixel, the contour degradation of the moving image as shown in FIG.
[0009]
In a liquid crystal display device, a so-called "hold type" display in which an image is displayed during one frame period is performed. On the other hand, a CRT displays an image for a moment and is black in the remaining period, that is, a so-called "impulse". The "type" is displayed. The cause of a blurred image when a moving image is displayed on a liquid crystal display device is strongly affected by this. If an impulse-type display can be performed, the moving image can be displayed finely on the liquid crystal display device without blurring.
[0010]
As a method for overcoming this problem, there have been reported a method of improving a liquid crystal material or a display mode constituting a liquid crystal layer of a liquid crystal display panel and a method of using a direct type backlight as a light source. In the case of using a direct-type backlight, a plurality of linear lamps (such as cold cathode fluorescent lamps) are arranged in a direction parallel to the gate line just below (the back surface) of the main surface of the liquid crystal display panel. This is an illumination method called backlight blinking that shifts the timing of the lighting start time from the top to the bottom of the display screen and synchronizes with the scanning cycle of the image display signal (see Patent Document 1).
[0011]
In the conventional blinking for controlling the lighting time of the light source, the D / D converter for driving the linear lamp is configured to directly turn on / off the input voltage of the linear lamp by a blinking signal. When the lamp is off, it is completely turned off. In addition, other techniques for improving the moving image of the liquid crystal display device include, for example, “Patent Document 2”, “Patent Document 3”, “Patent Document 4”, and “Patent Document 5”. Also, a liquid crystal display device provided with a light source device adopting a so-called burst drive (Burst Operation) for stopping a voltage pulse supplied to the drive circuit of the linear lamp for each frame period for a certain period is disclosed in Japanese Patent Application Laid-Open No. H10-163,086. And "Patent Document 7".
[0012]
[Patent Document 1] JP-A-11-109921
[Patent Document 2] Japanese Patent Publication No. 08-500915
[Patent Document 3] JP-A-11-202285
[Patent Document 4] JP-A-11-202286
[Patent Document 5] JP-A-11-237606
[Patent Document 6] JP-A-11-299254
[Patent Document 7] JP-A-2000-78857
[0013]
[Problems to be solved by the invention]
By adopting the above-described lamp driving method, it is possible to avoid the occurrence of a certain degree of moving image contour deterioration and improve the moving image display characteristics. However, the backlight blinking in the above-described conventional technique is to blink (turn on / off) a linear lamp, which is a light source, in synchronization with a frame period, and the linear lamp is completely turned off in an off state. (Discharge has stopped). Therefore, the luminance of the display screen is reduced by the period of turning off, and the linear lamp starts the next discharge from the state in which the discharge is stopped, so that the decrease in luminous efficiency is reduced and the delay in the rise of light emission is delayed. Therefore, it is difficult to secure sufficient luminance of the screen together with the existence of the light-off state.
[0014]
An object of the present invention is to improve screen brightness when using blinking of a linear lamp, suppress blurring when displaying a moving image, and provide a liquid crystal display device with excellent moving image display characteristics and high luminance, and a driving method thereof. Is to provide.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method of turning on / off a light source in synchronization with a frame period, by setting a lamp current of an off-line lamp to a value smaller than that of an on-line lamp without completely turning off the lamp. Lighting at a luminance lower than the luminance in the ON state is continued. In addition, a driving method was adopted in which the on / off duty was set to 30% to 60%, and the tube current ratio in the off state was set to 30% to 50% in the on state. The term “off” in the present invention means that the linear lamp is lit while the discharge of the linear lamp continues but the tube current is smaller than that when the lamp is on. In the following examples, the above-mentioned “at the time of off” of the present invention is also referred to as “brightness reduction lighting”.
[0016]
This makes it possible to provide a difference between the on-state luminance and the off-state luminance. With this configuration, the same blinking effect as that of the related art can be obtained, and the discharge of the linear lamp is continuously illuminated at a low luminance even when the liquid crystal display is turned off. Is suppressed.
[0017]
The configuration of the liquid crystal display device of the present invention for realizing the above driving method is as follows. That is, a liquid crystal display panel, comprising a lighting device having a linear lamp installed on the back of the liquid crystal display panel, and a brightness control circuit for controlling the brightness of the lighting device,
A D / D converter for supplying a lighting voltage to the linear lamp, a transformer having an output of the D / D converter connected to a primary side and a secondary side connected to the linear lamp, and detecting tube current information. A tube current detector, a switch circuit for generating blinking drive information with reference to a blinking signal and a linear lamp state signal (ON state and OFF state), and blinking drive information output from the switch circuit And a brightness control circuit including a calculation circuit that calculates tube current information detected by the tube current detector to generate a brightness modulation command signal and controls a light source brightness modulation output of the D / D converter,
The tube current of the linear lamp is controlled by supplying the light source luminance modulation output of the D / D converter to the primary side of the transformer.
[0018]
The switch circuit includes a first integrated circuit that generates a blinking current based on an externally input blinking signal, and a transistor circuit that generates blinking drive information from the blinking current output from the first integrated circuit. And a second integrated circuit that generates a luminance modulation command signal based on blinking drive information output from the transistor circuit.
[0019]
Also provided is to adjust a transmission condition of the blinking drive information from the transistor circuit to the first integrated circuit to change a light source luminance modulation output of the D / D converter based on the luminance modulation command signal. The resistance was made variable.
[0020]
The tube current detector detects the tube current of the linear lamp by being connected in series with the linear lamp on the secondary side of the transformer or connected in series with the primary side of the transformer.
[0021]
According to the configuration of the present invention, it is possible to provide a difference between the luminance when the linear lamp is turned on and the luminance when the linear lamp is turned off. Since the illumination is performed at a low luminance, it is possible to obtain a liquid crystal display device in which blurring of a moving image is improved by suppressing a decrease in luminance due to blinking.
[0022]
It should be noted that the present invention is not limited to the above configuration and the configuration of the embodiment described later, and it is needless to say that various changes can be made without departing from the technical idea of the present invention.
[0023]
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram for explaining a control circuit of a linear lamp for explaining a first embodiment of the liquid crystal display device of the present invention. In the figure, reference numeral CFL denotes a cold cathode fluorescent lamp as a linear lamp, DDC denotes a DC (direct current) -DC (direct current) converter (hereinafter referred to as D / D converter), INV denotes an inverter, and SSR denotes a tube current detector. , BCT are luminance control circuits. The D / D converter is a dimming circuit that adjusts the brightness of the cold cathode fluorescent lamp CFL, and details thereof will be described later. The inverter INV has a transformer TR whose primary side is connected to the D / D converter DDC and whose secondary side is connected to the high voltage side (Hot Side) of the cold cathode fluorescent lamp CFL. Although not shown in FIG. 1, a power supply current is supplied to the D / D converter DDC from a circuit serving as a power supply input unit. The D / D converter adjusts this power supply current and supplies it to the transformer TR.
[0024]
When the burst driving of the linear lamp discussed in the above-mentioned Patent Documents 6 and 7 is applied to the liquid crystal display device of the present embodiment, a burst signal (Burst Signal) is input to a power input unit, and this is input to the power supply input unit. In response, the power supply current intermittently output from the power supply input unit is supplied to the D / D converter. The D / D converter adjusts the power supply current intermittently input from the power supply input unit to adjust the value of the current output to the transformer TR. One of the driving methods of the liquid crystal display device according to the present invention is in the form of adjusting the output current of the D / D converter as described later. In the step of intermittently outputting a current from the D / D converter to the transformer TR, the timing is controlled by the power input unit, and the amount of the current is controlled by the D / D converter.
[0025]
In the liquid crystal display device by the burst drive, it is described that the power supply current is output “intermittently” from the power supply input section, but the power supply input section outputs the power supply current in accordance with the burst signal as described later. It does not always turn off completely, and sometimes outputs a weak current such as a dark current during the turn-off period of the power supply current output. In any case, the current output from the D / D converter to the transformer TR is modulated according to the burst signal. The brightness of the cold cathode fluorescent lamp CFL increases in a certain period within one frame period (lighting state) in response to the fluctuation of the current output from the D / D converter to the transformer TR, and in the remaining period. (The so-called light-off state).
[0026]
On the other hand, the brightness control circuit BCT includes a switch circuit SC and an arithmetic circuit LS. In addition to the light source device employing the burst drive, a liquid crystal display device having a light source device in which the luminance of the linear lamp is modulated for each frame period (a liquid crystal display device driven by blinking) includes a D / D converter. The brightness of the linear lamp is modulated according to the intermittently output current. In the liquid crystal display device of the present embodiment, the current output from the D / D converter is transmitted not only to the primary side of the transformer TR but also to the switch circuit SC of the brightness control circuit BCT. _ON (A signal for increasing the brightness of the cold cathode fluorescent lamp CFL) and a dark state signal D _OF (Signal for lowering the luminance of the cold cathode fluorescent lamp CFL) is input to the switch circuit SC of the luminance control circuit BCT.
[0027]
Bright state signal D alternately input to switch circuit SC _ON And dark state signal D _OF Means the timing of the luminance modulation of the cold cathode fluorescent lamp CFL as described above. The timing of the luminance modulation is one frame period, in which the cold cathode fluorescent lamp CFL is in a dark state (also called a turn-off period or “off time” for convenience) and in a bright state (for convenience). Turn-on period or "on-time"). The ratio of the period during which the cold-cathode fluorescent lamp CFL is in the bright state in one frame period (the so-called “on-time ratio”) is, for example, the bright state signal D to the brightness control circuit BCT for one frame period. _ON Of the input period (hereinafter referred to simply as “duty”), which will be described later.
[0028]
The switch circuit SC supplies a current (hereinafter, tube current) flowing from the high voltage side to the low voltage side (Cold Side) of the cold cathode fluorescent lamp CFL in the dark state, and the cold cathode fluorescent lamp CFL in the bright state. A blinking signal BK that is determined based on a certain time is also input. The blinking signal BK indicates a tube current corresponding to the dark state of the cold cathode fluorescent lamp CFL (also referred to as a turn-off period or “off” for convenience), for example, the bright state of the cold cathode fluorescent lamp CFL (for convenience). (Also referred to as turn-on period or "on-time"). As a result, the switch circuit SC outputs a signal obtained by multiplying the luminance modulation timing of the cold cathode fluorescent lamp CFL by the luminance ratio according to the blinking signal BK, and outputs the signal to the arithmetic circuit provided in the luminance control circuit BCT. Transmit to LS.
[0029]
The current (hereinafter, tube current) generated between the electrodes (between the high voltage side and the low voltage side) of the cold cathode fluorescent lamp CFL in accordance with the output current from the D / D converter is also calculated through the tube current detector SSR. LS. The cold cathode fluorescent lamp CFL also functions as a capacitive element in a secondary circuit (high voltage side) of the transformer TR. The change in the capacitance generated between the electrodes of the cold cathode fluorescent lamp CFL reflects the lighting state of the cold cathode fluorescent lamp CFL (including the above-mentioned off state) and the value of the tube current actually generated in the cold cathode fluorescent lamp CFL. Decide. Therefore, the tube current sent from the tube current detector SSR to the arithmetic circuit LS reflects the lighting state (lighting luminance) of the cold cathode fluorescent lamp CFL.
[0030]
The arithmetic circuit LS generates a luminance modulation command signal BMC with reference to the output from the switch circuit SC and the tube current from the tube current detector SSR, and transmits this to the D / D converter. In other words, the brightness control circuit BCT according to the present invention provides the current output timing from the D / D converter (the bright state signal D in each frame period). _ON Period and dark state signal D _OF The lighting information of the cold-cathode fluorescent lamp CFL is fed back to the distribution of the period and the current ratio in accordance therewith to generate a luminance modulation command signal BMC, which is input to the D / D converter. As a result, the cold cathode fluorescent lamp CFL emits light at a luminance corresponding to each of the above-described ON state (the above-described period of the bright state) and the OFF state (the above-described period of the dark state) for each frame period. .
[0031]
The luminance modulation command signal BMC output from the luminance control circuit BCT is supplied to the D / D converter DDC, and the driving voltage V _in To control the current flowing to the primary side of the transformer TR of the inverter INV. At this time, when the driving condition of the cold cathode fluorescent lamp CFL is the brightness lowering lighting state, the D / D converter DDC sets the tube current of the cold cathode fluorescent lamp CFL in the off state to a value smaller than that in the on state and does not completely turn off the lamp.
[0032]
The tube current at the time of off and the duty at the time of on are 30% to 60%, and the tube current at the time of off is 30% to 50% at the time of on. By setting it to 50% of the time, the object of the present invention is achieved.
[0033]
According to the present embodiment, it is possible to provide a difference between the luminance when the cold cathode fluorescent lamp CFL is turned on and the luminance when the cold cathode fluorescent lamp CFL is turned off. However, since illumination at a low luminance is continuously performed, a decrease in luminance due to blinking is suppressed, and a liquid crystal display device with improved moving image blur can be obtained.
[0034]
FIG. 2 is a block diagram for explaining a control circuit of a linear lamp for explaining a second embodiment of the liquid crystal display device of the present invention. In the figure, the same reference numerals as those in FIG. 1 correspond to the same functional parts. In the first embodiment described above, the tube current detector SSR is connected in series with the cold cathode fluorescent lamp CFL on the secondary side of the transformer TR of the inverter INV, but in this embodiment, the tube current detector SSR is connected in series with the primary side of the transformer TR. The configuration is the same as that of the first embodiment except that the configuration detects the tube current of the cold cathode fluorescent lamp CFL.
[0035]
Also in this embodiment, the driving condition signal (lighting state signal D) of the cold cathode fluorescent lamp CFL corresponding to the blinking signal BK _ON And brightness reduction lighting state signal D _OF ) And the tube current detected by the tube current detector SSR are calculated by an arithmetic circuit LS to generate a luminance modulation command signal BMC.
[0036]
The luminance modulation command signal BMC output from the luminance control circuit BCT is supplied to the D / D converter DDC, and the driving voltage V _in To control the current flowing to the primary side of the transformer TR of the inverter INV. At this time, when the driving condition of the cold cathode fluorescent lamp CFL is the brightness lowering lighting state, the D / D converter DDC sets the tube current of the cold cathode fluorescent lamp CFL in the off state to a value smaller than that in the on state and does not completely turn off the lamp.
[0037]
Similarly to the first embodiment, in this embodiment, the tube current at the time of OFF and the duty at the time of ON are set to 30% to 60%, and the tube current at the time of OFF is set to 30% to 50% of the ON time. The object of the present invention is achieved by setting the duty to 50% and the tube current when off to 50% when on.
[0038]
According to the present embodiment, it is possible to provide a difference between the luminance when the cold cathode fluorescent lamp CFL is turned on and the luminance when the cold cathode fluorescent lamp CFL is turned off. Since illumination with low luminance is continuously performed, a decrease in luminance due to blinking is suppressed, and a liquid crystal display device with improved moving image blur can be obtained.
[0039]
FIG. 3 is a driving waveform diagram of the cold cathode fluorescent lamp for explaining the tube current waveform in the embodiment of the present invention in comparison with the tube current waveform obtained by the conventional blinking control. In the figure, INV is a control waveform of the inverter INV, _L1 Is the waveform of the tube current in the embodiment of the present invention; _L2 Shows a conventional tube current waveform. The inverter is controlled like the waveform INV based on the blinking signal. By controlling the inverter, the driving of the conventional cold-cathode fluorescent lamp is controlled by the waveform I. _L2 As shown in (1), no tube current flows during the off period (at the time of off) within one frame, and the discharge stops (I _L2OF = 0).
[0040]
In contrast, in the embodiment of the present invention, the tube current I _L1OF As shown by, the tube current of 30% to 60% of the ON period (at the time of ON) flows, and the discharge continues. Although the on / off duty in one frame period is shown as 50% in FIG. 3, the object of the present invention can be achieved by adjusting this duty in the range of 30% to 60%.
[0041]
FIG. 4 is a luminance response waveform diagram of the cold cathode fluorescent lamp for explaining the luminance response in the embodiment of the present invention in comparison with the luminance response by the conventional blinking control. In the drawing, INV indicates a control waveform of the inverter INV, BL1 indicates a luminance response waveform of the cold cathode fluorescent lamp in the embodiment of the present invention, and BL2 indicates a luminance response waveform of the conventional cold cathode fluorescent lamp. In the conventional driving method, since the discharge of the cold cathode fluorescent lamp is stopped during the off period, it takes time to start the discharge during the on period, and a delay occurs until a predetermined luminance is reached.
[0042]
That is, as shown by the waveforms BL1 and BL2 in FIG. 4, the time at which the luminance reaches 90% from the time T at which the off period is switched to the on period is t1 in the control of the present invention, and t2 in the conventional control. <T2. That is, it can be seen that the luminance according to the control of the present invention is higher than the luminance according to the conventional control, as indicated by the area of the luminance response waveform in FIG.
[0043]
Next, the effect of improving moving image blur according to the present invention will be described with reference to FIGS. FIG. 5 is a state diagram of moving image blur (outline blur) when a black vertical line displayed on the screen is moved in the scanning line direction by the driving method of the present invention. FIG. 6 is a diagram of the vertical line shown in FIG. FIG. 4 is an explanatory diagram of a luminance profile. FIG. 7 is a state diagram of moving image blur when a vertical line displayed on the screen is moved in the scanning line direction by the conventional blinking driving method, and FIG. 8 is a diagram showing the luminance profile of the vertical line shown in FIG. FIG.
[0044]
5 and 7, reference numeral ED is a vertical line main body portion, B1 is a rear edge blur of the vertical line moving direction S, B2 is a front edge blur of the vertical line moving direction S, WB1 is a rear edge blur width, WB2 indicates a front edge blur width. Also, the horizontal axis of the luminance profile shown in FIGS. 6 and 8 is the distance in which the scanning direction on the screen is represented by the number of pixels, and the vertical axis is the luminance (unit: cd / m). ³ , Cd: candela), and WB1 and WB2 indicate the widths of the rear edge blur B1 and the front edge blur B2 in FIGS. The width of the rear edge blur B1 and the width of the front edge blur B2 are both indicated by the width between 10% and 90% of the luminance drop amount.
[0045]
In the present invention, as described with reference to FIG. 4, the cold cathode fluorescent lamp is driven for each frame such that the first half has an off period, that is, a low luminance state, and the second half has an on period, that is, a high luminance state. On the other hand, in the conventional driving method, the cold cathode fluorescent lamp is driven in each frame such that the first half thereof has an off period, that is, a state caused by stopping the discharge of the cold cathode fluorescent lamp, and the second half has an on period, that is, a high luminance state. The decrease in luminance at the time of transition from the off period to the on period appears to be slightly insufficient in the present invention as compared with the related art.
[0046]
However, in the screen luminance according to the present invention, in the vertical line main body portion ED, as shown in FIG. 6, the luminance of the black line when the luminance drop amount is 10% is suppressed lower than that of the conventional art, and the contrast is improved. . Further, when the brightness of the liquid crystal screen when the entire screen was displayed in white was compared, it was observed that the brightness of the present invention was improved by 110% to 145% as compared with the related art.
[0047]
9 and 10 are circuit diagrams for explaining a specific example of a control circuit for a linear lamp in the liquid crystal display device of the present invention, and FIG. 10 shows a D / D converter circuit section in FIG. This circuit corresponds to the first embodiment of the present invention described with reference to FIG. As shown in FIGS. 9 and 10, this circuit for driving the cold cathode fluorescent lamp CFL as a linear lamp includes a power input blinking PWU, a D / D converter circuit section DDC, an inverter circuit section INV, a tube current detecting section. It is composed of an SSR and a brightness control circuit unit BCT. Among the element codes in the figure, those with an R in the head are resistance elements, those with a C in the head are capacitance elements, those with the Q in them are transistors, and those with a D are heads. A diode with a ZD prefix indicates a Zener diode, and an IC with a prefix indicates an integrated circuit (logic element).
[0048]
The power input unit PWU is connected to the input power V _in And the stabilized power supply voltage V _DD Is supplied to the D / D converter circuit unit DDC. The D / D converter circuit unit DDC has a circuit configuration as shown in FIG. _DD Is supplied to the inverter circuit unit INV to control the current and voltage on the primary side of the transformer of the inverter circuit unit INV. The inverter circuit section INV has a booster circuit and a transformer TR, and supplies a high-frequency current (tube current) to the cold cathode fluorescent lamp CFL connected to the secondary side thereof.
[0049]
The tube current detector SSR detects the tube current I flowing through the cold cathode fluorescent lamp DFL. _L Is supplied to the luminance control circuit unit BCT and the inverter circuit unit INV. The brightness control circuit unit BCT includes a first logic element IC1 for inputting a blinking signal BK and a blinking drive signal S _igBin And a second logic element IC2.
[0050]
In the conventional blinking drive, the voltage (V _DD ) And a current output together with a blinking signal (a signal indicating a luminance modulation signal of a cold cathode fluorescent lamp) is input to a DD converter circuit unit DDC (light control circuit), and the DD converter circuit unit DDC responds to the blinking signal. (V) supplied to the inverter circuit _DD ) And the current was adjusted. On the other hand, in the present circuit, the blinking signal BK and the output timing signal (D in FIGS. 1 and 2) of the current and the voltage according to the ON and OFF states of the cold cathode fluorescent lamp CFL are supplied from the power input unit PWU. _ON And D _OF ) Are referred to each other by the switch circuit SC, and the output signal Sig from the switch circuit SC corresponding to the result is output. _Bln And I of the cold cathode fluorescent lamp CFL _L And an arithmetic circuit LS, which will be described later, refers to each other, and outputs an output signal (the above-described luminance modulation command signal) BMC from the arithmetic circuit LS according to the result to the DD converter circuit section DDC, and the transformer TR of the inverter circuit section INV Of the cold cathode fluorescent lamp CFL (corresponding to the tube current) flowing through the primary side of the cold cathode fluorescent lamp CFL.
[0051]
In FIG. 9, the switch circuit SC shown in FIGS. 1 and 2 includes a first logic element IC1 and a transistor Q14 operated by the output current thereof, and the operation circuit LS includes a second logic element IC2. The output timing signal from the transistor Q7 of the power input unit PWU is also input to the second logic element IC2, which adjusts the output timing of the luminance modulation command signal BMC.
[0052]
The output timing signal from the power supply input unit PWU is input to the first logic element IC1 through the resistance element R38, and the blinking signal BK is input to the first logic element IC1 as a signal having a voltage amplitude of 5V. The first logic element IC1 outputs a current signal I corresponding to the blinking signal BK. _Bln Is output. This current signal I _Bln Is modulated in accordance with the ratio of the tube current between the ON state and the OFF state determined by the blinking signal BK, and the ON / OFF state of the cold cathode fluorescent lamp CFL defined by the output timing signal from the power input unit PWU. Is supplied to the base of the transistor Q14. Current signal I _Bln Current generated between the collector and the emitter of the transistor Q14 by the output signal (blinking drive information) Sig _Bln Is input to the second logic element IC2.
[0053]
The second logic element IC2 includes a tube current I of the cold cathode fluorescent lamp CFL detected by the tube current detector SSR. _L Is also entered. Blinking driving information Sig _Bln And tube current I _L Are referred to each other by the second logic element IC2, and are important factors for determining the output of the luminance modulation command signal BMC. Therefore, the current paths to the respective second logic elements IC2 are also improved. You. Blinking driving information Sig _Bln Of the current path, the resistance element R36 in the middle of the current path and the reference potential V of the brightness control circuit unit BCT. _EE A variable resistor is used for the resistance element R22 for determining the potential of this path with respect to.
[0054]
These resistance values correspond to the blinking drive information Sig to the second logic element IC2 when the cold cathode fluorescent lamp CFL is turned off. _Bln Adjusted so that the input is not interrupted. Tube current I _L The path of the reference potential V and the reference potential V of the brightness control circuit unit BCT _EE Are directly connected by the resistance element R35, so that the potential of this path is changed to the reference potential V. _EE Only uniquely determine. The tube current I from the output terminal of the tube current detection unit SSR to the input terminal of the second logic element IC2 is _L The reference potential line V _EE -Not electrically connected to any wiring other than Line. Therefore, the second logic element IC2 stores the blinking drive information Sig. _Bln The desired luminance modulation ratio of the cold cathode fluorescent lamp CFL transmitted as _L And information on the lighting state of the cold-cathode fluorescent lamp CFL transmitted as "1".
[0055]
The second logic element IC2 in FIG. 9 includes the blinking drive information S as the arithmetic circuit LS in FIG. _igBin And light source drive information (tube current I _L ) Is output to the D / D converter circuit unit DDC.
[0056]
In the D / D converter circuit section DDC shown in FIG. 10, the blinking signal BK and the tube current I from the second logic element IC2 of the luminance control circuit section BCT are output. _L The voltage output according to the logical sum of _FB Finally, the operating condition of the switching element Q9 composed of NPN-type and PNP-type bipolar transistors, which is arranged complementarily to the D / D converter circuit unit DDC, is changed.
[0057]
As described above, a method of giving a voltage variation to the D / D converter circuit unit DDC from the source other than the voltage input unit PWU to the switching element Q9 for current modulation is already known as an initial condition adjustment method for driving the inverter circuit unit INV. A novel feature of the present invention is that this voltage fluctuation is generated according to the logical sum of the blinking signal and the driving condition (tube current) of the cold cathode fluorescent lamp. That is, in the present invention, the current on the primary side of the transformer TR is modulated in accordance with the logical sum of the blinking signal and the driving condition (tube current) of the cold cathode fluorescent lamp, and the voltage is modulated together with this.
[0058]
Therefore, the lighting of the cold cathode fluorescent lamp due to the difference in both the current value (tube current) and the voltage value required for lighting the cold cathode fluorescent lamp at each of the inevitable brightness when changing the brightness of the cold cathode fluorescent lamp Instability and the accompanying discharge stop in the cold cathode fluorescent lamp are avoided. This can be applied not only to a cold cathode fluorescent lamp but also to a light source utilizing discharge.
[0059]
That is, in order to prevent instability of the discharge occurring when the luminance of a light source such as a cold cathode fluorescent lamp is modulated, the discharge information in the light source is fed back to the luminance modulation control together with the blinking signal, and the luminance modulation command signal is referred to by referring to both of them. The driving method of the present invention for controlling the D / D converter circuit unit DDC by generating the image signal is applicable not only to a cold cathode fluorescent lamp but also to a general light source utilizing a discharge phenomenon, such as a xenon lamp or a fluorescent lamp.
[0060]
【The invention's effect】
As described above, according to the present invention, even when the cold cathode fluorescent lamp is turned off, a tube current smaller than the tube current at the time of on is caused to flow, and a difference between the luminance at the time of on and the luminance at the time of off is provided. A similar blinking effect is obtained. In addition, since the discharge is continued even at the time of off-state and illumination with low luminance is performed, a decrease in luminance due to blinking is suppressed, and a liquid crystal display device with improved moving image blur can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a control circuit of a linear lamp illustrating a first embodiment of a liquid crystal display device of the present invention.
FIG. 2 is a block diagram illustrating a control circuit of a linear lamp illustrating a second embodiment of the liquid crystal display device of the present invention.
FIG. 3 is a driving waveform diagram of a cold cathode fluorescent lamp for explaining a tube current waveform according to an embodiment of the present invention by comparing it with a tube current waveform obtained by conventional blinking control.
FIG. 4 is a luminance response waveform diagram of a cold cathode fluorescent lamp for explaining a luminance response in the embodiment of the present invention in comparison with a luminance response by a conventional blinking control.
FIG. 5 is a state diagram of moving image blur when a vertical black line displayed on a screen is moved in a scanning line direction by the driving method of the present invention.
FIG. 6 is an explanatory diagram of a luminance profile of a vertical line shown in FIG.
FIG. 7 is a state diagram of moving image blur when a vertical line displayed on a screen is moved in a scanning line direction by a conventional blinking driving method.
FIG. 8 is an explanatory diagram of a luminance profile of a vertical line shown in FIG. 7;
FIG. 9 is a circuit diagram illustrating a specific example of a control circuit for a linear lamp in the liquid crystal display device of the present invention.
FIG. 10 is a diagram illustrating a D / D converter circuit unit of FIG. 9;
FIG. 11 is a schematic diagram illustrating a mechanism of occurrence of moving image contour deterioration when a moving image is displayed on a display device having a hold characteristic.
[Explanation of symbols]
CFL: cold cathode fluorescent lamp as linear lamp, DDC: D / D converter, INV: inverter, SSR: tube current detector, BCT: brightness control circuit , TR, transformer, SC, switch circuit, LS, arithmetic circuit, BK, blinking signal, SSR, tube current detector, BMC, brightness modulation Command signal.

Claims (7)

A liquid crystal display panel, a lighting device having a linear lamp installed on the back of the liquid crystal display panel, and a brightness control circuit for controlling the brightness of the lighting device,
A D / D converter for supplying a lighting voltage to the linear lamp, a transformer having an output of the D / D converter connected to a primary side and a secondary side connected to the linear lamp, and detecting tube current information. A tube current detector, a switch circuit for generating blinking drive information with reference to a blinking signal and a linear lamp state signal (ON state and OFF state), and blinking drive information output from the switch circuit And a brightness control circuit including a calculation circuit that calculates tube current information detected by the tube current detector to generate a brightness modulation command signal and controls a light source brightness modulation output of the D / D converter,
A liquid crystal display device, wherein a tube current of the linear lamp is controlled by supplying a light source luminance modulation output of the D / D converter to a primary side of the transformer. The switch circuit includes a first integrated circuit that generates a blinking current based on an externally input blinking signal, and a transistor circuit that generates blinking drive information from the blinking current output from the first integrated circuit. The liquid crystal display device according to claim 1, further comprising: a second integrated circuit that generates a luminance modulation command signal based on blinking drive information output from the transistor circuit. A variable resistor provided for adjusting a transmission condition of the blinking drive information from the transistor circuit to the first integrated circuit to change a light source luminance modulation output of the D / D converter based on the luminance modulation command signal. The liquid crystal display device according to claim 1, further comprising: 4. The liquid crystal display device according to claim 1, wherein the tube current detector is connected in series with the linear lamp on a secondary side of the transformer. 5. The liquid crystal display device according to claim 1, wherein the tube current detector is connected in series to a primary side of the transformer. A liquid crystal display panel, a lighting device having a linear lamp installed on the back of the liquid crystal display panel, and a brightness control circuit for controlling the brightness of the lighting device,
A D / D converter for supplying a lighting voltage to the linear lamp, a transformer having an output of the D / D converter connected to a primary side and a secondary side connected to the linear lamp, and detecting tube current information. A tube current detector, a switch circuit for generating blinking drive information with reference to a blinking signal and an on state and an off state of the linear lamp, blinking drive information output from the switch circuit, and the tube current A brightness control circuit comprising a calculation circuit for calculating tube current information detected by the detector to generate a brightness modulation command signal and controlling a light source brightness modulation output of the D / D converter; And
When turning on / off the linear lamp in synchronization with the frame period, the lamp current of the linear lamp at the time of off is set to a value smaller than that at the time of on, and the lamp is not completely turned off and has a lower luminance than the luminance of the on state. The method of driving a liquid crystal display device, characterized in that lighting of is continued. 7. The driving of the liquid crystal display device according to claim 6, wherein the duty in one on / off frame is 30% to 60%, and the tube current ratio in the off state is 30% to 50% in the on state. Method.

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