JPH1031204A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device with excellent display quality in a wide temp. range by correcting increase in interasurface dispersion of a pixel electrode voltage accompanying temp. rise. SOLUTION: A controller 4 receives various signals, and controls a data signal outputted by a data driver 3 and a scan signal outputted by a scan driver 2 to drive a thin film transistor(TFT) liquid crystal panel 1. A temp. compensation circuit 5 is constituted of a temp. sensor 5-1 and a correction voltage generation circuit 5-2, and setting up the temp. sensor 5-1 on a casing and detecting the temp. of the panel casing at an operation time, and generating a high level voltage and a low level voltage of a scan signal pulse corresponding to the output of the temp. sensor 5-1 by the correction voltage generation circuit 5-2 to supply them to the scan driver 2. The high level voltage and low level voltage of the scan signal pulse generated by the temp. compensation circuit 5 automatically adjust so as to lower the voltage level of the scan signal pulse at a high temp. time and increase the voltage level at a low temp. time.

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 more particularly to an active matrix driven liquid crystal display device capable of preventing display problems caused by temperature changes.

[0002]

2. Description of the Related Art Liquid crystal display devices have been used in various devices including so-called notebook computers and portable devices because of their characteristics of being thin, lightweight and low power. Among them, the demand for a liquid crystal display device using an active matrix driving method is increasing due to features of high-speed response, high definition display, and multi-gradation display.

An active matrix type liquid crystal panel generally includes a transparent pixel electrode and a thin film transistor (Thin Fi).
a semiconductor substrate on which an lm Transistor (TFT) is arranged;
It consists of a counter substrate with one transparent electrode formed on the entire surface, and a liquid crystal sealed between the two substrates so as to oppose each other. A predetermined voltage is written, and the transmittance of the liquid crystal is changed by a voltage difference between each pixel electrode and a counter substrate electrode (hereinafter, referred to as “common electrode”) to perform screen display.

A data line for transmitting a gradation voltage signal (data signal) to be written to each pixel electrode is provided on a semiconductor substrate.
And a scanning line for transmitting a T switching control signal (scanning signal).

FIG. 5 shows a structure of a typical semiconductor substrate, and FIG. 6 shows a signal waveform diagram of a scanning signal, a data signal and a pixel electrode voltage in one pixel.

Referring to FIG. 5, a semiconductor substrate includes M rows and N rows.
It is composed of TFTs and pixel electrodes arranged in an array of columns (where M and N are arbitrary natural numbers), and M scanning lines and N data lines that are orthogonal to each other.
FIG. 5 also shows the storage capacity representing the gate storage type.

A pulse-like scanning signal is sent to each scanning line, and when the scanning signal of the m-th scanning line (where m is a natural number not less than 1 and not more than M) is at a high level, N leads to the scanning line. All the TFTs are turned on, and the gray scale voltage (data signal) sent to the data line in each column is written to each pixel electrode in the m-th row.

Next, the scanning signal becomes low level and TF
When T changes to the off state, the gray scale voltage written to each pixel electrode is changed until 1
It is held during the frame (see FIG. 6).

A predetermined voltage is written to all the pixel electrodes by sequentially sending a scanning signal to the scanning lines from the first row to the Mth row, and the screen display is performed by rewriting in a frame cycle. Is going. Note that the scanning signal is set to a sufficiently high voltage and the low level voltage is set to a sufficiently low voltage compared to the data signal in order to sufficiently write to the pixel electrode and suppress a leak current from the pixel electrode. .

Further, when a DC voltage is applied to the liquid crystal, display quality is degraded due to the polarization action of impurity ions and the like contained in the liquid crystal. Therefore, AC driving for changing the polarity of the pixel electrode voltage with respect to the common electrode for each frame is performed. Generally done.

Further, when the gate signal switches from the high level to the low level, the electric charge of the capacitance attached to the pixel electrode is also redistributed. , And the effective voltage of the pixel electrode becomes lower than the writing voltage by the feedthrough voltage. Therefore, a DC voltage is applied to the liquid crystal only by the feed-through voltage. Therefore, the common electrode voltage is adjusted so that the DC voltage is hardly applied.

By the way, in the liquid crystal display device, when the temperature changes, the display quality deteriorates due to various factors. One of these factors is the temperature dependence of the alignment state of the liquid crystal. For this reason, the liquid crystal transmittance changes when the temperature changes for a fixed liquid crystal application voltage. Therefore, in order to accurately perform the gradation display, it is necessary to perform some kind of temperature correction according to the temperature change.

Therefore, as a liquid crystal display device having a function for correcting the voltage (gradation voltage) to be written to the pixel electrode according to the temperature, for example, Japanese Patent Application Laid-Open No. 2-271390 discloses a liquid crystal display device having a display luminance over a wide temperature range. In order to provide a liquid crystal display device that does not change, the temperature of the liquid crystal panel is detected by a temperature sensor, one of a plurality of applied voltage correction tables is selected according to the detected output, and the selected applied voltage correction table is selected. Is read out as digital gradation data, and the read data is converted into an analog signal by a D / A converter and supplied to a driver of a liquid crystal panel. Liquid crystal display device in which correction data for correcting gradation data is selected so that It is draft.

This prior art, as shown in FIG. 11, has an application (gradation voltage) correction table 124 corresponding to the temperature, reads out the digital correction data according to the output of the temperature sensor 125, and performs D / A The analog voltage is converted by the converter 127 and a gradation voltage is supplied to the X driver 117 so that the liquid crystal transmittance of each gradation does not change even with a change in temperature.

Japanese Patent Application Laid-Open No. 5-45623 discloses that
There has been proposed a liquid crystal monitor temperature compensating circuit in which a common voltage for AC driving or an inversion reference voltage of a data signal is changed in accordance with a temperature change of an on-voltage of a TFT. Further, in Japanese Patent Application Laid-Open No. Hei 7-191608, a temperature measuring section measures the temperature of a liquid crystal panel or an ambient temperature, and a liquid crystal driving voltage correction section lowers the voltage level of the liquid crystal driving voltage at high temperatures based on the measured temperature. In addition, there has been proposed a liquid crystal display device in which a liquid crystal driving voltage is automatically corrected to a high voltage level at a low temperature. These prior arts all perform temperature correction of a gradation voltage and a common electrode voltage in order to prevent a change in transmittance of liquid crystal due to temperature.

[0016]

In these prior arts, accurate gradation display can be performed ideally by correcting the gradation voltage and the common electrode voltage in accordance with the ambient temperature change. it can.

However, when the TFT panel has a large screen, the scanning lines and data lines become long wirings, a delay occurs in the pulse signal due to wiring capacitance and resistance, and the delay changes the effective voltage of the pixel electrode. For this reason, even when the same gradation voltage is written, the effective voltage of the pixel electrode varies within the panel surface.

Such in-plane variation of the pixel electrode voltage (effective value) is caused by a difference between the positive and negative voltages of the pixel electrode voltage (effective value) depending on the screen position, particularly when a still image is displayed for a long time. Occurs, and a DC voltage is applied to the liquid crystal.

FIG. 7 is a diagram schematically showing the waveform of the pixel electrode voltage with respect to the common electrode voltage Vcom, and shows the pixel electrode voltage (effective value). In the figure, the solid line shows the waveform of the effective voltage at a screen position close to the scan driver and without a scan signal delay, and the broken line shows the waveform of the effective voltage at a screen position with a scan signal delay away from the scan driver. .

As shown in FIG. 7, the common electrode voltage Vco
m is set to an intermediate value between the positive and negative voltages so that no DC voltage is applied to the liquid crystal at the screen position where there is no delay in the scanning signal. On the other hand, at the screen position where the scanning signal is delayed, the effective voltage is higher due to the signal delay than at the screen position where the signal is not delayed.
A difference occurs between the positive and negative voltages with respect to the DC voltage, and a DC voltage is applied to the liquid crystal. For this reason, at the screen position where the scanning signal is delayed, the display quality deteriorates, such as flickering of the screen such as flicker or the occurrence of a still image afterimage due to the polarization action of impurity ions contained in the liquid crystal. ing.

The in-plane variation of the pixel electrode voltage (effective value) is generally relatively small in an environment where there is almost no change in temperature, and often causes no problem. The in-plane variation of the electrode voltage (effective value) is increased, and the DC voltage applied to the liquid crystal is increased, thereby deteriorating the display quality.

The following describes in detail how the in-plane variation of the pixel electrode voltage (effective value) increases as the temperature rises. An example of a scanning signal delay in which the signal amplitude is large and the influence of the signal delay is large will be described.

In general, one pixel of a TFT panel is represented by an equivalent circuit as shown in FIG. Referring to FIG. 8, the TFT 43 and the pixel electrode 44 are sandwiched between the (n-1) th scanning line 40 and the (n) th scanning line 41 (where n is a natural number of 2 or more), and The signal is output in the order of the scanning line 40 and the scanning line 41.

The gate of the TFT 43 is connected to the scanning line 41, and the drain (source) and the source (drain) of the TFT 43 are connected to the data line 42 and the pixel electrode 44, respectively.

A liquid crystal capacitance Clc is inserted between the pixel electrode 44 and the common electrode 45, and has a capacitance Cgs between the pixel electrode 44 and the nth scanning line 41.
And the (n−1) th scanning line 40.

Assuming that the voltage of the common electrode 45 is Vcom and the data signal (grayscale voltage) of the data line 42 is Vs, when the scanning signal of the scanning line 41 is a high level voltage (Vgh),
The TFT 43 is turned on, and the gradation voltage Vs is written to the pixel electrode 44. At this time, the scanning signal of the scanning line 40 is at a low level (Vgl).

When the charges of the capacitors Clc, Cs, and Cgs are q1, q2, and q3, respectively, the charges stored in the capacitors when the TFT 43 is on are represented by the following equations (1) to (3). The following relationship is established.

Vs-Vcom = q1 / Clc (1) Vs-Vgl = q2 / Cs (2) Vs-Vgh = q3 / Cgs (3)

If the total sum of the charges stored in the pixel electrode 44 is Q, the following equation (4) is obtained.

Q = q1 + q2 + q3 (4)

From the above equations (1) to (3) and the above equation (4), it can be seen that the following equation (5) holds.

[0032]

(Equation 1)

Next, consider a case where the scanning signal of the scanning line 41 changes from a high level voltage to a low level voltage and the TFT 43 is turned off.

At a screen position where there is no delay in the scanning signal, the scanning signal instantaneously changes from the high level voltage to the low level voltage, so that the TFT 43 is turned off instantaneously, and the total charge Q of each capacitor on the pixel electrode side becomes , Stored as is.

The scanning signal of the scanning lines 40 and 41 is a low level voltage (Vgl), the pixel electrode voltage when the TFT 43 is off is Vs', and the charges of the respective capacitors Clc, Cs and Cgs at this time. To q1 'and q
Assuming 2 ′ and q3 ′, the relations shown in the following equations (6) to (9) hold.

Vs'-Vcom = q1 '/ Clc (6) Vs'-Vgl = q2' / Cs (7) Vs'-Vgl = q3 '/ Cgs (8) Q = q1' + q2 '+ q3' … (9)

From the above equations (6) to (8) and (9), the following equation (10) is derived.

[0038]

(Equation 2)

From the above equations (5) and (10), the following equation (1)
1).

[0040]

(Equation 3)

Here, the second term on the right side of the above equation (11) indicates a change in the pixel electrode voltage caused by the change of the scanning signal of the scanning line 41 from the high level to the low level. Called "feedthrough".

In the actual driving of the liquid crystal panel, the TFT
Since the time during which is turned on is sufficiently shorter than the time when the TFT is turned off, the effective voltage held at the pixel electrode can be regarded as Vs'.

On the other hand, at a screen position where the scanning signal is delayed,
The TFT is not instantaneously switched from the on-state to the off-state, but is on until the scanning signal drops from the high level voltage to the TFT threshold voltage due to signal delay.

The pixel electrode voltage at this time gradually decreases from the already written gradation voltage Vs because the amount of charge stored in the capacitor Cgs changes as the scanning signal decreases from the high level voltage. . However, since the TFT is turned on due to the delay of the scanning signal, a new charge flows from the data line to the pixel electrode. Due to the delay of the scanning signal, the amount of newly introduced charge is represented by Q ″, the pixel electrode voltage when the scanning signal becomes a low level voltage is represented by Vs ″, and the charges of the capacitors Clc, Cs, and Cgs are represented by q, respectively.
Assuming that the scanning signal has a low level voltage, the following equations (12) to (14) hold.

Vs ″ −Vcom = q1 ″ / Clc (12) Vs ″ −Vgl = q2 ″ / Cs (13) Vs ″ −Vgl = q3 ″ / Cgs (14) Q + Q ″ = q1 ″ + q2 ″ + q3 ″… (15)

From the above expressions (12) to (14) and (15), the following expression (16) is derived.

[0047]

(Equation 4)

The following equation (17) is derived from the above equations (5) and (16).

[0049]

(Equation 5)

Here, the second term on the right side of the above equation (17) represents the feedthrough amount at the screen position where the scanning signal is delayed.

From the comparison with the above equation (11), it has been shown that the in-plane variation of the pixel electrode voltage (effective value) due to the delay of the scanning signal is caused by the variation of the feedthrough amount.

The magnitude of the variation of the pixel electrode voltage (effective value) is determined by the difference Δ between the above equations (17) and (11).
It can be expressed as the following equation (18).

[0053]

(Equation 6)

In addition, in the above equation (18), considering the parameter depending on the temperature, it is expressed as the following equation (19).

[0055]

(Equation 7)

In the above equation (19), the charge amount Q ″ (T)
Is caused by the temperature dependence of the TFT characteristics.

As shown in FIG. 9, it is known that the temperature dependency of the TFT characteristics is such that the drain-source current (hereinafter referred to as “drain current”) under a constant gate voltage increases as the temperature rises. I have. Therefore, at a certain current value, the drain current becomes sufficiently small.
If the source-to-source voltage is regarded as the threshold voltage of the TFT, the threshold voltage of the TFT decreases as the temperature rises.

Therefore, at the screen position where the scanning signal delay is large, the charge inflow increases as the temperature rises due to the temperature characteristics of the TFT, and further, the charge inflow is performed longer due to the decrease in the TFT threshold voltage. (T) increases with an increase in temperature.

The liquid crystal capacitance Clc (T) can be known from the temperature dependence of the liquid crystal dielectric constant. FIG. 10 shows the measured value of the liquid crystal dielectric constant in the direction perpendicular to the panel surface, and the liquid crystal capacitance Clc (T) is proportional to this dielectric constant.

The liquid crystal dielectric constant has a temperature characteristic that decreases as the temperature rises, and therefore, the liquid crystal capacitance Clc (T) has a temperature dependency that decreases as the temperature rises. Further, both the capacitances Cgs and Cs are constant independently of the temperature. Therefore, from the above equation (19), it can be seen that the in-plane variation Δ (T) of the pixel electrode voltage (effective value) due to the delay of the scanning signal increases as the temperature rises.

From the above description, it has been shown that the in-plane variation of the pixel electrode voltage (effective value) increases as the temperature rises.

As described above, when the in-plane variation of the pixel electrode voltage (effective value) is increased, the DC voltage applied to the liquid crystal which is generated in a part of the panel surface is also increased. There's a problem.

In order to solve such a problem, in the correction of the gradation voltage and the common electrode voltage according to the temperature change as in the above-described prior art, even if the entire panel can be uniformly corrected, Of the pixel electrode voltage (effective value) cannot be corrected.

Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to correct an increase in in-plane variation of a pixel electrode voltage due to a rise in temperature and to improve display quality in a wide temperature range. It is to provide a liquid crystal display device.

[0065]

In order to achieve the above object, a liquid crystal display device according to the present invention is provided with a temperature sensor for detecting the temperature of the panel housing when the liquid crystal display device is operating, inside or on the side of the panel housing. The high level voltage or both the high level voltage and the low level voltage of the scanning signal pulse are changed according to the output of the temperature sensor, and the voltage level is automatically adjusted so as to lower the voltage level at high temperature and to increase the voltage level at low temperature. It is characterized by including a temperature compensation circuit.

The principle of the present invention will be described below. First, the operation when the high level voltage of the scanning signal pulse is changed will be described.

In the above equation (19), Q ″ represents a new delay time from the high level voltage to the TFT threshold voltage while the scanning signal changes from the high level voltage to the low level voltage. Represents the amount of charge flowing into the.

In order to reduce the Q ″, the high-level voltage of the scanning signal may be reduced to shorten the delay time of the scanning signal. By decreasing the high-level voltage as the temperature rises, the Q ″ may be reduced. An increase in (T) is suppressed, whereby an increase in Δ (T), that is, an increase in in-plane variation of the pixel electrode voltage (effective value) can be suppressed, and a decrease in display quality can be prevented.

[0069]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

Referring to FIG. 1, in the embodiment of the present invention, a data driver 3 for outputting a voltage signal to be written to each pixel in a liquid crystal display panel and a scanning signal for controlling each switching element in the liquid crystal panel 1 are provided. It comprises an active matrix driven liquid crystal display device having a scanning driver 2 for outputting.

In FIG. 1, a controller 4 receives a video signal, a clock, a vertical and horizontal synchronizing signal, and controls a data signal output from a data driver 3 and a scanning signal output from a scanning driver 2 so as to control the TFT liquid crystal. The panel 1 is driven.

The temperature compensating circuit 5 includes a temperature sensor 5-1.
And a correction voltage generation circuit 5-2. The temperature sensor 5-1 is installed inside or on the side of the panel housing to detect the temperature of the panel housing during operation of the liquid crystal display device and generate a correction voltage. The circuit 5-2 generates a high-level voltage and a low-level voltage of a scanning signal pulse corresponding to the output of the temperature sensor 5-1 and supplies them to the scanning driver 2.

The high-level voltage and low-level voltage of the scanning signal pulse generated by the temperature compensating circuit 5 reduce the voltage level of the scanning signal pulse at high temperatures and prevent the low-level voltage at low temperatures, in order to prevent the display quality from deteriorating due to temperature changes. Automatically adjust to increase the voltage level.

The functions and effects actually obtained by the liquid crystal display device according to the embodiment of the present invention will be described below.

FIG. 2 shows, as a comparative example, the relationship between the in-plane variation Δ of the scanning signal high level voltage and the pixel electrode voltage (effective value) in an active matrix driven liquid crystal display device without the temperature compensation circuit 5 of FIG. It is a figure which shows the result of having measured the relationship in different temperature. The rhombus, white circle, and black circle symbols in the figure are the measurement results at 5 ° C., 25 ° C., and 45 ° C., respectively, and each measurement point is connected by a straight line. In addition,
Even when both the high-level voltage and the low-level voltage of the scanning signal are simultaneously changed, the same tendency as in FIG. 2 is obtained.
A description thereof will be omitted.

Referring to FIG. 2, in the liquid crystal display device without temperature compensation circuit 5, since the high level voltage of the scanning signal is constant, the in-plane variation of the pixel electrode voltage increases as the temperature increases. . This means that the display quality decreases as the temperature increases.

Therefore, a case where a temperature compensation circuit 5 is added to the liquid crystal display device according to the embodiment of the present invention will be considered. In the temperature compensation circuit 5, for example, 5 ° C., 25 ° C.,
The scanning signal high level voltage corresponding to 5 ° C. is respectively
20.7 V, 18.2 V, and 16.75 V, the voltage levels are set to be lower as the temperature rises.
Therefore, the in-plane variation Δ of the pixel electrode is approximately 0.225 V
(Shown by a broken line in the figure). Therefore, a constant display quality can be maintained irrespective of a temperature change.

When the high-level voltage of the scanning signal is simply reduced, the writing speed to the pixel electrode is reduced and the display quality is reduced. However, when the temperature is increased, the writing speed is reduced due to the temperature dependence of the TFT characteristics. Since it acts so as to increase, the display quality is not affected even if the high level voltage of the scanning signal is slightly lowered with an increase in temperature.

As described above, in the liquid crystal display device according to the embodiment of the present invention shown in FIG. 1, the high level voltage of the scanning signal pulse or both the high level voltage and the low level voltage are detected by the temperature sensor 5-1. Change according to the output of
By providing a temperature compensating circuit 5 that automatically adjusts the voltage level to lower at high temperature and raises the voltage level at low temperature, it is possible to prevent the deterioration of display quality due to the in-plane variation of the pixel electrode voltage due to the temperature change. Can be.

[0080]

EXAMPLE Next, as an example of the present invention, a specific configuration example of a temperature compensation circuit that can be used in the liquid crystal display device described as the embodiment of the present invention will be described.

[Embodiment 1] FIG. 3 is a diagram showing a configuration of a first embodiment of a temperature compensation circuit in a liquid crystal display device according to the present invention. Referring to FIG. 3, the temperature compensation circuit includes a temperature sensor 21, an A / D converter (ADC) 24 for converting an analog output of the temperature sensor 21 into a digital signal, a storage circuit 25 such as a read-only memory (ROM), and a storage. It can be easily configured using a general temperature compensation circuit including a D / A converter (DAC) 26 that reads data from the circuit 25 and outputs a voltage. In FIG. 3, a thermistor 21 is used as a temperature sensor, and a voltage at a connection point 23 between the thermistor 21 and the resistance element 22 is input to an A / D converter 24 and converted into a digital signal. In accordance with the digital signal, high-level voltage or low-level voltage data of a scanning signal pulse preset in the storage circuit 25 is selected, and the voltage data is converted into an analog signal by the D / A converter 26 to obtain the scanning signal. A high level voltage (Vgh) or a low level voltage (Vgl) is supplied to the scan driver.

As the data to be set in the storage circuit 25 in advance, an arbitrary temperature correction table having an optimum scan signal voltage output with respect to the temperature can be set.

Although a thermistor is used as a temperature sensor in FIG. 3, a general electronic element or IC used for detecting a temperature change can also be used as a temperature sensor.

[Embodiment 2] FIG. 4 is a diagram showing a configuration of a second embodiment of a temperature compensation circuit which can be used in the liquid crystal display device of the present invention.

Referring to FIG. 4, the temperature compensation circuit in this embodiment does not have a storage circuit as in the first embodiment, but includes a general temperature compensation circuit including a temperature sensor and a differential amplifier. It can be easily configured using.

FIG. 4A shows a configuration example of a temperature compensating circuit, in which a bipolar transistor 3 is used as a temperature sensor.
1 and the junction temperature coefficient of the bipolar transistor 31 is used. Resistance elements 35, 36
, A reference voltage V0 is generated and input to the non-inverting (+) terminal of the operational amplifier 32. The output terminal of the operational amplifier 32 is connected to the inverting (-) terminal via the resistance element 34.

The transistor 31 has a base and a collector connected to the power supply VDD, and an emitter connected to the power supply VSS via the resistance element 37. The connection point between the emitter of the transistor 31 and the resistor 37 is connected to the inverting terminal of the operational amplifier 32 via the resistor 33.

In such a circuit configuration, the voltage at the connection point between the emitter of transistor 31 and resistance element 37 is set to V1
Then, when the threshold voltage of the transistor 31 (that is, the base-emitter voltage V _BE ) changes due to a temperature change, the value of V1 also changes accordingly. Further, since the operational amplifier 32 and the resistance elements 33 and 34 are general differential amplifiers, if the resistance values of the resistance elements 33 and 34 are Rs and Rf, respectively, according to the values of Rs and Rf,
The difference voltage between the reference voltage V0 and the voltage V1 is amplified, added (subtracted) to the reference voltage V0, and output from the operational amplifier 32.

Assuming that the output voltage of the operational amplifier 32 is Vout, by a simple calculation, It has the relational expression.

V1 sets the resistance values of the resistance elements 35, 36 and 37 so as to be higher than the reference voltage V0.
When f> Rs, the voltage V1 and the output voltage Vout have characteristics as shown in FIG. 4B with respect to temperature.

This is because the temperature of the transistor 31 increases as the temperature rises.
, The threshold voltage (base-emitter voltage V _BE ) slightly decreases, so that the voltage V1 also increases accordingly, and the output voltage Vout decreases. The amount of change in the output voltage Vout is a value obtained by amplifying the amount of change in the voltage V1 at a magnification of the resistance ratio Rf / Rs.

As described above, since the voltage level decreases as the temperature rises, it can be used as the temperature compensation circuit of the liquid crystal display device described in the embodiment.
Since the change in the threshold voltage of the transistor with respect to the temperature changes substantially linearly, the scanning signal high-level voltage is also corrected substantially linearly with respect to the temperature.

The optimum correction value of the scanning signal high-level voltage for preventing the deterioration of the display quality is often non-linear with respect to the temperature change, so that the temperature compensation circuit having the built-in storage circuit as in the first embodiment is required. Although it is effective to use it, there is a problem that the circuit becomes complicated.

On the other hand, in the temperature compensation circuit shown in the second embodiment, the correction value is determined by linearly approximating the optimum correction value of the scanning signal high-level voltage which is non-linear with respect to the temperature. Fig. 4
By setting the reference voltage V0 and the resistance ratio Rf / R shown in (a), a temperature compensation circuit having a simple circuit configuration can be provided.

Further, as the temperature compensating circuit, a circuit having the same function as a combination of various temperature sensors and amplifiers other than the above can be used.

[0096]

As described above, according to the liquid crystal display device of the present invention, the temperature sensor for detecting the temperature of the panel housing during the operation of the liquid crystal display device is provided inside or on the side of the panel housing to perform scanning. The high-level voltage or both the high-level voltage and the low-level voltage of the signal pulse are changed according to the output of the temperature sensor, and the voltage level of the scanning signal pulse is automatically reduced so as to decrease at a high temperature and to increase the voltage level at a low temperature. By providing the temperature compensation circuit, it is possible to prevent the in-plane variation of the pixel electrode voltage (effective value) from increasing due to the temperature rise, and to prevent the display quality of the liquid crystal display device from deteriorating due to the temperature change. .

The reason is as described above, but will be briefly described below.

The in-plane variation of the pixel electrode voltage (effective value) is such that the switching of the TFT from the ON state to the OFF state is delayed in the screen position where the scanning signal is delayed, and the writing to the pixel electrode is performed in the screen position where there is no signal delay. This is because the writing is performed for a longer time, and when the temperature rises, the writing speed increases due to the temperature dependency of the TFT characteristics and the like, and the in-plane variation of the pixel electrode voltage (effective value) increases. Therefore, if the scanning signal high-level voltage is reduced as the temperature rises,
Since the delay of the scanning signal is reduced, the in-plane variation of the pixel electrode voltage (effective value) can be suppressed from expanding, and the display quality can be prevented from lowering.

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining the principle of the embodiment of the present invention. As a comparative example, the variation in the pixel electrode voltage of the liquid crystal display device due to the temperature and the embodiment of the present invention are not provided with the temperature compensation circuit. FIG. 4 is a diagram for explaining the principle of variation compensation according to a mode.

FIG. 3 is a diagram showing a configuration example of a temperature compensation circuit in a liquid crystal display device according to the present invention as a first embodiment of the present invention.

FIG. 4 is a diagram showing another configuration example of the temperature compensation circuit in the liquid crystal display device according to the present invention as a second embodiment of the present invention.

FIG. 5 is a diagram showing a structure of a conventional active matrix panel.

FIG. 6 is a driving waveform diagram of a conventional active matrix panel.

FIG. 7 is a waveform diagram for explaining a problem of the related art.

FIG. 8 is a diagram showing an equivalent circuit of one pixel of the liquid crystal display device.

FIG. 9 is a diagram showing temperature characteristics of a TFT.

FIG. 10 is a diagram showing a temperature characteristic of a liquid crystal dielectric constant.

FIG. 11 is a diagram illustrating a configuration of a liquid crystal display device including a conventional temperature compensation circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 TFT liquid crystal panel 2 Scan driver 3 Data driver 4 Controller 5 Temperature compensation circuit 21 Thermistor 22 Resistance element 23 Terminal 24 A / D converter (ADC) 25 Storage circuit (ROM) 26 D / A converter (DAC) 31 Transistor 32 Operational amplifier ( Amplifier) 33 resistive element (Rs) 34 resistive element (Rf) 35 resistive element 36 resistive element 37 resistive element 40 scan line (n-1) 41 scan line (n) 42 data line 43 TFT (thin film transistor) 44 pixel electrode 45 common electrode

Claims (3)

[Claims] An active matrix liquid crystal display device comprising a data driver for outputting a voltage signal to be written to each pixel in a liquid crystal display panel and a scan driver for outputting a scan signal for controlling each switching element in the panel. A temperature sensor for detecting the temperature of the panel casing during operation of the liquid crystal display device is provided inside or on the side of the panel casing, and the high-level voltage and / or the low-level voltage of the scanning signal pulse are changed according to the output of the temperature sensor. A liquid crystal display device comprising: a temperature compensating circuit for automatically adjusting the voltage level of the scanning signal pulse to decrease at high temperature and increasing the voltage level of the scanning signal pulse at low temperature. 2. A storage unit for storing high-level voltage or low-level voltage data of the scanning signal pulse selected in accordance with an output of the temperature sensor, wherein the temperature compensating circuit stores voltage data from the storage unit. And a D / A converter for reading the scan signal and supplying the scan signal to the scan line driver, wherein the scan driver outputs a scan signal having a high level voltage and a low level voltage according to the output of the temperature sensor. 2. The liquid crystal display device according to claim 1, wherein: 3. An element having a predetermined temperature characteristic is used as the temperature sensor, and a voltage obtained through the element is amplified to lower the voltage level of the scanning signal pulse at a high temperature and the scanning signal pulse at a low temperature. 2. The liquid crystal display device according to claim 1, wherein the voltage is automatically adjusted so as to increase the voltage level of the pulse.