KR100824857B1 - Flat panel device having ambient light sensing circuit - Google Patents

Abstract

A flat panel display having an ambient light sensing circuit is provided to manufacture a thinner display device by employing a low temperature polycrystalline silicon thin film transistor(LTPS-TFT). An ambient light sensing circuit(100) includes a photo detector, a first capacitor, a second capacitor, and a transistor. An ambient light controller(200) receives an 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) 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 light. An OLED(Organic Light Emitting Device) panel(500) receives the light emitting control signal from the power controller and emits light. A data driver(400) supplies data voltage to the OLED panel, and a scan driver(600) supplies scan signal to the OLED panel.

Description

Flat panel display device having ambient light sensing circuit {FLAT PANEL DEVICE HAVING AMBIENT LIGHT SENSING 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.

Figure 3 shows the current flow during the initialization period by the ambient light sensing circuit of the present invention.

Figure 4 shows the current flow during the ambient light sensing period by the ambient light sensing circuit of the present invention.

Figure 5 shows the current flow during the ambient light sensing and compensation period by the ambient light sensing circuit of the present invention.

Figure 6 shows the current flow during the buffering period by the ambient light sensing circuit of the present invention.

7 is an equivalent circuit diagram of capacitive elements for error compensation analysis in an ambient light sensing circuit according to the present invention.

8 is a graph simulating the change of the output voltage according to the change in the ambient light of the ambient light sensing circuit according to the present invention.

9 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.

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

FIG. 11A is a circuit diagram illustrating an example of a pixel circuit in an organic EL panel of a flat panel display, and FIG. 10B 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 S7; 7th switch

S8; An eighth 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 having an ambient light sensing circuit. And a flat panel display having an ambient light sensing circuit.

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 a dark place, 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 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 light receiving element that flows current in proportion to ambient light, and a first battery that is electrically charged and discharged after being charged at a voltage of a first power source. A capacitive element, a second capacitive element electrically connected to the first capacitive element to provide a coupling voltage, and after the first capacitive element and the second are electrically connected to the second capacitive element A digital value is calculated by calculating a current ambient light using an ambient light sensing circuit comprising a transistor for flowing a current from the first power source corresponding to a coupling voltage of a capacitive element, and an output signal of the ambient light sensing circuit as an input signal. A timing for outputting a control signal suitable for the current ambient light by using the ambient light control processing unit for outputting the signal and the output signal of the ambient light control processing unit as an input signal A control unit, a power control unit outputting a power supply voltage suitable for current ambient light by using the output signal of the timing control unit as an input signal, and an organic electroluminescent panel which emits light by using the power supply voltage of the power supply control unit as an input signal; .

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 may include 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.

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

A third capacitive element for increasing the reverse bias capacitance of the light receiving element may be further electrically connected to the first capacitive element of the ambient light sensing circuit.

The light receiving element, the first capacitive element, and the second capacitive element of the ambient light sensing circuit are electrically connected and initialized between a first power source and a second power source, and the first capacitive element is electrically connected to the light receiving element. The first capacitive element is discharged according to the ambient light incident on the light receiving element, and the second capacitive element and the transistor are electrically connected between a first power source to adjust the threshold voltage of the transistor. The capacitive element compensates for and the first capacitive element and the second capacitive element are electrically connected to each other so that the transistor generates a current corresponding to the coupling voltage of the first capacitive element and the second capacitive element. You can print

The light receiving element of the ambient light sensing circuit may be any one selected from a PIN diode, a PN diode, and a photo coupler.

A first switch for electrically connecting the light receiving element to the first power source or the first capacitive element may be further connected to the light receiving element of the ambient light sensing circuit.

A second switch for electrically connecting the first capacitive element to the first power supply or the second capacitive element may be further connected to the first capacitive element of the ambient light sensing circuit.

A third switch for supplying a first power supply is electrically connected to the first electrode of the transistor in the ambient light sensing circuit, and a fourth switch is electrically connected between the second electrode and the control electrode of the transistor. A fifth switch for supplying a second power source may be electrically connected to the second electrode, and an output terminal for outputting a current may be formed between the first electrode and the third switch of the transistor.

An eighth switch for supplying a first power source to the light receiving element, the first capacitive element, and the second capacitive element may be further connected to the first power source of the ambient light sensing circuit.

The first electrode of the third capacitive element of the ambient light sensing circuit is electrically connected to the first capacitive element through a sixth switch and to a first power source through a seventh switch, and the second electrode is a second power source. Can be electrically connected to the

Among the ambient light sensing circuits, a first power supply is provided between the light receiving element, the first capacitive element, and the second capacitive element and the first power source to supply the first power to the light receiving element, the first capacitive element, and the second capacitive element. The eighth switch may be further electrically connected.

The ambient light control processor may be electrically connected to an output terminal of the transistor in the ambient light sensing circuit.

The ambient light control processor includes an analog digital converter electrically connected to the first electrode of the transistor, a first memory electrically connected to the analog digital converter to store a digital value according to a current ambient light state, and the first memory. And a second memory electrically connected to the memory to calculate and output the brightness of the current ambient light, and a second memory electrically connected to the controller to store digital values obtained from ambient light having various brightnesses in advance.

The analog to digital converter 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 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.

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.

As shown in FIG. 1A, the ambient light sensing circuit 100 according to the present invention includes a light receiving element PD, a transistor T1, a first capacitive element C1, a second capacitive element C2, and a second light source. Tri-capacitive element C3, first switch S1, second switch S2, third switch S3, fourth switch S4, fifth switch S5, sixth switch S6, The seventh switch S7 and the eighth switch S8 are included.

The light receiving device PD plays a role of flowing a constant current according to ambient light. In the light receiving device PD, a cathode may be electrically connected to the first power source VDD, and an anode may be electrically connected to the second power source VSS. In addition, the light receiving device PD may be any one selected from a PIN diode, a PN diode, a photo coupler, and an equivalent thereof electrically connected in a reverse direction between the first power source VDD and the second power source VSS. It does not limit the kind. In addition, the first power source VDD may have a relatively higher potential than the second power source VSS.

A first switch S1 may be electrically connected to the light receiving element PD to electrically connect the light receiving element PD to the first power supply VDD or the second capacitive element C2. In the first switch S1, a first electrode is electrically connected to the first capacitive element C1, that is, the first node N1, and a second electrode is electrically connected to the cathode of the light receiving element PD. The first control signal may be applied to the control electrode. The first switch S1 may be any one selected from a transistor and an equivalent thereof, but is not limited thereto.

After the first capacitive element C1 is charged with the voltage of the first power source VDD, the first capacitive element C1 is electrically connected to the light receiving element PD and discharges to a predetermined voltage. In the first capacitive element C1, the first electrode may be electrically connected to the first power source VDD, that is, the first node N1, and the second electrode may be electrically connected to the second power source VSS. .

Here, the first capacitive element C1 has a second switch S2 electrically connecting the first capacitive element C1 to the first power supply VDD or the second capacitive element C2. Can be connected. That is, in the second switch S2, a first electrode is electrically connected to the second node N2, in other words, the first power source VDD, and the second electrode is the first capacitive element C1. The second control signal may be electrically connected to the first node N1 and may be applied to the control electrode. The second switch S2 may be any one selected from a transistor and its equivalent, but is not limited thereto.

The transistor T1 is electrically connected to the second capacitive element C2, that is, the third node N3, so that the coupling of the first capacitive element C1 and the second capacitive element C2 is performed. It outputs a constant current according to the voltage of the second capacitive element (C2) changed through. In the transistor T1, a first electrode is electrically connected to a second electrode of the third switch S3, and a second electrode is electrically connected to the second electrode of the fourth switch S4. The voltage of the second capacitive element C2 changed through the coupling of the first capacitive element C1 and the second capacitive element C2 may be applied. In addition, the third switch S3 has a first electrode electrically connected to the first power supply VDD, a second electrode electrically connected to the first electrode of the transistor T1, and a third control to the control electrode. A signal can be applied. In addition, the fourth switch S4 has a first electrode electrically connected to the control electrode of the transistor T1, a second electrode electrically connected to the second electrode of the transistor T1, and a first electrode to the control electrode. Control signals may be applied. By the fourth switch S4, the transistor T1 may have a diode connection structure. In addition, a fifth switch S5 may be further connected between the second electrode of the transistor T1 and the second power source VSS. In the fifth switch S5, a first electrode is electrically connected to a second electrode of the transistor T1, a second electrode is electrically connected to the second power source, and a third control signal is applied to a control electrode. Can be. Here, the third switch S3, the fourth switch S4, and the fifth switch S5 may all be any one selected from a transistor and its equivalent, but are not limited thereto.

The second capacitive element C2 is electrically connected between the first capacitive element C1 and the transistor T1 to compensate for the threshold voltage V _TH of the transistor T1. . That is, in the second capacitive element C2, a first electrode is electrically connected to the second node N2, and a second electrode is electrically connected to the control electrode of the transistor T1, that is, the third node N3. Can be connected. The second capacitive element C2 may be formed of low temperature polycrystalline silicon thin film transistors (LTPS-TFTs) using the excimer laser annealing (ELA) method. In this case, due to the energy variation of the excimer laser, the electrical characteristics of the transistor, such as the threshold voltage variation, are not uniform, and serve to compensate for the threshold voltage variation.

The third capacitive element C3 is electrically connected in parallel to the first capacitive element C1, that is, the light receiving element PD, so that relatively very bright light is incident on the light receiving element PD, thereby providing a first light source. When the capacitive element C1 is quickly discharged, it serves to increase the reverse bias capacitance of the light receiving element PD. That is, the combined reverse bias capacitance of the first capacitive element C1 and the third capacitive element C2 acts on the light receiving element PD, thereby extending the overall discharge time to enable accurate ambient light detection. Play a role. The third capacitive element C3 has a first electrode electrically connected to the first capacitive element C1 through a sixth switch S6 and to a first power source VDD through a seventh switch S7. The second electrode may be electrically connected to the second power source VSS. In the sixth switch S6, a first electrode is electrically connected to the first electrode of the third capacitive element C3, and a second electrode is electrically connected to the first electrode of the first capacitive element C1. The fourth control signal may be applied to the control electrode. In the seventh switch S7, a first electrode is electrically connected to the first power supply VDD, a second electrode is electrically connected to a second electrode of the third capacitive element C3, and a subsidiary part of the control electrode is provided. Four control signals can be applied.

Meanwhile, in the present invention, an eighth switch S8 may be further electrically connected between the second node N2 and the first power source VDD. In the eighth switch S8, a first electrode is electrically connected to the first power supply VDD, a second electrode is electrically connected to the second node N2, and a first control signal is applied to the control electrode. Can be.

In addition, according to an exemplary embodiment of the present invention, an output load 110 may be connected between the first electrode of the transistor T1 and the second electrode of the third switch S3, and a fourth capacitive element may be connected to the output load 110. C4) may be connected. 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.

In addition, in the present invention, the transistor T1, the first switch S1 to the eighth switch S8 may be any one selected from a polysilicon thin film transistor, an amorphous silicon thin film transistor, an organic thin film transistor, and an equivalent thereof. However, the type of the transistor T1 is not limited to the present invention.

In addition, when the transistor T1, the first switch S1 to the eighth switch S8 are polysilicon thin film transistors, it is a laser crystallization method, a metal induction crystallization method, a high pressure crystallization method, and an equivalent method thereof, which is a low-temperature crystallization method. It may be formed by any one method selected from, but the present invention is not limited to the method of manufacturing the 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.

Further, the transistor T1, the first switch S1 to the eighth switch S8 may be formed of any one selected from a P channel transistor, an N channel transistor, and an equivalent thereof, but the type is not limited thereto. Of course, the transistor T1, the first switch S1 to the eighth switch S8 may be configured by mixing a P-channel transistor and an N-channel transistor.

The first power source VDD connected to the third switch S3, the first power source VDD connected to the seventh switch S7, and the first power source VDD connected to the eighth switch S8 are the same. Voltage or different voltages. Of course, the voltage of the first power source VDD connected to the third switch S3 is the value obtained by subtracting the threshold voltage Vth from the first power source VDD so that the transistor T1 can operate. Of course, it should be set to be greater than the voltage of the second power supply (VSS) connected to. In addition, the second power source VSS connected to the light receiving element PD, the first capacitive element C1, and the third capacitive element C3 is the second power source VSS connected to the fifth switch S5. It may be the same voltage or different voltages.

Meanwhile, as shown in FIG. 1B, another ambient light sensing circuit 101 according to the present invention may include the circuit 100 having the connection positions of the first power source VDD, the light receiving element PD, and the second power source VSS. Can be different from. That is, as shown in FIG. 1B, the first power source VDD may be electrically connected directly to the cathode of the light receiving element PD, and the second power source VSS may be electrically connected to the eighth switch S8. In addition, a first switch S1 may be electrically connected to an anode of the light receiving element PD.

Accordingly, in the circuit 100, when the reverse current flows through the light receiving element PD, the first capacitive element C1 is discharged. In the circuit 101 of FIG. 1B, the light receiving element PD is discharged. When the reverse current flows through the first capacitive element C2, the first capacitive element C2 is charged. Therefore, in the circuit 100 shown in FIG. 1A, as the reverse current through the light receiving element PD increases, the voltage through the coupling of the first capacitive element and the second capacitive element is relatively small, but FIG. 1B. In the circuit 101 shown in FIG. 1, as the reverse current through the light receiving element PD increases, the voltage through the coupling of the first capacitive element and the second capacitive element becomes relatively large. Of course, the voltage of the first power supply VDD connected to the light receiving element PD must be higher than the voltage of the second power supply VSS connected to the eighth switch S8 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 light sensing circuit 100 according to the present invention, for example, performs the initialization process T1 of the circuit for about 100 ms, performs the sensing process T2 of ambient light for about 10.6 Hz, and for about 4 ms. The sensing and compensation process T3 of ambient light may be performed, and the buffering process T4 may be performed for about 2 ms. Of course, four control signals, that is, a first control signal, a second control signal, a third control signal, and a third 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 very bright, the fourth control signal and the sub-fourth control signal are further applied to the ambient light sensing circuit 100, but the timing diamonds for the fourth control signal and the sub-fourth control signal are different. Gram is omitted. However, the fourth control signal and the sub- fourth control signal will be described in detail below.

The operation of the present invention will be described with reference to FIGS. 1A, 2 and 3 to 6. The first switch S1 to the eighth switch S8 are assumed to be P-channel transistors.

First, as shown in FIGS. 2 and 3, in the initialization process T1, the low level first control signal is applied to the control electrodes of the first switch S1, the fourth switch S4, and the eighth switch S8. Respectively, the low level second control signal is applied to the control electrode of the second switch S2, the high level third control signal is applied to the control electrode of the third switch S3, and the low level subtitle. The three control signal is applied to the control electrode of the fifth switch S5.

Therefore, only the first switch S1, the second switch S2, the fourth switch S4, the fifth switch S5, and the eighth switch S8 are turned on.

As described above, the X first power source VDD, the eighth switch S8, the second switch S2, the first switch S1, the light receiving element PD, and the second power source VSS are connected to the current path. By forming, a predetermined current flows through the light receiving element PD. Of course, this current increases approximately in proportion to the ambient light.

In addition, the first capacitor VDD, the eighth switch S8, the second switch S2, the first capacitive element C1, and the second capacitor VSS form a current path, thereby providing the first capacitor. Sung element C1 is initialized. That is, the first capacitive element C1 is charged by a voltage corresponding to the difference between the first power source VDD and the second power source VSS.

In addition, the first power supply VDD, the second capacitive element C2, the fourth switch S4, the fifth switch S5, and the second power supply VSS form a current path, thereby providing the second capacitance. Sung element C2 is initialized. That is, the second capacitive element C2 is charged by a voltage corresponding to the difference between the first power source VDD and the second power source VSS.

Subsequently, as shown in FIGS. 2 and 4, in the sensing process T2 of the ambient light, the first control signal of the low level is generated by the first switch S1, the fourth switch S4, and the eighth switch S8. Respectively applied to the control electrode, a high level second control signal is applied to the control electrode of the second switch S2, a high level third control signal is applied to the control electrode of the third switch S3, and low The third control signal of the level is applied to the control electrode of the fifth switch S5.

Therefore, only the first switch S1, the fourth switch S4, the fifth switch S5, and the eighth switch S8 are turned on.

As described above, the first capacitive element C1, the first switch S1, the light receiving element PD, and the second power source VSS form a current path, thereby providing the first capacitive element C1. Discharge while passing a constant current through the first switch (S1) and the light receiving element (PD). Of course, when the ambient light is bright, the first capacitive element C1 discharges rapidly while a relatively large amount of current flows, and slowly discharges while a relatively small current flows when the ambient light is dark.

Meanwhile, the first power supply VDD, the second capacitive element C2, the fourth switch S4, the fifth switch S5, and the second power supply VSS still form a current path to form the second capacitance. The component C2 continues to be charged by a voltage corresponding to the difference between the first power source VDD and the second power source VSS.

Subsequently, as shown in FIGS. 2 and 5, in the sensing and compensating process T3 of the ambient light, the first control signal having a low level is the first switch S1, the fourth switch S4, and the eighth switch S8. Are applied to the control electrodes of the control panel, high level second control signals are applied to the control electrodes of the second switch S2, and low level third control signals are applied to the control electrodes of the third switch S3. The high level sub-third control signal is applied to the control electrode of the fifth switch S5.

Therefore, only the first switch S1, the third switch S3, the fourth switch S4, and the eighth switch S8 are turned on.

As described above, the first capacitive element C1, the first switch S1, the light receiving element PD, and the second power source VSS still form a current path, thereby providing the first capacitive element C1. Discharge while flowing a predetermined current through the first switch (S1) and the light receiving element (PD).

On the other hand, the current from the first power supply (VDD) is supplied to the output load 110 through the third switch (S3). Since the fourth capacitive element C4 is connected to the output load 110 as is well known, the fourth capacitive element C4 is charged with a voltage by the first power supply VDD.

In addition, since the transistor T1 is diode connected by the fourth switch S4, the transistor T1 is connected to the second capacitive element C2, that is, the third node N3 from the first power supply VDD. is applied by a voltage obtained by subtracting the threshold voltage (V _TH), is also the voltage of the first power source (VDD) and the second capacitive element (C2) that is, the second node (N2) is via an eighth switch (S8) As a result, the threshold voltage V _TH of the transistor T1 is preliminarily stored in the second capacitive element C2. In other words, the threshold voltage V _TH of the transistor T1 is stored in the second capacitive element C2 in advance so that its threshold voltage is canceled during the operation of the transistor T1 later. That is, the transistor T1 always outputs a constant voltage without being affected by the threshold voltage variation.

Subsequently, as shown in FIGS. 2 and 6, in the buffering process T4, the first control signal having a high level is applied to the control electrodes of the first switch S1, the fourth switch S4, and the eighth switch S8. Respectively, a low level second control signal is applied to the control electrode of the second switch S2, a high level third control signal is applied to the control electrode of the third switch S3, and The third control signal is applied to the control electrode of the fifth switch S5.

Therefore, only the second switch S2 and the fifth switch S5 are turned on. Accordingly, the voltage of the second capacitive element C2 changed through the coupling of the first capacitive element C1 and the second capacitive element C2 becomes the control electrode voltage of the transistor T. Accordingly, the transistor T1 flows a current corresponding to the voltage of the changed second capacitive element C2 through the coupling of the first capacitive element C1 and the second capacitive element C2. .

That is, current flows from the fourth capacitive element C4 through the output load 110, the first electrode and the second electrode of the transistor T1, the fifth switch S5, and the second power source VSS. do. Of course, accordingly, the voltage of the fourth capacitive element C4 is gradually decreased, and the second capacitive element (C) changed through coupling of the first capacitive element C1 and the second capacitive element C2 ( The voltage of C2) converges to the value obtained by subtracting the threshold voltage of the transistor T1.

Meanwhile, the voltage of the first capacitive element C1 depends on the ambient light incident on the light receiving element PD. That is, when the ambient light is relatively bright, a relatively large amount of current flows through the light receiving element PD, and the first capacitive element C1 is relatively discharged. That is, the voltage of the first capacitive element C1 becomes relatively small.

In addition, if the ambient light is relatively small, a relatively small current flows through the light receiving element PD to discharge the first capacitive element C1 relatively small. In other words, the voltage of the first capacitive element C1 is maintained to be relatively large.

 Therefore, a voltage applied to the control electrode of the transistor T1 according to the ambient light (second capacitive element C2 through coupling of the first capacitive element C1 and the second capacitive element C2). Voltage), and eventually, the transistor T1, the fifth switch S5, and the second power supply VSS are disconnected from the output load 110 connected to the transistor T1, that is, the fourth capacitive element C4. The amount of current flowing through the discharge (discharge amount) also varies.

Of course, since the analog-to-digital converter senses the voltage remaining in the fourth capacitive element C4, for example, a voltage value related to ambient light is obtained as an analog value.

In other words, when the ambient light incident through the light receiving element PD is relatively small, the current flowing therein becomes small, thereby coupling the first capacitive element C1 and the second capacitive element C2. The change in voltage of the second capacitive element C2 through is relatively small. Accordingly, the dischargeable voltage of the fourth capacitive element C4 through the transistor T1 is relatively small, and thus the voltage remaining in the fourth capacitive element C4 is relatively large. In other words, the output voltage becomes relatively large.

In addition, when the ambient light incident through the light receiving element PD is relatively large, the current flowing therein becomes large, and accordingly, the second through coupling of the first capacitive element C1 and the second capacitive element C2 is increased. The voltage change of the capacitive element C2 becomes relatively large. Therefore, the discharge voltage of the fourth capacitive element C4 through the transistor T1 is relatively large, and thus the remaining voltage remaining in the fourth capacitive element C4 is relatively small. That is, the output voltage is relatively small.

Meanwhile, the operation of the third capacitive element C3 by the fourth control signal and the fourth control signal will be described.

When a lot of light suddenly enters the light receiving element PD, the voltage charged in the first capacitive element C1 is quickly discharged through it. That is, since the first capacitive element C1 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, when the output voltage through the output terminal (for example, the voltage input to the analog-to-digital converter) continues to fall below the threshold for a predetermined time, the present invention uses the sub- fourth control signal as a feedback signal. After applying to the control electrode of the switch S7, the fourth control signal is then applied to the control electrode of the sixth switch S6.

Then, the first power source VDD is supplied to the third capacitive element C3 to perform a charging operation, and then the third capacitive element C3 is the first capacitive element C1, that is, a light receiving element. Connected in parallel to PD.

Therefore, since the first capacitive element C1 and the third capacitive element C3 are connected to the light receiving element PD in parallel, the reverse bias capacitance increases. In other words, the capacity that can flow through the light receiving element PD increases.

 Accordingly, a current flows through the light receiving element PD for a time sufficient to sense ambient light. Of course, the remaining voltage remaining in the first capacitive element C1 and the third capacitive element C3 contributes to the operation of the transistor 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.

7 is an equivalent circuit diagram of a capacitive element for error compensation analysis in the ambient light sensing circuit according to the present invention.

Referring back to FIG. 1A, the equivalent parasitic capacitive element Cpara of the first capacitive element C1, the second capacitive element C2, and the transistor T1 is shown as an equivalent circuit, as shown in FIG. 7. do.

Referring to this, the voltage (Vgate = Q / C) applied to the control electrode of the transistor T1 is calculated as shown in the following equation.

Here, V _integrate is the voltage of the first capacitive element (C1), V _th is the voltage of the second capacitive element (C2), C _para is the capacitance of the parasitic capacitive element of the transistor (T1).

As described in the above equation, the voltage applied to the control electrode Vgate of the transistor T1 is a threshold voltage value stored in the second capacitive element C2 in a function related to the voltage of the first capacitive element C1. Is the value of minus. Therefore, in the present invention, the output voltage of the ambient light sensing circuit 100 is not only proportional to the voltage of the first capacitive element C1, but also the threshold of the transistor T1 by the second capacitive element C2. It can be seen that the voltage is also compensated.

In other words, the voltage that the fourth capacitive element C4 discharges and converges during the buffering process T4 is relatively small when the control electrode voltage Vgate = Q / C of the transistor T1 is small. If the control electrode voltage is large, it is relatively large.

Of course, a small control electrode voltage of the transistor means that a lot of light is incident on the light-receiving element, and a large current flows. A large control electrode voltage of the transistor means that a small light is incident on the light-receiving element. It means flow.

8 is a graph simulating the change of the output voltage according to the change in the ambient light of the ambient light sensing circuit according to the present invention. Here, the graph of FIG. 8 is a result obtained during the buffering process T4, where X axis means time (ms) and Y axis means voltage (V).

As described above, in the buffering process T4, the voltage applied to the control electrode of the transistor T1 varies according to the ambient light, and the analog voltage value output through the output load 110 also varies. That is, when the ambient light incident through the light receiving element PD is small, the current flowing thereto is relatively small, and the output voltage is relatively high.

In addition, when the ambient light incident through the light receiving element PD is large, the current flowing therein is relatively large, and the output voltage is relatively small.

For example, when a small current of approximately 11pA flows through the light receiving element PD, the output voltage converges to a value of approximately 7.9961 to 7.9965V. At this time, the deviation of the output voltage is approximately 400nV.

In addition, when a large current of approximately 1881pA flows through the light receiving element PD, the output voltage converges to a value of approximately 3.0938 to 3.11849V. At this time, the deviation of the output voltage is approximately 24.7mV.

Here, humans are generally known to recognize the ambient light in log scale units. In other words, small changes in ambient light (e.g. in a dark room) can be easily perceived as slight changes in ambient light, while small changes in daylight can be noticeable in relatively large conditions (e.g. under sunlight). can not do it.

Therefore, as in the present invention, it is preferable that an output voltage having a small deviation is output in a state where the ambient light is relatively small. In addition, even when an output voltage having a relatively large deviation is output in a state in which the ambient light is relatively large, it can be seen that there is no big problem in using the output voltage since humans do not feel it anyway.

9 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 the first electrode of the transistor T1. Of course, the above-described output load 110 and the fourth capacitive element C4 may be embedded 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, although the third switch S3 is illustrated as being formed in the ambient light control processing unit 200 in the drawing, the present invention is not limited thereto. That is, the third switch S3 may be formed in the ambient light sensing circuit 100. 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, the one-chip form of the ambient light control processing unit 200 is not limited, and it may be formed on a substrate such as an organic electroluminescent panel.

For example, the third switch S3 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.

10 is a block diagram showing the 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 serves to supply a data voltage to the organic electroluminescent panel 500, and the scan driver 600 turns off 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. 11A is a circuit diagram showing an example of one pixel circuit among organic electroluminescent panels of a flat panel display, and FIG. 11B is a timing diagram thereof.

As shown in FIG. 11A, the pixel circuit includes 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 supply line VSS to supply the auto zero line An to supply the auto zero signal, the light emission control line En to supply the light emission control signal, the first to fourth transistors T1, T2, T3, 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, while some reference numerals overlap with those used in FIGS. 1 to 10, it is noted that the reference numerals shown here are limited to FIGS. 11A and 11B only.

As illustrated in FIG. 11B, 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. 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 illustrated in FIG. 11B (indicated by 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 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.

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 (16)

A light receiving element that flows current in proportion to ambient light, a first capacitive element charged with a voltage of a first power source, and then discharged by being connected to the light receiving element, and a second capacitive element connected to the first capacitive element And a current flowing from the first power source in response to the voltage of the second capacitive element changed through coupling of the first capacitive element and the second capacitive element after being connected to the element and the second capacitive element. An ambient light sensing circuit consisting of a transistor; An ambient light control processor configured to calculate a current ambient light by using the output signal of the ambient light sensing circuit as an input signal and output the digital ambient value; A timing controller configured to output a control signal suitable for current ambient light by using the output signal of the ambient light control unit as an input signal; A power control unit outputting a power supply voltage suitable for current ambient light by using the output signal of the timing control unit 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 the power control unit outputs a power voltage proportional to an ambient light obtained from the ambient light sensing circuit. The flat panel display of claim 1, wherein a third capacitive element for increasing a reverse bias capacitance of the light receiving element is further connected to the first capacitive element of the ambient light sensing circuit. The method of claim 1, wherein the light receiving element, the first capacitive element, and the second capacitive element of the ambient light sensing circuit are connected and initialized between the first power source and the second power source, The first capacitive element is connected to the light receiving element, and the first capacitive element is discharged according to ambient light incident on the light receiving element. The second capacitive element and the transistor are connected to a first power source, and the second capacitive element compensates for the threshold voltage of the transistor, The first capacitive element and the second capacitive element are connected, and the transistor outputs a current corresponding to the voltage of the second capacitive element changed through coupling of the first capacitive element and the second capacitive element. Flat display device characterized in that. The flat panel display of claim 1, wherein the light receiving element of the ambient light sensing circuit is one selected from a PIN diode, a PN diode, and a photo coupler. The flat panel display of claim 1, wherein a first switch connecting the light receiving element to a first power source or a first capacitive element is further connected to the light receiving element of the ambient light sensing circuit. The flat panel display of claim 1, wherein a second switch connecting the first capacitive element to a first power supply or a second capacitive element is further connected to the first capacitive element of the ambient light sensing circuit. . According to claim 1, A third switch for supplying a first power source is connected to the first electrode of the transistor of the ambient light sensing circuit, A fourth switch is connected between the second electrode and the control electrode of the transistor, A fifth switch for supplying a second power source is connected to the second electrode of the transistor, And an output terminal configured to output a current between the first electrode and the third switch of the transistor. The flat panel display of claim 10, wherein the fifth switch is turned on and the voltage charged to the output load connected through the output terminal is discharged to the second power source through the transistor and the fifth switch. The method of claim 5, wherein the first electrode of the third capacitive element of the ambient light sensing circuit is connected to the first capacitive element through a sixth switch, to a first power source through a seventh switch, and to a second electrode. The flat panel display, characterized in that connected to the second power source. The method of claim 1, wherein the first power of the ambient light sensing circuit further comprises an eighth switch for supplying a first power to the light receiving element, the first capacitive element and the second capacitive element. Flat panel display. The flat panel display of claim 1, wherein the ambient light control processor is connected to an output terminal of a transistor in the ambient light sensing circuit. 15. The method of claim 14, wherein the ambient light control processing unit An analog-digital converter connected to the first electrode of the transistor; 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 15, wherein the analog to digital converter 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.

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