JPH1020275A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce shadowing by correcting the increase of an effective voltage due to a crosstalk noise generated in a non-selective voltage of a common driver by the output change of a segment driver. SOLUTION: The voltage waveform of a common electrode is discribed by a dot line in SEG1, SEG2. In order to prevent the generation of difference in an effective voltage by causing a crosstalk noise in the common electrode, correcting signals CC1, CC2 are formed from the crosstalk noise and the output waveform of SEG2 is corrected (d). At this time, at the changing point of the output signal of a segment driver at the time of white background display of the segment driver, the rise noise of the output signal of segment driver shown by SEG1 and the fall noise of the output signal of segment driver shown by SEG2 are detected by a circuit for detecting a crosstalk noise propagating to the common driver side as the crosstalk noise amount generated on a non- selected level VM, respectively, and outputted to the driver as CC1, CC2 pulse signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a driving method for a matrix type liquid crystal display device and a technique effective when applied to a driving circuit.

[0002]

2. Description of the Related Art STN (Super Twisted)
Nematic) simple matrix type liquid crystal display devices are widely used as display devices such as notebook personal computers.

FIG. 7 is a block diagram showing a schematic configuration of a conventional simple matrix type liquid crystal display device of the STN system, 101 is a display control device, 102 is a power supply circuit, 103
Is a conversion circuit, and LCD is a liquid crystal display panel.

A liquid crystal display panel LCD includes a pair of glass substrates disposed to face each other with a liquid crystal interposed therebetween. One of the glass substrates has a liquid crystal side surface extending in the X direction and having a Y direction.
The m common electrodes (scanning lines) arranged in the direction are formed, and each of the m common electrodes is connected to the corresponding common driver (IC-C1 to IC-C5).

On the liquid crystal side of the other glass substrate, there are formed n segment electrodes (data lines) extending in the Y direction and juxtaposed in the X direction. The segment electrodes are divided into upper and lower two, and each of the n divided segment electrodes is connected to a corresponding upper segment driver (IC-U1 to IC-U).
n) or each of the corresponding lower segment drivers (IC-L1 to IC-Ln).

The intersections between the plurality of segment electrodes and the plurality of common electrodes constitute a pixel area, and each of the upper segment drivers (IC-U1 to IC-Un) and each of the lower segment drivers (IC-L1 to IC-L1). IC-Ln) and the common drivers (IC-C1 to IC-C5) apply respective drive voltages to the plurality of segment electrodes and the plurality of common electrodes to drive the pixels.

In FIG. 7, a liquid crystal panel control device 101
Is based on a display control signal and display data transferred from the host computer or the like, and each segment driver (IC-U1 to IC-Un, IC-L1 to IC-Ln)
And controls each common driver (IC-C1 to IC-C5).

The power supply circuits 102 have different V
H, VM, VL, VxH, VxL, VxC, Vcc,
A voltage of GND is generated, and VH, VM, Vcc and GN are generated.
The voltage of D is applied to each segment driver (IC-U1 to IC-
Ln) and VxH, VM, VxL and VxC
Voltage of each common driver (IC-C1 to IC-C5)
To supply.

In the simple matrix type liquid crystal display device, the driving voltages applied to the plurality of segment electrodes and the plurality of common electrodes are inverted at a predetermined cycle so that no DC voltage is applied to the liquid crystal. A so-called AC drive method is employed.

FIG. 8 is a diagram for explaining a data line driving voltage applied to a segment electrode and a scanning line driving voltage applied to a common electrode of the conventional STN simple matrix type liquid crystal display device shown in FIG. FIG.

As shown in FIG. 8, for example, an AC signal M
Is High level, the drive voltage VL is supplied from the power supply circuit 102 to each segment electrode of data “1”, and the power supply circuit 1 is supplied to each segment electrode of data “0”.
02, the driving voltage VH is supplied and applied. Also,
When the AC signal M is at the low level, the drive voltage V from the power supply circuit 102 is applied to each segment electrode of data “1”.
H is supplied, and the drive voltage VL is supplied from the power supply circuit 102 and applied to each segment electrode of data “0”.

Similarly, when the AC signal M is at a high level, the drive voltage VxH supplied from the power supply circuit 102 is applied to the selected common electrode, and the AC signal M is Low.
When the level is at the level, the drive voltage VxL supplied from the power supply circuit 102 is applied to the selected common electrode, and the AC signal M is applied to the non-selected common electrode.
Regardless of the level or the low level, the power supply circuit 10
2 is applied.

FIG. 9 shows each segment driver (IC-U1 to IC-Un, IC-L1 to IC-Ln) shown in FIG.
FIG. 2 is a block diagram showing a schematic configuration of the embodiment.

The segment driver shown in FIG. 9 includes a shift register circuit 511, a bit latch circuit BR, a line latch circuit LR, a selector circuit 514, an output buffer circuit 515, and a random logic circuit 510.

Next, the operation of the segment driver shown in FIG. 9 will be described.

The shift register circuit 511 is provided with a display data latch clock C input from the display controller 501.
Based on L2, a signal for capturing data of the bit latch circuit BR is generated and output to the bit latch circuit BR.

The bit latch circuit BR latches 8-bit display data Din input from the display control device 501 based on a data capture signal input from the shift register circuit 511.

The line latch circuit LR latches the display data captured by all the bit latch circuits BR based on the output timing control line clock CL1 and outputs the latched display data to the selector circuit 514.

The selector circuit 514 converts the voltage level of the display data input from the line latch circuit LR to a high voltage level for driving the liquid crystal, and outputs the converted data to the output buffer circuit 515.
Output to

The output buffer circuit 515 includes a power supply circuit 1
A data signal line drive voltage of 02 to 3 levels is supplied. The output buffer circuit 515 receives one of the three levels of data signal line drive voltages supplied from the power supply circuit 102 from the selector circuit 514. And output to each segment electrode (data signal line) based on the high voltage level display data and the AC signal M.

In this case, each segment driver (IC
-U1 to Un, IC-L1 to Ln) output carry signals (EI / O1 or EI / O2),
The carry signal of the previous stage is directly input to the carry inputs of the segment drivers (IC-U1 to Un and IC-L1 to Ln) of the next stage. Ln), the display data fetch operation is controlled, and erroneous display data is transferred to each of the segment drivers (IC-U1 to Un, IC-
L1 to Ln).

When the segment driver shown in FIG. 9 is arranged above the liquid crystal display panel LCD and when arranged below the liquid crystal display panel LCD, the output terminals of the output buffer circuit 515 are inverted left and right. It is necessary to invert the data signal line drive voltage from the output buffer circuit 515 output to each segment electrode left and right.

The random logic circuit 510 shown in FIG.
Is an output buffer circuit 5 output to each segment electrode.
Left and right inversion (SHL) of data signal line drive voltage from 15
Is performed, the 8-bit display data Din input from the display control device 501 is rearranged. Note that DIS
P is a display display off signal.

Each common driver (IC-C) shown in FIG.
1 to IC-C5) select a common electrode driven every one horizontal scanning time by an internal logic circuit according to the frame signal FLM input from the display control device 101 and the clock CL1, and select the selected common. A voltage VxH or a voltage VxL supplied from the power supply circuit based on the AC signal M to the electrodes is output from the liquid crystal drive voltage output circuit to the common electrode, and a common electrode other than the selected common electrode is output. For the power supply circuit 102
Is output from the liquid crystal drive voltage output circuit to the common electrode.

In this case, each common driver (IC-C
1 to IC-C5) output a carry signal as an output signal via an output buffer.
The signal is directly input to the carry input of the next stage common driver, and the carry signal is used to sequentially select the common electrodes driven every horizontal scanning time.

[0026]

In the above prior art, as shown in FIG. 10, the display screen of the matrix type display device has a ruled line (black or white) on a white background or a black background.
Is displayed, a luminance difference (shadowing) occurs with the background part A even when the same white background as that of the background part (A in the figure) is displayed on the upper and lower parts (B in the figure) of the ruled line. As shown in FIG. 11, the brightness difference is changed from the segment driver output to the common driver via the liquid crystal capacitance by changing the polarity of the output waveform of the segment electrode at points (1) and (2) as shown in FIG. Current flows into the output electrode of
This is caused by distortion (crosstalk noise) of the output waveform of the non-selection level VM of the common driver.

SEG1 in FIG. 11 shows the voltage waveform output to the upper and lower portions B of the ruled line in FIG.
3 shows a voltage waveform output. Due to the above-described crosstalk noise, the voltage of the common electrode corresponding to SEG1 and SEG2 has noise as shown by a voltage waveform shown by a dotted line. Due to this crosstalk noise, the effective voltage increases in SEG1 and decreases in SEG2. As a result, a difference in effective voltage is generated between SEG1 and SEG2, and a luminance difference (shadowing) occurs even though the same display is performed in portions A and B in FIG.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art, and an object of the present invention is to generate a non-selection voltage of a common driver by a change in output of a segment driver in a liquid crystal display device. Another object of the present invention is to provide a technique capable of reducing shadowing by correcting an increase in an effective voltage due to crosstalk noise.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0030]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

In order to achieve the above object, a circuit for detecting the generation of crosstalk noise propagating to the common driver at the segment driver output signal change point when the segment driver (white or black) background display is performed. The driver output signal rising noise and the segment driver output signal falling noise are each detected as the amount of crosstalk noise that propagates to the common driver output waveform, and output to the driver as a correction pulse signal.

The driver determines whether or not to output the same data as the background data. When outputting data that is not the same as the background data, an arbitrary voltage is output without outputting the output voltage for the width of the correction pulse signal. Output.

As a result, the output voltage is not output during the period in which the effective voltage is increasing due to the crosstalk noise, and an arbitrary voltage is output. Therefore, the increase in the effective voltage can be corrected, and the shadowing can be reduced.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention applied to a simple matrix type liquid crystal display device of the STN mode will be described below in detail with reference to the drawings.

In all the drawings for describing the embodiments of the present invention, components having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

FIG. 1 shows a driver output waveform for driving a liquid crystal display device according to an embodiment of the present invention, and timings of correction signals and the like. FIG. 2 shows an embodiment of the present invention. 1 shows a driving circuit for driving a liquid crystal display device. FIG. 1 shows a case in which black ruled lines are displayed on a white background. M is an AC signal, and CC1 and CC2 are waveform correction signals. SE
G1 and SEG2 are the same as in FIG. 10, SEG1 is the driver output waveform for displaying the upper and lower parts of the ruled line (B in FIG. 10), and SEG2 is the driver output waveform for outputting the white background (A in FIG. 10). The voltage waveform of the common electrode is indicated by a dotted line in SEG1 and SEG2.

Crosstalk noise is applied to the common electrode,
In order to prevent a difference in effective voltage, correction signals CC1 and CC2 are formed from crosstalk noise, and SEG2
Are corrected (shown by (d) in FIG. 1).

At this time, a circuit (shown in FIG. 4) for detecting crosstalk noise propagating to the common driver side at the segment driver output signal change point in the white background display of the segment driver rises the segment driver output signal shown in SEG1. The noise (1) and the falling noise (2) of the segment driver output signal shown in SEG2 are detected as the amount of crosstalk noise generated at the non-selection level VM of the common driver, and are output to the driver as CC1 and CC2 pulse signals.

FIG. 3 is a block diagram showing one embodiment of the correction signal generation circuit. In this circuit, a change in the voltage VM output from the power supply circuit is detected by a crosstalk detection circuit.

FIG. 4 is a circuit diagram showing an embodiment of the crosstalk detecting circuit. The crosstalk detection circuit CD1 forms a correction signal CC1 from crosstalk noise, and the crosstalk detection circuit CD2 forms a correction signal CC2.
The crosstalk detection circuit CD1 detects a change in the voltage VM by detecting a voltage difference between the voltage VL and the voltage VM by the differential amplifier AMP1, and forms a correction signal CC1. Similarly, the crosstalk detection circuit CD2 is a differential amplifier AMP
2 to detect a voltage difference between the voltage VH and the voltage VM, thereby detecting a change in the voltage VM and forming a correction signal CC2.

Due to the correction signals CC1 and CC2 and the alternating signals M 'and DISP, VH is not output at the (1) point of SEG2 in FIG.
, W), and outputs a voltage VM. Further, at point (2) of SEG2, the voltage VM is output for the High width of CC2 without outputting VL. Thereby, the ruled line portion (SE
G2) can be corrected to the same effective voltage as the background portion (SEG1), so that the occurrence of shadowing can be suppressed.

FIG. 5 shows a circuit diagram of an embodiment of the present invention, and FIG. 6 shows a crosstalk detecting circuit. In this circuit, C
It is simplified to one C signal. In this embodiment, since only the basic circuit is described, the booster circuit and the like are omitted.

[0043]

According to the present invention, there is an effect that shadowing can be reduced. Further, there is an effect that an increase in power consumption and a decrease in effective voltage can be suppressed regardless of the phase of the AC signal and the phase of the line clock.

[Brief description of the drawings]

FIG. 1 is a liquid crystal driving waveform diagram of a liquid crystal display device according to the present invention.

FIG. 2 is a drive circuit diagram of the liquid crystal display device according to the present invention.

FIG. 3 is a block diagram of a crosstalk detection circuit of the liquid crystal display device according to the present invention.

FIG. 4 is a crosstalk detection circuit diagram of the liquid crystal display device according to the present invention.

FIG. 5 is a drive circuit diagram of the liquid crystal display device according to the present invention.

FIG. 6 is a block diagram of a crosstalk detection circuit of the liquid crystal display device according to the present invention.

FIG. 7 is a block diagram illustrating a schematic configuration of a conventional liquid crystal display device.

FIG. 8 is a liquid crystal driving waveform diagram of the liquid crystal display device.

FIG. 9 is a block diagram of a liquid crystal driving device.

FIG. 10 is a schematic configuration diagram of a panel display screen of a conventional liquid crystal display device.

FIG. 11 is a liquid crystal drive waveform diagram of a conventional liquid crystal display device.

[Explanation of symbols]

101: display control device, 102: power supply circuit, 103: conversion circuit, LCD: liquid crystal display panel, IC-U1 to IC
-Un, IC-L1 to IC-Ln ... Drain driver,
IC-C1 to IC-C5 ... Common driver, CC1, C
C2: correction signal, CL1: line clock, M, M '...
AC signal, SEG1 ... data line to be displayed as background, SE
G2: Data line for displaying ruled lines, BR: Bit latch circuit, LR: Line latch circuit, Yn: Output.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shinji Yasukawa 3681 Hayano Mobara-shi, Chiba Hitachi Device Engineering Co., Ltd. (72) Inventor Toshimitsu Matsudo 3300 Hayano Mobara-shi Chiba Pref. 72) Inventor Tatsuhisa Fujii 3300 Hayano, Mobara-shi, Chiba Pref., Electronic Device Division, Hitachi, Ltd.

Claims (2)

[Claims] 1. A liquid crystal display device comprising a liquid crystal display element and a liquid crystal drive circuit for driving the liquid crystal display element, wherein the liquid crystal drive circuit has a common driver, a segment driver, and a correction signal circuit. The signal circuit forms a correction signal from noise generated in the output signal of the common driver, and the segment driver outputs a voltage for correcting the noise in accordance with the correction signal when outputting a voltage in a direction opposite to the noise. A liquid crystal display device characterized by the above-mentioned. 2. A liquid crystal display device according to claim 1, wherein said segment driver has a correction signal input terminal.