JPH06214528A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To substantially attain reduction of the amplitude of an AC video signal by half and to suppress power consumption further by lowering the power source voltage of a video waveform conversion means. CONSTITUTION:In a liquid crystal display device provided with the video waveform conversion means 100 pulsating the DC level of the AC analog video signal equivalent to the potential of the common electrode of a liquid crystal panel, first capacitor group 321-32n by the number of pixels of one horizontal scanning line successively sampling the output of the video waveform conversion means 100 synchronizing with a pixel clock and voltage applying means 361-36n transferring the charge stored on the first capacitor group 351-35n to second capacitor group 351-35n synchronizing with a horizontal scanning signal and simultaneously impressing the charge stored on the second capacitor group 351-35n to the data lines of respective pixels of one horizontal scanning line of the liquid crystal panel, this device is constituted so that the ground side electrodes of the first capacitor group 321-32n or the second capacitor group 351-35n are connected in common, and the potential of the ground side electrode is switched between ground potential and the potential equivalent to the applied voltage of the common electrode of the liquid crystal panel.

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,
More specifically, the present invention relates to a power saving technique for a liquid crystal display device that displays an analog video signal. Generally, a flat panel display such as a liquid crystal display device is a CRT (cathoderay tub).
e) It is superior to a display in terms of installability and power consumption, and in particular, it is widely used in portable computers and the like, but due to the long life requirement of the battery, further power reduction is required.

[0002]

2. Description of the Related Art FIG. 5 is a schematic block diagram of a liquid crystal display device. Reference numeral 1 is a video waveform converting means for amplifying the input analog video signal Vin and converting it into an alternating current. here,
The purpose of alternating current (to be exact, pulsating current) is to prevent deterioration of the liquid crystal, and the magnitude relationship between the black level and the white level potential is exchanged for each horizontal scanning signal or each vertical synchronizing signal. The direct current level of the alternating (pulsating) video signal Vac is applied to the potential (so-called common voltage Vcm) of the common electrode 2a of a large number of pixel capacitors C _LC (one of which is shown in the figure) constituting the liquid crystal panel 2. Corresponding, based on this Vcm,
Vac is generated so that the polarities of the black level and white level potentials alternate with each other.

Reference numeral 3 indicates that Vac is sequentially sampled in pixel units.
Pulling and horizontal scanning of the sampling voltage
Many data lines D of the liquid crystal panel 2 are synchronized with the signals.₁
~ D _nData driver for simultaneous application to 4 and 4 for horizontal scanning
A large number of scan lines S of the liquid crystal panel 2 in synchronization with the signals
₁~ S_mAre sequentially selected and the selected scan line is
Scan driver for applying a constant ON voltage Von, 2b
Is turned on by Von and the voltage on the data line is
Capacity C_LCSelect transistor (TFT: thin f)
ilm transistor).

FIG. 6 is a schematic block diagram of the data driver 3. In this figure, the data driver 3 is composed of n blocks 3 _{1 to} 3 _n , where n is the number of pixels forming one horizontal scanning line of the liquid crystal panel 2, and each block has the same structure. is there. The block 3 ₁ will be described as a representative. 5 ₁ is a pre-stage switch which is turned on in response to the clock signal TE ₁ of the first pixel, and 6 ₁ is a pre-stage switch 5 _1.
The previous-stage capacitor for accumulating a part of Vac (the part corresponding to the first pixel) that has passed through, 7 ₁ is a buffer amplifier, 8 ₁
Is a horizontal scanning signal or a signal TLE synchronized with the horizontal scanning signal
Secondary switch which is turned on in response, 9 ₁ subsequent capacitor to accumulate captures preceding capacitor 6 ₁ charge during secondary switch ₈₁ ON period, the 10 ₁ is a buffer amplifier.

According to such a configuration, the signals TE _{1 to} T
Sequentially preceding capacitor Vac in synchronization with E _n 5 ₁ to 5
sampled _n, then, in synchronism with the signal TLE stored charge in each of the former capacitor 5 ₁ to 5 _n to can be transferred to the subsequent stage capacitor 9 ₁ to 9 _n at a time, display this transfer charge of n pixels as the voltage O ₁ ~ O _n, the liquid crystal panel 2
Can be applied to the data lines D _{1 to} D _n .

That is, as shown in the waveform chart of each part in FIG. 7, first, Vac is sampled at the falling timing of the signal TE ₁ synchronized with the pixel clock # 1 of the first pixel, and the sampling charge is sampled in the first pixel. It is stored in the previous stage capacitor 6 ₁ . V _F1 represents the holding voltage of the _first- stage capacitor 6 ₁ of the first pixel. Next, Vac is sampled at the falling timing of the signal TE ₂ synchronized with the pixel clock # 2 of the second pixel, and the sampling charge is stored in the pre-stage capacitor 6 ₂ of the second pixel. V _F2
Represents the holding voltage of the pre-stage capacitor 6 ₂ of the second pixel. Then, this operation is sequentially executed up to the last pixel (n pixels), and all the preceding stage capacitors 6 ₁ , 6 ₂ are synchronized with the pixel clock #n of the last pixel, that is, at the rising timing of the signal TLE synchronized with the horizontal scanning signal. ......, subsequent capacitor 9 ₁ charge of 6 _n, 9 _2, ..., are transferred to 9 _n, the transfer charge display voltage O _1, O _2, ..., are output as O _n.

[0007]

However, in such a conventional liquid crystal display device, the alternating video signal Va is used.
Since c is sampled in pixel units and the sampling voltage is directly applied to the data lines D _{1 to} D _n , the amplitude of the AC video signal Vac is large and the power consumption of the video waveform converting means is large. There was a point.

FIG. 8 is a waveform diagram of the alternating video signal Vac. Vac is a signal that periodically repeats the positive polarity period and the negative polarity period with the common voltage Vcm as a reference level (DC level), and is a pulsating signal to be precise. There is a potential relationship of “Vcm <white level <black level” during the positive polarity period and “black level <white level <Vcm” during the negative polarity period (however, in the case of a normally white liquid crystal panel).
The liquid crystal panel displays a gradation corresponding to the potential difference with respect to Vcm. For example, in a typical normally white liquid crystal panel, a gradation corresponding to a white level is displayed when the potential difference with respect to Vcm is 2V, and a gradation corresponding to a black level is displayed when the potential difference is 5V.

Therefore, the amplitude of Vac is Vcm + 7V
Then, the potential (+7) corresponding to the black level in the positive polarity period
V + 5V = + 12V) to a potential (+ 7V−5V = + 2V) corresponding to the black level in the negative polarity period, which is 10V _PP , but in order to generate such a large Vac, at least a magnitude exceeding this amplitude is required. Power supply voltage (generally +
15 V) is required, and the power consumption of the video waveform converting means increases accordingly. [Object] Therefore, an object of the present invention is to substantially halve the amplitude of an AC video signal and to lower the power supply voltage of the video waveform converting means to further suppress power consumption.

[0010]

In order to achieve the above object, the present invention amplifies an input analog video signal and synchronizes the analog video signal before or after amplification with a horizontal scanning signal or a vertical scanning signal. And the AC waveform is converted into an alternating current, and the DC level of the AC analog video signal is pulsated as a potential equivalent to the common electrode of the liquid crystal panel, and the output of the video waveform converting means is synchronized with the pixel clock. The first capacitor group for the number of pixels of one horizontal scanning line to be sequentially sampled, and the charges accumulated in the first capacitor group are transferred to the second capacitor group in synchronization with the horizontal scanning signal, and A liquid crystal display device comprising: a voltage applying unit that simultaneously applies charges accumulated in the second capacitor group to a data line of each pixel of one horizontal scanning line of the liquid crystal panel. The first capacitor group and the second
The ground side electrode of the capacitor group is commonly connected, and the potential of the ground side electrode can be switched between the ground potential and the potential corresponding to the applied voltage (common voltage) of the common electrode of the liquid crystal panel. It is characterized by

[0011]

According to the present invention, the potential of the ground side electrode of the first capacitor group or the second capacitor group is switched to 0V and the common voltage for each one horizontal scanning period or one vertical scanning period. Therefore, instead of the conventional alternating video signal (see FIG. 8) whose polarity alternates with the common voltage as a reference, 0
It is possible to use an AC video signal whose amplitude is from V to a potential corresponding to a black level (in the case of normally white type liquid crystal), and this amplitude is almost half that of a conventional AC video signal. Since it corresponds to the amplitude, the power supply voltage of the video waveform converting means can be lowered to further suppress the power consumption.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are views showing a first embodiment of a liquid crystal display device according to the present invention, which is an NTSC (National Television).
This is an example of application to a liquid crystal display device that displays a video signal of the System Committee system.

In FIG. 1, reference numeral 100 is a video waveform converting section as a video waveform converting means. The video waveform conversion unit 100 receives the input analog video signal Vin
(It is a unipolar signal and its amplitude is 0.7 in the video signal part.
V _PPmax ), and Vi before or after amplification
n is subjected to alternating waveform conversion processing different from the conventional one,
When the video signal after the waveform conversion processing is represented by the code Vac ′,
As shown in the upper part of FIG. 2, this Vac ′ has a positive polarity period having an amplitude from 0 V to a potential (+7 V) corresponding to a black level and a negative polarity period having the same amplitude for one horizontal scanning period or one vertical period. It is generated as a signal that is alternately repeated for each scanning period. In the positive polarity period, 0V <white level <black level, and in the negative polarity period, 0V <black level <white level (however, in the case of normally white liquid crystal),
The amplitude of any period is the same as that of the conventional AC video signal (see FIG. 8).
It is almost half of the reference value).

Reference numeral 30 denotes n corresponding to the number of pixels of one horizontal scanning line.
(3n in the case of color liquid crystal) is a data driver including the same configuration blocks 30 ₁ to 30 _n , and each block 30 ₁ to 30 _n has a pixel clock signal TE _i (i is A pre-stage switch 31 _i that sequentially turns on in response to pixel numbers 1 to n), and a pre-stage capacitor 32 _i that accumulates Vac ′ that has passed through the pre-stage switch 31 _i .
The buffer amplifier 33 _i , the rear-stage switch 34 _i that is turned on in response to the horizontal scanning signal or the signal TLE synchronized with the horizontal scanning signal, and the charge of the front-stage capacitor 32 _i is captured and accumulated during the ON period of the rear-stage switch 34 _i. Although the latter stage capacitor 35 _i and the buffer amplifier 36 _i for outputting the display voltage O _i are provided, it is conventional in that the ground side electrode of the preceding stage capacitor 32 _i is connected to the voltage switching section 38 via the common wiring 37. Different from the example.

Here, the voltage switching section 38 responds to a predetermined timing signal TMG by setting it to 0V and a common voltage (+7).
The voltage corresponding to V) is switched and the switched voltage is output as the voltage VLS of the common wiring 37. The signal TMG is one cycle of the alternating analog signal Vac ′ generated in the signal generating circuit (not shown). This is a synchronizing signal. In the figure, the voltage switching unit 38 is composed of a switch 38a and a + 7V power source 38b for convenience, but a ground potential (0V) and a potential corresponding to the voltage applied to the common electrode of the liquid crystal panel (common voltage Vcm) are used. It is not limited to this as long as it can switch.

In such a configuration, the front capacitor 32 _i, AC video signal Va shown in the upper part of FIG. 2
A charge corresponding to the amplitude of c'is accumulated. This charge is transferred to the latter stage capacitor 35 _i at the timing of the signal TLE and is output to the data line D _i as the display voltage O _i , but the potential of the ground side electrode of the preceding stage capacitor 32 _i is V.
Because switched into two stages of 0V and + 7V by LS, when the VLS = 0V, while the accumulated charge of the preceding capacitor 32 _i is output as display voltage O _i, when the VLS = + 7V is front capacitor 32 _i
The display voltage O _i having a magnitude obtained by adding the accumulated charge of +7 V and +7 V is output.

That is, in FIG. 2, the video signal Vac 'in the positive polarity period accumulated in the preceding stage capacitor 32 _i.
Is transferred to the latter-stage capacitor 35 _i in synchronization with the signal TLE and output as the display signal O _i . In this case,
Since VLS is switched to +7 V corresponding to the common voltage Vcm, the amplitude of the display signal O _{i in} the positive polarity period is V.
From the potential of LS (+ 7V) to the potential (V
(cm + 5V = + 12V).

On the other hand, the video signal Vac 'in the negative polarity period accumulated in the front stage capacitor 32 _i is transferred to the rear stage capacitor 35 _i in synchronization with the signal TLE and is also output as the display signal O _i. , VLS are switched to the ground potential (0 V), the potential (+) at which the amplitude of the display signal O _{i in} the negative polarity period corresponds to the black level.
2V) to a potential (+ 7V) corresponding to Vcm.

Therefore, an AC-converted video signal whose amplitude is halved
Even if Vac 'is used, the conventional alternating video signal Vac
Display having the same amplitude and potential level (see FIG. 8)
Voltage O _iCan be output, and the video waveform conversion unit 10
The power supply voltage supplied to 0 is reduced,
Power consumption can be suppressed. 3 and 4 show the present invention
It is a figure which shows the 2nd Example of the liquid crystal display device which concerns on. Na
The same reference numerals are given to the constituent elements common to the first embodiment.
The description will be omitted.

In this embodiment, instead of the pre-stage capacitor 32 _i , the ground side electrode of the post-stage capacitor 35 _i is connected to the voltage switching section 38 via the common wiring 37, and as shown in FIG. VLS = + 7V is maintained during the negative polarity period of the video signal, and VLS = 0 during the negative polarity period.
The difference is that V is maintained. With such a configuration as well, the display voltage O _i having the same amplitude and potential level as the conventional alternating video signal Vac (see FIG. 8) can be output, and the power supply voltage supplied to the video waveform conversion unit 100 can be supplied. It is possible to reduce the power consumption of the converter 100, and further, according to the second embodiment, the post-stage capacitor that performs the accumulation operation in the cycle of one horizontal scanning period that is much longer than the pixel clock. Since the electrode voltage of 35 _i is manipulated, even if the power source impedance of the voltage switching unit 38 is somewhat high, the storage operation of the post-stage capacitor 35 _i can be accurately performed, and the power source system can be easily designed. .

[0021]

According to the present invention, since it is configured as described above, the amplitude of the alternating video signal can be substantially halved, and the video waveform converting means (the video waveform converting section 10 in the embodiment).
The power supply voltage of 0) can be lowered to further suppress the power consumption.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment.

FIG. 2 is an operation waveform diagram of the first embodiment.

FIG. 3 is a configuration diagram of a second embodiment.

FIG. 4 is an operation waveform diagram of the second embodiment.

FIG. 5 is a conceptual block diagram of a liquid crystal display device.

FIG. 6 is a configuration diagram of a conventional example.

FIG. 7 is an operation waveform diagram of a conventional example.

FIG. 8 is a potential level diagram of an AC video signal of a conventional example.

[Explanation of symbols]

D _{1 to} D _n : Data line Vin: Analog video signal 2: Liquid crystal panel 2a: Common electrode 32 _{1 to} 32 _n : Pre-stage capacitors (first capacitor group) 34 _{1 to} 34 _n : Post-stage switch (voltage applying means) 35 _{1 to} 35 _n : post-stage capacitors (second capacitor group) 36 _{1 to} 36 _n : buffer amplifier (voltage applying unit) 100: video waveform converting unit (video waveform converting unit)

Claims (2)

[Claims] 1. Amplifying an input analog video signal,
Video in which an analog video signal before or after amplification is converted into an alternating current in synchronization with a horizontal scanning signal or a vertical scanning signal, and a direct current level of the alternating analog video signal is pulsated as a potential equivalent to a common electrode of a liquid crystal panel. Waveform conversion means and a first number corresponding to the number of pixels of one horizontal scanning line for sequentially sampling the output of the video waveform conversion means in synchronization with a pixel clock.
And the electric charges accumulated in the first capacitor group are transferred to the second capacitor group in synchronization with the horizontal scanning signal, and the electric charges accumulated in the second capacitor group are transferred to the liquid crystal panel 1 In a liquid crystal display device including a voltage applying unit that applies simultaneously to data lines of pixels of a horizontal scanning line, the ground side electrodes of the first capacitor group or the second capacitor group are commonly connected, and A liquid crystal display device, characterized in that the potential of the ground side electrode can be switched between a ground potential and a potential corresponding to a voltage (common voltage) applied to a common electrode of a liquid crystal panel. 2. The liquid crystal display device according to claim 1, wherein the timing of switching the potential of the ground side electrode is synchronized with one cycle of the alternating analog signal.