JPH01281497A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the display performance of linearity and contrast by correcting at least the DC level or the amplitude of a display signal in accordance with the output of an average level detecting means so that it is matched to the standardized transmittance characteristic to voltage of a liquid crystal panel. CONSTITUTION:Primary color signals, for example, red R, green G, and blue B including color information and luminance information or including only luminance information are obtained in outputs 22-24 of a primary color signal output circuit, and they are transmitted to the next stage. A block 19 consists of a pedestal clamping circuit 12, an average level detecting circuit 13 which detects the average level of the display signal, namely, an average picture level APL, and an amplitude correcting circuit 14 which corrects the amplitude of the display signal in accordance with the output of the average level detecting circuit 13 so that it is matched to the Va-to-T characteristic of a liquid crystal panel 16. Consequently, one of the DC level and the amplitude of the display signal is satisfactorily corrected. Thus, the display performance of linearity and contrast is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device, and particularly to a liquid crystal display device for displaying images.

[Prior Art] As is well known, a liquid crystal display device displays characters and images by utilizing a phenomenon in which the transmittance of a liquid crystal panel changes when a voltage is applied. FIG. 6 shows an example of a typical voltage versus normalized transmittance characteristic (hereinafter abbreviated as Va versus characteristic) of a normally black mode liquid crystal panel using TN liquid crystal.

In the figure, the horizontal axis is the applied voltage Va (volts), and the vertical axis is the normalized transmittance T (%).On the other hand, in the conventional liquid crystal display device, as shown in Figure 7, the applied voltage Va (volts) is the applied voltage. The display signal is applied to the liquid crystal panel 3 through the signal processing circuit 2 to perform the display, and the display signal is applied to the liquid crystal panel 3 through the signal processing circuit 2, and the display signal is applied to the liquid crystal panel 3 through the signal processing circuit 2. The voltage was applied to a liquid crystal panel having the characteristics shown in Figure 6.

The details of the conventional horizontal iA of the above signal processing circuit can be found in the document ``Japan Broadcasting Corporation Participating NED Color Television Textbook J, [Nikkei Electronics Magazine, September 10, 1984 issue, pages 211 to 240'', etc. It has been described.

[Problems to be Solved by the Invention] In the Va vs. vs. vs. characteristics shown in FIG. 6, γ (gamma) in region I between white circles 4 and 5 is almost constant, so display with good linearity is possible. It is. On the other hand, white circle 5
The area sandwiched between and white circle 6] ■ has poor display linearity because γ changes. Therefore, if linearity is given priority, contrast should be sacrificed by about 30% to display within the range of area I. On the other hand, if priority is given to contrast, areas I
and area II.

The present invention solves the above-mentioned problem of being forced to choose between linearity and contrast, and provides an easy-to-understand WLff with excellent display performance in both linearity and contrast. [Means for Solving the Problems] The present invention provides a signal processing circuit and a liquid crystal panel so that a display signal inputted from outside the merchant is supplied to the liquid crystal panel via the signal processing circuit. In the liquid crystal display device, the signal processing circuit includes average level detection means for detecting the average level of the display signal inputted from the outside, and detects the DC level and amplitude of the display signal according to the output of the average level detection means. The above-mentioned problem is solved by providing a liquid crystal display device comprising means for correcting at least one of the voltage and normalized transmittance characteristics of the liquid crystal panel. Furthermore, it is an object of the present invention to more effectively solve the above problem by providing a liquid crystal display device in which a means for performing γ correction is added to the liquid crystal display device.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a block diagram of the liquid crystal display device of the present invention. In the same figure, 7 is an input terminal into which a display signal (for example, an NTSC decoded video signal, etc.) is input, 8 is a band amplification circuit for amplifying a chroma signal, 9 is a color synchronization circuit, 10 is a color demodulation circuit,
11 is a primary color signal output circuit. The outputs 22, 23, and 24 of the primary color signal output circuit are primary color signals containing color information and luminance information or only luminance information (for example, red [R], green [G]).
and blue [B] are obtained and transmitted to the next stage. Block 19 surrounded by the 0-dot line is the essential part of the present invention.
A pedestal clamp circuit 12 (to which the primary color signal is input), an average level detection circuit 13 that detects the average level of the display signal (here, the primary color signal), that is, the average picture level APL. It is composed of a width correction circuit 14 that corrects the amplitude of the display signal according to the output of the average level detection circuit 13 so as to match the Va vs. T characteristics of the liquid crystal panel 16 as shown in FIG. 3 Here, it is also possible to achieve the object of the present invention by correcting the DC level without relying on the amplitude correction for the display signal, and in that case, the DC level correction circuit 14 is used in place of the amplitude correction circuit 14. Further, the block 14 can be configured to include both an amplitude correction circuit and a DC level correction circuit.

In other words, the amplitude correction and the DC level correction are corrections for the AC component and DC component included in the display signal, respectively. At the output 25 of the block 19, a display signal matching the Va vs. T characteristic of the liquid crystal panel 16 is obtained. Figure 1 shows an embodiment of a color liquid crystal display device, and blocks 19, 20, and 21 have the same structure, and detect and correct the average level of the R, G, and B primary color signals, respectively. It adds An uncorrected primary color signal is input to the input end 22, 23, 24 of each block, and a corrected primary color signal is obtained at the respective output end 25.26.27. Block 15 is connected to node 25.26.2
The primary color No. 53 obtained in step 7 was changed to the pixel color scheme of the liquid crystal panel 16 (
It has a function of chronologically arranging the signals (R, G, H) and a function of forming an AC inverted display signal for driving the liquid crystal. Blocks 17 and 18 are h
These are a column driver and a U row driver for driving the liquid crystal panel 1G.

Objective: Among the components of the second block 19, the average level detection circuit is realized, for example, by a passive or active low-pass filter, an integrator, or the like.

In addition, the amplitude correction circuit can be realized by, for example, a reverse type or forward type automatic gain control circuit (hereinafter abbreviated as AGC) using a common emitter amplifier using a transistor, an AGC using differential amplification, etc. The average level correction circuit is realized by, for example, a level shift circuit using a diode or a transistor, a DC level setting circuit using a capacitor and a resistor, or the like.

Next, the present invention will be explained in detail using FIGS. 2 and 3. Assume now that a display signal is generated according to the prior art so as to operate the liquid crystal panel in the region (2) and region (II) of the Va vs. T characteristic. In FIG. 2, a display signal 30 is a display signal with a low average level generated by the conventional method, that is, the whole is blackish; In the 1-display code 30, which indicates a display signal that is closer to white, 34 is a white part, and 35 is a black part.In the 1-display code 31, 36 is a white part, and 37 is a black part, with the pedestal level 33 being the reference. At this time, the ratio of the potential of the next part to the potential of the white part is equal for the image display signals 3o and 31.At this time, since the display signal 30 exists within the Va contrast characteristic region I, the contrast ratio of the display is approximately 6= 1 has been taken. On the other hand, since the display signal 31 is applied over a wide range of area II, the contrast of the display is reduced to about 2.2+1, resulting in an unclear display.In order to solve the above-mentioned pressure, the present invention performs the following corrections to the display signal.

The average levels APL of the two display signals 30 and 31 are 1 and 2, respectively, as shown in FIG. 3(a). This V1. V* is detected by the average level detection circuit 13 in FIG. Further, the display signal correction circuit of the present invention is configured as shown in FIG. By passing through 19, the display signal 31 is converted into a display signal as shown at 32 in FIG. . As a result, V in Figure 2
It can be seen from the attT characteristics that the display contrast is improved to about 5:l. When a DC level correction circuit is used, the contrast is improved by shifting the entire display signal 31 in FIG. 2 to the lower potential side, that is, m1'l1lI.

Another embodiment of the present invention is shown in FIG.
Another example of the configuration of the display signal correction circuit 19 shown in the figure is shown. In FIG. 4, 40 and 42 are the input terminal and output terminal of the display signal correction circuit, respectively. The display signal correction circuit shown in the figure is obtained by adding a gamma correction circuit 41 to the block 19 shown in FIG. *Has a structure. The gamma correction circuit is realized as an amplifier whose gain is variable using a diode or a transistor as a switch.

According to the display signal correction circuit 1819 shown in FIG.
A corrected display signal is obtained as shown at 32 in the figure, and a display with improved contrast is realized. However, since the operating range of the corrected signal extends to region II due to the Va contrast characteristics, the problem of loss of linearity on the white side remains. In order to solve this gap, a gamma correction circuit shown at 41 in FIG. 4 is added, and the gamma correction circuit 41 has a function of converting the conventional display signal shown at 43 in FIG. 5 into a display signal shown at 44. Configure it to protect against. In other words, when the gamma correction circuit 41 inputs a linear tone signal (for example, 43 in FIG. 5), it generates a non-linear tone signal (for example, in FIG. 44
) has the ability to output merchants. By doing so, a liquid crystal display device with improved not only contrast but also linearity can be realized.

[Effects of the Invention] The gist of the present invention can be roughly divided into two. The first gist is the display (
The average W4 level of the C signal is detected and the display is applied to the liquid crystal panel accordingly (correction is made to the amplitude of the W4 signal or the DC level. By doing this, it is possible to use specific numerical values in the example. A significant improvement in the contrast ratio as shown in FIG. However, only a small increase in hardware is required to apply the correction.

The second gist of the present invention is to add gamma correction means to the first gist. In this way, by first optimizing the amplitude and DC level of the display signal and then applying gamma correction, it is possible to create an impeccable display (especially image display) with significantly improved not only contrast but also linearity. This is achieved through manufacturing and purchasing.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the present invention in detail. FIG. 2 is a t: eye diagram illustrating the operation of the embodiment of the present invention. 3(a) and 3(b) are diagrams for explaining the operations of the average level detection circuit and amplitude correction circuit shown in FIG. 1. FIG. FIG. 4 is a diagram for explaining another embodiment of the present invention. FIG. 5 is a diagram for explaining the operation of another embodiment of the present invention. FIG. 6 is a diagram showing a typical example of the voltage versus normalized transmission/retention properties of a liquid crystal panel. FIG. 7 is a diagram for explaining the prior art. Applicant Seiko Epson Co., Ltd. Agent Patent Attorney Masatoshi Kamiyanagi (and 1 other person)'% 33
Hede enter 9 Luci N le 2nd figure 杢り '/EF 迿子'E-"'Fe (T) 3rd figure 4th figure 5t Figure 7

Claims (2)

[Claims] (1) In a liquid crystal display device that includes a signal processing circuit and a liquid crystal panel and is configured to supply a display signal input from the outside to the liquid crystal panel via the signal processing circuit, the signal processing circuit comprising average level detection means for detecting the average level of the input display signal; and according to the output of the average level detection means, at least one of the DC level and amplitude of the display signal is adjusted to the voltage versus normalized transmittance characteristic of the liquid crystal panel. 1. A liquid crystal display device characterized by comprising means for correcting it to suit. (2) The liquid crystal display device according to claim 1, wherein the signal processing circuit further comprises means for performing gamma correction on the corrected display signal.