KR100892792B1 - Ambient light sensor circuit for flat panel display device - Google Patents

Abstract

The present invention relates to an ambient light sensing circuit for a flat panel display device, and the technical problem to be solved is to detect the ambient brightness and output by adjusting the output current, to automatically adjust the screen brightness of the flat panel display according to the ambient brightness have.

To this end, the present invention provides a transistor electrically connected to a first power source, a first capacitive element electrically connected between a control electrode of the transistor, and a first reference power source, and an electrical connection between the first capacitive element and a second reference power source. The coupling voltage between the first capacitive element and the second capacitive element is electrically connected between the connected second capacitive element and the first reference power source and the third reference power source to flow current in response to ambient light. A first switch for controlling and a first switch electrically connected to the transistor, the first switch for outputting current from the first power supply through the transistor in accordance with coupling voltages of the first capacitive element and the second capacitive element; It is electrically connected between the first light receiving element and the first capacitive element, and blocks the leakage current of the first light receiving element, thereby preventing the coupling voltage of the first capacitive element and the second capacitive element from changing. It discloses an ambient light sensor circuit for a flat panel display device includes a second switch for.

Flat panel display, switch, temperature, leakage current, light receiving element

Description

AMBIENT LIGHT SENSOR CIRCUIT FOR FLAT PANEL DISPLAY DEVICE}

The present invention relates to an ambient light sensing circuit for a flat panel display device, and more particularly, to detect an ambient light and adjust an output current to automatically adjust the screen brightness of the flat panel display device according to the ambient light. To a 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). 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 user manipulation, but is generally designed to display the screen at a constant brightness regardless of the ambient brightness. . For example, a typical flat panel display device 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 dark 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 for a long time in a place where the surrounding brightness is relatively dark, thereby increasing the power consumption rate.

In addition, in the conventional flat panel display, when manufacturing the ambient light sensing circuit for sensing the ambient brightness, a sensor, a substrate, and a circuit should be formed on a substrate separate from the main substrate on which the flat panel is formed, and electrically connected to the main substrate. By doing so, there is a problem in that the size and thickness of the flat panel display device is increased and power consumption is also increased.

In addition, the ambient light sensing circuit of the conventional flat panel display has a problem in that the output current is changed due to the light leakage current during the ambient light sampling period, thereby not accurately sampling the ambient light.

Furthermore, the conventional ambient light sensing circuit has a problem in that the output current of the ambient light sensing circuit is changed due to the temperature leakage current as the ambient temperature increases, thereby not accurately detecting the ambient light.

SUMMARY OF THE INVENTION The present invention has been made to overcome the above-described problems, and an object of the present invention is to detect the ambient brightness and adjust the output current to automatically adjust the screen brightness of the flat panel display according to the ambient brightness. An optical sensing circuit is provided.

In addition, another object of the present invention is to form an ambient light sensing circuit on the same substrate as the substrate on which the pixel circuit is formed to prevent the size and thickness of the flat panel display from becoming unnecessarily large and to reduce power consumption. An ambient light sensing circuit is provided.

In addition, another object of the present invention is to flatten the light leakage current applied to the light receiving element in the ambient light sampling period, and prevent the output current from changing due to the light leakage current, it is possible to accurately sample the ambient light It is to provide an ambient light sensing circuit.

In addition, another object of the present invention is to provide an ambient light sensing circuit for a flat panel display that can prevent the output current of the ambient light sensing circuit from fluctuating due to the temperature leakage current as the ambient temperature of the flat panel display increases. There is.

In order to achieve the above object, an ambient light sensing circuit for a flat panel display device according to the present invention includes a transistor electrically connected to a first electrode at a first power supply, and a first electrode electrically connected between a control electrode of the transistor and a first reference power supply. A first capacitive element, a second capacitive element electrically connected between the first capacitive element and a second reference power source, and an electrical connection between the first reference power source and the third reference power source in response to ambient light A first light receiving element for adjusting a coupling voltage between the first capacitive element and the second capacitive element by flowing a current, and electrically connected to the transistor, the first capacitive element and the second capacitor A first switch and a current between the first light receiving element and the first capacitive element for outputting a current from the first power source through the transistor according to a coupling voltage of the active element; The second switch may be electrically connected to the second light blocking device to block a leakage current of the first light receiving device, and to prevent a coupling voltage between the first capacitive device and the second capacitive device from changing.

An electrical connection between the first reference power supply and the second switch, wherein a first reference voltage is applied from the first reference power supply to the first capacitive element and the second capacitive element through the second switch; It may further include a third switch.

The electronic device may further include a fourth switch electrically connected between the control electrode of the transistor and the second electrode of the transistor to connect the transistor to a diode structure.

The electronic device may further include a fifth switch electrically connected between the first switch and the reference current source and applying a reference current to the transistor through the first switch to apply a constant voltage to the control electrode of the transistor. .

The transistor is electrically connected to the first switch, and in response to a coupling voltage between the first capacitive element and the second capacitive element, the transistor outputs a constant current from the first power supply through the first switch. It may further include a sixth switch for transmitting to.

The display device may further include a third capacitive element electrically connected to the second capacitive element in parallel to increase a reverse bias capacitance of the first light receiving element.

The electronic device may further include a seventh switch electrically connected between the second capacitive element and the third capacitive element to connect the third capacitive element to the second capacitive element in parallel.

An electrical connection between the first reference power supply and the second switch, wherein a first reference voltage is applied from the first reference power supply to the first capacitive element and the second capacitive element through the second switch; A third switch, a fourth switch electrically connected between a control electrode of the transistor and a second electrode of the transistor, a fourth switch connecting the transistor in a diode structure, and electrically connected between the first switch and a reference current source. A fifth switch configured to apply a reference current to the transistor through the first switch to apply a constant voltage to the control electrode of the transistor, and electrically connected to the first switch, In response to the coupling voltage of the second capacitive element, the transistor outputs a constant current from the first power supply through the first switch. A sixth switch transferring to the power terminal, a third capacitive element electrically connected in parallel with the second capacitive element, and increasing a reverse bias capacitance of the first light receiving element, and the second capacitive element; The electronic device may further include a seventh switch electrically connected between the third capacitive elements to connect the third capacitive element to the second capacitive element in parallel.

The first light receiving device may be any one selected from a PIN diode, a PN diode, and a photocoupler, wherein an anode is electrically connected to the first reference power source, and a cathode is electrically connected to a third reference power source.

The third reference voltage applied from the third reference power supply may be greater than the first reference voltage applied from the first reference power supply.

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

The third reference voltage applied from the third reference power supply may be smaller than the first reference voltage applied from the first reference power supply.

The second light receiving device may further include a second light receiving device electrically connected between the first light receiving device and the fourth reference power source and detecting only a leakage current according to an increase in temperature since no ambient light is incident to the light receiving layer.

The leakage current caused by the temperature increase, which is the current flowing through the second light receiving element, is removed from the current flowing through the first light receiving element, and current corresponding to ambient light is applied to the first capacitive element and the second capacitive element. The coupling voltage can be adjusted.

The second light receiving device may further include a second light receiving device electrically connected between the first light receiving device and the fourth reference power source and detecting only a leakage current according to an increase in temperature since no ambient light is incident to the light receiving layer.

A reference sensor having a temperature sensor sensing a temperature, an ambient light detection time corresponding to the sensed temperature electrically connected to the temperature sensor, and a peripheral value electrically connected to the reference value and output from the reference value The electronic device may further include a controller configured to supply a first control signal to the first switch in response to the light detection time.

A reference sensor having a temperature sensor sensing a temperature, an ambient light detection time corresponding to the sensed temperature electrically connected to the temperature sensor, and a peripheral value electrically connected to the reference value and output from the reference value A first control signal for the first switch, a second control signal for the second switch and a third switch, a third control signal for the fourth switch, a fourth control signal for the fifth switch, and a sixth switch in response to a light sensing time; The control unit may further include a controller configured to supply a sixth control signal to the fifth control signal and the seventh switch.

A first switching transistor electrically connected between a first electrode and a second electrode between the first capacitive element and the second capacitive element, and a control electrode electrically connected to a second sub-control signal; The first and second electrodes may be electrically connected to each other, and the control electrode may further include a second switching transistor electrically connected to the third sub-control signal.

The second switch, the fourth switch, and the seventh switch may be formed of two transistors connected in series.

The ambient light sensing circuit for a flat panel display according to the present invention can automatically adjust the screen brightness of the flat panel display according to the ambient brightness by sensing the ambient brightness and adjusting the output current.

In addition, as described above, the ambient light detection circuit for a flat panel display according to the present invention forms an ambient light detection circuit on the same substrate as the substrate on which the pixel circuit is formed, thereby preventing the size and thickness of the flat panel display device from becoming unnecessarily large, Power can be reduced.

Further, as described above, the ambient light sensing circuit for a flat panel display according to the present invention cuts off the light leakage current applied from the light receiving element in the ambient light sampling period, and prevents the output current from being changed due to the light leakage current, thereby preventing the ambient light. Can be sampled accurately.

As described above, the ambient light sensing circuit for a flat panel display according to the present invention can prevent the output current of the ambient light sensing circuit from fluctuating due to the temperature leakage current as the ambient temperature of the flat panel display increases.

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 coupled to another part, this includes not only a case where it is directly connected but also a case where another element is connected in between.

1A to 1C, a circuit diagram illustrating an ambient light sensing circuit for a flat panel display device according to an exemplary embodiment of the present invention is shown.

First, as shown in FIG. 1A, the ambient light sensing circuit for a flat panel display device includes a transistor Tr1, a first capacitive element C1, a second capacitive element C2, a third capacitive element C3, and a third capacitor. 1st light receiving element PD1, 1st switch S1, 2nd switch S2, 3rd switch S3, 4th switch S4, 5th switch S5, 6th switch S6, 5th 7 switch S7 is included. In this case, the second reference power supply V _REF2 and the third reference power supply V _REF3 are electrically connected to the first power supply VDD to receive the first voltage, which is the same as the ambient light sensing circuit for the flat panel display of FIG. 1. Can work. Hereinafter, for convenience of description, each reference power source and a reference voltage have the same reference numerals. That is, the first reference power supply and the first reference voltage are V _REF1 , the second reference power supply and the second reference voltage are V _REF2, and the third reference power supply and the third reference voltage are V _REF3 . Reference numerals are used.

The transistor Tr1 includes a first electrode (source or drain), a second electrode (drain or source), and a control electrode (gate electrode). The transistor Tr1 has a first electrode electrically connected to the first power supply VDD and a second electrode electrically connected to the first electrode of the first switch S1 and the second electrode of the fourth switch S4. The control electrode is electrically connected to the first electrode of the fourth switch S4 and the second electrode of the first capacitive element C1. The transistor Tr1 may be any one selected from an amorphous silicon thin film transistor, a polysilicon thin film transistor, an organic thin film transistor, a nano thin film semiconductor transistor, and an equivalent thereof as a P-channel transistor, but the material or type thereof is not limited thereto.

In addition, when the transistor Tr1 is a polysilicon thin film transistor, it may be formed by any one method selected from a laser crystallization method, a metal induced crystallization method, a high pressure crystallization method, and an equivalent method, but in the present invention, the polysilicon It does not limit the manufacturing method of a thin film transistor.

For reference, the laser crystallization method is a method of crystallizing amorphous silicon, for example by irradiating an excimer laser, the metal-induced crystallization method is the crystallization from the metal is started by placing a metal, for example, a predetermined temperature on the amorphous silicon The high pressure crystallization method is a method of crystallizing amorphous silicon by applying a predetermined pressure, for example.

The first capacitive element C1 has a first electrode formed between the second electrode of the second capacitive element C2 and the second electrode of the second switch S2 and the second electrode of the seventh switch S7. The second electrode is electrically connected to the first node N1, and the second electrode is electrically connected to the control electrode of the transistor Tr1 and the first electrode of the fourth switch S4. The first capacitive element C1 stores a voltage corresponding to the voltage difference between the first electrode and the second electrode of the first capacitive element C1 and adjusts a coupling voltage with the second capacitive element C2. Is generated and applied to the control electrode of the transistor Tr1.

In the second capacitive element C2, a first electrode is electrically connected to the second reference power supply V _REF2 , and the second electrode is connected to the first electrode and the second switch of the first capacitive element C1. It is electrically connected to the first node N1 between the second electrode of S2 and the second electrode of the seventh switch S7. The second capacitive element C2 stores a voltage corresponding to the voltage difference between the first electrode and the second electrode of the second capacitive element C2, and adjusts a coupling voltage with the first capacitive element C1. Is generated and applied to the control electrode of the transistor Tr1. In addition, the second capacitive element C2 increases the reverse bias capacitance of the first light receiving element PD1 to improve the signal retention characteristic.

In the third capacitive element C3, a first electrode is electrically connected to the second reference power supply V _REF2 , and a second electrode is electrically connected to the first electrode of the seventh switch S7. The third capacitive element C3 stores a voltage corresponding to the voltage difference between the first electrode and the second electrode of the third capacitive element C3 and increases the reverse bias capacitance of the first light receiving element PD1. The signal holding characteristic is improved.

An anode of the first light receiving element PD1 is electrically connected between the first electrode of the second switch S2 and the second electrode of the third switch S3, and the cathode of the first light receiving element PD1 is a third reference. It is electrically connected to the power supply V _REF3 . In this case, the third switch S3 may apply the first reference voltage V _REF1 to the anode of the first light receiving device PD1 when the first electrode is electrically connected to the first reference power supply V _REF1 and turned on. The first reference voltage V _REF1 may be lower than the third reference voltage V _REF3 . In addition, the first light receiving device PD1 may be any one selected from a PIN diode, a PN diode, a photo coupler, and an equivalent thereof, but the type of the first light receiving device PD1 is not limited thereto. The first light receiving element PD1 charges the first capacitive element C1 and the second capacitive element C2 by flowing a current from the third reference voltage V _REF3 in response to ambient light.

The first switch S1 has a first electrode electrically connected to the second electrode of the transistor Tr1 and the second electrode of the fourth switch S4, and the second electrode is connected to the fifth switch S5 and the fifth electrode. It is electrically connected to the second contact node N2 of the six switch S6. The first switch S1 may be turned on / off by a first control signal by applying a first control signal to the control electrode. The first switch S1 may be formed of any one selected from N-channel or P-channel low temperature crystallized polysilicon and its equivalents, but is not limited thereto. The first switch S1 initializes the first capacitive element C1 to a constant voltage or corresponds to a coupling voltage of the first capacitive element C1 and the second capacitive element C2. A predetermined amount of current applied from the first power supply VDD through the transistor Tr1 is output to the output terminal I _OUT .

In the second switch S2, a first electrode is electrically connected to an anode of the first light receiving element PD1 and a second electrode of the third switch S3, and the second electrode is the first capacitive element C1. Is electrically connected to the first electrode of the second electrode and the second electrode of the second capacitive element C2. The second switch S2 may be turned on / off by a second control signal by applying a second control signal to the control electrode. The second switch S2 may be formed of any one selected from N-channel or P-channel low temperature crystallized polysilicon and its equivalents, but is not limited thereto. The second switch S2 is turned off to block the light leakage current of the first light receiving element PD1 from being applied to the first capacitive element C1 and the second capacitive element C2, thereby providing a first capacitive characteristic. The coupling voltage between the element C1 and the second capacitive element C2 is prevented from changing.

In the third switch S3, a first electrode is electrically connected to the first reference power supply V _REF1 , and a second electrode is connected to the anode electrode of the first light receiving element PD1 and the first switch of the second switch S2. Is electrically connected to the electrode. The third switch S3 may be turned on / off by a third control signal by applying a third control signal to the control electrode. The third switch S3 may be formed of any one selected from N-channel or P-channel low temperature crystallized polysilicon and its equivalents, but is not limited thereto. The third switch S3 is turned on to transfer the first reference voltage V _REF1 applied to the first electrode to the first capacitive element C1 and the second capacitive element C2.

In the fourth switch S4, a first electrode is electrically connected between the control electrode of the transistor Tr1 and the second electrode of the first capacitive element C1, and the second electrode is a second electrode of the transistor Tr1. It is electrically connected between the electrode and the first electrode of the first switch S1. The fourth switch S4 may be turned on / off by a third control signal by applying a third control signal to the control electrode. The fourth switch S4 may be formed of any one selected from N-channel or P-channel low-temperature crystallized polysilicon and its equivalents, but is not limited thereto. The fourth switch S3 is turned on to connect the transistor Tr1 to the diode structure.

In the fifth switch S5, a first electrode is electrically connected to the second electrode of the first switch S1 and the first electrode of the sixth switch S6, that is, the second node N2. It is electrically connected to this reference current source I _REF . The fifth switch S5 may be turned on / off by a fourth control signal by applying a fourth control signal to the control electrode. The fifth switch S5 may be formed of any one selected from N-channel or P-channel low-temperature crystallized polysilicon and equivalents thereof, but the type and material are not limited thereto. The fifth switch S5 is turned on to apply a reference current applied from the reference current source I _REF to the transistor Tr1 through the first switch S1. At this time, when the transistor Tr1 is connected in a diode structure and the first reference voltage V _REF1 is applied to the first node N1, the first capacitive element C1 and the second capacitive element C2 are connected. The coupling voltage is maintained at a constant voltage.

The sixth switch S6 has a first electrode electrically connected to the first node N1, which is between the second electrode of the first switch S1 and the first electrode of the fifth switch S5, and the second electrode. Is electrically connected to the output terminal I _OUT . The sixth switch S6 may be turned on / off by a fifth control signal by applying a fifth control signal to the control electrode. The sixth switch S6 may be formed of any one selected from N-channel or P-channel low temperature crystallized polysilicon and the equivalent thereof, but is not limited thereto. The sixth switch S6 has a predetermined amount of current applied from the first power supply VDD through the transistor Tr1 in response to the coupling voltage of the first capacitive element C1 and the second capacitive element C2. Output to the output terminal (I _OUT ).

In the seventh switch S7, a first electrode is electrically connected to the second electrode of the third capacitive element C3, and the second electrode is connected to the second electrode and the first capacitive element of the second switch S2. It is electrically connected between the first electrode of C1) and the second electrode of the second capacitive element C2. The seventh switch S7 may be turned on / off by a sixth control signal by applying a sixth control signal to the control electrode. The seventh switch S7 may be formed of any one selected from N-channel or P-channel low temperature crystallized polysilicon and its equivalents, but is not limited thereto. The sixth switch S7 is turned on when a large amount of light is suddenly incident on the first light receiving element PD1 to connect the third capacitive element C3 and the second capacitive element C2 in parallel to each other. The signal holding characteristic is improved by increasing the reverse bias capacitance of the single light-receiving element PD1.

Next, as shown in FIG. 1B, the ambient light sensing circuit for the flat panel display device includes the first switch S1 to the seventh switch S7 as the P-channel transistor in the ambient light sensing circuit for the flat panel display device shown in FIG. 1A. The case is made, the operation of each device and the circuit is the same as in Figure 1a.

Finally, as shown in FIG. 1C, the ambient light sensing circuit for the flat panel display device includes the second switch S2, the fourth switch S4, and the ambient light sensing circuit for the flat panel display device shown in FIG. 1B. The seventh switch S7 includes two transistors connected in series, and the two transistors are P-channels, and the operation of each device and the circuit is the same as in FIG. 1A. When the second switch S2, the fourth switch S4, and the seventh switch S7 are turned off, the leakage current flowing through each switch causes the gate electrodes of the first node N1 and the transistor Tr1 to be turned off. The voltage is affected. Therefore, when the switch is formed by connecting two transistors in series, it is possible to reduce the leakage current of the switch, thereby compensating a phenomenon that the voltages of the gate electrodes of the first node N1 and the transistor Tr1 change due to the leakage current. can do.

2A and 2B, a timing diagram of the ambient light sensing circuit for the flat panel display device of FIGS. 1A to 1C is shown. The timing diagram of FIG. 2A is a case where the first switch S1 to the seventh switch S7 are P-channel transistors, and the timing diagram of FIG. 2B is the N-channel transistor of the first switch S1 to seventh switch S7. Figure 1 shows the case. Since the first switch S1 to the seventh switch S2 of FIGS. 2A and 2B are turned on at the low level when the P-channel transistor is turned on, and are turned on at the high level when the N-channel transistor is operated, the same operation is performed. Hereinafter will be described in detail with reference to Figure 2a.

As shown in FIGS. 2A and 2B, the timing diagram of the ambient light sensing circuit for a flat panel display device includes an initialization period T1, an ambient light detection period T2, and a sampling period T3. Five control signals, i.e., the first control signal, the second control signal, the third control signal, the fourth control signal, and the fifth control signal for the initialization period T1, the ambient light detection period T2, and the sampling period T3. The control signal is applied to the ambient light sensing circuit for the flat panel display.

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

First, in the initialization period T1, the first control signal, the second control signal, the third control signal, and the fourth control signal of a low level are applied to the ambient light sensing circuit for the flat panel display device so that the first switch S1 and the second control signal are applied. The switch S2, the third switch S3, the fourth switch S4, and the fifth switch S5 are turned on, and a fifth control signal of a high level is applied to turn off the sixth switch S6.

The fifth switch S5 is turned on to transfer the reference current of the reference current source I _REF to the first switch S1, and the first switch S1 is turned on to transfer the reference current to the second electrode of the transistor Tr1. To pass. At this time, the fourth switch S4 is turned on to connect the transistor Tr1 to the diode structure. Since the transistor Tr1 is connected in a diode structure and a reference current is constantly applied to the second electrode, the voltage applied to the control electrode of the transistor Tr1 is maintained at a constant voltage V _A.

The third switch S3 is turned on to transfer the first reference voltage applied from the first reference power supply V _REF1 to the second switch S2 and the first light receiving device PD1, and the second switch S2. Is turned on to transfer the reference voltage to the first node N1. The reference voltage applied to the first node N1 is transferred to the first capacitive element C1 and the second capacitive element C2.

The first capacitive element C1 includes the first reference voltage V _REF1 applied to the first electrode of the first capacitive element C1 and the control electrode voltage V of the transistor Tr1 applied to the second electrode. _The voltage corresponding to the difference of _A ) is stored. The second capacitive element C2 is formed by a difference between the second reference voltage V _REF2 applied to the first electrode of the second capacitive element C2 and the first reference voltage V _REF1 applied to the second electrode. The corresponding voltage will be stored. That is, when constant values of the first reference voltage V _REF1 , the second reference voltage V _REF2 , and the reference current I _REF are applied, the first capacitive element C1 and the second capacitive element C2 are applied. The voltage stored in is initialized constantly.

In the next ambient light detection period T2, a second control signal of a low level is applied to turn on the second switch S2, and a first control signal, a third control signal, a fourth control signal, and a fifth control of a high level are applied. The signal is applied to turn off the first switch S1, the third switch S3, the fourth switch S4, the fifth switch S5, and the sixth switch S6.

The second switch S2 is turned on so that a reverse current formed between the first electrode and the second electrode of the first light receiving element PD1 is a contact point between the first capacitive element C1 and the second capacitive element C2. Is applied to the first node N1. In this case, the reverse current formed through the first light receiving element PD1 depends on the brightness of the ambient light. That is, when the ambient light becomes dark, the current flowing through the first light receiving element PD1 becomes small, and when the ambient light becomes bright, the current flowing through the first light receiving element PD1 becomes large.

The reverse current formed through the first light receiving element PD1 is applied to the first node N1, which is a contact point between the first capacitive element C1 and the second capacitive element C2, and thus the first node N1. The voltage of V is changed by the voltage V corresponding to the reverse current from the first reference power supply V _REF1 to become V _REF1 + _ΔV . In this case, the first reference power supply V _REF1 is a voltage applied to the first node N1 in the initialization period T1.

As the voltage of the first node N1 is changed, the voltage of the second electrode of the first capacitive element C1 and the second capacitive element C2 correspond to the changed voltage of the first node N1. The storage voltage is changed. That is, the voltage of the first node N1 is changed by ΔV in response to the reverse current formed through the first light receiving element PD1, and the second voltage is corresponding to the changed voltage of ΔV of the first node N1. Since the voltage stored in the capacitive element C2 is changed and charged by ΔV, and the voltage stored in the first capacitive element C1 is kept unchanged, the voltage of the second electrode of the first capacitive element C1 is It is changed by ΔV. Therefore, the coupling voltage of the first capacitive element is changed corresponding to the changed voltage of the first node N1.

Here, the charging speed of the second capacitive element C2 is rapidly charged when the ambient light is relatively bright, and slowly charged when the ambient light is relatively dark.

Lastly, in the sampling period T3, the first control signal and the fifth control signal having a low level are applied to turn on the first switch S1 and the sixth switch S6, and the second control signal and the third control signal with the high level are turned on. The control signal and the fourth control signal are applied to turn off the second switch S2, the third switch S3, the fourth switch S4, and the fifth switch S5.

The first switch S1 is turned on and outputs a current applied from the transistor Tr1 to the output terminal I _OUT through the sixth switch S6. In this case, the transistor Tr1 is configured to supply the current I _{REF -ΔI} corresponding to the coupling voltage of the first capacitive element C1 and the second capacitive element C2 to the first switch S1 and the sixth switch. Output to the output terminal (I _OUT ) through (S6). That is, the coupling voltage of the first capacitive element C1 and the second capacitive element C2 is applied to the control electrode of the transistor Tr1, and when the coupling voltage is small, a relatively large current is applied to the transistor Tr1. The output voltage is output to the output terminal (I _OUT ) through, and if the coupling voltage is large, a relatively small current is output to the output terminal (I _OUT ) through the transistor Tr1.

Here, ΔI is a change amount of the voltage ΔV corresponding to the reverse current formed through the first light receiving element PD1 is applied to the first node N1 so that the current flowing through the transistor Tr1 is changed. In the case of ΔI, the coupling voltage of the first capacitive element C1 and the second capacitive element C2 becomes the control electrode voltage of the transistor Tr1. Therefore, when the coupling voltage is small, ΔI becomes small. If the coupling voltage is large, ΔI becomes large.

In this manner, when light is relatively incident on the first light receiving element PD1, the current flowing through the first light receiving element PD1 is relatively small, so that the first capacitive element C1 and the second capacitive element are reduced. The coupling voltage by (C2) becomes relatively small. Then, the current I _{REF -ΔI} flowing through the transistor Tr1 becomes relatively large. In addition, when a relatively strong light is incident on the first light receiving device PD1, the current flowing through the first light receiving device PD1 becomes relatively large, and accordingly, the first capacitive element C1 and the second capacitive element C2 are thus increased. The coupling voltage of becomes relatively large. Then, the currents I _{REF -ΔI} flowing through the transistor Tr1 are relatively small.

In addition, the second switch S2 is turned off to separate the first light receiving element PD1 and the first node N1, and the first light receiving element PD1 is generated in response to the ambient light in the sampling period T3. The light leakage current is applied to the first node N1 to prevent the coupling voltage between the first capacitive element C1 and the second capacitive element C2 from changing.

Meanwhile, referring to the operation of the third capacitive element C3 according to the sixth control signal, when a sudden strong light is incident on the first light receiving element PD1, the second capacitive element C2 is rapidly charged. As the second capacitive element C2 is charged too quickly, it is difficult to secure a reliable output voltage from the transistor Tr1, and thus accurate ambient light sensing operation is impossible.

In order to prevent such a phenomenon, the present invention, when the output current continues to be below the threshold point for a predetermined time to the output terminal (I _OUT ) as a feedback signal, by applying a sixth control signal to a low level to turn on. Then, the third capacitive element C3 is connected in parallel with the second capacitive element C2.

Therefore, in the first light receiving device PD1, the two second capacitive elements C2 and the third capacitive element C3 are connected in parallel, thereby increasing the capacitance of the capacitive element and further increasing the reverse bias capacitance. do. Of course, the second capacitive element C2 and the third capacitive element C3 affect the coupling voltage between the first capacitive element C1, and this coupling voltage is again influenced by the operation of the transistor Tr1. Will contribute. Accordingly, the transistor Tr1 operates in a reliable operation section, thereby ensuring a stable output voltage. That is, since the third capacitive element C3 is connected to the second capacitive element C2 in parallel, the first light receiving element PD1 can detect the ambient light smoothly.

Referring to FIG. 3, a circuit diagram illustrating an ambient light sensing circuit for a flat panel display according to another exemplary embodiment of the present invention is shown.

As shown in FIG. 3, the ambient light sensing circuit for the flat panel display is similar to the ambient light sensing circuit shown in FIG. 1A. However, the cathode and the anode of the first light receiving element PD1 are connected to each other in reverse, so that the cathode is electrically connected between the first electrode of the second switch S2 and the second electrode of the third switch S3, and the anode is connected to the third electrode. It is electrically connected to a reference power supply V _REF3 . In this case, when the first electrode is electrically connected to the first reference power supply V _REF1 and turned on, the third switch S3 applies the first reference voltage V _REF1 to the cathode of the first light receiving device PD1. The first reference voltage V _REF1 may be at a higher level than the third reference voltage V _REF3 . Therefore, in the ambient light sensing circuit of FIG. 1A, as the current in the reverse direction increases through the first light receiving element PD1, the second capacitive element C2 is charged and coupled by the first capacitive element C1. Although the voltage is increased, the ambient light sensing circuit of FIG. 3 causes the second capacitive element C2 to be discharged as the reverse current increases through the first light receiving element PD1 and is discharged by the first capacitive element C1. The coupling voltage is reduced.

Referring to FIG. 4, a circuit diagram illustrating an ambient light sensing circuit for a flat panel display according to another exemplary embodiment of the present invention is shown.

As shown in FIG. 4, the ambient light sensing circuit for the flat panel display is similar to the ambient light sensing circuit shown in FIG. 1A. However, the transistor Tr2 is configured as an N-channel transistor, and the operation is performed in the same manner as the ambient light sensing circuit of FIG. 1A. In the ambient light sensing circuit of FIG. 1, the first switch S1, the fourth switch S4, the fifth switch S5, and the sixth switch S6 are electrically connected to the second electrode of the transistor Tr1. Since the transistor Tr2 is an N-channel transistor, the first switch S1, the fourth switch S4, the fifth switch S5, and the sixth switch S6 are electrically connected to the first electrode. Since the ambient light sensing circuit for the flat panel display of FIG. 4 is the same as the ambient light sensing circuit for the flat panel display of FIG. 1A except that the transistor uses an N-channel transistor in the P channel, the operation of the ambient light sensing circuit is illustrated in FIGS. The same operation as described in Figures 2a and 2b.

Referring to FIG. 5, a circuit diagram illustrating an ambient light sensing circuit for a flat panel display according to another exemplary embodiment of the present invention is shown.

As shown in FIG. 5, the ambient light sensing circuit for the flat panel display is similar to the ambient light sensing circuit shown in FIG. 4. However, the cathode and the anode of the first light receiving element PD1 are connected to each other in reverse, so that the cathode is electrically connected between the first electrode of the second switch S2 and the second electrode of the third switch S3, and the anode is connected to the third electrode. It is electrically connected to a reference power supply V _REF3 . In this case, when the first electrode is electrically connected to the first reference power supply V _REF1 and is turned on, the third switch S3 applies the first reference voltage V _REF1 to the cathode of the first light receiving device PD1. The first _reference voltage V _REF1 may be at a higher level than the third reference voltage V _REF3 . In the ambient light sensing circuit of FIG. 4, as the current in the reverse direction increases through the first light receiving element PD1, the second capacitive element C2 is charged and the coupling voltage by the first capacitive element C1 is increased. Although increased, the ambient light sensing circuit of FIG. 5 has the second capacitive element C2 discharged and the coupling by the first capacitive element C1 as the reverse current increases through the first light receiving element PD1. The voltage decreases.

Referring to FIG. 6, a circuit diagram illustrating an ambient light sensing circuit for a flat panel display according to another exemplary embodiment of the present invention is shown.

As shown in FIG. 6, the ambient light sensing circuit for the flat panel display is similar to the ambient light sensing circuit shown in FIG. 1A. However, the ambient light sensing circuit further includes a second light receiving element PD2 electrically connected to the anode of the first light receiving element PD1 and includes a light blocking plate, and the other elements are the same as the ambient light sensing circuit of FIG. 1A. It works. The second light receiving element PD2 has a cathode electrically connected to an anode electrode of the first light receiving element PD1, and an anode is electrically connected to a fourth reference power supply V _REF4 . In this case, the first reference voltage V _REF1 may be at a lower level than the third reference voltage V _REF3 , and the fourth reference voltage V _REF4 may be at a lower level than the first reference voltage V _REF1 . (low level).

Here, the first light receiving element PD1 changes the coupling voltage of the first capacitive element C1 by flowing a current from the third reference voltage V _REF3 in response to the ambient light when the ambient light is incident to the ambient light. The device C2 is charged, and as the temperature increases, the current flowing through the first light receiving device PD1 also increases. That is, leakage current is generated. Since the second light receiving element PD2 includes a light blocking plate, the current change occurs due to the same temperature increase as the first light receiving element PD1, but there is no change in current due to ambient light incident. Therefore, since the difference between the current flowing through the first light receiving element PD1 and the current flowing through the second light receiving element PD2 becomes a current according to ambient light, a voltage corresponding thereto can be applied to the first node N1. That is, it is possible to prevent the output current from fluctuating with the leakage current according to the temperature. The first light receiving element PD1 and the second light receiving element PD2 are light receiving elements having the same characteristics, and the temperature characteristics are also the same.

In other words, the current flowing through the first light receiving device PD1 is a current Idark from the third reference voltage V _REF3 in response to the ambient light and the current Idark according to the temperature increase, and the second light receiving device PD2 is Since the light blocking plate is included, the current flowing in the second light receiving element PD2 flows only the current Idark according to the temperature increase. Therefore, the difference between the current flowing through the first light receiving element PD1 and the current flowing through the second light receiving element PD2 leaves only the current I _photo from the third reference voltage V _REF3 in response to ambient light. Therefore, the current flowing to the ambient light sensing circuit through the second switch S2 flows only the current I _photo according to the ambient light which is not affected by the temperature change, and thus the output current is changed by removing the leakage current according to the temperature. This can be prevented.

 3 to 5 further includes a second light receiving element PD2 including a light shielding plate in the ambient light sensing circuit of FIGS. 3 to 5, and the ambient light sensing circuit of FIGS. Can be prevented.

Referring to FIG. 7, a circuit diagram illustrating an ambient light sensing circuit for a flat panel display according to another exemplary embodiment of the present invention is shown.

As shown in FIG. 7, the ambient light sensing circuit for the flat panel display is similar to the ambient light sensing circuit shown in FIG. 1A. However, the ambient light sensing circuit of FIG. 1A further includes a temperature sensor, a reference value (LUT), and a controller, and other elements operate in the same manner as the ambient light sensing circuit of FIG. 1A.

The temperature sensor is electrically connected to the reference value LUT to sense the temperature of the ambient light sensing circuit, and transfers the sensed temperature as the reference value LUT.

The reference value is electrically connected between the temperature sensor and the controller to transmit the ambient light detection time corresponding to the sensed temperature to the controller. In this case, the reference value LUT is a curve in which the characteristic of the reference value is illustrated in FIG. 8 in the form of a memory in which the ambient light sensing time corresponding to the sensed temperature is stored.

The controller is electrically connected between the first to sixth control signals and the reference value LUT. The reference value LUT outputs an ambient light detection time corresponding to a temperature sensed by a temperature sensor and applies it to the controller, and applies an ambient light detection time according to a temperature to the first to sixth control signals. At this time, as the temperature increases, the leakage current increases, so that the ambient light sensing time decreases. When the temperature decreases, the leakage current does not occur. Therefore, the ambient light sensing time increases compared to when the temperature is high, and is output through the transistor Tr1. The current output to the terminal I _OUT is kept constant.

 The ambient light sensing circuit of FIGS. 3 to 5 further includes a temperature sensor, a reference value (LUT), and a controller, and the ambient light sensing circuit of FIGS. 3 to 5 also outputs by adjusting the ambient light sensing time in response to leakage current according to temperature. The fluctuation of the current can be prevented.

Referring to FIG. 8, a characteristic curve showing a reference value of the ambient light sensing circuit for the flat panel display of FIG. 7 is illustrated.

As shown in FIG. 8, the characteristic curve showing the reference value of the ambient light sensing circuit for the flat panel display device shows that the leakage current of the light receiving element increases as the sensing temperature applied from the temperature sensor increases, and the ambient light increases as the leakage current increases. The detection time is reduced. This increases the leakage current of the light receiving element if the sensing temperature applied from the temperature sensor is increased, thereby reducing the ambient light detection time. This is because the time for which the voltage is applied from the first light receiving element PD1 to the first node N1 between the first capacitive element C1 and the second capacitive element C2 is reduced, so that the first capacitive element The time for charging C1 and the second capacitive element C2 is reduced. That is, it is possible to reduce the ambient light sensing time that the current increases due to the temperature, thereby preventing the current output to the output terminal I _OUT from changing.

9, a circuit diagram illustrating an ambient light sensing circuit for a flat panel display according to another exemplary embodiment of the present invention is shown.

As shown in FIG. 9, the ambient light sensing circuit for the flat panel display is similar to the ambient light sensing circuit shown in FIG. 1A. However, the ambient light sensing circuit of FIG. 1A further includes a first switching transistor ST1 and a second switching transistor ST2, and other devices operate in the same manner as the ambient light sensing circuit of FIG. 1A.

The first switching transistor ST1 includes a first electrode (source or drain), a second electrode (drain or source), and a control electrode (gate electrode). In the first switching transistor ST1, a first electrode and a second electrode are electrically connected to a first node N1 between the first capacitive element C1 and the second capacitive element C2. The first switching transistor ST1 may be turned on / off by a second sub control signal by applying a second sub control signal to the control electrode. At this time, the second sub-control signal is a signal opposite to the second control signal, when the second control signal is a high level, the second sub-control signal is a low level, when the second control signal is a low level, The two-part control signal goes high.

As shown in FIG. 9, the first switching transistor ST1 may use a P-channel transistor, and when the second switch S2 also uses the same P-channel transistor, when the first switching transistor ST1 is turned on. The second switch S2 is turned off, and when the first switching transistor ST1 is turned off, the second switch S2 is turned on. In other words, the opposite operation. The first switching transistor ST1 may be an N-channel transistor, but the second switch S2 should also be an N-channel transistor.

When the first switching transistor ST1 is turned on and the second switch S2 is changed from the ambient light sensing period T2 at which the second switch S2 is turned off to the sampling period T3, the second switch S2 is turned off. At the moment, the voltage of the control electrode of the transistor Tr1 is increased due to the switching error, thereby lowering the output current. This may be compensated by the first switching transistor ST1.

The second switching transistor ST2 includes a first electrode (source or drain), a second electrode (drain or source), and a control electrode (gate electrode). In the second switching transistor ST2, a first electrode and a second electrode are electrically connected to the control electrode of the transistor Tr1. The second switching transistor ST2 may be turned on / off by a third sub control signal by applying a third sub control signal to the control electrode. In this case, the third sub control signal is a signal opposite to the third control signal. When the third control signal is high level, the third sub control signal becomes low level, and when the third control signal is low level. , The third sub-control signal is at a high level.

As shown in FIG. 9, the second switching transistor ST2 may use a P-channel transistor, and when the fourth switch S4 uses the same P-channel transistor, the second switching transistor ST2 is turned on. The fourth switch S4 is turned off, and when the second switching transistor ST2 is turned off, the fourth switch S4 is turned on. In other words, the opposite operation. The second switching transistor ST2 may be an N-channel transistor, but at this time, the fourth switch S4 should also be an N-channel transistor.

When the second switching transistor ST2 is turned on and the fourth switch S4 is changed from the initialization period T1 at which the fourth switch S4 is turned off to the ambient light sensing period T2, the fourth switch S4 is turned off. When the switching error occurs, the voltage of the control electrode of the transistor Tr1 is increased to decrease the output current. The second switching transistor ST2, which is a dummy switch, is turned on to compensate for this.

 The first and second switching transistors ST1 and ST2 are further included in the ambient light sensing circuit of FIGS. 3 to 5, and the second and fourth switches of the ambient light sensing circuit of FIGS. The switching error of S4 increases the voltage of the control electrode of the transistor, thereby reducing the output current.

What has been described above is only one embodiment for implementing the ambient light sensing circuit for a flat panel display device according to the present invention, and the present invention is not limited to the above embodiment, as claimed in the following claims. Without departing from the gist of the present invention, anyone of ordinary skill in the art will have the technical spirit of the present invention to the extent that various modifications can be made.

1A to 1C are circuit diagrams illustrating an ambient light sensing circuit for a flat panel display according to an exemplary embodiment of the present invention.

FIG. 2 is a timing diagram of an ambient light sensing circuit for the flat panel display of FIG. 1A.

3 is a circuit diagram illustrating an ambient light sensing circuit for a flat panel display according to another exemplary embodiment of the present invention.

4 is a circuit diagram illustrating an ambient light sensing circuit for a flat panel display according to another exemplary embodiment of the present invention.

5 is a circuit diagram illustrating an ambient light sensing circuit for a flat panel display according to another exemplary embodiment of the present invention.

6 is a circuit diagram illustrating an ambient light sensing circuit for a flat panel display according to another exemplary embodiment of the present invention.

7 is a circuit diagram illustrating an ambient light sensing circuit for a flat panel display according to another exemplary embodiment of the present invention.

FIG. 8 is a characteristic curve illustrating a reference value of the ambient light sensing circuit for the flat panel display of FIG. 7.

9 is a circuit diagram illustrating an ambient light sensing circuit for a flat panel display according to another exemplary embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

PD1; A first light receiving element PD2; Second light receiving element

S1; First switch S2; Second switch

S3; Third switch S4; 4th switch

S5; Fifth switch S6; 6th switch

S7; Seventh switch C1; First capacitive element

C2; Second capacitive element C3; Third capacitive element

Tr1; Transistor (P-channel) Tr2; Transistor (N channel)

ST1; A first switching transistor ST2; 2nd switching transistor

LUT; Reference value

Claims (20)

A transistor electrically connected with the first electrode to the first power source; A first capacitive element electrically connected between a control electrode of the transistor and a first reference power source;  A second capacitive element electrically connected between the first capacitive element and a second reference power source; It is electrically connected between the first reference power source and the third reference power supply to flow a current in response to ambient light, thereby reducing the coupling voltage of the first capacitive element and the charge / discharge voltage of the second capacitive element. A first light receiving element for adjusting; A first switch electrically connected to the transistor and configured to output a current from the first power source through the transistor according to a coupling voltage of the first capacitive element; And A second switch electrically connected between the first light receiving element and the first capacitive element and blocking a leakage current of the first light receiving element to prevent the coupling voltage of the first capacitive element from changing Ambient light sensing circuit for a flat panel display comprising a. The method of claim 1, Is electrically connected between the first reference power supply and the second switch, and a first reference voltage is applied from the first reference power supply to the first capacitive element and the second capacitive element through the second switch. An ambient light sensing circuit for a flat panel display further comprising a third switch. The method of claim 1, And a fourth switch electrically connected between the control electrode of the transistor and the second electrode of the transistor to connect the transistor in a diode structure. The method of claim 1, And a fifth switch electrically connected between the first switch and a reference current source and applying a reference current to the transistor through the first switch to apply a constant voltage to the control electrode of the transistor. An ambient light sensing circuit for a flat panel display device. The method of claim 1, The transistor is electrically connected to the first switch, and in response to a coupling voltage between the first capacitive element and the second capacitive element, the transistor supplies a constant current from the first power source to an output terminal through the first switch. The ambient light sensing circuit for a flat panel display further comprises a sixth switch for transmitting. The method of claim 1, And a third capacitive element electrically connected in parallel with the second capacitive element to increase the reverse bias capacitance of the first light receiving element. The method of claim 6, And a seventh switch electrically connected between the second capacitive element and the third capacitive element, the seventh switch connecting the third capacitive element in parallel with the second capacitive element. Ambient light sensing circuit for display devices. The method of claim 1, An electrical connection between the first reference power supply and the second switch, wherein a first reference voltage is applied from the first reference power supply to the first capacitive element and the second capacitive element through the second switch; Third switch; A fourth switch electrically connected between the control electrode of the transistor and the second electrode of the transistor to connect the transistor to a diode structure; A fifth switch electrically connected between the first switch and a reference current source and applying a reference current to the transistor through the first switch to apply a constant voltage to the control electrode of the transistor; The transistor is electrically connected to the first switch, and in response to a coupling voltage between the first capacitive element and the second capacitive element, the transistor supplies a constant current from the first power source to an output terminal through the first switch. A sixth switch for transmitting; A third capacitive element electrically connected in parallel with the second capacitive element to increase a reverse bias capacitance of the first light receiving element; And And a seventh switch electrically connected between the second capacitive element and the third capacitive element, the seventh switch connecting the third capacitive element in parallel with the second capacitive element. Ambient light sensing circuit for display devices. The method of claim 8, The first light receiving element is any one selected from among a PIN diode, a PN diode, and a photocoupler, wherein an anode is electrically connected to the first reference power source and a cathode is electrically connected to a third reference power source. Ambient light sensing circuit. The method of claim 9, And a third reference voltage applied from the third reference power supply than the first reference voltage applied from the first reference power supply. The method of claim 8, The first light receiving element is any one selected from a pin diode, a PN diode, and a photocoupler, the cathode of which is electrically connected to the first reference power source and the anode of which is electrically connected to a third reference power source. Ambient light sensing circuit. The method of claim 11, And a third reference voltage applied from the third reference power supply is smaller than the first reference voltage applied from the first reference power supply. The method of claim 1, And a second light receiving element electrically connected between the first light receiving element and the fourth reference power source, the second light receiving element sensing only a leakage current according to an increase in temperature since ambient light is not incident including a light blocking layer. Ambient light sensing circuit for display devices. The method of claim 13, The leakage current caused by the temperature increase, which is the current flowing through the second light receiving element, is removed from the current flowing through the first light receiving element, and current corresponding to ambient light is applied to the first capacitive element and the second capacitive element. An ambient light sensing circuit for a flat panel display, characterized in that the coupling voltage is adjusted. The method of claim 8, And a second light receiving element electrically connected between the first light receiving element and the fourth reference power source and detecting only a leakage current according to an increase in temperature since ambient light is not incident including a light blocking layer. Ambient light sensing circuit for flat panel display. The method of claim 1, A temperature sensor for sensing a temperature; A reference value stored in the ambient light detection time corresponding to the sensed temperature electrically connected to the temperature sensor; And And a control unit electrically connected to the reference value and supplying a first control signal to the first switch in response to an ambient light detection time output from the reference value. Circuit. The method of claim 8, A temperature sensor for sensing a temperature; A reference value stored in the ambient light detection time corresponding to the sensed temperature electrically connected to the temperature sensor; And Electrically connected to the reference value, the first control signal to the first switch, the second control signal to the second switch and the third switch, and the fourth switch to correspond to the ambient light sensing time output from the reference value. And a control unit for supplying a third control signal, a fourth control signal to the fifth switch, a fifth control signal to the sixth switch, and a sixth control signal to the seventh switch. . The method of claim 1, A first switching transistor electrically connected between a first electrode and a second electrode between the first capacitive element and the second capacitive element, and a control electrode electrically connected to a second sub-control signal; And a second switching transistor electrically connected to a first electrode and a second electrode, and a control electrode electrically connected to a third sub-control signal, to the transistor. The method of claim 8, A first switching transistor electrically connected between a first electrode and a second electrode between the first capacitive element and the second capacitive element, and a control electrode electrically connected to a second sub-control signal; And a second switching transistor electrically connected to the first electrode and the second electrode, and a control electrode electrically connected to a third sub-control signal. The method of claim 8, And the second switch, the fourth switch, and the seventh switch are configured of two transistors connected in series.

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