Display apparatus

A configuration for decreasing the leakage electric current of a transistor for control for controlling an electric potential holding operation of a control electrode of a transistor for drive for flowing an electric current through a display device by adjusting the output electric potential of an electric potential source is disclosed.

BACKGROUND OF THE INVENTION

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 planar 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, “J. Applied Physics”, 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 inFIG. 3has proposed in Japanese Patent Application Laid-Open No. 2001-056667 and U.S. Pat. No. 6,229,506. The drive circuit copies an input electric current (idata) to supply the electric current to OEL13. The drive method is an electric current control type method of using an electric current as an input to set the electric potential of the control electrode of a transistor11. The method has a technical advantage of the capability of supplying a substantially same electric current as an input electric current to the OEL13without being affected by the threshold value of the transistor11and a deteriorated voltage of the OEL13.

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.

SUMMARY OF THE INVENTION

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:

preparing a display unit; and

adjusting an electric potential to be applied to the display unit; wherein

the display unit includes:

a plurality of wirings for a scanning signal;

a plurality of wirings for a modulation signal; and

a plurality of pixel circuits connected to be in a matrix connection with the plurality of wirings for a scanning signal and the plurality of wirings for a modulation signal; and wherein

each of the plurality of pixel circuits includes:

a display device;

a transistor for drive having a control electrode and two primary electrodes; and

a transistor for control having a control electrode and two primary electrodes, wherein

the transistor of drive is configured so that one of the two primary electrodes is connected to the display device to flow a drive electric current, which should be flown into the display device, through the transistor of drive between the two primary electrodes thereof, and

the transistor for control is configured so that one of the primary electrodes is connected to the control electrode of the transistor for drive, and that the transistor for control switches a state of the transistor for drive between a state of setting up an electric potential of the control electrode of the transistor for drive and a state of holding the set electric potential in accordance with the scanning signal to be applied to the control electrode through the wiring for the scanning signal; and

the display unit further includes:

a first common electrode, to which one primary electrode of the two primary electrodes of the transistor for drive is commonly connected, the one primary electrode being not the primary electrode connected to the display device in each of at least a part of the plurality of pixel circuits; and

a second common electrode, to which an electric potential different from an electric potential applied to the first common electrode is applied, for commonly applying the former electric potential to the display device of the part or all of the plurality of pixel circuits; wherein

the step of adjusting an electric potential is a step of adjusting an electric potential which an electric potential source for applying the electric potential to the first common electrode can output to bring the electric potential near to one to be applied to the second common electrode.

A second aspect of the present invention is a manufacturing method of an image display apparatus having the steps of:

preparing a display unit; and

adjusting an electric potential to be applied to the display unit; wherein

the display unit includes:

a plurality of wirings for a scanning signal;

a plurality of wirings for a modulation signal; and

a plurality of pixel circuits connected to be in a matrix connection with the plurality of wirings for a scanning signal and the plurality of wirings for a modulation signal; and wherein

each of the plurality of pixel-circuits includes:

a display device;

a transistor for drive having a control electrode and two primary electrodes; and

a transistor for control having a control electrode and two primary electrodes, wherein

the transistor of drive is configured so that one of the two primary electrodes is connected to the display device to flow a drive electric current, which should be flown into the display device, through the transistor of drive between the two primary electrodes thereof, and

the transistor for control is configured so that one of the primary electrodes is connected to the control electrode of the transistor for drive, and that the transistor for control switches a state of the transistor for drive between a state of setting up an electric potential of the control electrode of the transistor for drive and a state of holding the set electric potential in accordance with the scanning signal to be applied to the control electrode through the wiring for the scanning signal; and

the display unit further includes:

a first common electrode, to which one primary electrode of the two primary electrodes of the transistor for drive is commonly connected, the one primary electrode being not the primary electrode connected to the display device in each of at least a part of the plurality of pixel circuits; and

a second common electrode, to which an electric potential different from an electric potential applied to the first common electrode is applied, for commonly applying the former electric potential to the display device of the part or all of the plurality of pixel circuits; wherein

the step of adjusting an electric potential is a step of adjusting an electric potential which an electric potential source for applying the electric potential to the second common electrode can output to bring the electric potential near to one to be applied to the first common electrode.

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;

the plurality of pixel circuits connected to be in the matrix connection includes a plurality of pixel circuits each including display devices corresponding to a predetermined color different from the color;

the display unit further includes a third common electrode to which a primary electrode being not one to which the display device is connected between two primary electrodes of the transistor for drive in each of the plurality of pixel circuits including the display devices corresponding to the predetermined color; and

the step of adjusting an electric potential includes a step of adjusting an electric potential which an electric potential source for applying an electric potential to the third common electrode to bring the electric potential near to an electric potential which should be applied to the second common electrode.

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;

the plurality of pixel circuits connected to be in the matrix connection includes a plurality of pixel circuits each including display devices corresponding to a predetermined color different from the color;

the display unit further includes a fourth common electrode commonly applying an electric potential to a display device of each of the the plurality of pixel circuits including the display devices corresponding to the predetermined color; and

the step of adjusting an electric potential includes a step of adjusting an electric potential which an electric potential source for applying an electric potential to the fourth common electrode to bring the electric potential near to an electric potential which should be applied to the first common electrode.

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:

a plurality of wirings for a scanning signal;

a plurality of wirings for a modulation signal; and

a plurality of pixel circuits connected to be in a matrix connection with the plurality of wirings for a scanning signal and the plurality of wirings for a modulation signal; and wherein

each of the plurality of pixel circuits includes:

a display device;

a transistor for drive having a control electrode and two primary electrodes; and

a transistor for control having a control electrode and two primary electrodes, wherein

the transistor of drive is configured so that one of the two primary electrodes is connected to the display device to flow a drive electric current corresponding to a plurality of on-states different from each other of the display device through the transistor for drive between the two primary electrodes thereof, and

the transistor for control is configured so that one of the primary electrodes is connected to the control electrode of the transistor for drive, and that the transistor for control switches a state of the transistor for drive between a state of setting up an electric potential of the control electrode of the transistor for drive and a state of holding the set electric potential in accordance with the scanning signal to be applied to the control electrode through the wiring for the scanning signal; and

the plurality of pixel circuits includes first pixel circuits including the display devices corresponding to a predetermined color, and second pixel circuits including the display devices corresponding to a color different from the predetermined color;

the image display apparatus further includes:

a first common electrode, to which one primary electrode of the two primary electrodes of the transistor for drive is commonly connected, the one primary electrode being not the primary electrode connected to the display device in each of the first pixel circuits and the second pixel circuits; and

a second common electrode, to which an electric potential different from an electric potential applied to the first common electrode is applied, for commonly applying the former electric potential to the display device of each of the first pixel circuits and the second pixel circuits;

a first electric potential source;

an adjustment circuit for adjusting an electric potential which the first electric potential source can generate to apply the adjusted electric potential to the first common electrode; and

a second electric potential source for applying an electric potential to second common electrode, wherein the adjustment circuit is a circuit for adjusting the electric potential which the first electric source can generate to bring the electric potential near to the electric to be applied to the second common electrode.

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:

a plurality of wirings for a scanning signal;

a plurality of wirings for a modulation signal; and

a plurality of pixel circuits connected to be in a matrix connection with the plurality of wirings for a scanning signal and the plurality of wirings for a modulation signal; and wherein

each of the plurality of pixel circuits includes:

a display device;

a transistor for drive having a control electrode and two primary electrodes; and

a transistor for control having a control electrode and two primary electrodes, wherein

the transistor of drive is configured so that one of the two primary electrodes is connected to the display device to flow a drive electric current corresponding to a plurality of on-states different from each other of the display device through the transistor for drive between the two primary electrodes thereof, and

the transistor for control is configured so that one of the primary electrodes is connected to the control electrode of the transistor for drive, and that the transistor for control switches a state of the transistor for drive between a state of setting up an electric potential of the control electrode of the transistor for drive and a state of holding the set electric potential in accordance with the scanning signal to be applied to the control electrode through the wiring for the scanning signal; and

the plurality of pixel circuits includes first pixel circuits including the display devices corresponding to a predetermined color, and second pixel circuits including the display devices corresponding to a color different from the predetermined color;

the image display apparatus further includes:

a first common electrode, to which one primary electrode of the two primary electrodes of the transistor for drive is commonly connected, the one primary electrode being not the primary electrode connected to the display device in each of the first pixel circuits and the second pixel circuits; and

a second common electrode, to which an electric potential different from an electric potential applied to the first common electrode is applied, for commonly applying the former electric potential to the display device of each of the first pixel circuits and the second pixel circuits;

a first electric potential source for applying an electric potential to the first common electrode;

a second electric potential source; and

an adjustment circuit for adjusting an electric potential which the second electric potential source can generate to apply the adjusted electric potential to the second common electrode, wherein the adjustment circuit is a circuit for adjusting the electric potential which the second electric source can generate to bring the electric potential near to the electric to be applied to the first common electrode.

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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

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 inFIG. 6. InFIG. 6, a display unit605includes red pixel circuits (each denoted by a letter R in the drawing), green pixel circuits (each denoted by a letter G in the drawing), and blue pixel circuits (each denoted by a letter B in the drawing). Each pixel circuit severally includes an OEL device having one of red, green and blue luminance colors. Incidentally,FIG. 6shows an example in which the pixel circuits are linearly arranged both in row directions and in column directions, but various arrangements such as one in which red, green and blue pixel circuits are triangularly arranged can be adopted.

Moreover, the display unit605includes a scanning circuit601and a modulation circuit602. Each pixel circuit and the scanning circuit601are connected with each other by means of a scanning signal wiring606. Each pixel circuit and the modulation circuit602are connected with each other by means of a modulation signal wiring607. A scanning signal is applied to the pixel circuits on each row through the scanning signal wiring606, and a modulation signal is applied to the pixel circuit on which the scanning signal is applied through the modulation signal wiring607. 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 device603being a first electric potential source can output by means of a DC-DC converter604is commonly supplied to each pixel circuit through a first common electrode608.

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 electrode609.

A suitable form of each pixel circuit is shown inFIG. 3. Although the scanning signal wiring606is shown to be one to each pixel circuit inFIG. 6for the same of a clear expression, it is suitable to connect at least two modulation signal wirings606to each pixel circuit in case of adopting an electric current programming type pixel circuit shown inFIG. 3. To put it concretely, it is suitable to use a scanning signal wiring606for supplying a scanning signal Vg1to a transistor for control4ofFIG. 3, and a scanning signal wiring606for applying a scanning signal Vg2to a transistor5for setting up a signal writing timing and a transistor12for preventing an electric current from flowing through an OEL device13at the time of signal writing. Incidentally, the cathode electrode of the OEL device13being a display device is a solid electrode common to all pixels, which is connected to the second common electrode609. The pixel circuit is configured to include a transistor for drive11for flowing a desired drive electric current into the display device, the display device13connected to the transistor for drive11in series between the first common electrode608and the second common electrode609, and the transistor for control4connected to the control electrode of the transistor for drive11for switching the electric potential setting state and the electric potential holding state of the control electrode.

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 drive11is set up at the control electrode (gate) of the transistor for drive through the transistor for control4. 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 inFIG. 3is an electric current programming type configuration. In the configuration, a modulation electric current signal (idata ofFIG. 3) is applied to the modulation signal wiring607. The electric current signal flowing through the modulation signal wiring607flows through the two principal electrodes of the transistor for drive11. In addition, the transistor for control4functions as a path for setting up the electric potential at the control electrode of the transistor for drive11, and the electric potential according to the modulation electric current flowing between the principal electrodes of the transistor for drive11is set up as the control electric potential of the control electrode of the transistor for drive11.

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 capacitor17inFIG. 3) additionally.

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 ofFIG. 3. Incidentally, because thin film transistors are used as transistors in the preferred embodiments described later, transistors in the following description are notated as TFT's. Moreover, because organic electroluminescence devices are used in the preferred embodiments described later as display devices, the organic electroluminescence devices are notated as OEL's. In the present embodiment, polysilicon is formed on a glass substrate, and TFT's are formed by means of the polysilicon. However, the material of the TFT's is not limited to one having crystallinity such as the polysilicon, but amorphous silicon can be also used.

A capacitor17is connected between the input-output first electrode and the control electrode of the TFT11(a first transistor). Moreover, the input-output second electrode of the TFT11is connected to the input-output first electrode of the TFT12. The input-output second electrode of the TFT12is connected to the electrode on one side of the organic EL light emitting device13. The electrode on the other side of the organic EL light emitting device13is connected to the common solid electrode connected to the second common electrode609. On the other hand, two input-output electrodes of the TFT4(a second transistor) functioning as a switch are connected to the control electrode and the input-output second electrode of the TFT11, respectively. Moreover, the input-output second electrode of the TFT11is connected to the input-output electrode on one side of the TFT5being 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 TFT5. The voltage of the control electrode of the TFT4is controlled by the scanning signal Vg1. Moreover, it is needed that the on states and the off states of the TFT5and the TFT12are different from each other. Accordingly, in the configuration ofFIG. 3, the TFT's having a carrier polarity different from each other are used as the TFT5and the TFT12, and thereby the voltages of the control electrodes of the TFT's5and12can be controlled by means of a single scanning signal Vg2.

Next, the operation of the drive circuit is described with the timing chart ofFIG. 4being also referred to. First, the luminance signal idata is set up. After that, the scanning signal Vg1becomes a low level, and the p-channel type TFT4turns on. At the same time, the scanning signal Vg2takes a high level, and then the n-channel type TFT5turns on to flow the electric current of the luminance signal idata through the TFT11between the source thereof and the drain thereof. Moreover, the turning of the scanning signal Vg2to the high level turns the p-channel type TFT12off to cut off the electric current to the OEL13.

During this period, the gate voltage of the TFT11, through which the electric current of the luminance signal idata flows between the source and the drain, is accumulated in the capacitor17. Consequently, when the scanning signal Vg1being the gate voltage of the p-channel type TFT4is turned to the high level again as shown inFIG. 4to turn the TFT4off, and when the scanning signal Vg2being the gate voltage of the p-channel type TFT12is turned to the low level again to turn the TFT12on and to turn the TFT5off, an electric current14, the amount of which is the same as that of the luminance signal idata, flows through the source and the drain of the TFT11from a power supply15for making the OEF13emit light.

By the above-mentioned series of operations, the p-channel type TFT11copies the luminance signal idata to perform a constant electric current operation.

Next, a leakage electric current of the TFT4, which the drive circuit of the present invention aims to suppress, is described.

As described above, when the luminance signal idata flows through the TFT11between the source thereof and the drain thereof, the scanning signal Vg1turns to the low lever, and the p-channel type TFT4turns on. When the gate voltage of the TFT11is accumulated in the capacitor17, the TFT4is turned off. The voltage of the TFT4between 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 TFT4between the source thereof and the drain thereof, Vdd denotes the electric potential applied to the first common electrode608, TFT11_Vgs denotes the voltage of the TFT11between the gate thereof and the source thereof, TFT12_Vds denotes the voltage of the TFT12between the source thereof and the drain thereof, OEL_V denotes the voltage of the OEL13between the anode thereof and the cathode thereof, and Vcom denotes the electric potential applied to the second common electrode609.

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 inFIG. 5, and a leakage electric current flows without control of a gate electric potential. The charge of the holding capacitor17changes owing to the leakage electric current. As a result, the gate electric potential of the TFT11changes, and the electric current flowing through the OEL17changes according to the change of the gate electric potential of the TFT11. Thereby, the luminance of the OEL13also changes. Consequently, as shown inFIG. 4, even when the scanning signal Vg2is the low level, the drive electric current rises, and the luminance of the OEL13also rises as the rise of the drive electric current.

The state of the leakage electric current of the transistor for control4sometimes 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 electrode608is 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 electrode608. Thereby, the leakage electric current of the transistor for control4is suitably suppressed.

Moreover, as another embodiment, a configuration in which the electric potential applied to the second common electrode609is 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 electrode608; 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 electrode609to 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.

FIG. 1is a view substantially equivalently showing a state of connecting a pixel circuit being the present embodiment, a power supply device being an electric potential source, a ground unit being an electric potential source, and a DC-DC converter being an adjustment circuit to each other.

In the light emitting device drive circuit of the present embodiment shown inFIG. 1, the voltage of the TFT4between the source thereof and the drain thereof is controlled by a DC-DC converter (shown as a variable voltage source) provided on the opposite side of the transistor for control11to the display device13.

To put it more concretely, the DC-DC converter604controls the voltage of the TFT4between the source thereof and the drain thereof in order to satisfy OEL_V, i.e. the V–I characteristic of the OEL13, which does not damage the constant electric current property of the OEL13, and further in order to correct the increase of voltage at the time of the deterioration of the OEL13. To put it concretely, the DC-DC converter604lowers 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 electrode609).

At the time of the adjustment of the electric potential, the gate electric potential of the transistor for drive11is set up by performing electric current programming actually, and by making the OEL device13emit 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 TFT4between the source thereof and the drain thereof, the leakage electric current flowing through the transistor for control4between 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 TFT11can be suppressed at the time of a series of drive of the drive circuit having the form shown inFIG. 1, and thereby the variation of the electric current flowing through the OEL13can be suppressed. Consequently, the variation of the luminance of the OEL13can be suppressed.

In the drive circuit shown inFIG. 1, the luminance signal idata is first set up. After that, the scanning signal Vg1turns to the low level, and the p-channel type TFT4turns on. At the same time, the scanning signal Vg2turns to the high level, and the n-channel type TFT5turn on to flow the electric current of the luminance signal idata through the TFT11between the source thereof and the drain thereof.

Moreover, the p-channel type TFT12turns off at the change of the scanning signal Vg2to the high level, and the TFT12cuts off the electric current to the OEL13. During this period, the gate voltage of the TFT11, through which the electric current of the luminance signal idata flows between the source thereof and the drain thereof, is accumulated in the capacitor17. Then, the scanning signal Vg1being the gate voltage of the p-channel type TFT4is again turned to the high level as shown inFIG. 4to turn the TFT4off. Then, when the scanning signal Vg2being the gate voltage of the p-channel type TFT12is turned to the low level again to turn the TFT12on and to turn the TFT5off, an electric current14, the amount of which is the same as that of the luminance signal idata, flows through the source and the drain of the TFT11from the DC-DC converter604to the second common electrode609for making the OEF13emit light. At this time, the DC-DC converter604performs the adjustment for lowing the voltage of the TFT4between the source thereof and the drain thereof, and thereby, as described above, the voltage satisfying OEL_V, i.e. the V–I characteristic of the OEL13, which does not damage the constant electric current property of the OEL13, is applied to the series of devices of the TFT11, TFT4, TFT12and the OEL13with the consideration of the increase of voltage at the time of the deterioration of the OEL13.

By the above-mentioned series of operations, the p-channel type TFT11copies the luminance signal idata to perform a constant electric current operation. Because the voltage of the TFT4between 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 TFT11is kept to be constant, and also the electric current flowing through the OEL13can be kept to be constant. Consequently, the luminance of the OEL13can be kept to be constant while emitting light.

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, inFIG. 6, the adjustment circuit is arranged to adjust the electric potential to be applied to the first common electrode608, but in the present embodiment, the adjustment circuit is arranged to adjust the electric potential to be applied to the second common electrode609. To put it concretely, the adjustment circuit is provided between the ground unit being the second electric potential source and the common electrode to which the display device of each pixel circuit is commonly connected.

A schematic circuit diagram equivalently showing the configuration of the drive circuit of the present embodiment is shown inFIG. 2. As described above, the light emitting device drive circuit of the present embodiment controls the voltage of the TFT4between the source thereof and the drain thereof with the adjustment circuit (shown as a variable voltage source19) provided on the second common electrode side.

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 electrode609controls the voltage of the TFT4between the source thereof and the drain thereof in order that the voltage of the OEL13OEL_V which does not damage the constant property of the OEL13may be obtained, namely the V–I characteristic of the OEL13may be satisfied, with the increase of the voltage of the OEL13at 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 electrode608). Thereby, the voltage of the TFT4between the source thereof and the drain thereof is lowered.

By lowering the voltage of the TFT4between the source thereof and the drain thereof, the leakage electric current flowing through the TFT4between 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 ofFIG. 2, which will be described in the following, the variation of the gate electric potential of the TFT11can be suppressed, and the variation of the electric current flowing through the OEL13can be suppressed. Consequently, the variation of the luminance of the OEL13can be suppressed.

In the drive circuit shown inFIG. 2, first, the luminance signal idata is set up. After that, the scanning signal Vg1becomes a low level, and the p-channel type TFT4turns on. At the same time, the scanning signal Vg2takes a high level, and then the n-channel type TFT5turns on to flow the electric current of the luminance signal idata through the TFT11between the source thereof and the drain thereof. Moreover, the turning of the scanning signal Vg2to the high level turns the p-channel type TFT12off to cut off the electric current to the OEL13. During this period, the gate voltage of the TFT11, through which the electric current of the luminance signal idata flows between the source thereof and the drain thereof, is accumulated in the capacitor17. Then, when the scanning signal Vg1being the gate voltage of the p-channel type TFT4is turned to the high level again as shown inFIG. 4to turn the TFT4off, and when the scanning signal Vg2being the gate voltage of the p-channel type TFT12is turned to the low level again to turn the TFT12on and to turn the TFT5off, an electric current14, the amount of which is the same as that of the luminance signal idata, flows through the source and the drain of the TFT11from a power supply15to a variable voltage source19for making the OEF13emit light. At this time, the adjustment circuit lowers the voltage of the TFT4between the source thereof and the drain thereof according to the set gate voltage o the TFT11while controlling the voltage in order that the voltage OEL_V which does not damage the constant electric current property of the OEL13, namely which satisfies the V–I characteristic of the OEL13, may be applied to the serried of devices of the TFT11, the TFT14, the TFT12and the OEL13, with the increase of the voltage of the OEL13at the time of the deterioration thereof being considered.

By the above-mentioned series of operations, the p-channel type TFT11copies the luminance signal idata to perform a constant electric current operation. Because the voltage of the TFT4between 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 TFT11is suppressed, and also the variation of the electric current flowing through the OEL13can be suppressed.

In Embodiment 1 and Embodiment 2, pixel circuits having the display devices corresponding to different colors are commonly connected to the first common electrode608.

Now, the characteristics of the display devices sometimes differ from each other at every corresponding color. For example, in the case where the OEL13described above is made of a different organic material to each color, the voltage threshold value until the OEL13emits light and the electric current-voltage characteristic at the time of light emission differ in each color material. Consequently, the voltage Vds of the TFT4between 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 ofFIG. 8. As described above, the following formula is effective: TFT4_Vds=(Vdd−TFT11_Vgs−TFT12_Vds−OEL_V−Vcom). Consequently, when the voltage-electric current characteristic of each light emitting material of R, G and B differ from each other (or changes), the voltage of the TFT4between the source thereof and the drain thereof differs from each other (changes). The voltage-electric current characteristic of each of the R, the G and the B pixel materials is different from each other owing to the following primary factors and the like. InFIG. 8, GVth denotes a voltage at which an electric current begins to flow in a G pixel1_2material; BVth denotes a voltage at which an electric current begins to flow in a B pixel1_3material; RVth denotes a voltage at which an electric current begins to flow in a R pixel1_1material; ΔGV denotes an electric current increasing rate to a voltage in the G pixel1_2material; ΔBV denotes an electric current increasing rate to a voltage in the B pixel1_3material; and ΔRV denotes an electric current increasing rate to a voltage in the R pixel1_1material. Consequently, the voltages of the TFT's4between their sources and their drains of the drive circuits provided in the G pixel1_2, the B pixel1_3and the R pixel1_1are different from each other in their initial states even at the same luminance. Moreover, the voltages of the TFT's4between their sources and their drains are different from each other also owing to the differences of ΔV's. Furthermore, the electric current-voltage characteristics of the R, the G and the B light emitting materials change also owing to time degradation.

In this case, as a configuration capable of more suitably suppressing the leakage electric currents between the sources and the drains of the TFT's4driving 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 electrode608. In the present embodiment, a plurality of pixel circuits corresponding to red is commonly connected to a first common electrode704; a plurality of pixel circuits corresponding to green is commonly connected to a third common electrode705; and a plurality of pixel circuits corresponding to blue is commonly connected to a fifth common electrode706. Moreover, an electric potential is applied to the first common electrode704through a DC-DC converter701being an adjustment circuit for adjusting the electric potential output from the power supply device603; an electric potential is applied to the third common electrode705through a DC-DC converter702for adjusting the electric potential output from the power supply device603; and an electric potential is applied to the fifth common electrode706through a DC-DC converter703for adjusting the electric potential output from the power supply device603. 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 circuit701is 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 circuit702is 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 circuit703is 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.

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, inFIG. 7, the plurality of adjustment circuits are arranged to adjust the electric potential to be applied to the first common electrode704, the third common electrode705and the fifth common electrode706, respectively. However, in the present embodiment, the adjustment circuits for respective colors are arranged to adjust the electric potentials on the opposite sides of the display devices to the ones on which the transistors for drive are connected. Although an electric potential can be applied commonly to all of the pixel circuits through the second common electrode609in Embodiment 1, Embodiment 2 and Embodiment 3 described above, the cathode electrodes of the display devices are arranged to respective colors in the present embodiment.

Then, the cathode electrodes of the display devices of a plurality of pixel circuits corresponding to red are commonly connected to a second common electrode903; the cathode electrodes of the display devices of a plurality of pixel circuits corresponding to green are commonly connected to a fourth common electrode902; and the cathode electrodes of the display devices of a plurality of pixel circuits corresponding to blue are commonly connected to a sixth common electrode901. Moreover, an electric potential is applied to the second common electrode903from a DC-DC converter906being an adjustment circuit for adjusting the electric potential output from the ground unit; an electric potential is applied to the fourth common electrode902from a DC-DC converter905for adjusting the electric potential output from the ground unit; and an electric potential is applied to the sixth common electrode901from a DC-DC converter904for 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 inFIG. 10can be used as the configurations of the scanning circuit601and the modulation circuit602described with regard to each embodiment.

FIG. 10shows a V shift register1003constituting the scanning circuit601, an H shift register1002constituting the modulation circuit602, and a latch1001. A scanning signal is applied to the scanning signal wiring from the V shift register1003, and a modulation signal is applied to the modulation signal wiring from the latch1001. A display control unit36includes a controller37and a picture signal conversion memory38. Image data and a timing control signal, if necessary, are input into the display control unit36, and the display control unit inputs a timing signal such as a shift pulse and a start pulse, and a video signal into the scanning circuit601and the modulation circuit602.