JPS6294828A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To eliminate a flicker on a screen due to variation in the light transmissivity of a liquid crystal panel which is being driven by allowing a driving circuit to start driving the panel when a back light source is turned off. CONSTITUTION:When a write instruction is supplied from an external input device 8, a display control part 4 outputs a write state signal from a terminal B. A blink signal which indicates the on-off state of the back light source, on the other hand, is outputted from a back light source driving part 3 from a terminal A. Those two signals are inputted to a gate circuit 9 to become a NAND signal, which is supplied as a shift clock to the shift register of a scanning-side driving part 6. Those two signals are also supplied as latch pulses to a terminal C of the display control part 4 and a signal-side driving part 7. This control part 4 counts leading edges of the C terminal input and places the B terminal output in a nonwrite state when the counted value reaches the specific number of scans.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transmission type ferroelectric liquid crystal display device having a backlight source.

[Summary of the Disclosure] The present specification and drawings describe a transmissive liquid crystal display device having a backlight source, in which the backlight source is switched on and off at high frequency, and even if a display control circuit issues a command to change the display content. By not driving the scanning line immediately and starting scanning after waiting for the backlight source to turn off, it is possible to eliminate flickering on the screen due to changes in light transmission of the liquid crystal panel during driving. .

[Prior Art] A twisted nematic (TN) type liquid crystal element is commonly used as a liquid crystal display element. This element utilizes the property of TN liquid crystal, which transmits light when voltage is applied and blocks light when no voltage is applied (or vice versa). On the other hand, liquid crystal elements using ferroelectric liquid crystals that have a memory property of molecular orientation even when no voltage is applied have attracted attention in recent years.

[Problems to be Solved by the Invention] However, when the present inventors drove the above-mentioned ferroelectric liquid crystal element in a matrix manner, pixels on a scanning line to which no scanning signal was applied had no signal from the display signal line. +V or -■ display signal will be applied, but this +■ or -
It has been observed that even if V is a voltage below the threshold value, the amount of transmitted light changes temporarily while V is applied. below,
This will be explained with reference to FIG. 83 and FIG. FIGS. 3 and 4 show changes over time in the amount of transmitted light when pulse voltages above and below the threshold are applied. When a pulse higher than the threshold is applied, the cell that was in the light-blocking state is shown in Figure 3 (a).
), the cell changes to a transparent state, and the cell that was in the transparent state changes to a blocked state, as shown in FIG. 3(b). On the other hand, when a pulse of f14 value or less is applied, the cell that was in the light-blocking state momentarily transmits light and then returns to the steady-blocking state again, as shown in the 4th IN (a), and the cell that was in the transmitting state As shown in FIG. 4(b), the amount of transmitted light momentarily decreases and then returns to the steady transmission state.

That is, during the scanning period, not only the pixels on the selected scanning line but all the pixels exhibit changes in the amount of transmitted light, and the amount of light varies depending on the voltage applied to the signal electrode 43.
There was a problem in that the entire screen flickered, making it extremely difficult for the user to see and having an adverse effect on the eyes.

The present invention has been made in view of the problems of the prior art described above.
The object is to provide a display device that is flicker-free and easy to see.

c. Means for Solving Problems] The liquid crystal display device according to the present invention is composed of a transmissive ferroelectric liquid crystal panel having a backlight source, a stationary circuit of the panel, and a display control circuit. By switching on and off at high frequency, even if the display control circuit issues a command to change the display content, it does not immediately drive the scanning line, but waits for the backlight source to turn off before starting scanning. be.

Further, in the liquid crystal display device according to the present invention, it is desirable that the blinking frequency of the backlight source is 100t(z or more).

[Function] Scanning starts when the back light source is turned off, so it is not only effective against write portions due to voltages north of the threshold value, but also against instantaneous changes in transmitted light amount due to voltages below the threshold value in other pixels. Even on one screen, the change is not felt.

[Example] FIG. 1 is a schematic configuration diagram of a liquid crystal display device according to the present invention. In FIG. 1, when a write command is given from an external input device 8, the 1 display control section 4 outputs a write status signal from the B terminal. On the other hand, the back light source drive unit 3 outputs a blinking signal from the A terminal indicating whether the back light source is on or off.

These two signals enter the gate circuit 9, become a HAND signal, and are supplied to the shift register of the scanning side drive section 6 as a shift clock, and are also sent to the C terminal of the display control section 4 and the signal side drive section 7 as a latch pulse. will also be supplied.

The display control section 4 counts the rising edge of the C terminal input, and when a predetermined number of scan lines is reached, the B terminal output is set to a non-writing state. Note that, in parallel with these operations, the display control section 4 also performs an operation of sending data from the video memory to the shift register of the signal side drive section 7.

The rJtlz diagram shows the above operation as a timing diagram of each signal. In FIG. 2, L is the brightness of the back light source, A is the blinking signal output from the A terminal of the back light source control section 3, B is the write state signal output from the B terminal of the display control section 4, and C is the gate circuit. N of A and B with the output signal of 9
Shows an AND signal. a shift register of the scanning side drive unit 6;
Since both the C terminal of the display control unit 4 and the latch of the signal side drive unit 7 are triggered by the falling edge of the C signal, the time T
Even if the write state signal of the display control section 4 is outputted to I by external input, scanning is started at time T2. In this way, by delaying the scan start time in synchronization with the turning off of the back light source, it is possible to make the back light source turn off during the scanning period. Therefore, changes in transmittance caused by application of an electric field to the liquid crystal cell do not cause screen flickering, and an easy-to-read display screen can be obtained.

Note that if the blinking frequency of the backlight source is too low, it will itself be perceived as flickering to the human eye, so it is desirable that it be at least 100 Hz or higher. Therefore, the light-off period during the patent cycle, which is characterized by a lighting duty, is less than 5 m5ec, but since the ferroelectric liquid crystal has an extremely fast response speed, it is quite possible to complete scanning within this period.

Next, one embodiment of the liquid crystal cell used in the present invention will be described.

FIG. 5 schematically depicts an example of a ferroelectric liquid crystal cell. 31 and 31' are In2O3, 51102 and I
A substrate (glass plate) coated with a transparent electrode such as TO (Indium-Tin-Oxide), between which a liquid crystal molecular layer 32 is oriented perpendicular to the glass surface.
C" phase liquid crystal is sealed. The thick line 33 represents the liquid crystal molecule, and this liquid crystal molecule 33 has a dipole moment (on CP) 34 in the direction perpendicular to the molecule. When a voltage above a certain threshold is applied between the electrodes of the substrates 31 and 31'h, the helical structure of the liquid crystal molecules 33 is unraveled, and the liquid crystal molecules are arranged so that all dipole moments (Pyo) 34 are directed in the direction of the electric field. The orientation direction of the liquid crystal molecules 33 can be changed.The liquid crystal molecules 33 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. It is easy to understand that by placing polarizers arranged in the same relationship, it becomes a liquid crystal optical modulation element whose optical properties change depending on the polarity of applied voltage.Furthermore, if the thickness of the liquid crystal cell is made sufficiently thin (for example, 1 end) As shown in Figure 6, even when no electric field is applied, the helical structure of the liquid crystal molecules is released (non-helical structure), and its dipole moment) P or P' is directed upward (
34a) or downward (34b). When such a cell is subjected to an electric field E or E' of different polarity above a certain threshold value for a predetermined period of time as shown in FIG.
The dipole moment changes direction to an upward direction 34a or a downward direction 34b corresponding to the electric field vector of the electric field E or E',
Accordingly, the liquid crystal molecules are aligned in either the first alignment state 35 or the second alignment state 35'.

There are two advantages to using such a ferroelectric liquid crystal as an optical modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has a bistable state. To explain the second point using the example jf Fig. 6,
When the electric field E is applied, the liquid crystal molecules are aligned in a first alignment state 35, but this state remains stable even when the electric field is turned off. or,
When an opposite electric field E' is applied, the liquid crystal molecules are oriented to a second alignment state 35' and change their orientation, but they remain in this state even after the electric field is turned off.

Further, as long as the electric field E does not exceed a certain threshold value, each orientation state is maintained. In order to effectively realize such fast response speed and bistability, it is preferable for the cell to be as thin as possible, and in general, the cell should be as thin as possible.
．． 5, to 20 JL, especially 1p to 5 JL are suitable. A liquid crystal-electro-optical device having a matrix electrode structure using ferroelectric liquid crystals of this type has been proposed by Clark and Ragaval in US Pat. No. 4,387,924, for example.

FIG. 7 is a schematic diagram of a cell 41 having a matrix electrode structure in which a ferroelectric liquid crystal is sandwiched between.

42 is a scanning electrode group, and 43 is a signal electrode group.

FIGS. 8(a) and 8(b) show the electrical signals applied to the selected scanning electrode 42(S) and the electricity applied to the other scanning electrodes (unselected scanning electrodes) 42(r+), respectively. FIGS. 8(C) and 8(d) represent the electrical signal applied to the selected signal electrode 43(s) and the electrical signal applied to the unselected signal electrode 43(n), respectively. In Figures (a) to (d), the horizontal axis represents time and the vertical axis represents voltage. For example, when displaying a moving image, the scanning electrode groups 42 are sequentially and periodically selected. Now, the threshold voltage for providing the first stable state of a liquid crystal cell having bistability is V th+ ,
-vth2 threshold voltage to give the second stable state
Then, the electric signal given to the selected scanning electrode 42(s) is V at phase (time) 1+ and 1■ at phase (time) b, as shown in FIG. 8(a). It is an alternating voltage like that. In addition, other scanning electrodes 4
2(n) is in a grounded state as shown in the eighth UA(b), and is an electrical signal O. On the other hand, the electric signal returned to the selected signal electrode 43(s) is V as shown in FIG. 8(C), and the unselected signal electrode 43(s)
The electric signal given to 3(n) is 1.2 as shown in FIG. 8(d).

In the above, the voltage V is set to a desired value that satisfies V<Vth+<2v and -V>-Vth2>-2V. The voltage waveform applied to each pixel when such an electrical signal is given is rjS9
As shown in the figure. 9(a) to 9(d) correspond to pixels A, B, C, and D in FIG. 7, respectively. That is,
As is clear from FIG. 9, a voltage of 2v exceeding the threshold value V thl is applied to the pixel A on the selected scanning line at phase t2. In addition, in the case of pixel B existing on the same scanning line, the voltage -2 exceeding the threshold value -Vth2 at phase t1
v is applied. Therefore, depending on whether a signal electrode is selected on the selected scanning electrode line, if the signal electrode is selected, the liquid crystal molecules are aligned in the first stable state, and if not selected, the liquid crystal molecules are aligned in the second stable state. Align the orientation to a stable state. In any case, it has nothing to do with the previous history of each pixel.

On the other hand, as shown in pixels C and D, on the unselected scan line, the voltage applied to all pixels C and D is +V
or -■, neither of which exceeds the threshold voltage. Therefore, the liquid crystal molecules in each pixel C and D maintain the orientation corresponding to the signal state when scanned last time without changing the orientation state.

[Effects of the Invention] As explained above, according to the present invention, the backlight source is made to blink at a constant frequency, and after the display control circuit issues a write command, the drive circuit waits for the timing when the backlight source is turned off, and then By driving the panel, it is possible to eliminate flickering on the screen due to unchanged light transmission of the liquid crystal panel during driving, and to obtain an easy-to-read display device.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of a liquid crystal display device, Figure 2 is a timing diagram of each signal, Figures 3 and 4 are diagrams showing the optical response state of a liquid crystal cell, Figures 5 and 6 are diagrams showing ferroelectric FIGS. 7 to 9 are explanatory views of driving the matrix display panel. l...Liquid crystal panel, 2...Back light source, 3...Back light source drive unit, 4...Display control unit, 6...Scanning side drive unit, 7...Signal side drive unit, 9 ...Gate circuit.

Claims (1)

[Claims] 1) Consists of a transmissive ferroelectric liquid crystal display panel having a backlight source, a drive circuit for the panel, and a display control circuit, which causes the backlight source to blink at a constant cycle, and a A liquid crystal display device, wherein the output write signal is temporarily maintained, and a drive circuit starts driving the panel when the backlight source is turned off. 2) The liquid crystal display device according to claim 1, wherein the back light source has a blinking frequency of 100 Hz or more.