JP5589250B2 - Active matrix display device - Google Patents

Description

  The present invention relates to a display device that performs gradation display by an amount of current, such as an organic electroluminescent element.

  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.

Problems to be solved by the invention

  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.

  An example of an active matrix display device using a transistor having a semiconductor layer is shown in FIG. Each pixel includes a plurality of transistors (switching elements) 73, a storage capacitor 74, and an organic light emitting element 72, as indicated by 79.

  In the row selection period (period A) of one frame, the transistor 73 turns on the transistors 73a and 73b by the output from the gate driver 70, and turns off the transistor 73d. Conversely, in the non-selection period (period B), the 73d transistor is turned on, and the 73a and 73b transistors are turned off.

  By this operation, in period A, the amount of current flowing through the transistor 73c is determined according to the current value output from the source driver 71, the gate voltage is determined from the relationship between the source-drain current of the transistor 73c and the gate voltage, and the gate voltage The electric charge corresponding to is stored in the storage capacitor 74. In the period B, the gate voltage of the transistor 73c is set in accordance with the amount of charge accumulated in the period A. Therefore, the same current as the current flowing in the transistor 73c in the period A flows in the transistor 73c in the period B. The organic light emitting element 72 is caused to emit light through 73d. The amount of charge in the storage capacitor 74 changes according to the amount of current in the source signal line, and the light emission intensity of the organic light emitting element 72 changes.

  As a display pattern, it was found that the luminance of pixels when not lit differs between when a current is passed through a certain source signal line in the order of lighting and non-lighting and when current is passed in the order of non-lighting and non-lighting. In the order of lighting and non-lighting, the non-lighting pixels lighted about 0.5, assuming that the luminance at lighting is 1 and the luminance at non-lighting is 0. In addition, when the non-lighting signal is continuously supplied within the same frame period after the lighting signal is supplied once, the luminance of the non-lighting pixels gradually decreases from 0.5, the frame frequency is 60 Hz, the number of display rows In the case of 220 lines, the luminance is 0 from the 6th to 7th lines.

  On the other hand, when the lighting signal was sent after the non-lighting, the lighting luminance was 0.8 at first, but it was possible to display with luminance 1 from the third row.

  This is because the output of the source driver changes the current value according to the display pixel, but the current waveform supplied to each pixel is distorted by the wiring resistance and stray capacitance of the source signal line, and the desired current value Is not stored as the charge of the storage capacitor 74 in each pixel. That is, it was found that the ability to write a desired current value was small.

  In particular, it has been found that a change from a large current value to a small current value takes about twice as much as a change from a small current value to a large current value.

  It was confirmed that the influence of waveform rounding is reduced by reducing the frame frequency and taking more writing time for each line, and the above problem is improved.

  When the frame frequency is slowed, if the off-state characteristics of the transistor 73 are poor, the charge amount of the storage capacitor 74 changes due to the leakage of the transistor 73, and furthermore, the amount of current of the organic light emitting element 72 also changes, thereby generating flicker. .

  Therefore, in order to obtain a flicker-free display, it is necessary to reduce the rounding of the current waveform so that a desired current value flows within the selection period regardless of the current value flowing to the pixel displayed immediately before. There is.

Means for solving the problem

  In order to solve the above problems, an active matrix display device according to the present invention includes a means for applying a predetermined voltage to a source signal line, a means for flowing a predetermined amount of current, the voltage applying means for a source signal line, A switching means for switching between the current flowing means is provided, and the change in the amount of current flowing in the source signal line is accelerated by the change in the video signal.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 2 is a diagram showing a driving circuit for organic light emitting elements for two pixels connected to one source signal line in the first embodiment of the present invention.

  In the present invention, the current source 10 for supplying a desired current corresponding to the display gradation and the voltage source 18 for applying a predetermined voltage are provided so that the power source input to the source signal line can be switched by the power source switching means 19. It is characteristic that it was made.

  The size of each pixel of a display unit such as a mobile phone and a monitor is about 100 μm wide and about 250 μm long. The current value necessary for the source signal line to obtain a luminance of 100 candela / square meter is the display color and external quantum efficiency. Depending on the case, it is about 1 μA.

  To supply 1 μA to the EL element 16, the power source switching means 19 selects the current source 10 on the source driver side, and the current source 10 sets the flowing current value to 1 μA.

  In the selected row, a signal for conducting the transistor 17 is applied to the gate signal line (1) 12, and a non-conducting signal is applied to the gate signal line (2) 13. On the contrary, in the non-selected row, the signal is not applied to the gate signal line (1) 12. A conduction signal is applied to the conduction signal and the gate signal line (2) 13.

  Thereby, in the selected row (the first row in this example), the current of the source signal line 11 flows into the pixel through the transistors 17b and 17c. Since the current path in the pixel is only connected to the EL power supply line 15a through the transistor 17a, a current of 1 μA also flows through the transistor 17a, and charges corresponding to the gate voltage at this time are stored in the storage capacitor 14a. In the non-selection period, the transistor 17d becomes conductive and the transistors 17b and 17c become non-conductive. Therefore, the current flowing through the transistor 17a is defined based on the charge accumulated in the storage capacitor 14a in the selection period, and the EL element 16a A current of 1 μA flows.

  Therefore, in order to flow a desired current value (for example, 1 μA) to the EL element 16a, it is necessary to store charges in the storage capacitor 14a so as to give a gate voltage that causes the transistor 17a to flow a desired current value in the selection period. .

  However, when the stray capacitance 20 exists in the source signal line 11, a rounded waveform determined by the wiring resistance of the source signal line 11 and the time constant of the stray capacitance 20 is observed. When gradation display is performed using current values, this waveform rounding also varies depending on the current value flowing through the source signal line, and the smaller the current value, the longer it takes to rise and fall. For example, when the wiring capacitance is 100 pF and the wiring resistance is 500 ohms, it is necessary for the current value of the source signal line and the current value of the contact 1001 to change from 0.24 μA to 40 nA when the current value of the current source 10 is changed. The time required for the change from 300 nsec to 40 nA to 0.24 μA was 250 μsec.

  Since the amount of charge movement per unit time is small in the low current region, it is difficult to charge and discharge the charge accumulated in the stray capacitance 20.

  For example, as shown in FIG. 35, when the ON period of the gate signal line (1) 12 is changed to 64 μs and 256 μs, the output current almost equal to the input current was obtained in 256 μs. On the other hand, at 64 μsec, it was found that the output current differs from the input with a focus on a low current (0.7 μA or less).

  For this reason, in the conventional gradation display method using current, the minimum time of one horizontal scanning period is 300 μsec. In this case, when the number of scanning lines is 220 as in a mobile phone, it is necessary to drive one frame at about 10 Hz. Depending on the off characteristics of the transistor 17, the charge amount of the storage capacitor 14 changes, and the EL element 16 Flicker occurs due to a change in the current flowing through the.

  In addition, when a voltage value is applied to the source signal line, the voltage value of the contact 1001 is about 1 μsec, which is determined by only the wiring resistance of the source signal line and the time constant of the stray capacitance 20 regardless of the voltage value. 10 is faster than when the voltage value corresponding to the current value of the contact 1001 is determined.

  Therefore, in order to shorten one horizontal scanning period, in the present invention, when the current waveform changes from a low current (black display) to a high current (white display), a high current (white display) changes to a low current. I thought to use that it was no longer than when it changed to (black display).

  As shown in FIG. 3A, the power source switching means 19 is switched to the voltage source 18 side at the beginning of one horizontal scanning period, and the black signal current value flows through the voltage of the source signal line 22a using this voltage source 18. The voltage is the same as the current state (discharge voltage application period 24). Next, the power source switching means 19 is switched to the current source 10 side, and a desired current value corresponding to the video signal is passed through the source signal line 22a by the current source 10 (video signal current application period 25).

  FIG. 4 shows the voltage application period dependency of the output current with respect to the input current. When the input current is 1 μA, the output is almost 1 μA regardless of the voltage application time. When the input current is as small as 40 nA (assuming black display), if there is no voltage application period, the output is 0.65 μA, 4 μs or more and 0.38 μA, and even if it is 4 μs or more, the output is not affected. Accordingly, since it is desired to lengthen the current display period, the discharge voltage application period 24 may be 4 μsec at the maximum, and preferably the source signal line has a black voltage value if 0.5 μsec to 3 μsec. In addition, the time for the video signal current application period 25 to change from black display to a desired current is about 250 μs from black display, which takes the longest time, to white display, and also changes from white display to black display in halftone display. Since it is shorter than the time required for this, it takes about 270 μsec, and one horizontal scanning period is about 270 μsec, which is 90% shorter than the conventional 300 μsec, and low flicker display is possible.

  Furthermore, in the discharge voltage application period 24, by applying a source voltage such that the luminance is 0.01 candela / square meter or less, the luminance at the time of black display is lowered, and an image in which black is displayed can be displayed. it can. For example, a voltage close to the voltage supplied from the EL power supply line 15 may be applied to the source signal line 11. In order to apply a voltage close to the EL power supply voltage to the source signal line 11 during current driving, it is necessary to supply a very small current (several nA). The specification of the source signal line voltage at several nA current has been described so far. Thus, it takes several hundred microseconds to 1 millisecond, which is difficult. Thus, voltage insertion in the present invention is effective for performing black display in a short time.

  When a scanning line moves from one line (N line: N is a natural number) to the next line (M line: M is a natural number other than N), there is a period in which all lines are not selected. As shown in FIG. 3 (b), when the gate control signal is active (all rows are in a non-selected state), a voltage value for displaying black is applied, and the video signal current corresponding to the selected row is applied during the selection period. Further, as shown in FIG. 3C, the black voltage application period may extend over all rows in a non-selected state and part of one row selection period.

  The purpose of applying the black voltage is to charge the stray capacitance 20 of the source signal line 11 to the black state. Therefore, even if the pixel transistor connected to the source signal line 11 is in a non-conductive state, There is no problem.

  In order to lengthen the current writing time necessary for the original gradation display, when there is an all-row non-selection period, it is preferable that the voltage application period includes the all-row non-selection period.

  Further, the voltage applied to the source signal line 11 during the voltage application period is not necessarily a voltage for displaying black. However, when the current source 10 changes the voltage to a voltage value corresponding to a predetermined current value, white display is performed. Therefore, it is preferable that the voltage value of the voltage source 18 is a value on the other side of the black signal voltage with respect to the intermediate value between the white signal voltage and the black signal value voltage.

(Embodiment 2)
In the first embodiment, a discharge voltage application period 24 is provided, and a voltage for displaying a black signal is applied so that the source signal line can be easily changed to a current indicating black.

  As a result, the voltage change amount of black and the gradation near black is small, so that one horizontal scanning period can be displayed in 200 μs to 230 μs. Further, since the amount of current is maximum at the time of white display, the discharge rate of the stray capacitance 20 existing in the source signal line 11 is fast, and one horizontal scanning period is about 180 μs despite the large change amount. It was possible to display. On the other hand, the gradation from black near the middle of white and black is less than half the amount of current when white is displayed, so the charge discharge rate of the stray capacitance 20 is halved, so one horizontal period takes as long as about 250 μsec. .

  In view of this, in the discharge voltage application period 24, instead of applying a voltage for displaying a black signal, it was considered to apply different voltages in several stages according to the gradation of the video signal to be displayed next.

  FIG. 5 shows an internal block of the source driver 71 of the display device of the present invention for realizing this. The gradation data detection means 52 detects the gradation of the input video signal, and controls the amount of current flowing through the source signal current source 53 based on the detection result, and at the same time, selects one of the plurality of voltage sources 54a to 54c. select. Further, the output of the voltage application period control unit 51 is changed by the horizontal synchronization signal to control the voltage application period and the current application period.

  In FIG. 2, when writing a signal from the source signal line 11 to the pixel, the transistors 17b and 17c are in a conductive state and the transistor 17d is in a non-conductive state. Therefore, an equivalent circuit for one pixel at this time is shown in FIG. Show.

  When a predetermined current I is passed through the source signal line 124 by the current source 125, a current having a current amount I also flows through the transistor 121. As can be seen from FIG. 6A, since the source or drain of the transistor 121 and the gate have the same potential, when the gate voltage and the drain current of the transistor 121 are in the relationship as shown in FIG. The potential of the line 124 varies depending on the current value.

  For example, when the current flowing through the source signal line 124 changes from I1 to I2, the potential of the source signal line 124 changes from Vdd−V1 to Vdd−V2. The same applies to the case where the current changes from I1 to I3.

  As shown in FIG. 6C, the time required for the current value change varies depending on the current value after the change, and it takes t4-t1 time from I1 to I2 as indicated by the solid line 126, as indicated by the dotted line 127. It can be seen that from I1 to I3 takes t3-t1 time, and that the change takes longer as the current value is smaller. This is because it takes time to charge and discharge the stray capacitance 123 in the source signal line 124 using a low current.

  Therefore, considering that it takes time to change in the low current region (gradation close to black), a different voltage value is applied to each display gradation or multiple display gradations to reduce the amount of change. The writing time was shortened.

  For example, in the case of 16 gradation display, voltages corresponding to gradations 1, 2, and 4 are prepared. In gradation 1, corresponding voltages are applied during the voltage application period, and in gradations 2 and 3, gradation 2 is supported. By applying a voltage corresponding to gradation 4 in the case of gradation 4 or higher, the time required for writing, particularly the writing time in a low current region that takes time can be shortened. The scanning period may be 220 μsec regardless of the display gradation.

  Similarly, in the case of other gradation numbers, the voltage values applied by the plurality of voltage sources in FIG. 5 are allotted at equal intervals by the number of voltage sources 54 from the maximum voltage value and the minimum voltage value necessary for gradation expression. It is better to set the voltage value than in the low current region rather than the measured voltage value.

  Further, although the number of power supplies to be prepared depends on the voltage amplitude that the source signal line 124 can take, it is desirable that the number be about five at most because of the increase in the circuit scale of the source driver and the improvement in image quality due to the increase in the number of power supplies.

(Embodiment 3)
An organic light emitting element is given as a display device that performs gradation control with current. As one of methods for realizing a multi-color display device using organic light-emitting elements, there is a method of arranging multi-colors by arranging red light-emitting elements, green light-emitting elements, and blue light-emitting elements.

  Since the emission efficiency, the mobility of carriers in the organic layer, and the energy difference from the electrode to the organic layer are different for each emission color, the relationship between current and luminance, voltage and luminance, and current and voltage is different for each emission color. For example, as shown in FIG. 36A, the luminance differs for the same voltage value, and as a result, the light emission start voltage also takes a value different from V1 for element G and V2 for element R. Further, as shown in FIG. 36B, the light emission start current is also different.

  In the first embodiment, there is one type of voltage value during the voltage application period. In this embodiment, when a voltage is applied with the same voltage value to the display device composed of the two types of elements G and R shown in FIG. 36, the voltage corresponding to J2 that is the black display current value of the element R is all source signals. When applied to the line, the source signal line connected to the element G does not have the potential corresponding to the black display, and it is necessary to change the potential of the source signal line for the black display that takes the longest time. On the other hand, when a voltage corresponding to J1 is applied to the source signal line, a voltage value higher than the black display voltage value is applied to the element R, and the source signal does not have a voltage application period. There is a problem that the voltage amplitude becomes large.

  Therefore, when an element having a different light emission start current value is formed by the source signal line, a black signal voltage can be adjusted by providing a different voltage source for each source signal line having at least an element having a different light emission start current value. What should I do? In the case of the display device formed by the R and G elements in FIG. 36, two voltage sources 54 in the configuration of FIG. 7 are prepared, and the source signal line in which the elements R are arranged and the source signal line in which the elements G are arranged are different. Provide a voltage source.

  Further, in order to further shorten the writing time, as in the second embodiment, a plurality of voltage sources are prepared for each signal line, and the applied voltage value is changed according to the gradation. Good.

(Embodiment 4)
As the frame frequency becomes faster, one horizontal scanning period becomes shorter. Therefore, when the frequency is fast, the voltage values of the plurality of voltage sources implemented in the second embodiment are voltage values corresponding to the vicinity of the black display that takes time to write. Prepare mainly. On the other hand, if the frame frequency is made slow, it takes a long time to change the voltage, so the way of taking the voltage value may be shifted to the white display side. Thereby, it is possible to improve the brightness at the time of white display, leading to an improvement in contrast.

  In a display device such as a portable information terminal that requires low power driving, the full screen is displayed when the button 184 shown in FIG. 8 is operated, but only a part is displayed when the button 184 is not operated for a long time, such as in standby. There is a case where the partial display mode is performed to reduce power consumption. Since the number of display lines is reduced in this partial display mode, the frame frequency can also be lowered, and the circuit can be operated using an oscillation frequency different from that in full screen display.

  FIG. 9 shows a block diagram of a controller and a source driver unit of a display device having a plurality of oscillators, a switching circuit, and a frequency dividing circuit and corresponding to a plurality of frame frequencies. The gradation display is performed by outputting the data read from the memory 86 to the source signal line via the selector 88 by controlling or selecting the current source 90 by the gradation control unit 87. The voltage value of the applied voltage is determined by the voltage control means 85 and the voltage generator 89, and the voltage control means 85 can receive the output of the oscillation frequency detection means 83 and change the voltage value according to the frequency. As a result, it is possible to change the voltage values of the plurality of voltage sources during the voltage application period according to the difference in the frame frequency, and to perform optimum gradation display.

  In addition to the portable information terminal, for example, when used as a television, the frame rate differs depending on the video signal transmission method. In the case of creating a display device that supports both types, the video signal processing circuit 194 detects the transmission method and changes the combination of voltage values of a plurality of voltage sources in the television shown in FIG. Key display is possible.

(Embodiment 5)
In the black voltage application performed in the first embodiment, the voltage value corresponding to the current value at the time of black display is applied using the current-voltage characteristic of the transistor 17a of FIG. However, since the voltage value for the same current may vary depending on the position of the substrate between lots, it is necessary to adjust the input voltage value for each display device in order to apply the optimum black voltage value.

  Adjustment for each display device is not desirable because it complicates the manufacturing process. Therefore, since the variation in the voltage value is smaller between the pixels in the display device than between the lots, when at least one test transistor is created in the display device and a current for black display is passed through the transistor, It was considered that a necessary gate voltage of a transistor was detected and a voltage value corresponding to the result was applied to the source signal line. The circuit configuration is shown in FIG.

  A current value representing a black signal is passed through the source signal line 100. At this time, the same current value also flows through the drain of the transistor 98, the potential difference between the contact 99 and the EL power supply line 96 is detected by the voltage detection means 91, and the detection result is input to the voltage generation means 92, and the voltage source of FIG. The voltage value corresponding to 18 is changed. The selector 93 controls the voltage application period and the current period.

  In this method, a black display voltage can always be applied even if the current vs. voltage characteristics of the drive transistor vary between lots, so that black floating due to variations in transistor formation can be prevented.

  In addition, by passing current values corresponding to various gradations to the source signal line 100, the voltage at that time can be detected by the voltage detection means 91 and applied to the source signal line using the voltage generation means 92 and the selector 93. Therefore, the present invention is not necessarily limited to the time of applying a black signal, and is generally applicable to the case of applying a voltage corresponding to a certain gradation.

(Embodiment 6)
The change in the current value of the source signal becomes faster as the current value after the change becomes larger. As shown in FIG. 6C, when the current I1 changes to I2 or I3, the change to I3 having a larger current value can be changed in a shorter time. This is because the current value is changed by extracting or accumulating the charge of the floating capacitance 123 of the source signal line by the current source 125, so that the high current region where a large amount of charge can flow can be changed more quickly. is there.

  Therefore, by utilizing the fact that the rising time of the waveform is shortened when a large amount of current is passed, it is at least three times the predetermined current value for the display gradation from the beginning of one horizontal scanning period shown in FIG. Apply a current value of 10 times or less. In a subsequent period 135, a predetermined current value is passed. As a result, the current value has changed as indicated by 131 (dotted line) in the prior art, whereas the rise can be accelerated as indicated by 132 (solid line). As a result, the writing time is shortened, and one horizontal scanning period 134 can be shortened, and writing can be performed in 230 μsec. Unlike the first to fifth embodiments, this method eliminates the need for a power source, a voltage generation unit, and a selector, so that a source driver with a small circuit scale can be realized.

  During black display, the writing speed can be increased by increasing the current by 3 to 10 times. However, since the luminance increases as the current increases, black floating may occur when the current value is increased by 10 times. In addition, when the source current value in the next scanning period is smaller than the source current value in the previous scanning period, the luminance is increased, so that there is a risk that the contrast may decrease even if the writing speed is increased. is there.

  Therefore, as shown in FIG. 13, a black signal voltage insertion period 144 is provided at the beginning of one horizontal scanning period in the same manner as in the first to fifth embodiments, and then a period 145 in which a current value of 3 to 10 times is passed. A period 146 for supplying a current value corresponding to the gradation is provided.

  When the current value changes from a small value to a large value, the current value changes 3 times or more and 10 times or less, and changes quickly as shown by 142 (solid line) compared to the conventional rise 141 (dotted line). Can do.

  When the current value changes from a large value to a small value, the black signal voltage insertion period 144 can change the state to the black state instantaneously (at least within 4 μsec), so that the falling can be changed quickly.

  FIG. 7 shows a circuit configuration for realizing such a waveform. This can be realized with substantially the same configuration as in the first embodiment, and by changing the output of the gradation data detection means 52 during the horizontal scanning period, a period of 3 to 10 times the predetermined current and a predetermined current value You can make a period to flow. As a result, one horizontal scanning period can be scanned in 150 μsec.

(Embodiment 7)
According to the sixth embodiment, for example, a display device having 220 scanning lines can be operated at a frame frequency of 30 Hz. As a result, display with less flicker is possible. However, when it is applied to a frame frequency of 60 Hz as in a television, luminance increases during black display and luminance decreases during white display due to insufficient writing.

  Furthermore, the method shown in FIGS. 14 and 15 was considered as a method for increasing the writing time. As shown in FIG. 15, a voltage value corresponding to the gradation is applied to the source signal line at the beginning of one horizontal scanning period (gradation display 114 corresponding to the voltage value). The speed of voltage change at this time is 2 μsec or less because it is determined by the wiring constant of the source signal line and the time constant determined by the stray capacitance. In the pixel configuration shown in FIG. 2, if the current is allowed to flow through the EL element 16 as it is, the current value changes by the same amount as the change amount when the relationship between the gate voltage and the drain current of the transistor 17a or 17e changes for each pixel. As the luminance of the EL element 16 changes, display unevenness occurs. Therefore, in the remaining period 115, a current corresponding to the current value is supplied to the source signal line, thereby changing the gate voltage of the transistor 17a or 17e so that a predetermined drain current flows. As a result, variations in the current-voltage characteristics of the transistors are corrected, and a display device without display unevenness is realized.

  The circuit configuration at this time is shown in FIG. 14, and the grayscale data detection means 52 provided for each source signal line controls the source signal current source 53 and the voltage source 104, and the current amount or voltage value for each grayscale. To change. As a result, the voltage and current values are changed for each display gradation during the periods 114 and 115, and the switching means 106 for determining which of the source signal current source 53 and the voltage source 104 is connected to the source signal line is horizontal. By controlling the voltage application period control unit 51 controlled by the synchronization signal, the lengths of the periods 114 and 115 can be varied in the horizontal scanning period 113.

  Even during the writing time, the amount of change in the current during the gradation display according to the current is at most about 50 μs because it is at most within the range of variations in the current-voltage characteristics of the transistors.

  The voltage application period may be at most 3 μs and the current writing time may be about 20 μs. Therefore, when the number of scanning lines is 220, driving at 60 Hz is possible, and flickerless driving can be realized.

  Therefore, considering the margin, it is desirable that the voltage application period be 1% or more and 50% or less of one horizontal scanning period depending on the frame frequency.

(Embodiment 8)
FIG. 16 shows a source driver section output stage according to the present invention. Reference numeral 263 denotes a digital-analog converter that converts an X-bit video signal into an analog signal, and reference numeral 264 denotes a reference voltage line that determines the maximum value of the analog voltage output. In the present invention, the voltage value applied to the reference voltage line 264 can be changed by selecting one of the plurality of voltage values generated by the reference voltage generation unit 261 according to the clock and the horizontal synchronization signal 267 by the selection unit 262. It is a feature.

  FIG. 17 shows a timing chart when the input video signal is 8 bits. Assuming that the voltage value of the source signal line 265 corresponding to the required maximum luminance is V1, the voltage V2 in FIG. 17 may be a voltage not less than 3 times and not more than 10 times V1. Further, the period during which V2 is applied to the reference voltage may be from one fifth to one half of the horizontal scanning period. In addition, when the gradation expression is performed using the source signal line voltage, it is shorter and it may be 1 μs or more and 5 μs or less.

  When the input video signal data is FF by the operation of the reference voltage, the voltage V2 is first output to the source signal line, and then V1 is output by the change of the reference voltage. When the input data is 00, a voltage of 0 is always applied to the output to the source signal line. Further, among the values in the meantime, when the reference voltage value is V2, a voltage not less than 3 times and not more than 10 times the predetermined output voltage is output, and when the reference voltage value is V1, the predetermined voltage value is output.

  In this way, by controlling the source signal line voltage, the waveform rounding due to the stray capacitance of the source signal line 76 can be reduced in the display device configured as shown in FIG. 34, and a panel having a size of about 2 type. If so, the writing time per line can be driven in about 150 μsec.

(Embodiment 9)
FIG. 1 is a diagram showing a circuit for one pixel, a source signal line, and a current source for performing gradation display in the ninth embodiment of the present invention.

  FIG. 18 shows a timing chart. The gate signal line (1) 12 becomes conductive during the row selection period (here, since the transistor 17 in FIG. 1 is a P-channel transistor, it becomes conductive at a low level), and the gate signal line (2) 13 is in the non-selection period. Make it conductive.

  As a result, in the row selection period, the transistors 17b, 17c, and 17j are turned on, and 17d is turned off, equivalently, a circuit as shown in FIG. Flows through the transistors 17a and 17i, and the sum Iin of the current Ia flowing through the transistor 17a and the current Ii flowing through the transistor 17i flows through the source signal line 11. In addition, electric charges are accumulated in the storage capacitor 14 so that the gate voltage is such that the sum of the current values flowing through the transistors 17a and 17i becomes Iin.

  Conversely, the transistor 17d is turned on and the transistors 17b, 17c, and 17j are turned off during the non-selection period, so that an equivalent circuit as shown in FIG. 19B is obtained, and the EL power line 15 is connected to the EL element 16 through the transistor 17a. Current flows. The amount of current is determined by the amount of charge stored in the storage capacitor 14, and a current corresponding to the charge held in the selection period flows. That is, the current Ia flows through the transistor 17a during the non-selection period, and the current Ia also flows through the EL element 16.

  Since the current flowing through the EL element becomes Ia with respect to the current Iin = Ia + Ii flowing through the source signal line, the current value flowing through the source signal line is increased without changing the luminance of the EL element by adjusting the current value Ii. In addition, since the charge and discharge of the charge of the stray capacitance 20 existing in the source signal line 11 is accelerated, the value of the current flowing through the source signal line becomes a predetermined value in a shorter time than conventional.

  Here, the relationship between the currents Ia and Ii can be adjusted by the channel width and channel length of the transistors 17a and 17i. FIG. 20 shows the relationship between the channel size of the two transistors, the current value of the current source 10 that determines the current flowing through the source signal line 11, and the current value flowing through the EL element 16.

  When the channel size of the transistor 17i is the same as that of the transistor 17a, the current flowing through the EL element 16 is half of the current flowing through the source signal line 11. As shown in FIG. 19A, the current flowing through the source signal line flows through both the transistors 17a and 17i. If variations due to the film forming process are ignored, the current characteristics between the gate voltage and the source / drain of the two transistors are the same, and the same voltage is applied to the gates. Since the current that flows through the EL element is only the current that flows through the transistor 17a, it is half of the current that flows through the source signal line 11.

  When the channel width and the channel length of the transistor 17i are changed, the characteristics of the gate voltage to the source-drain current change. When the channel width is widened or the channel length is shortened, the current easily flows through the transistor 17i. The ratio of the current flowing through the EL element 16 to the current flowing through the line 11 can be reduced. As an example, FIG. 20 shows a case where the channel width is 9 times that of the transistor 17a, the channel width is tripled, and the channel length is ３. In either case, the current flowing through the EL element 16 is 1/10 of the current flowing through the source signal line 11.

  The time t required to change the current value of the source signal line is t = C · V / I, where C is the size of the stray capacitance, V is the voltage of the source signal line, and I is the current flowing through the source signal line. The ability to increase the current value by a factor of 10 indicates that the time required to change the current value can be shortened to nearly 1/10. As a result, when the number of scanning lines is 220, it can be driven at a frame frequency of 60 Hz.

(Embodiment 10)
In the ninth embodiment, the time taken to change to a predetermined current is shortened by increasing the value of the current flowing through the source signal line by 10 times, but the current is ideally 0 at the time of black display. The current of about tens of nA flows due to the leakage current of the transistor and the leakage of the transistor constituting the current source. However, in order to prevent black floating, the smaller the current value, the better. It is easy to invite.

  Therefore, as shown in FIG. 21, the power source switching means 19 is provided in the source signal line 11 so that the output of the current source 10 or the voltage source 18 is applied to the source signal line, and the voltage source 18 has a current flowing through the transistor 17a. A source signal line voltage is applied so as to be about several tens of nA. The power source switching means 19 selects the voltage source 18 for about 1 to 5 μs at the beginning of the horizontal scanning period, and selects the current source 10 for the remaining period. As shown in FIG. 3A, the source signal line 11 has a discharge voltage application period and a video signal current application period, and a voltage value indicating black display is always applied to the source signal line at the beginning of the horizontal scanning period. Is done. By this operation, it is possible to eliminate the phenomenon of slight lighting during black display.

  On the other hand, for each gradation other than black, the larger the value of the current flowing during the current application period, the easier it is to change, and the gradation that takes the longest time to change is the gradation one above black. The time t required for the current change is expressed by t = CV / I (C: stray capacitance existing in the source signal line, V: source signal line voltage, I: current flowing in the source signal line), and C is a floor. V is constant regardless of the tone and is determined by the size of the display device. When a P-channel transistor is used, V increases as the black signal is increased and I decreases as the black signal is increased. This is because it takes time to change. Here, for the sake of explanation, it is assumed that the gradation indicating black is gradation 0, the gradation with the next highest luminance is gradation 1, and the gradation value is increased one by one as the luminance increases.

  As shown in FIG. 3, when a black voltage is applied at the beginning of the horizontal scanning period, a period of gradation 0 always exists regardless of the video signal displayed on the previous line, and a predetermined gradation is included in the same horizontal scanning period. If the current value can be changed to a predetermined value, a predetermined gradation can be displayed.

  The change takes the longest in the case of gradation 1 display. If gradation can be changed from gradation 0 to gradation 1 in one horizontal scanning period, all gradations can be displayed.

  In the pixel configuration shown in FIG. 22 (a) and in the pixel configuration shown in FIG. 21 (b) (the current value flowing through the source signal line 11 is 10 times the current value flowing through the EL element 16). In such a combination of transistors 17a and 17i), when the horizontal scanning period is set to 75 μs, the gradation 1 is displayed, and the capacitance of the source signal line is changed, the current flowing through the EL element 16 with respect to a predetermined current It is the figure which showed how much can be flowed. When it is 100%, it indicates that the current can be changed to a predetermined current value, and when it is less than that, it indicates that the time required for the change is later than 75 μsec, indicating that the predetermined gradation display cannot be performed.

  Since a deviation of about 10% with respect to the predetermined current value (luminance) cannot be visually confirmed, it is practically 90% to 100%. The source signal line capacitance allowable under this condition operates only at 2 pF or less in the pixel configuration of FIG. 2, but can operate at 27 pF or less in the pixel configuration shown in FIG. In the case of a display device of about 2 type, the capacitance parasitic to the source signal line is about 15 to 20 pF including the output stage of the driver IC, and the tenth embodiment in which the current value of the source signal line is increased 10 times is used. Thus, it is possible to drive at a frame frequency of 65 Hz or less, and display with less flicker is possible. It can also be applied to televisions.

  The capacitance parasitic on the source signal line 11 varies depending on the size of the display device. If it is 15 type, it will be about 50 pF. In this case, even if writing is performed with the source signal line current set to 10 times the EL current, only about 70% can be written. Therefore, if the number of scanning lines is equal, for example, the channel size ratio is increased by 15 times to 60 Hz. It turned out that driving becomes possible.

  As described above, according to the tenth embodiment of the present invention, a predetermined current value is written within a predetermined horizontal scanning period by changing the size of the channel regions of the drive transistors 17a and 17i according to the size of the display device. It becomes possible.

(Embodiment 11)
In the tenth embodiment, when the horizontal scanning period is a period in which a current value several times a predetermined current value flows through the black signal voltage application period, the source signal line is driven at 60 Hz even if the capacitance is 20 pF. Realized.

  Due to variations in the gate threshold voltage of the transistors 17a and 17i in FIG. 21 within the panel, the current value flowing through the EL element 16 with respect to black voltage application differs, and when the threshold voltage is low, a large amount of current flows and black is floated. Occur.

  In order to solve this problem, considering the variation of the gate threshold voltage of the transistors in the panel, the black voltage should be applied higher so that the luminance becomes black display even if the transistor through which the most current flows is used. In this case, however, the amount of change in the current value from gradation 0 to gradation 1 becomes large in the pixel using the transistor through which the most current flows, and the time required for the change to the predetermined current value becomes long. As a result, for example, when the black voltage is increased by 0.5 V, the source signal line capacitance value that can be written in the horizontal scanning period of 75 μsec with respect to the change from gradation 0 to gradation 1 is about 2 pF. Become.

  As in the tenth embodiment, the ratio of the channel region sizes of the transistors 17a and 17i may be changed. However, in the eleventh embodiment, it is allowed by increasing the current value of the gradation other than the gradation 0. Considered increasing the capacity value. A current source for supplying a current value corresponding to each gradation is prepared, and a plurality (α) of current sources for supplying a larger current are prepared. FIG. 21 shows a case where α is 4. For the gradation 0, the current source 0 is used as before, and for the gradation 1, the current source 5 is used instead of the current source 1. The current source 6 is used for the gradation 2, and the current source (i + 4) is used for the gradation i in the following order.

  As a result, the current flowing through the source signal line at the time of each gradation display increases, so that the current value changes more quickly. FIG. 23 shows whether a predetermined current value can be written in 75 μsec with respect to the source signal line capacitance when the current source 1 is used for gradation 1 (a) and when the current source 5 is used (b). In the tenth embodiment, gradation expression could not be made unless it was 2 pF or less, but in the eleventh embodiment, it was possible to write up to 20 pF or less.

  Further, even when this method is not used together with the voltage application period, the current value of each gradation increases, so that the writing time can be shortened.

  Note that the number of current sources is not necessarily the number of gradations + α, and there may be no α current sources that are not necessary for gradation display. In the eleventh embodiment, the four power supplies from the current source 1 to the current source 4 are not necessary configuration requirements.

(Embodiment 12)
When gradation display is performed using current values, current sources corresponding to each gradation are supplied to the source signal line as a method for supplying current corresponding to each gradation by at least the number of gradations, and according to the input data. There is a method of selecting and outputting one.

  In this method, when the number of gradations increases, the number of necessary current sources also increases, and the area of the source driver increases.

  When the current value is Ik at the gradation k, the current value is IL at the gradation, and IL = Ik × 2, two current sources having the conventional output current values Ik and IL are required. .

  As shown in FIG. 1, when the transistor 17 is formed for one pixel and the ratio of the sizes of the transistors 17a and 17i in the channel region is changed, the current value flowing through the EL element 16 with respect to the same source signal line 11 current is The relationship changes as shown in FIG.

  Here, paying attention to the transistor 17j, if the channel sizes of the transistors 17a and 17i are the same, the gray level L is always non-conductive, and the gray level k is the same as the gate signal line (1) 12. When the operation is performed, the current flowing to the source signal line 11 flows to the EL element 16 as it is because it is the same as having no 17i transistor at the time of gradation L display. The source signal line current value at this time is IL.

  On the other hand, the current flowing through the EL element 16 is halved with respect to the value of the current flowing through the source signal line 11 during gradation k display. Therefore, in order to flow the necessary current Ik to the EL element 16, a current amount of Ik × 2 is required for the source signal line.

  If this method is used, since IL = Ik × 2, it is possible to use the same current value IL for gradation k, so that the number of necessary current sources can be reduced. The transistor 17j is operated from the gradation 0 to P, and is always in a non-conductive state at the gradation P + 1 or higher, so that the current flowing through the source signal line 11 for each gradation is shown by the solid lines (252, 253, 254) in FIG. It changes as shown. When the current value is Ip + 1 or more, the same current value may be obtained for two gradations, so that the number of necessary current sources can be reduced and the chip area of the source driver can be reduced.

  Further, since the minimum value of the current flowing through the source signal line 11 is larger than that in the conventional example (dotted line 251 in FIG. 24), the influence of waveform rounding due to the stray capacitance parasitic on the source signal line 11 can be reduced. Writing can be performed in a shorter horizontal scanning period.

  As in the tenth embodiment, even in the case where writing is performed by multiplying the source signal line current several times in all gradations, the source signal is sufficient in the gradation where writing can be performed sufficiently compared with the low luminance region. Even if the magnification of the current flowing through the line with respect to the EL current is reduced, if the current value is larger than that at the time of gradation 1 display, the writing time will not be short and writing in the same horizontal scanning period is possible. Rather, there is an advantage that low power consumption driving is possible by reducing the value of the current flowing through the source signal line 11.

  In the above description, the channel sizes of the transistors 17a and 17i are the same and the current value is doubled. However, depending on the relationship between the gray level and the current value flowing through the source signal line, triple, ten times, etc. The same effect can be obtained by adjusting the magnification and changing the same source current value so that two gradations are included, as indicated by solid lines 252 and 254 in FIG. It is desirable to increase the magnification as the slope of the dotted line shown in the conventional example increases. When the gradient is large, a combination of two or more multiple magnifications is used, such as 4 times from gradation 0 to gradation P, 2 times from gradation P + 1 to Q, and 1 time from gradation Q + 1 or more. May be.

  In order to perform such an operation, it is necessary to cause the conventional transistor 17j in FIG. 1 to perform at least two different operations depending on the input gradation. Therefore, as shown in FIG. 25, the magnification changing means 343 is provided, and the output thereof is ANDed with the gate signal line (1) 345 to be input to the gate of the transistor 17j. In FIG. 25, since the transistor 17j is a P channel, the magnification changing means 343 outputs a high level below the gradation P, and outputs a low level above the gradation P + 1, so that the transistor 17j is above the gradation P + 1. The source signal line current is always equal to the EL element current in a non-conductive state, and it is possible to flow current values with different magnifications depending on the channel size ratio of the transistors 17j and 17a below the gradation P.

  A current to be supplied to the source signal line 11 is selected by the current switching unit 342 by the input video signal 341 among the plurality of current sources 344, and a predetermined current is supplied when the power source switching unit 19 selects the current source. To. In FIG. 25, the voltage source 18 is used to prevent black floating at the time of gradation 0 display. However, the number of current sources 344 can be reduced regardless of the presence or absence of the voltage source 18. Does not have to be affected.

  By using the above invention, even if the capacitance value parasitic on the source signal line is 25 pF, the horizontal scanning period can be written in 65 μsec, and display with less flicker is possible.

  FIG. 8 shows an example in which a demodulator, an antenna 181 and a button 184 are attached to a display portion 182 using at least one of the forms of the present invention, and a form information terminal is formed by a housing 183.

  FIG. 5 shows a display device 191 using at least one of the modes of the present invention, with a video signal input 196 and a video signal processing circuit 194 attached thereto, and a television set with a housing 197.

  In the embodiment of the present invention, the source driver 71 and the gate driver 70 in FIG. 34 may be formed on a glass substrate of a display device using low-temperature polysilicon. Alternatively, the source driver 71 and the gate driver 70 may be formed as semiconductor circuits and combined with the display panel. Alternatively, one driver may be formed of low-temperature polysilicon on the glass substrate of the display device, the other is formed as a semiconductor circuit, and combined with the display panel.

  In the embodiment of the present invention, as a method for changing the ratio between the current value flowing through the source signal line and the current value flowing through the EL element, FIG. 1 shows a circuit example using at least two drive transistors. The arrangement location of the transistor 17j may be configured so that no current flows when one of the two transistors 17a and 17i is turned on, for example, as shown in FIG. 26, FIG. 27, or FIG. Even if they are arranged, the same effect can be obtained. Regardless of these drawings, the transistor 17j can be inserted at any position as long as the above-described purpose is achieved.

  In this example, a P-channel transistor has been described as an example of a switching element. However, an N-channel transistor or a combination thereof can be similarly realized. For example, in the case of the pixel configuration shown in FIG. 2, when N channel transistors are used for the voltage values applied to the gate signal line (1) 12 and the gate signal line (2) 13, the logic level of the P channel transistor is considered. An inversion signal of the signal may be input, and the current source 10 is reversed in the direction in which the current flows, and the voltage supplied from the EL power source line 15 is lower than the terminal voltage opposite to the power source switching unit 19 of the current source 10. By doing so, it can be similarly realized. That is, the purpose of accelerating the charge / discharge of the stray capacitance 20 existing in the source signal line 11 is the same only by reversing the relationship between the direction of the current and the potential.

  FIG. 29 shows an example of a configuration for changing the current ratio in the case of an N-channel transistor.

  Although the description has been given with respect to the pixel configuration of the dynamic current copier, the present invention can be similarly applied to the pixel of the current mirror configuration as shown in FIG. Even in the case of the current mirror configuration, when a row is selected, the transistor 177d is turned on and the transistor 177b is turned off, and the current source 170 uses the EL power supply line 175, the transistors 177a and 177d, and the source signal line 171 according to the gradation. Therefore, when stray capacitance exists in the source signal line 171, it is difficult to charge and discharge charges accumulated in the stray capacitance in the low current region when the current value of the current source 170 changes. The problem is the same. Therefore, the effect of increasing the writing speed can be obtained by implementing the present invention.

  As shown in FIG. 31, transistors 177m and 177n are added and the gate signal line (1) 172 is connected to the gate electrode of 177n to change the current flowing through the source signal line and the current flowing through the EL element. This can be realized by changing the channel size of the transistors 177m and 177a.

  In addition, by independently controlling the gate terminal of the transistor 177n instead of the gate signal line (1) 172, for example, any one of those that are always non-conductive or perform the same operation as the gate signal line (1) 172 depending on the gradation. By selecting these, the ratio of the source signal line current to the EL element current can be changed for each display gradation.

  As a result, the current value flowing through the source signal line can be increased, so that the change in the current value can be accelerated.

  The transistors 17b, 17c, 17d, 17j, 177b, 177d, and 177n used as transistors in the present invention have been described using thin film transistors as an example. Similar effects can be obtained by using MIM).

  Further, although an EL element has been described as a display element, an organic electroluminescence element, an inorganic electroluminescence element, a light emitting diode, or the like may be used.

  Further, it can be applied to a light modulation panel such as a liquid crystal. In FIG. 2, the EL element 16 may be a liquid crystal layer.

  Similarly, a configuration as shown in FIG. 32A is also conceivable as a pixel configuration for driving the EL element with a current value. The difference from FIG. 1 is that the switching transistor is connected to the power supply line, not the EL element.

  Hereinafter, the operation in the pixel configuration of FIG.

  The transistors 17c, 17b, and 17j are turned on by the gate signal line (1) 391. Further, the transistor 17d is turned off by the gate signal line (2) 392. The storage capacitor 14 stores a voltage corresponding to the sum of the currents flowing through the transistors 17a and 17i so as to be equal to the source signal line current value. The ratio of the current values flowing through the transistors 17a and 17i is determined by the ratio of the channel length and the ratio of the channel width.

  Next, by operating the gate signal lines (1) and (2), the transistors 17c, 17b, and 17j are turned off, the transistor 17d is turned on, and current flows from the EL power supply line 393 to the transistor 17a and the PL element 16. . The current value at this time is the same as the current value flowing from the source signal line current to the transistor 17a.

  Thus, as in the configuration of FIG. 1, the ratio of the current value with respect to the source signal line and the current value flowing through the EL element can be changed by changing the ratio of the channel sizes of the at least two drive transistors 17a and 17i. The amount of current flowing through the source signal line becomes larger than that of the conventional configuration, and the effect of reducing the rounding of the waveform due to the stray capacitance 20 can be obtained in the same manner as the configuration of FIG.

  Further, by increasing the value of the current flowing through the source signal line of each gradation several times (about 5 to 10 times for a 2 type panel) by implementing the present invention, the step size of the current step of each gradation can be increased. Therefore, it is possible to increase the allowable range of the output variation of the current source corresponding to each gradation configured in the source driver.

  In addition, there is an advantage that current adjustment is easy.

  This can be implemented by providing power source switching means 179 in the source signal line 171 and switching between the current source 170 and the voltage source 178.

Effect of the invention

  As described above, according to the present invention, the source signal line has the switching means, and the voltage application period and the current application period are provided within one horizontal scanning period so that the charges accumulated in the stray capacitance existing in the source signal line can be quickly obtained. By changing the amount of charge corresponding to a predetermined gradation, one horizontal scanning period can be shortened and flickerless driving can be realized.

  In addition, a period in which a current value of 3 to 10 times the current value corresponding to the display gradation is provided in one horizontal scanning period is used to change the charge accumulated in the floating capacitance existing in the source signal line. By shortening the time required, and by making the current value passed through the source signal line about 10 times the EL current value, one horizontal scanning period can be shortened and flickerless driving can be realized. In general, if the current value is at least larger than the product of the source capacitance value and the source voltage divided by one horizontal operation period, the current value corresponding to each gradation can be written in the horizontal operation period.

  The figure which showed the circuit for 1 pixel in the 9th Embodiment of this invention   The figure which showed the pixel, source signal line, and power supply by the 1st Embodiment of this invention   The figure which showed the timing of the voltage application period and the current application period in the horizontal scanning period   Diagram showing voltage application period dependency of output current for white display and black display   The figure which showed the relationship between the source driver part in the 2nd Embodiment of this invention, a power supply part, and a source signal line   The figure which showed the equivalent circuit at the time of the current writing from the source signal line to a certain pixel, the current voltage characteristic of the transistor in a pixel, and the waveform of a source signal line   The figure which showed the structure of the source driver part in the 3rd and 6th embodiment of this invention   The figure of the portable information terminal incorporating the display apparatus in embodiment of this invention   The block diagram of the controller and source driver in the 4th Embodiment of this invention   The figure which showed the television incorporating the display apparatus in embodiment of this invention   Block diagram for generating a voltage corresponding to the source signal line current in the fifth embodiment of the present invention   The figure which showed the waveform of the electric current which flows into the source signal line in the 6th Embodiment of this invention   The figure which showed the waveform of the electric current which flows into the source signal line in the 6th Embodiment of this invention compared with the prior art at the time of a rise and fall   The block diagram of the source driver in the 7th Embodiment of this invention, and the figure which showed the structure of the pixel part   Timing chart in the seventh embodiment of the present invention   The figure which showed the source signal line output using the digital analog converter in the 8th Embodiment of this invention   The figure which showed the change of the reference voltage in the horizontal scanning period in the 8th Embodiment of this invention   The figure which showed the relationship between the source signal line current in the 9th Embodiment of this invention, and the electric current which flows into an EL element   The figure which showed the conduction | electrical_connection state of each transistor at the time of flowing current into a source signal line in the circuit structure shown in FIG. 1, and flowing current into an EL element   The figure which showed the change of the current value of the current source by the change of the channel size of the transistor in FIG. 1 in the 9th Embodiment of this invention, and the current value which flows through an EL element.   The figure which showed the circuit for 1 pixel in the 10th Embodiment of this invention   A diagram showing how much data can be written with respect to a predetermined current value by the source signal line capacity when the horizontal scanning period is 75 μsec.   The figure which shows how much can be written with respect to a predetermined electric current value by the change of a source signal line capacity | capacitance in the 11th Embodiment of this invention when a horizontal scanning period is 75 microseconds   The figure which showed the relationship between the gradation and the electric current which flows into a source signal line in 12th Embodiment of this invention   The figure which showed the circuit structure for changing the ratio of the electric current value sent to a source signal line, and the electric current value sent to an EL element with a gradation   The figure which showed the circuit structure for changing the ratio of the electric current value sent through a source signal line, and the electric current value sent through an EL element   The figure which showed the circuit structure for changing the ratio of the electric current value sent through a source signal line, and the electric current value sent through an EL element   The figure which showed the circuit structure for changing the ratio of the electric current value sent through a source signal line, and the electric current value sent through an EL element   The figure which showed the circuit structure for changing the ratio of the electric current value sent to a source signal line, and the electric current value sent to an EL element when an N channel transistor is used   The figure which showed embodiment of this invention when a pixel became a current mirror structure   In the current mirror configuration, the current value flowing to the source signal line can be made different from the current value flowing to the EL element.   The figure which showed the circuit structure for changing the ratio of the electric current value sent to a source signal line in the case of changing not an EL element but an EL current line into a conduction | electrical_connection non-conduction state by a transistor, and the electric current value sent to an EL element   The figure which showed allocation of the current source with respect to the gradation in the 11th Embodiment of this invention   The figure which showed the structure of the conventional display apparatus   Diagram showing the relationship between input current and output current when the scanning time of the gate signal line is changed   The figure which showed the difference of the voltage-luminance characteristic and the current density-luminance characteristic of the organic light emitting element by the difference in display color

10 Current source 11 Source signal line 12 Gate signal line (1)
13 Gate signal line (2)
14 Storage Capacitor 15 EL Power Supply Line 16 EL Element 17 Transistor 18 Voltage Source 19 Power Supply Switching Means 20 Floating Capacitor

Claims (1)

An active matrix display device,
Two drive transistors;
A signal line connection transistor that forms a current path from a source signal line to the two driving transistors;
A power connection transistor that forms a path for supplying a current from a power source to the two driving transistors;
The two driving transistors are supplied with current from the power supply connection transistor or the signal line connection transistor, and include a magnification adjusting transistor inserted in series with one of the two driving transistors,
When the power connection transistor is turned on, the magnification adjustment transistor is turned off.
By not supplying a current through one of the driving transistors to the display element,
An active matrix display device, wherein an amount of current flowing through the source signal line when the magnification adjustment transistor is in a conductive state and a current flowing through the display element when the magnification adjustment transistor is in a non-conductive state are different.

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