KR19980048655A - Temperature Compensation Circuit of Liquid Crystal Display - Google Patents

Abstract

In the liquid crystal display device, the image quality deteriorates due to distortion of the pixel voltage due to deterioration of the liquid crystal or leakage current generated by parasitic capacitance according to an external temperature. Thus, a method for reducing the distortion of the pixel voltage has been developed. The present invention provides a gate voltage and a common voltage by providing an auxiliary voltage unit for correcting changes due to temperature changes in the gate voltage generator and the common voltage generator. It is directed to reducing the distortion of the pixel voltage by minimizing the variation of.

Description

Temperature Compensation Circuit of Liquid Crystal Display

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature compensating circuit of a liquid crystal display, wherein a temperature compensating circuit is provided to compensate for a liquid crystal voltage between a pixel electrode and a common electrode, which is changed according to a temperature change occurring in a common electrode and a gate electrode. The purpose is to apply a compensation signal to the gate electrode.

Currently, LCDs are generally used in two ways, segment type used in calculators and active matrix type used in computer monitors and TVs. Among them, an active matrix type liquid crystal display device (hereinafter referred to as TFT-LCD) has a signal inverted at every vertical and horizontal period output from a signal inversion driving circuit (not shown) as shown in FIG. The data signal of the odd pixel is sampled by the first shift resist 111, and the signals of the plurality of odd pixels are sampled and held by the first holding part 112 for one horizontal scanning period of the panel 100. The upper source driver for supplying each odd-numbered data line and the data signal of the even-numbered pixel are respectively sampled and held by the second shift resist and the second holding part 122 in accordance with the input signal. A gate which sequentially outputs a gate control signal for each horizontal scanning period along the gate lines G1, G2, G3 ... of the TFTs of the panel 100 and the lower source driver 120 to supply the first data line The drive unit 130, The common electrode voltage driver 140 supplies a common voltage applied to the common electrode of the panel.

In the general TFT-LCD configured as described above, a signal inverted at vertical and horizontal periods is first output from a signal inversion driving circuit (not shown) and input to the upper and lower source drivers 110 and 120.

First, the first shift register 111 of the upper source driver 110 samples an image signal to display the radix pixels d1, d3,... In the horizontal direction from the input image signal. The signals are thus held in the plurality of odd pixels sampled in the first holding unit 112 for one horizontal scanning period 1H and input to the data lines.

Similarly, the lower source driver 120 samples the data signals of the even-numbered pixels d2, d4,... In the second shift resist 121. The sampled signal is held in the first holding unit 122 for one horizontal scanning period and input to the data line. In addition, the gate driver 130 sequentially outputs signals that are sequentially turned on by one horizontal scanning period along each gate line g1, g2,...

That is, a data signal corresponding to an image signal from the upper source driver 110 and the lower source driver 120 is supplied to the drain terminal of the TFT of the unit pixel through the data line, and the gate pulse voltage output from the gate driver 130 is output. At this high level, the TFTs of the respective unit pixels connected to the gate lines are in a conductive state to supply data voltages to the storage capacitor Cs and the liquid crystal capacitor, and the inverted signals are supplied from the Vcom driver to drive the liquid crystal.

At this time, in order to prevent deterioration of the liquid crystal, the liquid crystal is driven by alternately inverting the Vcom voltage and the polarity of the image signal. That is, AC driving is performed by inverting the image signal applied to the display electrode of the liquid crystal and the Vcom voltage applied to the counter electrode at the vertical and horizontal periods. By inverting the polarity of the image signal and the common electrode signal in this manner, deterioration of the liquid crystal is prevented by applying a constant voltage to the liquid crystal at all times, and thus, flickering and the like can be improved by inverting the vertical and horizontal periods.

However, when the difference between the data voltage and the common electrode voltage is applied to the liquid crystal, a phenomenon in which the transmittances of the liquid crystal are different at the time of inversion of the data voltage polarity, i.e., positive and negative, appears. This is different depending on the magnitude of the applied data voltage, so that the difference is minimized by adjusting the inverted reference voltage of the common electrode at the initial stage of panel manufacturing.

On the other hand, when the deterioration of the liquid crystal due to the external temperature and the light source occurs, a change in the TV (Transmission-Voltage) characteristics of the liquid crystal display occurs, which causes the initial state of the Vcom driver or the image signal inversion reference voltage at an initial temperature at an optimal temperature. Even if it is adjusted to, if the temperature rises or falls below room temperature, the transmittance of the liquid crystal panel changes, causing deterioration of image quality.

2 is a graph showing a change in the T-V curve of the liquid crystal display according to the temperature change of the liquid crystal display. The TV curve of the LCD is to the right of the TV curve when the temperature of the LCD rises above the reference temperature and to the left of the TV curve when the temperature of the LCD falls below the reference temperature. Move. Since the transmittance at the same voltage changes as the temperature changes as described above, it is necessary to adjust the voltage difference between the common electrode applied to the liquid crystal and the data voltage in accordance with the change of temperature in order to obtain a desired transmittance. In general, a compensation signal according to a change in temperature is applied to the common electrode voltage to prevent a change in transmission characteristics due to a change in temperature.

As shown in Fig. 2A, a voltage having a transmittance of 50% is Vb at a general reference temperature (25 ° C), a voltage having a transmittance of 50% when the temperature rises, and a voltage having a transmittance of 50% when the temperature drops. Assume Vc. Then, the change in the pixel voltage according to the change in temperature can be approximated by a linear graph as shown in FIG. 2B.

The prior art JP-5-307169 applies a compensation signal to the common electrode to compensate for the change in the T-V curve with temperature. However, JP-5-307169 does not show a clear solution to the problem that when the voltage of the common electrode Vcom is changed by the compensation signal, the gate signal should be changed accordingly.

FIG. 3 shows the common electrode signal 200 corrected by applying a compensation signal ⑦⑧ for compensating for the change of the TV characteristic according to the temperature change when the floating gate is driven to the common electrode. As described above, when the compensation signal is not applied, the voltage difference (①②) between the common electrode signal and the gate signal is the same regardless of the polarity. However, when the compensation signal is applied, the value (③④) varies depending on the polarity. As described above, when the difference between the common electrode voltage and the gate voltage varies depending on the polarity, the leakage current value changes according to the polarity, thereby causing flicker and the like, thereby degrading the image quality. ⑤ denotes the amplitude of the gate voltage, and ⑥ denotes the amplitude of the common voltage to which the compensation signal is not applied.

That is, a means for compensating for the liquid crystal driving voltage which is changed by the variation of the common voltage and the gate voltage according to the temperature change is necessary.

1 is a block diagram showing a driving circuit of a general liquid crystal display device.

Figure 2 shows the state diagram of the T-V characteristic curve with the change of temperature.

3 is a view showing waveforms of a compensation signal for compensating for a change in T-V characteristic during driving of a floating gate.

4 is a schematic configuration diagram of a temperature compensation circuit of the liquid crystal display device of the present invention;

5 is a circuit diagram showing a temperature compensation circuit according to an embodiment of the present invention.

6 is a timing chart of the output when the temperature is lowered than the reference temperature in the temperature compensation circuit of the present invention.

FIG. 7 illustrates waveforms of a gate signal and a common electrode signal when the common electrode is driven by an alternating current in the present invention.

DESCRIPTION OF SYMBOLS 100 Liquid crystal panel 110 Upper source driver 111 First shift resist

112: first holding portion 120: lower source driving portion 121: first shift resist

122: first holding unit 130: gate driver 140: common electrode voltage driver

10: signal inversion driving circuit 200: compensated common electrode signal

310: gate signal generator 311: common electrode signal generator 312: common electrode signal correction

313: gate signal compensator 314: compensation signal generator 315: temperature detector

400: gate signal 410: corrected gate signal 420: common electrode signal

430: corrected common electrode signal

A1, A2, A3, A4, A5, A6, A7: Operational Amplifier

D1, D2, D3, D4: Signal line G1, G2, G3: Scan line

Dt: Temperature detector

PCS: Polarity Control Signal

①, ②: Voltage difference between gate voltage and common electrode signal before correction

③, ④: Voltage difference between gate voltage and common electrode signal after common electrode signal correction

⑤: amplitude of gate voltage ⑥: amplitude of common voltage to which compensation signal is not applied

⑦, ⑧: compensation signal voltage

⑨, ⑩, ⑬: voltage difference between common electrode signal and gate-off voltage without compensation signal

⑪, ⑫, ⑭, ⑮: voltage difference between common electrode signal to which compensation signal is applied and gate-off voltage

The present invention is a temperature compensation circuit of a liquid crystal display device for compensating for a change in transmission characteristics according to a temperature change of the liquid crystal display device. The temperature compensating circuit of the liquid crystal display of the present invention includes a gate voltage generating means 310 for applying a gate voltage to a gate line, a common voltage generating means 311 for applying a common voltage to a common electrode, a reference temperature and an actual value. A temperature detecting means 315 for detecting the temperature of the liquid crystal, a compensation signal generating means 314 for detecting a difference voltage between the reference voltage applied to the liquid crystal at the reference temperature and the actual voltage applied to the liquid crystal at the actual temperature, and the compensation signal And a gate voltage correction means 313 for outputting the difference voltage detected by the generating means in combination with the gate voltage, and a common voltage correction means 312 for outputting the difference voltage in combination with the common voltage.

4 is a schematic configuration diagram of a temperature compensation circuit of the liquid crystal display device of the present invention. The output of the compensation signal generator 314, which receives the output of the temperature detector 315, is input to the gate signal compensator 313 and the common electrode voltage compensator 312. The output of the common electrode voltage generator 311 and the output of the gate signal generator 310 are applied to the common electrode Vcom and the gate electrode G through respective correction units.

The compensation signal generating means 314 is connected to a non-inverting input terminal to input a reference signal (Vref), and is connected to the inverting input terminal actual voltage generated at the actual temperature of the liquid crystal detected by the temperature sensor A first amplifying means (A1) comprising an actual input terminal for inputting a; The actual temperature of the liquid crystal detected by the temperature sensor connected in parallel with the first amplification means, connected to a non-inverting input terminal to input a reference voltage, connected to a ground terminal in parallel, and connected to an inverting input terminal. A second amplifying means (A2) comprising an actual input terminal for inputting an actual voltage generated in the circuit; The output terminal of the second amplifying means is connected to a non-inverting input terminal, and the output of the first amplifying means comprises a third amplifying means A3, which is a means for determining a feedback resistance value. The means for determining the feedback resistance value is composed of a switch element such as a transistor and a resistor.

The gate voltage correction means 313 further includes: fourth amplification means A4 for applying the difference voltage to the inverting input terminal; An output of the fourth amplifier and the gate voltage Vg output from the gate voltage generator (not shown) are configured by the fifth amplifier A5 applied to the non-inverting input terminal. In addition, the common voltage correction means (312) and the sixth amplification means (A6) for applying the difference voltage to the inverting input terminal; An output of the sixth amplifying means and a seventh amplifying means A7 are applied to the common voltage Vcom output from the common voltage generator (not shown) to the non-inverting input terminal.

Hereinafter, the temperature compensation circuit of the liquid crystal display according to the embodiment of the present invention will be described with reference to FIG. Fig. 6 shows the waveform of the signal Vd applied to the temperature compensation circuit of the present invention.

(Example)

The reference input value Vref of the non-inverting input terminal of the first operational amplifier and the second operational amplifier is equal to the output value of the temperature detector at the reference temperature (for example, 25 ° C.). The output of the temperature detector and the reference input are input to the terminals of the first and second operational amplifiers. The first operational amplifier outputs the difference voltage between the reference input Vref and the output Vt of the temperature detector. The second operational amplifier outputs a polarity of a positive voltage when Vref > Vt and a polarity of a negative voltage when Vref < Vt. On / off of switch 1 (SW1) and switch 2 (SW2) is determined depending on whether the polarity output from the second operational amplifier is (+) or (-). When the temperature is higher than the reference temperature, the switch 2 is turned on so that the output of the third operational amplifier A3 is (1 + R2 / R1 = α), and when the temperature is lower than the reference temperature, the switch 1 is turned on. Amplified by (1 + R3 / R1 = β).

The compensation signal generating means 420 of the temperature compensation circuit of this embodiment is a first operation amplifier for outputting the difference between the reference input and the output from the temperature detecting means 410 as described above, and the reference input and the temperature detection. And a second operational amplifier for comparing the output from the means and a third operational amplifier for amplifying the output of the first operational amplifier in accordance with a set gain determined by the second operational amplifier.

Whether the output of the third operational amplifier is input to the fourth and sixth amplifiers by the polarity control signal (PCS) 500, or to the fifth and sixth amplifiers, which are non-inverting adders, Is determined. Does the polarity control signal add a compensation signal to the gate signal and the common electrode signal by turning on / off the switch 3 (SW3) and the switch 4 (SW4) or the switch 5 (SW5) and the switch 6 (SW6) for each gate signal period? Decide whether to subtract.

When the switch 3 and the switch 5 are turned on by the polarity control signal, the output of the fifth amplifier becomes a gate signal to which the compensation signal is added, and the output of the sixth amplifier becomes a common electrode signal to which the compensation signal is added. When switches 4 and 6 are turned on, the output of the fifth amplifier becomes a common electrode signal to which a compensation signal is added.

FIG. 7 is a timing diagram when the temperature of the liquid crystal display falls below the reference temperature so that the output of the first amplifier comes out as a positive value. If the temperature falls, the difference between the common electrode voltage Vcom and the pixel electrode voltage Vdata must be greater than the reference temperature. The output of the first amplifier is a positive value, and this value is the inverting amplifiers 4 and 6 amplifiers. It becomes negative. The fourth and sixth amplifiers lower the level of the common electrode voltage and the gate electrode voltage to increase the difference between the common electrode voltage and the pixel electrode voltage than the reference temperature. Since it does not occur, the deterioration of image quality can be prevented.

7A is a waveform diagram of a gate signal and a common electrode signal according to the temperature compensation circuit of the present invention when the common electrode is driven by alternating current, and FIG. 7B is a view of the waveform of the temperature compensation circuit of the present invention when the common electrode is driven by DC. A waveform diagram of a gate signal and a common electrode signal.

7A and 7B, the common electrode signal and the gate signal before the compensation signal is applied are indicated by solid lines, and the common electrode signal and the gate signal to which the compensation signal is applied are indicated by dotted lines. As can be seen in FIG. 7A, the voltage difference ⑩, 간의 between the common electrode signal and the gate-off voltage before the compensation signal is applied, and the voltage difference ⑪, ⑫ between the common electrode signal to which the compensation signal is applied and the gate-off voltage are the same. As shown in FIG. 7B, the voltage difference 의 between the common electrode signal and the gate-off voltage before the compensation signal is applied and the voltage difference ⑬, 차 between the common electrode signal to which the compensation signal is applied and the gate-off voltage are the same.

According to the present invention, by receiving the output of the temperature detector, the compensation signal generator generates a compensation signal and applies a signal corrected according to the compensation signal to the gate electrode and the common electrode, thereby preventing a change in the transmission amount according to the change of temperature, When the compensation signal is applied only to the electrode, the flicker caused by the variation of the leakage current value can be prevented, so that the image quality deterioration of the liquid crystal display device can be prevented.

In addition, the temperature compensation circuit of the present invention corrects both the gate voltage and the common electrode signal and applies them together to maintain the voltage difference between the gate voltage and the common electrode signal, thereby reducing the influence on the voltage charged in the pixel before the temperature change. It also has the effect of making the liquid crystal panel operate stably.

Claims (11)

Gate voltage generating means for generating a gate voltage; Common voltage generating means for generating a common voltage; Compensation signal generating means for detecting a difference voltage between the reference voltage applied to the liquid crystal at the reference temperature and the actual voltage applied to the liquid crystal at the actual temperature; Gate voltage correction means for outputting a corrected gate voltage by adding the difference voltage generated by the compensation signal generator and the gate voltage generated by the gate voltage generator; And a common voltage correction means for outputting a common voltage corrected by adding the difference voltage generated in the correction signal generator and the common voltage generated in the common voltage generator. In claim 1, the compensation signal generating means is connected to the non-inverting input terminal and the reference input terminal for inputting a reference signal, First amplification means connected to an inverting input terminal and configured to input an actual voltage generated at an actual temperature of the liquid crystal detected by the temperature sensor; Connected in parallel with the first amplifying means, A reference input terminal connected to the non-inverting input terminal and inputting a reference voltage, and a reference input terminal connected in parallel with the ground terminal; Second amplifying means connected to the inverting input terminal and configured to input an actual voltage generated at an actual temperature of the liquid crystal detected by the temperature sensor; A non-inverting input terminal connected to an output terminal of the second amplifying means, And a third amplifying means comprising an output of said first amplifying means comprising means for determining a feedback resistance value. The temperature compensation circuit according to claim 2, wherein the means for determining the feedback resistance value comprises a switching element for selecting the feedback resistance. The temperature compensation circuit according to claim 1, wherein the compensation signal generating means comprises a temperature detecting means and a correction voltage detecting means. The temperature compensation circuit according to claim 4, wherein the temperature detection means uses a temperature sensor. The apparatus of claim 4, wherein the correction voltage detecting means comprises: a reference input terminal connected to the non-inverting input terminal to input a reference signal; First amplifying means connected to an inverting input terminal and configured to input an actual voltage generated at an actual temperature of the liquid crystal detected by the temperature detecting means; Connected in parallel with the first amplifying means, A reference input terminal connected to the non-inverting input terminal and inputting a reference voltage, and a reference input terminal connected in parallel with the ground terminal; Second amplifying means connected to the inverting input terminal and configured to input an actual voltage generated at an actual temperature of the liquid crystal detected by the temperature sensor; A non-inverting input terminal connected to an output terminal of the second amplifying means, And a third amplifying means comprising an output of said first amplifying means comprising means for determining a feedback resistance value. The temperature compensation circuit according to claim 6, wherein the means for determining the feedback resistance value comprises a switching element for selecting the feedback resistance. The gate voltage correction means of claim 1, further comprising: third amplifying means for applying the difference voltage to an inverting input terminal; And a fourth amplifying means for applying the output of the third amplifying means and the gate voltage output from the gate voltage generator to a non-inverting input terminal. 3. The apparatus of claim 1, wherein the common voltage correcting means includes: third amplifying means for applying the difference voltage to an inverting input terminal; And a fourth amplifying means for applying the output of the third amplifying means and the common voltage output from the common voltage generator to the non-inverting input terminal. A gate voltage is applied to the gate terminal of the thin film transistor; A pixel voltage applied to the pixel electrode through the source terminal and the drain terminal of the thin film transistor; A driving method of a liquid crystal display device which operates by driving a liquid crystal by a voltage difference from a common voltage applied to a common electrode by a common voltage applying means, Compensating for the gate voltage and applying the change in the voltage difference generated by an external temperature change to the gate electrode; And driving the voltage difference to compensate for the common voltage and apply it to the common electrode. The method of claim 10, further comprising: a voltage difference between the gate voltage and the common voltage before compensating for the change; And the voltage difference between the gate voltage and the common voltage after compensating for the change is the same.