JP2630012B2 - Liquid crystal display - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device that can be used for a display such as a projection television receiver, a viewfinder for a television camera, and OA equipment.

2. Description of the Related Art In recent years, liquid crystal display devices are already in a practical stage, such as being used for displays of pocket-sized television receivers, projection television receivers, viewfinders for television cameras, OA equipment, and the like. In particular, in terms of image quality, each pixel has a thin film transistor (TF)
T) The active matrix type provided with a switch is excellent as a liquid crystal driving technique, and various signal processing methods are being studied to improve the image quality.

Hereinafter, a conventional liquid crystal display device will be described with reference to FIGS. 3 and 4. FIG. FIG. 3 is an equivalent circuit diagram of the liquid crystal display device, 21 is a horizontal scanning circuit, 22 is a vertical scanning circuit, 23 is an analog switch, 24 is a signal line, 25 is a gate signal line, 26 is a pixel switch, and 27 is a pixel capacitance. Element.

FIG. 4 shows a cross-sectional structure of the pixel unit 30. In the figure, 31
Is a TFT substrate, 32 is a pixel electrode, 33 is a common electrode, 34 is a liquid crystal, 3
5 is a glass substrate, 36 is a polarizing plate A, 37 is a polarizing plate B, and 38 is a black matrix. Black matrix 38
Is for blocking light leaking from the liquid crystal 34 '(region B) displaced by the potential of the signal line 24 or the gate signal line 25.

However, in the above-described conventional liquid crystal display device, in the voltage generated when the video signal Ls is written to the pixel capacitor 27, the potential to be written to the n-th row pixel capacitor and (n +
1) Since the potentials to be written to the pixel capacitance elements in a row are different, the potential difference in each pixel switch 6 increases, and a leakage current due to the potential difference flows through the pixel switches 6,
There have been problems of lowering the contrast and generating crosstalk.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a liquid crystal display device which suppresses a leak current flowing through a pixel switch and has excellent image quality.

Means for Solving the Problems A pixel portion in which pixels are arranged in a matrix, a signal line for transferring a signal commonly connected to pixels in each column, and an end of the signal line sandwiching the pixel portion And a gate signal line serving as a common gate electrode of the pixel transistors in each row in a liquid crystal display device, wherein a signal is sent from the signal line to the pixels every row from a blanking period of one horizontal period. Is transferred, and the potential of the signal line is made equal to the potential of the common electrode by the reset switch during at least the video holding period other than the blanking period.

Operation According to the present invention, with the above structure, a leak current due to a potential difference in each pixel can be reduced, so that image quality can be improved.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows an equivalent circuit of this embodiment, in which 1 is a horizontal scanning circuit, 2 is a vertical scanning circuit, 3 is an analog switch, 4 is a signal line, 5 is a gate signal line, 6 is a pixel switch. , 7 are pixel capacitors, 8 is a reset switch, 9 is a capacitor, and 10 is a transfer gate.
Is [Phi _T is a terminal for drive terminal of the transfer gate 10, V _com is to be connected to the common electrode at the same potential. The capacitance of the capacitance element 9 is set sufficiently larger than the parasitic capacitance of the signal line 4.

Next, FIG. 2 shows the structure of the pixel section 11 of the liquid crystal display device in this embodiment. In the figure, 12 is a TFT substrate, 13 is a pixel electrode, 14 is a common electrode, 15 is a liquid crystal, 16 is a glass substrate, 17
Denotes a polarizing plate A, and 18 denotes a polarizing plate B.

The operation principle of the liquid crystal display device configured as described above will be described. The capacitance element 9 and the transfer gate 10 shown in FIG.
Sample-and-hold circuit configured to, the sample after being stored in the video signal L _S once capacitive element 9 by a hold circuit, a transfer gate 10 during the horizontal blanking period by,
The data is written to the pixel capacitor 7 through the signal line 4 and the pixel switch 6. The signal line 4 is set to the same potential as the common electrode 14 by the reset switch 8 during the video holding period other than the horizontal blanking period. Next, a timing chart of signals of the present invention will be described with reference to FIG. As shown in FIG. 5, one horizontal period has a blanking period a and a video holding period b other than the blanking period, and the driving terminal (Φ _T ) of the transfer gate 10 applies signals during the blanking period. The signal is transferred to the pixel, and at the same time, the signal is written to the pixel capacitor 7 through the signal line 4. A drive signal waveform of the transfer gate shown by a [Phi _VT. Here, the signal (Φ _Vn ) is written to the n rows of pixel capacitance elements in one horizontal period A, and the signal (Φ _{Vn + 1} ) is
Since the data is written to the (n + 1) -th row of pixel capacitors in one horizontal period B, the potential written to each pixel capacitor differs. Then, the reset switch 8 connected to the driving terminal [Phi _R is closed at least in the blanking period of one horizontal period, the operation of opening the image holding period. Φ _VR
Indicated by Therefore, the signal line is set to the same potential as the common electrode 14 by the reset switch 8 during the video holding period other than the horizontal blanking period, and as a result, the leak current due to the potential difference applied to each pixel switch 6 can be reduced. Can be suppressed and the occurrence of crosstalk can be suppressed, and the image quality can be improved.

In this embodiment, Al is used as the conductive thin film electrode material of the signal line 4 or the gate signal line 5. However, other conductive materials such as Cr, Ti, Au, and polysilicon may be used. Similar effects can be obtained.

As is clear from the above embodiment, the present invention transfers a signal from a horizontal scanning circuit through a signal line during a horizontal blanking period, and reduces the potential of the signal line during a video holding period other than the horizontal blanking period. By maintaining the same potential as the common electrode, a leak current due to a potential difference in each pixel can be reduced, so that a liquid crystal display device having excellent image quality can be provided.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram of a main part of a liquid crystal display device according to an embodiment of the present invention, FIG. 2 is a sectional view of a main part of a pixel portion of the liquid crystal display device, and FIG. FIG. 4 is a sectional view of an essential part of the liquid crystal display device, and FIG. 5 is a timing chart of signals of the liquid crystal display device in one embodiment of the present invention. 4 ... signal line, 5 ... gate signal line, 11 ... pixel part, 13
... pixel electrode, 14 ... common electrode, 15, 15 '... liquid crystal, 17
...... Polarizing plate A, 18 ... Polarizing plate B.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Fumiaki Emoto 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Kazunori Kobayashi 1006 Kazuma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

(57) [Claims] 1. A pixel section in which pixels are arranged in a matrix, a signal line commonly connected to pixels in each column for transferring a signal, and a signal line interposed between the pixel sections are provided at an end of the signal line. A reset signal and a gate signal line serving as a common gate electrode of the pixel transistors in each row, a signal is transferred from the signal line to the pixel for each row during a blanking period of one horizontal period. As well as
A liquid crystal display device wherein the potential of the signal line is made equal to the potential of a common electrode by the reset switch at least in a video holding period other than a blanking period.