JP2938674B2 - Driving device for liquid crystal display element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a matrix type LC.
The present invention relates to a liquid crystal display element driving device for driving a liquid crystal display element such as D (liquid crystal display) by a voltage averaging method.

[0002]

2. Description of the Related Art When an LCD is driven by a voltage averaging method,
A scanning voltage is sequentially applied to a plurality of scanning electrodes extending in the horizontal direction, and a signal voltage is applied to a plurality of signal electrodes extending in the vertical direction in synchronization with the scanning voltage. As a result, a driving voltage that is a difference voltage between the scanning voltage and the signal voltage is applied to each pixel at the intersection of the scanning electrode and the signal electrode, and a desired character or graphic is displayed on the LCD.

In order to pixels to ON state (optical lighting state), Von = Vop / BIAS × ( (BIAS 2 + DUTY-1) / DUTY) it is necessary to apply the ^half of the effective voltage.

Similarly, in order to set the pixel to the OFF state (optically unlit state), an effective voltage of Voff = Vop / BIAS × (((BIAS−2) ² + DUTY−1) / DUTY) ^1/2 Must be applied.

Here, Vop is a constant voltage set in advance according to the liquid crystal material, and BIAS is a value equal to DUTY ^1/2 +1. DUTY is set according to the number of pixels of the LCD. For example, when the LCD has pixels of 400 dots in the vertical direction, DUTY is usually set to 200 and 480
If you have a dot pixel, DUTY is usually set to 240.

Since the liquid crystal display element is a capacitive element, the waveform of the driving voltage is distorted due to the inversion of the scanning voltage and the signal voltage. Therefore, the effective voltage Von or Voff decreases or increases. As a result, uneven brightness occurs due to the pixels. That is, shadowing occurs.

Assuming that the capacitance of the liquid crystal display element is C and the loop resistance is R, the drop of the effective voltage due to shadowing is Vop / BIAS × (1− (1-1.5 C · R · N · F) ^{1 / 2} ) proportional to Here, N is the number of reversals of the voltage level of the signal voltage, and F is the reciprocal of the frame time, that is, the scanning frequency.

Therefore, by setting BIAS to be large, the amount of decrease in the effective voltage is reduced, thereby preventing shadowing.

[0009]

However, in the above conventional configuration, as shown in FIG. 6, when a vertically extending bar graph 52 is displayed in black (OFF state) at the lower center of the LCD 51, the bar graph 52 is displayed. There is a problem that the brightness of the extended white (ON state) area 53 becomes higher than the brightness of the white areas 54 on the both sides of the bar graph 52.

Hereinafter, the cause of the shadowing will be described with reference to FIGS. 7 and 8. FIG.

A scanning voltage is sequentially applied to the scanning electrode for each pulse of the clock signal 55 in FIG. 7A, and the level of the scanning voltage is based on an AC signal 56 (FIG. 7B). At a predetermined cycle. On the other hand, a signal voltage ((c) in the figure) is applied to each signal electrode in synchronization with the clock pulse, and the level of the signal voltage is also applied to the AC signal 56 similarly to the level of the scanning voltage. Has been reversed based on.

In the figure, voltage levels V ₀ and V ₅ indicate a signal voltage for turning on a pixel (hereinafter referred to as a lighting voltage), and voltage levels V ₂ and V ₃ turn off a pixel. A signal voltage for setting a state (hereinafter, referred to as a non-lighting voltage) is shown. Note that the voltage level V ₁
And V ₄ are scanning voltages applied to unselected scanning electrodes (hereinafter, referred to as non-selection voltages).

When the AC signal is inverted, the level of the scanning voltage and the level of the signal voltage are inverted, so that charging and discharging occur in all pixels. At this time, as shown in FIG. 8, the waveform 57 of the non-selection voltage is greatly distorted by a transient phenomenon.

As shown in a bar graph 52 of FIG.
When most of the pixels are in the ON state, the waveform 57 of the non-selection voltage is on the lighting voltage side (the voltage level V in the figure).
Distortion toward ₀ ). Conversely, as the area 54, if most of each pixel of the LCD51 is OFF state, the waveform 57 of the non-selection voltage is distorted to a non-lighting voltage side (voltage level V ₂ side in the figure) (Fig. 8 ).

For this reason, in the pixel on the signal electrode where the non-lighting voltage is applied for a long time as in the region 53,
The effective value of the drive voltage increases. On the other hand, in pixels on the signal electrode to which the lighting voltage is constantly applied as in the regions 54, the effective value of the drive voltage decreases. This allows
Shadowing of a type in which the luminance of the region 53 is higher than the luminance of the regions 54 on both sides occurs.

In the case of the bar graphs 61 to 63 in FIG. 6, shadowing of a type different from the above-described shadowing occurs. That is, when the bar graphs 61 to 63 are displayed by a so-called net in which black (OFF state) and white (ON state) are alternately arranged, the bar graphs 61 to 63 are displayed.
The brightness of the white regions 71 to 73 on the extension of
The brightness is lower than the brightness of the white areas 54 on the background on both sides of.

Hereinafter, the cause of the shadowing will be described with reference to FIGS. 9 and 10. FIG.

FIG. 9 (a) shows the scanning electrodes in the same manner as described above.
The scanning voltage is sequentially applied for each pulse of the clock signal 55, and the level of the scanning voltage is inverted at a predetermined cycle based on the AC signal 56 (FIG. 9B). On the other hand, a signal voltage ((c) in the figure) is applied to each signal electrode in synchronization with the clock pulse, and the level of the signal voltage is the same as the level of the scanning voltage.
Has been inverted based on

When the AC signal is inverted, the level of the scanning voltage and the level of the signal voltage are inverted, so that charging and discharging occur in all pixels. At this time, as shown in FIG. 10,
The waveform 58 of the non-selection voltage is greatly distorted by a transient phenomenon.

Further, since the signal voltage is alternately switched to the lighting voltage or the non-lighting voltage in order to display the bar-like bar graphs 61 to 63, the waveform 59 of the signal voltage is further greatly distorted by the transient phenomenon.

Assuming that the number of times the signal voltage switches to the lighting voltage or the non-lighting voltage is N, Von and Voff are respectively
It is represented by the following equation.

[0022] Von = Vop / BIAS × (( BIAS 2 + DUTY-1-G) / DUTY) 1/2 Voff = Vop / BIAS × (((BIAS-2) 2 + DUTY-1-G) / DUTY) 1 / ² Here, G = 6C ・ RN ・ DUTY ・ F.

Therefore, in the regions 71 to 73, the region 54
, The effective value of the drive voltage decreases. This causes shadowing of a type in which the luminance of the regions 71 to 73 is lower than the luminance of the regions 54 on both sides.

In the case where characters are displayed vertically as in the area 64, the luminance of the white areas 65, 65 on the extension of the area 64 is the same as that in the case of the bar graphs 71 to 73.
It is lower than the luminance of the white area 54, 54 of both sides of the background area 64.

For the above shadowing, BI
The conventional shadowing prevention method that increases AS cannot cope sufficiently.

[0026]

In order to solve the above-mentioned problems, a driving device for a liquid crystal display element according to the present invention applies a scanning voltage to a scanning electrode sequentially, and synchronizes with a signal electrode in synchronization with the scanning voltage. Apply a signal voltage according to the display data to
In addition, in the liquid crystal display element driving device for displaying the display data on the liquid crystal display element by inverting the voltage level of the scanning voltage and the voltage level of the signal voltage in a predetermined cycle in response to the AC signal , the AC signal Running with the reversal of
In order to correct the effective value of the signal <br/> No. voltage transients caused by charge and discharge between the scan electrodes and the signal electrodes, said per the periodic
The signal a correction voltage according to changeover times of the signal voltage
It is characterized in that a correction means for applying to the electrode is provided.

[0027]

With the above arrangement, the scanning voltage is sequentially applied to the scanning electrodes, the signal voltage corresponding to the display data is applied to the signal electrodes in synchronization with the scanning voltage, and the voltage level of the scanning voltage and the signal voltage are applied. Voltage level according to the AC signal.
In a liquid crystal display element driving device that displays display data on the liquid crystal display element by inverting the liquid crystal display element in response to a predetermined period, a scanning electrode and a signal electrode accompanying the inversion of the AC signal are used.
In order to correct the effective value of the transient component of the signal voltage due to the charge and discharge between the, button switches the mode of the signal voltage per the periodic
Since the correction means for applying the correction voltage according to the number of times of the change is provided, it is possible to prevent the effective value of the signal voltage of the specific signal electrode from increasing or decreasing due to the transient phenomenon . This makes shadowing less likely to occur.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the matrix type LCD driving apparatus according to the present embodiment has a CPU (central processing unit) for processing data such as characters sent from input means (not shown) such as a keyboard. Unit) 1 and CPU 1
(Random access memory for video) 3 for storing display data from the VRAM 3, and an LCD controller 5 for reading out the display data stored in the VRAM 3 and performing control for display on the LCD panel 12.

Between the CPU 1 and the VRAM 3 and LC
A BUS (bus) arbiter 2 between the D controller 5 and the VRAM 3 for controlling the CPU 1 and the LCD controller 5 not to access the VRAM 3 at the same time.
・ 4 are provided.

Further, the driving device of the LCD of this embodiment is
A counter 6, a signal generating circuit 7 for AC conversion,
A drive voltage generation circuit 8 for generating six different levels of voltages for driving the CD panel 12, a switch unit 9 for switching the drive voltage from the drive voltage generation circuit 8, an LCD
Driver 10.1 of signal electrode (column electrode) of panel 12
0, a driver 11 for the scanning electrodes of the LCD panel 12 is provided.

The LCD controller 5 outputs the frame signal 13, the clock signal 14, and the display data read from the VRAM 3 as a data signal 15. LC
The frame signal 13 from the D controller 5 is input to a reset terminal (R) of the counter 6. The clock signal 14 from the LCD controller 5 is output to the counter 6
Input terminal (>), signal generation circuit 7, driver 1
It is input to 0.10.11.

The counter 6 outputs a display period signal 16 to the switch section 9 based on the frame signal 13 and the clock signal 14. The signal generation circuit 7 converts the AC signal 17 based on the clock signal 14 into the driver 10.1,
Output to 0.11.

In the liquid crystal display device driving apparatus of the present embodiment, after displaying one frame of display data on the LCD panel 12, a reduction or increase in the effective voltage caused during the display period is canceled. The correction voltage is applied to the signal electrodes of the LCD panel 12 from the drivers 10. Here, when a period during which the correction voltage is applied is referred to as a correction period, one frame period in the present embodiment is obtained by adding a correction period (= X × 1 clock period) to a display period (= DUTY × 1 clock period). Period. X is set to an appropriate integer value for correction.

[0035] For example, (Vop / BIAS) a correction voltage and V, when the applied only M × 1 clock period during the correction period, Von = Vop / BIAS × ( (BIAS 2 + DUTY-1-G + M) / (DUTY + X )) ^1/2 Voff = Vop / BIAS × (((BIAS-2) ² + DUTY-1-G + M) / (DUTY + X)) ^1/2 G = 6CＣRNＲ (DUTY + X) ・ F Here, C and R are respectively the capacitance and loop resistance of the liquid crystal display element, N is the number of times the voltage level of the signal voltage switches, and F is the reciprocal of the frame time, that is, the scanning frequency.

Therefore, if M is set so as to satisfy M = G, the G term is canceled out, so that shadowing can be reduced.

As an example, an LC of 640 × 480 dots
The case where the D panel 12 is driven will be described below with reference to FIG.

The frame signal 13 is composed of pulses output for each frame as shown in FIG. 2A, and the clock signal 14 is composed of one pulse as shown in FIG.
It consists of pulses output every clock.

If DUTY = 240 and X = 15, one frame period is 255 × 1 clock period. The display period signal 16 is at the high level in the former 240 × 1 clock period of one frame period, as shown in FIG.
It becomes low level during the subsequent 15 × 1 clock period.
The display period coincides with a period in which the display period signal 16 is at a high level, and display data is displayed on the LCD panel 12 during this period. On the other hand, the correction period is the display period signal 16.
During the low level period, and the correction voltage is applied during this period.

For example, if F = 60 Hz and CR = 0.5 μs, then M = 0.046N from the above equation. 0.046 × 2
Since 0 = 0.92 ≒ 1, the correction voltage is applied for one clock period every time the signal voltage is switched to the lighting voltage and the non-lighting voltage approximately 20 times.

FIG. 3 shows an example of the change over time of the signal voltage applied to the signal electrodes S ₁ , S ₂ , S ₃ .

In the drawing, in the display period, hatching indicates a period in which a lighting voltage (voltage level V ₀ or V ₅ ) is applied, and white blank indicates a non-lighting voltage (voltage level V ₂ or V ₃ ). Shows the period of time.

On the other hand, in the correction period, as in the display period, hatching indicates a period in which a correction voltage equal to the lighting voltage (voltage level V ₀ or V ₅ ) is applied. (Voltage level V ₁ or V ₄ )
The period during which the correction voltage equal to is applied is shown.

As described above, in this embodiment, the voltage level applied during the white blank period is switched depending on whether the white blank period belongs to the display period or the correction period. The switching of the voltage level is performed by the switch unit 9. That is, the voltage level applied from the drive voltage generation circuit 8 to the drivers 10 is switched by controlling the switch section 9 with the display period signal 16.

The signal electrodes S ₁ , S ₂ , S ₄ , S ₅ , S ₇ ,
In S ₈ , the number of times of switching between the lighting voltage and the non-lighting voltage is a standard value, and as shown in FIG. 2D, when the correction voltage is applied for five clock periods corresponding to M = 5, , G are canceled out.

[0046] In the signal electrodes S _3, the lighting voltage and the non-lighting voltage has switched alternately, often switched times. At this time, since G increases, M needs to be larger than the above value. Therefore, as shown in FIG. 2E, for example, when M = 15, the G term is canceled.

[0047] In the signal electrodes S _12, a long period in which the lighting voltage is applied, is less switched times. At this time,
Since G becomes smaller, M must be smaller than the above value. Therefore, as shown in FIG. 2F, for example, when M = 0 , the term of G is canceled.

The value of M is determined by the LCD controller 5
Is transmitted to the drivers 10 as a data signal 15 during the correction period indicated by the display period signal 16.

FIG. 4 shows a specific example of the drive voltage generating circuit 8 and the switch section 9 used in the above-mentioned liquid crystal display element driving device.

The driving voltage generating circuit 8 includes five resistors 21 to 21.
25 and five operational amplifiers 26.
The resistors 21 to 25 are connected in series, and voltages V _DD and V _EE from a power supply are applied to both ends. The voltages divided by the resistors 21 to 25 are respectively input to the operational amplifiers 26... And the voltage levels V _{1 to} V ₅ are output from the operational amplifiers 26.
Is output. The voltage level V ₀ is such that the voltage V _EE from the power supply is directly extracted.

The switch section 9 comprises a flip-flop comprising an inverter 36 and four FETs (field effect transistors) 37... And four switches comprising FETs 31 to 34. Voltage levels V _{1 to} V ₄ from the drive voltage generation circuit 8 are input to the sources of the FETs 31 to 34, respectively, and the drains are connected to the drivers 10.

In the above configuration, the FETs 31 and 33
Is turned on in accordance with the level of the display period signal 16. Thereby, _one of the voltage levels V ₁ and V ₃ from the drive voltage generation circuit 8 is selected, and
It can be input to the driver 10. Similarly, one of the FETs 32 and 34 is turned on in accordance with the level of the display period signal 16, whereby
One of the voltage levels V ₄ and V ₂ from the drive voltage generation circuit 8 can be selected and input to the drivers 10.

The clock signal 14 'in the figure is obtained by inverting the clock signal 14.

A second embodiment of the present invention will be described below with reference to FIG. For convenience of explanation, members having the same functions as those shown in the drawings of the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 5, the matrix-type LCD driving apparatus of this embodiment has an M generating circuit 4 for determining the value of M based on a data signal 15 and a clock signal 14.
2 is provided. Switching between the voltage levels V _{0 to} V ₅ in the display period and the correction period is performed by a switch unit 40 a provided in the driver 40 of the signal electrode. Switching between the voltage levels V ₁ and V ₄ of the scanning voltage
As in the related art, the operation is performed by the switch unit 41a provided in the driver 41 of the scanning electrode. The display period signal 16 is L
Generated by the CD controller 5.

As described above, the driving device of the liquid crystal display element of the present embodiment has a configuration in which the M generating circuit 42 is added to the driving device of the conventional liquid crystal display element. And shadowing can be easily prevented.

[0057]

As described above, the driving device for a liquid crystal display element according to the present invention has a structure in which a scanning electrode is provided in accordance with inversion of an alternating signal.
In order to correct the effective value of the signal voltage for the transient phenomenon caused by charging and discharging with the signal electrode, the signal
Since the correction means for applying the correction voltage according to the number of pressure switchings is provided, it is possible to prevent the effective value of the signal voltage of the specific signal electrode from increasing or decreasing due to the transient phenomenon . This produces an effect that shadowing hardly occurs.

[Brief description of the drawings]

FIG. 1, showing a first embodiment of the present invention, is a block diagram illustrating a configuration of a main part of a driving device of a liquid crystal display element.

FIG. 2 is a waveform diagram for explaining the operation of the driving device of the liquid crystal display element of FIG.

FIG. 3 is an explanatory diagram corresponding to the waveforms of FIGS. 2 (d) to (f).

FIG. 4 is a circuit diagram showing a specific example of a driving device of the liquid crystal display element of FIG. 1;

FIG. 5, showing a second embodiment of the present invention, is a block diagram illustrating a configuration of a main part of a driving device of a liquid crystal display element.

FIG. 6 is an explanatory diagram showing shadowing in a conventional LCD.

FIG. 7 is a waveform diagram for explaining a cause of occurrence of shadowing in which the luminance of FIG. 6 increases.

8 is a partially enlarged view of the waveform of FIG. 7C at the time of inversion.

FIG. 9 is a waveform diagram for explaining a cause of occurrence of shadowing in which luminance decreases in FIG. 6;

FIG. 10 is a partially enlarged view of the waveform of FIG. 9C when the waveform is inverted.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 CPU 3 VRAM 5 LCD controller 6 counter 7 signal generation circuit 8 drive voltage generation circuit 9 switch section 10 signal electrode driver 11 scan electrode driver 12 LCD panel 13 frame signal 14 clock signal 15 data signal 16 display period signal 40 signal electrode Driver 41 Scan electrode driver 42 M generation circuit

Claims (1)

(57) [Claims] 1. A scanning voltage is sequentially applied to a scanning electrode, a signal voltage corresponding to display data is applied to a signal electrode in synchronization with the scanning voltage, and a voltage level of the scanning voltage and a voltage level of the signal voltage are applied. the drive device for a liquid crystal display device for displaying the display data on the liquid crystal display element by in response to an AC signal is inverted at a predetermined cycle, between the scanning electrodes and signal electrodes associated with the inversion of the switching signal
Discharge in order to correct the effective value of the transient component of the signal voltage by, changeover times of the signal voltage per the period of
A driving device for a liquid crystal display element, further comprising a correction unit for applying a correction voltage according to the number to the signal electrode .