JP2000275619A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a liquid crystal display device to perform highly accurate temperature compensation in the thermal transient state of the device. SOLUTION: In the case of starting the supply of electric power to the liquid crystal display device, a temperature detector 151a, whose temperature coefficient is matched with that corresponding to the state when the temperature variation of the whole liquid crystal display device is in a thermal transient state, is connected to a power circuit 140 by a change-over circuit 152 to adjust the drive voltage, based on the detected temperature. After the lapse of a certain time, a temperature detector 151b, whose temperature coefficient is matched with that of corresponding to the equilibrium state, is connected to the power circuit 140 to adjust the voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a liquid crystal display device capable of performing high-accuracy temperature compensation in driving a liquid crystal panel.

[0002]

2. Description of the Related Art The temperature coefficient of an active liquid crystal panel using a TFD (Thin Film Diode) element is generally about 120 mV / degree in terms of a driving voltage. For this reason, in the conventional liquid crystal display device,
The temperature is detected using a temperature-sensitive element such as a diode or a thermistor, and the drive voltage is adjusted according to the detected temperature.
Thus, even if the ambient temperature changes, the positive voltage and the negative voltage applied to the liquid crystal are balanced to prevent the application of the DC voltage and to obtain the maximum contrast. The temperature coefficient was set to a value adjusted to a drive voltage at which the maximum contrast was obtained when the temperature change of the entire apparatus was in an equilibrium state. Further, since the temperature sensing element is disposed on the internal substrate of the liquid crystal display device, there is a temperature difference between the liquid crystal panel and the temperature sensing element. The temperature difference was determined as a constant value to determine a temperature coefficient, and drive adjustment was performed.

[0003]

In the conventional liquid crystal display device, when the temperature change of the entire device is in an equilibrium state, the difference between the actual temperature of the liquid crystal panel and the temperature detected by the temperature sensing element is a constant value. Therefore, temperature compensation can be accurately performed. However, during the period from when the power of the liquid crystal display device is turned on until the temperature change of the entire device reaches an equilibrium state, the difference between the actual temperature of the liquid crystal panel and the temperature detected by the temperature sensing element is large. For this reason, in the transient state, there is a problem that accurate temperature compensation is difficult, a maximum contrast cannot be obtained, and a DC voltage is applied to the liquid crystal to deteriorate display characteristics.

The present invention has been made in view of such circumstances, and an object of the present invention is to perform temperature compensation with high accuracy until the temperature of the entire device reaches an equilibrium state. It is to provide a liquid crystal display device which can perform.

[0005]

In order to achieve the above object, a liquid crystal display device of the present invention includes a plurality of temperature sensing elements for detecting the temperature of a liquid crystal panel, outputs a signal corresponding to the detected temperature, and outputs signals different from each other. A liquid crystal display device comprising: a plurality of temperature detectors having a temperature coefficient; and a voltage adjusting circuit that adjusts a liquid crystal driving voltage according to an output signal of the temperature detector, wherein a temperature change of the entire liquid crystal display device is Switching means for switching an output signal of the temperature detector to be input to the voltage adjusting circuit when the liquid crystal display device is in a transient state and when the entire temperature change of the liquid crystal display device is in an equilibrium state. .

According to the above configuration of the present invention, the temperature detector for measuring the temperature of the liquid crystal panel is divided into a time until the temperature change of the entire device reaches an equilibrium and a time when the temperature changes to the equilibrium.
By switching the temperature detector used for temperature correction,
Temperature correction can be performed more accurately. Since the temperature sensing element is mounted on the internal substrate of the liquid crystal display device, there is a difference between the measured temperature and the actual panel temperature. In the transitional state until the equilibrium is reached, the difference gradually increases, and in the equilibrium state, the difference becomes constant. In the transient state, a temperature detector having a temperature coefficient taking into account the temperature difference is used. Since the temperature difference is constant in the equilibrium state, a temperature detector having the same temperature coefficient as that of the related art is used. This allows accurate temperature compensation even in a transient state.

Further, in the present invention, the switching means switches an output signal of a temperature detector input to the voltage adjusting circuit at a timing when a predetermined time has elapsed from the start of power supply to the liquid crystal display device. And

[0008] With the above configuration, by making the switching time constant, it is possible to use a simple timer circuit for switching, so that the temperature compensation circuit can be simplified.

Further, in the present invention, the switching timing is the time from the start of power supply to the liquid crystal display device until the difference between the temperature of the liquid crystal panel and the temperature detected by the temperature detector becomes substantially constant. Desirably.

[0010] According to the above configuration, the time required for the temperature change of the entire apparatus to become substantially equilibrium is reached, so that the allowable range can be set wide.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment> A liquid crystal display device according to an embodiment of the present invention will be described.

<Liquid Crystal Display> FIG. 1 is a block diagram showing an electrical configuration of a liquid crystal display 100 of the present invention. As shown in this figure, in the liquid crystal display panel 10 in the liquid crystal display device 100, a plurality of pixels 16 are formed at each intersection of i data lines X1 to Xi and j scanning lines Y1 to Yj, Each pixel 16 includes a liquid crystal display element (liquid crystal layer) 1
8 and a TFD (Thin Film Diode) element 20 are connected in series. In the figure, the TFD element 20 is connected to the data line side and the liquid crystal layer 18 is connected to the scanning line side. Conversely, the TFD element 20 is connected to the scanning line side and the liquid crystal layer is connected to the liquid crystal layer. 18 may be connected to the data lines.

Next, the scanning line signal driving circuit 110 drives each of the scanning lines Y1 to Yj, and the data signal driving circuit 120 drives each of the data lines X1 to Xi. In the normal mode, the drive control circuit 130 generates various signals to be described later based on image signals and synchronization signals supplied from the outside, and controls the scan signal drive circuit 110 and the data signal drive circuit 120, respectively. However, when a test signal is input at the time of inspection, the drive control circuit 130 shifts to a test mode in which the screen is divided, and generates various signals based on a test image signal and a synchronization signal output from the test data output circuit 132. Then, the scanning signal driving circuit 110 and the data signal driving circuit 120 are controlled respectively. Here, the test mode refers to a special mode used in an inspection process after assembling the liquid crystal display device 100 as a module, and the normal mode refers to a general mode used in other normal display states. Mode. The test data output circuit 132 generates a test image signal and a data signal when a test signal is input.

On the other hand, the power supply circuit 140 generates and outputs voltages V0 to V7 used for the liquid crystal display device from the power supply voltage Vcc. The magnitude relationship between the voltages V0 to V7 is as follows.
The voltage V0 has the highest level, and thereafter has a relationship in which the voltages V0 and V7 become lower in order, and the potential relationship between the data signals V3 and V4
Are obtained by inverting the polarities of the voltages V0, V1, and V2 based on the intermediate value of the voltages V7, V6, and V5. Further, the temperature compensation circuit 150 is configured to perform temperature compensation by changing the voltages V1 and V2 according to the temperature of the liquid crystal display panel 10 detected by the temperature compensation circuit 150.

Hereinafter, the power supply circuit 140 and the temperature compensation circuit 150 will be described.

<Power Supply Circuit> Next, the configuration of the power supply circuit 140 will be described with reference to FIG. The power supply circuit 140
A power supply 141 and an intermediate voltage generation circuit 142 are provided. The power supply 141 generates the voltages V0, V3, V4, and V7, and the intermediate voltage generation circuit 142 controls the power supply 1
41, generate voltages V1, V2, V5 and V6 which are intermediate voltages of the voltages V0, V3, V4 and V7. And the voltage
V0 to V7 are supplied to the scanning signal driving circuit 110, and voltages V3 and V4 are supplied to the data signal driving circuit 120. In this embodiment, since the voltage V4 is used as the ground potential, actually, the seven types of voltages V0, V1, V2, V3, V5, V6, and V7 excluding the voltage V4 are used as the scanning signal driving circuit 110. , And the voltage V3 is supplied to the data line driving circuit 120.

Here, the intermediate voltage generating circuit 142 has a voltage adjusting circuit 142a, and this configuration is, for example, as shown in FIG.
By adjusting the variable resistor VR1 in 2a, the voltages V1, V2
Can be increased or decreased in the same direction. Although not shown, a similar circuit is provided for the voltages V6 and V5, and the voltages V6 and V5 are adjusted simultaneously with the adjustment of the voltages V1 and V2. Further, the intermediate voltage generation circuit 142
The configuration is such that temperature compensation is performed by changing the voltages V1 and V2 according to the temperature of the liquid crystal display panel 10 detected by the temperature compensation circuit 150.

<Temperature Compensation Circuit> Next, the temperature compensation circuit 150
Will be described with reference to FIG. Temperature compensation circuit 1
50 includes a temperature detector 151 and a switching circuit 152 as switching means.

The temperature detector 151 is a temperature sensor 151b such as a thermistor adapted to a temperature coefficient when the temperature change of the liquid crystal display device is in a transient state and a temperature detector 151b adapted to a temperature coefficient when the temperature is in an equilibrium state. It consists of two types. The temperature detector 151 has, for example, a configuration as shown in FIG. A voltage detected by a temperature-sensitive element such as a thermistor is output by a differential amplifier including an operational amplifier. The temperature coefficient can be adjusted by the resistance value connected to the operational amplifier. For example, in the transient state, if the thermistor is of a type whose resistance value changes non-linearly with respect to temperature and the resistance value is adjusted so that the temperature coefficient becomes larger than that in the equilibrium state, accurate temperature compensation can be performed.

On the other hand, the switching circuit 152 is provided with a timer 153 so as to switch when a certain period of time has elapsed from the start of power supply to the liquid crystal display device. As a result, immediately after the start of power supply, the temperature detector 151a having the temperature coefficient set in the transient state is connected to the intermediate voltage generation circuit 142, and the drive voltage is corrected according to the detected temperature of the liquid crystal display panel 10. You. Then, after a certain period of time, the connection is switched to the temperature detector 151b having the temperature coefficient set in the equilibrium state, and the drive voltage is corrected.

The output voltage of one of the temperature detectors according to the detected temperature is applied to the intermediate voltage generation circuit 14 shown in FIG.
V1 and V2 can be increased or decreased in the same direction by the output voltage of the temperature detector.
The output voltage from the non-inverting amplifier is connected to an addition circuit that adjusts V1 and V2, and the voltage change amount, that is, the temperature coefficient can be adjusted by adjusting the resistance value of the addition circuit. This allows adjustment even when the temperature coefficient differs between V1 and V2. Although not shown, a similar circuit is provided for the voltages V5 and V6, and the voltages V5 and V6 are adjusted simultaneously with the adjustment of the voltages V1 and V2.

Here, as shown by the characteristics in FIG. 5, the average temperature of the liquid crystal display panel 10 gradually rises from the room temperature RT by turning on the power supply, and is maintained for a certain period of time.
At the point in time when T has elapsed, the temperature is saturated at the temperature Tha, and an equilibrium state is reached. The time ST may need to be about one hour depending on the screen size and the model. On the other hand, the temperature detected by the temperature sensing element has a difference from the actual temperature of the liquid crystal display panel as shown in the characteristics, and the difference gradually increases after the power is turned on. However, the temperature difference becomes substantially constant during a time period ST0 shorter than the time period ST.
It is better to set the interval from T0 to ST, for example, about 20 minutes. In addition, until the temperature reaches the equilibrium state, the temperature detector 151b is set so that the temperature coefficient increases as the temperature increases, considering that the temperature difference increases. In the present embodiment, in this section (for example, 20 minutes after the power is turned on), the output of the temperature detector 151a is used for temperature compensation,
In the subsequent sections, the output of the temperature detector 151b in which the temperature coefficient is set in the equilibrium state is used for temperature compensation. In the present embodiment, the output of the temperature detector 151a is used for temperature compensation in this section (for example, 20 minutes after the power is turned on), and the temperature detector 151b in which the temperature coefficient is set in the equilibrium state in the subsequent sections. Is used for temperature compensation. As described above, the temperature is switched to the optimum temperature detector according to the state of the temperature change to perform the temperature compensation, so that accurate temperature compensation can be performed even in a transient state.

<Other Embodiments> In the embodiment of the present invention described above, an example in which two temperature detectors are used has been described. However, the present invention is not limited to this, and a temperature coefficient having a different temperature coefficient is used. It goes without saying that two or more detectors may be used to switch two or more times to perform temperature correction.

[0025]

As described above, according to the present invention, when the temperature of the entire liquid crystal display device is in a transient state, it is possible to accurately correct the temperature of the drive voltage.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a liquid crystal display device of the present invention.

FIG. 2 is a block diagram showing a configuration of a power supply circuit and a temperature compensation circuit in the same liquid crystal display device.

FIG. 3 is a circuit diagram showing a main configuration of a drive voltage adjustment circuit and an intermediate voltage generation circuit in the power supply circuit.

FIG. 4 is a circuit diagram showing a configuration of a main part of a temperature detector in the temperature compensation circuit.

FIG. 5 is a characteristic diagram showing a temperature change from power-on in the same liquid crystal display device.

[Explanation of symbols]

 10 Liquid crystal display panel 16 Pixel 18 Liquid crystal layer 20 TFD element 100 Liquid crystal display device 110 Scanning signal drive circuit 120 Data signal drive circuit 130 Drive control circuit 140 Power supply circuit

Claims (3)

[Claims] 1. A plurality of temperature detectors including a plurality of temperature sensing elements for detecting a temperature of a liquid crystal panel, outputting a signal corresponding to the detected temperature, and having different temperature coefficients from each other, and an output signal of the temperature detector. A voltage adjustment circuit for adjusting the liquid crystal drive voltage in response to the change in the temperature of the entire liquid crystal display device in a transient state and the equilibrium state of the temperature change in the entire liquid crystal display device. And a switching unit for switching an output signal of the temperature detector to be input to the voltage adjustment circuit. 2. The apparatus according to claim 1, wherein the switching unit switches an output signal of the temperature detector input to the voltage adjustment circuit at a timing when a predetermined time has elapsed from the start of power supply to the liquid crystal display device. 2. The liquid crystal display device according to 1. 3. The method according to claim 1, wherein the predetermined time is a time period from the start of power supply to the liquid crystal display device until the difference between the temperature of the liquid crystal display device and the temperature detected by the temperature detector becomes substantially constant. 3. The liquid crystal display device according to claim 2, wherein: