Computer graphics processing and selective visual display system – Display driving control circuitry – Waveform generator coupled to display elements
Reexamination Certificate
2001-08-27
2003-10-21
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Display driving control circuitry
Waveform generator coupled to display elements
C345S209000, C345S204000, C345S087000, C345S053000, C345S094000
Reexamination Certificate
active
06636208
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Technical Field of the Invention
This invention relates to a liquid crystal driving circuit device for driving a liquid crystal display panel and a the liquid crystal display device having the liquid crystal driving circuit device.
2. Prior Art
In driving a liquid crystal display panel, a voltage to be supplied to a pixel electrode is reversed every one line or one field. This is for prevention of deterioration of the pixel. For example, a gate voltage supplied to a certain row is expressed as a waveform shown in
FIG. 4
, and is constituted by a gate OFF level waveform of the driving voltage waveform reversing every one line and a gate ON level waveform for turning TFT on in the case of the liquid crystal display panel having a matrix type of TFTs (a thin film transistor). The voltage becomes a level designated as the gate ON level waveform and then TFT is turned into ON, when TFT in this row is selected. A gate voltage signal is generated by selecting a signal from a driving circuit for generating the gate OFF level waveform and a signal from the driving circuit for generating the gate ON level waveform by the switch circuit.
FIG. 3
shows an example of the driving circuit for generating the gate OFF level waveform of this gate voltage signal. The driving waveform having an amplitude value Vdv alternating between 0 V and a negative voltage is supplied from an amplitude source
50
. In the driving waveform, a direct current component is cut off by a capacitor
51
and an alternating current component is derived out, and the direct current component is combined with the voltage made by dividing means having a resistor
52
and a resistor
53
. The direct current component is a direct current voltage value obtained by dividing, with the resistor
52
and the resistor
53
, a voltage difference between 0V at one end of the resistor
52
and a negative voltage VLC from a voltage source
54
at one end of the resistor
53
. This combined driving waveform is sent to the switch circuit
55
.
PROBLEMS TO BE SOLVED BY THE INVENTION
In this prior liquid crystal driving circuit device, when the driving waveform is switched from the gate OFF level waveform to the gate ON level waveform by the switch circuit
55
in order to turn TFT on, there were problems as follows.
The direct current voltage value VLdc in a point A caused by the dividing means is VLdc=−R
1
×Ia where Ia is a current value which flows to the resistor
52
. And a reference symbol R
1
is a resistance value of the resistor
52
. When TFT of this row is selected, the voltage level designated as said gate ON level is selected, and a panel driving current Idc corresponding to this voltage level flows to the dividing means. The direct current voltage value VLdc in the point A at this time becomes VLdc=−R
1
×Ia+(R
1
∥R
2
)×Idc, where the resistance R
2
is a resistance value of the resistor
53
and R
1
∥R
2
means R
1
×R
2
/(R
1
+R
2
). As is apparent from this formula, the direct current voltage value VLdc in the point A is varied in response to the value of Idc. In order to minimize this variation, the current Ia should be made larger than the panel driving current Idc by minimizing the resistances R
1
and R
2
.
On the other hand, there has been the problem that power consumption becomes larger when this current Ia is large, because the current Ia is a current only for generating the direct current voltage value VLdc. In order to minimize this current Ia, it is preferable that the resistances R
1
and R
2
are large.
Furthermore, the voltage source for supplying the alternating current component of a gate OFF level is preferably supplied by only the voltage source for driving the amplitude source
50
, not from the voltage source for generating the direct current component. The reason is that electric power loss becomes large, because said electric power losses of the alternating current component is consumed in the power source for generating said negative voltage VLC, especially in the case that a voltage level of the power source for generating the negative voltage VLC is larger than a voltage level of the power source for generating the alternating current component sent by the amplitude source
50
.
The object of the invention is to provide a liquid crystal driving circuit device in which variation in a direct current is smaller and is less in electric power loss.
MEANS FOR SOLVING THE PROBLEMS
A liquid crystal driving circuit device according to the invention is comprises
AC generating means for generating an alternating current component of said drive signal;
a capacitive element with one terminal connected with said AC generating means;
a current limitation means with one terminal connected with the other terminal of said capacitive element;
and DC generating means for generating a direct current component of said drive signal, said DC generating means having an output connected with the other terminal of said current limitation means,
wherein said capacitive element eliminates a direct current component of an output signal from said AC generating means, and wherein said current limitation means limits a current caused by a voltage difference between a voltage at the other terminal of said capacitive element and a voltage at said output,
further wherein an amplitude value of the alternating current component from said AC generating means and an amplitude value of the alternating current component of a signal from said output of said DC generating means are approximately the same.
Since the amplitude value of the alternating current component from the AC generating means and the amplitude value of the alternating current component of a signal from said output of the DC generating means are approximately the same, and said capacitive element is used, the voltage source for supplying the alternating current component of the gate OFF level can be supplied from the voltage source supplied to the AC generating means. Moreover, the panel driving current generated in turning on TFT prevents from flowing into the DC generating means by the current limitation means, whereby electric power to be consumed by the DC generating means can be minimized.
In the liquid crystal display device having the liquid crystal driving circuit device according to the invention, electric power loss may be reduced by a large amount.
EMBODIMENT OF THE INVENTION
Embodiments according to the invention will be described below.
FIG. 1
is a circuit block diagram showing one embodiment according to the invention. The amplitude source
50
supplying the driving voltage with the amplitude value Vdv is connected with an end of one side of the capacitors
3
and
51
respectively. The other end of the capacitor
51
is connected with each end of the resistors
52
and
53
and with an input of a buffer amplifier
1
. The other end of the resistor
52
is connected at a ground of 0V. The other end of the resistor
53
is connected with the voltage source
54
which supplies the negative voltage VLC. One end of the resistor
2
is connected with output of the buffer amplifier
1
, and the other end is connected with the other end of the capacitor
3
and the switch circuit
55
.
An operation of this liquid crystal driving circuit device will be described below. The direct current component of the drive signal having the amplitude value Vdv from the amplitude source
50
is cut by the capacitor
3
. The direct current component of this drive signal is given as the following description. A voltage difference between 0V and the negative voltage VLC is divided by a resistance division of the resistors
52
and
53
. The divided voltage through the buffer amplifier
1
and the resistor
2
is combined with the alternating current component of said driving signal passed through the capacitor
3
. The drive signal combined with the divided voltage is supplied to a gate electrode of TFT through the switch circuit
55
.
The resistors
52
and
53
may be lar
Kamiya Takeo
Watanabe Hidetoshi
Koninklijke Philips Electronics , N.V.
Shalwala Bipin
Shapiro Leonid
Watanabe Hidetoshi
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