JPH05188881A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To suppress the increase of driving power for a common electrode with the increase of a driving current in the case of inverted drive by complementing one part of the driving current required for the common electrode with current supply from a switch means. CONSTITUTION:The level of a potential outputted from a control means 4 to a switch S1. is held at a potential, in which an MOS transistor is turned off, and just for fixed time when the output voltage of an operational amplifier 2a is switched from H (logic voltage higher than +5V) to L (lower than the logic voltage), the level of the potential outputted from the control means 4 to the switch S1 is changed. Then, the MOS transistor is turned on, and one part of charges stored in a liquid crystal equivalent capacitor is returned to a power supply circuit 3. The current due to the returned charges is charged through a diode D1 to a capacitor C1, and the current voltage charged in the capacitor C1 is transformed to +5V by a resistor R1 and a Zener diode Z1 and supplied through a resistor R2 and the control means 4, etc., as the logic voltage.

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, for example, the present invention relates to a liquid crystal display device that is suitable for use in the field of active matrix liquid crystal display panels and that operates with low power consumption. In recent years, for example, with the miniaturization of information terminal devices such as computer systems, many small-sized, low-power-consumption liquid crystal display devices have been developed as display devices.

In order to reduce the power consumption, the conventional driving method in which the common electrode is fixed to a constant voltage is changed to the inversion driving method so that the driving voltage of the data driver which consumes the most current is lowered. The power was being reduced. However, in the inversion driving method, although the total power of the liquid crystal display device is reduced, the drive power of the common electrode is increased.

Therefore, it is required to suppress the driving power of the common electrode.

[0004]

2. Description of the Related Art As a conventional liquid crystal display device of this type,
Generally, there is known one in which a common electrode is driven by using a high-speed and high-output operational amplifier. The reason why such a high-speed and high-output op-amp is used is to set the common electrode of the capacitive load to a predetermined voltage in a short time, but since the frequency of inversion increases, the charge / discharge current also increases. The maximum charge / discharge current is obtained when 1-line inversion is performed.

The charging / discharging is usually charging from a positive power supply (high potential power supply) and discharging to a negative power supply (low potential power supply or ground), and the common electrode is divided into a plurality of parts. The same is true in the case.

[0006]

However, in such a conventional liquid crystal display device, since the common electrode, which is a capacitive load, is set to a predetermined voltage in a short time, the common electrode has a high output at a high speed. Since it is driven by a pair amplifier, there is a problem that the drive current of the common electrode is considerably increased in the case of performing the inversion drive, particularly the one-line inversion.

[Object] Therefore, an object of the present invention is to provide a liquid crystal display device which suppresses an increase in drive power of the common electrode due to an increase in drive current during inversion drive.

[0008]

In order to achieve the above object, a liquid crystal display device according to the present invention includes a liquid crystal display device having a plurality of common electrodes divided into one or a predetermined number of systems, and a liquid crystal display device of the liquid crystal display device. Common electrode drive means for driving the common electrode via a drive line connected to each of the common electrodes, power supply current supply means for supplying a power supply current to the common electrode drive means, the power supply current supply means, and the common A switch means for connecting and disconnecting the electrode drive means and a drive line connecting the common electrode and a control means for controlling connection and disconnection of the switch means are provided, and the drive line is different depending on the common electrode drive means. When the common electrode is driven by periodically switching between two types of potentials, a predetermined period is started from the timing when each drive line switches from the high potential state to the low potential state. Connect the control means and the drive line in said switching means and said power current supplying means, are configured to return a part of the drive current to the power supply current supplying means.

In this case, when the common electrode is divided into a plurality of systems, the sum of the areas of the plurality of common electrodes driven at a high potential and the areas of the plurality of common electrodes driven at a low potential at a predetermined timing. It is effective to set the switching timing of the power supply current driving means in synchronism with the connection timing of the switch means by configuring the power supply current driving means with a switching regulator. is there.

[0010]

According to the present invention, when the common electrode is driven by periodically switching the drive line between two different kinds of potentials by the common electrode drive means, that is, when the common electrode is driven in reverse, each drive is performed. During the predetermined period from the timing when the line switches from the high potential state to the low potential state, the control unit controls the switch unit, and the drive line and the power supply current supply unit are connected, so that a part of the drive current is It is returned to the power supply current supply means.

That is, in the power supply current supply means,
Since a part of the drive current required for driving the common electrode by the common electrode drive means is supplemented by the current supply from the switch means, it is possible to suppress an increase in the drive power of the common electrode due to an increase in the drive current during the inversion drive.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 to 4 are diagrams showing an embodiment of the liquid crystal display device according to the present invention, and FIG. 1 is a block diagram showing the overall configuration of the present embodiment,
2 and 3 are circuit diagrams showing the configuration of the main part of FIG.

First, the structure will be described. Liquid crystal table of this embodiment
The display device is roughly classified into a liquid crystal display unit 1 and a common electrode driver.
Common electrode driver 2 which is a step, and power source current supply means
Power supply circuit 3, switch S as switch means₁~ S_n,
It is composed of the control means 4. In the figure, DL₁~ DL
_nIs a drive line for a common electrode (not shown), IL₁~ IL _nIs
Switch S₁~ S_nWith the power line that connects the
is there.

The liquid crystal display means 1 comprises a data driver 5, a gate driver 6 and a liquid crystal panel 7. The data driver 5 supplies a voltage for driving liquid crystal to a data bus. The gate driver 6 is a gate bus. As shown in FIG. 2, the liquid crystal panel 7 is arranged at the intersection of the data bus and the gate bus, which supplies a voltage for opening and closing a switching element group such as a TFT (Thin Film Transistor) arranged above. A voltage is applied to the liquid crystal 7b through the switching element 7a to change the transmittance of the liquid crystal 7b which is the pixel.

The common electrode driver 2 is as shown in FIG.
Is composed of an operational amplifier 2a and has a drive line DL₁~ DL_nTo
LCD panel divided into N (where N ≧ 0) systems through
The common electrode of the rule 7 is driven. The power supply circuit 3 is
As shown in FIG. 3, the diode D₁, Capacitor C₁,
Resistance R ₁, R₂, Zener diode Z₁(in this case,
(The logic voltage is a Zener voltage slightly higher than + 5V)
Consists of a voltage generator for driving the liquid crystal,
A power supply current is supplied to the bars 2, 5 and 6.

As shown in FIG. 2, the switches S _{1 to} S _n are provided between the drive lines DL _{1 to} DL _n and the power supply circuit 3, and their gates receive a control signal from the control means 4.
It is composed of a transistor T _i , and returns a part of the energy accumulated in the common electrode to the power supply circuit 3 by opening and closing at a predetermined timing. The control means 4 controls each driver 2, based on a timing signal supplied from the outside.
The timing signals for controlling the switches 5 and 6 and the switches S _{1 to} S _n are generated and output.

Next, the operation will be described. Under normal conditions, the potential level output from the control means 4 to the switch S _i is
The MOS transistor T _i is held at a potential to be turned off, and the output voltage of the operational amplifier 2a is switched from "H" (logic voltage is +5 V or more) to "L" (logic voltage or less) for a fixed time. The potential level output from the control means 4 to the switch S _i is changed, the MOS transistor T _i is turned on, and a part of the charge accumulated in the liquid crystal equivalent capacitance is returned to the power supply circuit 3.

The current due to the returned charge is the diode D ₁
Charged in the capacitor C ₁ via the current voltage charged in the capacitor C ₁ is converted by resistor R ₁ and the Zener diode Z ₁ to + 5V, the control unit 4 such as a logic voltage through the resistor R ₂ Supplied. The diode D ₁ is for preventing backflow of the current charged in the capacitor C ₁ , and the resistor R ₂ is a balance resistor for adjusting the potential difference between the voltage generated by the power supply circuit 3 and the voltage supplied from the outside. ..

FIG. 4 is a timing chart for explaining an operation example of this embodiment. In the figure, a to d are a to a of FIG.
shows the timing signal on the signal line shown in d, e _i ,
c _i represents the current flowing through the i-th signal line shown in e and c of FIG. The signal a is an AC timing signal generated from a plurality of control signals input from the outside, and includes a frame synchronization signal (Vsync) and a line synchronization signal (Hsyn).
c), or the line synchronization signal divided. An AC control signal b for the common electrode is generated by the AC timing signal a, and the common electrode is inverted based on the AC control signal b.

That is, in the present embodiment, the signal d is generated in synchronization with the timing when the potential of the signal c changes from the high potential to the low potential, and the switch S _i is turned on only during this period, so that the common electrode driver 2 is conventionally used. A part of the current returned to the low potential power source side is returned to the power source circuit 3 via. In the figure,
e _i represents the current returned to the power supply circuit 3 via the switch S _i , and c _i represents the drive current of the i-th common electrode,
In the figure, it can be seen that the drive current C _i is supplemented in the present embodiment compared to the case where the present embodiment shown by the broken line is not applied.

FIG. 2 shows another example of the liquid crystal display device according to the present invention.
It is a figure showing an example and a circuit diagram showing the composition of the important section.
It In the figure, 8 is a step-up DC / DC converter, D₂~
D_FourIs a diode, C₂, C₃Is a capacitor, L₁A
Contactance, B₁Is a bipolar transistor, R ₃，
R_FourIs resistance.

In the above-mentioned embodiment, the recirculated electric power is converted into the power supply of the logic system, but in the present embodiment,
DC / which forms the switching regulator
It is used as an input power source of the DC converter. That is, in this embodiment, D that constitutes a switching regulator is used.
Switching timing of C / DC converter is MOS
By synchronizing with the on-timing of the transistor T _i, the circulation efficiency is improved.

Further, when a plurality of common electrodes are driven in reverse, by making the areas of the common electrodes driven with opposite polarities substantially equal, the average value of the return current becomes substantially constant, and the return efficiency is further improved. As described above, in this embodiment, when the common electrode is driven to be inverted, the electric charge charged in the capacitance of the common electrode can be returned to the power supply circuit and reused, so that the power consumption of the liquid crystal display device can be reduced. ..

In the above embodiment, the case where the step-up type DC / DC converter is used as the switching regulator has been described as an example. However, the present invention is not limited to this, and a high voltage type or a transformer may be used. The primary / secondary separation type used may be used. Further, it goes without saying that the switching element forming the switch is not limited to the MOS transistor and the bipolar transistor.

[0025]

According to the present invention, in the case of driving the common electrode by periodically switching the drive line between two different potentials by the common electrode driving means, that is, in the case of inverting the common electrode, By connecting the drive line and the power supply current supply means by the switch means for a predetermined period from the timing of switching each drive line from the high potential state to the low potential state, a part of the drive current is supplied to the power supply current supply means. Can be returned.

Therefore, the power supply current supply means can supplement a part of the drive current required for driving the common electrode by the common electrode drive means by supplying the current from the switch means, thereby increasing the drive current during the inversion drive. It is possible to suppress an increase in driving power of the common electrode that accompanies it.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of this embodiment.

FIG. 2 is a circuit diagram showing a configuration of a main part of FIG.

FIG. 3 is a circuit diagram showing a configuration of a main part of FIG.

FIG. 4 is a timing chart for explaining an operation example of the present embodiment.

FIG. 5 is a circuit diagram showing a main part configuration of another embodiment.

[Explanation of symbols]

1 Liquid Crystal Display Means 2 Common Electrode Driver (Common Electrode Driving Means) 2a Operation Amplifier 3 Power Supply Circuit (Power Supply Current Supply Means) 4 Control Means 5 Data Drivers 6 Gate Drivers 7 Liquid Crystal Panels 7a Switching Elements 7b Liquid Crystals 8 DC / DC Converters ( switching regulator) S ₁ to S _n switch (switch means) DL ₁ through DL _n drive lines IL ₁ ~IL _n power lines

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiko Kishida 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (3)

[Claims] 1. A liquid crystal display device having one or a plurality of common electrodes divided into a predetermined number of systems, and driving the common electrode via a drive line connected to each of the common electrodes of the liquid crystal display device. Common electrode drive means, power supply current supply means for supplying a power supply current to the common electrode drive means, connection and disconnection between the power supply current supply means, and a drive line connecting the common electrode drive means and the common electrode And a control means for controlling connection and disconnection of the switch means, wherein the common electrode driving means cyclically switches the drive line between two different types of potential In the case of driving, the drive line and the power supply current are controlled by the switch means by the control means for a predetermined period from the timing when each drive line switches from the high potential state to the low potential state. Connecting the feeding means, the liquid crystal display device and returning a portion of the drive current to the power supply current supplying means. 2. The sum of the areas of a plurality of common electrodes driven at a high potential and the sum of the areas of a plurality of common electrodes driven at a low potential at a predetermined timing are made substantially equal to each other. Item 3. A liquid crystal display device according to item 1. 3. The power supply current drive means is a switching regulator, and the switching timing of the power supply current drive means is set in synchronization with the connection timing of the switch means. Liquid crystal display device.