JP4088098B2 - EL display panel - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention performs current output for use in a display device that performs gradation display according to an amount of current, such as an organic electroluminescent element.For EL display panelRelated.
[0002]
[Prior art]
Since the organic light emitting element is a self light emitting element, a backlight required for a liquid crystal display device is unnecessary, and it is expected as a next generation display device from the advantages such as a wide viewing angle.
[0003]
Unlike organic light-emitting devices, the light emission intensity of the device and the electric field applied to the device are not proportional, and the light emission intensity of the device and the current density flowing through the device are proportional. In contrast to the variation in signal value, the variation in emission intensity can be reduced by performing gradation display by current control.
[0004]
An example of an active matrix display device using a switching element having a semiconductor layer is shown in FIG. Each pixel includes a plurality of switching elements 153, storage capacitors 154, and organic electroluminescent elements 152, as indicated by 159.
[0005]
In the row selection period (period A) of one frame, the switching element 153 makes the switching elements 153a and 153b conductive by the output from the gate driver 150, and makes the switching element 153d non-conductive. In the non-selection period (period B), 153d is turned on, and 153a and 153b are turned off.
[0006]
By this operation, in period A, the amount of current flowing through 153c is determined according to the current value output from the source driver 151, the gate voltage is determined from the relationship between the source-drain current of 153c and the gate voltage, and according to the gate voltage. The stored charge is stored in the storage capacitor 154. In the period B, the gate voltage of 153c is set according to the amount of charge accumulated in the period A. Therefore, the same current as the current flowing in 153c in the period A flows in 153c in the period B. The light emitting element 152 emits light. The amount of charge in the storage capacitor 154 changes according to the amount of current in the source signal line, and the light emission intensity of the organic light emitting element 152 changes.
[0007]
The driving semiconductor circuit used in this display device needs to be capable of controlling and outputting current.
[0008]
[Problems to be solved by the invention]
An input signal of the driving semiconductor circuit is generally given by a voltage. In order to output a current corresponding to a video signal, it is realized by converting a voltage into a current in the semiconductor circuit.
[0009]
For example, there is a method in which a voltage value corresponding to a video signal is connected to a gate electrode using a thin film transistor, a power source is connected to one of a source or drain electrode, and a current value corresponding to the video signal is extracted from the other. .
[0010]
In this method, if the current-voltage characteristics of the transistors vary, the output current differs for the same voltage, which may cause uneven display.
[0011]
[Means for Solving the Problems]
  The present invention includes a display region in which a pixel having an EL element is formed, and a current output circuit that supplies a signal current to the pixel, and the current output circuit has an N-bit input corresponding to the number of display gradations. signalA gamma correction unit for converting the N-bit input signal into a signal of (L + M) bits (L and M are integers of 1 or more), and at least oneThe ratio of channel length to channel width differs between the first transistor group and the first transistor group.At least oneA second transistor group;A plurality of first switch groups that perform control according to the L-bit input signal; and a plurality of second switch groups that perform control according to the M-bit input signal. The first transistor group operates at a first current increase rate with respect to the gray level, and the second transistor group operates at a second current increase rate with respect to the gray level. At least one first transistor group is connected to each of the switch groups, and at least one second transistor group is connected to each of the second switch groups,The EL display panel is characterized in that a current is supplied to the pixel.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0013]
(Embodiment 1)
FIG. 13 shows an example of a display device using an organic light emitting element having a passive matrix configuration. The segment signal lines 136 and the common signal lines 135 are arranged in a matrix, and the organic light emitting element 134 is formed at the intersection, and the display is sequentially performed.
[0014]
The common driver 133 selects a row of pixels that outputs current and outputs a specific luminance, and passes a current corresponding to the display gradation from the segment driver 131 to the pixels in the selected row one by one in order.
[0015]
For example, in FIG. 14, in order to pass a current corresponding to the display gradation through the organic light emitting elements in the second row (the second row is the selected row), the potential of the common signal line 135 is set to the second row (common signal line 135b). Only the potential is lowered, the common signal lines 135a and 135c in the other rows are made higher than the potential of the segment signal line 136, and in the pixels in the non-selected rows, the potential relationship is set to the cathode potential> the anode potential so that the non-light emitting state is obtained. . In this state, the current corresponding to the display gradation is supplied from the segment signal line 136 from the current source 141, so that each organic light emitting element in the second row emits light with a predetermined luminance. In this example, the second row emits light, but the display rows can be changed in order by lowering the potential of different rows in the common driver 133.
[0016]
In order to perform display without luminance unevenness in such a display device, in addition to forming the organic light-emitting element 134 to have a uniform thickness, the variation in the output of the current value supplied from the current source 141 of the segment driver 131 is small. is important.
[0017]
FIG. 15 shows an example of a display device using an organic light emitting element having an active matrix structure. In a certain horizontal scanning period, for example, the transistors connected to the gate signal line 1 (for example, 157a) in the first row are turned on, and the transistors connected to the gate signal lines 1 (157) in all other rows are turned off. To do. At this time, a current corresponding to the gradation data of the pixels in each column of the first row is passed through the source signal line 156 from the source driver 151, whereby charges corresponding to the amount of current are stored in the storage capacitor 154.
[0018]
The gate signal line 2 (158) makes the transistor connected to the gate signal line 2 (158) conductive when the transistors connected to the gate signal line 1 (157) in the same row are non-conductive. When the transistor connected to the gate signal line 1 is in a conductive state, a current corresponding to the amount of charge stored in the storage capacitor 154 flows through the organic light emitting element 152 by setting the transistor in a non-conductive state.
[0019]
Thereby, gradation display according to the amount of current output from the source driver 151 can be performed. In this case as well, as in the case of a display device having a passive matrix configuration, as one of the conditions for preventing display unevenness, it is necessary that the variation in current output with respect to the same gradation output is small.
[0020]
In FIG. 15, each pixel has a current copier configuration. However, even in a current mirror configuration as shown in FIG. 28, gradation display is performed by the current flowing through the source signal line 156, so that the same gradation output is made between the terminals. The variation in current output with respect to is required to be small.
[0021]
Charges are accumulated in the capacitor 289 in accordance with the current flowing through the source signal line 156 in the state shown in FIG. 28A by operating the gate signal lines 157 and 158. Next, a current flows to the organic light emitting element 285 through the transistor 281b according to the electric charge stored in the capacitor 289 in the state of FIG.
[0022]
Since the current flowing through the organic light emitting element 285 changes according to the current flowing through the source signal line 156, the current variation for each source signal line 156 is observed as display unevenness. Therefore, even in an active matrix display device using such a current mirror pixel, it is necessary to reduce variations in current output of the source driver 151.
[0023]
In a display device that performs gradation display based on the amount of current as described above, it is desirable to reduce the variation in current value with respect to the same gradation display between the terminals that output current.
[0024]
In the present invention, as a method for reducing the variation in the current value between the terminals, a reference current source 631 for generating a reference current is provided as shown in FIG. 8, and a current corresponding to the current of the reference current source 631 is set to a plurality of currents. A plurality of current sources 633 that output to the source 632 and output a corresponding current to each current source 632 are arranged so that one reference current source 633 is arranged for each source signal line; By arranging the current sources 631 and 632a and 632b and 633a in the vicinity, the current variation due to the variation in the threshold voltage of the transistor is reduced.
[0025]
In the gradation display, as shown in FIG. 2 or FIG. 3, a current source 81 that passes a certain ratio of current to the current that flows through the reference current source 633.Or 82A plurality of current sources 81 to be output and output by a switch 641Or 82This can be achieved by changing the number.
[0026]
In the case of FIG. 2, the value of the flowing current can be changed according to the values of the input data L0 to L4. The rate of change is determined by the value of the current flowing through one current source 81. This value is changed by changing the value of the current flowing through the current source 633n1 or by changing the ratio of the channel width and channel length of the transistor of the corresponding current source. The output current value can be arbitrarily designed.
[0027]
Similarly in FIG. 3, the output current value can be changed by the values from H0 to H5 and the values from AK0 to AK2.
[0028]
By changing the ratio of the channel width and channel length of the transistors 81 and 82, the ratio of the current flowing through the transistor 81 and the current flowing through the transistor 82 can be changed. For example, when the current flowing in 81 and the current flowing in 82 are set to have a ratio of 1: 3, the channel width of the transistor 81 is set to 1/3 of the channel width of the transistor 82 or the channel length of the transistor 81 is changed to the transistor 82. This can be realized by making the channel length three times as long.
[0029]
As a result, as shown in FIG. 16, the current increase rate can be changed between the low gradation side and the high gradation side. The ratio of the slopes 161 and 162 can be varied by changing the channel width or channel length ratio of the transistors 81 and 82. In addition, the overall inclination can be changed by adjusting the variable resistor 651 that adjusts the amount of current flowing through 631.
[0030]
The gradation R1 at which the current increase rate changes can be changed by changing the values of the values L0 to L4 and H0 to H5 with respect to the input data gradation.
[0031]
For example, when L0 to L4 and H0 to H5 are output for a 6-bit input signal as shown in FIG. Further, when output is as shown in FIG. 5, the increase rate changes at gradation 8 and when output is as shown in FIG. 4 to 6, gradations 0 to 18 are shown. From 19 onward, L0 to L4 have the same output as that of gradation 18, and the values of H0 to H5 are the values of H [5: 0]. A value increased by 1 from the gradation 18 is output.
[0032]
Accordingly, the present invention can be applied to display elements having different gamma characteristics.
[0033]
In the multi-color display, the configuration shown in FIG. 2 on the low gradation side and FIG. 3 on the high gradation side is required for each of the three display primary colors. Further, the configuration shown in FIG. A total of six are required.
[0034]
The current output from one of the transistors 81 to 83 is about several nA to 1 μA. On the other hand, as shown in FIG. 8, when the current is adjusted by the variable resistor 651, it is necessary to design at a maximum of about 300 kΩ to 500 kΩ considering the chip size of the IC. If the power supply voltage is 5 V, an output current of several nA is required. When taking it out, the current flowing through the variable resistor 651 needs to be about 10 μA. The output must be reduced to about 1/1000 of the input by the current mirror. The transistor 631 and the variable resistor 651 are large in size. A channel width of about 1 mm may be required. Therefore, reducing the number of transistors 631 and variable resistors 651 has a great effect on reducing the layout area of the circuit.
[0035]
Therefore, FIG. 1 shows a configuration in which the variable resistor 651 and the transistor 631 on the low gradation side and the high gradation side are shared.
[0036]
The current is distributed to the two current sources 631a and 631b using a current mirror with respect to the current source 15 serving as one reference. 631 further distributes the current to a plurality of current sources 632. In this figure, only one is shown because of complexity. The configuration below 632 is the same as in FIG. In this figure, three output transistors are shown. However, the present invention is not limited to this, and the configurations shown in FIGS. 2 and 3 may be used. According to the number of bits of the L or H signal line, the numbers 81 and 82 are changed as appropriate.
[0037]
One reference current source 15 is connected to low gradation side outputs and high gradation side outputs as many as the number of output signal lines. As a result, the largest transistor 15 and variable resistor 14 are required for each display color. The transistors 631a and 631b may be transistors having the same size as the transistor 632n. The current mirror of the transistors 631 and 632n is for distributing the current flowing through 631 to a plurality of current sources 632n. The current ratio is changed by the transistors 15 and 13 or 15 and 11 and 12.
[0038]
FIG. 9 shows the configuration so far as shown in FIG. In comparison, the circuit area can be reduced by reducing the number of the largest transistors 631 and the variable resistors 651 one by one in the configuration of FIG.
[0039]
To change the ratio of current increase rate between low gradation and high gradationVariable resistance 651aAnd by setting 651b separatelyIt can be carried out.Thus, for example, the current characteristic of any one of 71 and 72a to 72c in FIG.Can be set.
[0040]
In the configuration of FIG. 1, in order to change the ratio of the current increase rate between the low gradation side and the high gradation side, a function to change the number of transistors constituting the current source 15 and the current mirror is provided on the high gradation side. It was.
[0041]
The current flowing through the current source 15 becomes the smallest with respect to the current flowing through the current source 15 when all the switches 16 are open, and the current flowing through the 631a increases as the switch 16 is closed. On the other hand, since the current flowing through 631b is constant with respect to the current flowing through current source 15, the amount of current flowing through 82 can be changed by switch 16 with respect to the current flowing through 81. As a result, the gradation characteristics shown in 72a in FIG. 7 can be obtained when all the switches 16 are opened, and 72c in FIG. 7 can be obtained when all the switches 16 are closed.
[0042]
If the sizes of the transistors 631, 632, and 633 are equal on the low gradation side and the high gradation side, respectively, the ratio of the current increase rates on the low gradation side and the high gradation side is determined by the size ratio of the transistors 11 and 13 and 81 and 82. The value that minimizes is determined. The value that maximizes the ratio of the current increase rate on the low gradation side and the high gradation side is determined by the size of all the transistors 11 and 12 and the ratio of 13 and the size ratio of 81 and 82. Further, the minimum change amount of the increase rate ratio is determined by the size of the transistor 12.
[0043]
In this figure, the example in which the number of transistors 12 for adjusting the current flowing through 82b is three has been described, but the number of transistors 12 is not limited to three and any number may be used. In that case, the number of switches 16 is increased in accordance with the number of transistors. By controlling the switch 16, as shown in FIG. 7, the ratio of the current increase amount in the low gradation portion and the current increase amount in the high gradation portion can be changed.
[0044]
The transistor 12 is arranged in parallel through the transistor 11 and the switch 16 so as to change the ratio of the current increase amount with respect to the low gradation side, but conversely the current increase on the low gradation side with reference to the high gradation side. Even if the transistor 12 and the switch 16 are arranged in parallel with the transistor 13 so as to change the amount, it is also possible to change the ratio of the current increase amount between the low gradation side and the high gradation side.
[0045]
Further, it is possible to cope with the case where the control of the switch 16 is changed by the ambient temperature by using the temperature sensor, and the gamma characteristic of the display element is changed by the temperature. Similarly, if the switch 16 is controlled for each display color, the gamma characteristic can be changed for each display color.
[0046]
(Embodiment 2)
When the current is changed by the variable resistor 651, the current-voltage characteristic of the transistor 631 is non-linear. Therefore, the amount of change in the current value with respect to the resistance value varies depending on the resistance value as indicated by 121a in FIG. As the resistance value increases, the increase rate of the current value decreases.
[0047]
In order to keep the rate of change of current constant, the step size of the resistance value may be increased as the resistance value increases. It is difficult to put the step width in a tap such as an electronic volume.
[0048]
Therefore, as shown in FIG. 10, a plurality of transistors 101 and 102 are provided instead of the variable resistor 651, and the current flowing through the transistor 631 is controlled by setting the terminals AJ0 to AJ2 to either the ground potential or the power supply voltage. I tried to do it.
[0049]
The channel size of the transistor 101 is designed such that the current flowing through the transistor 631 is (minimum current value 122) × (current flowing through the transistor 631 / current flowing through the transistor 81).
[0050]
The channel size of the transistor 102 is designed so that the difference between the off-state current and the on-state current is (step size of current value) × (current flowing through 631 / current flowing through 81).
[0051]
Since the drain current of the transistor is determined by the gate-source voltage, the current flowing through 631 is (current flowing through the transistor 101) + (number of transistors 102 in the on state) × (current flowing through the transistor 102). Since the amount of change in the value can be controlled by the number of turning on the transistor 102, the current value can be changed at a constant rate.
[0052]
As a result, for example, the current flowing through 81 can be increased from 30 nA to 10 nA. For example, as shown in FIG. 17, if the relationship between gradation and current is a curve of 171, the relationship of the curve shown by 172 can be obtained by increasing the number of transistors 102 that are turned on.
[0053]
  Further, in the configuration of FIG. 10, it is possible to change the output current value depending on the temperature by changing the potential of AJ0 to AJ2 by using the temperature sensor and changing the potential of the temperature sensor. For example, when the brightness decreases for the same current value as the temperature rises, the same input gradation is used regardless of the temperature.InOn the other hand, in order to make the luminance constant, the number of transistors 102 having the gate electrode as a ground potential may be increased. The channel size of the transistor 102 may be set depending on the rate of change in luminance with respect to temperature.
[0054]
Note that the present invention can also be implemented in combination with the first embodiment. As shown in FIG. 18, transistors 11 and 12 and a switch 16 for changing the ratio between the high gradation side output and the low gradation side output are provided, and transistors 181 and 182 for adjusting the output current amount are provided. It is provided. Since the current source is formed of a p-type transistor unlike FIG. 10, the adjustment transistors 181 and 182 are formed of n-type transistors. Therefore, the voltage applied to the gate electrode is also opposite to the p-type. As a result, as shown in FIG. 19, using AJ0 to AJ2, the increase / decrease of the current amount in the entire gradation region is adjusted as in the relationship of 191 and 192, and the switch 16 increases the current level in the low gradation region with respect to the current increase amount. If the ratio of the current increase amount in the adjustment area is 191, it can be changed from 191a to 191b.
[0055]
(Embodiment 3)
FIG. 11 is a diagram showing a third embodiment of the present invention. The difference from FIG. 10 is that the amount of current flowing through 631 is not controlled by a change in the gate potential of the transistor, but the gate potential is fixed at a potential at which the transistor is turned on and the on / off state of the switch 112 is controlled. The difference is that the amount of current flowing to 631 is changed to adjust the output current.
[0056]
The current increase amount per gradation can be changed by the signal line data from AJ0 to AJ2, and as shown in FIG. 17, the current values in all gradation areas change as shown by the relationship indicated by 171 and 172. it can. Further, by using the configuration of FIG. 23 combined with the configuration of FIG. 1, the same effects as those of the second embodiment can be obtained.
[0057]
The channel size of the transistor 101 is designed such that the current flowing through the transistor 631 is (minimum current value 122) × (current flowing through the transistor 631 / current flowing through the transistor 81).
[0058]
The channel size of the transistor 112 is such that the current value when the gate potential is the substrate potential in the case of a p-type transistor and the power supply voltage in the case of an n-type transistor is (current value step size) × (current flowing through the transistor 631 / The current flows through the transistor 81).
[0059]
The current flowing through the transistor 631 is (current flowing through the transistor 101) + (the number of transistors 112 in which the switch 113 connected to the source or drain electrode is on) × (current flowing through one transistor 112). Therefore, the current value can be changed at a constant rate.
The following can be carried out in common with the second and third embodiments.
[0060]
FIG. 20 is a diagram in the case where an organic light emitting element as shown in FIG. 13 or 15 is used as a display panel of a portable information terminal. FIG. 21 shows a case where it is used in a digital still camera. Personal digital assistants, digital cameras, PDAs, digital video cameras, etc. are used regardless of whether they are outdoors or indoors, and display is possible under a wide range of conditions, such as when the illuminance of the display panel is several lux to several hundred thousand lux. At least in the sunlight, the peak luminance needs to be 500 candela / square centimeter. On the other hand, it may be about 100 to 200 candela / square centimeter indoors.
[0061]
In such devices, it is important to drive at low power in order to make the battery last longer. The peak luminance is 500 candela / square centimeter under sunlight and the indoor brightness is 100-200 candela / square centimeter. It is desirable to provide a function for reducing power consumption.
[0062]
Therefore, the magnitude of the output current is changed depending on the illuminance of the display panel. What is necessary is just to change the terminal voltage of AJ0 to AJ2 of FIGS. 10, 11, 18, and 23 by the light intensity which hits a panel or a housing | casing.
[0063]
As shown in FIG. 24, a light intensity detecting means 241 is provided on the housing or the display panel. If you already have an exposure meter, such as a digital camera or digital video camera, you may use it. The current control means 243 controls the value 244 from AJ0 to AJ2 based on the detection result 242, and the current flowing through the current source 15 is controlled. Accordingly, by increasing the peak luminance when the surrounding is bright and suppressing the peak luminance when the surrounding is dark, it is possible to reduce power consumption while maintaining visibility.
[0064]
In addition to changing the amount of current by the light intensity detection means 241, the user may be able to adjust the brightness of the display. For example, a command or the like is input to the current control unit 243 in FIG. 24 by operating the key 202 of the portable information terminal in FIG. 20, and the output of the current control unit 243 is changed. The same applies to digital cameras, digital video cameras, and PDAs. Similarly, in the television as shown in FIG. 22, the brightness can be adjusted by the switch 226. The brightness adjustment is not limited to a switch, and may be performed through a remote controller, for example. Further, the output of the current control means 243 may be controlled by a method of displaying a menu on the display panel so that the luminance can be controlled or by a touch panel structure.
[0065]
In FIG. 24, AJ0 to AJ2 control the switch 233. However, AJ0 to AJ2 shown in FIGS.
[0066]
In each of the above figures, the signal for controlling the current has been described with an example of 3 bits from AJ0 to AJ2. However, in order to increase the number of steps of current control, it is set to 4 bits or more, and the 2nd bit in the Nth bit.^(N-1)It can be similarly implemented by connecting a number of transistors. Further, for example, in FIG. 10, the current adjustment transistors 102 are all weighted with respect to the AJ signal by changing the number of transistors having the same channel size, but one transistor is connected to each AJ signal. Thus, the current amount may be weighted by changing the channel size.
[0067]
In general, for a color display panel, a driver that performs gradation output has outputs corresponding to the number of display lines in three systems of X, Y, and Z for displaying three primary colors. As shown in FIG. 25, the source driver 251 with respect to the display panel 253 is arranged in an upper part (FIG. 25A) or a lower part (FIG. 25B) with respect to the display unit 252. There is an implementation method.
[0068]
If the red pixel (R), the green pixel (G), and the blue pixel (B) are arranged in this order from the left in the display unit 252, the X output is shown in FIG. 25A in which the source driver 251 is arranged at the top. The R and Y outputs are connected to G and the Z output is connected to B. On the other hand, in FIG. 25B arranged at the bottom, the Z output is connected to R, the Y output is connected to G, and the X output is connected to B. That is, the display color of the driver output changes depending on the relationship between the driver 251 and the display unit 252. Therefore, it is difficult to design so that each current of XYZ outputs a current that matches a specific display color.
[0069]
On the other hand, the current vs. luminance characteristics are often different for each of the three primary colors of the display unit 252. Therefore, the output current value at the same gradation display differs for each display color. When three sets of the configurations of FIGS. 18 and 23 are incorporated for each output of XYZ, the display color can be changed by changing the voltage input from AJ0 to AJ2 according to the relationship between the output terminal XYZ and the three display colors. It becomes possible to output a current corresponding to the current-luminance characteristic.
[0070]
Further, by changing the operation of the switch 16 according to XYZ, the ratio of the current increase rate in the low gradation region and the high gradation region can be changed for each display color.
[0071]
Although the description has been given with the example in which the display unit 252 is configured with the three primary colors of light, the description can be similarly applied to the three primary colors of cyan, yellow, and magenta.
[0072]
In addition, the luminance of the organic light-emitting element with respect to the same current density varies with temperature. As shown in FIG. 26, the organic light emitting device has an organic layer 262 formed between two electrodes 261 and 263. By applying a voltage between the electrodes, electrons are emitted from the cathode 261 and holes from the anode 263 are organic. Implanted into layer 262. The injected electrons and holes move to the counter electrode by the electric field applied by the power source 264. In the movement process, electrons and holes are recombined to generate excitons. In the process of excitons transitioning from the excited state to the ground state, light having a wavelength corresponding to the energy of the excitons is emitted. In the transition process from the excited state to the ground state, the process of emitting light and the process of heat deactivation (non-emission) are in a competitive process, and as the temperature rises, the process of heat deactivation becomes dominant and the light intensity decreases. To do.
[0073]
Accordingly, as the temperature of the organic light emitting device generally increases, the luminance at the same current density decreases. The amount of this decrease varies depending on the material used for the organic layer 262, but the decrease is the same regardless of whether the organic layer 262 material is a fluorescent material or a phosphorescent material, and whether it is a low molecule or a polymer. is there.
[0074]
In this example, the organic layer 262 is formed of one layer, but may be formed of a plurality of layers, or one layer may be formed by mixing a plurality of materials. This is because even if the layer structure is changed, as long as light emission is via excitons, the process of emitting light by transitioning from the excited state to the ground state does not change.
[0075]
Since the luminance changes depending on the temperature even when the same current is flowing, the driver needs to have a function of making the luminance constant by changing the current output corresponding to the change in luminance depending on the temperature.
[0076]
A temperature detection unit 271 is provided to change the output current value according to the temperature, and the voltage value of AJ0 to AJ2 is changed to change the current flowing through the transistor 15 by changing the output of the current control unit 273 according to the temperature. The current value can be changed depending on the temperature.
[0077]
This can be achieved by increasing the number of switches 233 that are turned on so that the current flowing by the current control means 273 increases as the temperature increases.
[0078]
The minimum current value is when all the switches 233 are turned off. At that time, the current flowing through 15 is controlled by the transistor 231. The amount of compensation current due to temperature change is increased by changing the amount by which the switch 233 is turned on. Since it is for adjustment, the current flowing per transistor 232 is smaller than the current flowing through the transistor 231. By adjusting the channel size of 232 transistors with respect to H.231, the adjustment amount per stage can be changed. The size is determined to some extent depending on the display panel to be used. The number of adjustment stages is determined by the bit width of the adjustment control signal AJ (274), and can be adjusted to 8 stages in FIG. If eight or more adjustments are necessary, the number of adjustment control signals 274, switches 233, and transistors 232 may be increased. For example, if eight transistors 232 connected between the signal line of AJ3 and the switch 233d and between the switch 233d and the ground are provided, the adjustment can be made in 16 steps.
[0079]
In the above invention, the transistor has been described as a MOS transistor, but a MIS transistor or a bipolar transistor can be similarly applied.
[0080]
The present invention can be applied to any material such as crystalline silicon, low-temperature polysilicon, high-temperature polysilicon, amorphous silicon, and gallium arsenide compound.
[0081]
Although the organic light-emitting element has been described as the display element, any element can be used as long as the display element has a proportional relationship between current and luminance, such as an inorganic electroluminescence element and a light-emitting diode.
[0082]
【The invention's effect】
As described above, according to the present invention, in the current mirror circuit unit, the output current value with respect to the input current can be changed by changing the number of transistors on the output side with the switch. Since the current value can be changed by controlling the switch, the current value can be easily changed for each temperature, illuminance, and display color.
[0083]
Also, in order to adjust the current flowing to the reference current source, instead of using a variable resistor, a plurality of current sources are prepared, and the number of outputs of the plurality of current sources is controlled by a switch or the gate potential is operated. By making it possible to change the current value, the step size of the change in current can be made constant by making all the channel sizes of all of the plurality of current sources equal or all of the channel sizes equal.
[Brief description of the drawings]
FIG. 1 is a diagram in which a ratio of a current increase rate on a low gradation side and a current increase rate on a high gradation side can be changed according to the present embodiment.
FIG. 2 is a diagram showing a current output unit for low gradation side data
FIG. 3 is a diagram showing a current output unit for high gradation side data.
FIG. 4 is a diagram showing the relationship between the input gradation, the low gradation side data, and the high gradation side data when the change point of the current increase amount is gradation 4.
FIG. 5 is a diagram showing the relationship between the input gradation, the low gradation side data, and the high gradation side data when the change point of the current increase amount is gradation 8.
FIG. 6 is a diagram showing the relationship between input gradation, low gradation side data, and high gradation side data when the change point of the current increase amount is gradation 16.
FIG. 7 is a diagram showing the relationship between gradation and current in the first embodiment of the present invention.
FIG. 8 is a diagram showing a circuit configuration for distributing a reference current to each output.
FIG. 9 is a diagram showing a circuit for outputting a current from a reference current of a high gradation portion and a low gradation portion in a conventional embodiment.
FIG. 10 is a diagram showing a circuit in which a current flowing through a current source according to the second embodiment of the present invention is adjusted by a gate potential of a transistor connected to the current source;
FIG. 11 is a diagram in which a current flowing through a current source according to a third embodiment of the present invention can be adjusted by a switch control from a plurality of supplied current sources.
FIG. 12 is a diagram showing the relationship between the resistance value connected to the current source and the current flowing in the current source at that time
FIG. 13 is a view showing a display device using a passive matrix organic light emitting element.
14 is a diagram showing a driving method of the display device shown in FIG.
FIG. 15 shows a display device using an active matrix organic light emitting element.
FIG. 16 is a diagram showing the relationship between gradation and current
FIG. 17 is a diagram showing that the current can be changed for the same gradation in the second or third embodiment of the present invention;
FIG. 18 is a diagram in which the amount of current changing per gradation can be changed, and the amount of change can be varied between a low gradation portion and a high gradation portion.
19 is a graph showing the relationship between gradation and current in the circuit of FIG.
FIG. 20 is a diagram showing a portable information terminal using at least one of the embodiments;
FIG. 21 is a diagram showing a digital camera using at least one of the embodiments.
FIG. 22 shows a television using at least one of the embodiments.
FIG. 23 is a diagram in which the amount of current changing per gradation can be changed, and the amount of change can be varied between a low gradation portion and a high gradation portion.
FIG. 24 is a diagram showing a configuration in which the value of a current flowing through a current source can be changed according to ambient light intensity.
FIG. 25 is a diagram showing the connection relationship between the display colors of the output terminal and the display panel when the arrangement of the driver and the display unit is changed.
FIG. 26 is a diagram showing an example of an element structure of an organic light emitting element
FIG. 27 is a diagram showing a configuration in which the value of a current flowing through a current source can be changed depending on the ambient temperature
FIG. 28 is a diagram showing a pixel circuit when a configuration of each pixel is a current mirror configuration in a display device using an organic light emitting element having an active matrix configuration.
[Explanation of symbols]
11, 12, 13 transistor
14 Variable resistance
15 transistor
16 switches
81 Low gradation side output current control transistor
82 High gradation output current control transistor
631, 632, 633 transistor
641 switch

Claims (7)

A display region in which pixels having EL elements are formed;
A current output circuit for supplying a signal current to the pixel,
The current output circuit is
An N-bit input signal corresponding to the display gradation number ;
A gamma correction unit that converts the N-bit input signal into a signal of (L + M) bits (L and M are integers of 1 or more);
At least one first transistor group;
At least one second transistor group having a different ratio of channel length to channel width with respect to the first transistor group;
A plurality of first switch groups that perform control according to the L-bit input signal;
A plurality of second switch groups that perform control according to the M-bit input signal;
The gamma correction unit operates at a first current increase rate with respect to gradation by the first transistor group, and operates at a second current increase rate with respect to gradation by the second transistor group. And
At least one first transistor group is connected to each first switch group,
At least one second transistor group is connected to each of the second switch groups,
An EL display panel, wherein current is supplied to the pixel. The current output circuit includes a third transistor element that forms a current mirror circuit with the first and second transistor groups, and a current generation circuit that supplies a first current to the third transistor element. ,
2. The EL display panel according to claim 1, wherein the current generation circuit generates the first current by stepwise changing a current generated by a circuit having a resistor. Wherein at least one of the number of transistors of the first or second group of switches connected to said first or second transistor, wherein, wherein different for each said first or second switch Item 2. An EL display panel according to Item 1. Provided for each pixel having the EL element, a driving transistor for controlling the amount of current flowing through the EL element and a third switch connected to a source signal line for supplying current to the pixel having the EL element. And
The current output circuit outputs the current to the source signal line,
In the first period, the third switch is turned on; in the second period following the first period, the third switch is turned off;
The driving transistor is a p-type transistor,
The EL display panel according to claim 1, wherein the first transistor element group includes an n-type transistor. The display area corresponds to at least two display colors;
The EL display panel according to claim 2, wherein the current output circuit is provided for each display color. Temperature detecting means,
5. The EL display panel according to claim 2, wherein an output of the current generation circuit changes in accordance with an output of the temperature detection means. Comprising light detection means,
5. The EL display panel according to claim 2, wherein an output of the current generation circuit changes according to an output of the light detection means.

Images