JPH0661027B2 - Driving method for thin film EL display panel - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a matrix type thin film EL display device for displaying characters, figures, etc., and to a driving method for improving display quality and ensuring long-term reliability. .

2. Description of the Related Art A thin film EL display device operates as a light emitting display device by interposing a thin film EL element between matrix electrodes composed of scan electrodes and data electrodes and applying a pulse voltage between both electrodes. Normally, the write pulse voltage V _D is applied by line-sequential scanning along the scan electrodes, and after the scanning of one screen is completed, the refresh pulse voltage V _R having the opposite polarity to the write pulse voltage is applied to the entire surface of the EL display panel. ,
Arbitrary characters and figures can be displayed. Such a driving method is read as a simultaneous inversion refresh driving method,
Since the light is emitted twice in one frame by the write pulse voltage V _D and the refresh pulse voltage V _R , an EL display device with high brightness and no flicker can be realized. By the way, in a display device using this driving method, when a display pattern such as a fixed character or figure is kept in a light emitting state for a long time,
Even if the display is returned to the non-invention display, a display pattern remains (hereinafter referred to as a shift phenomenon). FIG. 3 shows the voltage / luminance characteristics when the shift phenomenon occurs. The brightness characteristic in which the shift phenomenon occurs with respect to the initial value of the brightness characteristic a is moved to the low voltage side as a whole as shown by b, and the saturated brightness is slightly lowered. That is, in the low luminance region is lowered to V _th 'from light emission start threshold voltage V _th, V initial value
_{At th} , a brightness of B _l ′ occurs. On the other hand, in the high luminance region, the luminance is B _h to B _h ′ at the operating voltage V _p .
Fall to. For this reason, particularly when the display pattern is changed to the non-light emitting pattern, what should originally have a brightness of zero emits light with a brightness of B _l ′, and the display pattern is exposed. This shift phenomenon tends to increase toward the upper and lower parts of the panel, and will be described in correspondence with the actual line-sequential scanning drive. FIG. 4 shows the voltage waveforms applied to the EL elements in the simultaneous inversion refresh driving method as A, B and C.
When the number of scanning electrodes is n, A is the first line (topmost panel), B is the 2nd / nth line (panel central portion), and C is the nth line.
It is an applied voltage waveform of a line (bottom of panel). The write pulse voltage V _D is once a frame by line sequential scanning,
The refresh pulse voltage V _R having the opposite polarity to the write pulse voltage V _D is applied to all the scan electrode lines at the end of the frame after the end of scanning to refresh all the picture elements. Now, the relationship of the applied voltage is V _D = V _R
Sufficient pulse voltage to emit light of> V _th . It is known that when the EL element emits light, internal polarization occurs at the interface of the EL layer, and this has a kind of memory effect that is superimposed on the next pulse voltage. In considering the charge Q of internal polarization,
The charge due to the write pulse voltage V _D is Q ⁺ , and the charge due to the reverse polarity refresh pulse voltage V _R is Q ⁻ . Since the charges (Q ⁺ , Q ⁻ ) are internally discharged, the longer the rest period, the larger the amount of attenuation. The deviated state of accumulation of the charge amount of the internal polarization at the EL layer interface is shown by a broken line, and the write pulse voltage V _D to the refresh pulse voltage V _R are applied to each of the A, B, and C scan lines.
Time t _d until application of voltage and refresh pulse voltage V _R
Time t _R from application of write pulse voltage to application of write pulse voltage V _D
In the relative comparison at A, the first line of A: | Q ⁺ · t _D |
<| Q ⁻ · t _R | ... (t _D > t _R ), B-th n / 2 line:
^{_{| Q + · t D | =}} | Q - · t R | ... (t D = t R) C n-th line ^{_{| Q + · t D |>}} | Q - · t R | ... (t D <t
_In the upper part except the central part, the internal polarization is larger in the overlap with the write pulse voltage V _D , while in the lower part, the internal polarization is larger in the weight by the refresh pulse voltage V _R.

D shows the average accumulated charge amount in each scanning line time during one frame, and the positive and negative accumulated charge amounts are offset to the EL layer interface with the n / 2th line as the zero center.

That is, since the phase difference between the write pulse voltage V _D and the refresh pulse voltage V _R basically becomes the difference in polarization amount, the difference in polarization amount becomes large between the write pulse voltage V _D and the refresh pulse voltage V _R. Is closer to each other, and the shift phenomenon tends to be remarkable in the upper and lower portions of the display pattern.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above, in the conventional simultaneous inversion refresh driving method, an asymmetrical phase relationship occurs between the write pulse voltage and the refresh pulse voltage, and the non-uniformity of the internal polarization causes non-uniformity of the display panel. Since the shift phenomenon at the upper and lower portions is strong, an afterimage is generated in a fixed pattern display for a long period of time, resulting in deterioration of display quality. The present invention has been made in order to improve the above in view of the above point, and it is an object of the present invention to provide a new driving method in which the shift phenomenon does not occur by making the amount of internal polarization uniform regardless of the position of the scanning electrode. To aim.

Means for Solving the Problems The present invention is a method for driving a thin film EL display panel in which the order of line-sequential scanning is reversed frame by frame in the simultaneous inversion refresh driving method.

Function The present invention cancels the imbalance of the internal polarization amount of the EL display element between the odd-numbered frame and the even-numbered frame by the above-described driving method, thereby making the internal polarization amount uniform as a whole, thereby preventing the shift phenomenon. it can.

EXAMPLE FIG. 1 is a waveform diagram of a pulse voltage applied to a thin film EL display panel for explaining an example of the present invention. here,
A, B, and C are the same as in FIG. 4 of the conventional example, where A is the first scan line, B is the n / 2th scan line, and C is the applied voltage waveform of the nth scan line. The drive system of the present invention will be described below. In the first frame, the writing pulse voltage V _D is line-sequentially scanned from the top to the bottom, and after the scanning is completed, all the scanning electrode lines are refreshed with a polarity opposite to that of the writing pulse voltage V _{D in} order to refresh the entire display panel. applying a pulse voltage _{V R.} In the next second frame, line-sequential scanning is performed from the bottom to the top in the line-sequential scanning direction, the write pulse voltage V _D is applied, and after the scanning is completed, the refresh pulse voltage V _R is similarly applied. . (That is, the first line scanned first in the first frame is scanned last in the second frame, and similarly, the nth line scanned last in the first frame is scanned first in the second frame.) In this way, the direction of line-sequential scanning is reversed for each frame. As is apparent, the phase relationship between the applied voltages (V _D , V _R ) in the odd frame and the even frame can be made symmetrical. A comparison of the charge amount of the internal polarization in this driving method similar to that in the case of FIG. 4 shows that between the first and second frames A first scanning line: | Q ⁺ · t _D1 | = | Q ⁻ · t _R1 |, | Q ⁺ · t _D2 | = | Q ⁻ · t _R2 | …… t _D = t _RB nth scan line: | Q ⁺ · t _D1 | = | Q ⁻ · t
^{_{R1 |, | Q + · t}} D2 | = | Q - · t R2 | ...... t D = t R C n-th scan _{^{line: | Q + · t D1 |}} = | Q - · t R1 |, | Q + _{· t D2 | = | Q -} · t R2 | ...... t D = t R becomes positive and negative charge amount becomes the same value in any scan line, the charge of the EL layer interface since uneven internal polarization is eliminated It is possible to prevent the shift phenomenon as a result without deviation of accumulation.

Since the accumulated charge amount is related to the applied voltage value, the condition of V _D = V _R is the most desirable. FIG. 2 shows a configuration example of the drive circuit. The thin film EL display panel 1 is provided with scan electrodes 2 and data electrodes 3 arranged in a matrix, and each electrode is connected to drive circuits 4, 5 and 6 which are composed of a shift register circuit, a latch circuit, and a high breakdown voltage driver circuit (not shown). Has been done. Here, 4 is a data side driving circuit, 5 is a scanning side odd frame driving circuit, and 6 is a scanning side even frame driving circuit. or,
Reference numerals 7, 8 and 9 are pulse voltage generation circuits for turning on and off the EL display panel, 7 is a data side modulation drive circuit, 8 is a scanning side modulation drive circuit, and 9 is a refresh drive circuit. One frame of data is stored in the display data signal by the one-frame memory circuit 10. Here, the output of the frame synchronization signal circuit 11 corresponds to the order from the upper part to the lower part of the scanning line in the odd-numbered frame, and reverse in the even-numbered frame. The display data is output from the 1-frame memory circuit 10 and input to the DATA terminal of the data side drive circuit 4 in the order corresponding to the lower part to the upper part of the scanning line. Similarly, for the scanning side, the output of the frame synchronization circuit 11 is sent to the scanning signal circuit 12, where the scanning signal output is supplied to the DAT of the scanning side odd frame driving circuit 5 in the odd frame.
It is supplied to the A terminal and to the DATA terminal of the scanning side even frame drive circuit 6 in the even frame. As a result, during odd-numbered frames, the scanning-side odd-numbered frame driving circuit 5 performs line-sequential scanning from the upper side to the lower side as indicated by the arrow. On the other hand, during even-numbered frames, the scanning-side even-numbered frame driving circuit 6 moves from the lower side to the upper side. Line-sequential scanning is performed. Since the DATA input signal of the data side drive circuit 4 is input corresponding to the scanning order of the line-sequential scanning of the scanning side drive circuits 5 and 6, the display panel 1 displays substantially corresponding to the display data signal. It In addition, here, since the line-sequential scanning direction is changed for each frame, two sets for the odd-numbered frame and the even-numbered frame are used as the scanning side drive circuit
If the shift register circuit in the drive circuit has a drive circuit configuration in which two or more shift register circuits are bidirectionally connected in parallel and each shift direction can be shared for each frame, scanning can be performed. Only one side drive circuit is required. Further, although the line-sequential scanning direction is reversed every frame in the embodiment, the number of frames required for line-sequential scanning from the upper or lower portion is not limited to this (for example, switching of the line-sequential scanning direction for every 10 frames, etc.). Needless to say, if the condition of () is satisfied, the polarization amount can be basically made uniform and the shift phenomenon can be prevented.

As described above, according to the present invention, in the simultaneous inversion refresh driving method, the driving method in which the scanning direction of the line-sequential scanning is reversed for each frame is performed, so that the interface of the EL elements is spread over the entire scanning line. By eliminating the bias of charge accumulation by making the amount of internal polarization uniform, it is possible to prevent a shift phenomenon in which an afterimage of a display pattern occurs over the entire surface of an EL display panel, and display quality is improved. Its practical effect is great.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing a voltage waveform applied to a thin film EL display panel in a method of driving a thin film EL display panel of the present invention,
FIG. 2 is a block diagram showing the configuration of a specific drive circuit of the same method, and FIG. 3 is a characteristic showing voltage-luminance characteristics of an EL element that has caused a shift phenomenon and a normal EL element in the display of a conventional thin film EL display device. FIG. 4 and FIG. 4 are waveform diagrams showing applied voltage waveforms for explaining a driving method of a conventional thin film EL display device. V _D ... write pulse voltage, V _R ... refresh pulse voltage, 1 ... thin film EL display panel, 4 ... data side drive circuit, 5 ... scan side odd frame drive circuit, 6 ... scan side even frame drive Circuit, 10 ... 1 frame memory circuit, 11 ... Frame synchronization signal circuit, 12 ... Scan signal circuit.

Claims (1)

[Claims] 1. A thin film EL display panel in which scan electrodes and data electrodes are arranged in a matrix is line-sequentially scanned by applying a write panel voltage along the scan electrodes, and a refresh pulse is applied to the entire surface of the EL display panel after one field scan is completed. A method for driving a thin film EL display panel, wherein the scanning direction of line-sequential scanning is reversed for each frame.