JPH0377916A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the contrast characteristic on a bright screen or dark screen by providing a detecting means and a brightness correcting means and variably correcting the DC level of a video signal in accordance with the detection of the brightness of the screen. CONSTITUTION:The detecting means 17 which detects the average level of the video signal and outputs the detection signal proportional to the brightness of the screen and the brightness correcting means 17 which varies the DC level of video signal by the detection signal are provided. The DC level of the video signal changes so as to decrease the average light quantity of the screen on the bright screen and the DC level of the video signal changes so as to increase the average light quantity of the screen on the dark screen so that the bright setting level of the liquid crystal panel is variably corrected. The change in the quantity of the transmitted light with the impressed voltage on the bright screen or the dark screen is increased n this way and the contrast characteristic is improved.

Description

[Detailed description of the invention] [Industrial usage total] The present invention relates to a liquid crystal display device using a liquid crystal spring.

[Conventional technology]

Conventionally, liquid crystal display devices such as liquid crystal television receivers are often formed using a TPT active matrix driving type liquid crystal panel.

Particularly when displaying on a large screen, the transmitted light of the liquid crystal panel is projected onto the screen via a projection lens, as described in, for example, Japanese Patent Application Laid-open No. 61-150487 (HO4N 9/31).

By the way, the above-mentioned liquid crystal panels include normally white panels in which the amount of transmitted light decreases when a voltage is applied to the liquid crystal cell, and normally black panels in which the amount of transmitted light increases when a voltage is applied.

The amount of transmitted light changes non-linearly with respect to the applied voltage in either normally white or normally black panels. For example, in the case of a normally white panel, the characteristics of the amount of transmitted light are shown in FIG.

In this case, even if the voltage of the video signal (primary color signal) as the applied voltage changes linearly with the brightness of the original image, the amount of transmitted light of the liquid crystal panel with respect to the applied voltage is the large amount of light (white) and the small amount of light (white). The amount of change relative to the applied voltage decreases as the amount of light increases and decreases.

Therefore, the contrast of the display screen based on the amount of light transmitted through the liquid crystal panel is compressed as the screen becomes larger and smaller.
Especially when the screen is extremely bright near the minimum and maximum applied voltage,
In a dark screen, a so-called saturated state is reached and contrast disappears, resulting in deterioration of contrast characteristics.

Then, the actual video signal is subjected to gamma correction to match the light emission characteristics of the CRT, and at this time, since the transmitted light amount characteristics of the liquid crystal panel and the light emission characteristics of CR'l' are different, the voltage of the video signal is applied as is. When applied as a voltage to the liquid crystal panel, the contrast characteristics of one display screen are further degraded.

Therefore, in many cases, in such a liquid crystal display device,
A correction circuit called an inverse gamma correction circuit corrects the characteristics of the video signal and corrects the range of applied voltage to a range in which the amount of transmitted light changes approximately linearly.

The characteristics of this correction are as follows for a normally white panel:
Ideally, the characteristic would be approximately as shown by the broken line in Figure 4, but in reality, it is set to the characteristic shown by the solid line in Figure 4, for example, based on approximation correction such as polygonal line approximation.

Note that the input voltage and output voltage in FIG. 4 indicate the input voltage and output voltage of the inverse gamma correction circuit, and the output voltage becomes the voltage applied to the liquid crystal panel.

When the approximation correction shown by the solid line in FIG. 4 is applied, the relationship between the voltage applied to the liquid crystal panel and the amount of transmitted light becomes approximately as shown in FIG. 5.

In addition, Japanese Patent Application Laid-Open No. 64-40893 (GO9G 3/
36) describes an inverse gamma correction circuit for a normally-plaque panel.

[Problem to be solved by the invention]

In the case of the conventional liquid crystal display device, even if the video signal V is subjected to inverse gamma correction, the contrast of the display screen is
As is clear from the figure, the transmitted light amount characteristic becomes non-linear and is compressed for high light intensity screens and low light intensity screens, and in the case of the same figure, it is especially noticeable for bright screens with transmitted light amount of 90% or more and dark screens with less than 20% transmitted light amount. Contrast characteristics deteriorate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device that improves contrast characteristics on bright screens and dark screens.

[Means to solve the problem]

In order to achieve the above object, the liquid crystal display device of the present invention includes a detection means for detecting the average level of a video signal for display driving the liquid crystal panel and outputting a detection signal proportional to the brightness of one screen.

and a brightness correction means for changing the DC level rough 1i of the video signal so as to correct the brightness setting level to the opposite of the detection signal, at least when the detection signal is a high light intensity screen or a small light intensity screen.

Further, when the contrast setting level is also corrected to further improve the contrast characteristics, the contrast setting level is corrected to the opposite of the detection signal using the detection signal of the detection means at least for a high light intensity screen or a low light intensity screen. It is also desirable to provide a contrast correction means for varying the AC frequency tV' of the video signal.

[For production]

In the case of the liquid crystal display device of the present invention configured as described above,
Based on a detection signal from the detection means that is proportional to the brightness of the screen, the brightness correction means variably corrects the DC level of the video signal at least when a bright screen with a large amount of light or a dark screen with a small amount of light is displayed.

With this variable correction, the DC level of the video signal changes so that the average amount of light on the screen decreases for bright screens, and the DC level of the video signal changes so that the average amount of screen light increases for dark screens. The brightness setting level is variably corrected.

In other words, the normal of the transmitted light amount characteristics in Fig. 3 or Fig. 5.
When using a white panel, for bright or dark screens where the amount of change in the amount of transmitted light decreases and the contrast becomes smaller, the brightness setting is performed by adjusting the applied voltage to a higher or lower value in the direction that the amount of change changes linearly. The level is corrected to low or high.

Therefore, the amount of transmitted light changes greatly with respect to the applied voltage on a bright screen or a dark screen, and contrast characteristics are improved.

Furthermore, when a contrast correction means is also provided.

By varying the correction of the AC level of the video signal based on the detection signal, AC changes in the video signal are suppressed on bright screens;
On dark screens, alternating current changes in the carp image signal are magnified, and the contrast setting level of the liquid crystal panel is also corrected.

Therefore, the contrast characteristics are further improved, particularly near the maximum light amount and the minimum light amount.

〔Example〕

One embodiment will be described below with reference to Figure '#J1 and Figure MIJ2.

Figure 2 shows the display drive block of a liquid crystal video projector that projects the transmitted light of the liquid crystal panel onto the screen to reproduce large-screen color. In the figure, (1) is the brightness/chroma processing circuit, and (2) is the Matrix episode! , (3r)
, (3g), (3b) are inverted comma correction circuits, (4r)
.

(4g), (4b) are DC regeneration circuits, (5r), (5
g) and (5b) are bright control circuits.

(6r), (6g), (6b) are display drive +7) 1M polarity 11ml1ll path, (7r).

(7g) and (7b) are transmissive liquid crystal panels of three primary colors R, G, and H, which are normally white panels using a TPT active matrix drive system.

(8r), (8g), (8b) are liquid crystal springs/' (7r
), (7g), (7b) horizontal drive circuit (X F
”) Iha), (9r), (9g), (9b) C liquid crystal bar* /L/(7r), (7g), (7b) vertical drive circuit (Y driver'), QO is a synchronous separation circuit, 0υ is a display drive timing control circuit.

@ is the bright contrast correction circuit, (l13.α→
is an operation volume for adjusting brightness and contrast; one end is connected to a power supply terminal (10B), and the other end is grounded via current limiting resistors (JR, Ql).

The correction circuit (2) is constructed as shown in Fig. 1, in which αη is an average level detection section forming the detection means, a transistor α barrel, a current limiting resistor,
(Consists of 2υ and 4 smoothing capacitors.

The wires are bright control circuits (5r), (5g), (5b)
This is a bright correction section that together with the brightness correction means forms a brightness correction means, and is composed of an operational amplifier (F), a transistor (C), and a current-limiting resistor (H). (c) is a contrast correction section that forms a contrast correction means together with the luminance/chroma processing circuit (1), and is composed of an operational amplifier, a transistor (to), and a current-limiting resistor au, +32J.

Reference numerals 1331 and 1341 are buffer amplifiers to which the operation volume (to), the brightness adjustment voltage Bx of the sliding piece Ql, and the contrast adjustment voltage Cx are input.

Then, the input video signal S obtained by reception, tape playback, etc.
i is divided into luminance signal Y and color difference signals R-Y, B-YK in the luminance/chroma processing circuit (1) and sent to the matrix circuit (2)
and is converted into eight primary color signals of R, G, and B through matrix processing in this matrix circuit (2).

These three primary color signals are corrected by the conventional inverse gamma correction circuits (Sr), (3g), (8b) with the characteristics shown in FIG.
4b) via the bright control circuit (5r), (5g),
(5b), and the DC level is varied according to the voltage of a 1-write control signal, which will be described later.

And bright control circuits (5r), (5g), (5b
), the output signal of the polarity inversion circuit (6r), (6g), (
6b) to each horizontal drive circuit (8r), (8g), (
8b).

Further, the input video signal Si is supplied to a sync separation circuit QO, and the sync signal of the input video signal Si, which has been demultiplexed and extracted by the sync separation circuit 00, is supplied to a timing control circuit Ql).

Then, the input video signal S is controlled by the timing control circuit αυ.
Various timing control signals synchronized with i are formed, and based on each timing control signal, a polarity inversion circuit (6r),
(6g), (6b) and horizontal drive circuit (8r),
(8g), (8b).

The operations of the vertical drive circuits (9r), (9g), and (9b) are controlled.

(7) Operation control LCD bar* fi/(?r), (
7g) and (7b), the voltages of the eight primary color signals of the horizontal drive circuits (8r), (8g), and (8b) based on the input video signal are applied.

And each liquid crystal spring tv (7r), (7g), (7b
) changes by 1, for example, according to the transmitted light amount characteristics shown in FIG.

At this time, use two reflective mirrors, dichroic honey, etc. to create the next optical system, and each liquid crystal spring /I/(7r) (7g)
, (7b), three primary color lights are projected onto each liquid stimulation panel (7b).
r), (7g), (7b) K! At the same time, image light of each primary color is combined to form color image light.

Further, the color image light is projected onto a screen via a projection lens, and the color image is displayed on a large screen on this screen.

The brightness level /l/ and contrast level of the display screen are adjusted by adjusting the operation volume α3, 04).

Glide correction 1F of bright contrast correction circuit (2)! in, contrast correction 174%, and shadow correction.

In other words, the set operation volume αi, (1
If the bright setting voltage and contrast setting voltage of the sliding piece in 4) are Bx and Cx, the constant voltages of both films are Bx and C.
x is the bright correction sound pan through the resistor (4), 3;
Contrast correction tps is applied to the transistor (a) on the side and the collector of the peak.

On the other hand, the negative polarity luminance signal -Y of the luminance/chroma processing circuit (1) is supplied to the average level detection section αη of the glide/contrast correction circuit (2).

Then, the luminance signal -Y is supplied to the base of the transistor rib of the detection part Q'i), and the collector and emitter current of this transistor α is the voltage of the luminance signal -Y.
changes in the opposite direction.

Furthermore, the collector voltage of the transistor (to), which is proportional to the collector and emitter currents, is smoothed by a capacitor (A), and the screen average level detection signal of the human-powered video signal Si is sent to the connection point between the resistor eυ and the capacitor (A). , a detection signal Di proportional to the brightness of the screen is generated.

Then, the detection signal Di is supplied to the non-inverting input terminal (+-) of the operational amplifier (goods) and the operational amplifier (
(to), the output signal of the wire is supplied to the base of the transistor (2), 00.

Furthermore, the collector and emitter currents of the transistors So and (7) change in proportion to the output signals of the operational amplifiers (c) and (e), and the transistor (
A), an emitter current of 00 is applied to the inverting input terminal of the operational amplifier ←).

Then, by the differential amplification of the operational amplifier ■ and the wire, the output signal of the operational amplifier (c) and the wire is adjusted so that the voltage of the inverting input terminal ←) and the detection signal Di of the non-inverting input terminal (→) are the same. Voltage changes.

Therefore, the collector and emitter currents of the transistors (to) and (g) change in proportion to the detection signal Di, and based on this change, the collector voltages of the transistors (a), . . . change inversely to the detection signal Di.

Therefore, the brightness adjustment voltage Bx, the transistor (e) based on the contrast adjustment voltage Cx, the brightness control signal of the collector of (■), the voltage gy of the contrast control signal,
Cy is corrected in a downward direction when the screen is bright, where the detection signal Di becomes large, and upward when the screen is dark, where the detection signal Di becomes small.

Then, depending on the voltage By of the bright control signal, the glide control circuits (5r), (5g), and (5b) vary the DC level A/(bedescle level 1v) of the input signal to the opposite of the voltage By. Base LCD spring! (7r), (7
The DC level of the applied voltage in g) and (7b) is controlled.

At this time, due to the voltage correction of the bright correction section (to).

Liquid crystal spring A/ (7r), (7g), (7b)
The foot setting V is adjusted so that it decreases when the screen is bright, where the average amount of transmitted light increases, and increases when the screen is dark, where the average amount of transmitted light decreases.

Therefore, in FIG. 5, for example, the screen in the nonlinear region where the amount of transmitted light is 90% or more shifts toward the linear region so as to become darker, and the dark screen where the amount of transmitted light is 20% or less shifts toward the linear region so that it becomes brighter.

Therefore, the change in the amount of light with respect to the applied voltage on bright and dark screens increases, resulting in greater brightness and darkness.
Gradation becomes clearer and contrast characteristics improve.

Also, depending on the voltage Cy of the contrast control signal, the brightness/
A chroma processing circuit (1) corrects the AC level (amplitude) of the input video signal Si to the opposite of the voltage Cy.

Based on this correction, the input image signal S when the screen is bright is
The change in AC level of input video signal Si is suppressed, and the change in AC level of input video signal Si when the screen is dark is magnified.
Control of I/(7r), (7g), (7b)-77,1
The setting level is corrected.

The amount of correction of this contrast setting level is used to supplementally correct the overdrawing when the light amount approaches 100% or 0% even after the brightness level correction and the brightness and darkness are compressed. is set to the amount.

Therefore, even extremely bright and extremely dark screens become brighter and brighter, and the contrast characteristics are further improved.

In the above embodiment, a device configured to perform inverse gamma correction is corrected at bright setting level/L/1 contrast setting level to display with extremely good contrast characteristics. (8r),
Similar effects can be obtained even when applied to a device in which (8g) and (8b) are omitted.

Furthermore, in order to simplify the configuration, the contrast correction section (to) may be omitted and only the glide setting level may be corrected.

Furthermore, based on the characteristics of the liquid crystal panel, if it is necessary to perform correction only for either a bright screen with a large amount of light or a dark screen with a small amount of light, use the brightness correction section or the contrast correction section (to). should be limited.

That is, when performing correction only on a bright screen, for example, as shown by the broken line in Figure 1, the transistor (c), C
Resistance (a), (to) and i< between emitter and ground of 11
, (the earth power supplies C171 and l381 are connected in series, and the base voltage of the transistors (E) and (to) is the bias power supply,
Resistance (goods) based on +381, +351,135,
Transistor (c), - until the divided voltage of CI4 is reached.
Just turn it off and limit the correction.

Furthermore, the circuit configuration etc. are not limited to the examples,
It can be applied even when the liquid crystal spring is a normally black panel, and can be applied to a wide variety of liquid crystal display devices.

〔Effect of the invention〕

Since the present invention is configured as described above, it produces the effects described below.

By providing the detection means and the glide correction means, based on the detection of the brightness of the 91 screen, the DC level of the video signal can be adjusted at least when the screen is bright with a large amount of light or a dark screen with a small amount of light.
L' is corrected again and the brightness setting level of the LCD panel is lowered on bright screens.

Rising on a dark screen.

Therefore, contrast characteristics on bright or dark screens can be improved.

Next, when a contrast correction means is also provided, based on the detection of screen brightness, the contrast setting level of the LCD panel is also corrected so that it becomes smaller for brighter screens and larger for darker screens, so that the contrast characteristics can be further improved. can be improved.

[Brief explanation of drawings]

Figures 1 and 2 show one embodiment of the liquid crystal display device of the present invention, Figure 1 is a wiring diagram of the main parts, Figure 2 is a circuit block diagram, and Figure 3 is a diagram showing applied voltage and transmission of the liquid crystal panel. Figure 4 is a diagram of the relationship with light intensity, Figure 4 is a characteristic diagram of reverse gamma correction, Figure 5 is a diagram of the liquid crystal spring μ.
FIG. 3 is a diagram showing the relationship between the applied voltage and the amount of transmitted light after reverse gamma correction. (7r), (7g), (7b)...LCD panel, (6
)... Glide contrast correction circuit, (17)
...Average rep/L' detection section. 4... Glide correction section, @... Contrast correction section. Figure 1

Claims (2)

[Claims] (1) A detection means for detecting the average level of a video signal for driving the display of a liquid crystal panel and outputting a detection signal proportional to the brightness of the screen. The apparatus is characterized by comprising bright correction means for varying the DC level of the video signal so as to correct the brightness setting level to the opposite of the detection signal, at least when the detection signal is a high light intensity screen or a low light intensity screen. LCD display device. (2) Contrast correction means is provided for varying the alternating current level of the video signal so as to correct the contrast setting level to the opposite of the detection signal, at least in the case of a high light intensity screen or a low light intensity screen, based on the detection signal of the detection means. The liquid crystal display device according to claim 1, characterized in that: