Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-10-04
2004-10-05
Nguyen, Chanh (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S204000
Reexamination Certificate
active
06801182
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a liquid crystal display (LCD), and more particularly, to a scan driving circuit and driving method for active matrix liquid crystal display (AMLCD).
BACKGROUND OF THE INVENTION
An active matrix liquid crystal display includes an array of thin film transistors (TFT) formed on a panel, which is controlled by external column and row signals to display images. A block diagram for a typical display system of an active matrix liquid crystal display is illustrated in
FIG. 1
, in which a liquid crystal controller
201
is provided with display data and synchronization signal by a signal bus
101
and transmits the display data and synchronization signal to a data driver
202
by a data signal bus
206
, a first line marker (FLM)
207
and a clock
208
to a scan driver
203
for the activation and operation of the scan driver
203
, and a crystal alternating signal
209
to a power supply
204
. The color tone voltages generated by the data driver
202
are transmitted to a liquid crystal panel
205
by a drain bus
210
, and the select/unselect signal generated by the scan driver
203
for scan lines are transmitted to the liquid crystal panel
205
by a gate bus
211
. Among the voltages generated by the power supply
204
, select voltage level Vgon
212
and unselect voltage level Vgoff
213
are supplied to scan driver
203
, and the opposite electrode voltage
214
of the liquid crystal panel
205
and color tone voltage
215
of the data driver
202
are supplied to the liquid crystal panel
205
. The TFT liquid crystal panel
205
includes a matrix crossed by the drain bus
210
and gate bus
211
, and at the cross point a cell is formed with a TFT switch
216
and a pixel liquid crystal
217
. The gate of the TFT device
216
is connected with the gate bus
211
, the drain of the TFT device
216
is connected with the drain bus
210
, the source
218
of the TFT device
216
is one of the electrodes of the pixel liquid crystal
217
, and the opposite electrode
219
of the pixel liquid crystal
217
is connected with an opposite electrode line
214
.
The liquid crystal display controller
201
converts the display data and synchronization signal transmitted by the signal bus
101
to be the display data and liquid crystal driving signal for driving the TFT liquid crystal display, and transmits the display data and liquid crystal driving signal to the data driver
202
by the signal bus
206
, the liquid crystal display driving signal to the scan driver
203
with the FLM
207
and clock
208
, and the liquid crystal alternating signal
209
to power supply
204
. The data driver
202
sequentially fetches the display data from the signal bus
206
, and, when the display data of a scan line is completely fetched, converts the display data to the color tone voltage corresponding to the scan line, which is in turn outputted from drain bus
210
, and the data driver
202
repeats the process for each scan line as such. Synchronized to the event that the data driver
202
outputs the color tone voltage to the liquid crystal panel
205
by the drain bus
210
, the scan driver
203
sequentially applies the select voltage to the gate bus
211
. When the select voltage Vgon is applied on the gate bus
211
, the TFT device
216
in the liquid crystal display panel
205
enters the selected state and applies the color tone voltage upon the pixel liquid crystal
217
by the drain bus
210
, such that the actual voltage applied upon the pixel liquid crystal
217
varies the twist angle of the liquid crystal to control the transmittance of light, thus implements color tone display. Furthermore, when the unselect voltage Vgoff is applied by the gate bus
211
, the TFT device
216
in the liquid crystal display panel
205
enters the unselected state and keeps the voltage applied on the liquid crystal
217
. Repeat the process during the interval of a frame, and all TFT devices
216
will be selected.
The resolution of an image is dependent on the number of the pixels, and since a scan line controls the on/off of a row of TFT devices, the more the pixels are in a TFT array, the more there are scan lines, and thus the number of pins of a liquid crystal display panel increase. As a result, it is harder to connect the scan driver to the liquid crystal panel. Besides the apparent difficulty of reducing the external circuit of a liquid crystal display, the prior art driver circuit is not formed directly on the panel, thus circuit integration and simplification cannot be achieved, and when a new technology has been developed, such as the case that low-temperature poly-silicon (LTPS) process is applied to fabricate the liquid crystal display, advantages cannot be exploited. With the increasing resolution and complexity of the liquid crystal display, those problems are getting even worse. Therefore, it would be desirable for a scan driving circuit and driving method to provide a large enough number of scan lines with less control signals.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a scan driving circuit and driving method for active matrix liquid crystal display with a plurality of switching devices formed on the liquid crystal display panel and coupled between a plurality of scan lines and a plurality of control signal input ports, in which the number of the control signal input ports are less than that of the scan lines, and one set of control signals coupled to the control signal input ports from outside of the panel to manipulate the switching devices to drive the scan lines. Thus the number of the pins that the panel has to provide to drive the scan lines is reduced in order.
Another object of the invention is the utilization of Metal-Oxide-Semiconductor (MOS) devices of the same conductivity type serving as the switching elements to simplify the circuit and its fabrication process.
Still another object of the invention is the formation of the switching devices with low-temperature poly-silicon MOS devices so as to reduce the cost and difficulty of fabrication.
Yet still another object of the invention is to provide sequential or back-and-forth pulse signals as the driving waveform of the set of control signals.
REFERENCES:
patent: 4842371 (1989-06-01), Yasuda et al.
patent: 5585815 (1996-12-01), Nakashima et al.
patent: 5648790 (1997-07-01), Lee
patent: 5701167 (1997-12-01), Yamazaki
Rao Yong-Nien
Tai Ya-Hsiang
Yang Ho-Hsin
Bell Paul A.
Nguyen Chanh
Prime View International Co. Ltd.
Rabin & Berdo P.C.
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