JPH0363691A - Gradation controller for el display device - Google Patents

Abstract

PURPOSE:To enable stable gradation control with good reproducibility without varying a field frequency by providing a current control circuit which varies a current flowing to each EL display element according to gradation data on the side of a column electrode. CONSTITUTION:A composite row driving circuit 35 supplies a composite raw driving signal Praw to FETs 21 - 23, the signal Prow falls to -130V in synchronism with a horizontal synchronizing signal HS, and the FETs 21 - 23 turn on in synchronism with the signal HS to apply -130V to row electrodes Y1 - Y3. A column voltage Pclm is applied from a column voltage supply circuit 60 to current control circuits 41 - 43 of a column driving circuit 40 and +80V is applied in synchronism with the horizontal synchronizing signal HS. Image data D is inputted to a control circuit 41 and currents applied to column electrodes X1 - X3 are varied and controlled according to its gradation data.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gradation control device for an EL display device that drives EL display elements arranged in a matrix to display gradations.

[Conventional technology]

E L (C1ecLro Lum1nescence
) Conventional techniques for reproducing gradations using display elements include the following.

■ Voltage modulation method ■ Pulse width modulation method (Japanese Patent Application Laid-open No. 117598-1982) ■ Pulse number modulation method (Japanese Patent Application Laid-open No. 172396-1982) [Problem to be solved by the invention] This is an attempt to vary the applied voltage, but the brightness of an EL display element rises sharply when it exceeds a predetermined threshold voltage, and this rise characteristic varies greatly from element to element, and is also subject to deterioration over time. The method (2) above, in which tone reproduction is performed by applying a plurality of voltages to the rising portion, has the disadvantage that stable tone reproduction cannot be achieved and the reproducibility is also poor.

Method (2) attempts to change the brightness by varying the pulse width of the drive pulse applied to the EL display element, but the relationship between the field (1 field - 1 screen) frequency and the pulse width of the drive pulse is Considering this, this method has the disadvantage that good gradation control cannot be performed due to the afterglow characteristic (tailing) of the EL display element. In other words, the frame frequency that can be visually recognized without flickering is generally at least about 6011z, and the number of row lines in a dot matrix EL display panel is 4.
00 lines, the scanning time for one line is approximately 40 μsec at the longest. Since the response speed of an EL display element is generally several microseconds, the pulse width of the signal used for gradation control is about 30 microseconds. on the other hand,
The afterglow of an EL display element usually lasts several hundred microseconds.

As described above, in this method (2), when considering matrix driving of the EL elements, there is a problem that the afterglow time of the EL elements is much longer than the driving pulse width, and good gradation reproduction cannot be achieved.

The method (2) attempts to perform gradation control by appropriately thinning out the drive pulses applied to each EL display element in frame units, but in this method, for example, in order to maintain the frame frequency at 6011z, 3rd level sunny 1
2 Q llz, a field frequency of 18011z is required at 4 gradations, and therefore, in order to realize this method, a high-speed EL drive circuit is required as the number of gradations increases, making it difficult to achieve multiple gradations. There is a problem.

This invention has been made in view of these circumstances, and aims to provide a gradation control device for an EL display device that can perform gradation control with stability and good reproducibility without changing the field frequency. It is.

[Means to solve the problem]

Therefore, in the present invention, an EL display device in which an EL display element is interposed between a row electrode and a column electrode arranged in a 7-trix arrangement, and the EL display element is driven by selectively setting each potential of the row electrode and column electrode. In this method, a current control circuit for varying the current flowing through each EL display element in accordance with gradation data is provided for each electrode on the column electrode side.

[Effect]

This invention focuses on the fact that the brightness of an EL display element, which is a capacitive load, is approximately proportional to the current, and by variably controlling the current flowing through the column electrode according to the gradation data of the EL display element. , which performs gradation reproduction.

〔Example〕

Hereinafter, the present invention will be described in detail according to embodiments shown in the accompanying drawings.

FIG. 4 is a model of a light emitting circuit of an EL display element. Since the EL display element 1 has an EL layer sandwiched between electrodes with a dielectric material, it can be equivalently regarded as a capacitive element. When voltage V is applied from AC pulse voltage FA2 to such an EL display element 1, E
A current I flows through the L display element 1 . The EL display element 1 starts emitting light when the electric field E applied to the EL display element 1 exceeds a certain predetermined threshold value. At this time, the faster the electric field E becomes stronger, that is, the larger the current ,
Even with pulses having the same pulse width, the brightness of the EL display element 1 increases.

That is, the current I is given by the following equation, but if C and V are constant, the relationship between the pulse rise time ts of the AC pulse power source 2 and the current I is as shown in FIG. 5, as can be seen from the above equation. Become. In other words, the shorter the pulse rise time, the
Current I becomes large (II>12).

FIG. 6 shows experimental results showing the relationship between pulse rise time ts and brightness (pulse width Tp and voltage V are constant), and the brightness of EL display element 1 is determined by pulse rise time ts.
is inversely proportional to. Furthermore, since the current I is proportional to the pulse rise time ts as shown in the previous equation, this experimental result also indicates that the larger the current I, the greater the brightness of the display element.
I can approve.

This invention focuses on this point, and in a dot matrix drive type EL display device, by variably controlling the current flowing through each pixel when voltage is applied to the light emitting pixels, it is possible to perform gradation display. .

FIG. 1 shows an embodiment of the present invention, and an EL display device 10 of this embodiment includes column electrodes X1 to X3 on the column side arranged in the X direction, and row electrodes arranged in the Y direction. side row electrodes Y1 to Y3 are provided. therefore,
This EL display device 10 includes EL display elements E1 to E9 forming a 3×3 pixel matrix.

The row drive circuit 20 includes field effect transistors (hereinafter referred to as FETs) 21 to 23 connected to row electrodes Y1 to Y3, respectively, and a switching circuit 30. A horizontal synchronizing signal H3 as shown in FIG. 3(d) is input to the switching circuit 30, and the switching circuit 30 switches the FETs 21 to 23 in synchronization with the horizontal synchronizing signal HS.
selectively turn on one by one in sequence.

The composite row drive circuit 35 receives a composite row drive signal Prow as shown in FIG. 3(a).
is supplied to FETs 21 to 23, and this signal P r
ow becomes 1]30V in synchronization with the horizontal synchronization signal H3. Further, as described above, the FETs 21 to 23 are also turned on for each row in synchronization with the horizontal synchronizing signal H3. Therefore, 130V is sequentially applied to the row electrodes Y1 to Y3 via FETs 21 to 23, respectively.

Note that, as shown in FIG. 3(a), the composite row drive signal P row becomes +210V every time the scanning of all rows, that is, the scanning of one screen, is completed, and this causes a refresh operation to prevent afterimages. Do this.

On the other hand, the column side electrodes X1 to X3 are driven by a column drive circuit 40. The column drive circuit 40 is
Separate current control circuits 41~ for each column electrodes X1~X3
43, and these current control circuits 41 to 43 selectively turn on and off the column electrodes X1 to X3 in accordance with the image data D, and perform gradation drive in accordance with the intermediate image data D.

A column voltage Pelm is applied from a column voltage supply circuit 60 to these current control circuits 41 to 43. This column voltage Pelm becomes +80V in synchronization with the horizontal synchronizing signal H8, as shown in FIG. 3(b).

FIG. 2 shows an example of the internal configuration of the current control circuit 41.

Other current control circuits 42 and 43 also have the same configuration as shown in the figure.

Column electrode X1 is connected to FET51 and FET52, p-channel FET51 is turned on when turning on EL display element E1, and n-channel FET52 is turned on when turning off EL display element E1.

Switching of the FET 51 is performed by a configuration including a shift register 53, a level shifter 54, a latch 55, and a D/A converter 56, and switching of the FET 52 is performed by a configuration including a shift register 53 and a latch 57.

The image data D is stored in the shift register 53 using the clock ck.
It is powered by humans. The shift register 53 is composed of a 1-bit off data section DB and a multi-bit gradation data section DA, and when turning off the EL display element, a signal of logical value 1 is manually input to the off data section DI3. Further, when turning on the EL display element, necessary gradation data is manually entered into the gradation data section DA. Note that the other current control circuit 42
．． 43 shift registers 53'53' are connected in series to the shift register 53.

The gradation data manually entered into the gradation data section is entered into the level shifter 54, and the level shifter 54 transfers the data to the FET.
The level is shifted to correspond to the source voltage Pelm of 51. The level-shifted gradation data is stored in the latch 55.
After being latched once, the D/A converter 56 converts it into an analog voltage corresponding to the grayscale data. The output voltage of the D/A converter 56 is applied to the gate of the FET 51, thereby reverse biasing the gate of the FET 51. That is, by varying the bias voltage applied to the gate of the FET 51 according to the gradation data, the FET
51 gate-source voltage V. 3 is varied in accordance with the gradation data, so that the current I flowing through the column electrode Xl is varied in accordance with the gradation data. That is, F.E.
Using the constant current characteristic of T, the current flowing through the column electrode X1 is variably controlled according to the gray scale.

On the other hand, when a current (2) flows through the column electrode X1, the EL display element E1 is gradually charged with the current I, and the terminal voltage of the EL display element E1 rises almost to the output voltage of the column voltage supply circuit 60 +80V. Further, at this time, the output voltage of -130V from the composite row drive circuit 35 is applied to the row electrode Y1, so the potential difference at the intersection of the column electrode X1 and the row electrode Y1 is approximately 210V, and the EL display element El is Light is emitted from the point at which the N level difference exceeds a predetermined threshold voltage. Then, the luminance of the light emitted at this time is at a level corresponding to the m flow value ■ flowing through the column electrode X+.

On the other hand, the off data portion of the shift register 53.

When a signal with a logical value of 1, that is, a high-level signal is input manually, this high-level signal is once latched by the latch 57 and then applied to the gate of the n-channel FET 52, which turns on the FET 52 and turns the column on. Electrode X1
is grounded. At this time, -130V is applied to the row electrode Y1.
is applied, the column electrode X1 and the row electrode Y1
The potential difference at the intersection with E1 is 130V, which does not exceed the threshold voltage of the ELL display element, so the EL display element E1 does not emit light.

In this way, when making the ELL display element emit light, a current corresponding to the 1-week data is passed through the ELL display element by manually inputting the image data D including gradation data corresponding to the light emission gradation level. In addition to driving the display element in gradation, when the ELL display element is not to emit light, the ELL display element is prevented from emitting light by manually inputting image data including off data.

Note that the image data D is supplied as shown in FIG. 3(C). That is, before the row electrode Y1 of the first row is scanned, the image data of the EL display elements E1 to E3 is sequentially supplied to each shift register 53, 53'53', and these image data E1 to E3 are Electrode Y1
is applied to each FET 51 and 52 at the same time when scanning is performed. Similarly, before the scanning of the row electrode Y2, the image data of the EL front display elements 4 to E6 is sequentially transferred to the shift register 53.53, and the image data of the EL display elements E7 to E9 is sequentially transferred to the shift register 53. '53'. When the scanning of one screen is completed, refresh driving is performed by a refresh pulse.

In this way, this embodiment uses the constant current characteristics of the FET to variably control the current supplied to the ELL display element to reproduce gradation, and the voltage between the gate and source of the p-channel FET 51 is By variably controlling vGs according to the gradation data, the current flowing through the column line can be varied,
As a result, the brightness of the ELL display element is changed according to the gradation data.

Therefore, in this embodiment, gradation can be reproduced without changing the field frequency, and the threshold voltage vth of the ELL display element and the applied voltages Pray and Pa1 can be reproduced without changing the field frequency.
Adjustment of m can be performed independently of gradation control,
This makes it possible to obtain gradation characteristics with good stability and reproducibility.

〔Effect of the invention〕

As explained above, according to the present invention, the brightness gradation is obtained by controlling the current to each ELL display pixel, so it is possible to easily achieve multi-gradation, and it is stable without changing the field frequency. It is possible to obtain a gradation display image with good reproducibility.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of the internal configuration of a current control circuit, FIG. 3 is a time chart explaining the operation of the embodiment, and FIG. 4 is an E
A model circuit diagram of the LL display element, FIG. 5 is a graph showing the relationship between pulse rise time and current, and FIG. 6 is a graph showing the experimental results of the relationship between luminance and pulse rise time. DESCRIPTION OF SYMBOLS 10...ELL display device, 20...Row drive circuit, 35...Composite row drive circuit, 40...
・Column drive circuit, 41, 42.43... Current control circuit, 51.52... FET, 53... Shift register, 60... Column voltage supply circuit, Y1 to Y39
6. Row electrodes, X1 to X3...Column electrodes, E1 to E
9. ,. EL display element. Figure 1 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] Row electrodes and column electrodes are arranged in a matrix,
By interposing EL display elements between these row electrodes and column electrodes, and selectively setting the respective potentials of these row electrodes and column electrodes, the EL
An EL display device for driving display elements, characterized in that a current control circuit for varying the current flowing through each EL display element according to gradation data is provided on each of the column electrodes. control device.