Computer graphics processing and selective visual display system – Display driving control circuitry – Waveform generator coupled to display elements
Reexamination Certificate
2000-03-24
2003-09-30
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display driving control circuitry
Waveform generator coupled to display elements
C345S690000, C345S094000, C330S255000
Reexamination Certificate
active
06628274
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to display drive devices and drive methods to drive displays such as liquid crystal displays. More specifically, the present invention relates to the improvement of drive output of display drive devices.
2. Description of Related Art
FIG. 21
schematically shows a structure of a flat display
700
. The flat display
700
contains a flat display
710
such as a liquid crystal panel, an X-driver
720
, a Y-driver
730
and a controller
740
. The X-driver reads display data equivalent to one row of the display from data line
761
based on a predetermined control signal
760
from controller
740
. Based on instructions from the controller
740
, the Y-driver applies row selection voltage successively to scan electrodes for the 1st to Nth rows of the display
710
. In association with this operation, the X-driver outputs voltage for display data of the one row to the signal electrodes for the 1st to Mth columns of the display
710
. In this way, a display corresponding to display data is realized.
Now, let us consider conventional display drive devices (e.g., X-drivers). For example, let us consider Japanese Laid-open Patent Application HEI 4-107594. This reference shows the use of operational amplifiers, as indicated by reference numerals
10
and
13
in FIG.
1
and
FIG. 3
of Patent Application HEI 4-107594. However, the amplifier only uses a transistor as a differential unit that has either an N-channel or a P-channel. Consequently, this operational amplifier presents a non-linear operation region
820
near the positive power supply potential, as shown in
FIG. 22
of the present patent application, in the response of the output voltage to input voltage. With such a characteristic, even when a high voltage is to be output to a signal electrode in response to data with a high gray-scale level, a sufficient voltage cannot be applied to the signal electrode. As a result, it will be difficult to obtain a gray-scale display demanded.
FIG. 22
of the present application shows an operational amplifier with an N-channel transistor for the differential unit, but using a P-channel transistor would also create a similar, albeit opposite, problem, as shown in
FIG. 23
of the present application.
Japanese Laid-Open Patent Application HEI 8-122733 shows a different example of a drive method of a display drive device (an X-driver) in which voltages of the same polarity are applied to adjacent signal electrodes (e.g.,
711
and
712
in
FIG. 21
of the present application) and voltages of the opposite polarity are applied in the next display cycle. This reference describes an amplifier A (
9
) that absorbs current and an amplifier B (
10
) that releases current. A switch SA (
11
) and a switch SB (
12
) are opened or closed to selectively use the amplifier A (
9
) or the amplifier B (
10
) according to the voltage to be applied to CL. Since this structure entails discrete switching between the two types of amplifiers whose circuits are separate from one another, the following problem occurs. Namely, the open/close control between the switch SA (
11
) and the switch SB (
12
) would ideally be conducted such that one of them turns on while the other turns off, and such switching should take place simultaneously. However, strictly speaking, the possibility that there would be a moment when both of the switches are on or both of the switches are off cannot be denied. In such cases, there would be a problem of an output short-circuit or an output open-circuit. Further, even when the open/close control is to take place successfully, since the two amplifiers with individual differences are combined, a non-linear operation part
890
is created, as shown in
FIG. 24
of the present application, resulting in display unevenness and display fluctuations.
In addition, although not shown in the figures, in a prior art circuit where an input voltage to an operational amplifier is selected, there is a possibility that a power supply voltage would be applied to individual transistors. Accordingly, transistors with a dielectric strength enough to withstand the power supply voltage have to be used. As a result, a large circuit area is required.
Furthermore, when using an operational amplifier with either a P-channel or an N-channel differential unit for one output, and forming a positive or a negative output by the differential output and a current source that operates by capacitive coupling with the differential output, the area required by a capacitor for the capacitive coupling has to be several times the area of the output transistor area, which consequently requires a large circuit area.
In a one-channel operational amplifier (
900
) in
FIG. 25
of the present application, where an output is formed by a differential output (
912
) and a current source (
930
) operating with a capacitive coupling (
920
), the linear operation region of the output tends to become narrower. Consequently, either the power supply voltage Vdd has to be raised or the transistor's threshold voltage has to be lowered. Additionally, because it requires a constant-current source (
930
) for the output, it was necessary to constantly supply a current to the output, which requires a large amount of current.
Therefore, the display device driving in the conventional technique has the following problems.
Namely, a proper voltage, that matches the gray-scale data, cannot be applied to liquid crystals in a non-linear operation region of the operational amplifier. As a result, a required gray-scale presentation cannot be obtained.
In a driving technique to cover a non-linear operation region by a pair of operational amplifiers having different polarities, problems, such as an output short circuit and an output open circuit, can occur.
In addition, when the operational amplifiers in the combination are switched from one to the other, a non-linear section appears in an output due to potential mismatching between the potentials at their junction, as shown in FIG.
24
. As a result, a smooth gray-scale transition cannot be obtained, resulting in problems such as display non-uniformity and display fluctuation.
Also, transistors with a dielectric strength greater than the power supply voltage have to be used. As a result, a large circuit area is required. A circuit that requires a greater capacity also requires a greater circuit area. Also, in a circuit that requires a constant-current source (
930
), a large amount of current is consumed.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, a display drive apparatus is provided for driving liquid crystals by applying a voltage to the liquid crystals based on gray-scale data representative of a display. The display drive apparatus includes a polarity control circuit that generates a polarity control signal based on a polarity signal; an input selection circuit that selects a predetermined reference voltage for driving the liquid crystals from a plurality of reference voltages provided from an input voltage generation circuit or a plurality of reference voltages generated within the input selection circuit based on an input signal representative of gray-scale data and the polarity control signal; a non-linear operation region identifying circuit that identifies a non-linear operation region in which an output signal from an operational amplifier does not follow an input thereto based on the input signal and the polarity control signal, and outputs an offset current generation control signal for supplementing the current of the output signal of the operational amplifier when an input voltage in the non-linear operation region is subjected to an operation amplification, wherein the operational amplifier inputs the preferred reference voltage selected by the input selection circuit and outputs at an output terminal an output signal that is operation-amplified according to the preferred reference voltage; and an offset current generation circuit that supplements the curren
Hogan & Hartson LLP
Saras Steven
Seiko Epson Corporation
Spencer William C.
LandOfFree
Display drive device, display device, hand-carry electronic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Display drive device, display device, hand-carry electronic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Display drive device, display device, hand-carry electronic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3023406