JPH01239590A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the color reproducibility of gradations by providing a generating means for black level potentials determined correspondingly to voltage-transmissivity characteristics of the primary colors of a liquid crystal panel, and determining the black levels corresponding to the primary colors unequivocally according to the state of a single bright level adjusting means. CONSTITUTION:A black level potential generating circuit 15 for R, G, and B is equipped with a bright level adjustment terminal 19 which can be operated from the outside of the liquid crystal display device, and its output terminals 26, 27, and 28 are connected to black level setting circuits 12, 13, and 14 for R, G, and B. The output terminal of a liquid crystal panel driving interface circuit 16 is connected to the liquid crystal panel 17 including an active matrix substrate and a color filter where the primary colors are arrayed. Consequently, the voltage-transmissivity characteristics of respective picture elements of R, G, and B can be represented while being shifted approximately by a constant voltage in the voltage-axis direction. Consequently, a reproduced image with improved half-tone color reproducibility is obtained.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a liquid crystal display device that displays full-color images using a liquid crystal panel. [Prior Art 1] Conventionally, a color image display device using a CRT has adjusted the flight level by means as shown in FIG. That is, red (R) and green (G) input from terminals 5.6.7.
, the pedestal level of the blue (B) primary color signal is set to a potential determined according to the value of the bright adjustment volume l. 2, 3.4 are R, G, respectively.
This circuit sets the black level of B. [Problems to be Solved by the Invention] There are two display modes for TN liquid crystals: a normally white type in which polarizing plates are arranged orthogonally, and a normally black type in which polarizing plates are arranged in parallel.Comparing the display performance of the two, it is found that It is generally known that normally black has better contrast when interrupted and normally white has better color reproducibility when displaying intermediate tones. FIG. 6 shows the relationship between the transmittance and the transmitted light wavelength of a normally black type TN liquid crystal panel. ■5, V2, V3, v4, ■5 are the voltages applied to the liquid crystal, each voltage 4. :V5>V,>V3>
There is a relationship of Vz>vl. Moreover, FIG. 7 is a graph obtained by replotting FIG. 6 with the applied voltage on the horizontal axis and the normalized transmittance on the vertical axis. (The normalized transmittance is the transmittance of the liquid crystal when it is saturated as 100 (%).) In Fig. 7, 8, 9, and 10 are respectively red, green, and It represents the normalized transmittance for blue transmitted light. From FIGS. 6 and 7, it can be seen that the transmittance when displaying halftones has a significant wavelength dependence. If a full-color display device using a normally black type TN liquid crystal panel with such characteristics is driven by a conventional drive circuit as shown in Figure 5, the color reproducibility of intermediate tones will deteriorate and the entire display will have a brownish tinge. This results in obtaining a reconstructed image. SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device using a normally black type TN liquid crystal panel that solves the above-mentioned problems of the prior art and has poor color reproducibility in intermediate tones.

[Means to solve the problem]

The present invention provides a liquid crystal display device configured to perform color display using a liquid crystal panel including an active matrix substrate and a color filter in which a plurality of primary colors are arranged, and a drive circuit including a color signal processing circuit. teeth,
The liquid crystal panel includes means for generating a black level potential determined in accordance with the voltage versus transmittance characteristics of each of the plurality of primary colors, and the black level potential corresponding to each of the plurality of primary colors is determined by the state of a single bright level adjustment means. The above-mentioned problem is solved by configuring it so that it is uniquely determined according to the . [Example] The present invention will be described in detail below with reference to the drawings. Various combinations of primary colors can be considered to constitute a color filter in a liquid crystal panel equipped with a color filter, but here we will consider the case where a color filter is constituted by the three primary colors of red (R), green (G), and blue (B). Let me explain using an example. FIG. 1 is a block diagram for explaining the present invention in detail. This figure shows a liquid crystal display device which obtains a full color image on a color liquid crystal panel 17 by inputting a decoded video signal to an input terminal 18. The input terminal I8 is connected to the color demodulation circuit 11, and the primary color (B, G, R1) output terminals 20.21.22 of the single color demodulation circuit 11 are connected to the black level setting circuits 12.13.14 for B, G, and R, respectively. Output terminals 23, 24, and 25 of the black level setting circuit are connected to the liquid crystal panel driving interface circuit 16. The black bell potential generation circuit I5 for R, G, and B is equipped with a light level adjustment terminal 19 that can be operated from the outside of the liquid crystal display device, and its output terminal 2
6, 27, and 28 are connected to black level setting circuits 12, 13, and 14 for B, G, and R, respectively. An output terminal of the liquid crystal panel driving interface circuit 16 is connected to a liquid crystal panel 17 including an active matrix substrate and a color filter in which a plurality of primary colors are arranged. Although the present invention is suitable for driving active matrix panels, it is also applicable to other liquid crystal panels. Black level potential generation circuit 15 for R, G, B and B, G, R
A specific example of the black level setting circuits 12, 13, and 14 is shown in FIG. In the same figure, resistance 29.30.31.32,
The capacitor 31 constitutes a black level potential generation circuit for RlG and B, and their output terminals 26, 27, and 28 are connected to the black level setting circuit as described above. When the liquid crystal panel 17 has voltage versus transmittance characteristics as shown in FIGS. 6 and 7,
The output terminal 26 of the DC potential generating circuit in FIG. 2 generates a DC potential corresponding to the black level of a B pixel, 27 a G pixel, and 28 a black level of an R pixel. The resistor 29 is a variable resistor, and its resistance value is determined by the black level adjustment terminal 19. The capacitor 31 is set to a sufficiently large capacitance value and plays an auxiliary role to shorten the charging and discharging time of a capacitor 38, which will be described later. Terminal 33 is connected to the power supply, and terminal 34 is connected to ground. Blocks 35, 36, and 37 are respectively B
A black level setting circuit for setting the black level of a display signal corresponding to a pixel, a G pixel, and an R pixel; 36 and 37
has the same circuit structure as 35. Black level setting circuit 3
5, a transistor 36 and a resistor 37 constitute a buffer amplifier, a capacitor 38 is provided to store black level information for B, and a switch 39 is composed of a transistor, a diode, etc. It is set to turn on only for a certain period of time. 40 is a buffer amplifier to the next stage. The main input terminal 41 of the black level setting circuit receives the B primary color signal from the color demodulation circuit 11, and the output terminal 42 outputs the B primary color signal with the black level set. Next, the operation and effect of the present invention will be explained. In the liquid crystal panel 17, the voltage versus transmittance characteristics of each pixel of R, G, and B can be approximately expressed as shifted by a certain voltage in the voltage axis direction as shown in FIG. 7. For example, the voltage versus transmittance characteristic of the B pixel. If the black level of the display signal for the B pixel is shifted to a higher voltage by V than that of the R pixel, good color reproduction can be obtained by correcting the black level of the display signal for the B pixel to a higher potential by V than that for the R pixel. I can do it. FIG. 3 shows the state of this correction. In the figure, 43 is an R pixel, 44
is the voltage transmittance characteristic of the B pixel, 45 is a display signal for the R pixel, and 48 is a display signal for the B pixel. The black level 49 (white level 50) of the B pixel is the black level 46 (white level 50) of the R pixel.
It can be seen that the voltage is shifted to a higher voltage by V compared to the white level 47). The voltage correction of the B pixel with respect to the R pixel described above is performed by adjusting each resistor 29, 30, 31, 3 so that the potential of the terminal 26 is higher by V than the potential of the terminal 28 in FIG.
This can be achieved by setting a value of 2. A resistor 29 is connected to the black level adjustment terminal, that is, the brightness adjustment terminal 19.
Although the value of can be changed somewhat, the above-mentioned correction amount V
does not change significantly, and V is determined to be a substantially constant value. The black level of the display signal for the G pixel is similarly corrected. As described above, the corrected black level potential is obtained at the terminals 26, 27, and 28, and the switch 39 is turned on only for a certain period when each primary color signal is at the black level or pedestal level during the horizontal blanking time. As a result, the voltage to be superimposed on the primary color signal applied to the terminal 41 is stored in the capacitor 38. According to the present invention, the display signal is corrected to suit each of the RlG and B pixels as described above. If the black level potential generation circuit for R, G, and B shown in FIG. 2 is configured as shown in FIG. 4, and the potentials obtained at terminals 26, 27, and 28 can be preset, it will be possible to compensate for variations in the liquid crystal panel. It becomes possible to respond to Also, terminal 2
It is more effective if the potential obtained in 6.27.28 has temperature characteristics matching the characteristics of the liquid crystal. The present invention can be applied to image monitors using liquid crystal panels, such as electronic viewfinders and liquid crystal TVs. [Effects of the Invention J The present invention has the effects described in the embodiments, and is applicable to a normally black type TN as shown in FIGS. 6 and 7.
By applying the present invention, which is an effective means to eliminate the inherent drawbacks of liquid crystal panels, that is, the inconvenience in color reproduction in intermediate tones, the advantages of normally black type TN liquid crystal panels can be improved. It becomes possible to bring out the contrast sufficiently. Furthermore, the present invention brings about the above-mentioned image quality improvement only by modifying the drive circuit without making any changes to the liquid crystal panel itself. Therefore, it is very advantageous in terms of cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining the present invention in detail. FIG. 2 is a diagram showing a specific example of the present invention. FIG. 3 is a diagram for explaining the present invention in detail. FIG. 4 is a diagram for explaining one specific example of the present invention. FIG. 5 is a diagram for explaining the prior art. FIG. 6 and FIG. 7 are diagrams for explaining the problems to be solved by the present invention. Applicant: Seiko Epson Corporation Figure 3! Kawara, -; Figure 6

Claims (2)

[Claims] (1) In a liquid crystal display device configured to perform color display using a liquid crystal panel including an active matrix substrate and a color filter in which a plurality of primary colors are arranged, and a drive circuit including a color signal processing circuit, the color signal processing circuit , comprising means for generating a black level potential that is determined corresponding to the voltage versus transmittance characteristics of each of the plurality of primary colors of the liquid crystal panel, and the black level potential corresponding to each of the plurality of primary colors is generated by a single bright level adjustment means. A liquid crystal display device characterized in that it is configured to be uniquely determined depending on a state. (2) The liquid crystal display device according to item 1, wherein the black level potential corresponding to each of the plurality of primary colors can be independently preset.