JP2003108065A - Active matrix type display device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce display irregularity due to dullness in current waveforms caused by a stray capacitance of a source signal line of a current driven active matrix type display device. SOLUTION: The value of a current which flows in the source signal line is increased in order to make electric charges accumulated in stray capacitance correspond to display gradation quickly. To accomplish the above, the channel size of a driving transistor of each pixel is changed for a case in which the transistor is connected to the source signal line and for a case in which the transistor is connected to a display element. For example, the current value which is to be applied to the source signal line is made ten times larger in a two type panel so that driving is conducted in a 75 μ second horizontal scanning interval even though the stray capacitance of the source signal line is twenty-five pF. Moreover, a gradation vs. luminance characteristic is improved by using the fact that the time required for the change is different for every gradation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, such as an organic electroluminescence device, which performs gradation display by the amount of current.

[0002]

2. Description of the Related Art Organic light emitting elements are self-luminous elements, and therefore, do not require a backlight, which is required in liquid crystal display devices, and have a wide viewing angle. Therefore, they are expected as next-generation display devices. .

[0003]

Unlike the organic light emitting device, the light emitting intensity of the device and the electric field applied to the device are not in a proportional relationship, but the light emitting intensity of the device and a current density flowing through the device are in a proportional relationship. In contrast to variations in element film thickness and variations in input signal value, variations in emission intensity can be reduced by performing gradation display by current control.

FIG. 39 shows an example of an active matrix type display device using a transistor having a semiconductor layer. As shown at 79, each pixel includes a plurality of transistors (switching elements) 73, a storage capacitor 74, and an organic light emitting element 72.

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

By this operation, in the period A, the amount of current flowing through the transistor 73c is determined according to the current value output from the source driver 71, and the transistor 73
The gate voltage is determined from the relationship between the source-drain current of c and the gate voltage, and the charge corresponding to the gate voltage is stored in the storage capacitor 7.
Accumulated in 4. 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 also flows in the transistor 73c in the period B, The organic light emitting device 72 emits light through 73d. Depending on the amount of current in the source signal line, the storage capacity 7
The charge amount of 4 changes, and the emission intensity of the organic light emitting element 72 changes.

As a display pattern, when a current is applied to a certain source signal line in the order of lighting and non-lighting,
It was found that the luminance of the non-illuminated pixels was different when the current was applied in the non-illuminated order. In the order of lighting and non-lighting, the non-lighting pixel was lit about 0.5 when the brightness when lighting was 1 and the brightness when non-lighting was 0. In addition, when the non-lighting signal continues to flow within the same frame period after the lighting signal is sent once, the brightness of the non-lighting pixels gradually decreases from 0.5, the frame frequency is 60 Hz, and the number of display rows is It was found that the luminance was 0 from the 6th to 7th rows in the case of 220 rows.

On the other hand, when the lighting signal was sent after the non-lighting, the lighting luminance was 0.8 at the beginning, but the luminance 1 was displayed from the third row.

This means that the output of the source driver changes the current value according to the display pixel, but the current waveform supplied to each pixel is blunted by the wiring resistance and the stray capacitance of the source signal line, which is desirable. Indicates that the current value of is not stored in each pixel as the charge of the storage capacitor 74. 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 and the above problems are improved by slowing down the frame frequency and increasing the writing time for each row.

When the frame frequency is slowed, if the off characteristic of the transistor 73 is poor, the charge amount of the storage capacitor 74 changes due to the leakage of the transistor 73, and the current amount of the organic light emitting element 72 also changes, so that flicker occurs. Occurs.

Therefore, in order to obtain a display without flicker, the rounding of the current waveform is reduced so that a desired current value flows within the selection period regardless of the current value passed through the pixel displayed immediately before. Need to

[0014]

In order to solve the above-mentioned problems, an active matrix type display device of the present invention comprises a means for applying a predetermined voltage to a source signal line, a means for supplying a predetermined amount of current, and a source. A switching means for switching between the voltage applying means and the current flowing means on the signal line;
The feature is that the change in the amount of current flowing through the source signal line is accelerated by the change in the video signal.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 2 is a diagram showing a drive circuit of an organic light emitting element 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 according to the display gradation and the voltage source 18 for applying a predetermined voltage are provided, and the power source switching means 19 supplies a power source to the source signal line. The feature is that it can be switched.

The size of each pixel in the display section of a mobile phone, a monitor and the like is about 100 μm in width and 250 μm in length, and the current value required for the source signal line to obtain a brightness of 100 candela / square meter is Although it depends on the external quantum efficiency, it is about 1 μA.

To flow 1 μA to the EL element 16,
On the source driver side, the power supply switching means 19 is the current source 10
Is selected, and the current value of the current source 10 is set to 1 μA.

In the selected row, the gate signal line (1) 12 is a signal for making the transistor 17 conductive, and the gate signal line (2) 13
A non-conduction signal is applied to the gate signal line (1) 12 and the non-conduction signal is applied to the gate signal line (2) 13 in the non-selected row.
A conduction signal is applied to.

As a result, in the selected row (the first row in this example), the current of the source signal line 11 flows inside the pixel through the transistors 17b and 17c. The current path in the pixel is the EL power supply line 1 through the transistor 17a.
Since it is only connected to 5a, transistor 1
A current of 1 μA also flows through 7a, and the charge for the gate voltage at this time is stored in the storage capacitor 14a. In the non-selection period, the transistor 17d becomes conductive and the transistor 17d
Since b and 17c are non-conductive, the storage capacitor 1
The current flowing in the transistor 17a is defined based on the charge accumulated in 4a, and a current of 1 μA flows in the EL element 16a.

Therefore, in order to flow a desired current value (for example, 1 μA) to the EL element 16a, electric charges are stored in the storage capacitor 14a so that the transistor 17a gives a gate voltage that allows a desired current value to flow during the selection period. There is a need.

However, when the stray capacitance 20 is present on the source signal line 11, a rounding of the 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 by the current value, this waveform rounding also varies depending on the current value flowing in the source signal line, and the smaller the current value, the longer it takes to rise and fall. For example, the wiring capacitance is 100 pF and the wiring resistance is 500.
When it is ohm, the current value of the source signal line and the current value of the contact 1001 are 0.24 when the current value of the current source 10 is changed.
The time required to change from μA to 40nA is 300μ
Second, the time required to change from 40 nA to 0.24 μA was 250 μsec.

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

For example, as shown in FIG. 40, when the ON period of the gate signal line (1) 12 is changed to 64 μsec and 256 μsec, almost the same output current as the input current is obtained at 256 μsec. On the other hand, it was found that at 64 μs, the output current was different from the input, centering on the low current (0.7 μA or less).

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

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

Therefore, in order to shorten one horizontal scanning period,
In the present invention, when the current waveform changes, a low current (black display)
It was thought that we should take advantage of the fact that the change from high current (white display) to high current (white display) is lower than the change from low current (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 voltage of the source signal line 22a is changed to the black signal current by using this voltage source 18. The voltage is set to the same voltage as the value is flowing (discharge voltage application period 24). Next, the power source switching means 19 is switched to the current source 10 side, and the current source 1
When 0, a desired current value according to the video signal is passed through the source signal line 22a (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. Input current is 4
When it is as small as 0 nA (assuming black display), the output is 0.65 μA without voltage application period and 0.38 μA for 4 μs or more.
Therefore, the output is not affected even if the time is 4 μsec or more. Therefore, 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 0.5 μsec to 3 μsec, and the source signal line has a black voltage value. Also, in the video signal current application period 25, the time required to change from black display to a desired current is about 250 μsec from black display to white display, which takes the longest time, and in the halftone display, the white display changes to the black display. Since it is shorter than the changing time and is about 270 μsec, one horizontal scanning period is about 270 μsec, which is 90% shorter than the conventional 300 μsec, and low flicker display is possible.

Further, during the discharge voltage application period 24, by applying a source voltage such that the brightness becomes 0.01 candela / square meter or less, the brightness at the time of black display is lowered, and an image in which black is displayed is displayed. can do. 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. To supply a voltage close to the EL power supply voltage to the source signal line 11 during current driving, it is necessary to supply a minute current (several nA),
It is difficult to specify the source signal line voltage at a current of several nA because it takes several hundreds of microseconds to 1 millisecond as described above. As described above, the voltage insertion in the present invention is effective for displaying black in a short time.

When there is a period in which all the rows are unselected when the scanning row moves from a certain row (N rows: N is a natural number) to the next row (M rows: M is a natural number which is not N) Has
As shown in FIG. 3B, 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. Alternatively, as shown in FIG. 3C, the black voltage application period may extend over the non-selected state of all rows and a part of the one-row selection period.

Since the purpose of applying the black voltage is to charge the floating capacitance 20 of the source signal line 11 to the black state, even if the pixel transistor connected to the source signal line 11 is in the non-conductive state, it is in the conductive state. But there is no problem.

In order to lengthen the current writing time required for the original gradation display, when the all-row non-selection period exists, the voltage application period preferably includes the all-row non-selection period.

Further, the voltage applied to the source signal line 11 during the voltage application period does not necessarily have to be a voltage for displaying black, but it can be changed to a voltage value corresponding to a predetermined current value by the current source 10. Since the black display takes longer than the white display, the voltage value of the voltage source 18 is preferably a value on the black signal voltage value side of the intermediate value between the white signal voltage and the black signal voltage.

(Second Embodiment) In the first embodiment,
By providing the discharge voltage application period 24 and applying the voltage for displaying the black signal, the source signal line can be easily changed to a current showing black.

As a result, the amount of voltage change in black and the gradation in the vicinity of black becomes small, so that one horizontal scanning period is 200 μm.
It was possible to display in seconds to 230 μs. In addition, since the amount of current is maximum during white display, the discharge speed of the electric charges of the stray capacitances 20 existing in the source signal line 11 is fast, and one horizontal scanning period is about 180 μsec, despite a large change amount.
It was possible to display. On the other hand, since the amount of current is less than half of that in the case of displaying white, the gray scale from black is higher than that between the middle of white and black, and the charge discharge speed of the floating capacitance 20 is halved. Therefore, one horizontal period takes about 250 μsec. .

Therefore, the discharge voltage application period 24
In the above, it was considered that instead of applying the voltage for displaying the black signal, the voltage of several different levels is applied 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 detecting 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, controls 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 a signal is written to the pixel from the source signal line 11, the transistors 17b and 17c are in the conductive state and the transistor 17d is in the non-conductive state. Therefore, an equivalent circuit for one pixel at this time is shown in FIG. Shown in a).

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 in FIG. 6 (a),
Since the source or drain and the gate of the transistor 121 have the same potential, when the gate voltage and the drain current of the transistor 121 have a relationship as shown in FIG. 6B, the potential of the source signal line 124 changes depending on the current value. To do.

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 when the current changes from I1 to I3.

As shown in FIG. 6 (c), the time required for changing the current value varies depending on the changed current value.
Takes t4-t1 hours as shown by the solid line at 126,
As shown by the dotted line 127, t1-t1 from I1 to I3
It can be seen that it takes time, and the smaller the current value, the longer the change takes. This is because it takes time to charge and discharge the floating 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 (gradient close to black), a different voltage value is applied for each display gradation or for each of a plurality of display gradations. To reduce the writing time.

For example, in the case of 16 gradation display, gradation 1
Voltages corresponding to 2 and 4 are prepared, a corresponding voltage is applied in the voltage application period in the gradation 1, a voltage corresponding to the gradation 2 is applied in the gradations 2 and 3, and a gradation 4 or more is applied. By applying the voltage corresponding to gradation 4, the time required for writing,
In particular, the writing time in the low current region, which takes a long time, can be shortened, and one horizontal scanning period may be 220 μsec regardless of the display gradation.

Similarly for other gradation numbers, the voltage values applied by the plurality of voltage sources in FIG. 5 are equal to the number of voltage sources 54 from the maximum voltage value and the minimum voltage value required for gradation expression, respectively. It is better to set the voltage value in the low current region than in the voltage value assigned to the interval.

The number of power supplies to be prepared is the source signal line 12
Although it depends on the voltage amplitude that 4 can take, about 5 is preferable at the maximum in consideration 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 sources.

(Embodiment 3) An organic light emitting element can be mentioned as a display device which controls gradation by current. As one of methods for realizing a multi-color display device using an organic light emitting element, there is a method of arranging a red light emitting element, a green light emitting element, and a blue light emitting element side by side to form a multi color display.

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 the current and the luminance, the voltage and the luminance, and the current and the voltage is different for each emission color. Different to For example, as shown in FIG. 41A, the brightness is different for the same voltage value, and as a result, the light emission start voltage is V1 for the element G and V2 for the element R.
Takes a value different from. Further, as shown in FIG. 41 (b), 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 mode, when voltage is applied to the display device including the two kinds of elements G and R shown in FIG. 41 at the same voltage value, the voltage corresponding to J2 which is the black display current value of the element R is applied to all sources. When applied to the signal line, the source signal line connected to the element G does not have a potential corresponding to black display, and it becomes necessary to change the potential of the source signal line for black display, which takes the longest time. Conversely, J
When the voltage corresponding to 1 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 voltage amplitude of the source signal is smaller than that in the case where the voltage application period does not exist. There is a problem of getting bigger.

Therefore, when an element having a different emission start current value is formed by the source signal line, a different voltage source is provided at least for each source signal line on which an element having a different emission start current value is formed, and the black signal voltage is increased. Can be adjusted. In the case of the display device formed by the R and G elements of FIG. 41, two voltage sources 54 having the configuration of FIG. 7 are prepared,
Different voltage sources are provided for the source signal line in which the element R is arranged and the source signal line in which the element G is arranged.

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

(Embodiment 4) As the frame frequency becomes faster, one horizontal scanning period becomes shorter. Therefore, when the frequency is faster, it takes time to write the voltage values of the plurality of voltage sources implemented in the second embodiment. The voltage value corresponding to the vicinity of the black display is prepared. On the other hand, when the frame frequency is slowed down, the time required for the voltage change can be lengthened, so that the voltage value may be shifted to the white display side.
As a result, it is possible to improve the brightness during white display, which leads to an improvement in contrast.

In a display device such as a portable information terminal which is required to be driven with low power, the entire screen is displayed when the button 184 shown in FIG. 8 is operated, but when the button 184 is not operated for a long time such as in standby, only a part of the screen is displayed. A partial display mode for displaying may be used to reduce power consumption. Since the number of display lines is reduced in the partial display mode, the frame frequency can 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 section 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 generation section 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. This changes the voltage value of multiple voltage sources during the voltage application period depending on the difference in frame frequency,
It is possible to perform optimum gradation display.

In addition to the portable information terminal, when it is used as, for example, a television, the frame rate is different when the video signal transmission system is different. When creating a display device compatible with both systems, in the television shown in FIG. 10, the video signal processing circuit 44 detects the transmission system and changes the combination of the voltage values of the plurality of voltage sources to obtain the optimum floor. It is possible to display the key.

(Fifth Embodiment) In the black voltage application performed in the first embodiment, the voltage value corresponding to the current value during black display is applied by using the current-voltage characteristic of the transistor 17a in FIG. It was However, since the voltage value for the same current may change between lots depending on the position of the substrate, 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 complicates the manufacturing process and is not desirable. Therefore, since the variation in voltage value is smaller between pixels in the display device than between lots, it is necessary when at least one test transistor is created in the display device and a current for black display is applied to the transistor. It was considered to detect the gate voltage of various transistors and apply a voltage value corresponding to the result 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 result of FIG. The voltage value corresponding to the voltage source 18 is changed. The voltage application period and the current period are controlled by the selector 93.

According to this method, the black display voltage can be always applied even if the current-voltage characteristics of the driving transistor vary from lot to lot, and therefore it is possible to prevent black floating due to variations in transistor fabrication.

By supplying current values corresponding to various gradations to the source signal line 100, the voltage at that time can be detected by the voltage detecting means 91, and the voltage generating means 92 and the selector 9 can be detected.
3 can be applied to the source signal line, the present invention is not necessarily limited to the case of applying the black signal, and is generally applicable to the case of applying a voltage corresponding to a certain gradation. It is possible.

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

Therefore, by utilizing the fact that the rising time of the waveform is shortened when a large amount of current is passed,
From the beginning of the horizontal scanning period to a certain period 133, a current value that is 3 times or more and 10 times or less the predetermined current value for the display gradation is supplied. In the subsequent period 135, a predetermined current value is passed. As a result, the current value changes as in 131 (dotted line) in the related art, but the rise can be accelerated as in 132 (solid line). As a result, the writing time can be shortened, the one horizontal scanning period 134 can be shortened, and the writing can be performed in 230 μsec. Unlike the first to fifth embodiments, this method does not require a voltage source, a voltage generator, and a selector, so that a source driver having a small circuit scale can be realized.

At the time of black display, the writing speed can be increased by multiplying the current by 3 to 10; however, the brightness increases as the current increases. Therefore, when the current value is multiplied by 10, black floating occurs. There are cases. 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 high, and thus there is a possibility that the contrast is deteriorated 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 as in the first to fifth embodiments, and then a current value of 3 times or more and 10 times or less is supplied. A period 145 and a period 146 in which a current value corresponding to gray scale is supplied are provided.

When the current value changes from a small value to a large value, a period 145 in which a current value of 3 times or more and 10 times or less flows
By a, compared with the conventional rising 141 (dotted line), 1
It can change rapidly as shown by 42 (solid line).

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

A circuit configuration for realizing such a waveform is shown in FIG. This can be realized with almost the same configuration as that of the first embodiment, and by changing the output of the gradation data detecting means 52 in the horizontal scanning period, a period of 3 times to 10 times the predetermined current and a predetermined current value are obtained. You can make a period to flush. As a result, it becomes possible to scan in one horizontal scanning period of 150 μsec.

(Embodiment 7) According to Embodiment 6, for example, a display device having 220 scanning lines can operate at a frame frequency of 30 Hz. This has made it possible to display with less flicker. However, when it is applied to a television with a frame frequency of 60 Hz, insufficient brightness causes an increase in brightness during black display and a decrease in brightness during white display.

Further, as a method for shortening the writing time, the method shown in FIGS. 14 and 15 was considered. As shown in FIG. 15, a voltage value according to gradation is applied to the source signal line at the beginning of one horizontal scanning period (gradation display 114 according to voltage value). The speed of voltage change at this time is 2 μsec or less because it is determined by the wiring resistance of the source signal line and the time constant determined by the stray capacitance. In the pixel configuration of FIG. 2, if a current is allowed to flow through the EL element 16 as it is, when the relationship between the gate voltage and the drain current of the transistor 17a or 17e changes for each pixel, the current value changes by the same amount as the change amount. The display unevenness occurs due to the change in the brightness of the EL element 16. Therefore, in the remaining period 115, a current corresponding to the current value is supplied to the source signal line, so that the gate voltage of the transistor 17a or 17e is changed so that a predetermined drain current flows. As a result, variations in 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, in which the source data current source 53 and the voltage source 104 are controlled by the gradation data detection means 52 provided for each source signal line.
The current amount or voltage value is changed for each gradation. As a result, the voltage and current values are changed for each display gradation in the period of 114 and 115, and the switching means 106 that determines 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 in the horizontal scanning period 113 can be varied.

Even in the writing time, the amount of change in the current during the gradation display depending on the current is within the range of the variation of the current-voltage characteristics of the transistor at most.
It takes about 50 μs.

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

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

(Embodiment 8) FIG. 16 shows an output stage of a source driver section according to the present invention. 263 is X
A digital-to-analog converter that converts a bit video signal into an analog signal, and 264 is a reference voltage line that determines the maximum value of the analog voltage output. According to 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. The feature is that they did it.

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 brightness is V1, the voltage V2 in FIG. 17 may be a voltage that is 3 times or more and 10 times or less than V1. In addition, the reference voltage V2
Is applied for more than 1/5 of the horizontal scanning period 2
It need only be a fraction or less. Further, the gradation is further shortened when the gradation is expressed by the source signal line voltage, 1 μsec or more and 5 μ
It may be less than a second.

When the input video signal data is FF by the operation of this reference voltage, the voltage of 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, the voltage of 0 is always applied to the output to the source signal line. Further, in the values in between, when the reference voltage value is V2, a voltage of 3 times or more and 10 times or less of the predetermined output voltage is output, and when the reference voltage value is V1, the predetermined voltage value is output.

By controlling the source signal line voltage in this way, it is possible to reduce the waveform rounding due to the stray capacitance of the source signal line 76 in the display device having the structure shown in FIG. With a panel, the writing time per line can be driven in about 150 μsec.

(Ninth Embodiment) FIG. 18 is a diagram showing a circuit for one pixel, a source signal line and a current source for gradation display in a ninth embodiment of the present invention.

FIG. 19 shows a timing chart. The gate signal line (1) 12 becomes conductive (because the transistor 17 in FIG. 18 is a P-channel transistor in this case) becomes conductive in the row selection period, and the gate signal line (2) 13 becomes in the non-selection period. Make it conductive.

As a result, during the row selection period, the transistors 17b, 17c and 17j are turned on and the transistor 17d is turned off, which is equivalently a circuit as shown in FIG. The current Ia flowing through the transistor 17a and the transistor 17i flow to the source signal line 11 through the transistors 17a and 17i.
The sum Iin of the current Ii flowing through the source signal line 11 flows. The storage capacitor 14 has transistors 17a and 1
The charges are accumulated so that the gate voltage is such that the sum of the current values flowing in 7i becomes Iin.

On the contrary, during the non-selection period, the transistor 17d is turned on and the transistors 17b, 17c and 17j are turned off, so that an equivalent circuit as shown in FIG.
Transistor 17a from EL power line 15 to EL element 16
An electric current flows through it. 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.

Current flowing in source signal line Iin = Ia + I
Since the current flowing through the EL element is Ia for i, the current value flowing through the source signal line can be increased without changing the brightness of the EL element by adjusting the current value Ii. Since the charge of the stray capacitance 20 existing in the charging circuit becomes faster, the current value flowing through the source signal line becomes a predetermined value in a shorter time than in the conventional case.

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. 21 shows the relationship between the channel size of the two transistors, the current value of the current source 10 that determines the current flowing in the source signal line 11, and the current value flowing in 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 the current flowing through the source signal line 11. The current flowing through the source signal line flows through both transistors 17a and 17i, as shown in FIG.
Ignoring the variation due to the film forming process, the two transistors have the same gate voltage-source / drain current characteristics, and since the same voltage is applied to the gates, currents flow evenly through the respective transistors. The current flowing through the EL element is only the current flowing through the transistor 17a, and is half the current flowing through the source signal line 11.

When the channel width and the channel length of the transistor 17i are changed, the characteristics of the current between the gate voltage and the source / drain are changed. If the channel width is widened or the channel length is shortened, the current easily flows in the transistor 17i. , EL for the current flowing in the source signal line 11
The ratio of the current flowing through the element 16 can be reduced. As an example, FIG. 21 shows the case where the channel width is 9 times that of the transistor 17a, the channel width is tripled, and the channel length is 1/3. In both cases, E with respect to the current flowing through the source signal line 11
The current flowing through the L element 16 becomes 1/10.

Time t required to change the current value of the source signal line
Is the magnitude of the stray capacitance, C is the voltage of the source signal line,
If the current flowing through the source signal line is I, then t = C · V /
Since it is I, the fact that the current value can be increased ten times means that the time required for changing the current value can be shortened to nearly one-tenth. Thus, when the number of scanning lines is 220, it is possible to drive at a frame frequency of 60 Hz.

(Embodiment 10) In Embodiment 9, the time until the current changes to a predetermined current is shortened by increasing the value of the current passed through the source signal line 10 times. Although it is 0, in actuality, about several tens of nA flows due to the leak current of the transistor and the leak of the transistor forming the current source. However, in order to prevent the black floating, it is better that the current value is smaller, and by increasing the current value. The method of increasing the changing speed tends to cause a decrease in contrast.

Therefore, as shown in FIG. 22, the source signal line 11 is provided with a power supply switching means 19 so that the output of the current source 10 or the voltage source 18 is applied to the source signal line. A source signal line voltage is applied so that the flowing current is about several tens nA.
The power supply switching means 19 has 1 or more and 5 at the beginning of the horizontal scanning period.
The voltage source 18 is selected for about μ seconds, and the current source 10 is used for the remaining period.
Select. As shown in FIG. 3A, the source signal line 1
1 has a discharge voltage application period and a video signal current application period, and a voltage value representing that the source signal line represents black is always applied at the beginning of the horizontal scanning period. By this operation, it is possible to eliminate the phenomenon of slight lighting when displaying black.

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
The gradation that takes the most time to change is the gradation one level above black. This is because the time t required for current change is 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 constant regardless of gradation and is determined by the size of the display device. This is because, when a P-channel transistor is used, V increases as the black signal increases, and I decreases as the black signal increases, so that it takes time to change the current as the gradation approaches black. Here, for the sake of explanation, it is assumed that the gradation indicating black is gradation 0, the gradation having the next highest brightness is gradation 1, and the gradation value is increased by 1 as the brightness increases.

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

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

FIG. 23 shows the pixel configuration shown in FIG. 2 (a)
And (b) in the case of the pixel configuration shown in FIG. 22 (a combination of transistors 17a and 17i such that the current value flowing through the source signal line 11 is 10 times the current value flowing through the EL element 16) is horizontally scanned. When the period is set to 75 μs and gradation 1 is displayed and the capacitance of the source signal line is changed,
FIG. 6 is a diagram showing how much a current flowing through an EL element 16 can flow with respect to a predetermined current. A value of 100% indicates that the current value could be changed up to a predetermined current value, and a value of less than 100% indicates that the time required for the change was slower than 75 μsec, indicating that predetermined gradation display was not possible.

Since a deviation of about 10% with respect to the predetermined current value (luminance) cannot be visually confirmed, it is practically 90% or more 10
It may be 0% or less. The allowable source signal line capacitance under this condition is only 2 pF or less in the pixel configuration shown in FIG. 2, but 27 pF or less is possible in the pixel configuration shown in FIG. In the case of a display device of about 2 type, the capacitance parasitic on the source signal line is 15 to 2 including the output stage of the driver IC.
It is about 0 pF, and by using the tenth embodiment in which the current value of the source signal line is multiplied by 10, the frame frequency of 65
It is possible to drive at less than Hz, and display with less flicker is possible. It can also be applied to televisions and the like.

The parasitic capacitance of the source signal line 11 changes depending on the size of the display device. 50pF if type 15
It will be about. In this case, even if the source signal line current is written 10 times as large as the EL current, only about 70% can be written. Therefore, when the number of scanning lines is the same, for example, by increasing the channel size ratio to 15 times, 6
It was found that 0 Hz drive is possible.

Thus, according to the tenth aspect of the present invention,
Depending on the size of the display device, drive transistors 17a and 1
By changing the size of the 7i channel region, it is possible to write a predetermined current value within a predetermined horizontal scanning period.

(Embodiment 11) In the tenth embodiment, when the horizontal scanning period is a period in which a black signal voltage application period and a current value that is several times the predetermined current value flow, the capacitance of the source signal line is It was possible to drive at 60 Hz even at 20 pF.

Due to variations in the gate threshold voltage of the transistors 17a and 17i in FIG. 22 within the panel, the value of the current flowing through the EL element 16 with respect to the application of the black voltage is different, and when the threshold voltage is low, a large amount of current flows so that black floats. The problem occurs.

In order to solve this problem, the variation in the gate threshold voltage of the transistor in the panel is taken into consideration, and the black voltage is increased so that the brightness which produces black display is obtained even if the transistor through which the most current flows is used. In this case, the amount of change in the current value from the gradation 0 to the gradation 1 is large in the pixel using the transistor through which the largest amount of current flows, and the time required for the change to the predetermined current value is long. Become. As a result, for example, when the black voltage is increased by 0.5 V, the source signal line capacitance value that is allowed to be written in the horizontal scanning period of 75 μs with respect to the change from the gradation 0 to the gradation 1 is about 2 pF. Become.

As in the tenth embodiment, the transistor 1
Although the ratio of the sizes of the channel regions of 7a and 17i may be changed, in the eleventh embodiment, it is possible to increase the allowable capacitance value by increasing the current value of the gradation other than gradation 0. Thought. A current source for supplying a current value corresponding to each gradation is prepared, and a plurality of (α) current sources for supplying a larger current are prepared. FIG. 22 shows the case where α is 4, and for gradation 0, the current source 0 is used as before, and gradation 1
, The current source 5 is used instead of the current source 1. Gradation 2
Current source 6, and the current source (i +
4) is used.

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. 24 shows whether the current can be written to a predetermined current value in 75 μs with respect to the source signal line capacitance when the current source 1 is used for the gradation 1 (a) and when the current source 5 is used (b). In the tenth embodiment, gradation expression was not possible unless the value was 2 pF or less, but in the eleventh embodiment, the gradation expression was 2
It is possible to write up to 0 pF or less.

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

The number of current sources is not necessarily the number of gradations + α, and α current sources not required for gradation display may be omitted. In the eleventh embodiment, the four power sources of current source 1 to current source 4 are not necessary configuration requirements.

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

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

Assuming that the current value is Ik at gradation k, the current value is IL at gradation L, and IL = Ik × 2, two current sources having conventional output current values of Ik and IL are provided. is necessary.

When the transistor 17 is formed for one pixel as shown in FIG. 18, when the ratio of the channel region sizes of the transistors 17a and 17i is changed, the EL element is applied to the same current to the source signal line 11. The value of the current flowing through 16 changes, and the relationship shown in FIG. 21 is obtained.

Here, paying attention to the transistor 17j, assuming that the transistors 17a and 17i have the same channel size, it is always in a non-conducting state in the case of the gradation L, and the gate signal line (1) in the case of the gradation k. ) 12, the current flowing through the source signal line 11 flows through the EL element 16 as it is, since it is the same as when there is no 17i transistor at the time of gradation L display. At this time, the source signal line current value is IL.

On the other hand, when displaying the gradation k, the source signal line 11
The current flowing through the EL element 16 is half the current flowing through the EL element 16. Therefore, a current amount of Ik × 2 is required for the source signal line in order to pass the necessary current Ik through the EL element 16.

By using this method, since IL = Ik × 2, the same current value IL can be used for gradation k and gradation L, so that the number of necessary current sources can be reduced. is there. By operating the transistor 17j from gradation 0 to P and keeping it non-conductive at gradation P + 1 or higher, the current flowing through the source signal line 11 for each gradation is represented 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, 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. 25), the influence of waveform rounding due to the stray capacitance parasitic on the source signal line 11 is reduced. Therefore, writing can be performed in a shorter horizontal scanning period.

As compared with the case of performing the writing by multiplying the source signal line current several times in all the gray scales as in the tenth embodiment, in the gray scales in which the writing can be sufficiently performed as compared with the low luminance region. , EL of the current flowing in the source signal line
Even if the magnification with respect to the current is reduced, if the current value is larger than that at the time of displaying the gradation 1, the writing time will not be insufficient and the writing can be performed in the same horizontal scanning period. 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 transistors 17a and 17
Although the description has been given by taking the example in which the channel value of i is the same and the current value is doubled, the magnification is adjusted to 3 times, 10 times, or the like according to the relationship between the gradation and the current value flowing in the source signal line, and FIG. The same effect can be obtained by changing so that two gradations are included for the same source current value as indicated by solid lines 252 and 254. It is desirable to increase the magnification as the slope of the dotted line shown in the conventional example increases. When the inclination is large, the gradation from 0 to P is multiplied by 4 and the gradation from P + 1 to Q is increased.
It is also possible to use a plurality of magnifications in combination of two or more, such as up to 2 times and up to 1 time at gradation Q + 1 or more.

In order to perform such an operation, the conventional method shown in FIG.
It is necessary to make at least two different operations for the eight transistors 17j depending on the input gradation. Therefore, as shown in FIG. 26, a magnification changing means 343 is provided, the output of the magnification changing means 343 is ANDed with the gate signal line (1) 345, and the result is input to the gate of the transistor 17j. In FIG. 26,
Since the transistor 17j is a P-channel, the magnification changing unit 343 outputs a high level below the gradation P and outputs a low level above the gradation P + 1 to obtain the gradation P +.
When it is 1 or more, the transistor 17j is always in a non-conducting state, and the source signal line current = EL element current, and when the gradation is P or less, a current value having a different magnification is supplied depending on the ratio of the channel sizes of the transistors 17j and 17a. It is possible.

The current flowing through the source signal line 11 is selected from the plurality of current sources 344 by the current switching means 342 according to the input video signal 341, and when the power source switching means 19 selects the current source, a predetermined current is supplied. Let it flow. In FIG. 26, the voltage source 18 is used in order to prevent black floating when displaying gradation 0. However, the effect of the present invention of reducing the number of current sources 344 is affected regardless of the presence of the voltage source 18. You don't have to, because you don't.

(Embodiment 13) In a display element which performs black display when the current value is the lowest, a voltage representing black is applied to the source signal line at the beginning of the horizontal scanning period, and black is generated due to an increase in luminance during black display. In order to prevent floating, it is possible to determine whether or not writing is insufficient by checking whether the black state can be changed to a predetermined current value within the horizontal scanning period.

FIG. 27 shows the relationship between the current flowing in the source signal line and the time required to change to the current value when the source signal line is in the black signal state and the source signal line has a certain capacitance. Is. The smaller the source current value,
It takes a long time to change. This is because when the time required for the change is t, the source signal line capacitance is C, the source current value is I, and the source signal voltage is V, t = CV / I. is there. Further, when the drive transistor 17a is a P-channel transistor as shown in FIG. 2, the source signal voltage decreases as the source signal current increases. The rate of decrease is determined by the relationship between the gate voltage of the transistor 17a and the source-drain current. As a result, when the current I decreases, the voltage V
Becomes larger, the time required to change to a predetermined current becomes rapidly longer than the rate of current decrease. for that reason,
A curve as shown in FIG. 27 will be drawn.

FIG. 28 shows the change over time in the ratio with respect to the predetermined current when three different currents are passed through the source signal line. Here, in the three currents I1, I2, and I3, I1
If there is a relationship of <I2 <I3, after the time t1, the I3 changes to 95%, the I2 changes to 88%, and the I1 changes to about 80%.

FIG. 29 shows how much of the predetermined current value for each source current value input can be changed after 65 μs (source signal line capacitance is 40 pF). It can be seen that the write rate increases exponentially.

In such a state, when the EL current (output current) is measured with one horizontal scanning period of 65 μsec,
As shown in FIG. 30, for the source signal line current (input current),
There is no proportional relationship, and the lower the current, the more the output current becomes smaller than the predetermined value, and when the gradation is set at equal intervals with respect to the input current, the obtained brightness (proportional to the output current) is gamma-corrected. As shown, the gradation near black changes gently, and the amount of change increases as it becomes white.

As described above, in all the gradations, it is not necessary to prepare the writing time so as to write at the predetermined brightness, and when the current values of the respective gradations are at equal intervals, the brightness becomes gentle as shown in FIG. Since it increases exponentially, when all gradations are displayed by a lamp, the gamma curve in which the input signal intensity versus the brightness is proportional to the 2.2 power is approximated, and the display quality can be improved.

FIG. 1 shows the structure of a gate driver provided with a function for changing the write time.
A gate enable pulse generator 412 is provided, and when the enable pulse is output, the transistors 17c and 17g (transistors on the path of the source signal line and the driving transistor) of the gate signal line (1) shown in FIG. In the non-conducting state, the writing time can be shortened. Other than this method, the frame frequency may be changed, or a blanking period may be provided for each frame to adjust the writing time.

FIG. 10 shows a television using the embodiment of the present invention. The adjusting unit 42 has a function of adjusting the gamma characteristic by changing the gate enable pulse generator 412 of FIG. 1 and changing the enable pulse width.

Further, the external switching means 413 may be provided to change the pulse width of the gate enable pulse by switching to provide a gamma curve adjusting function.

(Embodiment 14) When the enable pulse width is increased in FIG. 1, the writing time is shortened and the current value to be written becomes smaller than the predetermined current value. For example, in FIG. 28, assuming that the current value I3 is passed through the source signal line and the conduction period of the gate signal line (1) is t2, it becomes 50% with respect to the predetermined current value, and the brightness is reduced by half. vice versa,
By supplying a current value larger than a predetermined luminance to the source signal line in advance, and turning off the transistor connected to the source signal line at the time when the source signal line reaches the predetermined luminance from the black state, the display element is turned off. It was possible to increase the source signal line current with respect to the current flowing in, and to shorten the time required for the change.

This method also has an advantage that the permissible value of the variation in the current source output corresponding to each gradation can be increased because the difference in the current value between the gradations becomes large.

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 the display with less flicker can be performed.

FIG. 8 shows a display device 182 using at least one of the embodiments of the present invention, a demodulation device, an antenna 181, and a button 184 attached thereto, and a housing 183 to form a form information terminal. .

FIG. 10 shows a display device 41 using at least one of the embodiments of the present invention, to which a video signal input 46 and a video signal processing circuit 44 are attached, and a casing 47 is used as a television. .

In addition, in the embodiment of the present invention, FIG.
The source driver 71 and the gate driver 70 of 9 may be formed on the glass substrate of the display device using low temperature polysilicon. Alternatively, the source driver 71 and the gate driver 70 may be formed as a semiconductor circuit and combined with the display panel. Alternatively, one driver may be formed of low-temperature polysilicon on a glass substrate of a display device, the other driver may be formed as a semiconductor circuit, and combined with a display panel.

FIG. 18 shows a circuit example using at least two drive transistors as a method of changing the ratio of the current value flowing in the source signal line and the current value flowing in the EL element in the embodiment of the present invention. But transistor 1
The arrangement location of 7j may be such that no current flows when one of the two transistors 17a and 17i has the transistor 17d conducting, for example, as shown in FIGS.
2 or the same effect can be obtained by arranging as shown in FIG. In addition, regardless of these figures, the insertion position of the transistor 17j may be arbitrary as long as it is an offensive that achieves the above purpose.

In this example, a P-channel transistor has been described as an example of the switching element, but an N-channel transistor or a combination thereof can be similarly used. For example, in the case of the pixel configuration shown in FIG. 2, when an N-channel transistor is used for the voltage value applied to the gate signal line (1) 12 and the gate signal line (2) 13, the P-channel transistor is considered at the logic level. It is only necessary to input an inverted signal of the signal of (1), reverse the direction of current flow in the current source 10, and compare the voltage supplied from the EL power supply line 15 with the terminal voltage opposite to that of the power supply switching means 19 of the current source 10. It can be realized similarly by lowering it. In other words, the purpose of accelerating the charging and discharging of the electric charge 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. 34 shows an example of a structure for changing the current ratio in the case of an N-channel transistor.

Further, although the pixel structure of the dynamic current copier has been described, the present invention can be similarly applied to the pixel of the current mirror structure as shown in FIG. Even in the case of the current mirror configuration,
When a row is selected, the transistor 177d is turned on, the transistor 177b is turned off, and the current source 170 controls the EL power supply line 175 and the transistors 177a and 177.
d. Since the operation of flowing a current according to the gradation through the source signal line 171, when the source signal line 171 has a stray capacitance, when the current value of the current source 170 changes,
It is the same problem that it is difficult to charge and discharge the charge accumulated in the stray capacitance in the low current region. Therefore, by implementing the present invention, the effect of increasing the writing speed can be obtained.

To change the current flowing in the source signal line and the current flowing in the EL element, as shown in FIG. 36, transistors 177m and 177n are added and the gate signal line (1) 172 is connected to the gate electrode of 177n. This can be achieved by connecting and changing the channel size of the transistors 177m and 177a.

Further, by controlling the gate terminal of the transistor 177n independently instead of the gate signal line (1) 172, for example, it is always non-conductive or performs the same operation as the gate signal line (1) 172 depending on the gradation. It is possible to change the ratio between the source signal line current and the current flowing through the EL element for each display gray level by selecting any one of them.

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

Transistors 17b, 17c, 17d, 17j, 1 used as switching elements in the present invention.
Although 77b, 177d, and 177n are described using thin film transistors as an example, similar effects can be obtained by using not only thin film transistors but also varistor, thyristor, ring diode, thin film diode (TFD, MIM), and the like.

Although the EL element has been described as the 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 liquid crystal. In FIG. 2, the EL element 16 may be a liquid crystal layer.

Similarly, as a pixel configuration for driving the EL element by a current value, a configuration as shown in FIG. 37 (a) can be considered. The difference from FIG. 18 is that the switching transistor is connected to the power supply line instead of the EL element.

The operation of the pixel structure shown in FIG. 37A will be described below.

The gate signal line (1) 391 makes the transistors 17c, 17b and 17j conductive. Further, the gate signal line (2) 392 makes the transistor 17d non-conductive. The storage capacitor 14 has a transistor 17
The corresponding voltage is stored so that the sum of the currents flowing in a and 17i becomes the same value as the source signal line current value. The ratio of the current values flowing in 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) 391 and (2) 392, the transistors 17c and 17 are formed.
b and 17j are turned off, transistor 17d is turned on, and a current is supplied from the EL power source line 393 to the transistor 17
a and EL 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.

As a result, similarly to the configuration of FIG. 18, the ratio of the current value to the source signal line and the current value flowing in the EL element is changed by changing the ratio of the channel sizes of at least two drive transistors 17a and 17i. As compared with the conventional configuration, the amount of current flowing through the source signal line is increased, and the effect of reducing the rounding of the waveform due to the stray capacitance 20 can be obtained as in the configuration of FIG.

By implementing the present invention, the value of the current flowing through the source signal line of each gradation is multiplied by several times (about 5 to 10 times in the case of the 2 type panel), so that the step size of the current step of each gradation is 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.

There is also an advantage that the current can be easily adjusted.

Power source switching means 1 is connected to the source signal line 171.
It is possible to implement by providing 79 and switching between the current source 170 and the voltage source 178.

[0149]

As described above, according to the present invention, the source signal line has the switching means, the voltage application period and the current application period are provided within one horizontal scanning period, and the floating capacitance existing in the source signal line is accumulated. By quickly changing the generated charge to the amount of charge corresponding to a predetermined gradation, one horizontal scanning period is shortened,
Flickerless drive can be realized.

In addition, a period in which a current value of 3 times or more and 10 times or less of the current value corresponding to the display gray level is provided in one horizontal scanning period is provided, and the charge accumulated in the stray capacitance existing in the source signal line is provided. The time required to change
By making the value of the current flowing through the source signal line about 10 times the current value, one horizontal scanning period can be shortened and flickerless driving can be realized. Generally, if the current value is made larger than the value obtained by dividing the product of the source capacitance value and the source voltage by one horizontal operation period, the current value corresponding to each gradation can be written within the horizontal operation period.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a gate driver section in a thirteenth embodiment of the present invention.

FIG. 2 is a diagram showing a pixel, a source signal line, and a power supply according to the first embodiment of the present invention.

FIG. 3 is a diagram showing timings of a voltage application period and a current application period within a horizontal scanning period.

FIG. 4 is a diagram showing voltage application period dependence of output current for white display and black display.

FIG. 5 is a diagram showing a relationship between a source driver unit, a power supply unit, and a source signal line in the second embodiment of the invention.

FIG. 6 is a diagram showing an equivalent circuit at the time of writing a current from a source signal line to a pixel, current-voltage characteristics of a transistor in the pixel, and a waveform of the source signal line.

FIG. 7 is a diagram showing a configuration of a source driver section in the third and sixth embodiments of the present invention.

FIG. 8 is a diagram of a personal digital assistant incorporating a display device according to an embodiment of the present invention.

FIG. 9 is a block diagram of a controller and a source driver according to a fourth embodiment of the present invention.

FIG. 10 is a diagram showing a television incorporating a display device according to an embodiment of the present invention.

FIG. 11 is a block diagram for generating a voltage corresponding to a source signal line current according to a fifth embodiment of the present invention.

FIG. 12 is a diagram showing a waveform of a current flowing through a source signal line according to the sixth embodiment of the present invention.

FIG. 13 is a diagram showing a waveform of a current flowing through a source signal line in a sixth embodiment of the present invention in comparison with a conventional example at the time of rising and falling.

FIG. 14 is a diagram showing a block diagram of a source driver and a configuration of a pixel portion in a seventh embodiment of the present invention.

FIG. 15 is a timing chart in the seventh embodiment of the invention.

FIG. 16 is a diagram showing a source signal line output using a digital-analog converter according to an eighth embodiment of the present invention.

FIG. 17 is a diagram showing a change in reference voltage within a horizontal scanning period according to the eighth embodiment of the present invention.

FIG. 18 is a diagram showing a circuit for one pixel according to a ninth embodiment of the invention.

FIG. 19 is a diagram showing a relationship between a source signal line current and a current flowing through an EL element according to a ninth embodiment of the present invention.

20 is a diagram showing a conduction state of each transistor when a current flows through a source signal line and when a current flows through an EL element in the circuit configuration shown in FIG.

FIG. 21 is a diagram showing changes in the current value of the current source and the current value flowing in the EL element due to changes in the channel size of the transistor in FIG. 18 in the ninth embodiment of the present invention.

FIG. 22 is a diagram showing a circuit for one pixel in the tenth embodiment of the invention.

FIG. 23 is a diagram showing how much data can be written to a predetermined current value by the source signal line capacitance when the horizontal scanning period is 75 μsec.

FIG. 24 is a diagram showing to what extent writing can be performed for a predetermined current value due to a change in source signal line capacitance when the horizontal scanning period is 75 μs in the eleventh embodiment of the present invention.

FIG. 25 is a diagram showing a relationship between gradation and current flowing through a source signal line according to the twelfth embodiment of the present invention.

FIG. 26 is a diagram showing a circuit configuration for changing a ratio of a current value flowing in a source signal line and a current value flowing in an EL element according to a gradation.

FIG. 27 is a diagram showing a relationship between a source signal line current and a time required to reach the current value with respect to a certain source capacitance value.

FIG. 28 is a diagram showing that the time required to change to a predetermined current value is different for three different current values.

FIG. 29: When the source signal line capacitance is 40 pF, what percentage of each source signal current value up to a predetermined current value after 65 μs
Showing how much has changed

FIG. 30 is a diagram showing the relationship between the source signal input current and the current value output to the EL element when written in the ratio shown in FIG. 29.

FIG. 31 is a diagram showing a circuit configuration for changing a ratio of a current value flowing in a source signal line and a current value flowing in an EL element.

FIG. 32 is a diagram showing a circuit configuration for changing a ratio of a current value flowing in a source signal line and a current value flowing in an EL element.

FIG. 33 is a diagram showing a circuit configuration for changing the ratio of the current value flowing in the source signal line and the current value flowing in the EL element.

FIG. 34 is a diagram showing a circuit configuration for changing a ratio between a current value flowing in a source signal line and a current value flowing in an EL element when an N-channel transistor is used.

FIG. 35 is a diagram showing an embodiment of the present invention when a pixel has a current mirror configuration.

FIG. 36 is a diagram in which a current value flowing in a source signal line and a current value flowing in an EL element can be made different in a current mirror configuration.

FIG. 37 shows a circuit configuration for changing the ratio of the value of the current flowing through the source signal line and the value of the current flowing through the EL element when the transistor is used to change the EL current line, not the EL element, into the conductive / non-conductive state. Figure

FIG. 38 is a diagram showing allocation of current sources to gradations according to the eleventh embodiment of the present invention.

FIG. 39 is a diagram showing a configuration of a conventional display device.

FIG. 40 is a diagram showing the relationship between the input current and the output current when the scanning time of the gate signal line is changed.

FIG. 41 is a diagram showing the difference between the voltage-luminance characteristic and the current density-luminance characteristic of the organic light emitting element due to the difference in display color.

[Explanation of symbols]

10 current source 11 Source signal line 12 Gate signal line (1) 13 Gate signal line (2) 14 Storage capacity 15 EL power line 16 EL element 17 transistors 18 Voltage source 19 Power supply switching means 20 stray capacitance 410 OR 411 output buffer 412 Gate enable pulse generator 413 External switching means

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Claims (5)

[Claims] 1. An active matrix display device comprising: a current source, a voltage source, a switching means for selecting one of the current source and the voltage source output and outputting the source signal line, and a power source. Two driving transistors that control the supplied current, a signal line connecting transistor that forms a current path from the source signal line to the driving transistor, and a path that supplies the current of the driving transistor to the display element are formed. An EL connection transistor, wherein the switching means is provided during a period in which all the signal line connection transistors connected to the source signal line are in a non-conduction state or a period in which at least one signal line connection transistor is in conduction. In the first period, the voltage source is selected, in the other periods, the current source is selected, and the signal line connection is selected. Transistor a period of conductive state, an active matrix display device characterized by being shorter than the required period for current of the source signal line becomes a predetermined value. 2. An active matrix type display device, wherein an external switching means is used to change a horizontal scanning period or a time for which a current flowing in a source signal line is taken in, whereby an increase rate of luminance for each gradation can be adjusted. An active matrix type display device characterized in that 3. An active current flowing through the driving transistor to the source signal line through the driving transistor during the first period, and a current flowing through the driving transistor through the driving transistor during the second period. In the driving method of the matrix type display device,
The method of driving an active matrix display device, wherein the first period is shorter than a period required for the source signal line to change to a predetermined current value. 4. An active current flowing through the source signal line through the driving transistor in the first period and a current flowing through the driving transistor in the second period in the second period with respect to the driving transistor. In the method for driving a matrix display device, a voltage indicating a display minimum luminance is applied to the source signal line before the first period or at the beginning of the first period, and the source signal is applied in the first period. A method for driving an active matrix display device, wherein the line is shorter than a period required for changing to a predetermined current value. 5. A television set comprising the active matrix display device according to claim 2, a video signal input section, a video signal processing circuit, and an adjusting means.