JP2004184900A - Passive matrix type organic el display device and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a passive matrix type organic EL display device of which power consumption and cost are reduced and with which high quality picture display is achieved. <P>SOLUTION: The driving method of the passive matrix type organit EL display device characterized in that, upper bits of gradation data corresponding to display data are expressed by a current amplitude modulation gradation system and lower bits of the gradation data corresponding to the display data are expressed by a frame rate control gradation system, and the frame rate control gradation system is added to the current amplitude modulation gradation system to achieve the objectives, is provided to solve the above-described problem. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an organic EL display device and a driving method thereof, and more particularly, to a gradation control technology that enables a multi-gradation display in a passive matrix organic EL display device.
[0002]
[Prior art]
In recent years, a self-luminous organic EL display device using a light-emitting organic material has been developed. There are two types of organic EL display devices, a passive type (simple matrix type) and an active type (active matrix type).
In a passive matrix organic EL driving method, a pulse amplitude modulation (PHM) method, a frame modulation (FRC) method, or a pulse width modulation (PWM) method is often used for gradation control.
[0003]
Generally, in the PHM method, instantaneous luminance can be controlled by a current value (or a voltage value), so that high-speed gradation control is possible.
Since the organic EL element is a current control type element, it is generally driven with a constant current. However, conventionally, it has been difficult to perform multi-gradation display by constant current value control. The conventional method requires a large number of high-precision current sources with multi-level outputs, resulting in high costs.
[0004]
Further, in the FRC method, since gradation is expressed using a plurality of display frames, it takes time until the display is completed, and there is a problem that flicker occurs. Furthermore, it is necessary to perform frame control at a high speed as the number of gradations increases, but the response of the organic EL panel is limited, and power consumption increases. In order to solve this, the PWM method is often used conventionally.
[0005]
The PWM method is a method in which one row (row) selection period is divided into several sequences, and an ON sequence and an OFF sequence are allocated. The display is completed in one display frame. In this system, the number of sequence divisions is set finely in order to enable multi-gradation expression, but there is a drawback in that the drive frequency is increased, and image quality of a displayed image such as crosstalk is deteriorated. Also, by increasing the frequency, power consumption naturally increases.
In addition, as a special method, a gradation method combining the PWM method and the PHM method has been devised (for example, see Patent Document 1).
[0006]
[Patent Document 1]
JP-A-11-329721
[Problems to be solved by the invention]
However, in the PHM method, as described above, as the number of gradations increases, a multi-level constant current source is required to control the gradation. For example, to display 2 ⁿ gradations, 2 ^{n -1} types are required. Is required. Therefore, there is a problem that a large number of multi-level constant current sources for generating the current are required, and the control becomes more complicated as the number of the constant current sources increases.
In addition, it is difficult to stably manufacture a high-precision multi-level constant current source, and the chip size is increased.
[0008]
Further, in the PWM method, the number of sequence divisions in one row selection period is set to ²ⁿ depending on the gray scale of display data. As the number of gray scales increases, the number of sequence divisions naturally becomes smaller. As a result, a high-frequency drive pulse is generated at a certain grayscale level, so that the response of the organic EL panel cannot follow and there is a problem that image quality is deteriorated.
[0009]
Similarly, in the FRC method, control of N-1 fields (subframes) is required to represent N gradations. If the frame frequency is F [Hz] in order to prevent flicker and the like, it is necessary to process one field at a speed of about F × (N-1) [Hz]. Power consumption increases.
[0010]
Further, when performing multi-gradation display, there is a problem that the relationship between the current value flowing through the organic EL element and the emission intensity is not linear. That is, finer settings (gradation data) than the desired gradation (display data) are required. This is called gamma correction. Usually, gradation data in which one bit or more is added to the number of bits of display data is provided. , Display data and gradation data are made to correspond to each other, or calculation processing is performed. Then, there is a problem that this processing further increases power consumption.
[0011]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has a low power consumption and a low cost, and a passive matrix organic EL display device capable of displaying a high-quality image and a driving method thereof. The task is to provide
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, a first aspect of the present invention is a driving method of a passive matrix organic EL display device, wherein a higher-order bit of gray-scale data corresponding to display data is expressed by a gray scale method using current amplitude modulation. And the lower bits of the gradation data corresponding to the display data are represented by a frame rate control gradation method, and the frame rate control gradation method is added to the current amplitude modulation gradation method. And a driving method of the passive matrix type organic EL display device.
[0013]
Further, the current is controlled by a gray scale method based on current amplitude modulation for the upper bits of the gray scale data, and the current is controlled by the lower bit of the gray scale data by a frame rate control gray scale method. It is preferable to control the instantaneous luminance by supplying the anode to the anode of the organic EL display device.
[0014]
Further, in the method for driving a passive matrix type organic EL display device, the method further comprises a reference current source for generating a reference current value I ₀ , and one frame rate control current source which is turned on or off by the gradation data. And a current amplitude modulation current source corresponding to the number of higher-order bits of the grayscale data, and drives an anode of the organic EL display device to control light emission luminance of the organic EL element.
[0015]
.., M, the intensity of the current source for current amplitude modulation corresponding to the number of high-order bits of the gradation data is 2 ^k times the reference current value I _0. Is preferable.
[0016]
In addition, it is preferable that at all anodes of the organic EL display device, the emission luminance of the organic EL element is simultaneously controlled, and the gradation control is performed in one frame.
[0017]
Further, in the portion where the frame rate control is performed, it is preferable that the number of display gradations in one frame is controlled as an FC field, and the gradation display is completed in one frame.
[0018]
Further, in a portion for performing the frame rate control, a frame rate control gradation table for a freely settable number of display gradations is provided, and in each field constituting one frame, based on the frame rate control gradation table. Preferably, the frame rate control current source is turned on or off.
[0019]
Similarly, in order to solve the above problem, a second aspect of the present invention provides a method of driving the passive matrix organic EL display device, wherein the frame rate control gray scale method is changed to a gray scale method by the current amplitude modulation. In addition to the above, the current value flowing through the organic EL element is controlled to form one frame using FC fields, and the number of gradations CHM by current amplitude modulation and the number of fields which are the number of gradations by frame rate control Provided is a passive matrix organic EL display device which performs gradation display for the number of gradations represented by the product of FC and CHM × FC.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a passive matrix type organic EL display device of the present invention and a driving method thereof will be described in detail based on preferred embodiments shown in the accompanying drawings.
[0021]
The method of driving an organic EL display device according to the present invention is characterized in that, in a passive matrix duty driving method, when selecting a gradation from arbitrary gradation data corresponding to display data and performing multi-gradation display, the gradation data Are expressed by a current amplitude modulation (hereinafter referred to as CHM) gray scale method (Current High Modulation gray scale method; hereinafter referred to as CHM gray scale method), and the lower bits of the gray scale data are represented. Is expressed by a frame rate control gradation method (hereinafter, referred to as an FRC gradation method).
In this manner, a gray scale method in which the FRC gray scale method is added (plus) to the CHM gray scale method is referred to as a CpF (CHM plus FRC) gray scale method.
Hereinafter, first, the outline of the CpF gray scale method of the present invention will be described.
[0022]
The CpF gradation type organic EL display device includes a reference current source I ₀ , an FRC current source I ₀ controlled by gradation data corresponding to display data, a CHM current source I ₀ , 2I ₀ , 4I ₀ ,. ··· Has 2nI ₀ The anode (anode) of the organic EL display device is driven by a drive current value for each gradation determined by turning on or off the current source for each display gradation.
The CpF gradation method is a gradation method in which the above-described anode drive is executed for all the anodes and gradation control is performed in one frame. Therefore, a current source for FRC and a current source for CHM are provided for all anodes.
[0023]
In the CpF gradation method, for example, when gradation data has n bits, the data is divided into upper m bits and lower s bits, the upper m bits are allocated to the CHM unit, and the lower s bits are allocated to the FRC unit. Is expressed by the gray scale method.
The CHM unit, the state of the upper m bits, k = 0, 1, 2, · · ·, as m-1, current source weighted ^{2 k} times _{^{(2 0 I 0 = I 0}} , 2 1 I 0 _{^{= 2I 0, 2 2 I 0}} = 4I 0, ···, a ^{2 m-1} _{I 0),} respectively on or off.
[0024]
The FRC unit controls the number of display gradations (FC field). That is, gradation display is completed in the FC field. The FRC unit includes a frame rate control gradation table (FRC gradation table) for a freely settable number of gradations, and turns on or off the FRC current source I ₀ in each field based on the gradation table. Turn off.
[0025]
The upper bits of the gray scale data are controlled by a gray scale method using CHM, and a drive current for expressing the gray scale of the upper bits is determined. Similarly, the lower bits of the grayscale data are controlled by the FRC grayscale method to determine the drive current. Finally, the respective drive currents from the CHM section and the FRC section are combined, and the combined current is supplied to the anode of the organic EL panel.
As described above, in the CpF gray scale method, one frame is configured using the FC field by controlling the current flowing through the organic EL element, and the number of gray scales CHM in the CHM gray scale method and the FRC gray scale method are used. The product of the number of gradations, ie, the number of fields FC, and the display gradation control of CHM × FC are enabled.
[0026]
On the other hand, in order to realize n-bit grayscale data only by the CHM grayscale method, n current sources are required for one anode. However, in the CpF gradation method according to the present invention, the upper m bits in the n-bit gradation data are set to the CHM gradation method, and the lower s bits are set to the FRC gradation method. (M + 1) (m + 1 <n), which is the sum of the m current sources described above and one current source of the FRC section for the lower bits.
[0027]
Further, when the reference current source I ₀ is constituted by one unit transistor, each of the current sources are weighted as described above to represent the upper m bits, for conducting the current value of its provisions, respectively It requires 2 ^k-1 (k = 1, 2,..., M) unit transistors (1 + 2 + 4 +... +2 ^{m-1 in} total).
On the other hand, if the n-bit grayscale data is realized only by the CHM grayscale method, a total of 1 + 2 + 4 +... +2 ⁿ⁻¹ unit transistors are required (where m <n). .
In general, considering that the number of anodes in an organic EL display device is several hundred, the present invention is effective for significantly reducing the chip size.
[0028]
Further, the CpF gray scale method of the present invention is an addition of the CHM gray scale method to the FRC gray scale method, and requires 2 ^s fields for the lower s bits, but the upper m bits of the gray scale data are , Is completed in each field. Therefore, there is also an effect that there is little flicker and there is little splicing even if display data changes during display.
[0029]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Here, as an embodiment, an arbitrary 64 gradations are selected from the gradation data of 128 gradations (7-bit data), and the upper 4 bits (for 16 gradations) of the 7-bit data are selected by the CHM gradation method. Also, an example will be described in which the lower three bits (for eight gradations) are represented by the FRC gradation method.
[0030]
FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a passive matrix organic EL display device according to the present invention.
As shown in FIG. 1, the organic EL display device 10 according to the present embodiment includes an organic EL panel 12, a cathode driver (cathode driver) 14, an anode driver (anode driver) 16, and a display data RAM 18.
[0031]
FIG. 1 shows an example in which each color of RGB is processed in a time-division manner, but only one is displayed. However, gradation data generation and on / off data of each color of RGB may be provided in parallel.
Further, the display data RAM 18 is provided with a RAM decoder 32. Further, a controller 34 for controlling these components is provided.
[0032]
The controller 34 reads 16-bit display data (R (5 bits), G (6 bits), B (5 bits)) of the row to be displayed from the display data RAM 18 and reads the read display data into R, G, The data is converted into 7-bit gradation data D0, D1, D2, D3, D4, D5, D6 for each B. This conversion may be performed by a method such as interpolation.
[0033]
In the 7-bit gradation data, the upper 4 bits D6 to D3 are allocated to CHM, and the lower 3 bits D2 to D0 are allocated to FRC. From the upper 4 bits D6, D5, D4, D3 of grayscale data, 4-bit ON / OFF data CHM3, CHM2, CHM1, CHM0 is determined and fourth current value 8I that are based on each of which a reference current value _{I 0 0, 4I 0,} 2I _0, the switch signal of the current source for generating a _{I 0.}
Further, for the lower three bits D 2, D 1, and D 0 of the gradation data, the FRC sequence counter 42 determines 1-bit on / off data FRC (reference current value I ₀ ) from the FRC gradation table 44. Here, the FRC sequence counter 42 counts up for each field, and returns to 0 after counting 8 fields (1 frame).
[0034]
FIG. 2 shows the FRC sequence. FRC0 to FRC7 in the drawing mean lower three bits of values 0 to 7 of the gradation data. In the FRC section, on / off in each sequence is controlled according to the value for each field (FRC sequence) as shown in FIG. One frame is completed by eight fields in order to express the lower three bits (eight gradations) of the gradation data.
By doing so, there is an effect that the FRC sequence is updated for each field, ON and OFF are averaged, and flicker is reduced.
[0035]
The 1-bit FRC determined from the FRC gradation table 44 and the 4-bit CHM CHM3, CHM2, CHM1, and CHM0 are input to the anode driver 16 as on / off data.
FIG. 3 shows a schematic configuration of the anode driver 16.
[0036]
As shown in FIG. 3, the anode driver 16 of the present embodiment includes a reference current source 41, a plurality of drivers corresponding to each anode (anodes 0 to N), an anode 0 driver A0, an anode 1 driver A1,. , An anode N driver AN. Here, the anode 0 driver A0 includes a current source F0 for FRC and a current source C0 for CHM. Similarly, each anode i driver Ai (not shown) also includes an FRC current source Fi and a CHM current source Ci.
[0037]
As shown in FIG. 3, the 5-bit ON / OFF data CHM3, CHM2, CHM1, CHM0, and FRC are respectively supplied to the CHM current source Ci and the FRC current source Fi (i = 0,...) Of each anode i driver Ai. ., N).
In the CHM, a current source having four current values 8I ₀ , 4I ₀ , 2I ₀ , and I ₀ based on the reference current value I ₀ is used to realize the upper four bits of gradation data (16 gradations). Are generated ( _{0 to} 15I ₀ ), and these become the driving current of the anode (anode).
[0038]
FIG. 4 shows an example of a switch surrounded by a broken line B as shown in FIG. Although the switch in the illustrated example is configured using the flip-flop 46 and the two transistors 48a and 48b, it is not limited to this, and any switch having the same function may be used. Is also good.
[0039]
Hereinafter, the operation of the organic EL display device 10 according to the present embodiment will be described.
The controller 34 instructs the RAM decoder 32 of the display data RAM 18 to select display data to be displayed on the organic EL panel 12.
[0040]
The controller 34 reads the display data of the row to be displayed, converts the read data into 7-bit gradation data by the gradation selector 28, and selects 64 gradations designated from the 128 gradations represented by these 7 bits. The upper 4 bits of the gradation data are set to CHM, and the lower 3 bits are set to FRC. In the CHM, 16 kinds of current values for realizing 16 gradations of the upper 4 bits of the gradation data are generated. In the FRC, the lower 3 bits of the gradation data are converted by the FRC sequence counter 42 into the FRC gradation table 44. , One-bit on / off data is determined. Then, one bit from the FRC gradation table 44 and the upper four bits of the gradation data are latched as ON / OFF data by the corresponding anode driver (anode driver) 16.
[0041]
The controller 34 activates the cathode driver 14 corresponding to the row to be displayed when the ON / OFF data is latched in all the anode drivers 16 in the row to be displayed. Thus, the organic EL panel 12 is driven.
[0042]
After a certain time, the row electrode (cathode driver) being displayed is made inactive, and the same is repeated for the next row to be displayed.
[0043]
As described above, in the present embodiment, since the CpF (CHM plus FRC) gradation control is performed, the operating frequency is suppressed, and lower power consumption is possible as compared with the PWM and FRC gradation methods.
For example, when the minimum gradation is displayed by the PWM gradation method, a high-frequency minimum drive pulse having a minimum on-time of the sequence (one unit time), that is, a short duration, is generated, resulting in high-frequency operation and consumption. The power increases.
[0044]
In order to explain this in more detail, a case where a moving image is displayed will be specifically considered. In displaying a moving image, at a full moving image rate, 30 frames / second or more is required, but usually, a very common use is about 10 to 20 frames / second. Here, a case where 64 gradations are expressed at 20 frames / sec is taken as an example. For example, when the frequency of the minimum drive pulse required to drive an organic EL panel of 168 lines per frame used in a mobile phone or the like is estimated, in the case of the PWM gradation method, 63 (sequence) × 168 (lines) × 20 (frames / second), which is about 200 [KHz].
Similarly, in the FRC gradation method, it is 64 (field) × 168 (row) × 20 (frame / sec), which is about 215 [KHz].
[0045]
However, in the method of the present embodiment, it is 8 (fields) × 168 (rows) × 20 (frames / second), which is about 27 [KHz]. As a result, the operating frequency may be about 1/8 that of the conventional method such as PWM or FRC, the power consumption can be reduced to 1/8, and the power consumption can be reduced.
[0046]
Further, in the present embodiment, by performing the instantaneous luminance control based on the current value of the CpF gradation method, it is possible to escape from the high frequency operation by the conventional PWM method.
On the other hand, by using the CpF gray scale method, the frame time is shorter than that of the conventional FRC gray scale method, so that optimum gray scale control can always be performed, and high image quality with little image quality deterioration such as flicker and splicing can be obtained. Image display can be realized.
[0047]
Further, in the present embodiment, by using the CpF gray scale method, the number of constant current sources can be reduced with respect to the organic EL element compared to the conventional PHM gray scale method, and multi-gray scale expression can be performed at low cost. It becomes.
[0048]
As described above, the passive matrix type organic EL display device of the present invention and the driving method thereof have been described in detail. However, the present invention is not limited to the above embodiments, and does not depart from the gist of the present invention. Of course, various improvements and changes may be made.
[0049]
【The invention's effect】
As described above, according to the present invention, in the passive matrix type organic EL display device, the operating frequency is suppressed by controlling by the CpF gray scale method in which the FRC gray scale method is added to the CHM gray scale method. Power consumption and cost reduction can be achieved, optimal gradation control can be performed, and multi-tone expression can be performed at low cost.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a schematic configuration of an embodiment of a passive matrix organic EL display device according to the present invention.
FIG. 2 is an explanatory diagram illustrating an example of a driving method in an FRC section in the present embodiment.
FIG. 3 is a schematic configuration diagram illustrating an anode driver according to the embodiment.
FIG. 4 is a circuit diagram showing another example of the switch of the anode driver of FIG. 3;
[Explanation of symbols]
10 Organic EL Display 12 Organic EL Panel 14 Cathode Driver (Cathode Driver)
16 Anode driver (anode driver)
18 Display data RAM
28 Gradation selector 32 RAM decoder 34 Controller 41 Reference current source 42 FRC sequence counter 44 FRC gradation table 46 Flip-flops 48a, 48b Transistor

Claims (8)

A driving method of a passive matrix type organic EL display device,
The upper bits of the gray scale data corresponding to the display data are expressed in a gray scale method by current amplitude modulation,
Expressing lower bits of the gradation data corresponding to the display data by a frame rate control gradation method,
A method of driving a passive matrix organic EL display device, wherein the frame rate control gray scale method is added to the gray scale method by current amplitude modulation. The upper bits of the grayscale data are controlled in current by a grayscale method using current amplitude modulation, the lower bits of the grayscale data are controlled in current by a frame rate control grayscale method, and the respective currents are synthesized. The method according to claim 1, wherein the instantaneous luminance is controlled by supplying the luminance to the anode of the organic EL display device. The method of driving a passive matrix type organic EL display device according to claim 1, further comprising: a reference current source for generating a reference current value I _0, 1 or frame rate to be turned on or off by said gradation data A control current source, and a current amplitude modulation current source corresponding to the number of upper bits of the grayscale data,
A method for driving a passive matrix type organic EL display device, wherein an anode of the organic EL display device is driven to control light emission luminance of the organic EL element. The intensity of the current source for modulating the current amplitude for the number of upper bits of the gradation data is set to k = 0, 1, 2,..., M, and is 2 ^k times the reference current value I ₀ . A method for driving a passive matrix organic EL display device according to claim 3. 4. The driving method of a passive matrix organic EL display device according to claim 3, wherein the emission luminance of the organic EL element is simultaneously controlled in all anodes of the organic EL display device, and gradation control is performed in one frame. 4. The method of driving a passive matrix organic EL display device according to claim 3, wherein in the portion for performing the frame rate control, the number of display gradations in one frame is controlled as an FC field, and gradation display is completed in one frame. In the portion for performing the frame rate control, a frame rate control gradation table for a freely settable number of display gradations is provided, and in each field constituting one frame, based on the frame rate control gradation table, 4. The method for driving a passive matrix organic EL display device according to claim 3, wherein the current source for frame rate control is turned on or off. The method for driving a passive matrix organic EL display device according to any one of claims 1 to 7, wherein the frame rate control gradation method is added to the gradation method based on the current amplitude modulation, and a current flowing through the organic EL element. The value is controlled, one frame is configured using FC fields, and the product of the number of gradations CHM by current amplitude modulation and the number of fields FC, which is the number of gradations by frame rate control, is represented by CHM × FC. A passive matrix organic EL display device, which performs gradation display for the number of gradations.

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