CN112970055A - Pixel circuit, display device, driving method of pixel circuit, and electronic apparatus - Google Patents

Abstract

Provided is a pixel circuit provided with: a light-emitting Element (EL); a drive transistor (T2) having a first terminal connected to the anode of the light-emitting Element (EL); a sampling transistor (T3) having a second terminal connected to the gate of the drive transistor (T2) and sampling the signal voltage written to the drive transistor (T2); a light emission control transistor (T1) having a first terminal connected to the second terminal of the drive transistor (T2) and a second terminal connected to a power supply line for supplying a power supply voltage; and a reset transistor (T4) that resets the anode of the light emitting Element (EL) to a predetermined potential at a predetermined timing, the pixel circuit turning on the light emission control transistor (T1) and writing the power supply voltage to the second terminal of the drive transistor (T2) before the signal voltage is switched from the video signal of the previous frame to the threshold correction reference potential of the drive transistor (T2).

Description

Pixel circuit, display device, driving method of pixel circuit, and electronic apparatus

Technical Field

The present disclosure relates to a pixel circuit, a display device, a driving method of the pixel circuit, and an electronic apparatus.

Background

In recent years, in the field of display devices, a flat-type (flat-panel type) display device in which pixels including light emitting sections are arranged in a row and a column (matrix) has been mainstream. As one of the flat display devices, there is a so-called current-driven Electro-optical device using a light emission luminance that varies depending on a value of a current flowing through a light emitting portion, for example, an organic EL display device using an organic Electro Luminescence (EL) device.

In a flat display device such as this organic EL display device, transistor characteristics (for example, threshold voltage) of a driving transistor for driving an electro-optical element may vary from pixel to pixel due to process variations and the like. For example,patent document 1 discloses a technique of a display device capable of shortening the time for writing an initialization voltage to a gate node of a driving transistor when performing a correction operation of the characteristics of the driving transistor.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-34861.

Disclosure of Invention

Problems to be solved by the invention

However, when an image having a specific pattern is to be displayed, if a correction operation of the characteristics of the driving transistor is performed by using the technique disclosed inpatent document 1 or the like, for example, a phenomenon called lateral crosstalk may occur in which a luminance difference occurs in a white display portion.

Accordingly, in the present disclosure, a novel and improved pixel circuit, a display device, a driving method of a pixel circuit, and an electronic apparatus capable of preventing lateral crosstalk from occurring when an image having a specific pattern is displayed are proposed.

Means for solving the problems

According to the present disclosure, there is provided a pixel circuit including: a light emitting element; a driving transistor having a first terminal connected to an anode of the light emitting element; a sampling transistor, a second terminal of which is connected to the gate of the driving transistor, for sampling a signal voltage written in the driving transistor; a light emission control transistor having a first terminal connected to the second terminal of the driving transistor and a second terminal connected to a power supply line for supplying a power supply voltage; and a reset transistor that resets the anode of the light-emitting element to a predetermined potential at a predetermined timing, wherein the pixel circuit turns on the light emission control transistor and writes the power supply voltage to the second terminal of the drive transistor before the signal voltage is switched from the video signal of the previous frame to the threshold correction reference potential of the drive transistor.

Further, according to the present disclosure, there is provided a method of driving a pixel circuit, the pixel circuit including: a light emitting element; a driving transistor having a first terminal connected to an anode of the light emitting element; a sampling transistor, a second terminal of which is connected to the gate of the driving transistor, for sampling a signal voltage written in the driving transistor; a light emission control transistor having a first terminal connected to the second terminal of the driving transistor and a second terminal connected to a power supply line for supplying a power supply voltage; and a reset transistor that resets the anode of the light emitting element to a predetermined potential at a predetermined timing, the driving method of the pixel circuit including turning on the light emission control transistor and writing the power supply voltage to the second terminal of the drive transistor before the signal voltage is switched from the video signal of the previous frame to the threshold correction reference potential of the drive transistor.

Drawings

Fig. 1 is an explanatory diagram illustrating a configuration example of adisplay device 100 according to an embodiment of the present disclosure.

Fig. 2 is an explanatory diagram showing a more detailed configuration example of thedisplay device 100 of the same embodiment.

Fig. 3 is an explanatory diagram showing a more detailed configuration example of thedisplay device 100 of the same embodiment.

Fig. 4 is an explanatory diagram showing an extraction of the pixel circuit shown in fig. 3.

Fig. 5 is an explanatory diagram showing a comparative example of a driving method of thedisplay device 100 of the same embodiment.

Fig. 6 is an explanatory diagram showing an example of a display pattern displayed on thedisplay device 100.

Fig. 7 is an explanatory diagram showing an example of the driving timing in the comparative example.

Fig. 8 is an explanatory diagram showing an example of the driving timing in the comparative example.

Fig. 9 is an explanatory diagram showing an example of the driving timing in the comparative example.

Fig. 10 is an explanatory diagram showing an example of the driving timing in the comparative example.

Fig. 11 is an explanatory diagram illustrating a driving method of thedisplay device 100 according to the same embodiment.

Fig. 12 is an explanatory diagram showing an example of the driving timing.

Fig. 13 is an explanatory diagram showing an example of the driving timing.

Fig. 14 is an explanatory diagram showing an example of the driving timing.

Fig. 15 is an explanatory diagram illustrating a driving method of thedisplay device 100 according to the same embodiment.

Fig. 16 is an explanatory diagram illustrating a modification of the pixel circuit of thedisplay device 100 according to the same embodiment.

Fig. 17 is an explanatory diagram illustrating a driving example in thedisplay device 100 provided with the pixel circuit illustrated in fig. 16.

Fig. 18 is an explanatory diagram illustrating a driving example in thedisplay device 100 provided with the pixel circuit illustrated in fig. 16.

Fig. 19 is an explanatory diagram illustrating a driving example in thedisplay device 100 provided with the pixel circuit illustrated in fig. 16.

Fig. 20 is an explanatory diagram illustrating a driving example in thedisplay device 100 provided with the pixel circuit illustrated in fig. 16.

Detailed Description

Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configurations are denoted by the same reference numerals, and redundant description thereof is omitted.

The description is made in the following order.

1. Embodiments of the present disclosure

1.1. Description of the display device, the method of driving the display device, and the electronic apparatus according to the present disclosure

1.2. Example of configuration and operation

1.3. Modification example

2. Summary of the invention

<1 > embodiments of the present disclosure

[1.1 ] general description of a display device, a method of driving the display device, and an electronic apparatus according to the present disclosure ]

The display device of the present disclosure is a flat-type (flat-panel type) display device, and is configured by arranging a pixel circuit having a sampling transistor and a holding capacitor in addition to a driving transistor that drives a light emitting section. Examples of the flat display device include an organic EL display device, a liquid crystal display device, and a plasma display device. Among these display devices, an organic EL display device uses electroluminescence of an organic material, and uses an organic EL element, which utilizes a phenomenon of light emission when an electric field is applied to an organic thin film, as a light emitting element (electro-optical element) of a pixel.

An organic EL display device using an organic EL element as a light emitting portion of a pixel has the following characteristics. That is, since the organic EL element can be driven with an applied voltage of 10V or less, the organic EL display device consumes less power. Since the organic EL element is a self-luminous element, the organic EL display device has higher image visibility than a liquid crystal display device which is the same flat display device, and since an illuminating member such as a backlight is not required, it is easy to reduce the weight and thickness. Further, since the response speed of the organic EL element is very high, being about several microseconds, the organic EL display device does not generate a residual image when displaying a moving image.

The organic EL element is a self-light-emitting element, and is an electro-optical element of a current-driven type. As the current-driven electro-optical element, an inorganic EL element, an LED element, a semiconductor laser element, and the like can be exemplified in addition to the organic EL element.

A flat display device such as an organic EL display device can be used as a display unit (display device) in various electronic apparatuses including the display unit. As various electronic devices, in addition to the television system, the following can be exemplified: head mounted displays, Digital cameras, video cameras, game machines, notebook Personal computers, portable information devices such as electronic books, Personal Digital Assistants (PDAs), and portable communication devices such as cellular phones.

In the display device, the method of driving the display device, and the electronic apparatus of the present disclosure, the driving section may be configured to bring the source node into a floating state after bringing the gate node of the driving transistor into a floating state. In addition, the driving unit may be configured such that the signal voltage is written by the sampling transistor while the source node of the driving transistor is kept in a floating state. The initialization voltage can be configured as follows: is supplied to the signal line at a timing different from the signal voltage, and is written from the signal line to the gate node of the driving transistor by sampling by the sampling transistor.

In the display device, the method for driving the display device, and the electronic apparatus of the present disclosure including the above-described preferred configurations, the pixel circuit can be configured to be formed on a semiconductor such as silicon. In addition, the driving transistor can be formed as a P-channel transistor. For the following reason, a P-channel transistor is used as the driving transistor instead of an N-channel transistor.

In the case where a transistor is formed not on an insulator such as a glass substrate but on a semiconductor such as silicon, the transistor is not three terminals of source/gate/drain but four terminals of source/gate/drain/back gate (base). In addition, when an N-channel transistor is used as the driving transistor, the back gate (substrate) voltage is 0V, which has an adverse effect on operations of correcting variations in the threshold voltage of the driving transistor for each pixel.

In addition, compared with an N-channel transistor having an LDD (Lightly Doped Drain) region, a P-channel transistor not having an LDD region has a smaller variation in transistor characteristics, and is advantageous in miniaturizing a pixel and further in miniaturizing a display device. For this reason, when it is assumed that the driving transistor is formed on a semiconductor such as silicon, it is preferable to use a P-channel transistor instead of an N-channel transistor as the driving transistor.

In the display device, the method for driving the display device, and the electronic apparatus of the present disclosure including the above-described preferred configurations, the sampling transistor may be formed of a P-channel transistor.

Alternatively, in the display device, the method for driving the display device, and the electronic apparatus of the present disclosure including the above-described more preferable configuration, the pixel circuit may be configured to include a light emission control transistor for controlling emission/non-emission of the light emitting portion. In this case, the light emission control transistor may be formed of a P-channel transistor.

Alternatively, in the display device, the display device driving method, and the electronic apparatus according to the present disclosure including the above-described more preferable configuration, the storage capacitor may be connected between the gate node and the source node of the driving transistor. In addition, the pixel circuit can be configured to have an auxiliary capacitance connected between the source node of the driving transistor and a node of a fixed potential.

Alternatively, in the display device, the method for driving the display device, and the electronic apparatus of the present disclosure including the above-described more preferable configuration, the pixel circuit may be configured to have a switching transistor connected between the drain node of the driving transistor and the cathode node of the light emitting portion. In this case, the switching transistor may be formed of a P-channel transistor. In addition, the driving unit may be configured such that the switching transistor is turned on during a period in which the light emitting unit is not emitting light.

Alternatively, in the display device, the display device driving method, and the electronic apparatus according to the present disclosure including the above-described preferred configurations, the driving unit may set the signal for driving the switching transistor to the active state before the sampling timing of the initialization voltage of the sampling transistor. In addition, the light emission control transistor can be configured to be in an inactive state after a signal for driving the light emission control transistor is in an active state. In this case, the driving unit may be configured as follows: before a signal for driving the light emission control transistor is set to an inactive state, the sampling of the initialization voltage of the sampling transistor is completed.

[1.2. configuration example and operation example ]

Next, a configuration example of the display device according to the embodiment of the present disclosure will be described. Fig. 1 is an explanatory diagram illustrating a configuration example of adisplay device 100 according to an embodiment of the present disclosure. Hereinafter, a configuration example of thedisplay device 100 according to the embodiment of the present disclosure will be described with reference to fig. 1.

Thepixel portion 110 has a structure in which pixels each provided with an organic EL element and another self-luminous element are arranged in a matrix. Thepixel unit 110 includes scanning lines in a horizontal direction in units of rows with respect to pixels arranged in a matrix, and signal lines in columns orthogonal to the scanning lines.

Thehorizontal selector 120 sequentially transfers predetermined sampling pulses and sequentially latches image data by the sampling pulses, thereby distributing the image data to the respective signal lines. Further, thehorizontal selector 120 performs analog-to-digital conversion processing on the image data assigned to each signal line, respectively, thereby generating a drive signal representing the light emission luminance of each pixel connected to each signal line in a time-division manner. Thehorizontal selector 120 outputs the driving signal to the corresponding signal line.

Thevertical scanner 130 generates a drive signal for each pixel in response to the driving of the signal line of thehorizontal selector 120, and outputs the drive signal to the scanning line SCN. Accordingly, thedisplay device 100 sequentially drives the pixels arranged in thepixel portion 110 by thevertical scanner 130, and causes the pixels to emit light at the signal level of each signal line set by thehorizontal selector 120, thereby displaying a desired image in thepixel portion 110.

Fig. 2 is an explanatory diagram illustrating a more detailed configuration example of thedisplay device 100 according to the embodiment of the present disclosure. Hereinafter, a configuration example of thedisplay device 100 according to the embodiment of the present disclosure will be described with reference to fig. 2.

In thepixel unit 110,pixels 111R for displaying red,pixels 111G for displaying green, andpixels 111B for displaying blue are arranged in a matrix.

Thevertical scanner 130 includes an auto-zeroscanner 131, adrive scanner 132, and awrite scanner 133. By supplying signals from the scanners to the pixels arranged in a matrix in thepixel portion 110, on/off operations of the TFTs provided in the pixels are performed.

Fig. 3 is an explanatory diagram illustrating a more detailed configuration example of thedisplay device 100 according to the embodiment of the present disclosure. Hereinafter, a configuration example of thedisplay device 100 according to the embodiment of the present disclosure will be described with reference to fig. 3.

Fig. 3 illustrates a pixel circuit for one pixel arranged in a matrix in thepixel portion 110. The pixel circuit includes transistors T1 to T4, capacitors C1 and C2, and an organic EL element EL. Fig. 4 is an explanatory diagram showing an extraction of the pixel circuit shown in fig. 3.

The transistor T1 is a light emission control transistor that controls light emission of the organic EL element EL. The transistor T1 is connected between a power supply node of the power supply voltage VCCP and a source node (source electrode) of the transistor T2, and controls light emission/non-light emission of the organic EL element EL by being driven by a light emission control signal output from thedrive scanner 132.

The transistor T2 is a driving transistor for driving the organic EL element EL by causing a driving current corresponding to the holding voltage of the capacitor C2 to flow through the organic EL element EL.

The transistor T3 writes the signal voltage Vsig into the gate node (gate electrode) of the transistor T2 by sampling the signal voltage Vsig supplied from thewrite scanner 133.

The transistor T4 is a reset transistor connected between the drain node (drain electrode) of the transistor T2 and a current drain destination node (e.g., power supply VSS). The transistor T4 controls the organic EL element EL to emit no light during the non-emission period of the organic EL element EL under the drive of the drive signal from the auto-zeroscanner 131. The transistors T1 to T4 may be formed of P-channel transistors.

The capacitor C2 is connected between the gate node and the source node of the transistor T2, and holds a signal voltage Vsig written by sampling of the transistor T3. The capacitor C1 is connected between the source node of the transistor T2 and a node of a fixed potential (e.g., a power supply node of the power supply voltage VCCP). The capacitor C1 functions as follows: when the signal voltage is written, the source voltage variation of the transistor T2 is suppressed, and the gate-source voltage Vgs of the transistor T2 is set to the threshold voltage Vth of the transistor T2. Further, Cp is a parasitic capacitance between the signal line Data and the power supply voltage Vccp.

In thedisplay device 100, thepixel portion 110, thehorizontal selector 120, thevertical scanner 130, and the like are collectively formed on a transparent insulating substrate such as a glass substrate by polysilicon TFTs. Polysilicon TFTs cannot avoid variations in threshold voltage and mobility, and display devices using organic EL elements have a problem of deterioration in image quality due to these variations.

Therefore, it is conceivable to configure a pixel circuit with a circuit configuration shown in fig. 4, for example, and correct variations in threshold voltage and mobility of the driving transistor.

With regard to the driving method of thedisplay device 100 configured as described above, first, a driving method of a comparative example will be described with respect to the techniques prior to the technique of the present disclosure (i.e., the driving method of the embodiment).

Fig. 5 is an explanatory diagram illustrating a comparative example of a driving method of thedisplay device 100 according to the embodiment of the present disclosure. Fig. 5 shows the time passage of the horizontal synchronization signal XVD, the signal voltage Vdata, the signal DS from thedrive scanner 132, the signal WS from thewrite scanner 133, the signal AZ from the auto-zeroscanner 131. Fig. 5 also shows the Source potential Source and the Gate potential Gate of the transistor T2 and the time course of the Anode potential Anode of the organic EL element EL.

Until time t1, the light emission period of the previous frame is reached. Before time T1, signal DS changes from high to low, and transistor T1 changes from off to on. At time t1, signal AZ changes from high to low, the light emission period ends, and the extinction period starts. The reason for changing the signal AZ from high to low is to prevent a current from flowing into the organic EL element EL during a Vth correction period described later and the organic EL element EL emits light.

During a period from time t1 to t2, the signal voltage Vdata changes to the offset voltage Vofs. The offset voltage Vofs is a reference potential for Vth correction. Thereafter, at time T2, when the light extinction period ends and the Vth preparation period starts, the signal WS changes from high to low and the transistor T3 changes from off to on. When the transistor T3 is turned on, the gate of the transistor T2 is connected to the signal line Data, and the gate voltage of the transistor T2 falls to the offset voltage Vofs.

At time T3, the signal WS goes from low to high, and the transistor T3 turns from on to off. If the transistor T3 changes from on to off, the gate of the transistor T2 is disconnected from the signal line Data.

Thereafter, at time T4, the signal DS changes from low to high, and the transistor T1 changes from on to off. The pass signal DS is high, and enters the Vth correction period. During the Vth correction period, the gate-source voltage Vgs of the transistor T2 is set to the threshold voltage Vth of the transistor T2. Further, at time t5 during Vth correction, the signal AZ goes from low to high.

Thereafter, at time T6, the signal WS changes from high to low, and becomes a writing period of the signal voltage Vsig into the transistor T2. In this writing period, the gate potential of the transistor T2 becomes Vsig. At time T7, the signal WS goes from low to high, and the writing period of the signal voltage Vsig into the transistor T2 ends. At time T8, the signal DS changes from high to low, and the transistor T1 is turned on, thereby causing the organic EL element EL to emit light. In the light-emitting period, the source potential of the transistor T2 becomes the power supply voltage VCCP of the pixel circuit.

Fig. 6 is an explanatory diagram showing an example of a display pattern displayed on thedisplay device 100. As shown in fig. 6, a display pattern in which the background is made white (high gradation) and two black windows are provided therein is considered. Here, the line of only white (high-gradation) display pixels in the front stage (upper stage) of the black window is defined as the nth line, the first stage of the black window is defined as the n +1 th line, and the second stage of the black window is defined as the n +2 th line.

Fig. 7 is an explanatory diagram showing an example of the driving timing of the signal line Data of the nth row, the (n + 1) th row and the (n + 2) th row, the signal line Vccp for supplying the power supply voltage, and the signals WS, AZ and DS of the respective rows in the above comparative example.

Here, attention is paid to the fluctuation of the potential Vdata of the signal line Data. If the front stage of the nth row is white gray and Vsig is < Vofs, when the potential Vdata is switched to Vofs, the coupling enters the signal line Vccp in the positive potential direction via the parasitic capacitance Cp, and at this moment, the potential of the signal line Vccp increases by the coupling amount.

The potential supplied from the signal line Vccp is always supplied to all pixels through the metal power supply line, and therefore the potential of the signal line Vccp is about to return to Vccp, but if the wiring resistance increases by the enlargement and high definition of the pixel region, the slew rate becomes slow. At this time, the transistor T1 of the pixel circuit is turned on, and the potential Vccp is written to the source of the transistor T2.

However, if the potential Vccp is not returned to and the potential of the signal line Vccp is Vccp + α [ V ] even at the time point when the transistor T1 is turned off, the gate-source voltage Vgs of the transistor T2 at the start of Vth correction becomes larger.

For the n +1 th row, which is the starting row of the black window, the source voltage of the transistor T2 at the time of Vth correction also becomes Vccp + α [ V ] because the n-th row of the preceding row is white gradation.

On the other hand, for the n +2 th row, the black color signal is included in the previous row (Vsig > Vofs), the more black color signal pixels (i.e., the larger the width of the black window), the more the coupling enters the signal line Vccp in the negative potential direction when switching to Vofs. That is, the gate-source voltage Vgs of the transistor T2 during Vth correction tends to be small.

Fig. 8, 9, and 10 show the driving of the white pixels in the n-th row, the n + 1-th row, and the n + 2-th row in the above comparative example. In contrast to the driving of the n-th row and the n + 1-th row shown in fig. 8 and 9, in the driving of the n + 2-th row in fig. 10, the gate-source voltage Vgs of the transistor T2 before Vth correction becomes small as described above.

Thus, the gate potential Vg and the source potential Vs of the transistor T2 after correction in the n +2 th row become higher than those in the n +1 th row, and the gate-source voltage Vgs of the transistor T2 after writing the video signal in the n +2 th row becomes lower than those in the n +1 th row. That is, the current in the n +2 th row is smaller than the currents in the n +1 th row and the n +2 th row, and the white display in the n +2 th row is darker than the n +1 th row and the n +1 th row. That is, if the driving of the comparative example shown in fig. 5 is performed, the line becomes dark from the line next to the edge of the black window, and the crosstalk is visually recognized as shown in fig. 6.

Accordingly, in the embodiment of the present disclosure, there is provided a driving method of thedisplay device 100 that does not generate crosstalk in the case where the black window shown in fig. 6 is displayed.

Fig. 11 is an explanatory diagram illustrating a driving method of thedisplay device 100 of the embodiment of the present disclosure. Thedisplay device 100 according to the embodiment of the present disclosure has a different timing of transition of the state of the signal DS from thedrive scanner 132 than the comparative example described above. In the above comparative example, the signal DS changes from high to low in the light emission period of the previous frame, and after the potential of the signal line Data is switched to Vofs, the signal DS changes from low to high.

However, in thedisplay device 100 according to the embodiment of the present disclosure, the signal DS changes from high to low during the light emission period of the previous frame, and thereafter, the signal DS changes from low to high before the potential of the signal line Data is switched to Vofs. That is, thedisplay device 100 according to the embodiment of the present disclosure turns off the transistor T1 before the potential of the signal line Data is switched to Vofs.

Thedisplay device 100 according to the embodiment of the present disclosure is characterized in that the potential Vccp is written to the source of the transistor T2 without being affected by coupling by controlling the switching of the state of the signal DS in the above-described manner.

Fig. 12 to 14 are explanatory diagrams respectively illustrating driving of the n-th row, the n + 1-th row, and the n + 2-th row of the image shown in fig. 6 of thedisplay device 100 according to the embodiment of the present disclosure.

First, driving of the nth row of the image shown in fig. 6 of thedisplay device 100 according to the embodiment of the present disclosure will be described with reference to fig. 12. Fig. 12 shows the time passage of the horizontal synchronization signal XVD, the signal voltage Vdata, the signal DS from thedrive scanner 132, the signal WS from thewrite scanner 133, the signal AZ from the auto-zeroscanner 131. Fig. 12 also shows the Source potential Source and the Gate potential Gate of the transistor T2 and the time course of the Anode potential Anode of the organic EL element EL.

Until time t1, the light emission period of the previous frame is reached. Before time T1, signal DS changes from high to low, and transistor T1 changes from off to on. At time t1, signal AZ changes from high to low, the light emission period ends, and the extinction period starts. The reason for changing the signal AZ from high to low is to prevent a current from flowing into the organic EL element EL during a Vth correction period described later and the organic EL element EL emits light.

Next, at a time point of time T2, the signal DS changes from low to high, and the transistor T1 changes from on to off.

Thereafter, if the potential of the signal line Data changes to Vofs higher than Vsig at a point in time after the time t2 and before the time t3, coupling enters the signal line Vccp in the positive potential direction, and at that moment, the potential of the signal line Vccp rises by the coupling amount. However, at this point in time, the transistor T1 is turned off, and therefore the influence of the potential change of the signal line Vccp does not affect the source potential of the transistor T2. Therefore, even if the potential of the signal line Data changes to Vofs, the source potential of the transistor T2 is kept Vccp at Vref.

Thereafter, at time T3, when the light extinction period ends and the Vth preparation period starts, the signal WS changes from high to low and the transistor T3 changes from off to on. When the transistor T3 is turned on, the gate of the transistor T2 is connected to the signal line Data, and the gate voltage of the transistor T2 falls to the offset voltage Vofs.

At time T4, the signal WS goes from low to high, and the transistor T3 turns from on to off. If the transistor T3 changes from on to off, the gate of the transistor T2 is disconnected from the signal line Data. From time T4 into the Vth correction period, the gate-source voltage Vgs of the transistor T2 is set to the threshold voltage Vth of the transistor T2. Further, at time t5 in the Vth correction period, the signal AZ changes from low to high.

Thereafter, at time T6, the signal WS changes from high to low, and becomes a writing period of the signal voltage Vsig into the transistor T2. In this writing period, the gate potential of the transistor T2 becomes Vsig. At time T7, the signal WS goes from low to high, and the writing period of the signal voltage Vsig into the transistor T2 ends. At time T8, the signal DS changes from high to low, and the transistor T1 is turned on, thereby causing the organic EL element EL to emit light. In the light emission period, the source potential of the transistor T2 is the power supply voltage Vccp equal to Vref.

The same applies to the driving of the n +1 th row shown in fig. 13 and the driving of the n +2 th row shown in fig. 14. That is, in the present embodiment, the signal DS is high, and the source potential of the transistor T2 is not affected by coupling by changing the potential of the signal line Data at the timing when the transistor T1 is turned off.

As described above, thedisplay device 100 according to the embodiment of the present disclosure can prevent crosstalk from occurring when a special pattern such as a black window is displayed on a white background by controlling the switching of the state of the signal DS in the above manner, and can realize high-quality image display.

Thedisplay device 100 according to the embodiment of the present disclosure may write the potential Vofs to the gate of the transistor T2 in advance for one horizontal period or more before the horizontal period in which the Vth correction is performed. Fig. 15 is an explanatory diagram illustrating a driving method of thedisplay device 100 according to the embodiment of the present disclosure. Fig. 15 shows a case where the state of the signal line WS is changed in the (n + 1) th row and the (n + 2) th row in order to write the potential Vofs to the gate of the transistor T2 in the horizontal period immediately before the horizontal period for Vth correction.

By writing the electric potential Vofs to the gate of the transistor T2 in advance for one or more horizontal periods before the horizontal period for Vth correction, thedisplay device 100 according to the embodiment of the present disclosure can set the gate-source voltage of the transistor T2 at the start of Vth correction without being affected by the video signal of the previous frame.

Although the example in which the pixel circuit is configured by the P-type MOSFET has been described so far, even when the pixel circuit is configured by the N-type MOSFET, occurrence of crosstalk can be prevented and high-quality image display can be realized.

Fig. 16 is an explanatory diagram illustrating a modification of the pixel circuit in thedisplay device 100 according to the embodiment of the present disclosure. Fig. 16 shows a pixel circuit composed of four N-type MOSFETs.

The transistor T11 is a light emission control transistor that controls light emission of the organic EL element EL. The transistor T11 is connected between a power supply node of the power supply voltage VCCP and a source node (source electrode) of the transistor T12, and controls light emission/non-light emission of the organic EL element EL by being driven by a light emission control signal output from thedrive scanner 132.

The transistor T12 is a driving transistor, and drives the organic EL element EL by causing a driving current corresponding to the holding voltage of the capacitor C12 to flow through the organic EL element EL.

The transistor T13 writes the signal voltage Vsig into the gate node (gate electrode) of the transistor T12 by sampling the signal voltage Vsig supplied from thewrite scanner 133.

The transistor T14 is a reset transistor connected between the drain node (drain electrode) of the transistor T12 and a current drain destination node (e.g., power supply VSS). The transistor T14 controls the organic EL element EL to emit no light during the non-emission period of the organic EL element EL under the drive of the drive signal from the auto-zeroscanner 131. The transistors T11 to T14 may be formed of N-channel transistors.

In thedisplay device 100 including the pixel circuit shown in fig. 16, a case where an image having a black window shown in fig. 6 is displayed is considered. As described above, the line of only white (high gradation) display pixels in the front stage (upper stage) of the black window is defined as the nth line, the first stage of the black window is defined as the n +1 th line, and the second stage of the black window is defined as the n +2 th line.

Fig. 17 is an explanatory diagram illustrating an example of driving the (n + 1) th row in thedisplay device 100 including the pixel circuit shown in fig. 16. Fig. 18 is an explanatory diagram illustrating an example of driving the (n + 2) th row in thedisplay device 100 including the pixel circuit shown in fig. 16. Fig. 17 and 18 show the time passage of the signal voltage Vdata, the signal DS from thedrive scanner 132, the signal WS from thewrite scanner 133, and the signal AZ from the auto-zeroscanner 131. Fig. 17 and 18 also show the time transition of the source potential Vs and the gate potential Vg of the transistor T12. Fig. 17 and 18 also show the time course of the source potential Vs of the transistor T14.

At time t1, the signals WS, AZ go from low to high. Thereby, the transistors T13 and T14 are switched from off to on. When the transistor T13 is turned on, the gate potential of the transistor T12 becomes Vofs, and the source potential falls to Vss.

At time t2, signal AZ changes from high to low. Thereby, the transistor T14 is switched from on to off. With the transistor T14 turned off, the source potential Vs of the transistor T12 is disconnected from the power supply potential Vss, and starts rising due to the charge accumulated in the capacitor C12.

Thereafter, at time t3, signal WS changes from high to low. Thereby, the transistor T13 is switched from on to off. When the transistor T13 is turned off, the gate of the transistor T12 is disconnected from the signal line Data. At this time point t3, the potential of the signal line Data changes to Vsig.

Thereafter, at time t4, signal WS goes from low to high again. Thereby, the transistor T13 is switched from off to on. When the transistor T13 is turned on, the gate potential of the transistor T12 becomes Vsig.

Thereafter, at time t5, signal WS changes from high to low. Thereby, the transistor T13 is switched from on to off. At time t6, signal DS changes from high to low. Thereby, the transistor T11 is switched from on to off, and a current flows through the organic EL element EL, so that the organic EL element EL emits light.

When the pixel circuit shown in fig. 16 is driven in the above manner, when the signal voltage Vdata is switched from Vsig to Vofs at time T1, if there is no influence of coupling, the source potential of the transistor T12 changes as shown by the broken line. However, as described in the pixel circuit of the P-channel type, the potential of Vss written in the source of the transistor T12 fluctuates due to the influence of coupling via the parasitic capacitance.

In the pixel circuit of the n +1 th row shown in fig. 17 and the pixel circuit of the n +2 th row shown in fig. 18, the direction of the potential of the coupling changes, and the gate-source voltage Vgs of the transistor T12 at the start of Vth correction fluctuates during the Vth correction period from time T3 to T4. Further, the gate-source voltage Vgs of the transistor T12 after the video signal writing period from time T4 to T5 ends differs between the pixel circuit in the n +1 th row and the pixel circuit in the n +2 th row, and as a result, crosstalk occurs if thedisplay device 100 performs the driving shown in fig. 17 and 18.

Therefore, in the present embodiment, the timing of turning on and off the transistor T14, which determines the source node of the transistor T12 at the time of starting Vth correction, is set before the potential Vdata of the signal line is switched from Vsig in the preceding stage to Vofs. By performing the driving in the above manner, the present embodiment can perform the Vth correction of the transistor T12 without being affected by the coupling via the parasitic capacitance. In the present embodiment, the influence of coupling via the parasitic capacitance is eliminated, thereby preventing crosstalk from occurring.

Fig. 19 is an explanatory diagram illustrating a driving method of the (n + 1) th row in thedisplay device 100 including the pixel circuit shown in fig. 16 according to the present embodiment. In fig. 19, time passage of the signal voltage Vdata, the signal DS from thedrive scanner 132, the signal WS from thewrite scanner 133, and the signal AZ from the auto-zeroscanner 131 is shown. Fig. 19 also shows the time transition of the source potential Vs and the gate potential Vg of the transistor T12. Further, fig. 19 also shows a time passage of the source potential Vs of the transistor T14.

In the present embodiment, as shown in fig. 19, the signal AZ is switched from low to high at a time t1 before the potential Vdata of the signal line is switched from Vsig before to Vofs. By switching the signal AZ from low to high at the time point of time T1, the transistor T14 is switched from on to off. When the transistor T14 is turned off, even if the coupling when the signal voltage Vdata is switched from Vsig to Vofs enters the source potential Vs, the source potential Vs of the transistor T12 is not affected.

Therefore, thedisplay device 100 of the present embodiment can prevent crosstalk by performing the driving shown in fig. 19 to eliminate the influence of coupling via the parasitic capacitance.

Thedisplay device 100 according to the embodiment of the present disclosure may write the potential Vofs to the gate of the transistor T12 in advance for one horizontal period or more before the horizontal period for Vth correction.

Fig. 20 is an explanatory diagram illustrating a driving method of the (n + 1) th row in thedisplay device 100 including the pixel circuit shown in fig. 16 according to the present embodiment. The time passage of the signal voltage Vdata, the signal DS from thedrive scanner 132, the signal WS from thewrite scanner 133, and the signal AZ from the auto-zeroscanner 131 are shown in fig. 20. Fig. 20 also shows the time transition of the source potential Vs and the gate potential Vg of the transistor T12. Further, fig. 20 also shows a time passage of the source potential Vs of the transistor T14.

In the driving method shown in fig. 20, the signal WS is made high from low at a time point of time t1 in the horizontal period immediately preceding the horizontal period in which the Vth correction is performed. The transistor T13 becomes conductive by the signal WS going from low to high. When the transistor T13 is turned on, the potential Vofs is written to the gate of the transistor T12. At time T2, the potential of the signal line Data becomes Vsig, the signal WS changes from high to low, and the transistor T13 is turned off.

Thereafter, at a time point of time t3 before switching from Vsig of the preceding stage to Vofs, the signal AZ is switched from low to high. By switching the signal AZ from low to high at the time point of time T3, the transistor T14 switches from on to off. When the transistor T14 is turned off, even if the coupling when the signal voltage Vdata is switched from Vsig to Vofs enters the source potential Vs, the source potential Vs of the transistor T12 is not affected. Thereafter, the same driving as that shown in fig. 19 is performed.

Thus, thedisplay device 100 according to the embodiment of the present disclosure can set the gate-source voltage of the transistor T12 at the start of Vth correction without being affected by the video signal of the previous frame.

<2. summary >

As described above, according to the embodiments of the present disclosure, thedisplay device 100 can be provided, thedisplay device 100 can prevent crosstalk from occurring when a special pattern such as a black window is displayed on a white background, and can realize high-quality image display.

Also, an electronic device including the display device according to the embodiment of the present disclosure is also provided. An electronic device including the display device according to the embodiment of the present disclosure has two effects of optimizing contrast and preventing lateral crosstalk. Such electronic devices exist: mobile phones such as televisions and smartphones, tablet mobile terminals, personal computers, portable game machines, portable music playback devices, digital cameras, digital video cameras, watch-type mobile terminals, wearable devices, and the like.

Although the preferred embodiments of the present disclosure have been described in detail with reference to the drawings, the technical scope of the present disclosure is not limited to the above examples. It is obvious that a person having ordinary knowledge in the technical field of the present disclosure can conceive various modifications and alterations within the scope of the technical idea described in the claims, and it should be understood that these also belong to the technical scope of the present disclosure.

The effects described in the present specification are merely illustrative or exemplary and are not restrictive. That is, the technique of the present disclosure may produce other effects that are obvious to those skilled in the art from the description of the present specification, together with or instead of the above-described effects.

The following configurations also fall within the technical scope of the present disclosure.

(1) A pixel circuit includes:

a light emitting element;

a driving transistor having a first terminal connected to an anode of the light emitting element;

a sampling transistor, a second terminal of which is connected to the gate of the driving transistor, for sampling a signal voltage written in the driving transistor;

a light emission control transistor having a first terminal connected to the second terminal of the driving transistor and a second terminal connected to a power supply line for supplying a power supply voltage; and

a reset transistor that resets an anode of the light emitting element to a predetermined potential at a predetermined timing,

the pixel circuit turns on the light emission control transistor and writes the power supply voltage to the second terminal of the driving transistor before the signal voltage is switched from the video signal of the previous frame to the threshold correction reference potential of the driving transistor.

(2) The pixel circuit according to the (1), wherein,

the pixel circuit turns on the sampling transistor in one or more horizontal periods prior to a horizontal period in which the threshold correction of the driving transistor is performed, and sets a threshold correction reference potential to the gate of the driving transistor.

(3) The pixel circuit according to the (1) or (2), wherein,

the light emission control transistor is a P-channel transistor, and the first terminal of the light emission control transistor is a drain.

(4) The pixel circuit according to any one of the above (1) to (3), wherein,

the reset transistor is a P-channel type transistor.

(5) The pixel circuit according to any one of the items (1) to (4), wherein,

the driving transistor is a P-channel type transistor, the first terminal of the driving transistor is a drain, and the second terminal of the driving transistor is a source.

(6) The pixel circuit according to the (1) or (2), wherein,

the light emission control transistor is an N-channel transistor, and the first terminal of the light emission control transistor is a source.

(7) The pixel circuit according to any one of the (1), (2), and (6), wherein,

the reset transistor is an N-channel type transistor.

(8) The pixel circuit according to any one of the items (1), (2), (6), and (7), wherein,

the driving transistor is an N-channel type transistor, the first terminal of the driving transistor is a source, and the second terminal of the driving transistor is a drain.

(9) A display device is provided with:

a pixel array section in which the pixel circuit according to any one of (1) to (8) is arranged; and

and a drive circuit for driving the pixel array section.

(10) An electronic device is provided, which comprises a display panel,

a display device according to the above (9) is provided.

(11) A method of driving a pixel circuit, the pixel circuit comprising:

a light emitting element;

a driving transistor having a first terminal connected to an anode of the light emitting element;

a sampling transistor, a second terminal of which is connected to the gate of the driving transistor, for sampling a signal voltage written in the driving transistor;

a light emission control transistor having a first terminal connected to the second terminal of the driving transistor and a second terminal connected to a power supply line for supplying a power supply voltage; and

a reset transistor that resets an anode of the light emitting element to a predetermined potential at a predetermined timing,

the driving method of the pixel circuit includes turning on the emission control transistor and writing the power supply voltage to the second terminal of the driving transistor before the signal voltage is switched from the video signal of the previous frame to the threshold correction reference potential of the driving transistor.

Description of the symbols

100. A display device; 110. a pixel section; 111B, pixels; 111G, pixels; 111R, pixels; 120. a horizontal selector; 130. a vertical scanner; 131. an auto-zero scanner; 132. driving the scanner; 133. writing into a scanner; c1, a capacitor; c2, a capacitor; t1, a transistor; t2, a transistor; t3, a transistor; t4, transistor.

Claims (11)

1. A pixel circuit includes:

a light emitting element;

a driving transistor having a first terminal connected to an anode of the light emitting element;

a sampling transistor, a second terminal of which is connected to the gate of the driving transistor, for sampling a signal voltage written in the driving transistor;

a light emission control transistor having a first terminal connected to the second terminal of the driving transistor and a second terminal connected to a power supply line for supplying a power supply voltage; and

a reset transistor that resets an anode of the light emitting element to a predetermined potential at a predetermined timing,

the pixel circuit turns on the light emission control transistor and writes the power supply voltage to the second terminal of the driving transistor before the signal voltage is switched from the video signal of the previous frame to the threshold correction reference potential of the driving transistor.

2. The pixel circuit of claim 1,

the pixel circuit turns on the sampling transistor in one or more horizontal periods prior to a horizontal period in which the threshold correction of the driving transistor is performed, and sets a threshold correction reference potential to the gate of the driving transistor.

3. The pixel circuit of claim 1,

the light emission control transistor is a P-channel transistor, and the first terminal of the light emission control transistor is a drain.

4. The pixel circuit of claim 1,

the reset transistor is a P-channel type transistor.

5. The pixel circuit of claim 1,

the driving transistor is a P-channel type transistor, the first terminal of the driving transistor is a drain, and the second terminal of the driving transistor is a source.

6. The pixel circuit of claim 1,

the light emission control transistor is an N-channel transistor, and the first terminal of the light emission control transistor is a source.

7. The pixel circuit of claim 1,

the reset transistor is an N-channel type transistor.

8. The pixel circuit of claim 1,

the driving transistor is an N-channel type transistor, the first terminal of the driving transistor is a source, and the second terminal of the driving transistor is a drain.

9. A display device is provided with:

a pixel array section provided with the pixel circuit according to claim 1; and

and a drive circuit for driving the pixel array section.

10. An electronic device is provided, which comprises a display panel,

a display device according to claim 9 is provided.

11. A method of driving a pixel circuit, the pixel circuit comprising:

a light emitting element;

a driving transistor having a first terminal connected to an anode of the light emitting element;

a sampling transistor, a second terminal of which is connected to the gate of the driving transistor, for sampling a signal voltage written in the driving transistor;

a light emission control transistor having a first terminal connected to the second terminal of the driving transistor and a second terminal connected to a power supply line for supplying a power supply voltage; and

a reset transistor that resets an anode of the light emitting element to a predetermined potential at a predetermined timing,

the driving method of the pixel circuit includes turning on the emission control transistor and writing the power supply voltage to the second terminal of the driving transistor before the signal voltage is switched from the video signal of the previous frame to the threshold correction reference potential of the driving transistor.

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