Display device

Abstract

An object of the present invention is to increase the reliability in the level shift operation in a display device provided with a level shift circuit. The display device according to the present invention is characterized in that the above described level shift circuit comprises: a first thin film transistor having a semiconductor layer formed of a polysilicon layer; a waveform rectifying circuit connected to a second electrode of the above described first thin film transistor; and a constant current source and a switching element connected between the second electrode of the above described first thin film transistor and a reference power source, wherein a bias voltage is inputted into a control electrode of the above described first thin film transistor and an input signal is inputted into a first electrode of the above described first thin film transistor.

Description

[0001] This application claims the priority based on the Japanese application Japanese Patent Application No. 2008-103403 on April 11, 2008, and uses the content in this application. technical field [0002] The present invention relates to a display device, and more particularly to an active matrix display device in which a driving circuit (peripheral circuit) is formed around a display area on the same substrate on which active elements are formed. Background technique [0003] Conventionally, as a liquid crystal display device, an active matrix type liquid crystal display device having an active element for each pixel and switching the active element is known. [0004] As one of such active matrix liquid crystal display devices, a thin film transistor whose semiconductor layer is formed of a polysilicon layer (hereinafter referred to as a polysilicon thin film transistor) is known as an active element. Furthermore, in this type of liquid crystal display device, since the ...

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Problems solved by technology

[0013] However, the threshold voltage of a polysilicon thin film transistor is generally large, and its variation is also large. Therefore, for example, even when the input signal is at an H level, the output voltage may not rise to a predetermined voltage.

[0014] Therefore, in the level conversion circuit described in Patent Document 1, there is a problem that when the pulse-shaped enable signal ENA is input to the gate 112 of the polysilicon thin film transistor 111 and the polysilicon thin film transistor 111 performs a pulse operation, The drain 114 cannot rise to the specified voltage, which impairs the stability of the level conversion operation

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