WO2006121137A1

WO2006121137A1 - Display apparatus and display panel driving method

Info

Publication number: WO2006121137A1
Application number: PCT/JP2006/309522
Authority: WO
Inventors: Shinichi Ishizuka
Original assignee: Pioneer Corporation
Priority date: 2005-05-10
Filing date: 2006-05-02
Publication date: 2006-11-16

Abstract

A display apparatus and a display panel driving method comprising the steps of supplying a drive current from a power supply means to capacitive light emitting elements of the display panel each set to emit a light in each of subframes used for gray-scale display; counting, as a number of light emitting pixels, the number of the capacitive light emitting elements of the display panel each set to emit a light during a predetermined one of the successive subframes; determining the value of the drive current flowing in the display panel during the predetermined subframe; and adjusting the output voltage of the power supply means such that the measured drive current value is within acceptable limits of the reference current value established for the light emitting pixels.

Description

DISPLAY DEVICE AND DISPLAY PANEL DRIVING METHOD

Technical field

The present invention relates to a display device using a display panel made of a capacitive light emitting element such as an organic electroluminescence element, and a method for driving the display panel.

Background art

Thin display panels are required for image display devices used in mobile terminals such as mobile phones. A liquid crystal display panel is usually used for a conventional thin display panel, but a display panel formed by arranging a plurality of organic EL luminescence elements (organic EL elements) in a matrix is only thin. In addition, since it is lightweight, it is considered promising as an image display device for portable terminals.

There are two methods for driving organic EL elements: current drive and voltage drive. The organic EL element emits light with a luminance corresponding to the supplied current level. In a current-driven display device, the current level supplied to the organic EL element is generally controlled to a constant current, and in a voltage-driven display device, the voltage applied to the organic EL element is generally controlled to a constant voltage. ing.

By the way, the EL element has a problem that its characteristics change with temperature and time. As shown in Fig. 1, the characteristics of the drive current flowing through the EL element and the forward voltage of the EL element change with changes in temperature. From the characteristics in Fig. 1, it can be seen that for the same drive current, the forward voltage decreases at high temperatures and increases at low temperatures. In addition, as shown in Fig. 2, it is found that the forward voltage increases over time. I'm crazy. Thus, when the forward voltage of the EL element changes with temperature and time, there is a disadvantage that the brightness of the EL element is lowered.

As a conventional technique for dealing with this, Japanese Patent Application Laid-Open No. 2004-271 755 measures the actual drive current flowing in the display panel and compares it with the panel drive current estimated from the display data. An organic EL display device that adjusts the black level voltage according to the above is shown.

Japanese Patent Laid-Open No. 2004-252216 discloses that a peak current value is measured when a display unit having an active matrix structure is driven by a pulse width modulation (PWM) method, and a peak current amount is measured according to the measured value. A display device is shown in which the average luminance of a display image is determined from the ratio of the average current amount to, and the luminance is adjusted by controlling the voltage applied to the self-luminous element based on this information.

In Japanese Patent Laid-Open No. 2004-252036, a driving current is applied to the measuring EL element to detect the forward voltage of the measuring EL element, and the driving voltage is applied to the display EL element based on the forward voltage. An active drive type light-emitting display device for supplying a light source is shown.

However, in any conventional apparatus, even if the forward voltage of a capacitive light emitting element such as an organic electroluminescence element changes, the light emission luminance is not controlled to be the initial luminance, and the display luminance of the entire display panel is not controlled. It did not eliminate the shortcoming of the decline.

Disclosure of the invention

The problems to be solved by the present invention include the above-mentioned drawbacks as an example, and the forward voltage of a capacitive light emitting element such as an organic electroluminescence element of a display panel is W

3 It is an object of the present invention to provide a display device and a display panel driving method capable of preventing a decrease in display luminance even when the display changes.

The display device according to the first aspect of the present invention provides a display panel composed of a plurality of capacitive light emitting elements arranged in a matrix, and a plurality of gradation display subframe periods within a period of each frame of input video data. A display device that performs gradation display by setting each of the plurality of capacitive light emitting elements to emit light or not emit light for each subframe corresponding to a luminance gradation indicated by input video data, The display panel emits light for each subframe and power supply means for supplying a driving current to the set capacitive light emitting element, and the display panel within a predetermined subframe period of the continuous subframes. A light emitting pixel number counting unit that counts the number of light emitting pixels set and the number of set capacitive light emitting elements as the number of light emitting pixels, and a driving power that flows to the display panel within a period of the predetermined subframe. Measuring means for measuring the value, and control means for adjusting the output voltage of the power supply means so that the drive current value measured by the measuring means is within the allowable range of the reference current value for the number of light emitting pixels. It is characterized by having

The display panel drive method of the second invention of the present application is for a display panel composed of a plurality of capacitive light emitting elements arranged in a matrix shape, for a plurality of gradation displays within the period of each frame of input video data. A display panel that provides a sub-frame period and performs gradation display by setting each of the plurality of capacitive light-emitting elements to emit light or not emit light for each sub-frame corresponding to the luminance gradation indicated by the input video data A driving current is supplied from the power supply means to the capacitive light emitting element set to emit light of the display panel for each subframe, and a period of a predetermined subframe among the continuous subframes The number of capacitive light-emitting elements set in the display panel is set to emit light Counting as the number of pixels, measuring the drive current value flowing through the display panel within the period of the predetermined sub-frame, and measuring drive current value within the allowable range of the reference current value for the number of light-emitting pixels And adjusting the output voltage of the power supply means.

The display device of the third invention of the present application provides a display panel composed of a plurality of capacitive light emitting elements arranged in a matrix, with a plurality of gradation display subframes within a period of each frame of input video data. A display that performs gradation display by setting a period and setting each of the plurality of capacitive light emitting elements to light emission or non-light emission for each gradation display subframe according to the luminance gradation indicated by the input video data. An apparatus for providing a current measurement subframe that is different from a period of the plurality of gradation display subframes within a specific frame period of the input video data; Display pattern setting means for setting each of the plurality of capacitive light emitting elements to emit light or not according to a predetermined display pattern within a period, and the capacitive light emitting element set to emit light of the display panel Power supply means for supplying a drive current to the power supply, a measurement means for measuring a drive current value flowing through the display panel within a period of the current measurement subframe, and a drive current value measured by the measurement means And control means for adjusting the output voltage of the power supply means so as to be within an allowable range of the reference current value. The display panel drive method according to the fourth invention of the present application is for a display panel composed of a plurality of capacitive light emitting elements arranged in a matrix, for displaying a plurality of gradations within each frame of input video data. A sub-frame period is provided, and gradation display is performed by setting each of the plurality of capacitive light-emitting elements to emit light or not to emit light for each gradation display sub-frame corresponding to the luminance gradation indicated by the input video data. A driving method for performing the input projection A current measurement subframe period different from a period of the plurality of gradation display subframes within a specific frame period of image data is provided, and the plurality of capacitive light emission within the current measurement subframe period Each element is set to light emission or non-light emission according to a predetermined display pattern, a drive current is supplied from the power supply means to the capacitive light emitting element set to light emission of the display panel, and the period of the current measurement subframe The drive current value flowing in the display panel is measured in the inside, and the output voltage of the power supply means is adjusted so that the measured drive current value is within the allowable range of the reference current value. Yes.

Brief Description of Drawings

FIG. 1 is a diagram showing a forward voltage-one drive current characteristic.

FIG. 2 is a graph showing the time-forward voltage characteristics.

FIG. 3 is a flock diagram showing a configuration of a display device to which the first and second inventions of the present application are applied.

FIG. 4 is a circuit diagram showing a configuration of a light emitting circuit for each pixel of the display panel in the apparatus of FIG.

FIG. 5 shows a frame modulation method.

Fig. 6 is a flowchart showing the panel applied voltage adjustment operation executed by the controller.

FIG. 7 is a diagram showing a gray scale display subframe for performing the panel applied voltage adjustment operation.

FIG. 8 is a hook diagram showing another configuration of the display device to which the first and second inventions of the present application are applied. . FIG. 9 is a flowchart showing the panel applied voltage adjustment operation executed by the controller in the apparatus of FIG.

FIG. 10 is a block diagram further illustrating another configuration of the display device to which the first and second inventions of the present application are applied. -Fig. 11 is a flowchart showing the panel applied voltage adjustment operation executed by the controller in the apparatus of Fig. 10.

FIG. 12 is a block diagram showing the configuration of a display device to which the third and fourth inventions of the present application are applied.

FIG. 13 is a flowchart showing the panel applied voltage adjustment operation executed by the controller in the apparatus of FIG. ― Fig. 14 is a diagram showing a sub-frame for gradation display within a specific frame and a sub-frame for current measurement.

FIG. 15 is a hook diagram showing another configuration of the display device to which the third and fourth inventions of the present application are applied.

FIG. 16 is a flowchart showing the panel applied voltage adjustment operation executed by the controller in the apparatus of FIG.

FIG. 17 is a hook diagram showing another configuration of the display device to which the third and fourth inventions of the present application are applied.

FIG. 18 is a flowchart showing the panel applied voltage adjustment operation executed by the controller in the apparatus of FIG.

FIG. 19 is a diagram showing an example in which a drive current measurement period is provided within each EL element of the display panel (a subframe in which this reverse bias voltage is applied). BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows a configuration of a display device to which the first and second inventions of the present application are applied. This display device includes a display panel 1 1, a scanning line driving circuit 1 2, a data line driving circuit 1 3, a current detection circuit 14, a variable power supply 1 5, and a controller 17.

The display panel 11 is an active matrix type composed of m × n pixels, and has an electroluminescence (EL) light emitting circuit 11 i to ll _m , _n for each pixel. EL light-emitting circuits 1 1 i to ll _m and _n all have the same configuration, are connected to the scanning line driving circuit 12 via scanning lines Al to An, and are connected to data lines via data lines B 1 to Bm. Connected to drive circuit 1 3.

Since the light emitting circuits 1 1 ^ i to ll _m , _n all have the same configuration as described above, the configuration of the light emitting circuit 11 1 will be described.

The light-emitting circuit 1 1 i has two FETs 21 and 22 and a capacitor 23 for driving the organic EL element 24 as shown in FIG. The gate G of FET 21 is connected to a scanning line A 1 to which a scanning signal is supplied, and the source S of FET 21 is connected to a data line B 1 to which a data signal is supplied. The drain D of FET 21 is connected to the gate G of FET 22 and is connected to one terminal of the capacitor 24. The source S of the FET 22 is connected to the common power line 25 together with the other terminal of the capacitor 23. The drain D of the FET 22 is connected to the anode of the EL element 24, and the cathode of the EL element 24 is connected to the ground.

Light emitting circuit 11 1 to ll _m , _n The light emission luminance of each EL element 24 is controlled in order to obtain a display gradation in accordance with the image data. As a bell, a frame modulation method that controls the drive period within one frame is adopted. In the frame modulation method, as shown in Fig. 5, one frame is divided into multiple (N) subframes SF1, SF2, SF3, ... SFN FET 2 only during the subframe period selected according to the video data. By using 2 in a saturated state (on state) and supplying a certain level of drive current, the light emission or non-light emission state is performed in subframe units. Each subframe SF1, SF2, SF3, ... SFN period is divided into writing period and display period. The writing period is a period for determining whether FET 22 is set to the on state or the off state in the scanning line order in each subframe. The display period is set when the writing period is set to the on state. This is the period during which the EL element 24 emits light.

The controller 17 generates a scanning control signal and a data control signal in the writing period according to the input image data. The scanning control signal indicates the selected scanning line and is supplied to the scanning line driving circuit 12, and the data control signal indicates the data line corresponding to the EL element to emit light and is supplied to the data line driving circuit 13.

Although each of the scanning line driving circuit 12 and the data line driving circuit 13 is not specifically shown, it includes a power source and a switch circuit. The scanning line driving circuit 12 sequentially selects the scanning lines A 1 to An for each subframe in accordance with the scanning control signal in the writing period, and supplies the scanning signal to the selected scanning line. The data line driving circuit 13 selects the data lines B1 to Bm according to the data control signal, and supplies a data signal to the selected data line. Emitting circuit 1 1 E ~ 1 l _m, the output voltage of the variable power source 1 5 is supplied via the current detection circuit 1 4 as a power supply voltage to the common power supply line 2 5 which is a power supply unit with respect to _n. For example, in the subframe where the EL element 2 4 of the light emitting circuit 1 1 i emits light, When a scanning signal is supplied to the gate G of the FET 2 1 via the scanning line A'l during the period, the FET 2 1 is turned on by the supply of the scanning signal, and to the source S via the data line B 1 A current corresponding to the voltage of the supplied data signal is supplied from the source S to the drain D. Capacitor 23 is charged and the voltage is supplied to the gate G of FET 22 and FET 22 is turned on. The FET 22 supplies a drive current corresponding to the data signal supplied to the gate G to the EL element 24 and causes the EL element 24 to emit light. The light emission continues until at least the end of the display period of the subframe.

Current detecting circuit 1 4 detects the values of the drive current from the variable power supply 1 5-emitting circuit 1 1 to 1 l _m, Ru is supplied to the _n. A controller 17 is connected to the detection output terminal of the current detection circuit 14.

In addition to generating the above scanning control signal and data control signal, the controller 17 performs the panel applied voltage adjustment operation so that the EL elements of all the pixels of the display panel 11 are set to emit light in one subframe. The number of pixels that emit light, that is, the number of light-emitting pixels, and the current detection circuit 14 calculate the unit drive current value by dividing the detected drive current value by the number of light-emitting pixels. A division function, a function for comparing the unit drive current value and the reference current value, and a voltage adjustment function for controlling the output voltage of the variable power source 15 according to the comparison result are provided. Note that each of these functions operates in the panel applied voltage adjustment operation described below by the controller 17 executing, for example, a program. However, the light emitting pixel number counting circuit, the divider, the comparison circuit, and the voltage adjustment are performed. A hardware circuit may be provided.

Next, the panel applied voltage adjustment operation executed by the controller 17 will be described using the flowchart of FIG. The controller 17 determines whether or not the period of the gradation display subframe for performing the panel applied voltage adjustment operation has come (step S 1). As shown in Fig. 7, the gray scale display subframe that performs the panel applied voltage adjustment operation is a subframe for gray scale display SF1, SF2, SF3, ... within one specific frame. In the subframe). The specific frame may be every frame, a predetermined number of frame intervals, or the specific frame interval may be shortened over time. Also, it may be a frame when the power is turned on. ■

As the gradation display sub-frame Λ for performing the panel applied voltage adjustment operation, a sub-frame whose display period is longer than the writing period is used. In a subframe in which the display period is shorter than the writing period, light may not be emitted simultaneously for all the scanning lines during the display period. In other words, even if the display period of the scanning line A 1 ends in the same subframe, the writing period does not end in the scanning line An. Therefore, a sub-frame having a display period in which a period in which the drive current value flowing through all the EL elements set to emit light in one sub-frame can be measured accurately is obtained.

When the controller 17 determines that the period of the gradation display subframe for performing the panel applied voltage adjustment operation is reached, the display pattern assigned to the subframe according to the image data is displayed on the display panel 11. Execute the operation to be displayed (step S2). The controller 17 first generates a scan control signal and a data control signal in the writing period of the gradation display subframe that performs the panel applied voltage adjustment operation. The scanning control signal indicates the selected scanning line and is supplied to the scanning line driving circuit 12, and the data control signal corresponds to the EL element for each scanning line to be emitted in the display pattern. Indicates a data line and is supplied to the data line driving circuit 13. The scanning line drive circuit 12 sequentially selects the scanning lines A 1 to An in accordance with the running control signal during the writing period, and supplies the scanning signal to the selected scanning line. The data line driving circuit 13 selects the data lines B1 to Bm according to the data control signal, and supplies the data signal to the selected data line. Therefore, the light emitting circuit 1 1 l _m , i 1 1 ₂ to 1 l _m , ₂ ,..., 1 1 _{n to} ll _m , _n are charged in the light emitting circuit capacitor 2 3 at the light emitting position of the display pattern in this order. On the other hand, since the EL elements 24 are turned on, the drive current is supplied to the EL elements 24. Emitting circuit 1 1 _n ～Ll _m, writing period ends for _n, all the light-emitting circuit 1 _1:, E to 1 l _m, when _n is shifted to the display period, EL device driving current is supplied The display panel 11 displays the above assigned display pattern.

The controller 17 counts the number of pixels set for light emission among all the pixels of the display panel 11 in the gradation display subframe that performs the panel applied voltage adjustment operation (step S 3). For example, the above-mentioned data control signal indicates light emission / non-light emission of all pixels, that is, light emitting circuits 1 1 _n to: I l _m , _n by logical values, and therefore emits the number of logic 1 indicating light emission. Count as the number of pixels.

The controller 17 reads the drive current value detected by the current detection circuit 14 during the measurement period of the display period (Step S4), and divides the read drive current value by the number of light emitting pixels. The unit drive current value is calculated (step S5). Then, the unit drive current value is compared with the reference current value (step S6), and the comparison result is determined (step S7). The reference current value is a preset drive current value that flows through one light emitting circuit during light emission. When the drive current value is lower than the allowable range of the reference current value, the controller 17 increases the output voltage of the variable power source 15 by a certain voltage (step S8), and the drive current value is equal to the reference current value. If it is higher than the allowable range, the output voltage of the variable power source 15 is reduced by a constant voltage (step S 9). By repeating steps S4 to S9, the drive current value is made substantially equal to the reference current value.

Therefore, even if the forward voltage of the EL element of the display panel 11 changes, it is possible to prevent a change in the drive current caused by the change, and thus it is possible to prevent the display brightness of the display panel 11 from being lowered.

In the embodiment described above, every time the drive current is measured, the unit drive current value is compared with the reference current value, but the drive current is measured several times, and the average drive current value is calculated and averaged. Even if the unit current value of the drive current value is compared with the reference current value, it is good.

In the above-described embodiment, the unit drive current value is calculated by dividing the measured drive current value by the number of light emitting pixels and divided by the reference current value. However, the number of light emitting pixels is added to the reference current value. Multiplication may be performed to compare the reference current value X the number of light emitting pixels and the measured drive current value.

Furthermore, the current detection circuit 14 is inserted between the variable power supply 15 and the display panel 11 1 only during the drive current measurement period, and the variable power supply 15 and the display panel 11 are directly connected during other periods. You may do it.

In addition, the configuration of each of the light emitting circuits 11 to 1 l _m and _n is shown in FIG. 4, but the configuration of the light emitting circuit is not limited to this, and the present invention is a display provided with a light emitting circuit of another configuration for each pixel. It can also be applied to the panel.

FIG. 8 shows another configuration of the display device to which the first and second inventions of the present application are applied. The This display device includes a display panel 1 1, a scanning line drive circuit 1 2, a data line drive circuit 1 3, a current detection circuit 14, a controller 1 7, a power supply 3 1, and an on-voltage variable circuit 3 2. The display panel 11, the scanning line driving circuit 12, the data line driving circuit 13, the current detection circuit 14 and the controller 17 are the same as those in the display device shown in FIG.

The power supply 31 outputs a fixed voltage. The output voltage of the power supply 31 is supplied to the common power supply line 25 via the current detection circuit 14 for the light emitting circuits 11 i to ll _m , _n . On voltage variable circuit 32 changes the ON voltage supplied as a data signal emitting circuit 1 of the display from the data line driving circuit 1 3 panel 1 1 1 to 1 l _m, the _n. The on-voltage is a gate voltage applied to the FET 22 via the FET 21 when the FET 21 is turned on in order to cause the EL element 24 of the light emitting circuit to emit light. The on-voltage is changed in response to a command from controller 17. In addition, when the on-voltage is changed by the on-voltage variable circuit 32, the gate voltage applied to the FET 22 changes, and as a result, the FET 22 operates in the active region and the EL element is connected via the FET 22. The drive current value supplied to 24 changes. In FIG. 8, the data line drive circuit 13 is specifically shown only with a configuration including a switch 13 that supplies a data signal to the data line B 1, but the same applies to each of the data lines B 2 to Bm. is there. The switch 13 selects either the ON voltage supplied from the ON voltage variable circuit 32 or the OFF voltage equal to the ground potential, for example, according to the data control signal supplied from the controller 17. And supplied to the data line B 1 as a data signal. The off voltage is a gate voltage applied to the FET 22 via the FET 21 when the FET 21 is turned on so that the EL element 24 of the light emitting circuit does not emit light. The panel applied voltage adjustment operation executed by the controller 17 in the display device of FIG. 8 is shown in the flowchart of FIG.

Steps S 1 to S 7 of the panel applied voltage adjustment operation in FIG. 9 are the same as steps S 1 to S 7 of the panel applied voltage adjustment operation shown in FIG. When the drive current value is lower than the allowable range of the reference current value in step S7, the controller 17 increases the output voltage (on voltage) to the on-voltage variable circuit 3 2 by a constant voltage (step S). 10), if the drive current value is higher than the allowable range of the reference current value, the ON voltage variable circuit 32 reduces the output voltage by a constant voltage (step S 1 1). By repeating steps S 4 to S 7, S 10 or S I 1, the drive current value is made approximately equal to the reference current value. Note that the constant voltage in steps S 10 and S 11 may be different from the constant voltage in steps S 8 and S 9 described above.

FIG. 10 further shows another configuration of the display device to which the first and second inventions of the present application are applied. The display device in FIG. 10 includes a display panel 1 1, a scanning line drive circuit 1 2, a data line drive circuit 1 3, a current detection circuit 1 4, a variable power supply 1 5, a controller 1 7, and an on-voltage variable circuit 3 2. I have. Display panel 1 1, Scan line drive circuit 1 2, Data line drive circuit 1 3, Current detection circuit 1 4, Variable power supply 1 5 and controller 17 are the same as those in the display device shown in Fig. 3. The on-voltage variable circuit 32 is the same as that in the display device shown in FIG.

The panel applied voltage adjustment operation executed by the controller 17 in the display device of FIG. 10 is shown in the flowchart of FIG.

The panel application voltage adjustment operation in Fig. 11 is a combination of the panel application voltage adjustment operation in Fig. 6 and the panel application voltage adjustment operation in Fig. 9. Step S 2! ~ S 2 3 Equivalent to S 1 to S 3 described above. Steps S 2 4 to S 29 are operations for adjusting the output voltage (ON voltage) of ON voltage variable circuit 3 2, and steps S 3 0 to S 3 5 are the output voltage (power supply voltage) of variable power supply 15 ) Is an operation to adjust. By repeating steps S 2 4 to S 3 5, the drive current value is substantially equal to the reference current value.

In each of the above embodiments, the panel applied voltage adjustment operation may be performed for each R GB. In other words, the controller 17 is detected by the current detection circuit 14 and the current detection circuit 14 which counts the number of pixels in which the EL elements of all the pixels of the display panel 11 are set to emit light, that is, the number of light emitting pixels. The division function that calculates the unit drive current value by dividing the drive current value by the number of light emitting pixels, the function that compares the unit drive current value and the reference current value, and the variable power supply 1 5 ( A voltage adjustment function for controlling the output voltage of the on-voltage variable circuit 3 2) is provided for each RGB.

As described above, according to the first and second inventions of the present application, the driving current is supplied from the power supply means to the capacitive light emitting element set to emit light of the display panel for each gradation display subframe, and the continuous sub The number of capacitive light elements set as the light emission of the display panel and the number of light emitting pixels within the predetermined subframe period of the frame is counted as the number of light emitting pixels, and the drive current value that flows through the display panel within the predetermined subframe period Is measured, and the output voltage of the power supply means is adjusted so that the measured drive current value is within the allowable range of the reference current value for the number of light emitting pixels. Therefore, it is possible to prevent the display brightness of the display panel from being lowered even if the forward voltage of the individual capacitive light emitting elements of the display panel changes. Also, there is an advantage that no special subframe other than the gradation display subframe is required for brightness adjustment. FIG. 12 shows the configuration of a display device to which the third and fourth inventions of the present application are applied. The display device includes a display panel 11, a scanning line driving circuit 12, a data line driving circuit 13, a current detection circuit 14, a variable power source 15, a comparison circuit 16 and a controller 17.

The display panel 11, the scanning line driving circuit 12, the data line driving circuit 13, the current detection circuit 14 and the variable power source 15 are the same as those of the display device shown in FIG.

The comparison circuit 16 is connected to the detection output terminal of the current detection circuit 14. The comparison circuit 16 compares the drive current value detected by the current detection circuit 14 with the reference current value. When the current detection circuit 14 detects the drive current value as a voltage level, a voltage value corresponding to the reference current value is supplied to the comparison circuit 16. The reference current value is a preset current value in a predetermined measurement display pattern. The comparison result of the comparison circuit 16 is supplied to the controller 17.

The controller 17 controls the output voltage of the variable power source 15 so that the drive current value becomes equal to the reference current value according to the comparison result of the comparison circuit 16.

Next, the panel applied voltage adjustment operation executed by the controller 17 will be described with reference to the flowchart of FIG.

The controller 17 determines whether or not the current measurement subframe period has come (step S 51). As shown in Fig. 14, the current measurement subframes are arranged separately from the subframes for gradation display SF1, SF2, SF3, ... SFN in a specific frame. In Fig. 14, the current measurement subframe is arranged between the grayscale display subframes. The specific frame may be every frame or a predetermined number of frame intervals. Also, it may be a frame when the power is turned on. If the controller 17 determines that the current measurement subframe period has come, it performs an operation to display the measurement display pattern on the display panel 11 (step S 5 2). As shown in Fig. Γ4, the current measurement subframe consists of a writing period and a display period. The measurement period for measuring the drive current is located in the display period. Scan control signals and data control signals are generated during the writing period of the current measurement subframe. The scanning control signal indicates the selected scanning line and is supplied to the scanning line driving circuit 12, and the data control signal indicates the data line corresponding to the EL element that should emit light in the measurement display pattern, and the data line driving circuit 1 3 To be supplied. The scanning line driving circuit 12 sequentially selects the scanning lines A :! to An in accordance with the scanning control signal in the writing period, and supplies the scanning signals to the selected scanning lines. The data line driving circuit 13 selects the data lines B 1 to B m according to the data control signal and supplies the data signal to the selected data line. Therefore, the capacitor 23 of the light emitting circuit at the light emitting position of the display pattern for measurement in the light emitting circuits 1 1 i to ll _m , _n is charged and the EL element 24 is turned on. 24 4 is supplied with drive current. As a result, the EL element to which the drive current is supplied during the display period emits light, and the display panel 11 displays the measurement display pattern.

The controller 17 causes the comparison circuit 16 to read the drive current value detected by the current detection circuit 14 during the above measurement period (step S 53). The comparison circuit 16 compares the read drive current value with the reference current value, and the comparison result is read by the controller 17 (step S54). When the drive current value is lower than the allowable range of the reference current value, the controller 17 increases the output voltage to the variable power source 15 by a certain voltage (step S 5 5), and the drive current value becomes the reference current value. Value tolerance ffl If it is higher, the output voltage of the variable power source 15 is reduced by a constant voltage (step S 5 6). By repeating steps S 53 to S 56, the drive current value is almost equal to the reference current value.

Therefore, even if the forward voltage of the EL element of the display panel 11 changes, it is possible to prevent a change in the drive current caused by the change, and thus it is possible to prevent the display brightness of the display panel I 1 from being lowered.

In the above embodiment, the subframe for current measurement is provided separately from the subframes SF1, SF2, SF3, ... SFN for gradation display, but the subframes SF1, SF2, SF for full tone display are provided. SF3, ... Any one subframe of SFN may be used as a current measurement subframe. Gradation display subframes SF1, SF2, SF3, ... When SFN is weighted and the duration of each subframe is different, the shortest subfield is set as the current measurement subframe. The influence on the displayed contents can be minimized.

Further, the display pattern for measurement in the above-described embodiment covers one line in the vertical direction of the display panel 11 or light emission of one EL element in several lines, or one line or several lines in the horizontal direction. It is a pattern that emits light from an EL element. By using such a display pattern for measurement, the degree to which the display of the display pattern for measurement influences the display corresponding to the input image data can be kept low. However, if the drive current is measured with only a part of the pixels on the display panel, it is possible that the total current value is not reflected. Therefore, each time the current measurement subframe is installed, the measurement display pattern on the display panel It is also possible to reflect the entire current value by moving the light emitting part by, measuring each movement, and averaging them. . The display pattern for measurement may be a display pattern that lights up all over. In this way, the entire current value can be reflected.

FIG. 15 shows another configuration of the display device to which the third and fourth inventions of the present application are applied. This display device includes a display panel 11, a scanning line drive circuit 2, a data line drive circuit 13, a current detection circuit 14, a comparison circuit 16, a controller 17, a power supply 31, and an on-voltage variable circuit 32. The display panel 11, the scanning line driving circuit 12, the data line driving circuit 13, the current detection circuit 14, the comparison circuit 16 and the controller 17 are the same as those in the display device shown in FIG.

The power supply 31 outputs a fixed voltage. The output voltage of the power supply 31 is supplied to the common power supply line 25 via the current detection circuit 14 for the light emitting circuits 11 i to ll _m , _n . On voltage variable circuit 32 changes the ON voltage supplied from the data line driving circuit 13 emitting circuit 1 1 to 1 l _m of the display panel 1 1, the _n as data signals. The on-voltage is a gate voltage applied to the FET 22 via the FET 21 when the FET 21 is turned on in order to cause the EL element 24 of the light emitting circuit to emit light. The on-voltage is changed in response to a command from controller 17. Further, when the on-voltage is changed by the on-voltage variable circuit 32, the gate voltage applied to the FET 22 changes. As a result, the FET 22 operates in the active region and the EL element 24 is operated via the FET 22. The drive current value supplied to the voltage changes. In FIG. 15, only the configuration of the data line driving circuit 13 including the switch 13 for supplying the data signal to the data line B 1 is specifically shown, but the same applies to each of the data lines B 2 to Bm. . Either the ON voltage supplied from the ON voltage variable circuit 32 or the OFF voltage equal to the voltage V _A , for example, is selected. Selected according to the data control signal and supplied to the data line B1 as a data signal. The off-voltage is a gate voltage that is applied to FET 2 2 via FET 21 when FET 21 is turned on so that EL element 24 of the light emitting circuit does not emit light.

The panel applied voltage adjustment operation executed by the controller 17 in the display device of FIG. 15 is shown in the flowchart of FIG.

Steps S 5 1 to S 5 4 of the panel applied voltage adjusting operation in FIG. 16 are the same as steps S 5 l ^ S 5 4 of the panel applied voltage adjusting operation shown in FIG. When the controller 17 determines that the drive current value is lower than the allowable range of the reference current value in step S54, the controller 17 increases the output voltage (on voltage) by a constant voltage to the on-voltage variable circuit 3 2 (step S5). 7) If the drive current value is higher than the allowable range of the reference current value, the ON voltage variable circuit 32 reduces the output voltage by a constant voltage (step S 58). By repeating steps S 5 3, S 5 4, S 5 7 or S 5 8, the drive current value is made substantially equal to the reference current value. The constant voltage in steps S 5 7 and S 5 8 may be different from the constant voltage in steps S 5 5 and S 5 6.

FIG. 17 further shows another configuration of the display device to which the third and fourth inventions of the present application are applied. The display device shown in Fig. 7 has a display panel 1 1, a scanning line drive circuit 1 2, a data line drive circuit 1 3, a current detection circuit 1 4, a variable power supply 1 5, a comparison circuit 1 6, a controller 1 7, and a variable ON voltage. Circuit 3 2 is provided. Display panel 1 1, Scan line drive circuit 1 2, Data line drive circuit 1 3, Current detection circuit 1 4, Variable power supply 1 5, Comparison circuit 1 6 and controller 1 7 are in the display device shown in Figure 12 The on-voltage variable circuit 32 is the same as that in the display device shown in FIG.

Fig. 17 Panel application zero executed by controller 17 in display device of 7 • The pressure adjustment operation is shown in the flowchart in Fig. 18.

The panel applied voltage adjustment operation in Fig. 18 is a combination of the panel applied voltage adjustment operation in Fig. 13 and the panel applied voltage adjustment operation in Fig. 16. Steps S 6 1 and S 6 2 are equal to S 5 1 and S 5 2 described above. Steps S 6 3 to S 6 6 are operations for adjusting the output voltage (ON voltage) of the ON voltage variable circuit 3 2. Steps S 6 7 to S 70 are output voltages of the variable power source 15 (power supply voltage) This is an operation for adjusting. By repeating steps S 63 to S 70, the drive current value is made substantially equal to the reference current value. '

FIG. 19 shows an example in which a drive current measurement period is provided within a subframe period in which a reverse bias voltage is applied to each EL element of the display panel. It is known that the EL element has a refreshing effect that the function of the EL element is restored when a reverse voltage, that is, a reverse bias voltage is sometimes applied to the EL element whose function is deteriorated due to repeated light emission. Yes. Therefore, by providing the drive current measurement period within the subframe period during which the reverse bias voltage is applied, the pixel selection time can be shared, and one frame compared to the case where the current measurement subframe is provided independently. It is possible to shorten the period other than the period of the sub-frame for gradation display.

Further, in each of the above-described embodiments, a voltage-driven display device is shown, but the present invention can also be applied to a current-driven display device. Although an example using an active matrix type display panel has been shown, the present invention can also be applied to a display device that drives a passive matrix type display panel.

Alternatively, the measurement display pattern may be displayed for each RGB, and the power supply voltage applied to the display panel for each RGB may be controlled. In either case, power can be measured with a single drive current measurement. The voltage (or on-voltage) may be controlled, or the power supply voltage (or on-voltage) may be controlled by taking the average of the measurement results of several drive current values.

As described above, according to the third and fourth aspects of the present application, the current measurement subframe period different from the periods of the plurality of gradation display subframes within the specific frame period of the input video data is set. And a plurality of capacitive light emitting elements are set to emit or not emit light during the period of the current measurement subframe, and a driving current is supplied from the power supply means to the capacitive light emitting elements set to emit light of the display panel. The drive current value flowing through the display panel is measured within the current measurement subframe period, and the output voltage of the power supply means is adjusted so that the measured drive current value falls within the allowable range of the reference current value. It is broken. Therefore, even if the forward voltage of each capacitive light emitting element of the display panel changes, it is possible to prevent the display brightness of the display panel from being lowered.

Claims

The scope of the claims ·

1. For a display panel composed of a plurality of capacitive light emitting elements arranged in a matrix, a plurality of gradation display subframe periods are provided within each frame period of the input video data, and the input video data indicates A display device that performs gradation display by setting each of the plurality of capacitive light emitting elements to emit light or not emit light for each subframe corresponding to a luminance gradation,

Power supply means for supplying a drive current to the capacitive light emitting element set to emit light of the display panel for each subframe;

A number-of-light-emitting pixel counting means for counting the number of capacitive light-emitting elements set to emit light of the display panel as the number of light-emitting pixels within a period of a predetermined sub-frame among the consecutive sub-frames;

Measuring means for measuring a drive current value flowing in the display panel within a period of the predetermined subframe;

Control means for adjusting the output voltage of the power supply means so that the drive current value measured by the measurement means falls within the allowable range of the reference current value for the number of light-emitting pixels. Display device.

2. The control means divides the drive current value measured by the measurement means by the number of light emitting pixels to calculate a unit drive current value, and a division means; and the unit drive current value and a single unit Comparing means for comparing a reference current value for the capacitive light emitting element, and voltage adjusting means for adjusting an output voltage of the power supply means in accordance with a comparison result of the comparing means. Item 1. A display device according to item 1.

3. The frame including the predetermined subframe is immediately after the display device is turned on. The display device according to claim 1, wherein the display device is a frame.

4. The display device according to claim 1, wherein the frame including the predetermined subframe is a frame of the input video data.

5. The display device according to claim 1, wherein the frame including the predetermined sub-frame is every predetermined number of frames of the input video data.

6. In the predetermined subframe, the capacitive light emitting element in which a writing period in which each of the plurality of capacitive light emitting elements is set to emit light or not emit light for each gradation display subframe is set to emit light. 2. The display device according to claim 1, wherein the display device has a subframe shorter than a display period in which a drive current is supplied to the display frame.

7. The power source unit, the light emitting pixel number counting unit, the measuring unit, and the control unit are provided for each of RGB colors of light emitted from the capacitive light emitting element. Display device. '

8. The output voltage of the power supply means adjusted by the control means changes the source voltage of the driving transistor of each of the capacitive light emitting elements set as the light emission of the display panel, thereby setting the light emission. 2. The display device according to claim 1, wherein a driving current value of the capacitive light emitting element changes. ― '

9. The output voltage of the power supply means adjusted by the control means changes the gate voltage of the driving transistor of each of the capacitive light emitting elements set as the light emission of the display panel, thereby setting the light emission. 2. The display device according to claim 1, wherein a driving current value of the capacitive light emitting element changes.

1 0. The output voltage of the power supply means adjusted by the control means is the source voltage of the driving transistor of each of the capacitive light emitting elements set to emit light of the display panel. 2. The display device according to claim 1, wherein the drive voltage value of the capacitive light emitting element set as the light emission is changed by changing the gate voltage and the gate voltage.

1 1. For a display panel composed of a plurality of capacitive light emitting elements arranged in a matrix, a plurality of gradation display subframe periods are provided within each frame period of the input video data. A display panel driving method for performing gradation display by setting each of the plurality of capacitive light emitting elements to emit light or not emit light for each of the sub-frames corresponding to the luminance gradation shown in FIG.

A driving current is supplied from the power supply means to the capacitive light emitting element set to emit light of the display panel for each subframe,

The number of capacitive light emitting elements set to emit light of the display panel within a predetermined subframe period of the consecutive subframes is counted as the number of light emitting pixels, and the display is performed within the predetermined subframe period. Measure the drive current flowing through the panel,

A drive method characterized by adjusting the output voltage of the power supply means so that the measured drive current value falls within an allowable range of reference current values for the number of light emitting pixels.

1 2. For a display panel consisting of a plurality of capacitive light emitting elements arranged in a matrix, a plurality of gradation display subframe periods are provided within the period of each frame of the input video data. A display device that performs gradation display by setting each of the plurality of capacitive light emitting elements to emit light or not emit light for each gradation display subframe corresponding to a luminance gradation indicated by data,

A current measurement subframe period different from a period of the plurality of gradation display subframes within a specific frame period of the input video data is provided, and the current measurement subframe is provided. Display pattern setting means for setting each of the plurality of capacitive light emitting elements to emit or not emit light according to a predetermined display pattern within a subframe period;

Power supply means for supplying a driving current to the capacitive light emitting element set to emit light of the display panel;

Measuring means for measuring a drive current value flowing through the display panel within a period of the current measurement subframe;

And a control means for adjusting an output voltage of the power supply means so that a drive current value measured by the measurement means falls within an allowable range of a reference current value.

13. The display device according to claim 12, wherein the specific frame is a frame immediately after the display device is turned on.

14. The display device according to claim 12, wherein the specific frame is a frame of the input video data.

15. The display device according to claim 12, wherein the specific frame is every predetermined number of frames of the input video data.

16. The display device according to claim 12, wherein the current measurement subframe is provided in common with a reverse bias application subframe that applies a reverse bias voltage to the plurality of capacitive light emitting elements. . .

17. The display device according to claim 12, wherein the predetermined display pattern is a pattern for lighting at least one line in a vertical direction or a horizontal direction of the display panel.

1 8. The predetermined display pattern is a pattern for lighting the entire screen of the display panel. The display device according to claim 12, wherein the display device is a screen.

19. The display device according to claim 12, wherein the control unit adjusts an output voltage of the power source unit applied to the display panel for each R GB of the emission color of the capacitive light emitting element.

21. The display device according to claim 12, wherein the current measurement subframe is one of the gradation display subframes.

2 1. The output voltage of the power supply means adjusted by the control means changes the source voltage of the driving transistor of each of the capacitive light emitting elements set as the light emission of the display panel, thereby setting the light emission. The display device according to claim 12, wherein a driving current value of the capacitive light emitting element changes.

2 2. The output voltage of the power supply means adjusted by the control means changes the gate voltage of the driving transistor of each of the set capacitive light emitting elements with the fluorescence of the display panel, and thereby the light emission and setting 13. The display device according to claim 12, wherein a drive current value of the capacitive light emitting element is changed.

2 3. The output voltage of the power supply means adjusted by the control means changes the source voltage of the driving transistor of each of the set capacitive light emitting elements and the gate voltage of the display panel, and the gate voltage. 13. The display device according to claim 12, wherein a drive current value of the capacitive light emitting element set as the light emission changes accordingly.

2 4. For a display panel consisting of a plurality of capacitive light emitting elements arranged in a matrix, a plurality of gradation display subframe periods are provided within each frame of the input video data, and the input video data is displayed. The plurality of capacitive occurrences corresponding to the luminance gradation indicated by The display panel driving method for performing gradation display by setting each of the optical elements to emit light or not to emit light for each gradation display subframe,

A period of a current measurement subframe that is different from a period of the plurality of gradation display subframes within a period of a specific frame of the input video data is provided, and the plurality of capacitors are included in the period of the current measurement subframe. Each light emitting element is set to light emission or non-light emission according to a predetermined display pattern,

A driving current is supplied from the power supply means to the capacitive light emitting element set to emit light of the display panel;

A drive current value flowing in the display panel within a period of the current measurement subframe is measured;

A drive method characterized in that the output voltage of the power supply means is adjusted so that the measured drive current value falls within an allowable range of the reference current value.