Patent Application
20050059185
This application claims priority from Japanese Patent Applications No. 2003-288401 filed Aug. 7, 2003, No. 2003-288520 filed Aug. 7, 2003 and No. 2004-221606 filed Jul. 29, 2004, which are hereby incorporated by reference herein.
1. Field of the Invention
The present invention relates to a display apparatus. In particular, the present invention relates to a display apparatus including a plurality of pixel circuits each having display devices, transistors for drive and transistors for control.
2. Description of Related Art
A method for performing a drive with a constant electric current is known as a drive circuit. For example, as a light emitting device suitable for being driven by an electric current, a light emitting device (hereinafter referred to as an LED), an organic electroluminescent device (hereinafter referred to as an organic EL device or as an OEL device), and the like can be cited. The characteristics of these light emitting devices scarcely depend on temperature, and an emission intensity curve almost linear to an electric current can be obtained. Consequently, a method of a constant electric current drive has been proposed.
In the following, an organic EL device is exemplified, and a conventional electric current drive for light emission is described.
The organic EL device is featured by planer self emitting light from a thin film stocked layer capable of high intensity emission. The organic EL device can realize high efficient light emission at a low voltage by increasing the number of function stacked layers of organic layers, see “Applied Physics Letters”, U.S., 1987, Vol. 51, p. 913, “Applied Physics Letters”, U.S. 1989, Vol. 65, p. 3610. As described above, because the organic EL device is driven to emit light by a constant electric current, some constant electric current driving schemes have been proposed.
For example, a drive circuit as shown in
Moreover, Japanese Patent Application Laid-Open No. S63-280300 discloses an information display apparatus arranging a plurality of display dots therein. Each of the display dots composed of collected light emitting diodes having different luminance colors. In particular, Japanese Patent Application Laid-Open No. S63-280300 discloses a configuration including a power supply for supplying a voltage to the light emitting diodes per each luminance color.
Moreover, Japanese Patent Application Laid-Open No. 2002-23666 discloses a plurality of configurations of an electronic display apparatus using cathode common type LED's emitting a plurality of color beams. One of the configurations uses an independent switching power supply outputting different DC voltages to respective colors. The other configuration uses a combination of simple power supply circuits for voltage adjustment.
Moreover, Japanese Patent Application Laid-Open No. H10-232649 discloses a configuration in which selection transistors and drive transistors are controlled by binary signals of on/off respectively, and in which peculiar voltage values or electric current values are variably output from a variable drive power supply during each sub-frame period.
It is a subject of the present invention to realize a display apparatus capable of realizing high grade display.
A first aspect of the present invention is a manufacturing method of an image display apparatus including the steps of:
A second aspect of the present invention is a manufacturing method of an image display apparatus having the steps of:
Incidentally, in the first aspect, it is preferable to set that the plurality of pixel circuits, in which the transistors for drive are commonly connected to the first common electrode, includes the display devices corresponding to a same color;
Incidentally, in the second aspect, it is preferable that the plurality of pixel circuits, to which the second electrode applies the electric potential, includes the display devices corresponding to a same color;
Moreover, in the first or the second aspect, it is preferable that one of the two primary electrodes of the transistor for control, the primary electrode being not one connected to the control electrode of the transistor for drive, is connected to one of the two primary electrodes of the transistor for drive, the primary electrode is connected to the display device.
Moreover, a configuration in which the display element is an organic electroluminescence device can be preferably adopted in the first or the second aspect.
Moreover, another aspect of the present invention is an image display apparatus, comprising:
Now, a configuration in which the second electric potential source is an electric potential source applying a ground potential, and a configuration in which the first electric potential source is a power supply apparatus for generating a predetermined electric potential.
Moreover, a further aspect of the present invention is an image display apparatus, comprising:
Now, a configuration in which the second electric potential source is an electric potential source applying a ground potential, and a configuration in which the first electric potential source is a power supply apparatus for generating a predetermined electric potential.
The present invention can be especially suitably applied to a configuration using self emitting light type display devices as display devices. To put it concretely, the present invention can be especially suitably applied to a configuration using electroluminescence display devices, especially suitably organic electroluminescence display devices. Moreover, the present invention can be especially suitably applied to a configuration in which each display device is driven by an active matrix drive.
The configuration of an image display apparatus of a first embodiment is shown in
Moreover, the display unit 605 includes a scanning circuit 601 and a modulation circuit 602. Each pixel circuit and the scanning circuit 601 are connected with each other by means of a scanning signal wiring 606. Each pixel circuit and the modulation circuit 602 are connected with each other by means of a modulation signal wiring 607. A scanning signal is applied to the pixel circuits on each row through the scanning signal wiring 606, and a modulation signal is applied to the pixel circuit on which the scanning signal is applied through the modulation signal wiring 607. Thereby, the light emitting state of each pixel circuit is set.
Moreover, an electric potential obtained by adjusting an electric potential which a power supply device 603 being a first electric potential source can output by means of a DC-DC converter 604 is commonly supplied to each pixel circuit through a first common electrode 608.
Moreover, an electric potential supplied from a ground unit being a second electric potential source is commonly supplied to each pixel circuit through a second common electrode 609.
A suitable form of each pixel circuit is shown in
An electric potential for flowing a drive electric current corresponding to a plurality of on states between the two principal electrodes (source and drain) of the transistor for drive 11 is set up at the control electrode (gate) of the transistor for drive through the transistor for control 4. The plurality of on states does not mean switching between two values of on and off, but means a state of flowing a drive electric current of a certain value significant correspondingly to a modulation signal, and another state of flowing another drive electric current of another significant value.
As a configuration for setting up an electric potential corresponding to a modulation signal as the electric potential of the control electrode of a transistor for drive, a configuration in which a modulation signal wiring and the control electrode of the transistor for drive are connected to the two principal electrodes (the electrodes other than a control electrode and concretely corresponding to the source electrode and the drain electrode) of the transistor for control, respectively, wherein a modulation electric potential applied to a modulation signal through the transistor for control is written as an electric potential of the control electrode of the transistor for drive, can be adopted as a simpler configuration. The configuration is a voltage programming type configuration.
On the other hand, the example shown in
In both of the voltage programming configuration and the electric current programming configuration, the transistor for control is turned off after the elapse of a voltage setting period, and the electric potential of the control electrode of the transistor for drive is kept. In this state, an electric current flowing between the principal electrodes of the transistor for drive flows through the display device, and thereby the display device emits light.
Incidentally, in both of the voltage programming configuration and the electric current programming configuration, when it is difficult to hold the electric potential of the control electrode of the transistor for drive only by the capacitance of the control electrode, it is suitable to use capacitance for holding the electric potential (corresponding to a hold capacitor 17 in
In the configuration of holding the electric potential of the control electrode of the transistor for control by turning off the transistor for control as described above, a peculiar problem is generated.
In the following, the problem is concretely described by exemplifying the electric current programming configuration of
A capacitor 17 is connected between the input-output first electrode and the control electrode of the TFT 11 (a first transistor). Moreover, the input-output second electrode of the TFT 11 is connected to the input-output first electrode of the TFT 12. The input-output second electrode of the TFT 12 is connected to the electrode on one side of the organic EL light emitting device 13. The electrode on the other side of the organic EL light emitting device 13 is connected to the common solid electrode connected to the second common electrode 609. On the other hand, two input-output electrodes of the TFT 4 (a second transistor) functioning as a switch are connected to the control electrode and the input-output second electrode of the TFT 11, respectively. Moreover, the input-output second electrode of the TFT 11 is connected to the input-output electrode on one side of the TFT 5 being a switch for switching the input electric current (idata) between the input thereof and the cut-off thereof. The input electric current (idata) is input through the input-output electrode on the other side of the TFT 5. The voltage of the control electrode of the TFT 4 is controlled by the scanning signal Vg1. Moreover, it is needed that the on states and the off states of the TFT 5 and the TFT 12 are different from each other. Accordingly, in the configuration of
Next, the operation of the drive circuit is described with the timing chart of
During this period, the gate voltage of the TFT 11, through which the electric current of the luminance signal idata flows between the source and the drain, is accumulated in the capacitor 17. Consequently, when the scanning signal Vg1 being the gate voltage of the p-channel type TFT 4 is turned to the high level again as shown in
By the above-mentioned series of operations, the p-channel type TFT 11 copies the luminance signal idata to perform a constant electric current operation.
Next, a leakage electric current of the TFT 4, which the drive circuit of the present invention aims to suppress, is described.
As described above, when the luminance signal idata flows through the TFT 11 between the source thereof and the drain thereof, the scanning signal Vg1 turns to the low lever, and the p-channel type TFT 4 turns on. When the gate voltage of the TFT 11 is accumulated in the capacitor 17, the TFT 4 is turned off. The voltage of the TFT 4 between the source thereof and the drain thereof at this time is TFT4_Vds=(Vdd−TFT11_Vgs−TFT12_Vds−OEL_V−Vcom), where TFT4_Vds denotes the voltage of the TFT 4 between the source thereof and the drain thereof, Vdd denotes the electric potential applied to the first common electrode 608, TFT11_Vgs denotes the voltage of the TFT 11 between the gate thereof and the source thereof, TFT12_Vds denotes the voltage of the TFT 12 between the source thereof and the drain thereof, OEL_V denotes the voltage of the OEL 13 between the anode thereof and the cathode thereof, and Vcom denotes the electric potential applied to the second common electrode 609.
Now, the relationship between a voltage between a source and a drain of a transistor, and an electric current between the source and the drain of the transistor in the off state thereof shows the qualification as a graph in
The state of the leakage electric current of the transistor for control 4 sometimes differs in every display unit to be manufactured. Accordingly, in the present embodiment, a prepared display unit is actually driven to emit light, and the luminance of the emitted light of the display device is measured. Then, the electric potential to be applied to the first common electrode 608 is adjusted in order that the variation of the luminance of the emitted light can be suppressed. To put it concretely, all white display is performed in the same condition as that at the time of actual image display, and the luminance of the all white display is measured with a photomultiplier for one frame. Then, the operation condition of a DC-DC converter being an adjustment circuit is adjusted to lower the electric potential to be applied to the first common electrode 608. Thereby, the leakage electric current of the transistor for control 4 is suitably suppressed.
Moreover, as another embodiment, a configuration in which the electric potential applied to the second common electrode 609 is adjusted can be adopted.
Moreover, as a further embodiment, the following configuration can be also adopted. That is, in the configuration, an electric potential is applied to a pixel circuit including a display device corresponding to a predetermined color through the first common electrode 608; an electric potential is applied to a pixel circuit including a display device corresponding to another predetermined color through a third common electrode; an electric potential is applied to a pixel circuit including a display device corresponding to further predetermined color through a fifth common electrode; the electric potential applied to the first electrode is set up as described above; the electric potential applied to the third electrode is also set up similarly; and the electric potential applied to the fifth electrode is also set up similarly. Incidentally, the electric potentials applied to the first, the third and the fifth common electrodes can suitably differed from each other according to each color display device.
Moreover, as a still further embodiment, the following configuration may be adopted. That is, in the configuration, the electric potential supplied from the second common electrode 609 to the other end of a display device is not applied to the whole pixel circuit through the common solid electrode, but is applied only to the pixel circuits including display devices of a predetermined color; the electric potential is applied to the pixel circuits including display devices of another predetermined color through a fourth common electrode; and the electric potential is applied to the pixel circuits including display devices of a further predetermined color through a sixth common electrode. In the configuration, the electric potentials to be applied to the second, the fourth and the sixth common electrodes can be set up similarly to the above.
In the following, each embodiment will be described more minutely.
(Embodiment 1)
In the light emitting device drive circuit of the present embodiment shown in
To put it more concretely, the DC-DC converter 604 controls the voltage of the TFT 4 between the source thereof and the drain thereof in order to satisfy OEL_V, i.e. the V-I characteristic of the OEL 13, which does not damage the constant electric current property of the OEL 13, and further in order to correct the increase of voltage at the time of the deterioration of the OEL 13. To put it concretely, the DC-DC converter 604 lowers the voltage TFT4_Vds by lowering the electric potential corresponding to the voltage Vdd of the formula TFT4_Vds=(Vdd−TFT11_Vgs−TFT12_Vds−OEL_V−Vcom) (by bringing the electric potential corresponding to the voltage Vdd near to the electric potential applied to the second common electrode 609).
At the time of the adjustment of the electric potential, the gate electric potential of the transistor for drive 11 is set up by performing electric current programming actually, and by making the OEL device 13 emit light on the basis of the programming to measure the luminance variation during one frame with a photomultiplier. The setting of the electric potential is performed to be able to suppress the luminance variation detected by the measurement.
Incidentally, one execution of the setting of the electric potential by means of the adjustment circuit at the manufacturing of the image display apparatus is sufficient, and the adjusted electric potential may be fixed. However, the adjustment may be performed by a user or a person in charge of maintenance of the image display apparatus as the need arises after the use of the image display apparatus for some periods.
By lowering the voltage of the TFT 4 between the source thereof and the drain thereof, the leakage electric current flowing through the transistor for control 4 between the principal electrodes thereof (or the source thereof and the drain thereof) can be suppressed. As a result, the variation of the gate electric potential of the TFT 11 can be suppressed at the time of a series of drive of the drive circuit having the form shown in
In the drive circuit shown in
Moreover, the p-channel type TFT 12 turns off at the change of the scanning signal Vg2 to the high level, and the TFT 12 cuts off the electric current to the OEL 13. During this period, the gate voltage of the TFT 11, through which the electric current of the luminance signal idata flows between the source thereof and the drain thereof, is accumulated in the capacitor 17. Then, the scanning signal Vg1 being the gate voltage of the p-channel type TFT 4 is again turned to the high level as shown in
By the above-mentioned series of operations, the p-channel type TFT 11 copies the luminance signal idata to perform a constant electric current operation. Because the voltage of the TFT 4 between the source thereof and the drain thereof is suppressed to be low, the leakage electric current is suppressed, and the gate electric potential of the TFT 11 is kept to be constant, and also the electric current flowing through the OEL 13 can be kept to be constant. Consequently, the luminance of the OEL 13 can be kept to be constant while emitting light.
(Embodiment 2)
In Embodiment 1, the configuration in which the adjustment circuit adjusts the electric potential to be applied to the principal electrode being not the one connected to the display device among the principal electrodes of the transistor for drive is shown. In the present embodiment, a configuration in which the adjustment circuit adjusts the electric potential applied to the opposite side of the transistor for drive to the side on which the transistor for drive is connected is adopted. To put it concretely, in
A schematic circuit diagram equivalently showing the configuration of the drive circuit of the present embodiment is shown in
The setting up of the electric potential of the adjustment circuit can be performed similarly to Embodiment 1. To put it concretely, the measurement of luminance is performed, and the electric potential is adjusted in order to suppress the variation of luminance.
To put it more concretely, the adjustment circuit provided on the side of the second common electrode 609 controls the voltage of the TFT 4 between the source thereof and the drain thereof in order that the voltage of the OEL 13 OEL_V which does not damage the constant property of the OEL 13 may be obtained, namely the V-I characteristic of the OEL 13 may be satisfied, with the increase of the voltage of the OEL 13 at the time of deterioration thereof being considered. The means raises the electric potential corresponding to the electric potential Vcom in the formula TFT4_Vds=(Vdd−TFT11_Vgs−TFT12_Vds−OEL_V−Vcom) (bringing the electric potential near to the electric potential applied to the first common electrode 608). Thereby, the voltage of the TFT 4 between the source thereof and the drain thereof is lowered.
By lowering the voltage of the TFT 4 between the source thereof and the drain thereof, the leakage electric current flowing through the TFT 4 between the source thereof and the drain thereof can be suppressed. As a result, at the time of a drive of the drive circuit having the form of
In the drive circuit shown in
By the above-mentioned series of operations, the p-channel type TFT 11 copies the luminance signal idata to perform a constant electric current operation. Because the voltage of the TFT 4 between the source thereof and the drain thereof is suppressed to be low, the leakage electric current is suppressed, and the variation of the gate electric potential of the TFT 11 is suppressed, and also the variation of the electric current flowing through the OEL 13 can be suppressed.
(Embodiment 3)
In Embodiment 1 and Embodiment 2, pixel circuits having the display devices corresponding to different colors are commonly connected to the first common electrode 608.
Now, the characteristics of the display devices sometimes differ from each other at every corresponding color. For example, in the case where the OEL 13 described above is made of a different organic material to each color, the voltage threshold value until the OEL 13 emits light and the electric current-voltage characteristic at the time of light emission differ in each color material. Consequently, the voltage Vds of the TFT 4 between the source thereof and the drain thereof changes according to the changes of the voltage threshold value and the electric current-voltage characteristic, and then the value of the leakage electric current also changes to each organic material. Moreover, the electric current-voltage characteristics of the R, the G and the B pixel materials also change owing to time degradation, and the way of the changes differs to each organic material.
Now, the reason why the voltage of a TFT between the source thereof and the drain thereof differ to each pixel circuit corresponding to each color is described on the basis of
In this case, as a configuration capable of more suitably suppressing the leakage electric currents between the sources and the drains of the TFT's 4 driving the light emitting devices having the different characteristics, a configuration of individually adjusting the electric potential applied to the pixel circuit corresponding to each color through the common electrode is preferable. Accordingly, the present embodiment adopts the following configuration. That is, a common electrode through which an electric potential is applied to a principal electrode being not one to which a display device is connected among the principal electrodes of a transistor for drive of each pixel circuit is provided to each color. Then, the electric potential to be applied to the common electrode of each color is individually adjusted.
The portions common in those of Embodiment 1 and Embodiment 2 are denoted by the same marks as those of Embodiment 1 and Embodiment 2.
The points different from those of Embodiment 1 and Embodiment 2 are as follows. That is, in Embodiment 1 and Embodiment 2, the pixel circuits corresponding to different colors are commonly connected to the first common electrode 608. In the present embodiment, a plurality of pixel circuits corresponding to red is commonly connected to a first common electrode 704; a plurality of pixel circuits corresponding to green is commonly connected to a third common electrode 705; and a plurality of pixel circuits corresponding to blue is commonly connected to a fifth common electrode 706. Moreover, an electric potential is applied to the first common electrode 704 through a DC-DC converter 701 being an adjustment circuit for adjusting the electric potential output from the power supply device 603; an electric potential is applied to the third common electrode 705 through a DC-DC converter 702 for adjusting the electric potential output from the power supply device 603; and an electric potential is applied to the fifth common electrode 706 through a DC-DC converter 703 for adjusting the electric potential output from the power supply device 603. The output electric potential of each adjustment circuit is individually adjusted.
To put it concretely, display of red is performed by driving the pixel circuits corresponding to red, and the luminance is measured. Then, the output electric potential of the adjustment circuit 701 is adjusted in order to suppress the luminance variation of red in a period of a frame. Next, only the pixel circuits corresponding to green are driven to perform the display of green, and the luminance measurement thereof is performed. Then, the output electric potential of the adjustment circuit 702 is adjusted in order to suppress the luminance variation of green in a period of a frame. Next, only the pixel circuits corresponding to blue are driven to perform the display of blue, and the luminance measurement thereof is performed. Then, the output electric potential of the adjustment circuit 703 is adjusted in order to suppress the luminance variation of blue in a period of a frame.
Thereby, the electric potentials to be applied to the transistors for drive can be adjusted to each color.
(Embodiment 4)
In Embodiment 3, the configuration in which the electric potentials applied to the principal electrodes being not ones to which the display devices are connected among the principal electrodes of the transistors for drive are adjusted by the adjustment circuits provided to respective colors is shown. In the present embodiment, a configuration in which the electric potentials applied to the sides of the display devices opposite to ones on which the transistors for drive are connected are adjusted by the adjustment circuits is adopted. To put it concretely, in
Then, the cathode electrodes of the display devices of a plurality of pixel circuits corresponding to red are commonly connected to a second common electrode 903; the cathode electrodes of the display devices of a plurality of pixel circuits corresponding to green are commonly connected to a fourth common electrode 902; and the cathode electrodes of the display devices of a plurality of pixel circuits corresponding to blue are commonly connected to a sixth common electrode 901. Moreover, an electric potential is applied to the second common electrode 903 from a DC-DC converter 906 being an adjustment circuit for adjusting the electric potential output from the ground unit; an electric potential is applied to the fourth common electrode 902 from a DC-DC converter 905 for adjusting the electric potential output from the ground unit; and an electric potential is applied to the sixth common electrode 901 from a DC-DC converter 904 for adjusting the electric potential output from the ground unit. The output electric potential of each adjustment circuit is individually adjusted. The concrete method of the adjustment is the same as that of Embodiment 3.
Incidentally, each embodiment has been described above. The configuration shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-288401 (PAT. | Aug 2003 | JP | national |
| 2003-288520 (PAT. | Aug 2003 | JP | national |
| 2004-221606 (PAT. | Jul 2004 | JP | national |
