Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-10-16
2004-10-19
Shankar, Vijay (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S090000, C345S092000, C345S099000, C345S102000
Reexamination Certificate
active
06806855
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal panel driving circuit. More particularly, the present invention relates to a liquid crystal panel driving circuit, in which a distortion of a wave form of an output or an oscillation of an operational amplifier for driving a liquid crystal panel that is caused by an influence of a self-inductance of a flexible substrate can be suppressed, when a flexible substrate is used as a medium through which a liquid crystal panel driving circuit and a liquid crystal panel are connected.
2. Description of the Related Art
A liquid crystal panel driving circuit is disposed at an input stage of a liquid crystal panel. This liquid crystal panel driving circuit has a plurality of operational amplifiers corresponding to the number of drive lines. A TFT type liquid crystal panel has transistors (TFTs) arrayed in a form of matrix. Each of the operational amplifiers of the liquid crystal panel driving circuit is connected to, for example, a source of this transistor by the first signal line. Then, the liquid crystal panel serving as a capacitance load is charged and discharged through this transistor. Incidentally, another second signal line is connected to a gate of the transistor. An on/off control of a predetermined transistor is carried out in accordance with an input signal through the second line.
FIG. 8
is a view showing an arrangement of a conventional operational amplifier for a liquid crystal panel. As shown in
FIG. 8
, an operational amplifier
806
a
for a liquid crystal panel contains an operational amplifier element
806
. The operational amplifier element
806
has a non-inverting input terminal
801
to receive an input signal. An output terminal
802
of the operational amplifier element
806
is connected as a voltage follower to an inverting input terminal
803
so as to form a negative feedback circuit. Typically, the output terminal
802
of the operational amplifier element
806
is connected through a flexible substrate
804
to a liquid crystal panel
805
serving as a load.
Here, the operation of the conventional liquid crystal panel driving circuit is described with reference to FIG.
9
.
FIG. 9
is a conceptual view of the conventional liquid crystal panel driving circuit. A liquid crystal panel driving circuit
906
shown in
FIG. 9
is provided with: an operational amplifier group
901
composed of a plurality of operational amplifiers; a D/A converter group
902
composed of a plurality of D/A converters; and an output terminal group
903
composed of a plurality of output terminals. The D/A converter group
902
is connected to an input stage of the operational amplifier group
901
.
The output terminal group
903
is connected to the liquid crystal panel
905
through a flexible substrate group
904
composed of a plurality of flexible substrates.
The operational amplifier group
901
is composed of the operational amplifiers
806
a
shown in FIG.
8
. Thus, the output terminals of the respective operational amplifiers of the operational amplifier group
901
are connected as the voltage follower so as to form the negative feedback circuit.
The operational amplifier group
901
performs an impedance conversion on an analog signal outputted by the D/A converter group
902
. The operational amplifier group
901
charges and discharges the liquid crystal panel
905
serving as the capacitance load, on the basis of the signal on which the impedance conversion is performed.
An invention in relation to a drive of a liquid crystal display using an operational amplifier, especially, an invention in relation to a power supply of a liquid crystal display driving circuit is disclosed in Japanese Laid Open Patent Application (JP-A-Showa, 62-83724). The technique disclosed in this gazette is the liquid crystal display driving circuit having the feature of protecting an oscillation of an operational amplifier by adding four resistors to a power supply circuit in which a six-level voltage is generated by using two kinds of power supplies, five resistors and four operational amplifiers. That is, this technique can protect a current increase caused by the oscillation of the operational amplifier. Incidentally, in order to protect the current increase, an output signal of the operational amplifier is outputted through the resistor and supplied to the liquid crystal panel.
Conventionally, the liquid crystal panel driving circuit has been optimally designed by referring to an equivalent circuit of a liquid crystal panel. However, if a reactance component of the flexible substrate is large, the inductance component causes high impedance to be generated in a high frequency band. This high impedance brings about the situation that a signal to be attenuated by the liquid crystal panel is fed back to the liquid crystal driving circuit
906
without any attenuation. For this reason, in the high frequency band, the influence of the high impedance causes the deterioration of the frequency property of the operational amplifier group
901
. The deterioration of the frequency property results in the oscillation of the operational amplifier group
901
.
Usually, the inductance component has a value of about 0.5 &mgr;H, although it is changed depending on the size of the liquid crystal panel. In the case of this condition, the input of a drive signal having a drive frequency of about 200 MHz may result in an occurrence of an oscillation.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-explained problems.
Therefore, an object of the present invention is to provide a liquid crystal panel driving circuit and a method of driving a liquid crystal panel, in which even if an inductance component is added between an operational amplifier and a liquid crystal panel, the operational amplifier is not oscillated.
Another object of the present invention is to provide a liquid crystal panel driving circuit and a method of driving a liquid crystal panel, in which even if an inductance component is added between an operational amplifier and a liquid crystal panel, a speed for driving the liquid crystal panel are not deteriorated.
Still another object of the present invention is to provide a liquid crystal panel driving circuit and method of driving a liquid crystal panel, in which even if an inductance component is added between an operational amplifier and a liquid crystal panel, a static current are not deteriorated.
In order to achieve an aspect of the present invention, the present invention provides a liquid crystal panel driving circuit including an operational amplifier which outputs an output signal based on an image signal and an feedback signal corresponding to the output signal without a high frequency content; and a flexible substrate with an inductance wherein the output signal pass through to a liquid crystal display via the inductance.
In the liquid crystal panel driving circuit, the operational amplifier may includes an operational amplifier element including a non-inverting input terminal supplied with the image signal, an inverting input terminal supplied with the feedback signal and an output terminal outputting the output signal; and a negative feedback circuit formed between the output terminal and the inverting input terminal.
In the liquid crystal panel driving circuit, the negative feedback circuit may include a low pass filter attenuating the high frequency content.
In the liquid crystal panel driving circuit, the low pass filter may includes a resistor connected between the inverting input terminal and the output terminal; and a capacitor connected between the inverting input terminal and an power supply.
In the liquid crystal panel driving circuit, the low pass filter may includes a plurality of resistors connected in series between the inverting input terminal and the output terminal; and a plurality of capacitors connected in parallel to each other through the resistors, wherein one end of the each of plurality of capacitors is connected to a conn
Kato Fumihiko
Miura Makoto
Dharia Prabodh M.
McGinn & Gibb PLLC
NEC Electronics Corporation
Shankar Vijay
LandOfFree
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