JP4550372B2 - Active matrix display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an active matrix display device in which a display screen is configured by arranging display pixels including self-luminous elements such as organic electroluminescence (hereinafter referred to as EL) elements in a matrix.
[0002]
[Prior art]
2. Description of the Related Art Planar active matrix display devices are widely used as display devices for personal computers, portable information terminals, and televisions. In recent years, as such a flat-type active matrix display device, an organic EL display device using a self-luminous element such as an organic EL element has attracted attention and has been actively researched and developed. This organic EL display device does not require a backlight that obstructs the reduction in thickness and weight, is suitable for moving image reproduction because of its high-speed response, and further has a feature that it can be used even in cold regions because the luminance does not decrease at low temperatures. .
[0003]
In general, an organic EL display device includes a plurality of display pixels arranged in a plurality of rows and a plurality of columns and constituting a display screen, a plurality of scanning lines extending along each row of display pixels, and a column of display pixels. A plurality of extended signal lines, a scanning line driving circuit for driving each scanning line, a signal line driving circuit for driving each signal line, and the like are provided. Each display pixel includes an organic EL element that is a self-light-emitting element and a pixel circuit that supplies a drive current to the organic EL element. Each pixel circuit includes a pixel switch arranged in the vicinity of the intersection of the scanning line and the signal line, a driving transistor configured by a thin film transistor connected in series with an organic EL element between a pair of power supply lines, and a gate control voltage of the driving transistor The capacitor element that holds The pixel switch is turned on in response to the scanning signal supplied from the corresponding scanning line, and takes in the video signal supplied from the corresponding signal line. This video signal is written as a gate control voltage in the holding capacitor and held for a predetermined period. Then, the driving transistor supplies a current amount corresponding to the gate control voltage written in the storage capacitor to the organic EL element to perform a light emitting operation.
[0004]
An organic EL element has a structure in which a light emitting layer, which is a thin film containing a fluorescent organic compound, is sandwiched between a cathode electrode and an anode electrode, and excitons are injected by injecting electrons and holes into the light emitting layer and recombining them. And emits light by light emission generated when the exciton is deactivated. The organic EL element emits light with a luminance corresponding to the amount of supplied current, and is 100 to 100,000 cd / m even at an applied voltage of 10 V or less. ² A certain level of brightness can be obtained.
[0005]
In such an organic EL display device, a thin film transistor used as a driving transistor is formed using a semiconductor thin film formed on an insulating substrate such as glass. Therefore, drive transistor characteristics such as threshold voltage Vth and carrier mobility μ tend to vary depending on the manufacturing process and the like. When the threshold voltage Vth of the driving transistor varies, it is difficult to cause the organic EL element to emit light with appropriate luminance, and luminance variation occurs between a plurality of display pixels, causing display unevenness.
[0006]
Conventionally, in order to avoid such an influence due to the variation in the threshold voltage Vth, a display device in which a threshold cancel circuit is provided in all display pixels has been proposed (for example, Patent Document 1). Each threshold cancellation circuit is configured to initialize the control voltage of the driving transistor using a reset signal supplied from the signal line driving circuit prior to the video signal. As another display device, a display device has been proposed in which a video signal is written by a current signal to reduce the influence of variation in threshold voltage in a driving transistor and to uniform light emission luminance (for example, a patent). Reference 2).
[0007]
[Patent Document 1]
US Pat. No. 6,229,506
[0008]
[Patent Document 2]
US Pat. No. 6,373,454
[0009]
[Problems to be solved by the invention]
In the display device described above, the pixel circuit of each display pixel suppresses leakage current and maintains the gate control voltage of the driving transistor at a desired value, so that a plurality of switches are connected in series between the gate and drain of the driving transistor. Has been. Each of these switches is composed of a thin film transistor, and is simultaneously turned on and off. However, when these switches are switched from on to off, a feedthrough voltage ΔVp is generated due to a parasitic capacitance formed between the gate and source of the switch. When a plurality of switches are provided, the feedthrough voltage generated by these switches flows into the storage capacitor, and the gate control voltage of the driving transistor is changed. For this reason, variations occur in the gate control voltage of the drive transistor, resulting in luminance variations among a plurality of display pixels. Such variation in luminance between display pixels appears as display unevenness, which degrades display quality.
[0010]
The present invention has been made in view of the above points, and an object of the present invention is to provide an active matrix display device with reduced display unevenness and improved display quality.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, an active matrix display device according to an aspect of the present invention includes a plurality of display elements arranged in a matrix, a first terminal connected to a first power supply terminal, and a second terminal connected to the display. A driving transistor connected to the element and having a control terminal connected to the first terminal via a storage capacitor; and each of the driving transistors formed in a transistor and connected in series between the control terminal and the second terminal; A plurality of switches that are controlled to be turned on and off in response to a control signal, and the scanning line between the plurality of switches and the other switches except the switch provided on the most control terminal side of the driving transistor. A delay element connected to delay the on / off switching timing of the other switch with respect to the switch provided on the most control terminal side; It is characterized that there was example.
[0012]
An active matrix display device according to another aspect of the present invention includes a plurality of display pixels arranged in a matrix and a plurality of first and second pixels connected to each row of the display pixels and provided independently. A scanning line and a plurality of signal lines connected to each column of the display pixels,
Each display pixel includes a self-light emitting element that emits light in response to a supply current, a pixel switch that is on / off controlled according to a control signal from the first scanning line, and that captures a video signal on the signal line, and the pixel switch. A storage capacitor for holding a control voltage corresponding to the captured video signal, and the self-light emission according to the control voltage connected in series with the self-light-emitting element between the first and second voltage power supplies and held in the storage capacitor A driving transistor that outputs an amount of current supplied to the element, each formed by a thin film transistor, connected in series between the gate and drain of the driving transistor, and turned on / off in response to a control signal from the first scanning line A plurality of first switches that are connected between the drive transistor and the self-light-emitting element in response to a control signal from the second scan line. A second switch that is controlled to be turned on and off, and a first switch other than the first switch provided on the most gate side of the drive transistor among the plurality of first switches, and the first scanning line , And between the first scanning line and the pixel switch, and delays the on / off switching timing of the other first switch and the pixel switch with respect to the first switch on the most gate side. It is characterized by including an element.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an active matrix organic EL display device according to a first embodiment of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 1, the organic EL display device includes an organic EL panel 10 and a controller 12 that controls the organic EL panel 10.
[0014]
The organic EL panel 10 is arranged in a matrix on a light-transmitting insulating substrate 8 such as a glass plate, and is connected to each row of display pixels, each of which is connected to each row of display pixels mx that constitutes a display region 11. A first scanning line Y (1 to m) and a second scanning line Bg (1 to m) provided independently for each m lines, and n signal lines X (1) connected to each column of display pixels, respectively. N), a scanning line driving circuit 14 that sequentially drives the first and second scanning lines Y and Bg for each row of display pixels, and a signal line driving circuit 15 that drives the plurality of signal lines X1 to Xn. .
[0015]
Each display pixel PX includes an organic EL element 16 that functions as a display element and is a self-light-emitting element, and a pixel circuit 18 that supplies a drive current to the organic EL element. As shown in FIGS. 1 and 2, the pixel circuit 18 is a current signal type pixel circuit that controls light emission of the organic EL element 16 in accordance with a video signal including a current signal, and includes a pixel switch 20, a drive transistor 22, and a plurality of pixels. For example, three first switches 24a, 24b, and 24c, a second switch 26, a holding capacitor 28, and a resistance element 30 that functions as a delay element are provided. Here, the pixel switch 20, the driving transistor 22, the first switch 24, and the second switch 26 are configured by the same conductivity type, for example, a P-channel type thin film transistor. The resistance element 30 is formed of, for example, lightly doped drain (LDD) type polysilicon into which impurities are implanted, and the resistance value is set to several MΩ.
[0016]
The drive transistor 22 is connected in series with the organic EL element 16 between the first voltage power supply Vdd and the second voltage power supply Vss, and outputs a current amount corresponding to the video signal to the organic EL element. The first and second voltage power sources Vdd and Vss are set to potentials of +10 V and 0 V, for example. The storage capacitor 28 is connected between the first terminal and the control terminal of the drive transistor 22, here, between the source and the gate, and holds the gate control potential of the drive transistor 22 determined by the video signal. The pixel switch 20 is connected between the corresponding signal line X and the drain of the driving transistor 22, and its gate is connected to the corresponding first scanning line Y via the resistance element 30. The pixel switch 20 takes in the video signal from the corresponding signal line X in response to the control signal Sa supplied from the first scanning line Y.
[0017]
The first switches 24a, 24b, and 24c that function as switches in the present invention are connected in series between the second terminal and the control terminal of the driving transistor 22, here, the drain and the gate, and among these first switches, The first switch 24 a is connected closest to the gate side of the drive transistor 22. The gate of the first switch 24a connected to the most gate side of the driving transistor 22 is connected to the first scanning line Y without passing through the resistance element 30, and the gates of the other first switches 24b and 24c are respectively resistance elements. The first scanning line Y is connected through 30. The first switches 24a, 24b, and 24c are turned on (conductive state) and turned off (non-conductive state) in response to the control signal Sa from the first scanning line Y, and the connection between the gate and drain of the drive transistor 22 is performed. While controlling non-connection, current leakage from the storage capacitor 28 is regulated.
[0018]
The second switch 26 is connected between the drain of the drive transistor 22 and one electrode of the organic EL element 16, here, the anode, and the gate thereof is connected to the second scanning line Bg independent of the first scanning line Y. It is connected. The second switch 26 is ON / OFF controlled by the control signal Sb from the second scanning line Bg, and controls connection / disconnection between the drive transistor 22 and the organic EL element 16.
[0019]
In the present embodiment, the thin film transistors constituting the pixel circuit are all formed in the same process and the same layer structure, and are top gate thin film transistors using polysilicon as the semiconductor layer. By constituting all the thin film transistors with the same conductivity type, an increase in the number of manufacturing steps can be suppressed. The second switch 26 may be formed of a thin film transistor having a conductivity type different from that of the pixel switch 20 and the first switch 24, here, an n-type thin film transistor, and the gate of the second switch 26 may be controlled by the first scanning line Y. In this case, the gate of the second switch is preferably controlled with the same waveform as that of the pixel switch 20 and the first switches 24 b and 24 c, that is, it is preferably connected to the scanning line Y via the resistance element 30. As a result, the number of wirings in the display area can be reduced.
[0020]
Next, the configuration of the first switch, the drive transistor, and the organic EL element 16 will be described in detail with reference to FIG. Here, the first switch 24a among the first switches will be described as a representative.
The P-channel type thin film transistor that constitutes the drive transistor 22 and the first switch 24a includes a semiconductor layer 50 made of polysilicon formed on the light-transmissive insulating substrate 8, and the semiconductor layer includes a source region 50a and a drain region. 50b and a channel region 50c located between the source and drain regions. A gate insulating film 52 is formed over the semiconductor layer 50, and a gate electrode G is provided on the gate insulating film so as to face the channel region 50c. An interlayer insulating film 54 is formed over the gate electrode G, and a source electrode (source) S and a drain electrode (drain) D are provided on the interlayer insulating film. The source electrode S and the drain electrode D are connected to the source region 50a and the drain region 50c of the semiconductor layer 50 through contacts formed through the interlayer insulating film 54 and the gate insulating film 52, respectively. The drain electrode D of the first switch 24 a is connected to the gate electrode G of the drive transistor 22 through a wiring formed on the gate insulating film 52.
The thin film transistors constituting the pixel switch 20, the first switches 24b and 24c, and the second switch 26 are also formed in the same structure as described above. Of the three first switches 24a, 24b, 24c, the channel region 50c of the first switch 24a connected to the gate side of the driving transistor 22 is the channel of the other first switches 24b, 24c, pixel switch 20. The channel area is smaller than that of the region. In the present embodiment, the channel length L of the first switch 24 a is shorter than the channel length L of the first switches 24 b and 24 c and the pixel switch 20. For example, the channel length L of the first switch 24a is 3 μm, the channel length L of the first switches 24b and 24c is 4 to 9 μm, and the channel width is 3 μm in common for all switches.
[0021]
As shown in FIG. 3, a plurality of wirings are provided on the interlayer insulating film 54. A protective film 56 is formed on the interlayer insulating film 54 so as to cover the source electrode S, the drain electrode D, and the wiring. Further, a hydrophilic film 58 and a partition film 60 are laminated on the protective film 56 in this order.
[0022]
The organic EL element 16 has a structure in which an organic light emitting layer 64 containing a luminescent organic compound is sandwiched between an anode 62 and a cathode 66. The anode 62 is made of a transparent electrode material such as ITO (indium tin oxide) and is provided on the protective film 56. Of the hydrophilic film 58 and the partition wall film 60, the portion on the anode 62 is removed by etching. An anode buffer layer 63 and an organic light emitting layer 64 are formed on the anode 62, and a cathode 66 made of barium / aluminum alloy is laminated on the organic light emitting layer 64 and the partition wall film 60.
[0023]
In the organic EL element 16 having such a structure, when the holes injected from the anode 62 and the electrons injected from the cathode 66 recombine inside the organic light emitting layer 64, organic molecules constituting the organic light emitting layer are formed. Is excited to generate excitons. The excitons emit light in the process of radiation deactivation, and the light is emitted from the organic light emitting layer 64 to the outside through the transparent anode 62 and the light-transmissive insulating substrate 8.
[0024]
Here, a case has been described in which the anode 62 is connected to the first voltage power supply Vdd and the cathode 66 is connected to the second voltage power supply Vss via the second switch 26 and the P-channel type drive transistor 22. The cathode 66 may be connected to the drain of the driving transistor 22 through the drain of the second switch 26, and the anode 62 may be connected to the second voltage power source Vss. In either case, it is necessary to form the light emitting surface side with a transparent conductive material. For example, when the cathode electrode 66 is disposed on the light emitting surface side, alkaline earth metal and rare earth metal are light-transmitting. This can be achieved by forming a thin film.
[0025]
On the other hand, the controller 12 shown in FIG. 1 is formed on a printed circuit board disposed outside the organic EL panel 10 and controls the scanning line driving circuit 14 and the signal line driving circuit 15. The controller 12 receives a digital video signal and a synchronization signal supplied from the outside, and generates a vertical scanning control signal for controlling the vertical scanning timing and a horizontal scanning control signal for controlling the horizontal scanning timing based on the synchronizing signal. The scanning control signal and the horizontal scanning control signal are supplied to the scanning line driving circuit 14 and the signal line driving circuit 15, respectively, and the digital video signal is supplied to the signal line driving circuit 15 in synchronization with the horizontal and vertical scanning timings.
[0026]
The signal line driving circuit 15 converts the video signals Data1 to Data sequentially obtained in each horizontal scanning period under the control of the horizontal scanning control signal into an analog format, and supplies them in parallel to the plurality of signal lines X as current signals. The scanning line driving circuit 14 includes a shift register, an output buffer, etc., sequentially transfers a horizontal scanning start pulse supplied from the outside to the next stage, and outputs two types of control signals to the display pixels PX in each row via the output buffer. That is, the control signal Sa and the control signal Sb are supplied. Thus, the first and second scanning lines Y and Bg are driven by the control signal Sa and the control signal Sb, respectively, in one horizontal scanning period different from each other.
[0027]
The operation of the pixel circuit 18 based on the output signals of the scanning line driving circuit 14 and the signal line driving circuit 15 will be described with reference to the timing chart shown in FIG.
For example, the scanning line driving circuit 14 generates a pulse having a width (Tw-Starta) corresponding to each horizontal scanning period from the start signal a (Starta) and the clock a (Clka), and outputs the pulse as the control signal Sa. To do. Further, the scanning line driving circuit 14 inverts the control signal Sa to generate the control signal Sc.
[0028]
The operation of the pixel circuit 18 is divided into a video signal writing operation and a light emission operation. At time t1 in FIG. 4, the control signal Sa is at a level at which the first switch and the pixel switch are turned on, in this case, low level, and the control signal Sb is at a level at which the second switch is turned off, in this case, high level. As a result, the pixel switch 20 and the first switches 24a, 24b, and 24c are turned on (conductive state) and the second switch 26 is turned off (non-conductive state), and the video signal writing operation is started. Here, the control signal Sa is directly input from the first scanning line Y to the first switch 24a, and the resistance element 30 is input from the first scanning line Y to the first switches 24b and 24c and the pixel switch 20. Is input via. Therefore, as shown in FIGS. 2 and 5, the control signal waveform at the point A located on the gate side of the first switch 24a is the point B located on the gate side of the first switches 24b and 24c and the pixel switch 20. Displaces to the on level (low level) side earlier than the control signal waveform. Thereby, the first switches 24b and 24c and the pixel switch 20 are turned on with a slight delay from the first switch 24a.
[0029]
In the video signal writing period (t1 to t2), the drive transistor 22 is in a diode connection state, and the video signal DATA is taken in from the corresponding signal Y through the pixel switch 20. That is, the current flowing between the source and drain of the drive transistor 22 is set to a desired constant current by the signal line X and the pixel circuit connected to the analog conversion circuit which is a constant current source. Then, the gate-source potential of the drive transistor 22 corresponding to this amount of current is written in the storage capacitor 28 as a gate control voltage.
[0030]
Next, at the time point t2, the control signal Sa and the control signal Sc become high level and low level, respectively, the pixel switch 20 and the first switches 24a, 24b, and 24c are turned off, and the second switch 26 is turned on. Thereby, the video signal writing operation 2 is finished, and the light emission operation is started. Here, as described above, the first switches 24 b and 24 c and the pixel switch 20 are driven by the control signal Sa via the resistance element 30. Therefore, as shown in FIG. 5, when the control signal Sa rises from the low level to the high level, the control signal waveforms at the point A located on the gate side of the first switch 24a are the first switches 24b and 24c and the pixel switch. Displace to the high level side earlier than the control signal waveform at point B located on the gate side of 20. Therefore, the first switch 24a is turned off first, and the first switches 24b and 24c and the pixel switch 20 are switched to the off state with a delay from the first switch 24a.
[0031]
Note that the delay period from when the first switch 24a is turned off to when the first switches 24b and 24c and the pixel switch 20 are turned off can be adjusted by selecting the resistance value of the resistive element 30, and the wiring time constant of the scanning line For example, it is set to 0.2 μs or more, more desirably 1 μs or more, so as to be above.
[0032]
During the light emission period, the drive transistor 22 supplies a current amount corresponding to the video signal to the organic EL element 16 by the gate control voltage written in the storage capacitor 28. Thereby, the organic EL element 16 emits light, and the light emission operation is started. The organic EL element 16 maintains the light emitting state until the control signal Sa is supplied again after one frame period.
[0033]
As described above, in the organic EL display device according to this embodiment, the resistive element 30 is provided between the gates of the first switches 24b and 24c and the pixel switch 20 and the first scanning line Y, and the gate of the driving transistor 22 is the most. After the first switch 24a is turned off at the end of the video signal writing operation by delaying the on / off switching timing of the first switches 24b, 24c and the pixel switch 20 with respect to the first switch 24a adjacent to the first switch 24a. The first switches 24b and 24c and the pixel switch 20 are switched off. Therefore, even when a feedthrough voltage is generated when the first switches 24b and 24c and the pixel switch 20 are switched off, the first switch 24a that has been turned off first causes the feedthrough voltage to move to the gate side of the drive transistor 22. It can be prevented from flowing. As a result, it is possible to reduce the variation and variation in the gate control voltage of the drive transistor 22 due to the feedthrough voltage and to suppress the variation in luminance among a plurality of display pixels while reliably performing the video signal writing operation. It becomes. From the above, it is possible to obtain an active matrix organic EL display device that prevents display unevenness and improves display quality.
[0034]
Furthermore, according to the present embodiment, the channel area of the first switch 24a closest to the gate of the drive transistor 22 is formed smaller than the channel areas of the first switches 24b and 24c and the pixel switch 20, It is possible to reduce the feedthrough voltage and its variation generated when the first switch 24a is switched on and off. Therefore, fluctuations and variations in the gate control voltage of the drive transistor 22 can be further reduced. As a result, variations in luminance among a plurality of display pixels can be reduced and display unevenness can be reduced.
[0035]
In the above-described embodiment, the resistance element 30 is used as the delay element of the display pixel. However, the present invention is not limited to this, and other delay elements can be applied. In the organic EL display device according to the second embodiment of the present invention shown in FIG. 6, the delay element is constituted by the diode element 70. The diode element 70 is formed of a thin film transistor, and has a source connected to the first scanning line Y and a drain connected to the first switches 24 b and 24 c and the gate of the pixel switch 20. The gate of this thin film transistor is connected to the source. As a result, the drive transistor is diode-connected and functions as the diode element 70.
In the second embodiment, other configurations are the same as those of the first embodiment described above, and the same reference numerals are given to the same portions, and detailed description thereof is omitted.
[0036]
According to the second embodiment, the diode element 70 is provided between the gates of the first switches 24b and 24c and the pixel switch 20 and the first scanning line Y, so that it is closest to the gate of the driving transistor 22. The on / off switching timing of the first switches 24b and 24c and the pixel switch 20 can be delayed with respect to the first switch 24a. In particular, by using the diode element 70, it is possible to provide a difference in the fall of the control signal and the delay at the rise. That is, as shown in FIGS. 6 and 7, when the control signal Sa falls from the high level to the low level, the diode element 70 is turned on and operates with a forward current, and its resistance is small. Therefore, the control signal waveform at the point B located on the gate side of the first switches 24b and 24c and the pixel switch 20 falls almost simultaneously with the control signal waveform at the point A located on the gate side of the first switch 24a. The first switches 24b and 24c and the pixel switch 20 are turned on with a short delay with respect to the first switch 24a.
[0037]
On the other hand, when the control signal Sa rises from the low level to the high level, the diode element 70 is turned off and operates by a leakage current between the source and drain. Therefore, the resistance of the diode element 70 is increased. In this case, the delay of the rise of the control signal waveform at the point B is larger than the rise of the control signal waveform at the point A. Therefore, the first switch 24a is turned off first, and the first switches 24b and 24c and the pixel switch 20 are switched to the off state with a delay from the first switch 24a.
[0038]
From the above, it is possible to reduce fluctuations and variations in the gate control voltage of the drive transistor 22 due to the feedthrough voltage, and to suppress luminance variations among a plurality of display pixels. In addition, the delay can be increased only when the switch is turned off, and the display pixel is operated at a higher speed than when a delay is generated in both the rise and fall of the control signal by the resistance element. be able to. The magnitude of the delay at the rise and fall of the control signal can be adjusted by the value of W / L (channel width / channel length) of the diode element.
[0039]
According to the organic EL display device according to the third embodiment of the present invention shown in FIG. 8, the delay element of each display pixel PX includes a first diode element 70a that operates with a forward current when the control signal Sa falls. The second diode element 70b operates with a forward current when the control signal rises. The first diode element 70a is formed of a thin film transistor, and has a source connected to the first scanning line Y and a drain connected to the first switches 24b and 24c and the gate of the pixel switch 20, respectively. The gate of the thin film transistor is connected to its source. Thereby, the thin film transistor is diode-connected and functions as the first diode element 70a.
[0040]
The second diode element 70b is formed of a thin film transistor, and has a source connected to the first scanning line Y and a drain connected to the first switches 24b and 24c and the gate of the pixel switch 20, respectively. Further, the gate of this thin film transistor is connected to its drain. Thereby, the thin film transistor is diode-connected and functions as the second diode element 70b. The first and second diode elements 70a and 70b are configured in the reverse direction using a common source and drain, that is, the diode elements in the reverse direction are connected in parallel.
In the third embodiment, other configurations are the same as those of the first embodiment described above, and the same reference numerals are given to the same portions, and detailed description thereof is omitted.
[0041]
According to the third embodiment, as shown in FIGS. 8 and 9, at the fall of the control signal Sa, the forward current operation of the first diode element 70a causes the control signal to fall at the point B. A delay is generated, and when the control signal Sa rises, a delay is generated in the fall of the control signal at the point B by the forward current operation of the second diode element 70b. Therefore, both the falling and rising of the control signal can be adjusted by the forward current of the diode element, and the falling and rising can be individually controlled. Therefore, the same operational effects as those of the above-described embodiment can be obtained, and the degree of freedom in design can be increased.
[0042]
The pixel circuit of the organic EL display device is not limited to the current signal method, and may be configured as a voltage signal method pixel circuit. FIG. 10 shows a display pixel PX of an organic EL display device according to the fourth embodiment of the present invention. Each display pixel PX includes an organic EL element 16 that is a self-light-emitting element and a pixel circuit 18 that supplies a drive current to the organic EL element. The pixel circuit 18 is a voltage signal type pixel circuit that controls light emission of the organic EL element 16 in accordance with a video signal composed of a voltage signal. The pixel circuit 18 includes a pixel switch 20, a drive transistor 22, and a plurality of, for example, three first switches 24a and 24b. 24c, second switch 26, holding capacitors 28a and 26b, and resistance element 30 functioning as a delay element. The pixel switch 20, the drive transistor 22, the first switches 24a, 24b, 24c, and the second switch 26 are configured by the same conductivity type, for example, a P-channel type thin film transistor.
[0043]
The source of the driving transistor 22 is connected to the first voltage power supply Vdd. A storage capacitor 28a is connected between the gate and source of the drive transistor 22, and first switches 24a, 24b, and 24c are connected in series between the gate and drain.
The gate of the drive transistor 22 is connected to the drain of the pixel switch 20 via the storage capacitor 28b, and the source of the pixel switch is connected to the signal line X. The drain of the drive transistor 22 is connected to the anode of the organic EL element 16 via the second switch 26, and the cathode of the organic EL element is connected to the second voltage power supply Vss.
[0044]
The gate of the first switch 24a connected to the most gate side of the driving transistor 22 is connected to the first scanning line Y without passing through the resistance element 30, and the gates and pixel switches of the other first switches 24b and 24c. Each of the 20 gates is connected to the first scanning line Y via the resistance element 30.
[0045]
A video signal DATA that is output from a signal line driving circuit (not shown) and that is a voltage signal is input to each pixel circuit 18 via a signal line X. Further, the pixel switch 20, the first switches 24a, 24b, 24c and the second switch 26 are turned on and off by a control signal Sa and a control signal Sb generated by a scanning line driving circuit (not shown), respectively.
[0046]
In the fourth embodiment, other configurations are the same as those of the above-described embodiment, and the same reference numerals are given to the same portions, and detailed description thereof is omitted. Also in the fourth embodiment having the above-described configuration, by providing the resistance element 30, the first switches 24b and 24c and the pixel switch 20 are turned on / off with respect to the first switch 24a closest to the gate of the driving transistor 22. The timing can be delayed, and the first switches 24b and 24c and the pixel switch 20 can be turned off after the first switch 24a is turned off first. As a result, an active matrix organic EL display device with improved display quality can be obtained in which the video signal writing operation is reliably performed and the fluctuation and variation in the gate control voltage of the drive transistor 22 due to the feedthrough voltage are reduced. It is done.
In the fourth embodiment, the delay element may be the diode element shown in FIG. 6 or 8 instead of the resistance element.
[0047]
The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.
[0048]
In the above-described embodiment, the thin film transistors constituting the pixel circuit are all configured with the same conductivity type, here the P channel type, but the present invention is not limited to this, and all the thin film transistors are configured with N channel type thin film transistors. Is also possible. It is also possible to form a pixel circuit with a mixture of different conductive type thin film transistors, such as a pixel switch, an N channel type thin film transistor for the first switch, and a P channel type thin film transistor for the drive transistor and the second switch. It is.
[0049]
Furthermore, the semiconductor layer of the thin film transistor is not limited to polysilicon, but may be composed of amorphous silicon. In the display pixel, the number of first switches is not limited to three, and may be two or four or more. In addition, the self-light-emitting elements constituting the display pixels are not limited to organic EL elements, and various light-emitting elements capable of self-light emission are applicable.
[0050]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide an active matrix display device with reduced display unevenness and improved display quality.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of an organic EL display device according to an embodiment of the present invention.
FIG. 2 is a diagram showing an equivalent circuit of display pixels in the organic EL display device.
FIG. 3 is a cross-sectional view showing a part of the organic EL display device.
4 is a timing chart for explaining the operation of the display pixel shown in FIG. 2;
FIG. 5 is a diagram showing a control signal waveform for controlling on / off of a switch in the display pixel.
FIG. 6 is a diagram showing an equivalent circuit of a display pixel in an organic EL display device according to a second embodiment of the present invention.
FIG. 7 is a view showing a control signal waveform for controlling on / off of a switch in a display pixel of the organic EL display device according to the second embodiment.
FIG. 8 is a diagram showing an equivalent circuit of a display pixel in an organic EL display device according to a third embodiment of the present invention.
FIG. 9 is a view showing a control signal waveform for turning on / off a switch in a display pixel of the organic EL display device according to the third embodiment.
FIG. 10 is a diagram showing an equivalent circuit of a display pixel in an organic EL display device according to a fourth embodiment of the present invention.
[Explanation of symbols]
12 ... Controller, 14 ... Scan line drive circuit,
15 ... signal line drive circuit, 16 ... organic EL element, 18 ... pixel circuit,
20 ... Pixel switch, 22 ... Drive transistor,
24a, 24b, 24c ... first switch,
26 ... second switch, 28, 28a, 28b ... holding capacity,
30 ... Resistance element 62 ... Anode electrode 64 ... Organic light emitting layer,
66 ... Cathode electrode, 70 ... Diode element,
70a ... 1st diode element, 70b ... 2nd diode element,
PX ... display pixel, Vdd ... first voltage power supply, Vss ... second voltage power supply,
Y: first scanning line, X: signal line, Bg: second scanning line.

Claims (10)

A plurality of display elements arranged in a matrix;
A drive transistor having a first terminal connected to the first power supply terminal, a second terminal connected to the display element, and a control terminal connected to the first terminal via a storage capacitor;
A plurality of switches each formed by a transistor and connected in series between the control terminal and the second terminal and controlled to be turned on and off in response to a control signal from a scanning line;
Of the plurality of switches, the switch is connected between the scanning line and the other switch except the switch provided on the most control terminal side of the drive transistor, and the switch provided on the most control terminal side. A delay element for delaying the on / off switching timing of the other switch,
An active matrix display device comprising: The active matrix display device according to claim 1, wherein the delay element is configured by a resistance element. 3. The active matrix display device according to claim 2, wherein the resistance element is made of lightly doped drain type polysilicon. The active matrix display device according to claim 1, wherein the delay element is configured by a diode element. The delay element includes a first diode element that operates with a forward current when the control signal rises, and a second diode element that operates with a forward current when the control signal falls. The active matrix display device according to claim 1. The display device is an active matrix display device according to any one of claims 1, characterized in that that are controlled by a current signal 5. 7. The active matrix display device according to claim 1, wherein the display element is a light emitting element having an organic light emitting layer between opposed electrodes. 8. The active matrix display device according to claim 1, wherein the driving transistor and the switch are formed of a thin film transistor using polysilicon as a semiconductor layer. 9. The active switch according to claim 8, wherein a switch connected to the most control terminal side of the drive transistor among the plurality of switches has a channel area smaller than a channel area of another switch. Matrix type display device. A plurality of display pixels arranged in a matrix, a plurality of first and second scanning lines connected to each row of the display pixels and provided independently, and a plurality connected to each column of the display pixels Signal line, and
Each display pixel includes a self-light emitting element that emits light in response to a supply current, a pixel switch that is on / off controlled according to a control signal from the first scanning line, and that captures a video signal on the signal line, and the pixel switch. A storage capacitor for holding a control voltage corresponding to the captured video signal, and the self-light emission according to the control voltage connected in series with the self-light-emitting element between the first and second voltage power supplies and held in the storage capacitor A driving transistor that outputs an amount of current supplied to the element, each formed by a thin film transistor, connected in series between the gate and drain of the driving transistor, and turned on / off in response to a control signal from the first scanning line A plurality of first switches that are connected between the drive transistor and the self-light-emitting element in response to a control signal from the second scan line. A second switch that is controlled to be turned on and off, and, among the plurality of first switches, a first switch other than the first switch provided on the most gate side of the driving transistor, and the first scanning line And a delay that delays on / off switching timings of the other first switch and the pixel switch with respect to the first switch on the most gate side, between the first scanning line and the pixel switch. An active matrix display device comprising an element.

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