Shift register circuit and image display comprising the same

Abstract

In a shift register circuit, a defective operation while an output signal is not outputted and a drive capability lowering while the output signal is outputted are prevented. A unit shift register comprises a first transistor for supplying a clock signal inputted to a first clock terminal to an output terminal, and the first transistor is driven by a drive circuit. A second transistor is connected between the gate of the first transistor and the output terminal and has a gate connected to the first clock terminal. The second transistor connects the gate of the first transistor to the output terminal based on the clock signal when the gate of the first transistor is at L (Low) level.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a shift register circuit and more particularly, to a shift register circuit used in such as a scan line drive circuit in an image display and comprising only the same conductivity type field effect transistor.[0003]2. Description of the Background Art[0004]According to an image display such a liquid crystal display (referred to as the “display” hereinafter), a gate line (scan line) is provided with respect to each pixel row (pixel line) of a display panel in which a plurality of pixels are arranged like a matrix, and the display image is updated by sequentially selecting and driving the gate line every cycle of one horizontal period of a display signal. Thus, as a gate line drive circuit (scan line drive circuit) for sequentially selecting and driving the pixel line, that is, the gate line, a shift register that makes one round of shifting for one frame period of the display signal can b...

AI Technical Summary

Benefits of technology

[0014]It is an object of the present invention to provide a shift register circuit in which a defective operation is prevented while an output signal is not outputted and drive capability is prevented from being lowered while the output signal is outputted.

[0016]The level of the control electrode of the first transistor sufficiently rises because a current does not flow in the switching circuit while the output signal (first clock signal transmitted to the output terminal through the first transistor) is outputted, so that the drive capability of the first transistor can be highly kept. Thus, the rising and falling speed of the output signal can be increased, which contributes to the high speed operation. In addition, since the switching circuit is turned on when the output signal is not outputted (non-selected period), the control electrode of the first transistor is discharged and kept at L level. Thus, it is prevented that the first transistor is turned on and the output signal unnecessarily becomes H level in the non-selected period. That is, both effect that the defective operation is prevented in the non-selected state and effect that the drive capability is prevented from being lowered while the output signal is outputted.

Problems solved by technology

Thus, when the gate potential exceeds the threshold voltage of the first transistor, the first transistor to be kept in the off state is unnecessarily turned on, which causes a defective operation of the unit shift register.

In this case, the problem is that the rising and falling speeds of the output signal are lowered and it is difficult to implement the high-speed operation.

Especially, since it is necessary to charge the gate line at high speed to activate it in order to ensure sufficient writing time of data to the pixel, in the gate line drive circuit of the display, lowering in the drive capability of the first transistor, that is, lowering in the drive capability of the unit shift register becomes a big problem.

As a result, when the drive capability of the first transistor is not sufficiently ensured, the problem the high speed operation is difficult arises again.

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