JPH027780A - Active matrix liquid crystal display driver - Google Patents

Abstract

PURPOSE:To reduce flicker by adopting a segmented common electrode and supplying an AC amplitude modulation pulse on a common potential. CONSTITUTION:The common electrode 9 is segmented for each row so as to supply a signal independently for each row and when a FET 3 is turned off, an AC signal in which the envelope of the amplitude peak varies opposite to the voltage drop is applied to other common electrodes 9 clipping the liquid crystal 1 while superimposed on the common potential so that the brightness change in each picture element due to the voltage drop caused during one frame of gate nonselection period caused by the effect of the resistive component of the liquid crystal 1 or the like. Thus, the brightness change is reduced considerably in average over each frame.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a driving device that can reduce flicker in an active matrix liquid crystal display.

[Conventional technology]

FIG. 3 is an equivalent circuit diagram of a conventional active matrix liquid crystal display. In the figure, 1 is a liquid crystal cell arranged in a matrix, 2 is a storage capacitor connected in parallel with each liquid crystal cell 1, and 3 is connected to one electrode (drain electrode or pixel electrode) of each liquid crystal cell 1. These three elements constitute one pixel. 4 is the manual electrode (source electrode) of FET3 for each column of the matrix
A plurality of X electrodes are commonly connected to each other, and a plurality of Y electrodes 5 are commonly connected to the gate electrodes of the FETs 3 for each row of the matrix. 6 is a scanning circuit that sequentially applies scanning pulses to the Y electrodes 5; 7 is a scanning circuit that samples and holds the video signal, converts the video signal for one horizontal scanning line into parallel video signals of the number of X electrodes, and sends them to the X electrodes 4; This is a serial/parallel conversion circuit that applies voltage. A common electrode 8 is commonly connected to the other electrode of all liquid crystal cells 1.

Next, a method of driving this display device will be explained.

Now, if the i-th row of the Y electrode is Yi, each ti of the Y electrode 5,
For example, the scanning circuit 6 applies waveform signals having timings such as those shown in FIG. 5 to the electrodes Y1 to Y4. When this scanning pulse is applied to the gate of FET3, all FET3 in the selected row are turned on,
A charge corresponding to the parallel video signal is charged from the X electrode 4 to the storage capacitor 2 via the FET 3. and FET3
Even when the storage capacitor 2 is turned off, a voltage corresponding to the video signal continues to be applied to the liquid crystal due to the charge stored in the storage capacitor 2, so that the transmitted light of each liquid crystal cell can be controlled by the video signal and displayed.

However, since there is a problem that the lifetime of the liquid crystal will be shortened if voltage of the same polarity is continuously applied to the liquid crystal, it is possible to use a liquid crystal that has the same transmitted light characteristics even if the polarity of the voltage applied to the liquid crystal is reversed Signal processing is performed such that the potential of the pixel electrode is inverted with respect to the potential Vc of the common electrode 8 at a frame period.

The above is an explanation of the driving method of an ideal active matrix liquid crystal display, but in reality, when the FET is OFF (non-selection period), the charge charged in each pixel by the resistance bone RLCD of the liquid crystal is transferred to the common electrode. Due to the influence of leakage, etc., the potential of each pixel fluctuates within the frame period.

FIG. 4 is a diagram illustrating fluctuations in the potential of the pixel electrode due to the influence of RLC0 in one frame of a certain pixel. The drop caused by RLCD in Figure 4 becomes approximately zero when RLCD becomes infinite, and if there are no fluctuation factors other than RIll, it will remain the same for one frame at positive polarity or negative polarity. Since voltage continues to be applied to the liquid crystal, the brightness does not change from frame to frame over time, and no flicker is felt.

[Problem to be solved by the invention]

The driving method of the conventional active matrix liquid crystal display is as described above, so in reality, RLCD0
Since the value is finite, there are problems such as brightness changes within one frame due to various influences, such as flickering.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to provide a driving device for an active matrix liquid crystal display that can reduce the above-mentioned flicker.

[Means to solve the problem]

The driving device for an active matrix liquid crystal display according to the present invention segments a common electrode in units of rows, and applies each common electrode (common line) to each pixel electrode potential within one frame period corresponding to that line. An alternating current amplitude modulation pulse that can cancel luminance changes due to average fluctuations over a frame is superimposed on the common potential and supplied.

[Effect]

In this invention, since the common electrode is segmented, it is possible to supply a correction pulse for brightness fluctuations whose temporal phase is aligned with the time point at which each pixel is selected to the common electrode of that pixel. Since the pulse is a signal in which an AC amplitude modulation pulse that can cancel the average brightness change over each frame within one frame period of that pixel is superimposed on the common potential, the above brightness change is significantly reduced and flicker is eliminated. Can be reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, l indicates liquid crystal cells arranged in a matrix, 2 indicates a storage capacitor connected in parallel with each liquid crystal cell 1, and 3 indicates one electrode (drain electrode or pixel electrode) for each liquid crystal cell 1. ), and these three elements constitute one pixel. 4 is a plurality of X electrodes commonly connected to the input electrode (source electrode) of the FET 3 for each column of the matrix, and 5 is a plurality of Y electrodes commonly connected to the gate electrode of the FET 3 for each row of the matrix. 6 is a scanning circuit that sequentially applies scanning pulses to the Y electrodes 5; 7 is a scanning circuit that samples and holds the video signal to convert the video signal for one horizontal scanning line into parallel video signals of the number of X electrodes, and applies the same to the X electrodes 4; This is a serial/parallel conversion circuit. Reference numeral 9 denotes a plurality of C electrodes (common lines) which are commonly connected to the other electrodes arranged in a matrix in each row of the liquid crystal cell 1;
is a common line driver that applies a common electrode potential and a correction pulse to each common line.

Next, a method of driving this device will be explained.

It is assumed that the i-th electrode of the X electrode 5 in FIG. 1 is Yi, and the yti-th row electrode of the C electrode 9 is Ci. Common line driver 1
0, a signal such as 01 to C4 shown in FIG. 2, which is formed by symmetrically superimposing rectangular wave pulses on the common electrode potential Vc, is applied to each C electrode 9. Furthermore, the scanning circuit 6 allows the X electrodes 5 to be connected to Y1 to Y1 shown in FIG. 2, as in the conventional example.
A scanning pulse such as Y4 is applied. Furthermore, when this scanning pulse is applied to the gate of the FET 3, all the FETs 3 in the selected row are turned on, and the storage capacitor 2 is charged with an electric charge corresponding to the parallel video signal from the X electrode 4 via the FET 3. This is also the same as in the conventional example.

Here, when FET3 is turned off, a voltage drop occurs during one frame of the gate non-selection period due to the influence of the liquid crystal resistance RLCll, etc., as shown in FIG. An alternating current signal whose amplitude peak value envelope is in the opposite direction to the voltage drop is superimposed on the common potential and applied to the other common electrode 9 sandwiching the liquid crystal so as to compensate for changes in pixel brightness. Therefore, the above luminance change can be canceled. In other words, the liquid crystal in TN (twisted nematic) mode responds not to the potential difference applied between its ends but to its effective value, so as mentioned above, the D of the common electrode
By superimposing a signal obtained by amplitude modulating the AC bone on the common electrode while keeping the C potential constant, it is possible to correct the brightness change described above.

Note that the common electrode is segmented for each row because the phase of the luminance change described above differs depending on the writing time to each pixel, so in order to cope with this, it is possible to supply signals independently for each row. .

Furthermore, although only frames at a certain time have been described above, when a moving image is displayed, the potential of the pixel electrode changes depending on each frame, and the intensity of flicker varies depending on the frame. however,
Even if the amount of fluctuation in the potential of the pixel electrode changes throughout all frames, the tendency does not change, so by superimposing a correction pulse on the Ci electrode that can compensate for the medium level of the fluctuation. , the luminance change can be significantly reduced on average over each frame.

In the above embodiment, a case was explained in which a rectangular waveform pulse as shown in FIG. It may also be a triangular wave or the like (which produces the same effect as the above embodiment).

〔Effect of the invention〕

As described above, according to the present invention, a common electrode is segmented, and an alternating current is applied to the common electrode, which can cancel the luminance change caused by the average fluctuation over each frame within one frame period of the pixel electrode potential corresponding to the line. Since the amplitude modulation pulse is supplied superimposed on the common potential, the average luminance change within one frame over each frame can be reduced, and flicker can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining a driving device for an active matrix liquid crystal display according to an embodiment of the present invention, FIG. 2 is a diagram showing the timing and waveforms of each part of FIG. 1, and FIG. FIG. 4 is a block diagram illustrating a driving device for a matrix liquid crystal display, and is a diagram illustrating dynamic characteristics per pixel. 1 is a liquid crystal cell, 2 is a memory capacitor, 3 is an FET, 4
5 is an X electrode, 5 is a Y electrode, 6 is a scanning circuit, 7 is a serial/parallel conversion circuit, 8 is a common electrode, 9 is a common electrode, and 10 is a common line driver (common electrode driving means). Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] (1) In a driving device for an active matrix liquid crystal display, a common electrode is provided segmented for each row, and each common electrode cancels brightness changes due to fluctuations in the pixel electrode potential corresponding to that line within its holding period. 1. An active matrix liquid crystal display driving device comprising: common electrode driving means for supplying an AC amplitude modulated pulse that can be applied in a manner superimposed on a common potential.