JPH075850A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To drive an intermediate size panel using an analog driver having a comparatively low sampling speed by sorting video signals by one line inputted time sequentially, lowering transfer speed of one pixel, and inputting them to plural analog drivers. CONSTITUTION:Video signals outputted from CCD shift register A and B are inputted to an analog driver 3 consisting of a sample-and-hold circuit and a driving circuit. And the lower side analog driver 3 drives an odd numbered signal line electrode extended in the longitudinal direction of a liquid crystal panel 4, and the upper side analog driver 3 drives an even numbered signal line electrode extended in the longitudinal direction of a liquid crystal panel 4. And when a transfer clock is an odd numbered clock, a switch 1 is connected to the contact (b) side and the video signal is supplied to the CCD register B, and when even numbered, the switch 1 is connected to the contact (a) side and the video signal is supplied to the CCD register A. Thus, transfer operation is performed with frequency of half of a transfer clock of an original video signal by switching operation of the switch 1, and a reduced video signal is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a technique effectively used for driving an active matrix liquid crystal display panel using TFTs (thin film transistors) with an analog driver.

[0002]

2. Description of the Related Art Generally, as one method for realizing multi-color display on a flat display panel, a liquid crystal matrix panel is provided with three colored layers of red (R), green (G) and blue (B).
There has been proposed a display device which obtains a multi-color image with gradation by applying voltages with different time widths to the row and column electrodes in correspondence with the matrix electrodes provided on the substrates sandwiching the liquid crystal.

In such a full-color liquid crystal matrix panel of the additive color mixing system, as shown in FIG. 5, a coloring layer R is provided for each pixel in the horizontal scanning direction of the liquid crystal panel 101.
This is realized by arranging dot electrodes corresponding to G and B, outputting a voltage applied to each image electrode from the signal side drive circuit 102, and sequentially scanning the row electrodes by the scan side drive circuit 103.

FIG. 6 shows a typical signal side driving circuit in the case where a video signal is a time series such as a television. The signal side drive circuit 104 includes input lines for the video signals S corresponding to the respective dots of R, G and B, and a sample hold circuit (S / H) 105 for sampling the respective video signals.
And an output buffer (B
uf) 106, as shown in FIG. 7, the video signal S is sampled at different timings (sampling timing signals C1 to C3) for each output of the liquid crystal drive circuit and output to the liquid crystal panel. Hereinafter, a drive circuit of this type will be referred to as an analog driver. Examples of such an analog driver include “HD66300” sold by Hitachi, Ltd. and “μPD16407” sold by NEC Corporation.

[0005]

The display device currently used in terminals of office automation equipment is a medium size panel having 640 × 3 dots in the horizontal direction and 480 dots in the vertical direction, and the display speed of the screen is It is about 60 Hz. Therefore, it is necessary to fetch the video signal into the liquid crystal drive circuit at the speed of the equation (1) per dot. 60 × 640 × 3 × 480 = 55.3MHz ・ ・ ・ ・ ・ ・ ・ (1)

On the other hand, the above analog driver has a maximum sampling speed of about 30 MHz, and therefore cannot drive the above-mentioned middle-sized panel. In other words, the analog driver is used exclusively for small televisions.

An object of the present invention is to provide a liquid crystal display device capable of driving a medium-sized panel capable of full-color display while using a low speed analog driver. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0008]

The outline of a typical one of the inventions disclosed in the present application will be briefly described as follows. That is, the video signals for one line, which are input in time series, are distributed and input to a plurality of analog shift registers to reduce the transfer rate per pixel, and a plurality of analogs including a sample hold circuit and a drive circuit. Type in the driver.

[0009]

According to the above means, the speed of the image signal input to the analog driver can be reduced by the analog shift register, so that the medium-sized panel can be driven by using the analog driver having a relatively slow sampling speed. It will be possible.

[0010]

1 is a schematic block diagram of an embodiment of a liquid crystal display device according to the present invention. Although not particularly limited, each circuit block except the liquid crystal panel in each circuit block in the figure is configured by a semiconductor integrated circuit device of one chip. Each of these semiconductor integrated circuit devices is formed on one semiconductor substrate such as single crystal silicon by a known MOS integrated circuit manufacturing technique.

The video signal is sent to the CCD via the switch 1.
(Charge transfer element) It is supplied to the shift register 2. CC
The D shift register 2 is composed of two CCD shift registers A and B. The video signals input in time series are alternately switched by the switch 1 for each pixel signal unit and supplied to the CCD shift register 2.

The video signals output from the CCD shift registers A and B are input to the analog driver 3 including a sample hold circuit and a drive circuit. The analog driver 3 is composed of two parts which are distributed above and below the liquid crystal panel. That is, the lower analog driver 3
Drive the odd-numbered signal line electrodes extended in the vertical direction of the liquid crystal panel 4, and the upper analog driver drives the even-numbered signal line electrodes extended in the vertical direction of the liquid crystal panel 4.

The scanning line driving circuit 5 forms a selection signal for sequentially selecting the scanning line electrodes extending in the lateral direction of the liquid crystal panel 4. The scanning line driving circuit 5 takes in a pulse input at the beginning of the frame as a start signal, sequentially shifts it by a shift register to form a selection signal, and outputs the driving signal of the scanning line electrode through an output buffer. .

When the number of output terminals of the analog driver is smaller than the number of signal line electrodes of the liquid crystal display panel, a plurality of analog drivers are arranged substantially in series to correspond to the signal line electrodes of the liquid crystal panel. Form the drive signal. This also applies to the scanning line drive circuit,
When the number of output terminals of the scanning line driving circuit configured by one semiconductor integrated circuit device is small with respect to the number of scanning line electrodes of the liquid crystal display panel, a plurality of scanning line driving circuits are connected in series, The scanning line electrodes are sequentially selected.

FIG. 2 shows the CC in the liquid crystal display device.
A timing diagram is shown to explain the operation of the D shift register. The switch 1 is switched by a transfer clock corresponding to each pixel of the video signal. That is,
When the video signal D11 corresponding to the first clock is input, the switch 1 is connected to the contact b side and the CCD
The video signal D11 is supplied to the shift register B side. When the video signal D12 corresponding to the second clock is input, the switch 1 is switched to the contact a side and CC
The video signal D12 is supplied to the D shift register A side.

Similarly, the switch 1 is connected to the contact b side at the odd-numbered transfer clock to supply the video signal at that time to the CCD shift register B, and the switch 1 at the even-numbered transfer clock. Is connected to the contact a side, and the video signal at that time is supplied to the CCD shift register A.

By switching the switch 1 as described above,
The time-series video signal is one of the transfer frequencies of the original video signal.
Converted to a frequency reduced to / 2. The CCD shift registers A and B are set to 1 of the transfer clock of the original video signal.
1 by performing the transfer operation with the transfer clock of the frequency of / 2
A video signal having a frequency reduced to / 2 is formed.

As a result, when the liquid crystal panel 4 of FIG. 1 has 640.times.3 dots in the horizontal direction and 480 dots in the vertical direction as described above, the input video signal is 55.3 MHz.
However, by using the switch 1 and the CCD shift register as described above, it is possible to reduce the frequency to a low frequency such as 27.7 MHz, which is half the frequency. As a result, as the analog driver 3 distributed above and below the liquid crystal display panel, the existing one for a small television receiver can be used as it is.

The CCD shift registers A and B need only perform a shift operation of at least 1 bit. In response to this, the selection timing on the scanning line side may be delayed by the above-mentioned 1 bit. It should be noted that if the selection time on the scanning line side has a certain time margin such as a horizontal blanking period, there is no problem because the selection timing is only advanced by one bit.

When the 1-bit CCD shift register as described above is used, the CCD shift register may be built in the input section of the analog driver 3. In this case, instead of the CCD shift register, an analog shift register using a sampling hold circuit may be used.

As a CCD shift register, in the case of a liquid crystal display panel having 640 × 3 dots as described above, 3
The 20 × 3 bit configuration may be delayed by one line to supply the video signal to the analog driver. In this case, the frame signal input to the scanning line drive circuit may be generated with a delay of one line.

FIG. 3 is a block diagram of another embodiment of the liquid crystal display device according to the present invention. In this embodiment, in order to further lower the frequency of the video signal input to the analog driver, the following configuration is adopted.

In this embodiment, the signal line electrodes of the liquid crystal panel 4 are divided into upper and lower parts and left and right parts, and four analog drivers 3 of A to D, which are composed of a total of four sample hold circuits and drive circuits, are provided. . Each of the four analog drivers A to D may be composed of one semiconductor integrated circuit device. If the number of output terminals is small for the signal line electrodes that the analog driver 3 handles, the plurality of semiconductor integrated circuit devices are used. It may be configured.

In this embodiment, two CCD analog shift registers are provided for each of the four analog varieties A to D. A changeover switch 2 and a changeover switch 3 are provided on the input side and the output side of the CCD analog shift register paired like the CCD analog shift registers A1 and A2, respectively. These input-side and output-side changeover switches 2 and 3 are reciprocal switches. For example, when the changeover switch 2 selects the CCD shift register A1, the changeover switch 3
Selects the CCD shift register A2.
In other words, when the video signal is being input to one CCD shift register A1, the video signal already fetched is being output from the other CCD shift register A2.

The CCD shift registers B1, B2 to D paired with the other analog drivers B to D are also paired.
1, D2 are provided, the changeover switch 2 is provided on each input side, and the changeover switch 3 is provided on the output side. A video signal is input to the changeover switch 2 through the changeover switch 1.

FIG. 4 shows the CC in the liquid crystal display device.
A timing diagram is shown to explain the operation of the D shift register. When capturing the video signal of the first row of the liquid crystal panel 4, the switch 2 selects the CCD shift registers A1 to D1 and the switch 3 selects the CCD shift registers A2 to D2. For the video signal of the first row in the left half of the liquid crystal panel 4, the switch 1
Selects the CCD shift registers A1 and C1 and alternately inputs them to the video signal. Then, for the video signal corresponding to the right half of the liquid crystal panel, the switch 1 selects the CCD shift registers B1 and D1 to alternately input the video signal. At this time, the CCD shift registers A1 and C1
And holds the captured image signal after stopping the transfer operation.

When the video signal of the first row is completed and the video signal of the second row is input as described above, the switch 2 and the switch 3 are switched, and the switch 2 is the CCD shift register. A2 to D2 are selected, and the switch 3 selects CCD shift registers A1 to D1.

For the video signal of the second row in the left half of the liquid crystal panel 4, the switch 1 selects the CCD shift registers A2 and C2 to alternately input the video signals. Then, for the video signal corresponding to the right half of the liquid crystal panel, the switch 1 switches the CCD shift registers B2 and D.
2 is selected and video signals are alternately input. When capturing the latter half of the video signal, the CCD shift registers A2 and C2 stop the transfer operation and hold the captured image signal.

In parallel with the above-described operation of capturing the video signal of the second row, the CCD shift registers A1 to D
The transfer operation of the video signal of the first row fetched in 1 is performed to cause the corresponding analog drivers A to D to input the video signal. At this time, analog driver A ~
In D, the transfer rate can be reduced to 1/4 of the original video signal.

As a result, it becomes possible to drive a larger liquid crystal panel or a liquid crystal panel having a high density of pixels by using the above analog driver. In the liquid crystal display device of the present application, pixels are driven by analog signals, whereas full-color display is possible in contrast to a liquid crystal device in which a grayscale voltage is applied to perform multicolor display.

The effects obtained from the above embodiment are as follows. That is, (1) a plurality of analog drivers including a sample hold circuit by distributing video signals for one line, which are input in time series, and inputting them to an analog shift register composed of a plurality of pixels to reduce the transfer rate per pixel. By inputting into, it is possible to obtain the effect that it becomes possible to drive a medium-sized panel using an analog driver having a relatively slow sampling rate.

(2) C as an analog shift register
By using the CD shift register, it is possible to obtain the effect of realizing full-color display of a medium-sized or larger liquid crystal panel while utilizing the existing semiconductor integrated circuit device.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention of the present application is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. Needless to say. For example, a larger liquid crystal panel can be driven by increasing the number of divisions such as dividing the analog driver for driving the signal line electrodes of the liquid crystal panel into left and right. Further, a configuration may be adopted in which a CCD shift register is incorporated in the analog driver and the analog signal serially taken in by the CCD shift register is directly transferred in parallel to the sample / hold circuit. INDUSTRIAL APPLICABILITY The present invention can be widely used for driving a TFT active matrix type liquid crystal panel by an analog video signal.

[0034]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows. That is, one-line video signals input in time series are distributed and input to a plurality of analog shift registers to reduce the transfer rate per pixel and input to a plurality of analog drivers including a sample hold circuit. This makes it possible to drive the medium-sized panel using the analog driver having a relatively low sampling rate.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a liquid crystal display device according to the present invention.

2 is a timing diagram for explaining the operation of the CCD shift register of FIG.

FIG. 3 is a block diagram showing another embodiment of the liquid crystal display device according to the present invention.

4 is a timing diagram for explaining the operation of the CCD shift register of FIG.

FIG. 5 is a schematic block diagram showing an example of a liquid crystal display device.

FIG. 6 is a block diagram showing an embodiment of a signal side drive circuit in a conventional liquid crystal display device.

7 is a waveform chart for explaining an example of the operation of the signal side drive circuit of FIG.

[Explanation of Codes] 1 ... Switch, 2 ... CCD shift register, 3 ... Analog driver (sample hold circuit and drive circuit), 4
... liquid crystal panel, 5 ... scanning line drive circuit, S1 to S3 ... switch, 101 ... liquid crystal panel, 102 ... signal side drive circuit,
103 ... Scan side drive circuit, 104 ... Signal side drive circuit, 1
05 ... Sample and hold circuit, 106 ... Output buffer.

Claims (2)

[Claims] 1. A time-series input video signal for one line is distributed and input to an analog shift register consisting of a plurality of pixels to output at a reduced transfer rate per pixel, and these output signals are sampled. A liquid crystal display device characterized by being input to a plurality of analog drivers including a hold circuit. 2. The liquid crystal display device according to claim 1, wherein the analog shift register uses a CCD shift register.