JPH084330B2 - Liquid crystal display device - Google Patents

Description

The present invention relates to a liquid crystal display device for displaying a still image.

[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 video signal of a television is supplied, and a signal from the input terminal (1) is a switching element M, which is, for example, an N-channel FET.
₁ 、 M ₂・ ・ ・ Lines L ₁ , L _{2 in the} vertical (Y-axis) direction through Mm
... Supplied to Lm. Note that m is a number corresponding to the number of pixels in the horizontal (X axis) direction. Further, an m-stage shift register (2) is provided, and clock signals Φ _1H and Φ _2H of m times the horizontal frequency are supplied to the shift register (2), and clocks from respective output terminals of the shift register (2). Pixel switch signals φ _H1 , φ _H2 ... φ _Hm sequentially scanned by the signals φ _1H and φ _2H are supplied to the respective control terminals of the switching elements M _{1 to} Mm. The shift register (2) is supplied with a low potential (V _SS ) and a high potential (V _DD ) and drive pulses of these two potentials are formed.

Further, for example, N-channel FE is provided in each line L _{1 to} Lm.
Switching element consisting of T M ₁₁ , M _21, ... M _n1 , M ₁₂ , M ₂₂
··· _{M n2,} ··· M _1m, one end of the M _2m ··· Mnm is connected. Note that n is a number corresponding to the number of horizontal scanning lines. The other ends of the switching elements M _{11 to} Mnm are respectively connected to the liquid crystal cell C ₁₁ ,
It is connected to the target terminal (3) through C ₂₁ ··· Cnm.

Further, an n-stage shift register (4) is provided, and horizontal frequency clock signals Φ _1V and Φ _2V are supplied to the shift register (4), and the clock signal Φ _1V from each output terminal of the shift register (4). , the scanning line switch signal phi _V1 sequentially scanned by Φ _2V, φ _V2 ··· φ _Vn is,
The gate lines G ₁ , G ₂ ... G _{n in the} horizontal (X-axis) direction are used to switch the switching elements M _{11 to} Mnm in each column (M ₁₁ to Mn) in the X-axis direction.
It is supplied to the control terminals for each of M _1m ), (M _{21 to} M _2m ) ... (M _{n1 to} Mnm). The shift register (4)
Also, V _SS and V _DD are supplied similarly to the shift register (2).

That is, in this circuit, the shift register (2),
In (4), the clock signals Φ _1H , Φ as shown in FIGS.
_2H , Φ _1V and Φ _2V are supplied. Then, from the shift register (2), as shown in FIG.
_{H1 to} φ _Hm are output, and the sixth from the shift register (4).
As shown in FIG. D, φ _V1 to φ _Vn are output every horizontal period. Further, a signal as shown in FIG. 6E is supplied to the input terminal (1).

When φ _V1 and φ _H1 are output, the switching elements M ₁ and M _{11 to} M _1m are turned on, and the input terminal (1) → M ₁
→ L ₁ → M ₁₁ → C ₁₁ → The current path of the 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 C _11. . Therefore, the charge corresponding to the potential difference due to the signal of the first pixel is sampled and _{held in} the capacity of the cell C ₁₁ . The light transmittance of the liquid crystal is changed according to this charge amount. The same operation is sequentially performed on the cells C _{12 to} Cnm, and when the signal of the next field is supplied, each cell C ₁₁
The charge amount of ~ Cnm is rewritten.

In this way, the light transmittance of the liquid crystal cells C _{11 to} Cnm is changed corresponding to each pixel of the video signal, and this is repeated sequentially to display a television image.

By the way, when displaying with a liquid crystal, an AC drive is generally used in order to improve its reliability and life. For example, in displaying a television image, a signal obtained by inverting the video signal for each field or frame is supplied to the input terminal (1). 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 Vt for each field or frame.

By the way, in the above-mentioned device, there is a demand to display 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, and the read signal is phase-inverted for each field and the above-mentioned input is performed. It is proposed to supply the terminal (1). However, the memory for one field or one frame as described above is large in size and expensive, and it is difficult to apply it to general consumer equipment.

On the other hand, as disclosed in, for example, Japanese Patent Laid-Open No. 58-107782, it has been proposed to display a still image by utilizing the memory function of the liquid crystal cell C. That is, this device
In a liquid crystal video display drive circuit having a first sample-hold circuit for supplying a plurality of pixels with a video signal whose polarity is inverted for each pixel in time series, the video signal is inverted and then the first sample-hold circuit is provided. Inverting means for supplying, a second sample hold circuit for reading out the video signals from the plurality of pixels in time series, a video signal from an external terminal or a video signal from the second sample and hold circuit is switched to switch the And a liquid crystal video display drive circuit having switching means for supplying to the inverting means.

However, in this device, as described in the publication, the image shifts by one pixel in the scanning direction every time one field is displayed. For this reason, a measure such as reversing the scanning direction is performed for each field, but a large-scale circuit is required to switch the scanning direction in this way, and one pixel is alternately shifted for each field. Since the state remains, this may cause flicker or the like.

Further, the signal of the liquid crystal cell C is taken out, this signal is returned to the liquid crystal cell C again, and this is repeated to display a still image. Therefore, if there is a distortion in the transmission characteristic of the signal during this time, this distortion will occur. The image quality is accumulated and is significantly deteriorated in a short time. On the other hand, it has been shown that the gain of the inverting means is adjusted, but it is impossible to perform such adjustment completely, and it is extremely difficult to display a normal still image for a long time. Is.

On the other hand, it is conceivable to correct the distortion due to a gain error or the like by normalizing the signal for each predetermined level range to, for example, its center level. However, in this case, in order to determine the above-mentioned predetermined level range, for example, a comparator is provided by the number of the boundaries of the level range, or at the half point of the maximum amplitude (V _{DD to} V _SS ) of the signal. A method is used to determine whether it is above or below it, then determine the top and bottom at 1/4 equally divided points, and then repeat 1/8 and 1/16 to determine the level range. If the resolution of the conversion is to be improved, the former may have a complicated and enormous configuration, and the latter may not be able to perform processing in one pixel clock period.

Further, when a signal is taken out from the liquid crystal cell C, if there is a residual charge in the floating capacitance of the signal line, the signal is also deteriorated by this, and it becomes impossible to display a still image for a long time.

[Problems to be solved by the invention]

Conventional devices have been configured as described above. Therefore, in the conventional device, the image quality is extremely deteriorated when the configuration is complicated or when a still image is displayed for a long time.
Further, there is a problem that the normalization resolution cannot be sufficiently large.

[Means for solving problems]

According to the present invention, a video signal whose polarity is inverted with respect to the reference potential for each field is generated via the first horizontal switch elements M _{B1 to} M _Bm driven by the pixel switch signals sequentially formed by the horizontal pixel clock. The number of column lines L _{1 to} L _m equal to the number of supplied horizontal pixels, the row lines G _{1 to} G _n equal to the number of horizontal scanning lines selected by the scanning line switch signal, and the above-mentioned column lines and row lines. A liquid crystal display device comprising liquid crystal display cells C _{11 to} C _nm arranged in a matrix, each pixel switch element M _{11 to} M _nm being driven by the scanning line switch signal at an intersection, The second horizontal switching element M _{A1 to} M _{Am in} parallel with the first horizontal switching element
Is provided, the video signal stored in the liquid crystal display cell is taken out through the pixel switch element and the second horizontal switch element in at least one field period of the video signal, and the polarity of the taken out signal is inverted. (14)
In addition, the polarity of the video signal is normalized (15) for each predetermined level range, and means for writing the inverted and normalized signal into the liquid crystal display cell again, and the horizontal direction of the video signal on each column line are provided. Reset voltage (3) via switch elements M _{R1 to} M _Rm that are turned on for each blanking period
And a means for supplying the liquid crystal display device.

[Action]

According to this device, since the signal taken out from the liquid crystal cell C is returned to the same liquid crystal cell C, the image shift does not occur, no special scanning or the like is required, and the drive circuit or the like is the conventional one. Can be used as is. Further, since the signal is normalized and the potential of the signal line is reset, the image quality is not deteriorated by these, and good still image display can be performed for a long time. Furthermore, since the normalization is performed only on one side of the polarity of the video signal, the resolution of the normalization circuit can be easily increased.

〔Example〕

In FIG. 1, two switching elements M _A1 , M _{B1 to} M _Am , M _Bm are provided in parallel in place of the switching elements M _{1 to} Mm. And each adjacent switching element
The gate terminals of M _A2 and M _B1 , M _A3 and M _B2 ... Are connected to each other, and the pixel switch signals φ _H1 , φ _H2 ...
・ Is supplied. The pixel switch signal φ _HO is supplied to the gate terminal of the switching element M _A1 . Furthermore, the input terminal (1) has a normal display / still image display switch (11)
Through the normal display side contact N of the switching elements M _{B1 to} M
Connected to _Bm . In addition, the connection midpoint of the switching elements M _{A1 to} M _Am is connected to the amplifier (12), the output end of this amplifier (12) is connected to the capacitor (13), and this output end is normalized through the inverting circuit (14). Circuit (Normalizer) (15)
And a delay circuit (16) having a signal delay time equal to that of the normalization circuit (15). And this normalization circuit (15)
The output end of the delay circuit (16) is selected by the field changeover switch (17) and connected to the still image display side contact S of the changeover switch (11). Also respectively connected switching elements M _R1, M _R2 ··· M _Rm to the respective signal lines L ₁ to L m, a predetermined voltage source through the switching element M _R1 ~M _Rm, for example connection to the target terminal (3) To be done.

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

As a result, for example, the signal of the liquid crystal cell C corresponding to the next pixel switch signal φ _H2 in the phase of the pixel switch signal φ _H1 of one field is taken out, and this signal is output from the amplifier (1
It is stored in the capacitor (13) through 2) and the inverting circuit (1
4), Pixel switch signal φ _H2 through normalization circuit (15)
Are written in the same liquid crystal cell C in the phase of. Here, if the potential of the signal from the liquid crystal cell C is v _S and the capacitance of the capacitor (13) is C _S , the capacitance of the amplifier (12) is C _{P and} the hot side potential v ′ _S of the capacitor (13). Is Becomes And if the gain of the inverting circuit (14) is -A,
The potential v ″ _S of the output of this inverting circuit (14) is Becomes So that this potential becomes v ″ _S = −v _S −
By determining the value of A, the same inverted signal is rewritten in 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 have the original polarity, and a time equal to the processing time in the normalizing circuit (15) is delayed by the delay circuit ( It is delayed in 16) and rewritten in the liquid crystal cell C. As a result, a still image is displayed by AC driving.

In this case, since the normalization circuit (15) normalizes only one field and does not normalize the other field, for example, in the case of a video signal as shown in FIG. Polarity is inverted Vt to V _SS
Normalization should be performed only in the level range of. That is, the input / output characteristics of the normalization circuit (15) may 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 determination is half that of the conventional one. Can be simplified and the processing time can be shortened.

Further, the horizontal blanking signal φ _HBLK is supplied to the gate terminals of the switching elements M _{R1 to} M _Rm . Therefore, the signal lines L _{1 to} Lm are reset to the target voltage every horizontal blanking. Therefore, the signal remaining in each signal line is reset, and an unnecessary signal is not mixed in when the signal of the liquid crystal cell C is taken out.

Although a still image is displayed in this way, the above-mentioned device has a very simple structure and the signal is not deteriorated even when it is displayed for a long time.
A good still image can always be displayed. Furthermore, since the normalization is performed only on 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 the normalization is performed every other field in the above-mentioned example, the normalization is performed once every two fields, and the setting condition of -A becomes slightly stricter than the conventional one. Therefore, in order to reduce it, a circuit as shown in FIG. 4 is used. In this figure, the structure of the liquid crystal display is omitted.

In this figure, the output terminal of the amplifier (12) is directly connected to the output terminal of the field selector switch (2)
2) is selected and connected to the normalization circuit (15), and the output end of the normalization circuit (15) is passed through the inverting circuit (23) or directly selected by the field change-over switch (24) and the switch (11). ) Still side contact S of.

Therefore, in this circuit, in one field, the signal from the amplifier (12) is inverted before the normalization circuit (15).
Is supplied to the liquid crystal cell C and the normalized signal is directly rewritten, and in the other field, the amplifier (12) is supplied.
Is directly supplied to the normalization circuit (15), and the normalized signal is inverted and rewritten in the liquid crystal cell C. As a result, also in this circuit, a still image is displayed by AC driving, and at this time, the normalizing circuit (15) is supplied with a signal having only one polarity.

In this circuit, the above-mentioned gain A adjustment is performed by the amplifier (12).
The gain of the inverting circuits (21) and (23) is set to -1. Further, at this time, a circuit having a gain of 1 is provided also in the position shown by the broken line in parallel with the inverting circuits (21) and (23). Therefore, a differential amplifier can be used to obtain inverting and direct outputs from the positive and negative output terminals. Inversion circuit (21) (23)
The positions of the switches (22) and (24) may be reversed.

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

Further, the shift registers (2) and (4) described above may be provided outside the IC constituting the device.

Further, the display can be applied to both dot sequential and line sequential.

〔The invention's effect〕

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, the image shift does not occur, no special scanning or the like is required, and the drive circuit or the like is the conventional one. Can be used as is. Further, since the signal is normalized and the potential of the signal line is reset, the image quality is not deteriorated by these, and good still image display can be performed for a long time. Furthermore, since the normalization is performed only on one side of the polarity of the video signal, the resolution of the normalization circuit can be easily increased.

[Brief description 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. L _{1 to} Lm are vertical signal lines, G _{1 to} Gn are gate lines, M _{1 to} Mm, M
₁₁ ~ Mnm, M _A1 ~ M _Am , M _B1 ~ M _Bm are switching elements, (1
4) is an inverting circuit, (15) is a normalization circuit, and (16) is a delay circuit.

Claims (1)

[Claims] 1. A horizontal line to which a video signal whose polarity is inverted with respect to a reference potential is supplied for each field via a first horizontal switch element driven by a pixel switch signal sequentially formed by a horizontal pixel clock. The number of column lines equal to the number of pixels, the row lines equal to the number of horizontal scanning lines selected by the scanning line switch signal, and the pixels driven by the scanning line switch signal at the intersections of the column lines and the row lines. A liquid crystal display device comprising a switch element and liquid crystal display cells arranged in a matrix, wherein a second horizontal switch element is provided in parallel with the first horizontal switch element, and at least one of the video signals is provided. The video signal stored in the liquid crystal display cell in the field period is taken out through the pixel switch element and the second horizontal switch element. Then, the polarity of the extracted signal is inverted, the polarity of the extracted signal is normalized for each predetermined level range, and the inverted and normalized signal is written into the liquid crystal display cell again, and the column lines. And a means for supplying a reset voltage via a switch element that is turned on every horizontal blanking period of the video signal.