KR20210081221A - Pixel circuit and display apparatus for minimizing leakage current and control method thereof - Google Patents

Abstract

The present specification is to provide a technology capable of preventing leakage of current in a circuit for driving a pixel. A pixel driving circuit according to the present specification includes a MOSFET to which a signal related to driving of a light emitting diode is input, and a leakage current prevention voltage may be applied to a body terminal of the MOSFET. In addition, it is possible to prevent leakage current generated after the MOSFET is turned off by appropriately charging a parasitic capacitor present in the display panel.

Description

PIXEL CIRCUIT AND DISPLAY APPARATUS FOR MINIMIZING LEAKAGE CURRENT AND CONTROL METHOD THEREOF

The present invention relates to a display device, and more particularly, to a display device having a circuit capable of minimizing a leakage current in a pixel.

1 is a block diagram schematically illustrating the configuration of a general display device.

Referring to FIG. 1 , the display device 10 may include a display panel 11 , a scan driving circuit 12 , a data driving circuit 13 , and a controller 14 . The display panel 11 may include a plurality of pixels (PX). The plurality of pixels PX may be arranged in a matrix form m X n (m, n is a natural number).

Each pixel PX may include a plurality of light emitting devices. The light emitting device may be a light emitting diode (LED). For example, one pixel PX may include a light emitting device composed of red (R), green (G), and blue (B).

Each pixel PX may include a pixel driving circuit for driving a plurality of light emitting devices. The pixel driving circuit may drive a turn-on or turn-off operation of the light emitting device according to a control signal output from the scan driving circuit 12 and/or the data driving circuit 13 . When the driving method of the display panel 11 is an active matrix method, the pixel driving circuit may include at least one thin film transistor and at least one capacitor. The capacitor stores a voltage related to driving the light emitting device, and the voltage stored in the capacitor causes the light emitting device to emit light during one frame through discharge.

FIG. 2 is a signal timing reference diagram for inputting data to a pixel included in the display device shown in FIG. 1 .

Referring to FIG. 2 , the scan driving circuit 12 sequentially outputs signals to a plurality of scan lines Scan① to Scanⓜ. Through this, only pixels connected to any one scan line among the plurality of pixels may be driven. For example, pixels connected to the first scan line Scan① may be driven during the first scan driving period, and pixels connected to the second scan line Scan② may be driven during the second scan driving period.

Since one pixel includes a plurality of light emitting devices, a time for charging a capacitor related to an operation of each light emitting device may be allocated without overlapping with each other. Accordingly, the data driving circuit 13 may output a gradation voltage to each pixel through data lines. Although one data line is connected to a plurality of pixels in the longitudinal direction, only pixels connected to the scan line selected by the scan driving circuit 12 may be driven during the one scan driving period. For example, the data driving circuit 13 may output a gradation voltage to a pixel connected to the first data line Data 1 during a driving period of the pixels connected to the first scan line Scan 1 . More specifically, a gradation voltage may be charged to a capacitor included in each light emitting device.

3 is an exemplary diagram of a general pixel driving circuit.

Referring to FIG. 3 , a typical pixel driving circuit may include two switching elements implemented as MOSFETs. First, a scan line may be connected to a gate terminal of one MOSFET and a data line may be connected to a drain terminal. Accordingly, when the V _Scan voltage is applied to the gate terminal, the MOSFET is turned on, and at this time, the V _Data voltage applied to the drain terminal may be charged in the capacitor C _{x .} Thereafter, when the V _Scan voltage becomes OV, the remaining MOSFET is turned on by the voltage charged in _{the capacitor C x to drive the light emitting device LED.}

However, in the case of a pixel implemented as a micro LED recently, the pixel driving circuit also became smaller as the size of the LED became smaller. When a capacitor is implemented in a reduced pixel driving circuit, a problem arises that the capacitance of the capacitor is limited to a capacity of about ^{femto (10 -15 , f)F.} In addition, due to the implementation of the reduced size MOSFET in the reduced pixel circuit, a leakage current is generated.

On the right side of FIG. 3, a situation in which leakage current occurs after the capacitor is charged is shown. In this case, the direction of the leakage current may vary according to the magnitude of the voltage charged in the capacitor. The magnitude of the voltage charged in the capacitor corresponds to the _{V Data voltage.} Regardless of the magnitude of the V _{Data voltage, the magnitude (I Leakage} ) of the current flowing through the light emitting device (LED) is changed.

That is, the generation of the leakage current changes the amount of light originally set to be emitted by the light emitting device (LED), so that the color representation of the pixel becomes inaccurate and causes the quality of the display device to deteriorate. Accordingly, there is a need for a method capable of preventing leakage current of the pixel driving circuit.

Republic of Korea Patent Publication No. 10-2017-0111788

An object of the present specification is to provide a technology capable of preventing current leakage in a circuit for driving a pixel.

The present specification is not limited to the above-mentioned problems, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

A pixel driving circuit according to the present specification for solving the above problems includes: a first MOSFET connected on a pixel line connecting between positive and negative power; a light emitting diode connected between the first MOSFET and the positive power supply or between the first MOSFET and the negative power supply; a second MOSFET turned on by a signal output from the scan driving circuit connected to the gate terminal and outputting a signal output from the data driving circuit connected to the input terminal to the gate terminal of the first MOSFET to an output terminal; and a pixel capacitor connected between the gate terminal of the first MOSFET and the positive power supply or between the gate terminal of the first MOSFET and the negative power supply; wherein a preset leakage current prevention voltage is provided at the body terminal of the second MOSFET can be authorized

According to an embodiment of the present specification, the second MOSFET may be an N-type MOSFET, and the leakage current prevention voltage may be a voltage higher than a voltage for turning off the second MOSFET. In this case, the leakage current prevention voltage may be less than or equal to the lowest grayscale voltage of the signal output from the data driving circuit.

According to another embodiment of the present specification, the second MOSFET may be a P-type MOSFET, and the leakage current preventing voltage may be lower than a voltage for turning off the second MOSFET. In this case, the leakage current preventing voltage may be greater than or equal to the highest grayscale voltage of the signal output from the data driving circuit.

A pixel driving circuit according to the present specification includes: a display panel including a plurality of pixel driving circuits; a scan driving circuit connected to any one of the plurality of scan lines to drive the pixel driving circuits arranged in a row direction; and a data driving circuit for outputting signals related to driving of a plurality of light emitting devices included in each pixel to the pixel driving circuits arranged in the longitudinal direction through a plurality of data lines; have.

The scan driving circuit according to the present specification may turn on a plurality of pixel driving circuits included in the pixel at different times. In addition, the display device according to the present specification may further include a demultiplexer for connecting the data driving circuit and a plurality of pixel driving circuits included in the pixel at different time points.

In this case, the scan driving circuit may turn on each pixel driving circuit included in the pixel for a preset charging time, and the charging times of each pixel driving circuit may be spaced apart.

The demultiplexer may connect the data driving circuit and each pixel driving circuit included in the pixel for a longer time than the charging time.

In addition, the signal related to driving of the plurality of light emitting devices may include a voltage for charging the parasitic capacitor.

Other specific details of the invention are included in the detailed description and drawings.

According to the present specification, it is possible to more accurately drive a pixel by minimizing a leakage current. Through this, accurate color expression and reproducibility can be improved even in small displays using micro LEDs.

Effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

1 is a block diagram schematically illustrating the configuration of a general display device.
FIG. 2 is a signal timing reference diagram for inputting data to a pixel included in the display device shown in FIG. 1 .
3 is an exemplary diagram of a general pixel driving circuit.
4 is a circuit diagram of a pixel driving circuit according to the first embodiment of the present specification.
5 is a circuit diagram of a pixel driving circuit according to a second embodiment of the present specification.
6 is a circuit diagram of a pixel driving circuit according to a third embodiment of the present specification.
7 is a circuit diagram of a pixel driving circuit according to a fourth embodiment of the present specification.
8 is a schematic configuration diagram of a display device ( ) according to the present specification.
9 is a block diagram of a demultiplexer according to the present specification.

Advantages and features of the invention disclosed herein, and methods of achieving them, will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present specification is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only the present embodiments allow the disclosure of the present specification to be complete, and those of ordinary skill in the art to which this specification belongs. It is provided to fully inform those skilled in the art (hereinafter 'those skilled in the art') the scope of this specification, and the scope of the present specification is only defined by the scope of the claims.

The terminology used herein is for the purpose of describing the embodiments and is not intended to limit the scope of the present specification. As used herein, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, “comprises” and/or “comprising” does not exclude the presence or addition of one or more other components in addition to the stated components. Like reference numerals refer to like elements throughout, and "and/or" includes each and every combination of one or more of the recited elements. Although "first", "second", etc. are used to describe various elements, these elements are not limited by these terms, of course. These terms are only used to distinguish one component from another. Accordingly, it goes without saying that the first component mentioned below may be the second component within the spirit of the present invention.

Unless otherwise defined, all terms (including technical and scientific terms) used herein may have the meaning commonly understood by those of ordinary skill in the art to which this specification belongs. In addition, terms defined in a commonly used dictionary are not to be interpreted ideally or excessively unless specifically defined explicitly.

In the following embodiments, “ON” used in connection with a device state may refer to an activated state of the device, and “OFF” may refer to an inactive state of the device. As used in connection with a signal received by a device, “on” may refer to a signal that activates a device, and “off” refers to a signal that deactivates a device. The device can be activated by a high voltage or a low voltage. For example, a P-type MOSFET is activated by a low voltage at the gate terminal, and an N-type MOSFET is activated by a high voltage. Accordingly, it should be understood that the "on" voltages for a P-type and N-type transistor are opposite (low vs. high) voltage levels.

When an element is referred to as being “connected to” or “coupled to” another element with another element, it means that it is directly connected or coupled to another element, or with the other element intervening. including all cases. On the other hand, when one element is referred to as "directly connected to" or "directly coupled to" with another element, it indicates that another element is not interposed therebetween.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

4 is a circuit diagram of a pixel driving circuit according to the first embodiment of the present specification.

5 is a circuit diagram of a pixel driving circuit according to a second embodiment of the present specification.

6 is a circuit diagram of a pixel driving circuit according to a third embodiment of the present specification.

7 is a circuit diagram of a pixel driving circuit according to a fourth embodiment of the present specification.

4 to 7 , the pixel driving circuit 100 according to the present specification may include a first MOSFET M1, a light emitting diode LED, a second MOSFET M2, and a pixel capacitor C _X . have.

The first MOSFET M1 may be connected on a pixel line connecting between the positive power Vcc and the negative power GND.

The light emitting diode LED may be connected between the first MOSFET M1 and the positive power supply Vcc or between the first MOSFET M1 and the negative power supply GND. The light emitting diode may be red (R), green (G), blue (B), or white (W), and may have various other colors. Also, the light emitting diode (LED) may be a micro LED (typically an LED having a width of 1 to 100 μm) or an OLED.

The second MOSFET M2 is turned on by a signal output from the scan driving circuit 120 connected to the gate terminal, and the signal output from the data driving circuit 130 connected to the input terminal is applied to the first MOSFET The gate terminal of (M1) can output to the output terminal.

The pixel capacitor C _X may be connected between the gate terminal of the first MOSFET M1 and the positive power Vcc or between the gate terminal of the first MOSFET M1 and the negative power GND. The pixel capacitor C _X serves to store a signal related to the brightness of light to be output by the light emitting diode LED during one frame, that is, a voltage. That is, the pixel driving circuit 100 according to the present specification may be a circuit for an analog driving type pixel.

Differences between the embodiments shown in FIGS. 4 to 7 will be described. In the first embodiment shown in FIG. 4 and the third embodiment shown in FIG. 6 , the first MOSFET M1 is an N-type MOSFET, and the second embodiment shown in FIG. 5 and the fourth embodiment shown in FIG. 7 . In an embodiment, the first MOSFET M1 is a P-type MOSFET. In the first and third embodiments, the light emitting diode (LED) is connected between the positive power supply (Vcc) and the first MOSFET (M1), and the pixel capacitor (C _X ) is the first MOSFET (M1) ) and connected between the negative power supply (GND). In the second and fourth embodiments, the light emitting diode (LED) is connected between the first MOSFET (M1) and the negative power supply (GND), and the pixel capacitor (C _X ) is the positive power supply (Vcc). ) and the gate terminal of the first MOSFET M1. That is, a connection position of the light emitting diode LED and the pixel capacitor C _{X may be determined according to the type of the first MOSFET M1 .} On the other hand, the portion connected to the remaining terminals of the first MOSFET M1, that is, the portion connected to the opposite side to the light emitting diode (LED), represents the remaining elements necessary for the pixel driving circuit 100 according to the present specification, and those of ordinary skill Various known elements may be included in the box.

Meanwhile, the pixel driving circuit 100 according to the present specification is characterized in that a preset leakage current prevention voltage is applied to the body terminal of the second MOSFET M2. The level of the leakage current prevention voltage may be different depending on the type of the second MOSFET M2. First, the magnitude of the leakage current prevention voltage will be described while explaining the operation of the first embodiment shown in FIG. 4 .

In the first embodiment shown in FIG. 4 , the second MOSFET M2 is an N-type MOSFET. _{The signal V Scan} output from the scan driving circuit 120 may have a size of 0V to VA _{A. The signal V Scan} output from the scan driving circuit 120 may be input to the gate terminal of the second MOSFET M2 . Accordingly, the second MOSFET M2 may be turned off at 0V and turned on _{at V A .} While the second MOSFET M2 is turned on, the data driving circuit 130 may output a signal V _Data related to driving of the light emitting diode LED to the second MOSFET M2 . _{The signal V Data} output from the data driving circuit 130 may have a size between V ₁ to V _{2 .} In the first embodiment, V ₁ may correspond to the lowest gray voltage, and V ₂ may correspond to the highest gray voltage. _{The signal V Data} output from the data driving circuit 130 is stored in the pixel capacitor C _X , and then the second MOSFET M2 is turned off. In the prior art, after the second MOSFET M2 is turned off, a leakage current may be generated by the voltage stored in _{the pixel capacitor C X .} However, in the pixel driving circuit 100 according to the present specification, a voltage having a preset magnitude is applied to the body terminal of the second MOSFET M2 to prevent leakage current. In the first embodiment, the leakage current prevention voltage may have a magnitude _{of V 1 .}

The second embodiment shown in FIG. 5 differs in that the type of the first MOSFET M1 is P-type. Accordingly, among the _{signals V Data} output from the data driving circuit 130 _{, V 1} may correspond to the highest gradation voltage, and V ₂ may correspond to the lowest gradation voltage. However, the leakage current prevention voltage may have the same magnitude _{as V 1 .}

The third embodiment shown in FIG. 6 differs in that the type of the second MOSFET M2 is a P type. In this case, the second MOSFET M2 may be turned off at 0V and turned off at V _A . In the third embodiment, the leakage current prevention voltage may have a magnitude _{of V 2 .}

Finally, the fourth embodiment shown in FIG. 7 differs in that the type of the first MOSFET M1 is P-type and the type of the second MOSFET M2 is P-type. Accordingly, among the _{signals V Data} output from the data driving circuit 130 _{, V 1} may correspond to the highest gradation voltage, and V ₂ may correspond to the lowest gradation voltage. In addition, the second MOSFET M2 may be turned off at 0V and turned on at V _A . In the fourth embodiment, the leakage current prevention voltage may have a magnitude _{of V 2 .}

To summarize what has been described above, it is as follows. When the second MOSFET M2 is an N-type MOSFET, the leakage current prevention voltage may be higher than a voltage that turns off the second MOSFET M2 . In addition, the leakage current prevention voltage may be less than or equal to the lowest grayscale voltage of the signal output from the data driving circuit 130 . When the second MOSFET M2 is a P-type MOSFET, the leakage current prevention voltage may be lower than a voltage that turns off the second MOSFET M2 . In addition, the leakage current prevention voltage may be greater than or equal to the highest grayscale voltage of the signal output from the data driving circuit 130 .

Meanwhile, the pixel driving circuit 100 according to the present specification may be a component of a display device.

8 is a schematic configuration diagram of a display device according to the present specification.

The display device according to the present specification may include a display panel 110 , a scan driving circuit 120 , a data driving circuit 130 , and a controller 140 . The display panel 110 may include a plurality of pixels. Each pixel may include the pixel driving circuit 100 according to the present specification. Since each pixel may include a plurality of light emitting devices, each pixel may include a plurality of pixel driving circuits 100 . The scan driving circuit 120 may be connected to any one of a plurality of scan lines to drive pixel driving circuits arranged in a row direction. The data driving circuit 130 may output a signal related to driving of a plurality of light emitting devices included in each pixel to the pixel driving circuits arranged in the vertical direction through a plurality of data lines. Other matters are the same as or similar to those of the display device illustrated in FIG. 1 , or detailed descriptions thereof will be omitted since they may be sufficiently added to the level of those skilled in the art.

Meanwhile, the display device according to the present specification may further include a configuration for preventing leakage current. Referring to FIG. 8 , it can be seen that the demultiplexer 131 is illustrated in the data driving circuit 130 unlike the conventional display device. The prevention of leakage current through the demultiplexer 131 will be described.

9 is a block diagram of a demultiplexer according to the present specification.

Referring to FIG. 9 , it can be seen that video data is input from the left side of the demultiplexer 131 . The video data is a signal output from the data driving circuit 130 . The demultiplexer 131 may connect the data driving circuit 130 and the plurality of pixel driving circuits 100 included in the pixel at different times. In addition, the scan driving circuit 120 may turn on the plurality of pixel driving circuits 100 included in the pixel at different times. Accordingly, signals may be sequentially input to the pixel driving circuit at different times.

_{Meanwhile, in FIG. 9 , a parasitic capacitor C Y} positioned between the plurality of pixel driving circuits 100 and the demultiplexer 131 can be seen. The parasitic capacitor C _Y represents a capacitor that may be generated by the characteristics of a material in the process of configuring the display panel 110 as an equivalent circuit. Since the parasitic capacitor C _{Y is generated in a larger area than the pixel capacitor C X} included in each pixel driving circuit 100 , it may have a relatively larger capacitance. For example, if _{the size of the pixel capacitor C X} is about a femto (10 ^-15 , f)F, the parasitic capacitor C _Y has a capacity of about a pico (10 ^{-12, p)F} can

9 shows timings with respect to the turn-on time of each switching element. The scan driving circuit 120 according to the present specification turns on each pixel driving circuit 100 included in the pixel for a preset charging time, and the charging times of each pixel driving circuit 100 may be spaced apart. . In addition, the demultiplexer 131 may connect the data driving circuit 130 and each pixel driving circuit 100 included in the pixel for a longer time than the charging time.

For example, a grayscale voltage related to driving a pixel may be applied to a _{pixel capacitor C X_R} related to a red LED during a time when the SW-R switch and V _{Scan_R are turned on together.} Thereafter, although the V _{Scan_R} is turned off, the SW-R switch may further maintain a turned-on state for a predetermined time. In this case, the parasitic capacitor C _{X_R} related to the red LED may be charged more than the red LED and the pixel capacitor C _{X_R .} Thereafter, the SW-R switch is also turned off, and the red LED and the pixel capacitor C _{X_R} are in a floating state until the red LED and the pixel capacitor C _{X_R are next charged.} As described above with reference to FIGS. 4 to 7 , the V _Scan signal is a signal for turning on or off the second MOSFET M2, and the problem is that leakage current occurs after the second MOSFET M2 is turned off. _{At this time, since the parasitic capacitor C Y} in a state in which a constant voltage is charged is connected to the input terminal of the second MOSFET M2 , current leakage from the _{pixel capacitor C X can be prevented.} Other switch elements in the demultiplexer 131 may operate in the same manner. On the other hand, Figure 9 shows the V _Scan time is turned, the parasitic capacitor (C _X) after being off more charge is set variously in consideration of the size and the capacity or the pixel capacitor (C _X) of the parasitic capacitor (C _Y) can Also, when outputting a signal related to driving of the plurality of light emitting devices, the data driving circuit 130 may include a voltage for charging _{the parasitic capacitor C Y .}

On the other hand, although it is illustrated that the demultiplexer 131 is included in the data driving circuit 130 for convenience of understanding and simplification of the drawing, it is possible to exist outside the data driving circuit 130 or to exist only a part of it outside. Do.

In the above, the embodiments of the present specification have been described with reference to the accompanying drawings, but those of ordinary skill in the art to which this specification belongs can realize that the present invention may be embodied in other specific forms without changing the technical spirit or essential features thereof. you will be able to understand Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

100: pixel driving circuit
110: display panel 120: scan driving circuit
130: data driving circuit 131: demultiplexer
140: control unit

Claims (1)

a first MOSFET connected on a pixel line connecting between the positive and negative power;
a light emitting diode connected between the first MOSFET and the positive power supply or between the first MOSFET and the negative power supply;
a second MOSFET turned on by a signal output from the scan driving circuit connected to the gate terminal and outputting a signal output from the data driving circuit connected to the input terminal to the gate terminal of the first MOSFET to an output terminal; and
A pixel driving circuit comprising: a pixel capacitor connected between the gate terminal of the first MOSFET and the positive power supply or between the gate terminal of the first MOSFET and the negative power supply,
A pixel driving circuit, characterized in that a preset leakage current prevention voltage is applied to the body terminal of the second MOSFET.

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