JPH0442653B2 - - Google Patents

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] This 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 rewrite display content, scanning is performed immediately. without driving the line,
By waiting for the backlight source to turn off before starting scanning, it is possible to eliminate flickering on the screen due to changes in the light transmittance of the liquid crystal panel while it is being driven.

[Prior art] The liquid crystal display elements commonly used are:
It is a twisted nematic (TN) type liquid crystal element. This element transmits light when voltage is applied and blocks light when no voltage is applied (or vice versa).
This takes advantage of the characteristics of type liquid crystal. 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-described ferroelectric liquid crystal element in a matrix, pixels on a scanning line to which no scanning signal was applied were supplied with +V or - from the display signal line. A display signal of V is applied, but it has been found that even if +V or -V is a voltage below the threshold value, the amount of transmitted light changes temporarily while it is being applied. This will be explained below with reference to FIGS. 3 and 4. 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 equal to or higher than the threshold value is applied, the cells that were in the light-blocking state shift to the light-transmitting state as shown in FIG. 3a, and the cells that were in the light-transmitting state shift to the blocking state as shown in FIG. 3b. On the other hand, when a pulse below the threshold is applied, the cell that was in the light blocking state momentarily transmits light as shown in Figure 4a and then returns to the steady blocking state, and the cell that was in the transmitting state returns to the steady blocking state. As shown in FIG. 4b, the amount of transmitted light is momentarily reduced and then returned 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 a change in the amount of transmitted light, and the amount of light varies depending on the voltage applied to the signal electrode 43, so flickering occurs on the entire screen. This poses a problem in that it is extremely difficult for the user to see and has an adverse effect on the eyes.

The present invention has been made in view of the problems of the prior art described above, and an object of the present invention is to provide a flicker-free and easy-to-read ferroelectric liquid crystal device.

[Means for Solving the Problems] The present invention provides: a scanning signal lines and information signal lines that intersect at intervals; a matrix of pixels formed at the intersections; and the scanning signal lines and information signal lines. a liquid crystal panel having a ferroelectric liquid crystal disposed between the ferroelectric liquid crystal and the ferroelectric liquid crystal that is oriented in one of the orientation states and the other orientation state depending on the polarity of the applied voltage; b. a light source arranged to illuminate the liquid crystal panel from the back by outputting a light/dark discrimination signal that changes periodically between the bright and dark states, and sequentially scans and selects the scanning signal line; By applying a scanning selection signal and applying an information signal corresponding to the information to the information signal line in synchronization with the scanning selection signal, writing to pixels on the scanning signal line selected for scanning is performed. , a driving means for applying a scanning non-selection signal to the scanning signal line which is not selected for scanning so that the pixel on the scanning signal line which is not selected for scanning so that the pixel maintains its written state; d. means for generating a write instruction signal for instructing the driving means to write; In this state, when the dark discrimination signal of the light/dark discrimination signal and the write instruction signal are both inputted, the driving means causes the scanning signal line to be This is a ferroelectric liquid crystal device having a synchronizing means for outputting a scanning selection signal to perform writing. Further, in the liquid crystal display device according to the present invention, it is desirable that the blinking frequency of the back light source is 100 Hz or more.

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

[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 the external input device 8, the display control section 4 outputs a write command signal from the B terminal. On the other hand, the back light source driving section 3 outputs a bright/dark identification 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 NAND signal, and are supplied as a shift clock to the shift register of the scanning side drive section 6, and the display control section 4.
It is also supplied as a latch pulse to the C terminal of and the signal side drive unit 7. 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.

FIG. 2 shows the above operation using a timing diagram of each signal. In FIG. 2, L is the brightness of the back light source, A is the brightness discrimination signal output from the A terminal of the back light source control section 3, B is the writing state signal output from the B terminal of the display control section 4, and C is the gate. The output signal of circuit 9 shows the NAND signal of A and B. Since the shift register of the scanning side drive unit 6, the C terminal of the display control unit 4, and the latch of the signal side drive unit 7 are all triggered by the falling edge of the C signal, the display control unit is activated by external input at time _T1 . Even if the write instruction signal No. 4 is output, 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 the transmittance of the liquid crystal cell due to the application of an electric field do not appear as flickering on the screen, making it possible to obtain an easy-to-read display screen.

Note that if the blinking frequency of the backlight source is too low, it will be perceived as flickering to the human eye, so it is desirable that it be at least 100Hz or higher. Therefore, if the lighting duty is 50%, then 1
The light-off period during the cycle is 5 msec or less, but since the response speed of ferroelectric liquid crystal is extremely fast, 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 In ₂ O ₃ , SnO ₂
It is a substrate (glass plate) coated with transparent electrodes such as ITO (Indium-Tin-Oxide), etc., and SmC ^* phase liquid crystal with the liquid crystal molecular layer 32 oriented perpendicular to the glass surface is sealed between them. There is. A thick line 33 represents a liquid crystal molecule, and this liquid crystal molecule 33 has a dipole moment P⊥34 in a direction perpendicular to the molecule. Boards 31 and 3
When a voltage higher than a certain threshold is applied between the electrodes 1', the helical structure of the liquid crystal molecules 33 is unraveled, and the orientation direction of the liquid crystal molecules 33 can be changed so that the dipole moment P⊥34 is all oriented in the direction of the electric field. can. The liquid crystal molecules 33 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. Therefore, for example, polarizers arranged in a crossed nicol position can be placed above and below the glass surface. For example, it is easily understood that the liquid crystal optical modulation element is a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of applied voltage. Furthermore, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1μ), the helical structure of the liquid crystal molecules unravels (non-helical structure) even when no electric field is applied, as shown in Figure 6, and the bipolar structure The child moment P or P' takes either an upward direction 34a or a downward direction 34b. When an electric field E or E' with a different polarity above a certain threshold value is applied to such a cell for a predetermined time as shown in FIG.
Corresponding to the electric field vector of E', the upward direction 34a or
The direction is changed from the downward direction 34b, and 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. The second point will be explained with reference to FIG. 6, for example. When the electric field E is applied, the liquid crystal molecules are aligned in a first alignment state 35, and this state remains stable even when the electric field is turned off. Moreover, when an electric field E' in the opposite direction is applied, the liquid crystal molecules are aligned to the second alignment state 35' and the orientation of the molecules is changed.
It remains in this state even if the electric field is turned off.
Also, as long as the applied electric field E does not exceed a certain threshold,
They are still maintained in their respective orientation states. In order to effectively realize such fast response speed and bistability, it is preferable for the cell to be as thin as possible, generally 0.5μ to 20μ, especially 1μ to 5μ.
is suitable. A liquid crystal electro-optical device having a matrix electrode structure using this type of ferroelectric liquid crystal has been proposed, for example, by Clark and Ragaval in US Pat. No. 4,367,924.

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. 8a and 8b show electrical signals applied to the selected scanning electrode 42s and electrical signals applied to the other scanning electrodes (unselected scanning electrodes) 42n, respectively, and FIGS. 8c and d show the electrical signals applied to the selected scanning electrode 42s, respectively. The electric signal applied to the selected signal electrode 43s and the electric signal applied to the unselected signal electrode 43n are shown. In FIGS. 8a to 8d, the horizontal axis represents time and the vertical axis represents voltage. for example,
When displaying a moving image, the scanning electrode group 42
are selected sequentially and periodically. Now, if the threshold voltage for providing the first stable state of the liquid crystal cell having bistable property is Vth ₁ , and the threshold voltage for providing the second stable state is -Vth ₂ , then the selected scan electrode 42s The electrical signal given to
As shown in , the voltage is alternating such that it is V at phase (time) t ₁ and −V at phase (time) t ₂ . Further, the other scanning electrodes 42n are in a grounded state as shown in FIG. 8b, and have an electric signal O. On the other hand, the selected signal electrode 43
The electric signal applied to s is V as shown in FIG. 8c, and the unselected signal electrode 43n
The electrical signal applied to is -V as shown in Figure 8d.

In the above, the voltage V is set to a desired value that satisfies V<Vth ₁ <2v and -V>-Vth ₂ >-2V. FIG. 9 shows a voltage waveform applied to each pixel when such an electric signal is applied. 9a to 9d 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 _Vth1 is applied to the pixel A on the selected scanning line at phase _t2 . In addition, for pixel B existing on the same scanning line, the _threshold value -
A voltage of −2V exceeding Vth ₂ is applied. Therefore,
Depending on whether or not a signal electrode is selected on the selected scanning electrode line, if 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. 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 unselected scanning lines, the voltages applied to all pixels C and D are +V or -V, 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 described above, according to the present invention, the drive circuit causes the back light source to blink at a constant frequency, and after the display control circuit issues a write command, the drive circuit controls the back light source at a timing when the back light source is turned off. By driving the panel, flickering of the screen due to changes in the light transmittance of the liquid crystal panel during driving can be eliminated, and an easy-to-read display device can be obtained.

[Brief explanation of drawings]

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

Claims (1)

[Scope of Claims] 1a A scanning signal line and an information signal line that intersect with each other at intervals, a matrix of pixels formed at the intersections thereof, and a voltage source arranged between the scanning signal line and the information signal line. a liquid crystal panel having a ferroelectric liquid crystal that is oriented in either one of the orientation states and the other orientation state depending on the polarity of the voltage; b. the amount of emitted light changes periodically between a bright state and a dark state; a light source arranged to output a bright/dark discrimination signal according to the bright state and the dark state and illuminate the liquid crystal panel from the back; c. sequentially scan and select the scanning signal lines and apply a scanning selection signal; By applying an information signal corresponding to the information to the information signal line in synchronization with the scanning selection signal, writing is performed to the pixels on the scanning signal line selected for scanning, and writing is performed on the pixels on the scanning signal line that is not selected for scanning. For pixels on the signal line, driving means applies a scanning non-selection signal to the scanning signal line which is not selected for scanning so that the pixel maintains its written state; d. instructing the driving means to write; means for generating a write instruction signal, and (e) writing to a pixel on a scanning signal line selected for scanning when the amount of light emitted from the light source is in a dark state, and when the amount of light emitted from the light source is in a bright state, writing is performed on a pixel on a selected scanning signal line; In order to prevent writing to the pixels on the scan signal line, the driving means outputs a scan selection signal to the scan signal line when both the dark discrimination signal of the light/dark discrimination signal and the write instruction signal are input. A ferroelectric liquid crystal device characterized in that it has a synchronizing means for writing data.