KR100784016B1 - External light sensor and liquid crystal display device using the same - Google Patents

Abstract

The present invention relates to an external light sensor that can increase the reliability of the external light detection performance and reduce the power consumption.

The external light sensor of the present invention is a first transistor connected between a first power supply and a second power supply having a lower voltage value than the first power supply and turned on or off in response to a control signal, and the first transistor. And a sensing unit connected between the second power source and the second power source to control an amount of current flowing from the first transistor to the second power source in response to the intensity of external light, and a gate electrode having a second transistor connected to the second power source. The apparatus further includes at least one amplifier connected to an output of the detector and at least one noise canceller connected between the detector and the amplifier.

As a result, power consumption is reduced by sensing the intensity of external light and controlling the brightness of light generated by the backlight. In addition, the amplification part improves the driving force that enables the external light sensor to drive an application circuit connected to its output terminal. In addition, by providing a noise removing unit to stabilize the output voltage of the external light sensor regardless of the process parameters of the transistors included in the amplifier, it is possible to improve the reliability when detecting the external light.

Description

Optical Sensor for detecting Peripheral Light and Liquid Crystal Display Device Using the Same}

1 is a view showing a conventional liquid crystal display device.

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

3 is a circuit diagram illustrating an example of an external light sensor shown in FIG. 2.

4 is a circuit diagram illustrating an equivalent circuit of the external light sensor shown in FIG. 3.

5 is a waveform diagram illustrating a method of driving the external light sensor illustrated in FIG. 3.

FIG. 6 is a waveform diagram illustrating an output voltage according to time of the external light sensor illustrated in FIG. 3.

FIG. 7 is a circuit diagram illustrating another example of the external light sensor illustrated in FIG. 2.

<Explanation of symbols for main parts of the drawings>

2, 20: pixel portion 3, 30: black matrix

4, 40: scan driver 6, 60: data driver

8, 80: gamma voltage supply unit 10, 100: timing control unit

12, 120: backlight driver 14, 140: backlight

110: external light sensor 112: detection unit

114: amplifier 116: noise canceling unit

The present invention relates to an external light sensor and a liquid crystal display using the same, and more particularly, to an external light sensor and a liquid crystal display using the same to increase the reliability of the external light detection performance and to reduce power consumption.

Recently, various flat panel displays have been developed to reduce weight and volume, which are disadvantages of cathode ray tubes. Flat display devices include Liquid Crystal Display (LCD), Field Emission Display (FED), Plasma Display Panel (PDP) and Light Emitting Display (LED). There is this.

Here, the liquid crystal display device has been attracting attention as an alternative means to overcome the disadvantages of the conventional cathode ray tube due to the advantages of miniaturization, light weight, and low power, and now portable devices such as mobile phones and portable digital assistants (PDAs). In addition, it is installed in medium and large-sized monitors and TVs. Such a liquid crystal display device is a transmissive display device and displays a desired image by adjusting the amount of light passing through the liquid crystal layer by refractive index anisotropy of liquid crystal molecules.

1 is a view showing a conventional liquid crystal display device. In FIG. 1, an active matrix liquid crystal display device is illustrated.

Referring to FIG. 1, in the conventional LCD, m × n liquid crystal cells Clc are arranged in a matrix type, and m data lines D1 to Dm and n scan lines S1 to Sn cross each other. And a pixel portion 2 having a thin film transistor (hereinafter referred to as TFT) at its intersection, a scan driver 4 for supplying a scan signal to the scan lines S1 to Sn, and data lines A data driver 6 for supplying a data signal to D1 to Dm, a gamma voltage supply unit 8 for supplying a gamma voltage to the data driver 6, a scan driver 4 and a data driver 6 And a timing controller 10 for supplying a control signal to the backlight, and a backlight driver 12 for driving the backlight 14 for supplying light to the liquid crystal cells Clc.

The pixel portion 2 includes a plurality of liquid crystal cells Clc arranged in a matrix at the intersections of the data lines D1 to Dm and the scan lines S1 to Sn. The TFTs formed in each of the liquid crystal cells Clc supply a data signal supplied from the data line D to the liquid crystal cell Clc in response to a scan signal supplied from the scan line S. In addition, a storage capacitor Cst is formed in each of the liquid crystal cells Clc. The storage capacitor Cst is formed between the pixel electrode of the liquid crystal cell Clc and the front scan line S, or is formed between the pixel electrode of the liquid crystal cell Clc and the common electrode line, so that the liquid crystal cell Clc is stored for one frame. Keep the voltage constant. Here, a black matrix 3 is formed between the adjacent liquid crystal cells Clc and at the outer edge of the pixel portion 2 to absorb the light incident from the adjacent cell or the outer portion of the pixel portion 2 to prevent a decrease in contrast. do.

The scan driver 4 sequentially supplies a scan signal to the scan lines S1 to Sn in response to the scan control signal SCS supplied from the timing controller 10, thereby providing a scanning signal of the pixel unit 2 to which the data signal is supplied. Select the horizontal line.

The data driver 6 converts the digital video data R, G, and B into analog gamma voltages corresponding to grayscale values, that is, data signals, in response to the data control signals DCS supplied from the timing controller 10, This data signal is supplied to the data lines D1 to Dm.

The gamma voltage supply unit 8 supplies a plurality of gamma voltages to the data driver 6.

The timing controller 10 scans the scan control signal SCS for controlling the scan driver 4 and the data driver 6 using the vertical / horizontal synchronization signals Vsync and Hsync and the clock signal CLK supplied from the outside. And a data control signal DCS. The scan control signal SCS for controlling the scan driver 4 includes a gate start pulse, a gate shift clock, a gate output enable, and the like. The data control signal DCS for controlling the data driver 6 includes a source start pulse, a source shift clock, a source output signal, and a polarity signal. Etc. are included. In addition, the timing controller 10 rearranges and supplies the data R, G, and B supplied from the outside to the data driver 6.

The backlight driver 12 supplies a driving voltage (or driving current) for driving the backlight 14 to the backlight 14. Then, the backlight 14 generates light corresponding to the driving voltage (or driving current) supplied from the backlight driver 12 and supplies the light to the pixel unit 2.

In the above-described liquid crystal display device, the backlight 14 always irradiates the pixel portion 2 with light of constant brightness. However, although a large amount of light is not required in a place where the brightness of the surrounding environment is relatively high and a relatively high recognition level, power consumption of the backlight 14 is increased by supplying light having a constant brightness to the pixel unit 2. . In fact, more than 80% of the power consumed for driving the liquid crystal display is consumed in the backlight 14. Therefore, in order to reduce the power consumption, it is necessary to reliably sense the external light to reduce the amount of light generated by the backlight 14 when the external light is detected below a predetermined brightness.

Accordingly, an object of the present invention is to provide an external light sensor and a liquid crystal display device using the same to increase the reliability of the external light sensing performance and to reduce power consumption.

In order to achieve the above object, a first aspect of the present invention is a first power supply connected between a first power supply and a second power supply having a lower voltage value than the first power supply and turned on or off in response to a control signal. A second transistor connected between the transistor and the first transistor and the second power source to control an amount of current flowing from the first transistor to the second power source in response to the intensity of external light, and a gate electrode connected to the second power source It includes a sensing unit having a, at least one amplification unit connected to the output terminal of the sensing unit and at least one noise removing unit connected between the sensing unit and the amplification unit provides an external light sensor.

Preferably, the channel width of the second transistor is set to 1000 μm to 56000 μm so that the capacitance of the parasitic capacitor inside the second transistor may be 1 pF or more. The noise canceller includes at least one capacitor and a plurality of switches. The noise canceller includes a first switch located between an output terminal of the detector and a gate electrode of at least one transistor included in the amplifier, a second switch located between a reference power supply and one terminal of the capacitor, A third switch connected between the other terminal of the capacitor and the output terminal of the amplifier, a fourth switch positioned between one terminal of the capacitor and the gate electrode of at least one transistor included in the amplifier, And a fifth switch located between the other terminal and the output terminal of the sensing unit. The first to third switches are turned on or off by the same switching pulse. The fourth and fifth switches are turned on or off by the same switching pulse. The amplifier includes a third transistor connected between the first power supply and the second power supply and turned on in response to a bias signal, and connected between the third transistor and the second power supply, and a gate electrode of the noise removing unit. It includes a fourth transistor connected to at least one switch included in. The first and second transistors are N-type transistors. The first transistor is an N-type transistor, and the second transistor is a P-type transistor.

According to a second aspect of the present invention, there is provided a pixel unit including a plurality of liquid crystal cells, at least one external light sensing sensor provided in a black matrix area formed at an outer edge of the pixel unit and generating a detection signal corresponding to the intensity of external light; And a backlight driver configured to control a brightness of light generated by the backlight in response to the sensing signal and a backlight for supplying light to the pixel unit, wherein the external light sensor has a first power supply and a voltage value lower than that of the first power supply. A first transistor connected between a second power source and turned on or off in response to a control signal, and connected between the first transistor and the second power source and corresponding to the intensity of external light from the first transistor; A sensing unit for controlling an amount of current flowing to a second power supply and having a second transistor having a gate electrode connected to the second power supply And also provides a liquid crystal display device further comprising: removing at least one of the noise which is connected between at least one amplification unit connected to the sensing unit output terminal, the sensing unit and the amplifying portion.

Preferably, the channel width of the second transistor is set to 1000 μm to 56000 μm so that the capacitance of the parasitic capacitor inside the second transistor may be 1 pF or more. The noise canceller includes at least one capacitor and a plurality of switches. The noise canceller includes a first switch located between an output terminal of the detector and a gate electrode of at least one transistor included in the amplifier, a second switch located between a reference power supply and one terminal of the capacitor, A third switch connected between the other terminal of the capacitor and the output terminal of the amplifier, a fourth switch positioned between one terminal of the capacitor and the gate electrode of at least one transistor included in the amplifier, And a fifth switch located between the other terminal and the output terminal of the sensing unit. The first to third switches are turned on or off by the same switching pulse. The fourth and fifth switches are turned on or off by the same switching pulse. The amplifying unit is connected between the first power supply and the second power supply and is turned on in response to a bias signal, and is connected between the third transistor and the second power supply, and a gate electrode is connected to the noise suppressor. And a fourth transistor connected to the at least one switch included in the reject. The gate electrode of the second transistor is located in the opening of the black matrix.

Hereinafter, the present invention will be described in detail with reference to FIGS. 2 to 7 in which preferred embodiments of the present invention may be easily implemented by those skilled in the art.

2 is a view showing a liquid crystal display device according to an embodiment of the present invention. Although FIG. 2 illustrates an active matrix liquid crystal display, the present invention is not limited thereto.

2, a liquid crystal display according to an exemplary embodiment of the present invention includes a pixel unit 20, a scan driver 40, a data driver 60, a gamma voltage supply unit 80, a timing controller 100, and external light. The sensor 110 is provided with a backlight driver 120 and a backlight 140. Here, the external light sensor 110 is formed in at least one region of the black matrix 30 formed on the outer edge of the pixel portion 20. An opening 35 is formed in the black matrix 30 formed on at least one region of the external light detecting sensor 110 such that external light is incident on at least one region of the external light detecting sensor 110 through the opening 35. do. When external light is incident on the external light sensor 110, the external light sensor 110 generates a detection signal corresponding to the intensity of the external light to control the backlight driver 120.

The pixel portion 20 includes a plurality of liquid crystal cells Clc arranged in a matrix at the intersections of the data lines D1 to Dm and the scan lines S1 to Sn, and at least formed on each of the liquid crystal cells Clc. One thin film transistor (hereinafter referred to as TFT) and a storage capacitor Cst are included. The TFT supplies the data signal supplied from the data line D to the liquid crystal cell Clc in response to the scan signal supplied from the scan line S. In FIG. The storage capacitor Cst is formed between the pixel electrode of the liquid crystal cell Clc and the front scan line S, or is formed between the pixel electrode of the liquid crystal cell Clc and the common electrode line, so that the liquid crystal cell Clc is stored for one frame. Keep the voltage constant. Then, in the liquid crystal cells Clc, when the scan signal is supplied to the scan line S, the arrangement angle of the liquid crystal is changed, and the light transmittance is changed according to the changed arrangement angle to display a desired image. . Here, a black matrix 30 is formed between each of the liquid crystal cells Clc and the outer edge of the pixel portion 20 so as to absorb the light incident from the neighboring cell or the outer portion of the pixel portion 20 to prevent a decrease in contrast. .

The scan driver 40 sequentially supplies a scan signal to the scan lines S1 to Sn in response to the scan control signal SCS supplied from the timing controller 100, so that the scan driver 40 supplies the data signal. Select the horizontal line.

The data driver 60 converts the digital video data R, G, and B into an analog gamma voltage corresponding to the gray scale value, that is, a data signal in response to the data control signal DCS supplied from the timing controller 100. This data signal is supplied to the data lines D1 to Dm.

The gamma voltage supply unit 80 supplies a plurality of gamma voltages to the data driver 60.

The timing controller 100 controls the scan driver 40 and the data driver 60 to control the scan driver 40 and the data driver 60 by using the vertical / horizontal synchronization signals Vsync and Hsync and the clock signal CLK. And a data control signal DCS. In this case, the scan control signal SCS for controlling the scan driver 40 includes a gate start pulse, a gate shift clock, a gate output enable, and the like. The data control signal CS for controlling the data driver 60 includes a source start pulse, a source shift clock, a source output signal, and a polarity signal. Etc. are included. In addition, the timing controller 100 rearranges the data R, G, and B supplied from the outside and supplies the data to the data driver 60.

The external light sensor 110 is formed in at least one region of the black matrix 30 formed on the outer edge of the pixel unit 20. In this case, at least one region of the external light sensor 110, in particular, a region to which external light is supplied, is located in the opening 35 of the black matrix 30. That is, at least one region of the external light sensor 110 is exposed to external light, whereby external light is incident on the external light sensor 110. The external light sensor 110, which receives external light, generates a detection signal corresponding to the intensity of external light and supplies it to the backlight driver 120 to control the backlight driver 120.

The backlight driver 120 supplies a driving voltage (or driving current) for driving the backlight 140 to the backlight 140. In this case, the backlight driver 120 controls the brightness of the light generated by the backlight 140 by changing the value of the driving voltage (or driving current) in response to the detection signal supplied from the external light sensor 110. For example, when the backlight driver 120 receives a detection signal corresponding to a low intensity of external light from the external light sensor 110, the driving voltage of the backlight 140 may be increased by a predetermined value corresponding to the intensity of the external light. Alternatively, by lowering the driving current, the luminance of light generated by the backlight 140 may be reduced to reduce power consumption. However, when the backlight driver 120 receives a corresponding detection signal from the external light sensor 110 when the intensity of external light is greater than a predetermined intensity, the size of the driving voltage (or driving current) of the backlight 140 is increased. By not changing the brightness of the light generated by the backlight 140 is not reduced to prevent the visibility of the pixel portion 20 is lowered. Meanwhile, in FIG. 2, the external light sensor 110 is illustrated as one, but the present invention is not limited thereto. For example, a plurality of external light detection sensors 110 may be provided in the black matrix region 30. That is, the number of the external light detecting sensors 110 may be variously set to at least one.

The backlight 140 generates light corresponding to a driving voltage (or driving current) supplied from the backlight driver 120 and supplies the light to the pixel unit 20.

In the liquid crystal display according to the embodiment of the present invention described above, the external light sensor 110 is provided to sense the intensity of the external light, thereby controlling the brightness of the light generated by the backlight 140 in response thereto. As a result, power consumption can be reduced. In addition, when the intensity of the external light is detected to be greater than or equal to a predetermined value, the brightness of the light generated by the backlight 140 may not be reduced, thereby preventing deterioration of the viewing characteristics.

3 is a circuit diagram illustrating an example of an external light sensor shown in FIG. 2. 4 is a circuit diagram illustrating an equivalent circuit of the external light sensor shown in FIG. 3.

3 and 4, the external light sensor 110 shown in FIG. 2 includes a detector 112 for outputting a detection signal corresponding to the intensity of the external light, and a detection signal supplied from the detector 112. The noise canceling unit 116 is connected between the amplifying unit 114 and the sensing unit 112 and the amplifying unit 114 to amplify to stabilize the output signal Vout output to the external light sensor 110 by removing noise. ).

The sensing unit 112 includes first and second transistors M1 and M2 connected in series.

The first transistor M1 is set as an N-type transistor, the first electrode of the first transistor M1 is connected to the first power source VDD, and the second electrode of the second transistor M2 is connected to the first transistor M2. It is connected to the output terminal of the first electrode and the detector 112. The gate electrode of the first transistor M1 is connected to a control terminal to receive a control signal Vreset. Here, various signals may be used as the control signal Vreset. For example, one of the scan signals supplied from the scan driver 40 may be supplied as the control signal Vreset. The first transistor M1 is turned on or turned off in response to a control signal Vreset supplied to its gate electrode. For example, the first transistor M1 is turned on when the high-level control signal Vreset is supplied to supply the first power supply VDD to the first electrode of the second transistor M2. In this case, the turn-off state is maintained.

The second transistor M2 is also set as an N-type transistor, and the first electrode of the second transistor M2 is connected to the second electrode of the first transistor M1 and the output terminal of the sensing unit 112. The second electrode is connected to a second power supply VSS having a voltage value lower than that of the first power supply VDD. The gate electrode of the second transistor M2 is connected to its second electrode and the second power supply VSS. That is, the gate electrode of the second transistor M2 is connected to a second electrode supplied with a lower voltage than the first electrode, so that the second transistor M2 is connected in a reverse diode-connection form. The gate electrode of the second transistor M2 is positioned in the opening 35 of the black matrix 30 to receive external light. The second transistor M2 controls the amount of current flowing from the first transistor M1 to the second power source VSS in response to the intensity of the external light. In other words, when the external light is supplied, the second transistor M2 operates as a current source for flowing a current corresponding to the intensity of the external light. Here, when the second transistor M2 is connected in an inverted diode form, the current value corresponding to the intensity of the external light changes almost linearly, thereby improving the reliability of the external light sensing performance. At this time, the parasitic capacitor Cp is generated in the second transistor M2. The parasitic capacitor Cp is generated in parallel with the current source, and when the control signal Vreset is supplied, the first transistor M1 is provided. The electric charge corresponding to the difference between the first power source VDD and the second power source VSS supplied from the battery is charged. However, the parasitic capacitor Cp of the second transistor M2 should be formed to have a sufficient capacity of 1 pF or more. To this end, the second transistor M2 is formed to have a channel width of 1000 μm or more, for example, 1000 μm to 56000 μm.

The amplifier 114 includes third and fourth transistors M3 and M4 connected in series between the first power source VDD and the second power source VSS.

The first electrode of the third transistor M3 is connected to the first power supply VDD, and the second electrode is connected to the first electrode and the output terminal of the fourth transistor M4. The gate electrode of the third transistor M3 is connected to the bias terminal to receive the bias signal Vbias. The third transistor M3 has a larger current than that flowing through the sensing unit 112 in response to a sufficiently large bias signal Vbias, for example, a current value of several hundred times the current flowing through the sensing unit 112. It operates as a constant current source through which a current with (hereinafter referred to as Io) flows.

The first electrode of the fourth transistor M4 is connected to the second electrode and the output terminal of the third transistor M3, and the second electrode is connected to the second power source VSS. The gate electrode of the fourth transistor M4 is connected to the first and fourth switches SW1 and SW4 included in the noise removing unit 116. In this case, the gate electrode of the fourth transistor M4 is connected to the output terminal of the sensing unit 112 when the first switch SW1 is turned on, and when the fourth switch SW4 is turned on, the noise canceling unit ( It is connected to one terminal of the second capacitor C2 of 116. The internal resistance value of the fourth transistor M4 is changed corresponding to the voltage value supplied to its gate electrode.

Here, the third and fourth transistors M3 and M4 are shown as P-type transistors, but the present invention is not limited thereto. For example, the third and fourth transistors M3 and M4 may be set as N-type transistors. In this case, the transistor connected to the first power supply VDD is connected to at least one switch included in the noise canceling unit 116, and the transistor connected to the second power supply VSS receives the bias signal Vbias. .

The noise removing unit 116 includes first to fifth switches SW1 to SW5 and a first capacitor C1. Here, for convenience, the first to fifth switches SW1 to SW5 are illustrated by a simple switch symbol, but the first to fifth switches SW1 to SW5 may be implemented as a transmission gate that receives a switching pulse. In this case, the first to third switches SW1 to SW3 are supplied with the first switching pulse and turned on or off at the same time, and the fourth and fifth switches SW4 to SW5 are supplied with the second switching pulse. It is set to turn on or off at the same time.

The first switch SW1 is positioned between the output terminal of the detector 112 and the gate electrode of the fourth transistor M4 of the amplifier 114. The first switch SW1 is turned on when the first switching pulse is supplied from the outside to connect the output terminal of the sensing unit 116 and the gate electrode of the fourth transistor M4.

The second switch SW2 is positioned between the reference power supply and one terminal of the first capacitor C1. The second switch SW2 is turned on when the first switching pulse is supplied from the outside to connect the reference power supply to the first capacitor C1.

The third switch SW3 is positioned between the other terminal of the first capacitor C1 and the output terminal of the amplifier 114 (that is, the common node of the third transistor M3 and the fourth transistor M4). . The third switch SW3 is turned on when the first switching pulse is supplied from the outside to connect the first capacitor C1 and the output terminal of the amplifier 114.

The fourth switch SW4 is positioned between one terminal of the first capacitor C1 and the gate electrode of the fourth transistor M4. The fourth switch SW4 is turned on when the second switching pulse is supplied from the outside to connect the first capacitor C1 and the gate electrode of the fourth transistor M4.

The fifth switch SW5 is positioned between the other terminal of the first capacitor C1 and the output terminal of the sensing unit 112. The fifth switch SW5 is turned on when the second switching pulse is supplied from the outside to connect the first capacitor C1 and the output terminal of the sensing unit 112.

One terminal of the first capacitor C1 is connected to the second and fourth switches SW2 and SW4, and the other terminal is connected to the third and fifth switches SW3 and SW5. The first capacitor C1 charges a charge corresponding to the difference between the voltages supplied to both terminals thereof.

Hereinafter, an operation process and effects of the above-described external light sensor 110 will be described in detail with reference to FIGS. 5 and 6.

First, when the high-level control signal Vreset is supplied to the sensing unit 112 during the t1 period, the first transistor M1 is turned on, whereby the first power source VDD turns on the second transistor M2. Is supplied to the first electrode. Then, the parasitic capacitor Cp of the second transistor M2 is charged with a charge corresponding to the difference between the first power source VDD and the second power source VSS. Here, the high-level control signal Vreset is supplied only for a predetermined time.

Subsequently, when external light is incident on the gate electrode of the second transistor M2, in particular, the second transistor M2, the second transistor M2 corresponds to the intensity of the external light from the first transistor M1 to the second power source VSS. Current). At this time, since the second transistor M2 is connected in an inverted diode form, the current value flowing through the second transistor M2 changes almost linearly in response to the intensity of the external light. As a result, the electric charges charged in the parasitic capacitor Cp of the second transistor M2 are discharged. Since the current flowing through the second transistor M2 is proportional to the intensity of the external light, the amount of charge discharged is also the intensity of the external light. Each has a different discharge voltage curve. As a result, the voltage value of the sensing signal supplied to the noise canceling unit 116 through the output terminal of the sensing unit 112 is changed in proportion to the intensity of the external light.

Thereafter, when the first switching pulse SWP1 is supplied to the noise removing unit 116 during the t2 period, the first to third switches SW1 to SW3 are turned on. When the first switch SW1 is turned on, the first sensing signal Vin1 output from the sensing unit 112 is supplied to the gate electrode of the fourth transistor M4. When the second switch SW2 is turned on, the reference voltage Vref is supplied to one terminal of the first capacitor C1, and when the third switch SW3 is turned on, the first capacitor C1 is turned on. The output voltage Vout of the amplifying unit 114 is supplied to the other terminal of. Therefore, when the capacitance of the first capacitor C1 is C, the amount of charge Q1 charged in the first capacitor C1 while the first switching pulse SWP1 is supplied is expressed by Equation 1.

Here, the output voltage Vout of Equation 1 is the voltage Vin1 supplied to the gate electrode of the fourth transistor M4, the threshold voltage Vth3 of the third transistor M3, and the current flowing through the third transistor M3 ( A value determined by the process transconductance parameter Kp with respect to Io) and the channel width versus channel length W / L of the fourth transistor M4, and the output voltage Vout is expressed by Equation 2 below.

Therefore, Equation 3 can be obtained by substituting the output voltage Vout of Equation 2 into Equation 1.

Thereafter, when the second switching pulse SWP2 is supplied to the noise removing unit 116 during the t3 period, the fourth to fifth switches SW4 and SW5 are turned on. When the fourth switch SW4 is turned on, the gate voltage Vg4 of the fourth transistor M4 is supplied to one terminal of the first capacitor C1. In this case, the gate voltage Vg4 of the fourth transistor M4 is set as the first sensing signal Vin1. When the fifth switch SW5 is turned on, the sensing signal output from the sensing unit 112 is supplied to the other terminal of the first capacitor C1. At this time, since the control signal Vreset is supplied to the sensing unit 112 during the t3 period, the second sensing signal Vin2 different from the first sensing signal Vin1 is supplied from the sensing unit 112. Therefore, the charge amount Q2 charged in the first capacitor C1 while the second switching pulse SWP2 is supplied is expressed by Equation 4.

Here, Equation 2 may be obtained by arranging Equation 2 with respect to the first detection signal Vin1 and substituting Equation 4.

At this time, the amount of charge Q1 charged in the first capacitor C1 while the first switching pulse SWP1 is supplied and the amount of charge Q2 charged in the first capacitor C1 while the second switching pulse SWP2 is supplied. ) Are the same, so Q1 of equation (3) and Q2 of equation (5) are the same. Therefore, by solving this by Q1 = Q2 and arranging the output voltage Vout, Equation 6 can be obtained.

Referring to Equation 6, the output voltage Vout of the external light sensor 110 is noise due to the threshold voltage Vth3 of the third transistor M3 and the process transconductance parameter Kp of the fourth transistor M4. Does not include That is, the output voltage Vout of the external light sensor 110 is the reference voltage Vref and the first and second sensing signals Vin1 and Vin2 regardless of process variables of the third and fourth transistors M3 and M4. As determined by), the output of the external light sensor 110 is stabilized. For example, when the external light of the same intensity is supplied and the threshold voltage Vth3 fluctuation range of the third transistor M3 is ± 0.5V, when the noise canceller 116 is not present, as shown in FIG. Vout) fluctuation range is about 1V, but when the noise canceling unit 116 is provided, the output voltage Vout fluctuation is approximately 10mV, which is reduced to 1/100 compared with the case where the noise canceling unit 116 is not present. As a result, the output of the external light sensor 110 corresponding to the intensity of the external light is stabilized to further improve the reliability of the external light detection performance.

In addition, in the operation of the external light sensor 110, the amplifier 114 is larger than the current flowing through the detector 112 in response to the bias signal Vbias supplied from the outside, for example, several hundred times. A third transistor M3 serving as a constant current source for flowing a large current Io and a fourth transistor M4 whose internal resistance changes in response to the sensed signal are amplified to amplify the current to amplify the sensed signal. It plays a role. As such, the detection signal output from the detection unit 112 is amplified by the amplification unit 114 and output to the outside of the external light detection sensor 110, whereby the external light detection sensor 110 is connected to its output terminal. The driving force capable of driving the is improved.

The backlight driver 120 is connected to the output terminal of the external light sensor 110, and the backlight driver 120 receives the amplified detection signal and controls the brightness of the light generated by the backlight 140 in response thereto. That is, the backlight driver 120 decomposes the signal into the minimum detectable level in response to the change of the amplified detection signal Vout output from the external light sensor 110 and adjusts the light generated by the backlight 140 according to each level. Control the brightness. For example, if the minimum output voltage Vout change value that the backlight driver 120 can detect is 0.2V and the change value of the current corresponding thereto is 10 pA, the second transistor M2 depends on the intensity of the external light. When a current of 50 pA to 400 pA flows, the intensity of external light may be decomposed to 35 levels to control the luminance of light generated by the backlight 140. Although not shown, at least one application circuit may be further connected between the output terminal of the external light sensor 110 and the backlight driver 120. Here, by implementing the active sensing unit 112 using the first and second transistors M1 and M2, the outputs of the amplifier 114 and the noise canceling unit 116 or the application circuits of the following stages are output. It can be stabilized.

Meanwhile, in FIGS. 3 and 4, all of the first and second transistors M1 and M2 included in the sensing unit 112 are illustrated as N-type transistors, but the present invention is not limited thereto. For example, as shown in FIG. 7, the second transistor M2 ′ may be formed as a P-type transistor. In this case, the P-type transistor can stably change the current value according to the change of the voltage supplied to the gate electrode, and thus can supply a stable sensing signal to the output terminal of the sensing unit 112. Here, the external light sensor 110 illustrated in FIG. 7 is the external light sensor 110 illustrated in FIGS. 3 and 4 except that the second transistor M2 ′ is formed as a P-type transistor. Since it is the same as, detailed description thereof will be omitted.

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various modifications are possible within the scope of the technical idea of the present invention.

As described above, according to the external light sensor and the liquid crystal display using the same, the power consumption is reduced by sensing the intensity of the external light to control the brightness of the light generated by the backlight. In addition, by connecting the second transistor in the form of an inverted diode so that the charged charge is discharged in proportion to the intensity of the external light, reliability in detecting the external light can be improved. In addition, by providing an amplifying unit for amplifying a sensing signal output from the sensing unit, the driving force for the external light sensor to drive the application circuit connected to its output terminal is improved. In addition, a noise removing unit may be provided between the sensing unit and the amplifying unit to stabilize the output voltage of the external light sensor regardless of process variables of the transistors included in the amplifying unit.

Claims (17)

A first transistor connected between a first power supply and a second power supply having a lower voltage than the first power supply and turned on or off in response to a control signal; And A first electrode connected between the first transistor and the second power source to control an amount of current flowing from the first transistor to the second power source in response to an intensity of external light, and a gate electrode connected to the second power source and connected to a reverse diode; A sensing unit having two transistors, And at least one amplifier connected to the output of the detector and at least one noise remover connected between the detector and the amplifier. According to claim 1, The channel width of the second transistor is an external light sensor, characterized in that set to 1000㎛ to 56000㎛. According to claim 1, The noise canceling unit includes at least one capacitor and a plurality of switches. The method of claim 3, wherein The noise canceling unit A first switch positioned between an output terminal of the sensing unit and a gate electrode of at least one transistor included in the amplifying unit; A second switch located between a reference power supply and one terminal of the capacitor; A third switch connected between the other terminal of the capacitor and the output terminal of the amplifier; A fourth switch positioned between one terminal of the capacitor and a gate electrode of at least one transistor included in the amplifier; And And a fifth switch located between the other terminal of the capacitor and the output terminal of the sensing unit. The method of claim 4, wherein The first to third switches are external light sensor, characterized in that turned on or off by the same switching pulse. The method of claim 4, wherein And the fourth and fifth switches are turned on or off by the same switching pulse. According to claim 1, The amplification unit A third transistor connected between the first power supply and the second power supply and turned on in response to a bias signal; And And a fourth transistor connected between the third transistor and the second power supply and having a gate electrode connected to at least one switch included in the noise canceling unit. According to claim 1, And the first and second transistors are N-type transistors. According to claim 1, And the first transistor is an N-type transistor, and the second transistor is a P-type transistor. A pixel unit including a plurality of liquid crystal cells; At least one external light detection sensor provided in a black matrix area formed at an outer edge of the pixel unit and generating a detection signal corresponding to the intensity of external light; A backlight for supplying light to the pixel portion; And A backlight driver configured to control luminance of light generated by the backlight in response to the detection signal; The external light sensor may include a first transistor connected between a first power supply and a second power supply having a lower voltage than the first power supply and turned on or off in response to a control signal, the first transistor, and the A sensing unit including a second transistor connected between a second power source to control an amount of current flowing from the first transistor to the second power source in response to an intensity of external light, and a gate electrode connected to the second power source and connected to a second diode And at least one amplifier connected to the output of the detector and at least one noise canceller connected between the detector and the amplifier. The method of claim 10, The channel width of the second transistor is set to 1000㎛ 56000㎛ liquid crystal display device. The method of claim 10, The noise canceling unit includes at least one capacitor and a plurality of switches. The method of claim 12, The noise canceling unit A first switch positioned between an output terminal of the sensing unit and a gate electrode of at least one transistor included in the amplifying unit; A second switch located between a reference power supply and one terminal of the capacitor; A third switch connected between the other terminal of the capacitor and the output terminal of the amplifier; A fourth switch positioned between one terminal of the capacitor and a gate electrode of at least one transistor included in the amplifier; And And a fifth switch positioned between the other terminal of the capacitor and the output terminal of the sensing unit. The method of claim 13, And the first to third switches are turned on or off by the same switching pulse. The method of claim 13, And the fourth and fifth switches are turned on or off by the same switching pulse. The method of claim 10, The amplification unit A third transistor connected between the first power supply and the second power supply and turned on in response to a bias signal; And And a fourth transistor connected between the third transistor and the second power supply, and a gate electrode connected to at least one switch included in the noise canceling unit. The method of claim 10, The gate electrode of the second transistor is positioned in the opening of the black matrix.

Images