JPS5953890A - Tone display system for el display - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to a gradation display method f in a display device in which EL (electroluminescence) type display elements are arranged in a matrix.

(L)) Technical background and prior art+bL In a display system in which display elements are arranged in a matrix, each element is sequentially scanned, and information to be displayed is provided in synchronization with the scanning, the EL display elements themselves Because they do not have sufficient memory capacity, they must find some way to store information. Therefore, conventionally 1112Tr-IC
A circuit scheme has been proposed. This method stores information as a voltage on a capacitor, and each pixel is provided with a transistor for driving an element, a transistor for selecting an address, and a capacitor for storing data.

FIG. 1 shows this 2Tr=IC circuit type EL display device. In FIG. 1, a plurality of pixels are arranged in a matrix of m pixels in the vertical direction and n pixels in the horizontal direction. Each pixel is EL
2 for controlling the display of the display element ELlj.
It is provided with a number of biting transistors A, Qij, DΔ-j and a data storage capacitor Cij. That is, for example, the pixel in the first row and first column is a display element ELIl, a transistor Dll for driving the element, a transistor AQ11 for data selection, and a capacitor C1 for data storage.
Consists of l.

The gate terminals of the data selection transistors AQ and ij are connected to the 1-transistor Q for address selection corresponding to that row.
It is commonly connected to the emitter terminals of 1 to Qm, while its drain terminal is commonly connected to each of the data lines corresponding to that column.

Each pace of the transistors Qi'-Qm for address selection has a scan terminal S, which is an output line of the scan control circuit SCN.
01 to SCm are connected. Scan control circuit SON
is composed of a shift register (shift) 5vs SFT
Each time one is input, data is output in parallel at the scan end.

Next, the display operation will be briefly explained.

In synchronization with the shift pulse SFT, each scan terminal S01 to SCm of the scan control circuit SON sequentially outputs a scan signal. Now, considering the point in time when the null signal is output from the scan terminal SC1, the transistor Q, II''i for selecting 7FL/s is turned on, and the gate terminal of the transistor AQ+1-AQ, tn for selecting data in the first row is The strobe signal STB is input in synchronization with this Nucan pulse, and each data line D] to Dn
Output more data. The output of data lines D1 to Dn is 1
' The data selection transistor A (Il
Only l and lj are transistors Q and 1 for address selection.
．． The corresponding capacitor C1j? via the data selection transistor AQ1j? , 47 charges. This charging potential is set higher than the threshold level of the driving transistor I)lj, and its discharge time constant is set longer than the scanning period l frame. Charging of the capacitor C1j turns on the driving transistor Dij, and the display element E
Drive L1j. Note that one terminal of each display element ELi j is connected to a pulse oscillator, and this oscillator has a ±100 to
A pulse pulse signal of 200 (V) is applied. As described above, among the pixels whose scan terminal SCi is set to 11', the capacitor Cij corresponding to the pixel whose data line DI-Dn is set to ``1'' is charged, and the corresponding display element E is charged.
LL j lights up.

Now, if we look at the state of each display element in such a display device, we can see that the capacitor for data storage is charged and its charge w.
When the L potential exceeds the threshold level, the element lights up. Then, when the capacitor gradually discharges and its potential drops below the above-mentioned level, the element becomes non-lit. That is, since the element has two states, lit and non-lit, and the luminance of the element in the lit state is constant, it was not possible to display images in gradations.

(C) Object and Structure of the Invention The object of the invention is to enable gradation display of images in an FiL type display device.

Gradation control may include changing the ratio of light emitting time and non-light emitting time of a display element within a unit time according to brightness information.1 Changing the light emitting brightness of a display element depending on brightness information, but this method The invention is based on the former control method. That is, the present invention focuses on the fact that an EL display device has a data storage capacitor corresponding to the display element, and by changing the potential charged in this capacitor based on luminance information, By changing the ratio of lighting time to non-lighting time, images can be displayed in gradations.

(2)) Embodiments of the Invention The gradation display method according to the present invention will be explained in detail below with reference to the drawings. shows the signal waveform in the main part of this circuit. The connection status of the transistor 'rrl, T172 data storage capacitor Cs, display element EL, etc. is the same as that of the conventional one, but the transistor l1l
A gain select circuit SEL is provided before r1. The input of this brightness select circuit SEL is brightness information J)B corresponding to the image, and its output is a data signal DA, which is connected to the drain terminal of the transistor Trl. This brightness select circuit SEL performs the following functions.

That is, it has a function of determining the value of the brightness information DB and sending out a data signal DA having a voltage value corresponding to the chain.

For example, if the luminance information DB has a 2-bit configuration, FIG.
), ((!1. (Data signal D as shown in (1)
A1 to DA3 are output according to their values. data signal D
Al~DA3 17) i positive value” 1~V 3haV 1
<'V 2 (V 3 ) function fK is set.

A scanning signal Se is applied to the gate terminal of the transistor 1'r.
A N (see FIG. 3 (8,) i) is applied at a predetermined period. Every time this scanning signal SCΔN arrives, the control circuit Tr1 becomes conductive, and the capacitor OR is light-loaded. Of course, this capacitor C
The potential charged to 6 changes depending on the voltage value applied to the data signal. Specifically, when the data signal DA is DAI, that is, the voltage terminal is
In the case of 2, the charging potential becomes F;2 (E2>El),
In the case of DA3, it becomes 3 (E3>E2) (Figure 8 (
'El) , (f) , 'F)Zanzhou), capacitor CG
When we look at the relationship between the potential of capacitor C3 and the threshold voltage of qTr2 as it discharges, we see that since the discharge time constant is the same in both cases, the potential of capacitor C8 becomes the threshold voltage. The time to reach the lred voltage is different. That is, the charging potential is E
In the case of l, it becomes tl, and in the case of E2, it becomes ts in the case of j 2 + E 3. (tx<tg<t a ) Kot7J
Since the transistor Tr2 is in a conductive state during FRjnfJ tt, tg, and ts, voltage waveforms as shown in FIG. Emits light. Therefore, when the data signal DA is DAI, only tl of one period of the scanning signal 5CAN is in the light emitting state, in the case of DAz, only tg is in the light emitting state, and in the case of DA2, only ts is in the light emitting state. In this way, the ratio between the lighting time and the non-lighting time within a predetermined time is controlled according to the brightness information corresponding to the image, thereby making it possible to display the image in gradations.

In the above embodiment, the voltage m of the data signal DA(7) is changed depending on the luminance information, and as a result, the charging potential of the data storage capacitor is controlled. However, assuming that the voltage value of the data signal is constant, The time width may be changed depending on the luminance information. Furthermore, the voltage value or time width of the scanning signal 5CAH may be changed depending on the luminance information without changing the data signal DA. However, when controlling the charging potential based on the time width of each signal, it is necessary to consider the time widths of the opposing signals.

(e) As described in detail, the present invention utilizes a data storage capacitor required for a display device;
Since the charging potential is changed according to the luminance information, i? It becomes possible to perform gradation display even in the F:L type display device without using 1';

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional EL display device, FIGS. 2 and 3 are related to the present invention, FIG. 2 is a control circuit constituting one pixel, and FIG. 3 is a main part in FIG. 2. 2 is a flowchart showing waveforms of FIG. In the figure, DB is brightness information, SEL is brightness select circuit, D
A, DAl, DA2. D113 is a data signal, 5
CAN is a scanning signal, EL is a display element, and es is a data storage capacitor.

Claims (1)

[Claims] M) In a display device having capacitors for data storage arranged in an IJ-shaped configuration and corresponding to each of Y12L type display elements, the data storage is A gradation display method in an EL display device characterized by changing the charging potential of a capacitor.