KR20080039719A - LCD Display - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device for compensating a gate low voltage in order to control a TFT off current that changes according to ambient temperature characteristics of a liquid crystal panel. A driving voltage generation circuit for compensating and outputting the gate low voltage by the temperature sensing means when generating a low voltage; A data driving circuit receiving the gamma reference voltage to generate a gray scale voltage; A gate driving circuit to which a gate on / off voltage is applied from the driving voltage generating circuit; And a liquid crystal panel driven by the gray voltage and the gate on / off voltage to implement an image.

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY DEVICE}

1 is a block diagram showing a driving voltage generating circuit of a liquid crystal display according to the related art.

2 is a graph showing that the off current of a TFT increases due to an increase in the ambient temperature of the liquid crystal display according to the related art.

3 is a block diagram of a liquid crystal display according to the present invention.

4 is a circuit diagram illustrating a DC / DC converter and a gate voltage compensator of FIG. 3 as an example.

5 is a circuit diagram illustrating a DC / DC converter and a gate voltage compensator of FIG. 3 according to another embodiment;

FIG. 6 is a circuit diagram illustrating a DC / DC converter and a gate voltage compensator of FIG. 3 as still another embodiment; FIG.

Explanation of symbols on the main parts of the drawings

200: driving voltage generation unit 200a: step-down unit

200b: DC / DC converter 200c: gamma voltage generator

200d: gate voltage compensator 202: data driver

204: gate driver 210: liquid crystal panel

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display, and more particularly, to compensate for a gate low voltage in order to control a TFT off current that varies according to ambient temperature characteristics of a liquid crystal panel, thereby improving cross-talk phenomenon on a screen. It is related to

As the information society in the 21st century develops, the demand for a display device for displaying an image is increasing in various forms. Recently, various flat panel displays such as LCD, Plasma Display Panel (PDP), Electro Luminescent Display (ELD), and Vacuum Fluorescent Display (VFD) are utilized. Among them, the liquid crystal display is not only capable of driving at low power but also image quality characteristics. This is particularly excellent and widely used.

In general, a liquid crystal panel including two substrates facing each other and liquid crystal injected between the substrates is used. Of course, the two substrates of the liquid crystal panel include an array substrate on which a thin film transistor (TFT) is formed and a color filter substrate on which a color filter is formed, and a backlight device for supplying light to the liquid crystal panel, a liquid crystal panel, A frame for accommodating and supporting the backlight device is modularized to form an LCD device.

Among these LCD modules, we will briefly examine the driving voltage circuit. 1 is a block diagram showing a driving voltage generating circuit of a liquid crystal display according to the prior art. In general, a liquid crystal display device such as a notebook computer appropriately converts a commercial AC voltage of 100 to 220V from the outside to be used in the LCD module unit. For example, when the predetermined AC / DC adapter 10 configured separately from the LCD module unit is connected to an outlet, the commercial AC voltage is output at DC 12V.

The step-down part 20b receives the DC 12V voltage from the AC / DC adapter 10 and generates and outputs a new DC voltage in the range of approximately 3V to 5V. Of course, such a step-down circuit has already been known.

Meanwhile, the DC / DC converter 20c converts the DC voltage provided from the step-down part 20b to generate at least one different DC voltage. Specifically, the common voltage Vcom is generated by the common voltage generator by generating a power supply voltage Vdd for adjusting the liquid crystal transmittance in the LCD panel unit or by using a common voltage signal provided from the DC / DC converter 20c. Generated and provided to the LCD panel. In addition, it generates various voltages required to drive the LCD, such as generating gate voltages (Vgl and Vgh) for generating gate signal voltages.

Among them, the power supply voltage generated from the DC / DC converter 20c is applied to the gamma voltage generation unit 20d to generate a plurality of gamma reference voltages Vref for driving the pixels of the liquid crystal panel, and the gamma The reference voltage Vref is provided to a data driver (not shown) again.

Of course, the process so far has described the case where the external commercial power supply voltage is used in the liquid crystal display device. However, if there is no supply of such a commercial power supply voltage, the liquid crystal display device is driven by using the battery provided in the battery pack 20a as shown in the drawing. In this regard, the AC / DC adapter 10 described above. The output voltage of is only replaced by the battery voltage. In other words, DC 12V is applied to the battery voltage similarly to the output voltage of the AC / DC adapter 10.

As a result, the gamma voltage is generated by generating one power supply voltage regardless of whether the input voltage to the DC / DC converter 20c through the step-down part 20b is by using a commercial power supply voltage or a battery voltage. As a result, the gamma reference voltage Vref is generated by distributing a fixed power supply voltage of approximately 10V.

In the conventional configuration, the gate voltages Vgl and Vgh are sequentially applied along the gate lines of the liquid crystal panel through the gate driver (not shown). Substantially, the liquid crystal display device is a liquid crystal panel as shown in FIG. 2. Since the TFT off current increases with the increase of the ambient temperature, this causes a problem that cannot escape from the cross-talk phenomenon.

Therefore, in order to solve such a problem, the present invention uses a temperature sensing means such as a thermistor whose resistance value changes according to temperature characteristics, and configures a gate voltage compensator and compensates for the gate low voltage. have.

And the achievement of this object can be further embodied through the present invention. That is, when the liquid crystal display according to the exemplary embodiment of the present invention generates a gamma reference voltage and a gate low voltage by applying a predetermined voltage from the outside or the inside, the liquid crystal display device compensates the gate low voltage by a temperature sensing means and outputs the gate low voltage. A driving voltage generating circuit; A data driving circuit receiving the gamma reference voltage to generate a gray scale voltage; A gate driving circuit to which a gate on / off voltage is applied from the driving voltage generating circuit; And a liquid crystal panel driven by the gray voltage and the gate on / off voltage to implement an image.

In addition, the driving voltage generation circuit of the liquid crystal display device according to an embodiment of the present invention includes a step-down means for generating a predetermined voltage by receiving a predetermined voltage from the outside or inside; DC / DC conversion means for receiving a predetermined voltage from the step-down means and outputting a constant voltage (Vdd) and a gate low voltage; Gamma voltage generating means for generating at least one gamma reference voltage by dividing the constant voltage from the DC / DC converting means; And a gate low voltage compensating means for receiving the gate low voltage from the DC / DC converting means and compensating the gate low voltage by the temperature sensing means.

On the other hand, the liquid crystal display according to another embodiment of the present invention generates a gate low compensation voltage by the temperature sensing means when the gamma reference voltage and the gate low compensation voltage Vglc are generated by receiving a predetermined voltage from the outside or the inside. A driving voltage generating circuit for outputting; A data driving circuit receiving the gamma reference voltage to generate a gray scale voltage; A gate driving circuit to which a gate on / off voltage is applied from the driving voltage generating circuit; And a liquid crystal panel to which the gray voltage and the gate on / off voltage are applied.

In addition, the driving voltage generation circuit of the liquid crystal display according to another embodiment of the present invention includes a step-down means for generating a predetermined voltage by receiving a predetermined voltage from the outside or inside; DC / DC conversion means for compensating and outputting a voltage fed back by the temperature sensing means when generating a constant voltage (Vdd) and a gate low compensation voltage by receiving a predetermined voltage from the step-down means; And gamma voltage generating means for dividing the constant voltage from the DC / DC converting means to generate at least one gamma reference voltage.

Next, the above configuration will be described in detail with reference to the accompanying drawings. 3 is a block diagram illustrating a liquid crystal display device applied to an LCD TV according to the present invention in terms of driving voltage. As shown in the figure, the step-down portion 200a is usually converted to a DC 12V voltage by receiving a commercial power supply voltage of AC 220V or 100V from the outside.

The DC 12V voltage is again applied to the DC / DC converter 200b to generate the constant voltage Vdd necessary for generating the gray scale voltage, as well as the common voltage (not shown) applied to the common electrode of the liquid crystal panel. Gate signal voltages Vgl and Vgh are generated for gate on / off.

The gate voltage compensator 200d according to the present invention compensates the gate low voltage Vgl output from the DC / DC converter 200b as the voltage increases with the temperature change of the liquid crystal panel to compensate the gate voltage. To the driver 204. Of course, the gate voltage compensator 200d is preferably configured by a temperature sensing means such as a thermistor, which will be described later.

After the gate driver 204 receives the gate high voltage Vgh and the gate low compensation voltage Vglc compensated from the gate voltage compensator 200d, which are not shown in the drawing but do not require any compensation, the liquid crystal panel The gate signal voltage for turning on / off the gate element of the TFT (Thin Film Transistor) formed at 210 is generated.

Meanwhile, the gamma voltage generator 200c divides the constant voltage from the DC / DC converter 200b to generate gamma reference voltages of various levels. For example, when N reference voltages are required, N + 1 The resistors are connected in series to obtain a predetermined voltage.

The data driver 202 receives the gamma reference voltage from the gamma voltage generation unit 200c and divides the N reference voltages, respectively, to separate the gamma reference voltages corresponding to 64 or 256 gray levels. The partial pressure is also configured by connecting a plurality of resistors in series similarly to the generation principle of the gamma reference voltage, except that the number is the same as the number of gradation voltages required for the LCD model. .

In the liquid crystal panel 210, a thin film transistor array substrate on which gate lines, data lines, and TFT elements are formed, and a color filter substrate on which color filters and a common electrode are formed are bonded through a series of processes, and the liquid crystals formed between the liquid crystals injected therebetween. In the TN mode, the above gate signal voltage and gray voltage are applied to the thin film transistor array substrate and twisted the liquid crystal at a set angle by a voltage difference from the common voltage applied to the common electrode on the color filter substrate ( twisted).

4 is a circuit diagram illustrating a gate voltage compensator 200d interlocked with the DC / DC converter 200b of FIG. 3. As shown in the figure, the DC / DC converter 200b related to the generation of the gate low voltage Vgl according to the present invention first needs the capacitor C1 and the input terminal of the PWM IC 200b1 to stabilize the predetermined DC voltage. The inductance L1 is configured.

The PWM IC 200b1 includes an oscillator (not shown) that generates a square wave with a substantially constant frequency therein, and a triangular wave generator (not shown) that generates a triangular wave using a square wave generated by the oscillator. Here, the PWM IC 200b1 includes a negative charge pumping part when generating the gate low voltage Vgl using the input voltage Vin. For example, when using TPS65161 from TEXAS INSTRUMENTS as a PWM IC, drive pin of the negative charge pump (DRN), feedback pin of negative charge pump (FBN) and internal reference output for negative charge pumping Typically a terminal such as 1.213V) can be used.

As the output terminal of the PWM IC 200b1 as described above, the cathode of the first diode D1 and the anode of the second diode D2 are connected in common to the negative drive terminal DRN, and the anode of the first diode D1 is connected. The first resistor R1 and the second resistor R2 are connected in series between the anode and the cathode of the second diode D2 and grounded, and the connection node of the first resistor R1 and the second resistor R2 is grounded. Is connected to the feedback terminal FBN of the PWM IC 200b1 to form the voltage divider resistors R1 and R2. Of course, the capacitors C3 and C4 and the load resistor R3 are connected in parallel in order to obtain an optimum output voltage from the voltage dividing resistor means R1 and R2 including the first resistor R1 and the second resistor R2. As a result, the DC / DC converter 200b for generating the gate low voltage Vgl is configured.

The ambient temperature of the liquid crystal panel is between the contact point of the anode and load resistor R3 of the first diode D1 constituting the DC / DC converter 200b and the output terminal of the gate low compensation voltage Vglc. By connecting a plurality of Negative Temperature Coefficient Thermistors whose resistance decreases as they rise, the gate voltage compensator 200d according to the present invention is configured to generate a gate compensation voltage.

Now, the operation principle will be briefly described with reference to the above configuration. For example, in the present invention, it is assumed that a more stable DC 12V voltage is applied through the capacitor C1 and the inductance L1 configured at the input terminal of the PWM IC 200b1. In this case, the DC 12V voltage applied to the input terminal of the PWM IC 200b1 is pumped down by the first and second diodes D1 and D2 configured in the switching of the PWM IC 200b1 and the output terminal of the PWM IC 200b1. It is output as a negative voltage of -6V (pumping down), and the voltage is again used to generate a feedback voltage by the voltage dividing resistor means R1 and R2, thereby making the voltage of -6V more stable at both ends of the load resistance R3. Voltage is applied.

The voltage of -6V across both ends of the load resistor R3 is applied to the liquid crystal panel by compensating for the voltage between both ends of the negative characteristic thermistor whose resistance value decreases as the ambient temperature of the liquid crystal panel rises. For example, assuming that the compensation voltages of thermistors Th1 to Thn according to the ambient temperature change of the liquid crystal panel are -0.5V, the applied voltage to the liquid crystal panel is -5.5V.

However, this operation assumes that the gate low voltage Vgl applied to the liquid crystal panel is designed to be -5V. Therefore, the voltage applied to both ends of the load resistor R3 depends on how much the off current at the gate threshold voltage Vth of the TFT is changed when the liquid crystal panel is driven for about 1000 hours based on the ambient temperature of 25 ° C. The voltage at both ends of (R3) can be changed.

For example, when the liquid crystal display is driven for 1000 hours as in the above case, if the gate low voltage of the liquid crystal panel is in the range of -2V to -2V initially set to maintain the same off current according to the ambient temperature change. The voltage across both ends of the load resistor R3 needs to be designed to be -7V in consideration of margin, so that the off current of the TFT of the liquid crystal display device after 1000 hours of driving is changed. It can be prevented. Of course, this can be adjusted by resetting the resistance values of the voltage dividing resistor means R1 and R2 configured at the output terminal of the PWM IC 200b1. Consequently, the compensation range of the gate low voltage Vgl according to the present invention is 25 ° C. It may be desirable to be in the range of 0 to -2V with respect to the gate low voltage (Vgl) fixed to.

However, the gate low voltage compensator 200d according to the present invention may be configured as a temperature sensing means such as a positive temperature thermistor whose resistance value increases in proportion to the temperature as shown in FIG. 5. It may be. However, in contrast to the case where the gate low voltage compensator 200d shown in FIG. 4 is constituted by a temperature sensing means such as a negative characteristic thermistor, the load resistor R3 constituting the DC / DC converter 200b and The gate voltage compensator 200d according to the present invention is constructed by generating a gate compensation voltage by connecting a plurality of static thermistors Th1 to Thn whose resistance values increase in parallel with an increase in the ambient temperature of the liquid crystal panel. .

Furthermore, the gate low voltage compensator 200d according to the present invention, which is constituted by a temperature sensing means such as a thermistor, uses the thermistors Th1 and Th2 directly as a voltage divider as shown in FIG. As a result, the feedback voltage to the PWM IC 200b1 is changed as a result of the rising, and the compensated gate low voltage Vglc is applied to the liquid crystal panel.

Specifically, once again, the output terminal of the PWM IC 200b1 connects the cathode of the first diode D1 and the anode of the second diode D2 to the negative drive terminal DRN in common. The first thermistor Th1 and the second thermistor Th2 are connected in series between the anode of the diode D1 and the cathode of the second diode D2, and the first thermistor Th10 and the second thermistor ( By connecting the connection node of Th2 to the feedback terminal FBN of the PWM IC 200b1, the divided voltage sensing means Th1 and Th2 are constituted.

Of course, the capacitors C3 and C4, the zener diode ZD1, and the load resistor R3 are used to obtain a stable output voltage to the divided temperature sensing means Th1 and Th2 with the first thermistor Th1 and the second thermistor Th2. In parallel, the gate voltage compensator 200d for generating the gate row compensation voltage Vglc may be configured. As a result, the gate row compensation voltage Vglc is generated.

In this case, the first thermistor Th1 and the second thermistor Th2 constituting the partial pressure temperature sensing means Th1 and Th2 whose resistance values change with the change of the ambient temperature of the liquid crystal panel have the same temperature characteristics. Therefore, according to this principle, the compensated gate row compensation voltage Vglc is generated according to the change of the ambient temperature of the liquid crystal panel. This can be explained by the following equation.

Vgl = Vref (Th1 / Th2)

Here, Vref = -1.213V means a reference voltage applied to the REF terminal of the PWM IC 200b1.

In the above equation, the partial pressure temperature detection means (Th1, Th2) consisting of the first thermistor (Th1) and the second thermistor (Th2) simultaneously changes the resistance value according to the temperature rise, so that the room temperature or absolute temperature 25 As the temperature becomes higher than the gate low voltage Vgl fixed at ° C, a lower negative voltage may be applied to the liquid crystal panel.

However, on the other hand, the partial pressure temperature sensing means Th1 and Th2 shown in FIG. 6 above constitute only one of the two first thermistors Th1 and the second thermistor Th2 as a temperature sensing means such as a thermistor. In addition, the other one of the temperature sensing means may be composed of a resistor R to compensate for the gate low voltage Vgl according to the increase in the ambient temperature of the liquid crystal panel.

As a result of the configuration up to now, the liquid crystal display according to the present invention configures the gate voltage compensator by using a temperature sensing means such as a thermistor whose resistance value changes as the ambient temperature of the liquid crystal panel increases, thereby compensating for the gate low voltage. The cross talk phenomenon in the LCD panel could be improved.

Claims (15)

A driving voltage generation circuit for generating a gamma reference voltage and a gate low voltage by receiving a predetermined voltage from the outside or the inside, and compensating and outputting the gate low voltage by a temperature sensing means; A data driving circuit configured to generate the gray scale voltage by receiving the gamma reference voltage; A gate driving circuit to which a gate on / off voltage is applied from the driving voltage generating circuit; And And a liquid crystal panel to which the gray voltage and the gate on / off voltage are applied. The driving voltage generating circuit of claim 1, further comprising: step-down means for generating a predetermined voltage by receiving a predetermined voltage from the outside or the inside; DC / DC conversion means for receiving a predetermined voltage from the step-down means and outputting a constant voltage (Vdd) and a gate low voltage; Gamma voltage generating means for generating at least one gamma reference voltage by dividing the constant voltage from the DC / DC converting means; And a gate low voltage compensating means for receiving the gate low voltage from the DC / DC converting means and compensating the gate low voltage by the temperature sensing means to output the gate low voltage. The method of claim 1, wherein when the gate low voltage is applied with a predetermined DC voltage to generate a pumped-down negative voltage, the voltage of the first diode D1 and the cathode of the first diode D1 is applied to the negative drive terminal DRN. A PWM IC for commonly connecting the anode of the diode D2; The anode and the second resistor (D2) of the second diode (D2) by connecting the first resistor (R1) and the second resistor (R2) in series between the anode of the first diode (D1) and the cathode of the second diode (D2) The connection node of R2 is grounded, and is produced by voltage divider means for connecting the connection node of the first resistor R1 and the second resistor R2 to the feedback terminal of the PWM IC. . The liquid crystal display device according to claim 1, wherein the temperature sensing means is a thermistor. Step-down means for generating a predetermined voltage by receiving a predetermined voltage from the outside or the inside; DC / DC conversion means for amplifying a predetermined voltage from the step-down means and outputting a constant voltage (Vdd) and a gate low voltage; Gamma voltage generating means for generating at least one gamma reference voltage by dividing the constant voltage from the DC / DC converting means; And And a gate low voltage compensating means for receiving a gate low voltage from the DC / DC converting means and compensating the gate low voltage by a temperature sensing means. 6. The driving voltage generation circuit of a liquid crystal display device according to claim 5, wherein the temperature sensing means is a thermistor. The cathode of claim 5, wherein the gate low voltage is applied with a predetermined DC voltage to generate a pumped-down negative voltage. The cathode of the first diode D1 and the second diode D2 are applied to the negative drive terminal DRN. A PWM IC commonly connecting the anodes of < RTI ID = 0.0 > The anode and the second resistor (D2) of the second diode (D2) by connecting the first resistor (R1) and the second resistor (R2) in series between the anode of the first diode (D1) and the cathode of the second diode (D2) The connection node of R2 is grounded, and is produced by voltage divider means for connecting the connection node of the first resistor R1 and the second resistor R2 to the feedback terminal of the PWM IC. Driving voltage generation circuit. A driving voltage generation circuit which generates and outputs a gate row compensation voltage by a temperature sensing means when a gamma reference voltage and a gate row compensation voltage Vglc are generated by receiving a predetermined voltage from outside or inside; A data driving circuit configured to generate the gray scale voltage by receiving the gamma reference voltage; A gate driving circuit to which a gate on / off voltage is applied from the driving voltage generating circuit; And And a liquid crystal panel to which the gray voltage and the gate on / off voltage are applied. The method of claim 8, wherein the gate row compensation voltage is applied with a predetermined DC voltage to generate a pumped-down negative voltage. The voltage of the first diode D1 is applied to the negative drive terminal DRN. A PWM IC for commonly connecting the anodes of the two diodes D2; An anode and a second diode D2 are connected in series between an anode of the first diode D1 and a cathode of the second diode D2 in series. The connection node of the second temperature sensing means Th2 is grounded, and the divided temperature sensing means for connecting the connection node of the first temperature sensing means Th1 and the second temperature sensing means Th2 to the feedback terminal of the PWM IC. Liquid crystal display characterized in that it is generated by. The method of claim 8, wherein the gate row compensation voltage is applied with a predetermined DC voltage to generate a pumped-down negative voltage. The voltage of the first diode D1 is applied to the negative drive terminal DRN. A PWM IC for commonly connecting the anodes of the two diodes D2; The anode and the second diode D2 are connected in series between the first temperature sensing means Th1 and the second resistor R2 between the anode of the first diode D1 and the cathode of the second diode D2. The connection node of the resistor R2 is grounded, and is generated by the voltage dividing temperature sensing means for connecting the connection node of the first temperature sensing means Th1 and the second resistance R2 to the feedback terminal of the PWM IC. A liquid crystal display device. The liquid crystal display device according to claim 8, wherein the temperature sensing means is a thermistor. Step-down means for generating a predetermined voltage by receiving a predetermined voltage from the outside or the inside; DC / DC conversion means for compensating and outputting a voltage fed back by the temperature sensing means when generating a constant voltage (Vdd) and a gate low compensation voltage by receiving a predetermined voltage from the step-down means; And And a gamma voltage generating means for generating at least one gamma reference voltage by dividing the constant voltage from the DC / DC converting means. The method of claim 12, wherein when the gate row compensation voltage is applied with a predetermined DC voltage to generate a pumped-down negative voltage, the voltage of the first diode D1 and the cathode of the first diode D1 is applied to the negative drive terminal DRN. A PWM IC for commonly connecting the anodes of the two diodes D2; An anode and a second diode D2 are connected in series between an anode of the first diode D1 and a cathode of the second diode D2 in series. The connection node of the second temperature sensing means Th2 is grounded, and the divided temperature sensing means for connecting the connection node of the first temperature sensing means Th1 and the second temperature sensing means Th2 to the feedback terminal of the PWM IC. The driving voltage generation circuit of the liquid crystal display device, characterized in that generated by. The method of claim 12, wherein when the gate row compensation voltage is applied with a predetermined DC voltage to generate a pumped-down negative voltage, the voltage of the first diode D1 and the cathode of the first diode D1 is applied to the negative drive terminal DRN. A PWM IC for commonly connecting the anodes of the two diodes D2; The anode and the second diode D2 are connected in series between the first temperature sensing means Th1 and the second resistor R2 between the anode of the first diode D1 and the cathode of the second diode D2. The connection node of the resistor R2 is grounded, and is generated by the voltage dividing temperature sensing means for connecting the connection node of the first temperature sensing means Th1 and the second resistance R2 to the feedback terminal of the PWM IC. A drive voltage generation circuit of a liquid crystal display device. The driving voltage generation circuit of a liquid crystal display device according to claim 12, wherein the temperature sensing means is a thermistor.

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