JPH0981088A - Automatic lcd contrast adjusting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a screen more easy to see by automatically setting the number of black dots on an LCD screen, that is, the proper contrast corresponding to the area ratio between brightness and darkness. SOLUTION: This circuit is constituted of a display dot counter circuit 11 fetching the display data signal 101 from a display data control circuit 2 to count the number of black dots on an LCD 3 and outputting a dot count signal 102 by performing a ranking in the order of increasing the number of black dots, an analog voltage generating circuit 12 generating the liquid crystal contrast voltage 104 corresponding to the ranked dot count signal 102 and a contrast adjusting power source 13 supplying the power source 103 of the liquid crystal contrast voltage 104.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic contrast adjusting circuit for an LCD (liquid crystal device), and more particularly to an automatic contrast adjusting circuit for automatically setting an optimum contrast corresponding to a light / dark area ratio of a screen.

[0002]

2. Description of the Related Art Conventionally, an automatic contrast adjusting circuit of this type of LCD, for example, in Japanese Patent Laid-Open No. 149409/1992, directly detects a difference in light transmittance between liquid crystal elements in a dark and light portions on a screen, and this difference, that is, The contrast voltage applied to the LCD is automatically controlled so that the contrast becomes the set optimum value.

That is, since the LCD has a characteristic that the contrast of the screen changes due to changes in the operating environment temperature and environmental voltage, such an automatic control circuit is provided in order to stabilize it.

[0004]

As described above, the conventional LC is used.
In the D contrast automatic adjustment method, the contrast is adjusted by performing the face-to-face detection of the difference in the light transmittance of the liquid crystal element in the bright and dark parts. That is, in general, when the area of the dark portion of the screen is large, the contrast is small, and when the area is small, it is easier to see the contrast, and better image quality cannot be obtained only by detecting the contrast directly. There is a problem.

[0005]

The LCD automatic contrast adjustment circuit of the present invention counts the number of black dots from a display data signal for one screen, and divides the count value into ranks in descending order of the number of black dots. Separately, a display dot counter circuit for outputting a dot count signal and an analog voltage generating circuit for determining a predetermined optimum liquid crystal contrast voltage based on the dot count signal and applying it to the LCD are provided.

[0006]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.

In FIG. 1, the LCD contrast automatic control circuit 1 checks the presence / absence of an input from the display data control circuit 2, fetches the display data signal 101, counts the number of black dots on the screen of the LCD 3, and determines the order of the number of black dots. A display dot counter circuit 11 that ranks and outputs a dot count signal 102, and a liquid crystal contrast voltage 10 that corresponds to the ranked dot count signal 102.
4 and a contrast adjusting power supply 13 for supplying a power supply 103 for the liquid crystal contrast voltage 104.

Next, the detailed operation of the circuit of FIG. 1 will be described. FIG. 2 is a block diagram showing a circuit of the display dot counter circuit 11. In FIG. 2, the display data signal 101 from the display data control circuit 2 is composed of a display data upper screen signal (HSYNC), a display data screen signal (YSYNC), an operation start signal (FRM) and a display data shift clock signal CLK. ing. The latch circuit 111 is
The display data signal 101 is input and the data is held by the internal flip-flop. The held signal is compared with the comparator 114 via the synchronous counter 112 and the decoder 113.
Is input to.

The comparator 114 compares a preset setting value with a numerical value obtained by the decoder 113, and outputs a detection signal only when the coefficient value is larger than the setting value. Comparator 1
The set value of 14 is divided into several types and determined according to the number of dots displayed on the liquid crystal screen. The signal output from the comparator 114 is held by a flip-flop inside the latch circuit 115, and then output to the analog voltage generation circuit 12 as a dot count signal 102 that is ranked into four types of A, B, C, and D. To be done.

FIG. 3 is a block diagram showing a circuit of the analog voltage generating circuit 12. In FIG. 3, as the dot count signal 102, only the signal designated by the voltage selector circuit 121 is output as ON. This output signal is applied to the analog switch 122, and the analog switch 122 selects the voltage from the contrast adjusting power supply 13 and outputs the appropriate contrast voltage 104 inversely proportional to the number of black dots measured to the LCD 3. To do.

The contrast adjusting power source 13 is a power source for supplying a contrast voltage to the LCD 3, and is classified by the display dot count circuit 11 into ranks according to the number of signal divisions (A, B, C, D). The setting of the voltage corresponding to each rank is decided into the categories (E, F, G, H).

In this way, the LCD 3 can be maintained in a clearer state by the LCD contrast automatic control circuit 1 receiving an appropriate contrast voltage corresponding to the number of black dots, that is, the ratio of the bright and dark areas of the screen.

The LCD automatic contrast control circuit may be used alone, but by using it together with a control circuit which has been used conventionally for detecting direct contrast and stabilizing it, a better image quality can be obtained. realizable.

[0014]

As described above, as described above, the LC according to the present invention
The automatic contrast adjustment circuit D counts the number of black dots displayed on the screen and applies an appropriate contrast voltage corresponding to the screen to the LCD, and thus has the effect of making the screen easier to see.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram of a display data control circuit in FIG.

FIG. 3 is a block diagram of an analog voltage generation circuit in FIG.

[Explanation of symbols]

 1 LCD contrast automatic control circuit 2 Display data control circuit 3 LCD 11 Display dot counter circuit 12 Analog voltage generation circuit 13 Contrast adjustment power supply

Claims (1)

[Claims] 1. A display dot counter circuit for counting the number of black dots from a display data signal for one screen, dividing the count value into ranks in descending order of the number of black dots, and outputting a dot count signal for each rank. An automatic contrast adjustment circuit for an LCD, comprising: an analog voltage generation circuit for determining a predetermined optimum liquid crystal contrast voltage based on the dot count signal and applying the same to the LCD.