Electro-optical device

• US 5,585,949 A
• Filed: 11/03/1994
• Issued: 12/17/1996
• Est. Priority Date: 03/25/1991
• Status: Expired due to Term

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Hiroki, Masaaki, Mase, Akira, Yamazaki, Shunpei
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US08/334,383
• Time in Patent Office: 775 Days
• Field of Search: 354/54, 354/55, 354/57, 354/58, 354/59, 354/60, 354/61, 354/87, 357/23.13-257, 340/784, 257/56, 257/355, 257/356, 257/357, 257/358, 257/359, 257/360, 257/363, 257/532, 361/340, 361/784, 361/345, 361/92, 361/56, 361/9, 361/111
• US Class Current: 349/41
• CPC Class Codes: G02F 1/136204 Arrangements to prevent high voltage or static electricity failures

Abstract

A display device with over voltage protection circuits having zener diode characteristics. The protection circuits have pairs of TFTs connected to resistive dividers. Each resistive divider provide the voltage set levels for one direction of overvoltage application.

Claims

1. An electro-optical device, comprising:

a pair of signal lines having a matrix configuration disposed on a substrate;

a plurality of pixel electrodes formed on the substrate;

at least one thin film transistor disposed at each pixel electrode, with one of an input and output side connected to said pixel electrode and the other of the input side and the output side thereof connected to a first signal line of said pair of signal lines having a matrix configuration, and a gate of said thin film transistor connected to a second signal line of said pair of signal lines having a matrix configuration; and

a protective circuit having zener diode characteristics connected to a signal source which is one of said first signal line and said second signal line, to protect said thin film transistor against overvoltages emanating from said signal source, said protective circuit comprising first and second protective TFTs, each with gate, source, and drain connections, and first and second voltage divider means, each of said first and second voltage divider means providing a respective first resistance and a second resistance;

such that the drain of said first protective TFT is connected to a terminal other than said first signal line and said second signal line, said source of said first protective TFT is connected through said first voltage divider means to said signal source so that the first resistance of said first voltage divider means is interposed between said first protective TFT source and said signal source, and said gate of said first protective TFT is connected through said first voltage divider means to said signal source so that said second resistance of said first voltage divider means is provided between said first protective TFT gate and said signal source, and

such that said drain of said second protective TFT is operably connected to said signal source, said source connection of said second protective TFT is connected through said second voltage divider means to said terminal so that said first resistance of said second voltage divider means is provided between said second protective TFT source connection and said terminal, with said gate of said second protective TFT connected through said second voltage divider means to said terminal so that said second resistance of said second voltage divider means is provided between said second protective TFT gate and said terminal; and

wherein values of said first and second resistances of the first and second voltage divider means, respectively, are selected to provide a current diverting operation of said first and second protective TFTs at predetermined overvoltage levels.

2. The electro-optical device of claim 1 wherein a plurality of said protective circuits are connected between the signal source and the thin film transistor.

3. An electro-optical device, comprising:

a pair of signal lines having a matrix configuration disposed on a substrate;

a plurality of pixel electrodes formed on the device;

at least one thin film transistor disposed at each pixel electrode, with one of an input and output side connected to said pixel electrode and the other of the input side and the output side thereof connected to a first signal line of said pair of signal lines having a matrix configuration, and a gate of said thin film transistor connected to a second signal line of said pair of signal lines having a matrix configuration; and

a protective circuit having zener diode characteristics connected to a signal source which is one of said first signal line and said second signal line, to protect said transistors against overvoltages emanating from said signal source, said protective circuit comprising an N-channel protective TFT and a P-channel protective TFT, with input terminals, output terminals, and gate terminals respectively of each protective TFT being mutually connected, and a voltage divider means for providing a first resistance and a second resistance;

wherein said output terminals of said protective TFTs are connected to a terminal other than said first signal line and said second signal line and input terminals of said protective TFTs are connected through said first resistance of said voltage divider means to said signal source, and said gates of said protective TFTs are connected through said second resistance of said voltage divider means to said signal source, and wherein values of said first and second resistances of the voltage divider means are selected to provide a current diverting operation of said first and second protective TFTs at a predetermined overvoltage level.

4. The electro-optical device of claim 3, wherein a plurality of said protective circuits are connected between the signal source and the protected thin film transistors.

5. An electro-optical device, comprising:

a plurality of pixel electrodes formed on a substrate;

thin film transistors provided at said pixel electrodes to switch said pixel electrodes;

a pair of signal lines having a matrix configuration disposed on said substrate, and signal lines being connected to said thin film transistors to supply signals thereto;

a protective circuit connected to a signal source which is one of said signal lines to protect said thin film transistors against overvoltage emanated from said signal source, said protective circuit comprising a protective TFT and a voltage dividing means having series connected two resistances,

such that said protective TFT and said two resistances are connected in series between said signal source and a terminal other than said signal lines;

one of the source and drain regions of said protective TFT is connected to either one of said signal source or said terminal;

the other one of the source and drain regions is connected to one end of said series connected two resistances; and

a gate of said protective TFT is connect to a point between said two resistances,

wherein the values of said two resistances are respectively selected to provide a current diverting operation of said protective TFT at a predetermined overvoltage level.

6. An electro-optical device comprising:

a pair of signal lines having a matrix configuration disposed on a substrate;

a plurality of pixel electrodes provided on said substrate;

at least one transistor disposed at each pixel electrode, with one of an input and output side connected to said pixel electrode and the other of the input and output side thereof connected to a first signal line of said pair of signal lines having a matrix configuration, and a gate of said transistor connected to a second signal line of said pair of signal lines having a matrix configuration; and

a protective circuit having zener diode characteristics connected to a signal source which is one of said first signal line and said second signal line, to protect said transistor against overvoltages emanating from said signal source, said protective circuit comprising a protective TFT and a voltage divider means, said divider means providing a first resistance and a second resistance,

such that a drain of said protective TFT is connected to a terminal other than said signal source, a source of said protective TFT is connected through said divider means to said signal source so that said first resistance is interposed between said source of said protective TFT and said signal source, and a gate of said protective TFT is connected through said divider means to said signal source so that said second resistance is provided between said gate and said signal source,

wherein values of said first and second resistances are selected to provide a current diverting operation of said protective TFT at predetermined overvoltage levels.

7. An electro-optical device comprising:

a pair of signal lines having a matrix configuration disposed on a substrate;

a plurality of pixel electrodes provided on said substrate;

at least one transistor disposed at each pixel electrode, with one of an input and output side connected to said pixel electrode and the other of the input and output side thereof connected to a first signal line of said pair of signal lines having a matrix configuration, and a gate of said transistor connected to a second signal line of said pair of signal lines having a matrix configuration; and

a protective circuit having zener diode characteristics and comprising a first protective circuit portion and a second protective circuit portion, each of said first protective circuit portion and said second protective circuit portion being connected between a signal source which is one of said first signal line and said second signal line, and a terminal other than said signal source, to protect said transistor against overvoltages emanating from said signal source, each of said first and second protective circuit portions comprising first and second protective transistors and first and second voltage divider means, each of said first and second voltage divider means providing a respective first resistance and a second resistance;

such that a drain of said first protective transistor is connected to said terminal, a source of said first protective transistor is connected through said first voltage divider means to said signal source so that said first resistance of said first voltage divider means is interposed between said first protective transistor source and said signal source, and a gate of said first protective transistor is connected through said first voltage divider means to said signal source so that said second resistance is provided between said first protective transistor gate and said signal source; and

such that a drain of said second protective transistor is operably connected to said signal source, a source of said second protective transistor is connected through said second voltage divider means to said terminal so that said first resistance of said second voltage divider means is provided between said second protective transistor source and said terminal, with a gate of said second protective transistor connected through said second voltage divider means to said terminal so that said second resistance of said second voltage divider means is provided between said second protective transistor gate and said terminal; and

wherein values of said first and second resistances of the first and second voltage divider means, respectively, are selected to provide a current diverting operation of said first and second protective transistors at predetermined overvoltage levels.

8. An electro-optical device comprising:

a pair of signal lines having a matrix configuration disposed on a substrate;

a plurality of pixel electrodes provided on said substrate;

at least one transistor disposed at each pixel electrode, with one of an input and output side connected to said pixel electrode and the other of the input and output side thereof connected to a first signal line of said pair of signal lines having a matrix configuration, and a gate of said transistor connected to a second signal line of said pair of signal lines having a matrix configuration; and

a protective circuit having zener diode characteristics and comprising a first protective circuit portion and a second protective circuit portion, each of said first protective circuit portion and said second protective circuit portion being connected between a signal source which is one of said first signal line and said second signal line, and a terminal other than said signal source, to protect said transistor against overvoltages emanating from said signal source, each of said first protective circuit portion and said second protective circuit portion comprising an N-channel protective transistor and a P-channel protective transistor and a voltage divider means for providing a first resistance and a second resistance, with input terminals, output terminals and gates respectively of said N-channel protective transistor and said P-channel protective transistor being mutually connected in each of said first protective circuit portion and said second protective circuit portion,

wherein said output terminals of said N-channel transistor and said P-channel transistor of each of said first and second protective circuit portions are connected to said terminal other than said signal source, and input terminals of said N-channel transistor and said P-channel transistor of each of said first and second protective circuit portions are connected through said first resistance of the corresponding voltage divider means to said signal source, and said gates of said N-channel transistor and said P-channel transistor of each of said first and second protective circuit portions are connected through said second resistance of the corresponding voltage divider means to said signal source, and

wherein values of said first and second resistances of the voltage divider means of each of said first and second protective circuit portions are selected to provide a current diverting operation of the corresponding N-channel transistor and P-channel transistor.