KR20090043167A - A liquid crystal display device and a method for driving the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display and a driving method thereof capable of preventing image quality defects due to variations in leakage current of a photoelectric conversion element. ; A current-voltage converter converting the photocurrent from the photoelectric converter into an optical voltage; An analog-digital converter for converting the optical voltage from the current-voltage converter into digital data; A pulse width modulator for converting a duty rate of an optical control signal according to the digital data from the analog-digital converter and supplying it to the backlight; And the current-voltage conversion according to any one of an output from the photoelectric converter, an output from the current-voltage converter, an output from the analog-digital converter, and an output from the pulse width modulator. It characterized in that it comprises a control unit for controlling the output of the negative.

LCD, photoelectric conversion element, photo sensor, backlight

Description

A liquid crystal display device and a method for driving the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a driving method thereof capable of preventing image quality defects due to variations in leakage current of a photoelectric conversion element.

Liquid crystal displays display an image by adjusting light transmittance of liquid crystal cells according to a video signal.

Among the liquid crystal display devices, an active matrix type liquid crystal display device in which switching elements are formed for each liquid crystal cell is advantageous in implementing a moving image because active control of the switching element is possible. As a switching element used in an active matrix type liquid crystal display device, a thin film transistor (hereinafter, referred to as TFT) is mainly used.

Since the liquid crystal display uses a liquid crystal that is a non-luminescent material, it is essentially provided with a backlight for providing light. Conventional liquid crystal display device includes a backlight control unit for changing the brightness of the backlight according to the light from the external environment.

The backlight controller receives a light current from a sensor called a photoelectric conversion element that senses external light and converts the light into a light current corresponding to the light intensity, and controls the brightness of the backlight according to the magnitude of the light current.

Since the photoelectric conversion element has a large leakage current variation between the same kind of devices, the photoelectric conversion device may also have a variation between liquid crystal display devices of the same product having the same photoelectric conversion device.

Therefore, it is necessary to inspect the photoelectric conversion element before commercializing the liquid crystal display. The inspection process may include providing inspection light having a predetermined illuminance to the photoelectric conversion element, determining whether illuminance of the light emitted from the backlight is at a target value, and backlight controller according to the determination result. Adjusting the value of the internal element, that is, the variable resistor.

At this time, in the related art, since the operator directly adjusts the variable resistance using the adjusting rod, it takes a long time and it is difficult to adjust the variable resistance to an accurate value.

The present invention has been made to solve the above problems, and provides a liquid crystal display device and a driving method thereof which can automatically and accurately correct the internal resistance of the backlight controller according to the illuminance of the inspection light from the outside. The purpose is.

According to an aspect of the present invention, there is provided a liquid crystal display device including: a photoelectric conversion unit generating a photo current according to inspection light from the outside; A current-voltage converter converting the photocurrent from the photoelectric converter into an optical voltage; An analog-digital converter for converting the optical voltage from the current-voltage converter into digital data; A pulse width modulator for converting a duty rate of an optical control signal according to the digital data from the analog-digital converter and supplying it to the backlight; And the current-voltage conversion according to any one of an output from the photoelectric converter, an output from the current-voltage converter, an output from the analog-digital converter, and an output from the pulse width modulator. It characterized in that it comprises a control unit for controlling the output of the negative.

In addition, the driving method of the liquid crystal display device according to the present invention for achieving the above object comprises the steps of: generating a photo current according to the inspection light from the outside; Converting the photocurrent into a photovoltage; Converting the optical voltage into digital data; Converting a duty rate of an optical control signal according to the digital data and supplying it to a backlight; and the optical voltage according to any one of the optical current, the optical voltage, the digital data, and the optical control signal. It characterized by including the step of controlling.

The liquid crystal display and the driving method thereof according to the present invention have the following effects.

The liquid crystal display according to the present invention includes a control unit which can automatically correct the resistance value according to the inspection light. Therefore, the work time can be reduced, and the resistance value can be corrected accurately.

1 is a view showing a liquid crystal display device according to an embodiment of the present invention.

As shown in FIG. 1, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal panel 111 having a display portion 111a and a non-display portion 111b, and a non-display portion 111b of the liquid crystal panel 111. And a driver IC (D-IC) (Integrated Circuit) for receiving images from the outside through FPC 170 (Flexible Printed Circuit) and displaying an image on the display unit 111a, and the liquid crystal panel ( A backlight BL positioned under the 111 to provide light toward the display portion 111a of the liquid crystal panel 111, and a non-display portion 111b of the liquid crystal panel 111 to receive light from the outside; A plurality of photoelectric conversion unit 120 for sensing and generating a photo current (photo current).

The liquid crystal panel 111 has a plurality of gate lines GL and a plurality of data lines DL that cross each other.

One pixel cell receives a thin film transistor TFT that switches a data signal from the data line DL in response to a scan pulse from the gate line GL, and receives a data signal from the thin film transistor TFT. A pixel electrode (not shown), a common electrode (not shown) positioned opposite to the pixel electrode, and positioned between the pixel electrode and the common electrode to adjust the amount of light transmission according to an electric field generated between the two electrodes. A liquid crystal layer (not shown).

A liquid crystal capacitor Clc having the liquid crystal layer as a dielectric is formed between the common electrode and the pixel electrode, and an insulating film is shown between the pixel electrode and a front gate line GL overlapping a part of the pixel electrode. Storage capacitor Cst is formed as a dielectric.

The driver IC D-IC includes a gate driver (not shown) for driving the gate lines GL and a data driver (not shown) for driving the data lines DL.

The gate driver may include a shift register (not shown) that sequentially generates scan pulses in response to a gate control signal from a timing controller (not shown), and a swing width of the scan pulses suitable for driving the liquid crystal cell Clc. And a level shifter (not shown) for shifting to a level, and an output buffer (not shown) for buffering and outputting the output from the level shifter. The gate driver turns on the thin film transistors connected to the gate line GL by supplying a scan pulse to the gate line 46 to supply the pixel voltage of the data signal, that is, the analog gamma compensation voltage. 1 Select pixel cells of a horizontal line. Data signals generated from the data driver are supplied to pixel cells of one horizontal line selected by being synchronized with the scan pulse.

In addition, the driver IC (D-IC) further includes a backlight controller 200, wherein the backlight controller 200 receives the light current from the photoelectric converter 120 to expose the liquid crystal display device. The intensity of light in the current environment is measured, and the brightness of the backlight BL is adjusted according to the measured result. For example, the backlight controller 200 lowers the brightness of the backlight BL when the surroundings are bright, and conversely, increases the brightness of the backlight BL when the surroundings are dark.

2 is a diagram illustrating a backlight controller 200 according to an exemplary embodiment of the present invention, and FIG. 3 is a detailed configuration diagram of the current-voltage converter 211 of FIG. 2.

First, as described above, the photoelectric conversion unit 120 detects light from the outside and generates a photocurrent Ic according to the intensity of the light. It includes.

As illustrated in FIG. 2, the backlight controller 200 includes a current-voltage converter 211, an analog-to-digital converter (ADC), and a pulse width modulator (PWM) ( Pulse Width Modulation), and a control unit 222.

The current-voltage converter 211 converts the photocurrent Ic from the photoelectric converter 120 into an optical voltage Vc, and the analog-digital converter ADC is the current-voltage converter. The optical voltage Vc from 211 is converted into digital data, and the pulse width modulator PWM converts the optical control signal CS_BL according to the digital optical data Dc from the analog-digital converter ADC. The duty rate of the light source is converted to the backlight BL. In addition, the controller 222 may include the photocurrent Ic from the photoelectric converter 120, the photovoltage Vc from the current-voltage converter 211, and the analog-to-digital converter ADC. The output of the current-voltage converter 211 is controlled in accordance with any one of the optical data Dc and the optical control signal CS_BL from the pulse width modulator PWM.

The backlight BL emits brighter light as the duty rate of the light control signal CS_BL is higher, and emits darker light as the duty rate of the light control signal CS_BL is lower.

As illustrated in FIGS. 2 and 3, the current-voltage converter 211 includes an operational amplifier (OPA), a resistor 230, and a switch SW.

A photocurrent Ic from the photoelectric converter 120 is input to the inverting terminal (−) of the amplifier OPA, and an offset voltage Voffset is input to the non-inverting terminal (+).

As shown in FIG. 3, the resistor unit 230 includes a plurality of resistors R connected in parallel, and one terminal of each resistor R is an inverting terminal (−) of the amplifier OPA. ) Are commonly connected. The resistors R have different resistance values.

The switch SW electrically connects between the other terminal of any one of the plurality of resistors R and an output terminal of the amplifier OPA according to the switch control signal CS_SW from the controller 222.

4 is a detailed block diagram of the controller 222 of FIG. 2.

As illustrated in FIG. 4, the controller 222 includes a comparator 411, a selector 412, a storage 413, and a switch controller 414.

The comparison unit 411 compares the reference value preset according to the inspection light with the value of the output from the analog-to-digital converter ADC, and the selection unit 412 from the comparison unit 411. According to the comparison result, one of the pre-stored correction values is selected and stored in the storage unit 413, and the switch controller 414 controls the switch SW based on the correction value stored in the storage unit 413. A switch control signal CS_SW is generated for controlling.

The selector 412 includes a look up table 521 and a correction value selector 522.

The lookup table 521 stores a difference value between the output value from the analog-to-digital converter ADC and the reference value, and a plurality of correction values corresponding to the difference values. That is, FIG. 5 illustrates correction values stored in the lookup table 521. As illustrated in FIG. 5, each digital correction value represents a resistance value of each resistor R. As shown in FIG.

The correction value selector 522 selects one correction value from the lookup table 521 based on the difference value from the comparison unit 411, and selects the correction value from the lookup table 521 to the storage unit 413. Save it.

The driving method of the liquid crystal display according to the present invention configured as described above and the leakage current deviation correction method in the liquid crystal display having the above structure will be described.

First, inspection light having arbitrary illuminance is irradiated to the photoelectric conversion element PTr. Then, the photoelectric conversion element PTr generates a photocurrent Ic corresponding to the intensity of the inspection light and supplies it to the inverting terminal (−) of the amplifier OPA.

Then, the amplifier OPA converts the photocurrent Ic from the photoelectric conversion element PTr into the photovoltage Vc. In this case, a resistor R selected in advance is provided between the inverting terminal (-) and the output terminal of the amplifier OPA. The preselected resistor R has a resistance value selected under the condition of assuming that the leakage current of the photoelectric conversion element PTr is within an allowable reference value, and the digital correction value corresponding to this resistance value is stored in the storage unit 413. In the default state. The optical voltage Vc output from the amplifier OPA is input to the analog-to-digital converter ADC.

The analog-to-digital converter ADC converts the optical voltage Vc, which is an analog signal, to optical data Dc, which is a digital signal, and supplies the optical voltage Dc to the pulse width modulator PWM. Then, the pulse width modulator PWM adjusts the duty ratio of the light control signal CS_BL according to the size of the optical data Dc. For example, if the value of the optical data Dc is large, bright light may be emitted. If the value of the optical data Dc is small, dark light may be emitted.

The comparator 411 receives the optical data Dc from the analog-digital converter ADC and compares the optical data Dc with a preset reference value. The reference value is a digital value set according to the illuminance of the inspection light.

Herein, the operation of the comparison unit 411 when the difference between the optical data Dc and the reference value occurs, that is, when the default resistance value is incorrect, will be described below.

That is, the comparison unit 411 calculates the difference between the optical data Dc and the reference value, and supplies the calculated value to the correction value selector 522. The correction value selector 522 selects a correction value corresponding to the calculated value from the lookup table 521, and stores the selected correction value in the storage unit 413. Accordingly, the correction value stored by default in the storage unit 413 is replaced with a new, that is, corrected correction value. Then, the switch controller 414 controls the switch SW to select a resistor R having a resistance value corresponding to the new correction value stored in the storage unit 413.

On the other hand, when there is no difference between the optical data Dc and the reference value (the calculated value is 0), that is, when the default resistance value is correct, the comparison unit 411 performs one of the following two operations. Can be done.

First, the comparison unit 411 calculates a difference between the optical data Dc and a reference value, that is, calculates a value of 0, and supplies the calculated value to the correction value selector 522. The correction value selecting unit 522 selects the calculated value, that is, a correction value corresponding to 0 from the lookup table 521, and stores the selected correction value in the storage unit 413. This selected correction value is eventually the same as the correction value previously stored in the storage 413.

Second, the comparison unit 411 compares the magnitude between the optical data Dc and the reference value and does not proceed to the next operation when there is no difference between the optical data Dc and the reference value. In other words, the comparing unit 411 does not output any control signal for operating the correction value selecting unit 522. Accordingly, the correction value previously stored in the storage unit 413 is maintained as it is. In this case, a separate correction value for 0 does not need to be stored in the lookup table 521.

On the other hand, the storage unit 413 may be used EEPROM (Electrically Erasable and Programmable Read Only Memory), the storage unit 413 is corrected when the operating power (PO) and the write signal (WS) from the outside supplied The correction value provided from the value selector 522 is stored. However, when the operation power source PO and the write signal WS are not supplied, the previously stored correction value is maintained even when the correction value is provided from the correction value selecting unit 522.

Therefore, after the corrected correction value is stored in the storage unit 413 through this process, the operation power source PO and the write signal WS are blocked so that the correction value is not changed to another value.

Meanwhile, in the present invention, the control unit 222 representatively shows an embodiment in which the value of the resistor R is controlled by using the optical data Dc from the analog-to-digital converter ADC. The controller 222 may use the resistor R by using any one of the optical voltage Vc from the current-voltage converter 211 and the optical control signal CS_BL from the pulse width modulator PWM. You can also control the value of.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and it is common in the art that various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

1 is a view showing a liquid crystal display device according to an embodiment of the present invention.

2 is a diagram illustrating a backlight controller according to an exemplary embodiment of the present invention.

3 is a detailed configuration diagram of the current-voltage converter of FIG. 2.

4 is a detailed configuration diagram of the control unit of FIG. 2.

5 is a diagram illustrating correction values stored in a lookup table.

Claims (9)

Photoelectric conversion unit for generating a photo current in accordance with the inspection light from the outside; A current-voltage converter converting the photocurrent from the photoelectric converter into an optical voltage; An analog-digital converter for converting the optical voltage from the current-voltage converter into digital data; A pulse width modulator for converting a duty rate of an optical control signal according to the digital data from the analog-digital converter and supplying it to the backlight; And, An output of the current-voltage converter according to any one of an output from the photoelectric converter, an output from the current-voltage converter, an output from the analog-digital converter, and an output from the pulse width modulator. And a control unit for controlling the liquid crystal display. The method of claim 1, The current-voltage converter An amplifier receiving an optical current from the photoelectric conversion unit through an inverting terminal and an offset voltage through a non-inverting terminal; A plurality of resistors having one terminal connected to the inverting terminal in common; And a switch for electrically connecting the other side of any one of the plurality of resistors to an output terminal of the amplifier according to an output from the controller. The method of claim 2, The control unit, A comparison unit comparing a reference value preset according to the inspection light with a value of an output from the analog-digital converter; A selection unit for selecting any one of pre-stored correction values according to a comparison result from the comparison unit and storing the selected correction value in a storage unit; And, And a switch controller for controlling the switch based on the correction value stored in the storage unit. The method of claim 3, wherein The selection unit, A look-up table storing a difference value between the output value from the analog-digital converter and the reference value and a plurality of correction values corresponding to each difference value; And, And a correction value selection unit for selecting a correction value from the lookup table based on the difference value from the comparison unit, and storing the selected correction value in the storage unit. The method of claim 3, wherein And the storage unit is EEPROM (Electrically Erasable and Programmable Read Only Memory). Generating a photo current according to inspection light from the outside; Converting the photocurrent into a photovoltage; Converting the optical voltage into digital data; Converting a duty rate of an optical control signal according to the digital data and supplying the duty ratio to a backlight; and And controlling the optical voltage in accordance with any one of the optical current, the optical voltage, the digital data, and the optical control signal. The method of claim 6, An amplifier having a plurality of resistors arranged in parallel between an inverting terminal and an output terminal is used to convert the optical current into an optical voltage, and the controlling of the optical voltage may include: Inputting a photocurrent to the inverting terminal of the amplifier; Inputting an offset voltage to the non-inverting terminal of the amplifier: Selecting one of the plurality of resistors according to any one of the photocurrent, the photovoltage, the digital data, and the photocontrol signal to electrically connect the inverting terminal and the output terminal. Method of driving a liquid crystal display device characterized in that. The method of claim 7, wherein Controlling the optical voltage, Comparing a value of the digital data with a reference value preset according to the inspection light; And, And selecting any one of the resistors and electrically connecting the inverting terminal and the output terminal according to the comparison result. The method of claim 8, Selecting any one of the resistors according to the comparison result and electrically connecting between the inverting terminal and the output terminal, Setting and storing a difference value between the digital data value and the reference value and a plurality of correction values corresponding to each difference value; Selecting a correction value based on a difference value generated according to the comparison result, and storing the selected correction value; And, And selecting one of the resistors and electrically connecting the inverting terminal and the output terminal based on the selected and stored correction value.

Images