JPH0614720B2 - LCD 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 Figure 8, (1) is an input terminal to which a video signal of the television is supplied through the switching elements M _1, M ₂ ...... M _m signal from the input terminal (1) is made of each example N-channel FET It is supplied to lines L ₁ , L ₂ ... L _m in the vertical (Y-axis) direction. Note that m is horizontal (X
This is a number corresponding to the number of pixels in the (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 this shift register (2) Pixel switch signals φ _H1 , φ _H2, ... φ _Hm that are sequentially scanned by the signals φ _1H and φ _2H are switching elements M _{1 to} M _m.
Is supplied to each control terminal of. A low potential (V _SS ) and a high potential (V _DD ) are supplied to the shift register (2), and drive pulses of these two potentials are formed.

Further, the switching elements M ₁₁ , M _21, ... M _n1 , respectively composed of, for example, N-channel FETs are provided on the respective lines L _{1 to} L _m .
One end of M ₁₂ , M ₂₂ ...... M _n2 , ...... M _1m , M _2m ...... M _nm 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} M _nm are respectively connected to the liquid crystal cell C.
₁₁ 、 C ₂₁・ ・_・ Connected to the target terminal (3) through C _nm .

Further, an n-stage shift register (4) is provided, and horizontal frequency clock signals Φ _1V and Φ _2V are provided in the shift register (4).
Are supplied, and scanning line switch signals φ _V1 , φ _V2, ... φ _{vn, which} are sequentially scanned by the clock signals Φ _1V and Φ _2V from the output terminals of the shift register (4), are in the horizontal (X-axis) direction. the gate lines _{G 1, G} 2 ...... _{G n} through the switching element M ₁₁ ~M _nm in the X-axis direction each column of _{(M 11 ~M 1m), (} M
_{21 to} M _2m ) ... (M _{n1 to} M _nm ) are supplied to the respective control terminals. Incidentally, V _SS and V _DD are supplied to the shift register (4) as well as the shift register (2).

That is, in this circuit, the shift registers (2) and (4) have clock signals Φ _1H and Φ _2H , as shown in FIGS.
Φ _1V and Φ _2V are supplied. Then, from the shift register (2), as shown in FIG. 9C, φ _H1 to φ _Hm for each pixel period.
Is output, and φ _V1 to φ _Vn are output from the shift register (4) every horizontal period as shown in FIG. 9D. Further, a signal as shown in FIG. 9E 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. It 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 as above is sequentially performed for the cells C _{12 to} C _nm , and when the signal of the next field is supplied, each cell C 12
The charge amount of _{11 to} C _nm is rewritten.

In this way, the light transmittance of the liquid crystal cells C _{11 to} C _nm 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, when displaying a television image, a signal obtained by inverting the video signal for each field or frame is input terminal (1).
Supply to. That is, the input terminal (1) is supplied with an inverted signal for each field or frame as shown in FIG. 9E.

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, 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 and hold circuit for supplying a video signal whose polarity is inverted for each screen to a plurality of pixels in time series, the video signal is inverted and supplied to the first sample and hold circuit Inverting means, a second sample hold circuit for reading 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 hold circuit, and the inversion is performed. And a switching means for supplying the means to the 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, since 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. 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.

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] The conventional device is configured as described above. Therefore, the conventional device has a problem that the configuration is complicated and the image quality is extremely deteriorated when a still image is displayed for a long time.

[Means for solving problems]

According to the present invention, the number of column lines L _{1 to} L _m equal to the number of horizontal pixels to which a video signal is supplied via the horizontal switch elements driven by the pixel switch signals sequentially formed by the horizontal pixel clock, and the scanning line switches. Row lines G _{1 to} G _n equal to the number of horizontal scanning lines selected by signals, and pixel switch elements M _{11 to} M _nm driven by the scanning line switch signals at intersections of the column lines and row lines, respectively. Equipped with
In a liquid crystal display device having liquid crystal display cells C _{11 to} C _nm arranged in a matrix, the horizontal switch elements are commonly connected to a signal path for supplying the video signal and are turned on in the first half of the pixel switch signal. First
Switch element and the video signal stored in the liquid crystal display cell during the ON period of the first switch element M _A are extracted via the pixel switch and the horizontal switch element, and the extracted signal is inverted ( 14) means for supplying the inverted signal to the signal path through the second switch element M _B which is turned on in the latter half of the pixel switch signal, and the horizontal line of the video signal to each column line. A liquid crystal display device comprising a plurality of third switch elements M _{R1 to} M _Rm which are turned on for each blanking period and supply a reset voltage (3).

[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 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.

〔Example〕

In Figure 1, an input terminal (1) the normal display side contact N of the normal display / still image display changeover switch (11), through the switching element M _B, is connected to the switching element M ₁ ~M _m. Further, the switching element M _B and the switching element M
_The midpoint of connection with _{1 to} M _m is connected to the amplifier (12) via the switching element M _A , the output end of this amplifier (12) is connected to the capacitor (13), and this output end is connected to the inverting circuit (14 ) To a normalizer (normalizer) (15). The output end of the normalization circuit (15) is connected to the still image display side contact S of the changeover switch (11). Further, the switching elements M _R1 , M _R2, ... Are respectively connected to the signal lines L _{1 to} L _m.
M _Rm is connected and is connected to a predetermined voltage source, for example, a target terminal (3) through the switching elements M _{R1 to} M _Rm .

In this device, the switching elements M _A and M _B
To the gate terminal of the switch, switch signals φ _A and φ _B as shown in C and D are supplied to pixel switch signals φ _H1 and φ _H2 as shown in _A and _B of FIG. Note that similar switch signals φ _A and φ _B are formed for the following pixel switch signals φ _H3 .

As a result, for example, the signal of the corresponding liquid crystal cell C is extracted in the first half of the pixel switch signal φ _H1 , and this signal is amplified.
It is stored in the capacitor (13) through the (12) and the inverting circuit (1
4) is written in the same liquid crystal cell C in the latter half of the pixel switch signal φ _H1 through. Here the potential of the signal from the liquid crystal cell C and v _s, and the capacitance of the capacitor (13) and C _s, the capacitance of the amplifier (12) as C _p, the hot side of the condenser (13) potential v _'s Is Becomes When the gain of the inverting circuit (14) is -A, the output potential v ″ _s of this inverting circuit (14) is Becomes Therefore, by setting the value of -A so that this potential becomes v ″ _s = −v _s , the same inverted signal is rewritten in the liquid crystal cell C, and a still image is displayed by AC driving. Is done.

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} L _m 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-described device has an extremely simple structure and does not deteriorate the signal even when the display is performed for a long time. Images can be displayed.

By the way, in the above-mentioned device, it is impossible to completely determine the value of -A in the above-mentioned manner. Therefore, the normalization circuit (15) is provided in the above device. That is, the input / output characteristics of the normalization circuit (15) are as shown in FIG. 3, and by providing this, even if there is some error in the value of −A, the output signal (rewrite signal) is always output. Can be a constant value.

That is, such a normalizing circuit (15) may not be provided, but by providing it, it is possible to display a still image for a longer time.

Further, FIG. 4 shows a case where the number of liquid crystal cells C is tripled to colorize the display, and circuits corresponding to respective colors (red, green, blue) are provided in parallel (R, G, B). These are simultaneously driven to perform the same operation as described above. In this case, the processing of taking out, inverting and rewriting the signal from the liquid crystal cell C described above requires a processing time because it includes a capacitor.
The processing time can be lengthened. It should be noted that this configuration can also be applied to the case of increasing the density of an image by displaying a single color.
On the contrary, it can be applied to the case where a low-speed circuit having a long processing time is used.

By the way, in the above configuration, the normalization circuit (15R) (15G) (15
In B), the processing time is short, but the circuit scale is large. Therefore, as shown in FIG. 5, the switching elements M _01B , M _02B , and M _03B simultaneously synchronize the three pixels of the signal supplied in series, and the buffer circuit (via the capacitors (16R) (16G) (16B)). 17R) (17G) (17
B) and supplies this signal to the switching elements M _BR , M _BG , M _BB.
To each of the same liquid crystal cells as described above via the liquid crystal cells, and the switching elements M _AR , M _AG , M _AB , the amplifier (12
R) (12G) (12B), capacitor (13R) (13G) (13B), inverting circuit
The signals are taken out through (14R), (14G) and (14B), serialized by the signal switching elements M _01A , M _02A and M _03A and supplied to the normalization circuit (15). Note that FIG. 6 shows a time chart of each switching. This also makes it possible to perform still image display similar to that described above.

Further, FIG. 7 shows a case in which 6 pixels are arranged in parallel to increase the density of the image or the speed of the circuit. In this case, two sets of circuits are provided for every three systems (suffixes O and E are added). (Shown), and these are driven in parallel. In this case, the normalization circuits (15O) and (15E) can also be made relatively slow.

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.

The shift registers (2) and (4) described above are I
It may be provided outside C.

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 extracted from the liquid crystal cell C is returned to the same liquid crystal cell C, no image shift occurs, no special scanning or the like is required, and the drive circuit etc. are the same as those of the conventional one. Can be used. Further, since the potential of the signal line is reset, the image quality is not deteriorated by these, and it becomes possible to display a good still image for a long time.

[Brief description of drawings]

FIG. 1 is a block diagram of an example of the present invention, FIGS. 2 to 7 are diagrams for explaining the same, and FIGS. 8 and 9 are diagrams for explaining a conventional device. L _{1 to} L _m are vertical signal lines, G _{1 to} G _n are gate lines,
M _{1 to} M _m , M _{11 to} M _nm , M _A , M _B , and M _{R1 to} M _Rm are switching elements, (14) is an inverting circuit, and (15) is a normalizing circuit.

Claims (1)

[Claims] 1. A number of column lines equal to the number of horizontal pixels to which a video signal is supplied via a horizontal switch element driven by a pixel switch signal sequentially formed by a horizontal pixel clock, and selected by a scan line switch signal. The number of horizontal scanning lines is equal to the number of horizontal scanning lines, the pixel switching elements driven by the scanning line switching signals are provided at the intersections of the column lines and the row lines, and the liquid crystal display cells are arranged in a matrix. In the liquid crystal display device, a first switch element that is connected to a signal path that supplies the video signal in common to the horizontal switch element and is turned on in the first half of the pixel switch signal, and the first switch element is turned on. During the period, the video signal stored in the liquid crystal display cell is taken out through the pixel switch and the horizontal switch element, Means for inverting the output signal and supplying the inverted signal to the signal path via a second switch element that is turned on in the latter half of the pixel switch signal; A liquid crystal display device comprising a plurality of third switch elements that are turned on for each horizontal blanking period of a signal and supply a reset voltage.