Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1998-10-30
2001-11-13
Shalwala, Bipin (Department: 2778)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S098000, C345S100000, C345S204000
Reexamination Certificate
active
06317121
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display apparatus, and more particularly to a liquid crystal display apparatus which has a level shifting function or device.
2. Description of the Prior Art
Generally, a liquid crystal display apparatus displays pictures for video signals by controlling the light transmissivity of a liquid crystal. Generally, the liquid crystal display apparatus includes a liquid crystal panel arranged in a matrix type, driving integrated circuits (D-ICs) for driving the liquid crystal matrix, and a programmable logic device (PLD) for generating various control signals in the shape of pulse to control the D-ICs. The liquid crystal display apparatus further includes a level shifting device, depending upon whether either amorphous silicon thin film transistors (TFTs) or poly silicon TFTs were arranged to the liquid crystal panel to serve as a switch, for selectively switching data signals applied to liquid crystal cells. The level shifting device is needed since a driving voltage level of amorphous silicon TFTs is different from poly silicon TFTs.
As shown in
FIG. 1
, a liquid crystal display apparatus employing a liquid crystal panel
10
, in which amorphous silicon TFTs are arranged together with liquid crystal cells, includes D-ICs
12
and a PLD
14
. The PLD
14
generates timing control signals for controlling the operations of the D-ICs
12
, and transfers video data from the outside thereof to the D-ICs
12
disposed on the edges of the liquid crystal panel
10
. The timing control signals outputted from the PLD
14
and the video data have a swing width of 5.0 V or 3.3 V that is equal to a driving voltage of amorphous silicon TFT. The D-ICs
12
switch the amorphous silicon TFTs on the liquid crystal panel
10
and applies signal voltages corresponding the video data to the liquid crystal cells, thereby displaying a picture corresponding to the video data.
As shown in
FIG. 2
, a liquid crystal display apparatus employing a liquid crystal panel
20
, in which poly silicon TFTs having an operating voltage level above 20 V higher than that of the amorphous silicon TFT are arranged together with liquid crystal cells, further includes a level shifting device
22
in addition to the D-ICs
12
and the PLD
14
. The level shifting device
22
is connected between the PLD
14
and the D-ICs
12
to shift voltage levels of both timing control signals to be transferred from the PLD
14
to the D-ICs
12
and video data such that swing widths of the timing control signals and the video data increase from 5.0 V or 3.3 V to 20 V. Using the timing control signals and the shifted video data level, the D-ICs
12
drives the liquid crystal panel
20
comprising the poly silicon TFTs.
In order to shift the voltage levels of the timing control signals and the video data simultaneously, the level shifting apparatus comprises a number of level shifters.
Usually, amplifiers as shown in
FIG. 3
are used for the number of level shifters included in the level shifting apparatus. The amplifier includes an operational amplifier
30
for receiving an input signal in a shape of pulse having a swing width V
1
at the non-inverting terminal (+) thereof, a first resistor R
1
connected between the inverting terminal (−) of the operational amplifier
30
and a ground GND, and a second resistor R
2
connected between the inverting terminal (−) and the output terminal of the operational amplifier
30
.
The amplifier
30
is driven with a high level voltage V+ and a low level voltage V− and amplifies the input signal on the non-inverting terminal (+) thereof by a voltage amplification ratio Av corresponding to a resistance ratio of the first resistors R
1
to the second resistor R
2
plus
1
, i.e., Av=1+R
1
/R
2
. As a result, a pulse signal having a swing width corresponding to a difference between the high level voltage V+ and the low level voltage V− is outputted at the output terminal of the operational amplifier
30
. If the difference voltage between the high level voltage V+ and the low level voltage V− is 20 V, then a pulse signal having a swing width of 20 V is outputted at the output terminal of the operational amplifier
30
.
Alternatively, a comparator as shown in
FIG. 4
may be used for the level shifters included in the level shifting apparatus. The comparator
40
has an inverting terminal (−) for receiving a reference voltage and a non-inverting terminal (+) for receiving an input signal in a shape of pulse having a swing width of V
1
. The reference voltage is set to have a voltage lower than the highermost voltage level and higher than the lowermost voltage level.
Accordingly, a pulse signal corresponding to a difference voltage between the high level voltage V+ and the low level voltage V− emerges at the output terminal of the comparator
40
. If the voltage difference between the high level voltage V+ and the low level voltage V− is 20 V, then a pulse signal having a swing width of 20 V is outputted at the output terminal of the comparator
40
.
The above amplifier and comparator have a complicate circuit configuration because they require a relatively large number of circuit devices. This results in a complication in a circuit configuration of the level shifting apparatus as well as having a difficulty in simplifying the liquid crystal display apparatus. Also, the amplifier and the comparator used for the level shifter waste a relatively large amount power and have a slow response speed.
SUMMARY OF THE INVENTION
An object of the present invention is to solve at least the problems and disadvantages of the background and prior art.
Another object of the present invention is to simplify the circuit configuration.
A further object of the present invention is to minimize a signal delay.
In order to achieve this and other objects of the invention, a liquid crystal display apparatus according to the present invention comprises a liquid crystal panel including poly silicon thin film transistors and liquid crystal cells, a plurality of driving integrated circuits for driving the liquid crystal panel, control means for generating timing control signals and data signals, each having a small swing width, required to control the plurality of driving integrated circuits, and a plurality of level shifting means for shifting each voltage level of the timing control signals and the data signal to be transferred from the control means to the driving integrated circuits, wherein each of said level shifting means includes a first voltage source for generating a high level voltage signal, a second voltage source for generating a low level voltage signals, and switching control means, being responsive to any ones of the timing control signals and the data signals, for complementarily transferring the high level voltage signal and the low level voltage signal to the driving integrated circuits.
The present invention may be achieved in a whole or in parts by a display apparatus comprising: a display panel including a plurality of pixels; a plurality of driving integrated circuits for driving the display panel; a control circuit that generates timing control signals and data signals; and a plurality of level shifting cells for shifting voltage levels of at least one of the timing control signals and the data signal to be transferred from the control circuit to the driving integrated circuits wherein each of the level shifting cells includes a first switch coupled for receiving a high level voltage signal; and a second switch coupled for receiving a low level voltage signal, said first and second switches being complementarily responsive to at least one of the timing control signals and the data signals for one of the high and low voltage signals corresponding driving integrated circuit.
The present invention may be achieved in a whole or in parts by an integrated switching device for a display panel responsive to at least one
Fleshner & Kim LLP.
Lewis David L
LG Electronics Inc.
Shalwala Bipin
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