Coded data generation or conversion – Converter compensation
Reexamination Certificate
2000-12-08
2002-08-20
Young, Brian (Department: 2819)
Coded data generation or conversion
Converter compensation
C345S098000, C345S209000
Reexamination Certificate
active
06437716
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a gray scale display reference voltage generating circuit for use in an LCD(Liquid Crystal Display) drive unit or the like and to an LCD drive unit employing the circuit.
The above-mentioned gray scale display reference voltage generating circuit is a circuit for forming intermediate voltages in between two voltages. For example, in an LCD drive section or the like in an active matrix system LCD device, intermediate voltages are formed by resistance division. Then, resistors for resistance division have a resistance ratio called the gamma (&ggr;) correction, and according to this resistance ratio, the optical characteristics of a liquid crystal material are corrected to provide more natural gray scale display.
Reference will be made below to the construction of an LCD device provided with the aforementioned gray scale display reference voltage generating circuit, the construction of a TFT (Thin Film Transistor) type LCD panel in the LCD device, an LCD drive waveform and a source driver for the LCD panel.
FIG. 6
shows a block diagram of a TFT system LCD device as a representative example of the active matrix system. This LCD device is separated into an LCD section and an LCD drive circuit (LCD drive section) for driving the LCD section. The above-mentioned LCD section has a TFT system LCD panel
1
. Then, the LCD panel
1
is internally provided with an LCD element (not shown) and an opposite electrode (common electrode)
2
described in detail later.
On the other hand, the LCD drive circuit includes a source driver assembly
3
, a gate driver assembly
4
and a controller
5
, which are constructed of ICs (Integrated Circuits) as well as an LCD drive power supply
6
. The controller
5
inputs display data D and a control signal S
1
to the source driver assembly
3
and inputs a vertical synchronization signal S
2
to the gate driver assembly
4
. Further, a horizontal synchronization signal is inputted to the source driver assembly
3
and the gate driver assembly
4
.
In the above-mentioned construction, the externally inputted display data is inputted as the display data D that is a digital signal to the source driver assembly
3
via the controller
5
. Then, the source driver assembly
3
time-sharingly divides the inputted display data D, latches the data into a first source driver through an n-th source driver and thereafter subjects the latched data to D/A (Digital-to-Analog) conversion in synchronization with the horizontal synchronization signal inputted from the controller
5
. Then, a gray scale display use analog voltage (referred to as a gray scale display voltage hereinafter) formed by subjecting the time-sharingly divided display data D to D/A conversion is outputted to the corresponding LCD element inside the LCD panel
1
via a source signal line (not shown).
FIG. 7
shows the construction of the LCD panel
1
. The LCD panel
1
has pixel electrodes
11
, pixel capacitors
12
, TFTs
13
for controlling the turning-on and -off of a voltage to be applied to the pixel electrodes
11
, source signal lines
14
, gate signal lines
15
and an opposite electrode
16
(corresponding to the opposite electrode
2
of FIG.
6
). In this case, an LCD element A of one pixel is constructed of the pixel electrode
11
, the pixel capacitor
12
and the TFT
13
.
The aforementioned gray scale display voltages corresponding to the brightnesses of the pixels to be used for display are applied from the source driver assembly
3
of
FIG. 6
to the source signal lines
14
. On the other hand, scanning signals for successively turning on the TFTs
13
arranged in the direction of column is applied from the gate driver assembly
4
to the gate signal lines
15
. Then, via each TFT
13
in the ON-state, the gray scale display voltages of the source signal lines
14
are applied to the pixel electrodes
11
connected to the drains of the TFTs
13
and elective charges are accumulated in the pixel capacitors
12
provided between the pixel electrode and the opposite electrode
16
. Thus, the light transmittance of the liquid crystals is changed in accordance with the gray scale display voltage, executing pixel display.
FIG.
8
and
FIG. 9
show an example of an LCD drive waveform. In FIG.
8
and
FIG. 9
, the reference numerals
21
and
25
denote the drive waveforms of one source driver of the source driver assembly
3
, while the reference numerals
22
and
26
denote the drive waveforms of one gate driver of the gate driver assembly
4
. The reference numerals
23
and
27
denote the potential of the opposite electrode
16
, while the reference numerals
24
and
28
denote the voltage waveforms of the pixel electrode
11
. In this case, the voltage applied to the liquid crystal material is a potential difference between the pixel electrode
11
and the opposite electrode
16
and is indicated by the hatching in the figures.
For example, in the case of
FIG. 8
, the TFT
13
is turned on only when the level of the drive waveform
22
of the gate driver is at H-level, by which a voltage of the difference between the drive waveform
21
of the source driver and the potential
23
of the opposite electrode
16
is applied to the pixel electrode
11
. Subsequently, the level of the drive waveform
22
of the gate driver comes to be at L-level, by which the TFT
13
is turned off. In this case, due to the provision of the pixel capacitor
12
for the pixel, the aforementioned voltage is retained.
The same thing can be said for the case of FIG.
9
. It is to be noted that FIG.
8
and
FIG. 9
respectively show the cases where different voltages are applied to the liquid crystal material. In the case of
FIG. 8
, the application voltage is higher than that of FIG.
9
. As described above, by varying the voltage applied as an analog voltage to the liquid crystal material, the light transmittance of the liquid crystals is varied in an analog manner, providing multilevel gray scale display. It is to be noted that the number of levels of gray that can be provided for display depends on the number of analog voltages to be selectively applied to the liquid crystal material.
FIG. 10
shows a block diagram of an example of the n-th source driver constituting part of the source driver assembly
3
of FIG.
6
. The display data D of the inputted digital signal has display data (DR, DG, DB) of R (red), G (green) and B (blue) . Then, the display data D is once latched into an input latch circuit
31
and thereafter time-sharingly stored into a sampling memory
33
in accordance with the operation of a shift register
32
that effects shifting by a start pulse SP and a clock CK supplied from the controller
5
. Subsequently, the data are collectively transferred to a hold memory
34
on the basis of the horizontal synchronization signal (not shown) supplied from the controller
5
. It is to be noted that the reference letter S denotes a cascade output.
A gray scale display reference voltage generating circuit
39
generates a reference voltage at each level on the basis of a voltage VR supplied from an external reference voltage generating circuit (corresponding to the LCD drive power supply
6
of FIG.
6
). The data in the hold memory
34
is transmitted to a D/A converter circuit (Digital-to-Analog converter circuit)
36
via a level shifter circuit
35
and converted into an analog voltage on the basis of the reference voltage at each level from the gray scale display reference voltage generating circuit
39
. Then, the analog voltage is outputted as the aforementioned gray scale display voltage from an LCD drive voltage output terminal
38
to the source signal lines
14
of the LCD elements A by an output circuit
37
. That is, the number of levels of the reference voltages becomes the number of levels of gray that can be provided for display.
FIG. 11
shows the construction of the gray scale display reference voltage generating circuit
39
generating intermediate voltages for outputting a plurality of reference voltages as
Nguyen John
Sharp Kabushiki Kaisha
Young Brian
LandOfFree
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