JPH05307169A - Common electrode driving circuit for liquid crystal display device - Google Patents

Abstract

PURPOSE:To maintain picture quality in an optimum state even though the ambient temperature of a liquid crystal display device is charged. CONSTITUTION:The common electrode 14 of a liquid crystal panel 13 is driven by output Vo from an operational amplifier 12 through a DC cut capacitor 16. The amplifier 12 amplifies the output Vi which is made to be AC from a liquid crystal controlling circuit 11 as an inverting amplifier. An amplification factor is corrected by a thermistor 21 thermally connected to the liquid crystal panel 13 in terms of temperature. When the temperature of the panel 13 rises, the resistance value Rs of the thermistor 21 falls, and the amplitude of the output Vo becomes small. And when the temperature falls, the resistance value Rs rises, so that the amplitude of the output Vo becomes large. Thus, the change of light transmittance and the responsive characteristics caused by the temperature change of the liquid crystal is corrected, so that high-quality picture can be maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a common electrode driving circuit of a liquid crystal display device for displaying image data using liquid crystal display elements as pixels.

[0002]

2. Description of the Related Art A conventional common electrode drive circuit is shown in FIG. Alternating signal V from liquid crystal control circuit 1
i is derived. The alternating signal Vi is amplified by the operational amplifier 2 and drives the common electrode 4 of the liquid crystal panel 3.
The regulator 5 is a variable resistor VR and outputs a bias voltage for driving the common electrode 4. In the common electrode 4,
The output voltage Vo from the operational amplifier 2, which is DC-cut by the capacitor 6, is superimposed on the bias voltage and is given. The gain of the operational amplifier 2 is set by the resistance value R1 of the resistor 7 and the resistance value R2 of the resistor 8. Output Vo
Bleeder voltage Vre generated at the connection point of the resistor 9 having the level resistance value R3 and the resistor 10 having the resistance value R4
It is set based on f. As the power supply voltage, a positive voltage VsH and a negative voltage VsL are applied.

FIG. 7 shows a liquid crystal control circuit 1 shown in FIG.
And the output voltages Vi and Vo of the operational amplifier 2 are shown respectively. The output voltages Vi and Vo are rectangular waves whose levels change every horizontal scanning period 1H for displaying the liquid crystal panel 3. In the drive circuit shown in FIG. 6, the operational amplifier 2 is applied to the output Vi from the liquid crystal control circuit 1 having a constant amplitude E.
Since the gain of is constant, the amplitude A of its output Vo is also constant.

[0004]

In the conventional driving circuit as shown in FIG. 6, the alternating voltage Vo having a constant amplitude is applied to the common electrode 4 of the liquid crystal panel 3 to drive the driving circuit as shown in FIG. To do. However, in the liquid crystal display element that constitutes the liquid crystal panel 3, the response speed and the light transmittance change according to the ambient temperature as a characteristic peculiar to the liquid crystal. As a result, even if the applied voltage Vo to the liquid crystal panel 3 is set so that the maximum contrast is obtained at room temperature, the original contrast cannot be obtained when the ambient temperature rises and falls. For this reason, the driving cannot be performed in the optimum state, and the image quality of the display by the liquid crystal panel 3 is deteriorated.

It is an object of the present invention to provide a common electrode drive circuit for a liquid crystal display device which eliminates the above-mentioned conventional drawbacks and can drive a liquid crystal panel under optimum conditions even when the ambient temperature changes. ..

[0006]

The present invention provides a common electrode drive circuit for a liquid crystal display device, which comprises a plurality of pixel electrodes arranged in a two-dimensional matrix and a common electrode provided so as to face the pixel electrodes. A temperature detecting means for detecting the temperature of the liquid crystal display device, and a temperature correction responding to the output from the temperature detecting means and controlling the signal voltage applied to the common electrode so as to correct the change in the physical properties of the liquid crystal according to the detected temperature. And a means for driving the common electrode of the liquid crystal display device.

[0007]

According to the present invention, the common electrode driving circuit of the liquid crystal display device includes the temperature detecting means and the temperature correcting means. The temperature correction means controls the voltage applied to the common electrode so as to correct the change in the physical properties of the liquid crystal according to the temperature of the liquid crystal display device detected by the temperature detection means. As a result, even if the ambient temperature changes and the response speed or light transmittance of the liquid crystal changes, the voltage applied to the common electrode of the liquid crystal display device is controlled to prevent deterioration of contrast and display with good image quality. It can be performed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic electrical structure of an embodiment of the present invention. From the liquid crystal control circuit 11, the alternating signal Vi is derived as a rectangular wave whose polarity is inverted every horizontal scanning period 1H. This alternating signal Vi is the operational amplifier 1
It is amplified by 2 and its output voltage becomes Vo. A bias voltage from the adjuster 15 is applied to the common electrode 14 of the liquid crystal panel 13. The regulator 15 has a positive power supply voltage V
The output from the movable contact of the variable resistor VR connected between sH and the negative power supply voltage VsL is given to the common electrode 14.
The output Vo from the operational amplifier 12 is DC-cut by the capacitor 16 having the capacitance C and is given to the common electrode 14. In this way, the common electrode 14 is given the AC output Vo by being superimposed on the bias voltage.

A resistor 17 having a resistance value R1 is connected between the output of the liquid crystal control circuit 11 and the inverting input of the operational amplifier 12. A resistor 12 having a resistance value R2 is connected between the inverting input of the operational amplifier 12 and the output. At the non-inverting input of the operational amplifier 12, a bleeder voltage Vre obtained by dividing the negative power supply voltage VsL by a resistor 19 having a resistance value R3 and a resistor 20 having a resistance value R4.
f is given. A thermistor 21 having a resistance value Rs is connected in parallel to the resistor 18. The thermistor 21 serves as a temperature detecting means and is a liquid crystal panel 13 which is a liquid crystal display device.
Mounted in a heat-bonded state.

FIG. 2 shows a schematic electrical configuration related to the liquid crystal panel 13. The liquid crystal panel 13 includes a TFT matrix 100 in which thin film transistors (hereinafter abbreviated as “TFT”) are arranged in a two-dimensional matrix. The TFT matrix 100 has n scan electrodes 101.
And 3 m signal electrodes 102. In this embodiment, one picture element is composed of three picture element electrodes 103, and color display is performed. The gate G is connected to the scan electrode 101 to which a signal is applied, and the source S is connected to the signal electrode 102 to which a signal is applied. The TFT 104 is
The pixel electrode 103 is driven. The pixel electrode 103 opposes the counter electrode 105 with a space therebetween.
A liquid crystal is filled in the gap between 03 and 105. TFT
When 104 is activated, the display mode of the liquid crystal changes, and the display in that pixel can be performed. LCD panel 13
Displays the image as a whole by combining the displays of the picture elements arranged in a matrix. Counter electrode 105
Is usually arranged in common to all pixel electrodes 103.
It is a conductive layer and is driven by applying an alternating signal as the common electrode 14. The AC signal is applied to the common electrode 14 because the characteristics of the liquid crystal deteriorate when the liquid crystal layer between the pixel electrode 103 and the counter electrode 105 is driven by direct current.

The TFT matrix 100 is driven by a picture element electrode driving circuit 150 provided around the TFT matrix 100.
The pixel electrode drive circuit 150 includes a control circuit 16
0, source driver 200 and gate driver 300
Is included. The control circuit 160 gives a control signal for adjusting the display timing to the source driver 200 and the gate driver 300 on the basis of the synchronization signal.

The source driver 200 includes a shift register 210, a sample hold circuit 220 and an output buffer 230. An analog image signal to be displayed as an image is serially given to the shift register 210. The shift register 210 converts an analog image signal into a parallel signal and supplies it to the sample hold circuit 220 as an image signal for each signal electrode 102. The sample hold circuit 220 samples and holds the analog image signal for each horizontal scanning period. The output buffer 230 gives the held analog image signal to each signal electrode 102.

The gate driver 300 includes a shift register 310, a level shifter 320 and an output buffer 330.
including. The shift register 310 is supplied with a signal for selecting one of the n scan electrodes 101 from the control circuit 160. The level shifter 320 shifts the output voltage level of the shift register 310. The output buffer 330 provides the output of the level shifter 320 to the scan electrode 101.

The operational amplifier 12 shown in FIG. 1 operates as an inverting amplifier which is a temperature correction means. The input / output characteristics follow the following formula (1).

[0015]

[Equation 1]

However, the bleeder voltage Vref is expressed by the following equation (2).

[0017]

[Equation 2]

Rs // R2 indicates that it is in parallel, and its value is expressed by the following equation (3).

[0019]

[Equation 3]

FIG. 3 shows the temperature change of the resistance value Rs of the thermistor 21. The resistance value Rs increases as the temperature decreases. Such a negative characteristic thermistor 21 is used in the liquid crystal panel 13
When the temperature is detected by mounting the temperature sensor at a low temperature, the parallel resistance value expressed by the equation (3) increases at low temperature, so that the amplitude of the output Vo expressed by the equation (1) increases and decreases at high temperature.

FIG. 4 shows an example of the relationship between the applied voltage Vs of the liquid crystal used in the liquid crystal panel 13 and the light transmittance T. It is assumed that there is a difference in applied voltage by ΔVx at a transmittance of 50% between room temperature (+ 25 ° C.) and low temperature (−10 ° C.). At this time, the amplitude needs to increase from the amplitude A1 at room temperature to the amplitude A2 at low temperature, as indicated by Vo in FIG. Such temperature correction may satisfy the following relational expression of Equation 4, where Rs1 and Rs2 are the resistance values of the thermistor 21 up to room temperature and low temperature, respectively.

[0022]

[Equation 4]

Similarly at high temperature (+ 60 ° C.), ΔV
It can be corrected so that the AC output Vo amplitude is reduced by x. Further, among the characteristics of the liquid crystal panel 13, the response speed and the like have the same temperature change as the light transmittance characteristics, and thus can be similarly corrected. Therefore, the common electrode drive circuit of the liquid crystal panel 13 in the present embodiment is driven in the optimum state even when the ambient temperature changes, and it is possible to always obtain a constant high image quality.

In the above embodiment, the temperature of the liquid crystal panel 13 is detected by the thermistor 21 and the amplification factor of the operational amplifier 12 is corrected, but the amplification factor may be corrected by another method. Of course. Further, the temperature of the liquid crystal panel 13 is detected, and the liquid crystal control circuit 11
It goes without saying that the output Vi from the above may be controlled.

[0025]

As described above, according to the present invention, the temperature of the liquid crystal display device is detected by the temperature detecting means, the voltage applied to the common electrode of the liquid crystal display device is controlled according to the detected temperature, and the ambient temperature Changes in the physical properties of the liquid crystal due to changes and the like can be corrected. As a result, changes in light transmittance, response speed, and the like are reduced, and reductions in contrast such as the contrast optimally adjusted at room temperature due to temperature changes are reduced, and display with good image quality can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic electrical configuration of an embodiment of the present invention.

2 is a block diagram showing a schematic electrical configuration for driving picture element electrodes of the liquid crystal panel 13 shown in FIG.

FIG. 3 is a graph showing temperature characteristics of the thermistor 21 shown in FIG.

FIG. 4 is a graph showing temperature characteristics of light transmittance of the liquid crystal panel 13 shown in FIG.

5 is a waveform diagram showing an operating state according to the embodiment shown in FIG.

FIG. 6 is a block diagram showing a schematic electrical configuration of a conventional common electrode drive circuit.

7 is a waveform chart showing the operation of the drive circuit shown in FIG.

[Explanation of symbols]

 11 Liquid Crystal Control Circuit 12 Operational Amplifier 13 Liquid Crystal Panel 14 Common Electrode 15 Regulator 16 Capacitor 17 to 20 Resistance 21 Thermistor 100 TFT Matrix 101 Scanning Electrode 102 Signal Electrode 103 Picture Element Electrode 104 TFT 105 Counter Electrode 150 Picture Element Electrode Driving Circuit 160 Control Circuit 200 Source driver 300 Gate driver

Claims (1)

[Claims] 1. A temperature of a liquid crystal display device is detected in a common electrode drive circuit of a liquid crystal display device, which has a plurality of pixel electrodes arranged in a two-dimensional matrix and a common electrode provided facing the pixel electrodes. And a temperature correction unit that responds to the output from the temperature detection unit and controls the signal voltage applied to the common electrode so as to correct the change in the physical properties of the liquid crystal according to the detected temperature. A common electrode drive circuit for a liquid crystal display device.