JPH0661028B2 - Liquid crystal display - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and in particular, a screen is divided into a plurality of blocks, and a voltage applied to a liquid crystal layer in each block is reversed in polarity for two frame times. However, the present invention relates to a liquid crystal display device that is suitable for preventing the occurrence of display unevenness in a liquid crystal display device that is driven by alternating current and driven in a time division manner.

[Background of the Invention]

When a liquid crystal display element is driven in a time-division manner, a voltage averaging method is generally used as a driving method, and the polarity is inverted within one frame time (a time for scanning all scanning lines once) to be converted into an alternating current. (Hereinafter, referred to as A method) and one that inverts the polarity in two frame times to make alternating current (hereinafter referred to as B method) 2
There are different types of methods. For these driving methods, see, for example, Nikkei Electronics August 16, 1980, pp. 150-1.
It is discussed in detail on page 74.

The time-division driving method of the liquid crystal display element is also described in the above-mentioned document, but at present, in order to reduce the load on the driver LSI, the B-method driving is mainly used as the time division number increases. ing.

A screen division method is used as the number of display pixels increases. For example, as shown in FIG. 1, the screen is divided into two parts in the vertical direction and is driven. A liquid crystal panel 3 consisting of 2n scanning lines is scanned with a first block 3a consisting of scanning lines X _{1 to} X _n. Second block 3 consisting of lines X _{n + 1 to} X _2n
It is divided into two, and each scanning line is driven with a 1 / n duty.

FIG. 2 is a block diagram for explaining an example of a conventional liquid crystal display device. In FIG. 2, 1 is composed of a liquid crystal panel in which a plurality of liquid crystal pixels are arranged in a matrix and a liquid crystal drive circuit thereof. 2, a controller circuit for controlling the operation of the liquid crystal module 1 is a commercially available product, for example, a liquid crystal controller board CB1026R manufactured by Hitachi Ltd. 3 is a liquid crystal panel 4a, 4b shown in FIG. Are signal lines Y ₁ in the Y-axis direction of the first block 3a and the second block 3b of the liquid crystal panel 3, respectively.
Y ₂ , Y _3, ... Segment side drive circuit for outputting a signal voltage to Y _m , 5 is a scanning line (X ₁ , X ₂ ,
X ₃ , ... X _n ) and (X _{n + 1} , X _{n + 2} , X _{n + 3} , ... X _{2 n} ) are sequentially output to the scanning side drive circuit, and 6 is a segment. A liquid crystal driving power supply circuit for supplying a predetermined voltage for driving the side driving circuits 4a and 4b and the scanning side driving circuit 5 by the voltage averaging method, and 7 is a latch signal C as a timing signal for operating the liquid crystal module 1.
L ₁ , a data shift signal CL _2, and a timing generation circuit for outputting an AC signal M for inverting the polarity of the applied voltage; 8 is a power supply circuit for supplying a predetermined voltage to the liquid crystal drive power supply circuit 6; D ₁ , D ₂ is the signal electrodes Y ₁ , Y ₂ , ... Of the first block 3a and the second block 3b of the liquid crystal panel 3, respectively.
A data terminal for serially inputting ON / OFF information of all pixels on Y _m , and f _F is a frame signal input terminal.

3 (a) to 3 (d) show timings of output signals in the B system drive of the controller circuit 2 shown in FIG.

In such a configuration, on / off information signals of all pixels on a certain scanning line are serially input to the data terminals D ₁ and D ₂ . Segment side driving circuit 4a, a shift register in 4b is slide into shift Yotsute data to the data shift signal CL _2. Then, when the serial data is full in the shift register, the latch signal CL ₁ is output and latched by the latch circuit. It is possible to switch the analog multiplexer according to the latch data, output a selection / non-selection pulse, and light an arbitrary dot. In this case, the latch signal CL ₁ has a relationship of generating a signal at each time obtained by dividing the frame period γ _F by the time division number n and latching the data. Further, in this B system drive, as described above, 2
The polarity of the liquid crystal drive waveform is inverted in the frame to make a complete AC, and the AC signal M having a period twice the frame period γ _F is used to make a complete AC.

Liquid crystal panel shown in FIG. 1, that is, the scanning lines total number 2n present, a first block 3a consisting of the scanning lines _X 1 to X _n, is divided into two blocks of the second block 3b consisting of the scanning line _{X n} + 1 _~X2n The liquid crystal panel 3 and the liquid crystal driving power supply circuit 6 as shown in FIG.
When the black pattern is lit up and displayed on the entire surface of the liquid crystal panel 3 by the system drive, as shown in FIG. 5, the first scanning line X ₁ of the first block 3a and the first scanning line X ₁ of the second block 3b are displayed.
It was observed that the display on _{n + 1} was lighter than the other scan lines. The mechanism of occurrence of this phenomenon is
In the case of the system drive, the start point of the polarity inversion of the drive waveform applied to the liquid crystal layer, that is, the switching point of the alternating signal M is the first scan line X ₁ and the second block 3b of the first block 3a, respectively. Since it corresponds to the _first scanning line X _{n + 1} , it can be considered as follows.

That is, when the alternating signal M is switched, the polarity of the voltage applied to the liquid crystal layer is inverted, and a large transient current flows into the resistor R ₄ (LSI latch-up prevention resistor) of FIG. _The voltage waveform applied to the scanning lines X ₁ and X _{n + 1} is distorted by the resistance capacitance circuit of ₄ and the capacitance C of the liquid crystal layer, and the effective voltage value of these scanning lines is different from the effective voltage value of the other scanning lines. This causes unevenness in display.

Here, R ₁ and R 4 in FIG. ₄ are resistors for preventing the latch-up of the LSI, and R ₂ and R ₃ are predetermined voltages when the liquid crystal is driven by the voltage averaging method. Is the resistance needed to provide. Further, the transistor used for the V ₀ receiving port of the power supply circuit is for making the power supply circuit on the user side less likely to be affected.

As a measure for solving the display unevenness problem, it is conceivable to reduce the value of the resistor R ₄ , but this is not preferable from the viewpoint of preventing the latch-up of the LSI and the capacitance C of the liquid crystal.
It is impossible to set the value to zero, and it has been impossible to eliminate display unevenness.

[Object of the Invention]

Therefore, the present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a liquid crystal display device that prevents the occurrence of display unevenness that occurs when the polarity of a drive waveform is inverted. It is in.

[Outline of Invention]

In order to achieve such an object, according to the present invention, when a drive waveform applied to a liquid crystal layer is polarity-reversed in two frame times and is made alternating, the switching point of polarity reversal is sequentially moved on the display screen. is there.

Example of Invention

 Next, embodiments of the present invention will be described in detail with reference to the drawings.

In one embodiment of the present invention, as shown in FIG.
LCD module 1 and controller circuit 2 (Hitachi LCD control board CB available as Ichisaka product)
₁₀₂₆ R can be used) and a counter circuit 10 that counts the latch signal CL ₁ and outputs a new AC signal M ′ (commercially available Hitachi 4-Dual 4-bit)
Binary Counter HD74HC393 can be used). The E _x -OR 6 Figure is used for AC-driving the liquid crystal panel, M "was convex an exclusive OR of the original output signal M of the AC signal M and Kauta 'from the controller It is an output signal.

Here, the new alternating signal M'is originally the alternating signal M (in the case of the B system, at a frequency of 1/2 of the frame frequency 1 / γ _F ,
By setting the count so that it does not become an integer multiple of the frequency of the (signal synchronized with this), the start point of the polarity inversion of the drive waveform is not fixed to a specific scan line in each block of the liquid crystal panel, and the display This is to improve the unevenness.

FIG. 7 shows the timing of these signals.
In the B mode drive, if the number of time divisions in a block with a liquid crystal panel is n and the pulse count number of the latch signal CL ₁ is P (the frequency division number of CL ₁ is 1 / 2P), the frame period γ _F The number of pulses of the latch signal CL ₁ is n = mP + Q (1) where m is a positive integer and P> Q, Q ≠ O. Here, preferably, if the count number P of CL ₁ is selected so that −5 ≦ Q ≦ 5, the movement of the scanning line where polarity inversion occurs becomes smooth.

In FIG. 7, the period γ _M of the M signal and the period γ of the M ′ signal
_Since the relation of _M ′ is set so that 1 / γ _M ′ does not become an integral multiple of 1 / γ _M , the starting point of the polarity reversal of the voltage applied to the liquid crystal layer, that is, the new alternating signal M ′ The switching point is not fixed to a specific scanning line, that is, the scanning line which is the starting point of the polarity reversal is moved and dispersed for each frame, so that display unevenness does not occur. Arrow in Fig. 8 →
Shows the movement of the switching point of the alternating signal M ′ for each frame.

Example CL ₁ count number P: 16 Frame frequency _F : 80 Hz Frequency of signal M: 40 Hz The frequency of the new alternating signal M'is In the embodiment, it is 250 Hz. Further, when the count number P used in the embodiment is substituted into the equation (1), Q becomes 4, and this numerical value indicates that the start point of the polarity inversion for each frame corresponds to 4 cycles of CL _1. In the embodiment, it is 10 mSec. By selecting Q between -5 and 5, the display unevenness that occurs at the time of polarity reversal is dispersed over the entire display surface, which cannot be detected practically, and the problem of display unevenness can be solved.

Although the frame frequency is set to 80 Hz in the embodiment, the present invention is not limited to this, and the frame frequency range is 40 to 80 Hz, and the time division number n is 16 to 300.
The same effect is achieved in the range up to. The count number P of CL ₁ can be a value that satisfies the expression (1).

In the embodiment, the reason why P is as large as 6 is
The effect of preventing the display unevenness that occurs when the liquid crystal panel in which the frequency characteristics of the threshold voltage V _th of the liquid crystal of the L and D panels 3 in the figure drop at a low frequency as shown in FIG. It was because I aimed at. New AC signal M ″
Is a widely used controller circuit IC,
Since it can be manufactured by only adding two CMOS circuits, there is no problem in terms of cost increase. Also, the whole circuit including the counter circuit can be handled at the same time as the conventional circuit when viewed from the outside, and therefore the system compatibility is good.

Although the division of the latch signal CL ₁ in the binary counter in the above-mentioned embodiment having conducted, the present invention is not limited thereto, and means also E _x -OR for AC driving the liquid crystal
Of course, the method using the gate is not limited.

〔The invention's effect〕

As described above, according to the present invention, when the display screen is divided into a plurality of blocks and the time-division driving is performed, the position of the scanning line where the polarity inversion starts is moved and dispersed for each frame, so that the display unevenness is surely prevented. It is possible to obtain a liquid crystal display device having high image quality, which is an extremely excellent effect.

[Brief description of drawings]

FIG. 1 is a diagram showing an example in which a screen of a liquid crystal panel is vertically divided into two parts, and FIG. 2 is a block diagram of a liquid crystal module for explaining an example of a conventional drive circuit for a liquid crystal display device, and FIG.
(a) to (d) are operation timing diagrams of FIG. 2, FIG. 4 is a circuit diagram showing an example of the liquid crystal driving power supply circuit of FIG. 2, and FIG.
FIG. 6 is a diagram for explaining the occurrence of display unevenness that occurs when the liquid crystal panel of FIG. 1 is fully illuminated, FIG. 6 is a circuit diagram for explaining an example of the liquid crystal display device according to the present invention, and FIGS. FIG. 6 is an operation timing chart, and FIG. 9 is a diagram showing the frequency dependence of the threshold voltage of the liquid crystal panel. 1 ... Liquid crystal module, 2 ... Controller circuit, 3 ...
... Liquid crystal panel, 4a, 4b ... Segment side drive circuit,
5 ... Scanning side drive circuit, 6 ... Liquid crystal drive power supply circuit, 7
...... Timing generator circuit, 8 …… Power supply circuit, 10 …… Counter circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Sakuma, 3300, Hayano, Mobara, Chiba Prefecture, within the Mobara Plant, Hitachi, Ltd. (72) Inventor, Kiyoshige Kinugawa, 3300, Hayano, Mobara, Chiba, Ltd., within the Mobara Plant, Hitachi, Ltd.

Claims (1)

[Claims] 1. A liquid crystal panel, in which liquid crystal pixels are arranged in a matrix, is divided into a plurality of blocks in the scanning direction, and the voltage applied to the liquid crystal pixels in each block is reversed in polarity for 2 frame times to make alternating current. A liquid crystal display device that is dividedly driven, in which a scanning line at which polarity inversion of a voltage applied to a liquid crystal pixel starts is moved for each frame.