KR101437689B1 - Photo-sensor and Driving Method thereof - Google Patents

Abstract

The present invention relates to a photo sensor for compensating a threshold voltage of a transistor element for detecting a light field.

The photosensor is a high potential voltage source generating a high potential voltage; A base voltage source generating a base voltage; A control signal generator for sequentially generating a first control signal, a second control signal, and a third control signal; A sensor transistor element connected between the first node, the second node and the base voltage source; A capacitor connected to the sensor transistor element via a first node to charge a threshold voltage of the sensor transistor element; A first transistor element that is turned on in accordance with the first control signal and supplies the high potential voltage to the first node; A second transistor element which is turned on in accordance with the second control signal to short-circuit the first node and the second node to charge the threshold voltage of the sensor transistor element to the capacitor; And a third transistor element which is turned on in accordance with the third control signal to supply the high-potential voltage to the sensor transistor element.

Photo sensor, threshold voltage, deviation

Description

[0001] Photoelectric sensor and driving method [0002]

The present invention relates to a photo sensor for compensating a threshold voltage of a transistor element for detecting a light field and a driving method thereof.

The photosensor senses the light by using a phenomenon in which photo current flows in the semiconductor layer of the transistor element when the light is irradiated. Such a photosensor has been applied to various fields, and recently it has been applied to various display devices.

A liquid crystal display device of an active matrix driving type displays an image using a thin film transistor (hereinafter referred to as "TFT") as a switching element. This liquid crystal display device can be downsized as compared with a cathode ray tube (CRT), and is applied to a display device in a portable information device, an office machine, a computer, etc., and is rapidly applied to a television, thereby rapidly replacing a cathode ray tube. When a photosensor is formed on a glass substrate of such a liquid crystal display device, the film quality of the glass substrate is relatively uneven. Therefore, driving characteristics of the photosensor vary depending on the glass substrate and the position of the glass substrate on which the photosensor is to be formed have.

1 shows a conventional photo sensor.

Referring to Fig. 1, the photosensor includes a TFT, an operational amplifier OPamp connected to the TFT, and a variable resistor R. When light is received by the semiconductor layer of the TFT, the TFT generates an output voltage proportional to the photodetector. The operational amplifier OPamp amplifies the output of the TFT by its gain.

When such a photosensor is formed on a glass substrate of a liquid crystal display device, the threshold voltage (Vth) of the TFT is changed according to the glass substrate and the position of the glass substrate, as shown in FIG. As a result, an output deviation can be generated between the photo sensors having the deviation of the threshold voltage of the TFT. In order to compensate for such a deviation, the conventional technique adjusts the gate-source voltage Vgs of the TFT to the first variable resistor R1 or adjusts the gain of the operational amplifier OPamp to the second variable resistor R2 have.

However, when the threshold voltage of the photosensor TFT is compensated by a variable resistor, the operation time is excessively shortened and the productivity of the liquid crystal display device is lowered, and it is difficult to compensate the variation of the photosensor characteristic by a satisfactory level.

Accordingly, it is an object of the present invention to provide a photo sensor for automatically compensating a threshold voltage of a TFT that senses light in a photo sensor, and a driving method thereof.

According to an aspect of the present invention, there is provided a photosensor including: a high potential voltage source generating a high potential voltage; A base voltage source generating a base voltage; A control signal generator for sequentially generating a first control signal, a second control signal, and a third control signal; A sensor transistor element connected between the first node, the second node and the base voltage source; A capacitor connected to the sensor transistor element via a first node to charge a threshold voltage of the sensor transistor element; A first transistor element that is turned on in accordance with the first control signal and supplies the high potential voltage to the first node; A second transistor element which is turned on in accordance with the second control signal to short-circuit the first node and the second node to charge the threshold voltage of the sensor transistor element to the capacitor; And a third transistor element which is turned on in accordance with the third control signal to supply the high-potential voltage to the sensor transistor element.

The control signal generator generates a fourth control signal to overlap the second half of the third control signal, and applies the fourth control signal to the capacitor.

A method of driving a photosensor according to an embodiment of the present invention includes: connecting a first node connected to a gate electrode of the sensor transistor element to the high potential voltage source during a first period, Initializing a voltage and charging a capacitor connected to the first node; Connecting the first node to a second node connected to a drain terminal of the sensor transistor element for inducing a discharge of the capacitor through the sensor transistor element to cause the capacitor to have a threshold voltage of the sensor transistor element Storing; And driving the sensor transistor element by supplying the high potential voltage to the second node during a third period.

The method of driving a photosensor according to another embodiment of the present invention further includes supplying an external voltage to the capacitor for a part of the latter period of the third period.

A photosensor and a driving method thereof according to an embodiment of the present invention detect a threshold voltage of a sensor transistor element and then drive a sensor transistor element with the threshold voltage so that a deviation of a threshold voltage Can be automatically compensated.

Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS. 3 to 8. FIG.

Referring to FIG. 3, the photosensor 100 according to the first embodiment of the present invention includes first through fourth TFTs T 1 through T 4, and a capacitor C. Each of the TFTs is implemented as an n-type MOS-FET.

The first TFT T1 resets the gate voltage of the fourth TFT T1 to the high potential source VDD. A reset signal RESET is applied to the gate terminal of the first TFT T1. The drain terminal of the first TFT T1 is connected to the high potential source VDD and the source terminal of the first TFT T1 is connected to the first node n1.

The second TFT T2 charges the capacitor C with the gate voltage-source voltage Vgs of the fourth TFT T4 to the high potential voltage VDD. A threshold voltage sensing signal VTH-SEN is applied to the gate terminal of the second TFT T2. The drain terminal of the second TFT T2 is connected to the second node n2 and the source terminal of the second TFT T2 is connected to the first node n1.

The third TFT T3 supplies the high potential voltage VDD to the drain electrode of the fourth TFT T4. The driving signal DRV is applied to the gate terminal of the third TFT T3. The drain terminal of the third TFT T3 is connected to the high potential source VDD and the source terminal of the third TFT T3 is connected to the second node n2. The source terminal of the third TFT T3 is connected to the output terminal from which the sensed voltage is outputted.

The fourth TFT T4 is driven when the third TFT T3 is turned on to sense light. The gate terminal of the fourth TFT T4 is connected to the first node n1 and the drain terminal of the fourth TFT T4 is connected to the second node n2. The source terminal of the fourth TFT T4 is connected to the ground voltage source GND.

The first to third TFTs (T1 to T3) are covered by the light shielding member so as not to be exposed to external light to malfunction, and the fourth TFT (T4) is exposed to external light since external light must be sensed.

One terminal of the capacitor C is connected to the first node n1 and the other terminal is connected to the ground voltage source GND. The capacitor C serves to detect the threshold voltage of the fourth TFT T4 by charging the threshold voltage of the fourth TFT T2 by the second TFT T2.

The operation of the photo sensor 100 will be described with reference to FIG.

4 is a waveform diagram showing a driving method of the photosensor 100 according to the first embodiment of the present invention.

3 and 4, the first TFT T1 is turned on in response to the reset signal RESET at the same time as the start of the first period t1 and is turned on during the first period t1 And maintains the ON state to supply the high potential voltage VDD to the first node n1. During the first period, the second and third TFTs (TFT2 and TFT3) remain off. During the first period t1, the gate voltage of the fourth TFT T4 rises to the high-potential voltage VDD, and the capacitor C charges the high-potential voltage VDD. At the end of the first period t1, the first TFT T1 is turned off. During the first period t1, the gate voltage of the fourth TFT T4 is initialized to a high potential voltage.

The second TFT T2 is turned on in response to the threshold voltage sensing signal VTH-SEN at the start of the second period t2 in the first period t1. The second TFT T2 maintains the on state during the second period t2. During the second period, the first and third TFTs (TFT1, TFT3) remain off. The first node n1 is shorted to the second node n2 due to the ON operation of the second TFT T2 and the fourth TFT T4 is turned on with the voltage charged in the capacitor C. After the voltage of the capacitor C is discharged through the drain-source terminal of the fourth TFT T4 until the voltage of the capacitor C becomes the gate-source voltage of the fourth TFT T4, C becomes lower than the gate-source voltage of the fourth TFT T4, the fourth TFT T4 is turned off. Therefore, during the second period T2, only the gate-source voltage of the fourth TFT T4, that is, the threshold voltage, is charged in the capacitor C after the discharge.

The third TFT T3 is turned on in response to the driving signal DRV in the second period t2, and at the beginning of the third period t3. The third TFT T3 maintains the on state during the third period t3. During the third period, the first and second TFTs (TFT1 and TFT2) remain off. The gate-source voltage of the fourth TFT T4 becomes the threshold voltage of the fourth TFT T4 due to the voltage charged in the capacitor C due to the ON operation of the third TFT T3, An increased current flows in the drain-source channel of the transistor T4 according to the photocathode. Therefore, during the third period, the source terminal of the fourth TFT (T4) is applied with a voltage varying in accordance with the photodetection of the fourth TFT (T4).

As a result, the photosensor 100 according to the first embodiment of the present invention and the driving method thereof periodically initialize the gate voltage of the sensor TFT T4, and then the threshold voltage of the sensor TFT T4 is detected Stores the voltage in the capacitor C and then drives the sensor TFT T4 with the threshold voltage of the sensor TFT T4 stored in the capacitor C. Therefore, even if the threshold voltage characteristic differs according to the sensor TFT T4, all the sensor TFTs T4 detect the light receiving state in a state where the sensor TFTs T4 are turned on with their threshold voltages, so that the driving voltage deviation of the sensor TFTs T4 is automatically compensated do.

5 shows a photosensor 100 according to a second embodiment of the present invention.

Referring to FIG. 5, the photosensor 100 according to the second embodiment of the present invention includes first through fourth TFTs T1 through T4, and a capacitor C. Each of the TFTs is implemented as an n-type MOS-FET. In this embodiment, the connection relation of each element is substantially the same as that of the first embodiment described above, and a detailed description thereof will be omitted.

The fourth TFT T4 can raise the gate voltage at which the fourth TFT T4 can be turned on due to the rise of the drain voltage when the high potential voltage VDD is applied to its drain terminal. In consideration of this, the photosensor 100 according to the second embodiment of the present invention applies the high-potential voltage VDD to the fourth TFT T4 (T4) in order to compensate the threshold voltage deviation of the fourth TFT T4 and the rise of the drain voltage, And then applies a capacitor control signal CON to the capacitor C to raise the voltage.

6 is a waveform diagram showing a driving method of the photosensor 100 according to the second embodiment of the present invention. FIG. 6 also shows experimental results when the three TFTs having different threshold voltage characteristics are applied to the fourth TFT T4 which is the sensor TFT of the photosensor 100 according to the second embodiment of the present invention.

5 and 6, the first TFT T1 is turned on in response to the reset signal RESET at the same time as the start of the first period t1, and is turned on during the first period t1 And maintains the ON state to supply the high potential voltage VDD to the first node n1. During the first period, the second and third TFTs (TFT2 and TFT3) remain off. During the first period t1, the gate voltage of the fourth TFT T4 rises to the high-potential voltage VDD, and the capacitor C charges the high-potential voltage VDD. At the end of the first period t1, the first TFT T1 is turned off. During the first period t1, the gate voltage of the fourth TFT T4 is initialized to a high potential voltage.

The second TFT T2 is turned on in response to the threshold voltage sensing signal VTH-SEN at the start of the second period t2 in the first period t1. The second TFT T2 maintains the on state during the second period t2. During the second period, the first and third TFTs (TFT1, TFT3) remain off. The first node n1 is shorted to the second node n2 due to the ON operation of the second TFT T2 and the fourth TFT T4 is turned on with the voltage charged in the capacitor C. After the voltage of the capacitor C is discharged through the drain-source terminal of the fourth TFT T4 until the voltage of the capacitor C becomes the gate-source voltage of the fourth TFT T4, C becomes lower than the gate-source voltage of the fourth TFT T4, the fourth TFT T4 is turned off. Therefore, during the second period T2, only the gate-source voltage of the fourth TFT T4, that is, the threshold voltage, is charged in the capacitor C after the discharge.

In the second period t2, the third TFT T3 is turned on in response to the driving signal DRV at the start of the third period t3a. And the third TFT T3 remains on for the third and third time periods t3. During the third and third time periods, the first and second TFTs (TFT1 and TFT2) are kept off. The third TFT T3 maintains the ON state during the third period t3b and the capacitor control signal CON is supplied to the capacitor C following the third period t3a. As a result, the gate-source voltage of the fourth TFT T4 becomes the threshold voltage of the fourth TFT T4 due to the voltage charged in the capacitor C, and the drain-source channel of the fourth TFT T4 An increased current flows according to the photocathode. Therefore, during the third period, the source terminal of the fourth TFT (T4) is applied with a voltage varying in accordance with the photodetection of the fourth TFT (T4).

6, three TFTs (tran7, tran8, and tran9) having different threshold voltage characteristics are connected to the fourth TFT (T4) of the photosensor 100 according to the second embodiment of the present invention ), The sensor output voltage Vds is constant even though the threshold voltages of the TFTs are different from each other, so that it is confirmed that the threshold voltage deviation of the TFT is compensated.

7 shows a liquid crystal display device according to the first embodiment of the present invention.

7, the liquid crystal display according to the first embodiment of the present invention includes a liquid crystal display panel 70, a timing controller 71, a data driving circuit 72, a gate driving circuit 73, a photosensor 100 A sensor driving circuit 77, a luminance control circuit 78, an inverter 79,

The liquid crystal display panel 70 includes a display area 70A in which a pixel array is formed and a non-display area 70B outside the display area 70A. M × n liquid crystal cells Clc arranged in a matrix form by the intersection structure of m data lines 74 and n gate lines 75 are formed in the display region 70A.

In the lower glass substrate of the liquid crystal display panel 70, a plurality of data lines 74, a plurality of gate lines 75, TFTs, and a storage capacitor Cst are formed in the display region 70A. The liquid crystal cell Clc is connected to the TFT and controls the transmittance of incident light from the backlight unit 80 according to the electric field between the pixel electrodes 1 and the common electrode 2 to display an image. A photosensor 100 is formed in the non-display area 70B on the lower glass substrate of the lower portion 70 of the liquid crystal display panel together with the pixel array of the display area 70A. The photocensor 100 has the same circuit configuration as the embodiment of FIG. 3 or 5 described above.

On the upper glass substrate of the liquid crystal display panel 70, a black matrix, a color filter, and the like are formed.

The common electrode 2 is formed on an upper glass substrate in a vertical electric field driving method such as a TN (Twisted Nematic) mode and a VA (Vertical Alignment) mode. The common electrode 2 is formed of an IPS (In Plane Switching) mode, an FFS (Fringe Field Switching) Is formed on the lower glass substrate together with the pixel electrode 1 in the same horizontal electric field driving system.

On the upper glass substrate and the lower glass substrate of the liquid crystal display panel, a polarizing plate orthogonal to the optical axis is attached, and an alignment film is formed to set a pre-tilt angle of the liquid crystal at the interface with the liquid crystal.

The timing controller 71 receives the timing signals such as the vertical / horizontal synchronizing signals Vsync and Hsync, the data enable signal, the dot clock signal DCLK and the fixed clock signal FCLK, 72, and the gate driving circuit 73. The gate driver circuit 73, These control signals include a gate timing control signal GDC and a data timing control signal DDC. Further, the timing controller 71 supplies the digital video data RGB to the data driving circuit 72.

The data driving circuit 72 includes a plurality of data drive ICs. The data driving circuit 72 latches the digital video data RGB in accordance with the data timing control signal DDC and then converts the digital video data RGB into an analog positive / negative gamma compensation voltage, Lines 74, respectively.

The gate driving circuit 73 sequentially supplies gate pulses to the gate lines 75 in response to the gate timing control signals.

The sensor driving circuit 77 generates control signals RESET, VTH_SEN, DRV, and CON to control the TFTs of the photosensor 77 as shown in FIGS. 4 and 5 to drive the photosensor 100.

A high potential source VDD and a ground voltage source GND are supplied to the photosensor 100 and control signals are supplied from the sensor driving circuit 77. The photosensor 100 senses the brightness of the surrounding environment under the control of the sensor control regolator 77 and outputs a sensor signal indicating its surrounding brightness. The luminance control circuit 78 amplifies the output of the photosensor 100 and converts it into digital data. The brightness control circuit 78 determines the brightness of the surrounding environment according to the output of the photosensor 100 and increases the brightness control value for controlling the brightness of the backlight unit 80 as the brightness of the surrounding environment is higher. The inverter 79 adjusts the brightness according to the brightness control value from the brightness control circuit 78.

Therefore, the liquid crystal display according to the first embodiment of the present invention adjusts the brightness of the backlight unit 20 according to the brightness of the surroundings sensed by the photosensor 100, .

8 shows a liquid crystal display device according to a second embodiment of the present invention. In FIG. 8, substantially the same constituent elements as those of the embodiment of FIG. 7 described above are denoted by the same reference numerals, and a detailed description thereof will be omitted.

8, a liquid crystal display according to a second embodiment of the present invention includes a liquid crystal display panel 70, a timing controller 81, a data driving circuit 72, a gate driving circuit 73, a photosensor 100, a sensor driving circuit 77, a data modulation circuit 82, an inverter 83, and a backlight unit 80.

The timing controller 71 receives the timing signals such as the vertical / horizontal synchronizing signals Vsync and Hsync, the data enable signal, the dot clock signal DCLK and the fixed clock signal FCLK, 72, and the gate driving circuit 73. The gate driver circuit 73, The timing controller 71 supplies the digital video data RGB to the data modulation circuit 82 and the digital video data RGB 'modulated by the data modulation circuit 82 to the data driving circuit 72 Supply. Further, the timing controller 71 analyzes the digital video data (RGB) and generates a dimming signal for raising the brightness of the bright image relative to the dark image.

The inverter 79 drives the light source of the backlight unit 80 by a PWM (Pulse Width Modulation) modulation method in accordance with the dimming signal from the timing controller 81 in accordance with the driving signal of the light source of the backlight unit.

The data modulation circuit 82 amplifies the output of the photosensor 100 and converts it into digital data. The data modulation circuit 82 determines the brightness of the surrounding environment according to the output of the photosensor 100 and increases the value of the digital video data RGB as the brightness of the surrounding environment is higher, . The data modulation circuit 82 may incorporate a look-up table for automatically selecting the brightness signal of the surrounding environment, that is, the data modulated in accordance with the output of the sensor.

Accordingly, the liquid crystal display according to the second embodiment of the present invention increases the data value displayed on the liquid crystal display panel 70 according to the brightness of the surroundings sensed by the photosensor 100, The phenomenon of degradation can be reduced.

7 and 8, the liquid crystal display device according to the third embodiment of the present invention combines the circuits of FIGS. 7 and 8 to determine a data value And the brightness of the backlight unit 80 is increased.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. For example, while the embodiments of the photosensor have been described above with reference to an n-type MOS-FET, the transistor elements constituting the photosensor may be implemented as a p-type MOS-FET. In this case, the control signal for controlling the transistor elements of the photosensor must be generated with a low logic voltage as opposed to Fig. 4 or Fig. In addition, the transistor elements constituting the photo sensor may be implemented as a combination of a p-type MOS-FET and an n-type MOS-FET, that is, CMOS transistors. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

1 is a circuit diagram showing a conventional photo sensor;

FIG. 2 is a waveform diagram showing threshold voltage characteristics of three TFTs in which a threshold voltage deviation exists. FIG.

3 is a circuit diagram showing a photosensor according to a first embodiment of the present invention;

Fig. 4 is a waveform diagram showing control signals of the photosensor shown in Fig. 3; Fig.

5 is a circuit diagram showing a photosensor according to a second embodiment of the present invention;

6 is a waveform diagram showing control signals of the photosensor shown in Fig. 5; Fig.

7 is a block diagram showing a liquid crystal display device according to the first embodiment of the present invention.

8 is a block diagram showing a liquid crystal display device according to a second embodiment of the present invention.

Description of the Related Art

70: liquid crystal display panel 71, 81: timing controller

72: Data driving circuit 73: Gate driving circuit

77: sensor driving circuit 78: luminance control circuit

79: Inverter 80: Backlight unit

82: Data modulation circuit 83: Inverter

Claims (9)

A high potential voltage source generating a high potential voltage; A base voltage source generating a base voltage; A control signal generator for sequentially generating a first control signal, a second control signal, and a third control signal; A sensor transistor element connected between the first node, the second node and the base voltage source; A capacitor connected to the sensor transistor element via a first node to charge a threshold voltage of the sensor transistor element; A first transistor element that is turned on in accordance with the first control signal and supplies the high potential voltage to the first node; A second transistor element which is turned on in accordance with the second control signal to short-circuit the first node and the second node to charge the threshold voltage of the sensor transistor element to the capacitor; And And a third transistor element that is turned on in accordance with the third control signal to supply the high-potential voltage to the sensor transistor element. The method according to claim 1, Wherein the first control signal is applied to the gate terminal of the first transistor element, the drain terminal of the first transistor element is connected to the high potential voltage source, and the source terminal of the first transistor element is connected to the first node Wherein the photo sensor comprises: 3. The method of claim 2, Wherein the second control signal is applied to a gate terminal of the second transistor element, a drain terminal of the second transistor element is connected to the second node, and a source terminal of the second transistor element is connected to the first node Wherein the photo sensor comprises: The method of claim 3, The third control signal is applied to the gate terminal of the third transistor element, the drain terminal of the third transistor element is connected to the high potential voltage source, and the source terminal of the third TFT (T3) (n2) and the output terminal. 5. The method of claim 4, Wherein a gate terminal of the sensor transistor element is connected to the first node, a drain terminal of the sensor transistor element is connected to the second node, and a source terminal of the sensor transistor element is connected to the base voltage source Photo sensor. The method according to claim 1, Further comprising a light shielding member for shielding the first to third transistor elements; Wherein the sensor transistor element is exposed to external light. The method according to claim 1, Wherein the control signal generator comprises: Generates a fourth control signal to overlap the second half of the third control signal, and applies the fourth control signal to the capacitor. A method of driving a photosensor including a high potential voltage source generating a high potential voltage, a ground voltage source generating a low voltage, and a sensor transistor element for sensing light, A first node connected to a gate electrode of the sensor transistor element is connected to the high potential voltage source for a first period to initialize a gate voltage of the sensor transistor element to the high potential voltage and a capacitor connected to the first node Charging; Connecting the first node to a second node connected to a drain terminal of the sensor transistor element for inducing a discharge of the capacitor through the sensor transistor element to cause the capacitor to have a threshold voltage of the sensor transistor element Storing; And And driving the sensor transistor element by supplying the high potential voltage to the second node during a third period. 9. The method of claim 8, Further comprising the step of supplying an external voltage to the capacitor during a part of the latter period of the third period.

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