JP2007156460A5 - - Google Patents

Description

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

The present invention relates to a pixel circuit that drives a light-emitting element arranged for each pixel and a driving method thereof, a display device including the pixel, a driving method thereof, and an electronic apparatus including the display device . More specifically, controls the amount of current flowing through the light-emitting element such as an organic EL element by the insulating gate field effect transistor provided in each pixel circuit, relates to a pixel circuit and the like which constitute the pixels of the so-called active matrix display device .

An image display device, for example, in a liquid crystal display, arranged a number of liquid crystal pixels in a matrix, by controlling the transmission intensity or the reflection intensity of the incident light for each pixel in accordance with image information to be displayed, to display an image . This also applies to an organic EL display using an organic EL element as a pixel, but unlike a liquid crystal pixel , the organic EL element is a self-luminous element. Therefore, the organic EL display has a high image visibility than a liquid crystal display, a backlight is unnecessary, has advantages such as high response speed. Also, the brightness level of each light-emitting element (gradation) can be controlled by a current value flowing thereto, differs significantly from the voltage-controlled, such as a liquid crystal display in that a so-called current-controlled.

In the organic EL display, similarly to the liquid crystal display, there are a simple matrix method and an active matrix method as driving methods. The former has a simple structure, large, and, because of a problem such as it is difficult to realize a high-definition display, is currently developing an active matrix system has been popular. In this method, a current flowing through a light emitting element in each pixel circuit is controlled by an active element (generally a thin film transistor or TFT) provided in the pixel circuit, and is described in the following patent documents.
JP 2003-255856 A JP 2003-271095 A JP 2004-133240 A JP 2004-029791 A JP 2004-093682 A

A conventional pixel circuit is arranged at a portion where a row scanning line supplying a control signal and a column signal line supplying a video signal intersect, and at least a sampling transistor, a pixel capacitor , a drive transistor, and a light emission Element. The sampling transistor conducts in response to a control signal supplied from the scanning line, and samples the video signal supplied from the signal line. The pixel capacitance holds an input voltage corresponding to the sampled video signal. The drive transistor supplies an output current during a predetermined light emission period in accordance with the input voltage held in the pixel capacitor . In general, the output current, the carrier mobility and the threshold voltage of the channel region of the drive transistor, having a dependency. Light-emitting element, the output current supplied from the drive transistor, emits light at a luminance corresponding to the video signal.

In the drive transistor, an output current flows between the source and the drain in accordance with the input voltage held in the pixel capacitor , and this current flows in the light emitting element. In general, the light emission luminance of a light emitting element is proportional to the amount of current . Further , the output current of the drive transistor is controlled by the gate / source voltage, that is, the input voltage written to the pixel capacitor . The conventional pixel circuit controls the amount of current supplied to the light emitting element by changing the input voltage applied between the gate / source of the drive transistor in accordance with the video signal .

Here, the operation characteristics of the drive transistor is expressed by the following equation (1).

Formula (1)
I _ds = (1/2) μ (W / L) C _ox ( V _gs −V _th ) ²

In the transistor characteristic formula (1) , I _ds represents a drain current flowing between the source and the drain, and is an output current supplied to the light emitting element in the pixel circuit. V _gs represents a gate-source voltage applied to the gate with reference to the source, and is the above-described input voltage in the pixel circuit. V _th is the threshold voltage of the transistor. Further, mu denotes the mobility of a semiconductor thin film constituting the channel region of the transistor. In addition , W represents the channel width, L represents the channel length, and C _ox represents the capacitance of the gate insulating film . As is apparent from the transistor characteristic equation (1) , when the thin film transistor operates in the saturation region, the gate-source voltage V _gs exceeds the threshold voltage V _th and becomes on, and the drain current I _ds. Flows. When principle view, as shown above transistor characteristic equation (1) is, if the gate / source voltage V _gs constant, always drain current I _ds of the same amount is supplied to the light emitting element. Therefore, if video signals of the same level are supplied to all the pixels constituting the screen, all the pixels should emit light with the same luminance, and the uniformity of the screen should be obtained.

However , in reality, thin film transistors (TFTs) composed of a semiconductor thin film such as polysilicon have variations in individual device characteristics. In particular, the threshold voltage V _th is not constant and varies from pixel to pixel. As apparent from the transistor characteristic equation (1) , when the threshold voltage V _th of each drive transistor varies, the drain current I _ds varies even if the gate-source voltage V _gs is constant, and the pixel since thus variations in brightness for each impairs the uniformity of the screen. Conventionally , a pixel circuit incorporating a function for canceling variation in threshold voltage of a drive transistor has been developed, and is disclosed in, for example , Patent Document 3 described above.

However, the ability to cancel the variations in the threshold voltage (threshold voltage correction function) conventional display device incorporating the pixel circuits, the configuration is complicated, has become an obstacle to miniaturization or high definition of pixels. The pixel circuits incorporating a conventional threshold voltage correction function is not efficient, has led to complication of the circuit design. In addition, the pixel circuit including a conventional threshold voltage correction function, since the number of components is relatively large, resulting in decrease in yield.

In view of the above-described problems of the conventional technology, the present invention aims to improve the efficiency and simplification of a pixel circuit having a threshold voltage correction function, thereby achieving higher definition and improved yield of a display device. Objective. In order to achieve this purpose , the following measures were taken. That is, the display device according to the present invention includes a pixel array section and a scanner section and a signal section, the pixel array having scanning lines arranged in rows, and signal lines arranged in columns, both consists of a matrix of pixels disposed at the intersection, the signal unit, and supplies the video signal to the signal lines, the scanner unit supplies a control signal to the first scan line and the second scan line The pixels are sequentially scanned for each row. Each pixel includes a sampling transistor, a pixel capacitor connected thereto, a drive transistor connected thereto, a light emitting element connected thereto, and a switching transistor connecting the drive transistor to a power source. The sampling transistor conducts in response to a control signal supplied from the first scanning line and samples the signal potential of the video signal supplied from the signal line into the pixel capacitor. The pixel capacitor applies an input voltage to the gate of the drive transistor in accordance with the signal potential of the sampled video signal. The drive transistor, the output current corresponding to the input voltage supplied to the light emitting element, the output current has a dependency on a threshold voltage of the drive transistor. The light emitting element during the light emission period, emits light at a luminance corresponding to the signal potential of the video signal by the supplied output current from the drive transistor. The switching transistor is rendered conductive in response to the control signal supplied from the second scan line, in the light emitting period to connect the drive transistor to the power supply, the non-emission period in the non-conductive state, the drive transistor Disconnect from the power supply. As a feature, the scanner unit outputs respectively control signals to the first scan line and the second scanning line in the horizontal scanning period, and on-off controlling the sampling transistor and the switching transistor, the threshold of the output current preparation operation for resetting the pixel capacitor to correct the dependence on voltage, the correction operation of writing a voltage for canceling the threshold voltage to the pixel capacitor was reset, and the video of the corrected pixel capacitor A sampling operation for sampling the signal potential of the signal is executed.

On the other hand , the signal unit switches the video signal between the first fixed potential , the second fixed potential, and the signal potential during the horizontal scanning period, so that the preparation operation, the correction operation, and the sampling are performed. A potential necessary for the operation is supplied to each pixel through a signal line. In this case, the signal unit is to enable the preparation operation First and subsequently supplying a first fixed potential at the high level (high potential) is switched to the second fixed potential low-level (low potential), and further, a low-level The correction operation is executed while the second fixed potential (low potential) is maintained, and then the sampling operation is executed by switching to the signal potential. Further, the signal unit includes a signal generation circuit for generating a signal potential, a first fixed potential and a second fixed potential is inserted into the signal potential output from the signal generating circuit, than Te, and a first fixed potential first 2 and an output circuit that synthesizes a video signal in which a fixed potential and a signal potential are switched and outputs the synthesized video signal to each signal line. In this case, the signal unit, the normal rated the exceed no signal potential and the rated outputs a video signal obtained by synthesizing the ultrasonic El first fixed potential, said signal generation circuit, the exceeded no signal potential rated while one of ordinary withstand voltage for generating to said output circuit is a high breakdown voltage to deal with rated Exceeding first fixed potential.

  In one aspect, the drive transistor has an output current dependent on a carrier mobility of a channel region in addition to a threshold voltage, and the scanner unit applies a control signal to the second scan line during a horizontal scan period. In order to further control the switching transistor and cancel the dependence of the output current on the carrier mobility, the output current is taken out from the drive transistor in a state where the signal potential is sampled, and this is output to the pixel. An operation of correcting the input voltage by performing negative feedback to the capacitor is executed.

The display device according to the present invention includes a pixel array and a scanner and driver, the pixel array, the scanning lines arranged in rows, and signal lines arranged in columns, at respective intersections consists of a disposed a matrix of pixels, said driver supplies a video signal to the signal lines, the scanner sequentially pixel for each row by supplying a control signal to the first scan line and the second scan line Each pixel includes a sampling transistor, a pixel capacitor connected thereto, a drive transistor connected thereto, a light emitting element connected thereto, and a switching transistor connecting the drive transistor to a power source, The sampling transistor conducts in response to a control signal supplied from a first scanning line and samples a signal potential of a video signal supplied from the signal line into the pixel capacitor, The elementary capacitor applies an input voltage to the gate of the drive transistor according to the signal potential of the sampled video signal, the drive transistor supplies an output current according to the input voltage to the light emitting element, and The light emitting element emits light with luminance corresponding to the signal potential of the video signal by the output current supplied from the drive transistor during the light emission period , and the switching transistor is turned on according to the control signal supplied from the second scanning line. and, in the light emitting period to connect the drive transistor to the power supply, the non-emission period in the non-conductive state, disconnecting the drive transistor from a power source, the scanner, and the first scan line in the horizontal scanning period A control signal is output to each of the second scanning lines, and the sampling transistor and the switching transistor are controlled to be turned on / off. Switch between performing the sampling operation for sampling the signal potential of the correcting operation and the video signal for correcting the variation of the output current, the driver, the video signal in the horizontal scanning period, a fixed potential and the signal potential , following Te, a potential necessary for the correction operation and the sampling operation and supplying via the signal line to the pixel.

Specifically said driver includes a signal generation circuit for generating a signal potential, the fixed potential is inserted into the signal potential output from the signal generating circuit, than Te, the video signal switched and the fixed potential and the signal potential And an output circuit for combining and outputting to each signal line. In this case, the driver normal rated the exceed no signal potential and the rated outputs a video signal obtained by synthesizing the ultrasonic el fixed potential, the signal generating circuit of the normal to generate exceed no signal potential rated has a breakdown voltage, characterized by high breakdown voltage to deal the rated Exceeding fixed potential only the output circuit.

According to the present invention, the display device incorporates a threshold voltage correction function in each pixel circuit. In this display device, within one horizontal scanning period (1H) assigned to each row of pixels, a threshold voltage correction preparation operation by gate potential coupling, an actual threshold voltage correction operation, and a signal potential sampling operation of a video signal And go. Thereby, the number of elements constituting each pixel circuit can be reduced to three transistors, one capacitor, and one light emitting element. Accordingly , the number of power supply lines and gate lines (scanning lines) can be reduced, and the crossover between wirings can be greatly reduced, whereby the yield of panels constituting the display device can be improved. At the same time , high definition panels can be achieved. In the present invention, not only sampling scanning but also correction operation is executed within the horizontal scanning period, so that a fixed potential for control is supplied from the signal line in addition to the signal potential. Thus , the display device of the present invention can send not only image data but also a fixed voltage for controlling the pixel circuit from the signal line to the pixel array of the panel. As a result , a means for correcting characteristic variations of drive transistors included in each pixel circuit can be configured with a small number of elements. In addition , even if the fixed voltage for controlling the pixel circuit is higher than the maximum rated voltage of a general driver IC, it is only necessary to increase the breakdown voltage of the output circuit section, and it is not necessary to increase the breakdown voltage of the driver IC. The increase in the physical size of the driver, such as an increase in the size of the driver and an increase in the pitch, could prevent an increase in the cost of the IC, and it was possible to cope with a high-resolution panel.

Hereinafter , embodiments of the present invention will be described in detail with reference to the drawings. First , with reference to FIG. 1, a reference example of the display device on which the present invention is based will be briefly described. As shown, the active matrix display device has a pixel array 1 and the peripheral circuit portion as a main part. Circuit part around a horizontal selector 3, a write scanner 4, the drive scanner 5, a first correcting scanner 71, and the like second correcting scanner 72. Pixel array 1 is composed of the scanning lines WS in rows, and columns of the signal line SL, and the pixel circuits 2 arranged in a matrix form at the intersection of both. For ease of understanding in the figure, it is expanded display only one pixel circuit 2. The signal line SL is driven by the horizontal selector 3. The horizontal selector 3 forms a signal unit and supplies a video signal to the signal line SL. The scanning line WS is scanned by the write scanner 4. Incidentally, in parallel with the scanning lines WS, another scan line DS, AZ1 and AZ2 are also wired. The scanning line DS is scanned by the drive scanner 5. The scanning line AZ1 is scanned by the first correction scanner 71. The scanning line AZ2 is scanned by the second correction scanner 72. The write scanner 4, the drive scanner 5, the first correction scanner 71, and the second correction scanner 72 constitute a scanner unit, which sequentially scans pixel rows every horizontal scanning period. Each pixel circuit 2, when selected by the scanning line WS, samples the video signal from the signal line SL. Further, when selected by the scanning line DS, the light emitting element EL included in the pixel circuit 2 is driven in accordance with the sampled video signal. In addition, the pixel circuit 2, when scanned by the scanning lines AZ1, AZ2, performs predetermined correction operation.

The pixel circuit 2 includes five thin film transistors Tr ₁ to Tr ₄ and Tr _d , one capacitor element (pixel capacitor) C _s , and one light emitting element EL. Transistors Tr ₁ ~ Tr ₃ and Tr _d is an N-channel polysilicon TFT. Only the transistor Tr ₄ is a P-channel type polysilicon TFT. One capacitor element C _s constitutes the pixel capacitor of the present pixel circuit 2. The light emitting element EL is , for example , a diode type organic EL element having an anode and a cathode. However , the present invention is not limited to this, and the light emitting element generally includes all devices that emit light by current drive.

Drive transistor Tr _d which is the center of the pixel circuit 2, a gate G is connected to one end of the pixel capacitor C _s, the source S is also connected to the other end of the pixel capacitor C _s. The gate G of the drive transistor Tr _d via a switching transistor Tr _2, and is connected to another reference potential V _ss1. The drain of the drive transistor Tr _d via the switching transistor Tr _4, are connected to a power supply V _cc. The gate of the switching transistor Tr ₂ is connected to the scanning line AZ1. The gate of the switching transistor Tr ₄ is connected to the scanning line DS. The anode of the light emitting element EL is connected to the source S of the drive transistor Tr _d, the cathode is grounded. This ground potential may be expressed as V _cath . Further , the switching transistor Tr ₃ is interposed between the source S of the drive transistor Tr _d and a predetermined reference potential V _ss2 . The gate of the transistor Tr ₃ is connected to the scanning line AZ2. On the other hand , the sampling transistor Tr ₁ is connected between the signal line SL and the gate G of the drive transistor Tr _d . The gate of the sampling transistor Tr ₁ is connected to the scanning line WS.

In such a configuration, the sampling transistor Tr ₁ conducts according to the control signal WS supplied from the scanning line WS during a predetermined sampling period, and samples the video signal V _sig supplied from the signal line SL into the pixel capacitor C _s . . The pixel capacitor C _s applies an input voltage V _gs between the gate G and the source S of the drive transistor Tr _d in accordance with the sampled video signal V _sig . Drive transistor Tr _d during a predetermined light emission period, the output current I _ds according to the input voltage V _gs, supplied to the light emitting element EL. Note that the output current (drain current) I _ds is the carrier mobility μ and the threshold voltage V _th of the channel region of the drive transistor Tr _d, having any dependency. The light emitting element EL emits light with luminance according to the video signal V _sig by the output current I _ds supplied from the drive transistor Tr _d .

As a feature of this reference example, the pixel circuit 2 includes a correction unit including switching transistors Tr ₂ to Tr ₄ , and emits light in advance in order to cancel the dependency of the output current I _{ds on} the carrier mobility μ. The input voltage V _gs held in the pixel capacitor C _s at the beginning of the period is corrected. Specifically, the correcting means ( Tr ₂ to Tr ₄ ) operate in a part of the sampling period according to the control signals WS and DS supplied from the scanning lines WS and DS, and the video signal V _sig is sampled. In this state, the output current I _ds is taken out from the drive transistor Tr _d and negatively fed back to the pixel capacitor C _s to correct the input voltage V _gs . Further, the correcting means ( Tr ₂ to Tr ₄ ) detects the threshold voltage V _th of the drive transistor Tr _d in advance of the sampling period in order to cancel the dependence of the output current I _{ds on} the threshold voltage V _th . In addition , the detected threshold voltage V _th is added to the input voltage V _gs .

For this reference example, the drive transistor Tr _d, while the drain of N-channel transistor is connected to the power supply V _cc side, the source S is connected to the light emitting element EL side. In this case, the correction means described above takes out the output current I _ds from the drive transistor Tr _d at the beginning of the light emission period that overlaps the latter part of the sampling period, and negatively feeds back to the pixel capacitor C _s side. At this time , the correcting means causes the output current I _ds extracted from the source S side of the drive transistor Tr _d at the beginning of the light emission period to flow into the capacitance of the light emitting element EL. Specifically, the light emitting element EL, a diode-type light-emitting device having an anode and a cathode, while the cathode side of the anode side is connected to the source S of the drive transistor Tr _d is grounded. With this configuration, the correcting means ( Tr ₂ to Tr ₄ ) sets the anode / cathode of the light emitting element EL in a reverse bias state in advance, and outputs the output current I _ds extracted from the source S side of the drive transistor Tr _d. When the LED flows into the light emitting element EL, the diode type light emitting element EL is caused to function as a capacitive element. Incidentally, the correcting means can adjust the time width t extracting an output current I _ds of the drive transistor Tr _d within the sampling period, thereby to optimize the negative feedback amount of the output current I _ds to the pixel capacitor C _s Yes.

FIG. 2 is a schematic view of a pixel circuit portion extracted from the display device shown in FIG. For ease of understanding, the video signal V _sig sampled by the sampling transistor Tr ₁ , the input voltage V _gs and output current I _{ds of} the drive transistor Tr _d , and the capacitance component C _oled of the light emitting element EL, etc. It has been added. Hereinafter , the operation of the pixel circuit 2 according to the reference example will be described with reference to FIG.

FIG. 3 is a timing chart of the pixel circuit shown in FIG. With reference to FIG. 3, the operation of the pixel circuit according to the reference example shown in FIG. 2 will be described more specifically. 3, along the time axis T, are a waveform of the control signals applied to the scanning lines WS, AZ1, AZ2 and DS. In order to simplify the notation, the control signals are also represented by the same reference numerals as the corresponding scanning lines. Since the transistors Tr ₁ , Tr ₂ , and Tr ₃ are N-channel type, they are turned on when the scanning lines WS, AZ 1, and AZ 2 are at a high level and turned off when they are at a low level. On the other hand , since the transistor Tr ₄ is a P-channel type, it is turned off when the scanning line DS is at a high level and turned on when it is at a low level. Note that this timing chart, with the control signals WS, AZ1, AZ2, DS waveform is represented the potential change of the drive transistor Tr _d potential change and the source S of the gate G of the.

In the timing chart of FIG. 3 , timings T1 to T8 are defined as one field (1f). Each row of the pixel array is sequentially scanned once during one field. The timing chart represent the control signals WS, AZ1, AZ2, DS of waveforms applied to the pixels of one row.

At timing T0 before the field starts, all control line numbers WS, AZ1, AZ2, DS are at a low level. Accordingly, the N-channel transistors Tr ₁ , Tr ₂ , Tr ₃ are in the off state, while only the P-channel transistor Tr ₄ is in the on state. Therefore, the drive transistor Tr _d is because it is connected to the power source V _cc through transistor Tr ₄ in the ON state and supplies the output current I _ds to the light emitting element EL in accordance with the predetermined input voltage V _gs. Therefore, the light emitting element EL emits light at the timing T0. At this time, the input voltage V _gs applied to the drive transistor Tr _d is represented by the difference between the gate potential (G) and the source potential (S).

At the timing T1 when the field starts, the control signal DS is switched from the low level to the high level. Thus, the transistor Tr ₄ is turned off and the drive transistor Tr _d is disconnected from the power supply V _cc, light emission is stopped into the non-emission period. Therefore, at the timing T1, all the transistors Tr ₁ to Tr ₄ are turned off.

Subsequently , at timing T2, since the control signals AZ1 and AZ2 are at a high level, the switching transistors Tr ₂ and Tr ₃ are turned on. As a result, the gate G of the drive transistor Tr _d is connected to the reference potential V _ss1 , and the source S is connected to the reference potential V _ss2 . Here, V _ss1 - V _ss2> meets the _{V th, V ss1 - V ss2} = By the V _gs> V _th, to prepare for the V _th correction, which is performed in the subsequent timing T3. In other words, the period T2-T3 corresponds to a reset period of the drive transistor Tr _d. Further, when the threshold voltage of the light emitting element EL is V _thEL , V _thEL > V _ss2 is set. Thereby, a minus bias is applied to the light emitting element EL, and a so-called reverse bias state is obtained. This reverse bias state is necessary for normal V _th correction operation and mobility correction operation to be performed later.

Timing was T3, the control signal AZ2 at low level, and, and the control signal DS is also low immediately. Thereby , the transistor Tr ₃ is turned off, while the transistor Tr ₄ is turned on. As a result , the drain current I _ds flows into the pixel capacitor C _s and the V _th correction operation is started. This time, the gate G of the drive transistor Tr _d is held in V _ss1, flows current I _ds to the drive transistor Tr _d is cut off. When cut off , the source potential (S) of the drive transistor Tr _d becomes V _ss1 −V _th . Drain current returned to the high level again a control signal DS at the timing T4 after the cut-off and turns off the switching transistor Tr _4. Furthermore, the control signal AZ1 is also returned to the low level, the switching transistor Tr ₂ is also turned off. As a result, V _th is held and fixed in the pixel capacitor C _s . In this manner, the timing T3-T4 is a period for detecting the threshold voltage V _th of drive transistor Tr _d. Here, this detection period T3-T4, is referred to as V _th correction period.

Thus, after the V _th correction switches the control signal WS to the high level at a timing T5, writing the video signal V _sig in the pixel capacitor C _s to turn on the sampling transistor Tr _1. The pixel capacitance C _s is sufficiently smaller than the equivalent capacitance C _oled of the light emitting element EL. As a result, most of the video signal V _sig is written into the pixel capacitor C _s . To be precise, the difference V _sig of V _sig against the V _ss1 - V _ss1 is written to the pixel capacitor C _s. Accordingly, the voltage V _gs between the gate G and the source S of the drive transistor Tr _d is a level _obtained by adding V _th previously detected and held to V _sig −V _ss1 sampled this time , ( V _sig −V _ss1 + V _th ). Since, for purposes of explanation simplicity, when V _ss1 = 0V (0 volts), the gate / source voltage V _gs is as shown in the timing chart of FIG. 3, the V _sig + V _th. Sampling of such video signal V _sig, the control signal WS is performed until time T7 back to low level. That is, the timing T5-T7 corresponds to the sampling period.

Control signal DS goes low at the timing T6 prior to timing T7 to the end of the sampling period, the switching transistor Tr ₄ are turned on. Thus, the drive transistor Tr _d is connected to the power supply V _cc, the pixel circuit goes to the light emission period from the non-emission period. Thus, the sampling transistor Tr ₁ is still turned on and, in the period T6-T7 in which the switching transistor Tr ₄ enters the ON state, the mobility correction of the drive transistor Tr _d. That is , in this reference example , the mobility correction is performed in a period T6-T7 in which the latter part of the sampling period and the head part of the light emission period overlap. In the beginning of the emission period of the mobility correction is performed, the light emitting element EL, because in fact is in a reverse bias state, are not able to emit light. In the mobility correction period T6-T7, a state in which the gate G of the drive transistor Tr _d is fixed at the level of the video signal V _sig, the drain current I _ds flows to the drive transistor Tr _d. Here, V _ss1 - V _th <By setting the V _thEL, the light emitting element EL to be placed in a reverse bias state, exhibits a simple capacitance characteristics, rather than diode characteristics. Therefore , the current I _ds flowing through the drive transistor Tr _d is written into a capacitance C = C _s + C _oled that combines both the pixel capacitance C _s and the equivalent capacitance C _oled of the light emitting element EL. Thus, the source potential of the drive transistor Tr _d (S) is rises. In the timing chart of FIG. 3 , this increase is represented by ΔV. The rise ΔV eventually, it means that subtracted from the voltage V _gs between the gate / source held in the pixel capacitor C _s, it will be multiplied by the negative feedback. Thus, by negatively feeding back the output drain current I _ds of the drive transistor Tr _d also to the input voltage V _gs of the drive transistor Tr _d, it is possible to correct the mobility mu. Note that the negative feedback amount (increase) ΔV can be optimized by adjusting the time width t of the mobility correction period T6-T7.

At timing T7, the control signal WS becomes low level, and the sampling transistor Tr ₁ is turned off. As a result, gate G of drive transistor Tr _d is separated from the signal line SL. Since the application of the video signal V _sig is released, drive the gate potential of the transistor Tr _d (G) becomes possible increase, rises as with the source potential (S). Meanwhile, the pixel capacitance C _s gate / source voltage V _gs held in maintains the value of _{(V sig -ΔV + V th)} . With increasing the source potential (S), the reverse bias state of the light emitting element EL is because it is eliminated, the inflow of the output current I _ds, the light emitting device EL actually starts emitting light. Relationship between the drain current I _ds and the gate / source voltage V _gs at this time, by substituting V _sig -ΔV + V _th to V _gs of the previous transistor characteristic expression (1), the following formula (2) As given.

Formula (2)
I _ds = kμ ( V _gs −V _th ) ² = kμ ( V _sig −ΔV) ²

In the above formula (2) , k = (1/2) (W / L) C _ox . From this characteristic equation (2) , it can be seen that the term V _th is canceled and the output current I _ds supplied to the light emitting element EL does not depend on the threshold voltage V _th of the drive transistor Tr _d . Basically, the drain current I _ds is determined by the voltage of the video signal V _sig. In other words, the light emitting element EL will emits light at a luminance corresponding to the video signal V _sig. At that time , V _sig is corrected by the feedback amount ΔV. This correction amount ΔV is just serves to cancel the effect of the mobility μ is located in the coefficient of the characteristic equation (2). Accordingly, the drain current I _ds will be substantially dependent only on the video signal V _sig.

Finally, the control signal DS reaches the timing T8 is at a high level, the switching transistor Tr ₄ is turned off, the light emission is finished, the field is completed. Thereafter, proceeds to the next field, again, V _th correction operation, mobility correction operation and light emitting operation will be repeated.

However , in the pixel circuit according to this reference example, five types of transistors Tr ₁ , Tr ₂ , Tr ₃ , Tr ₄ , Tr _d , three types of power supply lines V _ss1 , V _ss2 , V _cc , and four types of gate lines. (Scanning lines) WS, DS, AZ1 and AZ2 need to be formed, and crossover with power supply lines and signal line lines increases. This causes to lower the yield. Furthermore, high definition becomes difficult in terms of layout. In a high-definition panel, it is necessary to reduce the number of elements in order to increase the yield.

FIG. 4 shows the overall configuration of the display device according to the present invention, which is an active matrix type having a threshold voltage ( V _th ) correction function. As shown in the figure, this active matrix display device is composed of a pixel array 1 as a main part and a peripheral circuit part. Circuit part around a horizontal selector 3, a write scanner 4, and the like Dora Lee Busukyana 5. Pixel array 1, a scanning line (first scanning line) WS of rows, and a and column-like signal line SL, and the pixel arranged at the intersection of both the matrix R, G, and B. Order to enable a color display, but are prepared three primary colors pixel of RGB, the invention is not limited thereto. Pixels R, G, B, respectively, are formed in the pixel circuit 2. The signal line SL is driven by the horizontal selector 3. The horizontal selector 3 forms a signal unit, and generally uses a driver IC, and supplies a video signal to the signal line SL. The scanning line WS is scanned by the write scanner 4. Incidentally, in parallel with the first scanning line WS, the second scanning line DS is also wired. The second scanning line DS is scanned by the drive scanner 5. The write scanner 4 and the drive scanner 5 constitute a scanner unit, which sequentially scans a row of pixels every horizontal scanning period. Each pixel circuit 2 samples a video signal from the signal line SL when selected by the first scanning line WS. Further, when selected by the second scanning line DS, the light emitting element included in the pixel circuit 2 is driven in accordance with the sampled video signal. In addition, the pixel circuit 2, when controlled by the first scanning line WS and second scanning lines DS in the horizontal scanning period, performing a predetermined correction operation.

Pixel array 1 described above, typically, it is formed on an insulating substrate such as glass, and has a flat panel. Transistors constituting the pixel circuits 2 is formed of an amorphous silicon thin film transistor (TFT) or a low-temperature polysilicon TFT. For amorphous silicon TFT, a scanner unit panel and is configured by a different TAB, it is connected to the flat panel by flexible cables. Similarly, the signal portion may be constituted by an external driver IC, is connected at full les carboxymethyl Bull cable to a flat panel. In the case of the low-temperature polysilicon TFT, the signal portion and the scanner portion can be formed of the same low-temperature polysilicon TFT, so that the pixel array portion, the signal portion, and the scanner portion can be integrally formed on the flat panel.

FIG. 5 is a circuit diagram showing a configuration of the pixel circuit 2 incorporated in the display device according to the present invention shown in FIG. The pixel circuit 2 includes a sampling transistor Tr ₁ , a pixel capacitor C _s connected thereto, a drive transistor Tr _d connected thereto, a light emitting element EL connected thereto, and a drive transistor Tr _d as a power source V _cc . And a switching transistor Tr ₄ to be connected.

The sampling transistor Tr ₁ is turned on in response to the control signal WS supplied from the first scanning line WS, and samples the signal potential V _sig of the video signal supplied from the signal line SL into the pixel capacitor C _s . The pixel capacitor C _s applies an input voltage V _gs between the gate G and the source S of the drive transistor Tr _d in accordance with the signal potential V _sig of the sampled video signal. Dora Lee Bed transistor Tr _d supplies an output current I _ds according to the input voltage V _gs to the light emitting element EL. Note that the output current I _ds has a dependency on the threshold voltage V _th of the drive transistor Tr _d. During the light emission period, the light emitting element EL emits light with luminance corresponding to the signal potential V _sig of the video signal by the output current I _ds supplied from the drive transistor Tr _d . S w Tsu quenching transistor Tr ₄ is conducts in response to the control signal DS supplied from the second scanning line DS, connect the drive transistor Tr _d during the emission period to the power source V _cc, in a non-conductive state in the non-emission period ringing, disconnect the drive transistor Tr _d from the power supply V _cc.

As a characteristic matter, the scanner unit composed of the write scanner 4 and the drive scanner 5 outputs control signals WS and DS to the first scanning line WS and the second scanning line DS in the horizontal scanning period (1H), respectively, and the sampling transistor The preparatory operation (V _th correction preparatory operation) for resetting the pixel capacitor C _s to correct the dependence of the output current I _{ds on} the threshold voltage V _th by controlling on / off of the Tr ₁ and the switching transistor Tr ₄ is reset. writing a voltage for canceling the threshold voltage V _th to the pixel capacitor C _s correction operation (V _th correction operation), and the sampling operation for sampling the signal potential V _sig of the video signal to the corrected pixel capacitance C _s Execute. On the other hand , the signal unit configured by the horizontal selector (driver IC) 3 transmits a video signal between the first fixed potential V _ssH , the second fixed potential V _ssL, and the signal potential V _sig during the horizontal scanning period (1H). in switching, than Te, the above-mentioned preparation operation, a potential necessary for the correction operation and the sampling operation, and supplies via the signal line SL to the pixels.

Specifically, the horizontal selector 3 first high level to allow the first fixed potential V _ssH supplied subsequently by the low level (low potential) second preparation operation is switched to a fixed potential V _ssl of (high potential) Further, the correction operation is performed in a state where the second fixed potential V _ssL at the low level (low potential) is maintained, and thereafter , the sampling operation is performed by switching to the signal potential V _sig . As described above, the horizontal selector 3 is composed of a driver IC, a signal generating circuit for generating a signal potential V _sig, first fixed potential V _ssH and second fixed signal potential V _sig output from the signal generating circuit insert the potential V _ssl, than Te, and an output circuit for outputting to the first fixed potential V _ssH a second fixed potential V _ssl and signal potential V _sig and is synthesize the video signal that switches the signal lines SL Including. Preferably , the driver IC constituting the horizontal selector 3 outputs a video signal obtained by synthesizing the signal potential V _sig not exceeding the normal rating and the first fixed potential V _ssH exceeding the rating. In this case , the signal generation circuit included in the driver IC has a normal breakdown voltage to generate the signal potential V _sig that does not exceed the rating, while the output circuit has a high breakdown voltage to cope with the first fixed potential V _ssH that exceeds the rating. Has been.

In the drive transistor Tr _d , the output current I _ds depends on the carrier mobility μ in the channel region in addition to the threshold voltage V _th . In this case , the scanner unit composed of the write scanner 4 and the drive scanner 5 outputs a control signal to the second scanning line DS in the horizontal scanning period (1H) to further control the switching transistor Tr ₄ and output current I _ds. In order to cancel the dependence on the carrier mobility μ, the output current is taken out from the drive transistor Tr _d while the signal potential V _sig is sampled, and this is negatively fed back to the pixel capacitor C _s to obtain the input voltage V _gs . Execute the operation to be corrected.

FIG. 6 is a schematic diagram in which a portion of the pixel circuit 2 is taken out from the display device shown in FIG. For easy understanding, the video signal V _sig sampled by the sampling transistor Tr ₁ , the input voltage V _gs and output current I _{ds of} the drive transistor Tr _d , and the capacitance component C _oled of the light emitting element EL are written. In addition. Further , the scanning lines WS and DS connected to the gates of the transistors are also written. The pixel circuit 2 is in the horizontal scanning period (1H), performs a V _th correction preparation operation, the actual correction operation, the sampling operation of the signal potential V _sig. Thus, the pixel circuit 2 can be configured with three transistors Tr ₁ , Tr ₄ , Tr _d , one pixel capacitor C _s, and one light emitting element EL. Compared to the pixel circuit incorporating a V _th correction function according to the reference example shown in FIG. 1, at least the transistor two possible reduction. Thus, it is possible to reduce the power line and the gate line, which leads to improved yield of the panel. Also, by simplifying the layout of the pixel circuit, it is also possible high definition.

FIG. 7 is a timing chart of the pixel circuit shown in FIGS. Referring to FIG. 7, specifically the operation of the pixel circuit shown in FIGS. 5 and 6, and will be described in detail. 7, along the time axis T, the scanning lines WS, are a waveform of the control signal applied to the DS. In order to simplify the notation, the control signals are also denoted by the same reference numerals as the corresponding scanning lines. In addition , the waveform of the video signal applied to the signal line is also shown along the time axis T. As shown in the figure, this video signal is sequentially switched to a high potential V _ssH , a low potential V _ssL , and a signal potential V _sig within each horizontal scanning period (1H). Since the transistor Tr ₁ is an N-channel type, it is turned on when the first scanning line WS is at a high level and turned off when it is at a low level. On the other hand , since the transistor Tr ₄ is a P-channel type, it is turned off when the second scanning line DS is at a high level and turned on when it is at a low level. Note that this timing chart, the control signals WS, together with the waveform of the DS waveform and the video signal, is represented the potential change of the drive transistor Tr _d potential change and the source S of the gate G of the.

In the timing chart of FIG. 7 , timings T1 to T8 are defined as one field (1f). Each row of the pixel array is sequentially scanned once during one field. Timing diagram represents the control signals WS is applied to the pixels of one row, the waveform of the DS.

First, at timing T1, the non-emission by turning off the switching transistor Tr _4. At this time, the source potential of the drive transistor Tr _d, since there is no power supply from the power source V _cc, is lowered to the cut-off voltage V _thEL of the light-emitting device EL.

Next, at timing T2, to turn on the sampling transistor Tr _1. However, it is _preferable to raise the potential of the signal line to the high potential V _ssH before this because the writing time can be shortened. High potential V _ssH is written into the gate G of the drive transistor Tr _d in that to turn on the sampling transistor Tr _1. At this time, coupling enters the source potential via the pixel capacitor C _s and the source potential rises. Although the source potential rises once, it is discharged through the light emitting element EL, so that the source potential becomes V _thEL again. At this time, the gate potential remains at the high potential V _ssH . In this way, by raising the potential of the signal line to the high potential V _ssH , the source potential can be once raised from V _thEL and then reliably set to V _thEL .

Next, at timing Ta, while turning on the sampling transistor Tr _1, it changes the video signal to the low potential V _ssl. This potential change is coupled to a source potential through the pixel capacitor C _s. The amount of coupling at this time is determined by C _s / ( C _s + C _oled ) × ( V _ssH −V _ssL ). At this time, the gate potential of the low potential V _ssl, the source potential V _thEL - represented by _{- (V ssL V ssH) C} s / (C s + C oled) ×. Here, the source potential is desirably set to a potential at which the light emitting element EL continues to be cut off after the subsequent V _th correction and mobility correction. Also, by preparing coupling so that V _gs > V _th , preparation for V _th correction can be made. As described above , the V _th correction preparation operation can be performed even in a circuit in which transistors, power supply lines, and gate lines are reduced. That is , the timings T2 to Ta are included in the correction preparation period. The level of low potential V _ssl and the high potential V _ssH, taking into account the volume ratio of the light emitting element capacitor C _oled the pixel capacitor C _s, satisfy the drive preparative transistor Tr _d is V _gs> V _th condition, and , V _th correction and mobility emitting element EL corrected completion after this is set to be the potential to continue to cut off.

In the above description , the video signal is once raised to the high potential V _ssH and then lowered to the low potential V _ssL to lower the source potential of the drive transistor Tr _d , so that the condition of V _gs > V _th is _satisfied. Is set.

However, the present invention is not limited to this operation, basically lowers the source potential from V _thEL by dropping the video signal to the low potential V _ssl, and, V _gs> V _th for the drive transistor Tr _d pixel capacitance C _s that can satisfy that the light-emitting device capacitance C _oled, low potential V _ssl level, may if the relationship of the high potential V _ssH level.

However, as in the present embodiment, once the raised video signal to the high potential V _ssH, by lowering the low potential V _ssl, quickly and reliably, the source potential of the drive transistor Tr _d is V _gs> It satisfies the condition of V _th, and, V _th correction and mobility emitting element EL corrected completion after this can be set so that the potential continues to cutoff.

As will be described later, the signal potential V _sig is written into the pixel capacitor C _s after V _th correction. That is, the potential of the signal line is changed from the low potential V _ssl to the signal potential V _sig, and writes the signal potential V _sig of the video signal to the pixel capacitor C _s. At this time, voltage actually held in the pixel capacitor C _s is determined by the capacitance division of the light emitting element capacitor C _oled the pixel capacitor C _s. In this case, since the pixel capacitance C _s is smaller than the light emitting element capacitance C _oled , the potential variation on the gate side is larger than the potential variation on the source side of the drive transistor Tr _d , the potential difference between the source and gate is widened, and the actual signal is Can write. Therefore, if a margin on the amplitude of original signal potential V _sig, it is possible to write the signal potential V _sig of operational sufficient video signal to the pixel capacitor C _s.

As described above, the display device according to the present invention sets V _gs by coupling through the pixel capacitor C _s in the V _th correction preparation operation and the signal potential V with respect to the pixel capacitor C _{s in} the signal write operation ( sampling operation). Write _sig . In any operation, by setting the level of the low potential V _ssL or the signal potential V _sig appropriately according to the capacitance ratio between the pixel capacitance C _s and the light emitting element capacitance C _oled , V _th correction preparation is possible without causing mutual troubles. Operations and signal writing operations can be performed.

Thereafter, when the switching transistor Tr ₄ is turned on with the gate G held at the low potential V _ssL at the timing T 3, a current flows through the drive transistor Tr _d and V _th correction is performed as in the reference example. A current flows until the drive transistor Tr _d is cut off. When the drive transistor Tr _d is cut off, the source potential of the drive transistor Tr _d becomes V _ssL −V _th . Here, V _ssl - there needs to be V _th <V _thEL.

Thereafter, at the timing T4, V _th correction turns off the switching transistor Tr ₄ is terminated. That is, the timing T3~T4 is a V _th correction period.

Thus, after the V _th correction at the timing T3 to T4, the potential of the signal line leading to timing T5 is changed from the low potential V _ssl to the signal potential V _sig. Thereby , the signal potential V _sig of the video signal is written into the pixel capacitor C _s . Compared to the equivalent capacitance C _oled of the light-emitting device EL, pixel capacitor C _s is sufficiently small. As a result, most of the signal potential V _sig is written in the pixel capacitor C _s. Accordingly, the voltage V _gs between the gate G and the source S of the drive transistor Tr _d becomes a level ( V _sig + V _th ) obtained by adding the previously detected and held V _th and the signal potential V _sig sampled this time. That is , the input voltage V _gs for the drive transistor Tr _d is V _sig + V _th . The sampling operation of the signal potential V _sig is performed until timing T7 when the control signal WS returns to the low level. That is , timings T5 to T7 correspond to the sampling period.

The pixel circuit according to the present invention corrects the mobility μ in addition to the correction of the threshold voltage V _th described above. The mobility μ is corrected at timings T6 to T7. This point will be described later in detail. As a conclusion, as shown in the timing chart, the correction amount ΔV is subtracted from the input voltage V _gs .

When it is time T7, the control signal WS is the sampling transistor Tr ₁ becomes a low level to turn off. As a result, the gate G of the drive transistor Tr _d is disconnected from the signal line SL. Since the application of the signal potential V _sig of the video signal is released, the gate potential (G) of the drive transistor Tr _d can be increased and increases with the source potential (S). Meanwhile, the pixel capacitance C _s gate / source voltage V _gs held in maintains the value of _{(V sig -ΔV + V th)} . With increasing the source potential (S), the reverse bias state of the light emitting element EL is because it is eliminated, the light emitting element EL by the inflow of the output current I _ds actually starts emitting light. The relationship between the drain current I _{ds and the} gate / source voltage V _gs at this time is given by the above-described equation (2) . It can be seen from this characteristic equation (2) that the term V _th is canceled and the output current I _ds supplied to the light emitting element EL does not depend on the threshold voltage V _th of the drive transistor Tr _d . Basically, the drain current I _ds is determined by the signal potential V _sig of the video signal. In other words, the light emitting element EL emits light with a luminance corresponding to the signal potential V _sig of the video signal. At that time , the signal potential V _sig is corrected by the feedback amount ΔV. This correction amount ΔV is just serves to cancel the effect of the mobility μ is located in the coefficient of the characteristic equation (2). Accordingly, the drain current I _ds practically becomes possible to rely only on the signal potential V _sig of the video signal.

Finally, reaching the timing T8, the control signal DS is switching transistor Tr ₄ is turned off at a high level, the light emission is finished, the field is completed. After this, move to the next field, again, V _th correction preparation operation, V _th correction operation, the mobility correction operation and light emitting operation are repeated. Thus, in this embodiment, the threshold voltage correction preparation operation (V _th correction preparation operation) by gate potential coupling and the actual threshold voltage correction are performed within one horizontal scanning period (1H) assigned to each row of pixels. An operation (V _th correction operation) and a sampling operation of the signal potential V _sig are performed. However, the present invention is not limited to this, and the threshold voltage correction preparation operation, the actual threshold voltage correction operation, also perform a sampling operation of the signal potential V _sig, over a plurality of horizontal scanning periods . For example, carried out in a horizontal scanning period preceding the threshold voltage correction preparation operation and the threshold voltage correction operation, the sampling operation of the signal potential V _sig can be carried out in the horizontal scanning period assigned to the pixel rows.

FIG. 8 is a circuit diagram showing the state of the pixel circuit 2 in the mobility correction period T6-T7. As illustrated, the mobility correction period T6-T7, the sampling transistor Tr ₁ and the switching transistor Tr ₄ is one that is turned on, the remaining switching transistor Tr ₃ off. In this state, the source potential (S) of the drive transistor Tr _d is V _ssL −V _th . This source potential S is also the anode potential of the light emitting element EL. As described _above, V ssL - V _th <By setting the V _thEL, the light emitting element EL is placed in a reverse bias state, and to exhibit a simple capacitance characteristics, rather than diode characteristics. Therefore , the current I _ds flowing through the drive transistor Tr _d flows into the combined capacitance C = C _s + C _oled of the pixel capacitance C _s and the equivalent capacitance C _oled of the light emitting element EL. In other words, a part of the drain current I _ds is negatively fed back to the pixel capacitor C _s and the mobility is corrected.

Figure 9 is a graph of the transistor characteristic expression (2) described above, take the I _ds on the vertical axis, taking the signal potential V _sig on the horizontal axis. The characteristic formula (2) is also shown below the graph. In the graph of FIG. 9, a characteristic curve is drawn in a state where the pixel 1 and the pixel 2 are compared. The mobility μ of the drive transistor Tr _d of the pixel 1 is relatively large. Conversely, the relatively small mobility μ of the drive transistor Tr _d included in the pixel 2. Thus, in the case of constituting the drive transistor Tr _d like poly-silicon thin film transistor, the mobility μ it is inevitable that variations between the pixels. For example , when the signal potential V _sig of the video signal of the same level is written in both the pixels 1 and 2, the output current I _ds1 ′ flowing through the pixel 1 having the high mobility μ is moved without any mobility correction. A large difference is generated as compared with the output current I _ds2 ′ flowing in the pixel 2 having a small degree μ. Thus, since a large difference between the output current I _ds due to variation in the mobility μ occurs, so that the impairing the uniformity of the screen.

Therefore , in the present invention, the variation in mobility is canceled by negatively feeding back the output current to the input voltage side. As is clear from the transistor characteristic equation, the drain current I _ds increases as the mobility increases. Therefore, the negative feedback amount ΔV increases as the mobility increases. As shown in the graph of FIG. 9, the negative feedback amount ΔV1 of large pixel 1 of the mobility μ is greater than the negative feedback amount ΔV2 of small pixels 2 mobility. Accordingly , the larger the mobility μ is, the more negative feedback is applied, and the variation can be suppressed. As shown, when applying a correction of the mobility in large pixel 1 mu [Delta] V1, the output current is large drops from I _ds1 'to I _ds1. On the other hand, the correction amount ΔV2 of small pixels 2 mobility μ is small, the output current I _ds2 'is not lowered so much to I _ds1. Consequently, I _ds1 and I _ds2 become substantially equal, variations in mobility is canceled. Cancellation of variations in mobility, so carried out in the entire range of the signal potential V _sig from the black level to the white level, uniformity of the screen becomes very high. In summary, when there is a different pixel 1 and pixel 2 mobility correction amount ΔV1 of the larger mobility pixel 1 is increased with respect to the correction amount ΔV2 of small pixels 2 mobility. That is , as the mobility increases , ΔV increases and the decrease value of I _ds increases. As a result , the current values of the pixels having different mobilities are made uniform, and variations in mobility can be corrected.

Hereinafter, for reference, with reference to FIG. 10, performs numerical analysis of the mobility correction described above. As shown in FIG. 10, in a state where the transistor Tr ₁ and Tr ₄ are turned on, and analyzes by taking the source potential of the drive transistor Tr _d to the variable V. When the source potential of the drive transistor Tr _d the (S) to is V, the drain current I _ds flowing through drive transistors Tr _d, are as shown in the following equation (3).

Formula (3)

Further , due to the relationship between the drain current I _ds and the capacitance C (= C _s + C _oled ), I _ds = dQ / dt = CdV / dt is established as shown in the following formula (4) .

Formula (4)

In equation (4) by substituting the equation (3), integrating both sides. Here, the initial state of the source potential V is - and V _th, the mobility correction time (time width T6-T7) and t. Solving this differential equation, the pixel current for the mobility correction time t is given by the following equation (5).

Formula (5)

FIG. 11 is a graph of the equation (5) , in which the vertical axis represents the output current I _ds and the horizontal axis represents the signal potential V _sig of the video signal. The mobility correction time t = 0us as parametric meter is set in the case of 2.5us and 5 us. Furthermore, as also the parameter mobility mu, certain relatively small when 0.8μ relatively large when 1.2μ for parameters. It can be seen that the mobility variation is sufficiently corrected at t = 2.5 us as compared to the case where the mobility correction is not substantially applied at t = 0 us. Those without mobility correction that there is variation of 40% I _ds is suppressed to less than 10% multiplied by the mobility correction. However, the longer the correction period as t = 5 us, conversely, the variation of the output current I _ds according to the difference of the mobility μ increases. Thus, in order to apply appropriate mobility correction, it is necessary to set t to an optimal value. In the case of the graph shown in FIG. 11, the optimum value is in the vicinity of t = 2.5 us.

As described above, in the present invention, the V _th correction preparation operation by switching the gate potential from the high potential to the low potential and the V _th correction operation are performed within 1H, and then the video signal is transmitted within the same horizontal scanning period. Write. By this operation, the power supply line N'ya switching transistor by sharing the 3 kinds of power which is conventionally required in the signal line, it is possible to reduce the gate line, forming a pixel circuit of the third transistor 1 volume that Can do. As described above, the yield of the panel can be improved. In addition, high definition can be achieved by reducing the layout. In this embodiment, the mobility correction is performed by turning on the switching transistor Tr ₄ while the sampling transistor Tr ₁ is turned on. However, the mobility is set by making the sampling transistor Tr ₁ and the switching transistor Tr ₄ non-overlapping. Even in a simple V _th correction operation without correction, the number of wirings and transistors can be similarly reduced. Further, the circuit of this embodiment, the drive to the switching transistor other than the transistor Tr _d was used N-channel type, the characteristics of each transistor may also P-channel type even N-channel type.

Finally, an embodiment of the data driver constituting the signal unit (horizontal selector) of the display device according to the present invention will be described. In the present embodiment, the data driver arranged in the column direction of the image display device and used to display image data can switch and output a signal potential representing image data and a fixed potential for pixel circuit control, and, fixing the potential for the pixel circuit control, when requesting a higher voltage amplitude than the maximum rated voltage of a general data driver, the image data signal potential and a pixel circuit controlling fixed potential near the output terminal portion By increasing the breakdown voltage of only the switch function part to be switched, the necessary functions can be realized in the driver manufacturing process without the need to change to a higher breakdown voltage process, change the circuit size, increase the terminal pitch, etc. Is.

FIG. 12 shows an example of a pixel circuit (A) and a drive waveform (B) of an image display device in which a signal potential representing image data and a fixed potential for controlling a pixel circuit are mixed in a signal line . The pixel circuit shown in FIG. 5A includes three transistors , one pixel capacitor, and one light emitting element EL, and the pixel circuit according to the embodiment of the present invention shown in FIG. Is generalized. The signal potential V _sig of the video signal is supplied from the signal line SL. The voltage value of the signal potential V _sig, and drives the drive transistor Tr _d, causes the light emitting element EL in desired brightness. In this image display device, since the characteristic variation of the drive transistor Tr _d directly affects the image quality at this time, the pixel capacitance C _s is used to correct this variation during the correction period. When performing this correction operation, a fixed potential V _st for control is sent from the signal line SL to the pixel circuit using the drive waveforms of the scan pulse WS and the scan pulse DS. In conventional image display apparatus, image data system signal line and the drive control system signal lines of are separated, when inputting a signal of the control system will place another wiring and the scanning pulse. However, if the number of elements in the pixel circuit increases, the yield deteriorates due to transistor defects, and the area required for one pixel circuit increases. Therefore, adverse effects such as a decrease in physical resolution can be considered. the number of elements of the circuit to minimize, in order to correct the variation of the drive transistor Tr _d from the signal line SL, and a signal potential V _pc corresponding to the image data, the fixed potential V _st for pixel circuit control, sampling It is necessary to transmit separately at the time of correction and time of correction.

At this time, the fixed voltage V _st for controlling the pixel circuit is not necessarily in the same range as the signal voltage V _{pc of the} image data. As examples of the waveform timing chart of (B), the control signal voltage V _st, when higher than the image signal voltage V _pc is considered, and, V _st if higher than the rated voltage of the data driver IC There is also. The normal driver output is indefinite (high impedance) during the non-display period. In this pixel circuit, V _st and V _pc are separated into the sampling period and the correction period, and the voltage between them is at the ground level GND. It may be necessary to fix.

The block structure of satisfying the data driver IC3 of the driving waveform, shown in FIG. 13. A portion surrounded by a square solid line is a high withstand voltage output circuit unit 32. If only a circuit in this is increased by increasing the wiring film thickness, the image signal generation circuit unit 31 has a normal withstand voltage. And can be made by a process. The output circuit unit 32 includes voltage switching switches SW1 and SW2. However, since the control signal for the switch SW1 and the control signal for the switch SW2 are logic signals for controlling ON / OFF of the switch, there is no need to increase the breakdown voltage.

The output terminal 31B of the image signal generation circuit unit 31 outputs output voltages V _pc1 to V _pcn having the image display system power supply voltage V _pc as a maximum voltage. This output voltage is sent to the switch SW1 and switched to a fixed voltage for controlling the pixel circuit. Fixed voltage for the pixel circuit control is a logic pulse having an amplitude of the control system power supply voltage V _st. The output of the switch SW1 is sent to the switch SW2. This switch SW2 selects a signal or GND in order to fix the output terminal to the GND level when V _pc1 to V _pcn and V _st are switched. As a result, as the final output signal V _sig is the final output end 32B, control system power supply voltage maximum value to V _st or image display system power supply voltage to the maximum value V _pc1 ~ V _pcn, or, GND level voltage Is output.

The display device according to the present invention has a thin film device configuration as shown in FIG. This figure shows a schematic cross-sectional structure of a pixel formed on an insulating substrate. As shown in the figure, the pixel includes a transistor portion (a single TFT is illustrated in the figure) including a plurality of thin film transistors, a pixel capacitor such as a storage capacitor, and a light emitting portion such as an organic EL element. A transistor portion and a pixel capacitor are formed on the substrate by a TFT process, and a light emitting portion such as an organic EL element is stacked thereon. A transparent counter substrate is pasted thereon via an adhesive to form a flat panel.

The display device according to the present invention includes a flat module-shaped display as shown in FIG. For example , a pixel array part in which pixels made up of organic EL elements, thin film transistors, thin film capacitors, etc. are integrated in a matrix is provided on an insulating substrate, and an adhesive is provided so as to surround the pixel array part (pixel matrix part). The display module is formed by attaching a counter substrate such as glass. This transparent counter substrate, if necessary, a color filter, a protective layer may be also provided with a light shielding film. For example, an FPC (flexible printed circuit) may be provided in the display module as a connector for inputting / outputting a signal to / from the pixel array unit from the outside.

  The display device according to the present invention described above has a flat panel shape and is input to an electronic device such as a digital camera, a notebook personal computer, a mobile phone, or a video camera, or an electronic device. It is possible to apply to the display of the electronic device of all fields which display the image signal produced | generated in the inside as an image or an image | video. Examples of electronic devices to which such a display device is applied are shown below.

FIG. 16 shows a television to which the present invention is applied, which includes a video display screen 11 including a front panel 12, a filter glass 13, and the like, and is manufactured by using the display device of the present invention for the video display screen 11. .

FIG. 17 shows a digital camera to which the present invention is applied, in which the top is a front view and the bottom is a back view. This digital camera includes an imaging lens, a light emitting unit 15 for flash, a display unit 16, a control switch, a menu switch, a shutter 19, and the like, and is manufactured by using the display device of the present invention for the display unit 16.

Figure 18 shows a notebook personal computer over the present invention is applied, the body 20 includes a keyboard 21 which is operated to input characters and the like, the body cover includes a display unit 22 for displaying an image, the It is manufactured by using the display device of the invention for the display portion 22 thereof.

FIG. 19 shows a mobile terminal device to which the present invention is applied. The left side shows an open state and the right side shows a closed state. The portable terminal device includes an upper housing 23, a lower housing 24, a connecting portion (here, a hinge portion) 25, a display 26, a sub-display 27, a picture light 28, a camera 29, and the like, and includes the display device of the present invention. The display 26 and the sub-display 27 are used.

  FIG. 20 shows a video camera to which the present invention is applied. The video camera includes a main body 30, a lens 34 for photographing a subject, a start / stop switch 35 at the time of photographing, a monitor 36, etc. on the side facing forward. It is manufactured by using the device for its monitor 36.

It is a block diagram which shows the display apparatus concerning a reference example. It is a schematic diagram which shows the pixel circuit taken out from the display apparatus shown in FIG. 3 is a timing chart for explaining the operation of the display device shown in FIGS. 1 and 2. 1 is a block diagram showing an overall configuration of a display device according to the present invention. It is a block diagram which shows the structure of the pixel circuit contained in the display apparatus concerning this invention. FIG. 6 is a schematic diagram illustrating a pixel circuit cut out from the display device illustrated in FIG. 5. 6 is a timing chart for explaining the operation of the display device according to the present invention shown in FIGS. 4 and 5. It is a circuit diagram similarly used for operation | movement description. It is a graph similarly provided for operation explanation. It is a circuit diagram similarly used for operation | movement description. It is a graph similarly provided for operation explanation. It is a schematic diagram with which it uses for description of the data driver concerning this invention. It is a circuit diagram which shows the structural example of the data driver concerning this invention. It is sectional drawing which shows the device structure of the display apparatus concerning this invention. It is a top view which shows the module structure of the display apparatus concerning this invention. It is a perspective view which shows the television set provided with the display apparatus concerning this invention. It is a perspective view which shows the digital still camera provided with the display apparatus concerning this invention. 1 is a perspective view illustrating a notebook personal computer including a display device according to the present invention. It is a schematic diagram which shows the portable terminal device provided with the display apparatus concerning this invention. It is a perspective view which shows the video camera provided with the display apparatus concerning this invention.

1 ... pixel array, 2 ... pixel circuit, 3 ... horizontal selector (driver IC), 4 ... write scanner, 5 ... drive scanner, Tr ₁ ... sampling transistor, Tr ₄ · ..Switching transistors, Tr _d ... Drive transistors, C _s .. pixel capacitance, EL.

Claims (11)

A sampling transistor, a drive transistor, and a switching transistor, each including a light emitting element and a pixel capacitor, and a field effect transistor;
In the drive transistor, the gate is connected to one of the source and drain of the sampling transistor and one end of the pixel capacitor, and one of the source and drain is connected to the other end of the pixel capacitor and the light emitting element,
In the switching transistor, one of the source and the drain is connected to the other of the source and the drain of the drive transistor, and the other of the source and the drain is connected to a power source.
In a state where the switching transistor is non-conductive and the sampling transistor is conductive, the potential applied to the gate of the drive transistor from the other of the source and drain of the sampling transistor is changed from the first fixed potential of high potential to the second potential of low potential. After switching to a fixed potential, so that the voltage between the gate of the drive transistor and one of the source and drain exceeds the threshold voltage of the drive transistor by coupling through the pixel capacitance,
By connecting the other of the source and drain of the drive transistor to the power supply with the switching transistor in a conductive state, the potential of one of the source and drain of the drive transistor is set to a potential obtained by subtracting the threshold voltage of the drive transistor from the second fixed potential. A method for driving a pixel circuit, which includes a step of bringing the pixel closer together. 2. The pixel circuit driving method according to claim 1, wherein after the step, a signal potential is applied to the gate of the drive transistor from the other of the source and drain of the sampling transistor through the sampling transistor in a conductive state. When a signal potential is applied to the gate of the drive transistor, a current flows through the drive transistor having the other of the source and drain connected to the power source by the conductive switching transistor, and the potential of one of the source and drain of the drive transistor The driving method of the pixel circuit according to claim 2, wherein the voltage changes. After applying a signal potential to the gate of the drive transistor, the sampling transistor is turned off, and a current corresponding to the value of the voltage between the gate of the drive transistor held in the pixel capacitor and one of the source and drain 3. The pixel circuit driving method according to claim 2, wherein the light-emitting element emits light by flowing into the light-emitting element through a drive transistor in which the other of the source and the drain is connected to a power source by the switching transistor in a conductive state. A sampling transistor, a drive transistor, and a switching transistor, each including a light emitting element and a pixel capacitor, and a field effect transistor;
In the drive transistor, the gate is connected to one of the source and drain of the sampling transistor and one end of the pixel capacitor, and one of the source and drain is connected to the other end of the pixel capacitor and the light emitting element,
In the switching transistor, one of the source and the drain is connected to the other of the source and the drain of the drive transistor, and the other of the source and the drain is a pixel circuit connected to a power source,
In a state where the switching transistor is non-conductive and the sampling transistor is conductive, the potential applied to the gate of the drive transistor from the other of the source and drain of the sampling transistor is changed from a first fixed potential having a high potential to a first potential having a low potential. After the voltage between the gate of the drive transistor and one of the source and drain exceeds the threshold voltage of the drive transistor by being switched to 2 fixed potential and coupled through the pixel capacitance,
When the switching transistor is turned on and the other of the source and drain of the drive transistor is connected to the power supply, the potential of one of the source and drain of the drive transistor is a potential obtained by subtracting the threshold voltage of the drive transistor from the second fixed potential. Pixel circuit that can be approached toward It has pixels arranged in a matrix,
Each pixel includes a light emitting element, a pixel capacitor, and a field effect transistor, a sampling transistor, a drive transistor, and a switching transistor,
In the drive transistor, the gate is connected to one of the source and drain of the sampling transistor and one end of the pixel capacitor, and one of the source and drain is connected to the other end of the pixel capacitor and the light emitting element,
In the switching transistor, one of the source and the drain is connected to the other of the source and the drain of the drive transistor, and the other of the source and the drain is connected to a power source.
In a state where the switching transistor is non-conductive and the sampling transistor is conductive, the potential applied to the gate of the drive transistor from the other of the source and drain of the sampling transistor is changed from the first fixed potential of high potential to the second potential of low potential. After switching to a fixed potential, so that the voltage between the gate of the drive transistor and one of the source and drain exceeds the threshold voltage of the drive transistor by coupling through the pixel capacitance,
By connecting the other of the source and drain of the drive transistor to the power supply with the switching transistor in a conductive state, the potential of one of the source and drain of the drive transistor is set to a potential obtained by subtracting the threshold voltage of the drive transistor from the second fixed potential. A method for driving a display device, which includes a step of bringing them closer together. The method for driving a display device according to claim 6, wherein after the step, a signal potential is applied from the other of the source and drain of the sampling transistor to the gate of the drive transistor through the sampling transistor in a conductive state. When a signal potential is applied to the gate of the drive transistor, a current flows through the drive transistor having the other of the source and drain connected to the power source by the conductive switching transistor, and the potential of one of the source and drain of the drive transistor The method for driving a display device according to claim 7, wherein the voltage changes. After applying a signal potential to the gate of the drive transistor, the sampling transistor is turned off, and a current corresponding to the value of the voltage between the gate of the drive transistor held in the pixel capacitor and one of the source and drain The display device driving method according to claim 7, wherein the light-emitting element emits light by flowing into the light-emitting element through a drive transistor in which the other of the source and the drain is connected to the power source by the conductive switching transistor. It has pixels arranged in a matrix,
Each pixel includes a light emitting element, a pixel capacitor, and a field effect transistor, a sampling transistor, a drive transistor, and a switching transistor,
In the drive transistor, the gate is connected to one of the source and drain of the sampling transistor and one end of the pixel capacitor, and one of the source and drain is connected to the other end of the pixel capacitor and the light emitting element,
In the switching transistor, one of the source and the drain is connected to the other of the source and the drain of the drive transistor, and the other of the source and the drain is connected to a power source,
In a state where the switching transistor is non-conductive and the sampling transistor is conductive, the potential applied to the gate of the drive transistor from the other of the source and drain of the sampling transistor is changed from a first fixed potential having a high potential to a first potential having a low potential. After the voltage between the gate of the drive transistor and one of the source and drain exceeds the threshold voltage of the drive transistor by being switched to 2 fixed potential and coupled through the pixel capacitance,
When the switching transistor is turned on and the other of the source and drain of the drive transistor is connected to the power supply, the potential of one of the source and drain of the drive transistor is a potential obtained by subtracting the threshold voltage of the drive transistor from the second fixed potential. A display device that can be brought closer to the screen. An electronic apparatus comprising the display device according to claim 10.