JP4039441B2 - Electro-optical device and electronic apparatus - Google Patents

Description

  The present invention relates to an electro-optical device that performs display of information equipment such as a television and a computer, and more particularly to an electro-optical device and an electronic device using an electro-optical element such as an organic EL (Electro Luminescence) element.

  In recent years, organic EL display devices have attracted attention as monitor displays for portable information devices such as mobile phones because of their characteristics of light weight, thinness, high brightness, and wide viewing angle. A typical active matrix organic EL display device is configured to display an image by a plurality of display pixels arranged in a matrix. The display pixel includes a pixel circuit for each pixel that is a minimum unit of display. This pixel circuit is a circuit for controlling the current or voltage supplied to the electro-optical element.

  In such an organic EL display device, a plurality of scanning lines are arranged along the rows of these display pixels, a plurality of data lines are arranged along the columns of these display pixels, and a plurality of pixel switches are connected to these scanning lines and It is arranged near the intersection of the data lines. Each display pixel includes at least an organic EL element, a driving transistor connected in series to the organic EL element between a pair of power supply terminals, and a holding capacitor that holds the gate voltage of the driving transistor. The selection switch of each pixel is turned on in response to the scanning signal supplied from the corresponding scanning line, and the video signal (voltage or current) supplied from the corresponding data line is directly or as a result of correcting the variation in pixel circuit characteristics. A gradation voltage is applied to the gate of the driving transistor. The drive transistor supplies a drive current corresponding to the gradation voltage to the organic EL element.

An organic EL element has a structure in which a light-emitting layer, which is a thin film containing a fluorescent organic compound of red, green, or blue, is sandwiched between a common electrode (cathode) and a pixel electrode (anode). Are excited and recombined to generate excitons, which emit light by light emission generated when the excitons are deactivated. In the case of a bottom emission type organic EL element, the electrode is a transparent electrode made of ITO or the like, and the common electrode (cathode) electrode is made of a reflective electrode obtained by reducing the resistance of an alkali metal or the like with a metal such as aluminum. . With this configuration, with an organic EL element alone, a luminance of about 100 to 100,000 cd / m ² can be obtained with an applied voltage of 10 V or less.

  As disclosed in Patent Document 1, each pixel circuit of the organic EL display device includes a thin film transistor (TFT) as an active element. This thin film transistor is formed by, for example, a low-temperature polysilicon TFT.

Japanese Patent Laid-Open No. 5-107561

  In order to improve display quality in this type of display device, it is desirable that the electrical characteristics of the pixel circuit be uniform across all pixels. However, low-temperature polysilicon TFTs tend to have characteristic variations during recrystallization, and crystal defects may occur. For this reason, in a display device using a thin film transistor made of a low-temperature polysilicon TFT, it is extremely difficult to make the electrical characteristics of the pixel circuit uniform over all pixels. In particular, when the number of pixels is increased to increase the definition of the display image or to increase the screen size, the possibility of variations in the characteristics of each pixel circuit is further increased, and the problem of deterioration in display quality becomes even more pronounced. In addition, due to the limitations of the laser annealing apparatus for recrystallization, it has been difficult to increase the substrate size like an amorphous TFT (α-TFT) and improve productivity.

  On the other hand, α-TFT has relatively few transistor variations, and has a track record of mass production of large-sized substrates in LCDs driven by alternating current. However, if gate voltage is constantly applied in one direction, the threshold voltage shifts. This adversely affects the image quality, such as the current value changes and the brightness decreases. Moreover, since the mobility of the α-TFT is small, there is a limit to the current that can be driven with a high-speed response, and only an n-channel TFT has been put into practical use.

  Further, to date, the organic EL element has a structure in which the TFT substrate side is the pixel electrode (anode) and the common electrode (cathode) is the surface side of the element due to limitations of the organic EL manufacturing technology that comes from the materials used. I don't get it. Therefore, in the conventional pixel circuit shown in FIG. 9, the relationship between the common electrode power supply 38, the pixel electrode (anode) of the organic EL element 16 and the P-channel drive TFT 61 is such that the drive transistor can operate in the saturation region as shown in FIG. Limited to connection relationships. Further, generally, when it is attempted to keep the luminance of the organic EL element constant, the resistance of the organic EL element increases with the passage of time. Therefore, the organic EL element must be driven with a constant current. For this reason, the drive circuit is composed of three or more TFTs, and a low-temperature polysilicon P-channel TFT capable of supplying a constant current regardless of load variation has been used as the drive TFT. Incidentally, in FIG. 9, when the drive transistor 61 is an n-channel TFT, the source electrode of the drive transistor 61 is on the organic EL element side (source follower), and the current value changes with load fluctuation.

Furthermore, the drive circuit requires a display data write preparation signal and a forced off signal in addition to the power supply wiring and the scanning line, and supplying these from the external driver IC is limited by the connection pitch of the connection terminals, It was difficult. There was a limit of 1 to 2 per pixel.
For this reason, it has been considered impossible to use an α-TFT for driving an organic EL element.

  The present invention has been made in view of such circumstances, and the object thereof can be configured by a drive element having a low driving capability such as an α-TFT in a circuit for driving a driven element such as an electro-optical element. It is an object to provide a drive circuit, a drive method, and an electro-optical device using the same.

  In order to solve the above problems, an electro-optical device according to the present invention is arranged corresponding to a plurality of scanning lines, a plurality of data lines, and an intersection of the plurality of scanning lines and the plurality of data lines. A plurality of pixels and a plurality of first power supply wirings, wherein each of the plurality of pixels includes an electro-optic element, a drive transistor connected to the electro-optic element, and the plurality of scanning lines. A first switch transistor whose conduction is controlled by a scanning signal supplied through a corresponding scanning line; a second switch transistor connected to the first switch transistor; a first electrode; A capacitor that forms a capacitance with an electrode, the first capacitor being connected between the gate and the source of the driving transistor via the first electrode; and the first switch transistor; A second capacitor connected in series between the gate of the driving transistor, a bias transistor connected between the gate and drain of the driving transistor, the second electrode, and a first predetermined potential; Switching means for controlling the electrical connection of the second switching transistor, and the conduction state of the second switching transistor and the bias transistor is controlled by a periodic signal different from the scanning signal supplied via the corresponding scanning line It is characterized by being.

In this configuration, since the charge holding capacitor is provided between the source electrode and the gate electrode of the driving transistor, the source and gate of the driving transistor are connected even if the electro-optic element is connected to the driving transistor as a source follower. The inter-voltage V _GS is maintained even if the source voltage changes. As a result, a drive current corresponding to the data signal supplied via the data line is supplied to the electro-optical element, and the electro-optical element can be operated with predetermined characteristics.

  Note that the electro-optical element applied to the electro-optical device according to the present invention converts an electrical action such as supply of current or application of voltage into an optical action such as change in luminance or transmittance, or an optical effect. The action is converted into an electric action. A typical example of such an electro-optical element is an organic EL element that emits light with luminance corresponding to a current supplied from a pixel circuit. However, the present invention can be applied to apparatuses using other electro-optical elements.

  In a preferred embodiment, each of the plurality of electro-optic elements is disposed at a different position in the plane. For example, the plurality of electro-optical elements are arranged in a matrix over the row direction and the column direction.

  Further, in the above-described electro-optical device, the first capacitor holds a data signal supplied via a corresponding data line among the first switch transistor and the plurality of data lines as a charge amount, and The second electrode is connected between the driving transistor and the electro-optic element, and is set to the first predetermined potential by conducting the switch means, and the corresponding data line among the plurality of data lines Before the data signal is supplied via the first switch transistor, the electrode on the side holding the data signal of the first switch transistor may be set to a second predetermined potential by conducting the second switch transistor. preferable.

  According to this configuration, the source electrode of the driving transistor to which the second electrode of the first capacitor for holding electric charge is connected is configured such that the data signal supplied via the data line drives and controls the driving transistor. Is set to the ground potential or a predetermined potential by the switch means. As a result, even when an electro-optic element is connected between the source electrode and the second power supply, the data signal is always written to a constant potential, so that the drive current of the drive transistor is 1: 1 to the data signal. Can be set to a value corresponding to. Therefore, the electro-optical element can be operated with predetermined characteristics.

  In a more specific aspect of the electro-optical device according to the invention, the predetermined potential is the same as the ground potential. According to this configuration, the ground potential can be used without increasing the number of power supplies of the electro-optical device, which leads to a reduction in power supply cost.

  In a more specific aspect of the electro-optical device according to the invention, the driving transistor is an n-channel transistor. According to this aspect, the performance of the drive circuit is improved by using the most suitable transistor in consideration of the performance of the transistor constituting the TFT substrate and the productivity of the TFT substrate without changing the conventional manufacturing method of the organic EL element. Can be achieved.

  In a further preferred embodiment, the driving transistor is an amorphous thin film transistor (α-TFT). According to this configuration, the pixel portion that occupies most of the area of the drive substrate can be configured with the same type of channel transistor, and thus the TFT substrate can be easily manufactured. A large electro-optical panel in which a large number of electro-optical elements are arranged in a matrix can be realized at an early stage by using an amorphous TFT technology that has established a large-size technology. Even when a polysilicon TFT is used, it is preferable that the pixel portion is composed of the same type of channel transistor because it is easy to optimize the TFT manufacturing conditions.

  In another aspect, before the data signal is supplied to each of the plurality of pixels via the corresponding data line among the plurality of data lines, the data signal of the first switch transistor is held on the side that holds the data signal The electrode is set to a second predetermined potential that is different from the first predetermined potential. According to this configuration, the data is initialized to a predetermined potential before the data signal is written to the drive control means, so that the gate voltage of the drive transistor can be changed to AC or the threshold compensation detection of the drive transistor can be detected as the value of the data signal. Since this can be performed without being influenced by the threshold voltage fluctuation of the driving transistor can be suppressed.

  In still another aspect, each of the plurality of pixels further includes a second switch transistor that controls a connection between an electrode on the data holding side of the first switch transistor and the second predetermined potential. The conduction state of the second switch transistor is controlled by a periodic signal supplied before the scanning signal for controlling the conduction state of the first switch transistor is supplied. According to this configuration, when initialization is required before writing a data signal to the drive control unit, the drive control unit can be initialized using another period that does not affect the data signal write timing. is there. Further, since the organic EL element does not emit light during this initialization period, this initialization period may be used as a light extinguishing period as a countermeasure against moving image blur.

  In yet another aspect, the periodic signal for controlling the conduction state of the second switch transistor is the scanning signal before the scan signal for controlling the conduction state of the first switch transistor is supplied. Supplied through either According to this configuration, when initialization is required before writing a data signal to the drive control means, a periodic write preparation signal can be used as a scanning signal. As a result, an increase in the internal circuit scale of the scan driver and the number of connection terminals between the scan driver and the organic EL panel can be suppressed, and initialization can be performed without affecting the sampling input time of the drive control means. This makes it easy to realize a large-scale and more complex matrix driving circuit than an LCD even when a transistor with low driving capability such as an α-TFT is used.

  Further, since the reset state is held until the next data signal is written to the pixel, this period can be set to the display-off state (drive-off state). The length of this display off period is determined by which scanning signal is used as the write preparation signal. Therefore, in the active display, the operation time duty of the electro-optic element can be changed as appropriate in accordance with the necessity of countermeasures against moving image blur. The operating time duty is preferably 60 to 10%.

  In another preferred embodiment, the second electrode is connected to a source of the drive transistor, and at least during the period in which the first capacitor holds a charge amount corresponding to the data signal, The potential difference between the source and the gate is kept constant. According to this configuration, the amount of charge held in the capacitor is held, and the potential difference between the source and the gate of the driving transistor is unchanged. For this reason, even if the drive transistor is connected to the electro-optical element as a source follower, a drive current corresponding to the data signal can flow.

  In a preferred aspect of the present invention, a data signal supplied to each of the plurality of pixels via a corresponding data line among the plurality of data lines is not supplied by the first switch transistor at the latest. The second electrode is set to the first predetermined potential. According to this aspect, even when the driving transistor connects the organic EL element to the source side, the gate voltage reference for controlling the driving current of the driving transistor is reached by the time when the writing of the data signal is completed. Since the source voltage is set to a predetermined potential, the capacitor can store charges corresponding to the data signal with the predetermined potential as a reference. As a result, the drive current of the drive transistor can be set to a value corresponding to the data signal on a one-to-one basis. Therefore, the organic EL element can emit light with a predetermined luminance.

  In a more preferred aspect, each of the plurality of pixels further includes a plurality of second power supply lines for supplying the first predetermined potential to the second electrode included in each of the plurality of pixels. According to this configuration, the first predetermined potential can be independently supplied to each of the pixels.

  In another aspect, the plurality of first power supply lines and the plurality of second power supply lines have the same metal wiring layer portion and are provided so as to cross each other. According to this configuration, since the first power supply wiring can be arranged with priority over other signal lines and power supply wiring, the first power supply wiring can be supplied with low impedance and low crosstalk. Further, the light shielding layer of the TFT can be efficiently formed using metal wiring.

  In still another aspect, the electro-optical element is an organic EL element. According to this configuration, the organic EL element has a low driving voltage, and with the progress of light emitting materials, etc., it has become possible to emit light with a high luminance with a gradually decreasing driving current, so a large-sized display can be realized with relatively low power consumption. it can.

  In a more specific aspect, the second switch transistor, the bias transistor, and the switch means are all controlled by a common signal. According to this configuration, the number of signal lines for controlling the second switch transistor and the switch means can be minimized, and a data signal can be accurately stored in the capacitor connected to the gate of the drive transistor.

  According to the present invention, since an electro-optic element using a conventional manufacturing method can be driven by a drive circuit composed of a mono-channel TFT such as an α-TFT, a large-size electro-optic device that has been impossible in the past can be realized. . In particular, when applied to an organic EL display, it is possible to obtain an active substrate that realizes a very thin and high-quality large-screen display. Also, in order to adjust the video with sharp outlines and display brightness over a wide range, even if multiple different types of periodic control lines are required in the scan line direction for each pixel drive circuit, the number of connection terminals is not increased. In addition, since it can be controlled by a combination of scanning lines, a display with higher definition and superior expressive power can be realized.

Example 1
Embodiments of the present invention will be described below with reference to the drawings. The form shown below shows one mode of the present invention, does not limit the present invention, and can be arbitrarily changed within the scope of the present invention. Further, in the respective drawings shown below, the dimensions and ratios of the respective constituent elements are appropriately changed from the actual ones in order to make the respective constituent elements large enough to be recognized on the drawings.

  First, a mode in which the electro-optical device according to the present invention is applied to an organic EL display device as a device for displaying an image will be described. FIG. 6 shows a configuration of the organic EL display device 110. The organic EL display device 110 includes an organic EL panel 111, a display module 100 including an external drive circuit that drives the organic EL panel 111, and a peripheral control unit.

  The display module 100 includes an organic EL panel 111 and an external drive circuit. The organic EL panel 111 includes a plurality of display pixels PX arranged in a matrix to display an image on a glass substrate, a plurality of scanning lines 11 arranged along the rows of the display pixels PX, and the display pixels PX. A plurality of data lines 12 and a plurality of pixel power supply lines 35 are provided along the column. The external driving circuit includes a scanning line driver 14 that drives a plurality of scanning lines, a pixel power supply circuit 19 that supplies a driving current to the organic EL elements in the display pixel PX, and a data line driver that outputs a pixel driving signal to the data lines. 15. The pixel power supply circuit 19 may not be necessary depending on the configuration of the display pixel PX.

In the display pixel circuit of FIG. 1 which is the first embodiment, each display pixel PX has an organic EL element 16 between the pair of first and second power supply terminals V _E and the ground power supply terminal GND. Drive transistor 17 that is an n-channel thin film transistor (TFT) connected in series to 16, a holding capacitor 18 that holds the gate voltage of the drive transistor 17, and an n-channel continuity in which the terminals of the organic EL element 16 have substantially the same potential. The transistor 22 includes a pixel selection switch 13 that selectively applies a video signal from the data line 12 to the gate of the driving transistor 17, and a reset transistor 23 that initializes the gate potential of the driving transistor 17 to a predetermined potential (Vee).

The power supply terminal V _E is set to a predetermined potential of + 28V, for example, and the ground power supply terminal GND is set to a potential of 0V that is lower than the predetermined potential, for example. All the transistors constituting the pixel circuit are n-channel TFTs. Each pixel selection switch 13 applies the gradation voltage Vsig of the video signal supplied from the corresponding data line 12 to the gate of the driving transistor 17 when driven by the scanning signal supplied from the corresponding scanning line 11. The drive transistor 17 supplies a drive current Id corresponding to the gradation voltage Vsig to the organic EL element 16. The organic EL element 16 emits light with a luminance corresponding to the drive current Id.

  The data line driver 15 converts the video signal output from the display controller 103 in each horizontal scanning period from a digital format to an analog format, and supplies the voltage of the video signal to the plurality of data lines 12 in parallel. The scanning line driver 14 sequentially supplies scanning signals to the plurality of scanning lines 11 in each vertical scanning period. The pixel selection switches 13 in each row are turned on for one horizontal scanning period by a scanning signal supplied in common from one of these scanning lines 11 until the scanning signal is supplied again after one vertical scanning period. Period (one frame) becomes non-conductive. The drive transistors 17 for one row supply drive currents corresponding to the voltages of the video signals supplied from the data lines 12 to which the pixel selection switches 13 are connected to the organic EL elements 16, respectively.

  Further, the scanning line driver 14 conducts the reset transistor 23 connected between the gate of the driving transistor 17 and the power source Vee prior to the output of each scanning signal, and temporarily sets the gate potential of the driving transistor to a predetermined voltage Vee. A periodic write preparation signal R is output so that a drive current does not flow through the organic EL element. As the write preparation signal R, as shown in FIG. 6, a signal of a scanning line that is output from each scanning line to the pixel circuit of one row or a specific row before the scanning line may be used. This can be realized by adding scanning lines, and does not increase the number of connection terminals between the organic EL panel 111 and the scanning line driver. Incidentally, the write preparation signal line 36 connected to the first stage pixel circuit may be a scan line output from the subsequent stage of the scan line driver 14. Since this reset state is held until the next data signal is written to the pixel, this period can be set as a forced display off period (drive off period). The length of this display off period is determined by which scanning signal is used as the write preparation signal. Therefore, in the active display, the light emission time duty of the organic EL element 16 can be changed as appropriate in accordance with the necessity of countermeasures against moving image blur. The light emission time duty is preferably 60 to 10%.

  The display pixel PX further includes a holding capacitor 18 connected between the gate electrode and the source electrode of the drive transistor 17 and a conduction transistor 22 connected between the source electrode and the GND electrode of the drive transistor 17. The scanning line 11 is connected to the gate electrode of the conduction transistor 22 and is turned on simultaneously with the conduction of the pixel selection switch 13. Thus, the gradation voltage Vsig of the video signal supplied from the corresponding data line 12 is accumulated in the holding capacitor 18 without being affected by the voltage between the terminals of the organic EL element 16. While the conducting transistor 22 is conducting, no current flows through the organic EL element 16, so the organic EL element 16 does not emit light. In synchronization with the conduction of the conducting transistor 22, a switch for making it non-conductive may be provided between the power source VE and the driving transistor 17.

Next, when the scanning line is in a non-selected state and the pixel selection switch 13 and the conducting transistor 22 are turned off, a constant current corresponding to the voltage stored in the holding capacitor 18 is supplied from the driving transistor 17 to the organic EL element 16. The organic EL element emits light. In this case, the source potential of the drive transistor 17 rises as the potential of the organic EL element 16 rises and becomes a source follower-like state, but the potential between the source and gate electrodes of the drive transistor is held by the holding capacitor 18. . The power supply terminal V _E is supplied with a voltage necessary for the drive transistor 17 to operate in the saturation region. As a result, the drive transistor 17 supplies a constant current corresponding to the gate potential to the organic EL element 16, and the organic EL element 16 emits light with a constant luminance for one frame period until the next write preparation signal R is input. become.

This series of timing charts is shown in FIG. In the figure, the gate voltage V _{GD as} viewed from the drain of the drive transistor 17 changes in an alternating manner. As a result, fluctuations in the threshold value of the drive transistor 17 that particularly require characteristic stability in order to maintain image quality are suppressed. In terms of the inferior driving capability of the α-TFT, a driving capability equivalent to that of the low-temperature polysilicon can be obtained by increasing the voltage by several tens of V compared to the case of the low-temperature polysilicon TFT.

In the above description, the source electrode of the conduction transistor 22 is connected to the common electrode (cathode) of the organic EL element 16, but may be connected by providing a specific voltage supply line in a range where the organic EL element 16 does not emit light. . If the specific voltage value is set to a value close to the threshold voltage of the organic EL element 16, there is also an effect of suppressing light emission delay due to a capacitor parasitic on the organic EL element. In order to suppress variation in characteristics of the drive transistor 17, the drive transistor 17 may be configured by connecting a plurality of transistors in parallel.
(Example 2)

  FIG. 3 is a display pixel circuit showing a second embodiment of the present invention. The display pixel PX in this figure includes a kick capacitor 20 connected in series between the pixel selection switch 13 and the gate electrode of the drive transistor 17, a bias transistor 21 connected between the gate electrode and the drain electrode of the drive transistor 17, and a drive transistor. The holding capacitor 18 connected between the gate electrode and the source electrode 17, the conduction transistor 22 that short-circuits between the pixel electrode and the common electrode (cathode) of the organic EL, and the connection point between the pixel selection switch 13 and the kick capacitor 20 and the power source Vee A threshold compensation circuit for the drive transistor 17 including the reset transistor 23 connected therebetween is included.

  Each transistor in the display pixel circuit is composed of an n-channel TFT, the pixel selection switch 13 is controlled by a scanning signal SEL from the outside, and the bias transistor 21, the conduction transistor 22 and the reset transistor 23 are by a write preparation signal R from the outside. Be controlled. By this control, the bias transistor 21 is turned on only while the predetermined voltage Vee is supplied via the reset transistor 23, and at the same time, the conduction transistor 22 is turned on and the ground potential GND is supplied to the source electrode of the drive transistor 17. At this time, the organic EL element 16 does not emit light.

  In this threshold value compensation circuit, a write preparation signal R is applied to the gate electrode of the reset transistor 23 prior to the periodically coming scanning signal SEL, and at the same time a predetermined voltage Vee is supplied via the reset transistor 23, the bias transistor 21 and the conduction transistor 22 become conductive. At this time, the power source VEL is in a high impedance state, but the current of the drive transistor 17 is changed until the gate voltage becomes equal to the threshold voltage Vth of the drive transistor 17 due to the current flowing through the bias transistor 21 from the residual charge on the power line 35. The node potential between the gate electrode and the kick capacitor 20 rises.

After the node potential is stabilized, the write preparation signal R becomes inactive (“L” level), whereby the reset transistor 23, the conduction transistor 22, and the bias transistor 21 become non-conduction. As a result, the second electrode of the holding capacitor 18 is set to the GND potential, and the organic EL element 16 enters a non-light emitting state. This state is maintained while the power supply VEL is in a high impedance state. That is, even if there is a time difference between the input timings of the write preparation signal R and the scanning signal SEL, the above state is maintained and the organic EL element 16 does not emit light. Next, when the scanning signal is applied to the gate electrode of the pixel selection switch 13 and the video signal voltage is supplied, the node potential V _G2 between the gate electrode of the driving transistor 17 and the kick capacitor 20 causes the threshold voltage Vth to be imaged. The level is added to the signal voltage. Next, after the scanning signal SEL is in a non-selected state and the pixel selection switch 13 becomes non-conductive, the power source VEL is supplied, and a predetermined driving current compensated for Vth is supplied from the power source VEL through the driving transistor 17 to the organic EL element. 16 flows. Here, as described in the first embodiment, the source potential of the drive transistor 17 increases in accordance with the increase in the interelectrode potential of the organic EL element, and becomes a source follower-like state. The potential between the gate electrodes is maintained. As a result, the drive current is determined by the potential difference between the predetermined voltage Vee and the video signal voltage, and the drive current is not affected even if the threshold voltage Vth of the drive transistor 17 varies.

FIG. 4 shows this series of timing operations. During the display, this series of operations is periodically repeated. In the figure, the gate voltage V _G2D viewed from the drain of the driving transistor 17 changes in an alternating manner with the GND potential interposed therebetween. As a result, fluctuations in the threshold value of the drive transistor 17 that particularly require characteristic stability in order to maintain image quality are suppressed.

  In order to suppress variation in characteristics, the drive transistor 17 may be arranged in parallel in the arrangement of the drive transistor in two directions, upper and lower, left and right, or a plurality of transistors as shown in FIG. Alternatively, a ring gate structure in which the electric field tends to be uniform may be used. (Example 3)

  A third embodiment of the present invention will be described based on the display pixel circuit shown in FIG. 5 and the timing chart of FIG. The display pixel PX of FIG. 5 is a current program type pixel circuit different from the first and second embodiments. The display pixel PX of FIG. 5 includes a pixel selection switch 50 connected to the data line 58, a conversion transistor 52 connected to the pixel selection switch 50 and the ground power supply wiring 60 (GND), and a gate electrode and a drain electrode of the conversion transistor 52. The gate electrode is connected to the gate electrode of the bias transistor 51 and the conversion transistor 52 connected between the conversion transistor 52 and the drive transistor 53 constituting the current mirror circuit, and is connected between the gate electrode of the drive transistor 53 and the organic EL element 16. A capacitor 55, a conduction transistor 54 connecting the pixel electrode (anode) and the common electrode (cathode) of the organic EL element 16, and a power source VEL connected to the drain electrode of the drive transistor 53.

  Each transistor in the display pixel circuit is composed of an n-channel TFT, the pixel selection switch 50 and the conduction transistor 54 are controlled by a scanning signal SEL from the outside, and the bias transistor 51 is a periodic erase signal ER from the outside. Be controlled.

  First, at the time of current programming, the scanning signal SEL and the erase signal ER are selected. However, the erase signal ER may be selected prior to the scanning signal SEL, as shown in FIG. 10, so that the bias transistor 51 is turned on and the gate electrode of the drive transistor 53 is substantially turned off. In this case, the erase signal ER may be used by ORing (ORing) any one of the scanning signal SEL and a plurality of scanning line outputs supplied before the scanning signal SEL. Thereby, the display off period for the moving image blur countermeasure described in the first and second embodiments can be set. As a result, a non-light emission period is always periodically inserted in one frame period of each pixel, and a phenomenon in which the outline of a moving image is blurred can be prevented. The ratio of the light emission time for preventing moving image blur is preferably 60 to 10% of the entire period.

  Next, when the scanning signal SEL is selected, the conducting transistor 54 is turned on, and the potential VELC of the source electrode of the driving transistor 53 becomes substantially the same potential as the ground power supply GND. At this time, since the pixel selection switch 50 and the bias transistor 51 are conductive, by connecting the current source CS corresponding to the video signal to the data line 58, the signal current corresponding to the luminance information of the video signal is connected to the conversion transistor 52. Iw flows. The current source CS is a variable current source that is in the data line driver 15 of FIG. 6 and is controlled according to luminance information. At this time, since the gate electrode and the drain electrode of the conversion transistor 52 are short-circuited by the bias transistor 51, the conversion transistor 52 operates in a saturation region. At this time, the gate-source voltage Vgs of the conversion transistor 52 is stored in the holding capacitor 55. Since the conducting transistor 54 is conducting while the scanning signal SEL is in the selected state, the current IEL does not flow through the organic EL element 16 even when the bias voltage Vgs is applied to the gate electrode of the driving transistor 53.

  Next, the scanning signal SEL and the erase signal ER are not selected. As a result, the pixel selection switch (transistor) 50, the bias transistor 51, and the conduction transistor 54 are rendered non-conductive, and the gate-source voltage Vgs stored in the capacitor 55 is maintained. Therefore, the drive transistor 53 in a current mirror relationship with the conversion transistor 52 flows the drive current reduced by the size ratio of the conversion transistor 52 and the drive transistor 53 from the power supply VEL to the organic EL element 16. The above operation is periodically repeated for each frame, and display is performed.

  Here, as described in the first embodiment, the source potential VELC of the drive transistor 53 increases in accordance with the increase of the potential of the organic EL element 16 and becomes a source follower-like state. As for the potential between the gate electrode and the gate electrode, the value at the time of current programming is maintained. As a result, a constant current corresponding to the luminance information of the video signal flows through the organic EL element 16, and the organic EL element 16 is driven so as to maintain the light emission luminance during a period (one frame) until the next current program is performed. The gate potentials of the conversion transistor 52 and the drive transistor 53 are biased in one direction and are subject to threshold fluctuations, but are compensated to absorb the threshold fluctuations during current programming.

  In order to increase the accuracy of the holding voltage Vgs at the time of current programming, a switch transistor is provided between the driving transistor 53 and the power source VEL, or the power source VEL is set to a high impedance as in the second embodiment to supply current to the organic EL element 16. You may make it not flow. Further, if the manufacturing method of the organic EL element advances and the anode common type organic EL element can be easily manufactured and the organic EL element 16 can be connected to the drain side of the driving transistor 53, the organic EL element 16 And the conduction transistor 54 connected in parallel with each other may be unnecessary. However, it is necessary when the organic EL element 16 is made to emit no light during current programming to the pixel circuit. Further, during current programming, the source electrode of the conduction transistor 54 is connected to a power supply different from the ground power supply GND, and the drain electrode is connected to the connection point between the organic EL element 16 and the driving transistor 53 to connect the organic EL element 16 and the driving transistor 53 to each other. A reverse bias may be applied.

  7 shows a planar structure around the display pixel PX in FIG. 3, and FIG. 8 shows a cross-sectional structure along the line AB in FIG. The metal wiring layer 35 shown in FIG. 8 is a power supply line VEL provided for each row of the display pixels PX, and is disposed in the region of the drive transistor 17, the conduction transistor 22, the pixel selection switch 13, and the bias transistor 21, and FIG. As shown in FIG. 8, it is formed so as to cover the channel region of the transistor. The holding capacitor 18 is formed by capacitive coupling between the metal wiring layer 35 and the gate wiring 17G, and the kick capacitor 20 is formed by capacitive coupling between the gate wiring 17G and the source electrode metal wiring 39 of the pixel selection switch 13. The capacitance values of the kick capacitor 20 and the holding capacitor 18 have extremely large values compared to the capacitance values formed parasitically at the nodes VG1 and VG2.

  In FIG. 7, the organic EL element 16 is arranged separately from the TFT arrangement region assuming bottom emission, but the top in which the organic EL element is formed using the entire pixel region on the planarized interlayer film 44. An emission structure is also possible. Also in this case, the ground power supply wiring 38 (GND) and the VEL power supply line 35 which is the drive power supply wiring of the light emitting element 16 have a portion in the same layer as the metal wiring layer (35, 39, etc.) shown in FIG. The power supply wiring 38 (GND) is arranged so as to cross the VEL power supply line 35. Since the common electrode which is the ground power supply GND of the light emitting element 16 is separately formed as the uppermost electrode of the light emitting element layer, the drive current for the light emitting element 16 does not have to flow directly to the ground power supply wiring 38 (GND). For this reason, even if a three-dimensional intersection with the VEL power supply line 35 is formed using a semiconductor island, it is difficult to affect the operation characteristics of the pixel circuit.

Next, a light-emitting element applicable to the present invention will be described.
The light-emitting element to which the present invention can be applied includes an organic EL element, a field emission element (FED), a surface conduction emission element (SED), a ballistic electron emission element (a light emitting organic material such as a low molecule, a polymer, or a dendrimer) ( Preferred examples include self-luminous elements such as BSD) and light-emitting diodes (LEDs).

  Note that examples of a driving device to which the present invention can be applied include a display using the above-described light emitting element, a writing head such as an optical writing type printer or an electronic copying machine, and the like. The electro-optical device of the present invention includes a large-screen television, a computer monitor, a display / lighting device, a mobile phone, a game machine, electronic paper, a video camera, a digital still camera, a car navigation device, a car stereo, a driving operation panel, a printer, The present invention can be applied to various electronic devices having a function of displaying an image, such as a scanner, a copier, a video player, a pager, an electronic notebook, a calculator, and a word processor.

1 is a diagram illustrating a configuration of a pixel circuit according to a first embodiment of the present invention. 3 is a timing chart for explaining the operation of the pixel circuit of FIG. 1. It is a figure which shows the structure of the pixel circuit which concerns on the 2nd Embodiment of this invention. 4 is a timing chart for explaining the operation of the pixel circuit of FIG. 3. It is a figure which shows the structure of the pixel circuit which concerns on the 3rd Embodiment of this invention. 1 is a block diagram illustrating a configuration of an electro-optical device according to an embodiment of the invention. FIG. It is a figure which shows the example of a plane layout of the pixel circuit which concerns on the 2nd Embodiment of this invention. It is a figure which shows the cross section of the pixel circuit which concerns on the 2nd Embodiment of this invention. It is a figure which shows the conventional pixel circuit. 6 is a timing chart for explaining the operation of the pixel circuit of FIG. 5.

Explanation of symbols

PX ... Pixel 11 ... Scanning line 12 ... Data line 13 ... Pixel selection switch 14 ... Scanning line driver 15 ... Data line driver 16 ... Light emitting element (organic EL element)
17... Drive transistor 18... Holding capacitor 19... Pixel power supply circuit 20... Kick capacitor 21... Bias transistor 22.
36 …… Write preparation signal line 37 …… Power supply line (VE)
38 …… Power supply line (GND)
39 …… Source metal wiring 70 …… Power supply line (Vee)
100 …… Display module 101 …… Power supply 102 …… Frame memory 103 …… Display controller 104 …… I / O
105 …… Microprocessor 110 …… Organic EL display device 111 …… Organic EL panel

Claims (15)

A plurality of scanning lines; a plurality of data lines; a plurality of pixels arranged corresponding to intersections of the plurality of scanning lines and the plurality of data lines; and a plurality of first power supply wirings. ,
Each of the plurality of pixels is supplied via a driving transistor, an electro-optical element connected between a source of the driving transistor and a first predetermined potential, and a corresponding scanning line among the plurality of scanning lines. A capacitor that forms a capacitance with the first switch transistor whose conduction is controlled by the scanning signal and the first electrode and the second electrode, and the first electrode is placed on the gate side of the driving transistor. A first capacitor connected between the gate and source of the drive transistor, a second capacitor connected in series between the first switch transistor and the gate of the drive transistor, a second switch transistor connected between the connection point and the second predetermined potential between said first switching transistor a second capacitor, the drive Switch and connected to bias transistor between the gate and drain of transistor, are short-circuited ends of the electrodes of the electro-optical element, to control the electrical connection between the first predetermined potential and said second electrode Means,
The electro-optical device, wherein conduction states of the second switch transistor and the bias transistor are controlled by a periodic signal different from a scanning signal supplied via the corresponding scanning line. The electro-optical device according to claim 1.
The first capacitor holds, as a charge amount, a data signal supplied via a corresponding data line among the first switch transistor and the plurality of data lines.
The second electrode is connected between the drive transistor and the electro-optic element, and is set to the first predetermined potential by conducting the switch means.
Before the data signal is supplied via the corresponding data line among the plurality of data lines, the electrode on the side of holding the data signal of the first switch transistor conducts the second switch transistor. electro-optical device characterized in that it is set to the second predetermined potential. The electro-optical device according to claim 1,
The electro-optical device, wherein the first predetermined potential is the same as a ground potential. The electro-optical device according to claim 3.
The electro-optical device, wherein the switch unit is controlled by the periodic signal. The electro-optical device according to any one of claims 1 to 4,
The electro-optical device, wherein the periodic signal is a signal different from a scanning signal supplied before a scanning signal for controlling a conduction state of the first switch transistor is supplied. The electro-optical device according to any one of claims 1 to 5,
An electro-optical device, wherein the bias transistor is turned on by the periodic signal to raise the gate voltage of the driving transistor to a threshold voltage of the driving transistor. The electro-optical device according to claim 6.
An electro-optical device that adjusts a gate voltage of the drive transistor by making the first switch transistor conductive by the scanning signal and supplying the data signal to the second capacitor. The electro-optical device according to claim 7.
The second electrode is connected to a source of the driving transistor;
An electro-optical device, wherein a potential difference between the source and the gate of the driving transistor is kept constant at least during a period in which the first capacitor holds a charge amount corresponding to the data signal. The electro-optical device according to claim 1,
Until the data signal supplied to each of the plurality of pixels via the corresponding data line among the plurality of data lines is cut off by the first switch transistor, the second electrode is The electro-optical device is set to the first predetermined potential. The electro-optical device according to claim 1,
2. An electro-optical device, wherein all transistors constituting each of the plurality of pixels have the same conductivity type. The electro-optical device according to claim 1,
The electro-optical device, wherein the driving transistor is an n-channel transistor. The electro-optical device according to any one of claims 1 to 11,
The electro-optical device, wherein the driving transistor is an amorphous thin film transistor. The electro-optical device according to any one of claims 1 to 12,
Each of the plurality of pixels further includes a plurality of second power supply lines for supplying the first predetermined potential to the second electrode included in each of the plurality of pixels. Optical device. The electro-optical device according to claim 1,
The electro-optical device is an organic EL element. An electronic apparatus comprising the electro-optical device according to claim 1.

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