JPH085992A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To widen a visual field angle range wherein an image is displayed with a proper gradation and proper gradations by suppressing the influence of variation in visual field angle on a liquid crystal panel. CONSTITUTION:A frame counter 101 counts frames, one by one, on the basis of an inputted frame signal F and a clock signal CLK and outputs a frame counter output corresponding to 0 or 1 to an address selector 102. The address selector 102 outputs an address selector output corresponding to an address to a ROM 103, which specifies a data table corresponding to input/output characteristics according to the inputted address selector output, and converts an image signal DATA for varying the input/output characteristics on the basis of the data table specified with the address selector output when the image signal DATA is inputted.

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 provided with a drive circuit for driving a liquid crystal panel, and more particularly to reducing the change in contrast when the viewing angle of the liquid crystal panel with respect to the image display surface is changed. The present invention relates to a liquid crystal display device including the image signal conversion circuit.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing a control circuit in a conventional liquid crystal display device, in which 701 is a horizontal synchronizing signal H.
S, vertical sync signal VS, frame signal F and clock signal C
A liquid crystal control signal creation circuit that creates and outputs a liquid crystal control signal by LK, 702 is a source driver that outputs a drive voltage according to the image signal DATA and the output from the liquid crystal control signal creation circuit 701, and 703 is a liquid crystal control signal creation circuit A gate driver that outputs a scanning signal according to the output of 701, and a liquid crystal panel 704 that displays an image according to the outputs of the source driver 702 and the gate driver 703.

FIG. 4 is a characteristic diagram showing the relationship between the signal value of the image signal and the drive voltage of the source driver to the liquid crystal panel. The source driver 702 increases the signal value of the input image signal DATA and the liquid crystal panel. The drive voltage V for 704 is reduced.

FIG. 5 is an explanatory diagram of a method of displaying the viewing angle with respect to the liquid crystal panel. The viewing angle when viewing the liquid crystal panel 704 from the normal direction orthogonal to the liquid crystal panel 704 in FIG. The viewing angle when the liquid crystal panel 704 is viewed at an angle α with respect to θ1 is θ2.

FIG. 8 is a characteristic diagram showing the relationship between the drive voltage for the liquid crystal panel and the transmittance of the liquid crystal panel. The drive voltage V output from the source driver 702 and the liquid crystal panel 704.
The transmittance T of the liquid crystal panel 704 changes according to the change of the viewing angle with respect to.

The operation of the conventional liquid crystal display device configured as shown in FIG. 7 will be described. The source driver 702 outputs the drive voltage V corresponding to the signal value of the image signal DATA according to the characteristics shown in FIG. 4 when the image signal DATA is input. Further, the liquid crystal control signal creation circuit 701 creates a liquid crystal control signal according to the input horizontal synchronizing signal HS, vertical synchronizing signal VS, frame signal F and clock signal CLK, and supplies the liquid crystal control signal to the liquid crystal panel 704 as a source driver. Output to 702 and gate driver 703. The source driver 702 receives the image signal DATA and the liquid crystal control signal, and thereby the liquid crystal panel
A drive voltage V corresponding to the image signal DATA is applied to 704, and the gate driver 703 outputs a scanning signal to the liquid crystal panel 704 when the liquid crystal control signal is input. The liquid crystal panel 704 displays the image corresponding to the image signal DATA by changing the transmittance when the driving voltage V is applied and the scanning signal is input.

Here, the solid line L1 in FIG. 8 shows the relationship between the drive voltage V and the transmittance T when the viewing angle with respect to the liquid crystal panel 704 is θ1, and the solid line L2 shows the viewing angle with respect to the liquid crystal panel 704. Shows the relationship between the drive voltage V and the transmittance T when θ is θ2.

[0008]

However, in the conventional liquid crystal display device, as shown in FIG.
Even if the values are the same, the transmittance T changes depending on the viewing angle. This is due to the optical characteristics of the liquid crystal element in the liquid crystal panel 704, but the change in the transmittance T due to the change in the viewing angle limits the viewing angle at which an image can be viewed with proper contrast and proper gradation. As a result, the expressiveness of contrast and gradation is lowered, so that the quality of the display image in the liquid crystal display device is lowered.

In view of the above problems, the present invention provides a liquid crystal display device capable of suppressing the influence of a change in the viewing angle on a liquid crystal panel and widening the viewing angle range in which an image is displayed with proper contrast and proper gradation. The purpose is to provide.

[0010]

In order to solve the above problems, the present invention changes the transmittance of a liquid crystal panel and the liquid crystal panel according to the signal value of an input image signal, and an image is displayed by the liquid crystal panel. A drive circuit to be displayed and at least two types of input / output characteristics for the input image signal, the type of the output characteristic is changed at a constant cycle, and the signal of the input image signal is made to correspond to the type of the input / output characteristic. An image signal conversion circuit for converting a value and outputting the value to the drive circuit is provided.

[0011]

According to the above means, since the liquid crystal panel has the characteristic that the transmittance changes according to the change of the viewing angle, the contrast and the gradation display for the user change according to the change of the viewing angle. By changing the type of input / output characteristics for each preset constant cycle, converting the signal value of the input image signal according to the type of input / output characteristics and outputting it to the drive circuit, it is appropriate for each constant cycle. Since the viewing angle at which the image can be viewed with the contrast and the appropriate gradation changes, the viewing angle range for the liquid crystal panel that can display the image with the appropriate contrast and the appropriate gradation is apparently widened.

[0012]

FIG. 1 is a block diagram showing an embodiment of a control circuit in a liquid crystal display device of the present invention. Members corresponding to those described with reference to FIG. To do. 101 is a frame counter that counts the number of frames for each frame, 102 is an address selector that outputs an address signal according to the output of the frame counter 101, and 103 is a data table specified according to the output of the address selector 102. A ROM (read only memory) that converts the signal value of the image signal DATA according to the data in the table, and 104 is a liquid crystal according to the liquid crystal control signal from the liquid crystal control signal generation circuit 701 and the image signal DATA converted by the ROM 103. The source driver applies a drive voltage V to the panel 704.

FIG. 2 is a timing chart showing changes in input / output signal waveforms and signal values with respect to the control circuit of this embodiment. The frame counter 101 counts the number of frames for each frame based on the input frame signal F and clock signal CLK. Where the frame counter
Reference numeral 101 is a 1-bit counter, which outputs a frame counter output Cf corresponding to a value of 0 or 1 to the address selector 102. When the frame counter output Cf corresponding to 0 is input, the address selector 102 outputs the address selector output Cs corresponding to the address A1 to the ROM 103,
When the frame counter output Cf corresponding to 1 is input, the address selector output Cs corresponding to the address A2 is output to the ROM 103.

In the ROM 103, a data table corresponding to the input / output characteristics is designated according to the inputted address selector output Cs, and the inputted image signal DATA is converted based on the data table designated by the address selector output Cs.

FIG. 3 shows the signal value of the image signal DATA from the outside and the image signal DA converted by the ROM in this embodiment.
It is a characteristic view which shows the relationship with the signal value of TA. In FIG. 3, the solid line M1 is the signal value D of the image signal DATA input from the outside.
_in and the signal value D of the image signal DATA converted based on the data table corresponding to the address A1 in the ROM 103
shows the relationship with _out , where the solid line M1 has a slope of 1
Is a straight line. A solid line M2 indicates the relationship between the signal value D _in of the image signal DATA input from the outside and the signal value D _out of the image signal DATA converted in the ROM 103 based on the data table corresponding to the address A2. .

When the data table corresponding to the address A1 is designated, that is, when the frame counter output Cf corresponds to 0, the ROM 103 converts the image signal DATA based on the characteristic shown by the solid line M1 in FIG. Output to the source driver 104. Here, since the solid line M1 is a straight line with a slope of 1, if the signal value D _in of the image signal DATA input to the ROM 103 is D1 to D4 as shown in FIG.
The signal value D _out of the image signal DATA output from the ROM 103 also becomes D1 to D4 and does not change.

When the data table corresponding to the address A2 is designated, that is, when the frame counter output Cf corresponds to 1, the ROM 103 outputs the image signal DATA based on the characteristic shown by the solid line M2 in FIG. The converted data is output to the source driver 104. Here, the ROM 103 is shown in FIG.
If the signal value D _in of the image signal DATA input to the ROM 103 is D1 to D3 as shown in FIG. 3, the signal value D _out of the image signal DATA is changed from D1 'to D based on the characteristic indicated by the solid line M2.
Change to 3 '.

Here, when the image signal DATA is converted based on the input / output characteristics shown by the solid line M1 in FIG. 3, the source driver 104 is operated when the user looks at the liquid crystal panel 704 at the viewing angle θ1 shown in FIG. , The drive voltage V so that the contrast and gradation of the image displayed on the liquid crystal panel 704 are optimized.
Of the liquid crystal panel 704 and the image signal DATA is converted based on the input / output characteristics shown by the solid line M2, when the user looks at the liquid crystal panel 704 at the viewing angle θ2 shown in FIG.
The magnitude of the drive voltage V is set so that the contrast and gradation of the image displayed on 704 are optimal.

FIG. 6 is a characteristic diagram showing the relationship between the drive voltage and the transmittance for the liquid crystal panel of this embodiment. LCD panel
The source driver 104 applies a drive voltage V to 704,
In addition, the gate driver 703 applies a scanning signal, so that the liquid crystal panel 704 sets the transmittance T so that the contrast and gradation of the image are optimized at the viewing angle θ1 or the viewing angle θ2 for each frame. Therefore, the LCD panel 704
It is possible to substantially prevent the apparent transmittance T from changing even when the viewing angle with respect to changes in the range of θ1 to θ2, and to keep the transmittance T with respect to the drive voltage V substantially constant as shown in FIG. It will be possible.

As described above, according to the liquid crystal display device of the present embodiment, the influence of the change in the viewing angle on the liquid crystal panel 704 can be suppressed, and the apparent change in the transmittance T can be suppressed to a small value. It is possible to widen the viewing angle range in which an image is displayed with proper gradation. As a result, it is possible to suppress deterioration of contrast and gradation expression even if the viewing angle with respect to the liquid crystal panel 704 is changed.

In the liquid crystal display device of this embodiment,
The ROM 103 has two kinds of input / output characteristics corresponding to the two viewing angles θ1 and θ2, and the input / output characteristics are changed for each frame, but the ROM 103 is made to correspond to three or more different viewing angles. It is possible to set three or more types of input / output characteristics, and even if the input / output characteristics are changed at a large cycle such as several frames instead of being changed every frame, or every line or one. It is possible to suppress the change of the transmittance T due to the change of the viewing angle even if the change is made in a small cycle such as every dot.

[0022]

As described above, according to the liquid crystal display device of the present invention, the viewing angle range in which an image is displayed with proper contrast and proper gradation can be widened without performing complicated image signal processing. Therefore, the quality of the displayed image can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a control circuit in a liquid crystal display device of the present invention.

FIG. 2 is a timing chart showing changes in input / output signal waveforms and signal values with respect to the control circuit of the present embodiment.

FIG. 3 is a characteristic diagram showing a relationship between a signal value of an image signal DATA from the outside and a signal value of an image signal DATA converted by a ROM in this embodiment.

FIG. 4 is a characteristic diagram showing a relationship between a signal value of an image signal and a driving voltage applied to a liquid crystal panel of a source driver.

FIG. 5 is an explanatory diagram of a method of displaying a viewing angle with respect to a liquid crystal panel.

FIG. 6 is a characteristic diagram showing the relationship between drive voltage and transmittance for the liquid crystal panel of this example.

FIG. 7 is a block diagram showing a control circuit in a conventional liquid crystal display device.

FIG. 8 is a characteristic diagram showing a relationship between a drive voltage for a liquid crystal panel and a transmittance of the liquid crystal panel.

[Explanation of symbols] [Explanation of symbols]

101 ... Frame counter, 102 ... Address selector,
103 ... ROM (Read Only Memory), 104 ... Source driver, 701 ... LCD control signal generation circuit, 7
03 ... Gate driver, 704 ... LCD panel, DATA ... Image signal, HS ... Horizontal sync signal, VS ... Vertical sync signal,
F ... Frame signal, CLK ... Clock signal.

Claims (1)

[Claims] 1. A liquid crystal panel, a drive circuit for changing the transmittance of the liquid crystal panel in response to a signal value of an input image signal to display an image on the liquid crystal panel, and at least two types for the input image signal. And an image signal conversion circuit that changes the type of the input / output characteristic at a constant cycle, converts the signal value of the input image signal according to the type of the input / output characteristic, and outputs the converted signal value to the drive circuit. A liquid crystal display device comprising: