KR100824859B1 - Flat panel device having ambient light sensor circuit - Google Patents

Abstract

A flat panel display having an ambient light sensing circuit is provided to improve visibility both at dark and bright areas by automatically adjusting screen brightness based on the current ambient brightness. An ambient light sensing circuit(100) includes first and second capacitors, a photo detector, and first and second switches. An ambient light controller(200) receives an analog output signal from the ambient light sensing circuit, calculates the ambient light, and converts the ambient light into a digital value. A timing controller(300), including a look-up table and a brightness selecting unit, receives an output signal from the ambient light controller and outputs a control signal according to the current ambient light. A power controller(800) receives an output signal from the timing controller and outputs a source voltage corresponding to the current ambient brightness. An OLED(Organic Light Emitting Device) panel(500) receives the source voltage from the power controller and emits light.

Description

Flat panel display device having ambient light sensing circuit {FLAT PANEL DEVICE HAVING AMBIENT LIGHT SENSOR CIRCUIT}

1A and 1B are circuit diagrams illustrating an ambient light sensing circuit according to the present invention.

2 is a timing diagram of an ambient light sensing circuit in accordance with the present invention.

3 is a circuit diagram illustrating current flow during a threshold voltage compensation period by the ambient light sensing circuit of the present invention.

4 is a circuit diagram showing the current flow during the ambient light sensing period by the ambient light sensing circuit of the present invention.

5 is a circuit diagram showing the current flow during the sampling period by the ambient light sensing circuit of the present invention.

6A to 6C are graphs simulating changes in output voltage according to changes in ambient light of the ambient light sensing circuit according to the present invention.

7 is a block diagram illustrating a state in which an ambient light control processor is further connected to an ambient light sensing circuit according to the present invention.

8 is a block diagram illustrating a configuration of a flat panel display device having an ambient light sensing circuit according to the present invention.

FIG. 9A is a circuit diagram illustrating an example of a pixel circuit in an organic EL panel of the flat panel display, and FIG. 9B is a timing diagram thereof.

<Description of Symbols for Main Parts of Drawings>

100; Ambient light sensing circuit T1; transistor

C1; First capacitive element C2; Second capacitive element

C3; Third capacitive element C4; Fourth capacitive element

PD; Light receiving element S1; First switch

S2; Second switch S3; 3rd switch

S4; Fourth switch S5; Fifth switch

S6; Sixth switch 110; Output load

200; Ambient light control processor 210; Analog to digital converter

220; First memory 230; Control

240; Second memory 300; Timing control

310; Brightness selector 320; Lookup table

400; A data driver 500; Organic electroluminescent panels

600; Scan driver 700; Light emission control driver

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat panel display having an ambient light sensing circuit. More particularly, the present invention relates to a flat panel display device that accurately detects ambient brightness and automatically adjusts screen brightness according to ambient brightness. The present invention relates to a flat panel display having an ambient light sensing circuit that can be implemented.

In general, a flat panel display means an organic light emitting display, a liquid crystal display, a plasma display, a field emission display, or the like. Such flat panel displays are not only thin, light in weight, but also increasingly small in power consumption, rapidly replacing conventional display devices made of Cathode Ray Tubes (CRTs). In addition, among the flat panel display devices, the organic light emitting display device and the liquid crystal display device can be easily manufactured in a small size, and can be used for a long time with a battery, and thus are widely used as display devices of portable electronic devices.

By the way, such a flat panel display device such as an organic light emitting display device or a liquid crystal display device can artificially adjust the screen brightness by a user's operation, but is generally designed to display the screen at a constant brightness regardless of the ambient brightness. For example, a conventional flat panel display is designed to have an optimal screen brightness in a room where ambient brightness is not bright. Therefore, the brightness of the screen is relatively too bright in the dark, the brightness of the screen is relatively too small under sunlight, there is a problem in visibility.

In addition, since the brightness of the screen is constantly set as described above, the conventional flat panel display has a problem in that the screen brightness is unnecessarily bright and the power consumption rate is large when the ambient brightness is relatively dark for a long time.

In addition, in the conventional flat panel display device, when manufacturing the ambient light sensing circuit for sensing the ambient brightness, a sensor, a substrate, and a processing circuit should be formed on a substrate separate from the main substrate on which the flat panel display panel is formed. There is a problem in that the size and thickness of the flat panel display device are increased, and power consumption is also increased due to the connection.

SUMMARY OF THE INVENTION The present invention has been made to overcome the above-mentioned conventional problems, and an object of the present invention is to provide a flat panel display having an ambient light sensing circuit capable of accurately detecting ambient brightness.

Another object of the present invention is to provide a flat panel display having an ambient light sensing circuit that can automatically adjust the brightness of the screen according to the ambient brightness.

Another object of the present invention is to provide a flat panel display having an ambient light sensing circuit that can implement an ambient light sensing circuit, a signal processing circuit, and the like as a low temperature crystallized polysilicon thin film transistor on a substrate on which a pixel circuit is formed.

In order to achieve the above object, a flat panel display device according to the present invention includes a transistor, a first capacitive element electrically connected to the transistor, and compensating a threshold voltage of the transistor; The second capacitive element connected to the first capacitive element and the second capacitive element, and electrically connected to each other to change coupling voltages of the first capacitive element and the second capacitive element when ambient light is incident thereon. A light receiving element, a first switch for supplying and charging a voltage of a first power supply to an output load, and an electrical connection between the transistor and the output load, thereby coupling the first capacitive element and the second capacitive element An ambient light sensing circuit comprising a second switch configured to discharge a voltage of an output load through the transistor in response to a voltage, and an analog of the ambient light sensing circuit An ambient light control processor for calculating the current ambient light as an input signal and outputting the current ambient light as a digital value, and outputting a control signal corresponding to the current ambient light using the output signal of the ambient light control processor as an input signal; A timing controller, a power controller for outputting a power voltage corresponding to current ambient light using the output signal of the timing controller as an input signal, and an organic electroluminescent panel for self-emission using the power voltage of the power controller as an input signal. Include.

The timing controller compares a lookup table storing data suitable for the current lighting and data obtained from the ambient light control processor with data stored in the lookup table, and selects a control signal suitable for the current lighting to control the power control unit. It includes a brightness selection unit for outputting.

The ambient light sensing circuit, the ambient light control processor, the timing controller, the power controller, and the organic electroluminescent panel may be formed on one substrate.

At least one of the ambient light sensing circuit, the ambient light control processor, the timing controller, the power controller, and the organic electroluminescent panel may be formed of a low temperature crystallized polysilicon thin film transistor.

The power control unit may output a power voltage having a magnitude proportional to the ambient light obtained from the ambient light sensing circuit.

In the ambient light sensing circuit, a third switch for applying a reference voltage is electrically connected to the first electrode of the first capacitive element, and the transistor is connected to the second electrode of the first capacitive element. The fourth switch for applying the reference voltage reflecting the threshold voltage of the transistor may be electrically connected.

The ambient light sensing circuit may further be electrically connected to a fifth switch for applying a reference voltage reflecting a threshold voltage to the transistor through a fourth switch.

The ambient light sensing circuit may further be electrically connected to a sixth switch configured to converge after the voltage charged to an output load of the transistor is discharged corresponding to the coupling voltages of the first capacitive element and the second capacitive element. have.

In the ambient light sensing circuit, a third capacitive element may be further electrically connected to increase the reverse bias capacitance of the light receiving element.

The ambient light sensing circuit may further include a seventh switch for electrically connecting them between the light receiving element and the third capacitive element.

The ambient light sensing circuit may be any one selected from a PIN diode, a PN diode, and a photo coupler, the cathode of which is electrically connected to a reference power source, and the anode of which is electrically connected to a second power source.

The ambient light sensing circuit may be any one selected from a PIN diode, a PN diode, and a photocoupler, the anode of which is electrically connected to a light receiving element, and the cathode of which is electrically connected to a second reference power source.

The ambient light sensing circuit may be electrically connected to an ambient light control processor to the output load.

The ambient light control processing unit is electrically connected to the output load, and converts the residual voltage value of the output load into a digital value, and is electrically connected to the analog digital converter to convert the digital according to the current ambient light condition. A first memory for storing a value, a controller electrically connected to the first memory to calculate and output a brightness of the current ambient light, a digital value electrically connected to the controller, and stored in advance from the ambient light having various brightnesses; It can be made by including a second memory.

The analog to digital converter of the ambient light control processor may include an output load electrically connected to the first electrode of the transistor, and a fourth capacitive element electrically connected between the output load and the second power source.

As described above, the flat panel display having the ambient light sensing circuit according to the present invention obtains output voltages of various levels in accordance with the ambient light, and automatically adjusts the brightness of the screen through the display device using the same, thereby enabling bright or dark places. In all places, the visibility of a flat panel display device becomes excellent.

In addition, as described above, the flat panel display having the ambient light sensing circuit according to the present invention automatically adjusts the power consumption according to the ambient light, thereby maintaining the optimum power consumption, and thus the usable time of the portable flat panel display. This lengthens.

In addition, as described above, the flat panel display having the ambient light sensing circuit according to the present invention includes an ambient light sensing circuit, an ambient light control processing unit, a timing control unit, a light emission control driver, a power supply control unit and an organic electroluminescent panel all on one substrate. By using the low temperature crystallized polysilicon thin film transistor process, the thickness of the flat panel display device can be made thinner.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings such that those skilled in the art may easily implement the present invention.

Here, the same reference numerals are attached to parts having similar configurations and operations throughout the specification. In addition, when a part is electrically connected to another part, this includes not only the case where it is directly connected but also the case where another element is connected in between.

1A and 1B are circuit diagrams illustrating an ambient light sensing circuit according to the present invention.

First, as shown in FIG. 1A, the ambient light sensing circuit 100 according to the present invention includes a transistor T1, a first capacitive element C1, a second capacitive element C2, and a third capacitive element C3. ), The light receiving element PD, the first switch S1, the second switch S2, the third switch S3, the fourth switch S4, the fifth switch S5, the sixth switch S6, and And a seventh switch S7.

The transistor T1 may include a first electrode (source or drain), a second electrode (drain or source), and a control electrode (gate electrode). The transistor T1 may be one selected from a polysilicon thin film transistor, an amorphous silicon thin film transistor, an organic thin film transistor, and an equivalent thereof, but the type or material of the transistor T1 is not limited to the present invention.

In addition, when the transistor T1 is a polysilicon thin film transistor, it may be formed by any one of low temperature crystallization methods selected from a laser crystallization method, a metal induced crystallization method, a high pressure crystallization method, and an equivalent method. It does not limit the manufacturing method of a polysilicon thin film transistor.

For reference, the laser crystallization method is a method of crystallizing amorphous silicon, for example by irradiating an excimer laser, and the metal-induced crystallization method is applied from the metal by applying a predetermined temperature, for example, with a metal on the amorphous silicon Crystallization is initiated, and the high-pressure crystallization method is a method of crystallizing amorphous silicon by applying a predetermined pressure, for example.

In addition, the transistor T1 may be any one selected from a P-channel transistor, an N-channel transistor, and an equivalent thereof, but is not limited thereto. In the following description, it is assumed that the transistor T1 is a P-channel transistor.

The first capacitive element C1 is electrically connected to the transistor T1 to compensate for the threshold voltage of the transistor T1. That is, in the first capacitive element C1, a first electrode is electrically connected to a contact point of the third switch S3 and the second capacitive element C2, that is, the first node N1. The contact between the control electrode of the transistor T1 and the fourth switch, that is, the second node N2 may be electrically connected. The first capacitive element C1 is a low temperature polycrystalline silicon thin film transistors (LTPS-TFTs) using the excimer laser annealing (ELA) method. Due to the energy variation of the excimer laser, the electrical characteristics of the transistor T1 such as the threshold voltage variation are not uniform, thereby compensating the threshold voltage variation. This will be described in detail below.

The second capacitive element C2 increases the reverse bias capacitance of the light receiving element PD so that the signal retention characteristic is improved. This will also be described in detail below. In the second capacitive element C2, a first electrode is electrically connected to the cathode of the light receiving element PD, that is, the first node N1, and the second electrode is an anode of the light receiving element PD, that is, the first electrode. It can be electrically connected to the two power supply (VSS).

The third capacitive element C3 is connected in parallel to the light receiving element PD, and serves to improve the signal retention characteristic by further increasing its reverse bias capacitance when the incident light amount suddenly increases. This will also be described in detail below. In the third capacitive element C3, the first electrode may be electrically connected to the seventh switch S7, and the second electrode may be electrically connected to the second power source VSS.

The light receiving element PD is electrically connected to the second capacitive element C2 and flows a constant current in response to ambient light, thereby discharging the second capacitive element C2 to a constant voltage. . That is, the light receiving element PD has a cathode, in another word, between the first capacitive element C1 and the third switch S3, and is electrically connected to the first node N1, and the anode has a second power source ( It may be any one selected from a PIN diode, a PN diode, a photo coupler, and an equivalent thereof electrically connected to the VSS, but the type or material of the light receiving device PD is not limited thereto.

The first switch S1 supplies a voltage of the first power supply VDD to the output load 110 to charge the fourth capacitive element C4 electrically connected thereto. The first switch S1 has a first electrode electrically connected to the first power supply VDD, and the second electrode is a contact between the second switch S2 and the output load 110, that is, the third node N3. The P electrode is a low temperature crystallized polysilicon transistor and the equivalent thereof to which the first control signal is applied. However, the type and material of the first switch S1 are not limited thereto. Substantially, the output load 110 may be, for example, an internal load of an analog to digital converter, and the fourth capacitive element C4 may be a parasitic capacitor formed in a wiring. However, the present invention is not limited to the configuration of the output load 110 and the fourth capacitive element C4.

The second switch S2 is electrically connected between the transistor T1 and the output load 110, and is formed through coupling of the first capacitive element C1 and the second capacitive element C2. The fourth capacitive element C4 connected to the output load 110 through the transistor T1 is discharged to the second power source VSS according to the voltage of the single capacitive element C1. That is, the second switch S2 is connected to the output load 110 so that the fourth capacitive element C4 charged with the voltage of the first power source VDD is connected to the second power source VSS through the transistor T1. To discharge). In the second switch S2, the first electrode is electrically connected to the output load 110, that is, the third node N3, and the second electrode is electrically connected to the first electrode of the transistor T1. The electrode may be any one selected from a P-channel low temperature crystallized polysilicon transistor to which a second control signal is applied and its equivalent. However, the type and material of the second switch S2 are not limited thereto.

The third switch S3 may be electrically connected to the first electrode of the first capacitive element C1 such that a reference voltage of the reference power supply V _REF is applied. In the third switch S3, a first electrode is electrically connected to the reference power supply V _REF , and a second electrode is connected to the first capacitive element C1, the second capacitive element C2, and the light receiving element. A P-channel low temperature crystallized polysilicon transistor and an equivalent thereof, which are electrically connected to the contacts between the PDs, that is, the first node N1 and to which the third control signal is applied. However, the type and material of the third switch S3 are not limited thereto.

The fourth switch S4 is configured such that the transistor T1 is diode-connected to the first capacitive element C1 so that the reference voltage reflecting the threshold voltage of the transistor T1 is the first capacitive element ( It is to be applied to C1). The fourth switch S4 has a first electrode electrically connected to the second electrode of the transistor T1, and the second electrode is disposed between the control electrode of the transistor T1 and the first capacitive element C1. The control electrode may be any one selected from a P-channel low temperature crystallized polysilicon transistor and an equivalent thereof, which are electrically connected to the second node N2 and to which the third control signal is applied. However, the type and material of the fourth switch S4 are not limited thereto.

The fifth switch S5 allows a reference voltage reflecting the threshold voltage to the transistor T1 to be applied through the fourth switch S4. In the fifth switch S5, the first electrode is electrically connected to the reference power supply V _REF , the second electrode is electrically connected to the first electrode of the transistor T1, and the control electrode is provided with a fourth control signal. It may be any one selected from the P-channel low temperature crystallized polysilicon transistor and the equivalent thereof. However, the type and material of the fifth switch S5 are not limited thereto.

The sixth switch S6 is configured such that a voltage charged in the output load 110 connected to the transistor T1, that is, the fourth capacitive element C4 connected thereto is applied to the first capacitive element C1 and the second capacitor. In response to the voltage of the first capacitive element C1 through the coupling of the conductive element C2, it is discharged toward the second power source VSS and serves to converge to a predetermined voltage. The sixth switch S6 has a first electrode electrically connected to a second electrode of the transistor T1, a second electrode electrically connected to a second power source VSS, and a fourth control signal to a control electrode. May be any one selected from an N-channel low temperature crystallized polysilicon transistor and an equivalent thereof. However, the type of the sixth switch S6 is not limited thereto.

The seventh switch S7 is electrically connected between the light receiving element PD and the third capacitive element C3, so that the third capacitive element C3 is electrically connected to the light receiving element PD. Be sure to In the seventh switch S7, the first electrode is electrically connected to the light receiving element PD, that is, the first node N1, and the second electrode is electrically connected to the first electrode of the third capacitive element C3. And a P-channel low temperature crystallized polysilicon transistor to which the fifth control signal is applied to the control electrode, and an equivalent thereof. However, the type and material of the seventh switch are not limited thereto.

Here, the third switch (S3) a reference voltage source (V _REF) connected to a reference voltage (V _REF) and the fifth switch (S5) is connected to each other may have different value may be a value equal to each other. Of course, the voltage of the reference power supply V _REF connected to the fifth switch S5 should be greater than the voltage of the second power supply VSS even if the threshold voltage Vth of the transistor T1 is subtracted.

Meanwhile, as illustrated in FIG. 1B, another ambient light sensing circuit 101 of the present invention may have a connection position of the light receiving device PD different from the circuit 100 described above. That is, as illustrated in FIG. 1B, an anode of the light receiving element PD is electrically connected to the reference power supply V _REF through the first node N1 and the third switch S3, and the cathode is another reference power supply. (V _REF2 ) may be electrically connected.

Accordingly, in the circuit 100, when the reverse current flows through the light receiving element PD, the second capacitive element C2 is discharged. In the circuit 101 shown in FIG. 1B, the light receiving element PD is discharged. When the reverse current flows through the second capacitive element C2, the second capacitive element C2 is charged. Therefore, in the circuit 100 shown in FIG. 1A, as the reverse current through the light receiving device PD increases, the voltage of the first capacitive device decreases according to the coupling of the first capacitive device and the second capacitive device. However, in the circuit 101 shown in FIG. 1B, the voltage of the first capacitive element increases according to the coupling of the first capacitive element and the second capacitive element as the reverse current through the light receiving element PD increases. . Of course, the voltage of the reference power supply V _REF2 connected to the light receiving element PD must be higher than the voltage of the reference power supply V _REF connected to the third switch S3 in the circuit 101 shown in FIG. 1B. Of course.

2 is a timing diagram of an ambient light sensing circuit in accordance with the present invention.

As shown in the drawing, the ambient light sensing circuit 100 according to the present invention may operate with one frame in which the flat panel display outputs one screen, that is, a period of approximately 16.7 ms. Therefore, the flat panel display device using the ambient light sensing circuit 100 according to the present invention automatically adjusts the screen brightness in response to the ambient brightness. Of course, the operation cycle of the ambient light sensing circuit 100 is only one example, and can be set in various cycles.

The ambient sensing circuit according to the present invention, for example, performs a threshold voltage compensation process T1 for approximately 400 Hz, performs an ambient light sensing process T2 for approximately 15 Hz, and a sampling process T3 for approximately 1000 Hz. ). Of course, four control signals, that is, a first control signal, a second control signal, a third control signal, and a fourth control signal, are applied to the ambient light sensing circuit 100.

As described above, the present invention allows the ambient light sensing circuit 100 to perform the ambient light sensing process T2 for the longest time, thereby improving the ambient light sensing efficiency.

In addition, in the present invention, when the ambient light is relatively bright, the fifth control signal is further applied to the ambient light sensing circuit 100, but the timing diagram for the fifth control signal is omitted. However, the operation of the seventh switch S7 by the fifth control signal will be described in detail below.

The operation of the present invention will be described with reference to FIGS. 2 and 3 to 5.

3 is a circuit diagram illustrating the current flow during the threshold voltage compensation process T1 by the ambient light sensing circuit 100 of the present invention.

As shown in FIGS. 2 and 3, in the threshold voltage compensation process T1, a low level third control signal is applied to the third switch S3 and the fourth switch S4, and the low level fourth control is performed. The signal is applied to the fifth switch S5. Therefore, only the third switch S3, the fourth switch S4, and the fifth switch S5 are turned on.

Accordingly, a current path is formed along the reference power supply V _REF , the third switch S3, the second capacitive element C2, the second capacitive element C2, and the second power source VSS. In addition, a current path is formed between the reference power supply V _REF , the third switch S3, and the first capacitive element C1, and the reference power supply V _REF , the fifth switch S5, and the transistor T1. ), A current path is formed between the fourth switch S4 and the first capacitive element C1.

Therefore, the second capacitive element C2 is charged by subtracting the voltage of the second power source VSS from the voltage of the reference power source _VREF . In addition, the voltage of the reference power supply V _REF is applied to the first electrode of the first capacitive element C1 through the third switch S3. In addition, a voltage V _REF -V _{TH obtained} by subtracting the threshold voltage V _TH of the transistor T1 from the voltage of the reference power supply V _REF is applied to the second electrode of the first capacitive element C1. Therefore, the threshold voltage V _TH of the transistor T1 is stored in the first capacitive element C1 in advance, so that the threshold voltage of the transistor T1 is later compensated for. That is, the transistor T1 always outputs a constant voltage without being affected by the threshold voltage variation. In other words, when the transistor T1 is a low-temperature crystallized polysilicon thin film transistor using an excimer laser annealing method, an electrical characteristic such as a threshold voltage variation is not uniform due to an energy variation of the excimer laser. The first capacitive element C1 is compensated for.

4 is a circuit diagram showing the current flow during the ambient light detection process (T2) by the ambient light detection circuit 100 of the present invention.

2 and 4, in the ambient light sensing process T2, the second capacitive element C2 is discharged in proportion to the ambient light incident thereto through the light receiving element PD. That is, a constant current flows from the second capacitive element C2 through the light receiving element PD to the second power source VSS. The current through the light receiving element PD is relatively large when the ambient light is bright and relatively small when the ambient light is dark.

As the voltage of the second capacitive element C2 changes as described above, the first capacitive element C1 of the first capacitive element C1 and the second capacitive element C2 are coupled to each other. The voltage is changed. More specifically, a voltage of V _REF -ΔV is applied to the first electrode of the first capacitive element C1, and V _REF -V _TH -ΔV is applied to the second electrode of the first capacitive element C1. Is applied. Therefore, a voltage of V _REF -V _TH -ΔV is applied to the control electrode of the transistor T.

In this case, the first control signal is applied to the first switch S1. Therefore, only the first switch S1 is turned on. Accordingly, a current path is formed along the first power source VDD, the first switch S1, the output load 110, and the fourth capacitive element C4. Accordingly, the fourth capacitive element C4 is charged by the voltage of the first power source VDD. Of course, the voltage of the first power source VDD is output through the output terminal.

FIG. 5 is a circuit diagram illustrating the current flow during the sampling process T3 by the ambient light sensing circuit 100 of the present invention.

As shown in FIGS. 2 and 5, in the sampling process T3, a low level second control signal is applied to the second switch S2, and a high level fourth control signal is applied to the sixth switch S6. Is approved. Therefore, only the second switch S2 and the sixth switch S6 are turned on. Here, since the fourth control signal is at a high level and the sixth switch S6 is, for example, an N-channel low temperature crystallized polysilicon transistor, the sixth switch S6 is turned on. Of course, the fourth control signal of the high level is also applied to the fifth switch S5, but since the fifth switch S5 is a P-channel low temperature crystallized polysilicon transistor, the fifth switch S5 is turned off. Keep it.

Accordingly, a current path is formed between the fourth capacitive element C4, the output load 110, the second switch S2, the transistor T1, the sixth switch S6, and the second power source VSS. . Of course, a voltage of V _REF -V _TH -ΔV is applied to the control electrode of the transistor T1 by the coupling of the first capacitive element C1 and the second capacitive element C2. That is, the voltage charged in the fourth capacitive element C4 is converged by discharging to a predetermined voltage corresponding to the voltage of V _REF -V _TH -ΔV applied to the control electrode of the transistor T.

After the fourth capacitive element C4 is discharged and converged to a predetermined voltage in this manner, the voltage remaining in the fourth capacitive element C4 is, for example, an analog-digital converter (not shown) through an output terminal. It is output on the back.

In this case, when the ambient light is incident to the light receiving element PD with a small amount, the second capacitive element C2 is discharged small and the ΔV becomes small accordingly. Therefore, the voltages V _REF -V _TH -ΔV applied to the control electrode of the transistor T1 are relatively large, and accordingly, the voltage at which the fourth capacitive element C4 can discharge becomes small. That is, the voltage remaining in the fourth capacitive element C4 after discharge and convergence to a predetermined voltage has a relatively large value.

In addition, a large amount of ambient light is incident on the light receiving element PD, and the second capacitive element C2 is largely discharged, thereby increasing ΔV. Accordingly, the voltages V _REF -V _TH -ΔV applied to the control electrode of the transistor T1 are relatively small, thereby increasing the voltage at which the fourth capacitive element C4 can discharge. . That is, after discharging and converging to a predetermined voltage, the voltage remaining in the fourth capacitive element C4 has a relatively small value.

In summary, when a large amount of ambient light is incident on the light receiving element PD, when the voltage (output voltage) of the fourth capacitive element C4 decreases and a small amount of ambient light is incident on the light receiving element PD, The voltage (output voltage) of the fourth capacitive element C4 is increased.

Meanwhile, operations of the seventh switch S7 and the third capacitive element C3 by the fifth control signal will be described.

When a lot of light suddenly enters the light receiving element PD, the voltage charged in the second capacitive element C2 is quickly discharged through it. That is, since the second capacitive element C2 is discharged too quickly, a reliable output voltage cannot be secured from the transistor T1, and thus accurate ambient light sensing operation is impossible.

In order to prevent such a phenomenon, the present invention uses the fifth control signal as the feedback signal when the output voltage through the output terminal (for example, the voltage input to the analog-to-digital converter) continues to be below the threshold for a predetermined time. It is applied to the control electrode of the switch S7.

Then, the third capacitive element C3 is connected to the light receiving element PD together with the second capacitive element C2 in parallel.

Therefore, since the second capacitive element C2 and the third capacitive element C3 are connected in parallel to the light receiving element PD, the reverse bias capacitance is further increased. In other words, the amount of current that can flow through the light receiving element PD increases.

 Accordingly, it is possible to send a current through the light receiving element PD for a time sufficient to sense ambient light. Of course, the remaining voltage remaining in the second capacitive element C2 and the third capacitive element C3 affects the voltage of the first capacitive element C1, and this voltage is again converted into the transistor ( Contribute to the operation of T1).

Therefore, the transistor T1 operates in a reliable operation section, and thus the output voltage is stabilized. In other words, the ambient light is detected smoothly.

6A to 6C are graphs simulating changes in output voltage according to changes in ambient light of the ambient light sensing circuit according to the present invention.

In this graph, the X axis represents time (ms) and the Y axis represents output voltage (Vout). Further, the graph of V _{G, T1 (fast)} is △ V _TH is -1V, △ mobility (mobility) is + 20% of the fast (fast) is a transistor, V _{G, T1 (normal)} is △ V _TH 0V, A normal transistor having 0% mobility and V _{G and T1 (slow)} mean a slow transistor having + 1V and -20% mobility of DELTA V _TH .

First, as shown in FIG. 6A, in the ambient light sensing circuit 100 according to the present invention, when the current flowing through the light receiving device PD is, for example, 25 pA, the output voltage through the output terminal is approximately 5.068 to 5.104 V. After discharge it converges. Here, in practice, the output voltage through the output terminal may be regarded as the output voltage of the fourth capacitive element C4.

In addition, as shown in FIG. 6B, the ambient light sensing circuit 100 according to the present invention has an output voltage of about 4.793 V to 4.825 V when the current flowing through the light receiving element PD is 120 pA, for example. Discharge to and converge.

In addition, as shown in FIG. 6C, the ambient light sensing circuit 100 according to the present invention has an output voltage of about 3.457 to 3.483 V when the current flowing through the light receiving element PD is, for example, 566 pA. Discharge to and converge.

As described above, in the ambient light sensing circuit 100 according to the present invention, as the current I _PIN through the light receiving element PD decreases, the output voltage Vout of the fourth capacitive element C4 increases. . In addition, in the ambient light sensing circuit 100 according to the present invention, as the current I _PIN through the light receiving element PD increases, the output voltage Vout through the fourth capacitive element C4 decreases.

Here, the ambient light sensing circuit 100 according to the present invention can be seen that the variation of the output voltage Vout is always constant regardless of whether the current I _PIN through the light receiving element PD is small or large. Therefore, the ambient light sensing circuit 100 according to the present invention provides an accurate output voltage Vout regardless of the intensity of the ambient light.

In addition, the ambient light sensing circuit 100 according to the present invention has a significant difference in the control electrode voltage of the transistor T1 due to the threshold voltage variation or the mobility difference. Since Vout) is constant, reliable ambient light can be detected.

In addition, the protruding waveform indicated by Vout in the graph is a waveform that appears because the first switch S1 is turned on during the ambient light sensing period T2 and the first power supply voltage VDD is output through the output terminal.

7 is a block diagram illustrating a state in which an ambient light control processor is further connected to an ambient light sensing circuit according to the present invention.

As shown, the present invention may further include an ambient light control processor 200 for signal processing from the ambient light sensing circuit 100. The ambient light control processor 200 includes an analog-digital converter 210, a first memory 220, a controller 230, and a second memory 240.

The analog-to-digital converter 210 is electrically connected through a contact between the first switch S1 and the second switch S2, that is, a third node N3. Of course, the above-described output load 110 and the fourth capacitive element C4 and the like are built in the analog-to-digital converter 210. Substantially, the output load is an internal load of the analog-to-digital converter, and the fourth capacitive element may be the capacitive component formed on the wiring. The analog-to-digital converter 210 serves to convert the analog output voltage value into a digital value and output the digital value.

The first memory 220 is electrically connected to the analog-to-digital converter 210, which temporarily stores a digital value according to a currently detected ambient light state.

The controller 230 is electrically connected to the first memory 220 to calculate and output the brightness of the currently detected ambient light.

The second memory 240 is electrically connected to the controller 230 to store digital values obtained from ambient light having various brightnesses in advance.

With this configuration, the present invention compares the sensed ambient light data input from the first memory 220 and the ambient light data of various brightness stored in the second memory 240 to calculate the current ambient light brightness. .

Meanwhile, in the drawing, the reference power supply V _REF and the fifth switch S5 and the second switch S2 electrically connected to the reference power supply V _REF are formed in the ambient light sensing circuit 100, and the first power supply VDD and first Although one switch S1 is illustrated as being formed in the ambient light control processing unit 200, the present invention is not limited thereto. That is, all of the above components may be formed in the ambient light sensing circuit 100 or in the ambient light control processor 200.

Substantially, the ambient light sensing circuit 100 is formed on a substrate such as an organic electroluminescent panel, whereas the ambient light control processing unit 200 may be separately formed as a one chip form. Of course, it is not limited to the ambient light control processing unit 200 in the form of such a one chip, which may be formed on a substrate such as an organic electroluminescent panel.

For example, the first switch S1 may be formed in the ambient light control processing unit 200 in the form of a one chip or in the ambient light sensing circuit 100 formed on the substrate.

8 is a block diagram illustrating a configuration of a flat panel display device having an ambient light sensing circuit according to the present invention.

The ambient light sensing circuit 100 and the ambient light control processing unit 200 are shown in a block diagram for convenience of description.

As illustrated, the flat panel display according to the present invention includes the timing controller 300, the data driver 400, the organic electroluminescent panel 500, in addition to the above-described ambient light sensing circuit 100 and the ambient light control processor 200. The scan driver 600, the emission control driver 700, and the power controller 800 may be further included. Of course, since the configuration and operation of the ambient light sensing circuit 100 and the ambient light control processor 200 have been described in detail above, the description thereof will be minimized.

In addition, the organic electroluminescent panel 500 includes a circuit unit and an organic emission layer forming one pixel, and the pixels are arranged in a matrix to display a still image or a moving image. That is, the organic electroluminescent panel 500 has a plurality of data lines D1 to Dm extending from the data driver 400, and a plurality of scan lines S1 to Sn extending from the scan driver 600. And a plurality of emission control lines E1 to En extending from the emission control driver 700, and a plurality of power lines PL extending from the power control unit 800.

The timing controller 300 may include a brightness selector 310 and a lookup table 320. The timing controller 300 compares the digital value input from the ambient light control processor 200 with a value previously stored in the lookup table 320 by the brightness selector 310, and outputs a control signal suitable for the power controller. Output to (800). Of course, the look-up table 320 is stored in advance the optimum control signal matching the digital value input from the ambient light control processing unit 200 for each of R, G, B.

Then, the power control unit 800 supplies the organic EL panel 500 with a suitable power voltage according to external ambient light. For example, when the detected ambient light is relatively bright, a relatively high power supply voltage is supplied to display a screen having a strong brightness through the organic EL panel 500. In addition, when the detected ambient light is relatively dark, a relatively low power supply voltage is supplied so that a screen having a weak brightness is displayed through the organic EL panel 500.

In this manner, the present invention provides a display device in which the brightness of a screen is automatically adjusted according to external ambient light.

Here, the data driver 400 supplies a data voltage to the organic electroluminescent panel 500, and the scan driver 600 is to be turned off and on with the pixels to be turned on in the organic electroluminescent panel 500. It serves to supply a scan signal to select a pixel. In addition, the emission control driver 700 determines the time when the pixel is actually turned on by supplying an emission control signal to the organic EL panel 500. The data driver 400, the scan driver 600, and the emission control driver 700 are well known to those skilled in the art, and thus detailed descriptions thereof will be omitted.

Meanwhile, the ambient light sensing circuit 100, the ambient light control processor 200, the timing controller 300, the data driver 400, the organic electroluminescent panel 500, the scan driver 600, and the light emission control driver described above. Naturally, both the 700 and the power controller 800 may be formed on a common substrate through a semiconductor process and a thick film process. Of course, the present invention is the ambient light sensing circuit 100, the ambient light control processor 200, the timing controller 300, the data driver 400, the scan driver 600, the light emission control driver 700 and the power control unit ( At least one of the 800 may be formed on a substrate or a chip different from the substrate on which the organic electroluminescent panel 500 is formed, but is not limited to the formation position of each of these components.

FIG. 9A is a circuit diagram showing an example of one pixel circuit among organic electroluminescent panels of a flat panel display, and FIG. 9B is a timing diagram thereof.

As shown in FIG. 9A, the pixel circuit supplies a scan line Sn for supplying a scan signal, a data line Dm for supplying a data voltage, a first power line VDD for supplying a first voltage, and a second voltage. The second power line VSS, the auto zero line An for supplying the auto zero signal, the light emission control line En for supplying the light emission control signal, and the first to fourth transistors T1, T2, T3, and T4. ), First and second capacitive elements C1 and C2, and an organic electroluminescent element OLED. Here, the voltage of the first power line VDD is relatively higher than the voltage of the second power line VSS. In addition, although some reference numerals overlap with those used in FIGS. 1 to 8, it is noted that the reference numerals shown here are limited to FIGS. 9A and 9B only.

As illustrated in FIG. 9B, when the low level control signal is supplied from the auto zero line An to the control electrode of the third transistor T3, the third transistor T3 is turned on. Subsequently, when the high level control signal is supplied from the emission control line En to the control electrode of the fourth transistor T4, the fourth transistor T4 is turned off. Then, while the first transistor T1 is connected in the form of a diode, the threshold voltage of the first transistor T1 is stored in the first capacitive element C1. When the auto zero signal becomes high again, and then a low level data voltage is applied from the data line Dm, the ratio of the first capacitive element C1 to the second capacitive element C2 is increased. The data voltage of which the threshold voltage is compensated for is supplied to the control electrode of the first transistor T1. (Data writing operation) When the light emission control signal is at a low level, a predetermined current is supplied to the organic light emitting diode OLED. ) And light emission occurs.

According to such a pixel circuit, the current flowing through the organic EL device flows only in response to the data voltage supplied from the data line, regardless of the threshold voltage of the first transistor.

Meanwhile, according to the present invention, the brightness of the screen is automatically adjusted according to the ambient brightness as described above. More specifically, the present invention allows the brightness (luminance) of the organic light emitting diode OLED to be adjusted by adjusting the voltage of the first power source VDD in the pixel circuit.

That is, the brightness of the organic light emitting diode OLED is controlled by adjusting the voltage of the first power source VDD shown in FIG. 9B (indicated by reference numeral V in the drawing). For example, when the ambient brightness is dark, by supplying a relatively small power supply voltage, the brightness of the organic light emitting diode OLED is relatively small so that a dark screen is displayed. In addition, when the ambient brightness is bright, by supplying a relatively high power supply voltage, the brightness of the organic light emitting diode OLED is relatively increased so that a bright screen is displayed.

As described above, the flat panel display having the ambient light sensing circuit according to the present invention obtains output voltages of various levels in accordance with the ambient light, and automatically adjusts the brightness of the screen through the display device using the same, thereby enabling bright or dark places. In all places, the visibility of a flat panel display device becomes excellent.

In addition, as described above, the flat panel display having the ambient light sensing circuit according to the present invention automatically adjusts the power consumption according to the ambient light, thereby maintaining the optimum power consumption, and thus the usable time of the portable flat panel display. This will be longer.

In addition, as described above, the flat panel display having the ambient light sensing circuit according to the present invention includes an ambient light sensing circuit, an ambient light control processing unit, a timing control unit, a light emission control driver, a power supply control unit and an organic electroluminescent panel all on one substrate. By using the low temperature crystallized polysilicon thin film transistor process, the thickness of the flat panel display device can be made thinner.

What has been described above is only one embodiment for implementing a flat panel display device having an ambient light sensing circuit according to the present invention, and the present invention is not limited to the above-described embodiment, and is claimed in the following claims. As described above, any person having ordinary knowledge in the field of the present invention without departing from the gist of the present invention will have the technical spirit of the present invention to the extent that various modifications can be made.

Claims (15)

A transistor, a first capacitive element connected to the transistor to compensate for a threshold voltage of the transistor, a second capacitive element connected to the first capacitive element, the first capacitive element and a second capacitive element A light receiving device which is connected to the device and changes the voltage of the first capacitive device through coupling of the first capacitive device and the second capacitive device when ambient light is incident; and a voltage of the first power supply to the output load. Ambient light comprising a first switch to supply and charge, and a second switch connected between the transistor and the output load to discharge the voltage of the output load through the transistor corresponding to the voltage of the first capacitive element. Sensing circuit; An ambient light control processor configured to calculate a current ambient light and output a digital value using the analog output signal of the ambient light sensing circuit as an input signal; A timing controller configured to output a control signal corresponding to current ambient light by using the output signal of the ambient light control unit as an input signal; A power controller configured to output a power voltage corresponding to current ambient light by using the output signal of the timing controller as an input signal; And, And an organic electroluminescent panel which emits light by using the power voltage of the power control unit as an input signal. The method of claim 1, wherein the timing controller A lookup table storing data suitable for the current lighting; And, And a brightness selector which compares data obtained from the ambient light control processor with data stored in the lookup table to select a control signal suitable for current lighting and output the selected control signal to the power control unit. The flat panel display of claim 1, wherein the ambient light sensing circuit, the ambient light control processor, the timing controller, the power controller, and the organic electroluminescent panel are formed on one substrate. The flat panel display of claim 1, wherein at least one of the ambient light sensing circuit, the ambient light control processor, the timing controller, the power controller, and the organic electroluminescent panel is formed of a low temperature crystallized polysilicon thin film transistor. The flat panel display of claim 1, wherein the power control unit outputs a power voltage having a magnitude proportional to the ambient light obtained from the ambient light sensing circuit. The method of claim 1, wherein the ambient light sensing circuit has a third switch connected to the first electrode of the first capacitive element to apply a reference voltage, and the transistor is connected to the second electrode of the first capacitive element. And a fourth switch connected to a diode connection so that a reference voltage reflecting the threshold voltage of the transistor is applied. The flat panel display of claim 6, wherein the ambient light sensing circuit further includes a fifth switch configured to apply a reference voltage reflecting a threshold voltage to the transistor through a fourth switch. The method of claim 1, wherein the ambient light sensing circuit discharges a voltage charged to an output load of the transistor in response to a voltage of the first capacitive element through coupling of the first capacitive element and the second capacitive element. And a sixth switch which is further converged so as to converge. The flat panel display of claim 1, wherein the ambient light sensing circuit further includes a third capacitive element to increase a reverse bias capacitance of the light receiving element. 10. The flat panel display of claim 9, wherein the ambient light sensing circuit further comprises a seventh switch for interconnecting the light receiving element and the third capacitive element. The flat panel display of claim 1, wherein the ambient light sensing circuit comprises at least one selected from among a PIN diode, a PN diode, and a photo coupler, the cathode of which is connected to a reference power source and the anode of which is connected to a second power source. Device. The flat panel of claim 1, wherein the ambient light sensing circuit is any one selected from among a PIN diode, a PN diode, and a photocoupler, the anode of which is connected to a reference power source and the cathode of which is connected to a second reference power source. Display device. The flat panel display of claim 1, wherein the ambient light sensing circuit is connected to the output load by an ambient light control processor. The method of claim 13, wherein the ambient light control processing unit An analog-digital converter connected to the output load and converting a residual voltage value of the output load into a digital value; A first memory connected to the analog to digital converter to store a digital value according to a current ambient light state; A controller connected to the first memory to calculate and output a brightness of current ambient light; And, And a second memory connected to the control unit to store digital values obtained from ambient light having various brightnesses in advance. The method of claim 14, wherein the analog to digital converter of the ambient light control processing unit An output load connected to the first electrode of the transistor; And, And a fourth capacitive element connected between the output load and the second power supply.

Images