JP2000056727A - Gradation driving device for display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize gradation display which does not require high-speed operation and high accuracy by making a signal driver simultaneously perform the gradation display by the current or voltage output control at plural values and the control of plural output time widths. SOLUTION: The signal driver simultaneously performs the gradation display by the current or voltage output control at plural values and the control of plural output time widths. In this gradation driving device, a shift register 20 decides timing for sampling a data signal from a clock and a start signal from a controller. A latch 21 latches plural signal data lines showing gradation in accordance with the timing of the output of the shift register 20 so as to temporarily store data. The latched data is decoded to two data in a time direction and a current output direction by a decoder 30. The output data from the decoder 30, that means, a current command value is one system and it is inputted in a D/A converter 21, D/A converted and inputted in a constant- current circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an LED and an organic EL.
For display devices that can drive halftone display by modulating the drive current or drive voltage and emit light instantaneously, such as light-emitting devices, discharge tubes, and electron-emitting devices, they do not require high-speed and high-precision circuits. The present invention realizes a driving device capable of performing various gray scale displays.

[0002]

2. Description of the Related Art FIG. 14 shows a configuration of a display device using a conventional LED or organic EL. In FIG. 14, reference numeral 10 denotes a matrix type display panel in which a plurality of signal lines and a plurality of scanning lines are combined, 11 denotes a signal driver for driving the signal lines, 12 denotes a scanning driver for driving the scanning lines, and 13 denotes a scanning driver for driving the scanning lines. It is a controller that controls the signal driver 11 and the scanning driver 12. When performing gradation driving, data corresponding to the image signal is input to the signal driver 11, and a gradation control function is provided inside the signal driver 11.

Conventionally, two methods have been used for this gradation control method. One of them is pulse width modulation (hereinafter referred to as PWM).
Will be described. FIG. 15 shows a configuration example of a signal driver according to this method.

In FIG. 15, reference numeral 20 denotes a shift register (hereinafter abbreviated as "SR") which determines a timing for sampling a data signal from a clock and a start signal from a controller. Reference numeral 21 denotes a latch which connects a plurality of signal data lines indicating gradations to S.S. R. And latches temporary data according to the output timing. A decoder 22 determines a PWM output timing based on the data stored in the latch 21, and outputs a pulse width modulated output last by a PWM circuit 23 to a signal line of a display panel. FIG. 16 shows an example of the output. The gray scale display is performed by controlling the time width from 100% to the LSB output of the minimum unit in accordance with the gray scale at which a constant output is desired to be displayed every one horizontal period in synchronization with the driving of the scanning line.

FIG. 17 shows a configuration example of another signal driver of the output amplitude modulation system, which will be described with reference to the drawing. FIG.
Those having the same functions as those described above are denoted by the same reference numerals and description thereof will be omitted. 2
Reference numeral 5 denotes a D / A circuit for converting data stored in the latch 21 into an analog current.
It is input to the reference current source of the current mirror constituted by 6, 27. By the function of the current mirror, this D / A25
Current of the same value as the output current of
The gradation display is performed by the current amplitude modulation according to the data signal. FIG. 18 shows an example of the output. 100% constant current over the effective scanning period within one horizontal period
To the minimum unit LSB to display gradation.

The above description has been made with reference to an example of the configuration of the current drive which is optimal for the LED and the organic EL. However, a device suitable for constant voltage drive such as a discharge tube can be dealt with by configuring the output unit with an amplifier. is there.

[0007]

Among the conventional examples described above, the PWM has a drawback that as the number of gray scale displays increases, the LSB of the minimum unit becomes narrower and a high-speed operation is required as a signal driver. Was. For example, considering an 8-bit, 256-gradation required for a natural image on a 640 × 480 display panel for a computer, a frame unit is 6 bits.
Assuming 0 frames / sec, the LSB width is 0.12 μs
And extremely high speed operation is required as a signal driver. In addition, in a display element such as an organic EL, in which not only a diode but also a capacitance is added in parallel as an equivalent circuit in a pixel unit, even if a signal driver operates at high speed, current escapes to the parallel capacitance, and light emission does not occur in an LSB unit. The phenomenon that gradation expression is impaired has occurred.

The other output amplitude modulation method has no problem of high-speed operation, but has a problem that the output deviation of the signal driver is severe when the number of gradations is large. For example, 10
A current driver that outputs 10 mA at 0% output, the LSB output at the time of 8-bit 256 gradation is 40 μA, and it is extremely severe industrially to guarantee this accuracy uniformly over all lines. More specifically, the accuracy of the D / A 25 and the current mirror 26 in FIG. 8 is important. If these are not integrated, the display panel cannot be commercialized. However, a monolithic IC integrates a large number of analog circuits with an accuracy of 1/256 or less. It was extremely difficult to do.

Further, in the organic EL panel, there is a problem that a gradation shift occurs when the rectification ratio of the element is poor, as a phenomenon when the output amplitude modulation control is performed. This will be described with reference to FIG. First, in driving the organic EL, reverse bias is applied to elements other than the selected line to prevent crosstalk (L1, L3). At this time, a certain element (E2
When the output current value is controlled in order to emit light at low luminance in 2), the voltage applied to this element is necessarily small (+1 V). At this time, in the other elements E12 and E32 in the same column that are reverse-biased, if the rectification ratio of the element is poor, a reverse current flows there and a phenomenon occurs in which the current flows toward the light emitting element.

For this reason, a phenomenon that the gradation is shifted occurs. As described above, when the output amplitude modulation is performed by the organic EL element, an improvement in the rectification ratio of the element itself is required. For example, 6
In the case of displaying 256 gradations on a 40 × 480 display panel, a rectification ratio of 2.5 × 10 ⁵ or more is required if the permissible error of the gradation shift is １ ／ or less of one gradation.

Although the rectification ratio of the element depends on the material and the configuration, it becomes more difficult to realize as the gradation becomes higher. Like this
Driving the organic EL element becomes even more difficult.

An example of a conventional application is disclosed in JP-A-9-101.
No. 759. This is a driving method in which a plurality of different output power supplies are prepared, and the respective power supplies are switched and added based on information that is present at certain time intervals.

In this application example, when driving a plurality of elements such as a panel, a plurality of drive circuits are required. At this time, in the voltage-controlled drive circuit, a constant voltage can be supplied to the plurality of drive circuits in the form of a common bus as a power supply, and the power supply outputs can be added by the individual drive circuits. However, when adding and outputting current like an organic EL element,
A constant current cannot be supplied in a common bus format. In other words, a constant current source of a certain value is used in common for a plurality of elements, and the output current amount of the power supply changes depending on the switching state, making constant current operation extremely difficult. In this case, a plurality of current sources, a plurality of switches, and a set of adders are required for each of the plurality of drive circuits, and there are problems such as the number of components and the complexity of the configuration.

[0014]

SUMMARY OF THE INVENTION The present invention provides a display panel capable of displaying a plurality of gradations, a signal driver for driving a plurality of signal lines of the display panel, and a plurality of scanning lines for the display panel. And a controller that controls the signal driver and the scanning driver, and the signal driver simultaneously performs a plurality of values of current or voltage output control and a plurality of output time widths to simultaneously perform gradation display. It enables high-speed operation and gradation display that does not require high precision.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) The principle of operation of the present invention is shown in FIG. FIG. 1 is a diagram showing the principle of operation, in which 4 bits and 16 gradations are divided in the time direction and 4 bits and 16 gradations are divided in the current (or voltage) output direction. Is what you do. Thereby, the LS in the time direction
B is about 2 μs, and the operating frequency is greatly reduced.
If the current output direction is 100 mA at 10 mA, then LS
B is about 0.6 mA, and the accuracy is reduced to about 1/16 of the whole. This makes it possible to industrially make a monolithic IC.

As can be seen from the time direction of FIG. 1, in this example, normal 4-bit coding, 0, 1, 2,.
0, 1, 1, 2, 4, 8 instead of 4, 8.
The reason for this is that if the coding is performed in a normal manner in both the time and current directions, the width starts from 0, so that both are in units of 15 LSB, thereby preventing the display of 15 × 15 = 225 gradations and 256 gradations from being disabled. .

There is a problem in that a combination which cannot be displayed particularly at a low value appears and a gradation jump occurs. For example, 3
After 0, only 32 can be displayed, and 31 cannot be displayed.
In the example of the present invention, one LSB unit is added in the time direction, and 1
It is intended to display in a combination of 6 × 15 = 240 gradations. In this case, the gradation does not reach the 256 gradations, but the gradation jump of a low value can be prevented, so that there is almost no practical problem. Of course, 1LSB may be increased in the current output direction. Further, both the output and the LSB unit are added, and 16 × 16 = 256.
Alternatively, a method of completely displaying the information may be adopted.

Further, there are various methods of dividing in a time direction and an amplitude value (current or voltage) direction. There are various methods depending on a decoding method, and the method may be selected according to the characteristics of the light emitting element. For example, the division may be performed as shown in FIGS.

FIG. 2 shows a method in which the amplitude value direction takes values at equal intervals, and the time direction takes a value proportional to a power of two, and a method of realizing a gradation by a combination of the two.

FIG. 3 shows a method in which the amplitude value direction takes a value proportional to a power of two, and the time direction takes values at equal intervals, and a gray scale is realized by a combination of the two.

FIG. 4 shows a method in which the amplitude direction also takes values at equal intervals, and the time direction also takes values at equal intervals.

The number of divisions shown is not limited to this, but may be any number. The output time need not be continuous, and may be output in a discontinuous form. Furthermore, L
The control may be performed in a form in which another SB unit is added.

(Second Embodiment) Next, an example of the configuration is shown in FIG. In FIG. 5, reference numeral 20 denotes a shift register (abbreviated as SR) which determines a timing for sampling a data signal from a clock and a start signal from a controller. Reference numeral 21 denotes a latch which connects a plurality of signal data lines indicating gradations to S.S. R. And latches temporary data according to the output timing. The latched data is decoded by the decoder 30 into two data in the time direction and the current output direction. Specifically, the output current value is changed according to the progress of the time axis within the effective scanning period. Therefore, the output data from the decoder, that is, the current command value is one system and is input to the D / A converter 31.

The D / A converted current command value is input to a constant current circuit composed of an operational amplifier 34, Tr33 and a current setting resistor R32. This constant current circuit is of a general feedback type, and controls the Tr 33 so that the difference between the power supply and the output voltage of the D / A converter 31 and the current determined by the setting resistor R32 become constant. With such a configuration, a constant current value based on a command from the decoder 30 is output. Therefore, the elements of the panel can be driven with a constant current value determined by the current command value.

Here, the decoder 30 is configured to use an FPGA (Fiel) so as to flexibly distribute the current value and the time width.
d Programmable Gate Array) may be used. This type of IC implements functions by executing a program on software and downloading the program to the IC. That is, the distribution of the current value and the time width can be programmed according to the characteristics of the panel to be connected, and the gray scale can be output with high accuracy.

Next, a distribution method in the decoder 30 will be described with reference to FIGS.

The distribution of the current value and the time width can be freely set by the decoder 30, but as an example, distribution of equal division as shown in FIG. 4 is considered. The input data is divided into upper n bits and lower m bits to express a gray scale.

For example, a 6-bit gray scale (64 gray scales) is expressed, a current value of 2 bits (4 gray scales) and a time width of 4 bits (16 gray scales).
(Gray scale). The decoding algorithm is as follows.

First, the upper 2 bits of the input data are latched as current value divided data [A], and the lower 4 bits are latched as time width divided data [B]. Next, over 16 sections,
The current value corresponding to the numerical value of the data [A] is output. In addition, 1 is added to the current value output for an interval corresponding to the numerical value of the data [B].

A specific description will be given with reference to FIGS. For example, assume that the input data is 38/64 gradation. In binary notation, it is [100110]. At this time, the divided current value data [A] = 2 [10] and the divided pulse width data [B] = 6 [110]. At this time, the output waveform is 16
Output two times the numerical value of data [A] over the section. In addition, a value 3 obtained by adding 1 to the output is output only for the section corresponding to the numerical value 6 of the data [B].

As a result, the current value output has a waveform as shown in FIG. 7, and the concept is to realize the gradation by stacking the minimum unit blocks of the current value output.

As described above, since the current output blocks are stacked, the distribution and the number of divisions can be arbitrarily changed. In other words, when changing the current into 16 and the time width into four, it is only necessary to change the number of bits of the data to be latched.
Further, when driving an organic EL panel, there is a problem that a gradation shift occurs in a panel having a low rectification ratio. On the other hand, by reducing the number of current divisions and increasing the number of divisions in the time direction, accuracy can be ensured. Although it depends on the characteristics of the panel, it is easier to ensure the accuracy if the number of time divisions is larger than the number of current divisions.

The distribution method and the algorithm of the decoder are not limited to those described above, and numerical values such as the number of distributions and the number of gradations are not limited thereto. The output is not limited to the current value, but may be a voltage output according to the panel to be driven.

(Third Embodiment) A case is considered where, for example, an organic EL element is driven by using the gradation realizing method and the distribution method described in the second embodiment. At this time, the organic EL
Driving must be performed in consideration of the characteristics of the device. FIG. 8 schematically shows driving of the organic EL element.

The driving circuit has the configuration shown in FIG. 5 and is simplified. At the time of driving, a current flows from the power supply to this element by a constant current circuit. It is considered that the organic EL has equivalently the rectification characteristics of the capacitor component 36 and the equivalent diode 35, and at this time, the equivalent capacitor 36 of the organic EL element is charged. In the method described in the second embodiment (FIG. 7), the current value must be reduced at some timing on the time axis. However, since the output stage of the constant current drive circuit does not include a circuit for reducing the current, the voltage of the charged equivalent capacitor cannot be reduced.

On the other hand, when the driving period ends, the operation shifts to the reverse bias operation, so that the path shown by the broken line in FIG. 8 is turned on, and the charged voltage can be dropped to GND. That is, although there is a means for setting the voltage of the equivalent capacitor 36 to GND, there is no means for reducing the voltage to a certain value during the driving period. Therefore, the algorithm of the distribution method as shown in FIG. 7 cannot drive the organic EL element well.

Therefore, the algorithm of the distribution output is improved. That is, since the voltage of the equivalent capacitor 36 can be changed in the charging direction, a method of changing the voltage only in the direction of increasing the current command value as shown in FIG. That is, the distribution method employs an algorithm that increases the minimum unit block of the current output in the direction opposite to the time axis.

As described above, by changing the current command value only in the increasing direction in accordance with the characteristics of the panel to be connected, it is possible to output gradation with high accuracy.

The driving circuit and the driving method are shown in FIGS.
However, the present invention is not limited to the method shown in FIG. The output shown in FIG. 10 may be used as the distribution method or the algorithm of the decoder. Any other method may be used as long as it employs an algorithm for changing the current command value only in the increasing direction. The output is not limited to the current value, but may be a voltage output according to the panel to be driven.

(Fourth Embodiment) Next, an example of the configuration is shown in FIG. 11 and will be described with reference to the drawings. In FIG. R.
The operation of the latch 21 and the latch 22 is the same as that of FIG. 15, and this data is decoded by the decoder 30 into two data in the time direction and the current output direction. The data in the current output direction is converted into an analog current value by a current output type D / A converter 31, input to a current mirror circuit including transistors 32 and 33, and output a predetermined current value. The data in the time direction is pulse width modulated by a PWM circuit 34 connected to the output of the current mirror, and a predetermined pulse width is output. As described above, a gray scale display in which the time and the current output are combined becomes possible. Since the present invention does not require a high speed, the D / A 31
By directly modulating the output of the above to perform an operation equivalent to PWM, a configuration in which the PWM 34 is omitted is also possible.

Various combinations are conceivable for the decoding method of the decoder 30. Here, it will be described that a certain decoding method has a problem, and a decoding method for preventing the problem will be described below. As a decoding method, there is a method in which the output current is binary-selected and the time direction is assigned to lower data.

As an example, FIG. 12 shows an example at the time of middle data slightly smaller than the MSB turning on. In this case, a pattern of half emission and half non-emission is obtained. When the data becomes slightly increased from that state, the MSB emits light as shown in the second half of FIG. 12, and the light emitting period is inverted within the horizontal period. On average, the luminescence intensity only increases as much as the data increases, but when such a pattern occurs in a moving image, the eye catches the moment when the luminescence pattern changes, and a contour pattern not found in the data is observed Is done. This phenomenon is remarkably seen as a pseudo contour of a moving image in a plasma display that generates gray scales by PWM-modulating a binary light emitting device in the time direction, and various countermeasures have been proposed at present.

Therefore, the present invention proposes a decorating method in which the upper bits are assigned in the time direction and the lower bits are set in the current output direction to increase the light emission time as much as possible. As a result, even when the data slightly increases from the middle data as shown in FIG. 13, there is almost no change in the time direction, and the moving image pseudo contour is not observed.

Note that what has been described in the above embodiments has described the drive of a display for an organic EL or LED suitable for current drive. However,
In the case where the voltage-current characteristics of the device can be made uniform or in the case of a display combined with a discharge tube, a voltage output is obtained. In this case, a voltage amplifier output may be used instead of a current mirror, and the configuration can be simplified.

[0045]

As described above, according to the present invention, a high-speed response of elements and a driving circuit and a high-gradation display can be realized without requiring high-precision amplitude control. And
A combination method without gradation skip is realized.

Further, since the control system can be programmed in accordance with the characteristics of the panel to be connected, the distribution of the current value and the time width and the number of divisions can be arbitrarily changed, and the gradation can be output with high accuracy. It becomes possible.

Further, the number of current divisions can be reduced and the number of divisions in the time direction can be increased in accordance with the characteristics of the panel to be connected, so that accuracy can be ensured.

Also, by changing the current command value only in the direction of increasing the current command value in accordance with the characteristics of the panel to be connected, it is possible to output the gradation with high accuracy.

Further, by adopting a decoding method without a pseudo contour of a moving image, a good image can be obtained even in a moving image.

Further, the structure is simple even for a panel of a current control type and a low rectification ratio such as an organic EL element.
It is possible to provide a driving method in which current accuracy and response speed are not strict, and display with high gradation can be performed. Then, a gradation distribution method suitable for the characteristics of the light emitting panel can be adopted, and gradation can be displayed with high accuracy.

[Brief description of the drawings]

FIG. 1 is a principle diagram of an embodiment of the present invention.

FIG. 2 is a principle diagram of the embodiment.

FIG. 3 is a principle diagram of the embodiment.

FIG. 4 is a principle diagram of the embodiment.

FIG. 5 is a configuration diagram of an embodiment of the present invention.

FIG. 6 is a diagram showing decoder input data according to the embodiment of the present invention;

FIG. 7 is an output waveform diagram of the embodiment of the present invention.

FIG. 8 is a schematic circuit diagram showing a driving principle of an embodiment of the present invention.

FIG. 9 is an output waveform diagram of the embodiment of the present invention.

FIG. 10 is an output waveform diagram of the embodiment of the present invention.

FIG. 11 is a diagram showing an example of the configuration of an embodiment of the present invention.

FIG. 12 is a diagram showing an example of a light emission pattern according to the embodiment of the present invention.

FIG. 13 is a diagram showing an example of a light emission pattern according to the embodiment of the present invention.

FIG. 14 is a configuration diagram of a display.

FIG. 15 is a configuration diagram of a conventional PWM method.

FIG. 16 is a diagram showing an example of a conventional PWM light emission pattern.

FIG. 17 is a configuration diagram of a conventional output modulation method.

FIG. 18 is a diagram showing an example of a light emission pattern of a conventional output modulation method.

FIG. 19 is a diagram showing a gradation shift when output amplitude modulation control is performed on an organic EL panel.

[Explanation of symbols]

 Reference Signs List 20 shift register (SR) 21 latch 30 decoder 31 D / A converter 32 current setting resistor R 33 Tr 34 operational amplifier

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/28 G09G 3/28 K 3/30 3/30 K H04N 5/66 H04N 5/66 A

Claims (15)

[Claims] A display panel capable of displaying a plurality of gradations;
A signal driver that drives a plurality of signal lines of the display panel, a scan driver that drives a plurality of scan lines of the display panel, and a display device including a controller that controls the signal driver and the scan driver, A gradation driving apparatus for a display panel, wherein the signal driver performs gradation output by simultaneously performing output control of a plurality of values of current or voltage and gradation display by controlling a plurality of output time widths. 2. A display panel capable of displaying a plurality of gradations,
A signal driver that drives a plurality of signal lines of the display panel, a scan driver that drives a plurality of scan lines of the display panel, and a display device including a controller that controls the signal driver and the scan driver, The signal driver performs gradation display by simultaneously performing current or voltage value output control of a value proportional to the factorial of 2 and gradation control by control of an output time width proportional to the factorial of two. A gradation driving device for a display panel. 3. A display panel capable of displaying a plurality of gradations,
A signal driver that drives a plurality of signal lines of the display panel, a scan driver that drives a plurality of scan lines of the display panel, and a display device including a controller that controls the signal driver and the scan driver, The signal driver divides the maximum value into n equal parts (n is an arbitrary integer)
A gradation driving device for a display panel, wherein the gradation display is performed by simultaneously performing the current value or voltage value output control of the set value and the gradation display by controlling the output time width proportional to the factorial of 2. 4. A display panel capable of displaying a plurality of gradations,
A signal driver that drives a plurality of signal lines of the display panel, a scan driver that drives a plurality of scan lines of the display panel, and a display device including a controller that controls the signal driver and the scan driver, The signal driver controls current or voltage output of a value proportional to the factorial of 2, and divides the maximum value into n equal parts (n is an arbitrary integer)
A gradation driving device for a display panel, wherein gradation display is performed by simultaneously performing gradation display by controlling the output time width of the set value. 5. A display panel capable of displaying a plurality of gradations,
A signal driver that drives a plurality of signal lines of the display panel, a scan driver that drives a plurality of scan lines of the display panel, and a display device including a controller that controls the signal driver and the scan driver, The signal driver divides the maximum value into n equal parts (n is an arbitrary integer)
Output value or voltage value output control and the maximum value
A gradation driving apparatus for a display panel, wherein gradation display is performed by simultaneously performing gradation display by controlling output time widths of equally divided values (m is an arbitrary integer). 6. A driving system in which the signal driver simultaneously performs a plurality of values of current or voltage output control and a plurality of output time width controls to perform gradation display, and is represented by n bits (n is an arbitrary integer). Current or voltage output control in which the amplitude is controlled at an interval of 1/2 ^m of the maximum value using the upper m bits (m is an arbitrary integer) of the gray scale data,
6. The grayscale driving device for a display panel according to claim 5, wherein a time width control for controlling a time width at an interval of 1/2 ^(nm) of a maximum value using ⁽ m) bits is performed. 7. A decoder according to claim 1, further comprising a decoder for separating the gradation command value into a plurality of current or voltage outputs and a plurality of output time widths. 4. The grayscale driving device for a display panel according to 1. 8. The grayscale driving apparatus for a display panel according to claim 7, wherein the decoder is capable of rewriting a control method. 9. The method according to claim 1, wherein the LSB of the voltage output having no current is output twice, the LSB of the output time width is output twice, or both have two LSBs.
The grayscale driving device for a display panel according to any one of the above. 10. The signal driver according to claim 1, wherein a plurality of values of current or voltage output control and a plurality of output time widths are simultaneously controlled to perform gray scale display, and decoding is performed so that the output time is long. Item 6. A gradation driving device for a display panel according to any one of Items 1 to 5. 11. The signal driver simultaneously controls current or voltage output of a plurality of values and gradation display by controlling a plurality of output time widths, and the current or voltage output changes only in the direction of increasing the value. The grayscale driving device for a display panel according to claim 1, wherein the driving is performed. 12. In a driving method in which the signal driver simultaneously controls a plurality of values of current or voltage output and controls a plurality of output time widths to perform gradation display, the number of output of the current or voltage output is determined by the number of output divisions. 6. The grayscale driving device for a display panel according to claim 1, wherein the number of divisions of the time width increases. 13. The grayscale driving apparatus for a display panel according to claim 1, wherein the current output control includes a constant current circuit. 14. The gradation driving device for a display panel according to claim 13, wherein the constant current circuit is constituted by a current mirror type or a current feedback type. 15. The gradation driving device for a display panel according to claim 1, wherein the display panel is formed of an organic EL, an LED, a discharge tube, or an electron-emitting device.