Shift register and liquid crystal display using the same

Details Shift register and liquid crystal display using the same Shift register and liquid crystal display using the same

2002-02-11

2004-02-10

Wong, Don (Department: 2821)

Computer graphics processing and selective visual display system

Plural physical display element control system

Display elements arranged in matrix

C345S103000, C315S169200

Reexamination Certificate

active

06690347

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shift register of a display device and a liquid crystal display (LCD) using the same, and more particularly, to a shift register generating a scanning signal for scanning gate lines in a gate line driving circuit of AMTFT-LCD (Active Matrix Thin Film Transistor Liquid Crystal Display) and for selecting a block of data lines in a data line block driving circuit.
2. Description of the Related Art
In these days, information processing devices have been rapidly developed in a trend with various architectures, functions and faster information processing speed. Information processed in these information processing devices has an electrical signal format. In order to visually confirm information processed in the information processing device, a display for a role as an interface should be provided.
LCDs have advantages such as the lighter weight, small size, high resolution, lower power consumption and friendly relation with environment and they render display of full colors compared with the traditional cathode ray tube (CRT). Such the advantages allow the LCDs to replace the CRTs and to be spotlighted as a next generation display.
LCDs apply an electric power to liquid crystal having a specific molecular configuration to vary the molecular arrangement of liquid crystal. The variation in the molecular configuration of liquid crystal causes a variation in optical properties such as birefringence, optical rotary power, dichroism and light scattering. The LCDs utilize such variations in optical properties to display an image.
The LCD device is largely sorted into a TN (Twisted Nematic) type and a STN (Super-Twisted Nematic) type. The liquid crystal display device is, according to the driving method, sorted into an active matrix display type, which uses a switching device and a TN liquid crystal, and a passive matrix type, which uses an STN liquid crystal.
A distinguishable difference of two types is in that the active matrix display type is applied to a TFT-LCD that drives the LCD by using a TFT and the passive matrix display type dispenses with a complicated circuit associated with a transistor because of using no transistor
TFT-LCD is divided into amorphous silicon TFT LCD (a-Si TFT-LCD) and polycrystalline silicon TFT LCD (poly-Si TFT-LCD). Poly-Si TFT-LCD has advantages of lower power consumption, lower price compared with a-Si TFT-LCD but has a drawback in that its manufacturing process is complicated. Thus, poly-Si TFT-LCD is mainly used in a small sized display such as mobile phones.
Amorphous-Si TFT-LCD is applied to a large screen sized display such as notebook personal computer (PC), LCD monitor, high definition (HD) television, etc., due to easy application of large screen and high production yield.
As shown in
FIG. 1
, poly-Si TFT LCD includes a data driving circuit
12
and a gate driving circuit
14
that are formed on a glass substrate
10
having a pixel array. A terminal part
16
is connected with an integrated printed circuit board (PCB)
20
using a film cable
18
. This structure saves the manufacturing costs and minimizes the power loss due to the integration of driving circuits.
As shown in
FIG. 2
, amorphous-Si TFT LCD has a data driving chip
34
formed on a flexible printed circuit board
32
in a manner of COF (Chip-On-Film). A data printed circuit board
36
is connected with a data line terminal of the pixel array through the flexible PCB
32
. A gate driving chip
40
is formed on a flexible PCB
38
in a manner of COF. A gate PCB
42
is connected with a gate line terminal through the flexible PCB
40
.
Recently, there is also disclosed a technique for removing the gate PCB from the LCD by employing an integrated PCB technique mounting a gate power supply part on the data PCB. Korean Patent Laid-Open Publication No. 2000-66493 previously filed by the present assignee discloses an LCD module employing an integrated PCB by which the gate PCB is removed.
However, although the integrated PCB is employed, the flexible PCB having the flexible PCB is still used. Thus, since multiple flexible PCBs should be assembled in a glass substrate, a fabrication process of a-Si TFT LCD, especially OLB (Outer Lead Bonding) process becomes complicated compared with that of poly-Si TFT LCD, whereby its fabrication costs becomes higher.
Thus, there are many endeavors for decreasing the number of the assembly process by simultaneously forming data driving circuit and gate driving circuit along with pixel array on a glass substrate in a-Si TFT LCD like poly-Si TFT LCD.
U.S. Pat. No. 5,517,542 discloses a technique for an a-Si TFT gate driving circuit formed on a glass substrate.
In the above U.S. Pat. No. 5,517,542, a shift register of the gate driving circuit uses three clock signals. Each stage of the shift register two clock signals of three clock signals, is enabled with an output signal of previous stage as an input signal, and maintains the disable state by feed backing an output of the second next stage.
Each stage in the U.S. Patent provides a voltage applied to gate of full-down transistor in a capacitor charge manner in order to maintain the disable status. Thus, when an increase in gate threshold voltage of the full-down transistor due to stress of the full-down transistor is elevated higher than the charge voltage of the capacitor, there may occur a turn-off of the full-down transistor in the disable status.
The above U.S. patent employs a power supply circuit elevating a VDD in proportional to the increase in the threshold voltage of the a-Si TFT LCD in order to prevent an error operation due to the increase in the threshold voltage.
SUMMARY OF THE INVENTION
Accordingly, it is a first object of the present invention to provide a shift register making it possible to perform a stable operation regardless of the fluctuation in the threshold voltage of a-Si TFT LCD on a use of a long-term by maintaining an input node of the full-down means at a coupled status with the power voltage.
It is a second object of the present invention to provide an LCD capable of minimizing the number of external connection terminals on the LCD panel for the connection with an external circuit by using two clock signals.
It is a third object of the present invention to provide an amorphous silicon LCD in which a data driving circuit is integrated on a substrate.
It is a fourth object of the present invention to provide a method for operating gate lines of an LCD.
It is a fifth object of the present invention to provide a method for block-operating data lines of an LCD.
To accomplish the first object, there is provided a shift register in which multiple stages are connected one after another to each other, the multiple stages having a first stage in which a start signal being coupled to an input terminal, the shift register sequentially outputting output signals of respective stages. The multiple stages has odd stages for receiving a first clock signal and even stages for receiving a second clock signal having a phase opposite to the first clock signal.
Each of the multiple stages has: a pull-up means for providing a corresponding one of the first and second clock signals to an output terminal; a pull-up driving means connected to an input node of the pull-up means, for turning on the pull-up means in response to a front edge of an input signal and turning off the pull-up means in response to an output signal of a next stage; a pull-down means for providing a first power voltage to the output terminal; and a pull-down driving means connected to an input node of the pull-down means, for turning off the pull-down means in response to a front edge of the input signal and turning on the pull-down means in response to the front edge of the output signal of the next stage.
Here, the first power voltage is a turn off voltage (VOFF, VSS) and the second power voltage is a turn on voltage (VON, VDD).
Preferably, each stage further comprises a turn-on preventing means connected to the input node of the pull-down m

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