JPH11297485A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption and prevent the generation of optical brightness irregularities. SOLUTION: An inverter circuit 10 for driving a fluorescent tube 100 for backlight is of a separate excitation type, and drive pulses P1, P2 are not generated by a drive pulse generator 1 in an image signal blanking period in which images are not displayed, so that the inverter circuit 10 is set in a non-actuated condition in the image signal blanking period to light off the fluorescent tube 100 for backlight. For each horizontal scan line of image signals, the drive pulses P1, P1 of a different cyclic periods for each horizontal scan line are generated from oscillators 14a, 14b by a reference signal which is synchronized with an integral multiples of the horizontal scan frequency, and the inverter circuit 10 is driven by the drive pulses P1, P2 to light the fluorescent tube 100 for backlight, thereby the optical brightness irregularities due to the fluorescent tube 100 is eliminated on a display surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and is suitable for driving a fluorescent tube for a backlight provided on the back of a transmission type liquid crystal display panel on which an image is displayed.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal display device for displaying an image or the like on a transmissive liquid crystal display panel, an entire display screen of the transmissive liquid crystal display panel for displaying an image is illuminated. A tube is provided.

FIG. 8 is a diagram showing an example of a configuration of a driving device for a fluorescent tube for a backlight applied to a conventional liquid crystal display device. In FIG. 8, a fluorescent tube 100 is provided on the rear surface of a transmission type liquid crystal display panel (not shown), and is a backlight fluorescent tube for irradiating the transmission type liquid crystal display panel from the rear side.

An inverter circuit 110 enclosed by a broken line is a self-excitation control type inverter circuit for driving the fluorescent tube 100. This inverter circuit 110 has a voltage input terminal t2
When a DC operating voltage Vcc is input from the power supply 1 via a choke coil L and a starting resistor R11 and the transistor Q11 is turned on, a current flows through the primary winding N11 of the transformer T11 to generate a voltage, and a transistor is connected to the feedback winding Nf. A voltage is induced in the direction in which Q11 is turned on. At this time,
The transistor Q12 is in a reverse bias state by a voltage induced in the feedback winding Nf, and is turned off.

When the transformer T11 becomes saturable, the voltage generated in the primary winding N11 decreases, the transistor Q11 turns off, and a back electromotive force is induced in the feedback winding Nf to turn on the transistor Q12. Thus, a current flows through the primary winding N12 of the transformer T11 to generate a voltage, and a voltage is induced in the feedback winding Nf in a direction in which the transistor Q12 is turned on.

When the transformer T11 becomes saturable again, the voltage generated in the primary winding N12 decreases, the transistor Q12 turns off, and the transistor Q11 turns on. Thereafter, the above operation, that is, the switching operation is performed. become. Such transistors Q11, Q
12, the switching operation of the primary winding of the transformer T11 and the resonance capacitor C connected in parallel with this primary winding.
11 determines its switching frequency.

As a result, the secondary winding N of the transformer T11
In step 21, a boosted alternating voltage is excited, and this alternating voltage causes a tube current to flow through the current limiting capacitor C12 to the fluorescent tube 100 connected to the connection terminals t22 and t23, thereby lighting the fluorescent tube 100. Like that.

[0008]

In the above-described backlight fluorescent tube 100, the inverter circuit 110 for driving the backlight fluorescent tube 100 is of a self-excited control type. During driving, the fluorescent tube 100 for the backlight is always in a lighting state, and there is a problem that power is extremely consumed.

In addition, for example, during a vertical blanking period of a video signal in which no video is displayed on the display screen of the liquid crystal display device, for example, the DC operating voltage Vcc supplied to the inverter circuit 110 is turned off, and the inverter circuit 110 is intermittently oscillated. However, when the power consumption of the fluorescent tube 100 is reduced, the inverter circuit 110 is turned off at a timing ignoring the zero cross point of the switching frequency of the inverter circuit 110, which is disadvantageous in terms of noise. was there.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and comprises a fluorescent tube for a backlight for irradiating a transmission type liquid crystal display panel from the back, and a fluorescent tube for a backlight. Driving means for driving the fluorescent tube, an oscillator capable of outputting a reference signal of a predetermined frequency, and a driving pulse generating means for generating a driving pulse for controlling the driving means based on the reference signal from the oscillator A blanking period extracting unit for extracting a blanking period included in the video signal; and a mute unit for suspending generation of a driving pulse in the driving pulse generating unit in the blanking period extracted by the blanking period extracting unit. In the blanking period of the video signal displayed on the transmissive liquid crystal display panel, the backlight fluorescent tube is turned off.

Further, the liquid crystal display device of the present invention comprises a fluorescent tube for a backlight for irradiating the transmission type liquid crystal display panel from the back, a driving means for driving the fluorescent tube for the backlight, and a horizontal scanning frequency of a video signal. A first oscillator capable of outputting an even-numbered reference signal of the video signal, a second oscillator capable of outputting a reference signal of an odd-numbered multiple of the horizontal scanning frequency of the video signal, and a horizontal scanning line of the video signal. Switching means for switching between the first oscillator and the second oscillator; drive pulse generation means for generating a drive pulse for controlling the drive means based on reference signals from the first and second oscillators; In the blanking period extracting means for extracting a blanking period included in the video signal, and in the blanking period extracted by the blanking period extracting means, the driving pulse in the driving pulse generating means is provided. And a mute means for suspending the generation of the image signal.In a blanking period of the video signal displayed on the transmission type liquid crystal display panel, the fluorescent tube for the backlight is turned off, and in a horizontal scanning period of the video signal, the switching means is used. Switching between the first oscillator and the second oscillator for each horizontal scanning line, generating a drive pulse synchronized with the reference signal of the first oscillator or the second oscillator by the drive pulse generation means, and The backlight fluorescent tube was driven.

The driving means is constituted by a separately-excited inverter circuit. Further, a light control means for controlling the luminance of the fluorescent tube for the backlight is provided.

According to the present invention, the driving means for driving the fluorescent tube for the backlight is of a separately excited type, and is driven by the driving pulse generating means during the vertical / horizontal blanking period of the video signal in which the video is not displayed. By preventing the generation of the pulse, the driving unit is deactivated, and the backlight fluorescent tube can be turned off.

In the horizontal scanning period of the video signal, a driving pulse synchronized with a reference signal from the first oscillator or the second oscillator is alternately generated for each horizontal scanning line, and a different period is set for each horizontal scanning line. By driving the driving means with the driving pulse, it is possible to eliminate optical brightness unevenness occurring on the display screen.

[0015]

Embodiments of the present invention will be described below. FIG. 1 is a diagram showing a configuration example of a driving device for a fluorescent tube for a backlight applied to the liquid crystal display device according to the present embodiment. In FIG. 1, a fluorescent tube 1
00 is provided on the back of a transmission type liquid crystal display panel (not shown),
This is a backlight fluorescent tube that illuminates the transmissive liquid crystal display panel from the back.

The inverter circuit 10 enclosed by a broken line is a separately-excited control type inverter circuit for driving the fluorescent tube 100. In the inverter circuit 10, both ends of a primary winding N1 of a transformer T1 and a resonance capacitor C11 connected in parallel are connected to collectors of transistors Q11 and Q12, respectively. The emitters of the transistors Q11 and Q12 are grounded, and the bases are input terminals t11 and t1, respectively.
2, an output terminal t of a drive pulse generator 1 described later
4, t5.

One of the secondary windings N2 of the transformer T1 is connected to a connection terminal t13 via a current limiting capacitor C12.
The other is connected to a terminal t14, and the fluorescent tubes 100 are connected to the terminals t13 and t14.

In the separately-excited control inverter circuit 10 having such a configuration, the transistors Q11, Q2 are driven by the drive pulses P1, P2 from the drive pulse generator 1.
Q12 is turned on / off alternately. As a result, a boosted alternating voltage is generated in the secondary winding N2 of the transformer T1, and this alternating voltage causes a tube current to flow through the current limiting capacitor C12 to the fluorescent tube 100 connected to the terminals t13 and t14. Then, the fluorescent tube 100 is turned on.

A driving pulse generator 1 for supplying a driving pulse to the inverter circuit 10 includes a flip-flop circuit 2, a sawtooth waveform generation circuit 5, a comparison circuit 3, and a mute circuit 4.

The sawtooth waveform generating circuit 5 includes a transistor Q
1 and Q2, and capacitors C1 and C2. The bases of the transistors Q1 and Q2 are connected to the output line of the flip-flop circuit 2. The collectors of the transistors Q1 and Q2 are connected to capacitors C1 and C2, respectively, to one end of which the DC operating voltage Vcc is applied. The emitter is grounded.

The comparison circuit 3 comprises comparators 3a and 3b, and one input terminal (+) of each of the comparators 3a and 3b.
Is connected to the collectors of the transistors Q1 and Q2, and the other input terminal (−) is connected to an output line of the light control unit 16 described later via a terminal t2.

The mute circuit 4 comprises a transistor Q3 and a resistor R1, a resistor R1 is connected between the base and the emitter of the transistor Q3, and a DC operating voltage Vc is connected to the emitter.
c has been supplied. The base is connected to an output line of a synchronizing signal synthesizing unit 15 to be described later via a terminal t3, and the collector is connected to an output line of the dimming unit 16.

The horizontal synchronizing clock generator 11 generates a clock synchronized with a horizontal synchronizing signal included in a video signal of an image displayed on a transmission type liquid crystal display panel (not shown). The horizontal synchronization clock output from 11 is supplied to the horizontal line discriminator 12 and the oscillators 14a and 14b.

The horizontal line discriminator 12 counts horizontal scanning lines of a video signal based on a horizontal synchronization clock. Then, it is determined whether the horizontal scanning line is an even-numbered line or an odd-numbered line, and the switching of the switch 13 is controlled based on the determination result. The horizontal line discriminator 12 is composed of, for example, a 9-bit counter, and counts horizontal scanning lines. Usually, VG is used for large display devices.
A (640 × 480 pixels) is displayed, and the display is performed at double speed (525 progressive display) through line tabler, so that the horizontal scanning lines are 480 lines. Therefore, the counter of the horizontal line discriminator 12 can be realized by resetting the counter at the 481th line and using the output (1, 0) of the least significant bit as the switching pulse of the switch 13.

The oscillators 14a and 14b are, for example, PL
L (Phase Locked Loop) circuit and voltage controlled oscillator VC
The PLL circuit controls the voltage controlled oscillator VCO based on the horizontal synchronization clock to output a reference signal synchronized with, for example, an even or odd multiple of the horizontal scanning frequency. Note that the oscillators 14a and 14b are not limited to the above-described configuration, and may be configured by, for example, a crystal oscillator or the like that can obtain an output of a predetermined oscillation frequency. In that case, it is of course unnecessary to input the horizontal synchronization clock.

The synchronizing signal synthesizing unit 15 includes the inverter circuit 1
5-1 and 15-2 and a NOR circuit 14-3. After inverting the horizontal synchronizing signal H and the vertical synchronizing signal V input to the inverter circuits 15-1 and 15-2, respectively, the NOR circuit At 15-3, the exclusive OR is obtained. That is, in the synchronizing signal synthesizing unit 15,
A composite synchronizing signal of a synchronizing negative polarity in which the horizontal synchronizing signal H and the vertical synchronizing signal V are synthesized by active low is obtained.

The light control section 16 is constituted by a comparator 16-1. One terminal (+) has a DC operating voltage Vc.
The voltage obtained by dividing c by the voltage dividing resistors R2 and R3 is input as a predetermined reference voltage, and the other terminal (−) is connected to the fluorescent tube 100.
The dimming control voltage VT for dimming the luminance of the pixel is input. For example, when the luminance of the fluorescent tube 100 is maximized, the dimming control voltage VT is set to 0 V so that the output level S3 of the comparator 16-1 becomes the reference voltage level. Further, when suppressing the luminance of the fluorescent tube 100, the dimming control voltage VT is increased so that the output level S3 of the comparator 16-1 is lower than the reference voltage level.

The operation of the driving apparatus for a fluorescent tube for a backlight according to the present embodiment as described above will be described with reference to the timing charts shown in FIGS. First, the basic operation of the backlight fluorescent tube driving device shown in FIG. 1 will be described with reference to the timing chart of FIG.

If, for example, a reference signal OSC as shown in FIG. 2A is inputted from one of the oscillators 14a and 14b to the terminal t1 of the driving pulse generator 1 shown in FIG. 1, a flip-flop circuit 2 outputs an output Q whose state is inverted at the rise of the reference signal OSC as shown in FIG. 6B and an inverted output Q # as shown in FIG.

The output Q of the flip-flop circuit 2 and the inverted output Q # are input to the bases of the transistors Q1 and Q2 of the sawtooth waveform generator 5, respectively. Then, when the transistor Q1 is turned on, the capacitor C1 connected to the collector of the transistor Q1 is charged by the DC drive voltage Vcc, and the collector voltage becomes “low” level. When the transistor Q1 is turned off, the capacitor C1 self-discharges and gradually discharges to the DC operating voltage Vcc, so that the collector voltage of the transistor Q1 becomes a sawtooth as shown in FIG. The waveform voltage becomes S1. Similarly, the transistor Q
2 is a sawtooth voltage S2 as shown in FIG.

The sawtooth voltage S1, S2 is applied to one input terminal (+) of comparators 3a, 3b provided in the comparison circuit 3, respectively. Also, the comparator 3
The output S3 of the light control section 16 is input to the other input terminal (-) of the terminals a and 3b via the terminal t2. Accordingly, when the output S3 as shown by the solid line in FIGS. 2D and 2E is applied from the light control section 16 to the comparators 3a and 3b, the comparator 3
Drive pulses P1 and P2 are output from a and 3b as shown by solid lines in FIGS. The drive pulses P1 and P2 are supplied to the inverter circuit 1 via terminals t4 and t5.
0 is applied to the bases of the transistors Q11 and Q12.

When an output S3 as shown by a broken line in FIGS. 2D and 2E is applied from the dimmer 16 to the comparators 3a and 3b, the comparators 3a and 3b output the same signal as shown in FIG. f),
(G) outputs drive pulses P1 and P2 indicated by broken lines, and the drive pulses P1 and P2 are applied to the transistors Q11 and Q1 of the inverter circuit 10 via the terminals t4 and t5.
2 is applied to the base.

That is, the output S of the dimmer 16 is controlled by the dimmer control voltage VT input to the dimmer 26.
3, the pulse width of the driving pulses P1 and P2 output from the comparators 3a and 3b of the comparison circuit 3 can be varied.

By driving the inverter circuit 10 by the driving pulses P1 and P2 generated by the driving pulse generator 1 in this manner, the alternating voltage is excited in the inverter circuit 10 and the fluorescent tube 100 is turned on as described above. Will do. Further, by varying the pulse widths of the driving pulses P1 and P2 generated by the driving pulse generator 1 by the dimming control voltage VT input to the dimming unit 16, the duty ratio of the luminance of the fluorescent tube 100 can be changed. The light can be variably adjusted. Therefore, the brightness of the fluorescent tube 100 that irradiates the transmissive liquid crystal display panel can be adjusted according to the use environment such as indoor or outdoor, for example.

When the pulse widths of the pulse outputs P1 and P2 of the driving pulse generator 1 are maximized so that the fluorescent tube 100 has the maximum brightness, as shown in FIGS. 2 (f) and 2 (g). By providing a period TD (dead time) during which both the pulse outputs P1 and P2 are turned off, both the transistors Q11 and Q12 of the inverter circuit 10 are prevented from being turned on.

Incidentally, the video signal of the video displayed on the liquid crystal display device includes a period in which video data is not included, that is, a vertical blanking period and a horizontal blanking period. The vertical blanking period depends on the television system, for example, one field (26) in the NTSC system.
2.5H), one frame (5
25H) includes 40H. Therefore, video signal 1
This means that a vertical blanking period of 40/525 (sec) is included per second.

Also, approximately 11 ×
Since a horizontal blanking period of (525-40) × 30 (μsec) is included, when the horizontal blanking period and the vertical blanking period are totaled, a video signal per second is about 0.236 (sec). ) Blanking period is included. In such a blanking period, since no image is displayed on the transmissive liquid crystal display panel, even if the backlight fluorescent tube 100 is turned on during this period, the light emission is not effectively used.

Therefore, in the present invention, the emission of the fluorescent tube 100 for the backlight is stopped during a period in which no image is displayed on the transmissive liquid crystal display panel, that is, in a horizontal / vertical blanking period of the video signal, thereby providing a fluorescent light. The power consumption of the tube 100 is reduced. For this reason,
In the present embodiment, a mute circuit 4 is provided in the drive pulse generator 1 and a synchronizing signal synthesizing unit 15 for synthesizing a vertical / horizontal synchronizing signal included in a video signal is provided.

FIG. 3 shows that in the above-described drive pulse generator 1, during the blanking period included in the video signal,
FIG. 5 is a timing chart for explaining an operation of stopping light emission of the fluorescent tube 100. FIG. 3A shows the waveform of the horizontal synchronizing signal H input to the synchronizing signal synthesizing section 15, and FIG. 3B shows the waveform of the vertical synchronizing signal V.
The horizontal synchronizing signals V and H are inverted by the inverters 15-1 and 15-2 of the synchronizing signal synthesizing section 15, and then the NOR circuit 15-H is inverted.
3 is input. The output S4 of the NOR circuit 15-3 includes a horizontal synchronizing signal H and a vertical synchronizing signal V as shown in FIG.
The output S4 is applied to the base of the transistor Q3 provided in the mute circuit 4 via the terminal t3.

Therefore, during the period when the transistor Q3 of the mute circuit 4 is turned on, that is, during the blanking period when the output S4 from the synchronizing signal synthesizing unit 15 is "low",
Dimming unit 1 connected to the collector of transistor Q3
The output line No. 6 is pulled up to the “high” level regardless of the output level S3 of the light control section 16.
As a result, during the blanking period of the video signal in which the video on the liquid crystal display device is not displayed, the comparators 3a,
Since the driving pulses P1 and P2 are not output from 3b and the inverter circuit 10 is in a non-operation state, the fluorescent tube 100 can be turned off.

With this configuration, as shown in FIG. 4A, the drive pulse P from the drive pulse generator 1 is supplied to the inverter circuit 10 during the vertical blanking period of the video signal.
1 and P2 are not supplied, and the inverter circuit 10 is in a non-operating state, so that the light emission of the backlight fluorescent tube 100 can be stopped. Also, as shown in FIG.
The horizontal blanking period of the video signal is also controlled by the inverter circuit 10.
Since the drive pulses P1 and P2 from the drive pulse generator 1 are not supplied to the inverter and the inverter circuit is in a non-operation state, the light emission of the backlight fluorescent tube 100 can be stopped.

As a result, the backlight fluorescent tube 10 can be used without lowering the brightness of the image displayed on the liquid crystal display device.
The power consumption at 0 can be reduced by about 23%. In particular, when applied to a large-screen liquid crystal display device in which the basic power required for the backlight is as large as several hundred watts, power consumption can be reduced in units of tens of watts. In addition, since the light control of the fluorescent tube 100 by the light control unit 16 can be used in combination, for example, indoors, the brightness of the fluorescent tube 100 is further reduced by the light control unit 16 to further reduce power consumption. Can also be planned.

When the above-described reference signal supplied to the driving pulse generator 1 is fixed, the switching frequency of the inverter circuit 10 becomes constant, so that a fixed optical brightness unevenness appears on the display screen. May occur. In particular, the switching frequency of the inverter circuit 10 is changed to the scanning frequency f (for example, 15.7342 KH) of the video signal.
When fixed to an integer multiple of z), it is expected that fixed optical fixed stripes (bright and dark patterns) will become clearer in synchronization with the image displayed on the display screen.

Therefore, in the present embodiment, for example, an even multiple of the horizontal scanning frequency f of the video signal (for example, 2 × f ×
m times, where m is a correction value), an oscillator 14a capable of generating a reference signal synchronized with a horizontal scanning frequency f
An oscillator 14b capable of generating a reference signal synchronized with an odd number of times (for example, 2.5 × f × m times) is provided.
The reference signal OSC supplied to the drive pulse generator 1 can be switched according to the odd-numbered horizontal scanning lines. The correction value m is a correction value for keeping the reference signals of the oscillators 14a and 14b within one horizontal scanning period.

With this configuration, when the even-numbered horizontal scanning lines are being scanned, the backlight fluorescent tube 100 is supplied with the reference signal 2f of the oscillator 14a as shown in FIG. The lamp current corresponding to
The light emission output of the fluorescent tube 100 at that time is obtained at a frequency 4f which is twice the lamp current. When the odd-numbered horizontal scanning lines are being scanned, a lamp current corresponding to the reference signal 2.5f of the oscillator 14b shown in FIG. Then, the light emission output of the fluorescent tube 100 at that time is obtained by the frequency 5f which is twice the lamp current.

As a result, the phase of the switching frequency of the inverter circuit 10 is shifted by 180 degrees between the even-numbered horizontal scanning lines and the odd-numbered horizontal scanning lines. Therefore, as shown in FIG. Since the portions and the dark portions are arranged in a checkered pattern, it is possible to prevent the occurrence of optical fixed stripes (light and dark patterns) due to the backlight on the display screen due to the interleaving effect. Further, since the switching frequency of the fluorescent tube 100 by the inverter circuit 10 is synchronized with the video signal, even if the switching frequency is switched for each horizontal scanning line, the switching is always performed at the timing of the zero cross point. No noise is generated.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this.
For example, the light emission of the backlight fluorescent tube 100 may be stopped only during the vertical blanking period of the video signal, or the light emission of the backlight fluorescent tube 100 may be stopped only during the horizontal blanking period. In the case of an image displayed in an interleaved manner, the oscillator 1
The switching between 4a and 14b may be switched on a field basis, for example, as shown in FIG.

[0048]

As described above, in the liquid crystal display device of the present invention, the driving means for driving the fluorescent tube for the backlight is of a separately excited type, and the vertical / horizontal signal of the video signal for which the video is not displayed is provided. In the ranking period, the drive pulse is not generated by the drive pulse generation means, so that the drive means is not operated and the fluorescent tube for the backlight can be turned off, thereby consuming the liquid crystal display without lowering the luminance of the liquid crystal display device. Power can be significantly reduced. In particular, when the present invention is applied to a large-screen liquid crystal display device in which the basic power required for the backlight is as large as several hundred watts, power consumption can be reduced in units of several tens of watts, which is very effective. Is done.

Further, according to the present invention, in the horizontal scanning period of a video signal, the first oscillator or the second oscillator is provided for each horizontal scanning line.
By alternately generating drive pulses synchronized with the reference signal from the oscillator of the above, and driving the drive means with drive pulses having a different cycle for each horizontal scanning line, an optical fixation generated on the display screen is achieved. There is also an effect that stripes can be eliminated.

Further, since the present invention can be used in combination with other dimming means for dimming the luminance of the fluorescent tube for the backlight, the power consumption can be further reduced depending on the use environment and the like. It is possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a driving device of a fluorescent tube for a backlight according to an embodiment of the present invention.

FIG. 2 is a timing chart for explaining a basic operation of the backlight fluorescent tube driving device according to the embodiment;

FIG. 3 is a timing chart for explaining an operation of suspending light emission of the fluorescent tube 100 in the backlight fluorescent tube driving device according to the present embodiment.

FIG. 4 is a diagram showing a state of light emission / pause of a video signal by a backlight fluorescent tube driving device according to the present embodiment.

FIG. 5 is a diagram showing a state of a lamp current and a light emission output of the fluorescent tube 100 according to the present embodiment.

FIG. 6 is a diagram showing a state of a bright portion and a dark portion of a display screen by a backlight according to the present embodiment.

FIG. 7 is a diagram for explaining another example of switching in the horizontal line discriminator according to the embodiment;

FIG. 8 is a diagram showing an example of a configuration of a conventional driving apparatus for a backlight fluorescent tube.

[Explanation of symbols]

1 drive pulse generator, 2 flip-flop circuit, 3
Comparison circuit, 4 mute circuit, 5 sawtooth waveform generator, 10 inverter circuit, 11 horizontal synchronization clock,
12 horizontal line discriminator, 13 switch, 14a, 1
4b oscillator, 15 synchronizing signal synthesizer, 16 dimmer, 100 fluorescent tube

Claims (6)

[Claims] 1. A backlight fluorescent tube for illuminating a transmissive liquid crystal display panel from the back, a driving unit for driving the backlight fluorescent tube, and an oscillator capable of outputting a reference signal of a predetermined frequency. A driving pulse generating unit for generating a driving pulse for controlling the driving unit based on a reference signal from the oscillator; a blanking period extracting unit for extracting a blanking period included in a video signal; The blanking period extracted by the period extracting unit includes a mute unit that suspends the generation of the driving pulse in the driving pulse generating unit. In the blanking period of the video signal displayed on the transmissive liquid crystal display panel, A liquid crystal display device wherein a backlight fluorescent tube is turned off. 2. The liquid crystal display device according to claim 1, wherein said driving means is constituted by a separately-excited control type inverter circuit. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal display device includes dimming means for dimming the luminance of the fluorescent tube for the backlight. 4. A fluorescent tube for a backlight for irradiating a transmissive liquid crystal display panel from behind, a driving unit for driving the fluorescent tube for a backlight, and a reference signal having an even multiple of a horizontal scanning frequency of a video signal. A first oscillator capable of outputting the reference signal; a second oscillator capable of outputting a reference signal having an odd multiple of the horizontal scanning frequency of the video signal; and the first oscillator according to a horizontal scanning line of the video signal. Switching means for switching between the second oscillator; drive pulse generation means for generating a drive pulse for controlling the drive means based on reference signals from the first and second oscillators; A blanking period extracting unit for extracting a included blanking period; and a driving pulse generated by the driving pulse generating unit during the blanking period extracted by the blanking period extracting unit. Mute means for suspending the generation, wherein the backlight fluorescent lamp is turned off during the blanking period of the video signal displayed on the transmission type liquid crystal display panel, and the switching is performed during the horizontal scanning period of the video signal. By means
The first oscillator and the second oscillator are switched for each horizontal scanning line, and the drive pulse generation means generates a drive pulse synchronized with a reference signal of the first oscillator or the second oscillator. A liquid crystal display device, wherein the driving means drives the fluorescent tube for the backlight. 5. The liquid crystal display device according to claim 4, wherein said driving means is constituted by a separately-excited inverter circuit. 6. The liquid crystal display device according to claim 4, wherein the liquid crystal display device includes dimming means for dimming the luminance of the backlight fluorescent tube.