JPS6169283A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To display good still pictures without deviation or the like of pictures for a log period by normalizing a video signal taken out from a liquid crystal cell simultaneously with polarity inversion and writing this signal in the same liquid crystal cell again. CONSTITUTION:A switch 17 is connected to a contact A in the side of a normalizing circuit 15 in one field and is connected to a contact B in the side of a delay circuit 15 in the other field. Then, a following picture element switch signal PHIH2 is stored in a capacitor 13 through an amplifier 12 with the phase of a picture element switch signal PHIH1 of one field and passes an inverting circuit 14 and the normalizing circuit 15 and is written in the same liquid crystal cell C with the phase of the picture element switch signal PHIH2. In the other field, the signal read out from the liquid crystal cell C is inverted again to the original polarity by the inverting circuit 14 and is delayed in the delay circuit by a time equal to the processing time in the normalizing circuit 15 and is written in the liquid crystal cell C again. Thus, still pictures are displayed by AC driving.

Description

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

[Conventional technology]

For example, it has been proposed to display television images using liquid crystals.

In FIG. 5, (1) is an input terminal to which a television video signal is supplied, and the signal from this input terminal (1) is transmitted to each switching element M1. It is supplied to lines LL, L2...Lm in the vertical (Y-axis) direction through M2...Mm. Furthermore, m
is a number corresponding to the number of pixels in the horizontal (X-axis) direction. Furthermore, an m-stage shift register (2) is provided, and a clock signal Φ□ of m times the horizontal frequency is sent to this shift register (2).
H1Φ2H is supplied, and pixel switch signals φH□, φH2...φ are sequentially scanned by clock signals Φ□H2Φ2H from each output terminal of this shift register (2).
H0 is supplied to each control terminal of switching elements M1 to Mm. Note that the shift register (2) is connected to a low potential (V s
s ) and a high potential (Voo) are supplied, and drive pulses of these two potentials are formed.

In addition, switching elements M11, M21, .
MyH, M12. M22...'M712+ HHH
M1. , M2. ...One end of Mnm is connected. Note that n is a number corresponding to the number of horizontal scanning lines. The other ends of the switching elements Mu to Mnm are connected to target terminals (
3).

Furthermore, an n-stage shift register (4) is provided, and this shift register (4) receives a horizontal frequency clock signal ΦiV.
r Φ2v is supplied, and the scanning line switch signal φV1 + is sequentially scanned by the clock signal ΦIVr Φ2v from each output terminal of this shift register (4).
φv2...φvn is the gate line G in the horizontal (X-axis) direction
l.

G2... Switching elements Mll to M through On
Each column of nm in the X-axis direction (MnmM1m), (Mzt
~M21)... (Mn□~Mnm) are supplied to the respective control terminals. Note that the shift register (4) is also supplied with vss and VDD in the same way as the shift register (2).

That is, in this circuit, the shift register (2).

(4) As shown in Fig. 6A and B, the lock signal Φ□
A, Φ2H%Φ1v, Φ2V are supplied. Then, as shown in FIG. 6C, the shift register (2) outputs φH□ to φHm for each pixel period, and the shift register (
From 4) onwards, φv is calculated every horizontal period as shown in the sixth diagram.
1 to φvn are output. Furthermore, a signal as shown in FIG. 6 is supplied to the human input terminal (1).

And when φVi + φH□ is output,
Switching elements M1 and M11 to Mi are turned on, and the input terminal (ll=M t −L L =M 1x = C
A current path of the sl-target terminal (3) is formed, and the potential difference between the signal supplied to the input terminal (1) and the target terminal (3) is supplied to the liquid crystal cell C1l. Therefore, the charge corresponding to the potential difference due to the signal of the first pixel is sampled and held in the capacitance of this cell CL1. The light transmittance of the liquid crystal changes depending on the amount of charge. A similar process is performed for the cells C12 to Cnm after Hilt, and the amount of charge in each of the cells C1i to Cnm is rewritten at the time when the next field signal is supplied.

In this way, corresponding to each pixel of the video signal! Cell C
The light transmittance of L1 to Cnm is changed, and this is sequentially repeated to display a television image.

By the way, when displaying with a liquid crystal, AC drive is generally used to improve its reliability and lifespan. For example, when displaying a television image, a signal obtained by inverting the video signal for each l field or frame is input to the input terminal (1).
supply to. That is, as shown in FIG. 6E, the input terminal (1) is supplied with a signal whose polarity is inverted with respect to the target potential VL for each field or frame.

By the way, in the above-mentioned apparatus, there is a demand for displaying an arbitrary television image as a still image. In that case, conventionally, for example, a memory for one field or one frame is provided, a desired image is stored in this memory, this is repeatedly read out, and the phase of the read signal is inverted for each field, as described above. It is proposed to supply the input terminal (1) of

However, the memory for one field or one frame as described above is itself large and has the same cost.
It is difficult to apply it to general consumer equipment.

In response to this, it has been proposed to display still images by utilizing the memory function of the liquid crystal cell C, as disclosed in, for example, Japanese Unexamined Patent Publication No. 58-H7782. That is, in this device, in a liquid crystal video display drive circuit having a first sample and hold circuit that supplies a video signal whose polarity is inverted for each screen to a plurality of pixels in time series, the video signal is inverted and the polarity of the video signal is inverted to the first sample and hold circuit. a second sample and hold circuit that reads out the video signals from the plurality of pixels in time series; and a video signal from an external terminal or a video signal from the second sample and hold circuit. and switching means for switching signals and supplying the signals to the inverting means.

However, in the case of this device, as described in the publication, the image shifts by one pixel in the scanning direction each time one field is displayed. For this reason, measures such as reversing the scanning direction are taken for each field, but switching the scanning direction in this way requires a large-scale circuit, and the scanning direction is shifted by one pixel alternately for each field. This may cause flicker or the like.

Also, since the signal from the liquid crystal cell C is extracted, this signal is returned to the liquid crystal cell C, and this process is repeated to display a still image, if there is any distortion in the signal transmission characteristics during this time, this distortion will occur. This accumulates and the image quality deteriorates significantly in a short period of time. On the other hand, it has been shown that the gain of the inversion method can be adjusted, but it is impossible to make such adjustment completely, and it is impossible to display a normal still image for a long time. It is extremely difficult.

On the other hand, it is conceivable to normalize the signal for each predetermined level range to its center level, thereby correcting distortion due to gain error or the like. However, in this case, in order to determine the above-mentioned predetermined level range, it is necessary to provide as many comparators as there are boundaries of the level range, or to use 1/1/2 of the maximum amplitude of the signal (Voo-VSs).
The method used is to use the bisecting point to determine whether it is above or below, then use the 1/4 dividing point to determine whether it is above or below, and then repeating 1/8, 1/16, etc. to determine the level range. If an attempt is made to improve the resolution of discrimination and normalization, the former method would require a complex and enormous configuration, while the latter method would be unable to perform processing in one pixel clock period.

Further, when a signal is extracted from the liquid crystal cell C, if there is a residual charge in the stray capacitance of the signal line, the signal will also be degraded, making it impossible to display a still image for a long time.

[Problem that the invention seeks to solve]

Conventional devices were constructed as described above. For this reason, in conventional devices, if the configuration is complicated or if a still image is displayed for a long time, the image quality will deteriorate significantly. Another problem is that the resolution of normalization cannot be made sufficiently large.

[Means for solving problems]

In the present invention, the number of column lines Lt+L2 equal to the number of horizontal pixels.
...A video signal whose polarity is inverted with respect to the reference potential every l field is supplied to Lm through a horizontal switch element which is turned on by a pixel switch signal sequentially formed by a horizontal pixel clock, and horizontal scanning is performed. A scanning line switch signal sequentially formed by a horizontal scanning clock is supplied to the row lines G1, G2, . . . Gn of a number equal to the number of lines. Pixel switch element M11°Mt2 that is turned on
. . Mnm are provided, and the video signal supplied to the column line via these pixel switch elements is connected to liquid crystal display cells C11°C12...Cnm, each of which constitutes one pixel.
In a liquid crystal display device designed to supply
The video signal stored in the liquid crystal display cell during at least one of the field periods of the video signal is taken out via the pixel switch element, and the polarity of the taken out signal is inverted (14) and the polarity is Normalize the video signal for each predetermined level range (15)L, apply this inverted and normalized signal to the liquid crystal display cell again, and apply it to each column line for each horizontal blanking period of the video signal. Third switch element M R1 that is turned on
, MF, 2, . . . , M are supplied with a reset voltage (3).

[Operation] According to this device, the signal taken out from the liquid crystal cell C is returned to the same liquid crystal cell C, so there is no image shift, etc., no special scanning is required, and the drive circuit etc. can be used as is.

In addition, since the signal is normalized and the potential of the signal line is set, the image quality will not deteriorate due to these.
Good still image display can be performed over a long period of time.

Furthermore, since normalization is performed on only one side of the polarity of the video signal, the resolution of the normalization circuit can be easily increased.

(Example) In FIG. 1, each of the switching elements M1 to Mm is replaced with two (solid switching elements MA□).

MBi to MAY and MB are provided in parallel. And the adjacent switching elements MA2, MB□, MA3
The gate terminals of MB2 and MB2... are connected to each other, and pixel switch signals φM11, φH2...
is supplied. Note that the pixel switch signal φHO is supplied to the gate terminal of the switching element MAI.

Further, the input terminal (1) is connected to the switching elements MB□ to MB, , l through the normal display side contact N of the normal display/still image display changeover switch (11). Also, the connection midpoint of switching elements MA, ~MAT11 is the amplifier (12
), and a capacitor is connected to the output terminal of this amplifier (12).
1 sensor (13) is connected, and this output terminal is connected to the inverting circuit (13).
4) Normalization circuit (normalizer) through (15)
and is equal to the delay time a of the signal in the normalization circuit (15) and is connected to the delay circuit II (16). The output terminals of the normalization circuit (15) and the delay circuit (16) are selected by the field changeover switch (17) and connected to the still image display side contact S of the changeover switch (11). Also, each signal line L
1 to Lm respectively have switching elements MR and MR2.
...MR,,l are connected, and this switching element MR
1 to MFun to a predetermined voltage source, for example, a target terminal (3).

In this device, in one field the switch (17) is connected to contact A on the normalization circuit (15) side, and in the other field it is connected to contact B on the delay circuit (16) side.

As a result, for example, a signal of the liquid crystal cell C corresponding to the next pixel switch signal φH2 is extracted at the phase of the pixel switch signal φH1 of one field, and this signal is sent to the amplifier (
12), and is stored in a capacitor (13) through an inversion circuit (14) and a normalization circuit (15), and is written into the same liquid crystal cell C with the phase of the pixel switch signal φH2. Here, if the potential of the signal from the liquid crystal cell C is I/S, and the capacitance of the capacitor (13) is Cs, then if the capacitance of the amplifier (12) is cP, the hot side potential v'8 of the capacitor (13) is , the gain is -A, then this inverting circuit (14)
By setting the value of -A so that the output potential becomes v't=-v, the same inverted signal is rewritten into the liquid crystal cell C.

On the other hand, in the other field, the signal read from the liquid crystal cell C is inverted again by the inverting circuit (14) to the original polarity, and the delay circuit (14) takes a time equal to the processing time of the normalizing circuit (15). (2) The data is rewritten to the liquid crystal cell C with a delay in step 6). As a result, still image display is performed using AC drive.

In this case, the normalization circuit (15) normalizes only one field and not the other field, so for example, if the video signal is as shown in Figure 2, one field Vt~V with reversed polarity
Normalization may be performed only within the SS level range. That is, the input/output characteristics of this normalization circuit (15) need only be as shown in FIG. As a result, even if there is some error in the value of -A, the output signal (rewrite signal) can always be kept at a constant value, and the range of level discrimination is 1/2 that of the conventional one.
Therefore, the configuration can be simplified and the processing time can be shortened.

Further, a horizontal blanking signal φHBLK is supplied to the gate terminals of the switching elements MR, -MRm.

Therefore, each signal line L1 to Lm is reset to the target voltage every horizontal blanking. Therefore, the signals remaining on each signal line are reset, and unnecessary signals are not mixed in when the signal from the liquid crystal cell C is extracted.

In this way, still images are displayed, and the above-mentioned device has an extremely simple configuration, and the signal does not deteriorate even when displayed for a long time, so it can always display a good still image. It is possible to display images every time. Furthermore, since normalization is performed on only one side of the polarity of the video signal, the resolution of the normalization circuit can be easily increased.

By the way, in the above-mentioned apparatus, since normalization is performed every other field in the above-mentioned example, normalization is performed once every two fields, and the setting conditions for -A are somewhat stricter than in the conventional case. In order to reduce this, a circuit as shown in Figure 4 is used. In this figure, the structure of the liquid crystal display section is omitted.

In this figure, the output terminal of the amplifier (12) is connected directly or through the inverting circuit (21) to the field selector switch (
22) and connected to the normalization circuit (15), and the output terminal of the normalization circuit (15) passes through the inversion circuit (23) or is directly selected by the field changeover switch (24) and is connected to the switch (11). ) is connected to the stay side contact S.

Therefore, in this circuit, in one field the signal from the amplifier (12) is inverted and then the normal r
The normalized signal is directly rewritten into the liquid crystal cell C, and the signal from the amplifier (12) is directly sent to the normalization circuit (15) in the other field.
The normalized 4g signal is inverted and rewritten to the liquid crystal cell C. As a result, a still image is displayed by the AC drive J in this circuit as well, and at this time, a signal of only one polarity is supplied to the normal north circuit +1 (15).

In which circuit, I145M with gain A mentioned above is an amplifier (
12) etc., and the gain of the inverting circuits (21) and (23) is set to -1. Also at this time, the inverting circuit (21) (
A circuit with a gain of 1 is also provided at the position shown by the broken line in parallel with 23). Therefore, a differential amplifier can be used to obtain inverted and direct outputs from its positive and negative output terminals. Furthermore, the inverting circuit (21) (23) and the switch (22)
The positions of (24) may be reversed.

Note that this device can be applied to an active matrix liquid crystal display device using TPT such as amorphous silicon, polysilicon, silicon on sapphire, and organic semiconductor.

Further, the above-mentioned shift registers (2+, (41) may be provided outside the IC constituting the device. -Furthermore, the display can be applied to either dot-sequential or line-sequential display.

[Effects of the Invention] According to the present invention, since the signal taken out from the liquid crystal cell C is returned to the same liquid crystal cell C, there is no occurrence of image shift, etc., there is no need for special scanning, etc., and the drive circuit etc. The conventional one can be used as is.

In addition, since the signal is normalized and the potential of the signal line is reset, the image quality will not deteriorate due to these.
Good still image display can be performed for a long time.

Furthermore, since normalization is performed on only one side of the polarity of the video signal, the resolution of the normalization circuit can be easily increased.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an example of the present invention, FIGS. 2 to 4 are diagrams for explaining the same, and FIGS. 5 and 6 are diagrams for explaining a conventional apparatus. L1 to Lin are vertical signal lines, G1 to Gn are gate lines, Ml to Mm, Mu to Mnm, MA,
~MAl, l. M31 to MBm are switching elements, (14) is an inversion circuit, (15) is a normalization circuit, and (16) is a delay circuit.

Claims (1)

[Claims] A video signal whose polarity is inverted with respect to a reference potential every field through horizontal switch elements that are turned on by pixel switch signals that are sequentially formed in column lines equal to the number of horizontal pixels by a horizontal pixel clock. , a scanning line switch signal formed sequentially by a horizontal scanning clock is supplied to the row lines equal to the number of horizontal scanning lines, and the scanning line switch signal is turned on at the intersection of each column line and row line, respectively. In a liquid crystal display device, a driven pixel switch element is provided, and the video signal supplied to the column line is supplied to each liquid crystal display cell constituting one pixel via these pixel switch elements, The video signal stored in the liquid crystal display cell during at least one of the field periods of the video signal is taken out via the pixel switch element, the polarity of the taken out signal is inverted, and the video signal of that polarity is converted into the video signal. The normalized signal is normalized for each predetermined level range, and the inverted and normalized signal is written into the liquid crystal display cell again, and a switch element that is turned on in each horizontal blanking period of the video signal is provided in each column line. 1. A liquid crystal display device characterized in that a reset voltage is supplied through the interface.